@prefix vivo: . @prefix edm: . @prefix ns0: . @prefix dcterms: . @prefix skos: . vivo:departmentOrSchool "Forestry, Faculty of"@en ; edm:dataProvider "DSpace"@en ; ns0:degreeCampus "UBCV"@en ; dcterms:creator "Chunsi, Khalid Salum"@en ; dcterms:issued "2011-03-16T20:51:42Z"@en, "1973"@en ; vivo:relatedDegree "Master of Forestry - MF"@en ; ns0:degreeGrantor "University of British Columbia"@en ; dcterms:description """The gluing properties of pyinkado (Xylia dolabriformis Benth.), thitya (Shorea obtusa Wall.), ingyin (Pentacme siamensis Kurz.), padauk (Pterocarpus macrocarpus Kurz.), in (Dipterocarpus tuberculatus Roxb.), and kanyin (Dipterocarpus sp.) from Burma were investigated. Three room temperature curing glues, phenol-resorcinol-formaldehyde (exterior), urea-formaldehyde (interior), and casein were used. Specific gravity, shrinkage, pH and extractive content were determined for each wood species and their influence on the gluing properties discussed. Block shear specimens for phenol-resorcinol-formaldehyde were tested dry, cold soak, boil and vacuum-pressure treated. Percent delamination was measured. Wood glued with urea-formaldehyde was tested dry and after cold soaking, whereas that glued with casein was only tested dry. In and kanyin (specific gravity 0.67 and 0.59, respectively) showed wood failure values above 90 percent and good shear strength with all the three glues. Pyinkado (specific gravity 0.75) showed high shear strength with all the three glues. It developed 81 percent wood failure with phenol-resorcinol-formaldehyde, 86 percent with urea-formaldehyde but only 22 percent wood failure with casein. Padauk (specific gravity 0.77) developed high shear strength with casein (2,709 psi), but slightly lower shear strength values with phenol-resorcinol formaldehyde (2,693 psi) and urea-formaldehyde (2,448 psi). It had 78 percent wood failure with phenol-resorcinol-formaldehyde and 87 percent with urea-formaldehyde but only 67 percent wood failure with casein. Ingyin and thitya (specific gravity 0.81 and 0.80, respectively) showed low shear strength and low wood failure percent with all the three glues. In and kanyin showed low percentage of extractives soluble in ether (1.8 and 1.3 percent, respectively), ethanol (0.5 and 1.4 percent, respectively), hot water (0.5 and 0.4 percent, respectively), and acetone (2.5 and 2.2 percent, respectively). No direct relationship was observed between percentage extractives in the solvents used and shear strength or gluability. If the influence of specific gravity is excluded, a trend of increase in glue joint strength with increase in wood pH was observed. The pH of the wood was from 4.47 to 5.09. The vacuum-pressure treatment reduced the dry shear strength of all species more so for in (37 percent) and kanyin (34 percent). All species, except ingyin and thitya, still showed high wood failure. High delamination percent was observed for pyinkado (22 percent), thitya (68 percent), and ingyin (34 percent), and low delamination for in (8 percent), kanyin (8 percent), and padauk (11 percent) with phenol-resorcinol-formaldehyde. The boil test was observed to reduce glue joint strength most for all species. The reduction was 57 percent for ingyin, 53 percent for in, 50 percent for kanyin, 30 percent for pyinkado and thitya, and 19 percent for padauk. Wood failure percent was high for all species except thitya and ingyin. Padauk, in and kanyin meet the requirements for exterior structural lamination with phenol-resorcinol-formaldehyde. Ingyin, thitya and pyinkado failed to meet the requirements. Padauk, pyinkado, ingyin, in and kanyin meet the minimum requirements for interior structural lamination with urea-formaldehyde. Kanyin, in and padauk are considered suitable for interior structural lamination with casein. Further study is recommended for ingyin, thitya, and pyinkado for gluing with phenol-resorcinol-formaldehyde for exterior structural lamination; pyinkado, ingyin and thitya for gluing with casein; and thitya for gluing with urea-formaldehyde for interior structural lamination."""@en ; edm:aggregatedCHO "https://circle.library.ubc.ca/rest/handle/2429/32519?expand=metadata"@en ; skos:note "THE GLUABILITY OF CERTAIN HARDWOODS FROM BURMA by KHALID SALUM CHUNSI Sc. (Hons) Forestry, University of Wales 1969 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF FORESTRY in the Department of Forestry We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA June, 1973 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make i t freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Khalid Sal urn Chunsi Department of Forestry The University of British Columbia Vancouver 8, Canada Date June 20, 1973 ABSTRACT The gluing properties of pyinkado (Xylia dolabriformis Benth.), thitya (Shorea obtusa Wall.), ingyin (Pentacme siamensis Kurz.), padauk (Pterocarpus macrocarpus Kurz.), in (Dipterocarpus tuberculatus Roxb.), and kanyin (Dipterocarpus sp.) from Burma were investigated. Three room temperature curing glues, phenol-resorcinolQformaldehyde (exterior), urea-formaldehyde (interior), and casein were used. Specific gravity, shrinkage, pH and extractive content were determined for each wood species and their influence on the gluing properties discussed. Block shear specimens for phenol-resorcinol-formaldehyde were tested dry, cold soak, boil and vacuum-pressure treated. Percent delamination was measured. Wood glued with urea-formaldehyde was tested dry and after cold soaking, whereas that glued with casein was only tested dry. In and kanyin (specific gravity 0.67 and 0.59, respectively) showed wood failure values above 90 percent and good shear strength with all the three glues. Pyinkado (specific gravity 0.75) showed high shear strength with all the three glues. It developed 81 percent wood failure with phenol-resorcinol-formaldehyde, 86 percent with urea-for-maldehyde but only 22 percent wood failure with casein. Padauk (specific gravity 0.77) developed high shear strength with casein (2,709 psi) , but slightly lower shear strength values with phenol-resorcinol formalde-hyde (2,693 psi) and urea-formaldehyde (2,448 psi). It had 78 percent i i i i i wood failure with phenol-resorcinol-formaldehyde and 87 percent with urea-formaldehyde but only 67 percent wood failure with casein. Ingyin and thitya (specific gravity 0.81 and 0.80, respectively) showed low shear strength and low wood failure percent with all the three glues. In and kanyin showed low percentage of extractives soluble in ether (1.8 and 1.3 percent, respectively), ethanol (0.5 and 1.4 percent, respectively), hot water (0.5 and 0.4 percent, respectively), and acetone (2.5 and 2.2 percent, respectively). No direct relationship was observed between percentage extractives in the solvents used and shear strength or gluability. If the influence of specific gravity is excluded, a trend of increase in glue joint strength with increase in wood pH was observed. The pH of the wood was from 4.47 to 5.09. The vacuum-pressure treatment reduced the dry shear strength of all species more so for in (37 percent) and kanyin (34 percent). All species, except ingyin and thitya, s t i l l showed high wood failure. High delamination percent was observed for pyinkado (22 percent), thitya (68 percent), and ingyin (34 percent), and low delamination for in (8 percent), kanyin (8 percent), and padauk (11 percent) with phenol-resorcinol-formaldehyde. The boil test was observed to reduce glue joint strength most for all species. The reduction was 57 percent for ingyin, 53 percent for in , 50 percent for kanyin, 30 percent for pyinkado and thitya, and 19 percent for padauk. Wood failure percent was high for all species except thitya and ingyin. Padauk, in and kanyin meet the requirements for exterior structural lamination with phenol-resorcinol-formaldehyde. Ingyin, thitya and pyinkado i v failed to meet the requirements. Padauk, pyinkado, ingyin, in and kanyin meet the minimum requirements for interior structural lamination with urea-formaldehyde. Kanyin, in and padauk are considered suitable for interior structural lamination with casein. Further study is recommended for ingyin, thitya, and pyinkado for gluing with phenol-resorcinol-for-maldehyde for exterior structural lamination; pyinkado, ingyin and thitya for gluing with casein; and thitya for gluing with urea-formaldehyde for interior structural lamination. TABLE OF CONTENTS Page ABSTRACT i i TABLE OF CONTENTS . . . • • v LIST OF TABLES xi LIST OF FIGURES xi i i ACKNOWLEDGEMENT xv INTRODUCTION • . . • \"1 1. Importance of Tropical Forests 1 2. Objective and Scope of the Study 3 LITERATURE REVIEW 5 1. Gluing, general 5 2. Specific Gravity . . . . 9 3. Effect of Extractives 12 4. Wettability 16 5. pH 19 6. Effect of Glue . . . . • 20 MATERIALS AND METHODS 23 1. Species . . . 23 2. Glues 24 2.1 Phenol-resorcinol-formaldehyde 24 2.2 Urea-formaldehyde 24 v vi Page 2.3 Casein 25 3. Experimental Procedure 25 3.1 Preliminary experiments . . 25 3.2 Main experiment gluing 26 3.2.1 Gluing with phenol-resorcinol-formaldehyde 27 3.2.2 Gluing with urea-formaldehyde 27 3.2.3 Gluing with casein 28 3.3 Specimen preparation 28 3.3.1 Block shear specimen . . 29 3.3.2 Delamination specimen 30 4. Testing Procedure . 30 4.1 Dry test , 30 4.2 Cold soak test 31 4.3 Boil test 31 4.4 Vacuum-pressure cyclic test 31 5. Determination of Specific Gravity and Shrinkage 33 5.1 Specific gravity 33 5.2 Volumetric shrinkage 33 5.3 Radial and tangential shrinkage 34 6. Extractive Content Determination 34 7. pH Determination 36 RESULTS 37 1. Basis of Judgement 37 2. Differences between Species within Glue 38 vii Page 2.1 Phenol-resorcinol-formaldehyde :,resin'adhesive 38 2.1.1 Dry test shear strength and wood failure 38 2.1.2 Cold soak test shear strength and percent wood failure . 