"Forestry, Faculty of"@en . "DSpace"@en . "UBCV"@en . "Badejo, Solomon Olufunmilayo Olubunmi"@en . "2010-02-16T02:32:07Z"@en . "1977"@en . "Master of Forestry - MF"@en . "University of British Columbia"@en . "The gluing properties of plantation-grown gmelina wood (Gmelina arborea Roxb.) from Nigeria were investigated. Three wood peeling temperatures - 20\u00B0C, 50\u00B0C and 85\u00B0C; two glue types - urea-formaldehyde (UF) and phenol-formaldehyde (PF); two glue spreads - 25 kg/MDGL (55 lb) and 32 kg/MDGL (70 lb); and two closed assembly times - 10 minutes and 20 minutes were used. Veneers from the sample logs were peeled tight and were 1.27 mm (0.05 in) thick. The specific gravity for the logs was determined and its influence on the probable end uses of gmelina plywood discussed.\r\nThree 5-ply plywood panels were made, for each treatment combination for 72 in all. A total of 1438 shear test specimens were used. The UF specimens were tested dry and after vacuum-pressure treatment whereas the PF specimens received vacuum-pressure and boil-dry-boil tests. Bond quality was evaluated on the basis of wood shear strength and percentage wood failure. Results were compared to the U.S., British and German Plywood Standards.\r\nWood peeling temperature was highly significant regardless of glue type and bond quality testing method. Heating of gmelina logs prior to peeling did not improve veneer peel-quality. Veneers were of the highest peel-quality (basis: Thickness variation and surface roughness) when logs were peeled at 20\u00B0C. The highest peeling temperature\r\n\r\nyielded the lowest peel-quality.\r\nBond quality, (percentage wood failure), was consistently reduced by increasing peeling temperature and was lowest at 85\u00B0C in all the UF and PF treatments, regardless of bond quality testing method.\r\nIgnoring glue spreads, panels made from veneers cut at temperatures of 50\u00B0C and 85\u00B0C gave the highest shear strength values among the UF treatments. On the other hand, panels from veneers cut at temperatures of 20\u00B0C and 85\u00B0C gave the highest shear strength values among the PF treatments.\r\nAll factors considered, treatment combination of Spread 55 - Time 20, arising from veneers cut at the control temperature of 20\u00B0C, gave an impressive bond quality in all the UF and PF treatments used.\r\nFive of the 12 PF treatments used, regardless of type of bond quality testing method, pass the U.S. Plywood Standard; one passes the British Standard; while all pass the German Standard. On the\r\nother hand, five of the 12 UF treatments from vacuum-pressure test\r\n\r\npass the U.S. Standard; two pass the British Standard; while all pass the German Standard. Furthermore, all the 12 UF treatments from dry test pass the U.S. Standard; six pass the British Standard; while all pass the German Standard.\r\n\r\nFrom the results obtained, plantation-grown Gmelina arborea wood from Nigeria, with a specific gravity of 0.41 \u00B1 0.027 (as determined), was found suitable for use as construction plywood, core and crossband veneer for decorative panel as well as container veneer and plywood.\r\nThe dominant factor accounting for the general trend of low percentage wood failure was attributed to veneer surface inactivation, resulting from surface aging of veneers."@en . "https://circle.library.ubc.ca/rest/handle/2429/20279?expand=metadata"@en . "PEELING, GLUING AND BONDING CHARACTERISTICS OF NIGERIAN PLANTATION-GROWN GMELINA ARBOREA (ROXB.) by SOLOMON OLUFUNMILAYO OLUBUNMI BADEJO B.Sc. (Hons.) Forestry, U n i v e r s i t y of Ibadan, 1973 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF FORESTRY i n the Department of Forestry We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA May, 1977 Solomon Olufunmilayo Olubunmi Badejo, 1977 In presenting th i s thes is in pa r t i a l fu l f i lment of the requirements for an advanced degree at the Univers i ty of B r i t i s h Columbia, I agree that the L ibrary sha l l make it f ree ly ava i lab le for reference and study. I further agree that permission for extensive copying of th i s thesis for scho lar ly purposes may be granted by the Head of my Department or by his representat ives. It is understood that copying or pub l i ca t ion of th is thes is for f inanc ia l gain sha l l not be allowed without my writ ten permission. Department of The Univers i ty of B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 ABSTRACT The gluing properties of plantation-grown gmelina wood (Gmelina arborea Roxb.) from Nigeria were investigated. Three wood peeling temperatures - 20\u00C2\u00B0C, 50\u00C2\u00B0C and 85\u00C2\u00B0C; two glue types -urea-formaldehyde (UF) and phenol-formaldehyde (PF); two glue spreads -25 kg/MDGL (55 lb) and 32 kg/MDGL (70 l b ) ; and two closed assembly times - 10 minutes and 20 minutes were used. Veneers from the sample logs were peeled t i g h t and were 1.27 mm (0.05 in) thick. The s p e c i f i c gravity for the logs was determined and i t s influence on the probable end uses of gmelina plywood discussed. Three 5-ply plywood panels were made, for each treatment combination for 72 i n a l l . A t o t a l of 1438 shear test specimens were used. The UF specimens were tested dry and a f t e r vacuum-pressure treatment whereas the PF specimens received vacuum-pressure and b o i l - d r y - b o i l t e s t s . Bond q u a l i t y was evaluated on the basis of wood shear strength and percentage wood f a i l u r e . Results were compared to the U.S., B r i t i s h and German Plywood Standards. Wood peeling temperature was highly s i g n i f i c a n t regardless of glue type and bond q u a l i t y t e s t i n g method. Heating of gmelina logs p r i o r to peeling did not improve veneer p e e l - q u a l i t y . Veneers were of the highest p e e l - q u a l i t y (basis: Thickness v a r i a t i o n and surface roughness) when logs were peeled at 20\u00C2\u00B0C. The highest peeling temperature - i i -- i i i -yielded the lowest peel-quality. Bond quality, (percentage wood failure), was consistently reduced by increasing peeling temperature and was lowest at 85\u00C2\u00B0C in 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\u00C2\u00B0C and 85\u00C2\u00B0C gave the highest shear strength values among the UF treatments. On the other hand, panels from veneers cut at temperatures of 20\u00C2\u00B0C and 85\u00C2\u00B0C gave the highest shear strength values among the PF treatments. A l l factors considered, treatment combination of Spread 55 -Time 20, arising from veneers cut at the control temperature of 20\u00C2\u00B0C, gave an impressive bond quality in 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; one passes the British Standard; while a l l pass the German Standard. On the other hand, five of the 12 UF treatments from vacuum-pressure test j pass the U.S. Standard; two pass the British Standard; while a l l pass the German Standard. Furthermore, a l l the 12 UF treatments from dry test pass the U.S. Standard; six pass the British Standard; while a l l pass the German Standard. - i v -From the results obtained, plantation-grown Gmelina arborea wood from Nigeria, with a specific gravity of 0.41 + 0.027 (as determined), was found suitable for use as construction plywood, core and crossband veneer for decorative panel as well as container veneer and plywood. The dominant factor accounting for the general trend of low percentage wood failure was attributed to veneer surface inactivation, resulting from surface aging of veneers. TABLE OF CONTENTS Page TITLE PAGE i ABSTRACT i i TABLE OF CONTENTS \y LIST OF TABLES i x LIST OF FIGURES \. x i i ACKNOWLEDGEMENT . . x i v 1.0 INTRODUCTION 1 1.1 Objective and scope of study . . . . 1 1.2 Background information on the Nigerian wood-based panel industry . . . . . . 3 1.2.1 Log supply s i t u a t i o n . . . . . . 3 1.2.2 Growth and y i e l d of gmelina i n Nigerian plantations . . . . . . . 4 1.2.3 An overview of the industry . . . . 6 1.2.3.1 Employment . . . . . . . 6 1.2.3122.3.2 Value-added 7 1.2.3.3 Development . . . . . . . 7 1.2.3.4 Export trade . . . . . . . 8 1.2.4 Prospects of development . . . . . 8 1.2.4.1 Domestic consumption of plywood . . . 8 1.2.4.2 U t i l i z a t i o n of wood-based panels . . . 9 2.0 LITERATURE REVIEW 11 2.1 General wood properties of gmelina . . . 11 2.2 Log heating . . . . . . . . 12 2.3 Log peeling . . . . . . . . 15 2.4 Veneer drying . . . . . . . 19 2.5 Adhesion and adhesives . . . . . . 21 2.5.1 Adhesion: Wood bonding theories . . . 21 2.5.1.1 Mechanical theory . . . . . . 21 2.5.1.2 Adsorption theory . . . . . . 22 -v-- v i -Page 2.5.2 Adhesives: UF and PF r e s i n adhesives 2.5.2.1 UF glue 2.5.2.2 PF glue 2.6 Factors a f f e c t i n g plywood bond q u a l i t y 2.6.1 Glue spread . . . . 2.6.2 Assembly time . . . . 2.6.3 Glueline thickness 2.6.4 Pressing . . . . . 2.6.5 Degree of cure . . . . 2. 7 Wp:SbmeP.Nat\u00C2\u00B1onalt;P/lywo6d :S.t_nrd;ards- andf Specif i c a t 2.7.1 B r i t i s h Standard . 2.7.2 Japanese Standard 2.7.3 German Standard 2.7.4 United States Standard 2.8 G l u a b i l i t y of Hardwoods 3.0 EXPERIMENTAL PROCEDURES 3.1 Experimental design . . , 3.2 Materials and preparation 3.2.1 Wood species cha r a c t e r i z a t i o n 3.2.1.1 S p e c i f i c gravity determination 3.2.1.2 Moisture content determination 3.2.1.3 Determination of the optimum lathe settings for peeling 3.2.2 Logoheating 3.2.3 Log peeling 3.2.4 Peel - q u a l i t y evaluation 3.2.4.1 Veneer roughness 3.2.4.2 Veneer thickness measurement 3.2.5 Veneer drying 3.2.6 Glues and glue mixing 3.2.6.1 IB-334 Plyophen 3.2.6.2 Monsanto UF 109 r e s i n with EK Hardener 3.2.7 Glue spread . . . . . ions 24 25 26 27 27 28 29 30 30 31 32 32 33 33 34 40 40 41 41 42 42 42 43 45 45 46 46 46 47 47 48 49 - v i i -Page 3.2.8 Plywood panel pressing . . . . . . 5 0 3.2.8.1 Press Pressure . . . . . . 50 3.2.8.2 Pressing Temperature and Time . . . 50 3.2.9 Test specimen preparation . . . . 51 3.2.10 Bond quality testing procedures . . . 51 3.2.10.1 Dry test 51 3.2.10.2 Vacuum-pressure test . . . . . 52 3.2.10.3 Boil-dry-boil-cool test . . . . 53 3.2.11 S t a t i s t i c a l analysis . . . . . 53 4.0 RESULTS 54 4.1 Moisture content and specific gravity of gmelina v logs used . . . . . . . . 54 4.2. Log heating and peeling . . . . . 54 4.3 Veneer peel-quality . . . . . . 55 4.4 Veneer moisture content prior to gluing . . 55 4.5 UF resin adhesive . . . . . . . 56 4.5.1 Dry test: Shear strength and wood failure percent . . . . . . . , 56 4.5.2 Vacuum-pressure test: Shear strength and wood failure percent . . . . . . . 56 4.6 PF resin adhesives' . . . . . . 57 4.6.1 Vacuum-pressure test: Shear strength and wood failure percent . . . . . . . 57 4.6.2 Boil-dry-boil test: Shear strength and wood failure percent . . . . . . . 57 4.7 Analysis of variance . . . . . . . 58 4.7.1 Factorial analysis . . . . . . 58 4.7.2 Duncan's multiple range test . . . . 59 5.0 DISCUSSION 60 5.1 Sample, specific gravity . . . . . 60 5.2 Log heating . . . . . . . . 60 5.3 Veneer peel-quality . . . . . . 61 5.3.1 Thickness . 61 - v i i i -6.0 5. 3.2 Roughness ; . 5.4 Plywood bond quality . . . . . 5.4.1 Treatment panels bonded with UF glue 5.4.1.1 Dry test: Shear strength and wood failure percent . . . . . . . 5.4.1.2 Vacuum-pressure test: Shear strength and woo< failure percent . . . . . 5.4.2 Treatment panels bonded with PF glue 5.4.2.1 Vacuum-pressure test: Shear strength and woo failure percent . . . . . 5.4.2.2 Boil-dry-boil test: Shear strength and wood failure percent . . . . . 5.4.3 Probable factors accounting for low percentage wood percentage wood failures in the treatment 5.4.4 Comparison of study results with some National Plywood Standards . . . . 5.4.4.1 U.S. Hardwood Plywood Standard 5.4.4.2 British Hard Plywood Standards 5.4.4.3 German Hardwood Plywood Standard 5.5 Probable end uses of Gmelina arborea Veneer and Plywood . . . . . . 5.5.1 Construction plywood . . . . 5.5.2 Core and Crossband veneer for decorative plywood . . . . . 5.5.3 Container veneer and plywood SUMMARY, SUGGESTIONS FOR FURTHER STUDIES AND CONCLUSION 6.1 Summary . . . . . . . . . 6.2 Suggestions for further studies . . . . 7 ft 7.4T-8.0 9/0 10..0 6;. 3T TConclusion BIBLIOGRAPHY TABLES FIGURES APPENDICES Page 61 62 62 62 64 65 65 67 69 73 73 77 78 78 78 79 80 82 82 85 85 86 100 123' 13 9 LIST OF TABLES Table Page 1 De'scrriptive 'features of Gmelina arborea logs used for study . . . . . . . . . 100 2 I n i t i a l and peeling moisture content (%) of the Gmelina arborea logs used for study . . . . 101 3 Specific gravity of the Gmelina arborea logs used for study . . . . . . . . . . 102 4 Water bath and log temperature changes against time of peeling - 50\u00C2\u00B0C . . . . . . . . 103 5 Water bath and log temperature changes against time of peeling - 85\u00C2\u00B0C 104 6 Lathe specifications for peeling . . . . . 105 7 Peel-quality attributes: Veneer roughness measurement. 106 8 Veneer peel-quality statistics - 1.27mm (0.05 in) Gmelina arborea green veneer . . . . . 107 9 Veneer moisture content prior to gluing . . . 108 10 Average shear strength and average wood failure of 5-ply Gmelina arborea Plywood bonded with Urea - For-maldehyde (UF) glue 109 11 Average shear strength and average wood failure of 5-ply Gmelina arborea Plywood bonded with Phenol-Formaldehyde (PF) glue . . . . . . . 110 -i x --x-Table Page 12 Within- and between-panel variation in bond quality of 5-ply:Gmelina arborea Plywood bonded with UF glue: Dry test, wood failure . . . . . . . I l l 13 Within- and between-panel variation in bond quality of 5-ply Gmelina arborea Plywood bonded with UF glue: Vacuum pressure test, wood failure . . . . 112 14 Within- and between-panel variation in bond quality of 5-ply Gmelina arborea Plywood bonded with PF glue: Vacuum pressure test, wood failure . . . . 113 15 Within- and between-panel variation in bond quality of 5-ply Gmelina arborea Plywood bonded with PF glue: Boil-dry-boil test, wood failure . . . . . 114 16 Analysis of variance for testing the effects of Peeling Temperature, Glue Spread and Closed Assembly Time on UF glue bond quality in 5-ply Gmelina arborea Plywood: Dry test . . . . . . . . . 115 17 Analysis of variance for testing the effects of Peeling Temperature, Glue Spread and Closed Assembly Time on UF glue bond quality in 5-ply Gmelina arborea Plywood: Vacuum pressure test . . . . . . . 116 18 Analysis of variance for testing the effects of Peeling Temperature, Glue Spread and Closed Assembly Time on PF glue bond quality in 5-ply Gmelina arborea Plywood: Vacuum pressure test . . . . . . . 117 19 Analysis of variance for testing the effects of Peeling Temperature, Glue Spread and. Closed Assembly Time on PF glue bond quality in 5-ply Gmelina arborea Plywood: Boil-dry-boil test . . . . . . . . 118 - x i -Table Page 20 Duncan's multiple range test for shear strength of Gmelina arborea Plywood bonded with UF glue . . 119 21 Duncan's multiple range test for wood failure of Gmelina arborea Plywood bonded with UF glue . . 120 22 Duncan's multiple range test for shear strength of Gmelina arborea Plywood bonded with PF glue. . . 121 23 Duncan's multiple.range test for wood failure of Gmelina arborea. Plywood bonded with PF glue. 122 LIST OF FIGURES Figure Page 1 Pattern of cut of test samples from logs for specific gravity and moisture content determination tests . . . . . . . . . . 123 2 Temperature changes within a log, 8 ft long and 7.7 in diameter: 50\u00C2\u00B0C heating . . . . . . . 124 3 Temperature changes within a log, 8 f t long and 8.0 i n diameter: 85\u00C2\u00B0C heating . . . . . . 125 4 Frequency distribution of visual veneer roughness . 126 5 Dependence of bond quality on peeling temperature and assembly time interaction: UF Dry test (shear strength) . . . . . . . . . 127 -6 Dependence of bond quality on peeling temperature, glue spread and closed assembly time interactions: UF Dry test (wood failure) . . . . . . 128 7 Dependence of bond quality on peeling temperature and glue spread interaction: UF Vacuum pressure test (shear strength) . . . . . . . . 129 8 Dependence of bond quality on peeling temperature and glue spread interaction: UF Vacuum pressure test (wood failure) . . . . . . . . 130 9 Dependence of bond quality on peeling temperature, glue spread and closed assembly time interactions: UF Vacuum pressure test (wood failure) . . . . 131 - x i i -- x i i i -Figure Page 10 Dependence of bond q u a l i t y on peeling temperature and glue spread i n t e r a c t i o n : PF Vacuum pressure test (shear strength) . . . . . . . . .. 132 11 Dependence of bond q u a l i t y on peeling temperature and closed assembly time i n t e r a c t i o n : PF Vacuum pressure test (shear strength). 233 12 Dependence of bond q u a l i t y on peeling temperature and\"\" assembly time i n t e r a c t i o n : PF Vacuum pressure test (wood f a i l u r e ) . . . . . . . .- . 134 13 Dependence of bond q u a l i t y on peeling temperature, glue spread and closed assembly time i n t e r a c t i o n : PF Vacuum pressure test (wood f a i l u r e ) . 135 14 Dependence of bond q u a l i t y on peeling temperature and closed assembly time i n t e r a c t i o n : PF B o i l - d r y - b o i l test (shear strength) . . . . . . . 136 15 Dependence of bond q u a l i t y on peeling temperature and glue spread i n t e r a c t i o n : PF B o i l - d r y - b o i l test (wood f a i l u r e ) . . . . . . . . . 137 16 Dependence of bond q u a l i t y on peeling temperature and closed assembly time i n t e r a c t i o n : PF B o i l - d r y - b o i l test (wood f a i l u r e ) . . . . . . . 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 in providing the logs. I am greatly indebted to the Western Forest Products Laboratory, Vancouver, Canada, for being allowed to use the Laboratory's f a c i l i t i e s . 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 criticism, and numerous helpful suggestions throughout the experimental work. 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 their 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 results; and Mr. Richard Yang (graduate student) who wrote the programme used. The financial backing of my employer, the Federal Department of Forestry, Ibadan, Nigeria, has also made the study possible. Finally, special thanks are due to my wife, Remi, who has patiently 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 (IUERO 1973) in which the Forest Products Research Laboratory (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 African country. In the same publication, the Centre Technique du Bois, Paris, France reported that gmelina wood i s moderately suited for construction plywood, container veneer and plywood, and inner plies for decorative panels. The sample logs used by the French research centre were obtained from the Ivory Coast, in West Africa. No published reports have been found on the gluability of this wood in Nigeria. The findings of the FPRL, Princes Risborough, England, are considered of significant importance to the wood-based panels industry in Nigeria for two reasons: 1. The United Kingdom is the most important single market for a l l wood products export from Nigeria, accounting for about 90% of the veneer and plywood export in 1972. 2. The current objective of management of gmelina plantations, in - 2 -at least two of the States in Nigeria, has incorporated future supply of sawlogs and veneer logs (Alade 1970, Enemuoh 1970). In the Western State\ for example, i t is 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. The following plywood production variables w i l l be used: 1. Three levels of wood peeling temperature 2. Two adhesive types 3. Two levels of glue spread 4. Two closed assembly times Results from this study could serve to indicate whether to accept or reject the suitability of gmelina wood for use as plywood. If results are encouraging, the study could, -have*. arapLmpact?'on . p._\u00C2\u00A7Lntat -onpmanage\u00E2\u0080\u0094entinand gen-the awdo de.ba sedwpariel aindus t ry.linn <\u00E2\u0080\u00A2; \u00E2\u0080\u00A2 \u00E2\u0080\u00A2 Nigeria^ -\u00E2\u0080\u00A2 t Now comprising three New States - Oyo, Ogun and Ondo after February 1976. The logs used for study were part of consignment of logs shipped to SNC-Rus'^ L i l t e d of Montreal, Canada, from Nigeria, for pulping studies. - 3 -1.2 Background Information on the Nigerian Wood-based Panel Industry 1.2.1 Log supply situation Log supply i s one of the major current problems confronting the Nigerian wood industries. Various studies (Okigbo 1964, Eklund et. a l . 1966, Wellwood 1966, Huuhtanen 1975) have indicated the serious-ness of this situation in the forseeable future. The problem of log supply is not peculiar to Nigeria. Grudzinski (1975) has indicated that this factor has posed a problem.in a l l areas of the world where the plywood mills are f a i r l y concentrated. Nevertheless, the Nigerian case has not resulted from industrial concentration as such but from a limited wood-resource base. The total land area in Nigeria is about 93 million ha of which the productive high forest reserves (the only source of industrial wood supply) accounts for only 1.9 million ha or about 2%. The growth rate and rate of forest regeneration after logging i s quite low. Natural regeneration.has been inadequate, even where attempts were made to induce i t (Lowe 1966). Bamgbala and.Oguntala (1970) put the timber 3 3 yield from the natural moist forest in Nigeria at about 35jmp_per ha. With a rotation of about 50.years in.the high forests, this seemed a low \ figure. Increasing efforts 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 failure 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 situation in Nigeria seems to depend on.the development of planta-tions of fast-growing species for sawlogs, veneerlogs and pulpwoods. As indicated by Fox (1972), the fast growth of planted trees is perhaps the most important advantage of the developing countries. The Federal and States governments in Nigeria seem committed to this concept as evidenced by their forest policy statements. Nigeria.has.a vast forest land, as distinct from productive high.forests, that accounts for about 35% of the total land area. With better land use planning, enough land could s t i l l easily be allocated to Forestry for afforestation purposes. Afforestation schemes were started in Nigeria before 1950. By 1950 and 1969, the country had a total 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 total of 61,548 ha by 1970 (Enabor 1973). Plantings are being stepped up in the poorly stocked, highly degraded and the savannah areas of the country with fast growing exotic and indigenouss. species. Gmelina. arborea is one of the major exotic species established in 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 yield of gmelina i n Nigeria. LT Gmelina has.become a popular plantation species in Nigeria for six major reasons: 1. The seeds are readily available. - 5 -2. . It is easy to propagate from seeds and cuttings_. 3. It coppices well. 4. It shows adaptability to a wide range of s o i l and climatic conditions. 5. It is fast growing and has abi l i t y to coppice for about 50 years (Scherpe 1968). 6. It suppresses the growth of weeds at an early age, thus reducing cleaning and weeding costs. Gmelina grows very well in 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 is 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 in another 7-year old plantation. 3 Chittenden et_r-.>al. (1964) quoted a yield of about 84 m per ha in a 12-year old plantation on poor sandy soils.of the Derived 3 Savannah Zone of Nigeria. They also reported a yield of about 252 m per ha on the most favourable Savanna sites and in the Rain Forest Zone, 10 and 8 years respectively, after planting. From studies conducted by 3 the Federal Department of Forestry, Ibadan, a yield of about 184 m per 3 ha, with a Mean Annual Increment of about 23-27 m was reported for an 8-year old gmelina plantation at Omo Forest Reserve (Modugu 1977). - 6 -1.2.3 An overview of the industry. Nigeria is a major African producer of wood-based panels. The 3 actual wood-based panels production for 1973 was 55,000 m (FAO 1975a) in the following product categories: 3 i ) Hardwood Plywood . . . . . . 45 ,100' m 3 i i ) Veneer Sheets . . . . . . 1,200 m 3 i i i ) Blockboard, Laminboard, Battenboard . . 8,700 m Total 55,000-m3. Wood-based industries have played a major role in the economy of Nigeria, contributing substantially to employment and value - added in manufacturing. Since the industrial survey publications in 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 for labor in Nigeria, apart from agriculture and fisheries (Adeyoju 1968). With a total employment of 11,910 workers in 1963, the wood-based industries accounted for 17.5% of the total employment in manufacturing. The total number of workers employed decreased to 11,240 and 11,540 in 1967 and 1969 resulting in a decreased share of 14.6% and II. 3% respectively, of the total 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 textile industries in the country's - 7 -manufacturing employment. 1.2.3.2 Value-added The value-added in the wood-based industries in 1963 was $13.1 million, representing 8.5% of the national total. Although by 1967, the value-added.in these industries had increased to $14.5 million, i t represented id a,reduced share of 5.9% of the value-added in a l l the manufacturing industries.-. Again an increase to.^$23.4 million by 1970 , accounted for only 4.2% of the national, total (Enabor 1976). Rate of expansion and.level of efficiency have been indicated as some of the factors controlling ',,to value-added . in manufacturing within the wood-based industries. Thus, the. small*\u00C2\u00BBscale of operations and inefficiency within the sawmilling .industry could.have significantly accounted for the decreased share of value-added in manufacturing from the wood-based industries. 