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Peeling, gluing and bonding characteristics of Nigerian plantation-grown Gmelina arborea (Roxb.) Badejo, Solomon Olufunmilayo Olubunmi 1977

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PEELING, GLUING AND BONDING CHARACTERISTICS OF NIGERIAN  PLANTATION-GROWN  GMELINA ARBOREA (ROXB.)  by SOLOMON OLUFUNMILAYO OLUBUNMI BADEJO B.Sc.  (Hons.) F o r e s t r y , U n i v e r s i t y o f Ibadan, 1973  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF FORESTRY i n the Department o f F o r e s t r y  We accept t h i s t h e s i s as conforming to the r e q u i r e d  THE  standard  UNIVERSITY OF BRITISH COLUMBIA May, 1977  Solomon Olufunmilayo Olubunmi Badejo, 1977  In p r e s e n t i n g t h i s  thesis  in p a r t i a l  fulfilment of  the requirements f o r  an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, the I  Library shall  f u r t h e r agree  for  freely available  that permission  r e f e r e n c e and  f o r e x t e n s i v e copying o f  this  representatives. thesis  It  is understood that  f o r f i n a n c i a l gain s h a l l  written permission.  Department of The  for  this  that  study. thesis  s c h o l a r l y purposes may be granted by the Head of my Department or  by h i s of  make i t  I agree  University of B r i t i s h  2075 Wesbrook P l a c e Vancouver, Canada V6T 1W5  Columbia  copying or p u b l i c a t i o n  not be allowed without my  ABSTRACT  The g l u i n g p r o p e r t i e s of p l a n t a t i o n - g r o w n gmelina wood (Gmelina a r b o r e a Roxb.) from N i g e r i a were i n v e s t i g a t e d .  Three wood  p e e l i n g temperatures - 20°C, 50°C and 85°C; two g l u e types urea-formaldehyde  (UF) and phenol-formaldehyde  (PF); two  glue spreads -  25 kg/MDGL (55 l b ) and 32 kg/MDGL (70 l b ) ; and two c l o s e d assembly - 10 minutes and 20 minutes were used. were p e e l e d t i g h t and were 1.27 g r a v i t y f o r the l o g s was  Veneers from the sample l o g s  (0.05 i n ) t h i c k .  specific  discussed.  Three 5 - p l y plywood combination f o r 72 i n a l l .  p a n e l s were made, f o r each treatment  A t o t a l o f 1438  shear t e s t specimens were  The UF specimens were t e s t e d dry and a f t e r vacuum-pressure  whereas the PF specimens Bond q u a l i t y was  r e c e i v e d vacuum-pressure  treatment  and b o i l - d r y - b o i l  tests.  e v a l u a t e d on the b a s i s of wood shear s t r e n g t h and  percentage wood f a i l u r e . and German Plywood  R e s u l t s were compared to the U.S.,  British  Standards.  Wood p e e l i n g temperature was  highly significant  of glue type and bond q u a l i t y t e s t i n g method. prior  The  determined and i t s i n f l u e n c e on the p r o b a b l e  end uses o f gmelina plywood  used.  mm  times  H e a t i n g of gmelina l o g s  to p e e l i n g d i d not improve veneer p e e l - q u a l i t y .  the h i g h e s t p e e l - q u a l i t y  regardless  Veneers were of  ( b a s i s : T h i c k n e s s v a r i a t i o n and s u r f a c e  when l o g s were p e e l e d a t 20°C.  -ii-  The h i g h e s t p e e l i n g  temperature  roughness)  -iiiyielded the lowest peel-quality. Bond quality, (percentage wood f a i l u r e ) , was  consistently  reduced by increasing peeling temperature and was lowest at 85°C i n a l l the UF and PF treatments, regardless of bond quality testing method. Ignoring glue spreads, panels made from veneers cut at temperatures of 50°C and 85°C gave the highest shear strength values among the UF treatments.  On the other hand, panels from veneers cut  at temperatures of 20°C and 85°C gave the highest shear strength values among the PF treatments. A l l factors considered, treatment combination of Spread 55 Time 20, a r i s i n g from veneers cut at the control temperature of 20°C, gave an impressive bond quality i n a l l the UF and PF treatments used. Five of the 12 PF treatments used, regardless of type of bond quality testing method, pass the U.S. Plywood Standard; the B r i t i s h Standard; while a l l pass the German Standard.  one passes On the  other hand, f i v e of the 12 UF treatments from vacuum-pressure test  j pass the U.S.  Standard;  two pass the B r i t i s h Standard;  pass the German Standard. dry test pass the U.S.  while a l l  Furthermore, a l l the 12 UF treatments from  Standard;  s i x pass the B r i t i s h Standard;  while a l l pass the German Standard.  -ivFrom the results obtained, plantation-grown Gmelina arborea wood from Nigeria, with a s p e c i f i c gravity of 0.41 + 0.027 (as determined), was found suitable for use as construction plywood, core and crossband veneer f o r decorative panel as well as container veneer and plywood. The dominant factor accounting f o r the general trend of low percentage wood f a i l u r e was attributed to veneer surface i n a c t i v a t i o n , r e s u l t i n g from surface aging of veneers.  TABLE OF CONTENTS Page TITLE PAGE  i  ABSTRACT  i i  TABLE OF CONTENTS  \y  LIST OF TABLES  ix  LIST OF FIGURES ACKNOWLEDGEMENT 1.0  \. .  .  xiv  INTRODUCTION  1  1.1  O b j e c t i v e and scope of study  1.2  Background i n f o r m a t i o n on the N i g e r i a n woodbased p a n e l i n d u s t r y  1.2.1  Log s u p p l y s i t u a t i o n  1.2.2  Growth and y i e l d plantations  1.2.3  .  .  .  1  .  .  .  .  .  .  3  .  .  .  .  .  .  3  .  4  o f gmelina i n N i g e r i a n .  Employment  1.2.3122.3.2  .  .  .  .  .  .  . .  .  . .  .  . .  . .  6 6  Value-added  7  1.2.3.3  Development  .  .  .  .  .  .  .  7  1.2.3.4  Export t r a d e  .  .  .  .  .  .  .  8  1.2.4  2.0  .  An overview o f the i n d u s t r y  1.2.3.1  x i i  P r o s p e c t s o f development  .  .  .  .  .  8  1.2.4.1  Domestic consumption o f plywood  .  .  .  8  1.2.4.2  U t i l i z a t i o n o f wood-based p a n e l s  .  .  .  9  LITERATURE REVIEW  11  2.1  G e n e r a l wood p r o p e r t i e s o f gmelina  2.2  Log h e a t i n g  .  .  .  .  .  .  .  .  12  2.3  Log p e e l i n g  .  .  .  .  .  .  .  .  15  2.4  Veneer d r y i n g  .  .  .  .  .  19  2.5  A d h e s i o n and a d h e s i v e s  .  .  .  21  2.5.1  .  . .  .  .  .  A d h e s i o n : Wood bonding t h e o r i e s  .  .  .  .  .  11  21  2.5.1.1  M e c h a n i c a l theory  .  .  .  .  .  .  21  2.5.1.2  A d s o r p t i o n theory  .  .  .  .  .  .  22  -v-  -vi-  Page 2.5.2  A d h e s i v e s : UF and PF r e s i n  2.5.2.1  UF glue  25  2.5.2.2  PF glue  26  2.6  27  F a c t o r s a f f e c t i n g plywood bond q u a l i t y  2.6.1  Glue spread  .  .  .  .  27  2.6.2  Assembly time  .  .  .  .  28  2.6.3  Glueline thickness  2.6.4  Pressing  2.6.5  Degree o f cure  2. 7  .  29  .  .  .  .  .  .  30  .  .  30  Wp:SbmeP.Nat±onalt;P/lywo6d :S.t_n d;ards- and S p e c i f i c a t i o n s r  2.7.1  B r i t i s h Standard  2.7.2  Japanese  2.7.3  German  2.7.4  United States  2.8 3.0  24  adhesives  f  32  .  32  Standard  33  Standard  33  Standard  34  G l u a b i l i t y o f Hardwoods  40  EXPERIMENTAL PROCEDURES 3.1  Experimental design  3.2  M a t e r i a l s and p r e p a r a t i o n  3.2.1  .  .  40  ,  41 41  Wood s p e c i e s c h a r a c t e r i z a t i o n  42  3.2.1.1  Specific gravity  determination  3.2.1.2  M o i s t u r e content  determination  3.2.1.3  D e t e r m i n a t i o n o f the optimum l a t h e s e t t i n g s  42  42  for peeling  43  3.2.2  Logoheating  3.2.3  Log p e e l i n g  3.2.4  Peel-quality evaluation  45 45 46  3.2.4.1  Veneer roughness  3.2.4.2  Veneer t h i c k n e s s measurement  46 46  3.2.5  Veneer d r y i n g  3.2.6  Glues and g l u e mixing  47 47  3.2.6.1  IB-334 Plyophen  3.2.6.2  Monsanto UF 109 r e s i n w i t h EK Hardener  3.2.7  Glue spread  31  .  .  .  .  .  48 49  -viiPage 3.2.8  Plywood panel pressing .  Press Pressure  3.2.8.2  Pressing Temperature and Time  .  .  Test specimen preparation  3.2.10  . .  3.2.10.1  Dry test  3.2.10.2  Vacuum-pressure test  3.2.10.3  Boil-dry-boil-cool  .  . .  .  .  . .  .50  . .  .  Bond quality testing procedures  3.2.11  50  .  50  .  51  .  51  .  51 .  .  test  S t a t i s t i c a l analysis  .  . .  .  .  52  .  .  53  .  .  53  .  .  .  RESULTS 4.1  54  4.2.  .  .  .  .  .  Log heating and peeling  .  .  .  54  .  .  .  55  4.5  UF resin adhesive . .  .  .  PF resin adhesives'  .  .  .  .  56  .  .  ,  56  .  .  .  .  .  56  .  .  .  .  57  .  .  .  .  .  .  57  B o i l - d r y - b o i l test: Shear strength and wood .  .  .  .  .  .  .  .  Analysis of variance  .  .  .  .  4.7.1  F a c t o r i a l analysis  .  .  .  .  4.7.2  Duncan's multiple range test  .  . .  .  58  .  58  .  59 60  5.1  Sample, s p e c i f i c gravity  5.2  Log heating  5.3  Veneer peel-quality Thickness  57 .  DISCUSSION  5.3.1  55  Vacuum-pressure test: Shear strength and wood  f a i l u r e percent . 4.7  .  .  Shear strength and wood  .  f a i l u r e percent . 4.6.2  .  Vacuum-pressure test: f a i l u r e percent .  4.6.1  .  .  Dry test: Shear strength and wood f a i l u r e percent  4.6  .  54  .  Veneer moisture content p r i o r to gluing .  .  .  .  4.4  .  .  .  Veneer peel-quality  4.5.2  .  .  4.3  4.5.1  v  Moisture content and s p e c i f i c gravity of gmelina logs used  5.0  .  3.2.8.1  3.2.9  4.0  .  .  .  .  .  .  . .  . .  .  .  . . .  .  .  60  .  .  60  .  .  61 61  -viiiPage 5. 3.2 5.4  Roughness  ;  61  .  Plywood bond quality  5.4.1  .  .  .  .  62  .  62  Treatment panels bonded with UF glue  5.4.1.1  Dry test: Shear strength and wood f a i l u r e percent  5.4.1.2  .  .  .  .  .  62  .  Vacuum-pressure test: Shear strength and woo< f a i l u r e percent  5.4.2  . .  .  .  .  64  .  65  Treatment panels bonded with PF glue  5.4.2.1  Vacuum-pressure test: Shear strength and woo f a i l u r e percent  5.4.2.2  .  .  .  65  .  B o i l - d r y - b o i l test: Shear strength and wood f a i l u r e percent  5.4.3  .  .  .  .  .  67  .  Probable factors accounting f o r low percentage  69  wood percentage wood f a i l u r e s i n the treatment 5.4.4  Comparison of study results with some National Plywood Standards  5.4.4.2  B r i t i s h Hard Plywood Standards  77  5.4.4.3  German Hardwood Plywood Standard  78  Probable end uses of Gmelina arborea Veneer and .  10..0  .  .  .  78  .  .  78  5.5.2  Core and Crossband veneer f o r decorative .  .  .  .  Construction plywood .  . .  79  .  80  Container veneer and plywood  SUMMARY, SUGGESTIONS FOR FURTHER STUDIES AND CONCLUSION  82  6.1  Summary  .  82  6.2  Suggestions f o r further studies  .  85  .  .  .  .  .  .  . .  . .  .  6;. 3 Conclusion  85  BIBLIOGRAPHY  86  T T  9/0  .  5.5.1  5.5.3  8.0  73  .  73  plywood  7.4T-  .  U.S. Hardwood Plywood Standard  Plywood  7 ft  .  5.4.4.1  5.5  6.0  .  TABLES  100  FIGURES  123'  APPENDICES  13 9  LIST OF TABLES Table 1  Page De'scrriptive 'features of Gmelina arborea logs used for study  2  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  102  .  .  .  .  .  .  .  .  103  Water bath and log temperature changes against time of peeling - 85°C  104  6  Lathe s p e c i f i c a t i o n s for peeling .  7  Peel-quality a t t r i b u t e s : Veneer roughness measurement.  8  Veneer peel-quality s t a t i s t i c s - 1.27mm (0.05 in) Gmelina arborea green veneer  9 10  101  Water bath and log temperature changes against time of peeling - 50°C  5  100  Specific gravity of the Gmelina arborea logs used f o r study  4  .  I n i t i a l and peeling moisture content (%) of the Gmelina arborea logs used f o r study  3  .  .  .  .  .  .  .  Veneer moisture content p r i o r to gluing  .  . .  105  . .  106  107 .  108  Average shear strength and average wood f a i l u r e of 5-ply Gmelina arborea Plywood bonded with Urea - Formaldehyde (UF) glue  11  109  Average shear strength and average wood f a i l u r e of 5-ply Gmelina arborea Plywood bonded with PhenolFormaldehyde  (PF) glue . -ix-  .  .  .  .  .  .  110  -xTable 12  Page Within- and between-panel v a r i a t i o n i n bond quality of 5-ply:Gmelina arborea Plywood bonded with UF glue: Dry test, wood f a i l u r e .  13  .  .  .  .  .  .  Ill  Within- and between-panel v a r i a t i o n i n bond quality of 5-ply Gmelina arborea Plywood bonded with UF glue: Vacuum pressure test, wood f a i l u r e  14  .  .  .  .  112  .  113  .  114  Within- and between-panel v a r i a t i o n i n bond quality of 5-ply Gmelina arborea Plywood bonded with PF glue: Vacuum pressure test, wood f a i l u r e  15  .  .  .  Within- and between-panel v a r i a t i o n i n bond quality of 5-ply Gmelina arborea Plywood bonded with PF glue: B o i l - d r y - b o i l test, wood f a i l u r e .  16  .  .  .  Analysis of variance f o r testing the effects of Peeling Temperature, Glue Spread and Closed Assembly Time on UF glue bond quality i n 5-ply Gmelina arborea Plywood: Dry test  17  .  .  .  .  .  .  .  .  .  115  Analysis of variance f o r testing the effects of Peeling Temperature, Glue Spread and Closed Assembly Time on UF glue bond quality i n 5-ply Gmelina arborea Plywood: Vacuum pressure test  18  .  .  .  .  .  .  .  116  Analysis of variance f o r testing the effects of Peeling Temperature, Glue Spread and Closed Assembly Time on PF glue bond quality i n 5-ply Gmelina arborea Plywood: Vacuum pressure test  19  .  .  .  .  .  .  .  117  Analysis of variance f o r testing the effects of Peeling Temperature, Glue Spread and. Closed Assembly Time on PF glue bond quality i n 5-ply Gmelina arborea Plywood: B o i l dry-boil test  .  .  .  .  .  .  .  .  118  -xi-  Table 20  Page Duncan's multiple range test f o r shear strength of Gmelina arborea Plywood bonded with UF glue  21  119  .  .  120  .  121  Duncan's multiple range test f o r shear strength of Gmelina arborea Plywood bonded with PF glue.  23  .  Duncan's multiple range test f o r wood f a i l u r e of Gmelina arborea Plywood bonded with UF glue  22  .  .  Duncan's multiple.range test f o r wood f a i l u r e of Gmelina arborea. Plywood bonded with PF glue.  122  LIST OF FIGURES Figure 1  Page  Pattern of cut of test samples from logs f o r s p e c i f i c gravity and moisture content determination tests  2  .  .  .  .  .  .  .  .  .  123  Temperature changes within a log, 8 f t long and 7.7 i n diameter: 50°C heating .  3  .  .  .  .  .  .  .  124  Temperature changes within a l o g , 8 f t long and 8.0 i n diameter:  85°C heating  .  .  .  .  .  .  4  Frequency d i s t r i b u t i o n of v i s u a l veneer roughness  5  Dependence of bond quality on peeling temperature  125 .  126  and assembly time i n t e r a c t i o n : UF Dry test (shear strength) -6  .  .  .  .  .  .  .  .  .  127  Dependence of bond quality on peeling temperature, glue spread and closed assembly time interactions: UF Dry  7  test (wood f a i l u r e )  .  .  .  .  .  .  128  Dependence of bond quality on peeling temperature and glue spread i n t e r a c t i o n : UF Vacuum pressure test (shear strength)  8  .  .  .  .  .  .  .  .  129  Dependence of bond quality on peeling temperature and glue spread i n t e r a c t i o n : UF Vacuum pressure test (wood f a i l u r e )  9  .  .  .  .  .  .  .  .  130  Dependence of bond quality on peeling temperature, glue spread and closed assembly time interactions: UF Vacuum pressure test (wood f a i l u r e ) -xii-  .  .  .  .  131  -xiii-  Figure 10  Page  Dependence of bond q u a l i t y glue spread i n t e r a c t i o n : (shear s t r e n g t h )  11  test  assembly  .  on p e e l i n g  . .  .  233  PF Vacuum p r e s s u r e t e s t  time i n t e r a c t i o n : .  .  .  Dependence o f bond q u a l i t y  .  glue spread i n t e r a c t i o n : .  .  .-  .  135  on p e e l i n g  .  temperature and  PF  Boil-dry-boil  .  .  on p e e l i n g  .  .  .  test  .  .  .  and c l o s e d  PF  (wood f a i l u r e )  time i n t e r a c t i o n : .  .  136  .  137  (wood  temperature  test  .  temperature and  PF B o i l - d r y - b o i l .  134  PF  Dependence o f bond q u a l i t y on p e e l i n g assembly  .  temperature,  time i n t e r a c t i o n :  time i n t e r a c t i o n :  Dependence of bond q u a l i t y  .  . . .  (wood f a i l u r e ) .  (shear s t r e n g t h )  failure)  temperature and""  on p e e l i n g  assembly  Dependence of bond q u a l i t y assembly  132  PF Vacuum p r e s s u r e  assembly  test  ..  temperature and  on p e e l i n g  closed  16  .  Dependence of bond q u a l i t y  Vacuum p r e s s u r e t e s t  15  .  time i n t e r a c t i o n :  glue spread and c l o s e d  14  .  (shear s t r e n g t h ) .  (wood f a i l u r e )  13  temperature and  PF Vacuum p r e s s u r e t e s t  Dependence o f bond q u a l i t y closed  12  .  on p e e l i n g  .  Boil-dry-boil .  .  .  .  138  ACKNOWLEDGEMENT The author wishes to express his gratitude to Dr. R. W. Wellwood of the Faculty of Forestry, who kindly arranged for the supply of the gmelina logs used.  His understanding, constant  advice and c r i t i c a l review of the draft made the study possible. Thanks are also due to SNC-Rust Company Limited, Montreal,  Canada for  i t s cooperation i n providing the logs. I am greatly indebted to the Western Forest Products Vancouver, Canada, for being allowed  to use the Laboratory's  Laboratory,  facilities.  Special thanks are due to Dr. W. V. Hancock, Dr. S. Z. Chow and Mr. J . R. T. Hailey (WFPL) for their constant assistance, constructive c r i t i c i s m , and numerous h e l p f u l suggestions work.  throughout the experimental  Dr. Hancock and Mr. Hailey read the thesis draft and made many  valuable comments.  Jack Williams and Les Rozon (Plywood Section, WFPL)  deserve my appreciation for their help during veneer cutting and gluing. Appreciations are also due to Mr. L. Valg, Dr. L. Paszner, and Dr. D. Haley, of the Faculty of Forestry for t h e i r help and assistance. Mr. Valg and Dr. Paszner read the thesis and offered valuable  advice.  I thank Dr. A. Kozak for his advice during the analysis of r e s u l t s ; and Mr. Richard Yang (graduate student) who wrote the programme used. The f i n a n c i a l backing of my employer, the Federal Department of Forestry, Ibadan, Nigeria, has also made the study possible. F i n a l l y , s p e c i a l thanks are due to my wife, Remi, who has p a t i e n t l y endured my absence from Nigeria for two years.  -xiv-  - 1 -  INTRODUCTION 1.1  Objective and Scope of Study This study proposes an hypothesis  that the wood of the  Nigerian plantation-grown Gmelina arborea Roxb. (referred to hereafter by i t s trade name, gmelina) can be peeled into high quality veneer and glued into commercially acceptable plywood. This investigation has been prompted by the publication of the International Union of Forestry Research Organizations i n which the Forest Products Research Laboratory  (IUERO 1973)  (FPRL), Princes Risborough,  England indicated that gmelina wood was an unsuitable plywood species. The research centre obtained i t s sample logs from Thailand, Sarawak and an unspecified A f r i c a n country.  In the same publication, the Centre  Technique du Bois, P a r i s , France reported that gmelina wood i s moderately suited for construction plywood, container veneer and plywood, and inner p l i e s for decorative panels.  The sample logs used by the French research  centre were obtained from the Ivory Coast, i n West A f r i c a .  No published  reports have been found on the g l u a b i l i t y of this wood i n Nigeria. The findings of the FPRL, Princes Risborough, England, are considered of s i g n i f i c a n t importance to the wood-based panels  industry  i n Nigeria f o r two reasons: 1.  The United Kingdom i s the most important single market for a l l wood products export from Nigeria, accounting  f o r about 90%  of the veneer and plywood export i n 1972. 2.  The current objective of management of gmelina plantations, i n  - 2 at least two of the States i n Nigeria, has incorporated future supply of sawlogs and veneer logs (Alade 1970, Enemuoh 1970). In the Western S t a t e \ f o r example, i t i s intended that about 30 trees per acre from the existing and future plantations w i l l be allowed to grow into sawlog and veneerlog sizes concurrent with pulpwood harvesting. To test the proposed-hypothesis, therefore, plywood panels 2 from plantation-grown 'gmelina wood  from Nigeria, w i l l be prepared, and  standard glueline tests w i l l be conducted. production variables w i l l be used: 1. Three l e v e l s of wood peeling 2.  Two adhesive types  3.  Two levels of glue spread  4.  Two closed assembly  The following plywood  temperature  times  Results from this study could serve to indicate whether to accept or reject the s u i t a b i l i t y  of gmelina wood f o r use as plywood.  If results are encouraging, the study could, -have*. arapLmpact?'on . p._§Lntat -onpmanage—entinand gen-the awdo de.ba sedwpariel aindus t ry.linn <•; • •• Nigeria^ •  t  Now comprising three New States - Oyo, Ogun and Ondo after February 1976. The logs used f o r study were part of consignment of logs shipped to SNC-Rus'^ L i l t e d of Montreal, Canada, from Nigeria, f o r pulping studies.  - 31.2  Background Information on the Nigerian Wood-based Panel Industry  1.2.1  Log supply s i t u a t i o n Log supply i s one of the major current problems confronting  the Nigerian wood industries. et. a l . 1966, Wellwood 1966,  Various studies (Okigbo 1964, Eklund Huuhtanen 1975) have indicated the serious-  ness of this s i t u a t i o n i n the forseeable future. supply i s not peculiar to Nigeria.  The problem of log  Grudzinski (1975) has indicated  that this factor has posed a problem.in a l l areas of the world where the plywood m i l l s are f a i r l y concentrated.  Nevertheless, the Nigerian case  has not resulted from i n d u s t r i a l concentration as such but from a limited wood-resource base. The t o t a l land area i n Nigeria i s about 93 m i l l i o n ha of which the productive high forest reserves (the only source of i n d u s t r i a l wood supply) accounts  for only 1.9 m i l l i o n ha or about 2%.  The growth rate  and rate of forest regeneration after logging i s quite low. regeneration.has been inadequate, induce i t (Lowe 1966).  Natural  even where attempts were made to  Bamgbala and.Oguntala (1970) put the timber 33  y i e l d from the natural moist forest i n Nigeria at about 35jmp_per ha. With a rotation of about 50.years in.the high forests, this seemed a low \ figure. Increasing e f f o r t s have been made to improve and restock the forests.  The two methods used to encourage the regeneration and growth  of the economically desirable tree species, are the Tropical Shelterwood System (T.S.S.) and the Enrichment. Planting.  Anakwenze (1966) and  Oseni and Abayomi (1970) have pointed.out that T.S.S. has proved a f a i l u r e in. Nigeria while Igugu and Bamgbala (1970) indicated that  - 4 Enrichment Planting has had l i t t l e success. In view of the foregoing, the long term prospect of wood supply s i t u a t i o n i n Nigeria seems to depend on.the development of plantations of fast-growing species f o r sawlogs, veneerlogs and pulpwoods. As indicated by Fox  (1972), the fast growth of planted trees i s perhaps the  most important advantage of the developing countries.  The Federal and  States governments i n Nigeria seem committed to this concept as evidenced by their forest p o l i c y statements.  Nigeria.has.a vast forest land, as  d i s t i n c t from productive high.forests, that accounts f o r about 35% of the t o t a l land area.  With better land use planning, enough land could  s t i l l e a s i l y be allocated to Forestry f o r a f f o r e s t a t i o n  purposes.  A f f o r e s t a t i o n schemes were started i n Nigeria before 1950. 1950 and 1969,  By  the country had a t o t a l of 7,468 ha and 51,560 ha of  planted areas respectively (Oseni and Abayomi 1970).  The planted area  was estimated to increase, to a t o t a l of 61,548 ha by 1970  (Enabor 1973).  Plantings are being stepped up i n the poorly stocked, highly degraded and the savannah areas of the country with f a s t growing exotic and indigenouss. species.  Gmelina. arborea i s one of the major exotic species  established i n the plantations.  In order to.safeguard the future  supply of timber, Nigeria proposes to establish a minimum of 12,140 ha of plantation, annually.  1.2.2  Growth and y i e l d of gmelina i n Nigeria. LT  Gmelina has.become a popular plantation species i n Nigeria f o r  s i x major reasons: 1.  The seeds are readily available.  - 5 2. . I t i s easy to propagate from seeds and cuttings_. 3.  I t coppices well.  4.  I t shows adaptability to a wide range of s o i l and climatic conditions.  5.  I t i s fast growing and has a b i l i t y to coppice for about 50 years (Scherpe 1968).  6.  I t suppresses the growth of weeds at an early age, thus reducing cleaning and weeding costs. Gmelina grows very well i n Nigeria.  In a 2-year old plantation,  the average g.b.h. (girth at breast height) recorded i s 38.1 cm with a height of 12.2 m(Alade 1970).  In another 7-year old plantation, the  mean g.b.h. of 298 trees thinned per acre i s 35.5 cm with a mean height of 8.5 m (Enemuoh 1970).  Aladejana (1971) also reported a mean g.b.h.  of 88.g cm with a corresponding height of 19p2cm>for 30 randomly selected trees i n another 7-year old plantation.  3 Chittenden et_r-.>al. (1964) quoted a y i e l d of about 84 m  per  ha i n a 12-year old plantation on poor sandy s o i l s . o f the Derived  3 Savannah Zone of Nigeria.  They also reported a y i e l d of about 252 m  per ha on the most favourable Savanna s i t e s and i n the Rain Forest Zone, 10 and 8 years respectively, a f t e r planting.  From studies conducted by  3 the Federal Department of Forestry, Ibadan, a y i e l d of about 184 m  per  3 ha, with a Mean Annual Increment of about 23-27 m  was reported f o r an  8-year old gmelina plantation at Omo Forest Reserve (Modugu 1977).  - 6 1.2.3  An overview of the industry. Nigeria i s a major African producer of wood-based panels. The 3  actual wood-based panels production f o r 1973 was 55,000 m i n the following product  (FAO 1975a)  categories: 3  i) ii) iii)  Hardwood Plywood .  .  .  .  .  .  Veneer Sheets  .  .  .  .  .  .  Blockboard, Laminboard, Battenboard  . Total  45 ,100'  m  1,200 m .  8,700 m  3 3  55,000-m3.  Wood-based industries have played a major role i n the economy of Nigeria, contributing substantially to employment and value - added i n manufacturing.  Since the i n d u s t r i a l survey publications i n Nigeria  have always treated a l l the wood-based industries as a single sector, i t i s d i f f i c u l t to appraise the percentage contribution being made by the wood-based panel industry.  Nevertheless, within the many wood-based  industries of the country, the sawmilling, wood-based panel and the furniture are the most important. I. 2.3.1  Employment The wood-based industries have been the largest employment  sector f o r labor i n Nigeria, apart from agriculture and f i s h e r i e s (Adeyoju 1968).  With a t o t a l employment of 11,910 workers i n 1963, the  wood-based industries accounted f o r 17.5% of the t o t a l employment i n manufacturing.  The t o t a l number of workers employed decreased to 11,240  and 11,540 i n 1967 and 1969 r e s u l t i n g i n a decreased share of 14.6% and I I . 3% respectively, of the t o t a l manufacturing employment. In "spite of these decreases, Enabor (1976), however, indicated that the wood-based industries s t i l l ranked second to the t e x t i l e industries i n the country's  - 7manufacturing employment. 1.2.3.2  Value-added The value-added i n the wood-based industries i n 1963 was  $13.1 m i l l i o n , representing 8.5% of the national t o t a l .  Although by  1967, the value-added.in these industries had increased to $14.5 m i l l i o n , represented id a,reduced share of 5.9% of the value-added i n a l l  it  the manufacturing industries.-. Again an increase to.^$23.4 m i l l i o n by 1970 , accounted for only 4.2% of the national, t o t a l (Enabor 1976).  Rate of  expansion and.level of e f f i c i e n c y have been indicated as some of the factors c o n t r o l l i n g ',,to value-added . in manufacturing within the woodbased industries.  Thus, the. small*»scale of operations and i n e f f i c i e n c y  within the sawmilling .industry could.have s i g n i f i c a n t l y accounted f o r the decreased share of value-added i n manufacturing from the wood-based industries. 1.2.3.3. Development Nigeria's production of wood-based panels began i n 1946 when the f i r s t veneer m i l l was established as part of African Timber and 3  Plywood (A.T.& P)  Company i n Sapele.  For-almost two decades, this was  the only operating m i l l i n the country, producing veneer and plywood f o r export and domestic consumption.  Now, there are four operating wood-  based panel m i l l s i n the country located at Sapele, Calabar, Ologbo and Epe.  Another wood processing complex, having f a c i l i t i e s for veneer and  plywood production i s planned f o r Ondo at an investment of about 3  A.T.& P. accounts for about.40% of Nigeria's production of plywood and as indicated by Wellwood (1966), i t was the largest of i t s kind i n the World, though no longer the most modern.  $20 m i l l i o n .  T h i s proposed m i l l i s expected  to s t a r t p r o d u c t i o n under  the 1976-1980 Development P l a n . 1.2.3.4  Export t r a d e There i s no c o - o p e r a t i v e s e l l i n g and s h i p p i n g of the wood-  based p a n e l s among the f o u r o p e r a t i n g m i l l s undertakes  the shipment of i t s p r o d u c t s .  i n the c o u n t r y .  Each  mill  Export t r a d e has accounted f o r  an i n c r e a s i n g share of the t o t a l wood-based p a n e l s p r o d u c t i o n over years. 1962 about  T h i s averaged  to 1968.  69%  (FAO  1975b) d u r i n g the fe.y^en y e a r p e r i o d of  Export t r a d e was  h i g h e s t i n 1970 when i t accounted f o r  91% of the t o t a l p r o d u c t i o n .  Due  to i n c r e a s e d domestic  consumption,  the share exported has decreased d r a m a t i c a l l y s i n c e then. I t was 45% i n 1971 t r a d e was  and from FAO  expected  the  e s t i m a t e s f o r 1972  to account f o r o n l y about  The main markets f o r veneer Germany, H o l l a n d , Denmark, I t a l y and  and 1973  (FAO  42% and 38%  about  1975b), export respectively.  and plywood are the U n i t e d Kingdom, the U n i t e d S t a t e s of  America.  However, the b u l k of the plywood exported goes to the U n i t e d Kingdom. Veneer and plywood have c o n t r i b u t e d an average  of $2.7  a n n u a l l y , to the N i g e r i a n f o r e i g n exchange e a r n i n g s s i n c e 1964. e a r n i n g s from these commodities account the t o t a l export e a r n i n g s of about (1972), and  $19.4  ( N i g e r i a 1972,  1.2.4  FAO  million  $10.1  f o r about million  27%,  million, Export  24% and 14% of  (1971), $10.6  million  (1973) r e s p e c t i v e l y from a l l wood p r o d u c t s  1974).  P r o s p e c t s of development  1.2.4.1  Domestic consumption of plywood A major p r o s p e c t f o r development of the wood-based p a n e l  - 9 -  industry i n Nigeria l i e s i n t e r n a l l y . for plywood.  There i s currently a booming trade  Apparent plywood consumption increased substantially from  9,000 m 3 i n 1962  to 26,000 m 3 i n 1971,  or an annual growth rate of 12.5%  giving an increase of about  (FAO 1975b). 3  estimated  to increase to 30,000 m  289%  Consumption was 3  and 34,000 m  i n 1972  and  1973  respectively. Of the t o t a l wood-based panel consumption i n 1967 plywood accounted f o r a share of about 64.3% This was  expected to increase, to 71.4%  and  1971,  and 66.7% respectively.  and 72.3%  by 1972  and  1973  respectively. 1.2.4.2 U t i l i z a t i o n of wood-based panels The major use of wood-based panels i n Nigeria i s i n manufacturing, accounting f o r about 50% of the t o t a l annual domestic consumption of veneer and plywood.  Paneling, boat building and wood-based components  j o i n t l y account for about 40%; while the remaining 10% goes into packaging and other forms of uses (Enabor 1972). The furniture industry has contributed a great deal to increased use of wood-based panels i n Nigeria and more furniture m i l l s are proposed for the country.  For the 1970-74 Development Plan Period, the Federal  and States governments  i n Nigeria proposed anrinViestmentmof.Labdutu  $2 million.on two wooden furniture f a c t o r i e s .  This i s considered  — an  incentive f o r further development within the wood-based panel industry. Development may  not .necessa-r-i_yatake" .a form of increased number of  operating m i l l s , but rather that of increased production capacity of the existing ones v i a higher output.  - 10 Enabor (1976) projected a consumption of 102,000 to 132,000 m  3  (r) of wood-based panels i n Nigeria by 1985.  a consumption of 231,000 to 363,000 m  3  S i m i l a r l y , he forecasted  (r) by 2000 A.D.  Even though  forecasts are sometimes erroneous, future consumption of wood-based panels, i n Nigeria, i s indeed anticipated to increase with growth i n 4 population  and higher per capita income.  The country's population increased from 56 m i l l i o n i n 1963, to an estimated 80 m i l l i o n i n 1973.  - 11 -  2.0  LITERATURE REVIEW T h i s l i t e r a t u r e review i n i t i a l l y  covers some o f the most  important p r o c e s s s t e p s i n plywood p r o d u c t i o n i n c l u d i n g : 1.  Log h e a t i n g  2.  Log  3.  Veneer d r y i n g  peeling  A f u r t h e r s e c t i o n o f the review f o c u s e s on adhesion of wood and f a c t o r s a f f e c t i n g plywood bond q u a l i t y as w e l l as some c h a r a c t e r i s t i c s o f the two  adhesives - phenol—formaldehyde  used to make e x p e r i m e n t a l plywood.  (PF) and urea—formaldehyde  Some o f the d i f f e r e n t  (UF)  national  plywood standards and s p e c i f i c a t i o n s used to e v a l u a t e study r e s u l t s ,  are  surveyed. As o n l y l i m i t e d i n f o r m a t i o n i s a v a i l a b l e on the g l u a b i l i t y o f gmelina wood, the c h a p t e r concludes by g i v i n g a g e n e r a l review o f the g l u a b i l i t y of hardwoods.  2.1  G e n e r a l Wood P r o p e r t i e s of Gmelina Gmelina wood i s d i f f u s e porous  and,  as i n d i c a t e d by Esan  f a s t growth does not change the d e n s i t y o f the wood.  Growth r i n g s  v i s i b l e and from s t u d i e s done on the wood grown i n T h a i l a n d (Lamb and N i g e r i a  (Esan 1966), they appeared  to be annual.  appearance i s straw y e l l o w to creamy white  (1966), are 1968)  The wood i n  (Lamb 1968).  He  (Lamb)  f u r t h e r r e p o r t e d t h a t s e l e c t e d samples o f the wood show f i d d l e back m o t t l i n g and a f i n e sheen on q u a r t e r sawn boards. i n d i c a t e d to c o n t a i n a h i g h r e s i n c o n t e n t .  Gmelina wood i s  Sample l o g s from N i g e r i a n  p l a n t a t i o n s were p e e l e d , i n the c o u n t r y , i n t o 2.25  mm  t h i c k veneers f o r  match s p l i n t s .  Veneers were found to be smooth, straight grained and of  medium texture. 'J.  2.2  Log  Heating Heating of logs before veneering i s a conditioning process  (TRADA 1967)  commonly practised i n the hardwood plywood industry.  It  decreases the r a t i o of compressive to t e n s i l e strength of wood thereby giving a more uniform material (Hancock 1977a). Several heating systems have so far been developed.  These  include c i r c u l a t i n g hot water, steam heating, e l e c t r i c a l heating, water/ a i r heating and high pressure heating (Seidel 1952; 1953 , 5  Lickess 1957;  Kubinsky and Sochor 1968).  F l e i s c h e r and Downs  Of/these, hot water  systems of heating are the most commonly practiced i n the plywood industry (Feihl 1972).  Hot water systems give better uniformity compared to steam-  ing, and also ensure freedom from block end s p l i t s (Fleischer 1959; Anon 1968). Heating of logs helps to p l a s t i c i z e the wood for best veneer cutting.  With most woods, the f i b e r s and hard knots present i n the wood  are softened and cutting becomes easier.  F l e i s c h e r (1948), Lutz (1960),  Anon (1968) and Palka (1974) reported that log peeling as a result of p r i o r heating becomes easier and smoother veneers are produced without excessive lathe checks.  Lathe checks, as ascertained by Chow (1974),  contribute i n large measure to reduced shear strength of plywood. Considerable reduction i n damage to lathe knives has been reported, when  O r i g i n a l not seen. Cited from reference of 0. F e i h l  1972.  - 13 peeling heated logs (Lickess 1957; F e i h l and Godin 1975).  Ellwood and  Erickson (1962) reported that there i s loss of moisture by vaporization when logs are steamed p r i o r to peeling.  There i s , generally, loss of  moisture through evaporation, as the heated logs begin to cool a f t e r removal from the heating mediums.  These must have f a c i l i t a t e d the  shorter veneer drying time resulting from heated logs indicated by Anon (1968) and Kollman et. a l . (1975).  