Preparation of chitin nanofibers (whiskers) and their application as property-recovery agents in re-processed polypropylene

Abstract

The possibility of recycling polypropylene (PP)-based automobile parts is among the most important strategies to restrict the environmental impact of vehicles after their life cycle. However, current recycling conditions often lead to changes in the structure and properties of PP. In this work, the hypothesis that whiskers derived from chitin could be used to recover the dynamic mechanical properties of re-processed PP to its original values was tested. PP was subjected to multiple extrusion cycles to simulate recycling conditions. Chitin whiskers were prepared by an acid treatment of chitin and were dispersed in both neat and re-processed PP. The obtained whiskers and nanocomposites were characterized using X-ray diffraction, infrared spectroscopy, dynamic scanning calorimetry, transmission electron, scanning electron and atomic force microscopies and dynamic mechanical analysis. Results indicated that oxidation of PP has occurred during re-processing. Moreover, chitin whiskers were synthesized and successfully incorporated in PP and re-processed PP. The nanocomposites showed lower values of crystallinity than neat and re-processed pure PP. Dynamic mechanical analysis showed that the behavior of storage elastic modulus as well as the loss tangent as a function of temperature of nanocomposites containing 1 wt% chitin whiskers in re-processed PP was similar to the one displayed by neat PP. The capability of the chitin whiskers to interact better with oxidized PP chains and to restrict crystallization would be responsible for their observed potential in recovering the dynamic mechanical behavior of re-processed PP to its original behavior.