1.2.3.3. Development Nigeria's production of wood-based panels began in 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 in Sapele. For-almost two decades, this was the only operating m i l l in the country, producing veneer and plywood for export and domestic consumption. Now, there are four operating wood-based panel mills in 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 for 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 in the World, though no longer the most modern. $20 m i l l i o n . This proposed m i l l i s expected to s t a r t production under the 1976-1980 Development Plan. 1.2.3.4 Export trade There i s no co-operative s e l l i n g and shipping of the wood-based panels among the four operating m i l l s i n the country. Each m i l l undertakes the shipment of i t s products. Export trade has accounted for an increasing share of the t o t a l wood-based panels production over the years. This averaged 69% (FAO 1975b) during the fe.y^en year period of 1962 to 1968. Export trade was highest i n 1970 when i t accounted f o r about 91% of the t o t a l production. Due to increased domestic consumption, the share exported has decreased dramatically since then. I t was about 45% i n 1971 and from FAO estimates f o r 1972 and 1973 (FAO 1975b), export trade was expected to account for only about 42% and 38% r e s p e c t i v e l y . The main markets for veneer and plywood are the United Kingdom, Germany, Holland, Denmark, I t a l y and the United States of America. However, the bulk of the plywood exported goes to the United Kingdom. Veneer and plywood have contributed an average of $2.7 m i l l i o n , annually, to the Nigerian foreign exchange earnings since 1964. Export earnings from these commodities account for about 27%, 24% and 14% of the t o t a l export earnings of about $10.1 m i l l i o n (1971), $10.6 m i l l i o n (1972), and $19.4 m i l l i o n (1973) resp e c t i v e l y from a l l wood products (Nigeria 1972, FAO 1974). 1.2.4 Prospects of development 1.2.4.1 Domestic consumption of plywood A major prospect for development of the wood-based panel - 9 -industry in Nigeria l i e s internally. There is currently a booming trade for plywood. Apparent plywood consumption increased substantially from 3 3 9,000 m in 1962 to 26,000 m in 1971, giving an increase of about 289% or an annual growth rate of 12.5% (FAO 1975b). Consumption was 3 3 estimated to increase to 30,000 m and 34,000 m in 1972 and 1973 respectively. Of the total wood-based panel consumption in 1967 and 1971, plywood accounted for a share of about 64.3% and 66.7% respectively. This was expected to increase, to 71.4% and 72.3% by 1972 and 1973 respectively. 1.2.4.2 Utilization of wood-based panels The major use of wood-based panels in Nigeria is in manufactur-ing, accounting for about 50% of the total annual domestic consumption of veneer and plywood. Paneling, boat building and wood-based components jointly account for about 40%; while the remaining 10% goes into packag-ing and other forms of uses (Enabor 1972). The furniture industry has contributed a great deal to increased use of wood-based panels in Nigeria and more furniture mills are proposed for the country. For the 1970-74 Development Plan Period, the Federal and States governments in Nigeria proposed anrinViestmentmof.Labdutu \u00E2\u0080\u0094 $2 million.on two wooden furniture factories. This is considered an incentive for further development within the wood-based panel industry. Development may not .necessa-r-i_yatake\" .a form of increased number of operating mills, but rather that of increased production capacity of the existing ones via higher output. - 10 -Enabor (1976) projected a consumption of 102,000 to 132,000 3 m (r) of wood-based panels in Nigeria by 1985. Similarly, he forecasted 3 a consumption of 231,000 to 363,000 m (r) by 2000 A.D. Even though forecasts are sometimes erroneous, future consumption of wood-based panels, in Nigeria, is indeed anticipated to increase with growth in 4 population and higher per capita income. The country's population increased from 56 million in 1963, to an estimated 80 million in 1973. - 11 -2.0 LITERATURE REVIEW This l i t e r a t u r e review i n i t i a l l y covers some of the most important process steps i n plywood production i n c l u d i n g : 1. Log heating 2. Log peeling 3. Veneer drying A further section of the review focuses on adhesion of wood and factors 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 of the two adhesives - phenol\u00E2\u0080\u0094formaldehyde (PF) and urea\u00E2\u0080\u0094formaldehyde (UF) used to make experimental plywood. Some of the d i f f e r e n t n a t i o n a l plywood standards and s p e c i f i c a t i o n s used to evaluate study r e s u l t s , are surveyed. As only l i m i t e d information i s a v a i l a b l e on the g l u a b i l i t y of gmelina wood, the chapter concludes by giving a general review of the g l u a b i l i t y of hardwoods. 2.1 General Wood Properties of Gmelina Gmelina wood i s d i f f u s e porous and, as indicated by Esan (1966), f a s t growth does not change the density of the wood. Growth rings are v i s i b l e and from studies done on the wood grown i n Thailand (Lamb 1968) and Nigeria (Esan 1966), they appeared to be annual. The wood i n appearance i s straw yellow to creamy white (Lamb 1968). He (Lamb) further reported that selected samples of the wood show f i d d l e back mottling and a fin e sheen on quarter sawn boards. Gmelina wood i s indicated to contain a high r e s i n content. Sample logs from Nigerian plantations were peeled, i n the country, into 2.25 mm thick veneers f o r match splints. Veneers were found to be smooth, straight grained and of medium texture. 'J. 2.2 Log Heating Heating of logs before veneering is a conditioning process (TRADA 1967) commonly practised in the hardwood plywood industry. It decreases the ratio of compressive to tensile strength of wood thereby giving a more uniform material (Hancock 1977a). Several heating systems have so far been developed. These include circulating hot water, steam heating, electrical heating, water/ air heating and high pressure heating (Seidel 1952; Fleischer and Downs 19535, Lickess 1957; Kubinsky and Sochor 1968). Of/these, hot water systems of heating are the most commonly practiced in the plywood industry (Feihl 1972). Hot water systems give better uniformity compared to steam-ing, and also ensure freedom from block end split s (Fleischer 1959; Anon 1968). Heating of logs helps to plasticize the wood for best veneer cutting. With most woods, the fibers and hard knots present in the wood are softened and cutting becomes easier. Fleischer (1948), Lutz (1960), Anon (1968) and Palka (1974) reported that log peeling as a result of prior heating becomes easier and smoother veneers are produced without excessive lathe checks. Lathe checks, as ascertained by Chow (1974), contribute in large measure to reduced shear strength of plywood. Considerable reduction in damage to lathe knives has been reported, when Original not seen. Cited from reference of 0. Feihl 1972. - 13 -peeling heated logs (Lickess 1957; Feihl and Godin 1975). Ellwood and Erickson (1962) reported that there is loss of moisture by vaporization when logs are steamed prior to peeling. There i s , generally, loss of moisture through evaporation, as the heated logs begin to cool after removal from the heating mediums. These must have facili 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 is essential for hardwoods from which lumber cores are to be cut. The optimum cutting temperature for any wood is a function of i t s specific gravity, presence of hard knots, tendencies for end splitting and color changes (Fleischer 1959). The heating period required to obtain such optimum temperature, as well as the rate of temperature changes within the wood to give i t , are functions of the green specific 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 air temperature (MacLean 1946, Fleischer 1959, Seidel 1952, Nakamichi\u00E2\u0080\u00A2 and Konno 1965, Altukhov 1965, Garrison 1967, Anon 1968, Feihl 1972, Feihl and Godin 1975). As cutting from too cold or too hot logs results in lower veneer peel-quality, (Feihl and Godin 1975),each wood species therefore cuts best within a certain temperature range. With too low a peeling temperature, loose or rough veneers are produced (Fleischer 1959; Feihl 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\u00C2\u00B0C. Optimum cutting temperatures vary between hardwoods and soft-woods . Fleischer (1959) stated that best cutting temperatures in hard-wood species are roughly related to the wood density. Hardwoods of low specific gravity (^=0.40) are reported to cut well at room temperature (the specific gravity of Gmelina. arborea used for 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\u00C2\u00B0C; while yellow birch is indicated to cut best at aet!emperaturefof.babouE171^C.Furthermore, Feihl and Godin (1975) pointed out that soft species such as poplar and basswood cut best at a temperature of about 32\u00C2\u00B0F (0\u00C2\u00B0C). Cutting temperatures have also been correlated to the veneer nominal thickness intended to be peeled irrespective 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. These studies were, however, conducted on softwood species. In their study on hardwood species, Wangaard and Saraos (1959) showed that there was an impressive degree of - 15 -improvement in the tightness of veneers obtained from white and red lauan bolts heated in water at about 71\u00C2\u00B0C compared to unheated bolts. 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 in uniform thickness, reasonable tightness and smoothness for gluing into plywood. These properties serve to achieve good bonding during gluing. As indicated by Bryant et. a l . (1965), poor glue bonds in core veneers, as well as excessive panel-thickness variation, are largely accounted for by the extent of veneer-thickness variation. They also pointed out that gluing of such veneers requires greater pressures in panel pressing so as to promote intimate contact between a l l the glued laminates. Lutz et. a l . (1969) also reported that variation in veneer thickness can cause problems of show-through of the core veneer in decorative panels. Various studies have revealed that efficient rotary-cutting of logs hinges on many variables. These include the log diameter, the moisture content of the wood, the knife pitch 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, significantly, the peel-quality obtained during rotary-cutting of logs (Fleischer 1949). For example, Kovanen (1963) demonstrated that tensile strength of Finnish birch veneers decreases with decreasing i n i t i a l log diameter. A similar - 16 -trend was reported by Cade and Choong (1969) in their study with Southern pine. From their study, veneer tensile strength perpendicular to the grain improves with increasing;log diameters. Sivananda et, a l . (1973) also ascertained that thickness variation 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 Feihl and Godin (1963) identified lathe adjustment as a key to proper cutting of thin veneers of uniform thickness. This adjustment has also been recognised essential (Fleischer 1956, Hancock and Hailey 1975) for cutting smooth veneers of uniform thickness. rToo. large a knife angle and insufficient nose-bar pressure were reported to influence veneer thickness variation (Barefoot and Salehuddin 1962) as well as resulting in loose and rough veneer (Feihl and Godin 1970). The pitch angle (the knife cutting angle) is the angle the plane of the knife tip 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 Feihl and Godin (1967) a l l refered to the pitch angle as a major factor responsible for veneer thickness uniformity. The knife angle used at any particular 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 Feihl (1976) for example, recommended jaUpixtcfojangle of. 90 30' when peeling veneers thinner than 0.84 mm (1/30 in.) for a l l diameters. To - 17 -maintain a constant bearing on the knife, i t has also been pointed out that the knife angle should decrease as the diameter of the log being v peeled decreases (Fleischer 1949 and 1956, Kovanen 1963, Palka and Holmes 1973). 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 in rub length gives superior results at small log diameters. For any particular wood, there i s an optimum range of pitch angle in cutting within which veneer peel-quality can be maximised. -Madison (1951) and (1957) found an optimum pitch angle of 89\u00C2\u00B050' and 90\u00C2\u00B0-93\u00C2\u00B0 adequate for peeling 0.32 cm (1/8 inch) thick Western larch veneer and 0.13 cm (1/20 inch) thick/aspen veneer respectively. A knife angle of 90\u00C2\u00B0 was indicated adequate (Wangaard and Saraos 1959) for cutting veneers of uniform thickness from Philippiah'- white and red lauan. For most species, they, and Feihl and Godin (1970) reported an optimum level of knife angle varying between 89\u00C2\u00B031' and 90\u00C2\u00B030' when peeling 0.32 cm (1/8 inch) thick veneers. Another lathe variable considered to play a dominant role in determining veneer peel-quality i s the pressure bar compression / (Fleischer 1949, Leney 1960, Koch 1964, Palka. 1970, Cumming and Collett 1970, Lutz 1974). 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 result in greater veneer tightness and smoothness. Barefoot and Salehuddin (1962) demonstrated that insufficient nose-bar pressure could influence variation in veneer thick-ness when peeling small diameter bolts from woods of Albizzia procera. The horizontal opening (gap) is the horizontal distance between - 18 -knife tip and bar tip and i t i s the main control on veneer roughness while the vertical opening (lead), which controls the veneer thickness va r i a b i l i t y , i s the vertical distance between knife tip and bar tip (Hancock and Feihl 1976). Fleisher (1949), Collins (1960), Feihl et. a l . (1963), Feihl (1964), Lutz and Patzer (1966) a l l recognised the size of the horizontal roller-bar 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 roller-bar 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. Feihl (1964) reported that the use of smaller gaps result in smoother but too thin veneers when peeling curly birch logs. The nose-bar lead i s not as important as the gap in determining veneer peel-quality. Fleischer (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, Feihl et- a l . 1963, Cumming and Collett 1970) have shown, however, that there i s an optimum range of gap and lead within which satisfactory veneer can be obtained. This optimum varies with species as well as veneer nominal thickness. Hancock and Feihl (1976) indicated that,generally, the gap is 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 is in good working condition. From the literature reviewed above, i t is quite obvious that a - 19 -judicio u s s e l e c t i o n of knife angle, h o r i z o n t a l and v e r t i c a l pressure bar openings w i l l serve to optimize veneer p e e l - q u a l i t y during cutting with respect to species, veneer nominal thickness and log s i z e . \"4j Veneer Drying Drying^of f r e s h l y cut veneers, when properly c o n t r o l l e d , reduces t h e i r moisture content to a l e v e l s u i t a b l e f o r gluing into plywood. The rate of veneer drying i s a function of the veneer i n i t i a l moisture content, i t s thickness, species, dryer temperature, i t s a i r v e l o c i t y and r e l a t i v e humidity (Bethel and Carter 1950, Bethel and Hader 1952, F l e i s c h e r 1953, Holden J r . 1956, M i l l i g a n and.Davies 1963, Lutz 1974). The condition of p e e l - q u a l i t y , e s p e c i a l l y the tightness of the veneer, was indicated by Bethel and Hader (1952) to a f f e c t veneer drying. Loose peeled veneers, as they pointed out, dry at a f a s t e r rate than t i g h t peeled veneers. The moisture present i n veneer p r i o r to drying a f f e c t s the t o t a l drying time. As sapwood and heartwood veneer pieces d i f f e r i n moisture content, e f f e c t i v e veneer segregation p r i o r to drying helps to improve the drying control ( C a r r o l l and.Dokken 1970). In hardwoods where d i s t i n c t i o n between sapwood and heartwood may be d i f f i c u l t , C a r r o l l and Dokken (1970) suggested the use of moisture meters to e f f e c t i v e l y achieve green s o r t i n g . V a r i a b i l i t y i n moisture content of the dried veneer sheets has been reported as one of the causes of under-cured and washed out g l u e - l i n e s and panel blow-ups during pressing (Fleischer 1958, Carroll'and~Dokken 1970). Comstock (1971) and Walters (1971) pointed out that the - 20 -density of the veneer may be a factor in the total drying time because : denser woods have slower drying time. ~ Bethel and Hader (1952) reported differences in the drying time of different 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 identified as an important factor (Comstock 1971, Lutz 1974) in controlling rate of veneer drying. This rate is a function of the veneer thickness (Bethel and Hader 1952, Fleisher 1953). They also reported that veneer drying time is a function of the dryer temperature. The higher the temperature, the more accelerated the drying becomes and the shorter the total drying time. Drying should, however, be cautiously carried out as excessive drying with too high temperature results in veneer surface inactivation. As defined by Chow (1969a), \"surface inactivation 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 failures in plywood. The inferior joints caused by increased drying temperature and time are pointed out by Currier (1958) to be results of reduced wettability of the veneers by the adhesives. Sisterhenm (1961) also showed that plywood made from Douglas-fir veneers dried to 232\u00C2\u00B0C (450\u00C2\u00B0F) developed a significantly lower bond quality compared to those made from veneers dried to a temperature of 191\u00C2\u00B0C (375\u00C2\u00B0F). Chow et. a l . (1973) further indicated that overdrying or underdrying of veneers seriously affect the - 21 -bond quality obtained. 'I Carroll and Dokken (1970) nevertheless reported that surface inactivation 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 is due to loss i n strength of wood and not necessarily that of an adhesion. They further indicated that veneer surface inactivation can be avoided by the use of lower temperature at the dry end of the dryer. 2._5 Adhesion and Adhesives 2.5.1 Adhesion: Wood bonding theories Adhesion in wood is a complicated phenomenon. There are many factors that influence bonding in wood,and as stated by Allen (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, joint quality in 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 solid have been ascribed (DeLollis 1968) to chemical bonds, mechanical entanglement, physical and chemical adsorption due to polar groups, electrostatic forces of attraction inherent in a l l matter and to combinations thereof. From DeLollis viewpoint,therefore, i t is quite obvious that mechanical and specific adhesion are essential to bonding in wood. 2.5.1.1 . Mechanical theory Mechanical adhesion in wood is effected by anchorage due to penetration into and hardening within capillaries in adherend surfaces - 22 -(Bikerman 1961, Heitler. 1966) . Marian and Stumbo (1962a) have indicated that mechanical adhesion certainly exerts an influence in wood, depending on joint 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 is essential 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 is insufficient.for bonding strength in wood. Total adhesion inwood is dependent upon mechanical and.specific adhesions (Kollman et- a l . 1975). Marian.and Stumbo (1962a), in a particularly elegant experiment,, indicated.that the physico-chemical forces are mainly responsible for adhesion in 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 is specific adhesion which results from forces of adhesion-acting-between the molecules of the wood and the adhesive. As indicated by Marian and Stumbo (1962a), specific adhesion .is caused by primary valence forces or secondary valence (Van der Waals) forces. Baier et. a l . (1968) and Zisman (1963) - 23 -reported that the three requirements necessary f o r developing a strong adhesive j o i n t are: 1. Good wetting by the adhesive l i q u i d . 2. S o l i d i f i c a t i o n . 3. S u f f i c i e n t deformability necessary to reduce the e f f e c t of e l a s t i c stresses i n the formation of the j o i n t . According to Marian and Stumbo (1962b), the wetting helps to a s s i s t spreading and penetration.of.the adhesive into the wood. DeBruyne and Houwink (1951) remarked i n t h e i r discussion of adhesion theory that wetting of the surface by the adhesive i s a necessary pre-r e q u i s i t e f o r good gluing. The mutual a t t r a c t i o n between the wood surface and the adhesive ( r e s u l t i n g from the adhesive wetting power) has been at 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 chemical phenomena (DeBruyne 1947). C o l l e t t (1972) ascertained.that the covalent bond plays a very important r o l e i n s p e c i f i c adhesion, while the i o n i c bond was i d e n t i f i e d as of l e s s e r importance. In t h i s connection,therefore, the forces of molecular a t t r a c t i o n were stated by Kollman etfj al_. (1975) to play an important r o l e i n the adhesion between wood and glue. Zisman (1965) also remarked that adhesion i s caused-by forces between molecules i n or near the surface of the two contacting materials and that these are p r i m a r i l y of van der Waals and hydrogen bonding type. A l l the foregoing emphasizes, the f a c t that an adhesive must spread and wet w e l l the wood substrate to ensure good bonding since the forces that are causing the a t t r a c t i o n between the wood and the glue act only over short distances (Zisman 1965). As i t i s , not a l l l i q u i d s that wet wood well can form strong j o i n t s with i t . In t h i s regard, the - 24 -i n t e r n a l cohesive strength of the adhesive i t s e l f on s o l i d i f i c a t i o n must be high i n order to obtain strong j o i n t s . _ . 2,. 5.2>. Adhesives: UF and PF r e s i n adhesives Choice and performance of any r e s i n adhesive f o r s a t i s f a c t o r y bonds i n wood varies with species. As indicated by Northcott and Hancock (1966), the service l i f e of any bond i s dependent on such factors as: 1. Conditions of service 2. Type of glue 3. Type of glue j o i n t 4. Properties of the substrate Investigating the gluing c h a r a c t e r i s t i c s of Determa (Ocotea rubra Mez) Thomas (1959) reported that s a t i s f a c t o r y bonds of maximum wood strength were e a s i l y obtained with the use of UF, RF and MF glues as well as casein glue. On the other hand, gluing was d i f f i c u l t with ,-\" PF glue. This, as he explained,was due to the wax-like substances present i n the wood. Thus, the i n c o m p a t i b i l i t y of the PF glue with Determa could be due to differ e n c e i n p o l a r i t y , which, as Thomas indicated, could r e s u l t i n the f a i l u r e of the glue to wet the wood or penetrate adequately. However, the concept of adhesive and adherent having s i m i l a r p o l a r i t y which was postulated by DeBruyne, was no longer considered a precondition f o r the formation of adhesive bond (DeBruyne 1962) . ThusiS; the d i f f i c u l t y encountered when gluing Determa wood with PF glue could have been duesmes0m&e&t$e\u00C2\u00A3tfJS@t6r\u00C2\u00A7^Gerieially, PF r e s i n adhesives require a c e r t a i n amount of water to react or polymerize - 25 -(Hancock 1977b). Furthermore, Laidlaw (1976) remarked that apart from choice of timber species i n plywood, manufacture, proper choice of adhesives serve to determine plywood strength as w e l l as i t s a b i l i t y to withstand environmental degrading e f f e c t s . UF and PF glues came into commercial use i n the plywood ind u s t r i e s at about 1930 (Parker and Taylor 1966, Kollman et. a l . 1975). These two synthetic glues have been widely used since then. A l o t of modifications have also been done, e s p e c i a l l y with the UF glue to improve upon d u r a b i l i t y and a b i l i t y to withstand exposures to adverse weather conditions. 2.5.2.1 UF glue UF glue produces a nearly c o l o r l e s s gluelirieo. The glue also has the a b i l i t y . t o cure at ambient temperatures. I t i s , however, unsuitable f o r service conditions of high humidity and temperatures above 60\u00C2\u00B0C (SIRA 1970). Blomquist and Olson (1957) indicated that plywood made with t h i s glue su f f e r s an appreciable losses i n j o i n t strength when exposed to temperatures from about 27\u00C2\u00B0C (80\u00C2\u00B0F) to 70\u00C2\u00B0C (158\u00C2\u00B0F). Bergin - (1958) also stated that at a temperature of about 70\u00C2\u00B0C and higher, d e t e r i o r a t i o n of the glue becomes more rapid. For these reasons,therefore, UF glue i s r e s t r i c t e d to i n t e r i o r uses. Compared to PF glue, UF i s d e f i c i e n t i n long-term d u r a b i l i t y . The v i s c o s i t y of the glue, i t s degree of cure and i t s adhesive formulation have been reported to influence the wood bond d u r a b i l i t y obtained with the use.of the UF glue. Rice (1965) investigated 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 d u r a b i l i t y . He reported that r e s i n v i s c o s i t y (a measure of molecular weights and dispersion) r e s u l t s i n a more durable glue-wood bond. Steiner (1973) further showed that molar r a t i o ranges of Formaldehyde/Urea (F/U) = 2.0 to 1.8 yielded slower bond d e t e r i o r a t i o n under accelerated aging conditions than resins with F/U r a t i o i n the range of 1.6 to 1.4. 2.5.2.2 - PF glue PF glue i s more durable.than UF glue. I t i s quite s u i t a b l e for service conditions of extreme temperature and humidity. Laidlaw (1976) experimented on the bond d u r a b i l i t y of plywood bonded with PF and UF glues, following a period of over 18 years of exposure. He found that the PF glues used without f i l l e r s or extenders or with only small addition of f i l l e r s maintained an e f f i c i e n t bond.over the prolonged test periods while the UF glues gave s a t i s f a c t o r y service f or shorter periods. Muller (1953)^ reported that the d u r a b i l i t y of phenolic wood glue j o i n t s i s correlated with the wood species used as w e l l as the glue-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 , extenders and hardeners are often used with the UF and PF glues. A f i l l e r i s used to control the flow of the r e s i n while the sole function of the extenders i s to reduce the amount of adhesives to be used to maintain.an e f f e c t i v e g l u e l i n e . Hardeners are a blend of materials designed to give optimum working properties and bond q u a l i t y ( H i l l 1952) and are e s s e n t i a l i n most cases i n glue mixes. A l l the foregoing emphasizes the f a c t that proper s e l e c t i o n of glue and i t s formulation are important factors i n gluing (Bryant and ^ O r i g i n a l not seen. Cited from reference of Kollman et , a l . 