Dynamic Mechanical Analysis of Biocomposites Produced from Recycled Polypropylene and Groundnut Shell Powder

Abstract

The increasing accumulation of plastic waste and agricultural residues has stimulated interest in developing value-added polymer composites through waste recycling and biomass utilisation. This study investigated the dynamic mechanical and thermal properties of recycled polypropylene (rPP) composites reinforced with groundnut shell powder at loadings of 1, 5, 10, and 15 wt%. The composites were fabricated using a two-roll mill at 160 °C for 10 min, followed by compression moulding at 170 °C for 10 min. Dynamic mechanical analysis (DMA) was performed over a temperature range of −40 to 150 °C at a heating rate of 3 °C min⁻¹, a frequency of 1 Hz, and a strain amplitude of 0.1%. Thermogravimetric (TG), derivative thermogravimetric (DTG), and differential thermal analyses were conducted from room temperature to 800 °C at a heating rate of 10 °C min⁻¹ under nitrogen. The unreinforced rPP exhibited a storage modulus of 1,375 MPa at 25 °C, whereas the composite containing 15 wt% groundnut shell powder exhibited a loss modulus of 67 MPa at the same temperature. Glass transition temperatures estimated from the loss modulus and tan δ curves differed by no more than 7 °C, with tan δ peaks occurring between approximately 0 and 20 °C. Thermal analysis revealed lignocellulosic decomposition in the approximate range of 200–380 °C for the groundnut shell powder, while the principal degradation of the rPP matrix occurred between approximately 400 and 484 °C. The composite containing 15 wt% filler reportedly exhibited the highest residual mass at 800 °C. Overall, the findings demonstrate the feasibility of incorporating groundnut shell powder into recycled polypropylene, with the 5 wt% formulation identified as a potentially promising composition based on its reported dynamic mechanical response. Further quantitative comparisons of mechanical performance and thermal stability are required to establish the optimum formulation and suitability for specific applications.