Compatibilizing effect of grafted recycled graphene on the viscoelasticity and mechanical performance of polypropylene composites

The interface problem encountered with the graphene addition in polyolefin composites is an important issue and it is necessary to use various compatibilizers to overcome this problem. Maleic anhydride grafted Polypropylene (MAPP), which is an extensively used compatibilizer in PP composites tends to eliminate these interfacial problems by interacting physically through PP chains and allows easier stress transmission from matrix to reinforcer. However, there is a lack of understanding about how this compatibilizer works with graphene-based PP composite systems since MAPP is mostly used to harmonize hydrophilic surfaces of fillers with non-polar PP. With this study, instead of direct usage of MAPP and GNP separately, waste tyre driven graphene nanoplatelets (GNP) was grafted by MAPP and the resulted material (MAPP-g-GNP) was compounded with PP by applying high shear rates at a melt phase. Effect of MAPP-g-GNP on the processability, viscoelastic response, and mechanical performance of PP composites were investigated, and high degree of interfacial enhancement was achieved by chemically combined MAPP with amphiphilic type of GNP in PP matrix. The use of MAPP-g-GNP at a loading ratio of 0.1 wt% resulted in 38% increase in flexural modulus and 26% in flexural strength and tensile modulus compared to neat PP. The two additives used in the PP composite (2 wt% MAPP and 0.1 wt % GNP) were reduced to a single additive (PP/MAPP-g-GNP) with a 95% weight reduction in the additive content of PP. Rheological studies support that MAPP is not as successful as MAPP-g-GNP in strengthening the interface when used alone with GNP due to the lower complex viscosity and the higher crossover frequency. This study contributes to the production of high-performance PP materials with a very low amount of combined GNP and compatibilizer by integrating the circularity approach in compound development by using GNP obtained from recycled and upcycled waste tyres.