Batey (1955) showed that tight  veneers produced from heated bolts reduce plywood face checking. Generally, Nakamichii.:and Konno (1965) pointed out that heating i s essential for hardwoods from which lumber cores are to be cut. The optimum cutting temperature for any wood i s a function of i t s s p e c i f i c gravity, presence of hard knots, tendencies f o r end s p l i t t i n g and color changes (Fleischer 1959).  The heating period  required to obtain such optimum temperature, as w e l l as the rate of temperature changes within the wood to give i t , are functions of the green s p e c i f i c gravity of the wood, the type of vat used for heating and i t s temperature and warm-up period, the i n i t i a l log temperature and diameter, the temperature required within the log as well as the outside a i r temperature (MacLean 1946, Fleischer 1959, Seidel 1952, Nakamichi• and Konno 1965, Altukhov 1965, Garrison 1967, Anon 1968, F e i h l 1972, F e i h l and Godin 1975). As cutting from too cold or too hot logs results i n lower veneer peel-quality, (Feihl and Godin 1975),each wood species therefore cuts best within a c e r t a i n temperature range.  With too low a peeling  temperature, loose or rough veneers are produced (Fleischer 1959; F e i h l and Godin 1970) while too high temperature tends to soften the  - 14 wood excessively thereby resulting In woolly-surfaced veneers. Palka (1974) reported that for most species, with the exception of low density ones (e.g. poplar and western red cedar), peel-quality improves when veneers are cut from logs heated, usually to a temperature range of 49-71°C. Optimum cutting temperatures vary between hardwoods and s o f t woods .  Fleischer (1959) stated that best cutting temperatures i n hard-  wood species are roughly related to the wood density.  Hardwoods of low  s p e c i f i c gravity (^=0.40) are reported to cut well at room temperature (the  s p e c i f i c gravity of Gmelina. arborea used f o r this study f a l l s  within this group of hardwoods).  Medium density hardwoods are reported  to cut well at a temperature of 60°C; while yellow b i r c h i s indicated to cut  best at aet!emperaturefof.babouE171^C.Furthermore,  F e i h l and Godin  (1975) pointed out that soft species such as poplar and basswood cut best at a temperature of about 32°F (0°C). Cutting temperatures have also been correlated to the veneer nominal thickness intended to be peeled i r r e s p e c t i v e of wood-type. Fleischer (1959) indicated that thin veneers of 0.16 cm (1/16 inch) or thinner cut at lower temperatures without serious degrade (the veneer nominal thickness peeled for this study also f a l l s within this group 0.127  cm [1/20 inch]). Many investigators (Fleischer 1948, Grantham and Atherton  1959, Corder and Atherton 1963, Hailey et a l . 1968) have reported on the various effects of heating on veneer cutting. however, conducted on softwood species.  These studies were,  In their study on hardwood species,  Wangaard and Saraos (1959) showed that there was an impressive degree of  - 15 improvement i n the tightness of veneers obtained from white and red lauan bolts heated i n water at about 71°C compared to unheated b o l t s . A l l the foregoing emphasizes the existence of an optimum cutting temperature for each wood.  2.3. Log Peeling One of the aims of rotary cutting of logs i s the production of veneers i n uniform thickness, reasonable tightness and smoothness f o r gluing into plywood. during gluing.  These properties serve to achieve good bonding  As indicated by Bryant et. a l . (1965), poor glue bonds  i n core veneers, as well as excessive panel-thickness v a r i a t i o n , are largely accounted  for by the extent of veneer-thickness v a r i a t i o n .  They  also pointed out that gluing of such veneers requires greater pressures i n panel pressing so as to promote intimate contact between a l l the glued laminates.  Lutz et. a l . (1969) also reported that v a r i a t i o n i n veneer  thickness can cause problems of show-through of the core veneer i n decorative panels. Various studies have revealed that e f f i c i e n t rotary-cutting of logs hinges on many v a r i a b l e s .  These include the log diameter, the  moisture content of the wood, the knife p i t c h angle, the nose-bar openings of the lathe, the lathe conditions and to a certain extent the lathe cutting speed. Log diameter has been found to influence, s i g n i f i c a n t l y , the peel-quality obtained during rotary-cutting of logs (Fleischer 1949). For example, Kovanen (1963) demonstrated that t e n s i l e strength of Finnish b i r c h veneers decreases with decreasing i n i t i a l log diameter.  A similar  - 16 trend was reported by Cade and Choong (1969) i n their study with Southern pine.  From t h e i r study, veneer t e n s i l e strength perpendicular to the  grain improves with increasing;log diameters.  Sivananda et, a l . (1973)  also ascertained that thickness v a r i a t i o n of Vellapine (Vateria, indica) veneers increased at reduced diameters of the logs. For production of veneer of high peel-quality, the lathe has to be accurately adjusted for proper knife angle and adequate nose-bar openings.  Panshin e_t. a l . (1962) and F e i h l and Godin (1963) i d e n t i f i e d  lathe adjustment as a key to proper cutting of thin veneers of uniform thickness.  This adjustment has also been recognised e s s e n t i a l  (Fleischer 1956, Hancock and Hailey 1975) for cutting smooth veneers of uniform thickness. Too. large a knife angle and i n s u f f i c i e n t nose-bar r  pressure were reported to influence veneer thickness v a r i a t i o n (Barefoot and Salehuddin 1962) as well as resulting i n loose and rough veneer (Feihl and Godin 1970). The p i t c h angle (the knife cutting angle) i s the angle the plane of the knife t i p and centre of rotation of /the.'rlathe spindles makes with the knife face (Hancock and Hailey 1975).  Fleischer  (1949),  Wangaard and Saraos (1959), Kovanen (1963), Knospe (1964), Barefoot and Salehuddin (1962) and F e i h l and Godin (1967) a l l refered to the p i t c h angle as a major factor responsible for veneer thickness uniformity. The knife angle used at any p a r t i c u l a r cutting period has been related to the veneer nominal thickness peeled.  Available studies indicated that  the angle should decrease as the veneer thickness decreases.  Hancock  and F e i h l (1976) for example, recommended jaUpixtcfojangle of. 90 30' when peeling veneers thinner than 0.84 mm  (1/30 in.) f o r a l l diameters.  To  - 17 maintain a constant bearing on the k n i f e , i t has also been pointed out that the knife angle should decrease as the diameter of the log being v peeled decreases Holmes 1973).  (Fleischer 1949 and 1956, Kovanen 1963, Palka and  This has been reinforced by Hancock and Hailey  (1977).  Their research study indicates that a modified pitch r a i l with a gradual increase i n rub length gives superior results at small log diameters. For any p a r t i c u l a r wood, there i s an optimum range of pitch angle i n cutting within which veneer peel-quality can be maximised. -Madison (1951) and (1957) found an optimum p i t c h angle of 89°50' and 90°-93° adequate f o r peeling 0.32 cm (1/8 inch) thick Western larch veneer and 0.13 cm (1/20 inch) thick/aspen veneer respectively.  A k n i f e angle of 90° was  indicated adequate (Wangaard and Saraos 1959) f o r cutting veneers of uniform thickness from Philippiah'- white and red lauan.  For most species,  they, and F e i h l and Godin (1970) reported an optimum l e v e l of k n i f e angle varying between 89°31' and 90°30' when peeling 0.32 cm (1/8 inch) thick veneers. Another lathe v a r i a b l e considered to play a dominant role i n determining veneer peel-quality i s the pressure bar compression (Fleischer 1949, Leney 1960, Koch 1964, Palka. 1970, 1970, Lutz 1974).  /  Cumming and C o l l e t t  Fleischer (1949) pointed out that within the range of  nose-bar settings, up to the point where over-compression  of veneer  occurs, increased pressure seemed to r e s u l t i n greater veneer tightness and smoothness.  Barefoot and Salehuddin  (1962) demonstrated that  i n s u f f i c i e n t nose-bar pressure could influence v a r i a t i o n i n veneer thickness when peeling small diameter bolts from woods of A l b i z z i a procera. The h o r i z o n t a l opening  (gap) i s the h o r i z o n t a l distance between  - 18 knife t i p and bar t i p and i t i s the main control on veneer roughness while the v e r t i c a l opening (lead), which controls the veneer thickness v a r i a b i l i t y , i s the v e r t i c a l distance between knife t i p and bar t i p (Hancock and F e i h l 1976). al.  Fleisher (1949), C o l l i n s (1960), F e i h l  et.  (1963), F e i h l (1964), Lutz and Patzer (1966) a l l recognised the size  of the horizontal r o l l e r - b a r openings as an important variable influencing veneer thickness, roughness and lathe check formation.  Lutz and Patzer  (1966) reported that the veneer nominal thickness decreased with a decreased  r o l l e r - b a r gap when cutting Southern pine and yellow-poplar  veneers.  Also from their study, use of smaller gap improved the  smoothness of veneers cut from yellow-poplar.  F e i h l (1964) reported  that the use of smaller gaps result i n smoother but too thin veneers when peeling curly b i r c h logs.  The nose-bar lead i s not as important as  the gap i n determining veneer peel-quality. F l e i s c h e r (1949),however pointed out that suitable veneer cutting i s obtained when the lead i s varied approximately  according to the nominal thickness of the veneer.  Various studies (Madison 1951 and 1957, F e i h l et- a l . 1963, Cumming and C o l l e t t 1970) have shown, however, that there i s an optimum range of gap and lead within which s a t i s f a c t o r y veneer can be obtained. This optimum varies with species as well as veneer nominal thickness. Hancock and F e i h l (1976) indicated that,generally, the gap i s 5 to 15% narrower than the thickness of the veneer being peeled.  They further  indicated that,irrespective of type of bar used during peeling, the gap for a given species and given thickness i s the same as long as the lathe i s i n good working condition. From the l i t e r a t u r e reviewed above, i t i s quite obvious that a  - 19 -  j u d i c i o u s s e l e c t i o n of k n i f e a n g l e , h o r i z o n t a l and v e r t i c a l p r e s s u r e b a r openings w i l l  s e r v e to o p t i m i z e veneer p e e l - q u a l i t y d u r i n g c u t t i n g w i t h  r e s p e c t to s p e c i e s , veneer nominal  "4j  t h i c k n e s s and l o g s i z e .  Veneer D r y i n g D r y i n g ^ o f f r e s h l y cut veneers, when p r o p e r l y c o n t r o l l e d ,  reduces t h e i r m o i s t u r e content t o a l e v e l s u i t a b l e f o r g l u i n g plywood.  The r a t e of veneer d r y i n g i s a f u n c t i o n o f the veneer  m o i s t u r e c o n t e n t , i t s t h i c k n e s s , s p e c i e s , d r y e r temperature, v e l o c i t y and r e l a t i v e h u m i d i t y 1952,  F l e i s c h e r 1953,  1974).  The  veneer, was drying.  into  ( B e t h e l and C a r t e r 1950,  Holden J r . 1956,  initial  itsair  B e t h e l and Hader  M i l l i g a n and.Davies  1963,  Lutz  c o n d i t i o n of p e e l - q u a l i t y , e s p e c i a l l y the t i g h t n e s s of the i n d i c a t e d by B e t h e l and Hader  (1952) to a f f e c t  veneer  Loose p e e l e d v e n e e r s , as they p o i n t e d out, d r y a t a f a s t e r  rate  than t i g h t p e e l e d v e n e e r s . The m o i s t u r e p r e s e n t i n veneer p r i o r to d r y i n g a f f e c t s t o t a l d r y i n g time.  the  As sapwood and heartwood veneer p i e c e s d i f f e r i n  m o i s t u r e c o n t e n t , e f f e c t i v e veneer s e g r e g a t i o n p r i o r to d r y i n g h e l p s to improve  the d r y i n g c o n t r o l  ( C a r r o l l and.Dokken 1970).  where d i s t i n c t i o n between sapwood and heartwood may  be  In hardwoods difficult,  C a r r o l l and Dokken (1970) suggested the use of m o i s t u r e meters to e f f e c t i v e l y a c h i e v e green s o r t i n g .  V a r i a b i l i t y i n m o i s t u r e content of  the d r i e d veneer s h e e t s has been r e p o r t e d as one of the causes of under-cured pressing  and washed out g l u e - l i n e s and p a n e l blow-ups d u r i n g  ( F l e i s c h e r 1958,  Carroll'and~Dokken  Comstock (1971) and W a l t e r s  1970).  (1971) p o i n t e d out that  the  - 20 density of the veneer may be a factor i n the t o t a l drying time because denser woods have slower  drying  time.  :  ~ Bethel and Hader (1952)  reported differences i n the drying time of d i f f e r e n t species.  Fleischer  (1953) also reported that redwood and sweetgum heartwood veneers dried at a s%ower^rateiithaney.el'lw^popl"arerie"artwood. The rate of heat transfer to veneer surfaces during drying was i d e n t i f i e d as an important factor (Comstock 1971, Lutz 1974) i n c o n t r o l l i n g rate of veneer drying. veneer thickness  This rate i s a function of the  (Bethel and Hader 1952, Fleisher 1953).  They also  reported that veneer drying time i s a function of the dryer temperature. The higher the temperature, the more accelerated the drying becomes and the shorter the t o t a l drying time. Drying should, however, be cautiously carried out as excessive drying with too high temperature results i n veneer surface i n a c t i v a t i o n . As defined by Chow (1969a), "surface i n a c t i v a t i o n i s due to the properties of veneer surfaces after thermal treatment whereby their reception of glue i s made d i f f i c u l t " .  Northcott  (1957) and Northcott et, a l . (1959)  pointed out that too high veneer drying temperatures and too long drying time are some of the factors inducing low wood f a i l u r e s i n plywood.  The  i n f e r i o r j o i n t s caused by increased drying temperature and time are pointed out by Currier (1958) to be results of reduced w e t t a b i l i t y of the veneers by the adhesives.  Sisterhenm (1961) also showed that plywood  made from Douglas-fir veneers dried to 232°C (450°F) developed a s i g n i f i c a n t l y lower bond quality compared to those made from veneers dried to a temperature of 191°C (375°F).  Chow et. a l . (1973) further  indicated that overdrying or underdrying of veneers seriously affect the  - 21 bond quality obtained. 'I  C a r r o l l and Dokken (1970) nevertheless reported that surface  i n a c t i v a t i o n occurs not as a result of the use of too high veneer drying temperature but that of overdrying at too high temperature.  According  to them, the.weaker bond quality obtained from such veneers i s due to loss i n strength of wood and not necessarily that of an adhesion.  They  further indicated that veneer surface i n a c t i v a t i o n can be avoided by the use of lower temperature at the dry end of the dryer.  2._5 2.5.1  Adhesion and Adhesives Adhesion: Wood bonding theories Adhesion i n wood i s a complicated phenomenon.  There are many  factors that influence bonding i n wood,and as stated by A l l e n (1967), i t i s often d i f f i c u l t to distinguish which factor i s dominant.  Apart from  the type of adhesive used, j o i n t quality i n an adhesive bond depends on the nature of the substrate and the conditions existing during the bonding process (Collett 1972).  The forces.that cause an adhesive to  wet, spread and attach to the surface of a s o l i d have been ascribed (DeLollis 1968) to chemical bonds, mechanical entanglement, physical and chemical adsorption due to polar groups, e l e c t r o s t a t i c forces of a t t r a c t i o n inherent i n a l l matter and to combinations thereof.  From  D e L o l l i s viewpoint,therefore, i t i s quite obvious that mechanical and s p e c i f i c adhesion are e s s e n t i a l to bonding i n wood. 2.5.1.1 . Mechanical theory Mechanical adhesion i n wood i s effected by anchorage due to penetration into and hardening within c a p i l l a r i e s i n adherend surfaces  - 22 (Bikerman 1961, Heitler. 1966) . Marian and Stumbo (1962a) have indicated that mechanical adhesion c e r t a i n l y exerts an influence i n wood, depending on j o i n t type and condition of surfaces of the adherend members.  They  stated further that rough or damaged surfaces w i l l influence mechanical adhesion but for smooth and undamaged surfaces, the influence i s minimized.  According to Parker and-Taylor (1966), highly polished  surfaces contain small peaks and. troughs.and.so w i l l give l i t t l e adhesion. Patton''. (1970) further stated that surface roughness i s e s s e n t i a l for good bonding.  Experimenting with planed, sanded, sawn and combed maple  wood.samples, Maxwell (1945), however, reported that the planed samples yielded stronger bonds and highest shear strength.  This tends to  disprove the mechanical adhesion theory, advanced by Bikerman  (1947),  which was based.on the inherent roughness of surfaces. In view of these findings, i t i s evident that mechanical i  adhesion alone i s i n s u f f i c i e n t . f o r bonding strength i n wood.  Total  adhesion inwood i s dependent upon mechanical and.specific adhesions (Kollman et- a l . 1975).  Marian.and Stumbo (1962a), i n a p a r t i c u l a r l y  elegant experiment,, indicated.that the physico-chemical forces are mainly responsible f o r adhesion i n wood.  According to them, mechanical  adhesion.only contributes about 10-20% of the total, adhesion strength. 2-.<5_. 1 ..'2 Adsorption theory The basis of this theory i s s p e c i f i c adhesion which results from forces of adhesion-acting-between the molecules of the wood and the adhesive.  As indicated by Marian and Stumbo (1962a), s p e c i f i c  adhesion .is caused by primary valence forces or secondary valence (Van der Waals) forces.  Baier et. a l . (1968) and Zisman (1963)  - 23  -  reported  t h a t the t h r e e requirements n e c e s s a r y  adhesive  joint  f o r developing  a strong  are:  1.  Good w e t t i n g by  the adhesive  liquid.  2.  Solidification.  3.  S u f f i c i e n t d e f o r m a b i l i t y necessary e l a s t i c s t r e s s e s i n the f o r m a t i o n According  a s s i s t spreading  to M a r i a n and  Stumbo  and p e n e t r a t i o n . o f . t h e  to reduce the e f f e c t of the  joint.  (1962b), the w e t t i n g adhesive  of  helps  to  i n t o the wood.  DeBruyne and Houwink (1951) remarked i n t h e i r d i s c u s s i o n of adhesion theory  that wetting  of the s u r f a c e by  r e q u i s i t e f o r good g l u i n g . s u r f a c e and  the adhesive  The  the adhesive  i s a necessary  pre-  mutual a t t r a c t i o n between the wood  ( r e s u l t i n g from the adhesive  power) has  been a t t r i b u t e d  to d i f f e r e n t p h y s i c a l and  1947).  (1972) a s c e r t a i n e d . t h a t the c o v a l e n t bond p l a y s a v e r y  Collett  important  r o l e i n s p e c i f i c adhesion, w h i l e  as of l e s s e r importance.  chemical  wetting  phenomena (DeBruyne  the i o n i c bond was  In t h i s c o n n e c t i o n , t h e r e f o r e ,  molecular  a t t r a c t i o n were s t a t e d by Kollman etfj al_.  important  r o l e i n the adhesion between wood and  identified  the f o r c e s of  (1975) to p l a y  glue.  Zisman  an  (1965)  a l s o remarked t h a t adhesion i s caused-by f o r c e s between m o l e c u l e s i n or near the s u r f a c e of the two p r i m a r i l y of van All spread  and wet  der Waals and  hydrogen bonding  t h a t these  are  type.  the f o r e g o i n g emphasizes, the f a c t t h a t an adhesive  must  w e l l the wood s u b s t r a t e to ensure good bonding s i n c e  f o r c e s t h a t are c a u s i n g  the a t t r a c t i o n between the wood and  o n l y over s h o r t d i s t a n c e s wet  c o n t a c t i n g m a t e r i a l s and  (Zisman 1965).  the g l u e  As i t i s , not a l l l i q u i d s  wood w e l l can form s t r o n g j o i n t s w i t h i t .  In t h i s r e g a r d ,  the  the act that  - 24 i n t e r n a l c o h e s i v e s t r e n g t h o f the adhesive be h i g h i n o r d e r to o b t a i n s t r o n g j o i n t s .  2,. 5.2>.  Adhesives:  UF and PF r e s i n  itself  on s o l i d i f i c a t i o n must _ .  adhesives  Choice and performance of any r e s i n adhesive bonds i n wood v a r i e s w i t h s p e c i e s . Hancock (1966),  for satisfactory  As i n d i c a t e d by N o r t h c o t t and  the s e r v i c e l i f e o f any bond i s dependent on such  factors as: 1.  Conditions of s e r v i c e  2.  Type of glue  3.  Type o f glue  4.  P r o p e r t i e s o f the s u b s t r a t e  joint  I n v e s t i g a t i n g the g l u i n g c h a r a c t e r i s t i c s o f Determa  (Ocotea  r u b r a Mez) Thomas (1959) r e p o r t e d t h a t s a t i s f a c t o r y bonds o f maximum wood s t r e n g t h were e a s i l y o b t a i n e d w i t h the use o f UF, RF and MF g l u e s as w e l l as c a s e i n g l u e . PF g l u e .  On the o t h e r hand, g l u i n g was d i f f i c u l t w i t h ,-"  T h i s , as he explained,was due to the w a x - l i k e  p r e s e n t i n t h e wood.  substances  Thus, the i n c o m p a t i b i l i t y o f the PF g l u e w i t h  Determa c o u l d be due t o d i f f e r e n c e i n p o l a r i t y , which, as Thomas i n d i c a t e d , c o u l d r e s u l t i n the f a i l u r e o f the glue to wet the wood o r p e n e t r a t e adequately. having  However, the concept  of adhesive  and adherent  s i m i l a r p o l a r i t y which was p o s t u l a t e d by DeBruyne, was no l o n g e r  c o n s i d e r e d a p r e c o n d i t i o n f o r t h e f o r m a t i o n of adhesive 1962) . ThusiS; the d i f f i c u l t y encountered  bond (DeBruyne  when g l u i n g Determa wood w i t h  PF g l u e c o u l d have been duesmes0m&e&t$e£tfJS@t6r§^Gerieially, adhesives  PF r e s i n  r e q u i r e a c e r t a i n amount o f water t o r e a c t o r p o l y m e r i z e  - 25 (Hancock 1977b).  Furthermore,  Laidlaw  (1976) remarked t h a t a p a r t  from  c h o i c e o f timber s p e c i e s i n plywood, manufacture, p r o p e r c h o i c e o f adhesives  s e r v e t o determine  withstand environmental  plywood s t r e n g t h as w e l l as i t s a b i l i t y t o  degrading  effects.  UF and PF g l u e s came i n t o commercial use i n the plywood i n d u s t r i e s a t about 1930 (Parker and T a y l o r 1966, Kollman e t . a l . 1975). These two s y n t h e t i c g l u e s have been w i d e l y used  s i n c e then.  A l o t of  m o d i f i c a t i o n s have a l s o been done, e s p e c i a l l y w i t h the UF g l u e to improve upon d u r a b i l i t y and a b i l i t y t o w i t h s t a n d exposures  t o adverse weather  conditions. 2.5.2.1  UF g l u e UF g l u e produces a n e a r l y c o l o r l e s s g l u e l i r i e o .  has  the a b i l i t y . t o cure a t ambient temperatures.  u n s u i t a b l e f o r s e r v i c e c o n d i t i o n s o f h i g h humidity above 60°C (SIRA 1970).  Blomquist  and Olson  The glue a l s o  I t i s , however, and  temperatures  (1957) i n d i c a t e d t h a t  plywood made w i t h t h i s glue s u f f e r s an a p p r e c i a b l e l o s s e s i n j o i n t s t r e n g t h when exposed to temperatures (158°F).  from about 27°C (80°F) to 70°C  B e r g i n - (1958) a l s o s t a t e d t h a t a t a temperature  o f about 70°C  and h i g h e r , d e t e r i o r a t i o n o f the g l u e becomes more r a p i d . r e a s o n s , t h e r e f o r e , UF g l u e i s r e s t r i c t e d to i n t e r i o r Compared to PF g l u e , UF i s d e f i c i e n t durability.  F o r these  uses.  i n long-term  The v i s c o s i t y of the g l u e , i t s degree o f cure and i t s  adhesive f o r m u l a t i o n have been r e p o r t e d to i n f l u e n c e the wood bond d u r a b i l i t y o b t a i n e d w i t h the use.of  the UF g l u e .  Rice  (1965)  i n v e s t i g a t e d the e f f e c t of r e s i n v i s c o s i t y on plywood bond He r e p o r t e d t h a t r e s i n v i s c o s i t y  durability.  (a measure o f m o l e c u l a r weights  and  d i s p e r s i o n ) r e s u l t s i n a more d u r a b l e glue-wood bond.  Steiner  (1973)  f u r t h e r showed t h a t molar r a t i o ranges of Formaldehyde/Urea (F/U) = to  1.8  2.0  y i e l d e d slower bond d e t e r i o r a t i o n under a c c e l e r a t e d a g i n g  c o n d i t i o n s than r e s i n s w i t h F/U  r a t i o i n the range of 1.6  to  1.4.  2.5.2.2 - PF g l u e PF g l u e i s more d u r a b l e . t h a n UF g l u e . for  s e r v i c e c o n d i t i o n s of extreme temperature  (1976) experimented  I t i s quite  suitable  and h u m i d i t y .  Laidlaw  on the bond d u r a b i l i t y of plywood bonded w i t h PF  and UF g l u e s , f o l l o w i n g a p e r i o d of over 18 y e a r s of exposure. t h a t the PF g l u e s used w i t h o u t f i l l e r s  He  found  or extenders o r w i t h o n l y s m a l l  a d d i t i o n of f i l l e r s m a i n t a i n e d an e f f i c i e n t bond.over the p r o l o n g e d  test  p e r i o d s w h i l e the UF g l u e s gave s a t i s f a c t o r y s e r v i c e f o r s h o r t e r periods.  M u l l e r (1953)^ r e p o r t e d t h a t the d u r a b i l i t y of p h e n o l i c wood  g l u e j o i n t s i s c o r r e l a t e d w i t h the wood s p e c i e s used as w e l l as the g l u e l i n e thickness. In  the plywood i n d u s t r i e s , f i l l e r s ,  o f t e n used w i t h the UF and PF g l u e s .  A filler  extenders and hardeners  are  i s used to c o n t r o l the  f l o w of the r e s i n w h i l e the s o l e f u n c t i o n of the extenders i s to reduce the amount o f a d h e s i v e s to be used t o m a i n t a i n . a n e f f e c t i v e Hardeners  are a b l e n d of m a t e r i a l s designed to g i v e optimum working  p r o p e r t i e s and bond q u a l i t y in  (Hill  1952)  and are e s s e n t i a l i n most cases  g l u e mixes. All  of  glueline.  the f o r e g o i n g emphasizes the f a c t t h a t p r o p e r  glue and i t s f o r m u l a t i o n are important f a c t o r s i n g l u i n g  ^ O r i g i n a l not seen.  C i t e d from r e f e r e n c e of Kollman  selection (Bryant and  et , a l .  1975.  - 27 iStensrud •! 1954) i n order to achieve the desired glue j o i n t quality and d u r a b i l i t y (Blomquist 1954).  2.6 2.6.1  Factors Affecting Plywood Bond Quality Glue spreading Proper glue spreading i s essential as i t ensures uniform  d i s t r i b u t i o n of the l i q u i d glue.  In order to obtain good wood-glue  bond, Brown et. a l . (1952) have emphasized that the glue must flow, transfer from spread to unspread surfaces, wet a l l surfaces, penetrate into the wood c a p i l l a r i e s , and s o l i d i f y into a strong substance.  The  flow of the glue i s retarded i f the glue rapidly hardens before pressure i s applied.  Thus, the r a p i d i t y with which the glue begins to set i s of  primary importance.  Penetration i s necessary to produce a strong  mechanical bond but i t should not be excessive, to avoid a starved glueline.  Depending on the adhesive, s o l i d i f i c a t i o n i s achieved by  curing or chemical polymerization, hardening by physical cooling, loss of solvent by evaporation, and g e l l i n g of a dispersed polymeric s o l i d (Collett 1972). Furthermore, the amount of glue spread and the nature of r e s i n formulation varies with respect to the type of glue and wood species.  J a r v i (1967) indicated that heavier glue spreads usually  require more press time.  He also pointed out that the glue mixes f o r  Southern pine require more phenolic r e s i n content than normally used f o r Douglas-fir.  This i s probably due to differences i n the degree of  absorptivity of the two species.  - 28 2.6.2  Assembly  time  In plywood manufacturing, assembly time i s the time elapsing between glue spreading and press closing.  As indicated by Chow et a l . —c<,.—- -  (1973) the assembly time allows f o r some moisture absorption by the veneer and some reduction i n v i s c o s i t y of glue due to moisture l o s s . This serves to ensure that there i s just the right amount of water i n the panel glueline during bond curing. There seems to be a correlation between the maximum assembly time allowed during gluing and the moisture content of the veneer.  At  low veneer moisture content, prolonged assembly time results i n (a starved, glueline condition.  This leads to a s i t u a t i o n whereby i t becomes  impossible for the glue to cure as most of the water i n the glue i s being readily absorbed into the wood while some i s l o s t through evaporation.  There i s thus a lack of cohesive strength i n the glueline and  this results i n low wood f a i l u r e . On the other hand, at higher veneer moisture content, prolonged assembly time i s e s s e n t i a l to f a c i l i t a t e high wood f a i l u r e results.  More so, as i t provides enough time for the excess water i n  the glueline to be evaporated.  For example, Northcott et"•aX. (1959)  reported that short assembly time can induce undercure of phenolic resins thereby producing low wood f a i l u r e . With long open assembly time, the PF r e s i n has been noted to lose much of i t s moisture and shows a darkening i n color as a result (Troughton and Chow 1972).  Martin (1956) attributed t h i s d i s c o l o r a t i o n  to quinone methide formation caused by oxidation.  As indicated by  Chow (1969b), this quinone methide.formation reduces, the number of  - 29 methylol groups present i n the PF r e s i n .  This makes covalent bonding with  wood i n e f f e c t i v e and therefore f a i l s to produce durable glue-wood bonds. However, with the addition of" polyethylene g l y c o l 200 to the PF r e s i n , Troughton and Chow (1972) were able to induce an increased wetting capacity of the glue on the treated wood thereby improving  the bond quality obtained  under prolonged open assembly time. I t has to be indicated that PF glues, generally, require a certain amount of water to ensure favourable curing or polymerization.  2.6.3  Glueline thickness Specific adhesion i n wood requires a strong continuous glueline  i n order to form a strong j o i n t .  Using 36 phenolic resins, Hse (1971)  correlated the glueline thickness to the bond quality produced i n Southern pine plywood.  He reported that surface tension, contact angle and curing  time were related to the glueline thickness within the panels.  According  to him, wet shear strength and percentage wood f a i l u r e increased with increased glueline'thickness. Rice (1965) indicated that too thin gluel i n e s may bring about l o c a t i o n a l starved spots a l l over the glueline. These spots may act as weak points as. well as stress concentration areas, thereby causing bond deterioration. Contrary to these findings, however, Brown et^ a l . (1952) stated that moderate over penetration.of glue, while maintaining a thin, uninterrupted and uniform glueline i s a requirement adhesion.  for mechanical and s p e c i f i c  Thin glueline was also reported best for bond quality i n wood  (Poletika 1943) . 7  Bergin (1969) showed that adhesive strength generally  decreases with an increase glueline thickness. 7  O r i g i n a l not seen.  Cited from reference of J.T. Rice 1965.  - 30 The  theory of c r a c k s  these c o n f l i c t i n g f i n d i n g s .  -  /seems to come i n t o p l a y w i t h regards  T h i c k g l u e l i n e s are viewed t o have a g r e a t e r  p o t e n t i a l f o r c r a c k development. than do account f o r the decreased  2.6.4  t h i n g l u e l i n e s " . t h i s tends to  strength associated with  thick gluelines.  Pressing A p p l i c a t i o n of p r e s s u r e  to the p a n e l assembly a f t e r g l u i n g  promotes good c o n t a c t between the glued veneer s u r f a c e s . p e n e t r a t i o n as w e l l as e n s u r i n g surfaces  (Chow e t . a l . 1973).  the wood, Kennedy kg/cm  I t also aids  good g l u e t r a n s f e r to the unspread veneer Depending on the compressive s t r e n g t h of  (1965) r e p o r t e d a p r e s s i n g p r e s s u r e  2 10.5  to  i n the range of  2 to 14.1  kg/cm  (150-200 p . s . i . ) f o r Canadian grown woods. 2  Freeman (1970) a l s o r e p o r t e d  a pressure  i n the range of 13.0  kg/cm  to  2 14.1  gk/cm  185-200 p . s . i . ) f o r most plywood m i l l s . Thus the amount of p r e s s u r e  used at any  time, seems to be  f u n c t i o n of the wood s t r e n g t h as w e l l as the p h y s i c a l c o n d i t i o n of wood s u r f a c e .  Freeman  (1970) i n v e s t i g a t e d the i n f l u e n c e of  v a r i a b l e s on bond q u a l i t y of Southern p i n e plywood. coarse g r a i n e f f e c t and higher pressures  s u r f a c e roughness induced  d u r i n g the p r e s s i n g time.  percentage wood f a i l u r e ) , as he  He  a the  production  reported  that  by i t might r e q u i r e  Bond q u a l i t y ( i n terms of  indicated, increased with increased  press  pressure. 2.6.5  Degree of The  adhesive  used.  cure  c u r i n g temperature of a g l u e l i n e depends on type of  resin  Chow et. a l . (1973) p o i n t e d out t h a t inadequate c u r i n g :  temperature r e s u l t s i n undercured bonds.  As  they  indicated, this  defect  - 31 can be accentuated by i n s u f f i c i e n t pressing time.  They further reported  that a minimum glueline temperature of about 139°C (250°F) i s necessary to pass the CSA 80% wood f a i l u r e standard with the use of the vacuumpressure-soak test. In his investigation of under-cure of phenolic glue bonds, Northcott (1955) showed that percent wood f a i l u r e was proportional to the degree of cure of the glue used.  Chow and Hancock (1969) revealed  from their simple?sject-rophotometriq method that the degree of cure of phenolic resins i s related to the wood f a i l u r e and shear strength of the tested plywood panels.  Bergin (1965) reported that the rate of cure of  casein glues varies with the curing temperature -7°C to 21°C (20°F to 70°F).  i n the range of about  Rate of cure decreased as the temperature,  decreased. Rudriicki"' (1976) found that the strength and d u r a b i l i t y of PF glue bonds are determined by the curing temperature, the curing time and the amount of hardener used. Generally, the curing process of the plywood panel glueline i s a complex one. As stated by Koch (1972), i t involves properties of the r e s i n and the wood, assembly times, prepressing procedures and hot pressing techniques.  2.7>  Some National Plywood.Standards and Specifications. Plywood bond quality evaluation and. s p e c i f i c a t i o n standards •  vary from one country to another.  While some countries assess plywood  bond by percentage wood f a i l u r e , some.favour shear strength as the major c r i t e r i o n of assessment.  A combination of these two c r i t e r i a i s  being used by the United States Department of Commerce for ^hardwood  - 32 and decorative plywood. Wood f a i l u r e has f o r long been indicated as an impracticable means of judging j o i n t strengths i n plywood.  Truax (1929) stated that  under good gluing conditions, j o i n t strengths are not seriously affected by the percentage wood f a i l u r e developed.  Northcott (1955) remarked that;,  i n order to use percentage wood f a i l u r e to estimate bond strength, there must be a correlation between i t and the shear strength.  However, from  his cleavage test (Northcott 1952) this correlation seemed not to e x i s t . He therefore concluded at that time that the wood f a i l u r e i s of no value i n judging plywood bond quality. The following analysis covers some of the world plywood standards and s p e c i f i c a t i o n s related to bond quality. Details are included i n Appendices 1-4.  2.7.1  British  Standard  The B r i t i s h Standard f o r hardwood plywood does not take into consideration plywood shear strength. of assessment.  Wood f a i l u r e i s the sole c r i t e r i o n  The BS 1455-1963 s p e c i f i c a l l y applies to plywood manufactured  from Tropical hardwoods (Appendix 1). Delamination test i s required f o r the glue bond between i n d i v i d u a l panels.  On the other hand, the adhesion  test  for the four kinds of bonding - WPB, BR, MR and INT (See Appendix 1) i n volves wood f a i l u r e reading.  Wood f a i l u r e i s read off on a Master Scale  of 0 to-10 corresponding to 0 to. 100% wood f a i l u r e . The B r i t i s h  Standard  considers an average wood f a i l u r e reading of 5 (50%) as adequate.  2.7.2  Japanese Standard The Japanese use the Export Standard s p e c i f i c a t i o n f o r  Japanese plywood. Shear strength i s the sole c r i t e r i o n used to assess the  - 33 plywood bond quality... Depending on the type of species used to make the plywood, minimum shear strength required for Japanese woods ranges between 2 2 7 kg per cm (100 p s i ) to about 10 kg per cm (142 p s i ) .  For t r o p i c a l  2 woods, the Japanese require only about 8 kg per cm  (110  > p s i ) minimum  shear strength (Appendix 2). 2.7.3  German Standard Just as with the Japanese standard, the German standard uses the  shear strength as the sole c r i t e r i o n of assessment of plywood bond quality. The standard consists of. a l o t of requirements. to cold-soaking and b o i l i n g cycles...  Some of these are related  The exterior, grade plywood i s 2  designated AW100.  