Effect of Recycling on the Thermal and Rheological Properties of PP/MWCNT Composites Used as Liner Materials

In this study, we developed polypropylene-based nanocomposites using different (0.3, 0.5, and 1 wt%) fillers of multi-walled carbon nanotubes (MWCNTs), with a particular focus on their applicability as lining materials for Type IV hydrogen storage tanks. The aim of this research was to improve the thermal stability and rheological behavior of PP, while also evaluating the recyclability of the resulting composites in order to support sustainability goals. A realistic recycling approach was simulated by producing original and regranulated (REG) samples using a twin-screw extruder. Thermal analysis showed that the incorporation of MWCNTs promoted crystallization, increasing both the degree of crystallinity and lamellar thickness, which are beneficial factors in terms of reducing gas permeability. Rheological tests showed increased storage and loss moduli in both nanocomposites and their recycled counterparts, especially at low frequencies. It is noteworthy that in REG samples with 0.3 and 1 wt% content, the zero-shear viscosity increased by approximately 50% and 90%, respectively, compared to pure PP. In our research, we produced nanocomposites that could offer significant advances in the field of hydrogen storage and liner materials, while the results of the regranulated composites could further enhance the sustainability of our materials.