39 2.1.3 Boil test shear strength and wood failure 40 2.1.4 Vacuum-pressure cyclic test shear strength, wood failure and percent delamination 40 2.2 Urea-formaldehyde resin adhesive 41 2.2.1 Dry test shear strength and wood failure 41 2.2.2 Cold soak test shear strength and wood failure 42 2.3 Casein glue 43 2.3.1 Dry test shear strength and wood failure 43 3. Variation within Species between Glues 44 3.1 Pyinkado 44 3.1.1 Dry test shear strength and wood failure 44 3.1.2 Cold soak test shear strength and wood failure 44 3.2 Thitya 45 3.2.1 Dry test shear strength and wood failure percent . . . . 45 3.2.2 Cold soak test shear strength and wood failure percent . 45 3.3 Ingyin 46 3.3.1 Dry test shear strength and wood failure percent . . . . 46 3.3.2 Cold soak test shear strength and wood failure percent . 46 3.4 Padauk 47 3.4.1 Dry test shear strength and wood failure percent . . . . 47 3.4.2 Cold soak test shear strength and wood failure percent . 47 3.5 In 47 vi i i Paoe 3.5.1 Dry test shear strength and wood failure percent . . . 47 3.5.2 Cold soak test shear strength and percent wood failure 48 3.6 Kanyin 48 3.6.1 Dry test shear strength and wood failure percent . . . 48 3.6.2 Cold soak test shear strength and wood failure percent 48 4. Effect of Treatment within Species 49 4.1 Phenol-resorcinol-formaldehyde adhesive 49 4.1.1 Pyinkado: Shear strength and wood failure percentage . 49 4.1.2 Thitya: Shear strength and wood ! failure percentage . 49 4.1.3 Ingyin: Shear strength and wood failure percentage . . 50 4.1.4 Padauk: Shear strength and wood failure percentage . . 50 4.1.5 In: Shear strength and wood failure percentage . . . . 50 4.1.6 Kanyin: Shear strength and wood failure percentage . . 51 4.2 Urea-formaldehyde adhesive 51 4.2.1 Pyinkado: Shear strength and wood failure percent . . 51 4.2.2 Thitya: Shear strength and wood failure percent . . . 51 4.2.3 Ingyin: Shear strength and wood failure percent . . . 52 4.2.4 Padauk: Shear strength and wood failure percent . . . 52 4.2.5 In: Shear strength and wood failure percent 52 4.2.6 Kanyin: Shear strength and wood failure percent . . . 52 5. Within Treatment between Species Variation 53 5.1 Phenol-resorcinol-formaldehyde: Shear strength and wood failure percent 53 5.2 Urea-formaldehyde adhesive: Shear strength and wood failure percent 54 ix Page 6. Specific Gravity 54 7. Radial, Tangential and Volumetric Shrinkage 55 8. pH 56 9. Extractives 56 9.1 Ether soluble extractives 56 9.2 Ethanol soluble extractives 57 9.3 Hot water soluble extractives 57 9.4 Acetone soluble extractives 57 DISCUSSION 58 1. Influence of Specific Gravity 58 1.1 Phenol-resorcinol-resin adhesive: Glue line dry shear strength and wood failure percent 58 1.2 Urea-formaldehyde resin adhesive: Glue line dry shear strength and wood failure percent 61 1.3 Casein: Glue line dry shear strength and wood failure percent 64 2. Influence of Extractives 67 2.1 Successive extraction . . . 71 2.1.1 Ether soluble extractives 71 2.1.2 Ethanol soluble extractives 72 2.1.3 Hot water soluble extractives 73 2.1.4 Total extract!ves= 73 2.2 Acetone soluble extractives 75 3. Influence of pH 77 4. Influence of Shrinkage on Shear Strength and Delamination 79 X Page 4.1 Shrinkage 79 4.2 Del ami nation percent 82 5. Comparison of Treatments 85 CONCLUSION 87 REFERENCES 91 APPENDIX 130 LIST OF TABLES Table Page 1 Moisture content change of wood during storage 96 2 Specific gravity, wood shear strength as tested and minimum acceptable glue line shear strength at 10 percent moisture content for the six Burmese woods . . . 97 3 Shear strength and wood failure of wood bonded with phenol-resorcinol-formaldehyde adhesive 98 4 Duncan's multiple range test for shear strength of laminated wood bonded with phenol-resorcinol-formaldehyde adhesive 100 5 Duncan's multiple range test for wood failure percent of wood bonded with phenol-resorcinol-formaldehyde \" '\\\\ adhesive 101 6 Percent delamination for wood bonded with phenol-resorcinol-formaldehyde adhesive and statistical comparison . . . . 102 7 Shear strength and wood failure of wood bonded with urea-formaldehyde adhesive 103 8 Statistical ranking by Duncan's test for shear strength and wood failure percent for wood bonded with urea-formaldehyde adhesive . . 104 9 Shear strength and wood failure percent for wood bonded with casein glue 105 10 Statistical ranking by Duncan's test for dry shear strength and wood failure percent of wood bonded with casein glue 106 11 Comparison of shear strength and wood failure percent for four treatments and three adhesives (urea-formaldehyde, phenol-resorcinol-formaldehyde and casein) 107 12 Specific gravity, shrinkage percent and green moisture content, as determined in the study of the six Burmese woods 108 xi xii Table Page 13 Statistical ranking of specific gravity of the six Burmese woods . . . 109 14 Average pH value for cold water extractions of the six Burmese woods . 110 15 Statistical ranking by pH for cold water extractions of the six Burmese woods Ill 16 Percentage of extractives soluble in ether, ethanol, hot water and acetone for the six Burmese woods . . . . 112 17 Statistical ranking by percentage of extractives soluble in ether, ethanol, water and acetone 113 LIST OF FIGURES Figure Page 1 Form and dimension of block shear test specimen 114 2 Shearing tool 115 3 Dry test shear strength and percent wood failure for wood bonded with phenol-resorcinol-formaldehyde resin adhesive 116 4 Cold soak shear strength and percent wood failure for wood glue with phenol-resorcinol-formaldehyde resin adhesive . . . 117 5 Boil test shear strength and percent wood failure for wood bonded with phenol-resorcinol-formaldehyde resin adhesive 118 6 Vacuum-pressure cyclic test shear strength and percent wood failure for wood glued with phenol-resorcinol-formaldehyde resin adhesive 119 7 Dry test shear strength and wood failure percent for wood glued with urea-formaldehyde resin adhesive . . . 120 8 Cold soak shear strength and wood failure percent for wood glued with urea-formaldehyde resin adhesive . . . 121 9 Dry test shear strength and percent wood failure for wood bonded with casein glue 122 10 Phenol-resorcinol-formaldehyde, urea-formaldehyde and casein dry test shear strength 123 11 Relationship between specific gravity and glue line dry shear strength for wood glued with phenol-resorcinol-formaldehyde resin adhesive 124 12 Relationship between specific gravity and glue line dry shear strength for wood glued with urea-formaldehyde resin adhesive 125 13 Relationship between specific gravity and glue line dry shear strength for wood glued with casein glue . . . . 126 xi i i xiv Figure Page 14 Relationship between pH of wood and glue line dry shear strength for wood glued with phenol-resorcinol-formaldehyde resin adhesive . . . 127 15 Relationship between pH of wood and glue line dry shear strength for wood glued with urea-formaldehyde resin adhesive 128 16 Relationship between pH of wood and glue line dry shear strength for wood glued with casein glue 129 ACKNOWLEDGEMENT The author wishes to express his gratitude to Dr. S.-Z Chow of the Western Forest Products Laboratory, Canadian Forestry Service, Vancouver and to Dr. R. W. Wellwood of the Faculty of Forestry without whose constant supervision and advice the study would not have been possible. Appreciation is also due to Mr. Henry N. Mukai of the Western Forest Products Laboratory for his help in the experimental work. The author is also grateful for being allowed to use the Forest Products Laboratory faci l i t ies. The author is greatly indebted to Canadian International Devel ment Agency both for financing the author's study in Canada and for providing the Burmese hardwoods used in the study. The author is also appreciative of the financial assistance obtained from the Faculty of Forestry, University of British Columbia. Thanks are also due to the Director of Forestry, Tanzania, for making i t possible for the author to study in Canada. xv INTRODUCTION 1. Importance of Tropical Forests Tropical forests (defined by climate) extend over 2,100 million ha.whereas temperate zone forests cover about 1 ,800 million ha. The world average is 1.6 ha. of forest land per capita while the tropics average 2 ha. of forest land per capita (Wangaard, 1966). Total broad leaved wood removals for 1967 for the world was 3 3 1,091 million m of which 771 million m was fuelwood and 320 million o m was industrial wood (Pringle, 1969). For temperate countries the 3 3 total removal was 451 million m of which 226 million m was fuelwood and 225 million was industrial wood. Broad leaved wood removals for 3 industrial use in the tropical countries amounted to 95 million m , 3 3 fuelwood 545 million m , making a total removal of 640 million m . Some tropical hardwoods are already well established in markets of the industrialized countries. For example 60 percent of the hardwood plywood consumed in the United States is imported and at least 90 percent of this is manufactured from lauan (Shorea, Parashorea and Pentacme spp.) timber of Southeast Asia (Stadelman, 1969). In 1967, the Philippines furnished 64 percent of Japan's imports of hardwood logs, as well as 80 percent of the logs imported by Korea. The Philippines produced a total of 3.3 bill ion bd. ft. of lauan in 1967, over 2.8 bill ion bd. ft. of which 1 2 was exported to Japan, Korea and Taiwan all in the form of logs. The lauan plywood produced by Japan, Korea and Taiwan was in turn exported, chiefly to the United States. There is a tremendous diversity in growth which is regarded as a vast reserve for man's utilization. The level of utilization of tropical forests is very low because of a number of factors, including: a) the fact that a substantial part of the forest is isolated from centres of population and is physically or economically inaccessible at present; b) the fact that innmany densely\"p'6pul:a'tedmparts\" o'f^the\"tropics the most accessible forests, have been rendered unproductive through over-cutting and abuse over long periods, in extreme cases to the point of conversion to barren land subject to erosion by wind and water; c) the fact that tropical forests are typically heterogenous and have a multiplicity of species, of which relatively few are currently marketable. This is a major limiting factor for their economic use. Under these circumstances, Wangaard (1966) reports that usable timber is actually scarce in many parts of the tropics; this, coupled with a low level of income, has resulted in a per capita consumption of processed or industrial wood that is generally far below the world average. Expressed per 1,000 population, the consumption of sawn wood for 1960, 3 3 for example, was approximately 10 m in Tropical Africa, 69 m in Latin 3 America and 12 m in the Tropical Asia Pacific region, as compared with 3 an average world wide consumption of 145 m . The usefulness of the tropical forest must therefore be increased to contribute more to the comfort and economic development of the peoples of these regions. 