Because of the large percentage of juvenile wood in small-diameter southern pine, this material has lower strength properties compared with the historic published values in the ASTM Standard D2555. Finding new, simple, and inexpensive ways of increasing these strength properties would increase the use of this material for residential construction. For this study, we chose in situ polymerization using the monomer 1,6-hexanediol dimethacrylate to enhance bending strength and stiffness. After determining the lower range of density, modulus of rupture (MOR), and modulus of elasticity (MOE) of juvenile wood from small southern pine logs, southern pine specimens were polymerized using both a vacuum-impregnation and a surface-application approach. The results showed some significant physical property increases for the fully impregnated material that used a large amount of monomer. Although the surface-application approach used less monomer, the physical properties of the juvenile wood did not increase as expected. Only the 1-minute dip treatment showed a significant increase in both bending stiffness and strength, with a weight gain of 11.9 percent. For the surface-application approach, monomer moving to the wood surface during polymerization reduced their effectiveness in increasing MOR and MOE to the expected levels. Therefore, the challenge is finding a method that maintains polymer loading inside the wood structure during the curing process.
The authors are, respectively, Research Forest Products Technologist, Economics and Statistics Research, and Research Chemist, Performance Enhanced Polymers, USDA Forest Serv., Forest Products Lab., Madison, Wisconsin (firstname.lastname@example.org, email@example.com); and Research Analyst and Professor, Dept. of Wood and Paper Sci., North Carolina State Univ., Raleigh (firstname.lastname@example.org, email@example.com). This paper was received for publication in April 2009. Article no. 10605.
*Forest Products Society member.