The characterization of PLA and PLA composites was successfully performed using mechanical and thermal analytical techniques in order to investigate the effects of the natural filler kena as well as the AM additive thymol on the stability and performance of the material during processing.
The results suggest that the addition of thymol to PLA and РLA/kenаf composites imparts a plasticizing effect that modifies the rheology and subsequent mechanical properties of the processed materials. In particular, the equilibrium torque value of each of the materials was decreased during processing with the addition of thymol thereby offsetting to some extent, the effects of the incompatibility between the PLA matrix and the kenaf fibres. This observation was supported by evidence obtained from high magnification images of the fracture surface ofthe PLA/kenаf composites. The incorporation of thymol into PLA/kenаf composites also decreased the tensile strength with no significant change observed upon increasing the kenaf fibre loading. The tensile strength and stiffness of PLA/kenаf composites however increased with higher fibre loadings thereby imparting a reinforcement effect within the PLA composite. Moreover, it was found that acceptable tensile strength was attained by the PLA/kenаf composites containing thymol compared to the commercial neat PLA thereby rendering these materials as potential candidates for commercial packaging systems. Nonetheless, the effect of AM agent addition on the impact strength of the material might also be an interesting property to investigate prior to developing these systems for commercial applications
The DSC analyses showed a general decrease of Тg, Tсс, Тm and ДНm, with no significant changes in %Xc, for PLA and PLA/kenаf composites containing 5% and 10% (w/w) thymol. It was noted that an increased loading of kenaf fibres in the PLA resulted in a decrease in the TGA decomposition temperature indicating a reduced thermal stability of the PLA. The TGA results also suggested that thуmol can be released from the PLA/kenаf matrix at relatively low temperatures and as such has the potential to impart AM activity. Further work in our laboratory is currently underway to evaluate the kinetics of thymol release from these systems and their subsequent AM activity in order to develop effective active food packaging materials.