1975. - 27 -iStensrud \u00E2\u0080\u00A2! 1954) in order to achieve the desired glue joint quality and durability (Blomquist 1954). 2.6 Factors Affecting Plywood Bond Quality 2.6.1 Glue spreading Proper glue spreading is essential as i t ensures uniform distribution of the liquid 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 capillaries, and so l i d i f y into a strong substance. The flow of the glue is retarded i f the glue rapidly hardens before pressure is applied. Thus, the rapidity with which the glue begins to set is of primary importance. Penetration is necessary to produce a strong mechanical bond but i t should not be excessive, to avoid a starved glueline. Depending on the adhesive, sol 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 gelling of a dispersed polymeric solid (Collett 1972). Furthermore, the amount of glue spread and the nature of resin 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 for Southern pine require more phenolic resin content than normally used for 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 . \u00E2\u0080\u0094c<,.\u00E2\u0080\u0094- -(1973) the assembly time allows for some moisture absorption by the veneer and some reduction in viscosity of glue due to moisture loss. This serves to ensure that there is just the right amount of water in 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 in (a starved, glueline condition. This leads to a situation whereby i t becomes impossible for the glue to cure as most of the water in the glue is being readily absorbed into the wood while some is lost through evapora-tion. There is thus a lack of cohesive strength in the glueline and this results in low wood failure. On the other hand, at higher veneer moisture content, prolonged assembly time is essential to f a c i l i t a t e high wood failure results. More so, as i t provides enough time for the excess water in the glueline to be evaporated. For example, Northcott et\"\u00E2\u0080\u00A2aX. (1959) reported that short assembly time can induce undercure of phenolic resins thereby producing low wood failure. With long open assembly time, the PF resin has been noted to lose much of i t s moisture and shows a darkening in color as a result (Troughton and Chow 1972). Martin (1956) attributed this discoloration to quinone methide formation caused by oxidation. As indicated by Chow (1969b), this quinone methide.formation reduces, the number of - 29 -methylol groups present in the PF resin. This makes covalent bonding with wood ineffective and therefore f a i l s to produce durable glue-wood bonds. However, with the addition of\" polyethylene glycol 200 to the PF resin, 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. It 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 in wood requires a strong continuous glueline in order to form a strong joint. Using 36 phenolic resins, Hse (1971) correlated the glueline thickness to the bond quality produced in 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 failure increased with increased glueline'thickness. Rice (1965) indicated that too thin glue-lines may bring about locational 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, uninter-rupted and uniform glueline i s a requirement for mechanical and specific adhesion. Thin glueline was also reported best for bond quality in wood (Poletika 1943) 7. Bergin (1969) showed that adhesive strength generally decreases with an increase glueline thickness. 7 Original not seen. Cited from reference of J.T. Rice 1965. - 30 -The theory of cracks /seems to come into play with regards to these c o n f l i c t i n g f i n d i n g s . Thick gluelines are viewed to have a greater p o t e n t i a l for crack development. than do t h i n gluelines\". t h i s tends to account f o r the decreased strength associated with thick g l u e l i n e s . 2.6.4 Pressing A p p l i c a t i o n of pressure to the panel assembly a f t e r gluing promotes good contact between the glued veneer surfaces. I t also aids penetration as w e l l as ensuring good glue transfer to the unspread veneer surfaces (Chow et. a l . 1973). Depending on the compressive strength of the wood, Kennedy (1965) reported a pressing pressure i n the range of 2 2 10.5 kg/cm to 14.1 kg/cm (150-200 p . s . i . ) for Canadian grown woods. 2 Freeman (1970) also reported a pressure i n the range of 13.0 kg/cm to 2 14.1 gk/cm 185-200 p.s.i.) for most plywood m i l l s . Thus the amount of pressure used at any time, seems to be a function of the wood strength as w e l l as the p h y s i c a l condition of the wood surface. Freeman (1970) investigated the influence of production v a r i a b l e s on bond q u a l i t y of Southern pine plywood. He reported that coarse grain e f f e c t and surface roughness induced by i t might require higher pressures during the pressing time. Bond q u a l i t y (in terms of percentage wood f a i l u r e ) , as he indicated, increased with increased press pressure. 2.6.5 Degree of cure The curing temperature of a g l u e l i n e depends on type of r e s i n adhesive used. Chow et.: a l . (1973) pointed out that inadequate curing temperature r e s u l t s i n undercured bonds. As they indicated, t h i s defect - 31 -can be accentuated by insufficient pressing time. They further reported that a minimum glueline temperature of about 139\u00C2\u00B0C (250\u00C2\u00B0F) is necessary to pass the CSA 80% wood failure standard with the use of the vacuum-pressure-soak test. In his investigation of under-cure of phenolic glue bonds, Northcott (1955) showed that percent wood failure 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 is related to the wood failure and shear strength of the tested plywood panels. Bergin (1965) reported that the rate of cure of casein glues varies with the curing temperature in the range of about -7\u00C2\u00B0C to 21\u00C2\u00B0C (20\u00C2\u00B0F to 70\u00C2\u00B0F). Rate of cure decreased as the temperature, decreased. Rudriicki\"' (1976) found that the strength and durability 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 is a complex one. As stated by Koch (1972), i t involves properties of the resin and the wood, assembly times, prepressing procedures and hot pressing techniques. 2.7> Some National Plywood.Standards and Specifications. Plywood bond quality evaluation and. specification standards \u00E2\u0080\u00A2 vary from one country to another. While some countries assess plywood bond by percentage wood failure, some.favour shear strength as the major criterion of assessment. A combination of these two cr i t e r i a i s being used by the United States Department of Commerce for ^ hardwood - 32 -and decorative plywood. Wood failure has for long been indicated as an impracticable means of judging joint strengths in plywood. Truax (1929) stated that under good gluing conditions, joint strengths are not seriously affected by the percentage wood failure developed. Northcott (1955) remarked that;, in order to use percentage wood failure 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 exist. He therefore concluded at that time that the wood failure i s of no value in judging plywood bond quality. The following analysis covers some of the world plywood standards and specifications related to bond quality. Details are included in Appendices 1-4. 2.7.1 British Standard The British Standard for hardwood plywood does not take into consideration plywood shear strength. Wood failure i s the sole criterion of assessment. The BS 1455-1963 specifically applies to plywood manufactured from Tropical hardwoods (Appendix 1). Delamination test is required for the glue bond between individual 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 failure reading. Wood failure i s read off on a Master Scale of 0 to-10 corresponding to 0 to. 100% wood failure. The British Standard considers an average wood failure reading of 5 (50%) as adequate. 2.7.2 Japanese Standard The Japanese use the Export Standard specification for Japanese plywood. Shear strength is the sole criterion 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 psi) to about 10 kg per cm (142 psi). For tropical 2 woods, the Japanese require only about 8 kg per cm (110 > psi) 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 criterion of assessment of plywood bond quality. The standard consists of. a lot of requirements. Some of these are related to cold-soaking and boiling cycles... The exterior, grade plywood i s 2 designated AW100. A minimum shear strength of 10 kg/cm (142 \u00E2\u0080\u009E 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 for hardwood and decorative plywood makes use of both the percentage wood failure.and shear strength to assess bond quality of plywood. The average wood failure for a particular panel under, test i s qualified by the average shear strength for such a panel. Specimens are subjected to dry, cyclic-soak and .cyclic-boil tests. There i s also a specified minimum per-centage wood failure, for individual specimen tested. For example, for an 2 average f a i l i n g load of between 18 to 25 kg per cm (250 to 350 psi) the minimum wood failure of test piece required i s an.average of 30% with each individual specimen not having less than 10%.wood failure (Appendix 4). Of the four plywood standards reviewed above, i t is the U.S., - 34 -B r i t i s h and German standards that w i l l be used to evaluate r e s u l t s from t h i s study. The U.S. standard i s favored because i t q u a l i f i e s the percentage wood f a i l u r e developed at t e s t i n g with the shear strength obtained. Furthermore, U.S.A. has been an important importer of veneer from Nigeria since 1970. The B r i t i s h standards w i l l be used because B r i t a i n i s the largest market f or Nigerian hardwood plywood. The Federal Republic of Germany i s another major European, market f or Nigerian wood products exports. 2.8]. G l u a b i l i t y of Hardwoods Various studies have been undertaken on the g l u a b i l i t y of T r o p i c a l and secondary hardwoods i n Europe, North America and Japan. Some of these studies, as shown below, are related to the e f f e c t s of wetting phenomenon on wood g l u a b i l i t y . Troop and Wangaard (1950) investigated the gluing c h a r a c t e r i s -t i c s of 29 t r o p i c a l American woods using RF and PRF glues. Assessing bond q u a l i t y i n terms of j o i n t shear strength and percentage wood f a i l u r e developed i n the standard block shear t e s t , they reported that many of the woods are sui 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 also showed.that shear strengths, and wood f a i l u r e values were, i n general, strongly correlated with s p e c i f i c gravity. Defective surfacing of the glued materials and nature of t h e i r chemical constituents are some of the reasons they suggested for some.abnormal r e s u l t s obtained with some of the species. Freeman (1959) conducted an experiment r e l a t i n g the w e t t a b i l i t y of wood to i t s . g l u e bond q u a l i t y . Using 22 hardwoods, he found that wettability, pH and specific gravity are closely related to glue bond quality. Glue bond quality improved with increasing wettability in the high density wood ( 0.80) glued with UF resin adhesive. With specific gravity below 0.80, Freeman discovered that wood specific gravity has more influence on bond quality than wettability. He further indicated that wood specific gravity, acidity and wettability seem to have potential significance in wood adhesion. Experimenting with 6 tropical hardwoods, Freeman and Wangaard (1960) investigated the effect of wettability 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 viscosity increase more rapidly in woods of ..high wettability than in those of low wettability. These factors are essential in achieving optimum conditions for specific gluing operations. Carstensen '(1961) studied the gluing characteristics of secondary hardwoods, including red alder (Alnus rubra Bong.), cottonwood (Populus trichocarpa Torr. and Gray) and aspen (Populus tremuloides Michx.) as well as some softwood veneers. He reported that within any one species, gluability w i l l vary accordingly because of the wide variations that exist in density, grain configuration, moisture content and veneer surface conditions. He attributed the gluing problems encountered to accumulation of resinous materials.on the veneer surfaces. Bodig (1962) studies wettability of 5 Philippine mahoganies as related to.their gluability. He reported that there i s a high degree of correlation between the indices of gluability and wettability. This, according to him, reinforces the validity of the specific adhesion thesis. - 36 -As he stated further, surface condition of wood has an important e f f e c t on i t s w e t t a b i l i t y . He also indicated that i t i s possible to predict r e l a t i v e g l u a b i l i t y values of an unknown species by simply measuring i t s w e t t a b i l i t y . Reporting on the g l u a b i l i t y of Tectona grandis L. (Teak) and Acacia catechu W i l l d . , Narayamurti et,. a l . (1962) showed that extractives present i n these species affected the gelation time of the animal glue and UF glue used to glue the woods. The g l u a b i l i t y of some C a l i f o r n i a hardwoods including black oak (Quercus k e l l o g g i i Newb.), chinkapin (Quercus muehlenbergii Englem.), madrone (Arbutus menziesii Pursh) and tanoak (Lithocarpus d e n s i f l o r a Rehd.) was investigated by Dost and Maxey (1964). They reported that a l l four woods glue w e l l with PF r e s i n adhesive and with e x t e r i o r PVA r e s i n emulsion. Lee (1964) studied the g l u a b i l i t y of Gmelina arborea Roxb. from Malaya. Even though he worked with a l i m i t e d number of test samples, he reported that the wood showed good gluing properties. The FPRL, Princes Risborough, England (1966) indicated from a con-signmentaof logs from Gambia\" that good corestock veneers-suitable for gluing int6i.p,lywood~can -be produced - from-gmelina^woodiwithoutwany p r i o r heating. \" ~J~SGoto et a l . (1967) investigated the e f f e c t s of s p e c i f i c g r a v i t y , w e t t a b i l i t y , pH and percentage of extractives on the gluing properties of 18 t r o p i c a l woods. UF glue, PF glue and PVA emulsion adhesives were used to glue the woods. The following findings were reported: i ) Glue-joint strength increased with increase of s p e c i f i c gravity, i i ) There i s a high 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 -s p e c i f i c gravity, i i i ) 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 gl u e - j o i n t strength and pH. iv ) The r e l a t i o n s h i p between gl u e - j o i n t strength and the percentage of extract e i t h e r by cold or hot water i s not s i g n i f i c a n t . Chen. (1970) studied 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 of 8 t r o p i c a l woods. Ten percent solutions of sodium hydroxide, acetone and alcohol benzene solvents were used. Gluing was achieved with UF and RF r e s i n adhesives. He reported that ex t r a c t i v e removal improved.wettability.and increased the.pH of the wood surface thereby giving a more favorable bond q u a l i t y . Using P h i l i p p i n e s .red lauan (Shorea. negrosensis Foxworthy ), Moriya et;. a l . (1971) investigated the gluing c h a r a c t e r i s t i c s of laminated wood from t h i s species. RF, PF, UF, PVA emulsion and casein adhesives were used to.glue the wood. From the block shear and delamination tests performed, glue j o i n t strength was reported to increase with increase i n wood s p e c i f i c g r a v i t y . Yamagishi and Honma.(1972) reported on mixed use of two d i f f e r e n t species i n bonding?/ some t r o p i c a l woods using UF and RF r e s i n adhesives. Bond q u a l i t y was evaluated dry and a f t e r c y c l i c treatments as w e l l as by delamination t e s t s . They indicated that difference of s p e c i f i c gravity between two species considerably influence.the glue bond d u r a b i l i t y . The higher the dif f e r e n c e , the greater the bond q u a l i t y degradation. They concluded that d i f f e r e n c e i n s p e c i f i c gravity i n the mix use should be maintained within +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 specific gravity on the gluability of the woods varied with type of glue. While the lighter woods glued easily 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 joint strength increased with increase in the pH of the wood, i f the influence of specific gravity was excluded. Three of the six woods he used met the requirements for exterior structural lamination with PRF glue. The FPRL,- Princes Risborough, England, and Centre Technique du Bois, Paris, France (IUFRO 1973) investigated some aspects of peeling, drying and gluing of Gmelina arborea Roxb. The former concluded that the wood is not suitable for use as plywood because of wild grain and poor gluability. The sample logs used were heated to 85\u00C2\u00B0C prior 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 prior to peeling or not. Tan (1974), studied the suitability of 9 Malayan hardwoods for plywood manufacture. Gluing was achieved with PF resin adhesives. He arrived at the following conclusions: i ) That wood bulk density is a dominant factor influencing the bonding a b i l i t y of the woods. Higher density woods (densities 3 3 3 3 of 0.64 g/cm , 0.66 g/cm , 0.80 g/cm and 0.88 g/cm respectively)' were found unsuitable for plywood manufacture because of low percentage wood failures developed. - 3 9 -i i ) That thermal-degradation, due.to increasing veneer drying duration, was s i g n i f i c a n t i n reducing bonding a b i l i t y of the woods. i i i ) That an adhesive formulation of higher v i s c o s i t y than those used for softwoods was found necessary to prevent over-penetration of glue. A l l the foregoing emphasizes the f a c t that bond q u a l i t y and d u r a b i l i t y of plywood bonded with d i f f e r e n t glues are strongly influenced by the wood species involved. - 40 -3.0 EXPERIMENTAL PROCEDURES 3.1 Experimental Design The design of the experiment included four v a r i a b l e s . These were two glue types, three peeling temperatures, two glue spreads and two closed assembly times. The experimental steps were as indicated below: Two glue types - phenol\u00E2\u0080\u0094formaldehyde (PF) and urea-formaldehyde (UF) r e s i n adhesives. Three veneer peeling temperatures - 20\u00C2\u00B0C (c o n t r o l ) , 50\u00C2\u00B0C and 85\u00C2\u00B0C. Two l e v e l s of glue spread -approximately 25 kg/MDGL (55 l b / / MDGL) and 32 kg/MDGL (70 lb.^/ MDGL). Two closed assembly times- 10 and 20 minutes. A l l combinations of the above variables gave 24 treatments. Three panels were made under each treatment, thus giving a t o t a l of 72 panels f o r the study. The veneer nominal thickness peeled was 1.27 mm (0.050 in) while the plywood assembly construction was 5-ply. Furthermore, two types of bond q u a l i t y tests were used to evaluate bond performance f o r each type of glue. The Dry and Vacuum-Pressure-Soak tests were used f o r a l l the treatments bonded with UF r e s i n adhesive while the B o i l - D r y - B o i l -Cool and Vacuum-Pressure-Soak tests were used f o r a l l the treatments bonded with PF r e s i n adhesive. J I M a t \"d p r i . - 41 -3.2 Materials and preparation The logs used for t h i s study were part of the consignment of logs shipped from Nigeria to.SNC-Rust Limited of Montreal, Canada, f o r pulping studies. They were kept i n cold, storage while i n Montreal f o r about a year p r i o r to t h e i r use for t h i s study. The ends and surfaces of the logs had considerably dried out by the time they ar r i v e d at the Western Forest Products Laboratory (WFPL), Vancouver (note the lower moisture content value of the sapwood compared to the heartwood i n Table 23). The logs were examined v i s u a l l y on a r r i v a l at WFPL and 10 logs deemed of reasonable diameters.for peeling were selected. One of these 10 logs (Log No. 10) was used f o r preliminary determination of optimum lathe settings for peeling while the remaining 9 logs (Nos. 1-9) were used for veneer production. Their diameters ranged between 15.4cm to 22.9cm (6-9 i n ) ; lengths were about 2.7m (9 f t ) . They were subjected to water spray for 7 days before any test was performed. Six out of the 9 logs used f o r veneer production contained tension wood. The sapwood thickness was quite small and averaged ,20 mm (0.8 i n ) . The logs were from a young plan t a t i o n because growth ri n g count put t h e i r ages at 8 to 12 years. Bark thickness averaged 5.1mm (0.2 i n ) . Furthermore, presence of knots ranged between 4 and 8 for the 9 logs. 3.2.1 Wood chara c t e r i z a t i o n Before the logs were peeled, preliminary i n v e s t i g a t i o n into the s p e c i f i c gravity arid moisture content of the samples were conducted for each of the logs -Nos- 1-9 from which veneers were obtained. The - 42 -sample's s p e c i f i c gravity was taken as an average of the nine r e s u l t s obtained. I t was also e s s e n t i a l , as part of the preliminary study, to determine the optimum lathe s e t t i n g f o r peeling of the species. Log No. 10 was used for t h i s i n v e s t i g a t i o n . 3.2.1.1 S p e c i f i c gravity determination S p e c i f i c gravity of each of the nine logs was determined by the -vblumelmeasur.ement...me.thod_in<.accofdancdawithwthe ASTMAStandards (ASTM 1975 No?^143^5;2)v,Fq.ur samples per log yielded a. t o t a l of 36 samples for the' s p e c i f i c gravity.determination. Figure 1 shows pattern of cut of test samples from a log. Both the a i r and oven.dried length, width and thickness of each specimen were taken.at three d i f f e r e n t places \u00E2\u0080\u0094 the ends and center of the specimen. A log s p e c i f i c gravity i s taken as the average of i t s four samples. 3.2.1.2 Moisture content determination The procedure for the determination of the moisture content of each of the nine logs also followed that of the s p e c i f i c gravity. I t was i n accordance with ASTM standards (A;STM 1975;:) .No. D143-52) . I t must be indicated, however, that the moisture content of the logs were determined p r i o r to peeling and, except for the c o n t r o l logs peeled at 20\u00C2\u00B0C (ambient temperature) moisture contents of the logs heated to 50\u00C2\u00B0C and 85\u00C2\u00B0C were also determined following heating operations. 3.2.1.3 Determination of the optimum.lathe settings f or peeling A l l peeling was done at\"the Western Forest Products Laboratory, Vancouver, on t h e i r experimental.lathe equipped with a s o l i d nose bar. Log No. 10 which was used for t h i s study was cut into two b o l t s of 1.1m long each. Based on past peeling experiences of hardwoods of s i m i l a r - 43 -veneer thickness (1.27mm), Hailey (1977a), recommended lathe settings of pressure bar horizontal and vertical openings of 1.112mm (0.044 in) and 0.254mm (0.010 in) respectively for rotary peeling of the f i r s t bolt from log No. 10. A pitch angle of 89\u00C2\u00B030' at 25.4cm (10 in) was used. The second bolt was peeled with the same settings but with a change in the pitch to 89\u00C2\u00B030' at 26.7cm (10-1/2 in). This latter 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 in Table 6.' 3.2.2 Log heating Prior to the heating operations a disk about 30.5cm (1 ft) long was cut from one end of each log. Logs were grouped by diameter to give more uniform heating. For this reason, therefore, log numbers 5, 8 6 and 7, with diameters of 19.1cm (7.4 in), 19.7cm (7.7 in) and 18.4cm (7.3: in) were used for the 50\u00C2\u00B0C heating. Similarly, for the 85\u00C2\u00B0C heating, log numbers 1, 3 and 9, with diameters of 22.2cm (8.8 in), 21.0cm (8.2 in) and 20.3cm (8.0 in) 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 in) were peeled at ambient temperature of about 20\u00C2\u00B0C. Following the MacLean (1946).procedures on rate of temperature changes in short-length .round timbers, the i n i t i a l heating time for the 8 . . . oSAverageifordrbothiLends;. *-%ra - 44 -50\u00C2\u00B0C heating was calculated at about 8 hours. S i m i l a r l y , the heating time was calculated at about 11 hours f o r the 85\u00C2\u00B0C heating with the use of h i s suggested formulae. However, due to c e r t a i n factors discussed below the ultimate heating time for the 85\u00C2\u00B0C heating exceeded the calculated time by about 8 hours. Logs were heated immersed i n c i r c u l a t i n g hot water with over-head spray. The temperature changes at the centre of the logs were determined by means of control logs i n which thermo-couples were inserted. The d r i l l e d holes, through which the thermo-couples passed, were t i g h t l y sealed with corks to prevent flow of hot water i n t o the logs. Due to procedural error, however, the temperature changes, 25.4mm (1 in) from the surfaces of the co n t r o l logs, were not measured with s i m i l a r uses of thermo-couples. This was not regarded as serious since a r e l a t i o n s h i p e x i s t s (MacLean 1946) whereby such temperature changes could be obtained. The i n i t i a l temperatures of the co n t r o l logs were taken one minute a f t e r inserting, the thermo-couples while the subsequent temperature changes within.the logs were observed at every one-hour i n t e r v a l . The vat temperature was maintained at a l e v e l s l i g h t l y higher than that required f or peeling. For the 50\u00C2\u00B0C peeling temperature, the vat was maintained at about 55\u00C2\u00B0C (122\u00C2\u00B0F) while i t was about 86\u00C2\u00B0C (190\u00C2\u00B0F) f o r the 85\u00C2\u00B0Cpeeling temperature. Because of possible technical problems with the heating, a temperature difference of + 2\u00C2\u00B0C i n the required peeling temperature was viewed as acceptable. - 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) bolts. 