Influences of epoxidized natural rubber and fiber modification on injection molded-pulp/poly(lactic acid) biocomposites: Analysis of mechanical-thermal and weathering stability

Abstract

Accelerated weathering tests were conducted to evaluate the weathering resistance of poly(lactic acid) (PLA) based biocomposites without and with epoxidized natural rubber (ENR), that were reinforced with unmodified wood pulp fiber (WP) and silanized wood pulp fiber (modified WP). Changes in mechanical and thermal properties and morphology were observed, and structural and chemical degradation were analyzed. The addition of ENR improved the impact strength of the biocomposites before weathering, acting as an impact modifier. After the weathering test, the flexural properties of PLA-based biocomposite with ENR and silanized wood pulp fiber (ENR-modified WP) was better than the flexural properties of a biocomposite without ENR. The biodegradability of the biocomposites largely depended on the PLA matrix. The modified fibers have lower UV absorbance and can protect composites from UV light better than unmodified fibers. ENR and modified WP helped prevented the degradation of PLA. While weathering reduced the molecular weight of the WP and modified WP biocomposites by 78% and 61%, respectively, the molecular weight of the same biocomposites with ENR decreased by 51% and 50%, respectively. The accelerated weathering test produced cracks and increased surface roughness in the biocomposites and the glass transition temperature was reduced as a result of crystallization and chain shortening. These indicated that the biocomposite based containing ENR and silanized wood pulp fiber had better weathering resistance due to lowest absorption of UV radiation which was more suitable for applications in construction, furniture, and exterior and interior decoration.