Polylactic Acid/Polymethylsilsesquioxane (PLA/PMSQ) Microparticle Composites: Development and Characterization

Polylactic acid (PLA) is a promising bio-based polymer, but its limited thermomechanical stability and low thermal conductivity restrict its use in thermoforming. This study aimed to investigate the influence of polymethylsilsesquioxane (PMSQ) microparticles (5–15 wt.%) on the thermal, mechanical, thermomechanical, rheological, and heat-transfer properties of PLA biocomposites prepared by melt blending and injection molding, with a focus on the thermomechanical properties and thermal conductivity. The results showed that PMSQ acted as an effective nucleating agent, reducing the cold crystallization temperature by up to 14 °C and increasing the crystallinity of PLA, while having little influence on its melting and glass transition temperatures. At 5 wt.% PMSQ, the storage modulus increased by 15% at 35 °C and the thermal conductivity improved by up to 23% at 75 °C, indicating enhanced thermomechanical stability and heat-transfer efficiency. In contrast, tensile strength, yield strength, and impact resistance decreased at higher PMSQ contents (10–15 wt.%), mainly due to particle agglomeration and the formation of defects observed by SEM. Rheological analyses further showed that PMSQ slightly modified the viscoelastic relaxation behavior of PLA. Among the investigated formulations, PLA containing 5 wt.% PMSQ provided the most favorable balance between thermal conductivity, thermomechanical and thermal stability, and mechanical performance. A limitation of the study is that the individual contribution of the coupling agent was not evaluated separately. Overall, the results demonstrate that low PMSQ contents represent an effective strategy for improving the thermal and thermomechanical performance of PLA and highlight the potential of PLA/PMSQ biocomposites for infrared-assisted thermoforming applications.