Rheological behavior of wood flour filled poly(lactic acid): Temperature and concentration dependence

The aim of this study is to evaluate the influence of temperature and filler concentration on the rheology of wood fiber filled poly(lactic acid). After measuring complex viscosity for various filler amounts (0–30 wt%) and temperatures (155–175°C), it has been found that a single master-curve can be obtained by shifting the curves diagonally onto the one of the neat matrix at a reference temperature. Considering only the complex viscosity of the neat matrix at all temperatures, the resulting pure thermal shifts can be fitted by a Williams–Landel–Ferry equation. The same procedure can be employed considering the complex viscosity of all composites at the reference temperature. Here, the concentration shifts are approximated by a Krieger–Dougherty equation. We propose that these two pure shift factors can be combined together, independently of each other, for predicting the complex viscosity of the composites at any temperature and filler amount. The main assumption of this procedure is that temperature and filler concentration effects must be disjoint. For validation, the predicted shift factors have been compared with the experimental ones related to composites tested at temperatures other than reference. The agreement is satisfactory, thus the hypotheses at the basis of this methodology are justified. POLYM. COMPOS., 40:E169–E176, 2019. © 2017 Society of Plastics Engineers.