UNIAXIAL MODELING OF VIBRATIONAL PROPERTIES OF CHEMICALLY MODIFIED WOOD

The effect of chemically modified wood structure on the specific longi tudinal dynamic Young's modulus (E'/gamma) and loss tangent (tan delta ) was analyzed by using rheological analogies. Comparison with experim ental data, after eliminating the effect of volume and weight increase , allowed an estimate of the changes of rigidity and viscosity of the amorphous regions of the cell wall (matrix). In a formaldehyde treatme nt, a rigidity increase and an even more pronounced viscosity increase were evidenced and attributed to matrix crosslinking. In acetylation and epoxide treatments, swelling alone would have decreased E'/gamma a nd increased tan delta; the observed tan delta decrease in the first c ase and the increase in the second was explained by the hydrophobic or hydrophilic nature of the respective bulking agents. PEG (polyethylen e glycol) molecules both provoked swelling and reduce matrix rigidity and viscosity. In the case of wood plastic composite with the filling of lumens only, the effect of the treatment depended greatly on the vi scoelastic properties of the resin introduced: usually the weight incr ease should induces a marked decrease of E'/gamma, and a simultaneous E'/gamma increase and a tan delta decrease are difficult to obtain.