Fundamentals of Flakeboard Manufacture: Viscoelastic Behavior of the Wood Component
Keywords:Viscoelasticity, wood polymers, pressing, wood composites, flakeboard, density gradient, environmental conditions
AbstractTheories of the viscoelastic behavior of amorphous polymers are reviewed and are used to describe the density gradient formation in flakeboard. This technique utilizes measured temperature and gas pressure at discrete locations inside a flake mat during hot pressing to predict the glass transition temperature of wood as a function of press time. The difference between the flake temperature and the predicted glass transition temperature is a relative indicator of the amount of flake deformation and stress relaxation at a location in the mat. A knowledge of the stress history imposed in the mat is then used to relate flake deformation and stress relaxation to the formation of a density gradient. This analysis allows for a significant portion of the density gradient to develop after the hot press has closed. Experimental data for various density gradients support the theories presented here.
Back, E. L. 1987. The bonding mechanism in hardboard manufacture. Holzforschung 41(4):247-258.nBack, E. L., and N. L. Salmen. 1982. Glass transitions of wood components hold implications for molding and pulping processes. Tappi 65(7):107-110.nBlankenhorn, P. R., D. E. Kline, and F. C. Beall. 1973. Dynamic mechanical behavior of black cherry (Prunus serotina Ehrh.). Wood Fiber 4(4):298-308.nBrady, D. E. 1987. The effect of hot-pressing parameters on resin penetration and flakeboard layer properties. Master's thesis, VPI&SU, Blacksburg, VA.nCasey, L. J. 1987. Changes in wood-flake properties in relation to heat, moisture, and pressure during flakeboard manufacture. Master's thesis, VPI&SU, Blacksburg, VA.nChristensen, R. M. 1982. Theory of viscoelasticity: An introduction, 2nd ed. Academic Press Inc. New York, NY.nChow, S. Z., and H. N. Mukai. 1972. Polymerization of phenolic resin at high vapor pressure. Wood Sci. 5(1):65-72.nCousins, W. J. 1978. Young's modulus of hemicellulose as related to moisture content. Wood Sci. Technol. 12:161-167.nEasterling, K. E., R. Harrysson, L. J. Gibson, and M. F. Ashby. 1982. On the mechanics of balsa and other woods. Proc. R. Soc. Lond. A383:31-41.nGeimer, R. L. 1980. Data basic to the engineering design of reconstituted flakeboard. Proc. Wash. St. Univ. Particleboard Symp. (April 1980). WSU, Pullman, WA.nGeimer, R. L., R. J. Mahoney, S. P. Loehnertz, and R. W. Meyer. 1985. Influence of processing-induced damage on strength of flakes and flakeboards. For. Prod. Lab. Res. Paper #463. U.S. For. Prod. Lab., Madison, WI.nGoring, D. A. I. 1971. Polymer properties of lignin and lignin derivatives. Pages 695-768 in K. V. Sarkanen and C. H. Ludwig, eds. Lignins: Occurrence, formation, structure, and reactions. Wiley- Interscience, New York, NY.nHumphrey, P. E. 1979. Fundamental aspects of wood particleboard manufacture. Ph.D. dissertation, Univ. of Wales, Bangor, Wales, U.K.nHunt, M. O., and S. K. Suddarth. 1974. Prediction of elastic constants of particleboard. For. Prod. J. 24(5):52-57.nIrvine, G. M. 1984. The glass transitions of lignin and hemicellulose and measurement by differential thermal analysis. Tappi 67(5):118-121.nKamke, F. A., and L. J. Casey. 1988a. Gas pressure and temperature in the mat during flakeboard manufacture. For. Prod. J. 38(3):41-43.nKamke, F. A., and L. J. Casey. 1988b. Fundamentals of flakeboard manufacture: Internal-mat conditions. For. Prod. J. 38(6):38-44.nKamke, F. A., and M. P. Wolcott. 1990. Fundamentals of flakeboard manufacture: Wood-moisture relationships. Wood Sci. Technol. In Press.nKapur, S., C. E. Rogers, and E. Baer. 1972. A mechanism for the β relaxations of wet nylon 6. Poly. Sci.: Poly. Phys. Ed. 10:2297-2300.nKelley, M. W. 1977. Critical literature review of relationships between processing parameters and physical properties of particleboard. Gen. Tech. Report FPL-10. U.S. For. Prod. Lab., Madison, WI.nKelley, S. S., T. G. Rials, and W. G. Glasser. 