A minimum shear strength of 10 kg/cm  (142 „  psi) i s  required for non-coniferous woods (Appendix 3). 2.7.4  United States Standard The U.S. Department of Commerce voluntary product standard  PS51-71 f o r hardwood and decorative plywood makes use of both the percentage wood failure.and shear strength to assess bond quality of plywood.  The  average wood f a i l u r e f o r a p a r t i c u l a r panel under, test i s q u a l i f i e d by the average shear strength f o r such a panel. cyclic-soak and . c y c l i c - b o i l tests.  Specimens are subjected to dry,  There i s also a specified minimum per-  centage wood failure, for i n d i v i d u a l specimen tested.  For example, f o r an  2 average f a i l i n g load of between 18 to 25 kg per cm  (250 to 350 p s i ) the  minimum wood f a i l u r e of test piece required i s an.average of 30% with each i n d i v i d u a l specimen not having less than 10%.wood f a i l u r e (Appendix 4). Of the four plywood standards reviewed above, i t i s the U.S.,  - 34 B r i t i s h and German standards t h a t w i l l be used to e v a l u a t e r e s u l t s t h i s study.  The U.S. s t a n d a r d i s f a v o r e d because  percentage wood f a i l u r e developed obtained.  from  i t q u a l i f i e s the  a t t e s t i n g w i t h the shear s t r e n g t h  Furthermore, U.S.A. has been an important i m p o r t e r o f veneer  from N i g e r i a s i n c e 1970.  The B r i t i s h standards w i l l be used  B r i t a i n i s the l a r g e s t market f o r N i g e r i a n hardwood plywood.  because The F e d e r a l  R e p u b l i c o f Germany i s another major European, market f o r N i g e r i a n wood products exports.  2.8]. G l u a b i l i t y o f Hardwoods V a r i o u s s t u d i e s have been undertaken  on the g l u a b i l i t y o f  T r o p i c a l and secondary hardwoods i n Europe, North America Some o f these s t u d i e s , as shown below, a r e r e l a t e d w e t t i n g phenomenon on wood Troop  and Japan.  to the e f f e c t s o f  gluability.  and Wangaard  t i c s of 29 t r o p i c a l American  (1950) i n v e s t i g a t e d the g l u i n g  characteris-  woods u s i n g RF and PRF g l u e s .  Assessing  bond q u a l i t y i n terms o f j o i n t shear s t r e n g t h and percentage wood f a i l u r e developed i n the s t a n d a r d b l o c k shear t e s t , they r e p o r t e d t h a t many o f the woods are s u i t a b l e f o r s t r u c t u r a l uses.  Results of t h e i r  study a l s o showed.that shear s t r e n g t h s , and wood f a i l u r e v a l u e s were, i n general, strongly correlated with s p e c i f i c gravity.  Defective surfacing  of the g l u e d m a t e r i a l s and n a t u r e o f t h e i r c h e m i c a l c o n s t i t u e n t s a r e some o f the reasons they suggested f o r some.abnormal r e s u l t s o b t a i n e d w i t h some of the s p e c i e s . Freeman (1959) conducted an experiment o f wood t o i t s . g l u e bond q u a l i t y .  r e l a t i n g the w e t t a b i l i t y  U s i n g 22 hardwoods, he found  that  w e t t a b i l i t y , pH and s p e c i f i c gravity are closely related to glue bond quality.  Glue bond quality improved with increasing w e t t a b i l i t y i n the  high density wood ( 0.80) glued with UF r e s i n adhesive.  With s p e c i f i c  gravity below 0.80, Freeman discovered that wood s p e c i f i c gravity has more influence on bond quality than w e t t a b i l i t y .  He further  indicated  that wood s p e c i f i c gravity, a c i d i t y and w e t t a b i l i t y seem to have potential significance i n wood adhesion. Experimenting with 6 t r o p i c a l hardwoods, Freeman and Wangaard (1960) investigated  the effect of w e t t a b i l i t y of wood on glue-line  behavior of two cold-setting urea resins.  They reported that during the  closed assembly period, glue-line solids content and v i s c o s i t y increase more rapidly i n woods of ..high w e t t a b i l i t y than i n those of low w e t t a b i l i t y . These factors are e s s e n t i a l i n achieving optimum conditions f o r s p e c i f i c gluing operations. Carstensen '(1961) studied  the gluing c h a r a c t e r i s t i c s of  secondary hardwoods, including red alder (Populus trichocarpa  (Alnus rubra Bong.), cottonwood  Torr. and Gray) and aspen (Populus tremuloides  Michx.) as well as some softwood veneers. species,  He reported that within any one  g l u a b i l i t y w i l l vary accordingly because of the wide variations  that exist i n density, surface conditions.  grain configuration,  moisture content and veneer  He attributed the gluing problems encountered to  accumulation of resinous materials.on the veneer  surfaces.  Bodig (1962) studies w e t t a b i l i t y of 5 Philippine mahoganies as related to.their g l u a b i l i t y .  He reported that there i s a high degree of  correlation between the indices of g l u a b i l i t y and w e t t a b i l i t y .  This,  according to him, reinforces the v a l i d i t y of the s p e c i f i c adhesion thesis.  - 36 As he  stated  further, surface  on i t s w e t t a b i l i t y .  He  -  condition  also indicated  of wood has  an important e f f e c t  that i t i s p o s s i b l e  r e l a t i v e g l u a b i l i t y v a l u e s of an unknown s p e c i e s  by  to p r e d i c t  simply measuring  its wettability. R e p o r t i n g on Acacia  the  UF  a f f e c t e d the g e l a t i o n time of the  and  extractives  animal g l u e  glue used to glue the woods. The  oak  (Teak)  c a t e c h u W i l l d . , Narayamurti et,. a l . (1962) showed that  p r e s e n t i n these s p e c i e s and  g l u a b i l i t y of Tectona g r a n d i s L.  g l u a b i l i t y of some C a l i f o r n i a hardwoods i n c l u d i n g  (Quercus k e l l o g g i i Newb.), c h i n k a p i n  madrone (Arbutus m e n z i e s i i Rehd.) was  Pursh) and  black  (Quercus m u e h l e n b e r g i i Englem.),  tanoak ( L i t h o c a r p u s  i n v e s t i g a t e d by Dost and Maxey (1964).  f o u r woods g l u e w e l l w i t h PF r e s i n adhesive and  densiflora  They r e p o r t e d  w i t h e x t e r i o r PVA  that a l l resin  emulsion. Lee from Malaya. he  reported  (1964) s t u d i e d  the g l u a b i l i t y of Gmelina a r b o r e a Roxb.  Even though he worked w i t h a l i m i t e d number of t e s t samples, that  The  the wood showed good g l u i n g  FPRL, P r i n c e s  signmentaof l o g s  properties.  Risborough, England  (1966) i n d i c a t e d from a  from Gambia" t h a t good c o r e s t o c k v e n e e r s - s u i t a b l e  int6i.p,lywood~can -be produced - from-gmelina^woodiwithoutwany p r i o r "  ~J~ Goto  et a l . (1967) i n v e s t i g a t e d  S  w e t t a b i l i t y , pH 18  and  t r o p i c a l woods.  UF  ii)  Glue-joint  glue, The  strength  PF  glue and  following increased  PVA  gluing  heating.  e f f e c t s of s p e c i f i c g r a v i t y ,  percentage of e x t r a c t i v e s on  used to g l u e the woods. i)  the  for  con-  the g l u i n g p r o p e r t i e s  of  emulsion adhesives were  f i n d i n g s were with increase  reported: of s p e c i f i c g r a v i t y ,  There i s a h i g h degree of c o r r e l a t i o n between w e t t a b i l i t y  and  - 37 specific iii)  gravity,  There was no s i g n i f i c a n t r e l a t i o n s h i p between g l u e - j o i n t s t r e n g t h and pH.  iv)  The r e l a t i o n s h i p between g l u e - j o i n t s t r e n g t h and the percentage of e x t r a c t e i t h e r by c o l d o r h o t water i s not s i g n i f i c a n t . Chen. (1970) s t u d i e d the e f f e c t of e x t r a c t i v e removal on  adhesion  and w e t t a b i l i t y o f 8 t r o p i c a l woods.  sodium h y d r o x i d e ,  acetone  Ten p e r c e n t s o l u t i o n s of  and a l c o h o l benzene s o l v e n t s were used.  G l u i n g was a c h i e v e d w i t h UF and RF r e s i n a d h e s i v e s . e x t r a c t i v e removal i m p r o v e d . w e t t a b i l i t y . a n d s u r f a c e thereby  i n c r e a s e d the.pH of the wood  g i v i n g a more f a v o r a b l e bond q u a l i t y .  U s i n g P h i l i p p i n e s .red l a u a n Moriya  He r e p o r t e d t h a t  (Shorea. n e g r o s e n s i s Foxworthy ) ,  et;. a l . (1971) i n v e s t i g a t e d the g l u i n g c h a r a c t e r i s t i c s o f l a m i n a t e d  wood from t h i s s p e c i e s .  RF, PF, UF, PVA emulsion  were used t o . g l u e the wood.  and c a s e i n  adhesives  From the b l o c k shear and d e l a m i n a t i o n  tests  performed, g l u e j o i n t s t r e n g t h was r e p o r t e d to i n c r e a s e w i t h i n c r e a s e i n wood s p e c i f i c  gravity.  Yamagishi and Honma.(1972) r e p o r t e d on mixed use o f two d i f f e r e n t s p e c i e s i n bonding?/  some t r o p i c a l woods u s i n g UF and RF r e s i n  Bond q u a l i t y was e v a l u a t e d d r y and a f t e r c y c l i c treatments delamination tests.  adhesives.  as w e l l as by  They i n d i c a t e d t h a t d i f f e r e n c e of s p e c i f i c  gravity  between two s p e c i e s c o n s i d e r a b l y i n f l u e n c e . t h e glue bond d u r a b i l i t y . The h i g h e r the d i f f e r e n c e , the g r e a t e r the bond q u a l i t y d e g r a d a t i o n . concluded  They  t h a t d i f f e r e n c e i n s p e c i f i c g r a v i t y i n the mix use should be  maintained  w i t h i n +0.12. ..The ,gluing' ;prope_rties of 6 hardwoods from Burma were i n v e s t i -  "  C r j o a i  (17  '  - 38 gated by Chunsi (1973) using PRF, UF and Casein glues..Among the many conclusions reached, he reported that influence of s p e c i f i c gravity on the g l u a b i l i t y of the woods varied with type of glue.  While  the l i g h t e r woods glued e a s i l y with the three glues, the medium density woods glued well with the UF and PRF glues but poorly with casein glue. With a l l three glues, the high density woods glued poorly.  He  concluded  further that glue j o i n t strength increased with increase i n the pH of the wood, i f the influence of s p e c i f i c gravity was six woods he used met with PRF  excluded.  Three of the  the requirements for exterior structural lamination  glue. The FPRL,- Princes Risborough, England, and Centre Technique du  Bois, P a r i s , France (IUFRO 1973)  investigated some aspects of peeling,  drying and gluing of Gmelina arborea Roxb.  The former concluded  that the  wood i s not suitable for use as plywood because of wild grain and poor gluability.  The sample logs used were heated to 85°C p r i o r to peeling.  On the other hand, the Research Centre at Paris  concluded  from  i t s study that gmelina wood glues moderately .well.- There was no. indication as to whether the sample logs were heated p r i o r to peeling or not. Tan  (1974), studied the s u i t a b i l i t y of 9 Malayan hardwoods for  plywood manufacture.  Gluing was  achieved with PF r e s i n adhesives.  He  arrived at the following conclusions: i)  That wood bulk density i s a dominant factor influencing the bonding a b i l i t y of the woods. of 0.64  g/cm  3  , 0.66  g/cm  3  , 0.80  Higher density woods (densities g/cm  3  and 0.88  g/cm  3  respectively)' were found unsuitable for plywood manufacture because of low percentage wood f a i l u r e s developed.  -  ii)  39  -  That t h e r m a l - d e g r a d a t i o n , due.to d u r a t i o n , was  i n c r e a s i n g veneer d r y i n g  s i g n i f i c a n t i n r e d u c i n g bonding  a b i l i t y of the  woods. iii)  That an adhesive f o r m u l a t i o n of h i g h e r v i s c o s i t y used f o r softwoods  was  found n e c e s s a r y to p r e v e n t  than  those  over-  p e n e t r a t i o n of glue. All  the f o r e g o i n g emphasizes the f a c t t h a t bond q u a l i t y  d u r a b i l i t y of plywood bonded w i t h d i f f e r e n t by the wood s p e c i e s i n v o l v e d .  g l u e s are s t r o n g l y  and  influenced  - 40 -  3.0 3.1  EXPERIMENTAL PROCEDURES Experimental  Design  The d e s i g n o f the experiment  included four v a r i a b l e s .  were two g l u e t y p e s , t h r e e p e e l i n g temperatures, two  c l o s e d assembly times.  These  two g l u e spreads and  The e x p e r i m e n t a l s t e p s were as i n d i c a t e d  below: Two g l u e types - phenol—formaldehyde  (PF) and  urea-formaldehyde  (UF) r e s i n a d h e s i v e s . Three veneer p e e l i n g temperatures  - 20°C  ( c o n t r o l ) , 50°C and 85°C.  Two l e v e l s of g l u e spread - a p p r o x i m a t e l y  25 kg/MDGL (55 l b / /  MDGL) and 32 kg/MDGL (70 lb.^/ MDGL). Two c l o s e d assembly t i m e s - 10 and 20 minutes. All  combinations  o f the above v a r i a b l e s gave 24 treatments.  p a n e l s were made under each treatment,  Three  thus g i v i n g a t o t a l of 72 p a n e l s  f o r the study. The veneer nominal  t h i c k n e s s p e e l e d was 1.27 mm  w h i l e the plywood assembly c o n s t r u c t i o n was 5 - p l y . types o f bond q u a l i t y each type o f g l u e . all  t e s t s were used  (0.050 i n )  Furthermore,  two  to e v a l u a t e bond performance f o r  The Dry and Vacuum-Pressure-Soak t e s t s were used f o r  the treatments bonded w i t h UF r e s i n adhesive w h i l e the B o i l - D r y - B o i l -  C o o l and Vacuum-Pressure-Soak t e s t s were used f o r a l l the treatments bonded w i t h PF r e s i n  J  I  Mat  adhesive.  "d p r i .  - 41 3.2  M a t e r i a l s and p r e p a r a t i o n The  l o g s shipped  l o g s used f o r t h i s study were p a r t o f the consignment o f from N i g e r i a to.SNC-Rust L i m i t e d o f M o n t r e a l ,  pulping studies.  They were kept i n cold, s t o r a g e w h i l e  about a y e a r p r i o r to t h e i r use f o r t h i s study. of the l o g s had c o n s i d e r a b l y  Table  23).  i n Montreal f o r  The ends and s u r f a c e s  d r i e d out by the time they a r r i v e d a t the  Western F o r e s t Products L a b o r a t o r y m o i s t u r e content  Canada, f o r  (WFPL), Vancouver (note the lower  v a l u e o f the sapwood compared to the heartwood i n  The l o g s were examined v i s u a l l y on a r r i v a l a t WFPL and 10  l o g s deemed o f reasonable these 10 l o g s  diameters.for  p e e l i n g were s e l e c t e d .  One of  (Log No. 10) was used f o r p r e l i m i n a r y d e t e r m i n a t i o n of  optimum l a t h e s e t t i n g s f o r p e e l i n g w h i l e were used f o r veneer p r o d u c t i o n .  the remaining 9 l o g s  (Nos.  T h e i r diameters ranged between 15.4cm  to 22.9cm (6-9 i n ) ; l e n g t h s were about 2.7m (9 f t ) . They were to water spray  f o r 7 days b e f o r e  (0.8  in).  in).  contained  The sapwood t h i c k n e s s was q u i t e s m a l l and averaged ,20 mm  The l o g s were from a young p l a n t a t i o n because growth r i n g  count put t h e i r ages a t 8 to 12 y e a r s . (0.2  subjected  any t e s t was performed.  S i x out o f the 9 l o g s used f o r veneer p r o d u c t i o n t e n s i o n wood.  1-9)  Bark t h i c k n e s s averaged  5.1mm  Furthermore, presence o f knots ranged between 4 and 8 f o r the  9 logs.  3.2.1  Wood c h a r a c t e r i z a t i o n Before  the l o g s were p e e l e d ,  preliminary investigation into  the s p e c i f i c g r a v i t y arid m o i s t u r e content  o f the samples were conducted  f o r each of the l o g s -Nos- 1-9 from which veneers were o b t a i n e d .  The  - 42 sample's s p e c i f i c g r a v i t y was obtained.  I t was  determine 10 was  taken as an average  of the n i n e  results  a l s o e s s e n t i a l , as p a r t of the p r e l i m i n a r y study, to  the optimum l a t h e s e t t i n g f o r p e e l i n g of the s p e c i e s .  used  3.2.1.1  for this  Log  No.  investigation.  Specific gravity  determination  S p e c i f i c g r a v i t y of each of the n i n e l o g s was  determined  -vblumelmeasur.ement...me.thod_in<.accofdancdawithwthe ASTMAStandards  by  (ASTM  the 1975  No?^143^5 2)v,Fq.ur samples per l o g y i e l d e d a. t o t a l of 36 samples f o r t h e ' ;  s p e c i f i c gravity.determination. samples from a l o g .  F i g u r e 1 shows p a t t e r n of cut of  Both the a i r and o v e n . d r i e d l e n g t h , width  t h i c k n e s s of each specimen were taken.at ends and  c e n t e r of the specimen.  the average 3.2.1.2  test  and  three d i f f e r e n t places —  A l o g s p e c i f i c g r a v i t y i s taken  the as  of i t s f o u r samples.  Moisture  content  The procedure  determination  f o r the d e t e r m i n a t i o n of the m o i s t u r e  content  of each of the n i n e l o g s a l s o f o l l o w e d t h a t of the s p e c i f i c g r a v i t y . I t was  i n accordance  w i t h ASTM standards (A STM 1975;:) .No. ;  D143-52) .  I t must be i n d i c a t e d , however, t h a t the m o i s t u r e the l o g s were determined  p r i o r to p e e l i n g and,  l o g s p e e l e d a t 20°C (ambient heated 3.2.1.3  to 50°C and  temperature) m o i s t u r e  85°C were a l s o determined  f o r the  control  c o n t e n t s of the l o g s  following heating operations.  D e t e r m i n a t i o n of the optimum.lathe s e t t i n g s f o r p e e l i n g A l l p e e l i n g was  done a t " t h e Western F o r e s t P r o d u c t s  Vancouver, on t h e i r e x p e r i m e n t a l . l a t h e equipped Log No.  except  content of  10 which was  l o n g each.  used  f o r t h i s study was  Laboratory,  w i t h a s o l i d nose b a r .  cut i n t o two b o l t s of  Based on p a s t p e e l i n g e x p e r i e n c e s of hardwoods of  1.1m  similar  - 43 veneer thickness (1.27mm), Hailey (1977a), recommended lathe settings of pressure bar horizontal and v e r t i c a l openings of 1.112mm (0.044 in) and 0.254mm (0.010 in) respectively f o r rotary peeling of the f i r s t bolt from l o g No. 10. A p i t c h angle of 89°30' at 25.4cm (10 i n ) was used. The second bolt was peeled with the same settings but with a change i n the p i t c h to 89°30' at 26.7cm (10-1/2 i n ) .  This l a t t e r t r i a l was %  found to improve the quality of the veneer obtained. In summary, therefore, the optimum.lathe settings determined for peeling 1.27mm veneer from Gmelina arborea logs (16.1 - 22.2cm diameter ranges) were presented i n Table 6.'  3.2.2  Log heating P r i o r to the heating operations a disk about 30.5cm (1 f t )  long was cut from one end of each l o g . give more uniform heating.  Logs were grouped by diameter to  For this reason, therefore, log numbers 5,  8 6 and 7, with diameters  of 19.1cm (7.4 i n ) ,  (7.3: in) were used f o r the 50°C heating.  19.7cm (7.7 i n ) and 18.4cm  S i m i l a r l y , f o r the 85°C  heating, log numbers 1, 3 and 9, with diameters of 22.2cm (8.8 i n ) , 21.0cm (8.2 i n ) and 20.3cm (8.0 i n ) were used.  The diameters of the  logs in.each of these two groups were.assumed close enough to ensure the use of the same heating time.  The remaining logs, with diameters of  19.8cm (7.8.in), 16.5cm (6.5 in) and 18.4cm (7.2 i n ) were peeled at ambient temperature of about 20°C. Following the MacLean (1946).procedures on rate of temperature changes i n short-length .round timbers, the i n i t i a l heating time f o r the 8 . . . oSAverageifordrbothiLends;. *-%ra  - 44 50°C h e a t i n g was was  c a l c u l a t e d a t about 8 h o u r s .  S i m i l a r l y , the h e a t i n g  time  c a l c u l a t e d a t about 11 hours f o r the 85°C h e a t i n g w i t h the use of h i s  suggested formulae.  However, due to c e r t a i n f a c t o r s d i s c u s s e d below  u l t i m a t e h e a t i n g time f o r the 85°C h e a t i n g exceeded the c a l c u l a t e d  the  time  by about 8 h o u r s . Logs were heated immersed i n c i r c u l a t i n g hot water w i t h o v e r head s p r a y .  The temperature changes  at the c e n t r e of the l o g s were  determined by means o f c o n t r o l l o g s i n which thermo-couples were inserted.  The d r i l l e d h o l e s , through which the thermo-couples passed,  were t i g h t l y s e a l e d w i t h c o r k s t o p r e v e n t f l o w o f h o t water i n t o the l o g s . Due  to p r o c e d u r a l e r r o r , however, the temperature changes, 25.4mm (1 i n )  from the s u r f a c e s of the c o n t r o l l o g s , were not measured w i t h s i m i l a r uses of thermo-couples.  T h i s was  relationship exists  (MacLean  c o u l d be o b t a i n e d .  The i n i t i a l  not regarded as s e r i o u s s i n c e a  1946) whereby such temperature  changes  temperatures of the c o n t r o l l o g s were  taken one minute a f t e r i n s e r t i n g , the thermo-couples w h i l e the subsequent temperature changes w i t h i n . t h e l o g s were observed a t every  one-hour  interval. The v a t temperature was m a i n t a i n e d a t a l e v e l s l i g h t l y h i g h e r than t h a t r e q u i r e d f o r p e e l i n g .  F o r the 50°C p e e l i n g temperature, the  v a t was m a i n t a i n e d a t about 55°C  (122°F) w h i l e i t was  f o r the 8 5 ° C p e e l i n g  temperature.  about 86°C  Because of p o s s i b l e t e c h n i c a l  (190°F) problems  w i t h the h e a t i n g , a temperature d i f f e r e n c e of + 2°C i n the r e q u i r e d p e e l i n g temperature was viewed as a c c e p t a b l e .  - 45 3.2.3  Log peeling As required for veneer cutting on the lathe, both the heated  and unheated logs were bucked into 1.3 to 1.4m  (51 to 53 in) b o l t s . A l l  nine bolts were rotary cut with the same lathe settings (already determined). Throughout the cutting process, the speed of the lathe was maintained at about 36.6  metresper minute (120 feet per minute). A l l the veneers were t i g h t l y cut.  After peeling, the veneer  sheets were clipped into pieces about 30cm wide (12 i n ) .  To ensure  adequate y i e l d of veneer f o r use, pieces as narrow as 15 to 18cm wide (6 to 7 in) were also preserved. During the peeling, gmelina wood was noted to produce no disagreeable odor.  In appearance, the peeled veneers (from heartwood)  were l i g h t to medium yellow i n color. straight grained.  Veneers were also noted to be  A l l veneer pieces were coded and stored i n moisture  proof p l a s t i c bags.  3.2.4  Peel-quality evaluation According to Hailey et. a l . (1968),.peel-quality i s a technical  term used i n describing or evaluating the e f f e c t of the peeling process on certain'^physical properties - namely; thickness, roughness and looseness - of green veneer sheets.  Since the veneers were peeled thin and  t i g h t , only two measures of veneer peel-quality were selected to evaluate the lathe settings used i n this study with the d i f f e r e n t peeling tures.  tempera-  These were veneer surface roughness and thickness v a r i a t i o n ; and  a l l evaluations were made with green veneer sheets.  - 46 3.2.4.1  Veneer roughnes s Veneer surface roughness was estimated i n terms of the reference  standard maintained at the Western Forest Products Laboratory (Northcott and Walser 1965) i n accordance with Hailey and Hancock (1973) description. A l l the clipped veneer sheets, irrespective of width, were used for roughness 3.2.4.2  test. Veneer thickness measurement Veneer thickness v a r i a t i o n was measured i n accordance with Hailey  and Hancock (1973) description. From each set of veneers obtained from a p a r t i c u l a r peeling temperature, 10 approximately 30 cm wide (12 in) veneer sheets were randomly selectee for veneer thickness measurements. 3.2.5  Veneer drying The choice of the drying procedures used i n this study were based on: 1.  The need to avoid, as much as possible, over- or under-drying  / - _.' '^r-of-tjie.-.yeneer sheetse (Theoef f ects~on_the; resultingl.plywood bond " J were, reviewed in'" Chapter two). 2.  Since t h i r t y days had elapsed between the peeling and drying of the veneer sheets, veneers were regarded to have lost a considerable amount of moisture. This was due to frequent removal of the sheets from the p l a s t i c bags i n which they were kept for roughness and thickness measurements.  3.  The l i k e l i h o o d of much  moisture content v a r i a b i l i t y among the sheets.  Furthermore, no past veneer drying studies of this wood were available V-  to work with. 4.  There was d i f f i c u l t y i n sorting the veneer sheets into moisture content grades with the use of the moisture meter. This was  . ^  due to the thinness of the veneer.  - 47 -  For these reasons, therefore, the conventional high temperature drying method was  avoided. Veneer was  dried i n a forced-air oven, operating at about  152m/  minute (500 ft/minute) a i r speed, while the dryer heating system wascompletely turned o f f .  For every batch-load of veneer i n the oven, 5  wetter and 5 d r i e r pieces were randomly selected and loaded along with the remaihingg sheets at d i f f e r e n t locations i n the oven.  These  10 pieces were continuously weighed until, they reached constant weights. A l l the batch-loads of the three sets of veneer reached constant weights between 5 to 7 hours.  The veneer sheets at this stage were regarded 9  to contain a moisture content i n the range required for gluing. Veneer moisture content checking p r i o r to gluing indicated that the veneer pieces attained an equilibrium moisture content of between 5.5% and regardless of peeling temperature  3.2.6  7.5%  level.  Glues and-glue mixing The two glue types used i n this study - UF and PF - are the  basic resin adhesives used i n the Nigerian veneer and plywood m i l l s . 3.2.6.1  IB-334 Plyophen On the advice of Dr. Chow and Mr. Hailey (Chow 1977, Hailey  1977b) of the Western Forest Products Laboratory, the PF glue chosen was IB-334 Plyophen  (PF IB-334 hereafter).  Afolayan (1974) used this glue  successfully to produce laminated veneer lumber using Canadian hardwood species. Veneers were stacked i n a controlled temperature-humidity (CTH) room operating at a dry-bulb temperature of about 26.7°C (80°F), a dewpoint temperature of about 6.1°C (43°F) and a r e l a t i v e humidity of 26%.  - 48 The PF IB-334 glue was c a l s L i m i t e d , P o r t Moody, B.C.  s u p p l i e d ready-mixed by R e i c h h o l d ChemiI t i s a l i q u i d water s o l u b l e p h e n o l i c  r e s i n , which produces h i g h q u a l i t y e x t e r i o r adhesives bonds f o r the plywood i n d u s t r y .  The  glue was  a l s o claimed to p r o v i d e e x c e l l e n t bonds  at c o m p e t i t i v e p r e s s times, as w e l l as b e i n g t o l e r a n t to c o n d i t i o n s of l o n g assembly times and h i g h ambient and s t o c k The percentage i s 26%  of PF s o l i d s i n the f i n a l mix  as opposed to about 23%.for  Furthermore,  temperatures. of PF IB-334 g l u e  s t a n d a r d PF glue f o r  softwoods.  t h e r e i s twice the c o n c e n t r a t i o n of wheat f l o u r i n t h i s  compared to the average  plywood mix  (See Appendix 5).  n e c e s s i t a t e d a reduced use of extender  T h i s has  mix  thus  i n o r d e r to accommodate the  a d d i t i o n a l wheat f l o u r . The v i s c o s i t y of the r e s i n i s about 370-470 cps H o l d t ) w h i l e . t h e v i s c o s i t y of the g l u e mix was by the manufacturer  1350  (Gardner-  cps at 25°C measured  with.No. 3 s p i n d l e 60 rpm LVF B r o o k f i e l d  The recommended g l u e spread was  27-30 kg/MDGL w h i l e h i g h e r spreads  about 34 kg/MDGL and 38 kg/MDGL can be used depending on how the wood i s ( A i n s l e y 1977)"^.  viscometer. of  porous  The mixing sequence of the PF IB-334 i s  shown i n Appendix 5. 3.2.6.2  Monsanto UF 109  r e s i n w i t h EK Hardener.  U n l i k e the PF IB-334 g l u e , the Monsanto UF 109 Hardener, was mix  glue, using  prepared at the Western F o r e s t Products L a b o r a t o r y .  i s " a s u i t a b l e glue f o r i n t e r i o r softwood.and hardwood plywood.  components of the EK Hardener are u r e a , ammonium c h l o r i d e sodium m e t a b i s u l f i t e , and walnut s h e l l f l o u r .  EK  The The  (NH^Cl),  The urea c o n s t i t u t e s the  P e r s o n a l communication. A i n s l e y i s on the s t a f f of the R e i c h h o l d Chemicals L i m i t e d t h a t s u p p l i e d the g l u e .  - 49 b u l k o f the hardener w h i l e the main f u n c t i o n o f the sodium m e t a b i s u l f i t e is  t o d i s p e r s e the wheat f l o u r .  at  the Western F o r e s t Products L a b o r a t o r y  29.8%  S i m i l a r mix f o r m u l a t i o n o f t h i s g l u e (Rozon 1977) contains, about  o f u r e a formaldehyde s o l i d s w i t h a v i s c o s i t y o f about  2944 cps  measured by No. 3 s p i n d l e a t 30 rpm LVF b r o o k f i e l d v i s c o m e t e r 1/2 hour a f t e r mixing.  The mixing sequence is.shown i n Appendix 6 ( s u p p l i e d by  Hart-z 11977-) . i  3.2.7  Glue  Spread  The  glue was spread a t about 25 kg/MDGL and 32 kg/MDGL  ./as Iftiied fo>- =" make a p a n e l .  v.  A mechanical  apply g l u e to v e n e e r s . difficult  I n a l l cases, f i v e veneers were assembled to g l u e spreader w i t h rubber r o l l s was used to  S i n c e the veneers were p e e l e d t i g h t , i t was q u i t e  to i d e n t i f y the s i d e w i t h the l a t h e checks  The veneers were t h e r e f o r e assembled w i t h o u t side to turn i n s i d e or outside.  F o r the  (the l o o s e s i d e ) .  c o n s i d e r a t i o n f o r which  50°C p e e l e d v e n e e r s , enough  m a t e r i a l s were not a v a i l a b l e f o r use i n a l l the 24 treatments fehe^study?. and  The veneers  from gmelina.wood were t h e r e f o r e used  crossbands w h i l e y e l l o w b i r c h veneers  used  assembled.  o f the same t h i c k n e s s were  3 plywood p a n e l s were  A f t e r g l u i n g e a c h p a n e l was coded and marked w i t h r e s p e c t  I t s g l u e - t y p e , p e e l i n g temperature,  time.  as c o r e s  f o r the p a n e l f a c e s and backs. F o r each o f the 24 treatments,  to  used i n  g l u e - s p r e a d and c l o s e d assembly  - 50 3.2.8  Plywood P a n e l p r e s s i n g  3.2.8.1  Press  Pressure  T r i a l p a n e l s were assembled u s i n g t h r e e l e v e l s of p l a t e n p r e s s u r e s of about 11 kg/cm 18 kg/cm  2  (250 p . s . i . ) .  2  The  (150 p . s . i . ) , 14 kg/cm  2  (200 p . s . i . ) and  t h r e e p a n e l s o b t a i n e d were a s s e s s e d on 2  b a s i s of the plywood k n i f e - t e s t .  the  The p l a t e n p r e s s u r e of 14 kg/cm  (200 p . s . i . ) gave the most f a v o u r a b l e r e s u l t .  A l l the assembled p a n e l s ,  t h e r e f o r e , i r r e s p e c t i v e of g l u e - t y p e , were p r e s s e d w i t h t h i s p l a t e n pressure. 3.2.8.2  P r e s s i n g Temperature and Time F o l l o w i n g i n d u s t r i a l p r a c t i c e , a p l a t e n temperature  was  used  of 127°C  f o r p r e s s i n g . t h e p a n e l s g l u e d w i t h UF r e s i n adhesive and  f o r those p a n e l s .glued w i t h PF r e s i n a d h e s i v e . were p r e s s e d w i t h two p a n e l s per p r e s s opening Monsanto UF  109  glue and  4.5  The  assembled  149°C  panels  f o r 5 minutes w i t h  the  minutes w i t h the PF IB-334 g l u e .  In summary, the f o l l o w i n g s p e c i f i c a t i o n s and p r e s s i n g s c h e d u l e were used when making a t y p i c a l , p a n e l assembly: 1.  F i v e - p l y , w i t h a g l u e spread of 25kg/MDGL or 32 kg/MDGL depending on treatment  2.  Ten minutes or 20 minutes c l o s e d assembly time depending on treatment  3.  combination.  combination.  P l a t e n temperature depending on glue  of about 127°C (260°F) or 149°C type. 2  4.  P r e s s p r e s s u r e of 14 kg/cm  5.  P r e s s i n g time of 5 minutes or 4.5 type and p l a t e n  6.  (300°F)  (200 p . s . i . ) minutes depending on  temperature.  H o t s t a c k i n g of the p a n e l s g l u e d w i t h PF f o r 10  minutes.  glue  - 51 3.2.9  T e s t Specimen P r e p a r a t i o n T e n s i o n - s h e a r specimens from the plywood p a n e l s produced  prepared i n accordance w i t h the requirements  were  o f the CSA and NBS s t a n d a r d s .  Because o f the s m a l l t h i c k n e s s o f the panel's however, d i f f i c u l t i e s were encountered when making grooves the p a n e l s .  on the 7.6cm (3 i n ) wide s t r i p s c u t from  The c i r c u l a r saw i n some cases c u t through the e n t i r e  t h i c k n e s s o f the c o r e - p l y i n s t e a d of the t w o - t h i r d s o f i t s p e c i f i e d .  Test  specimens- o b t a i n e d from such s t r i p s were regarded as " r e j e c t s " and were screened out o f the l o t s a f t e r  cutting.  Specimens were coded by p a n e l o f o r i g i n to f a c i l i t a t e between and w i t h i n p a n e l comparison failure.  Specimens were randomized :Testospecimens  used  i n t h i s study.  to f a i l u r e . . quality  f o r shear s t r e n g t h and percentage wood f o r the two types o f t e s t .  v a r y between 22 and 36 i n a l l the 24 treatments  In a l l , a t o t a l o f 1438 t e s t specimens were s t r e s s e d  Specimens were coded  and marked a c c o r d i n g to type o f bond  t e s t , p a n e l number, g l u e - t y p e , p e e l i n g temperature,  and assembly time.  glue spread  F o r example, a sample d e s i g n a t e d UF-20-55-10  i n d i c a t e s t h a t . t h e sample was from a p a n e l glued w i t h UF r e s i n  adhesive;  veneers were p e e l e d a t 20°C; p a n e l was g l u e d a t a spread o f 551b /MDGL (25 kg/MDGL) and p a n e l assembly was p r e s s e d a f t e r a c l o s e d assembly  time  of 10 minutes.  3.2.10.  Bond Quality"^"*" T e s t i n g Procedures  3.2.10.1  Dry T e s t The UF t e s t specimens were s t r e s s e d to f a i l u r e i n a Globe  Wood f a i l u r e r e a d i n g s , r e g a r d l e s s o f n b o n d - q u a l i t y t e s t i n g method, were based b o t h on g r o s s and f i n e f i b r e wood f a i l u r e s .  - 52 t e n s i o n - s h e a r machine i n accordance was  w i t h the NBS/CSA s t a n d a r d s .  a p p l i e d a t the r a t e of about 272 kg to 454 kg per minute  l b . per minute).  Load  (600 to  1000  The u l t i m a t e shear s t r e n g t h and wood f a i l u r e were  r e c o r d e d f o r each specimen. 3.2.10.2  Vacuum-Pressure T e s t T h i s t e s t was usedhto a s s e s s bond :qual>i>t-yl performance  i n a l l the treatments  used  i n t h i s study, i r r e s p e c t i v e of g l u e - t y p e . As  i n v e s t i g a t e d by Chow and Warren (1972), found was  to be.on a par w i t h the c y c l i c c o l d - s o a k t e s t .  -  The vacuum a p p l i e d  about 63.5cm (25 i n ) of mercury w h i l e the a i r p r e s s u r e a p p l i e d was  i n the. range>of about 4.6-4.9 kg/cm The was  the vacuum-pressure t e s t was  2  (65-70 p . s . i . ) .  e f f i c i e n c y of water p e n e t r a t i o n i n t o the t e s t  not i n v e s t i g a t e d i n s o f d e r to j u s t i f y  30 minutes as was  specimens  the use of a c y c l e g r e a t e r than  the case w i t h Tan's study  (Tan 1974).  T h i s was  h i s study i n v o l v e d the use of denser Malayan hardwoods whereas i s a low to medium d e n s i t y h a r d w o o d . ( s p e c i f i c g r a v i t y = 0.41). 30-minute c y c l e was  t h e r e f o r e viewed adequate.  because  gmelina The  Evidence of adequate  water p e n e t r a t i o n seemed to be p r o v i d e d by the wide d i f f e r e n c e s shown by the w o o d . f a i l u r e r e s u l t s between the d r y and vacuum p r e s s u r e t e s t s o f the treatments bonded w i t h UF g l u e ((Table.; lOO}.. Specimens were sheared w h i l e wet machine used  f o r the dry t e s t .  the wood f a i l u r e was overnight.  The  on the same Globe  shear s t r e n g t h was  e v a l u a t e d a f t e r oven-drying  by the water.  recorded while  the sheared  T h i s served to prevent r e a d i n g e r r o r s due  testing  to the  specimens darkening  - 53  -  3.2.10.3. B o i l - d r y - b o i l T e s t The  t e s t specimens glued w i t h PF r e s i n a d h e s i v e , were  s u b j e c t e d to b o i l - d r y - b o i l t e s t i n accordance standards.  The  room temperature  specimens were sheared wet i n water.  w i t h DIN68705 and  a f t e r h a v i n g been c o o l e d to  Shear s t r e n g t h was  and,as b e f o r e , wood f a i l u r e was  CSA  r e c o r d e d f o r each specimen  read a f t e r d r y i n g the sheared  specimens  o v e r n i g h t i n an oven.  3.2.11  S t a t i s t i c a l Analysis F a c t o r i a l . a n a l y s i s , was  t i o n of the main and  performed  to f a c i l i t a t e  the  i n t e r a c t i n g e f f e c t s that could evolve.  interpretaTreatments  were a n a l y s e d w i t h r e s p e c t to g l u e - t y p e as w e l l as type of bond t e s t used.  Shear s t r e n g t h and wood f a i l u r e were a n a l y s e d s e p a r a t e l y . A l s o based  on the a d v i c e of Dr. Kozak, F a c u l t y . o f F o r e s t r y ,  an a n a l y s i s of v a r i a n c e was  performed, f o r both the shear s t r e n g t h and  wood f a i l u r e a c c o r d i n g to type of t e s t . show the comparative  I t was  applied.  