2. Objective and Scope of the Study 3 One of the big problems in the utilization of tropical species is their great variation in properties. This necessitates a proper understanding of properties of individual species before they can be introduced for commercial processing. The problem is further magnified by the fact that there is usually a profusion of species within a given area, only a few of which can be removed and used economically. Research in the properties of tropical species is therefore a slow and costly process which many of the tropical countries can barely afford. This study was undertaken in an effort towards adding to infor-mation on some properties of tropical hardwoods. It is proposed to investigate the gluing properties of six species from Burma (Southeast Asia). The selection of these species was made by the Burmese Timber Authority - based on their commercial and economic availability as well as their differences in physical properties. Some of these woods are already being used for construction activities and are therefore familiar to the local people. The species which will be found suitable for gluing may be used for manufacturing laminated beams in a factory to be built by Canadian International Development Agency as part of industrial aid to Burma. The following will be investigated: * a) The gluing characteristics of the six wood samples using phenol-resorcinol-formaldehyde, urea-formaldehyde and casein glue formulations. All the glues are room temperature setting. * Any reference to the term 'species' used in this study refers only to the wood samples received and not necessarily..representative of the species in Burma. 4 b) The influence of wood specific gravity on the gluability of the wood samples. c) The amount of extractives in the individual wood samples and their influence on the gluing characteristics. d) The pH of the wood and its influence on gluability. e) Shrinkage properties of the wood samples and their effect on durability of the glue bonds. f) Effect of four different treatments on the strength of the wood glue bond. LITERATURE REVIEW 1. Gluing, general The gluing of hardwoods has been undertaken in Europe and North America for some time, but.comprehensive studies on the gluing of tropical hardwoods are not many. Troop and Wangaard (1950) studied the gluing properties of certain tropical American woods. The results of their preliminary survey of gluing properties of selected tropical woods indi-cated that many of them could be adapted to a number of industrial or structural uses. The gluing properties of each wood were based on joint strength and percentage of wood failure as developed in the standard block shear test. It is emphasized in their report that the gluing of these woods is important not only from the standpoint of assembly gluing as employed conventionally in fabricated wood products and structures, but in addition, from the standpoint of the more complete utilization that may be made possible through laminated and edge glued construction. Twenty-nine wood species were investigated using two adhesives, resorcinol-formaldehyde and phenol-resorcinol-formaldehyde. The authors recognised the fact that other types of adhesives and other gluing tech-niques may yield results different from theirs. Narayanamurti (1957) studied the gluability of Diospyros melanoxy- lon Roxb. and the various problems involved in gluing this species noted for its high density and high extractive content. Extractive removal 5 6 improved gluability. Narayanamurti et a l . (1962) reported on the gluing of Tectona grandis L. and Acacia catechu Willd. and the effect of extrac-tives from these species on the properties of animal glue and of urea-formaldehyde. Extractives from the two species affected gelation time of the glues. The gluing characteristics of secondary hardwoods, including red alder (Alnus rubra Bong.), cottonwood (Populus trichocarpa Torr. and Gray) and aspen (Populus tremuloides Michx.) were investigated by Carstensen (1961). In the same study he investigated the gluing characteristics of softwood veneers. He concludes that within any one species, wide variations exist in density, grain configuration, moisture content and veneer surface characteristics and that gluability will vary accordingly. Accumulation of resinous material on the surface and high percentage of summer wood may add to the gluing problems of the woods noted. Dost and Maxey (1964) reported on the gluing charactistics of some California hardwoods including black oak (Quercus kelloggii Newb.), chinkapin (Quercus muehlenbergii Engl em.), madrone (Arbutus menziesii Pursh) and tanoak (Lithocarpus densiflora Rehd.). They concluded that all four species glue well with phenol-formaldehyde adhesive and with exterior polyvinyl-acetate resin emulsion. Also, joint strength by species and \"stock treatment\" appeared closely related to \"stock density.\" In recent years many investigations on the gluing of tropical hardwoods have been carried out in Japan. The species investigated are from Southeast Asia. Among the notable contributions in this field are those discussed below. 7 The effect of specific gravity, wettability, pH and percentage of extractives on the glliability of eighteen tropical woods using urea-formaldehyde, phenol-formaldehyde adhesive and polyvinyl»acetate emulsion, was reported on by Goto et a l . (1967). The durability of the bond was tested by the drying-wetting cycle. They concluded that glue-joint strength increased with increase of specific gravity. There is a high degree of reverse correlation between wettability and specific gravity. There was no significant relationship between glue-joint strength and pH. They also reported that the relationship between glue-joint strength and the percentage of extract either by cold water or by hot water is not significant. Moriya et al . (1968) reported the gluing faculties of laminated wood made of fourteen species of Kalimantan woods with resorcinol resin adhesive, phenol-formaldehyde adhesive, urea-formaldehyde adhesive, polyvinyl-acetate resin emulsion adhesive, and casein adhesive. Glue bond durability was tested by del ami nation test and the dry strength by block shear test. The gluing properties of laminated wood made of keruing (Diptero- carpus spp.) grown in Malaya were investigated by Moriya et a l . (1969). The results showed that the gluing characteristics of keruing were un-satisfactory. Red lauan (Shorea negrosensis Foxworthy.) from the Philippines was used by Moriya et al . (1971) in their study on the gluing characteris-tics of laminated wood. The glues used included resorcinol-formaldehyde, phenol-formaldehyde, urea-formaldehyde adhesive, polyvinyl-acetate resin emulsion and casein. Block shear test and del ami nation test were used 8 to evaluate the strength and durability of the glue bond. One of the conclusions reached was that glue joint strength increases with increase in specific gravity of the wood. Sakuno and Goto (1970b) studied the gluability of thirty-six tropical woods using urea-formaldehyde resin adhesive and phenol-formaldehyde. They reported the coefficient of correlation between glue joint strength, wood failure and various properties including specific gravity, pH, ether soluble extractives and wettability. Their findings are elaborated below. Extractive removal from wood surface by solvent led to an increase in joint strength but the increase in strength varied with species irres-pective of glue. This was shown by Chen (1970) in his study on the effect of extractive removal on adhesion and wettability of eight tropical woods. The solvents used included a 10 percent solution of sodium hydroxide, acetone, and alcohol benzene. Urea-formaldehyde and resorcinol-formaldehyde resin adhesive were used to glue the wood. Extractive removal improved wettability and increased the pH of the wood surface. Some extractives of kapur (Dryobalanops spp.) were shown by Imamura et al . (1970) to inhibit the adhesion of veneer with phenol-formaldehyde adhesive and also the curing of paint film with unsaturated polyester resin varnish. Yamagishi and YoshvhirS (:]972)/oreport':6n; the use'''o'f two different species in bonding some tropical woods. They concluded that in using mixed species for plywood, careful consideration should be given to the specific gravity of the species. The difference in specific gravity between the species should be within +0.12. 9 2. Specific Gravity The effect of specific gravity on the gluing of wood has been studied by various workers. * Eickner (1942) investigated the gluing of fjfiteew species- using tr.e\"a*.¥briDa:l'dehydeJ,adhesi've:can.d.:casei.n.