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 tightly cut. After peeling, the veneer sheets were clipped into pieces about 30cm wide (12 in). To ensure adequate yield of veneer for 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 light to medium yellow in color. Veneers were also noted to be straight grained. A l l veneer pieces were coded and stored in moisture proof plastic bags. 3.2.4 Peel-quality evaluation According to Hailey et. a l . (1968),.peel-quality i s a technical term used in describing or evaluating the effect of the peeling process on certain'^physical properties - namely; thickness, roughness and loose-ness - of green veneer sheets. Since the veneers were peeled thin and tight, only two measures of veneer peel-quality were selected to evaluate the lathe settings used in this study with the different peeling tempera-tures. These were veneer surface roughness and thickness variation; and a l l evaluations were made with green veneer sheets. - 46 -3.2.4.1 Veneer roughnes s Veneer surface roughness was estimated in terms of the reference standard maintained at the Western Forest Products Laboratory (Northcott and Walser 1965) in accordance with Hailey and Hancock (1973) description. A l l the clipped veneer sheets, irrespective of width, were used for roughness test. 3.2.4.2 Veneer thickness measurement Veneer thickness variation was measured in accordance with Hailey and Hancock (1973) description. From each set of veneers obtained from a particular 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 in 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 thirty 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 plastic bags in which they were kept for roughness and thickness measurements. 3. The likelihood 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 in 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 in a forced-air oven, operating at about 152m/ minute (500 ft/minute) air speed, while the dryer heating system was-completely turned off. For every batch-load of veneer in the oven, 5 wetter and 5 drier pieces were randomly selected and loaded along with the remaihingg sheets at different locations in 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 in the range required for gluing. Veneer moisture content checking prior to gluing indicated that the veneer pieces attained an equilibrium moisture content of between 5.5% and 7.5% regardless of peeling temperature level. 3.2.6 Glues and-glue mixing The two glue types used in this study - UF and PF - are the basic resin adhesives used in the Nigerian veneer and plywood mills. 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 in a controlled temperature-humidity (CTH) room operating at a dry-bulb temperature of about 26.7\u00C2\u00B0C (80\u00C2\u00B0F), a dew-point temperature of about 6.1\u00C2\u00B0C (43\u00C2\u00B0F) and a relative humidity of 26%. - 48 -The PF IB-334 glue was supplied ready-mixed by Reichhold Chemi-cals Limited, Port Moody, B.C. I t i s a l i q u i d water soluble phenolic r e s i n , which produces high q u a l i t y e x t e r i o r adhesives bonds for the plywood industry. The glue was also claimed to provide excellent bonds at competitive press times, as w e l l as being tolerant to conditions of long assembly times and high ambient and stock temperatures. The percentage of PF s o l i d s i n the f i n a l mix of PF IB-334 glue i s 26% as opposed to about 23%.for standard PF glue for softwoods. Furthermore, there i s twice the concentration of wheat f l o u r i n t h i s mix compared to the average plywood mix (See Appendix 5). This has thus necessitated a reduced use of extender i n order 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 (Gardner-Holdt) while.the v i s c o s i t y of the glue mix was 1350 cps at 25\u00C2\u00B0C measured by the manufacturer with.No. 3 spindle 60 rpm LVF Brookfield viscometer. The recommended glue spread was 27-30 kg/MDGL while higher spreads of about 34 kg/MDGL and 38 kg/MDGL can be used depending on how porous the wood i s (Ainsley 1977)\"^. 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 with EK Hardener. Unlike the PF IB-334 glue, the Monsanto UF 109 glue, using EK Hardener, was prepared at the Western Forest Products Laboratory. The mix i s \" a s u i t a b l e glue for i n t e r i o r softwood.and hardwood plywood. The components of the EK Hardener are urea, ammonium chloride (NH^Cl), sodium me t a b i s u l f i t e , and walnut s h e l l f l o u r . The urea constitutes the Personal communication. Ainsley i s on the s t a f f of the Reichhold Chemicals Limited that supplied the glue. - 49 -bulk of the hardener while the main function of the sodium m e t a b i s u l f i t e i s to disperse the wheat f l o u r . Similar mix formulation of t h i s glue at the Western Forest Products Laboratory (Rozon 1977) contains, about 29.8% of urea formaldehyde s o l i d s with a v i s c o s i t y of about 2944 cps measured by No. 3 spindle at 30 rpm LVF br o o k f i e l d viscometer 1/2 hour a f t e r mixing. The mixing sequence is.shown i n Appendix 6 (supplied by Hart-z 11977-) . i 3.2.7 Glue Spread The glue was spread at about 25 kg/MDGL and 32 kg/MDGL ./as Iftiied fo>- =\" v . In a l l cases, f i v e veneers were assembled to make a panel. A mechanical glue spreader with rubber r o l l s was used to apply glue to veneers. Since the veneers were peeled t i g h t , i t was quite d i f f i c u l t to i d e n t i f y the side with the lathe checks (the loose s i d e ) . The veneers were therefore assembled without consideration f o r which side to turn i n s i d e or outside. For the 50\u00C2\u00B0C peeled veneers, enough materials were not ava i l a b l e f o r use i n a l l the 24 treatments used i n fehe^study?. The veneers from gmelina.wood were therefore used as cores and crossbands while yellow b i r c h veneers of the same thickness were used for the panel faces and backs. For each of the 24 treatments, 3 plywood panels were assembled. A f t e r g l u i n g e a c h panel was coded and marked with respect to Its glue-type, peeling temperature, glue-spread and closed assembly time. - 50 -3.2.8 Plywood Panel pressing 3.2.8.1 Press Pressure T r i a l panels were assembled using three l e v e l s of platen 2 2 pressures of about 11 kg/cm (150 p . s . i . ) , 14 kg/cm (200 p . s . i . ) and 2 18 kg/cm (250 p . s . i . ) . The three panels obtained were assessed on the 2 basis of the plywood k n i f e - t e s t . The platen pressure of 14 kg/cm (200 p.s.i.) gave the most favourable r e s u l t . A l l the assembled panels, therefore, i r r e s p e c t i v e of glue-type, were pressed with t h i s platen pressure. 3.2.8.2 Pressing Temperature and Time Following i n d u s t r i a l p r a c t i c e , a platen temperature of 127\u00C2\u00B0C was used f o r pressing.the panels glued with UF r e s i n adhesive and 149\u00C2\u00B0C for those panels .glued with PF r e s i n adhesive. The assembled panels were pressed with two panels per press opening for 5 minutes with the Monsanto UF 109 glue and 4.5 minutes with the PF IB-334 glue. In summary, the following s p e c i f i c a t i o n s and pressing schedule were used when making a t y p i c a l , panel assembly: 1. Five-ply, with a glue spread of 25kg/MDGL or 32 kg/MDGL depending on treatment combination. 2. Ten minutes or 20 minutes closed assembly time depending on treatment combination. 3. Platen temperature of about 127\u00C2\u00B0C (260\u00C2\u00B0F) or 149\u00C2\u00B0C (300\u00C2\u00B0F) depending on glue type. 2 4. Press pressure of 14 kg/cm (200 p . s . i . ) 5. Pressing time of 5 minutes or 4.5 minutes depending on glue type and platen temperature. 6. Hotstacking of the panels glued with PF for 10 minutes. - 51 -3.2.9 Test Specimen Preparation Tension-shear specimens from the plywood panels produced were prepared i n accordance with the requirements of the CSA and NBS standards. Because of the small thickness of the panel's however, d i f f i c u l t i e s were encountered when making grooves on the 7.6cm (3 in) wide s t r i p s cut from the panels. The c i r c u l a r saw i n some cases cut through the en t i r e thickness of the core-ply instead of the two-thirds of i t s p e c i f i e d . Test specimens- obtained from such s t r i p s were regarded as \" r e j e c t s \" and were screened out of the l o t s a f t e r cutting. Specimens were coded by panel of o r i g i n to f a c i l i t a t e between and within panel comparison f o r shear strength and percentage wood f a i l u r e . Specimens were randomized f o r the two types of te s t . :Testospecimens vary between 22 and 36 i n a l l the 24 treatments used i n th i s study. In a l l , a t o t a l of 1438 test specimens were stressed to failure.. Specimens were coded and marked according to type of bond qu a l i t y t e s t , panel number, glue-type, peeling temperature, glue spread and assembly time. For example, a sample designated UF-20-55-10 indicates that.the sample was from a panel glued with UF r e s i n adhesive; veneers were peeled at 20\u00C2\u00B0C; panel was glued at a spread of 551b /MDGL (25 kg/MDGL) and panel assembly was pressed a f t e r a closed assembly time of 10 minutes. 3.2.10. Bond Quality\"^\"*\" Testing Procedures 3.2.10.1 Dry Test The UF t e s t specimens were stressed to f a i l u r e i n a Globe Wood f a i l u r e readings, regardless ofnbond-quality t e s t i n g method, were based both on gross and f i n e f i b r e wood f a i l u r e s . - 52 -tension-shear machine i n accordance with the NBS/CSA standards. Load was applied at the rate of about 272 kg to 454 kg per minute (600 to 1000 l b . per minute). The ultimate shear strength and wood f a i l u r e were recorded for each specimen. 3.2.10.2 Vacuum-Pressure Test This test was usedhto assess 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 glue-type. As investigated by Chow and Warren (1972), the vacuum-pressure test was -found to be.on a par with the c y c l i c cold-soak t e s t . The vacuum applied was about 63.5cm (25 in) of mercury while the a i r pressure applied was 2 i n the. range>of about 4.6-4.9 kg/cm (65-70 p . s . i . ) . The e f f i c i e n c y of water penetration into the test specimens was not investigated insofder to j u s t i f y the use of a cycle greater than 30 minutes as was the case with Tan's study (Tan 1974). This was because h i s study involved the use of denser Malayan hardwoods whereas gmelina i s a low to medium density hardwood.(specific gravity = 0.41). The 30-minute cycle was therefore viewed adequate. Evidence of adequate water penetration seemed to be provided by the wide differences shown by the wood.failure r e s u l t s between the dry and vacuum pressure tests of the treatments bonded with UF glue ((Table.; lOO}.. Specimens were sheared while wet on the same Globe t e s t i n g machine used for the dry t e s t . The shear strength was recorded while the wood f a i l u r e was evaluated a f t e r oven-drying the sheared specimens overnight. This served to prevent reading errors due to the darkening by the water. - 53 -3.2.10.3. B o i l - d r y - b o i l Test The test specimens glued with PF r e s i n adhesive, were subjected to b o i l - d r y - b o i l test i n accordance with DIN68705 and CSA standards. The specimens were sheared wet a f t e r having been cooled to room temperature i n water. Shear strength was recorded for each specimen and,as before, wood f a i l u r e was read a f t e r drying the sheared specimens overnight i n an oven. 3.2.11 S t a t i s t i c a l Analysis Fa c t o r i a l . a n a l y s i s , was performed to f a c i l i t a t e the i n t e r p r e t a -t i o n of the main and i n t e r a c t i n g e f f e c t s that could evolve. Treatments were analysed with respect to glue-type as w e l l as type of bond q u a l i t y test used. Shear strength and wood f a i l u r e were analysed separately. Also based on the advice of Dr. Kozak, Faculty.of Forestry, an analysis of variance was performed, f o r both the shear strength and wood f a i l u r e according to type of t e s t . I t was hoped that t h i s would show the comparative performance of a treatment with the others. Where s i g n i f i c a n t differences were found, Duncan's New Mu l t i p l e Range test was applied. In order to f a c i l i t a t e easier f a c t o r i a l analysis of r e s u l t s (Kozak 1977), the same number, of test specimens was used i n a l l the treatments. Therefore, the treatment with the smallest number of specimens was used as a standard while the same.number of specimens were randomly selected, from the other treatments with the use of a Table of random numbers. Thus, 22 specimens, per treatment were used for the f a c t o r i a l analysis of variance. - 54 -4.0 RESULTS 4.1 Moisture content and specific 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 in Table 2. Values are shown separately for sapwood, heartwood and corewood. The sapwood initial.-MCsv are consistently lower than those of the heartwood in a l l the 9 logs. MC values are in the ranges of 41% to 107% and 67%.to 147% for the sapwood and heartwood respectively. The MC of the sapwood increased for three of the six heated logs while the heartwood MC decreased for four of the six heated logs. Nevertheless, the sapwood MCs? at peeling are s t i l l consistently lower than those of the heartwoods in a l l the logs. The average log specific gravity (sp.gr.) as well as mean and standard deviation of gmelina sample logs.used, is given in Table 3. The sp.gr. values for the 9 logs are based on ovendry weight and green volume and are in 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 temperature changes within.the log at positions.2.5cm (1 in) and 10.2cm (4 in) from the log surface are shown in Tables4 and 5 for the 50\u00C2\u00B0C and 85\u00C2\u00B0C (+2\u00C2\u00B0C) heating, respectively. These changes are shown graphically in Figures (Fig.) 2 and 3. The logs heated to 50\u00C2\u00B0C (+2\u00C2\u00B0C) attained that temperature at the calculated heating time of 8 hours (hr) while those heated to 85\u00C2\u00B0C (+2\u00C2\u00B0C) 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 distribution.of visual roughness measurements is given in Table 7 for the.veneers peeled from the control bolts (20\u00C2\u00B0C) and bolts heated to 50\u00C2\u00B0C and to 85\u00C2\u00B0C, and is.graphically presented in Fig. 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 for the veneers peeled from the control bolts (20\u00C2\u00B0C) and bolts.heated to 50\u00C2\u00B0C and 85\u00C2\u00B0C. 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\u00C2\u00B0C), bolts heated to.50\u00C2\u00B0C and bolts heated.to.85\u00C2\u00B0C respectively. Results show that peel-quality was best for the veneers peeled from the control bolts (20\u00C2\u00B0C) while bolts heated to 85\u00C2\u00B0C produced the roughest veneers. 4.4 Veneer moisture.content prior to gluing Table 9 shows the MC of the 10.pieces of veneer checked prior to gluing as well as the average MC for the 10 pieces. These averages are 6.6%, 6.4% and 6.4% for the veneers .peeled from the control bolts (20\u00C2\u00B0C) and bolts heated to 50\u00C2\u00B0C and 85\u00C2\u00B0C respectively. These values give no indication of overdrying of veneers with.the use of the forced-air drying technique. - 56 -4.5 UF r e s i n adhesive 4.5.1 Dry t e s t : Shear strength and wood f a i l u r e percent Table 10 summarizes the average.shear strength and percentage wood f a i l u r e f o r the 12 treatment combinations of: peeling temperature (PT) , glue spread (GS) and-closed assembly time (AT). Individual specimen minimum wood f a i l u r e in. each treatment combination i s also shown, as well as treatment codes used i n the study. This was done to f a c i l i t a t e comparison of bond, q u a l i t y r e s u l t s with the U.S. Plywood Standard. Plywood panels made .from veneers peeled at 85\u00C2\u00B0C (using a GS of 70 lb/MDGL and an AT of 20 min r) produced the highest shear strength of 389 p s i ; while those made from veneers peeled at 20\u00C2\u00B0C (using a GS of 55 lb/MDGL and an AT 20-min;:) produced the. highest percentage wood f a i l u r e of 70%. Generally, bond q u a l i t y i s best, at the PT of 20\u00C2\u00B0C. The mean, maximum, minimum and.range.of percentage wood f a i l u r e for each of the three panels produced f o r te s t i n g i n each of the 12 treatments are presented i n Table.12. 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 the panels, are noted. 4.5.2 Vacuum-pressure t e s t : 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 for the 12 treatment combinations of PT,.GS. and AT.subjected to t h i s test are also shown i n Table 10. Similar, to the dry t e s t , plywood panels made from veneers peeled at 85\u00C2\u00B0C(using a GS.of 70 lb/MDGL and an AT of 20 min : ) produced the highest shear strength of 307. p s i ; while those made from veneers - 57 -peeled at 20\u00C2\u00B0C (using a GS of 55 lb/MDGL and an AT of 20 min ) produced the highest percentage wood failure of 59%. Generally, bond quality i s best at the PT of 20\u00C2\u00B0C. There i s also a large va r i a b i l i t y in bond quality within and between panels as shown in Table 13. 4.6 PF resin adhesives 4.6.1 Vacuum-pressure test: Shear strength and wood failure percent Table 11 shows the average shear strength and percentage wood failure for the 12 treatment combinations of PT, GS and.AT. The minimum wood failure percent for each test specimen i s also shown as well as treatment codes used. Plywood panels made from.veneers peeled at 85\u00C2\u00B0C (using a GS of 70 lb/MDGL and an AT of 20 min. ) produced the highest wet shear strength of 405 psi; while those made from veneers peeled at 50\u00C2\u00B0C (using a GS of 70 lb/MDGL and an. AT of 20 min.) produced the highest percentage wood failure of 64%. Generally, panels.made from veneers peeled at 20\u00C2\u00B0C give ah impressive bond quality. The mean, maximum, minimum and range of percentage wood failure for each of the three panels produced for testing are presented in Table 14. Values are shown separately for each of the 12 treatments used. Large v a r i a b i l i t i e s in bond quality, within and between panels, are noted. 4.6.2 Boil-dry-boil test: Shear strength and wood failure percent The average shear strength and percentage wood failure for the 12 treatment combinations of PT, GS and AT are also summarized in - 58 -Table 11. The minimum wood failure percent for each test specimen i s also shown in 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\u00C2\u00B0C '\u00E2\u0080\u00A2 (using a GS of 70 lb/MDGL and an AT of 20 min\u00E2\u0080\u009E) produced the highest shear strength of 334 psi; while those made from veneers peeled at 50\u00C2\u00B0C (using a GS of 70.1b/MDGL and an AT of. 20 min .) produced the highest percentage wood failure of 66%. The mean, maximum, minimum and .range of percentage wood failure for each of the three panels produced.for testing are presented in Table 15. Values are shown separately for each.of the 12 treatments used. Large v a r i a b i l i t i e s in 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 failure for the.treatment panels, bonded with UF glue (factorial analysis) are summarized in Table 16; showing the significant main and interacting effects at the 0.01 and 0.05 levels. All. the significant interacting effects are graphically depicted in Fig. 5 and 6. Similarly, Table 17 summarizes the factorial analysis results of the vacuum-pressure test shear.strength and percentage wood failure for the treatment.panels bonded.with UF glue. The.significant inter-acting effects at 0.01 and 0.05 levels.are graphically depicted in Fig. 7 to 9. - 59 -The r e s u l t s of the vacuum-pressure test shear strength and percentage wood f a i l u r e f o r the panels bonded with PF glue are presented i n Table 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 e f f e c t s at the 0.01 and 0.05 l e v e l s . A l l . t h e s i g n i f i c a n t i n t e r a c t i n g e f f e c t s are graphically depicted i n F i g . 10 to 13. Table 19 shows the f a c t o r i a l analysis r e s u l t s of the B o i l - d r y -b o i l test shear strength, and percentage wood f a i l u r e f o r the treatment panels bonded with PF glue. 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 e f f e c t s i n th i s r e s u l t are gra p h i c a l l y depicted i n . F i g . 14 to 16. 4.7.2 Duncan's multiple range test The r e s u l t s of the. Duncan's multiple range test f o r d i r e c t comparison of the average shear strength and percentage wood f a i l u r e are presented i n Tables 20 and 21 for the treatment panels bonded with UF glue (Dry test and Vacuum-pressure test r e s p e c t i v e l y ) . S i m i l a r l y , r e s u l t s are shown i n Tables 22 and 23 for the treatment panels bonded with PF glue (Vacuum-pressure test and b o i l - d r y -b o i l test r e s p e c t i v e l y ) . - 60 -5.0 DISCUSSION 5.1 Sample specific gravity The mean sp. gr. of 0.41 + 0.027 found for the Nigerian plantation-grown gmelina logs used in this study compares favourably to a value of 0.41 + 0.060 reported by Nokoe-Sagary (1972) for 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 for 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 attain a temperature of 85\u00C2\u00B0C (+ 2\u00C2\u00B0C) required for their 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 for the 19-hour period did not arise for two reasons: 1. The water bath temperature did not at any time attain a tempera-. ture of 85\u00C2\u00B0C (+ 2\u00C2\u00B0C) 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\u00C2\u00B0C (+ 2\u00C2\u00B0C) required for their peeling without the vat maintaining that temperature. 5.3 Veneer peel-quality 5.3.1 Thickness As shown in 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\u00C2\u00B0C), bolts heated 8 hr, (to 50\u00C2\u00B0C) and bolts heated 19 hr., (to.85\u00C2\u00B0C) respectively. These averages are slightly 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\u00C2\u00B0C PT, thickness variation i s under best control because of i t s smallest.range compared to the other PTs. Generally, results show that veneer thickness variation i s under good control as the three means are equal at the 0.05 level. 5.3.2 Roughness As similarly shown in. Table 28, the average veneer roughnesses were 0.15 mm, 0.21 mm and 0.24 mm for the control bolts (20\u00C2\u00B0C), bolts' heated 8 hr, (to 50\u00C2\u00B0C)and bolts heated.19 hr. (to 85\u00C2\u00B0C) 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 for the three veneer PTs.of 20\u00C2\u00B0C, 50\u00C2\u00B0C and 85\u00C2\u00B0C. On the basis of these average and range values, the logs peeled at 20\u00C2\u00B0C give the best veneer smoothness results. Generally, veneer roughness is very good and well within the - 62 -limits for high quality veneer. In view of the above, therefore, i t can be stated that variation in thickness and roughness of veneer were not improved by heating the gmelina bolts to temperatures of 50\u00C2\u00B0C and 85\u00C2\u00B0C prior to peeling. Measure-ments by the visual roughness method indicated increased roughness at high PTs. Kinoshita. and Ohira. (1971), McMillin (1958) and Feihl (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 prior 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 failure percent The dry test shear strength results of the factorial analysis shown in Table 16 indicate that the PT and the GS are highly significant factors (i.e. significant at the 0.01 level). The interaction between PT and AT is significant, at the 0.05 level. The presence of this inter-action obscures any interpretation that could have been made on the main effects. This interaction may be more clearly understood by referring to Fig. 5. At the PT of 20\u00C2\u00B0C, AT of 10 and 20 min. have negligible influence on the shear strength of. the treatment panels bonded with UF glue. At the PT. of 50\u00C2\u00B0C, however, prolonged AT of 20 min results in lower shear strength. A mild effect i s produced at the highest PT of - 63 -85\u00C2\u00B0C with the AT of 20 min. producing a higher shear strength. Generally, plywood panels made from veneers cut at the PT of 85\u00C2\u00B0C produce^the highest shear strength at both levels 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 psi) given by the treatment combination of Spread 70 - Time 20 is not s t a t i s t i c a l l y significant at the 0.05 level from the dry shear strength of about 2 2 26.8 kg/cm (381 psi) and 25.5 kg/cm (362 psi) 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 psi) i s given by the treatment combination of Spread 55 - Time 10 at the PT of 20\u00C2\u00B0C. From the factorial analysis for wood failure shown in Table 16, the PT and the interaction of PT with GS and AT are highly significant. This interaction is better depicted in Fig. 6. Except for the treatment combination of Spread 70 - Time 20, bond quality, i n terms of percentage wood failure, i s consistently reduced at the higher PT for 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 failure) i s best for the plywood panels made from veneers cut at the PT of 20\u00C2\u00B0C. As shown in Table 21,. treatment UF-20-55-20 produced the highest percentage wood failure of 70%, which i s not significantly different at the 0.05 level from the percentage wood failures of 62% and 61% produced by treatments UF-20-70-10 and UF-50-70-20 respectively. The lowest percentage wood failure i s produced.by treatment UF-85-70-10. - 64 -5.4.1.2 Vacuum-pressure test: Shear strength and wood failure percent The factorial analysis results for the shear strength samples of the UF glued panels, subjected to vacuum-pressure test, follow the same pattern as the dry test. As.shown i n Table 17, the PT is highly significant (0.01 level) whereas the GS is significant at the 0.05 level. The interaction between the PT and GS is highly significant. As depicted in Fig. 7, bond quality, in terms of wet shear strength, i s slightly affected at both spread levels of 55 lb/MDGL and 70 lb/MDGL at the PT of 20\u00C2\u00B0C and 85\u00C2\u00B0C respectively. While wet shear strength is slightly higher with the higher spread at the PT of 20\u00C2\u00B0C, the lower spread, on the other hand, gives a slightly higher shear strength at the PT of 85\u00C2\u00B0C. The lower spread also gives higher shear strength at the PT of 50\u00C2\u00B0C. Generally, plywood panels made from veneers cut at the PT of 85.