Effect of the addition of cellulose filaments on the relaxation behavior of thermoplastics

Abstract

In this work, the effect of cellulose filaments (CFs) dispersion on the relaxation behavior of thermoplastics matrices was studied. The dispersion state of polystyrene/CF composites produced by two different processing methods, leading to two different dispersion qualities, was assessed using scanning electron microscopy (SEM), transmission electron microscopy, and small amplitude oscillatory shear (SAOS). Instead of the generally used plateau value of G′, the melt yield stress of the modified Carreau–Yasuda model was used to find an accurate value of the percolation threshold concentration. It was concluded that in this case, the process involving a solution mixing step led to a better dispersion than the process involving only melt mixing. Then, using the weighted relaxation spectra calculated using the Honerkamp and Weese method on SAOS results, it was shown that the better the dispersion, the more delayed the relaxation process of the polymer matrix. Finally, by studying the relaxation spectra as well as the melt yield stress of polypropylene/CF composites, it was possible to understand the evolution of their morphology upon CF concentration. It was shown that below 5 wt. %, a well dispersed network of CF was obtained, whereas from 5 to 15 wt. % CFs were agglomerating, then leading to a network of agglomerated fibers for concentrations above 15 wt. %. Those assessments done using SAOS results were confirmed by SEM.