1987. Relaxation behaviour of the amorphous components of wood. J. Mater. Sci. 22:617-624.nLaufenburg, T. L. 1983. Characterizing the nonlinear behavior of flakeboards. Wood Fiber Sci. 15(1):47-58.nLaufenburg, T. L. 1984. Flakeboard fracture surface observations and correlations with orthotropic failure criteria. J. Inst. Wood Sci. 10(2):57-65.nLaufenburg, T. L. 1986. Using gamma radiation to measure density gradients in reconstituted wood products. For. Prod. J. 36(2):59-62.nMaku, T., R. Hamada, and H. Sasaki. 1959. Studies on the particleboard. Rept. 4. Temperature and moisture distribution in particleboard during hot-pressing. Wood Research, Kyoto Univ. 21:34-46.nLaufenburg, T. L. Pecht, M. 1985. Creep of regain-rheologically simple hydrophyllic polymers. J. Strain Anal. 20(3):179-181.nPrice. E. W. 1976. Determining tensile properties of sweetgum veneer flakes. For. Prod. J. 26(10):50-53.nRials, T. G., and W. G. Glasser. 1986. Engineering plastics from lignin XIII. Effects of lignin structure on polyurethane network formation. Holzforschung 40(6):353-360.nSalmen, N. L. 1982. Temperature and water induced softening behaviour of wood fiber based materials. Ph.D dissertation, Dept. of Paper Tech., The Royal Inst. of Tech., Stockholm, Sweden. Paper I, p. 8.nSalmen, N. L. 1984. Viscoelastic properties of in situ lignin under water-saturated conditions. J. Mater. Sci. 19:3090-3096.nSalmen, N. L., P. Kolseth, and A. de Ruvo. 1985. Modeling the softening behaviour of wood fibres. J. Pulp Paper Sci. 11(4):J102-J107nSchafer, E. L. 1973. Effect of pyrolytic temperatures on the longitudinal strength of dry Douglas-fir. J. Test. Eval. 1(4):319-329.nSchajer, G. S. 1984. Dryrun: One dimensional wood drying computer program. Science and Process Control Unit, Solid Wood R & D, Weyerhauser Technology Center, Tacoma, WA. 45 pp.nSmith, D. 1982. Waferboard press closing strategies. For. Prod. J. 32(3):40-45.nStanish, M. A., G. S. Schajer, and F. Kayihan. 1985. Mathematical models of wood drying from heat and mass transfer fundamentals. Pages 360-367 in R. Toei and A. S. Mujumdar, eds. Drying '85. Hemisphere Publishing Corp., New York, NY.nStrickler, M. D. 1959. Properties of Douglas-fir flakeboard. For. Prod. J. 7:203-215.nSuchsland, O. 1962. The density distribution in flakeboard. Quart. Bull., Michigan Agri. Exp. Sta., Michigan State Univ. 45(1):104-121.nWagner, F. G., T. E. Harless, D. S. Ladd, P. H. Short, R. D. Seale, and D. E. Lyons. 1987. MSU-PDP: A microcomputer model to predict the density profile of particleboard. User's manual. Vs. 2.0. Miss. St. Univ., Starkville, MS.nWard, I. M. 1983. Mechanical properties of solid polymers, 2nd ed. Wiley-Interscience. New York, NY.nWilson, J., and R. L. Krahmer. 1976. Particleboard microscopic observations of resin distribution and board fracture. For. Prod. J. 26(11):42-45.nWolcott, M. P., B. Kasal, F. A. Kamke, and D. A. Dillard. 1989. Testing small wood specimens in transverse compression. Wood Fiber Sci. 21(3):320-329.n
The copyright of an article published in Wood and Fiber Science is transferred to the Society of Wood Science and Technology (for U. S. Government employees: to the extent transferable), effective if and when the article is accepted for publication. This transfer grants the Society of Wood Science and Technology permission to republish all or any part of the article in any form, e.g., reprints for sale, microfiche, proceedings, etc. However, the authors reserve the following as set forth in the Copyright Law:
1. All proprietary rights other than copyright, such as patent rights.
2. The right to grant or refuse permission to third parties to republish all or part of the article or translations thereof. In the case of whole articles, such third parties must obtain Society of Wood Science and Technology written permission as well. However, the Society may grant rights with respect to Journal issues as a whole.
3. The right to use all or part of this article in future works of their own, such as lectures, press releases, reviews, text books, or reprint books.