\u00C2\u00B0C, produce the highest shear strength values at the two spread levels. As shown in Table 20, the highest shear strength of about 22.4 2 -kg/cm (319 psi) given by treatment UF-85-55-20 is not\u00E2\u0080\u00A2significantly diffefentn t at the 0.05 level from those given by treatments UF-50-55-10 (20.7 kg/cm2 i.e. 295 psi), UF-50-55-20 (21.0 kg/cm2 i.e. 299 psi), UF-85-70-20 (21.6 kg/cm2 i.e. 307 psi) and UF-85-55-10 (20.7 kg/cm2 i.e. 295 psi). 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 in Table 17, the vacuum-pressure test wood failure results for the UF glued panels indicate that the PT and the GS v are highly significant factors, as well as the interaction between the PT, GS and the AT. The interaction between the PT and the GS is significant at the 0.05 level. As depicted for the interactions in - 65 -F i g . 8 and 9, bond q u a l i t y , i n terms of percentage wood f a i l u r e , i s co n s i s t e n t l y reduced at the PT of 50\u00C2\u00B0C and 85\u00C2\u00B0C. The lowest percentage wood f a i l u r e i s obtained at the PT of 85\u00C2\u00B0C for each of the treatment combinations. of Spread 55--^*Time\u00C2\u00A310*fSpread'^SS - Time 20, Spread 70 -Time 10 and Spread 70 - Time 20. As noted i n F i g . 9, the influence of treatment combinations of 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 treatments, at the PT of 20\u00C2\u00B0C, give the highest percentage wood f a i l u r e . At the PT of 50\u00C2\u00B0C, there i s no s i g n i f i c a n t influence of treatment combinations of 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 at t h i s PT i s best with the treatment combination of Spread 55 - Time 20. Each of the four treatment combinations exerts a d i s t i n c t influence on percentage wood f a i l u r e at the PT of 85\u00C2\u00B0C with treatment UF-85-55-20 giving the most.favourable r e s u l t . The wood f a i l u r e ranking in.Table 21 shows that the highest percentage wood f a i l u r e of 59% given by treatment UF-20-55-20 i s not r s i g n i f i c a n t l y . d i f f e r e n t J ; : at the 0.05 l e v e l from the value of 56% given by<..treaemgS4 UF-20-70-10. The lowest percentage wood f a i l u r e of 11% i s given by the treatment combination of Spread 70 - Time 10 at the PT of 85\u00C2\u00B0C. 5.4.2 Treatment panels bonded.with PF glue 5.4.2.1 Vacuum-pressure te s t : Shear strength and wood f a i l u r e percent More in t e r a c t i o n s of the main e f f e c t s are noted with the shear strength of the PF glued test samples subjected to vacuum-pressure test - 66 -than for the UF glued test samples. As noted in Table 18, PT, GS and AT are highly significant (at the 0.01 level). Similarly, the interaction between PT and AT is highly significant. The interaction between PT and GS is significant at the 0.05 level. Fig. 10 and 11 depict these inter-actions. As shown in Fig. 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\u00C2\u00B0C, whereas the spread of 70 lb/MDG gives the highest shear strength at the PT of 85\u00C2\u00B0C (Fig. 10). As shown in Fig. 11, wet shear strength is slightly higher with the AT of 10 mim at the PT of 50\u00C2\u00B0C whereas the AT of 20 min produces a slightly higher shear strength at the PT of 85\u00C2\u00B0C. Generally, plywood panels made from veneers.cut at the PT of.20\u00C2\u00B0C and 85\u00C2\u00B0C produce the highest wet shear strength values. From the shear strength ranking presented in Table 22, the highest shear strength value of about 28.5 2 kg/cm (405 psi) is given by the treatment combination of Spread 70 -Time 20 at the PT of 85\u00C2\u00B0C. This i s , however, not s t a t i s t i c a l l y s i g n i f i -2 cant at the 0.05 level from the values of about 27.9 kg/cm (397 psi) 2 and about 26.9 kg/cm (382 psi) given by the treatment combinations of Spread 70 - Time 10 (at PT of 20\u00C2\u00B0C) and Spread 70 - Time 10 (at PT of 2 85\u00C2\u00B0C). The lowest shear strength of about 21.7 kg/cm (308 psi) is given by the treatment combination of Spread 55 - Time 10 at the PT of 50\u00C2\u00B0C. The factorial analysis (Table 18) for the wood failure of the PF treatments subjected to vacuum-pressure test shows that the PT, AT, PT-AT interaction and PT-GS-AT interaction are a l l highly significant. The s i g n i f i c a n t i n t e r a c t i o n s are shown i n F i g . 12 and 13. F i g . 12 shows that bond q u a l i t y , i n terms of percentage wood f a i l u r e , i s lowest at the PT of 85\u00C2\u00B0C. Higher percentage wood f a i l u r e i s produced by the prolonged AT of 20 min.' at each l e v e l of PT as against the AT of 10 min The AT of 10 min. produces the highest percentage wood f a i l u r e at the PT of 20\u00C2\u00B0C; while the AT of 20 min. produces the highest percentage wood f a i l u r e at the PT of 50\u00C2\u00B0C. As shown i n . F i g . 13, percentage wood f a i l u r e decreased cons i s t e n t l y between 20\u00C2\u00B0C and 85\u00C2\u00B0C PT for each of the treatment combina-tions of Spread 55 - Time 20, Spread 70 - Time 10, Spread 70 - Time 20 and Spread 55 - Time 10. At the PT of 85\u00C2\u00B0C, the highest percentage wood f a i l u r e i s produced by.the treatment combination of Spread 55 -Time 20. For the three.treatment combinations of Spread 55 - Time 10, Spread 55 - Time 20 and Spread 70 - Time 10, the highest percentage wood f a i l u r e s are produced at the PT of 20\u00C2\u00B0C. For th i s p a r t i c u l a r t e s t , however, the highest and most favourable bond q u a l i t y i s given by the treatment combination of Spread 70 - Time 20 at the PT of 50\u00C2\u00B0C. From the wood f a i l u r e ranking presented i n Table 23, the percentage wood fa i l u r e ^ of 64% given 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 at the 0.5 l e v e l to the value shown by any other treatment. The lowest percentage wood f a i l u r e of 7% i s given by the treatment combination of Spread 55 - Time 10 at the PT of 85\u00C2\u00B0C. 5.4.2.2 B o i l - d r y - b o i l t e s t : Shear strength and wood f a i l u r e percent Shear strength r e s u l t s f o r t h i s test (Table 19) in d i c a t e that the PT, GS and AT are highly s i g n i f i c a n t . S i m i l a r l y , the i n t e r a c t i o n of the PT with the AT i s highly s i g n i f i c a n t . From F i g . 14., the lower AT - 68 -of 10 min. produces higher wet shear strength than the prolonged AT of 20 min. at the PT of 20\u00C2\u00B0C and 50\u00C2\u00B0C. At the PT of 85\u00C2\u00B0C, however, the pro-longed AT of 20min. gives a higher wet shear strength. Furthermore, with the AT of 10 min. the highest wet shear strength i s produced at the PT of 20\u00C2\u00B0C; whereas with the AT of 20 min. the highest wet shear strength i s given at the PT of 85\u00C2\u00B0C. Generally, plywood panels made from veneers cut at temperatures 20\u00C2\u00B0C and 85\u00C2\u00B0C.give the most favourable bond, q u a l i t y . From the shear strength ranking presented i n Table 22, the highest wet shear strength 2 of about 23.5 kg/cm (334 psi) i s given.by the treatment combination of Spread 70 - Time 20 at the PT of 85\u00C2\u00B0C. This, however, i s not s i g n i f i c a n t 2 at the 0.05.level from the values of about 22.6 kg/cm (322 p s i ) and 2 22.1 kg/cm (315 p s i ) given by the treatment combinations of Spread 70 -Time 10 (at the PT of 20\u00C2\u00B0C) and.Spread 70 - Time 10 (at the PT of 85\u00C2\u00B0C). 2 The lowest shear strength of 16.8.kg/cm (239 p s i ) i s given by the treatment combination of Spread 55 - Time 20 at the PT of 50\u00C2\u00B0C. Wood f a i l u r e r e s u l t s . f o r same test (Table 19) i n d i c a t e that the PT, GS and AT are highly s i g n i f i c a n t . 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 highly 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 gr a p h i c a l l y i n F i g . 15, the PT of 85\u00C2\u00B0C gives the lowest bond q u a l i t y (in terms of percentage wood f a i l u r e ) at each of the spread l e v e l s of 70 lb/MDGL and 50 lb/MDGL. With the lower spread, percentage wood f a i l u r e i s highest at the PT of 20\u00C2\u00B0C, while the higher spread gives the highest percentage wood f a i l u r e at the PT of 50\u00C2\u00B0C. F i g . 716 shows a.similar trend i n bond performance to F i g . 15. The prolonged AT of 20 min. r e s u l t s i n higher percentage wood f a i l u r e - 69 -than the lower AT of 10 min- at a l l three l e v e l s of PT. For the AT of 10 min., percentage wood f a i l u r e i s highest at the PT of 20\u00C2\u00B0C and lowest at the PT of 85\u00C2\u00B0C. For the'AT of 20 min,, percentage wood f a i l u r e i s highest at the PT of 50\u00C2\u00B0C and lowest at the PT of 85\u00C2\u00B0C. Generally, plywood.panels made from veneers cut at 50\u00C2\u00B0C gave the highest percentage wood f a i l u r e f o r th 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 ranking presented i n Table 23, the highest percentage wood f a i l u r e of 66% given by the treatment combination of Spread 70 - Time 20 at the PT of 50\u00C2\u00B0C i s s i g -n i f i c a n t l y c S _ f f e r e h t . V t \" t h e 0.05 ievei^to'the value shown by any other treatment. Thellowest percentage wood f a i l u r e of 12% i s given by treatment combina-tions of Spread 55 - Time 10 (at the PT of 50\u00C2\u00B0C) and Spread 55 - Time 10 (at the PT of 85\u00C2\u00B0C). 5.4.3 Probable factors accounting f o r low percentage wood f a i l u r e s i n the treatments. The following explanations are presented as the possible causes of low bond q u a l i t y performance (in terms of percentage wood f a i l u r e ) shown by the treatments, e s p e c i a l l y with the use of PF glue: 1. The veneers used f o r the study wereinbt obtained, from fresh logs. The logs peeled were from the consignment shipped from Nigeria to SNC-Rust Company Limited, of Montreal. They had been kept i n cold storage by the company for at least a year p r i o r to t h e i r use. The sapwood zone had dried out considerably and veneers from t h i s wood zone were also used when constructing c e r t a i n of the panels. D i s c o l o r a t i o n of such veneers to a dark brown or bl a c k i s h color had already occurred, as noticed at - 70 -peeling. Further veneer d i s c o l o r a t i o n occurred between the 30 days that expired between the peeling and drying of the veneers. 2. There i s also the problem of influence of surface aging of veneer p r i o r to gluing. Eighty days expired between the peeling and gluing of the veneers. Surface aging of wood has been reported 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 turn, the q u a l i t y of the glue bond (Gray 1962, Marian 1962, Marian and Stumbo 1962b, Stumbo 1964, Herczeg 1965 and C o l l e t t 1972). 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 also been noted i n Section 2.8. It was noticed that where the discolored veneers were used as cores, low or zero percentage wood f a i l u r e s were developed. No attempt was made to give the veneers l i g h t surface sanding p r i o r to gluing. The introduction of such a v a r i a b l e would have doubled the number of 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 impossible to include t h i s v a r i a b l e . Walters (1973), for example, reported that poor gluing resulted from decreased surface w e t t a b i l i t y and surface i n a c t i v a t i o n but could be improved upon by giving the veneers a l i g h t surface sanding p r i o r to gluing. He obtained higher percentage wood f a i l u r e f o r the sanded veneers compared to the unsanded veneers. Comparing the r e s u l t s of the PF treatments, vacuum-pressure t e s t , with the UF treatments, vacuum-pressure test (Tables 10 and 11), the PF IB-334 glue used seems to be more - 71 -se n s i t i v e to 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, than the Monsanto UF 109 glue used, thus accounting for i t s lower percentage wood f a i l u r e . 3. V a r i a b i l i t y i n bond q u a l i t y between and within panels i s a usual phenomenon. This i s i l l u s t r a t e d by Tables 12 to 15. Regardless of type of bond q u a l i t y t e s t , large v a r i a b i l i t y i n percentage wood f a i l u r e was observed with both the UF and PF treatments a l i k e . This i s indicated by '\u00C2\u00A3helwid\u00C2\u00A7 ranges shown i n columns 11-13 of Tables zl*2 tto 315 res p e c t i v e l y . In addition, and more l i k e l y , t h i s v a r i a b i l i t y i s the re s u l t of such factors as: i ) differences i n veneer moisture content at gluing, i i ) - spanel edge e f f e c t , i i i ) differences i n degree of cure of g l u e l i n e . i v ) numanrf-aetor introduced during veneer gluing e s p e c i a l l y with regards to the, open assembly time (Not introduced as a v a r i a b l e i n the study), v) stress concentrations inherent i n the test specimens during shear t e s t i n g . I t was noticed, f o r example, that longer open assembly time was used when gluing with the PF glue than the UF glue. This was due to the d i f f i c u l t y encountered while spreading the glue on the veneers. Because i t was les s viscous than the UF glue, i t was leaking out of the r o l l e r spreader. The glue was therefore spread on one face of the veneer then the piece was f l i p p e d over for the spreading of the other face. The e f f e c t of long open - 72 -assembly time on phenolic glue has been reviewed i n Section 2/6.2. 4. The PF.resin used was more caustic (pH 12.5 - 13.5) than the UF r e s i n (pH 8.4). The buffe r i n g capacity of the UF r e s i n , theref ore^would be low at high panel pressing. temperature of 127\u00C2\u00B0C (260\u00C2\u00B0F). Due to moisture and natural acids i n wood (uronic acids of hemicelluloses), hydrolysis condition may be created. This weakens the wood structure i n the v i c i n i t y of the g l u e l i n e , thereby causing f a i l u r e at lower shear loads with higher percentage wood f a i l u r e s as evidenced by vacuum-pressure r e s u l t s of both glues i n Tables 10 and 11. 5. As reviewed i n Section 2.1, the r e s i n content of gmelina wood i s high. The low percentage wood f a i l u r e s exihibitedvby the PF and UF treatments could, therefore, be due to interference of the wood extractives with the glues. The PF r e s i n has a pH of 12.5 to 13.5, which should be enough to saponify the extractives on the veneer surfaces (Chow 1977b). However, the PF treatments showed lower percentage wood f a i l u r e values compared to the UF treatments (UF has a pH of 8.5). This, seems to contradict the interference concept. The d e f i n i t e influence of the extractives of the wood on bond q u a l i t y i s therefore d i f f i c u l t to make. It i s the view of the writer that with fresh veneers, better bond q u a l i t y could be obtained with gmelina wood. - 73 -5.4.4 Comparison of study r e s u l t s with some National Plywood Standards As indicated i n Section 2.7, the U.S., B r i t i s h and German; Plywood Standards w i l l be used to assess bond q u a l i t y r e s u l t s obtained i n t h i s study. 5.4.4.1 U.S. Hardwood plywood standard Voluntary Product Standard PS 51-71 f o r Technical and Type I (both E x t e r i o r Grades) Hardwood plywood are: The s p e c i f i c a t i o n s of the U.S. Department of Commerce Average f a i l i n g load (psi) Average Wood f a i l u r e (%) Under 250 50 25 250 - 350 30 10 Above 350 15 10 PF treatments from t h i s study that meet the above Ex t e r i o r Grade Plywood requirements are as follows: - 74 -Average f a i l i n g Average Wood Individual Specimen Treatments L o a d ( p g i ) failure (%) minimum wood failure (%) 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 PF- B o i l - d r y - b o i l 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 As noted in the above comparison, three of the five treatments, from each of the bond.quality testing methods, passing the U.S. standard are treatment .combinations arising from the PT of 20\u00C2\u00B0C. The remaining two treatments come from the PT of 50\u00C2\u00B0C. No treatment combination arising from the PT of 85\u00C2\u00B0C meets this standard. It can therefore be concluded that a PT of 85\u00C2\u00B0C produces roughest veneers (compared to the PT of 20\u00C2\u00B0C and 50\u00C2\u00B0C) (Table 8) which, when glued into plywood, result in low bond quality - i n terms of percentage wood failure. Among the five treatments that meet the U.S. standard, the 2 shear strength of about 22.3 kg/cm (317 psi) 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 level to the value - 75 -2 of about 22.4 kg/cm (318 psi).obtained from treatment PF-20-55-20 (Vacuum-pressure t e s t ) . On the basis of the U.S. standard, therefore, treatment PF-20-55-20 may be of greater i n d u s t r i a l importance than treatment PF-50-70-20. I t f a c i l i t a t e s lower production costs because higher energy consumption i s required to heat logs to 50\u00C2\u00B0C as w e l l as higher adhesive cost at a spread of 70 lb/MDGL as against 55 lb/MDGL. However, where the industry hopes to maximise bond q u a l i t y with respect to shear strength and percentage wood f a i l u r e , treatment PF-50-70-20 i s most s u i t a b l e . Also comparing treatments PF-20-55-20 and: PF-20-70-10, the 2 shear strength of about 27.9 kg/cm (397 p s i ) obtained f o r the l a t t e r i s s t a t i s t i c a l l y d i f f e r e n t at the 0.05 l e v e l from the shear strength of 2 about 22.4 kg/cm (318 p s i ) obtained f o r the former. Treatment PF-20-55-20 may, however,be of i n d u s t r i a l importance because of for Gmelina arborea grown i n Niger i a , India, Gambia and Malaysia. This, as he indicated, puts the wood i n the r i g h t weight category f o r many uses. This study ;-has also demonstrated that the wood, glues e a s i l y depending on treatment combinations of peeling temperature, glue spread and closed assembly time. Therefore, Gmelina, arborea plywood may be considered s u i t a b l e for b u i l d i n g construction as subfloor, w a l l sheathing, roof sheathing and s i d i n g panels; o v e r l a i d panels; and concrete forms. 5.5.2 Core and Crossband veneer for decorative plywood S p e c i f i c gravity i s also one of the ph y s i c a l properties considered of major importance f o r core and crossband veneers f o r decora-t i v e plywood (Lutz 1971). For such a use, a t y p i c a l s p e c i f i c g ravity range of 0.32 to 0.45 i s required. The s p e c i f i c gravity of g'melina wood - 80 -(0.41 + 0.027) satisfies this requirement. On this basis, therefore, veneers from gmelina are quite suitable for use as core and crossbands for decorative plywood. As indicated by Lutz (1971), uniformity of wood structure is particularly desirable for crossband veneers meant to be used as decorative panels in order to minimize \"telegraphing\" of the grain to the face. Thus, diffuse-porous hardwoods like yellow birch and yellow-poplar have been reported as good veneer species. As a diffuse-porous hardwood, gmelina has been found from this study to yield relatively smooth veneers. Ease of gluing, straight and fine, uniform grain are other desirable veneer qualities when considering veneers for use as cores and crossbands for decorative plywood. As discussed in Section 2.1 and Section 3.2.3, gmelina wood satisfies these requirements. This seems to strengthen the suitability of gmelina wood for use as core and crossband veneers for decorative plywood for products like furniture, flush doors and case goods. 5.5.3 Container veneer and plywood Woods meant to be cut into veneers for use as container veneer and plywood are expected to possess the following physical and mechanical properties: specific gravity in the range of 0.36 to 0.65, light color, freedom.from odor, high stiffness (MOE), high shock resistance (MOR) and high strength in tension perpendicular to the grain. Since the only mechanical property measured in this study is 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 and MOR. However, on the basis of the shear strength and the physical pro-perty involving specific 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 container veneer and plywood. Since the veneers used f o r t h i s study were not obtained from fresh-cut gmelina logs, i t i s d i f f i c u l t to assess the s u i t a b i l i t y of the wood f o r use as decorative veneer and plywood on the basis of a t t r a c t i v e -ness and fi g u r e . - 82 -6.0 SUMMARY, SUGGESTIONS FOR FURTHER STUDIES AND CONCLUSION 6.1 Summary The data list e d below contribute to the knowledge of the bonding characteristics of Gmelina arborea wood: 1. Even though the presence of a significant interacting effect may obscure interpretation of a significant main effect in a s t a t i s t i c a l analysis, the effects of the peeling temperatures used are nevertheless found highly significant regardless of glue type and bond quality testing method. 2. Similarly, the effects of the glue spreads used (a major factor in total cost of plywood manufacture) are found highly significant in 3 of the 4 ANOVA's for shear strength results. 3. Veneers of the highest peel-quality are produced with the 20\u00C2\u00B0C (control) peeling temperature whereas the temperature of 85\u00C2\u00B0C yields veneers of the lowest peel-quality. 4. Thus, the study has demonstrated that gmelina wood can be satisfactorily rotary-cut into good veneers without any prior heating. 5. Bond quality, in terms of percentage wood failure, i s consistently reduced by increasing peeling temperature and i s lowest at the peeling temperature of 85\u00C2\u00B0C in a l l the UF and PF treatments used, reagrdless of bond quality testing method. 6. The peeling temperature of 20\u00C2\u00B0C (control) gives the best bond quality results in terms of percentage wood failure in a l l the UF treatments used, regardless of type of bond quality - 83 -testing method. 7. In spite of the distinctive performance of the treatment combination of Spread 70 - Time 20 at the peeling temperature of 50\u00C2\u00B0C, the treatments arising from the 20\u00C2\u00B0C (control) peeling temperature also give the most impressive bond quality results in terms of percentage wood failure in a l l the PF treatments regardless of bond quality testing method. 8. Among the UF treatments used, ignoring glue spreads, those arising from the peeling temperatures of 50\u00C2\u00B0C and 85\u00C2\u00B0C 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 arising from the peeling temperatures of 20\u00C2\u00B0C and 85\u00C2\u00B0C both give the highest shear strength values regardless of type of bond quality testing methods. 10. At the peeling temperature of 20\u00C2\u00B0C (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 failure values developed are not significant at the 0.05 level 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 significantly higher shear strength than treatment combination of Spread 55 - Time 20, while the latter has a significantly - 84 -higher percentage wood f a i l u r e i n one of the bond q u a l i t y t e s t i n g methods used. 11. At the peeling temperature of 50\u00C2\u00B0C, the highest percentage wood vfaiiureiisdeveloped with the treatment combination of Spread 70 -Time 20 regardless of glue type and bond q u a l i t y t e s t i n g method. 12. At the peeling temperature of 85\u00C2\u00B0C, the highest shear strength i s developed with the treatment combination of Spread 70 - Time 20 regardless of glue type and bond q u a l i t y t e s t i n g method. 13. A l l factors considered, the treatment combination of Spread 55 - Time 20, at the peeling temperature of 20\u00C2\u00B0C (c o n t r o l ) , gives an impressive bond q u a l i t y i n a l l the UF and PF treatments used. 14. Five of the 12 PF.treatments used, regardless of type of bond q u a l i t y 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; while a l l pass the German Standard. On the other hand, f i v e of the 12 UF treatments from vacuum-pressure test pass the U.S. Standard; two pass the B r i t i s h Standard; while a l l pass the German Standard. Furthermore, a l l the 12 UF treatments from dry t e s t pass the U.S. Standard; s i x pass the B r i t i s h Standard; while a l l pass the German Standard. 15. From the r e s u l t s of t h i s study, plantation-grown Gmelina arborea wood, with a s p e c i f i c gravity of 0.41 + 0.027 (as determined), i s s u i t a b l e f o r use as construction plywood, core and crossband veneer for decorative panel as w e l l as container veneer and plywood. - 85 -6.2 Suggestions for further studies Conclusive evidence has been presented f o r the s u i t a b i l i t y of Gmelina arborea wood f o r veneer and plywood production depending on the treatment combinations of wood peeling temperature, glue spread and 'closed assembly time. However, further work would be necessary to improve upon the bond q u a l i t y achieved with the wood, e s p e c i a l l y using PF r e s i n adhesive. Suggested areas of study are as follows: 1. Determination of the optimum peeling temperature. 2. E f f e c t s of veneer drying schedules on bonding c h a r a c t e r i s t i c s of the wood. 3. E f f e c t s of assembly time (open and c l o s e ) , pressing time, temperature and pressure t r i a l s on bond q u a l i t y . 4. Glue formulation and optimum glue spread t r i a l s . 5. Nature of the r e s i n present 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 of gmelina wood. 6.3 Conclusion The findings of t h i s study are considered of research, i n d u s t r i a l and economic importance to the wood-based panel industry i n Nig e r i a as w e l l as the States Forestry Services responsible f o r plantations establishment. Management of gmelina plantations i n Nigeria for future supply of veneer logs i s considered a j u s t i f i a b l e investment. - 86 --, BIBLIOGRAPHY Adeyoju, S.K. 1968. Forestry i n the nation a l economy of Nig e r i a . Unpubl. Diploma thesis i n Forestry. St. John's College, Oxford. Chaps. 4 and 5. Afolayan, A.A. 1974. 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Log Number Estimated' age from Growth Ring Count Noiotiknots present in 1 og Log d iameter* (cm) Bark th i ckness cm) Sapwood thickness (cm) Presence of Tension wood 1 8 5 22.2 4.1 2.8 Yes 2 !0 8 18.4 1.7 No 3 12 3 21.0 5.8 1.5 Yes 4 9 4 16.5 3.0 1 .8 Yes 5 10 6 19.1 4.6 2.0 No 6 8 5 1 9 - 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 * 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 (1968) , growth rings are noted to be v i s i b l e and usually annual for Gmelina arborea grown in Thailand. -101-Table 2. I n i t i a l and peeling moisture content {%) of the Gmelina arborea logs used for study. Log Peeli ng I n i t i a l MC Peeli ng MC Number temp( C) Sapwood Heartwood Corewood Sapwood Heartwood Corewood 2 20 90 124 132 124 132* 4 20 8 2 107 90 82 107 90* 8 20 96 114 104 96 - 114 104* 5 5 0 45 67 76 61 65 78 6 50 41 79 67 88 104 73 7 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. -102-Table 3. Spec i f ic gravity of the Gmelina arborea logs used for study. = Log Number 2 Log Average Spec i f ic Gravity Sample Mean Spec i f ic Gravity 1* 0.42 2 0.44 3 * 0.37 Mean = 0 . 