hoped t h a t t h i s would  performance of a treatment w i t h the o t h e r s . Where  s i g n i f i c a n t d i f f e r e n c e s were found, Duncan's New was  quality  M u l t i p l e Range t e s t  In order to f a c i l i t a t e e a s i e r f a c t o r i a l a n a l y s i s of  (Kozak 1977), the same number, of t e s t specimens was treatments. specimens was  used  results  i n a l l the  T h e r e f o r e , the treatment w i t h the s m a l l e s t number of used  as a s t a n d a r d w h i l e the same.number of specimens were  randomly s e l e c t e d , from the o t h e r treatments w i t h the use of a T a b l e of random numbers.  Thus, 22 specimens, per treatment were used  f a c t o r i a l a n a l y s i s of v a r i a n c e .  f o r the  - 54 4.0 4.1  RESULTS Moisture content and s p e c i f i c gravity of gmelina logs used The i n i t i a l and.peeling moisture contents (MCs) of the log  samples used are presented i n Table 2. sapwood, heartwood and corewood.  Values are shown separately f o r  The sapwood initial.-MCsv are consistently  lower than those of the heartwood i n a l l the 9 logs.  MC values are i n  the ranges of 41% to 107% and 67%.to 147% f o r the sapwood and heartwood respectively.  The MC of the sapwood increased f o r three of the s i x  heated logs while the heartwood MC decreased for four of the s i x heated logs.  Nevertheless, the sapwood MCs? at peeling are s t i l l  consistently  lower than those of the heartwoods i n a l l the logs. The average log s p e c i f i c gravity (sp.gr.) as w e l l as mean and standard deviation of gmelina sample logs.used, i s given i n Table 3. The sp.gr. values f o r the 9 logs are based on ovendry weight and green volume and are i n the range of 0.37  to 0.44.  This gives a sample mean of  0.41  with a standard deviation of 0.027.  4.2  Log heating and peeling The water bath temperature  changes as well as  changes within.the log at positions.2.5cm  temperature  (1 in) and 10.2cm (4 in) from  the log surface are shown i n Tables4 and 5 f o r the 50°C and 85°C (+2°C) heating, respectively. (Fig.) 2 and 3.  These changes are shown graphically i n Figures  The logs heated to 50°C (+2°C) attained that  temperature  at the calculated heating time of 8 hours (hr) while those heated to 85°C (+2°C) attained that temperature  at a heating time of 19 hrs  - 55 instead of the calculated time of 11 hrs. The lathe specifications.used for veneer cuttingare presented in Table 6.  4.3  Veneer peel-quality The frequency d i s t r i b u t i o n . o f v i s u a l roughness measurements i s  given i n Table 7 for the.veneers peeled from the control bolts  (20°C)  and bolts heated to 50°C and to 85°C, and i s . g r a p h i c a l l y presented i n F i g . 4.  The mean, maximum, minimum, standard deviation and range are  presented.in Table 8 for each of the veneer peel-quality attributes measured; namely veneer thickness and veneer roughness.  Veneer thick-  nesses were derived.from 10.specimens .each f o r the veneers peeled from the control bolts (20°C) and bolts.heated to 50°C and 85°C.  On the  other hand, the veneer roughness values, were derived, from 175, 194 and 173 specimens for the veneers peeled from the control bolts (20°C), bolts heated to.50°C and bolts heated.to.85°C  respectively.  Results show  that peel-quality was best for the veneers peeled from the control bolts (20°C) while bolts heated to 85°C produced the roughest veneers.  4.4  Veneer moisture.content p r i o r to gluing Table 9 shows the MC of the 10.pieces of veneer checked p r i o r  to gluing as well as the average MC f o r the 10 pieces. are 6.6%,  These averages  6.4% and 6.4% for the veneers .peeled from the control bolts  (20°C) and bolts heated to 50°C and 85°C respectively.  These values give  no i n d i c a t i o n of overdrying of veneers with.the use of the forced-air drying technique.  - 56 4.5  UF r e s i n a d h e s i v e  4.5.1  Dry t e s t : Shear s t r e n g t h and wood f a i l u r e p e r c e n t T a b l e 10 summarizes the average.shear s t r e n g t h and percentage  wood f a i l u r e f o r the 12 treatment combinations of: p e e l i n g (PT) , g l u e spread  (GS) a n d - c l o s e d assembly  time  (AT).  temperature  Individual  specimen minimum wood f a i l u r e i n . each treatment combination i s a l s o shown, as w e l l as treatment codes used i n the study. f a c i l i t a t e comparison o f bond, q u a l i t y  T h i s was done to  r e s u l t s w i t h the U.S. Plywood  Standard. Plywood p a n e l s made .from veneers p e e l e d a t 85°C ( u s i n g a GS o f 70 lb/MDGL and an AT o f 20 m i n ) produced r  the h i g h e s t shear s t r e n g t h o f  389 p s i ; w h i l e those made from veneers p e e l e d a t 20°C (using a GS o f 55 lb/MDGL and an AT 20-min ) produced ;:  f a i l u r e o f 70%.  the. h i g h e s t percentage wood  G e n e r a l l y , bond q u a l i t y  i s best, a t the PT o f 20°C.  The mean, maximum, minimum and.range.of f o r each o f the t h r e e p a n e l s produced treatments a r e p r e s e n t e d i n Table.12.  f o r testing  percentage wood f a i l u r e i n each of the 12  Large v a r i a b i l i t i e s i n bond  quality,  w i t h i n and between the p a n e l s , a r e noted.  4.5.2  Vacuum-pressure t e s t : Shear s t r e n g t h and wood f a i l u r e p e r c e n t The average shear s t r e n g t h and percentage wood f a i l u r e f o r the  12 treatment combinations o f PT,.GS. and A T . s u b j e c t e d t o t h i s t e s t a r e also  shown i n T a b l e 10. S i m i l a r , to the d r y t e s t , plywood p a n e l s made from veneers  p e e l e d a t 8 5 ° C ( u s i n g a GS.of 70 lb/MDGL and an AT o f 20 min ) produced :  the h i g h e s t shear s t r e n g t h o f 307. p s i ; w h i l e those made from veneers  - 57 peeled at 20°C (using a GS of 55 lb/MDGL and an AT of 20 min ) produced the highest percentage wood f a i l u r e of 59%. best at the PT of 20°C.  Generally, bond quality i s  There i s also a large v a r i a b i l i t y i n bond  quality within and between panels as shown i n Table 13.  4.6  PF resin adhesives  4.6.1  Vacuum-pressure test: Shear strength and wood f a i l u r e percent Table 11 shows the average shear strength and percentage wood  f a i l u r e f o r the 12 treatment combinations of PT, GS and.AT. The minimum wood f a i l u r e percent f o r each test specimen i s also shown as w e l l as treatment codes used. Plywood panels made from.veneers peeled at 85°C (using a GS of 70 lb/MDGL and an AT of 20 min. ) produced the highest wet shear strength of 405 p s i ; while those made from veneers peeled at 50°C (using a GS of 70 lb/MDGL and an. AT of 20 min.) produced the highest percentage wood f a i l u r e of 64%.  Generally, panels.made from veneers  peeled at 20°C give ah impressive bond quality. The mean, maximum, minimum and range of percentage wood f a i l u r e f o r each of the three panels produced f o r testing i n Table 14. used.  are presented  Values are shown separately f o r each of the 12 treatments  Large v a r i a b i l i t i e s i n bond q u a l i t y , within and between panels,  are noted.  4.6.2  Boil-dry-boil  test: Shear strength and wood f a i l u r e percent  The average shear strength and percentage wood f a i l u r e f o r the 12 treatment combinations of PT, GS and AT are also summarized i n  - 58 Table 11.  The minimum wood f a i l u r e percent f o r each test specimen i s  also shown i n order to f a c i l i t a t e comparison of bond quality  results  with the U.S. Plywood Standard. In this test, plywood-panels.made from.veneers peeled at 85°C ' • (using a GS of 70 lb/MDGL and an AT of 20 min„) produced  the highest  shear strength of 334 p s i ; while those made from veneers peeled at 50°C (using a GS of 70.1b/MDGL and an AT of. 20 min .) produced  the highest  percentage wood f a i l u r e of 66%. The mean, maximum, minimum and .range of percentage wood f a i l u r e for each of the three panels produced.for testing are presented i n Table 15.  Values are shown separately f o r each.of the 12 treatments  used.  Large v a r i a b i l i t i e s i n bond quality., within and between panels, are also noted.  4.7  Analysis of variance  4.7.1  Factorial  analysis  The results of the dry test shear.strength and percentage wood f a i l u r e f o r the.treatment panels, bonded with UF glue ( f a c t o r i a l analysis) are summarized i n Table 16; showing the s i g n i f i c a n t main and interacting effects at the 0.01 and 0.05 l e v e l s .  A l l . the s i g n i f i c a n t interacting  effects are graphically depicted i n F i g . 5 and 6. S i m i l a r l y , Table 17 summarizes the f a c t o r i a l analysis  results  of the vacuum-pressure test shear.strength and percentage wood f a i l u r e for the treatment.panels bonded.with UF glue.  The.significant  acting effects at 0.01 and 0.05 levels.are graphically to 9.  inter-  depicted i n F i g . 7  - 59 The r e s u l t s  o f the vacuum-pressure t e s t shear s t r e n g t h and  percentage wood f a i l u r e f o r the p a n e l s bonded w i t h PF g l u e a r e p r e s e n t e d i n T a b l e l o y ' showing the s i g n i f i c a n t main and i n t e r a c t i n g 0.01 and 0.05 l e v e l s . graphically  All.the  significant interacting  e f f e c t s a t the  e f f e c t s are  d e p i c t e d i n F i g . 10 to 13.  T a b l e 19 shows the f a c t o r i a l a n a l y s i s r e s u l t s o f the B o i l - d r y b o i l t e s t shear s t r e n g t h , and percentage wood f a i l u r e f o r the treatment p a n e l s bonded w i t h PF g l u e . t h i s r e s u l t are graphically  4.7.2  A l l the s i g n i f i c a n t i n t e r a c t i n g d e p i c t e d i n . F i g . 14 to 16.  Duncan's m u l t i p l e range t e s t The  r e s u l t s o f the. Duncan's m u l t i p l e range t e s t f o r d i r e c t  comparison o f the average  shear s t r e n g t h and percentage wood f a i l u r e  are p r e s e n t e d i n T a b l e s 20 and 21 f o r the treatment UF g l u e  effects i n  (Dry t e s t and Vacuum-pressure t e s t  p a n e l s bonded w i t h  respectively).  S i m i l a r l y , r e s u l t s a r e shown i n T a b l e s 22 and 23 f o r the treatment b o i l test  p a n e l s bonded w i t h PF g l u e respectively).  (Vacuum-pressure t e s t and b o i l - d r y -  - 60 -  5.0 5.1  DISCUSSION Sample s p e c i f i c gravity The mean sp. gr. of 0.41 + 0.027 found for the Nigerian  plantation-grown gmelina logs used i n this study compares favourably to a value of 0.41 + 0.060 reported by Nokoe-Sagary (1972) f o r Nigerian plantation-grown gmelina samples.  Lamb (1968) also reported a nominal  sp. gr. of 0.407 - 0.427 and 0.42 for work done on Gmelina arborea samples from Gambia and Malaysia respectively.  Furthermore, IUFRO (1973)  reported a sp. gr. value of 0.40 for Gmelina arborea samples from Thailand and Sarawak. The mean sp. gr. value of 0.41 +0.027 of this study, makes veneer and plywood produced.from.Gmelina  arborea wood suitable f o r  various end uses (elaborated further in_the discussion).  5.2  Log heating Because of technical problems with the heating, logs numbered  1, 3 and 9 did not a t t a i n a temperature of 85°C (+ 2°C) required f o r t h e i r peeling at the calculated time of 11 hr, but rather at an extended time of 19 hr.  The temperature regulator of the vat. had to be adjusted  several times before i t was able to give the required temperature.  The  question of overheating the log f o r the 19-hour period did not arise f o r two reasons: 1.  The water bath temperature did not at any time a t t a i n a tempera. ture of 85°C (+ 2°C) u n t i l 18-19 hr. heating period.  2.  The temperature within the log cannot exceed that of the  - 61 heating medium.  The logs can therefore not attain a tempera-  ture of 85°C (+ 2°C) required f o r t h e i r peeling without the vat maintaining that temperature.  5.3  Veneer peel-quality  5.3.1 Thickness As shown i n Table 8.9, the average veneer thicknesses were 1.25 mm, 1.22 mm and 1.19 mm; with standard deviations of 0.08 mm, 0.10 mm and 0.05 mm for the control bolts (20°C), bolts heated 8 hr, (to 50°C) and bolts heated 19 hr., (to.85°C) respectively.  These averages  are s l i g h t l y below the objective veneer nominal thickness of 1.27 mm (0.05 in) by about 2%, 4% and 6% respectively.  Even though the average  veneer thickness i s lowest at 85°C PT, thickness v a r i a t i o n i s under best control because of i t s smallest.range compared to the other PTs. Generally, results show that veneer thickness v a r i a t i o n i s under good control as the three means are equal at the 0.05 l e v e l .  5.3.2  Roughness As s i m i l a r l y shown in. Table 28, the average veneer roughnesses  were 0.15 mm, 0.21 mm and 0.24 mm f o r the control bolts (20°C), bolts' heated 8 hr, (to 50°C)and bolts heated.19 hr. (to 85°C) with standard deviations of 0.05 mm, 0.07 mm and 0.06 mm respectively.  The correspond-  ing veneer, roughness ranges are 0.12 mm,..0.38 mm and 0.38 mm f o r the three veneer PTs.of 20°C, 50°C and 85°C.  On the basis of these average  and range values, the logs peeled at 20°C give the best veneer results.  smoothness  Generally, veneer roughness i s very good and well within the  - 62 l i m i t s for high quality veneer. In view of the above, therefore, i t can be stated that v a r i a t i o n i n thickness and roughness of veneer were not improved by heating the gmelina bolts to temperatures of 50°C and 85°C p r i o r to peeling. Measurements by the v i s u a l roughness method indicated increased roughness at high PTs.  Kinoshita. and Ohira. (1971), McMillin (1958) and F e i h l (1964)  reported from.their studies on certain hardwoods (Philippine red lauan and yellow birch) that.improved veneer peel-quality was obtained when these woods were heated p r i o r to peeling.  Madison  (1957), however,  indicated that heating of quaking aspen (Populus tremuloides) and big tooth aspen (Populus grandidentata) bolts above room temperature increased the fuzziness of the veneer surfaces.  5.4  Plywood bond quality  5.4.1  Treatment panels bonded with UF glue  5.4.1.1  Dry-test: Shear strength and wood f a i l u r e percent The dry test shear strength results of the f a c t o r i a l analysis  shown i n Table 16 indicate that the PT and the GS are highly s i g n i f i c a n t factors ( i . e . s i g n i f i c a n t at the 0.01 l e v e l ) . PT and AT i s significant, at the 0.05  level.  The i n t e r a c t i o n between The presence of this i n t e r -  action obscures any interpretation that could have been made on the main effects. to F i g . 5.  This i n t e r a c t i o n may be more c l e a r l y understood by r e f e r r i n g At the PT of 20°C, AT of 10 and 20 min. have n e g l i g i b l e  influence on the shear strength of. the treatment panels bonded with UF glue.  At the PT. of 50°C, however, prolonged AT of 20 min  lower shear strength.  results i n  A mild effect i s produced at the highest PT of  - 63 85°C with the AT of 20 min. producing a higher shear strength. Generally, plywood panels made from veneers cut at the PT of 85°C produce^the highest shear strength at both l e v e l s of AT thus giving the most favourable bond quality on the basis of shear strength. At 2 this PT, the shear strength of about 28 kg/cm  (398 p s i ) given by the  treatment combination of Spread 70 - Time 20 i s not s t a t i s t i c a l l y s i g n i f i c a n t at the 0.05 l e v e l from the dry shear strength of about 2 2 26.8 kg/cm (381 p s i ) and 25.5 kg/cm (362 p s i ) given by the treatment combinations of Spread 70 - Time-10 and.Spread 55 - Time 10 respectively. 2 The lowest dry shear strength of about 21.5 kg/cm  (306 p s i ) i s given  by the treatment combination of Spread 55 - Time 10 at the PT of 20°C. From the f a c t o r i a l analysis for wood f a i l u r e shown i n Table 16, the PT and the interaction of PT with GS and AT are highly s i g n i f i c a n t . This i n t e r a c t i o n i s better depicted i n F i g . 6.  Except f o r the treatment  combination of Spread 70 - Time 20, bond q u a l i t y , i n terms of percentage wood f a i l u r e , i s consistently reduced at the higher PT f o r the remaining treatment combinations of Spread 5 5 - Time 10, Spread 55 - Time 20 and Spread 70 - Time 10 respectively.  Generally, bond quality (in terms of  percentage wood f a i l u r e ) i s best f o r the plywood panels made from veneers cut at the PT of 20°C. As shown i n Table 21,. treatment UF-20-55-20 produced the highest percentage wood f a i l u r e of 70%, which i s not s i g n i f i c a n t l y d i f f e r e n t at the 0.05 l e v e l from the percentage wood f a i l u r e s of 62% and 61% produced by treatments UF-20-70-10 and UF-50-70-20 respectively. lowest percentage wood f a i l u r e i s produced.by  The  treatment UF-85-70-10.  - 64 5.4.1.2  Vacuum-pressure test: Shear strength and wood f a i l u r e percent The f a c t o r i a l analysis results f o r the shear strength samples  of the UF glued panels, subjected to vacuum-pressure test, follow the same pattern as the dry test. significant  As.shown i n Table 17, the PT i s highly  (0.01 l e v e l ) whereas the GS i s s i g n i f i c a n t at the 0.05 l e v e l .  The i n t e r a c t i o n between the PT and GS i s highly s i g n i f i c a n t .  As depicted  i n F i g . 7, bond q u a l i t y , i n terms of wet shear strength, i s s l i g h t l y affected at both spread levels of 55 lb/MDGL and 70 lb/MDGL at the PT of 20°C and 85°C respectively.  While wet shear strength i s s l i g h t l y higher  with the higher spread at the PT of 20°C, the lower spread, on the other hand, gives a s l i g h t l y higher shear strength at the PT of 85°C.  The  lower spread also gives higher shear strength at the PT of 50°C. Generally, plywood panels made from veneers cut at the PT of 85.°C, produce the highest shear strength values at the two spread l e v e l s . As shown i n Table 20, the highest shear strength of about 22.4 kg/cm  2  (319 p s i ) given by treatment UF-85-55-20 i s n o t • s i g n i f i c a n t l y  d i f f e f e n t n t at the 0.05 l e v e l from those given by treatments UF-50-55-10 (20.7 kg/cm  2  i . e . 295 p s i ) , UF-50-55-20 (21.0 kg/cm  UF-85-70-20 (21.6 kg/cm  2  i . e . 295 p s i ) .  2  i . e . 299 p s i ) ,  i . e . 307 p s i ) and UF-85-55-10 (20.7 kg/cm  2  In this test, the lowest shear strength of about 17.5  2 kg/cm  (249 psi) i s given by treatment UF-50-70-20. As further shown i n Table 17, the vacuum-pressure test wood  f a i l u r e results f o r the UF glued panels indicate that the PT and the GS v are highly s i g n i f i c a n t factors, as w e l l as the i n t e r a c t i o n between the PT, GS and the AT.  The i n t e r a c t i o n between the PT and the GS i s  s i g n i f i c a n t at the 0.05 l e v e l .  As depicted f o r the interactions i n  - 65 Fig.  8 and 9, bond q u a l i t y ,  i n terms o f percentage wood f a i l u r e , i s  c o n s i s t e n t l y reduced a t the PT o f 50°C and 85°C.  The lowest percentage  wood f a i l u r e i s o b t a i n e d a t the PT o f 85°C f o r each of the treatment combinations. of Spread 55--^*Time£10*fSpread'^SS - Time 20, Spread 70 Time 10 and Spread 70 - Time 20. As noted i n F i g . 9, the i n f l u e n c e of treatment combinations o f Spread 55 - Time 20 and Spread 70 - Time 10 on percentage wood f a i l u r e i s not s i g n i f i c a n t .  These  two  t r e a t m e n t s , a t the PT o f 20°C, g i v e the  h i g h e s t percentage wood f a i l u r e . significant  At the PT o f 50°C, t h e r e i s no  i n f l u e n c e o f treatment combinations o f Spread 55 - Time 20  and Spread 70 - Time 20 on percentage wood f a i l u r e .  Bond q u a l i t y  PT i s b e s t w i t h the treatment combination of Spread 55 - Time 20. of  the f o u r treatment combinations e x e r t s a d i s t i n c t i n f l u e n c e  at  this  Each  on  percentage wood f a i l u r e a t the PT o f 85°C w i t h treatment UF-85-55-20 g i v i n g the m o s t . f a v o u r a b l e  result.  The wood f a i l u r e r a n k i n g i n . T a b l e 21 shows t h a t the h i g h e s t percentage wood f a i l u r e o f 59% g i v e n by treatment UF-20-55-20 i s not r  significantly .different : J ;  by<..treaemgS4 UF-20-70-10.  a t the 0.05  l e v e l from the v a l u e of 56% g i v e n  The lowest percentage wood f a i l u r e of 11% i s  g i v e n by the treatment combination of Spread 70 - Time 10 a t the PT of 85°C.  5.4.2  Treatment  5.4.2.1  p a n e l s bonded.with  Vacuum-pressure t e s t :  PF g l u e  Shear s t r e n g t h and wood f a i l u r e p e r c e n t  More i n t e r a c t i o n s of the main e f f e c t s s t r e n g t h o f the PF g l u e d t e s t  samples  are noted w i t h the shear  s u b j e c t e d to vacuum-pressure  test  - 66 than for the UF glued test samples. are highly s i g n i f i c a n t (at the 0.01  As noted i n Table 18, PT, GS and AT level).  between PT and AT i s highly s i g n i f i c a n t . GS i s s i g n i f i c a n t at the 0.05 actions.  S i m i l a r l y , the i n t e r a c t i o n  The i n t e r a c t i o n between PT and  l e v e l . F i g . 10 and 11 depict these i n t e r -  As shown i n F i g . 10, higher wet shear strength i s produced at  each of the PT with the higher spread of 70 lb/MDGL.  The spread of  55 lb/MDGL gives the highest shear strength at the PT of 20°C, whereas the spread of 70 lb/MDG gives the highest shear strength at the PT of 85°C (Fig. 10). As shown i n F i g . 11, wet shear strength i s s l i g h t l y higher with the AT of 10 mim  at the PT of 50°C whereas the AT of 20 min  produces a s l i g h t l y higher shear strength at the PT of 85°C.  Generally,  plywood panels made from veneers.cut at the PT of.20°C and 85°C produce the highest wet shear strength values.  From the shear strength ranking  presented i n Table 22, the highest shear strength value of about  28.5  2 kg/cm  (405 p s i ) i s given by the treatment combination of Spread 70 -  Time 20 at the PT of 85°C.  This i s , however, not s t a t i s t i c a l l y  signifi-  2 l e v e l from the values of about 27.9 kg/cm (397 p s i ) 2 and about 26.9 kg/cm (382 p s i ) given by the treatment combinations of cant at the 0.05  Spread 70 - Time 10 (at PT of 20°C) and Spread 70 - Time 10 (at PT of 2 85°C).  The lowest shear strength of about 21.7 kg/cm  (308 p s i ) i s  given by the treatment combination of Spread 55 - Time 10 at the PT of 50°C. The f a c t o r i a l analysis (Table 18) for the wood f a i l u r e of the PF treatments subjected to vacuum-pressure test shows that the PT,  AT,  PT-AT i n t e r a c t i o n and PT-GS-AT interaction are a l l highly s i g n i f i c a n t .  The s i g n i f i c a n t  interactions  t h a t bond q u a l i t y , the  PT o f 85°C.  a r e shown i n F i g . 12 and 13.  F i g . 12 shows  i n terms o f percentage wood f a i l u r e , i s lowest a t  Higher percentage wood f a i l u r e i s produced by the  p r o l o n g e d AT o f 20 min.' a t each l e v e l o f PT as a g a i n s t the AT o f 10 min The AT o f 10 min. produces of  the h i g h e s t percentage wood f a i l u r e a t the PT  20°C; w h i l e the AT o f 20 min. produces  the h i g h e s t percentage wood  f a i l u r e a t the PT o f 50°C. As shown i n . F i g . consistently tions  13, percentage wood f a i l u r e decreased  between 20°C and 85°C PT f o r each o f the treatment  combina-  o f Spread 55 - Time 20, Spread 70 - Time 10, Spread 70 - Time 20  and Spread 55 - Time 10.  A t the PT o f 85°C, the h i g h e s t percentage  wood f a i l u r e i s produced by.the treatment combination of Spread 55 Time 20.  F o r the t h r e e . t r e a t m e n t combinations of Spread 55 - Time 10,  Spread 55 - Time 20 and Spread 70 - Time 10, the h i g h e s t percentage wood f a i l u r e s a r e produced  a t the PT o f 20°C.  For this  particular  t e s t , however, the h i g h e s t and most f a v o u r a b l e bond q u a l i t y the  i s g i v e n by  treatment combination o f Spread 70 - Time 20 a t the PT o f 50°C. From  the wood f a i l u r e r a n k i n g p r e s e n t e d i n T a b l e 23, the percentage wood f a i l u r e ^ o f 64% g i v e n by the treatment i s s i g n i f i c a n t l y ' d i f f e r e n t the  0.5 l e v e l t o the v a l u e shown by any o t h e r treatment.  at  The lowest  percentage wood f a i l u r e o f 7% i s g i v e n by t h e treatment combination o f Spread 55 - Time 10 a t the PT o f 85°C. 5.4.2.2  Boil-dry-boil  t e s t : Shear s t r e n g t h and wood f a i l u r e p e r c e n t  Shear s t r e n g t h r e s u l t s the of  for this  PT, GS and AT a r e h i g h l y s i g n i f i c a n t .  test  (Table 19) i n d i c a t e  Similarly,  the PT w i t h the AT i s h i g h l y s i g n i f i c a n t .  that  the i n t e r a c t i o n  From F i g . 14., the lower AT  - 68 of 10 min. produces h i g h e r wet  shear s t r e n g t h than the p r o l o n g e d AT o f  20 min. a t the PT of 20°C and 50°C. longed AT of  At the PT of 85°C, however, the p r o -  20min. g i v e s a h i g h e r wet  w i t h the AT of 10 min.  the h i g h e s t wet  shear s t r e n g t h .  shear s t r e n g t h i s produced a t the  PT of 20°C; whereas w i t h the AT of 20 min. i s g i v e n a t the PT of  Furthermore,  the h i g h e s t wet  shear s t r e n g t h  85°C.  G e n e r a l l y , plywood p a n e l s made from veneers cut a t 20°C and 85°C.give the most f a v o u r a b l e bond, q u a l i t y .  From the shear  s t r e n g t h r a n k i n g p r e s e n t e d i n T a b l e 22, the h i g h e s t wet of about 23.5  kg/cm  2  temperatures  shear s t r e n g t h  (334 p s i ) i s given.by the treatment combination o f  Spread 70 - Time 20 a t the PT of 85°C.  T h i s , however, i s not  significant  2 at the 0 . 0 5 . l e v e l from the v a l u e s of about 22.6  kg/cm  (322 p s i ) and  2 22.1 kg/cm (315 p s i ) g i v e n by the treatment combinations of Spread 70 Time 10 (at the PT of 20°C) and.Spread 70 - Time 10 (at the PT of 8 5 ° C ) . 2 The lowest shear s t r e n g t h of 16.8.kg/cm  (239 p s i ) i s g i v e n by  treatment combination o f Spread 55 - Time 20 a t the PT of Wood f a i l u r e r e s u l t s . f o r same t e s t the PT, GS and AT are h i g h l y s i g n i f i c a n t .  the  50°C.  (Table 19) i n d i c a t e  that  S i m i l a r l y , the i n t e r a c t i o n s  between the PT and GS as w e l l as PT and AT are h i g h l y s i g n i f i c a n t . From the i n t e r a c t i o n shown g r a p h i c a l l y i n F i g . 15, the PT o f 85°C g i v e s the lowest bond q u a l i t y  ( i n terms of percentage wood f a i l u r e ) a t each of the  spread l e v e l s o f 70 lb/MDGL and 50 lb/MDGL.  With the lower s p r e a d ,  percentage wood f a i l u r e i s h i g h e s t a t the PT of 20°C, w h i l e the h i g h e r spread g i v e s the h i g h e s t percentage wood f a i l u r e a t the PT o f F i g . 716 shows a . s i m i l a r t r e n d i n bond performance  50°C.  to F i g . 15.  The p r o l o n g e d AT of 20 min. r e s u l t s i n h i g h e r percentage wood f a i l u r e  - 69 than the lower AT o f 10 min- a t a l l t h r e e l e v e l s o f PT.  F o r the AT o f  10 min., percentage wood f a i l u r e i s h i g h e s t a t the PT o f 20°C and lowest at the PT o f 85°C.  F o r the'AT o f 20 min,, percentage wood f a i l u r e i s  h i g h e s t a t the PT o f 50°C and lowest a t the PT of 85°C. plywood.panels  Generally,  made from veneers c u t a t 50°C gave the h i g h e s t percentage  wood f a i l u r e f o r t h i s p a r t i c u l a r t e s t .  From the wood f a i l u r e r a n k i n g  p r e s e n t e d i n Table 23, the h i g h e s t percentage wood f a i l u r e of 66% g i v e n by the treatment combination o f Spread  70 - Time 20 a t the PT o f 50°C  is sig-  n i f i c a n t l y S _ f f e r e h t . V t " t h e 0.05 i e v e i ^ t o ' t h e v a l u e shown by any o t h e r treatment. c  T h e l l o w e s t percentage wood f a i l u r e o f 12% i s g i v e n by treatment  combina-  t i o n s o f Spread 55 - Time 10 (at the PT o f 50°C) and Spread 55 - Time 10 (at the PT o f 85°C).  5.4.3  P r o b a b l e f a c t o r s a c c o u n t i n g f o r low percentage wood f a i l u r e s i n the treatments. The f o l l o w i n g e x p l a n a t i o n s a r e p r e s e n t e d as the p o s s i b l e  causes o f low bond q u a l i t y performance  ( i n terms o f percentage wood  f a i l u r e ) shown by the treatments, e s p e c i a l l y w i t h the use o f PF g l u e : 1.  The veneers used f o r the study wereinbt obtained, from logs.  The l o g s p e e l e d were from the consignment  N i g e r i a t o SNC-Rust Company L i m i t e d , o f M o n t r e a l .  fresh  shipped  from  They had been  kept i n c o l d s t o r a g e by the company f o r a t l e a s t a y e a r p r i o r to t h e i r use. veneers  The sapwood zone had d r i e d out c o n s i d e r a b l y and  from t h i s wood zone were a l s o used when c o n s t r u c t i n g  c e r t a i n o f the p a n e l s .  D i s c o l o r a t i o n o f such veneers  to a dark  brown o r b l a c k i s h c o l o r had a l r e a d y o c c u r r e d , as n o t i c e d a t  - 70 peeling.  F u r t h e r veneer d i s c o l o r a t i o n o c c u r r e d between the  30 days t h a t e x p i r e d between the p e e l i n g and d r y i n g of the veneers. 2.  There i s a l s o the problem o f i n f l u e n c e of s u r f a c e a g i n g of veneer p r i o r t o g l u i n g .  E i g h t y days e x p i r e d between the  p e e l i n g and g l u i n g o f the v e n e e r s .  S u r f a c e a g i n g o f wood has  been r e p o r t e d to d r a s t i c a l l y reduce i t s w e t t a b i l i t y and, i n t u r n , the q u a l i t y of the g l u e bond  (Gray 1962, M a r i a n  M a r i a n and Stumbo 1962b, Stumbo 1964, 1972).  Herczeg 1965  1962,  and  Collett  The r e l a t i o n s h i p between wood w e t t a b i l i t y and i t s  g l u a b i l i t y has a l s o been n o t e d i n S e c t i o n I t was  2.8.  n o t i c e d t h a t where the d i s c o l o r e d veneers were  used as c o r e s , low o r z e r o percentage wood f a i l u r e s were developed.  No attempt was  made to g i v e the veneers  s u r f a c e sanding p r i o r to g l u i n g .  light  The i n t r o d u c t i o n o f such a  v a r i a b l e would have doubled the number o f treatments used. Due  to the l i m i t e d amount of veneer a v a i l a b l e , i t was i m p o s s i b l e  to i n c l u d e t h i s v a r i a b l e .  Walters  (1973), f o r example,  r e p o r t e d t h a t poor g l u i n g r e s u l t e d from decreased  surface  w e t t a b i l i t y and s u r f a c e i n a c t i v a t i o n but c o u l d be  improved  upon by g i v i n g the veneers a l i g h t s u r f a c e sanding p r i o r to gluing.  He o b t a i n e d h i g h e r percentage wood f a i l u r e f o r the  sanded veneers compared to the unsanded v e n e e r s . Comparing the r e s u l t s o f the PF treatments, vacuump r e s s u r e t e s t , w i t h the UF t r e a t m e n t s , vacuum-pressure  test  (Tables 10 and 11), the PF IB-334 g l u e used seems to be more  - 71 s e n s i t i v e to s u r f a c e i n a c t i v a t i o n , r e s u l t i n g from s u r f a c e aging of v e n e e r s ,  than t h e Monsanto UF 109 g l u e used,  f o r i t s lower percentage wood 3.  thus  accounting  failure.  V a r i a b i l i t y i n bond q u a l i t y between and w i t h i n p a n e l s i s a u s u a l phenomenon.  T h i s i s i l l u s t r a t e d by T a b l e s  12 t o 15.  R e g a r d l e s s o f type o f bond q u a l i t y t e s t , l a r g e v a r i a b i l i t y i n percentage wood f a i l u r e was observed w i t h both the UF and PF treatments  alike.  T h i s i s i n d i c a t e d by '£helwid§  ranges  shown i n columns 11-13 o f T a b l e s zl*2 tto 315 r e s p e c t i v e l y . In a d d i t i o n , and more l i k e l y ,  this v a r i a b i l i t y  i s the  r e s u l t o f such f a c t o r s a s : i)  d i f f e r e n c e s i n veneer m o i s t u r e  content a t g l u i n g ,  i i ) - spanel edge e f f e c t , iii) iv)  d i f f e r e n c e s i n degree o f cure of g l u e l i n e . numanrf-aetor i n t r o d u c e d d u r i n g veneer w i t h regards to the, open assembly time  gluing especially (Not i n t r o d u c e d  as a v a r i a b l e i n the s t u d y ) , v)  s t r e s s c o n c e n t r a t i o n s i n h e r e n t i n the t e s t d u r i n g shear  specimens  testing.  I t was n o t i c e d , f o r example, t h a t l o n g e r open assembly time was used when g l u i n g w i t h the PF glue than the UF g l u e . due  to the d i f f i c u l t y encountered  the v e n e e r s .  T h i s was  w h i l e s p r e a d i n g t h e glue on  Because i t was l e s s v i s c o u s than the UF g l u e , i t  was l e a k i n g out o f the r o l l e r s p r e a d e r . spread on one f a c e of the veneer  The glue was t h e r e f o r e  then the p i e c e was f l i p p e d  f o r the s p r e a d i n g of the o t h e r f a c e .  over  The e f f e c t o f l o n g open  - 72 assembly time on p h e n o l i c  glue has been reviewed i n S e c t i o n  2/6.2. 4.  The P F . r e s i n used was more c a u s t i c UF r e s i n  (pH 8.4).  (pH 12.5 - 13.5) than the  The b u f f e r i n g c a p a c i t y of the UF r e s i n ,  t h e r e f o r e ^ w o u l d be low a t h i g h p a n e l p r e s s i n g . temperature o f 127°C  (260°F).  Due t o m o i s t u r e and n a t u r a l a c i d s i n wood  ( u r o n i c a c i d s of h e m i c e l l u l o s e s ) , h y d r o l y s i s c o n d i t i o n may be created.  T h i s weakens the wood s t r u c t u r e i n the v i c i n i t y o f  the g l u e l i n e , thereby c a u s i n g with higher pressure 5.  f a i l u r e a t lower shear  loads  percentage wood f a i l u r e s as evidenced by vacuum-  r e s u l t s o f both g l u e s  i n T a b l e s 10 and 11.  As reviewed i n S e c t i o n 2.1, the r e s i n content o f gmelina wood i s high. and  The low percentage wood f a i l u r e s e x i h i b i t e d v b y  UF treatments c o u l d , t h e r e f o r e , be due to i n t e r f e r e n c e of  the wood e x t r a c t i v e s w i t h the g l u e s . 12.5  the PF  to 13.5, which should  on the veneer s u r f a c e s  The PF r e s i n has a pH o f  be enough to s a p o n i f y  (Chow 1977b).  However, the PF treatments  showed lower p e r c e n t a g e wood f a i l u r e v a l u e s treatments  (UF has a pH o f 8.5).  the i n t e r f e r e n c e concept.  the e x t r a c t i v e s  compared t o the UF  T h i s , seems to c o n t r a d i c t  The d e f i n i t e i n f l u e n c e o f the  e x t r a c t i v e s o f the wood on bond q u a l i t y i s t h e r e f o r e  difficult  to make. I t i s the view o f the w r i t e r t h a t w i t h f r e s h v e n e e r s , b e t t e r bond q u a l i t y c o u l d be obtained  w i t h gmelina wood.  - 73 5.4.4  Comparison of study r e s u l t s w i t h some N a t i o n a l Plywood As i n d i c a t e d i n S e c t i o n 2.7,  the U.S.,  Standards  B r i t i s h and German;  Plywood Standards w i l l be used t o a s s e s s bond q u a l i t y r e s u l t s o b t a i n e d i n this  study.  5.4.4.1  U.S.  Hardwood plywood s t a n d a r d  The s p e c i f i c a t i o n s of the U.S. V o l u n t a r y Product Standard PS 51-71  Department o f Commerce  f o r T e c h n i c a l and Type I (both  E x t e r i o r Grades) Hardwood plywood a r e :  Average Wood failure (%)  Average f a i l i n g load (psi)  Under  250  50  25  250 -  350  30  10  Above  350  15  10  PF treatments from t h i s study t h a t meet the above E x t e r i o r Grade Plywood requirements are as  follows:  - 74 -  Treatments  Average f a i l i n g L  o  a  d  ( p g i )  Average Wood f a i l u r e (%)  Individual Specimen minimum wood f a i l u r e (%)  PF-Vacuum-Pressure 1. PF-20-55-20  318  45  15  2. PF-20-70-10  397  31  10  3. PF-20-70-20  337  34  10  4. PF-50-55-20  313  45  10  5. PF-50-70-20  317  64  30  1. PF-20-55-20  255  43  10  2. PF-20-70-10  322  38  10  3. PF-20-70-20  276  34  10  4. PF-50-55-20  239  46  10  5. PF-50-70-20  258  66  10  PF-Boil-dry-boil  As noted i n the above comparison, three of the f i v e treatments, from each of the bond.quality testing methods, passing the U.S. standard are  treatment .combinations a r i s i n g from the PT of 20°C.  two treatments come from the PT of 50°C.  The remaining  No treatment combination  a r i s i n g from the PT of 85°C meets this standard.  I t can therefore be  concluded that a PT of 85°C produces roughest veneers (compared to the PT of 20°C and 50°C) (Table 8) which, when glued into plywood, result i n low bond quality - i n terms of percentage wood f a i l u r e . Among the f i v e treatments that meet the U.S. standard, the 2 shear strength of about 22.3 kg/cm  (317 p s i ) obtained from treatment  PF-50-70-20 i s not s t a t i s t i c a l l y different  at the 0.05 l e v e l to the value  - 75 of  about  22.4 kg/cm  2  (318 p s i ) . o b t a i n e d from treatment  (Vacuum-pressure t e s t ) .  On the b a s i s of the U.S. s t a n d a r d , t h e r e f o r e ,  treatment PF-20-55-20 may be o f g r e a t e r i n d u s t r i a l treatment PF-50-70-20. h i g h e r energy  PF-20-55-20  importance  than  I t f a c i l i t a t e s lower p r o d u c t i o n c o s t s because  consumption  i s r e q u i r e d t o heat l o g s to 50°C as w e l l as  h i g h e r a d h e s i v e c o s t a t a s p r e a d o f 70 lb/MDGL as a g a i n s t 55 lb/MDGL. However, where the i n d u s t r y hopes t o maximise bond q u a l i t y w i t h r e s p e c t to  shear s t r e n g t h and percentage wood f a i l u r e ,  most  treatment PF-50-70-20 i s  suitable. A l s o comparing  treatments PF-20-55-20 and: PF-20-70-10, the 2  shear s t r e n g t h of about is  27.9 kg/cm  s t a t i s t i c a l l y different  (397 p s i ) o b t a i n e d f o r the l a t t e r  a t the 0.05 l e v e l from the shear s t r e n g t h o f  2 about  22.4 kg/cm  (318 p s i ) o b t a i n e d f o r the former.  