Structure-Property Relationships in Thermoplastic Cassava Starch/Candelilla Wax Biocomposites Reinforced with Pennisetum purpureum Fibers

Abstract

Thermoplastic starch-based composites often suffer from poor mechanical performance and high moisture sensitivity. This limits their practical applications. In this study, thermoplastic cassava starch modified with candelilla wax (TPCS/CW) was reinforced with Pennisetum purpureum fiber (PPF) at loadings ranging from 0 to 60 wt% using thermo-compression moulding. The structural, morphological, thermal, and mechanical properties of the composites were evaluated using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and mechanical testing. The results showed that fiber incorporation enhanced intermolecular interactions without altering the chemical structure of the starch matrix. Mechanical properties improved significantly with increasing fiber content, with tensile strength and modulus reaching optimum values of 9.14 MPa and 3.28 GPa, respectively, at 50 wt% PPF. Flexural strength and impact toughness also showed maximum values of 26.5 MPa and 4.97 kJ m⁻² at 50 wt% PPF. Thermogravimetric analysis indicated a slight reduction in onset degradation temperature with fiber addition, accompanied by a notable increase in char residue. However, excessive fiber loading (60 wt%) led to fiber agglomeration and reduced performance. These findings demonstrate that PPF is an effective reinforcement for TPCS/CW composites, with potential applications in biodegradable packaging, disposable products, and low-load structural components.