Effects of Graphene and Zinc Borate on Physical, Thermal, and Structural Properties of Recycled Polypropylene: An Experimental Study

Abstract

In this study, recycled polypropylene (RPP)-based nanocomposites were produced using graphene nanoplatelets (GNP) and zinc borate (ZB) as hybrid reinforcements at 0.5 and 1 wt%. The composites were fabricated via twin-screw extrusion and injection molding, and their physical, thermal, and structural characteristics were thoroughly examined. The addition of ZB and GNP significantly improved the Melt Flow Index (MFI) of RPP, indicating reduced viscosity and enhanced chain mobility. The highest MFI measured was 22.60 g/10 min for the blend containing 1 wt% ZB and 1 wt% GNP. This suggests that at these low filler concentrations, the primary mechanism is shear-assisted interfacial slippage rather than the formation of a complex rheological network. The most significant thermal enhancements were achieved with 0.5 wt% GNP, which raised the Vicat Softening Temperature (VST) and heat deflection temperature (HDT) by 8.87% and 7.16%, respectively. Oxidation Induction Time (OIT) results also demonstrated superior thermo-oxidative stability for this formulation, reaching 15.79 min and surpassing both neat RPP and ZB-only composites. Fourier transform infrared spectroscopy (FTIR) and x-ray diffraction (XRD) analyses confirmed that the crystalline structure of RPP remained unchanged, while field emission scanning electron microscopy (FE-SEM) images indicated a reasonably uniform filler distribution.