4 1 SD3 = 0 . 0 2 7 0.43 5 0 . 3 8 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 ( Ident i f ied by visual examination of Pith displacement). ) - 1 0 3 -Table 4 . Water bath and log temperature changes against time of heating - 5 0 C. Nominal heating temperature: 50\u00C2\u00B0cJ + 2\u00C2\u00B0C Wood Temperature at core, 4 in from Wood Temperature Heating Water Bath Log Surface, at 1 in from the Period Temperature recorded by Log Surface, (hours) (\u00C2\u00B0C) Thermocouples ( C) Est i ma ted 2 ( c) 0 2 1 . 5 1 7 . 8 1 8 . 8 1 46.6 2 0 . 1 2 7 . 9 2 4 6 . 4 2 5 . 3 3 0 . 7 3 4 5 . 6 3 0 . 1 3 6 . 0 4 4 5 . 0 3 3 . 9 3 7 . 7 5 4 8 . 8 3 6 . 9 4 2 . 2 6 5 2 . 9 3 8 . 0 4 7 . 9 7 5 3 . 0 3 9 . 8 5 0 . 0 8 5 4 . 4 41.6 5 1 . 8 1 A wood temperature of 5 0 C + 2 C was considered acceptable for the 50\u00C2\u00B0C heating since i t was d i f f i c u l t to control the temperature within the vat. 2 Using MacLean (1946) formulae -10^-Table 5 . Water bath and log temperature changes against time of heating - 8 5 C. Nominal heating temperature: 85\u00C2\u00B0C + 2\u00C2\u00B0C Wood Temperature at core, 4 in from Wood Temperature Heat i ng Water Bath Log Surface, at 1 in from the Per iod Temperature recorded by Log Surface, (hours) (\u00C2\u00B00 Thermocouples ( C) Estimated^ ( C) 0 2 0 . 1 1 7 . 7 1 8 . 4 1 5 0 . 5 1 9 . 2 2 9 . 3 2 7 0 . 4 2 5 . 1 41 . 4 3 8 1 . 6 4 5 . 0 6 0 . 0 4 8 1 . 4 6 0 . 1 64 . 3 5 8 1 . 5 64 . 9 6 8 . 0 6 8 1 . 5 6 7 . 4 7 2 . 5 7 8 1 . 6 6 8 . 9 7 6 . 2 8 8 1 . 5 6 9 . 9 7 7 . 5 9 8 1 . 4 7 0 . 8 7 8 . 8 1 0 ' 8 1 . 5 7 1 . 4 7 9 . 7 11 8 1 . 3 7 1 . 8 7 9 . 5 1 2 81 . 3 7 2 . 1 8 0 . 4 1 3 8 1 . 1 7 2 . 3 8 0 . 7 \" 14 8 0 . 9 7 2 . 4 8 0 . 4 1 5 8 2 . 1 7 2 . 3 8 1 . 7 1 6 8 2 . 3 7 2 . 3 8 1 . 8 1 7 8 2 . 9 7 2 . 6 8 2 . 4 18 87 .O 7 3 . 7 8 6 . 5 19 8 6 . 9 7 5 . 6 8 6 . 4 1 A Wood temperature of 85\u00C2\u00B0C + 2\u00C2\u00B0C was considered acceptable for the 85\u00C2\u00B0C heating. 2 Using MacLean ( 1 9 4 6 ) formulae. -105-Table 6 . Lathe spec i f icat ions for 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) Ver t i ca l Gap 0 . 2 5 mm ( 0 . 0 1 0 in) Veneer Thickness 1 . 2 7 mm ( 0 . 0 5 in) Nosebar Type Sol id nosebar Nosebar Face Angle 14\u00C2\u00B0 Knife Thickness 1 5 - 8 8 mm ( 5 / 8 ) in Knife Length 1 6 7-64 cm ( 6 6 in) Rockwel1 Hardness 5 6 Main Bevel 23\u00C2\u00B0 Cutting Angle (at 1 0 - 1 / 2 in) 8 9 \u00C2\u00B0 3 0 ' Speed of Cut 1 2 0 fpm Diameters of the bolts ranged between 1 6 . 5 cm ( 6 . 5 in) to 2 2 . 2 cm ( 8 . 8 in ) . -106-Table 1. Peel-qual i ty a t t r ibutes : Veneer roughness measurement. Total No.of Veneer sheets sampled Roughness in mm Frequency Scale Equivalent Equivalent Frequency % 2 0 C Peeling 175 0 . 0 0 0 0 . 0 0 5 0 . 0 1 0 0 . 0 0 0 . 1 3 0 . 2 5 0 143 32 0 . 0 8 1 . 7 18.3 5 0 C Peeling 1 9 4 0 1 2 3 0 . 0 0 0 0 . 0 0 5 0 . 0 1 0 0 . 0 1 5 0 . 0 0 0 . 1 3 0 . 2 5 0 . 3 8 2 6 5 1 2 0 7 1 . 0 33.5 6 1 . 9 3.6 8 5 C Peeling 173 0 1 2 3 4 0 . 0 0 0 0 . 0 0 5 0 . 0 1 0 0 . 0 1 5 0 . 0 2 0 0 . 0 0 0 . 1 3 0 . 2 5 0 . 3 8 0 . 5 1 0 2 6 1 3 2 1 3 2 0 . 0 1 5 . 0 7 6 . 3 7 . 5 1 . 2 -107-Table 8 . Veneer peel -qual i ty s t a t i s t i c s . 1 . 2 7 mm ( 0 . 0 5 ~ i n ) Gmelina arborea green veneer Veneer Attr ibutes Peel ing temperature Mean SD* Max Min Range (mm) (mm) (mm) (mm) (mm) 1 . Thickness 20\u00C2\u00B0C (Control) 1 . 2 5 0 . 0 8 1 . 3 7 1 . 1 7 0 . 2 0 50\u00C2\u00B0C (Heated 8 hr..) 1 . 2 2 0 . 1 0 1 . 3 2 1.04 0 . 2 8 85\u00C2\u00B0C (Heated 1 9 hr.-,) 1 . 1 9 0 . 0 5 1 . 2 7 1.14 c 0 . 1 3 2 . Roughness 20\u00C2\u00B0C (Control) 0.15 0 . 0 5 0 . 2 5 0.13 0 . 1 2 50\u00C2\u00B0C (Heated 8 hr..) 0 . 2 1 0 . 0 7 0 . 3 8 0 . 0 0 0 . 3 8 85\u00C2\u00B0C (Heated 19 hr. ) 0.24 0 . 0 6 0.51 0.13 0 . 3 8 N.B. Standard Deviation. - 1 0 8 -Table 9- Veneer moisture content pr ior to gluing. V E N E E R M O I S T U R E C O N T E N T {%) Sample V E N E E R P E E L I N G T E M P E R A T U R E C O Number 20 50 \u00C2\u00A75 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 . 6.6 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 Average 6.6 6.4 6.4 N.B. 1. CTH Room Conditions: Temperature = Dry bulb 80\u00C2\u00B0F; Dew. Point 43\u00C2\u00B0F Relative Humidity = 26%. 2. Time of conditioning in the CTH Room = 15 days. 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. DRY ' TEST VACUUM-PRESSURE TEST M i n imum Mini mum Mean Mean Spec imen No. of Mean Mean Spec imen No. of Treatments Shear Wood Wood Test Shear Wood Wood Test Strength Fa i1ure Fa i1ure Specimens Strength Fa i1ure Fa i1ure Specimens (psi) (*) (%) (psi) {%) (%) U F - 2 0 - 5 5 - 1 0 3 0 6 5 7 2 0 3 4 2 6 4 3 8 10 34 U F - 2 0 - 5 5 - 2 0 3 1 2 7 0 3 5 3 5 2 7 4 5 9 15 36 U F - 2 0 - 7 0 - 1 0 3 3 2 6 2 3 0 2 8 2 6 0 5 6 15 36 U F - 2 0 - 7 0 - 2 0 3 2 6 5 2 . 1 0 2 8 2 7 7 4 4 10 36 U F - 5 0 - 5 5 - 1 0 3 1 2 5 3 1 0 2 2 2 9 5 3 3 10 25 U F - 5 0 - 5 5 - 2 0 3 5 3 3 8 1 0 2 7 2 9 9 24 0 30 U F - 5 0 - 7 0 - 1 0 3 3 4 40 1 0 24 2 5 3 18 5 2 3 U F - 5 0 - 7 0 - 2 0 3 5 3 61 15 2 6 249 31 5 26 U F - 8 5 - 5 5 - 1 0 3 6 2 3 9 15 3 0 2 9 5 24 0 36 U F - 8 5 - 5 5 - 2 0 342 3 8 15 3 0 3 1 9 24 10 30 U F - 8 5 - 7 0 - 1 0 3 8 1 3 5 1 0 2 3 2 8 1 11 0 29 U F - 8 5 - 7 0 - 2 0 3 8 9 4 7 1 0 2 7 3 0 7 14 0 30 N.B. 1 . Figures rounded to the nearest unit. 2 . Treatment codes are as fol lows: e.g. U F - 2 0 - 5 5 - 1 0 I I -> Closed assembly time (min) \u00C2\u00BB Glue spread ( lb. IMDGL) ' > Peeling temperature (\u00C2\u00B0C) \u00E2\u0080\u00A2 >Glue used (Urea-forma 1 dehyde) Table 11. Average shear s trength and average wood f a i l u r e of 5-ply Gmelina arborea Plywood bonded with Phenol-Formaldehyde (PF). VACUUM PRESSURE TEST BOIL-\u00E2\u0080\u00A2DRY-BOIL TEST Minimum Minimum No. of Mean Mean Specimen No. of Mean Mean Specimen Shear Wood Wood Test Shear Wood Wood Test Treatments Strength Fa i 1 u re F a i l u r e Specimens Strength F a i l u r e Fa i1ure Specimens (psi) (%) (S) (psi) (*) {%) PF-20-55-10 346 20 0 36 288 21 5 35 PF-20-55-20 318 45 15 30 255 43 10 34 PF-20-70-10 397 31 10 31 322 38 10 33 PF-20-70-20 337 3*\u00C2\u00BB 10 30 276 31* 10 28 PF-50-55-10 309 16 0 25 247 12 0 26 PF-50-55-20 313 45 10 22 239 46 10 23 PF-50-70-10 354 20 0 35 304 30 5 35 PF-50-70-20 317 64 30 30 258 66 10 30 PF-85-55-10 321 7 0 36 259 12 0 33 PF-85-55-20 330 19 5 28 286 16 5 35 PF-85-70-10 382 15 0 29 315 16 0 22 PF-85-70-20 405 10 0 36 334 16 0 31 o I N.B. 1. Figures rounded to the nearest un i t , 2. Treatment codes are as fo l l ows : e.g. PF-20-55-10 L -> Closed assembly time (min) \u00E2\u0080\u00A2> Glue spread (lb/MDGL) \"> Pee l ing temperature (\u00C2\u00B0C) Glue used (Phenol-formaldehyde) Table 12. Within - and between - panel var iat ion in bond qual i ty of 5~ply Gmelina arborea. Plywood bonded with UF glue: Dry test wood f a i l u r e . Mean Wood Fai lure {%) Max.Wood Fai lure {%) Min.Wood Fa i1ure Range Panels Panels Panels Panels Treatments 1 2 3 1 2 3 1 2 3 1 2 3 UF-20-55-10 38 7 2 62 55 100 95 20 50 35 35 50 60 UF-20-55-20 77 69 63 95 95 85 55 55 35 40 40 50 UF-20-70-10 60 51 76 90 90 95 35 40 50 55 50 45 UF-20-70-20 43 57 51 85 90 9 0 10 25 20 75 65 70 UF-50-55-10 56* 46* 57 70 95 95 40 10 20 30 85 75 UF-50-55-20 . 2 9 * 47, 35* 45 80 90 15 15 10 30 65 ' 8 0 UF-50-70-10 5 2 * 23* 36 95 40 75 10 10 10 85 30 65 UF-50-70-20 65* 49* 71 95 90 95 30 15 45 65 75 50 UF-85-55-10 37 43 36 55 60 60 20 15 20 35 45 40 UF-85-55-20 25 48 47 45 9 0 100 1 5 1 5 15 30 75 85 UF-85-70-10 19 34 46 40 85 70 10 10 15 30 75 55 UF-85-70-20 47 48 46 9 0 75 75 20 10 15 70 65 60 N.B. * Panels with yellow birch veneers as faces and backs. 1. Figures rounded to the nearest unit. 2. The Grand Mean Wood Fai lure of the Means of the above 3 panels for a part icu lar 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. Table 1 3 - Within - and between - panel var iat ion in bond qual i ty of 5~ply Gmelina arborea Plywood bonded with UF glue: Vacuum-pressure test , wood f a i l u r e . Mean Wood F a i l u r e ft) Max. Wood F a i l u r e ft) Min.Wood F a i l u r e ft) Range Panels Panels Panels Panels Treatments 1 2 3 1 2 3 1 2 3 1 2 3 UF-20-55 -10 44 4 2 32 70 70 55 10 10 1 5 60 60 40 UF-20-55-20 60 67 51 95 95 90 2 5 20 15 7 0 75 75 UF-20-70-1.0 81 70 37 100 9 0 65 50 30 15 5 0 60 50 UF-20-70-20 42 3 1 5 8 9 0 60 95 10 10 20 80 50 75 UF-50-55-10 24* 38* 35 35 55 75 '5 20 10 20 35 65 UF-50-55-20 12* 47 14* 40 60 55 5 30 0 35 30 55 UF-50-70-10 2 3 * 17* 11 85 55 1 5 10 5 5 75 50 10 UF-50-70-20 16* 6* 68 40 10 85 5 5 35 35 5 50 UF-85-55 -10 11 39 21 30 65 50 0 0 0 30 65 50 UF-85-55-20 15 38 20 35 75 45 10 10 10 25 65 35 UF-85-70-10 7 7 18 20 20 60 0 0 0 20 20 60 UF-85-70-20 \u00E2\u0080\u00A2 \u00E2\u0080\u00A2-10 19 9 35 75 40 0 0 0 .75 40 N.B. * Panels with y e l l o w b i r c h veneers as faces and backs. 1. Figures rounded to the nearest u n i t . 2. Because of rounding, the Grand Mean Wood F a i l u r e of the means of the above 3 panels f o r a p a r t i c u l a r treatment may not be same as in Table 1 0 . Table 14. Within - and between - panel var iat ion in bond qual i ty of 5~ply Gmelina arborea. Plywood bonded with PF glue: Vacuum-pressure test , wood f a i l u r e . Mean Wood Fa i lure (%) Max.Wood Fai lure (%] ) Min.Wood Fa i1ure (*) Range Panels Panels Panels Panels Treatments 1 2 3 1 2 3 1 2 3 1 2 3 P F - 2 0 - 5 5 - 1 0 2 8 1 3 13 7 5 3 0 3 5 5 0 0 7 0 3 0 3 5 P F - 2 0 - 5 5 - 2 0 . 3 9 5 1 * 4 9 * 8 0 8 0 8 0 15 2 5 3 0 6 5 5 5 5 0 P F - 2 0 - 7 0 - 1 0 3 7 3 2 2 5 8 0 6 0 8 5 1 0 1 0 1 0 7 0 50 7 5 P F - 2 0 - 7 0 - 2 0 18 4 5 3 7 4 5 8 0 7 5 1 0 1 5 1 0 3 5 6 5 6 5 P F - 5 0 - 5 5 - 1 0 3 6 3 5 1 0 ' 1 5 8 0 0 0 0 1 0 1 5 8 0 P F - 5 0 - 5 5 - 2 0 3 8 3 1 5 2 9 0 7 5 9 5 1 0 1 0 1 0 8 0 6 5 8 5 P F - 5 0 - 7 0 - 1 0 21 8 * 2 9 * 5 0 2 5 7 0 0 0 0 5 0 2 5 7 0 P F - 5 0 - 7 0 - 2 0 64 6 8 * . . 5 2 * 9 5 9 5 8 0 3 5 3 0 3 5 6 0 6 5 5 0 P F - 8 5 - 5 5 - 1 0 6 8 7 .10 3 0 4 5 0 0 0 1 0 3 0 4 5 P F - 8 5 - 5 5 - 2 0 24 24 * 1 3 5 0 7 5 40 5 5 5 4 5 7 0 3 5 P F - & 5 - 7 0 - 1 0 1 5 2 8 8 3 0 6 5 3 0 5 5 0 2 5 6 0 3 0 P F - 8 5 - 7 0 - 2 0 4 3 1 8 1 5 1 0 5 5 0 0 0 1 5 1 0 5 5 N.B. * Panels with yellow birch veneers as faces and backs 1 . Figures rounded to the nearest un i t . 2. The Grand Mean Wood Fa i 1 ure of the means of the above 3 panels for a part icu lar 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 respectively. Half of the test samples of each of the panel was used for the above test while the other half was used for the test in Table 1 1 . Table 1 5 . Within - and between - panel var iat ion in bond qual i ty of 5~ply Gmelina arborea Plywood bonded with PF glue: Boi1 -dry-boi1 test, wood f a i l u r e . Mean Wood Fa i lure {%) Max.Wood Fai lure {%) Min.Wood Fa i1 lure (%) Range Panels Panels Panels Panels Treatments 1 2 3 1 2 3 1 2 3 1 2 3 P F - 2 0 - 5 5 - 1 0 31 1 2 1 2 9 0 3 5 2 0 5 5 5 8 5 3 0 1 5 P F - 2 0 - 5 5 - 2 0 3 5 . 42* . 5 3 * 9 0 . 7 5 9 0 1 0 1 5 1 0 8 0 . 6 0 8 0 P F - 2 0 - 7 0 - 1 0 3 9 \" 4 9 3 2 9 0 7 5 8 0 1 0 1 5 1 0 8 0 6 5 7 0 P F - 2 0 - 7 0 - 2 0 2 7 4 4 3 2 8 0 9 5 8 0 1 0 1 0 1 0 7 0 8 5 7 0 P F - 5 0 - 5 5 - 1 0 5 1 3 14 2 0 5 5 40 0 0 0 2 0 5 5 40 P F - 5 0 - 5 5 - 2 0 2 3 1 9 6 9 9 0 4 5 9 5 1 0 1 0 2 5 8 0 3 5 7 0 P F - 5 0 - 7 0 - 1 0 2 9 24* 3 4 * 40 5 5 9 0 5 1 0 5 3 5 4 5 8 0 P F - 5 0 - 7 0 - 2 0 18 8 5 * 8 2 * 5 5 1 0 0 9 5 1 0 5 0 7 0 4 5 5 0 2 5 P F - 8 5 - 5 5 - 1 0 2 0 1 2 7 5 5 4 5 2 5 0 0 0 5 5 4 5 2 5 P F - 8 5 - 5 5 - 2 0 11 2 2 13 15 5 5 40 5 5 5 1 0 5 0 3 5 P F - 8 5 - 7 0 - 1 0 14 6 2 2 4 5 1 0 5 5 0 0 0 4 5 1 0 5 5 P F - 8 5 - 7 0 - 2 0 1 21 . ' 1 8 4 5 3 5 6 0 0 0 0 4 5 3 5 6 0 N.B. * Panels with yellow birch veneers as faces and backs. 1. Figures rounded to the nearest un i t . 2 . The Grand Means of the three means above may not be same as in Table 11 due to rounding. -115-Table 1 6 . Analysis of variance for test ing the effects of peeling temperature, Glue Spread and Closed Assembly Time on UF Glue bond qual i ty in 5~ply Gmelina arborea Plywood: Dry test . Shear Strength r . . Degrees q ^ Mean F \u00E2\u0080\u00A2 Source or var ia t ion or j _ ~i n . . _ , Square Square Ratios ... Freedom \u00E2\u0080\u00A2 Peeling temperature (PT) 2 Glue Spread (GS) 1 Closed Assembly Time (AT) 1 PTxGS 2 PTxAT 2 GSxAT 1 PTxGSxAT 2 Error 2 5 2 Total 2 6 3 0 . l 6 7 8 4 E x l 0 6 8 3 9 2 0 . 31 . 2 6 * * 3 5 8 8 7 . 3 5 8 8 7 . 1 3 . 3 7 * * 2 9 2 0 . 0 2 9 2 0 . 0 1 . 2 2 6 5 3 2 . 1 3 2 6 6 . 1 1 . 0 9 1 9 4 4 2 . 9 7 2 1 . 1 3 . 6 2 * 541 . 2 3 541 . 2 3 0 . 2 0 1 3 3 9 6 . , 6 6 9 8.O 2 . 5 0 0 . 6 7 6 4 9 x 1 0 \u00C2\u00B0 2 6 8 4 . 5 0 . 9 2 3 0 4 x 1 . 0 Wood Fa i1ure Degrees _ c u c \u00C2\u00A3 . ^ . r Sum of Mean F Source of var iat ion or _ c D . Square Square Ratios Freedom Peeling temperature (PT) 2 1 8 6 1 2 9 3 0 6 . 2 1 8 . 1 2 * * Glue Spread (GS) 1 8 . 0 1 5 2 8 . 0 1 5 2 0 . 0 2 Closed Assembly Time (AT) 1 5 5 8 . 5 5 5 5 8 . 5 5 2 . 7 1 PTxGS 2 2 7 8 2 . 4 1 3 9 1 . 2 1 . 0 9 PTxAT 2 1 1 8 3 . 9 5 9 1 . 9 5 1 . 1 5 GSxAT 1 1 2 5 6 . 7 1 2 5 6 . 7 2 . 4 5 PTxGSxAT 2 9 4 5 9 . 4 , 4 7 2 9 . 7 9 . 2 1 * * Error _ 2 5 2 0 . 1 2 9 4 1 x 1 0 ? 5 1 3 . 5 4 Total 2 6 3 0 . 1 6 3 2 7 x 1 0 S ign i f icant at the 0 . 0 1 l e ve l . S ign i f icant at the 0 . 0 5 l e ve l . -116-Table 1 7 . Analysis of variance for test ing the effects of Peeling Temperature, Glue Spread and Closed Assembly Time on UF Glue bond qual i ty in 5 _ p l y Gmelina arborea. Plywood: Vacuum-pressure test. Shear Strength Degrees _ c u r r . . ..j. Sum or Mean F Source of var iat ion '.or _ . D . Square Square Ratios Freedom Peeling Temperature (PT) 2 44448 .0 22224.0 5 . 7 2 6 9 * * Glue Spread (GS) 1 1 9 6 0 5 . 0 1 9 6 0 5 . 0 5 . 0 5 1 8 * Closed Assembly Time (AT) 1 9 6 3 6 . 5 9 6 3 6 . 5 2.4832 PTxGS 2 34173.0 1 7 0 8 7 . ~ 4 . 4 0 3 0 * * PTxAT 2 I O O 6 9 . O 5 0 3 4 . 5 1.2973 GSxAT 1 3 5 2 . 3 7 352 .37 0.90800E-01 PTxGSxAT 2 1 7 7 8 . 0 , 8 8 9 . O 0.22909 Error 2 5 2 0 . 9 7 7 9 4 x 1 0 \u00C2\u00B0 3 8 8 0 . 7 Total 2 6 3 0 . 1 0 9 8 0 x 1 0 Wood Fa i 1 u re Source of var ia t ion Degrees .of Freedom Sum of Square Mean Square F Rat ios Peeling Temperature (PT) 2 44537.0 22269.0 49.693** Glue Spread (GS) 1 3000.4 3000.4 6.6954** Closed Assembly Time (AT) 1 606 .06 606.06 1.3524 PTxGS 2 3114.4 1557.2 3.4749* PTxAT 2 196.21 98.106 0.21893 GSxAT 1 836.74 836.74 1.8672 PTxGSxAT 2 6993.9 , 3497.0 7.8036** Error 252 0.11283x10\u00C2\u00B0 448.12 Total 263 0.17221x10\u00C2\u00B0 S ign i f icant S ign i f icant at the 0.01 l e ve l . at the 0.05 l e ve l . -117-Table 18. Analysis of variance for test ing the effects of Peeling Temperature, Glue Spread and Closed Assembly Time on PF Glue bond qua l i ty in 5 - p l y Gmelina arborea Plywood: Vacuum-pressure tes t . Shear Strength Source of var ia t ion Degrees of Freedom Sum of Square Mean Squa re F Rat ios Peeling Temperature (PT) 2 55543.0 27772.0 9-5261** Glue Spread (GS) 1 84209.0 84209.0 28.885** Closed Assembly Time (AT) 1 19605.0 19605.0 6.7247** PTxGS 2 19768.0 9884.2 3.3904* PTxAT 2 36216.0 1 8 1 0 8 . 6 . 2 1 1 3 * * GSxAT 1 1675.1 1675.1 0.57458 PTxGSxAT 2 6295.6 , 3147.8 1.0797 Error 2 5 2 0.73466x10? 2915.3 Total 263 0.95797xlOb Wood Fa i1 u rs \ Source of var ia t ion Degrees of Freedom Sum of Square Mean Square F Ratios Peeling Temperature (PT) 2 2 8 0 8 9 . 14044. 3 1 . 3 2 6 * * Glue Spread (GS) 1 1 2 0 9 . 2 1 2 0 9 . 2 2 . 6 9 7 1 Closed Assembly Time (AT) 1 2 2 6 4 4 . 2 2 6 4 4 . 5 0 . 5 0 7 * * PTxGS. 2 1 6 3 0 . 9 8 1 5 . 4 4 1 . 8 1 8 8 PTxAT 2 1 4 7 9 6 . 7 3 9 8 . 0 1 6 . 5 0 1 * * GSxAT 1 3 2 9 . 6 4 3 2 9 . 6 4 0 . 7 3 5 2 5 PTxGSxAT 2 5 0 4 1 . 1 , 2 5 2 0 . 5 5 . 6 2 2 0 * * Error 2 5 2 0 . 1 1 2 9 8 x 1 0 ; 4 4 8 . 3 4 Total 2 6 3 0 . 1 8 6 7 2 x 1 0 S ign i f icant at the 0.01 l e ve l . S ign i f icant at the 0.05 l e ve l . -118-T a b l e 19- A n a l y s i s o f v a r i a n c e f o r t e s t i n g t h e e f f e c t o f P e e l i n g Temperature,' Glue Spread and C l o s e d Assembly Time on PF Glue bond q u a l i t y i n 5 - p l y Gmelina a r b o r e a Plywood: B o i 1 - d r y - b o i 1 t e s t . Shear S t r e n g t h Degrees _ ^ u r r r Sum o f Mean F Source o f v a r i a t i o n o f _ _ D .. , Square Square R a t i o s Freedom P e e l i n g Temperature (PT) 2 49995. 24997. 9.16** G l u e Spread (GS) 1 99103. 99103. 3 6 . 3 1 * * C l o s e d Assembly Time (AT) 1 35352. 3 5 3 5 2 . 12.95** PTxGS 2 7302.8 3651.4 1.34 PTxAT 2 47467. 23734. 8.69** GSxAT 1 2578.1 2578.1 0.94 PTxGSxAT 2 20499. , 10250. 3.76 E r r o r 252 0.68786x10^ 2729.6 T o t a l 263 0.95015x10\u00C2\u00B0 Wood F a i l u r e Degrees _ c u \u00E2\u0080\u009E r Sum o f Mean Source o f v a r i a t i o n o t _ c D-.4--~,-^ , Square Square R a t i o s Freedom P e e l i n g Temperature (PT) 2 3 0 0 1 2 . 1 5 0 0 6 . 2 7 . 5 8 1 * * Glue Spread (GS) 1 3 8 6 4 . 0 3 8 6 4 . 0 7 . 1 0 2 1 * * C l o s e d Assembly Time (AT) 1 1 7 8 3 7 . 1 7 8 3 7 . 3 2 . 7 8 4 * * PTxGS 2 6 0 2 1 . 2 3 0 1 0 . 6 5 . 5 3 3 5 * * PTxAT 2 9 8 2 1 . 2 ; 4 9 1 0 . 6 9 . 0 2 5 8 * * GSxAT 1 9 8 5 . 2 3 9 8 5 . 2 3 1 . 8 1 0 9 PTxGSxAT 2 2 3 5 4 . 5 6 1177.3 c 2 . 1 6 3 8 E r r o r 2 5 2 0 . 1 3 7 1 0 x 1 0 ? 5 4 4 . 0 7 T o t a l 2 6 3 0 . 2 0 8 0 0 x 1 0 S i g n i f i c a n t a t the 0.01 l e v e l . S i g n i f i c a n t a t t h e 0.05 l e v e l . -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 Shear S t r e n g t h o f Gmeli na a r b o r e a . Plywood bonded w i t h UF G l u e . T R E A T M E N T R A N K I N G Dry T e s t 1 2 5 4 3 7 1 0 6 8 9 11 1 2 Treatment Mean 2 3 0 6 3 1 2 3 1 2 3 2 6 3 3 2 3 3 4 342 3 5 3 353 3 6 2 381 3 9 8 Vacuum P r e s s u r e T e s t 8 7 3 1 2 4 11 5 9 6 12 10 Treatment Mean 2 249 253 260 264 274 277 281 295 2 9 5 299 307 319 N.B. 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 2. Numbers above means r e f e r t o 1 UF-20-55-10 2 UF-20-55-20 3 UF-20-70-10 4 UF-20-70-20 5 UF-50-55-10 , 6 UF-50-55-20 l i n e a r e not s i g n i f i c a n t l y d i f f e r e n t a t t r e a t m e n t s as f o l l o w s : 7 U F - 5 0 - 7 0 - 1 0 8 U F - 5 0 - 7 0 - 2 0 9 U F - 8 5 - 5 5 - 1 0 1 0 U F - 8 5 - 5 5 - 2 0 11 U F - 8 5 - 7 0 - 1 0 1 2 U F - 8 5 - 7 0 - 2 0 -120-T a b l e 2 1 . Duncan'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 . Plywood bonded w i t h UF G l u e . Dry T e s t T R E A T M E N T R A N K I N G 11 10 6 9 7 12 Treatment Mean 2 3 5 3 8 3 8 3 9 40 4 7 ' 5 2 5 3 5 7 61 6 2 7 0 Vacuum P r e s s u r e T e s t 11 12 7 6 9 10 8 5 1 4 3 2 Treatment Mean 2 11 14 18 24 24 24 31 33 38 44 5 6 5 9 N.B. 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 not s i g n i f i c a n t l y d i f f e r e n t a t th e 5% l e v e l o f s i g n i f i c a n c e . 2 . Numbers above means r e f e r t o t r e a t m e n t s as f o l l o w s : 1 U F - 2 0 - 5 5 - 1 0 7 U F - 5 0 - 7 0 - 1 0 2 U F - 2 0 - 5 5 - 2 0 8 U F - 5 0 - 7 0 - 2 0 3 U F - 2 0 - 7 0 - 1 0 9 U F - 8 5 - 5 5 - 1 0 4 U F - 2 0 - 7 0 - 2 0 1 0 U F - 8 5 - 5 5 - 2 0 5 U F - 5 0 - 5 5 - 1 0 1 11 U F - 8 5 - 7 0 - 1 0 6 U F - 5 0 - 5 5 - 2 0 ' 1 2 U F - 8 5 - 7 0 - 2 0 -121-T a b l e 22. Duncan's M u l t i p l e Range T e s t f o r Shear S t r e n g t h d f Gmelina a r b o r e a . Plywood 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 G Vacuum P r e s s u r e T e s t 5 6 8 2 9 10 4 1 7 1 1 3 12 Treatment Mean 2 308 313 317 318 321 330 337 346 354 382 397 405 B o i 1 - d r y - b o i 1 T e s t 6 5 2 8 9 4 10 1 7 11 3 12 Treatment Mean 2 239 247 255 258 259 2 7 6 2 8 6 288 304 3 1 5 322 334 N.B. 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 not s i g n i f i c a n t l y d i f f e r e n t a t 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 above means r e f e r t o t r e a t m e n t s as f o l l o w s : 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 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 -122-T a b l e 23. Duncan'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 . Plywood bonded w i t h PF Gl u e . T R E A T M E N T R A N K I N G Vacuum P r e s s u r e T e s t 9 12 11 5 10 1 7 3 4 2 6 8 Treatment Mean 2 7 10 15 16 19 20 20 31 34 45 45 64 B o i 1 - d r y - b o i 1 T e s t 5 9 10 11 12 1 7 4 3 2 6 8 Treatment Mean 2 12 12 16 16 16 21 30 34 38 43 46 66 N.B. 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 d i f f e r e n t a t 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 above means r e f e r t o t r e a t m e n t s as f o l l o w s : 1 PF-20-55-10 2 PF-20-55-20 3 PF-20-70-10 4 PF-20-70-20 5 PF-50-55-10 6 PF-50-55-20 7 P F - 5 0 - 7 0 - 1 0 8 P F - 5 0 - 7 0 - 2 0 9 P F - 8 5 - 5 5 - 1 0 1 0 P F - 8 5 - 5 5 - 2 0 11 P F - 8 5 - 7 0 - 1 0 1 2 P F - 8 5 - 7 0 - 2 0 -123-Sapwood Test Sample Heartwood Test Sample Heartwood Test Sample Corewood H\u00E2\u0080\u009E Test Sample Thus, there are four test samples per log. The centre Sample i s used f o r moisture content determination Used for S p e c i f i c gravity. Figure 1. Pattern of cut of Test Samples from Logs for S p e c i f i c Gravity and Moisture Content Determination Tests. -124-Figure 2. \"Temperature Changes within a log 8ft long and 7.7 in diameter (50\u00C2\u00B0C Heating). -125-4 ^ ' ' -n r - i 10 12 14 16 18 19 Heating Time (hr) Figure 3. 100 -, 80 - \ 60 -J ko-20-\ '20\u00C2\u00B0 CC Pee 1ed Venee r s 0 5 10 Visual roughness (.001 inch) 50\u00C2\u00B0C Peeled Veneers T T 20 0 5 10 15 Visual roughness (.001 inch) Figure k. Frequency d i s t r i bu t i on of visual veneer roughness. 85\u00C2\u00B0C Peeled Veneers 5 10 15 20 25 Visual roughness (.001 Inch) -127-Figure 5. Dependence of bond qua l i ty 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 ry r Te s t (Shear Strength). -128- I 20 40 60 Peel ing Temperature Spread 70 lb/MDGL Spread 55 lb/MDGL 80 100 Figure 10. Dependence of bond qua l i t y on Peel ing Temperature and Glue Spread Interact ion-PF Vacuum-pressure Test (Shear Strength). \u00E2\u0080\u00A2133-in o. cn c 500-1 4ooH 300 H Time 20 min. Time 10 min. 20 40 60 Peel i n g Temperature S(\u00C2\u00B0.G') 80 100 Figure 11. Dependence of bond q u a l i t y on Pee l i n g Temperature and Closed Assembly Time Interaction-PF Vacuum-pressure Test (Shear Strength). -13**-Figure 12. Dependence of bond qual i ty on Peeling Temperature 'and .'Oiro's'e'd' Assembly .;T:ime;tl\"nteraiction-rPF Vacuum-pressure Test (Wood Fa i l u re ) . -135-70 60 i 50 3 -a O o 30 J 20 _J 10 -4 Spread 55\" Time 20 Spread 70-Time 10 Spread 70-Time 20 Spread 55\"Time 10 T 20 kO 60 P e e l i n g Temperature (\u00C2\u00B0(C)), 80 100 F i g u r e 13- Dependence o f bond q u a l i t y on P e e l i n g T e mperature, Glue Spread and C l o s e d Assembly Time I n t e r a c t i o n -PF Vacuum-pressure T e s t (Wood F a i l u r e ) . -136-D-c 400-1 300 H 200 H 20 r 40 Time 20 min. -\u00C2\u00A9T i me 10 min. T 60 80 Peeling Temperature (\u00C2\u00B06)v 100 Figure 14. Dependence of bond qual i ty on Peeling Temperature and Closed Assembly Time Interaction-PF Boi1-dry-boi1 Test (Shear Strength). -137-Figure 15. Dependence of bond qual i ty on Peeling Temperature and Glue Spread Interaction-PF Boi1-dry-boi1 Test (Wood Fa i1ure). -138-60 - i 20 40 60 80 100 Peeling Temperature (\u00C2\u00B0'C,) Figure 16. Dependence of bond quaj i ty on Peeling Temperature and Closed Assembly Time Interaction-PF Boi1-dry-boi1 Test (Wood Fa i l u re ) . -139-APPENDIX 1 B. S. 1455:1963 S p e c i f i c a t i o n for Plywood manufactured from T r o p i c a l Hardwoods. -140-SPECIFICATION F O R P L Y W O O D M A N U F A C T U R E D F R O M T R O P I C A L H A R D W O O D S B.S. 1455 : 1963 Price 10/6 net BRITISH S T A N D A R D S INSTITUTION INCORPORATED BY ROYAL CHARTER BRITISH STANDARDS HOUSE, TELEGRAMS: STANDARDS AUDLEY LONDON TELEPHONE: MAYFAIR 9000 -141-B.S. 1455 C O N T E N T S _o-operating organizations Foreword . . . . ' . Page . 2 . 5 SPECIFICATION 1. Scope . . 2. Definitions 3. Grade . 4. Cores . . . . . . . . . . . . 6 . . . . . . . . . . 6 . . . . . . . . . . 6 . 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 Page . APPENDICES A. Selection of samples from a consignment for testing B. Method of making the tests and assessing the results C Method of applying the k n i f c - t e s t . . . . . D. Method of determining moisture content. . . TABLES 1. Schedule of tests for proving compliance of the plywood with the requirement of its declared bonding . . . . . 2. Wet tests in hot water or steam. . . ... . . . 16. Manufacturer's warranty 8 IV. Bond quality No. V. Bond quality No. VI. Bond quality No. VII. Bond quality No. VIII. Bond quality No. 9 10 10 7 9 PLATES I. Tool for the knife-testing of plywood . . . 11 II. Knife-testing plywood. . . . . . . 11 HI. Bond quality No. 10' 8 in the Master Scale for 6 ^ assessing bond quality At in plywood by the knife . test . . . . . 14-19 -142- B.S. 1455 B R I T I S H S T A N D A R D S P E C I F I C A T I O N F O R P L Y W O O D \u00E2\u0080\u00A2 ' M A N U F A C T U R E D F R O M T R O P I C A L H A R D W O O D S F O R E W O R D 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. High strength plywood for aircraft. B.S. V35. Medium and low strength plywood for aircraft purposes. B.S. 10S3. British-made plywood for marine craft. ( B.S. 3444. Blockboard and laminboard. B.S (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 of this British Standard to British-made material has been removed. While this allows oversea producers, who supply by far the greater part of the plywood used in the United K ingdom, 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, s luing standards and tests o f their own which are well known in the U . K . market. The conditions of these are dictated by the woods available and internal requirements o f the particular producing country. If users in the United Kingdom 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 United 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 term4 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. N O T E I. Where metric equivalents are given, the British units arc to be regarded as the standard. The metric equivalents arc approximate. More accurate conversions should be based on the tables in U.S. 330, * Conversion factors and tables *. N O T E 2. In place ofthc customary, but incorrect, use o f the pound and kilopramm'e as units o f 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 one pound, or kilogramme respectively, give it an acceleration equal to that o f standard gravity. \u00C2\u00B0 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 wood-work', apply with the following modifications: 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 approx-imately 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 of firm smoothly 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\u00E2\u0084\u00A2 b\u00C2\u00AB filled with 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 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\u00C2\u00BBy 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 manu-facturing 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. 