Mathematical and experimental study on flow of wood plastic composite to acquire its constitutive equation

This article presents a study on the rheological behavior of wood plastic composites with a mathematical approach to acquire their melt constitutive equation. The wood plastic composites were produced with four compositions of high density polyethylene as the matrix and very fine wood particles, smaller than 50 µm in size, as the fillers: 40, 50, 60 and 70 wt% of wood content. Storage modulus ( G′), loss modulus ( G′′), complex viscosity ( η*) were measured for all four composites at a temperature of 170°C and for shear rates in the range of 1–500 rad/s. The results indicated a noticeable increase in all measured properties upon increasing the wood content. In mathematical approach, the main goal was to obtain the most fitted expression to relate shear stress with shear rate. Firstly power law model was applied considering a viscous behavior of the composites. In continue, generalized Maxwell model was used and the most fitted number of the elements in modeling was analyzed for various wood contents. Moreover, Cox–Merz rule was evaluated for the composites, where it showed that this rule is only valid for the composites in some special conditions.