--.He. concluded that there, was less difference between gluing characteristics of woods of different densities when glued with urea-formaldehyde adhesive than when glued with casein. Twenty-nine Tropical American woods were used by Troop and Wan-gaard (1950) in their study on gluing characteristics. Resorcinol and phenol-resorcincol-formaldehyde adhesives were used to glue the wood species. They observed that the general trend is that of increasing joint strength and decreasing wood failure with increase in specific gravity. They also observed some uneven character of trend of values for wood failure and shear strength in certain species. This was caused by interference with the adhesive. Such interference may have been introduced as a result of defective surfacing or i t may have been related to the character of chemical components, such as gums, resins, oils and waxes which occur in varying amounts as extractives. The effect of such interference, they contend, is partly obscured in shear strength data because of deviations of individual species from the strength values anticipated on the basis of specific gravity alone. Freeman (1959) studied the effect of specific gravity, pH and wettability on the strength of glue joints. It was found that specific gravity is of prime importance as far as failure in wood is concerned. High specific gravity increased bond strength. Original not seen. Cited from Troop and Wangaard (1950). 10 In his report on the gluing characteristics of softwood veneers and secondary hardwoods Carstensen (1961) concluded that within any one species, wide variations exist in density, grain configuration, moisture content and surface characteristics; gluability will therefore vary accordingly. Dost and Maxey (1964) report that joint strength by species and \"stock treatment\" appeared closely related to \"stock density.\" They found this trend in their study of the gluing characteristics of Cali-fornia hardwoods. The effect of specific gravity, wettability, pH and percentage of extractives on the gluability of eighteen tropica:! woodstwas-studied by Goto et a l . (1967). They found a high degree of correlation between glue joint strength and specific gravity. The glue joint strength in-creased with the increase of specific gravity. Of the four factors investigated, specific gravity was shown to have the most important effect on glue-joint strength followed by wettability. Yagishita and iKarasawa (.1969), in their study of fourteen species of Kalimantan woods, reported that the relation between bond strength and the. apparent specific gravity was that the species with higher specific gravity showed higher values of strength with phenol-formaldehyde adhesive and melamine-formaldehyde. This trend was not observed with urea-formaldehyde. In the literature reviewed above no attempt has been made [except generally for Troop and Wangaard (195' )] to distinguish the point up to which the statement that glue joint strength increases with the increase in specific gravity of the wood. Sakuno and Goto (1970b) in their study 11 on wood gluing established this point. They studied thirty-six species using urea-formaldehyde and phenol-formaldehyde glues. They concluded that the correlation between specific gravity and glue line shear strength was significant at the 5 percent level for both urea-formaldehyde and phenol-formaldehyde glues for values of specific gravity of 0.8 and below. For values above 0.8, the correlation between specific gravity and glue-line shear strength was not significant. For wood failure, however, the opposite was found to be the case. There was no correlation between wood failure and specific gravity for values of specific gravity of 0.8 and below, but above 0.8 there was significant correlation at the 5 percent level. Moriya et al . (1971), in their study on the gluing faculties of laminated wood made of red lauan sawn boards from the Philippines, reported on the effect of specific gravity on shear strength. They used ten species and five adhesives including resorcincol-formaldehyde, phenol-formaldehyde, urea-formaldehyde, polyvinyl-acetate resin emulsion adhesive and casein adhesive. Their results follow essentially the same pattern as those of Sakuno and Goto (1970b). Species with apparent specific gravity of above 0.8 exhibit lower strength properties than expected by extrapolation in all the five glues. Species with specific gravity of 0.8 or below follow the general pattern that glue line strength increases with increase in specific gravity. 12 3. Effect of Extractives Extractives have been known to interfere with gluing properties of wood for a long time but until now very l i t t le was known about the nature of these extractives and their mode of action, especially in tropi-cal hardwoods. Different species have different types of extractives. Extractive quantities vary within species and within tree. Heartwood normally has more extractives than sapwood. * Rapp (1948) studied the gluing characteristics of lignum vitae (Guaiacum officinale L.), a species which is known to be among the most diff icult to glue. He investigated the possibility of various surface treatments to improve the gluing performance by removal of at least part of the resinous extractives contained in this wood. The solvents used included carbon tetrachloride, benzene, acetoneand ethyl alcohol. None of these solvents was as successful as an application of 10 percent caustic soda solution wiped on the surface, allowed to remain for 10 minutes, and removed by washing with water. The results show an increase in shear strength and wood failure values, especially in the combination of sanding and caustic soda treatment. In one study carried out by Gamble Brothers Inc. i t is stated that the washing of the surface of teak, which contains an oily extractive, with acetone improved joint shear strength and wood failure. Troop and Wangaard (1950), on the other hand, report that Burma teak does not it Original not seen. Cited from Troop and Wangaard (1950). Original not seen. Cited from Troop and Wangaard (1950). 13 necessarily require preliminary treatment when glued with resorcinol adhesive. Narayanamurti (1957) summarised the importance of extractives in wood. He points out that the distribution of extractives varies both vertically and horizontally in a tall tree. Extractives affect the hygroscopicity, swelling and shrinkage of wood. The effect of ex-tractives on the gluing of wood is of special importance. He noted that different researchers observed during testing of glue joints that sapwood, which has a lower extractive content, can be glued better under some conditions and with certain adhesives than heartwood. He found that the gluability of Diospyros melanoxylon is improved by extraction and that other species which were treated with extractions from Diospyros melanoxylon lost considerably in glue joint strength. Narayanamurti et a l . (1962) discussed the influence of extractives on the setting of adhesives. Wood extractives affect the bonding of wood but their effect may vary from glue to glue. Extractives affect the viscosity and rigidity of glue. The effect of various extractives from Acacia catechu and teak on the gelation time and rigidity modulus of adhesive, \"animal\" glue and urea-formaldehyde was undertaken. They concluded that extractives affect gelation and rigidity of glues but the effect depends on the species being glued. Teak extractives were more effective than those of Acacia. Extractives from afrormosia' (Afrormosia elafa Harms.) i.nhibit the setting of most adhesives, particularly animal glue,acid set phenol-formaldehyde and polyvinyl acetate. This phenomenon was observed by 14 Chugg and Gray (1965). The same authors reportthat extractives lower the surface tension of the wood surface and reduce wettability, which is essential for a good glue bond. Most wood species contain traces of low molecular weight fatty acids or resins which could easily migrate to the surface during a drying or hot press operation forming an oriented surface layer. If the surface tension of the wood is sufficiently low the glue tends to display a definite receding angle of contact on some parts of the surface so that these remain completely free from the glue. This behaviour is more likely with glues possessing a high surface tension such as cold setting phenol-formaldehyde and urea-formaldehyde. Hancock (1964) reports that Douglas f i r veneer dried at high temperatures had fatty acids concentrated at the surface. The fatty acids were shown to reduce the wettability of veneer,and:affectt^ate\"'and \"depth of. penetration of glue. In a study on surface inactivation of wood at high temperatures, using wood microsections of white spruce [Picea glauca (Moench) Voss] that had had extractives removed to varying degrees, Chow (1971), con-cludes that extractives serve only as catalysts for oxidation and that when drying wood at temperatures over 180°C, in addition to oxidation, pyrolytic degradation occurred. Since no high temperatures were used either in drying the wood or in the hot press in this study, i t is not necessary to review in detail the effect of high temperature on wood surface inactivation. Goto et al . (1967), in their study of tropical woods, conclude that the relationship between the glue joint strength and percentage of extract either by cold water or by hot water was not significant. 