55-20 may, however,be o f i n d u s t r i a l cost  importance  because  Treatment  PF-20-  of<it-s.-lower g l u e  (both treatments a r e from t h e same P^TdaMgpWdta'cfefctihe.'-highest  ;  percenfeageKwood-failure va'l-u'es):be Nevertheless,- wft'ereiath^ui-ndustry hopes •: to.jmaximiseibond q u a l i t y inieterms.xoft^wood ' she'ariestrerTgtlSr^reatment PF^2a-r7i(D^10 i s most f a v o u r a b l e . T h i s same a n a l y s i s a p p l i e s e x a c t l y t o the f i v e treatments t h a t meet the U.S. s t a n d a r d . p r e f e r r e d because.of  Treatment  PF-Boil-dry-boil  PF-20-55-20 i s  advantage o f lower p r o d u c t i o n c o s t i n h e a t i n g and  a d h e s i v e c o s t ; treatment PF-50-70-20 i s p r e f e r r e d where b o t h h i g h shear s t r e n g t h and percentage wood f a i l u r e  a r e of prime  importance and  treatment PF-20-70-10 i s most f a v o u r e d where v e r y h i g h shear s t r e n g t h i s most  desirable.  - 76 UF treatments that, a l s o meet the U.S. s t a n d a r d a r e as f o l l o w s :  Average f a i l i n g Load ( p s i )  Treatments  Average Wood f a i l u r e (%)  I n d i v i d u a l Specimen minimum wood f a i l u r e  (%) UF-Dry T e s t A l l the Twelve Treatments used. UF-20-55-10 through UF-85-70-20  35-70  306-389  10-35  UF-Vacuum P r e s s u r e 1. UF-20-55-10  264  38  10  2. UF-20-55-20  274  59  15  3. UF-20-70-10  260  56  15  4. UF-20-70-20  277  44  10  5. UF-50-55-10  295  33  10  Since vacuum-pressure r e s u l t s g i v e b e t t e r i n f o r m a t i o n on bond q u a l i t y performance  than the dry t e s t , the f i v e  w i l l o n l y be viewed  as the UF treatments meeting  treatments l i s t e d above the U.S. s t a n d a r d .  Of  these f i v e t r e a t m e n t s , f o u r a r i s e from the PT o f 20°C and none from the 85°C. fails  T h i s a l s o suggests t h a t even w i t h the UF g l u e , the PT o f 85°C to produce plywood o f adequate  combination.  bond q u a l i t y r e g a r d l e s s treatment  Among the f i v e treatments l i s t e d , treatment UF-20-55-20  i s most favoured t o a plywood i n d u s t r y . c o s t because  h i g h e r energy  I t f a c i l i t a t e s lower p r o d u c t i o n  c o s t i s r e q u i r e d to heat l o g s to 85°C and  lower glue c o s t i s ensured a t a spread' o f 55 lb/MDGL as a g a i n s t 70 l b / MDGL.  High shear s t r e n g t h and percentage wood f a i l u r e a r e both maximised  - 77 i n the treatment.  A l l f i v e treatments are c o n s i d e r e d adequate  for  p r o d u c i n g I n t e r i o r grade plywood.  5.4.4.2  B r i t i s h Hardwood Plywood Standard The B r i t i s h Standard B.S.  1455:1963 f o r T r o p i c a l Hardwood  Plywood s p e c i f i e s an average percentage wood f a i l u r e of 50%. PF and UF treatments t h a t meet t h i s s t a n d a r d are as  Treatments  The  study  follows.  Average Wood f a i l u r e (%)  PF-Vacuum P r e s s u r e  64  PF-50-70-20 PF-Boil-dry-boil  66  PF-50-70-20 UF-Dry T e s t  UF-20-55-10  57  UF-20-55-20  70  UF-20-70-10  62  UF-20-70-20  52  UF-50-55-10  53  UF-50-70-20  61  UF-Vacuum P r e s s u r e  UF-20-55-20  59  UF-20-70-10  56  On the b a s i s o f the B r i t i s h Standard, the o n l y PF t h a t meets the s t a n d a r d  treatment  (PF-20-70-20) i s c o n s i d e r e d adequate  Weather and b o i l - p r o o f , B o i l - r e s i s t a n t and M o i s t u r e r e s i s t a n t grade plywood.  On the o t h e r hand, the two UF  f o r use as Exterior  treatments under Vacuum-  p r e s s u r e t e s t t h a t meet the s t a n d a r d are c o n s i d e r e d adequate  f o r use as  - 78 Interior  grade plywood.  Out o f these two treatments, however,  UF-20-55-20 i s o f g r e a t e r i n d u s t r i a l importance  than treatment  UF-20-70-10 s i n c e i t s spread o f 55 lb/MDGL ensures lower c o s t o f a d h e s i v e consumption  than the spread o f 70 lb/MDGL f o r the o t h e r treatment.  Its  h i g h e r percentage wood f a i l u r e o f 59% i s n o t s t a t i s t i c a l l y d i f f e r e n t a t the  0.01 l e v e l from the average of 56% f o r the o t h e r treatment. 12 German . 'iHardwood. Plywoods Standard  5.4.4.3  The German s t a n d a r d , Deutshe I n d u s t r i e Normen DIN .68705-1968 2 specifies  an average shear s t r e n g t h o f 10 kp/cm  (142 p s i ) .  A l l the 24  treatments used i n t h i s study, r e g a r d l e s s o f g l u e type and b o n d . q u a l i t y testing  methods, meet the German Hardwood Plywood Standard.  Shear 2  s t r e n g t h v a l u e s a r e i n the range o f about 16.8 t o 28.5 kg/cm  (239 to  405 p s i ) . Cost c o n s i d e r a t i o n may j u s t i f y  the use o f . t r e a t m e n t PF-20-55-20 2 and UF-20-55-20 with.average shear s t r e n g t h s o f about 22.4 kg/cm 2 (318 p s i ) and about 19.3 kg/cm pressure 5.5  (274 p s i ) r e s p e c t i v e l y under vacuum-  test.  P r o b a b l e end uses o f Gmelina a r b o r e a Veneer  and Plywood  From the f i n d i n g s o f t h i s study, Gmelina.arborea plywood i s s u i t e d f o r the f o l l o w i n g uses:  5.5.1  C o n s t r u c t i o n plywood Specific  g r a v i t y i n the range o f 0.41 to 0.55, i s one o f the  p h y s i c a l p r o p e r t i e s of. wood c o n s i d e r e d of.major importance t i o n plywood 12  (Lutz 1971).  With a s p e c i f i c g r a v i t y o f 0.41 + 0.027 as  1  Same as Japanese  f o r construc-  Standard •• hi:, s  found f o r Gmelina.arborea i n t h i s study, the wood i s m a r g i n a l l y  suitable  f o r c o n s t r u c t i o n plywood.  property  of major importance. study, t h e r e f o r e  Shear s t r e n g t h i s another m e c h a n i c a l  From the g l u e l i n e shear s t r e n g t h o b t a i n e d  i n this  (Table 1 1 ) , the wood i s q u i t e s u i t a b l e f o r c o n s t r u c t i o n 2  plywood.  T h i s ranges between 239 - 405 p s i (about 16.8 kg/cm  - 28.5  2 kg/cm ) f o r the PF treatments t h a t pass the v a r i o u s World plywood Standards a l r e a d y  discussed.  These shear s t r e n g t h v a l u e s  a b l y and i n some cases more f a v o u r a b l y 1972,  compare  (Hancock 1977c, Chow and Warren  W a l t e r s 1973, Hse 1971) t o the plywood shear s t r e n g t h s  found from  d i v e r s e s t u d i e s f o r some woods used f o r c o n s t r u c t i o n plywood. essential considerations (1968) r e p o r t e d arborea  favour^  Other  a r e moderate weight and ease of g l u i n g .  a d e n s i t y range o f 30 to 31 lb,/cu-<,ft  f o r Gmelina  %>  grown i n N i g e r i a , I n d i a , Gambia and M a l a y s i a .  i n d i c a t e d , puts the wood i n the r i g h t weight category study ;-has a l s o demonstrated t h a t the wood, glues  Lamb  T h i s , as he f o r many uses.  This  e a s i l y depending on  treatment combinations o f p e e l i n g temperature, glue spread  and c l o s e d  assembly time. Therefore,  Gmelina, a r b o r e a  plywood may be c o n s i d e r e d  f o r b u i l d i n g c o n s t r u c t i o n as s u b f l o o r , w a l l s h e a t h i n g , and  s i d i n g panels;  5.5.2  o v e r l a i d panels;  and c o n c r e t e  Core and Crossband veneer f o r d e c o r a t i v e  roof  suitable  sheathing  forms. plywood  S p e c i f i c g r a v i t y i s a l s o one o f the p h y s i c a l p r o p e r t i e s considered  o f major importance f o r core and crossband veneers f o r d e c o r a -  t i v e plywood  (Lutz 1971).  F o r such a use, a t y p i c a l s p e c i f i c g r a v i t y  range o f 0.32 t o 0.45 i s r e q u i r e d .  The s p e c i f i c g r a v i t y o f g'melina wood  - 80 (0.41 + 0.027) s a t i s f i e s this requirement.  On this basis, therefore,  veneers from gmelina are quite suitable for use as core and crossbands f o r decorative plywood.  As indicated by Lutz (1971), uniformity of wood  structure i s p a r t i c u l a r l y desirable for crossband veneers meant to be used as decorative panels i n order to minimize "telegraphing" of the grain to the face.  Thus, diffuse-porous hardwoods l i k e yellow b i r c h and  yellow-poplar have been reported as good veneer species.  As a d i f f u s e -  porous hardwood, gmelina has been found from this study to y i e l d r e l a t i v e l y smooth veneers.  Ease of gluing, straight and f i n e , uniform  grain are other desirable veneer q u a l i t i e s when considering veneers f o r use as cores and crossbands f o r decorative plywood.  As discussed i n  Section 2.1 and Section 3.2.3, gmelina wood s a t i s f i e s these requirements. This seems to strengthen the s u i t a b i l i t y of gmelina wood for use as core and crossband veneers for decorative plywood for products l i k e furniture, flush doors and case goods.  5.5.3  Container veneer and plywood Woods meant to be cut into veneers f o r use as container veneer  and plywood are expected to possess the following physical and mechanical properties: s p e c i f i c gravity i n the range of 0.36 to 0.65, l i g h t color, freedom.from  odor, high s t i f f n e s s (MOE), high shock resistance (MOR)  high strength i n tension perpendicular to the grain.  and  Since the only  mechanical property measured i n this study i s the shear strength, i t becomes d i f f i c u l t to access the gmelina veneers on the basis of MOE MOR.  and  However, on the basis of the shear strength and the physical pro-  perty involving s p e c i f i c gravity, color and odor (See Section 3.2.3),  - 81 gmelina wood i s s u i t a b l e . f o r  use as c o n t a i n e r veneer and plywood.  S i n c e the veneers used f o r t h i s study were n o t o b t a i n e d from f r e s h - c u t gmelina l o g s , i t i s d i f f i c u l t  to a s s e s s the s u i t a b i l i t y  wood f o r use as d e c o r a t i v e veneer and plywood ness and f i g u r e .  of the  on the b a s i s o f a t t r a c t i v e -  - 82 -  6.0 6.1  SUMMARY, SUGGESTIONS FOR FURTHER STUDIES AND CONCLUSION Summary The data l i s t e d below contribute  to the knowledge of the  bonding c h a r a c t e r i s t i c s of Gmelina arborea wood: 1.  Even though the presence of a s i g n i f i c a n t interacting e f f e c t may obscure interpretation of a s i g n i f i c a n t main e f f e c t i n a s t a t i s t i c a l analysis, the effects of the peeling  temperatures  used are nevertheless found highly s i g n i f i c a n t regardless of glue type and bond quality testing method. 2.  S i m i l a r l y , the effects of the glue spreads used (a major factor i n t o t a l cost of plywood manufacture) are found highly s i g n i f i c a n t i n 3 of the 4 ANOVA's f o r shear strength r e s u l t s .  3.  Veneers of the highest peel-quality (control) peeling  are produced with the 20°C  temperature whereas the temperature of 85°C  y i e l d s veneers of the lowest peel-quality. 4.  Thus, the study has demonstrated that gmelina wood can be s a t i s f a c t o r i l y rotary-cut  into good veneers without any p r i o r  heating. 5.  Bond quality, i n terms of percentage wood f a i l u r e , i s consistently reduced by increasing peeling lowest at the peeling  temperature and i s  temperature of 85°C i n a l l the UF and PF  treatments used, reagrdless of bond quality testing method. 6.  The peeling  temperature of 20°C (control) gives the best  bond quality results i n terms of percentage wood f a i l u r e i n a l l the UF treatments used, regardless of type of bond quality  - 83 testing method. 7.  In spite of the d i s t i n c t i v e performance of the treatment combination of Spread 70 - Time 20 at the peeling  temperature  of 50°C, the treatments a r i s i n g from the 20°C (control) peeling temperature also give the most impressive bond quality results i n terms of percentage wood f a i l u r e i n a l l the PF treatments regardless of bond quality testing method. 8.  Among the UF treatments used, ignoring glue spreads, those a r i s i n g from the peeling temperatures of 50°C and 85°C give the highest shear strength values regardless of type of bond quality testing methods.  In most cases, shear strength  differences are marginal between these two peeling temperatures. 9.  Among the PF treatments used, ignoring glue spreads, those a r i s i n g from the peeling temperatures of 20°C and 85°C both give the highest shear strength values regardless of type of bond quality testing methods.  10.  At the peeling temperature of 20°C (control), treatment combination of Spread 70 - Time 10 gives the most favourable bond quality among the UF treatments, regardless of type of bond quality testing method.  However, the shear strength and  percentage wood f a i l u r e values developed are not s i g n i f i c a n t at the 0.05 l e v e l from those given by treatment combination of Spread 55 - Time 20. Among the PF treatments, however, the treatment combination of Spread 70 - Time 10 develops a s i g n i f i c a n t l y higher shear strength than treatment combination of Spread 55 - Time 20, while the l a t t e r has a s i g n i f i c a n t l y  - 84 h i g h e r percentage wood f a i l u r e i n one o f the bond  quality  t e s t i n g methods used. 11.  At the p e e l i n g temperature vfaiiureiisdeveloped  of 50°C, the h i g h e s t percentage wood  w i t h the treatment combination of Spread  Time 20 r e g a r d l e s s of g l u e type and bond q u a l i t y 12.  At the p e e l i n g temperature  70 -  t e s t i n g method.  o f 85°C, the h i g h e s t shear s t r e n g t h  i s developed w i t h the treatment combination of Spread  70 - Time  20 r e g a r d l e s s o f glue type and bond q u a l i t y t e s t i n g method. 13.  A l l factors  c o n s i d e r e d , the treatment combination of Spread  - Time 20, at the p e e l i n g temperature  of 20°C  (control), gives  an i m p r e s s i v e bond q u a l i t y i n a l l the UF and PF treatments 14.  F i v e of the 12 PF.treatments quality  55  used.  used, r e g a r d l e s s of type of bond  t e s t i n g method, pass the U.S.  Plywood Standard;  one  passes the B r i t i s h Standard; w h i l e a l l pass the German Standard.  On the o t h e r hand, f i v e of the 12 UF  vacuum-pressure t e s t pass the U.S.  treatments  Standard; two pass  from  the  B r i t i s h Standard; w h i l e a l l pass the German Standard. Furthermore, U.S.  a l l the 12 UF  treatments from dry t e s t pass  Standard; s i x pass the B r i t i s h Standard; w h i l e a l l pass  the German Standard. 15.  the  From the r e s u l t s of t h i s study, p l a n t a t i o n - g r o w n a r b o r e a wood, w i t h a s p e c i f i c g r a v i t y  of 0.41  Gmelina  + 0.027 (as  determined), i s s u i t a b l e f o r use as c o n s t r u c t i o n plywood, c o r e and crossband veneer f o r d e c o r a t i v e p a n e l as w e l l as c o n t a i n e r veneer and plywood.  - 85 6.2  Suggestions f o r f u r t h e r  studies  C o n c l u s i v e evidence has been p r e s e n t e d f o r the s u i t a b i l i t y o f Gmelina a r b o r e a wood f o r veneer and plywood p r o d u c t i o n depending treatment combinations ' c l o s e d assembly  of wood p e e l i n g temperature,  on the  g l u e spread and  time.  However, f u r t h e r work would be n e c e s s a r y to improve  upon the  bond q u a l i t y a c h i e v e d w i t h the wood, e s p e c i a l l y u s i n g PF r e s i n a d h e s i v e . Suggested  areas o f study a r e as f o l l o w s :  1.  D e t e r m i n a t i o n o f the optimum p e e l i n g  2.  E f f e c t s o f veneer d r y i n g s c h e d u l e s on bonding of  3.  temperature. characteristics  the wood.  E f f e c t s o f assembly temperature  time  (open and c l o s e ) , p r e s s i n g  and p r e s s u r e t r i a l s  time,  on bond q u a l i t y .  4.  Glue f o r m u l a t i o n and optimum g l u e spread  trials.  5.  Nature o f the r e s i n p r e s e n t i n the wood and i t s e f f e c t on w e t t a b i l i t y and g l u a b i l i t y o f gmelina wood.  6.3  Conclusion The  f i n d i n g s o f t h i s study a r e c o n s i d e r e d o f r e s e a r c h ,  i n d u s t r i a l and economic importance  to the wood-based p a n e l i n d u s t r y i n  N i g e r i a as w e l l as the S t a t e s F o r e s t r y S e r v i c e s r e s p o n s i b l e f o r plantations establishment. for  Management o f gmelina p l a n t a t i o n s i n N i g e r i a  f u t u r e s u p p l y o f veneer l o g s i s c o n s i d e r e d a j u s t i f i a b l e  investment.  - 86 -,  BIBLIOGRAPHY  Adeyoju, S.K. 1968. F o r e s t r y i n the n a t i o n a l economy of N i g e r i a . Unpubl. Diploma t h e s i s i n F o r e s t r y . S t . John's C o l l e g e , O x f o r d . Chaps. 4 and 5. A f o l a y a n , A.A. 1974. 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D u r a b i l i t y of urea-formaldehyde a d h e s i v e s : E f f e c t s of molar r a t i o , second u r e a , and f i l l e r . F o r . Prod. J o u r .  23 (12): pp. 32-38. Stumbo, D.A. 1964. I n f l u e n c e o f s u r f a c e a g i n g p r i o r to g l u i n g on bond s t r e n g t h of D o u g l a s - f i r and Redwood. F o r . Prod. J o u r . 14(12):  582-589. TRADA.  1967. Plywood. I t s manufacture and uses. Timber Res. and A s s o c . , Hughenden V a l l e y , High Wycombe, Bucks. 43 pp.  Tan, B.H.  Dev.  1974. E f f e c t of veneer d r y i n g schedules on bonding c h a r a c t e r i s t i c s and s u i t a b i l i t y of n i n e Malayan hardwoods f o r plywood manufacture. Unpbl. B.S.F. t h e s i s , F a c u l t y of F o r e s t r y , U n i v . o f B.C., Vancouver, Canada. 180 pp.  Thomas, R.J.  1959.  G l u i n g c h a r a c t e r i s t i c s of Determa. F o r . Prod. J o u r .  9(8): 266-271. Troop, B.S. and F.F. Wangaard. 1950. The g l u i n g p r o p e r t i e s of c e r t a i n T r o p i c a l American woods. O f f i c e of Naval Res., Y a l e U n i v e r s i t y School of F o r . , New Haven, C o n n e c t i c u t . Techn. Rep. No. 4, 10 pp. Troughton, G.E. 1969. E f f e c t o f degree of cure on the a c i d h y d r o l y s i s r a t e s of formaldehyde glue-wood samples. J o u r . I n s t . Wood  S c i . 4(5): 51-56. . , S^.ZijChow. 1972. A study on the cause f o r v a r i a t i o n i n plywood bond q u a l i t y w i t h open assembly time. F o r . Prod.  Jour. 22(3): 55-58. Truax, T.R. 1929. The g l u i n g of wood. B u i . 1500. 23 pp.  U.S.  Dept. o f A g r i c ,  Tech.  W a l t e r s , E.D. 1971. S o r t i n g Southern p i n e green veneer to improve d r y i n g c o n t r o l . F o r . Prod. J o u r . 21(11): 52-59. W a l t e r s , E.O. 1973. The e f f e c t s of green veneer water c o n t e n t , d r y e r s c h e d u l e s , and w e t t a b i l i t y on g l u i n g r e s u l t s f o r Southern  p i n e veneer.  F o r . Prod. Jour. 23(6): 46-53.  Wangaard, F.F. and R.P. Saraos. 1959. E f f e c t o f s e v e r a l v a r i a b l e s on q u a l i t y o f r o t a r y - c u t veneer. F o r . Prod. J o u r . 9(6): 179-187. Wellwood, R.W. 1966. Forest Industries. Report to the govt, of Nigeria. FAO/UNDP, Rome. 64 pp. ±'.~j<  Xhs 1975 Wcrid Wocd  evjew-  VJoi„d  -99.Yamagishi, Y., and Y. Honma. 1972. Study on the g l u a b i l i t y o f t r o p i c a l woods.. I . Mixed use of.two d i f f e r e n t s p e c i e s i n bonding some , t r o p i c a l woods. Japan Wood Ind., Wood Tech. Assoc. 27-11: -  542-546. Zisman, W.A.  1963.  Influence of constitution  on a d h e s i o n .  I n d . Eng.  Chem. 55(10): 19-38. .  1965.  Improving the performance o f r e i n f o r c e d  Ind. Eng. Chem. 57(1): 26-34.  plastics.  -100Table 1.  Descriptive features of the Gmelina arborea. logs used for study.  Log Number  Estimated' age from Growth Ring Count  Noiotiknots present in 1 og  1  8  5  22.2  2  !0  8  18.4  3  12  3  21.0  4  9  4  5  10  6  Presence Sapwood Bark Log of d iameter* th i ckness thickness (cm) cm) Tension wood (cm)  2.8  Yes  1.7  No  5.8  1.5  Yes  16.5  3.0  1 .8  Yes  6  19.1  4.6  2.0  No  8  5  19-7  4.3  2.7  Yes  7  9  5  18.4  5.3  1.7  Yes  8  10  7  19.7  5.8  1.5  No  9  12  20.3  3.6  1.8  Yes  4.1  *  Average for both ends of the log.  1  It was found convenient to use growth rings to estimate age of the logs since, as reported by Lamb ( 1 9 6 8 ) , growth rings are noted to be v i s i b l e and usually annual f o r Gmelina arborea grown in Thailand.  -101Table 2.  Log Number  I n i t i a l and peeling moisture content {%) of the Gmelina arborea logs used for study.  Peeli ng temp( C)  I n i t i a l MC Sapwood Heartwood Corewood  2  20  90  124  132  4  20  82  107  90  8  20  96  114  5  50  45  6  50  7  Peeli ng MC Sapwood Heartwood Corewood 124  132*  82  107  90*  104  96  - 114  104*  67  76  61  65  78  41  79  67  88  104  73  50  107  147  118  105  149  139  1  85  53  123  103  45  76  111  3  85  59  128  101  67  120  81  9  85  91  115  107  78  85  79  Since these logs were not heated, peeling MCs were not determined.  They were assumed to be same as the i n i t i a l  MC previously determined.  -102Table 3.  S p e c i f i c g r a v i t y of the Gmelina arborea logs used for study. =  2  Log Number  Log Average S p e c i f i c Gravity  1*  0.42  2  0.44  3*  0.37  Sample Mean S p e c i f i c Gravity  Mean = 0 . 4 1 SD  3  =  0.027  0.43 5  0.38  6*  0.44  7*  0.41  8  0.41  g*  0.37  1  Determined by Volume Measurement Method.  2  Average for four test samples.  3  SD = Standard Deviation.  *  Logs with Tension wood ( I d e n t i f i e d by v i s u a l examination of P i t h displacement).  )  -103-  Table 4 .  Water bath and log temperature changes against time of heating - 5 0 C.  Nominal heating temperature: 50°cJ + 2°C  Heating Period (hours)  1  Water Bath Temperature (°C)  Wood Temperature at core, 4 in from Log Surface, recorded by Thermocouples ( C)  0  21.5  17.8  18.8  1  46.6  20.1  27.9  2  46.4  25.3  30.7  3  45.6  30.1  36.0  4  45.0  33.9  37.7  5  48.8  36.9  42.2  6  52.9  38.0  47.9  7  53.0  39.8  50.0  8  54.4  41.6  51.8  A wood temperature of 5 0 C + 2 C was considered acceptable for the  50°C  heating since i t was d i f f i c u l t to control the temperature  w i t h i n the vat. 2  Wood Temperature at 1 in from the Log Surface, Est i ma ted 2 ( c)  Using MacLean (1946) formulae  -10^-  Table 5 .  Water bath and log temperature changes against time of heating - 8 5 C.  Nominal heating temperature: 85°C + 2°C  Heat i ng Per iod (hours)  Water Bath Temperature (°0  20.1  17.7  18.4  1  50.5  19.2  29.3  2  70.4  25.1  41  3  81.6  45.0  60.0  4  81.4  60.1  64.3  5  81.5  64.9  68.0  6  81.5  67.4  72.5  7  81.6  68.9  76.2  8  81.5  69.9  77.5  9  81.4  70.8  78.8  71.4  79.7  '  81.5  .4  11  81.3  71.8  79.5  12  81.3  72.1  80.4  13  81.1  72.3  80.7  80.9  72.4  80.4  15  82.1  72.3  81.7  16  82.3  72.3  81.8  17  82.9  72.6  82.4  18  87.O  73.7  86.5  19  86.9  75.6  86.4  " 14  A Wood temperature of 85°C + 2°C was considered acceptable for the heating.  85°C 2  Wood Temperature at 1 in from the Log Surface, Estimated^ ( C)  0  10  1  Wood Temperature at core, 4 in from Log Surface, recorded by Thermocouples ( C)  Using MacLean  (1946)  formulae.  -105Table 6 .  Lathe s p e c i f i c a t i o n s f o r peeling:  1 . 2 7 mm ( 0 . 0 5 in) Gmelina arborea green veneer. 9 bolts sampled*  Horizontal Gap  1 . 1 1 mm (O.Okk in)  V e r t i c a l Gap  0.25  Veneer Thickness  1 . 2 7 mm ( 0 . 0 5  Nosebar Type  S o l i d nosebar  Nosebar Face Angle  14°  Knife Thickness  1 5 - 8 8 mm ( 5 / 8 )  Knife Length  167-64  Rockwel1 Hardness  56  Main Bevel  23°  Cutting Angle (at Speed of Cut  10-1/2  in)  89°  mm  (0.010  cm  (66  in) in)  in in)  30'  1 2 0 fpm  Diameters of the bolts ranged between 1 6 . 5 cm ( 6 . 5 in) to 22.2  cm  (8.8  in).  -106Table 1.  Peel-quality attributes: measurement.  Total No.of Veneer sheets sampled  Roughness Scale  Veneer roughness  in Equivalent  mm  Frequency  Equivalent Frequency  %  2 0 C Peeling  175  0.000  0.00  0  0.0  0.005  0.13  143  81.7  0.010  0.25  32  18.3  0  0.000  0.00  2  1  0.005  0.13  65  33.5  2  0.010  0.25  120  61.9  3  0.015  0.38  7  3.6  0  0.000  0.00  0  0.0  1  0.005  0.13  26  15.0  2  0.010  0.25  132  76.3  3  0.015  0.38  13  7.5  4  0.020  0.51  2  1.2  5 0 C Peeling 194  1.0  8 5 C Peeling  173  -107Table 8 .  Veneer p e e l - q u a l i t y s t a t i s t i c s . 1.27  Veneer A t t r i b u t e s  1.  2.  N.B.  Thickness  Roughness  mm ( 0 . 0 5 ~ i n ) Gmelina arborea green veneer  Peel ing temperature  Mean  SD*  Max  Min  Range  (mm)  (mm)  (mm)  (mm)  (mm)  20°C  (Control)  1.25  0.08  1.37  1.17  0.20  50°C  (Heated 8 hr..)  1.22  0.10  1.32  1.04  0.28  85°C  (Heated 1 9 hr.-,)  1.19  0.05  1.27  1.14  20°C  (Control)  0.15  0.05  0.25  0.13  0.12  50°C  (Heated 8 hr..)  0.21  0.07  0.38  0.00  0.38  85°C  (Heated 19 hr. )  0.24  0.06  0.51  0.13  0.38  Standard Deviation.  c  0.13  -108-  Table 9-  Sample  Veneer moisture content p r i o r to g l u i n g .  VENEER VENEER  M O I S T U R E P E E L I N G  CONTENT  T E M P E R A T U R E  Number  20  50  1  6.6  6.8  7.4  2  7.3  5-9  6.2  3  6.5  6.1  5.5  4  6.4  7.3  6.3  5  7.3  6.4  6  5.7  6.4  6.4  7  6.7  6.0  7.2  8  7.2  6.9  6.4  9  6.0  6.0  6.0  10  5.8  6.5  5.8  6.6  6.4  6.4  Average  N.B.  1. CTH Room Conditions:  §5  .  6.6  Temperature = Dry bulb 80°F; Dew. Point 43°F Relative Humidity = 2 6 % .  2. Time of conditioning in the CTH Room = 15 days.  {%) C O  Table 1 0 .  Average shear strength and average wood f a i l u r e of 5 p l y Gmelina arborea Plywood bonded with Urea-Formaldehyde (UF) glue. -  VACUUM-PRESSURE TEST  DRY ' TEST  Treatments  Mean Shear Strength (psi)  Mean Wood Fa i 1 u r e  M i n imum Spec imen No. of Wood Test Fa i 1 u r e Specimens  (*)  (%)  Mean Shear Strength (psi)  Mean Wood Fa i 1 u r e {%)  UF-20-55-10  306  57  20  34  264  38  UF-20-55-20  312  70  35  35  274  59  UF-20-70-10  332  62  30  28  260  56  UF-20-70-20  326  52  10  28  277  44  UF-50-55-10  312  53  10  22  295  33  353  38  10  27  299  10  UF-50-55-20  334  40  UF-50-70-20  353  61  UF-85-55-10 UF-85-55-20  362  UF-85-70-10  381  UF-50-70-10  342  .  38  15 15 15  35  10  47  10  39  0  34 36 36 36 25 30  5  23  249  30  295  30  319  23  281  11  0  27  307  14  0  389  N.B.  1.  Figures rounded to the nearest u n i t .  2.  Treatment codes are as f o l l o w s :  I  10 15 15 10 10  26  253  5 0  10  UF-20-55-10  ' •  I  ->  Closed assembly time (min)  » Glue spread ( l b . IMDGL) >  No. of Test Specimens  (%)  24 18 31 24 24  24  UF-85-70-20  e.g.  Mini mum Spec imen Wood Fa i 1 u r e  Peeling temperature (°C) >Glue used (Urea-forma 1 dehyde)  26 36 30 29 30  T a b l e 11.  Average shear s t r e n g t h and average wood f a i l u r e o f 5 - p l y Gmelina a r b o r e a Plywood bonded w i t h Phenol-Formaldehyde ( P F ) .  BOIL-•DRY-BOIL TEST  VACUUM PRESSURE TEST Mean Shear Strength (psi)  Treatments  346 318 397  PF-20-55-10 PF-20-55-20 PF-20-70-10 PF-20-70-20 PF-50-55-10 PF-50-55-20 PF-50-70-10 PF-50-70-20 PF-85-55-10 PF-85-55-20  337 309 313  354  317 321 330 382 405  PF-85-70-10 PF-85-70-20  N.B.  1.  Figures  Mean Wood Fa i 1 u re  Minimum Specimen Wood Failure  (%)  (S)  20 45 31 3*» 16 45 20  0 15 10 10 0 10 0 30 0 5 0 0  64  7  19  15 10  No. o f Test Specimens  Mean Shear Strength (psi)  Mean Wood Failure  288  21  255 322 276  43 38 3* 12  36 30 31 30 25 22 35 30 36 28 29 36  247  239 304 258 259 286 315 334  (*)  1  46  30 66 12 16 16 16  rounded t o the n e a r e s t u n i t ,  2. Treatment codes a r e as f o l l o w s : e.g.  PF-20-55-10  L  -> C l o s e d assembly •> Glue spread ">  time (min)  (lb/MDGL)  P e e l i n g temperature ( ° C ) Glue used  (Phenol-formaldehyde)  Minimum Specimen Wood Fa i1ure {%)  5 10 10 10 0 10  5  10 0 5 0 0  No. o f Test Specimens  35 34 33 28 26 23 35 30 33 35 22 31  o I  Table 12.  Within - and between - panel v a r i a t i o n in bond q u a l i t y of 5~ply Gmelina arborea. Plywood bonded with UF glue: Dry test wood f a i l u r e .  Mean Wood F a i l u r e  {%)  Max.Wood F a i l u r e {%)  Treatments  1  UF-20-55-10 UF-20-55-20 UF-20-70-10 UF-20-70-20 UF-50-55-10 UF-50-55-20 UF-50-70-10 UF-50-70-20 UF-85-55-10 UF-85-55-20 UF-85-70-10 UF-85-70-20  N.B.  38 77 60 43 56* .29* 52*  65* 37 25 19 47  2 72  69 51 57 46* 47, 23* 49* 43 48 34 48  3 62 63 76 51 57 35* 36 71  36 47 46 46  2  1  2  3  1  55 95 90 85 70 45 95 95 55 45 40  100 95 90 90 95 80 40 90 60  95 85 95  20 55 35 10 40 15 10 30 20  50 55 40 25 10 15 10 15 15  15  15  10 20  10 10  90  90  85 75  Panels  Panels  Panels  Panels  Range  Min.Wood Fa i1ure  90  95 90 75 95 60 100 70 75  3  1  2  3  35 35 50 20 20 10 10 45 20 15 15 15  35 40 55 75 30 30 85 65 35 30 30 70  50 40 50 65 85 65 30 75 45 75 75 65  60 50 45 70 75  '  80  65 50 40 85 55 60  *  Panels with yellow birch veneers as faces and backs.  1.  Figures rounded to the nearest u n i t .  2.  The Grand Mean Wood F a i l u r e of the Means of the above 3 panels for a p a r t i c u l a r treatment may not be same as in Table 10 due to rounding.  3.  Panels 1, 2 and 3 above are same as those in Table 13, respectively. Half of the test samples from each panel was used for the above.test while the other half was used for the test in Table 13.  Within - and between - panel v a r i a t i o n in bond q u a l i t y of 5 ~ p l y Gmelina Plywood bonded w i t h UF glue: Vacuum-pressure t e s t , wood f a i l u r e .  Table 1 3 -  Mean Wood F a i l u r e ft)  Max. Wood F a i l u r e ft) Min.Wood  1  Treatments  44 60 81 42 24* 12*  UF-20-55-10  UF-20-55-20 UF-20-70-1.0 UF-20-70-20 UF-50-55-10 UF-50-55-20 UF-50-70-10 UF-50-70-20  23*  16* 11 15 7 10  UF-85-55-10  UF-85-55-20 UF-85-70-10 UF-85-70-20 •  N.B.  2  3  1  2  3  42  32  70 95 60 55 60 55 10 65 75 20 75  55 90 65 95 75 55  67 70  37  70 95 100  31  58  90  38* 47 17* 6* 39 38 7 19  35 14*  35 40 85 40 30 35 20 35  51  11  68 21 20 18 9  90  Range  F a i l u r e ft)  Panels  Panels  Panels  Panels  arborea  15  85 50 45 60 40  1  2  10  10 20 30 10 20 30 5 5 0 10 0 0  25  50 10 '5 5 10 5 0 10 0 0  1  2  3  15  60  15 15 20 10 0 5 35 0 10 0 0  70  60 75 60 50 35 30 50 5 65 65 20 .75  40 75 50 75 65 55 10 50 50 35 60 40  3  50  80 20 35 75 35 30 25 20  •-  *  P a n e l s w i t h y e l l o w b i r c h v e n e e r s as f a c e s and backs.  1.  F i g u r e s rounded t o t h e n e a r e s t u n i t .  2.  Because o f r o u n d i n g , t h e Grand Mean Wood F a i l u r e o f t h e means o f t h e above 3 p a n e l s f o r a p a r t i c u l a r t r e a t m e n t may n o t be same as i n T a b l e 1 0 .  Table 14.  Within - and between - panel v a r i a t i o n in bond q u a l i t y of 5~ply Gmelina arborea. Plywood bonded with PF glue: Vacuum-pressure t e s t , wood f a i l u r e .  Mean Wood F a i l u r e (%)  Max.Wood F a i l u r e (%])  Panels Treatments  1  PF-20-55-10 PF-20-55-20  28  .  Min.Wood Fa i 1 u r e (*) Panels  Panels 2  3  1  2  75  30  35  5  80  80  2  3  1  13  13  Range Panels  3  1  2  0  0  70  30  35  15  25  30  65  55  50  10  10  70  50  75  3  39  51*  49*  80  60  85  10  80  75  10  15  10  35  65  65  15  80  0  0  0  10  15  80  75  95  10  10  10  80  65  85  25  70  0  0  0  50  25  70  35  30  35  60  65  50  PF-20-70-10  37  32  25  80  PF-20-70-20  18  45  37  45  PF-50-55-10  3  6  35  10  PF-50-55-20  38  52  90  29*  50  PF-50-70-10  21  31 8*  PF-50-70-20  64  68*  '  . .  52*  95  95  80  7  .10  30  45  0  0  0  10  30  45  *  13  50  75  40  5  5  5  45  70  35  PF-85-55-10  6  8  PF-85-55-20  24  24  PF-&5-70-10  15  28  8  30  65  30  5  5  0  25  60  30  PF-85-70-20  4  3  18  15  10  55  0  0  0  15  10  55  N.B.  * 1.  Panels with yellow b i r c h veneers as faces and backs Figures rounded to the nearest u n i t .  2. The Grand Mean Wood Fa i 1 ure of the means of the above 3 panels for a p a r t i c u l a r treatment may not be the same as in Table due to rounding. 3 . Panels 1 , 2 and 3 above are same as those in Table 1 5 r e s p e c t i v e l y . Half of the test samples of each of the panel was used f o r the above test while the other half was used f o r the t e s t in Table 1 1 .  Table 1 5 .  Within - and between - panel v a r i a t i o n in bond q u a l i t y of 5~ply Gmelina arborea Plywood bonded with PF glue: B o i 1 - d r y - b o i 1 t e s t , wood f a i l u r e .  Mean Wood F a i l u r e {%)  Max.Wood F a i l u r e {%)  Treatments  PF-20-55-10  1  31  PF-20-55-20  35  PF-20-70-10  39  Panels  Panels  Panels  Panels  Range  Min.Wood Fa i1lure (%)  2  2  3  1  2  3  1  2  3  1  12  12  90  35  20  5  5  5  85  30  15  .60  80  65  70  . 42*  .  "49  53*  90  32  90  .  75  90  10  15  10  80  75  80  10  15  10  80  3  PF-20-70-20  27  44  32  80  80  10  10  10  70  85  PF-50-55-10  5  13  14  95  70  20  55  40  0  0  0  20  55  40  PF-50-55-20  23  19  69  90  45  95  10  10  25  80  35  70  PF-50-70-10  34*  40  55  90  5  10  5  35  45  80  85*  82*  55  100  95  10  50  70  45  50  25  20  12  7  55  45  25  0  0  0  55  45  25  11  22  13  15  55  40  5  5  5  10  50  35  6  22  45  10  55  0  0  0  45  10  55  21 .  18  45  35  60  0  0  0  45  35  60  29  PF-50-70-20  18  PF-85-55-10 PF-85-55-20 PF-85-70-10  14  PF-85-70-20  1  N.B.  24*  '  *  Panels with yellow b i r c h veneers as faces and backs.  1.  Figures rounded to the nearest u n i t .  2.  The Grand Means of the three means above may not be same as in Table 11 due to rounding.  -115Table 1 6 .  Analysis of variance for t e s t i n g the e f f e c t s of peeling temperature, Glue Spread and Closed Assembly Time on UF Glue bond q u a l i t y in 5 ~ p l y Gmelina arborea Plywood: Dry t e s t . Shear  . . • Source or v a r i a t i o n r  Peeling temperature (PT) Glue Spread (GS) Closed Assembly Time (AT) PTxGS PTxAT GSxAT PTxGSxAT Error Total  Degrees or j _ , ... Freedom  Strength ^ _ Square q  •  Mean ~i Square  F  . . Ratios  n  2  0.l6784Exl0  83920.  31 . 2 6 * *  1  35887.  35887.  13 . 3 7 * *  1  2920.0  2920.0  1. 22  2  6532.1  3266.1  1. 09  2  19442.  9721.1  3. 62*  1  541.23  0. 20  2  13396.  541.23 6698.O  ,  252  0.67649x10°  263  0.92304x1.0  6  2. 50  2684.5  Wood Fa i 1 u r e . ^. Source of v a r i a t i o n £  Peeling temperature (PT) Glue Spread (GS) Closed Assembly Time (AT) PTxGS PTxAT GSxAT PTxGSxAT Error _ Total  Degrees r or Freedom  _ Sum of _ Square c  Mean Square u  c  F . Ratios c  D  2  18612  9306.2  18.12**  1  8.0152  8.0152  0.02  1  558.55  558.55  2.71  2  2782.4  1391.2  1.09  2  1183.9  591.95  1.15  1  1256.7  1256.7  2.45  2  9459.4  4729.7  9.21**  252  0.12941x10?  263  0.16327x10  S i g n i f i c a n t at the 0 . 0 1 l e v e l . S i g n i f i c a n t at the 0 . 0 5 l e v e l .  ,  513.54  -116Table 1 7 .  Analysis of variance f o r t e s t i n g the e f f e c t s of Peeling Temperature, Glue Spread and Closed Assembly Time on UF Glue bond q u a l i t y in 5 p l y Gmelina arborea. Plywood: Vacuum-pressure t e s t . _  Shear Strength Degrees ..j. '.or Freedom  . . Source of v a r i a t i o n r  Peeling Temperature (PT) Glue Spread (GS) Closed Assembly Time (AT) PTxGS PTxAT GSxAT PTxGSxAT Error Total  _ Sum or _ Square  Mean . Square  c  u  F . Ratios r  D  2  44448.0  22224.0  1  19605.0  19605.0  5.0518*  1  9636.5  9636.5  2  34173.0  2.4832  17087.  ~  5.7269**  4.4030**  2  IOO69.O  5034.5  1.2973  1  352.37  0.90800E-01  ,  352.37 889.O  252  0.97794x10°  3880.7  263  0.10980x10  2  1778.0  0.22909  Wood Fa i 1 u re Source of v a r i a t i o n Peeling Temperature (PT) Glue Spread (GS) Closed Assembly Time (AT) PTxGS PTxAT GSxAT PTxGSxAT Error Total  Degrees .of Freedom 2 1 1 2 2 1 2 252 263  S i g n i f i c a n t at the 0.01  level.  S i g n i f i c a n t at the 0.05  level.  Sum of Square 44537.0 3000.4 606.06  3114.4 196.21 836.74 6993.9 , 0.11283x10° 0.17221x10°  Mean Square  F Rat ios  22269.0 3000.4 606.06 1557.2 98.106 836.74 3497.0 448.12  49.693** 6.6954** 1.3524 3.4749* 0.21893 1.8672 7.8036**  -117-  Table 18.  Analysis of variance f o r t e s t i n g the e f f e c t s of Peeling Temperature, Glue Spread and Closed Assembly Time on PF Glue bond q u a l i t y in 5 p l y Gmelina arborea Plywood: Vacuum-pressure t e s t . -  Shear  Source of v a r i a t i o n  Peeling Temperature (PT) Glue Spread (GS) Closed Assembly Time (AT) PTxGS PTxAT GSxAT PTxGSxAT Error Total  Source of v a r i a t i o n Peeling Temperature (PT) Glue Spread (GS) Closed Assembly Time (AT) PTxGS. PTxAT GSxAT PTxGSxAT Error Total  Strength  Degrees of Freedom 2 1 1 2 2 1 2  55543.0 84209.0 19605.0 19768.0 36216.0 1675.1 6295.6 , 0.73466x10? 0.95797xlO  252  263  Wood Fa i1 u rs Degrees of Freedom  Mean Squa re  Sum of Square  27772.0 84209.0 19605.0 9884.2 18108.  1675.1 3147.8 2915.3  F Rat ios 9-5261** 28.885** 6.7247** 3.3904* 6.2113**  0.57458 1.0797  b  \ Mean Square  Sum of Square  F Ratios  2  28089.  14044.  31.326**  1  1209.2  1209.2  2.6971  1  22644.  22644.  50.507**  2  1630.9  815.44  1.8188  2  14796.  7398.0  16.501**  1  329.64  329.64  0.73525  2  5041.1  2520.5  5.6220**  252  0.11298x10;  263  0.18672x10  S i g n i f i c a n t at the 0.01 l e v e l . S i g n i f i c a n t at the 0.05 l e v e l .  ,  448.34  -118-  Table  19-  Analysis of variance f o r testing theeffect o f Peeling Temperature,' G l u e S p r e a d a n d C l o s e d A s s e m b l y T i m e o n PF G l u e bond q u a l i t y i n 5 p l y G m e l i n a a r b o r e a Plywood: Boi1-dry-boi1 t e s t . -  Shear Source o f v a r i a t i o n r  P e e l i n g T e m p e r a t u r e (PT) G l u e S p r e a d (GS) C l o s e d A s s e m b l y T i m e (AT) PTxGS PTxAT GSxAT PTxGSxAT Error Total  Strength  Degrees of , Freedom r  2 1 1 2 2 1 2 252 263  Wood „ Source o f v a r i a t i o n  P e e l i n g T e m p e r a t u r e (PT) G l u e S p r e a d (GS) C l o s e d A s s e m b l y T i m e (AT) PTxGS PTxAT GSxAT PTxGSxAT Error Total  _ ^ Sum o f _ Square  Mean _ Square  F .. Ratios  u  49995. 99103. 35352. 7302.8 47467. 2578.1 20499. , 0.68786x10^ 0.95015x10°  r  D  9.16**  24997. 99103.  36.31**  12.95** 1.34 8.69** 0.94 3.76  35352.  3651.4 23734. 2578.1 10250. 2729.6  Failure  Degrees ot ^ , Freedom r  _ Sum o f _ Square c  u  c  Mean D  Square  -.4--~,Ratios  2  30012.  15006.  27.581**  1  3864.0  3864.0  7.1021**  1  17837.  17837.  32.784**  2  6021.2  3010.6  2  9821.2  5.5335** 9.0258**  1  985.23  985.23  2  2354.5  1177.3  4910.6  ;  6  252  0.13710x10?  263  0.20800x10  S i g n i f i c a n t a t t h e 0.01  level.  S i g n i f i c a n t a t t h e 0.05  level.  544.07  1.8109 c  2.1638  -119-  T a b l e 20.  Duncan's M u l t i p l e Range t e s t f o r S h e a r S t r e n g t h o f G m e l i na a r b o r e a . P l y w o o d bonded w i t h UF G l u e .  T Dry  R  E  A  T  M  E  N  T  R  A  N  K  I  N  G  Test  Treatment Mean  2  1  2  5  4  3  7  306  312  312  326  332  334  8  7  3  1  2  4  249  253  260  264  274  277  10  342  6  8  9  353  353  362  5  9  6  295  295  299  11  12  381  398  Vacuum P r e s s u r e T e s t  Treatment Mean  N.B.  2  1. Means u n d e r s c o r e d by t h e sam t h e 5% l e v e l o f s i g n i f i c a n c e  11 281  l i n e a r e not s i g n i f i c a n t l y  2. Numbers a b o v e means r e f e r t o t r e a t m e n t s a s f o l l o w s :  1 2 3 4 5 6  UF-20-55-10 UF-20-55-20 UF-20-70-10 UF-20-70-20 UF-50-55-10 , UF-50-55-20  7  UF-50-70-10  8  UF-50-70-20  9  UF-85-55-10  10  UF-85-55-20  11  UF-85-70-10  12  UF-85-70-20  12 307  10 319  different at  -120-  Table 2 1 .  D u n c a n ' s M u l t i p l e Range t e s t f o r Wood F a i l u r e o f G m e l i n a a r b o r e a . P l y w o o d bonded w i t h UF G l u e .  T Dry  R  E  A  T  M  E  N  T  R  A  N  K  I  N  G  Test  Treatment  Mean  2  11  10  6  9  7  12  35  38  38  39  40  47  ' 52  53  57  61  62  70  11  12  7  6  9  10  8  5  1  4  3  2  11  14  18  24  24  24  31  33  38  44  56  59  Vacuum P r e s s u r e T e s t  Treatment  N.B.  Mean  2  1 . Means u n d e r s c o r e d by t h e same l i n e a r e n o t s i g n i f i c a n t l y t h e 5% l e v e l o f s i g n i f i c a n c e . 2.  Numbers a b o v e means r e f e r  t o t r e a t m e n t s as  follows:  1  UF-20-55-10  7  UF-50-70-10  2  UF-20-55-20  8  UF-50-70-20  3  UF-20-70-10  9  UF-85-55-10  4  UF-20-70-20  10  UF-85-55-20  5  UF-50-55-10  11  UF-85-70-10  6  UF-50-55-20'  12  UF-85-70-20  1  different at  -121Duncan's M u l t i p l e Range T e s t f o r S h e a r S t r e n g t h d f Gmelina a r b o r e a . P l y w o o d bonded w i t h PF G l u e .  T a b l e 22.  T  R  E  A  T  M  N  E  R  T  A  N  I  K  N  G  Vacuum P r e s s u r e T e s t  Treatment  Mean  Boi1-dry-boi1  Treatment  N.B.  Mean  2  5  6  8  2  9  10  308  313  317  318  321  330  6  5  2  8  9  4  239  247  255  258  259  276  4  1  7  337  346  354  10  1  7  286  288  304  1 1 3 382  12  397  405  3  12  Test  2  11 315  1. Means u n d e r s c o r e d by t h e same l i n e a r e n o t s i g n i f i c a n t l y t h e 5% l e v e l o f s i g n i f i c a n c e . 2. Numbers a b o v e means r e f e r  2 3 4 5 6  PF-20-55-10 PF-20-55-20 PF-20-70-10 PF-20-70-20 PF-50-55-10 PF-50-55-20  t o t r e a t m e n t s as f o l l o w s :  7 8 9 10 11 12  PF-50-70-10 PF-50-70-20 PF-85-55-10 PF-85-55-20 PF-85-70-10 PF-85-70-20  322  334  different at  -122-  T a b l e 23.  D u n c a n ' s M u l t i p l e Range t e s t f o r Wood F a i l u r e o f Gmelina a r b o r e a . P l y w o o d bonded w i t h PF G l u e .  T  R  E  A  T  M  E  N  T  R  A  N  K  I  N  Vacuum P r e s s u r e T e s t  Treatment Mean  Boi1-dry-boi1  Treatment Mean  N.B.  2  9  12  11  5  10  7  10  15  16  19  5  9  10  11  12  12  12  16  16  16  1 20  7 20  3 31  4  2  6  8  34  45  45  64  Test  2  1 21  7  4  3  2  6  8  30  34  38  43  46  66  1. Means u n d e r s c o r e d by t h e same l i n e a r e - n o t s i g n i f i c a n t l y t h e 5% l e v e l o f s i g n i f i c a n c e . 2. Numbers a b o v e means r e f e r t o t r e a t m e n t s a s f o l l o w s :  1 2 3 4 5 6  PF-20-55-10 PF-20-55-20 PF-20-70-10 PF-20-70-20 PF-50-55-10 PF-50-55-20  7  PF-50-70-10  8  PF-50-70-20  9  PF-85-55-10  10  PF-85-55-20  11  PF-85-70-10  12  PF-85-70-20  different at  G  -123-  Sapwood T e s t Sample Heartwood T e s t Sample Heartwood T e s t Sample  H„  Corewood T e s t Sample  Thus, t h e r e are f o u r t e s t samples p e r l o g .  The c e n t r e Sample i s used f o r m o i s t u r e content determination  Used f o r S p e c i f i c  F i g u r e 1.  gravity.  P a t t e r n o f c u t o f T e s t Samples from Logs f o r S p e c i f i c G r a v i t y and M o i s t u r e Content D e t e r m i n a t i o n T e s t s .  -124-  Figure 2. "Temperature Changes within a log 8 f t long and 7.7 i n diameter (50°C Heating).  -125-  4  ^  10  H e a t i n g Time  F i g u r e 3.  '  12 (hr)  '  14  -n  16  18  r-i  19  100 -,  85°C Peeled Veneers  50°C Peeled Veneers  '20° CC Pee 1ed Venee r s 80 -\  60 -J  ko-  20-\  0  5  0  10  Visual roughness (.001  inch)  5  T 10  T  15  5  20  Visual roughness (.001  Figure k. Frequency d i s t r i b u t i o n of v i s u a l veneer roughness.  inch)  10  15  Visual roughness (.001  20  25  Inch)  -127-  Figure 5. Dependence of bond q u a l i t y on Peeling Temperature - a nd C'i osed A; s s emb 1 y T i meI h t-e ra c t i 6n -U F ~ D r y Te s t r  :  (Shear Strength).  -128-  70  60  50  Spread 70-Time 20  <u u  3  40 i  ^Spread 55-Time 20 Spread 55 Time 10 -  o o  Spread 70-Time 10 30  0 0  20  40  80  60  R e e l i n g Temperature. ..(.°'C)  100  .  Figure 6. •Dependence' of bon'd q u a l i t y on Peeling Temperature, Glue spread and Closed "Assembly Time Interactions -UF Dry Test (Wood F a i l u r e ) .  -129-  ~  1  '  -r V  rSO  ,' ,00  Peeling Temperature (°C ) Dependence of bond q u a l i t y on Peeling Temperature ancl"G1 ue Spread "I ntferacV\Ion-OF -Vaeuum-pressurre^Test 5  (Shear Strength).  -130-  Spread 55 lb/MDGL  Spread 70/lb/MDGL  0  20  40 Peeling  u  bbn'd qual i ' t y ' o n » P e e l ing' Temperature  aaaanduS'lue;Spread _ , t (Wood Fai l u r e ) . f  80  Temperature  F i g u r e 8? Dependedce of  V'.nreerf  60  I htecaction-UFtJ/aGUum-pressure T e s t  -131-  0  ' 0  -  1  20  ,  ,  40  60  Peeling Temperature  -,  ,  80  100  (?C)  Figure ' 9 . Dependence of bond q u a l i t y on Peeling Temperature, Glue Spread and Closed Assembly Time Interactions -UF vacuum-pressure Test (Wood f a i l u r e ) .  -132-  500 - ,  ~  in Q.  1+00 Spread 70 lb/MDGL  c  Spread 55 lb/MDGL  1_ Z ro  300 H  > I 60  40  20 Peeling  80  100  Temperature  F i g u r e 10. Dependence of bond q u a l i t y on P e e l i n g Temperature and Glue Spread (Shear  Interaction-PF  Strength).  Vacuum-pressure  Test  •133-  500-1  in o.  4ooH Time 20 min. Time 10 min.  cn  c  300 H  20  40 P e e l i n g Temperature  60  80  100  S(°.G')  F i g u r e 11. Dependence o f bond q u a l i t y on P e e l i n g Temperature and C l o s e d Assembly Time  Interaction-PF  Vacuum-pressure T e s t (Shear  Strength).  -13**-  Figure 12. Dependence of bond q u a l i t y on Peeling Temperature 'and .'Oiro's'e'd' Assembly .;T:ime;tl"nteraiction-rPF Vacuum-pressure Test (Wood F a i l u r e ) .  -135-  70  i  60  50  3  30  J  -a O o  20 _J  10 -4  Spread  55"  Spread  70-Time  10  Spread  70-Time  20  Spread  55"Time  10  T  20 Peeling  Figure  13-  60  kO Temperature  80  (°(C)),  D e p e n d e n c e o f bond q u a l i t y o n P e e l i n g Glue Spread and C l o s e d Assembly -PF V a c u u m - p r e s s u r e  100  Test  Time  Temperature, Interaction  (Wood F a i l u r e ) .  Time  20  -136-  400-1  Time 20 min.  300 H  - © T i me 10 min.  D-  c  200 H  20  r  40  T  60  80  100  Peeling Temperature (°6)  v  Figure 14. Dependence of bond q u a l i t y on Peeling Temperature and Closed Assembly Time Interaction-PF Boi1-dry-boi1 Test (Shear Strength).  -137-  Figure 15. Dependence of bond q u a l i t y on Peeling Temperature and Glue Spread Interaction-PF Boi1-dry-boi1 (Wood Fa i1ure).  Test  -138-  60 - i  20  40  60  80  100  Peeling Temperature (°'C,) Figure 16. Dependence of bond q u a j i t y on Peeling Temperature and Closed Assembly Time Interaction-PF Boi1-dry-boi1 Test (Wood F a i l u r e ) .  -139-  APPENDIX 1  B. S. 1455:1963 S p e c i f i c a t i o n f o r Plywood manufactured from Hardwoods.  Tropical  -140-  SPECIFICATION F O R  PLYWOOD MANUFACTURED  FROM  TROPICAL  HARDWOODS  B.S. 1455 : 1963  Price  BRITISH  10/6  net  STANDARDS  INSTITUTION  INCORPORATED BY ROYAL CHARTER  BRITISH STANDARDS HOUSE, TELEGRAMS: STANDARDS A U D L E Y LONDON TELEPHONE: MAYFAIR 9000  B.S. 1455  -141-  CONTENTS Page _o-operating organizations Foreword . . . . ' .  . .  2 5  SPECIFICATION . . . . . . . . . . 6 1. Scope . . 2. Definitions . . . . . . . . . . 6 3. Grade . . . . . . . . . . . 6 4. Cores . . . 6 5. Assembly of veneers 6 6. Bonding . . . . 6 7. Delamination 7 8. Removal of metal clips 7 9. Scarf joints in boards . 1 10. Testing the quality of the adhesion and the kind of bonding in the plywood 7 11. Moisture content. . . . . . . . . . . ^ 12. Dimensions of plywood boards 7 13. Finishing . . . . . . . . . . . . 8 14. Re-testing. . . . . . . . . . . . 8 15. Marking . . . . . . . . . . . . 8 16. Manufacturer's warranty 8  Page . APPENDICES A. Selection of samples from a consignment for testing B.  Method of making the tests and assessing the results . .  9 10 10  TABLES 1. Schedule of tests for proving compliance of the plywood with the requirement of its declared bonding . . . . .  7  2. Wet tests in hot water or steam. . . ...  .  9  PLATES I. Tool for the knife-testing of plywood . . . II. Knife-testing plywood. . . . . . . HI. Bond quality No. 10'  11 11  C Method of applying the k n i f c - t e s t . . . . D. Method of determining moisture content. .  IV. V. VI. VII. VIII.  Bond quality Bond quality Bond quality Bond quality Bond quality  .  .  No. 8 in the Master Scale for No. 6 ^ assessing bond quality No. At in plywood by the knife . No. test . . . . . 14-19 No.  -142-  B.S. 1455  BRITISH S T A N D A R D SPECIFICATION F O R  PLYWOOD MANUFACTURED FROM TROPICAL  •  '  HARDWOODS  FOREWORD This British Standard prepared under the authority of the Timber Industry Standards Committee specifies requirements for plywood manufactured from tropical hardwoods and suitable for all general purposes. Although the scope of the previous issue was not restricted to tropical hardwoods, in practice these were the only species used for plywood manufacture in the U.K. This standard does not specify requirements for blockboards or plywood faced with decorative veneer nor certain specialitymateriais, some of which are covered by the following British Standards: B.S. 6V3. B.S. V35. B.S. 10S3. B.S. 3444. B.S  High strength plywood for aircraft. Medium and low strength plywood for aircraft purposes. British-made plywood for marine craft. Blockboard and laminboard. (in course of preparation) Plywood treated with preservatives or flame retardants or both. (  S P E C I A L N O T E In this revision the restriction o f applicability o f this British Standard to British-made material has been removed. While this allows oversea producers, who supply by far the greater part o f the plywood used in the United K i n g d o m , to comply with the standard i f they so wish, it should be borne in mind that the traditional suppliers to this country work to gradings, sluing standards and tests of their own which are well k n o w n in the U . K . market. The conditions o f these are dictated by the woods available and internal requirements of the particular producing country. If users in the United K i n g d o m require plywood from overseas producers'whose manufacture does not comply with this standard, they should consult their suppliers as to the material most nearly equivalent to the requirements o f this standard. Information as to the species, producing countries, sizes, grading and bonding o f plywood commonly available i n the U n i t e d K i n g d o m is given in B.S. ?493,' Information about plywood '.  The requirements have been modified in the light of experience, and the descriptions of adhesives in Clause 6 have been orought into conformity with those in B.S. 1203*. The dry test has been deleted as experience shows that the wet tests, and the mycological tests when appropriate provide sufficient control of bond quality. The term Grade ' used in this specification refers to the quality of the veneers forming the face and back of the plywood. According to the defects they contain, er.cli of the veneers classified by a number or symbol and the combination of these (e.g. 1 - 2, 2 - 2, or i) defines the grade of the plywood. The standard neither specifies nor gives advice upon the species of the timbers for plywood manufacture. Sources of supply and supplies themselves vary considerably over short periods, and any list of' approved * umbers would not only have to be long to bo comprehensive, but might well, by the omission of their names, piejudice the introduction of additional kinds. Purchasers and manufacturers should agree between themselves on the species that are to be used, having regard to the purpose for which the plywood is intended, particularly where immunity to insect attack is essential. The term ' Bonding * in this standard refers solely to the type of adhesive used in the manufacture of the plywood. It should be understood that although some types of adhesive have, over a period of years, proved themselves adequate to resist full exposure to weather, they do not impart this quality to the plywood as a material. It follows that when plywood is to be exposed to weather or to other severe conditions, not only must the appropriate type of adhesive be employed in its manufacture, but also the wood component must be of a suitable species or be treated with fungicidal or insecticidal preservatives, paints or other surface coatings according to circumstances. This standard does not cover such treatment or coating, which should be the subject of special arrangement between the parties concerned. Some of the te>ts for the compliance of the plywood with the bonding requirements (Clause 6 and the Appendices) arc of necessity somewhat lengthy and troublesome to make. The warranty (Clause 16) does not necessarily mean that the manufacturer has carried but all tlie tests set out in the Appendices, but, in cases of doubt or dispute, these Appendices enable the purchaser or an arbitrator to satisfy himself that the warranty is substantiated or otherwise. 4  N O T E I. Where metric equivalents are given, the British units arc to be regarded as the standard. T h e metric equivalents arc approximate. M o r e accurate conversions should be based o n the tables in U.S. 330, * Conversion factors and tables *. N O T E 2. In place o f t h c customary, but incorrect, use of the pound and kilopramm'e as units of force, the units called pound-force (abbreviation Ibf) and kilogramme-force (abbreviation kgf) have been used in this standard. These are forces which when acting on a body o f mass o n e p o u n d , o r kilogramme respectively, give it an acceleration equal to that o f standard gravity.  ° B.S. 1203, * Synthetic resin adhesives (phenolic and aminoplastic) for plywood. *  . 1455 : 1963  -143-  SPECIFICATION SCOPE  1. This British Standard covers plywood for general purposes manufactured from, tropical hardwoods with rotary-cut or sliced veneers bonded together with an adhesive. The term 'plywood' is intended to include ' multi-ply'.  DEFINITIONS  2. For .the purposes of this standard the definitions in B.S. 565, * Glossary of terms relating to timber and woodwork', apply with the following modifications:  to that used for bonding the veneers. No end joints are permissible. N O T R . Grade 2 venyer excluding pinhole* can be supplied l»y agreement between purchaser and 'supplier.  Grade 3 veneer. Grade 3 veneer may include wood defects, including worm-holes, which are excluded from Grades I and 2 in number and si/.o which do not impair the serviceability of the plywood. It may also include manufacturing defects, such as rough cutting, overlaps, gaps or splits, provided these do not affect the use of the plywood. No end joints are permissible. Other grades. Other grades, appropriate to the end use, may be agreed between purchaser and supplier.  Bonding. See Gluing. Discoloration. Areas, occurring in either streaks or patches, of colour different from that of the surrounding wood and differing from that normally associated with the species. Cluing. The process of uniting, by means of an adhesive, two or more pieces of wood. When used without qualification the t?nn implies a process characterized by continuity of the union over the whole of the areas of contact Rotary Cut {Peeled). (Veneer) produced in a continuous sheet by feeding a knife mounted parallel to the axis into ' a log rotating in a lathe. Cf. Sliced. Sliced {Flat cut). (Veneer) cut sheet by sheet from a stationary block of wood by a knife mounted approximately parallel with and moving to and fro across the longitudinal axis of the block. In some machines the knife is fixed and the block moves. Cf. Rotary cut.  GRADE  3. Plywood shall be graded according to the appearance of the face and back, each being assessed separately after the board has been made and not when in the form of veneer as defined in Clause 2. Grades of veneer are defined as follows: Grade 1 veneer. Grade 1 veneer shall be of one or two pieces offirmsmoothly cut veneer. When of two pieces the joint shall be approximately at the centre of the board. The veneers shall be reasonably matched for colour. The veneer shall be free from knots, worm and beetle holes, splits, dote, glue stains, filling or inlaying of any kind or other defects. No end joints are permissible. Grade 2 veneer. Grade 2 veneer shall present a solid surface free from open defects. When jointed, veneers need not necessarily be matched for colour or be of equal width. A few sound knots are permissible, with occasional minor discoloration and slight glue stains and isolated pinholes not along the plane of veneer. Occasional splits not wider than Yit in (0.8 mm) at any point and not longer than one tenth of the length of the panel or slightly ojvned joints mi™ b«filledwith a suitable filler. This grade shall admit neatly made repairs consisting of inserts of the same species as the veneer, which present solid, level, hard surfaces and are bonded with an adhesive equivalent  6  CORES  4. Core veneers may contain knots, open defects, gaps, overlaps or pleats, provided such defects will not cause undulations or impair the smooth finish of the surfaces required for painting or staining. No end joints are permissible. In the cores of plywood faced on at least one side with Grade 1 or Grade 2 vcr.cer, open defects and gaps in the ply adjacent to the. Grade 1 or Grade 2 vcr.cer shali not exceed Mo in (2.5 mm). It shall be at the purchaser's option to accept .the manufacturer's warranty of compliance (Clause 16) or to inspect the veneers before the plywood is assembled. ASSEMBLY OF VENEERS  '5. Unless otherwise specified by the purchaser, the direction of the grain of the veneer shall be at right angles in adjacent plies, except in the case of boards compiling an even number of plies, when the grain of the centre pair shall follow the same direction. The veneers forming any one ply and the corresponding ply on the opposite side of the central plane of the board shall be of the same thickness and species or of species known to be similar to one another in physical characteristics, and shall be cut by the same method, i.e. either all. totaiy-cut o." sliced. The tight side of the veneer should be turned outwards in faces and backs. Tapes shall not be used internally. When used for making edge joints or repairing splits in face veneers they shall be removed subsequently. This paragraph shall'apply unless otherwise agreed between purchaser and supplier. Ail plywood thicker than % in (10 mm) shall be made of not less than 5 plies. The core in 3 ply shall be not more than 60 per cent of the total thickness: for panels with more than three plies, the laces, and all plies running in the same direction as the faces, shall have a total or combined thickness of not less than 40 per cent and not more than 65 per cent'of the total thickness of the panel. In the dry state, no face ply shali be thicker than \s in (3 mm) and no inner ply shall exceed ?ie in (5 mm). BONDING  6. Bonding between veneers shall be WBP, BR, MR or INT defined* as follows, and these designatory letters siiiiil be toed i n u i a i k i n g iiic ply wOvu. • T h e s e designations are those used i n D.S. 1203, ' S y n t h e t i c resin adhesives (phenolic and aminbplastic) for plywood".  B.S. 1455 :  -144Tvpr t!/?/'.- V'fdihci und hoil-pioof. Adhesives of the type'- which by systematic tests and by their records in bcrviic oxer ni;inv v r . i r s h;ivi» heen nrovrd to n-iakr. joints '•«*.hly resistant to weather, micro-organisms, cold and .ling water,steam and dry lieat. :  Type BR: Boil, resistant. Joints made with these adhesives have good resistance to weather and to the boiling water test, but fail under the very prolonged exposure to weather that Type W B P adhesives will survive. The joints will withstand cold water for many years and are highly resistant to attack by micro-organisms. Type MR: Moisture-resistant and moderately weatherresistant. Joints made with these adhesives will survive full  TABU' 1. SCHEDULE OF TESTS FOR PROVING COMPLIANCE OF THE PLYWOOD WITH THE RFOniRF.MF-NT OF ITS DECLARED BONDING The letters show the appendices giving details of the tests. A dash indicates thatthe test named in the column is not applicable.  1 Donding  I  1  WBP  exposure to weather for only a few years. They will withstand cold water for a long period and hot water for a limited time, but fail under the boiling water test. They arc. resistant to attack by micro-organisms.  BR  Joints made with these adhesives arc resistant to coid water but are not required to withstand attack by micro-organisms.  INT  Type INT:  Interior.  0ELAMTNATION  7. The glue bond between individual plies shall be adequate"} and continuous over the entire area. Any board showing delaminatibn or blistering does not comply with the requirements of this standard. -  REMOVAL OF METAL CLIPS  8. All metal clips used for assembly during the manufacture of board shall be extracted or cut away in trimming before delivery. SCARF JOINTS (N BOARDS  9. When sizes larger than available press sizes are required, scarf joints through the thickness of the board shall be permitted by agreement with the purchaser. All scarf joints shall be bonded with the equivalent type of adhesive used for the manufacture of the boards themselves, and shall be made with the following inclinations: a. Board under Vi. in (13 mm) thick: Tin 10. b. Board Vi in (13 mm) thick and over: 1 in 8. N O T E . It should be noted thrst the glue line of any scarf joint is visible on the surface of the board.  TESTING THE QUALTTY OK THE ADHF.SION AND THE KIND OF BONDING LN THH rj.YV.OOD  10. The appropriate tests for adhesion in the four kinds of bonding arc set out in Table 1, which gives the requirements for the particular appendices concerned.  !  MR  Tests Wet test in hot water or fleam  1  jj !  Wet test in cold water  Mycolo;;ical test  A, B2o, C  A. B3  •  A, Bl, C i A, Bl. C j A, Bl, C  -  A, B&j, C  A, B3  A, B2o, C  A, B3  A, B26  —  •  When the adhesion of the plywood is tested by the methods described in Appendices A, B and C the results of the tests shall be as follows: Bonding WBP, BR and MR. The wet test in hot water or steam. (Appendix Bl) and the wet test in cold water (Appendix B2o). No glue line shall have a bond quality® of less than two, and the average value for all those tested shall be not less than five. Bonding INT. The wet test in cold water (Appendix B2b). At the conclusion of the test, none of the test pieces shall show any delamination, blistering on the surfaces or separation of the joints between veneers at the edges. Bonding WBP,. BR and MR. The mycological test (Appendix B3). At the conclusion of the test none of the test pieces shall show any delamination, blistering on the surfaces or separation of the joints between veneers at the . edges. MOIST'uRE CONTENT  11. At the time of leaving the factory, finished boards shall have a moisture content determined by the method described in Appendix D of 8 to 12 per cent. DIMENSIONS OF PLYWOOD BOARDS  12. The dimensions along the grain of the face veneer shall be quoted first. N O T E . It is not practicable to standardize the sizes of boards at present. Information on the sizes most commonly available are given in B.S. 3 4 9 3 , * Information about plywood ',  a. Length ant! width. The length or width of a. board shall not be less than the specified size nor more than y in (3 mm) greater than the specified size. b. Thickness. Unless otherwise agreed between purchaser and supplier, the nominal thickness shall be that of the board before sanding or scraping. The thickness of the board shall not differ from the nominal thickness by more than ± 5 per cent for boards up to and including V* in (6 mm) thick or ± 3 per cent for boards in excess of V* in (6 mm) thick. An additional allowance of 0 008 in (0-2 mm) per side shall be made for " scraping or sanding. 6  .r p e r s te o n y l e a t r n h e n c o il a d h e v e s is h a v eb e e ns h o w n ot n ie t h te s in r q e u r m i c e n . ti p t o 'Id rn ie to p r ra o tit n f *a d e q u e a t *s e eC a u ls e1 0 and a p p e n c d e is e r e f e r te h te r e n io.  7  1963 Squareness.  The lengths of the diagonals of a board shall not differ by more than in per foot (0-25 per cent) of the length of the diagonal. FINISHING  13. Boards shall be sanded or scraped both sides unless otherwise agreed between purchaser and supplier. RE-TESTING  14. In the event of failure to comply with any one of the test requirements given in Clauses 10 and 11, the plywood concerned need be re-tcsted only in respect of that requirement. If the rc-test fails, the batch shall be deemed not to comply with this British Standard.  N O T ! : . The mark U.S. 1455 on ilic product is a claim by ti;C manufacturer that it complies with the requirements pi this Uritish Standard. The Hrilish Standards Institution is the owner o f the registered certification trade mark shown below. This mark can be used only by manufacturers licensed under the certification mark scheme operated by the B.S.I. The presence of this mark on a product is an assurance that the goods have been produced to comply v.ith the requirements of the British Standard under a ssstem of supervision, control and testing operated durinp manufacture and inclv.din'j! periodical inspection at the manufacturer's works in accordance with the certification mark scheme of the B.S.I. Further particulars of the terms of licence may be obtained from the Director, British Standards Institution. 2 Park Street, London. W.I.  MARKING  15. Each board shall be marked with the following particulars and unless otherwise agreed the mark shall be near an edge on the back. a. Manufacturer's name or mark. b. Country of manufacture. e. The number of this British Standard, i.e. B.S. 1455. d. Grade for face and back (e.g. 2-3). For grades oilier than 1, 2 or 3 (see Clause 3) the grade mark shall be that agreed between purchaser and supplier. t. Bonding (i.e. WBP, BR, M R f.  Nominal thickness of board.  or INT).  MANUFACTURER'S WARRANTY  16. The marking of the boards by the manufacturer as set out in Clause 15 itself constitutes a warranty that the plywood complies with the appropriate rcquircmctits of this standard. In cases of dispute or doubt, Clause 10 indicates the procedure for testing the plywood for compliance with the requirements for bonding (Clause 6): the grade (Clause 3) can be decided by inspection.  -146-  APPENDIX 2  Export Standard  Specifications  of  Japanese Plywood, E x c e r p t s . (Japan).  1968.  -147-  EXPORT  ~  STANDARD  JAPANESE  ^ "  «o /sea  m a y-  SPECIFICATION  OF  PLYWOOD  Excerpted and Arranged for. Commercial Purposes  Effective January 1, 1968  The Japan Plywood Manufacturers' Association The Japan Specialty Plywood Manufacturers' Association The Japan Plywood Inspection Corporation Japan Plywood Exporters' Association  r  -148-  foreword •  T h i s publication has been excerpted and arranged f r o m B a s i c Rules of Inspection f o r Common Plywood and Specialty Plywood as set forth jointly by M i n i s t r y of A g r i c u l t u r e and F o r e s t r y , and M i n i s t r y of International T r a d e and Industry by joint Ordinance No. I . November 10, 1967.  History:  .  The F i r s t standards were promulgated in June, 1950. The F i r s t Revision was announced in August, 1951. T h e Second Revision was announced i n F e b r u a r y , 1954. The T h i r d Revision was announced in June, 1957. T h e F o u r t h Revision was announced in January, 1958. T h e F i f t h Revision was announced in May, 1963. T h e Sixth Revision was announced i n November, 1967.  Interpretation:  A n y dispute as to interpretation of this unofficial translation f o r c o m m e r c i a l purposes shall be f i n a l l y decided on the basis of the o r i g i n a l text in the Japanese language.  -149-  1. EXPORT STANDARD OF COMMON PLYWOOD  Page (I)  DOOR SKIN P L Y W O O D  3  1. Plywood with a face veneer .of domestic species 2.  (n) 1.  Plywood with a face veneer of lauan species  10  WALL. PANEL, P L Y W O O D  18  Plywood with a face veneer of domestic species  <1)  3  ." 18 18  Regular  (2) Rustic 2.  (HI)  f. • '  25 31  Plywood with a face veneer of lauan species  P L Y W O O D F O R G E N E R A L USES  . 38  1.  Plywood with a face veneer of domestic species  2.  Plywood with a face veneer of lauan species  47  ; . .  S E P A R A T E P A R A G R A P H - P h y s i c a l Inspection 1.  5  P n bonding T e s t  6. Type III soak delamination T e s t 7.  Moisture content Test  9  60  4. Tyne I =oak delamination T e s t 5. Type II soak delamination T e s t . .  57 -57  Cyelic-boilTest  2. Hot and cold soaking T e s t 3.  38  • 60 '.  60 61 61  -150-  SEPARATE  PARAGRAPH  P h y s i c a l Inspection  1. Cyclic-boil test (1) P r e p a r a t i o n of Specimen Specimens s h a l l be prepared in accordance with the following methods f r o m the part of sample which i s free f r o m any defect to affect bonding strength of the said specimen. a.  P'or 3 ply-plywood having face i-.nd back veneers in 1/16 i n . o r m o r e of thickness, four specimens s h a l l be prepared in . conformity to drawing A; and f o r the said plywood having face or back veneer in less than 1/16 in. of thickness o r a veneer s h e a r e d easily, four specimens s h a l l be prepared i n conformity to drawing B.  •  In this case, one half of total specimens s h a l l be prepared to c o m p r i s e r e g u l a r direction of core's r e v e r s e check and another half s h a l l be p r e p a r e d to involve contrary direction o f core's r e v e r s e check.  Tl 5— j H •'••>•»>  f —  "i  i  i  HI—  i H i , - ^ — — |  (Unit : inch)  b.  F o r 5 ply-plywood. 3 ply-plywood which c o m p r i s e s any two bonded layers respectively in a specimen shall be obtained by means of stripping surplus veneers and specimens shall be prepared f r o m the said 3 ply-plywood in conformity to drawing A.  57 -  -151-  (2) T e s t i n g method 'A specimen shall be submerged in boiling water for four hours and then d r i e d at a temperature of GO°C + 3°C during 20 hours. F u r t h e r m o r e , it shall be submerged again in boiling water for four hours and then, shall be continuously kept in the* said water until its temperature goes down to a r o o m temperature.  Bonding test  s h a l l be performed on this specimen under wet conditions.  (Bonding  test: Both ends of specimen a r e clamped by grips and a r e tensioned by a load velocity of 1, 320 Lb., maximum per minute and maximum load i s measured at the time of rupture.) (3) Successful standard of test Bonding strength of specimen shall be equal to o r m o r e than the standard figures of bonding strength stipulated in the following Table.  Standard F i g u r e s of bonding strength  Species of Wood  145 (Lbs. /sq. in. )  Birch Beech, Oak, Japanese Itaya Kaede (Maple), Japanese Akadamo (Elm), Japanese Shioji (Ash) and Japanese Yachidamo (Ash) Japanese Sen (Caster Arabia), Japanese Hohnoki (Magnolia), Japanese Katsura (Judaf. T r e e ) and Japanese Tabu (Lourel)  135  115  Japanese Shiba (Bass wood)  100  L a u a n and Others  110  Note-  1.  When a specimen c o m p r i s e s veneers of different wood species, the species having lowest standard figure, out of various standard figures of bonding strength for those species s h a l l be specified f o r the standard figure of this specimen.  - 58 -  -152-  2.  Bonding strength of specimen shall be calculated by the *. following formula. But, provided that a thickness ratio of c o r e sheet in proportion to face sheet is 1. 5 o r m o r e f o r this specimen, the above calculated figure shall be multiplied by a coefficient in column of the following table which is c l a s s i f i e d in conformity to thickness ratio in the said table and the multiplied figure s h a l l be specified as this bonding strength. Bonding strength Lb. /sq. in. =  P ^ , wherein p i s  m a x i m u m load (Lb.) in the test of bonding strength and b i s width of bonded surface (surface between both grooves) and h is length of bonded surface (surface between both grooves): T h i s f o r m u l a i s applicable f o r a specimen i n the f o r m of drawing A, and another specimen in the f o r m of drawing B which i s used f o r c y c l i c b o i l test and hot and c o l d soaking test.  , Bonding strength Lb. /sq. in. =  p b  ^  x 0. 9, wherein p, b  and h have the same significances with the above f o r m u l a : T h i s f o r m u l a i s applicable f o r a specimen i n the f o r m of drawing B which is used dry bonding strength test. T h i c k n e s s Ratio  Coefficient  1. 50 to less than 2. 00  1.1  2. 00 to less than 2. 50  1.2  2. 50 to less than 3. 00  1.3  3. 00 to less than 3. 50  1.4  3. 50 to less than 4. 00  1.5  4. 00 to less than 4. 50  1-7  4. 50 o r m o r e  2.0  Hot and cold soaking test (1) P r e p a r a t i o n of Specimen T o conform to the paragraph I-(l). (2) T e s t i n g method A specimen s h a l l be submerged in hot water at a temperature of 60°C + 3°C f o r three hours and then s h a l l be continuously kept i n the said water until the temperature goes down to a r o o m temperature.  - 50 -  -153Bonding test shall be performed for this specimen under wet conditions. (3) Successful standard of test. T o conform to the paragraph I-(3).  3.  Dry bonding test  (1) Preparation of specimen T o conform to the paragraph I-(l). (2) T e s t i n g method T e s t of bonding strength shall be performed f o r a specimen under common conditions. (3) Successful standard of test. T o c o n f o r m to the paragraph I-(3).  4. . Type I soak delamination test (1) Preparation of specimen F o u r specimens in size of 3 i n . square shall be prepared f r o m the part of sample which is free from any* defect to affect bonding strength of the s a i d specimen. (2) T e s t i n g method A specimen shall be submerged in boiling water f o r four hours and then d r i e d at a temperature of 60°C + 3°C during 20 hours. F u r t h e r m o r e , it s h a l l be again submerged in boiling water for four hours and d r i e d at temperature of 60"C + 3"C during three hours. (3) Successful standard of test. T h e part which does not delaminate in the s a m e bonded l a y e r of a specimen s h a l l have 2 i n . o r m o r e of length at the s i d e surface.  5. Type 11 soak delamination test (1) P r e p a r a t i o n of specimen T o c o n f o r m to the paragraph 4 - ( l ) . (2) T e s t i n g method A specimen shall be submerged in hot water at a temperature of 70°C + 3°C f o r two hours and then d r i e d at temperature of 60°C + 3°C during three hours. - 60 -  -154-  (3) Successful standard of test T o conform to the paragraph, 4-{3).  6. Type Hi soak delamination test (1)  P r e p a r a i i o n of specimen T o conform to the paragraph 4 - ( l ) .  (2) ' T e s t i n g method A specimen shall be submerged i n w a r m water at a temperature of 3 5 ° C ' + 3 C f o r two hours and then d r i e d at temperature of 60"C C  +3°C  during three hours. (3) S u c c e s s f u l standard of test. T o conform to the paragraph, 4-(3).  