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 compli-ance (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 character-istics, 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 in uiaiking iiic ply wOvu. \u00E2\u0080\u00A2These designations are those used in D.S. 1203, 'Synthet ic resin adhesives (phenolic and aminbplastic) for plywood\". 6 -144- B.S. 1455 : Tvpr 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 rs h;ivi\u00C2\u00BB heen nrovrd to n-iakr. joints '\u00E2\u0080\u00A2:\u00C2\u00AB*.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 weather-resistant. Joints made with these adhesives will survive full 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. Type INT: Interior. Joints made with these adhesives arc resistant to coid water but are not required to with-stand attack by micro-organisms. 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 inclina-tions: 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. . present only certain phenolic adhesiv have ben shown to inert this requiremt. t I'or interpretation of * adequate * se Clause 10 and apendices refred to therein. 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 Tests Donding ! Wet test in hot water or I fleam 1 Wet test in cold water Mycolo;;ical test WBP 1 j A, Bl, C A, B2o, C A. B3 BR j A, Bl, C \u00E2\u0080\u00A2 A, B&j, C A, B3 MR i A, Bl. C j A, B2o, C A, B3 INT ! - A, B26 \u00E2\u0080\u0094 \u00E2\u0080\u00A2 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\u00C2\u00AE 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. 3493 , * 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 y6 in (3 mm) greater than the specified size. b. Thickness. Unless otherwise agreed between pur-chaser 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 \u00C2\u00B1 5 per cent for boards up to and including V* in (6 mm) thick or \u00C2\u00B1 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. 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 require-ment. If the rc-test fails, the batch shall be deemed not to comply with this British Standard. 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, MR or INT). f. Nominal thickness of board. 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 . 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 S p e c i f i c a t i o n s of Japanese Plywood, Excerpts. (Japan). 1968. -147- ~ ^ \" may -\u00C2\u00ABo /sea r E X P O R T S T A N D A R D S P E C I F I C A T I O N O F J A P A N E S E P L Y W O O D 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 -148-foreword \u00E2\u0080\u00A2 This publication has been excerpted and arranged from Basic Rules of Inspection for Common Plywood and Specialty Plywood as set forth jointly by Ministry of Agriculture and Forestry, and Ministry of International Trade 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. The Second Revision was announced in February, 1954. The Third Revision was announced in June, 1957. The Fourth Revision was announced in January, 1958. The Fifth Revision was announced in May, 1963. The Sixth Revision was announced in November, 1967. Interpretation: Any dispute as to interpretation of this unofficial translation for commercial purposes shall be finally decided on the basis of the original text in the Japanese language. -149-1. EXPORT STANDARD OF COMMON PLYWOOD Page (I) DOOR SKIN PLYWOOD 3 1. Plywood with a face veneer .of domestic species 3 2. Plywood with a face veneer of lauan species 10 (n) WALL. PANEL, PLYWOOD 18 1. Plywood with a face veneer of domestic species .\" 18 <1) Regular 18 (2) Rustic 25 2. Plywood with a face veneer of lauan species 31 (HI) PLYWOOD FOR GENERAL USES . 38 1. Plywood with a face veneer of domestic species 38 f. \u00E2\u0080\u00A2 ' 2. Plywood with a face veneer of lauan species 47 S E P A R A T E PARAGRAPH - Physical Inspection ; . . 57 1. Cyelic-boilTest -57 2. Hot and cold soaking Test 5 9 3. P n bonding Test 60 4. Tyne I =oak delamination Test \u00E2\u0080\u00A2 60 5. Type II soak delamination Test.. '. 60 6. Type III soak delamination Test 61 7. Moisture content Test 61 -150-SEPARATE P A R AGRAPH Physical Inspection 1. Cyclic-boil test (1) Preparation of Specimen Specimens shall be prepared in accordance with the following methods from the part of sample which is free from 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 in. or more of thickness, four specimens shall be prepared in . conformity to drawing A; and for the said plywood having face or back veneer in less than 1/16 in. of thickness or a veneer sheared easily, four specimens shall be prepared in conformity to drawing B. \u00E2\u0080\u00A2 In this case, one half of total specimens shall be prepared to comprise regular direction of core's reverse check and another half shall be prepared to involve contrary direction of core's reverse check. Tl 5\u00E2\u0080\u0094 j H f \u00E2\u0080\u0094 i H I \u00E2\u0080\u0094 i H \u00E2\u0080\u00A2'\u00E2\u0080\u00A2\u00E2\u0080\u00A2>\u00E2\u0080\u00A2\u00C2\u00BB> \"i i i , - ^ \u00E2\u0080\u0094 \u00E2\u0080\u0094 | b. (Unit : inch) For 5 ply-plywood. 3 ply-plywood which comprises any two bonded layers respectively in a specimen shall be obtained by means of stripping surplus veneers and specimens shall be prepared from the said 3 ply-plywood in conformity to drawing A. 57 --151-(2) Testing method 'A specimen shall be submerged in boiling water for four hours and then dried at a temperature of GO\u00C2\u00B0C + 3\u00C2\u00B0C during 20 hours. Furthermore, 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 room temperature. Bonding test shall be performed on this specimen under wet conditions. (Bonding test: Both ends of specimen are clamped by grips and are tensioned by a load velocity of 1, 320 Lb., maximum per minute and maximum load is measured at the time of rupture.) (3) Successful standard of test Bonding strength of specimen shall be equal to or more than the standard figures of bonding strength stipulated in the following Table. Species of Wood Standard Figures of bonding strength Birch 145 (Lbs. /sq. in. ) Beech, Oak, Japanese Itaya Kaede (Maple), Japanese Akadamo (Elm), Japanese Shioji (Ash) and Japanese Yachidamo (Ash) 135 Japanese Sen (Caster Arabia), Japanese Hohnoki (Magnolia), Japanese Katsura (Judaf. Tree) and Japanese Tabu (Lourel) 115 Japanese Shiba (Bass wood) 100 Lauan and Others 110 Note- 1. When a specimen comprises veneers of different wood species, the species having lowest standard figure, out of various standard figures of bonding strength for those species shall be specified for 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 core sheet in proportion to face sheet is 1. 5 or more for this specimen, the above calculated figure shall be multiplied by a coefficient in column of the following table which is classified in conformity to thickness ratio in the said table and the multiplied figure shall be specified as this bonding strength. Bonding strength Lb. /sq. in. = P ^ , wherein p is maximum load (Lb.) in the test of bonding strength and b is width of bonded surface (surface between both grooves) and h is length of bonded surface (surface between both grooves): This formula is applicable for a specimen in the form of drawing A, and another specimen in the form of drawing B which is used for cyclic boil test and hot and cold soaking test. , p Bonding strength Lb. /sq. in. = b ^ x 0. 9, wherein p, b and h have the same significances with the above formula: This formula is applicable for a specimen in the form of drawing B which is used dry bonding strength test. Thickness 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 or more 2.0 Hot and cold soaking test (1) Preparation of Specimen To conform to the paragraph I-(l). (2) Testing method A specimen shall be submerged in hot water at a temperature of 60\u00C2\u00B0C + 3\u00C2\u00B0C for three hours and then shall be continuously kept in the said water until the temperature goes down to a room temperature. - 50 --153-Bonding 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 To conform to the paragraph I-(l). (2) Testing method Test of bonding strength shall be performed for a specimen under common conditions. (3) Successful standard of test. To conform to the paragraph I-(3). 4. . Type I soak delamination test (1) Preparation of specimen Four specimens in size of 3 in. square shall be prepared from the part of sample which is free from any* defect to affect bonding strength of the said specimen. (2) Testing method A specimen shall be submerged in boiling water for four hours and then dried at a temperature of 60\u00C2\u00B0C + 3\u00C2\u00B0C during 20 hours. Furthermore, it shall be again submerged in boiling water for four hours and dried at temperature of 60\"C + 3\"C during three hours. (3) Successful standard of test. The part which does not delaminate in the same bonded layer of a specimen shall have 2 in. or more of length at the side surface. 5. Type 11 soak delamination test (1) Preparation of specimen To conform to the paragraph 4-(l). (2) Testing method A specimen shall be submerged in hot water at a temperature of 70\u00C2\u00B0C + 3\u00C2\u00B0C for two hours and then dried at temperature of 60\u00C2\u00B0C + 3\u00C2\u00B0C during three hours. - 60 --154-(3) Successful standard of test To conform to the paragraph, 4-{3). 6. Type Hi soak delamination test (1) Preparaiion of specimen To conform to the paragraph 4-(l). (2) ' Testing method A specimen shall be submerged in warm water at a temperature of 35\u00C2\u00B0C'+3 CC for two hours and then dried at temperature of 60\"C +3\u00C2\u00B0C during three hours. (3) Successful standard of test. To conform to the paragraph, 4-(3). 7. Moisture content test (1) Preparation of specimen Two specimens sized appropriately shall be prepared from the part of sample which is free from any defect to affect moisture content of the said specimen. (2) Testing method After weight of specimen is balanced, the specimen shall be dried at a temperature of 100\u00C2\u00B0C to 105\u00C2\u00B0C until it reaches to constant weight. This weight will be balanced and a moisture content shall be measured by the following formula. But, when moisture content is measured by another process besides the above mentioned method with equal or more degree of accuracy, the measurement may be accorded with this latter process. Wl - W2 Moisture content (per cent) \u00C2\u00B0 \u00E2\u0080\u0094 x 100 W2 wherein Wj is a weight in gram before drying and W*2 is a bone dry weight in gram. (3) \u00E2\u0080\u00A2 Successful Standard of Test \u00E2\u0080\u00A2 13 per cont or less of moisture content for specimen. - 61 --155-APPENDIX 3 DIN 68705 Plywood Standards (translated) (Germany). 1968 : C01.4 January .190ft lilt Definitions Plywood General Recuirenents I H A R 2 2 F i \u00C2\u00AB 7 n ^ Sheet a 2 E Sperrholr-; Becriffe, Allgemeine Anforderungen, Priifung ! 2ais Standard applies to veneer boards and blockboards. It 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 \u00C2\u00A3 voca D o n d e a together with the grain running crosswise. Plywood (syabol SP according to DIN 4076 h s t y-sse-z -under revision) i s therefore a generic definition for various t y p e B of sheets. A * t distinction i s nade between: pa: a : '. D i to Dir; ^o?s) V e n e e r b o a r d c o n s i s the d i r e c t i o n s c f 2 . 2 . 31ockoos.rds a i l e l to tne o a a 1 1 y 2^. Veneer board (synbol HJ according to DIN 4076) . Plyvocd in which a l l plies 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 plies grain. l a m i n a t e d v e n e e r b o a r d (symbol Stf according sting cf at least five plies of veneer bonded to each other, in such a way that the \u00C2\u00A3~~ -1 of adjacent layers cross at angles of 45\u00C2\u00B0 or less. (symbol 71 according to Dili 4076) 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, in blockboards consisting of i'ive plies parallel to the bonded covering veneers. A l l layers are bonded together crossvise. Slockboards consisting of five plies are mainly produced to neet higher standards of surface condition and diuensional stability. . . A distinction i s nade b 8 2.2.1. L a n i n b o ;ween various blockboards, according to the type of core\", a r d c o r e (symbol SIAE according to DIH 4076) These are: - u \u00E2\u0080\u0094\u00E2\u0080\u0094. ' \u00E2\u0080\u0094 I \u00E2\u0080\u0094 \u00E2\u0080\u00A2 Karr.ov:, lemnated strips of wood consisting of rotary cut veneers up to 8on thick, bonded together and arranged edgewise to the plane of the board. 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. 2.2.3- U 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 2i1i_3ondin2 Choice of plywood bondings shall be governed by the climatic conditions and hunidity to which tne^boards or sheets are subjected in use. A distinction is aade between the following types of 3.1.1. X? 20 (interior plywood) \" 5 resistant whan used in rooas with generally low atnospheric huaidity (not weather-. con resistant). (exterior plywood) to the effects of the weather and humidity (weather-resistant).^ la additi== tc ties? boadinga the following types can. a l so be produced! . AV 100 2.5 resistan 5 .1 . 2 36ndi. N o t IS i7z 3 s : i i ; j r e s i s t ant \u00C2\u00AB i s i = s \u00C2\u00AB d i a v&'-rr -p to about c \" c -(set \u00C2\u00BB e a t i - r - r e s i s t 2 r : t } A ICC: \u00C2\u00A3 i a 7O0E9 with high atmospheric huaid i ty and r e s i s t a n t to occas ional contact with s-r-.iti t i e sheets or boards are protected against d i r e c t e f fect s o f the weather SzzzL^s ^ t s i s ' . e s : to t i e a c t i o s of cold and hot water ( l imi ted weather r e s i s t a n c e ) . \u00E2\u0080\u00A2 F a r t i i u . a r s r- ^ dimension 200 Z s h a f l \" J p l J tno cirection of the r;ram of the coverintr veneern O n \u00C2\u00BB of th. r^,r\u00C2\u00AB \u00E2\u0080\u00A2 \"\"UJ-1- \u00C2\u00B0PP-LJ fro* the cd,:e of the sheet, the others froa fhe inllle S the shlet\" ( ^ S I > e C l n s n B ttust C 0 O c Continued on panes 2 to 4 - Explanations on p'i\u00C2\u00A3\u00C2\u00AB 4 Allelnvukuut d.r Normblorlei durch Brulh-Veririeb OmbH, Berlin 30 und Kolo T 1 T U g n i M . ^ . Fac* 2 Dili 66705 Sheet 1 -157- 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 following short testa are s u f f i c i e n t f o r testing bonding provided the stated glues were used.\" Bondine; I? 20 (urea resins) Specimens immersed i n voter f o r 24 hours at a water temperature of 20 \u00C2\u00B0C + 2 dec-Bonding AV 100 (phenolic, phenolic-resorcin or reoorcin resins) a) Cold water test: r Specimens'immersed i n water for 24 hours at a water temperature of 20 \u00C2\u00B0C + 2 deg. b) B o i l i n g test with alternate heating and. cooling as follows: Boil i n g for 4 hours (100 \u00C2\u00B0C) Eeeoing for 16 to 20 hours i n hot a i r at 60 \u00C2\u00B0C + 2 deg i n a hot cabinet acco-cVi r - to DIN 50011 ~ \u00E2\u0080\u00A2 . \" B o i l i n g f o r 4 hours Cooling for 2 to 3 hours under water at a water temperature of 20 \u00C2\u00B0C + 5 defj. M o t e t Bonding IV* 67 (unextended or nelajaine-reinforced urea res ins) . Specimens immersed i n water for 3 hours at a water tesperature of 67 \u00C2\u00B0 C + 0.5 deg. Cool ing under water for 2 hours at a rater temperature of 20 \u00C2\u00B0 C + 5 deg. Bonding A ICO (nelamine res ins or mixtures of urea and melaaine res ins) Boiling for 6 hours (100 \u00C2\u00B0 C ) Coolins under water for 2 hours at a water temperature of 20 \u00C2\u00B0C + 5 deg. 4.1.1.3- Test procedure Knife tests according to DIU 53255 s h a l l be carried out on a l l p l i e s of the f i v e (ten) speciaens taken according to Section 4.1.1.1 and pretreated according to Section 4.1.1.2. 4.1.1.4. Assessment of test results Test results f o r a l l glue j o i n t s examined s h a l l be designated according to DIN 53255 by the following grading numbers: 1 excellent. bord?ng 3 adequate bonding 2 good bonding 4 inadequate bonding 4.1.2. S h e a r t e s t 4.1.2.1 Sampling and production of specimens At least ten simple tension/shear specimens s h a l l be prepared according to Din 53255 frcn every sheet to be tested (20 simple tension/shear specimens from sheets of bonding tyje A'W 1C0). In the case of sheets with f i v e and more layers bf veneer the.outer veneers shall\" be removed (e.g. by planing down) to three p l i e s . 4.1.2.2. Pretreatment of specimens according to Section 4.1.1.2. 4.1.2.3. Testing and evaluation Shear tests according to PITT 53255|irshall be carried out on the ten (20) specimens taken according to Section 4.1.2.1 and pretreated. according to Section 4.1.1.2, and the\" results evaluated. 4.2 . _Bendir^_strenrjth -The bending strength s h a l l be determined accordins to. DIK 52371 (at present s t i l l c i r c u l a t i n g as d r a f t ) . 4.3. Moisture content The moisture content s h a l l be determined according to DT.il 52183. 5. Quality safeguard Depeadins on the f i e l d of application of veneer boards and blockboards, they can or must be subjected to regular supervision of th e i r quality i n the form of a s t a t i s t i c a l q uality control (own supervision) and/or a supervision testing (outside supervision). \" . ft.1. S t a t i s t i c a l quality control (own supervision) 5.1.1. S a m p l i n g ?or ova supervision the number of sheets to be selected w i l l depend on the relevant production ' progrsrcse. At l e a s t one sheet must be taken at random from every l o t (consignment) ahi, i n the case of continuous production, at least one sheet d a i l y , and must be tested f o r the specified rvrcperties. 5.1.2. C o n t r o l c a r d s The results of own supervision s h a l l be recorded and entered on control card3. S t a t i s t i c evaluation covers r.ean values f o r sheets and a fluctuation measure. The fluctuation measure .chosen caa either be the variable s2, the standard variation s or span R. Supervision of -the span does not require any calculations but i t i a not suitable f o r systematic evaluations. For subsequent evaluations, for deciding whether several sheet or board thicknesses .-:r.d/or constructional combinations should be summarized under a basic l o t and f o r calculating varniar; and control l i n i t 3 i t i s necessary to calculate and determine the sua t o t a l of individual values Z x i and t h e i r squares Ex^ for each sheet tested. Warning and control l i m i t s for the control cards can be calculated the f i r s t time a f t e r testing ebout 25 sheets per l o t . They should be fixed annually and entered on new control cards. CY.TJ supervision records must be kept for at least f i v e years. 5.1.3* T e s t i n g n o n - c o n d i t i o n e d s p e c i n e n s Veneer boards and blockboards leaving the press frequently have a lower moisture content than i n t h e i r state of equilibrium i n a standard, climate 20/65 Dili 50014. As a rule adjustment of the noisturc content of sheets or boards to the standard climate takes about 7 days, even loader i n -158- DIH 68705 Sheet 1 Page 3 aec The teeting of non-conditioned bending specimens can produce systematic v a r i a t i o n s from measurements undertaken on conditioned specimens. Systematic variations i n bending properties cf non-conditioned specimens must therefore be taken into account by correction factors f o r the mean values and fo r the warning and control l i m i t s . Correction factors determined by experiment should be re-examined from time to time. 5.2._Superyision testing (outside supervision) Outride supervision testings must be carried out every .six months by an o f f i c i a l l y recognized material testing i n s t i t u t e on the basis of a supervision agreement, provided regular supervision i n accordance with regulations of building authorities does not take piece under the d i r e c t i o n of a recognised quality control body. A condition f o r carrying out outside supervision i s proof of properly conducted own supervision according to \" Section 5-1. 5-2.1. S a m p l i n g \u00E2\u0080\u00A2 ~~ In outside supervision three sheets or boards s h a l l always be selected at random from a lonrest possible production period by a representative of or person appointed by the super-visor;.' department and s h a l l be marked immediately so as to prevent confusion. A report cn selection 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 or his representative. This report must contain the following p a r t i c u l a r s : . e) Date and place of sampling; bJ Possible size of stocks from, which the sheets or boards are taken; c) Number and date of production of the boards or sheets belonging to the specimens taken at random; d) Particulars of how the sample sheets or boards were marked by the person selecting them; e; A statement to the effect that the specimen vas selected at random; f ) Fames'of persons present during selection of the specimen; g) Ko'ces on t-sstiag and evaluation of records from own supervision. The report s h a l l be submitted to the competent material testing i n s t i t u t e together with the specimen taken at random. N o t e : The fol lowing material tes t ing i n s t i t u t e s (shown i n a lphabet ica l order) are et present ava i l ab le for supervis ion t e s t i n g : Bayerische landesgewerbeanstalt, Niirnberg 2, Gewerbemuseuraplatz 2 Bundesforeehungsanstolt fiir For s t - und Holzwirtschaft , Heinbek be i Hamburg, Schlofl Bundesanstalt fi:r Kate r i a l priif ung (BAM), B e r l i n 5^ (Dahlem), Unter den Eichen 87 Forsehungsinst i tut fur Holz 'erks to f fe und Holzle ime, Karlsruhe-Durlach, Dieselstrafle 6 Forschungs- uod Materialprufungsamt fur das Bauwesen - Otto-Graf-In&titut - , S tut tgar t-Vaihiagen, Robert- ieieht-StraBe 209 I n s t i t u t fur Baustoffkunde und Stahlbeton der Technischen Hochschule Braunschweig, A n t l i c h e Katerialpru'funr;sanstalt fiir das Bauwesen, Braunschweig, BeethovenstraBe \u00E2\u0080\u009E , I n s t i t u t fiir Flugzeugbau und Leichtbau, Technische Hochschule Braunschweig, Braunschweig, Langer Kamp I9t> I n s t i t u t fiir Eolzforschung und Holzteehnik der Univers i ta t Kiinchen, Kiinchen 13, Winterers trade *\u00C2\u00BB5 I n s t i t u t fiir Katerialprufung und Foroehung des Bauwe6ens der Technischen Hochschule Hannover -.Ant l iche Katerialpri i fungsanstalt fur das Bauwesen, Hannover, iiienburger StraBe 3 Staa t l i cbe Katerialpri i fungsanstalt Darmstadt an der Technischen Hochschule Darmstadt S taa t l i cbes Katerialprufungsant Nordi-hein-tfestf a l e n , Dortmund-Aplerbeck, MarsbruchstraBe 186 Versuehsanatalt fur S t a h l , Holz und Steine - Katerialpri i fungsanstalt der Technischen Hochschule Kar l s ruhe , Karlsruhe, XaiserstraQe 12 ttllhelm-Klauditz-Institut fiir Eolzforschuag as der Technischen Hochschule Braunschweig, Braunschwelg-Kra lenr iede , Bienroder weg 51* * State tes t ing i n s t i t u t e s abroad can undertake qua l i ty supervis ion tes t ings i n cooperation 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 o w n s u p e r v i s i o n Vhen sanplir.-- according to S\u00C2\u00ABction 5.2.1 records of own supervision mentioned i n Section 5.1.2 s h a l l be tested. Designation rlywood'\"eheeus or boards in 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 side. C rher s.tnndr'rd.-\u00C2\u00BB *-C, o Weed, v.ood t u t o r i a l s and laminated boards; definitions and symbols Sri: *07\u00C2\u00A3 Tiyvco.-!; dir.cncions DIK 5001^ Tec^iri-;, of cart-rials, structural \u00E2\u0080\u00A2 components and equipment; standard climates Dili 51220 f.aterial testing machines; d e f i n i t i o n , general directions, c l a s s i f i c a t i o n DI\u00C2\u00AB 51221 Sheet 1 Tensile testing machines; general requirements Sheet 5 Tensile testing machines; small tensile testing machines (at present s t i l l c i r c u l a t i n g as draft) Dili 52153 Testin.-r of v.ocd; determination of moisture content DIN 53251 Testing of wood glues and wood bondings, determination of bonding strenjth; general directions DIH 53255 Testing of wood glues and wood bondings, determination of bonding strength of plywood bondings (veneer boards and blockboards) i n the t e n s i l e teBt and knife test BIN 66330 Veneers; definitions - - \u00E2\u0080\u00A2 DIN 68705 Sheet 2 Plywood f o r general purposes; quality conditions Sheet 3 Plywood; veneer boards for building, quality conditions Sheet 4 Plywood; building blockboarda, quality conditions (at 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 -159-Explanations Standard DIN 6 8 7 0 5 has been separated into several standard sheets and extended because a s ing le standard oheet con be adapted note ea s i ly to the l a t e s t s tate of technica l developments i n view o f the considerably wider f i e ld s of a p p l i c a t i o n . DIN 68705 Sheet 1 contains the general bases for plywood ouch as d e f i n i t i o n s , requireoenta, te s t ing spec i f i ca t ions and ins t ruc t ions for safeguarding q u a l i t y . DIN 63705 Sheet 2 contains the qua l i ty conditions for plywood U B e d for general purposes, i . e . mainly with regard to plywood used for furni ture , i n t e r i o r decoration of rooms and for pane l l ing i n a l l f i e l d s o f app l i ca t ion not subject to s t a t i c s t re s s . The qunl i ty requirements for these sheets or boards c h i e f l y cover bonding of the sheets and grading of the covering veneers. DIN 68705 Sheet 3 contains the q u a l i t y condit ions for veneer boards and DIN 68705 Sheet k (at present s t i l l c i r c u l a t i n g as draft) the qua l i ty conditions for b u i l d i n g blackboards. This Standard appl ies to plywood s p e c i a l l y su i tab le for use i n bu i ld ing by reason o f i t s cons t ruct ion , veneer thicknesses and types of wood. CJ o o-1: _> \u00E2\u0080\u00A2j c '5> _o o CJ VI 5 u ' c c t, Q a c o ,, 1 o IA '\u00E2\u0080\u00A2\"JE o ~j \u00C2\u00A3 (!)