15 But glue joint strength increased with the decrease of percentage of extract in the ether extraction when the effect of specific gravity is excluded. They further state that the value of pH and percentage extract have less important effects on the glue joint strength than wettability and specific gravity. Similar results were obtained by Sakuno and Goto (1970b) in their investigation of thirty-:s'tx species. --They report that tP$tifi£ngJue rjoyi,t strength ^she^ar strength jof figTue^oint/spe^'if-ic gravity) was significantly correlated with percent ether extract for urea-formaldehyde for woods of specific gravity 0.8 and below. There was no significant correlation at the 5 percent level of significance between glue joint strength and ether extract percent for wood species with specific gravity higher than 0.8. S ^ h J p - f r ^ :tne~-eJffecr of -•&U afMd?ar eM v&l;>9& iadhesri on, and wettabi iSiiywrT.Sojdi^ um: hydrox^dei S'ol ution (10 percent), acetone and alcohol benzene were the solvents for the extractives. The wood was glued with urea-formaldehyde and resorcinol-formaldehyde adhesives. Glue-joint strength was improved by all treatments in all but one species. In the case of the 10 percent solution of sodium hydroxide, some species were affected more by one treatment than the other, without regard for the adhesive used. Extractive removal improved wettability and increased pH of the wood in all species examined. A positive linear correlation existed between wettability and joint strength eojf.: blocks glued with urea-formaldehyde; however, no such correlation was observed for resorcinol-formaldehyde. Wood extractives of kapur wood (Dryobalanops spp.) inhibit the adhesion of veneer with phenol-formaldehyde adhesive. This was shown 16 by Imamura et al . (1970). They also found that the extractives inhibited the curing of paint film with unsaturated polyester resin varnish. It was shown in the same study that only certain portions of the extractives had inhibitory effect. Other extractives in the wood had no inhibition effect. Onishi and Goto (1971) report the effect of wood extractives on the gelation time of urea-formaldehyde resin adhesive. The influence of wood extractives with cold water, boiling water and alcohol benzene on the gelation time of urea-formaldehyde, and the compressive strength of setting material, was investigated. The results show that gelation time of urea-formaldehyde to which wood extractives were added increases with the increased amount of wood extractives with cold and boiling water. For cold water extractives i t was observed that the gelation time decreased with decrease in pH. Alcohol-benzene extracts also have effect on the gelation time of urea-formaldehyde though to a lesser extent than water extract. 4. Wettability An effective glue joint for structural purposes cannot be made unless a liquid adhesive spreads completely over the surface to be joined. Air bubbles from surface irregularities have to be displaced and chemical contact with the wood substrate made so that a permanent, high strength bond is developed between the glue and the wood. The physical quantities which determine effectiveness of spreading and adhesion are the surface 17 tension of the wood surface and the interfacial tension between the adhesive and the wood. Freeman (1959), Bodig (1962), Freeman and Wangaard (1960), Marian and Stumbo (1962) have demonstrated that glue bond strength can be cor-related with surface wettability. Patton (1970) reviews adhesion theory based on surface energetics. Gary (1962) has reviewed the concept of equilibrium contact angle and the methods of measuring i t on wood sur-faces. Most of the wettability measurements on wood have been made using homogeneous liquids such as water. Herczeg (1965), however, inves-tigated the wetting of wood by liquids having various surface tensions and pointed out the probability that bond strength is closely dependent upon wetting, spreading and surface tension of the adhesive. Bryant (1968) showed that bond quality is influenced by the wettability of wood by the resin and the wood surface. Freeman and Wangaard (1960) observed that during the period of closed assembly, prior to the application of gluing pressure, glue line solids content and viscosity increase more rapidly in the woods of high wettability than in woods of low wettability. Changes in wettability are due to contamination of the wood surface with active chemicals which reduce surface tension (Chugg and Gray, 1965). These chemicals may be traces of low molecular weight fatty acids or resins which migrate to the surface. They lower the surface tension of the wood surface and reduce wettability. Hse (1972) reports on the wettability of southern pine (species not mentioned) veneers by _3fhi^ty^si:x,'-exteteiaitegRtftfe: ph :erfofliEc'resiir adhesives having a wide range of physico-chemical properties. He also discusses 18 the effects of resin formulation on wettability as measured by contact angle, as well as the relationship between contact angle and bond quality. One of the important findings of the study is that contact angle was positively correlated with glue bond quality as tested by wet shear strength, percent of wood failure and percent del ami nation. Extractive removal improved wettability and increased pH of the wood in some tropical hardwoods studied by Chen (1970). He reports that a positive linear correlation existed between wettability and joint strength of blocks glued with urea-formaldehyde but no such correlation was observed for blocks glued with resorcinol-formaldehyde. A reverse correlation between wettability and specific gravity was observed by Goto et a l . (1967). Wettability increased with decrease in specific gravity. Glue joint strength increased with increase in wettability when the effects of specific gravity are excluded. Sakuno and Goto (1970a) studied the wettability of thirty,-six tropi woods and related wettability to glue joint strength and wood failure. They found that specific glue joint strength (shear strength/specific gravity) and wettability had significant correlation at 5 percent level for all species with specific gravity 0.8 and below, for both urea-formaldehyde and phenol-formaldehyde. No correlation was observed between specific glue joint strength and wettability at the 5 percent level for all species with specific gravity higher than 0.8. Significant corre-lation is reported at the 5 percent level between wood failure percent and wettability for phenol-formaldehyde for all species with specific gravity less than 0.8. There was no significant correlation at 5 percent 19 level between wood failure and wettability for species with specific gravity higher than 0.8. Since no actual wettability measurements were made in the present investigation on the gluing of the six Burmese hardwoods, no review of the methods of measuring wettability will be done. 5. pH Acidity or alkalinity of the wood have an effect on the setting of adhesives. The effect of pH on the strength of particleboard was studied by Kitahara and Mizumo (1961). They showed that the strength of particleboard was correlated with pH of the wood chips and that in some cases acid in the wood is sufficient to cure the urea resin adhesive. Chugg and Gray (1965) report that joints made with resorcinol adhesives display a marked change in strength with change of pH. Goto et a l . (1967) found that the relation between glue joint strength and pH is not significant, and that specific gravity and wett-ability are more important factors. Sakuno and Goto (1970a) report that pH affects the wettability of woods with specific gravity lower than 0.8. In a study of some tropical woods Chen (1970) reports that extrac-tive removal improved wettability and increased the pH of the wood in all species tested. The gelation time of urea-formaldehyde to which wood extractives were added increases with increased amount of extractives with cold or boiling water (Onishi and Goto, 1970). For cold water 20 extractives, a certain relationship was observed between the gelation time and the pH of wood, the gelation time decreasing with a decrease in pH of each wood. 6. Effect of Glue The chemical processes whereby most glues cure to give a final bond are influenced by a number of factors among which are the minor .. chemical components of the wood. Wood adhesives harden either by heating, cooling, by loss of water, by chemical action or by a combination of two or more of these. Premature solidification of an adhesive may in-terrupt the sequence in the glue line development at any point because each successive phase of this development requires mobility for optimum results. If solidification occurs before the transfer of the adhesive has been accomplished, wetting will also be prevented. It is here that the role of extractives may be sometimes very important. They may accel-erate the rate of setting,resulting in premature so l i d i f i c a t i o n , or they may retard i t , resulting in a weak joint. Different glues behave dif-ferently to similar extractives, depending on their formulation and other characteristics. Eickner (1942), in his investigation on the gluing characteristics of fifteen specdest;!concluded thatsthere\";was (less difference between gluing characteristics of woods of different densities when glued with urea-formaldehyde, than when glued with casein glue. Troop and Wangaard (1950) report that casein and vegetable glues do not seem to permit as f u l l a development of the strength of white 21 oak as do the animal, urea and resorcinol resin adhesives. When comparing mahogany and white oak they found that the non-resin adhesives showed appreciably lower wood failure values in the case of white oak. Yagishita and Karasawa (1969), in their investigation of adhesion i n \"f bunteenc speci es > ofuKael.i maatan, woods.,* observed-.that thei rel ati onshi p be-itw.eens bondgsttren:gth;'an,dpi.the2:app:a;rentvspecif.itt:gr.avj ty,,wastitha*- the speci es with higher specific gravity showed higher values of strength with phenol-and melamine-formaldehyde adhesives. This trend was not observed for urea-formaldehyde adhesive. Onishi and Goto (1971) studied the effects of wood extractives on the gelation time of urea-formaldehyde resin adhesive. They suggest that wood extractives have effects on the curing reaction of adhesives. The pH and buffer action of wood may affect the gelation of urea-formaldehyde resin adhesive because the rate of curing of this resin is closely depen-dent on pH. They concluded that wood extractives influence gelation time in that increased amounts of cold or boiling water extractives increased gelation time of urea-formaldehyde. The compressive strength and the ratio of plastic region to elastic of set gel decreased with increased gelation time. Yamagishi and Yoshihiro (1972) report on the mixed use of two different species in bonding some tropical woods. They found that the durability of the glue bond varied with the glue, and that specific gravity difference between two species considerably influence the glue bond durability, imoresxo with urea-formaldehyde than with resorcinol-formaldehyde adhes i ves. 22 Northcott,(1968) states that urea glues are susceptible to hy-drolysis and degrade much more rapidly under continuously wet systems than cyclic dry-wet bond degrade accelerating systems. Phenol-formaldehyde adhesives, on the other hand, are generally considered to be immune to hydrolysis and are more durable than wood, and are less degraded by continuously wet than by cyclic dry-wet bond degrade systems. He suggests that probably the degradation observed with fully cured phenol-formaldehyde adhesives is that of the wood rather than the glue. The conclusion reached in the study of influence of species and glues on bond durability is that durabilities of plywood bonded with different glues is strongly influenced by wood species. MATERIALS AND METHODS 1. Species Wood specimens from six species native to Burma were received in the form of sawn lumber with dimensions of 2 by 4 by 142 inches (5 by 10.by 3603cm)j8 There werectwelve..pieces .for.each of .the-s~peci.es. Eight of these pieces were made available for use in this study. Some of the pieces were quarter sawn and others flat sawn. For each species only heartwood was used. The wood specimens were comprised of the following species: Percentage of Burmese name Botanical name volume of com-mercial timber in Burma Pyinkado Xylia dolabriformis Benth. 