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AbstractThe potential for using pretreatment with cinnamon leaf oil or juniper foliage oil to improve the durability of viscoelastic thermal compression (VTC)–treated hybrid poplar was explored in a field termite test and a laboratory mold test. The addition of oils prior to VTC processing had variable effects on resistance to both mold and termite attack. Subsequent gas chromatography–mass spectroscopy assessment of residual oil components in VTC processed material suggested that the heating associated with the process was associated with substantial degradation of oil components that might help explain the lack of protective effect. The results suggest that further attempts to use essential oils to improve the durability of VTC processed materials must first explore less aggressive heating conditions to reduce the potential for thermal degradation of oil components while still achieving the attractive gains in physical properties associated with the process.

Unlike constant moisture effects on the behavior of composite materials, transient moisture effects are not well studied and known. Armstrong and Kingston have shown that the creep of wood under transient humidity levels could be greatly accelerated over that at any constant moisture content. Later this phenomenon was termed "mechano- sorptive". In this paper, the authors show that aramid fibers (Kevlar® 29, Kevlar® 49, and Kevlar® 149) and Kevlar® 49/epoxy composites exhibit mechano-sorptive phenomenon. Kevlar® composites were studied using both creep and dynamic mechanical analysis while undergoing desorption. Creep of single Kevlar® fibers was studied during relative humid ity conditions cycled between 5 % and 95 %. The results observed with Kevlar are consis tent with those reported for other natural polymeric materials.

An optimum amount of adhesive penetration is desirable for economy of production and development of bond strength in wood composites. A general method that allows quantitative measurement of gross adhesive penetration in wood is described. Staining techniques have been developed that can provide sharp contrast between a cured adhesive and the wood substrate using fluorescence microscopy. An image analysis system utilizes this contrast to quantify gross adhesive penetration in wood. An example of this technique is provided, whereby the effect of molecular weight distribution of phenol formaldehyde prepolymers on gross adhesive penetration into yellow poplar (Liriodendron tulipifera) flakes is observed and quantified. Adhesive penetration into wood flakes was shown to be correlated with the molecular weight distribution of the prepolymer, decreasing with higher weight average molecular weight. Gross adhesive penetration into hardwoods is likely to be dominated by flow into vessel elements, as demonstrated by the wood species studied here.