LAUSR

The exposure of wood to elevated temperatures during hot water extraction (HWE) has been shown to significantly influence a variety of physical and chemical properties of the wood. Aspen (Populus tremuloides) and hemlock (Tsuga canadensis) strands underwent HWE at 160 °C for four different periods of time. The weight loss (WL) associated with the processes ranged from 2.9 to 17.3% for the aspen, and from 2.9 to 12.8% for the hemlock. The higher WL associated with the hardwood was attributed to higher hemicellulose content in the hardwood than in the softwood as well as differences in chemical composition. Substantial increases in cell wall hardness (up to 34%) and modulus of elasticity (MOE) (up to 28%) were obtained at the intermediate extraction conditions. Extended exposure conditions resulted in decreases. The axial MOE of strands showed significant differences only in aspen. These changes are hypothesized to be related, in part, to changes in cellulose crystallinity.