21.5 Thitya Shorea obtusa Wall. f 5 5 Ingyin Pentacme siamensis Kurz. ^ ' Padauk Pterocarpussmaerocarpus.Kurz. 1.5 In Dipterocarpus tuberculatus Roxb. Kanyin Dipterocarpus sp. i 44.4 Moisture contents of the specimens were measured by taking samples one foot from the end of each board and averaging the results. The remainder of each board was then cut into two sections of 54 in. and one of 12 in. length. These boards were further sawn lengthwise into 1 by 4 by 54 in. and 1 by 4 by 12 in. dimensions. The long boards were reserved for the main experiment and the short boards for the preliminary experi-ments. 23 24 The sawn boards were then stacked with 1/2 in. spacers between boards in a 25 to 30 percent relative humidity room [dry bulb 80°F (26.7°C) and air speed approximately 200 feet per minute] to permit controlled drying of the material. Moisture contents were checked at time intervals shown in Table I using the ovendrying method (ASTM D 143-52). Prior to planing and gluing .the lumber was kept in the general laboratory condition which approximated 40 percent relative humidity and 70°F and EMC of about 8 percent. The moisture content of the wood at the time of gluing is shown in Table 1. 2. Glues Three glues were used in this study. They were supplied by Westport Chemicals Limited and the Borden Chemical Company (Canada) Limited. These glues include: 2.1 Phenol-resorcinol-formaldehyde Westport PRF 2947 Resin which, when mixed with 2947 Hardner, produces a phenol-resorcinol-formaldehyde resin adhesive that is suit-able for general gluing at temperatures of 70°F and above. It produces a waterproof and weather proof bond in accordance with CSA 0112.7-1960 (Specifications for Phenol and Resorcinol Resin Adhesives for Wood -Room and Intermediate Temperature curing). 2.2 Urea-formaldehyde Cascoresin 901-045 and 255-4812 catalyst supplied by Borden Chemical Company is a urea-resin based adhesive which cures to a water-resistant bond at temperatures of 70°F or higher in accordance with 25 CSA 0112.5-1960 (Specification for Urea Resin Adhesives for Wood - Room and High Temperature Curing). 2.3 Casein Casco-casein 402-003 supplied by Borden Chemical Company is room temperature curing and is recommended for interior use as specified in CSA 0112.3-1960 (Specification for Casein Glues for Wood). 3. Experimental Procedure 3.1 Preliminary experiments To determine the best conditions for gluing the wood specimens, 4 preliminary experiments were carried out using a 12 inch press. Only two glues, urea-formaldehyde and phenol-resorcinol resin adhesives were used. For each of the 6 species and glues, two boards each 1 by 4 by 12 inch were glued together. The lumber was planed before gluing to ensure identical thickness and smooth surface. To avoid any possible surface aging effects on gluing abil ity, the boards were glued within 4 to 6 hours after planing. Using a glue spread of 85 lb. per 1,000 sq. ft. of double glue line and recommended assembly times, the following conditions were tested: a) Gluing at room temperature (about 72°F) for 24 hours and 150 psi. The block shear strength and wood failure test indicated that the bond quality was substandard. b) Gluing at room temperature for 24 hours under 200 psi. The bond quality obtained was better than the f irst test, but far from satisfactory. c) Gluing and pressing at 100°F for 24 hours under 200 psi. The result was very satisfactory. 26 d) Using the conditions of the third preliminary experi-ment above, a different phenol-resorcinol glue provided by another adhesive manufacturer was evaluated. The results were satisfactory, but indicated that the bonding ability of the wood also differs with the adhesive used. 3.2 Main experiment gluing From the results of the preliminary experiment i t was decided to use 200 psi , 100°F and 24 hours clamp period for the main experiment for all the three glues. For each species and glue three boards were glued. The size of the press was the governing factor in determining the length of the laminations, each of which was 3/4 by 4 by 54 in. For each species and glue, six straight grain bi l lets, which were free from defects including knots, birds eye, short grain and any unusual discoloration from the shearing area, were selected. The grain direction in all the billets was parallel to the longest dimension. Just prior to gluing they were planed and assembled in pairs in such a way that each pair had approxi-mately the same specific gravity. All the surfaces of the wood remained unsanded and were free from dirt. The moisture content of the wood at the time of gluing is shown in Table 1. The range of the moisture content of pieces to be bonded in a single member did not exceed 5 percent (as determined by taking a 1 inch sample from the end and testing by the oven dry ing method), 27 3.2.1 Gluing with phenol-resorcinol-formaldehyde Glue was mixed according to the manufacturer's instructions and used within the recommended working l i fe . The spread used for phenol-resorcinol adhesive was 85 pounds per 1,000 square feet double spreading (one half of the spread was applied to each contacting surface). A grooved, rubber rolled mechanical spreader was used. The proper spread was obtained by weighing a piece of wood prior to the application of glue, then passing i t through the spreader so that glue is applied only on one side, and weighing i t again to deter-mine the amount of glue deposited on the surface. The spreader was then adjusted until just the right amount of glue was deposited on each board. For each press load, glue was applied to two pieces of each of the six species to produce one glued board per species. An open assembly time of 20 minutes and a closed assembly time of 35 minutes was used. This is within the 60 minutes total assembly time recommended by the manufac-turer. A pressure of 200 psi (which is within the range recommended for hardwoods by CS253-63 and confirmed by results of the preliminary experiments) was applied for all the six species for 24 hours. The press temperature was maintained at 100°F. The glued stock was removed after 24 hours and conditioned for 7 days before machining. Three glued stocks were made for each species. 3.2.2 Gluing with urea-formaldehyde- 2 ~ Vo . • z. Mixing of the glue was done according to manufacturer's instruc-tions. Enough glue was mixed and used before the expiration of the 28 working l i fe . Glue spread was 85 pounds per 1,000 square feet of joint area double spreading. A rubber rolled mechanical spreader was used, and steps were taken similar to those for phenol-resorcinol adhesive, to ensure the glue spread was as close as possible to the amount required. The assembly times were 5 minutes, open and 20 minutes closed. A pressure of 200 psi and a press temperature of 100°F was maintained for 24 hours. Each press load consisted of one glued stock per species. Three glued members were prepared for each species. • The members were conditioned in the laboratory before they were machined. 3.2.3 Gluing with Casco-casein Glue was mixed according to the manufacturer's instructions and used within the working l i fe . A glue spread of 85 pounds per 1,000 square feet of joint area double spread was used. Glue application procedures were similar to those for phenol-resorcinol and urea-formaldehyde resin adhesives. Assembly times were 15 minutes open and 25 minutes closed. Pressure of 200 psi and press temperature of 100°F was applied for 24 hours. Three glued members were prepared for each species. After removal from the press the members were conditioned for one week before machining. Some squeeze out was observed when pressure was applied in view of the heavy glue spreads. This is also true for the other two glues. 