The influence of mechanical recycling on the properties of thermotropic liquid crystalline polymer and long glass fiber reinforced polypropylene

The effect of mechanical recycling on the properties of injection-molded polypropylene (PP) reinforced with thermotropic liquid crystalline polymer (TLCP) or long glass fiber (GF) has been investigated. The 30 and 50 wt% in situ TCLP and GF reinforced composites were mechanically recycled for three processing cycles, using an injection molding machine with an end-gated plaque mold. The processing temperatures used in the mechanical recycling were determined using rheological and thermogravimetric analyses to minimize the degradation of polypropylene. Recycled TLCP/PP maintained its mechanical properties, and recycling had no significant influence on its morphological, thermal, rheological, and thermo-mechanical properties. Morphological investigation illustrated the regeneration of TLCP fibrils during the mold filling process of each recycle. By the addition of maleic anhydride-grafted polypropylene (MAPP), significant improvements in the mechanical properties of TLCP/PP without impact on recyclability were observed. In contrast, the tensile strength of 50 wt% glass fiber reinforced composite decreased 30% while the tensile modulus decreased 5% after the third recycle. Glass fiber filled polypropylene exhibited significant fiber shortening and was not able to regenerate fibers in processing. Fiber length attrition during the recycling process led to the deterioration of the mechanical properties of the recycled glass filled composites.