Microfibrillated cellulose for enhanced performance of PLA composites after soil degradation and water absorption

Poly (lactic acid) (PLA) composites can be a sustainable and biodegradable alternative to conventional synthetic plastics. It could be widely used across a range of applications, including trunk liners, door panels, and interior storage compartments, demonstrating its suitability for lightweight and durable interior applications. However, despite its versatility, overcoming the inherent limitations of PLA—particularly its relatively low degradation rate and water absorption —remains a challenge. In this study, the impact of integrating microfibrillated cellulose (MFC) as a reinforcement in PLA composites, specifically at fiber loadings of 0.5 wt% and 1.5 wt%, was comprehensively investigated through soil degradation and water absorption tests, examining their effects on mechanical, thermal, and morphological behavior. The MFC from curaua fibers utilized in the composites was pretreated with NaClO and NaOH solutions to optimize its interfacial properties. Interestingly, the composite with 0.5 wt% MFC showed delayed degradation and superior mechanical performance compared to the 1.5 wt% composite. Before degradation, the 0.5 wt% MCF/PLA composite had a flexural strength of 50.38 ± 2.83 MPa, statistically superior to the 44.09 ± 8.35 MPa of the 1.5 wt% composite. Under dry dynamic mechanical analysis (DMA) conditions (time mode and 1 Hz), the 0.5 wt% composite exhibited the highest storage modulus (3.13 GPa), notably higher than the 2.55 GPa recorded for the 1.5 wt% composite. After 90 days of soil exposure, the 0.5 wt% formulation retained significantly more strength (33.97 MPa) than the 1.5 wt% composite, which dropped to 13.07 MPa. The 0.5 wt% composite also showed the least affected increase in crystallinity after soil degradation (16.18%). Despite the 0.5 wt% composite absorbing slightly more water (nearly 1%) than the 1.5 wt% composite, it maintained a higher storage modulus under wet conditions (0.5% at 1.85 GPa vs 1.5% at 1.77 GPa at 1 Hz). These results revealed the complex interplay between the MFC content and composite characteristics. Furthermore, the intricate balance between degradability and water absorption is paramount when determining the optimal application of these biocomposites.