Recycling effects on the bending, rheological, and structural properties of glass fiber-reinforced isotactic polypropylene composites

In the present work, a combination of virgin polypropylene and E-glass fiber was subjected to ten (10) reprocessing cycles via extrusion and compression molding techniques to mimic recycling and its impacts on the bending properties of the composites. The samples were characterized using Fourier transform infrared (FTIR) spectroscopy, x-ray diffraction (XRD), scanning electron microscopy (SEM), and melt flow index (MFI). The results revealed a gradual depreciation in flexural properties after each reprocessing cycle. The XRD analysis indicated a substantial reduction of peak intensities, degrees of crystallinities, and average crystallite sizes, explaining the lowered flexural properties in addition to a possible reduction in glass fiber lengths (fiber attrition). Melt-processing behavior shows a progressive increase of MFI from 7 to 19.16 g/10 min, confirming the probable damage in molecular weight and loss of complex viscosity. Chemical and structural analysis showed no alteration in the polypropylene major functional groups. It is concluded that the reductions in molecular weight and composites' properties occurred due to chain scission from recycling effects; hence, glass fiber-reinforced polypropylene composites can be recycled only three (3) times unless it is refreshed by the addition of virgin parts to compensate for the lost property.

Automated summary

In this study, recycled polypropylene-E-glass fiber composites were investigated to evaluate the effect of recycling on bending properties. The results showed a gradual decrease in flexural properties with increasing reprocessing cycles. XRD analysis revealed reduced crystallinity and glass fiber length, while melt flow index increased, indicating damage to molecular weight and complex viscosity. The major functional groups of polypropylene remained unchanged. It was concluded that the composite properties and molecular weight can only be maintained through limited recycling or by incorporating virgin parts.