Effect of surface treatment of cellulose fiber (CF) on durability of PLA/CF bio-composites

Bio-composites made of polylactic acid (PLA) matrix reinforced with cellulose fibers (CF) were prepared using a twin-screw extruder and injection molding. The CFs were coated with epoxy-based surface treatment agents. Accelerated degradation tests were carried out on these PLA/CF composites at high temperatures (60 °C) or at constant temperature and constant humidity (60 °C/70% RH), and the higher-order structure changes and degradation characteristics of the molded products were evaluated. In the accelerated degradation test at 60 °C, the thermal and mechanical properties of PLA/CF composites showed no degradation, whereas at 60 °C and 70% RH, the melting point decreased ca. 25 °C and the storage modulus with increasing elapsed time decreased more than 50%. However, the thermal and mechanical properties of the PLA/CF composites treated with low-molecular-weight epoxy did not degrade, even at the high humidity of 70% RH. These results strongly suggest that the surface treatment agent not only improves interfacial adhesion between CF and PLA but also plays an important role in inhibiting degradation of the PLA matrix.