\u00E2\u0080\u00A2*. _-' *it u \u00C2\u00BB k 5 \u00E2\u0080\u0094 T 1. o b a t> o -U CD \"5 O e z unc 67^-419. DEUTSCHE NORMEN Plywood Veneer Boards for Building Quality Condition Sperrholz; Bau-Furnierplatten, Giitebedingungen o n Scooe This Standard applies to veneer boarda used for building; in general they shall he unsanded. Dili 68705 Sheet 2 applies to building plywood used for panellings. 2. Definitions d V e n e e r b o a r d u s e d f o r b u i particularly suitable for building applications. For further definitions, see DIN 68705 Sheet 1. 1 d i n g (synbol BFU), veneer board 3. Requirenents ^.1.^Covering veneers.and_under_veneers 3.1.1. T y p e s o'f w o o d The covering and under veneers of veneer boards used in 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. In view of their lower weather resistance, veneers made of Obeche, Ilonba, Samba and Wawa shall be inadmissible. o Z E o 1 a a - 5 3 O \u00E2\u0080\u00A26 o Z I 3.1.2. Q u a l i t y r e q u i r e m e n t s n The following are permissible: 3 Wood discolourations and colour faults provided they do not impair the stability of the veneers, jj Joints with slight faults only in the case of boards consisting of five and raore plies of veneer s Cracks, isolated, up to 3 ma wide in boards consisting of three plies of the veneer, up to 5. ma 4 wide in boards consisting of five and^more plies of veneer 3 isolated, completely intergrown knots and knot places up to 25 ma diameter in boards consisting of three plies of veneer, up to 60 mm diameter in board? consisting of five and more plies 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\u00C2\u00AB7 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 for the veneer board. Adhesive tapes which impair bonding stability shall be inadmissible. 2-2i_Cores 3.2.1. T y p e s o f w o o d A l l the types of wood mentioned in Section 3.1.1 can be used for cores (inner layers of veneer) regardless of the types of wood used for covering and under veneers, with the exception of Obeche, Ilomba, Samba and Wawa, provided quality specifications with regard to stability are satisfied. 3.2.2. Q u a l i t y r e q u i r e m e n t Board thickness No. of p l i e s up to 8 3 o v e r 8 to 1 5 5 O T e r 1 5 to 2 2 ' 7 o v e r 2 2 to 2 9 9 5 \u00E2\u0080\u00A2 m i The inner plies of veneer must satisfy requirements for 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 plies 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 stability are inadmissible. 3-3- Board structure Boards must be built 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 for the board thick-nesses listed below: The bonding of the veneer boards specified i n this 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 add i t ion to these bondings veneer boards Bay a l so be produced by the IW 67 oethod o f bonding. 3.5i_Bond_strength (quality limits) Bond strength must be at T o a s t 10 V-^/Cn2. at least.8 kp/cm2 in the case of inside veneers I consisting of coniferous woods. Those limiting values referto 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 limit. ^.. Hhndinff o^T^nerfrVj ^\"v.?.lity limits) Longitudinal bending strength must be at least 400 kp/cmc 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\u00C2\u00AB three average values for the boards may be more than 10 % below the limit. Continued on pages 2 and 3 Vpce 2 DIN 68705 Sheet 3 -161-2-7. niricnsi2Qs_S-I^_2\u00C2\u00A3IEi55i^l\u00C2\u00A3_Y2EiS*i2!12 Dili 4073 applies to length and width. 2.8i_Hoisture_content_ \u00E2\u0080\u00A2 The moisture content of veneer boards for building according to this Standard should be at least 6 c/i related to the kiln-dried weight. 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 plant pests i s no greater than that o f the types of wood employed. When using plywood i n bu i ld ing necessary steps must therefore 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 protect ion against moisture, regardless of the type of bonding (see also DIN 68800). When using wood preservatives care should be taken to see that they are compatible with the binders used. a. Testing ^.i^^ondin^ (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. . > if \"> ., \u00C2\u00AB\u00C2\u00BB-Vl. J' p r o d u a X .... P S 5 1 - 7 1 ,'.S>\" iC I I c Iv .... j f t S g g & j ^ ^ * \u00E2\u0080\u00A2 -165-UNITED STATES DEPARTMENT OF COMMERCE . Maurice 11. Stans, Secretary NATIONAL BUREAU OF STANDARDS \u00E2\u0080\u00A2 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\u00C2\u00BB describe the quality aspects of tin-product 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 and decorative; softwood plywood, decorative; veneer grades, decorative softwood and hardwood. 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'\u00C2\u00BB (Order by SD Catalog No. 03.20/2:51-71). Price 30 cent*. -166-Contents 1. Purpose \" \u00E2\u0080\u0094\u00E2\u0080\u00A2. 1 I. 1. Purpose : '- ' \u00E2\u0080\u0094 * 1 l b t e n d e d use \u00E2\u0080\u00A2 * 2. Scope ami Classification . : . 1 2.1. Scope . 1 \u00E2\u0080\u00A22.2. Classification , : : 1 2:2.3. Species - \u00E2\u0080\u00A2 '. : 1 2.2.2. Grades \u00C2\u00ABf vt-neers . 1 '2:2.3. Tyi-es of plywood - 1 2.2.4. C\u00C2\u00BBnsim\u00C2\u00BB-ii\"r;.5 > 1 II. 1'..\". Sizes jui'l '.hhl\u00C2\u00AB . \u00E2\u0080\u00A2 \u00E2\u0080\u0094 1 3. Ueo.uirvtncnt* \u00E2\u0080\u00A2- = \u00E2\u0080\u0094 \u00E2\u0080\u00A2 1 1. r\u00C2\u00BBen\u00C2\u00AB*rnl 1 3 2. Spn i<\u00E2\u0080\u00A2 \u00C2\u00AB for f t w , l i M c k s . ami inner plies . \u00E2\u0080\u0094 2 3.2.1. Slnties W:i-?pi>ries . 2 3.3. Veneer crade descriptions \u00E2\u0080\u0094 2 3.3.3. Premium erode (A) - 2 3.3.2. <5\"'Ml sTaclr U) \u00E2\u0080\u00A2 4 :;.:'..3. Sound prude (2) : : -_- . 4 3.3.-1. Utility ;:rnde (3) \u00E2\u0080\u00A2 4 3.3..1. Biu-kinc crane <4) 4 3.3. C. Specialty grade (SP) - 4 3.3.7. Softwood reneers \u00E2\u0080\u00A2 4 3.4. Thickness of veneers _ . \u00E2\u0080\u0094 _ _ \u00E2\u0080\u0094 4 o.\">. Lumber cores 4 3..1.1. Clear grade . . . 4 3..1.2. Sound crade \u00E2\u0080\u0094 . 4 3.0.3. Regular grade ; 6 3..\"..4. Clear edge \u00E2\u0080\u00A2 6 3.\"i.\"i. Banded core 6 3.C.. Parriclebonrd ond/hnrdboarri cores ' , G 3.7. Special cores - 6 3.5. Construction : \u00E2\u0080\u00A2 6 3.5.1. Special construction 7 3.0. Glue bond requirements 7 3.0.1. Technical Typo plywood 7 3.0.2. Type I plywood 7 3.0. 3. Type IT piywood . 7 3!'. t. Type II r plywood 7 3.10. Dimensions and tolerances \u00E2\u0080\u00A2- 7 3.10.1. Squareness \u00E2\u0080\u0094 1 3.10.2. Straichtness . 7 3.11. Snmlin? : 7 3.12. Moisture content '. 8 3.13. Factory finished panels 8 3.14. Marking ; \u00E2\u0080\u0094 _ 8 4. Inspection and Test Procedures . 8 4.1. General 8 4.2. Specimens for clue bond test ; - 1 8 4.2.1. Technical and Type I plywood 8 4.2.2. Type 11 plywood - 8 -1.2.3. Typo III plywood 8 4.3. Dry shear test 8 4.4. Cyclic-boil shenr test 9 4..\". Three-cycle s=nak test . \u00E2\u0080\u0094 '. \u00E2\u0080\u0094. 4.C Twtwycle son): trst - - - - - \u00E2\u0080\u0094 9 1.7. Moislnrc roriif.it test . .\u00E2\u0080\u0094 9 IVfuiitionsi \u00E2\u0080\u0094 iV Tiicntlfi'-ati\"\" 7. Ms:.ilifiotl lnspii-ti'ia ami T-.'stinj: Acency S. I'.tTociiTc 11nr\u00C2\u00BB. 0. Tlisf.-ry of l'roifvr 10 Ptanuiiis Cmiiiiiif'-e , \u00E2\u0080\u0094 1. Acceptors . \u00E2\u0080\u0094 \u00E2\u0080\u0094 \u00E2\u0080\u0094 Appendix \u00E2\u0080\u0094 : III 10 11 11 12 12 12 12 15 -167-V O L U N T A R Y P R O D U C T S T A N D A R D S 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 marking 'Hie objective of a Voluntary Product Standard is to establish requirements which \u00E2\u0080\u00A2 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 The 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 ap-propriate 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, distribu-tors, and users or consumers; (5) seeks satisfactory adjustment of valid points of disagree-ment; (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 Stand-ards, \"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, dis-tributors, 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. When the acceptances show general industry agreement, and when there is no substantive objec-tion 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. When 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 dis-tributors. Purchasers may order products that comply with Voluntary Product Standards and determine for themselves that their requirements are met. Manufacturers and distribu-tors 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 \u00E2\u0080\u0094 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 de-veloped under the Procedure* for the Development of Voluntary Product Standards, published by the U.S. Department of Commerce, as a revision of Commercial Standard CS 35-61, Hardwood Plytrood.-See Section 9, History of Project, for futher information.) . 1. PURPOSE 1.1. Purpose\u00E2\u0080\u0094The purpose of this Voluntary Product Standard is to establish nationally rec-ognized 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 hard-woods: however, certain softwood species are also used.1 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. 1.2. Intended use\u00E2\u0080\u0094The 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, con-tainers, and specialty products; and for marine applications.2 2. SCOPE AND CLASSIFICATION ?..L Scope\u00E2\u0080\u0094This Voluntary Product Stand-ard covers the principal types, grades, and con-structions of plywood made primarily with hard-wood faces. Included are requirements for wood species and veneer grading: for lumber, particle-board, 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 prod-ucts that conform to this Standard are included. 22. Classification\u00E2\u0080\u0094Plywood 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\u00E2\u0080\u0094The grades of ve-1 Th is Vnlnr tnrT rrn-iuct Stnndar.1 \u00C2\u00ABl*o Includes oertnln \u00E2\u0080\u00A2orotif* *ofnv\u00C2\u00ABort sp-rir.; fo r nnnconsfrnction Constrmr-..011 crnrt**? of \u00C2\u00ABoftiv.M*il nnt l hnrdwr . o t l pl.vtv.wnl nrc covered In the l. i|i\"-t rrtltlon i-f V\u00C2\u00AB.Iuntnr.v Prodm-t Sinmlnri l P S 1-Cfi. P o / f f o O ' / Pfyiro.x/. Construction nnil / f iVhi. ' rci / . 1 Ariri lt lnnnl product Information in IITIIII.IMP from th# Hnrd-wood Plywood Mi i i i i i f ; icnir . ' r i Atxnrlnt lon, 2310 S. Walter Reed Dr\rt. Ar l ington. Y l r c ln ln 22200. neers are listed below with the identification symbol for each grade: Premium grade (A) (1) Good grade Sound grade Utility grade Backing grade Specialty grade (2) (3) (4) (SP) 2.2.3. Typos of plyv/ood\u00E2\u0080\u0094The types of ply-wood are listed below in descending order of water-resistance, capability. (See table 5.) Technical \u00E2\u0080\u0094 (Exterior) Type I \u00E2\u0080\u00A2 \u00E2\u0080\u0094 (Exterior) Type II -\u00E2\u0080\u0094 (Interior) Type III \u00E2\u0080\u0094 (Interior)-2.2.4. Constructions \u00E2\u0080\u0094 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) Hardwood lumber core (3-ply, 5-ply, and 7-ply) Softwood lumber core (3-ply, 5-ply, and 7-ply) Particleboard core (3-ply and 5-ply) Hardboard core (3-ply) Special core (3-ply or more) 3. 5. 6. 7. 22.5. Sizes and thicknesses\u00E2\u0080\u0094Most combina-tions of length, width, and thickness are avail-able. 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 rang-ing from % to % inch. 3. REQUIREMENTS . 3.1. General\u00E2\u0080\u0094Products represented as com-plying with this Voluntary Product Standard shall meet all of the requirements specified here-in. Terms used in this Standard shall be as de-fined in section 5. 3.2. Species for faces, backs, and inner plies \u00E2\u0080\u0094The species for the face shall be any hardwood species, and if used for decorative faces, anv softwood species listed in table 1 may be used. The panels shall be identified by the species of 1 -169-the fare (sec The, species of the. buck und tlie inner plies msiy be any hardwood or soft-wood species. TABLE 1. Cat.itjories of commonly uird specie.) bused on specific gravity rmujei* as a face and when it consists of morn than one piece, it shall lie edge-matched aj outlined in Category-C Cate^.iry A species Category B specie* 1 species (0.5'J \u00C2\u00BBr more (O.-ia Ihroush 0.55 10.1-- or less speoifie gravity) specific gravity) | speeilie gravity Ash. Commercial 1 Asb, Black ] Alder, Red White ' .Wo-lire lAspcu P.eevb, American Bay Basswood, Birch, Yellow, Ce .inches for Category A species (see 3.2.1), 3 inches for Category B species, and 4 inches for Category C species. Core grades and core band-ing 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 sand-ing. . 3.5.1. Cl e a r g r a d e \u00E2\u0080\u0094 T h e wood strips shall be fu l l length or finger-jointed and shall be free of knots or other defects which would not properly shape or mold, except that discolorations will be permitted. Wood patches or plugs shall not be used, but wood filler will be permitted. 3-5^. Sound g r a d e \u00E2\u0080\u0094 T h e wood strips shall be f u l l length or finger-jointed and shall be free 4 T A U L K 4. Bvmmery of veneer characterise* and allcxal. JecU for Premium grade and Ooad P r o d ; decorative ioftwood tpeclcs Characteris t ics Discolorat ion Hur ls Knots I ' ln knots KlMlllll kllols Hplke knots F i l l ed knot holes ' Worm holes Open splits or jolntu 1)117.0 Rough cut Inconspicuous patches Pi tch streaks P i tch pockets Crow's foot JIatcl i ing R o t a r y \u00E2\u0080\u0094 Sliced \u00E2\u0080\u0094 Knot ty Ve. . Western Premium ( A ) No Yes Yes Yes Sl ight 94 m. No No No No Smal l Ema i l No Sl ight a or c Goor. (1) Whi te pine Premium ( A ) S l igh t Yes Yes Yes . Yes* Iv4 i n . No No No Inconspicuous Yes S m a l l S n a i l Occasional a o r e No Yes Yes Yes Slight % in . No No No . No Smal l Smal l No No a o r e Gcou (1) Slight Yes Yes Yes Yes\" 1V4 in . No No No Inconspicuous Yes Smal l Smal l N o a o r e Sliced \u00E2\u0080\u0094 Ver t ica l grain Characteristics S&i>WGG0 Percent* 25 10 10 Percent* CO 30 . 15 \u00E2\u0080\u00A2 T h e v Talues are the percentage of wood area remaining a i l h T f d to the fractured inr facc In tbc test area. hnrdwood face veneers on softwood inner plies '\u00E2\u0080\u00A2all also comply with the Exterior Type bond piirements specified in Voluntary Product otandard PS l-Gfi. Softwood Plytoood, Construc-tion and Industrial.* \u00C2\u00AB 8\u00C2\u00ABe footnote 3, page 6. 3.9.2. Type I plywood \u00E2\u0080\u0094 The glue bond of Type I plywood shall meet the same require-ments as Technical Type. 3.9.3. Type II plywood\u00E2\u0080\u0094The 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 \u00E2\u0080\u0094 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\u00E2\u0080\u0094The nom-inal dimensions of the plywood panels shall be as agreed upon between buyer and seller. The for the nominal dimensions shall be tolerances as follows Width: Length: Thickness: Unsanded Sanded: plus or minus 1/32 in plus or minus 1/32 in plus or minus 1/32 in 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 thickness of 14 i n o r more. .Vote: One inch equals 2.54 centimeters. 3.10.1. Squareness\u00E2\u0080\u0094Panels 4 feet by 4 feet or larger shall be square, within 3/32 inch.-Panels less than 4 feet in length or width shall be square within 1/1G inch. Squareness shall be de-length of the two termined by measuring the diagonals of the panel. 3.10.2. StraiRhtness\u00E2\u0080\u0094The edges of panels less than 8 feet long shall be such that a straight line from one corner to the adjacent corner shall fall within 1/10 inch of the panel edge. A de-parture of 3/32 inch will be permitted for panels 8 feet long and longer. 3.11. Sanding\u00E2\u0080\u0094-The. types of sanding shall be os described below. The type of sanding and the 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 \u00E2\u0080\u00A2 in handling the plywood during shipment or storage may require further sanding. No sanding\u00E2\u0080\u0094Surfaces need not be sanded nor tape removed. Ttough sanding\u00E2\u0080\u0094Sanding hit-or-miss. Tape re-moval is not required. Regular sanding\u00E2\u0080\u0094Surfaces shall be clean and free of tape. Sander streaks are not consid-ered defects. Polish sanding\u00E2\u0080\u0094Surfaces shall be clean and smoothly sanded. 3.12. Moisture content\u00E2\u0080\u0094The moisture con-tent of plywood panels at the time of shipment from the producing mill shall not exceed 12 per-cent of the ovendry weight, as determined an ac-cordance with 4.7. 3.13. Factory finished panels\u00E2\u0080\u0094The finish of factory finished panels shall be as agreed upon between buyer and seller. 3.14. Mark ing\u00E2\u0080\u0094Al 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 sym-bol of this Sandarcl, PS 51-71, the name or rec-ognized identification of the producer; the'species and grade of the face veneer; the type of ply-wood; 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 accom-panied by a written certification which states that the panels conform to all of the require-ments 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 ap-plicable (see section 7); and the specific intended use if container plywood. 4. INSPECTION AND TEST PROCEDURES 4.1. General\u00E2\u0080\u0094The inspection and test pro-cedures contained in this section are to be used to determine the conformance of products to the requirements of this Voluntary Product Stand-ard. 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 manufactur-ing process but shall keep such essential records as are necessary to document with a high degree of assurance his claim that all of the require-ments of this Standard have been met. Addition-al sampling and testing of the product, as may be agreed upon between purchaser and seller, is not precluded by this section. 4.2. Specimens for glue bond test\u00E2\u0080\u0094 4.2.1. Technical and Type I plywood \u00E2\u0080\u0094 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\u00E2\u0080\u0094A 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\u00E2\u0080\u0094-Three test speci-mens shall be cut from each panel selected: one from each end of the panel and one near the cen-ter of the panel (see table 7). TABLE 7. Test specimen sizes Type of plywood Specimen size Technical & Type I 3'A inch* by 1-inch specimens Type II (3-cycle) 5-inchb by 2-incb spccivuei;.-Type III (2-cyclc) G-inch by 6-inch specimens' a Parallel to the pniln of the outside venders In 7-. and l l - p ! y construction. Perpendicular to the grain of the outside veneers In 0- nnd !>-piy construction. The 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\u00E2\u0080\u0094Shear 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 speci-mens to insure that half of the lathe checks are \"pulled in tension and half are pulled in compres-sion, is described in American Society for Test-ing and Materials (ASTM) f) f>06-64, Stond.'rd Method of Test for Strength Properties of Ad-hesives in Plywood Type Constructio-n in Shtor by Tension Looding.* If the number of plies ex-ceeds three, the outer pairs of glue lines and in-nermost 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\u00C2\u00B0 1 square inch, as shown in figure 3. specimen A. Specimens of plywood with face plies 1/1R inch \u00E2\u0080\u00A2 L a t e r Issues of this publication may be u\u00C2\u00BBed providing the requirements ure applicable and ronalstent with the Issue de-dt--nnted. Copies of A S T M publication* are obtalnuble from the American Society for Test Inn and Materials. 191B Kace Street, Philadelphia, Pennsylvania 10103. 8 CUT 2/3 THROUGH CORE SPECIMEN A CUT 2 / 3 THROUGH CORE S P E C I M E N 8 FIOUBE 3. Plywood bond shear test specimens. or less in thickness shall be of the form shown in figure 3. speci.ntn B. in which the shear area shall be reduced to ty square inch without chang-ing 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 lum-r core plywood, particleboard core plywood, \u00C2\u00ABnd hardboard cove plywood, the core shall be cut away to 1/10 inch in thickness. \u00E2\u0080\u00A21.1. tyclic-boil uhear test \u00E2\u0080\u0094The specimens prepared as shown in figure 3 shall be boiled in water for 4 honi-s and then dried for 20 hours at a temperature of 145\u00C2\u00B15 \u00C2\u00B0F (63\u00C2\u00B13 \u00C2\u00B0C). They shall be boiled again for 4 hours, cooled in water, and then subjected while wet to the test described in 4.3. The values obtained from the six speci-mens shall meet the applicable requirements given in 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 soak test\u00E2\u0080\u0094The 5-inch by 2-inch specimens from eacli test panel shall be submerged in water at 75 = 5 \u00C2\u00B0F (24\u00C2\u00B13 \u00C2\u00B0C) for 4 hours and then dried at a temperature between 120 and 125 r F f4f' to 52 C C) for 10 hours with SufiioK-nt air 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 rvclfS 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 , l c M m 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 per-mitted by the grade shall be disregarded. Nine of the 10 specimens shall pass the first cycle and eight of the 10 specimens shall pass the third cycle. 4.6. Two-cycle soak test\u00E2\u0080\u0094The 6-inch by 6-inch specimens shall be submerged in water at 75 \u00C2\u00B1 5 \u00C2\u00B0F (24 \u00C2\u00B1 3 \u00C2\u00B0C) for 4. hours, and then dried at 75 \u00C2\u00B1 5 \u00C2\u00B0F 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 con-sidered as failing when any single delamination between two plies is greater than 2 inches in con-tinuous length, over Vi m depth at any point and 0.003 inch in width. Separation is de-termined with a 0.003-inch feeler gage. When this test is applied to lumber core or particle-boar;! 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. 4.7. Moisture content test \u00E2\u0080\u0094 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 \u00C2\u00B0F (100 to 105 \u00C2\u00B0C) 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: Orlclnnl weight \u00E2\u0080\u0094 o T m d r r weight x 1 0 0 = MoUture content Ovendry weight . {percent) 9 177 APPENDIX 5 The mixing sequence of the PF IB-334yGlue. 179 c . c . VJ.B. Smith Mr. F. Alan Tayelor, I n d u s t r i a l Development O f f i c e r , August 9, 1974 VANCOUVER, B.C. Dear Nr. Tayelor: B i l l Hancock has requested that I forward d e t a i l s on the glue aix we prepared f o r use in bonding veneer f o r ladder stock at our lab. The mixes r/.ade August 8th vjere formulated a3 follows: IB-33 4 Plyophen Water K'orprof i l Wheat Flour Soda Ash 5,872 gxas 1,781 gxas 93D RTP.S 900 gms *\u00C2\u00BB00 gns Mix 30 minutes on Bower Mixer at 4000 rpn IB-334 Plyophen Jater 8,985 gas 1,13? gras 20,000 gms Total piv. s o l i d s : 4 3.8% Phenol Formaldehyde s o l i d s : 26.0% Vis c o s i t y 3 25\u00C2\u00B0C \u00C2\u00A33 spindle 60 rpsi LVF Brookfield - 1350 cps This nix d i f f e r s fron a standard plywood mix on two points. F i r s t , the PF so l i d s are higher by approximately 3% - 26% as oppos-sd to 23%. Secondly, there i s twice the concentration of wheat f l o u r in t h i s nix as i n the average plywood mix. This formulation and r e s i n has previously been successfully used i n veneer laminating and appears to display the assembly ti n e tolerance required by the process. Should further assistance be required, please contact me. Yours very t r u l y , REICIIHOLD CHEMICALS LIMITED W. C. A i n s l i e , Wood Lab. Manager \u00E2\u0080\u00A2 V/CA/jia c.c. Dr. y. V. Hancock [to APPENDIX 6 The mixing sequence of the Monsanto UF 109 Glue. (8.1 M O N S A N T O UF109 R E S I N W I T H E K H A R D E N E R Mi x i n g D i r e c t i o n s 100 l b s . \u00C2\u00A35.43 15 l b s . o-<*'AZ \ lb. 100 l b s . 40 l b s . 6-S \"f739 Sff S7/4 90 lbs. _ji\u00C2\u00A3L\u00E2\u0080\u0094 345^ lbs.-i-6'S W A T E R at 65\u00C2\u00B0 - 70\u00C2\u00B0 F . M O N S A N T O E K C A T A L Y S T M i x 1 Minute S T E R O X C D W H E A T F L O U R M i x 5 Minutes o r U n t i l L u m p F r e e M O N S A N T O U F 1 0 9 R E S I N M i x 3 Minutes or U n t i l L ump F r e e M O N S A N T O U F 1 0 9 R E S I N M i x 5 Minutes with C o o l i n g Water i n J a c k e t T o t a l Weight of M i x The m i x e d glue w i l l have a working l i f e of 24 hours at 70\u00C2\u00B0 F . M i x e d glue left overnight should be m i x e d with a f r e s h batch before using. * The length of the m i x i n g time p r i o r to the addition of the r e s i n w i l l affect 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 w i l l reduce the v i s c o s i t y . ) HARDWOOD HOT PRESSING SCHEDULE* 0 UF-109 RESIN WITH EK HARDENER Si \ \) I } ) \u00E2\u0080\u0094 r \u00E2\u0080\u0094 P a nels Max. Di s t . p'SS No. ot per \u00C2\u00ABo!\u00C2\u00BBex Construction Center Time Settings F o r Press Time - Mins. 240\u00C2\u00B0 F. 260\u00C2\u00B0 F. 3/16 1/4 1/4 1/4* 3/S 1/2 1/2 3/4 3/4 3/4 O 3/4 3/4 183 , 208 . 207 .063 . 138 .181 . 136 .326 .329 .352 . 138 163 1/7H 1/6M 1/7H 1/6 or 1/7 1/10M 2xl/7H 1/10M 3xl/7H lxl/7H 1x1/ 10M 1/10 1/8 1/7H 1/7H . 262B Plywood 2xl/7H 2x3/16H 2xl/7H 1/2 Plywood 1/2 Plywood 5-1/4 5-1/2 5-3/4 3- 3/4 4- 3/4 6 5- 1/4 8-1/4 8-1/4 8-3/4 5-1/4 5-1/2 4- 3/4 5 5- 1/4 3- 1/4 4- 1/4 5- 1/2 4-i,'4 7-3/4 7- 3/4 8- 1/4 4-3/4 5 \u00C2\u00BB>' plus 1/2 min. for each additional 1/16 over the 3/4 . S OVERLAYS 1/4 with. 1/6 chipboard center - 2 panels per 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 or chipboard center 3-3/4 ABOVE TIME INCLUDE 15 SECS. CLOSING TIME AND 15 SECS. FOR CAULS. S P R E A D S Hemlock 62 , 1/10 \ ) 1/7 65 1/6 67 ^ Rough core add 3 to D lbs. Mahogany \" 57 60 62 Maximum recommended time assembly. Minimum recommended time assembly 8 hours 5 mins. \u00E2\u0080\u00A2 Note: Pressure 175 lbs. per square inch. Pressure with chipboard 150-160 lbs. per sq. xn. r e d u c e the press temperature to 220\u00C2\u00B0F. add "@en . "Thesis/Dissertation"@en . "10.14288/1.0075419"@en . "eng"@en . "Forestry"@en . "Vancouver : University of British Columbia Library"@en . "University of British Columbia"@en . "For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use."@en . "Graduate"@en . "Peeling, gluing and bonding characteristics of Nigerian plantation-grown Gmelina arborea (Roxb.)"@en . "Text"@en . "http://hdl.handle.net/2429/20279"@en .