Mechanical, thermal and morphological analysis of extrudate polypropylene reinforced with graphene nanoplatelets

Polypropylene (PP) is a prominent thermoplastic in engineering applications due to its low cost and ease of production. However, PP-based composites characteristically exhibit low strength, impact resistance and stiffness, which limit their application, resulting in frequent replacement and material waste. Graphene nanoplatelets (GNP) used as nanofillers have been widely studied to overcome these limitations. Yet, the challenge lies in determining the optimal GNP content to enhance the mechanical properties of PP. This study investigated the fabrication of PP/GNP nanocomposites with GNP contents of 1, 3, 5, 7, and 9 wt% using a twin-screw extruder at 170°C, followed by pelletisation. The extruded pellets were hot-compression moulded into 3 mm-thick sheets. The results show that tensile strength increased by 4.6% with 7 wt% GNP, while flexural strength improved by 30.1% with 5 wt% GNP. Impact strength increased by 140% with 7 wt% GNP compared to neat PP. SEM analysis indicates that nanocomposites with 5 wt% GNP are homogeneous and exhibit minimal porosity. Raman spectroscopy confirms the presence of PP and GNP components, consistent with DSC results, suggesting an organised semi-crystalline structure. TGA data indicate a gradual improvement in the thermal ability of the PP/GNP nanocomposites. This study identifies a 5 wt% GNP content as the optimal proportion, providing a balanced improvement in stiffness, strength, toughness and microstructural quality.