3.3 Specimen preparation It was intended in this study to investigate the performance of the adhesives and the species in laminated wood, as measured by resistance to shear by compression loading for all three glues; also resistance 29 to del ami nation during accelerated exposure to wetting and drying for phenol-resorcinol resin adhesive. In addition, the boil and cold soak treatment, normally used for plywood, was included to determine their effect on the glue-bond of laminated wood. 3.3.1 Block shear specimen Except for casein, from each of the glued stock thirty-six block shear specimens were cut according to CSA 0177-1965 with a slight modifi-cation, the specimen in this case being 1 1/2 by 1 3/4 by 2 in. (see Figure 1). This was because of the limited volume of material received, and the width being nominal 4 in. The 1/4 in. difference in width from the standard block shear specimen was considered to be of l i t t le significance to the validity of the test results. It has been proved by Strickler (1968) in a study on block shear specimen geometry that specimen width is of no significance to unit shear strength. Specimen length has significant effects on unit shear strength. For casein, ten shear block specimens were cut from each laminated piece for dry testing. The cut specimens were left in the air conditioned laboratory for two days before they were tested (dry). The cold soak test specimens and the boil test specimens were treated separately at periods no longer than a week from the time of cutting. The width and height of each specimen at the adhesive line was measured to the nearest 0.010 inch for determination of the shear area. For each species, ten specimens were randomly allocated from each of the three boards for dry block shear testing; ten from each board were used for the cold soak test; and ten for the boil test. For phenol-30 resorcinol resin adhesive, therefore, thirty specimens were used for each of the three-tests; 'TJii.r.tyspec-imens weredused fore case in for the dry test only. Urea-formaldehyde resin adhesive glued wood was tested in the dry condition and cold soaked only. 3.3.2 Delamination specimen In view of the size of the laminated stock, -four.--specimens, 3 inches along the grain and 4 inches across the grain were cut from each glued stock. Twelve specimens were used for each species for phenol-resorcinol resin adhesive. These were used for the vacuum-pressure cycle test (CSA 0177-1965). Only material as close as possible to flat sawn was used. 4. Testing Procedure 4.1 Dry test For block shear test for dry, cold soak and boil specimens, the block shear test method was used with the shear block area varying be-tween 2.6 and 2.8 sq.in.instead of the 3 sq. in.specified in CSA 0112.0 -1960. The standard block shearing tool containing a self aligning seat to ensure uniform distribution of the load was used (Figure 2). The load was applied by means of a Tinius 01 sen hydraulic testing machine at a continuous motion of the movable head at a rate of 0.015 in. per minute (+_ 25 percent) to failure. Shear stress at failure was recorded for each test block and shear strength at failure was calculated in pounds per square inch based 31 on the glue line area between the two laminations - measured to the nearest 0.01 sq.in.and rounded. Percent wood failure (the rupturing of wood fibers expressed as the percentage of the total area involved which shows such failure) was also recorded for each block. 4.2 Cold soak test Thirty specimens for each species for phenol-resorcinol and urea-formaldehyde resin adhesives were submerged in water at 70° to 75°F for 48 hours. Without drying, they were tested to failure as for the dry specimens. Shear strength and percent wood failure were recorded as for dry specimens. 4.3 Boil test Only specimens glued with phenol-resorcinol resin adhesive were used in this test. Thirty specimens for each species were submerged in boiling water for 4 hours, then dried in an oven at 140°F to 145°F for 20 hours, after which they were again submerged in boiling water for 4 hours, cooled in water at 70°F to 75°F and tested to failure while wet. Shear stress at failure and percent wood failure were recorded for each block. Shear strength in pounds per square inch was calculated as for the cold soak test specimens. 4.4 Vacuum-pressure cyclic test («\".\"/. J ' J 5 I S J J ) This test indicates the quality and durability of glued laminated timber with respect to high moisture conditions. Specimens 3 inches along the grain and 4 inches across the grain were used. Twelve specimens 32 glued with phenol-resorcinol resin adhesive were tested for each species. Specimens were placed in a vacuum-pressure tank which was then f i l led with water at room temperature. All end grain surfaces were exposed to water. A vacuum of 25 inches of mercury was drawn and held for 2 hours, after which i t was released and a pressure of 80 psi applied for two hours. The vacuum-pressure cycle was repeated. Specimens were removed from the tank and dried for a period of 88 hours in air at 80+5°F, and 25 to 30 percent relative humidity, moving at a velocity of 200 to 300 feet per minute. The entire soaking-drying cycle was repeated twice to comprise a total test period of 12 days. After drying for the last time the total length of open glue joints on the end grain surfaces of the specimens were measured to the nearest 1/16 inch. The total length of open glue joints on the two end grain surfaces of each specimen were expressed as a percentage of the entire length of glue lines exposed on these surfaces. This value was recorded as the percentage delamination of the specimen. The total delamination of the two end grain surfaces of the specimen at the con-clusion of the test should not exceed 10 percent of the total length of all glue lines on the two surfaces to pass as satisfactory (CSA 0177-65 1965). This figure is 8 percent as specified for hardwoods by U.S. Commercial Standard CS 253-63 (1963). After completion of the delamination test each block was cut into two shear block specimens (24 per species) and tested. Shear strength and percent wood failure were recorded as for the other block shear tests. 33 5. Determination of Specific Gravity and Shrinkage All specimens used for specific gravity and shrinkage tests were flat sawn. 5.1 Specific gravity Specific gravity was determined by obtaining the ovendry weight and green volume of four samples selected for each species. Only heart-wood was used for these determinations. For each species four specimens were cut, each 1 by 2 by 4 in. (instead of the standard 2 by 2 by 6 in. used in ASTM D 143-52) because of the restricted size of material received. The specimens were soaked in a tank f i l led with water for about five days at 120 psi to make sure they were saturated. Their cross-sectional and length dimensions were measured to the nearest 0.2 O) c 0) s_ +J oo XI E o CQ 1 0 0 0 -Pyinkado Thitya Ingyin Padauk r loo 80 Shear Strength Wood Failure -60 CD ~3 .40 o o -20 In Kanyin Figure 4. Cold soak shear strength and percent wood failure for wood glued with phenol-resorcinol-formaldehyde resin adhesive 3000 -r 2000 in Q. + J CT) O) S-+J oo O CQ 1 0 0 0 -_ 80 _ 60 • 100 Shear S t r e n g t h Wood F a i l u r e 40 £ o o 20 Pyinkado Figure 5. Thitya Ingyin Padauk In Kanyi n Boil test shear strength and percent wood failure for wood bonded with phenol-resorcinol-formaldehyde' resin adhesive' CO 3000 200O. c/i +-> CO CD S_ +-> oo -o c: o CO 1000-Pyinkado T h i t y a I n g y i n Padauk In Kanyin 1-100 - 80 60 ^ 5 CD 40 1 20 a m S h e a r S t r e n g Wood F a i l u r F i g u r e 6. Vacuum-pressure c y c l i c t e s t s h e a r s t r e n g t h and p e r c e n t wood f a i l u r e f o r wood g l u e d w i t h p h e n o l - r e s o r c i n o l -formaldehyde r e s i n a d h e s i v e 3000 H00 \" 8 0 She a r S t r e n g t h ~ 2 0 0 0 -in -M CD C CU S-4-> 00 1 •a c o CQ - 6 0 - 4 0 &9 -a o o Wood F a i l u r e 1000 _ 20 Pyinkado T h i t y a I n g y i n Padauk In Kanyin F i g u r e 7. Dry t e s t s h e a r s t r e n g t h and wood f a i l u r e p e r c e n t f o r wood g l u e d w i t h u r e a - f o r m a l d e h y d e r e s i n a d h e s i v e ro o 3000 n 2000 to C L 4-> C D CD 5-+-> LO ft \"looo CQ r-l 00' Byinkado hi t y a i n g y i n Padauk Kanyi n 80 •60 S h e a r S t r e n g t l Wood F a i l u r e CD 3 40 1 20 F i g u r e 8. C o l d soak s h e a r s t r e n g t h and wood f a i l u r e p e r c e n t f o r wood g l u e d w i t h u r e a - f o r m a l d e h y d e r e s i n a d h e s i v e , r o 3000 T -100 \"2000-to p-+-> CO c: OJ %-+-> C O -o o C Q 1000. Pyinkado hi.tya I n g y i n Padauk Tn Kanyin 80 - 60 3 - 40 o o 20 Shear S t r e n g t h Wood F a i l u r e F i g u r e 9. Dry t e s t s h e a r s t r e n g t h and p e r c e n t wood f a i l u r e f o r wood bonded with' c a s e i n g l u e ro ro 3000 ~ PR UF Cas 2000 -C L •)-> CD CJ i-OO T 3 E O CQ 1000 PR P^ up PR PR UF Cas •4-4 UF Cas UF PR Cas UF Cas CAS - Casein glue joint strength UF - Urea-formal dehyde resin adhesive glue joint strength PR - Phenol-resorcinol-formaldehyde resin adhesive glue joint strength Pyinkado Thitya Ingyin Padauk In Kanyi n Figure 10. Phenol-resorcinol-formaldehyde, urea-formaldehyde and casein dry test shear strength ro oo 3000 - i o Pyinkado 2800 ~ In o Padauk 2600 -to D-sz +-> CD c O Kanyin £2400 T h i t y a ° Q I n g y i n ca cu 2600 cu s_ S-n3 CU 2400 _ cu 2200 2000 Pyinkado O Padauk to ro CD (U E QJ 3 CJ3 2600 -Padauk 2400 2200 I n g y i n © Kanyin O T h i t y a 2000 4.40 4.50 T T 4.60 4.70 4.8.0 . PH 4.90 5.00 — i 5.10 F i g u r e 15. R e l a t i o n s h i p between pH o f wood and g l u e l i n e d r y s h e a r s t r e n g t h f o r wood g l u e d w i t h u r e a - f o r m a l d e h y d e r e s i n a d h e s i v e ro co 3000 O Pyinkado 2800 -O Padauk £ 2600 O In 2400 _ ^Kanyin O Thitya 2200 ~ O Ingyin 2000 4.40 4.50 4.60 4.70 4.80 4.90 5J0O 5.10 PH Figure 16. Relationship between pH of wood and glue line dry shear strength for wood glued with casein glue ro to APPENDIX APPENDIX I I. Species Description A. Pyinkado B. Thitya C. Ingyin D. Padauk E. In F. Kanyin 130 I. Species Description A. Pyinkado Xylia dolabriformis Benth. Family Leguminosae Pyinkado is one of the most useful of the structural woods of India and Burma (Titmuss, 1965). The timber is heavy, i t weighss from 55 to 65 lb per cu ft at 15 percent moisture.content and 72 lb per cu ft when green (44 percent moisture content) (Bri!ti!s!hoB6rofPHoddivbab's, 1956). It has a mild, non-distinctive smell, a grain that is shallowly inter-locked, with a moderately coarse but uniform texture. When freshly ' sawn the heartwood colour is of a red-brown shade, but this darkens after exposure to the air and the heartwood is then readily distinguishable from the thin brownish coloured sapwood. The planed surfaces of the wood have an oily appearance. Pyinkado is a difficult timber to work, either by hand or machine. It can be brought to a good surface and will respond satisfactorily to the normal