Viscoelastic properties of the matrix substance of chemically treated wood

The temperature variations of the storage modulus and the loss tangent along the grain for four kinds of chemically modified Sitka spruce (Picea sitchensis Carr.) woods were measured at 11 Hz over a temperature range of –150 to 200 °C. By using a cell-wall model in which the amorphous matrix substance is disposed parallel to the axis of cellulose fibrils inclined at an angle to the grain direction of the wood, the storage modulus, Em, and the loss tangent, tan m of the matrix substance were estimated, and the relaxation processes detected were discussed. In formalization, the restriction of the micro-Brownian motion of the main chains due to oxymethylene bridges between the hydroxyl groups resulted in a decrease in tan m above 0 °C. In acetylation and propylene oxide treatment, a marked reduction in Em was observed over the temperature range tested, by the introduction of bulky side chains, and the tan m remarkably increased in the high-temperature range. In polyethylene glycol (PEG) impregnation, the Em increased below 20 °C due to the freezing of the micro-Brownian motion of PEG molecules in the cell lumens as well as in the cell walls, while it was reduced above this temperature by the melting of PEG molecules.