Development of waste tire-derived graphene reinforced polypropylene nanocomposites with controlled polymer grade, crystallization and mechanical characteristics via melt-mixing

In the present work, single layer graphene nanoplatelets (GNPs) derived from waste tires by recycling and upcycling approaches were integrated in homopolymer (Homo-) and copolymer (Copo-) polypropylene (PP) matrices by fast and efficient mixing in the melt phase. The effect of GNP content on crystallization and mechanical behaviors was investigated in detail at different loading levels. Regarding isothermal and non-isothermal crystallization experiments, GNPs significantly accelerated the nucleation and growth of crystallites, and the crystallization degree in Homo-PP nanocomposites was slightly higher than that of Copo-PP based nanocomposites. Also, there was significant improvement in mechanical and thermal properties of GNP reinforced polymers compared to neat polymers. As the GNP concentration increased from 1 to 5 wt%, there was a gradual increase in flexural modulus and strength values. In tensile tests, an increase in GNP content in both polymer grades led to a slight increase in yield strength coming from the proper distribution of nano-reinforcement by creating stress concentration sites. After the yield point, Homo-PP based nanocomposites showed higher strain hardening than GNP reinforced Copo-PP owing to a high crystallization degree and linear chains of Homo-PP. This work showed that functionalized graphene can act as both nucleating and reinforcing agent in the compounding process and its exfoliation through polymer chains is much better in homopolymers at a faster and high shear rate