Elastic and yield behaviors of recycled polypropylene-based composites: Experimental and modeling study

In this work, stiffness and yield behaviors of recycled polypropylene (PP) based composites have been investigated by means of dynamic mechanical analysis (DMA) and split Hopkinson pressure bar (SHPB). It was found that the mechanical behaviors of non-recycled and recycled PP composites depend on temperature and frequency/strain-rate as well as on filler content and recycling cycle. For modeling the elastic modulus and yield stress, two new approaches were proposed. We extended a statistical stiffness model for neat polymers with temperature and frequency/strain-rate dependences by incorporating a Mori-Tanaka based approach and a two-population model to predict the elastic modulus of PP composites. By considering the initial modulus of neat PP and filler aspect ratio with reprocessing dependences, the predicted elastic modulus not only depended on the test temperature and frequency/strain-rate but also depended on the filler content and recycling number. To predict the yield behavior, we extended the modified cooperative model with temperature and strain rate dependences for neat polymers by incorporating a three-phase approach and a two-population model. In particular, the internal stress for neat PP and the interphase parameter B for PP-based composites were considered with reprocessing dependences. Predicted yield stresses by this new approach not only depended on the strain rate and temperature but also depended on the filler content and reprocessing number. A good agreement was found between experimental results and predictions.