Gluability of Out-of-service Utility Poles

This investigation determined the gluability of weathered, out-of-service southern yellow pine (SYP) (Pinus spp.) utility poles. Three types of adhesives were used: resorcinol-phenol formaldehyde (RPF), polyvinyl acetate (PVA), and casein. The poles consisted of two service duration groups: 5 and 25 years. Longer weathering caused greater reduction in creosote content, especially in the outer andupperportions, but resulted in better gluability. Gluability of 25-year service life poles was the best and most comparable to untreated SYP. Five-year in-service poles and fi-eshly treated poles showed less favorable gluability. Superior gluability was obtained using RPF followed consecutively by PVA and casein. In reutilization of out-of-service poles into engineered wood products, pieces that have retained sufficient creosote to be effective against decay should be placed into ground contact. Similarly, pieces of poles with lower creosote content, and consequently better gluability, would be better utilized in non-ground contact areas of engineered wood products. Latewood percentage and angle of growth ring to the glueline also affected gluability. Latewood correlated positively with shear strength and negatively with wood failure. The lower the angle of the growth ring, the higher the shear and the greater the wood failure. D i s p o s a l of weathered, out-of-service utility poles is a serious problem. Nearly 5 million metric tons of preservative-treated wood are disposed of annually into landfills (3). Moreover, about 2 millio~i 1n3 per year of weathered utility poles treated with creosote are available for recycling (4). Of the approximately 150 million wood poles in service carrying electrical transmission and distribution lines, I to 2 million poles are replaced each year. Approxin~ately 75 percent of the annual consumption of the poles consists of southern yellow pine (SYP) (Pinus spp.) (7). Creosote was used in 17 percent of U.S. pole production (1 1 million ft.') in 1993 and part of this volume was exported (2). I'opular waste disposal options, such as combustion and land-filling, are becoming more and more limited due to environmental regulations (8). Reutilization of waste poles by conversion to useful products, such as wood composite poles, can be regarded as one way to solve disposal problems. However, the remaining creosote content in the poles can affect the gluability of the sawn wood. In freshly treated poles, the creosote interferes with bonding due to poor contact between adhesive and wood substrate (9). As a result, fiber-toglue bond strength in treated wood is lower than that in untreated wood. After several years in service, the creosote in poles, due to weathering, can undergo changes in its content and composition, which may affect gluability. Therefore, before out-of-service poles can be properly utilized for engineered wood products such as composite poles, their gluing properties must be known. Contact angle and gluability are related when considering non-porous adherends and thermoplastic adhesives. However, for porous surfaces, such as wood, 'The authors are, respectively, Former Graduate Research Assistant, School of Forestry, Wildlife, and Fisheries, Louisiana State Univ. Agri. Center, Baton Rouge, LA 70803-6202; Principal Wood Scientist, Southern Res. Sta., USDA Forest Serv., Pinevitle, LA 7 1360; and Professor and Assistant Professor, School of Forestry, Wildlife, and Fisheries, Louisiana State Univ. Agri. Center. This paper No. 99-220653 is published with the approval of the Director of the Louisiana Agri. Expt. Sta. This paper was received for publication in November 1999. Reprint No. 9062. Forest Products Society Member. OForest Products Society 2000. Forest Prod. J. 50(10):76-81.