finishing agents; some care is needed in mortising and similar operations to avoid chipping out. Durability factors are high, and pyinkado is said to be a good species for use under water, as in piling; i t is classified as extremely diff icult to treat with preservative fluids. Although i t dries slowly, pyinkado can be seasoned satisfactorily either by air or kiln methods. Uses The wood is considered unsuitable for plywood manufacture because of its weight. In Burma and India pyinkado is ranked as one of the world's 131 132 best timbers for cross ties and also for bridges.. It is suitable for heavy structural work, piles,bridge girders, decking, dockwork and flooring. It is suited to these uses because of its great strength and its resis-tance to decay and termites. Macroscopic identification Pyinkado has a diffuse porous structure. Its growth rings are normally quite visible to the naked eye. It has moderately numerous pores which are arranged in clusters and individually. Orange-coloured gummy deposits may be present in the pores. It has vessel lines that are clearly visible to the naked eye. Numerous rays which are only visible under a lens on end section are present. V,Vasicentric parenchyma is visible under a lens, while fine lines of tissue may also be present. Ripple marks are not present in the species. B. Thitya Shorea obtusa Wall. Dipterocarpaceaefamily The species is practically identical to Indian sal (Shorea robusta Gaertn.). It is one of the heavier Shorea species, weighing 50 to 60 lb per cubic foot air dry (Titmuss, 1965). The species grows very commonly in association with ingyin (Pentacme siamensis Kurz.) and the two are used interchangeably in Burma. It has interlocked grain and a medium coarse texture. The heartwood of the species is a dark red-brown and quarter-sawn stock may show a striped figuring. The wood has a rather large number of resin canals in its structure, and these may result in splits during seasoning, an operation in which the wood also shows a tendency to warp. 133 Thitya is not an easy timber to work by hand, but does not cause trouble in machining. It is a very strong timber and is eminently suited for use for structural purposes, and also finds employment for flooring, bridging and similar work. It is also used for cross ties. Macroscopic identification The wood is diffuse porous with growth rings which are not very distinct. It has few medium-sized pores, uniformly distributed, which can be seen with the naked eye. Some of the pores are solitary but radial oblique clusters and pairs also occur. Vessel lines can be seen with the unaided eye. Its rays are moderately fine and are not always clearly distinct to the naked eye on end section. VMasicentric parenchyma is present in variable quantity, sometimes showing a tendency to become aliform. Narrow metatracheal lines of tissue may also be present. Small vertical canals with whitish deposits can be seen on all surfaces. In-distinct ripple marks may be seen sometimes. C. Ingyin Pentacme siamensis K'tirz. Dipterocarpaceae fami ly The wood of this species is hard, heavy and weighs 58 to 64 lb per cu ft air dry. The sapwood is greyish white and the heartwood is yellowish brown to red brown. The texture is medium to coarse and the grain is mostly interlocked. The wood seasons fairly well but slowly and is not liable to split and crack. It is very durable. It saws and machines with l i t t le difficulty especially in green condition. It finishes well. 134 Ingyin is used for floors, s i l l s , heavy construction, cross ties, tool handles and agricultural implements (Rodger, 1936). Macroscopic features of ingyin are similar to those of thitya. D. Padauk Pterocarpus macrocarpus Kurz. Leguminosae family Padauk is a fairly abundant tree and, next to teak, is the most valued uti l i ty timber in Burmese domestic usage. The wood weighs 50 to 60 lb per cu ft air dry. It is heavier and stronger than teak. It has very l i t t le sapwood which is greyish white. The heartwood is bright red to dark brick red with darker lines. The wood is hard and close grained. The interlocked grain produces a narrow ribbon grain figure. The growing tree is often 'girdled' as a pre-seasoning treatment, but during the drying operation surface cheeks are very likely to develop in the timber. The wood saws and works with some difficulty especially when dry, whilst the sawdust also irritates the nose and eyes. Generally i t can be clearly finished. It turns well, holds screws firmly but needs boring i f nailed. It polishes well when the grain is properly f i l led . Padauk is naturally durable for use in positions unprotected from the weather, and is especially resistant to \"white ant\" attack. It is diff icult to impregnate with wood preservatives. The wood is used for heavy construction and building purposes especially panelling, flooring beams, furniture. In the United States i t is used either in solid form or veneer in the manufacture of decorative panelling (Kukachka, 1962). It is said to be an important cabinet wood in Europe. 135 Padauk has a diffuse porous structure with growth rings distinct to the naked eye. Its largest vessels are clearly visible to the naked eye, but others are distinct under a lens. The vessels are solitary or in radial groups with open single perforation plates. Vessel lines are distinct to the naked eye. It has abundant metatracheal type of wood parenchyma. Paratracheal type parenchyma is also present. Ripple marks are present but are not usually visible to the naked eye; they are distinct under a hand lens. E. In Dipterocarpus tuberculatus Roxb. Dipterocarpaceaefamily In is a timber of Burmese origin but very similar woods (also produced by species of Dipterocarpus) are available from Malaya under such names as k'eruing and gurjun. It is appreciably denser than kleruing and gurjun. The wood weighs 51 to 54 lb per cu ft air dry. The moderately well defined sapwood of in is brownish-grey, while the heartwood is brownish-red; the latter may be of an extremely dark shade after prolonged exposure to the atmosphere. The grain is either straight or shallowly interlocked, the texture open but uniform, and the planed surfaces dull. It is not an easy wood to work with and resin exudation may cause some trouble in sawing or in the polishing process. The strength properties are good, the resistance to fungal infection is reasonable, but some insect damage may occur, though this is largely confined to the sapwood. In exposed conditions the wood lasts4 to 5 years. The response to preservative treatment is fairly satisfactory. It seasons 136 slowly, with some tendency to degrade, and is considered to be rather below average in respect of stability after seasoning. Air seasoning before kiln seasoning is recommended. The wood is used for heavy construction, railway wagon construction, house construction, Yarns'-, ~rafters~F'^ agricul-tural;1 i'mpTemeritsr: cultural ir:i\"\\n^i-s. Macroscopic identification The species is diffuse porous. The growth rings cannot be recog-nised. The pores are very large or large, quite distinct to the naked eye, evenly distributed and numerous. They are mostly solitary in arrange-ment but occasional pairs are present; some tyloses may be present. The coarse vessel lines can be seen with the naked eye. Rays are moderately few, fine and usually just visible to the naked eye on end section. Narrow wasicentric parenchyma (sometimes with a slight tendency to become aliform) and thin broken lines of metatracheal parenchyma may be seen under a hand lens. Ripple marks do not occur in the species but resin canals are present. F. Kanyin Dipterocarpus spp. The genus Dipterocarpus comprises a large number of species. The Dipterocarps are diff icult to separate both as standing trees and as sawn lumber (Stadelman, 1966). The wood weighs 40 to 49 lb per cu ft air dry. The sapwood is greyish-white and the heartwood is reddish-brown, dull with rough feel, even and coarse textured with characteristic odour. 137 It seasons moderately well but is liable to split i f left in large dimensions. Distortion, especially in the form of cupping is often considerable and slight collapse may occur. The wood is not resis-tant to termite attack or outside weathering. It is easy to impregnate with wood preservatives. It saws and machines well but does not take a good polish. It is used for railway carriage and wagon construction, bridge decking, boats, rough construction, house construction, rafters, beams and flooring. Macroscopic identification The species is diffuse porous. The growth rings cannot be recog-nised. The pores are very large or large, quite distinct to the naked eye, evenly distributed and numerous. They are mostly solitary in arrange-ment but occasional pairs are present; some tyloses may be present. The coarse vessel lines can be seen with the naked eye. Rays are moderately few, fine and usually just visible to the naked eye on end section. Narrow was:!'centric parenchyma (sometimes with a slight tendency to become aliform) and thin broken lines of metatracheal parenchyma may be seen under a hand lens. Ripple marks do not occur in the species but resin canals are present. APPENDIX II List of Abbreviations bd. ft. - board feet gr. vol. - green volume ha. - hectare hr - hour 3 lb/ft - pound per cubic foot m^ - cubic meter mc - moisture content ml - mi l l i l i ter od wt - oven dry weight psi - . pound per square inch r - roundwood' sp.gr. - specific gravity T/R - tangential/radial 138 "@en ; edm:hasType "Thesis/Dissertation"@en ; edm:isShownAt "10.14288/1.0075322"@en ; dcterms:language "eng"@en ; ns0:degreeDiscipline "Forestry"@en ; edm:provider "Vancouver : University of British Columbia Library"@en ; dcterms:publisher "University of British Columbia"@en ; dcterms:rights "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 ; ns0:scholarLevel "Graduate"@en ; dcterms:title "The gluability of certain hardwoods from Burma"@en ; dcterms:type "Text"@en ; ns0:identifierURI "http://hdl.handle.net/2429/32519"@en .