Rheological behavior of original and recycled cellulose–polyolefin composite materials

The effects of shear rate, fiber content and type of matrix on the melt rheological behavior of cellulose–reinforced polyolefin composites before and after their mechanical recycling was investigated, due to their relevance for the suitable engineering design of their processing operations. Original composites of HDPE or PP with residual Kraft pulp fiber contents of 10, 25, 40 and 48 wt% were obtained in a thermokinetic mixer. Five-cycle reprocessed composites were produced by successive injection molding. Capillary rheometry enabled us to obtain rheological curves for all these composites, and developing a new statistically checked modified Ostwald-de-Waele model for predicting their rheological behavior in real situations. The rheological data collected, along with SEM and TGA analysis, mainly revealed a more pronounced degradation of cellulose fibers for the HDPE-matrix reprocessed composites, a greater pseudoplasticity loss upon recycling for the PP-matrix composites than for HDPE-matrix ones, and that fiber’s dispersion was independent of matrices used.