No abstract

Biopolymers with universal accessibility and inherent biodegradability can offer an appealing sustainable platform to supersede petroleum-based polymers. In this research, a hybrid system derived from cellulose nanocrystals (CNCs) and zinc oxide (ZnO) nanoparticles was added into poly (lactic acid) (PLA) to improve its mechanical, thermal, and flame resistance properties. The ZnO-overlaid CNCs were prepared via the solvent casting method and added to PLA through the melt-blending extrusion process. The composite properties were evaluated using SEM, a dynamic mechanical analyzer (DMA), FTIR TGA, and horizontal burning tests. The results demonstrated that the incorporation of 1.5% nano-CNC-overlaid ZnO nanoparticles into PLA enhanced the mechanical and thermal characteristics and the flame resistance of the PLA matrix. Oxidative combustion of CNC-ZnO promoted char formation and flame reduction. The shielding effect from the ZnO-CNC blend served as an insulator and resulted in noncontinuous burning, which increased the fire retardancy of nanocomposites. By contrast, the addition of ZnO into PLA accelerated the polymer degradation at higher temperature and shifted the maximum degradation to lower temperature in comparison with pure PLA. For PLA composites reinforced by ZnO, the storage modulus decreased with ZnO content possibly due to the scissoring effect of ZnO in the PLA matrix, which resulted in lower molecular weight.

Composites of Poly(lactic acid) (PLA) and spherical zinc oxide (ZnO) nanoparticles were prepared using melt processing followed by injection molding. The effect of nanosized ZnO on the molecular structure, thermal properties, dynamic mechanical properties, and flow characteristics of PLA composites were analyzed. Scanning electron microscopy images illustrated the formation of ZnO aggregates through PLA matrix. The molecular weight of PLA-ZnO experienced a substantial decline by 55%, suggesting the presence of ZnO provoked degradation of PLA during composite preparation. Glass transition temperature of PLA-ZnO decreased by 18% as compared with pure PLA, confirming the deleterious role of ZnO in PLA. The ZnO nanoparticles acted as a reactant and increased the thermal degradation rate. However, the incorporation of ZnO into PLA increased the crystallinity up to 20% and the storage modulus of composites in glassy state by 10%. The higher peak value of tan δ in composites suggested the more viscous behavior, which was further supported by lower number average molecular weight. The complex viscosity of composites exhibited a large Newtonian region over low shear rate, followed by shear thinning phenomenon. A significant decrease (96%) in complex viscosity was observed with the addition of ZnO into PLA.