The Effect of Acetylation On The Shear Strength Development Kinetics of Phenolic Resin-To-Wood Bonds
Keywords:Acetylation, bond strength development, pressing temperature and pressing time, phenol formaldehyde
AbstractChemical pretreatment of materials used in wood-based composite products before lay-up and pressing has some advantages over the post-treatment of panels. However, pretreatment may affect the relationship between temperature and strength development rate of adhesive bonds (as well as final strengths). Such relationships affect minimum pressing times and the consequent economic viability of panel production. Acetylation is a possible chemical pretreatment. The effect of acetylation level on the strength development rates of small phenol-formaldehyde-to-wood test bonds was therefore investigated. Pieces of maple (Acer macrophyllum Pursh) measuring 0.8 X 20 X 106 mm were acet-ylated with acetic anhydride at 120° C to achieve weight percentage gains of 8.17, 11.62, and 14.49. Bonds were formed at pressing temperatures of 86° C, 97° C, 107° C, and 113° C for a variety of times and were immediately thereafter tested in shear mode. An automated bond formation and evaluation system (ABES) was used for this purpose. Four near-isothermal bond strength development curves were constructed for each acetylation level. The curves suggest differences in shear strength development rates at the early stages of bond development. Linearly regressed early rates were affected by both temperature and acetylation level, although the effect of acetylation level was small. Cold and fully cured bond strengths were impaired by acetylation; this is consistent with others' findings.
Bolton, A. J., and P. E. Humphrey. 1988. The hot pressing of dry-formed wood-based composites. Part I. A review of the literature, identifying the primary physical processes and the nature of their interaction. Holzforschung 42:403-406.nChow, P., Z. Bao, J. A. Youngquist, R. M. Rowell, J. H. Muehl, and A. M. Krzysik. 1996. Properties of hardboards made from acetylated aspen and southern pine. Wood Fiber Sci. 28(2):252-258.nGoldsthin, I. S., E. B. Jeroski, A. E. Lund, J. F. Nielson, and J. M. Weather. 1961. Acetylation of wood inlumber thickness. Forest Prod. J. 11:363-370.nGollab, L., and J. D. Wellons. 1990. Wood adhesion. Pages 598-610 in I. Skeist, ed. Handbook of adhesives. 3rd ed. Van Nostrand Reinhold, New York, NY.nGomez-Bueso, J., R. Torgilsson, M. Westin, P. Olesen, and R. Simonson. 1996. Properties of composites made from acetylated lignocellulosic fibers of different origins. Pages 432-440 in H. Kajita and K. Tsunoda, eds. Toward the new generation of bio-based composite products. Proc. Third Pacific Rim Bio-based Composites Symposium, December 2-5, Kyoto, Japan.nHumphrey, P. E. 1993. A device to test adhesive bonds. U.S. Patent number 5,176,028. U.S. Patent Office, Washington, DC.nHumphrey, P. E. 1996. Thermoplastic characteristics of partially cured thermosetting adhesive-to-wood bonds: The significance for wood-based composites manufacture. Pages 366-373 in H. Kajita and K. Tsunoda, eds. Toward the new generation of bio-based composite products. Proc. Third Pacific Rim Bio-based Composites Symposium, Kyoto, Japan.nHumphrey, P. E. 1997. Adhesive bond strength development in pressing operations: Some considerations. Pages 145-155 in Proc. First European Panel Products Symposium, Llandudno, Wales, U.K.nHumphrey, P. E., and D. Zavala. 1989. A technique to evaluate the bonding reactivity of thermosetting adhesives. J. Testing Eval. 7(6):323-328.nPizzi, A. 1994. Advanced wood adhesives technology. Marcel Dekker, Inc. New York, NY. pp. 119-126.nRowell, R. M. 1982. Distribution of acetyl groups in southern pine reacted with acetic anhydride. Wood Sci. 15:172-182.nRowell, R. M., and W. B. Banks. 1987. Tensile strength and toughness of acetylated pine and lime flakes. Br. Polymer J. 19:478-482.nRowell, R. M., A. M. Tillman, and R. Simonson. 1986. A simplified procedure for the acetylation of hardwood and softwood flakes for flakeboard production. J. Wood Chem. Technol. 6(3):427-448.nSheen, A. D. 1992. The preparation of acetylated wood fibre on a commercial scale. Pages 1-8 in D. V. Plackett and E. A. Dunningham, eds. Chemical modification of lignocellulosics. FRI Bulletin 176. New Zealand Forest Research Institute, Rotorua, New Zealand.nStamm, A. J., and H. Tarkow. 1947. Acetylation of wood and boards. U.S. Patent number 2,417,995. U.S. Patent Office, Washington, DC.nTarkow, H., A. J. Stamm, and E. C. O. Erickson. 1950. Acetylated wood. Forest Prod. Lab. Rep. 1593. USDA Forest Serv., Forest Prod. Lab., Madison, WI. 29 pp.nVick, C. B., and R. M. Rowell. 1990. Adhesive bonding of acetylated wood. Int. J. Adhesion and Adhesives 10(4):263-272.nYoungquist, J. A., and R. M. Rowell. 1986. Mechanical properties and dimensional stability of acetylated aspen flakeboard. Holz Roh-Werkst. 44:453-457.n
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