Influence of UV irradiation on mechanical properties and drop-weight impact performance of polypropylene biocomposites reinforced with short flax and pine fibers

Abstract

The design of biocomposite structures for outdoor applications should consider the influence of ultraviolet (UV) irradiation on the mechanical performances to more accurately determine their durability characteristics and prevent significant damage. Ultraviolet radiation causes the discoloration, surface roughness, mass loss, and degradation of the mechanical properties of biocomposites. In this study, the flexural strength and low-velocity impact response of polypropylene reinforced with short flax or pine fibers, which differed with respect to their physical and chemical properties, were investigated. Flax fibers are twice the length of pine fibers, and exhibit higher cellulose contents. Moreover, flax fibers have been demonstrated to increase the flexural strength and impact resistance of biocomposites. However, under UV irradiation, pine fibers containing more lignin dampened the degradation. Under photo-oxidative conditions, lignin is degraded to protect crystalline cellulose by acting as a light-absorbing compound. Non-destructive techniques such as Fourier transform infrared spectroscopy (FTIR), colorimetry, confocal imaging, acoustic emission, and CT scanning were therefore used to evaluate the effect of UV radiation on the chemical properties, color change, surface roughness, bending behavior, and drop-impact damage.