7. Moisture content test (1)  P r e p a r a t i o n of specimen Two  specimens s i z e d appropriately shall be prepared f r o m the part of  sample which i s f r e e f r o m any defect to affect moisture content of the said specimen. (2) T e s t i n g method A f t e r weight of specimen i s balanced, the specimen s h a l l be d r i e d at a temperature of 100°C to 105°C until it reaches to constant weight.  This  weight w i l l be balanced and a moisture content s h a l l be m e a s u r e d by the following formula. But, when moisture content is m e a s u r e d by another process besides the above mentioned method with equal o r m o r e degree of accuracy, the measurement may  be accorded with this latter process. Wl  -  Moisture content (per cent) °  W2 —  x 100  W2 wherein Wj  is a weight in g r a m before drying and W*2 i s a bone  dry weight in gram. (3) • Successful Standard of T e s t  •  13 per cont or less of moisture content f o r specimen.  - 61  -  -155-  APPENDIX 3  DIN 68705 Plywood Standards (translated) (Germany). 1968  :  lilt  January .190ft  C01.4  I  Plywood General Recuirenents  Definitions  F  HAR22  i«7n^ Sheet  Sperrholr-; Becriffe, Allgemeine Anforderungen, Priifung ! 2ais Standard applies to veneer boards and blockboards. I t specifies definitions, requirenents r and t-jmnrs which are applicable to a l l types of plywood regardless of i t s use. . r l y v o c a BZ-J.1 be ta>:en as meaning a l l sheets consisting of at least three superimposed layers of £ voca D o n d e a together with the grain running crosswise. Plywood (syabol SP according to DIN 4076 h y-sse-z -under revision) i s therefore a generic definition f o r various t y p e B of sheets. A * t distinction i s nade between: 2^. Veneer board (synbol HJ according to DIN 4076) . Plyvocd i n which a l l p l i e s consist of veneers and are bonded one on top of the other crosswise -' " the sheet. Y'ith an even nuaber of veneers the two innerraost p l i e s pa: a i l e l to tne grain. a 2 '. Di a : o a a 1 1 y l a m i n a t e d v e n e e r b o a r d (symbol Stf according to Dir; ^o?s) sting cf at least five plies of veneer bonded to each other, i n such a way that V e n e e r b o a r d c o n s i the s £ ~ ~ - of adjacent layers cross at angles of 45° or l e s s . the d i r e c t i o n s cf (symbol 71 according to Dili 4076) 2.2. 31ockoos.rds Plyvood consisting o f at least two covering; veneers and a core of adjacent strips of* wood. In"blockboards consisting o f three plies the direction of the grain of the .core runs crosswise, i n blockboards consisting of i'ive plies parallel to the bonded covering veneers. A l l layers are bonded together crossvise. Slockboards consisting of five p l i e s are mainly produced to neet higher standards of surface condition and diuensional s t a b i l i t y . . . A distinction i s nade b ;ween various blockboards, according to the type of core", These are: 8 2.2.1. L a n i n b o a r d c o r e (symbol SIAE according u to DIH ——. 4076) ' —I —• Karr.ov:, lemnated strips of wood consisting of rotary cut veneers up to 8 o n thick, bonded together and arranged edgewise to the plane of the board. s t  1  2.2.2. B o n d e d b l o c k b o a r d c o r e (s.yiabol ST according to DIN 4076) Xaainated strips of wood bonded together side by side and usually about 24 on hut not nore than 50 cr: wide.  2.2.3U n b o n d e d b l o c k b o a r d c o r e (synbol SH according to DUf 4076) Larjinated strips of wood arranged close together but not bonded and usually about 24 i n but not core than 50 nc wide. Keouirenents 2 1 _3ondin2 Choice of plywood bondings shall governed by the climatic conditions tne^boards or sheets are subjected i n use. A distinction i s aade i  be  i  3.1.1.  X?  20  to which betweenandthehunidity following types of  ( i n t e r i o r plywood)  low atnospheric huaidity (not weather-. and humidity (weather-resistant).^  con  resistant). " 5 resistant whan used i n rooas with generally 5.1.2 . AV 100 (exterior plywood) 36ndi. 2.5 resistan to the effects of weather N o t la additi== tc ties? boadinga the following types  the  can. a l s o be p r o d u c e d ! IS i7z 3 s : i i ; j r e s i s t a n t « i s i = s « d£ i ai a 7O0E9 with high atmospheric h u a i d i t y and r e s i s t a n t to o c c a s i o n a l c o n t a c t w i t h v&'-rr -p to about c " c - s-r-.iti t i e sheets or boards are p r o t e c t e d a g a i n s t d i r e c t e f f e c t s o f the weather (set »eati-r-resist2r:t} A ICC:  SzzzL^s  ^ t s i s ' . e s : to t i e a c t i o s of c o l d and hot water ( l i m i t e d weather r e s i s t a n c e ) . F a r t i i u . a r s r<!*uti=c to r * s tsr.ee r e f e r only to bonding. -in-  •  strength)  industrially t e.,.„-«. i i R S c-e c -^ . e s ^ 0 f 1 = ^  it  7 = short testings vmch are a^ents, other sr — short tests itr.air.r strer j? tic.-.. It i s ^;rin b wat:; and Lr.er.s soai i c 1.1.1. S=:tplir.r; r i v * cpecir.e:.s neasurir.R 200 u x c d  b  usually bonded with hardening synthetic resin glues whos long-ouration and outdoor tests. As a result; i t i s oocsible adjusted to the chemical basis of the resins. When uslnr other suitable for the appropriate bonding a entsmust be  £ofvS. ' '£-4%*°"-^ IE ffill ff l "»i«*«c. of .glue joints to mechanical destrucstill weJ? * " * * ° * S to MS 53255, usin n f test 100 un shall be taken f o r the knife test fron ever* sheet to < a  /  r  t h C  S h e a P  t C S t  a c c o r f i  G  *1 tno SVtfJill?'*** r ?coverintr £ ° ?veneern cirection of the?™* r;ram of° the  >- t h^. r^,r« dimension 200 •Z"" -s- h a°PPfl"J JplJ O n » of  fro* the cd,:e of the sheet, the others froa fhe inllle  S  1  E  C  he  T  a  E  e  8  f  b 0  d i n E  Allelnvukuut d.r Normblorlei durch Brulh-Veririeb OmbH, - Berlin 30 und Kolo  A W  100  UJ  the shlet" T1TU  (  ^  S I > e C l n s n B  1  L  ttust  C 0 O c  Continued on panes 2 to 4 Explanations on p'i£« 4 ^ .  g n i M .  Fac* 2  -157-  Dili 66705 Sheet 1  J  4.1.1.2. P r e t r e a t m e n t o f s p e c i m e n s The f o l l o w i n g short t e s t a are s u f f i c i e n t f o r t e s t i n g bonding provided the s t a t e d g l u e s were used." Bondine; I? 20 (urea r e s i n s ) Specimens immersed i n v o t e r f o r 24 hours a t a water temperature  of 20 °C + 2  dec-  Bonding AV 100 ( p h e n o l i c , p h e n o l i c - r e s o r c i n or r e o o r c i n r e s i n s ) a) Cold water t e s t : Specimens'immersed i n water f o r 24 hours at a water temperature o f 20 °C + 2 deg. b) B o i l i n g t e s t with a l t e r n a t e h e a t i n g and. c o o l i n g as f o l l o w s : B o i l i n g f o r 4 hours (100 °C) Eeeoing f o r 16 to 20 hours i n hot a i r a t 60 °C + 2 deg i n a hot c a b i n e t acco-cVi r - t o DIN 50011 ~ • . " B o i l i n g f o r 4 hours C o o l i n g f o r 2 to 3 hours under water at a water temperature o f 20 °C + 5 defj. r  M o t e t Bonding IV* 67 (unextended or nelajaine-reinforced urea r e s i n s ) Specimens immersed i n water for 3 hours at a water tesperature of 67 ° C + 0.5 C o o l i n g under water for 2 hours at a rater temperature of 20 ° C + 5 deg. Bonding A ICO (nelamine r e s i n s or mixtures of urea and melaaine r e s i n s )  Boiling for 6 hours (100  . deg.  °C)  Coolins under water for  2 hours at  a water temperature of 20 °C + 5 deg.  4.1.1.3- Test procedure K n i f e t e s t s a c c o r d i n g to DIU 53255 s h a l l be c a r r i e d out on a l l p l i e s o f the f i v e ( t e n ) speciaens taken a c c o r d i n g t o S e c t i o n 4.1.1.1 and p r e t r e a t e d a c c o r d i n g t o S e c t i o n 4.1.1.2. 4.1.1.4. Assessment of t e s t r e s u l t s Test r e s u l t s f o r a l l glue j o i n t s examined s h a l l be designated a c c o r d i n g to DIN f o l l o w i n g g r a d i n g numbers: 1 excellent. bord?ng  3 adequate bonding  2 good bonding  4 inadequate  4.1.2.  S h e a r  53255 by the  bonding  t e s t  4.1.2.1 Sampling and p r o d u c t i o n of specimens At l e a s t ten simple tension/shear specimens s h a l l be prepared according t o Din 53255 f r c n every sheet to be t e s t e d (20 simple tension/shear specimens from sheets of bonding t y j e A'W 1C0). I n the case of sheets with f i v e and more l a y e r s bf veneer the.outer veneers s h a l l " be removed ( e . g . by p l a n i n g down) t o three p l i e s . 4.1.2.2. Pretreatment of specimens a c c o r d i n g t o S e c t i o n 4.1.1.2. 4.1.2.3. T e s t i n g and e v a l u a t i o n Shear t e s t s a c c o r d i n g to PITT 53255 shall be c a r r i e d out on the ten (20) specimens taken a c c o r d i n g to S e c t i o n 4.1.2.1 and pretreated. according to S e c t i o n 4.1.1.2, and the" r e s u l t s e v a l u a t e d . 4.2 . _Bendir^_strenrjth The bending s t r e n g t h s h a l l be determined a c c o r d i n s to. DIK 52371 ( a t present s t i l l c i r c u l a t i n g as d r a f t ) . |ir  4.3. Moisture content The moisture content s h a l l be determined a c c o r d i n g t o DT.il 52183. 5. Q u a l i t y safeguard Depeadins on the f i e l d of a p p l i c a t i o n o f veneer boards and blockboards, they can o r must be subjected to r e g u l a r s u p e r v i s i o n of t h e i r q u a l i t y i n the form of a s t a t i s t i c a l q u a l i t y c o n t r o l (own s u p e r v i s i o n ) and/or a s u p e r v i s i o n t e s t i n g ( o u t s i d e s u p e r v i s i o n ) . " . ft.1. S t a t i s t i c a l q u a l i t y c o n t r o l (own s u p e r v i s i o n ) 5.1.1. S a m p l i n g ? o r ova s u p e r v i s i o n the number of sheets to be s e l e c t e d w i l l depend on the r e l e v a n t p r o d u c t i o n ' progrsrcse. At l e a s t one sheet must be taken a t random from every l o t (consignment) a h i , i n the case o f continuous p r o d u c t i o n , a t l e a s t one sheet d a i l y , and must be t e s t e d f o r the s p e c i f i e d rvrcperties. 5.1.2. C o n t r o l c a r d s The r e s u l t s o f own s u p e r v i s i o n s h a l l be recorded and entered on c o n t r o l card3. S t a t i s t i c e v a l u a t i o n covers r.ean values f o r sheets and a f l u c t u a t i o n measure. The f l u c t u a t i o n measure .chosen caa e i t h e r be the v a r i a b l e s2, the standard v a r i a t i o n s or span R. S u p e r v i s i o n of -the span does not r e q u i r e any c a l c u l a t i o n s but i t i a not s u i t a b l e f o r systematic e v a l u a t i o n s . For subsequent e v a l u a t i o n s , f o r d e c i d i n g whether s e v e r a l sheet o r board thicknesses .-:r.d/or c o n s t r u c t i o n a l combinations should be summarized under a b a s i c l o t and f o r c a l c u l a t i n g varniar; and c o n t r o l l i n i t 3 i t i s necessary to c a l c u l a t e and determine the sua t o t a l of i n d i v i d u a l v a l u e s Z x i and t h e i r squares Ex^ f o r each sheet t e s t e d . Warning and c o n t r o l l i m i t s f o r the c o n t r o l cards can be c a l c u l a t e d the f i r s t time a f t e r t e s t i n g ebout 25 sheets per l o t . They should be f i x e d annually and entered on new c o n t r o l c a r d s . CY.TJ s u p e r v i s i o n records must be kept f o r a t l e a s t f i v e y e a r s . 5.1.3* T e s t i n g n o n Veneer boards and blockboards i n t h e i r state of equilibrium n o i s t u r c content o f sheets o r  - c o n d i t i o n e d sp ec i n e n s l e a v i n g the press f r e q u e n t l y have a lower moisture content than i n a standard, c l i m a t e 20/65 Dili 50014. As a r u l e adjustment o f the boards to the standard c l i m a t e takes about 7 days, even l o a d e r i n  -158-  DIH  68705 Sheet 1 Page 3  aec The t e e t i n g of non-conditioned bending specimens can produce systematic v a r i a t i o n s from measurements undertaken on c o n d i t i o n e d specimens. Systematic v a r i a t i o n s i n bending p r o p e r t i e s c f non-conditioned specimens must t h e r e f o r e be taken i n t o account by c o r r e c t i o n f a c t o r s f o r the mean values and f o r the warning and c o n t r o l l i m i t s . C o r r e c t i o n f a c t o r s determined by experiment should be re-examined from time to time. 5.2._Superyision  t e s t i n g (outside  supervision)  Outride s u p e r v i s i o n t e s t i n g s must be c a r r i e d out every .six months by an o f f i c i a l l y recognized m a t e r i a l t e s t i n g i n s t i t u t e on the b a s i s o f a s u p e r v i s i o n agreement, p r o v i d e d r e g u l a r s u p e r v i s i o n i n accordance with r e g u l a t i o n s o f b u i l d i n g a u t h o r i t i e s does not take p i e c e under the d i r e c t i o n of a recognised q u a l i t y c o n t r o l body. A c o n d i t i o n f o r c a r r y i n g out outside s u p e r v i s i o n i s proof o f p r o p e r l y conducted own s u p e r v i s i o n a c c o r d i n g t o " S e c t i o n 5-1. 5-2.1. S a m p l i n g • ~~ In outside s u p e r v i s i o n three sheets o r boards s h a l l always be s e l e c t e d a t random from a l o n r e s t p o s s i b l e production p e r i o d by a r e p r e s e n t a t i v e o f o r person appointed by the supervisor;.' department and s h a l l be marked immediately so a s t o prevent c o n f u s i o n . A r e p o r t cn s e l e c t i o n of a random specimen s h a l l be drawn up by the person choosing the specimen and countersigned by the v.-orks manager o r h i s r e p r e s e n t a t i v e . T h i s r e p o r t must c o n t a i n the following particulars: . e) Date and p l a c e o f sampling; bJ P o s s i b l e s i z e o f stocks from, which the sheets o r boards are taken; c) Number and date o f production o f the boards o r sheets belonging t o the specimens taken at random; d) P a r t i c u l a r s of how the sample sheets o r boards were marked by the person s e l e c t i n g them; e; A statement t o the e f f e c t that the specimen vas s e l e c t e d a t random; f ) Fames'of persons present during s e l e c t i o n o f the specimen; g) Ko'ces on t-sstiag and e v a l u a t i o n o f records from own s u p e r v i s i o n . The r e p o r t s h a l l be submitted to the competent m a t e r i a l t e s t i n g i n s t i t u t e t o g e t h e r w i t h the specimen taken a t random. N o t e : The f o l l o w i n g m a t e r i a l t e s t i n g i n s t i t u t e s (shown i n a l p h a b e t i c a l o r d e r ) a v a i l a b l e for supervision t e s t i n g : B a y e r i s c h e l a n d e s g e w e r b e a n s t a l t , Niirnberg 2, Gewerbemuseuraplatz 2  are e t  present  Bundesforeehungsanstolt fiir F o r s t - und H o l z w i r t s c h a f t , Heinbek b e i Hamburg, Schlofl Bundesanstalt fi:r Kate r i a l priif ung (BAM), B e r l i n ^5 (Dahlem), Unter den E i c h e n 87 F o r s e h u n g s i n s t i t u t fur H o l z ' e r k s t o f f e und H o l z l e i m e , K a r l s r u h e - D u r l a c h , D i e s e l s t r a f l e 6 Forschungs- uod Materialprufungsamt fur das Bauwesen - O t t o - G r a f - I n & t i t u t - , S t u t t g a r t - V a i h i a g e n , R o b e r t - i e i e h t - S t r a B e 209 I n s t i t u t fur Baustoffkunde und S t a h l b e t o n der Technischen Hochschule Braunschweig, A n t l i c h e K a t e r i a l p r u ' f u n r ; s a n s t a l t fiir das Bauwesen, Braunschweig, BeethovenstraBe „ , I n s t i t u t fiir Flugzeugbau und L e i c h t b a u , Technische Hochschule Braunschweig, Braunschweig, Langer Kamp I9t> I n s t i t u t fiir E o l z f o r s c h u n g und H o l z t e e h n i k der U n i v e r s i t a t Kiinchen, Kiinchen 13, Winterers trade *»5 I n s t i t u t fiir K a t e r i a l p r u f u n g und Foroehung des Bauwe6ens der Technischen Hochschule Hannover . A n t l i c h e K a t e r i a l p r i i f u n g s a n s t a l t f u r das Bauwesen, Hannover, iiienburger StraBe 3 S t a a t l i c b e K a t e r i a l p r i i f u n g s a n s t a l t Darmstadt an der Technischen Hochschule Darmstadt S t a a t l i c b e s K a t e r i a l p r u f u n g s a n t Nordi-hein-tfestf a l e n , Dortmund-Aplerbeck, MarsbruchstraBe 186 Versuehsanatalt fur S t a h l , Holz und S t e i n e - K a t e r i a l p r i i f u n g s a n s t a l t der T e c h n i s c h e n Hochschule K a r l s r u h e , K a r l s r u h e , X a i s e r s t r a Q e 12 ttllhelm-Klauditz-Institut fiir E o l z f o r s c h u a g as der Technischen Hochschule Braunschweig, BraunschwelgK r a l e n r i e d e , B i e n r o d e r weg 5 * * 1  S t a t e t e s t i n g i n s t i t u t e s abroad can undertake q u a l i t y s u p e r v i s i o n t e s t i n g s i n c o o p e r a t i o n with one o f the above-mentioned German i n s t i t u t e s .  5.2.2. T e s t i n g o f own s u p e r v i s i o n Vhen sanplir.-- according t o S«ction 5.2.1 records o f own s u p e r v i s i o n mentioned i n S e c t i o n 5.1.2 s h a l l be t e s t e d . Designation rlywood'"eheeus o r boards i n storage dimensions s h a l l be marked by the manufacturer v i t h a sz?-~ on the r c c r c r s i d e .  C rher Sri: DIK Dili DI«  s.tnndr'rd.-»  *-C, o *07£ 5001^ 51220 51221  Dili 52153 DIN 53251 DIH  53255  BIN 66330 DIN 68705  Weed, v.ood t u t o r i a l s and laminated boards; d e f i n i t i o n s and symbols Tiyvco.-!; dir.cncions Tec^iri-;, of c a r t - r i a l s , s t r u c t u r a l • components and equipment; standard c l i m a t e s f . a t e r i a l t e s t i n g machines; d e f i n i t i o n , general d i r e c t i o n s , c l a s s i f i c a t i o n Sheet 1 T e n s i l e t e s t i n g machines; general requirements Sheet 5 T e n s i l e t e s t i n g machines; small t e n s i l e t e s t i n g machines ( a t present s t i l l c i r c u l a t i n g as d r a f t ) Testin.-r o f v.ocd; determination of moisture content T e s t i n g o f wood glues and wood bondings, determination o f bonding s t r e n j t h ; general d i r e c t i o n s T e s t i n g o f wood glues and wood bondings, determination o f bonding strength o f plywood bondings (veneer boards and blockboards) i n the t e n s i l e teBt and k n i f e t e s t Veneers; d e f i n i t i o n s -- • Sheet 2 Plywood f o r general purposes; q u a l i t y c o n d i t i o n s Sheet 3 Plywood; veneer boards f o r b u i l d i n g , q u a l i t y c o n d i t i o n s Sheet 4 Plywood; b u i l d i n g blockboarda, q u a l i t y c o n d i t i o n s ( a t present s t i l l c i r c u l a t i n g as d r a f t ) .  Pace 4  DIN 60705 Sheet 1 -159Explanations  Standard DIN 6 8 7 0 5 has been separated i n t o s e v e r a l standard sheets and extended because a s i n g l e standard oheet con be adapted note e a s i l y to the l a t e s t s t a t e o f t e c h n i c a l developments i n view o f the c o n s i d e r a b l y wider f i e l d s of a p p l i c a t i o n . DIN 68705 Sheet 1 c o n t a i n s the general bases for plywood ouch as d e f i n i t i o n s , r e q u i r e o e n t a , s p e c i f i c a t i o n s and i n s t r u c t i o n s f o r safeguarding q u a l i t y .  testing  DIN 63705 Sheet 2 c o n t a i n s the q u a l i t y c o n d i t i o n s f o r plywood U B e d f o r g e n e r a l purposes, i . e . mainly with regard to plywood used f o r f u r n i t u r e , i n t e r i o r d e c o r a t i o n o f rooms and f o r p a n e l l i n g i n a l l f i e l d s o f a p p l i c a t i o n not s u b j e c t to s t a t i c s t r e s s . The q u n l i t y requirements f o r these s h e e t s o r boards c h i e f l y cover bonding o f the sheets and grading o f the c o v e r i n g veneers. DIN 68705 Sheet 3 c o n t a i n s the q u a l i t y c o n d i t i o n s f o r veneer boards and DIN 68705 Sheet k (at p r e s e n t s t i l l c i r c u l a t i n g as d r a f t ) the q u a l i t y c o n d i t i o n s f o r b u i l d i n g b l a c k b o a r d s . T h i s Standard a p p l i e s to plywood s p e c i a l l y s u i t a b l e f o r use i n b u i l d i n g by reason o f i t s c o n s t r u c t i o n , veneer t h i c k n e s s e s and types o f wood.  DEUTSCHE N O R M E N  unc 67^-419.  Plywood Veneer Boards f o r Building Quality Condition o o-: •j c '5>_o o CJ _>  1  Sperrholz; Bau-Furnierplatten, Giitebedingungen  VI 5 c CJ c' t, u  Scooe Q a This Standard applies to veneer boarda used f o r building; i n general they shall he unsanded. c o ,, 1 o IA Dili 68705 Sheet 2 applies to building plywood used for panellings. '•"JE o (!)•*. _-'~j £ 2. Definitions *it u »k V e n e e r b o a r d u s e dd f o r b u i 5 —o Tb particularly suitable f o r building applications. 1 d i n g (synbol BFU), veneer board 1. o a For further definitions, see DIN 68705 Sheet 1. U t> CD O  z  "5 e  3. Requirenents ^.1.^Covering veneers.and_under_veneers 3.1.1. T y p e s o'f wood The covering and under veneers of veneer boards used i n building should be of the following types of woods Birch, beech, spruce, pine, linba, macore, mahogany species, gaboon, f i r or woods with similar or better weather resistance.  o  In view of their lower weather resistance, veneers made of Obeche, Ilonba, Samba and Wawa shall be inadmissible.  n  o Z  I n 3 jj s 4 3  3.1.2. Q u a l i t y r e q u i r e m e n t s The following are permissible: Wood discolourations and colour faults provided they do not impair the s t a b i l i t y of the veneers, Joints with slight faults only i n the case of boards consisting of five and raore plies of veneer Cracks, isolated, up to 3 ma wide i n boards consisting of three plies of the veneer, up to 5. ma wide i n boards consisting of five and^more plies of veneer isolated, completely intergrown knots and knot places up to 25 ma diameter i n boards consisting of three p l i e s of veneer, up to 60 mm diameter i n board? consisting of five and more p l i e s of veneer isolated bore holes caused by insects of their larvae Covering veneers should not be more than 2.5 mm, under veneers not more than 3«7 mm thick. . Covering and under veneers should be composed of strips of any width. Repairs to covering veneers shall be carried out by a method of bonding suitable f o r the veneer board. Adhesive tapes which impair bonding s t a b i l i t y shall be inadmissible. 2-2 _Cores 3.2.1. T y p e s of wood A l l the types of wood mentioned i n Section 3.1.1 can be used f o r cores (inner layers of veneer) regardless of the types of wood used f o r covering and under veneers, with the exception of Obeche, Ilomba, Samba and Wawa, provided quality specifications with regard to s t a b i l i t y are s a t i s f i e d . 3.2.2. Q u a l i t y r e q u i r e m e n t The inner p l i e s of veneer must satisfy requirements f o r covering veneer3 although a rather higher proportion of sound knots and bore holes caused by insects can be penaitted, provided these do not occur frequently or spread over the entire sheet of veneer. * The inner p l i e s of veneer should not be thicker than 3^7 mm. They may be composed of strips of any required width. Adhesive tapes which impair bond s t a b i l i t y are inadmissible. i  E  o 1  a  a  -5  3 O  3-3- Board structure Boards must be b u i l t up symmetrical to the middle plane with regard to veneer thicknesses and types of wood and must have the following minimum, nuaber of veneer plies f o r the board thicknesses l i s t e d below:  •6 o Z  The bonding of the veneer boards specified i n t h i s Standard must conform to the types of bonding IF 20 or AW 100 according to DIN 53705 Sheet 1.  Ii o t  e 1 In a d d i t i o n to  these bondings veneer boards Bay  Board t h i c k n e s s up to 8 o v e r 8 to 1 5 O T e r 1 5 to 2 2 o v e r 2 2 to 2 9  a l s o be produced by  the  IW 67 oethod o f  No.  of  plies  3 5 ' 7 9 bonding.  3.5 _Bond_strength (quality limits) i  Bond strength must be at T o a s t 10 V-^/ n . at least.8 kp/cm in the case of inside veneers I consisting of coniferous woods. Those limiting values r e f e r t o the average values for three boards' In this connection none of the three average values for the boards should be more than 10 ?i belo* the l i m i t . ^ . . Hhndinff o^T^nerfrVj ^"v.?.lity limits) 2  2  C  Longitudinal bending strength must be at least 400 kp/cm and cross bending strength at least 150 kp/cm^. These limiting values refer to average values from three boards. In this connection none of th« three average values for the boards may be more than 10 % below the l i m i t . c  5 •  mi  Continued on pages 2 and 3  Vpce 2 DIN 68705 Sheet 3  -161-  2-7. i i2Q _S-I^_2£IEi55i^l£_Y2EiS*i2!12 Dili 4073 applies to length and width. n  ricns  s  2.8 _Hoisture_content_ • The moisture content of veneer boards for building according to this Standard should be at least 6 /i related to the kiln-dried weight. i  c  Woods having good natural resistance should be used for plywood subjected for long periods to elevated ter.peratures and high humidity. Less resistant types or wood must be protected by a preservative. N o t e : Resistance of veneer boards for b u i l d i n g to animal and p l a n t pests i s no g r e a t e r than that o f the types of wood employed. When using plywood i n b u i l d i n g necessary steps must t h e r e f o r e be taken by c o n s t r u c t i v e m e a s u r e s to ensure the necessary p r o t e c t i o n against m o i s t u r e , r e g a r d l e s s o f the type o f bonding (see a l s o DIN 68800). When u s i n g wood p r e s e r v a t i v e s care should be taken to see that they are compatible with the b i n d e r s used.  a. Testing ^ . i ^ ^ o n d i n ^ (bond strength) Bor.d strength shall be tested by the shear test according to DIN 53255- Saraoling, production and pretreatment of specimens shall be carried out according to DIN 68705 Sheet 1. . -.2. Bending; strength Testing according to Dili 52371 (at present s t i l l circulating a3 draft) 4. ^. f-'oisture content . Testing according to.DIN.52183 <i  5. Quality safeguard Veneer boards for building according to this Standard must be subjected to regular quality supervision. Such quality supervision consists of a s t a t i s t i c quality control (own supervision) and a supervisory test (outside supervision). Attention i s drawn, i n connection with implementation of the quality safeguard, to the instructions of the Giiteschutzgemeinschaft Sperrholz o.V. (address: 63 Gie3en 1, Bahnhofstrafie 52-56) on quality supervision of veneer boards for.building.  5.1 i._2fB_§H225Zi5i22 ,  Own supervision shall be carried out according to DIN 68705 Sheet 1. 5.1.1. Q u a l i t y p r o p e r t i e s Own supervision of veneer boards for building shall cover bonding (determining bond strength in the shear test) and bending strength. ' When testing the bonding strength of bonding type AW 100 the only pretreatment given to the specimens shall be the cold water treatment according to DIN 68705 Sheet 1. 5.1.2. S a m p l i n g see DIN 6S705 Sheet 1. 5.1.3. Q u a i i t y l i m i t s The limiting values stated i n Section 3-6 shall be chosen as the lower warning boundary with a orcbable failing-short value of not more than 5 °,'«, where necessary taking into account the correction factor mentioned i n Section 5.1-3 ot DIN 68705 Sheet 1, January" 1968 edition. 5.2. Outside supervision Outside supervision shall be carried out according to DIN 68705 Sheet 1; 5.2.1. Q u a l i t y p r o p e r t i e s Outside supervision covers bonding (determining bonding strength i n the shear test) and the • bending strength. Wher. testing bonding strength i n bonding type AW 100 pretreatment of the specimens shall include the cold water treatment and the alternate boiling, heating and cooling treatment according to DIIT 65705 Sheet 1. 5.2.2. S a m p l i n g see DIN 63705 Sheet 1. 5.2.5. Q u a i i t y l i m i t s The requirements stated i n Sections 3-5 and 3-6 with regard to various properties must be satisfied. 5.2.4. T e s t i n g own s u p e r v i s i o n Vhr;a sampling eccording to DIN 63705 Sheet 1 records of own supervision (according to DIN 68705 Sheet 1)*shall be tested. " 6. D«tsirrhntion Vvneer uoard3 for building according to this Standard shall be marked by the manufacturer on the poorer side with a stamp showing the symbol BHJ for veneer board f o r building, the manufacturer's mark, board thickness, type of bonding and DIN number. Example: Veneer board for building, manufacturer  , hoard thlolrn-es 15 Ba, bondins AW 100  BHJ .... 15 AW 100 Dili 68705 Particulars used for designation (except f o r the manufacturer'a nark) may also be used f o r orders.  -162-  DIU 687C5 Sheet 3 Pace 3  Reference to f u r t h e r standards:  DIN DIN DIN Dili DIN  1052 4073 5216J 52371 53255  Wooden structures; calculation and construction Plywood; dimensions Testing of wood; deteraination of moisture content Testing of plywood; bending test (at present s t i l l circulating as draft) Testing of wood glues and wood bondings; determination of bond strength of plywood bondings (veneer boards and blockboards) i n the tensile test and i n the knife test  DIN 68330 Veneers; DIN 68705 Sheet 1 Sheet 2 Sheet 4  definitions Plywood; definitions, general requirements, testing ' Plywood f o r general purposes, quality conditions Plywood; blockboards for building, quality conditions (at present s t i l l circulating as draft) DIN 63800 Protection of wood used i n buildings *  •  ;  Explanations The s p e c i f i c a t i o n s g i v e n i n DIN 68705 Sheet 3 should be followed f o r veneer boards which are to be used c h i e f l y f o r wooden houses constructed i n panels and f o r l i g h t - w e i g h t r o o f s . T h i s Standard i s adapted to the r e l e v a n t supplementary r e g u l a t i o n s f o r DIM 1052. I t i n c l u d e s p a r t i c u l a r s o f approved v e n e e r s , bonding and q u a l i t y safeguards by own and outside s u p e r v i s i o n r e q u i r e d by the b u i l d i n g authorities. In d e f i n i n g s t r e n g t h r e q u i r e n e n t s the Advisory Committee proceeded on the b a s i n that plywood i s mainly s u b j e c t e d to bending s t r e s s e s i n wooden houses and l i g h t - w e i g h t r o o f s and r e o t r i c t e d the q u a l i t y safeguard, apart f r o a bonding s t r e n g t h , to one c h a r a c t c i j t . t r c , b e D d i n g s t r e n g t h . I s t h i s connection i s was assuaed that b e n d i n g - e l a s t i c modulus i s shown by experience to be l i n k e d c o r r e l a t i v e l y with bending s t r e n g t h . The bending Btrength therefore serves c h i e f l y as a c o n t r o l c h a r a c t e r i s t i c which can be subsequently checked i n a very simple manner. However, decigDero and s t r u c t u r a l a n a l y s t s need f u r t h e r i n f o r m a t i o n which i s l i s t e d i n the f o l l o w i n g T a b l e . Manufacturers o f veneer boards can vary t h e i r e l a s t o a e c h a n i c a l p r o p e r t i e s w i t h i n c e r t a i n l i m i t s by t h e i r choice o f woods and by the s t r u c t u r e o f the boards. T h i s l a t i t u d e could not be f u l l y taken i n t o account l n the T a b l e (approximate v a l u e s ) . In a r r i v i n g at c a l c u l a t i o n s f o r wooden c o n s t r u c t i o n s the l e a s t favourable t a b l e values are a p p l i c a b l e i n each case i f more advantageous v a l u e s cay not be used on the b a s i s o f a t e s t c e r t i f i c a t e o f a r e c o g n i z e d m a t e r i a l i n s t i t u t e i n an i n d i v i d u a l case or a c c o r d i n g to o t h e r German standards and s p e c i f i c a t i o n s .  B e a d i n g - e l a s t i c modolus along the g r a i n  £bll  a c r o s s the g r a i n (3 p l i e s )  *b-L  (5 aod more p l i e s ) G  shear  Lengthwise o r crosswise s w e l l i n g par percent change i n wood moisture C o e f f i c i e n t o f thermal c o n d u c t i v i t y (calculated value) Vapour d i f f u s i o n r e s i s t a n c e  . kg/m 3  e  • B u l k d e n s i t y u » 12 Si  Dyaanic modulus o f  Unit  Symbol  Property  factor  9L  kp/cm* *  Numerical value 500  to800  70000 to 120000  kp/cm»  7000 t o  12000  kp/cn*  30000 to  70000  kp/cm*  5000 * »  6000'  %  0.01 to 0.02  kcol/(mhdeg)  0,12 300 to 700  -163-  APPENDIX A  NBS V o l u n t a r y Product  Standard  PS 51-71  Hardwood and D e c o r a t i v e Plywood. U. S. Department o f Commerce, N a t i o n a l Bureau of  Standards.  _ i " -164UNITcO STATES ' PARtMfcM OF .: '•  HiViMERCE I.. (LIGATION  p r o d u a  :  t.' -•>> if ">  i  m  X  .,  «»-Vl.  J'  ....  P S  ,'.S>"  51-71  iC I  Ic  Iv  U.S. DEPARTMENT OF ' COMMERCE Hational Bureau cf Standards  .... j f t S g g & j ^ ^  *  •  -165-  UNITED STATES DEPARTMENT OF COMMERCE . Maurice 11. Stans, Secretary NATIONAL BUREAU OF STANDARDS • Lewis M. Rratiscomb, Director  Voluntary Product Standard PS 51-71 Hardwood and Decorative Plywood  Technical Slondsrds Coordinator: P. R. Sutula.'' Abstract Thla Voluntary Product Standard for hardwood and decorative plywood establishes the nationally rev.-oguiz'xJ marketing classifications, quality criteria, test methods, definitions, and giade-innrking and certification practices for plywood produced primarily from hardwoods. It is intended for voluntary use by refeit-nte in trade literature, catalogs, sales contracts, building codes, and procurement specifications t» describe the quality aspects of tinproduct and the means to determine conformance. Requirements are given for wood species, veneer grading* lumber-core, partieleboanl-core, hartlboard-core, shic bond, panel constructions, dimensions, moisture content, sanding, and finishing. Sampling and testing provisions cover dry shear, cyclic-boil, three cycle wet and dry, and cold soak test methods for plywood delamination determination:;, and field and laboratory moisture content measuring methods. A glossary of trade terms is provided for better communication and understanding, and provisions are made for panel grade-marking and certification to indicate -compliance. Key words: Decorative plywood; hardwood plywood; plywood, hardwood decorative; veneer grades, decorative softwood and hardwood.  and decorative; softwood plywood,  Nat. Bnr. Stand. (U.S.), Prod. Stand, r.1-71. 18 pages (January 1!>72) CODKX:XXPSAX For rale by tbe Superintendent of Documents. D.S. Government Printing Office. Washlnirton D C 204O'» (Order by SD Catalog No. 03.20/2:51-71). Price 30 cent*.  -166-  Contents 1. Purpose I. 1. Purpose 1lbtended 2.  "  —•.  . :  .  IVfuiitionsi  :  '.  •  : .  • •-  -  •  •  :  —  .  —  -  -_-  .  • -  •  .—__— .  .  .  —  .  ;  • '  -  , :  •  . •:  '.  —  .  _ . ;  -  1  -  —  . —  -  '.  -  —. .—  -  -  1 1 1 1 1  1  1 1  —  = —  .  —  1 1 2 2 2 2 4 4 4 4 4 4 4 4 4 4 6 6 6 G 6 6 7 7 7 7 7 7 7 1 7 7 8 8 8 8 8 8 8 8 8 8 9 9 9 10 11  Tiicntlfi'-ati""  11  7. Ms:.ilifiotl lnspii-ti'ia ami T-.'stinj: Acency S.  I'.tTociiTc  0.  Tlisf.-ry of l'roifvr  12  11nr».  12  Ptanuiiis Cmiiiiiif'-e  1. Acceptors . Appendix  .  .  >  4. Inspection and Test Procedures 4.1. General 4.2. Specimens for clue bond test 4.2.1. Technical and Type I plywood 4.2.2. Type 11 plywood -1.2.3. Typo III plywood 4.3. Dry shear test 4.4. Cyclic-boil shenr test 4..". Three-cycle s=nak test . 4.C Twtwycle son): trst 1.7. Moislnrc roriif.it test  10  : -  Ueo.uirvtncnt* 1. r»en«*rnl 3 2. Spn i<• « for f t w , l i M c k s . ami inner plies 3.2.1. Slnties W:i-?pi>ries 3.3. Veneer crade descriptions 3.3.3. Premium erode (A) 3.3.2. <5"'Ml sTaclr U ) :;.:'..3. Sound prude (2) : 3.3.-1. Utility ;:rnde (3) 3.3..1. Biu-kinc crane <4) 3.3. C. Specialty grade (SP) 3.3.7. Softwood reneers 3.4. Thickness of veneers _ o.">. Lumber cores 3..1.1. Clear grade 3..1.2. Sound crade 3.0.3. Regular grade 3.."..4. Clear edge 3."i."i. Banded core 3.C.. Parriclebonrd ond/hnrdboarri cores 3.7. Special cores 3.5. Construction 3.5.1. Special construction 3.0. Glue bond requirements 3.0.1. Technical Typo plywood 3.0.2. Type I plywood 3.0. 3. Type IT piywood 3!'. t. Type II r plywood 3.10. Dimensions and tolerances 3.10.1. Squareness 3.10.2. Straichtness 3.11. Snmlin? 3.12. Moisture content 3.13. Factory finished panels 3.14. Marking ;—  iV  1 * *  '—  use •  Scope ami Classification 2.1. Scope •2.2. Classification , 2:2.3. Species 2.2.2. Grades «f vt-neers '2:2.3. Tyi-es of plywood 2.2.4. C»nsim»-ii"r;.5 II. 1'..". Sizes jui'l '.hhl<n"«^'>«  3.  '-  :  ,  — —  12  —  12  — —  15  :  III  -167VOLUNTARY PRODUCT STANDARDS  Voluntary Product Standards are standards developed under procedures established by the Department of Commerce (15 C F T l Part 10, as amended. May -28. H'TO). The standards may include (1) dimensional requirements for standard sizes and types of various products, (2) technical requirements, and (3) methods of testing, grading, and m a r k i n g 'Hie objective of a Voluntary Product Standard is to establish requirements which • are in accordance with the principal demands of the industry and, at the same time, are not contrary to the public interest. Development of a VOLUNTARY PRODUCT STANDARD  T h e Office of Engineering Standards Services of the National Bureau of Standards has been assigned by the Department of Commerce the responsibility to work closely with scientific and trade associations and organizations, business firms, testing laboratories, and other appropriate groups to develop Voluntary Product Standard?. The Bureau has the following role i n the development process: It (1) provides editorial assistance in the preparation of the standard; (2) supplies such assistance and review as is required to assure the technical soundness of the standard; (3) acts as an unbiased coordinator in the development of the standard; (4) sees that the standard is representative of the views of producers, distributors, and users or consumers; (5) seeks satisfactory adjustment of valid points of disagreement; (6) determines the compliance with the criteria established in the Department's pro-, cedures cited above; and (7) publishes the standard. Industry customarily (1) initiates and participates i n the development of a standard; (2) provides technical counsel on a standard; and (3) promotes the use of. and support for, the standard. ( A group interested in developing a Voluntary Product Standard may submit a written request to the Office of Engineering Standards Services. National Bureau of Standards, "Washington, D.C. 20234.) A d r a f t of a proposed standard is developed in consultation with interested trade groups. Subsequently, a Standard Review Committee is established to review the proposed standard. T h e committee, appropriately balanced, includes qualified representatives of producers, distributors, and users or consumers of the product being standardized. When the committee approves a proposal, copies are distributed f o r industry consideration and acceptance. W h e n the acceptances show general industry agreement, and when there is no substantive objection deemed valid by the Bureau, the Bureau announces approval of the Voluntary Product Standard and proceeds with its publication. Use of a VOLUNTARY PRODUCT STANDARD T h e adoption and use of a Voluntary Product Standard is completely voluntary. Voluntary  Product Standards have been used most effectively in conjunction with legal documents such as sales contracts, purchase orders, and building codes. W h e n a standard is made part of such a document, compliance with the standard is enforceable by the purchaser or the seller along with other provisions of the document.  Voluntary Product Standards are useful and helpful to purchasers, manufacturers, and distributors. Purchasers may order products that comply with Voluntary Product Standards and determine f o r themselves that their requirements are met. Manufacturers and distributors may refer to the standards in sales catalogs, advertising, invoices, and labels on their product. Commercial inspection and testing programs may also be employed, together with grade labels and certificates assuring compliance, to promote even greater public confidence. Such assurance of compliance promotes better understanding between purchasers and sellers.  rv  —  168-  Voluntary Product Standard PS 51-71 (Supersedes CS- 35-61)  Hardwood and Decorative Plywood Effective August 15, 1971 (See section S.)  (This Standard, initiated by the Hardwood Plywood Manufacturers Association, has been developed under the Procedure* for the Development of Voluntary Product Standards, published b the U.S. Department of Commerce, as a revision of Commercial Standard C S 35-61, Hardwood Plytrood.-See Section 9, History of Project, for futher information.) . 1. PURPOSE  1.1. P u r p o s e — T h e purpose of this Voluntary Product Standard is to establish nationally recognized quality criteria for the principal types, grades, and sizes of hardwood and decorative plywood. The principal wood species used for hardwood and decorative plywood are hardwoods: however, certain softwood species are also used. The Standard is intended to provide producers, distributors, architects, contractors, builders, and users with a basis for common understanding of the characteristics of this product. 1  1.2. Intended u s e — T h e plywood covered by is Voluntary Product Standard is intended for use as decorative wall panels where esthetic characteristics are important; for cut-to-size and stock panels used for furniture, cabinets, containers, and specialty products; and for marine applications. 2  2. SCOPE AND CLASSIFICATION ?..L S c o p e — T h i s Voluntary Product Standard covers the principal types, grades, and constructions of plywood made primarily with hardwood faces. Included are requirements for wood species and veneer grading: for lumber, particleboard, and hardboard cores; and for glue bond, panel construction, moisture content, and panel dimensions and tolerances. Test procedures are provided for determining conformance with the. requirements. Definitions of trade terms, methods of ordering, and methods for identifying products that conform to this Standard are included. 22. Classification—Plywood covered by this Standard is rln=sifWi ns follows: 2.2.1. Species- -The most commonly marketed spories for plywood faces are listed in table 1. 2.2.2. Grades of veneers—The grades of veT h i s V n l n r t n r T rrn-iuct Stnndar.1 «l*o Includes oertnln •orotif* *ofnv«ort sp-rir.; f o r nnnconsfrnction Constrmr..011 crnrt**? of «oftiv.M*il n n t l h n r d w r . o t l pl.vtv.wnl nrc covered In the l.i|i"-t rrtltlon i-f V«.Iuntnr.v Prodm-t Sinmlnril P S 1-Cfi. 1  Po/ffoO'/  P f y i r o . x / . Construction  nnil  /fiVhi.'rci/.  Aririltlnnnl product Information in IITIIII.IMP from th# H n r d wood Plywood M i i i i i i f ; i c n i r . ' r i Atxnrlntlon, 2310 S. Walter Reed Dr\rt. A r l i n g t o n . Y l r c l n l n 22200. 1  neers are listed below with the identification symbol for each grade: Premium grade (A) Good grade (1) Sound grade (2) Utility grade (3) Backing grade (4) (SP) Specialty grade 2.2.3. Typos of plyv/ood—The types of plywood are listed below in descending order of water-resistance, capability. (See table 5.) Technical — (Exterior) Type I • — (Exterior) Type I I -— (Interior) Type I I I — (Interior)2.2.4. Constructions — The constructions, based on the kind of core, are listed below: 1." Hardwood veneer core (3-ply, 5-ply, etc. in odd numbers of plies) 2. Softwood veneer core (3-ply, 5-ply, etc. in odd numbers of plies) 3. Hardwood lumber core (3-ply, 5-ply, and 7-ply) Softwood lumber core (3-ply, 5-ply, and 7-ply) 5. Particleboard core (3-ply and 5-ply) 6. Hardboard core (3-ply) 7. Special core (3-ply or more) 22.5. Sizes and thicknesses—Most combinations of length, width, and thickness are available. The common panel sizes are 48 by 84 inches, 48 by 06 inches, and 48 by 120 inches (1 inch equals 25.4 millimeters) with thicknesses ranging from % to % inch.  3. REQUIREMENTS . 3.1. General—Products represented as complying with this Voluntary Product Standard shall meet all of the requirements specified herein. Terms used in this Standard shall be as defined in section 5. 3.2. Species for faces, backs, and inner plies — T h e species for the face shall be any hardwood species, and i f used for decorative faces, anv softwood species listed in table 1 may be used. The panels shall be identified by the species of  1  -169the fare (sec The, species of the. buck und tlie inner plies msiy be any hardwood or softwood species. T A B L E 1.  Cat.itjories of commonly uird specific gravity rmujei*  specie.) bused  as a face and when it consists of morn than one piece, it shall lie edge-matched aj outlined in  on  Category-C species Cate^.iry A species Category B specie* 1 (O.-ia Ihroush 0.55 10.1 - or less (0.5'J »r more specific gravity) | speeilie gravity speoifie gravity) ] Alder, Red Ash. Commercial 1 Asb, Black lAspcu White ' .Wo-lire Basswood, Bay P.eevb, American Ce<lar, Eastern American Birch, Yellow, Box MUler Red Sweet Cntivo Cherry, Black Buhinca Cedar, Western Chestnut, Elm. Rock Reel" American Madrone, Pacific Ceiba Cypress" Maple, Blnck Elm. American Cottonwood, (hard) (white, red,or Black Maple, Sugar pray) Cottonwood, (hard) Fir, Douglas" Eastern Oak, Commercial Gum, Black Pine, White and Red Ponderosa" Gum, Sweet Oak, Commercial Poplar, Yellow Hackberry White Lauan, (Philippine Redwood C"k, Oregon Willow, Block • Mahogany) PaUlao Pecan, Commercial Limba Magnolia Rosewood Mahogany, African Sa.-le Mahogany, Teak Honduras Maple, Red (soft) Maple, Silver (soft) Prima Vera Sycamore Tupelo, Water Walnut, American -  b  5  » Based on orendry i r e l j h t and volume at 12 percent content, b Softwood.  moisture  3.2.1. Species categories—Species of wood commonly used for veneers are listed in table 1 ai-.d are categorized by specific gravity for the purpose of establishing maximum veneer thicknesses (see table 5). The specific gravity ranges given in the three category headings shall also be used in determining the proper category for unlisted species. The Forest Products Laboratory in Madison, "Wisconsin, shall be considered as final JB valuator "of specific gravity data. 3~3. Veneer grade descriptions — The grade requirements and identification symbols for hardwood veneers are given in 3.3.1 through 3.3.6. Softwood veneer requirements are given" in 3.3.7. "When unsanded veneers are graded, such characteristics as patches, rough areas of grain, shallow depressions, open splits, and machine marks which may be corrected by sanding are not considered. Panels shall lie identified by the veneer grade of the face (see 3.14). A grading tolerance of n percent of the shipment or order will be permitted (see appendix). 3.3.1. Premium grade (A)—The veneer shall bo smooth, tight-cut, and full-length. "When used 2  BOOK M A T C H I N G  S U P MATCHING F I O U B E 1.  Face  matching.  table 2, and as illustrated in figure I. Edge joints shall be tight. The natural and other characteristics, the types of matching which will be permitted for each species, and the defects which will, not be permitted shall be as specified in table 2. Hardwood veneers of species not covered in table ii may contain small burls, occasional pin knots, color streaks or spots, inconspicuous small patches, and usual characteristics inherent iu the given species; however, knots (other than pin knots), wormholes, rough-cut veneer, splits, shake, and doze and other forms of decay will not be permitted.  -170-  R S | 5555| £2 55|- •= *5f 5|5l5 55 ii&l ; |5f5555J « « * 5 | 5 § S p l £ 55 555| • | U*i  iUii  I, ^f££  ii iiij  |, ^ 5 5 »S|5*« «  :  j ]| # 5 5 ffjj* 55  -  j ];•!&**! | * « * «  553 £ £ 5 £ | 55 HiS -  555 Ifia a. m l -  **** ~  i £  t  „  -  =55 5§355 55 £ ^ * 5 * £51 f i l l s 55 ml  *  555 5|555  -  5 5 § § f l l 5 Si a q  -  |i|555 5555s 55 iUz * 551 5 | l l l Si m l *  11  « « j «  * 1 «  I  ii\\\lii-n  m l  55 5§555 ii 5553 -  «£§§§{£*«£  55 ijiSi  £55 5|55^ M 555£ »  a  m l  -  m l  5  535 5 | l l i &i m i I laf  f|5i5 a m l -  | 5 5 § f f 5 5 5 ss 5535 J  a  •a 3  a "3  ** 0  v . -  1e  4£  555 5 f l l 5 it  mt  5511|||5 55 ssfg  * a | m&i  m l  551 f f 555 55 5555 J  ii  * s 3  II M  Hia  U  m  U  55| | | | | 5 55- a i l  i'4 | | l l 5 £ |3i55 *|£5s 55 5555 -  55 5 5 | | -  55| ||555 55 5555 551 § § | | 5 55 5 5 | |  ,?yiiii!ifi!iij  3  i t a  I o  S5s 56a  i l t i i l l i  -  J 7 /  3.3.2. Good grade ( 1 ) — T h e veneer shall be smooth, tight-cut, and full-length. W h e n used as a face and when it consists of more than one piece, the edge joints shall be tight. T h e pieces need not be matched for color or grain, but sharp contrasts between adjacent pieces of veneer with respect to grain, figure, and natural character markings will not be permitted. The natural and other characteristics which will be permitted for each species and the defects which will not be permitted shall be as listed in table 2. Veneers of species not covered i n table 2 may contain small burls, pin knots, color streaks or spots, inconspicuous patches, and usual characteristics inTABLE 3. Summary  of veneer characteristics  and allowable  Defects Sapwood Discoloration & Stain Mineral Streaks Sound Tight Burls Sound Tight Knots Knotholes Wonnholes Open Splits or Jolnta  Sound Grade (2)' Yes Yes Yes Max. diam. 1" Max. diam. % " No Filled or Patched" No  Doze & Decay  F i n n areas of dare  Rough Cut Patches Crossbreaks and Shake Bark Pockets B rashness Gum Spots Laps  herent in. the given species; however, knots (other than pin knots), wonnholes, rough-cut veneer, splits, shake, and doze and other forms of decay will J i o t be permitted. 3.3.3. S o u n d grade ( 2 ) — T h e veneer shall be free from open defects. Matching for grain or color is not required. The natural and other characteristics which will be permitted a n d the defects which will not be permitted shall be as listed in table 3. 3.3.4. U t i l i t y grade ( 3 ) — T h e natural a n d other characteristics which will be permitted a n d the defects which will not be permitted shall be as listed in table 3.  Small area Ye3  No No No Yes No  defect* of Sound, Utility, and Backing  Utility Grade (3)' Yes Yes Ye3 Yes Yes Max. di&r.i. 1" Yes Yes; 3 / 1 0 " for one-half length of panel Firm areas of doze in face. Areas of doze and decay in inner plies and backs provided serviceability of-panel is not impaired. Small area Ye? Max. 1" in length Yes No Yes Yes  » T»efects permitted In Premium and Oood Grades will be allowed 1 n thla grade (see tables 2 and 4). b CnHlled, Inconspicuous, vertical wonnholes not larger than 1/18 " ln diameter will be permitted in  3.3.5. B a c k i n g g r a d e ( 4 ) — T h e natural and other characteristics which will be permitted and thv defects which will not be permitted shall be aj listed in table 3. 3.3.6. S p e c i a l t y grade ( S P ) — T h i s grade shall include veneer possessing characteristics unlike any of those described for the above-mentioned grades. Characteristics shall be as agreed tipon between buyer and seller. Species such as wormy chestnut, birdseye maple, and English brown oak which have unusual decorative features are considered as Specialty Grade. ( W a l l panel veneer face grades generally fall in this category.) 3.3.7. S o f t w o o d v e n e e r s — T h e face grade requirements for certain decorative softwoods shall be as listed in table 4. A l l other softwoods for faces, backs, or inner plies shall meet the same grading requirements as specified for hardwoods in 3.3.1 through 3.3.6. 3.4. T h i c k n e s s o f v e n e e r s — T h e maximum veneer thicknesses shall be as provided in table 4  Grades  j Backing Grade (4) » JYes Yes Yes Yes Yes Max. dlaia. 3 " Yes 1" for one-fourth length of panel; for one half length of panel; " for full length of panel. Areas of doze and decay provided serviceability of panel is not impaired. Yes Yes Yes Yes Yes Yes Yes tropical nardwood9.  5. T h e minimum thicknesses of veneers shall be as agreed upon between buyer and seller. 3.5. L u m b e r c o r e s — L u m b e r cores shall be o f any species, except that mixing of species in a single core w i l l not be permitted. T h e maximum permissible, widths o f core strips shall lie 2V£> .inches for Category A species (see 3.2.1), 3 inches for Category B species, and 4 inches for Category C species. Core grades a n d core banding requirements shall be as described i n 3.5.1 through 3.5.5. Cores shall be conditioned after gluing to equalize moisture content before sanding. . 3.5.1. C l e a r g r a d e — T h e wood strips shall be full length o r finger-jointed and shall be free of knots or other defects which would not properly shape or mold, except that discolorations will be permitted. W o o d patches or plugs shall not b used, but wood filler will be permitted. 3-5^. S o u n d g r a d e — T h e wood strips shall be full length or finger-jointed and shall be free  T A U L K 4.  Bvmmery of veneer characterise*  and allcxal.  JecU for Premium g r a d e and Ooad P r o d ; decorative ioftwood tpeclcs  R o t a r y — Sliced — K n o t t y V e . . Western Premium ( A ) No Yes  Characteristics Discoloration Hurls Knots I'ln knots KlMlllll kllols  Hplke knots F i l l e d knot h o l e s ' W o r m holes Open splits or jolntu 1)117.0  Rough c u t Inconspicuous patches  Yes Yes Slight  94 m. No No No No Small Email No Slight a or c  P i t c h streaks P i t c h pockets C r o w ' s foot JIatcliing  W h i t e pine Gcou (1) Premium ( A ) Slight No Yes Yes  Goor. (1) Slight Yes  Yes Yes Slight % in. No No No . No Small  Yes Yes . Yes* Iv4 i n . No No No Inconspicuous Yes  Small No No a ore  Small Snail Occasional a ore  Yes Yes Yes" 1V4 i n . No No No Inconspicuous Yes Small Small No a ore  Sliced — V e r t i c a l g r a i n Douglas Mr Premium < A ) Characteristics Limited * S&i>WGG<! Yes' Heartwood No C o i c r streaks Slight Color v a r i a t i o n No M i n e r a l streaks Yes S a c u r l s No P i n iric.is No Knots No W o r m holes No Open splits or Joints No Shake o r doze No Rough cut No Crossbars Yes Inconspicuous patches Small P i t c h streaks No P i t c h pockets corf Matching  Redwood Premium ( A ) No Yes* No Slight Slight Yes Yes No ' No No No No No Yes No No cor f  • Randomly spaced for pleasing appearance, b Mnilminu 2 Inches. t Slip watched. Must be matched ln scouenco wits t i g i : B'.dt out i llripbl sapwood not permitted. • Six tir more nnnual rings per Inch. f Book matched. Matched for color and p a i n at the joints.  TABLE  L i m i t i n g factors G l u e horn! (3.0) A d h e s i v e performance (3.0) Species o r specific g r a v i t y category of veneer (3.2) Veneer edge joints (3.3) G r a d e of faces or face and back (3.3) G r a d e of hard wood inner plies adjacent to faces (3.3) M G r a d e of softwood inner plies adjacent to faces (3.3.7) G r a d e of other inner plies (3.3.1 through 3.3.7) G r a d e of lumber core (3.5) P a r l l c l e l i o a r d or hardboard core (3.0) M a x i m u m veneer thickness i n inches by specific g r a v i t y category (3.2.1): Category A Category II Category C Percentage of wood i n face d i r e c t i o n S a n d i n g (3.11) . .  5.  Limiting criteria for plywood  Technical (Exterior) F u l l y waterproof D r y and c y c l i c boll shear Specify  Type I * (Exterior) F u l l y waterproof D r y and cyclic boll shear Specify  Type I I (Interior) W a t e r resistant 3-eycle soak  Type H I (Interior) M o i s t u r e resistant 2-cycIe soak  Specify  Specify  N:» tape Specify 2 under A o r 1 3 under 2 2  N o tape Specify 2 or 3 .  Tape Specify 2 or 3"  Tape Specify 2or3  2 or 3  2or3  3 or 4  3 Or 4  2 or 3« (4 under 3 or 4) 3 or 4  N o t suitable N o t suitable  Specify Specify . •  Specify Specify  Specify Specify  1/12 1/10 1/8 40 to CO Specify  1/8 3/10 1/4 No limitation Specify  3/10 1/4 1/4 No l i m i t a t i o n Specify •  3/10 1/4 1/1 No l i m i t a t i o n Specify ..  11  • Not recommended for continuous exposure to moisture. ip Specify Grade 2 l o r solid inner piles. . . . .. „ . , t Whore 1/10 Inch or thicker faces are used, Grade 4 or better Inner piles are permitted.  c  e  3 or 4  173 of defects, except that discolorations, sound knots, and small open defects, if securely patched or plugged with wood or wood filler will he permitted. 3.5.3. R e g u l a r g r a d e — T h e wood strips shall be the same as sound grade, except that tightly butted end joints will be permitted. 3.5;4. C l e a r e d g e — T h e wood strips shall be "regular grade," except that the edge strips shall be iy incites or wider "clear grade" to permit shaping or molding. 3.5.5. B a n d e d core — T h e bands shall be "clear grade." The species, width, number of bands, and grade between bands shall be as agreed upon between buyer and seller. T h e types of banding shall be as follows: 1. Banded one end ( B l E ) 2. Banded two ends ( B 2 E ) 3. Banded one side ( B I S ) • 4. Banded two sides (B2S) 5. B a n d e d two ends and one side ( B 2 E 1 S ) 6. B a n d e d two sides and one end ( B 2 S 1 E ) 2  FACE »  Commercial Standard  C S 23R-06, Mat-formed  Wood Particlchoiird? JTardboard cores shall b in accordance with Commercial Standard C S 251-63, Hardbonrd* 3.7. Special c o r e s — C o r e s made of other material may be used providing all other applicable requirements of this Standard are met. 3.8. C o n s t r u c t i o n — P l y w o o d panels shall be constructed with an odd number of plies. A l l plies shall be combinations of species, thickness, and moisture content to produce a balanced panel. A l l inner plies, except the core or center ply, shall occur in pairs. P'.ach pair of inner plies shall be of the same thickness and direction of grain. Each, p l y of each pair shall be placed on * L a t e r Issues o f this publication may be used p r o v i d i n g the requirements are applicable and consistent w i t h the Issue designated. Copies are available from the Superintendent of Documents, U . S . Government P r i n t i n g Office. W a s h i n g t o n , D . C . J0402.  , •I  THREE-PLY VENEER CORE CONSTRUCTION  6  7. Banded two sides and two ends (B4) 3.6. P a r t i c l e b o a r d and h a r d b o a r d cores •— Particleboard cores shall be in accordance with  FIVE-PLY VENEER CORE CONSTRUCTION  FACE  FACE  (—.BACK  BACK  BANDS OR RAILS  CR0SS8ANDS CROSSBANOS  CORE  PIVSPLY LUMBER COHE CONSTRUCTION F I O U R B i. Typical  CORE (LUMBER.  PARTICLEBOARO.  OR HARDBOARD)  FIVE-PLY CONSTRUCTION WITH BANDING OR RAILING plywood  constructions—continued.  opposite sides of the core. The grain of all plies shall be at right angles to the grain of the adjacent plies and to the ends or edges of the panel. Some typical constructions are illustrated in figure 2. The limiting criteria for plywood panels shall be as provided in table 5 except for conincr plywood which shall utilize grade 4 or A.ev inner plies adjacent to the faces for each type. (See 3.14 for marking.) 3.8.1. Special construction—Because of special panel constructions and because of special face treatments, certain panels may deviate from a Hat surface prior to their application. Such devintion shall not prevent their taking the shape of the surface to which they are applied without the development of defects attributable to this deviation. 3.9. Glue bond requirements— 3.9.1. Technical Type plywood — The glue bond of Technical Type plywood panels shall meet the wood failure requirements given in table 6 when tested in accordance with 4.2, 4.3, and 4.4. Technical Type plywood constructed with  3.9.2. Type I plywood — The glue bond of Type I plywood shall meet the same requirements as Technical Type. 3.9.3. Type II plywood—The glue bond of Type II plywood shall be of such quality that specimens shall withstand the 3-cycle soak test described in 4.2 and 4.5. 3.9.4. Type III plywood — The glue bond of Type, III plywood shall be of such quality that specimens shall withstand the 2-cycle soak test described in 4.2 and 4.6. 3.10. Dimensions and tolerances—The nominal dimensions of the plywood panels shall be as agreed upon between buyer and seller. The tolerances for the nominal dimensions shall be as follows Width: plus or minus 1/32 in Length: plus or minus 1/32 in Thickness: Unsanded plus or minus 1/32 in Sanded: plus 0, minus 1/32 in except that a sanded tolerance of plus 0, minus 3/64 in will be permitted for panels having a nominal TABLE 6. Wood failure requirement* for Technical and Type I plywood glue bonds thickness of 14 i more. .Vote: One inch equals 2.54 centimeters. Minimum wood failure Avera.ce falling load 3.10.1. Squareness—Panels 4 feet by 4 feet Test piece Indiv. specimen averace or larger shall be square, within 3/32 inch.-Panels In/sq in. Percent* Percent* less than 4 feet in length or width shall be I'nder 230 25 CO square within 1/1G inch. Squareness shall be de2.-0 to .330 10 30 termined by measuring the length of the two Above 3.->0 10 . 15 diagonals of the panel. • T h e v Talues are the percentage of wood area r e m a i n i n g 3.10.2. StraiRhtness—The edges of panels a i l h T f d to the f r a c t u r e d i n r f a c c In tbc test area. less than 8 feet long shall be such that a straight hnrdwood face veneers on softwood inner plies line from one corner to the adjacent corner shall '•all also comply with the Exterior Type bond fall within 1/10 inch of the panel edge. A depiirements specified in Voluntary Product parture of 3/32 inch will be permitted for panels otandard P S l-Gfi. Softwood Plytoood, Construc8 feet long and longer. tion and Industrial.* 3.11. Sanding—-The. types of sanding shall be « 8«e footnote 3, page 6. os described below. The type of sanding and the no  r  -  7  175 number of surfaces of the. panels to he sanded shall he. as agreed upon between buyer and seller, except that, in no case shall the plywood be con-' sidered as ready for finishing because raised grain due to moisture absorption and marks made • in handling the plywood during shipment or storage may require further sanding. No sanding—Surfaces need not be sanded nor tape removed. Ttough sanding—Sanding hit-or-miss. Tape removal is not required. Regular sanding—Surfaces shall be clean and free of tape. Sander streaks are not considered defects. Polish sanding—Surfaces shall be clean and smoothly sanded. 3.12. Moisture content—The moisture content of plywood panels at the time of shipment from the producing mill shall not exceed 12 percent of the ovendry weight, as determined an accordance with 4.7. 3.13. Factory finished panels—The finish of factory finished panels shall be as agreed upon between buyer and seller. 3.14. M a r k i n g — A l l plywood represented as conforming to this Voluntary Product Standard shall be identified by either of the following methods: (a) Each panel shall be marked with the symbol of this Sandarcl, PS 51-71, the name or recognized identification of the producer; the'species and grade of the face veneer; the type of plywood; the symbol "CP," if container plywood; and the identity of the qualified inspection and testing agency, if applicable (see section 7), or (b) The shipment or order shall be accompanied by a written certification which states that the panels conform to all of the requirements of Voluntary Product Standard PS 51-71, and identifies the producer; the species and grade of the face veneer: the type of plywood; the qualified inspection and testing agency, if applicable (see section 7); and the specific intended use if container plywood. 4. INSPECTION AND TEST PROCEDURES  4.1. General—The inspection and test procedures contained in this section are to be used to determine the conformance of products to the requirements of this Voluntary Product Standard. Each producer or distributor who represents his products as conforming to this Standard may utilize statistically based sampling plans which are appropriate for each particular manufacturing process but shall keep such essential records as are necessary to document with a high degree of assurance his claim that all of the requirements of this Standard have been met. Additional sampling and testing of the product, as may be agreed upon between purchaser and seller, is not precluded by this section. 8  4.2. Specimens for glue bond test— 4.2.1. Technical and Type I plywood — Three test pieces shall be cut from each panel selected: one piece from each end of the-panel and one piece near the center of the punel. l/ich test piece shall be of sufficient size to provide at least six specimens for the dry shear test and six specimens for the cyclic-boil shear test (see table 7). 4.2.2. Type II plywood—A total of 10 t<-st. specimens shall be cut from each panel selected: two specimens from each end approximately at mid-width of the panel; two specimens from each edge approximately at mid-length of the panel; and two specimens near the center of the panel. Test, specimens shall not have common edges (see table 7). 4.2.3. Type III plywood—-Three test specimens shall be cut from each panel selected: one from each end of the panel and one near the center of the panel (see table 7). TABLE 7.  Test specimen  sizes  Type of plywood  Specimen size  Technical & Type I Type II (3-cycle) Type III (2-cyclc)  3'A inch* by 1-inch specimens 5-inch by 2-incb spccivuei;.G-inch by 6-inch specimens' b  a Parallel to the p n i l n of the outside venders In 7-. a n d l l - p ! y construction. Perpendicular to the grain of the outside veneers In 0- nnd !>-piy construction. T h e precedtii.it nppllr.-. to specimens for testing Ihe Innermost piles. Specimens for tesilrisr the outer plies shall always be parallel to the- (train of the face veneer lu the 3Vi Inch dimension. "J Parallel to the grain of the face veneers.  4.3. Dry shear test—Shear tests shall be conducted on specimens prepared as shown in figure 3. The ends of each specimen shall be gripped in test machine retaining jaws, and the load shall be applied at the rate of 600 to 1.000 pounds per minute. Specimen notching shall be accomplished in. such a way as to assure that when the specimens are subjected to loading, the lathe checks in the center ply of half of the. specimens will be in tension, while in the other half the lathe checks will be in compression. An explanation of one method of notching specimens to insure that half of the lathe checks are "pulled in tension and half are pulled in compression, is described in American Society for Testing and Materials (ASTM) f) f>06-64, Stond.'rd Method of Test for Strength Properties of A hesives in Plywood Type Constructio-n in Sh by Tension Looding.* If the number of plies exceeds three, the outer pairs of glue lines and innermost glue lines shall be tested with separate sets of test specimens. In plywood with face plies thicker than 1/16 inch, the shear area shall b° 1 square inch, as shown in figure 3. specimen A. Specimens of plywood with face plies 1/1R inch • L a t e r Issues of this publication may be u»ed p r o v i d i n g the requirements ure applicable and ronalstent w i t h the Issue de-dt-nnted. Copies of A S T M publication* are obtalnuble f r o m the A m e r i c a n Society for Test Inn and M a t e r i a l s . 191B K a c e Street, P h i l a d e l p h i a , P e n n s y l v a n i a 10103.  CUT  CUT 2/3 THROUGH CORE  SPECIMEN A  FIOUBE 3.  C  r  , l c M  m  / 3 THROUGH CORE  SPECIMEN 8  Plywood  bond shear test  or less in thickness shall be of the form shown i n figure 3. speci.ntn B. in which the shear area shall be reduced to ty square inch without changing the width of the specimen. Test machine loads obtained from specimens of ty square inch shear area shall be multiplied by 2 to convert to pounds per square inch and then reduced by 10 percent before comparing with the required -nhies set forth in table 6. For shear tests of l u m r core plywood, particleboard core plywood, «nd hardboard cove plywood, the core shall be cut away to 1/10 inch in thickness. tyclic-boil uhear test — T h e specimens prepared as shown in figure 3 shall be boiled in water f o r 4 honi-s and then dried for 20 hours at a temperature of 145±5 °F (63±3 °C). They shall be boiled again for 4 hours, cooled i n water, and then subjected while wet to the test described in 4.3. The values obtained from the six specimens shall meet the applicable requirements given i n table G. If the number of plies exceeds three, the outer pairs of glue lines and innermost glue lines shall be tested with separate sets of test pieces. 4.5. Three-cycle s o a k test—The 5-inch b y 2-inch specimens from eacli test panel shall be submerged in water at 75 = 5 °F (24±3 °C) for 4 hours and then dried at a temperature between 120 a n d 125 F f4f' to 52 C ) for 10 hours with SufiioK-nt a i r circulation to lower the moisture content (based on .ovendry weight) of specimens to a maximum of ^ percent. This cycle shall be repeated until all ^'ciim-ns fail or until three r v c l f S have been completed, whichever occurs first. A specimen shall be considered as failing when any single delnmination between two plies is greater than 2 inches in continuous length, over 14 i drpth at any point, and 0.003 ich in width, as determined by a feeler gage ,003-inch thick and V^-inch wide. Delamination duo to tape at-joint's of inner plies or defects permitted by the grade shall be disregarded. Nine of the 10 specimens shall pass the first cycle and  •1.1.  2  specimens.  eight of the 10 specimens shall pass the third cycle. 4.6. Two-cycle soak test—The 6-inch by 6inch specimens shall be submerged in water at 75 ± 5 °F (24 ± 3 °C) for 4. hours, and then dried at 75 ± 5 °F in an open room for 20 hours. . The cycle shall be repeated until all specimens fail or until two cycles have been completed, whichever occurs first. A specimen shall be considered as failing when any single delamination between two plies is greater than 2 inches in continuous length, over Vi depth at any point and 0.003 inch in width. Separation is determined with a 0.003-inch feeler gage. When this test is applied to lumber core or particleboar;! core, plywood, the core should be cut away to a depth of 1 inch on all four edges, leaving only enough core in this stress-relieved section to produce an approximate balance with the lace ply. Delamination due. to tape at joints of inner plies or defects permitted by the grade shall be disregarded. If there is a failure of more than one test specimen, the panel shall be classified as defective. m  4.7. Moisture content test — The. moisture content of the plywood shall be determined as follows: A small test specimen shall be cut from the sample panel; the test specimen shall meas.ure hot less than 0 square inches in area and shall weigh not less than 20 grams. A l l loose splinters shall be removed from the 'specimen. The specimen shall be immediately weighed to the nearest 0.1 of a gram, and the weight shall be recorded as the original weight. The specimen shall then be dried in an oven at 212 to 221 °F (100 to 105 °C) until constant weight is attained. After drying, the specimen shall be reweighed immediately, and this weight shall be recorded as the ovendry weight. The moisture content shall be calculated as follows: O r l c l n n l weight — oTmdrr Ovendry weight  weight .  x  1  0  0  =  M o U t u r e content {percent)  9  177  APPENDIX 5  The m i x i n g sequence of the PF  IB-334yGlue.  179 c.c.  VJ.B. S m i t h  Mr. F. A l a n T a y e l o r , I n d u s t r i a l Development  August 9, 1974  Officer,  VANCOUVER, B.C. Dear Nr. T a y e l o r : B i l l Hancock has requested t h a t I forward d e t a i l s on t h e glue a i x we prepared f o r use i n bonding veneer f o r l a d d e r stock a t our l a b . The  mixes r/.ade August 8th vjere formulated IB-334  Plyophen  Water K'orprof i l Wheat F l o u r Soda Ash Mix  a3 f o l l o w s :  5,872 gxas 1,781 gxas 93D RTP.S  900 gms *»00 gns  30 minutes on Bower Mixer a t 4000 r p n IB-334 Plyophen Jater  8,985 gas 1,13? gras 20,000 gms  T o t a l piv. s o l i d s : 4 3.8% Phenol Formaldehyde s o l i d s : 26.0% V i s c o s i t y 3 25°C £3 s p i n d l e 60 rpsi LVF B r o o k f i e l d - 1350 cps T h i s n i x d i f f e r s f r o n a standard plywood mix on two p o i n t s . F i r s t , the PF s o l i d s are h i g h e r by approximately 3% - 26% as oppos-sd t o 23%. Secondly, t h e r e i s twice t h e c o n c e n t r a t i o n of wheat f l o u r i n t h i s n i x as i n t h e average plywood mix. T h i s f o r m u l a t i o n and r e s i n has p r e v i o u s l y been s u c c e s s f u l l y used i n veneer l a m i n a t i n g and appears t o d i s p l a y t h e assembly t i n e t o l e r a n c e r e q u i r e d by the p r o c e s s . Should f u r t h e r a s s i s t a n c e be r e q u i r e d , p l e a s e c o n t a c t me. Yours very  truly,  REICIIHOLD CHEMICALS LIMITED  W. C. A i n s l i e , Wood Lab. Manager V/CA/jia c.c. Dr. y. V. Hancock  •  [to  APPENDIX 6  The m i x i n g sequence o f the Monsanto UF  109  Glue.  (8.1 M O N S A N T O UF109 RESIN WITH E K H A R D E N E R  Mixing Directions  100 £5.43  WATER  lbs.  MONSANTO E K  15 l b s .  Mix  6-S  \ lb.  o-<*'AZ 100  "f739  STEROX  Mix  CATALYST  1 Minute  WHEAT  lbs.  40  a t 65° - 70° F .  CD FLOUR  5 Minutes o r Until L u m p F r e e  MONSANTO UF109  lbs.  Sff  S7/4 90 lbs. _ji£L—  Mix  RESIN  3 Minutes or Until Lump  MONSANTO UF109 RESIN Mix  5 Minutes with Cooling Water in Jacket  345^  The  lbs.-i-6'S  T o t a l W e i g h t of M i x  m i x e d g l u e w i l l h a v e a w o r k i n g l i f e o f 24 h o u r s a t 70° F .  M i x e d g l u e l e f t o v e r n i g h t s h o u l d be m i x e d w i t h a f r e s h b a t c h before using.  *  T h e l e n g t h of the m i x i n g t i m e p r i o r to the a d d i t i o n o f the r e s i n w i l l a f f e c t the f i n a l v i s c o s i t y - i n c r e a s i n g the m i x i n g t i m e r e d u c e the v i s c o s i t y .  Free  will  )  HARDWOOD H O T PRESSING  SCHEDULE*  UF-109 RESIN W I T H E K H A R D E N E R 0  —r—  p'SS  Si  No. ot  Panels  Max. Dist.  per  «o!»ex  \ 3/16  183 , 208 . 207 .063  1/4 1/4 \) 1/4* I 3/S }) 1/2 1/2 3/4 3/4 3/4  O  1/7H 1/6M 1/7H 1/6 or 1/7  5-1/4 5-1/2 5-3/4 3- 3/4  4- 3/4 5 5- 1/4 3- 1/4  . 138 .181 . 136  1/10M 2xl/7H 1/10M  1/7H 1/7H . 262B Plywood  4- 3/4 6 5- 1/4  4- 1/4 5- 1/2 4-i,'4  .326 .329 .352  3xl/7H lxl/7H 1x1/ 10M  2xl/7H 2x3/16H 2xl/7H  8-1/4 8-1/4 8-3/4  7-3/4 7- 3/4 8- 1/4  1/2 Plywood 1/2 Plywood  5-1/4 5-1/2  4-3/4 5  . 138 163  3/4 3/4  Construction Center  T i m e Settings F o r P r e s s T i m e - Mins. 240° F. 260° F .  1/10 1/8  »>' plus 1/2 min. for each additional 1/16 over the 3/4 .  S  OVERLAYS 1/4 with. 1/6 chipboard center - 2 panels p e r opening 6 1/4 with 1/6 chipboard center and 1/30 - 1/16 face and back 3-3/4. 1/2 with 7/16 chipboard center and 1/30 - 1/16 face and back 3-3/4 3/4 with 11/16 lumber o r chipboard center 3-3/4 A B O V E T I M E I N C L U D E 15 S E C S . C L O S I N G T I M E AND 15 S E C S . F O R CAULS. SPREADS Hemlock  Mahogany " 57  62 65 1/6 67 ^ Rough core add 3 to D lbs.  , 1/10 \ ) 1/7  • Note:  60 62  Maximum recommended time assembly. Minimum recommended time assembly  8 hours 5 mins.  P r e s s u r e 175 lbs. per square inch. P r e s s u r e with chipboard 150-160 lbs. p e r sq. xn. r e d u c e the press temperature to 220°F. add  

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