Interfacial Engineering of Sustainable Microcrystalline Cellulose-Reinforced PLA/PHA Biocomposites for Enhanced Performance

The increasing demand for sustainable materials has accelerated the development of biodegradable polymer composites with enhanced multifunctional performance for engineering, packaging, and biomedical applications. In this study, poly(lactic acid) (PLA)/polyhydroxyalkanoate (PHA) biocomposites reinforced with microcrystalline cellulose (MCC) and a compatibilizer were fabricated by melt blending followed by compression molding. Fourier-transform infrared spectroscopy confirmed enhanced hydrogen-bonding interactions between MCC and the PLA/PHA matrix, indicating improved interfacial compatibility. X-ray diffraction and Differential scanning calorimetry revealed that MCC acted as an significant heterogeneous nucleating agent, increasing the crystallinity from 28.6% for the neat PLA/PHA blend (S0) to 40.1% while reducing the cold crystallization temperature from 115.2 to 110.5 °C and increasing the melting enthalpy from 29.8 to 38.9 J g−1. Thermogravimetric analysis demonstrated improved thermal stability, with the maximum degradation temperature increasing from 325.1 to 343.8 °C and the residual char yield increasing from 5.6% to 16.8%. Specimen S7, containing 6 wt.% MCC and 2 wt.% compatibilizer exhibited the optimum overall performance, achieving a tensile strength of 64 MPa, Young’s modulus of 2500 MPa, impact strength of 5.8 kJ/m2, cell viability of 98%, and 88.5% weight loss after 180 days of soil burial. These findings demonstrate that interfacial engineering with MCC and compatibilizer significantly enhances the structural, thermal, mechanical, biological, and biodegradation performance of PLA/PHA biocomposites, making them promising candidates for sustainable advanced packaging and biomedical applications.