UV accelerated aging of unidirectional flax composites: Comparative study between recycled and virgin polypropylene matrix

Previous studies on the photooxidation of natural fiber composites have focused on using short fibers and virgin matrices. In this work, unidirectional flax fiber composites with virgin and recycled polypropylene matrix were prepared by thermocompression to compare their accelerated aging. These composites were exposed to two accelerated xenon arc UV exposures where only the irradiance was modified. A multi-scale characterization was carried out to evaluate the consequences of the photooxidation on their mechanical and physicochemical properties with time. Results show that the photooxidation was limited to the surface. In addition, the photo -degradation of the surfaces of both composites was identified by the appearance of cracks, the variation of crystallinity, the decrease in weight average molar mass, and the appearance of new chemical products. These physicochemical variations are more evident with increasing irradiance. Despite these variations, the mechanical tensile properties of recycled matrix composites remain relatively indifferent to the two UV exposures compared to those with virgin polypropylene. It can be concluded that recycled polypropylene, if well selected, can replace virgin polypropylene in natural fiber composites for better mechanical resistance to photooxidation.

Automated summary

Previous studies have focused on photooxidation of natural fiber composites using short fibers and virgin matrices. This study compares the accelerated aging of unidirectional flax fiber composites with virgin and recycled polypropylene matrix prepared by thermocompression. The results show that photooxidation only occurs on the surface and can be identified through the appearance of cracks, variation of crystallinity, decrease in weight average molar mass, and presence of new chemical products. Despite these changes, the mechanical tensile properties of composites with recycled polypropylene remain relatively unaffected compared to those with virgin polypropylene. Therefore, well-selected recycled polypropylene can be used as a replacement for virgin polypropylene in natural fiber composites to enhance their mechanical resistance to photooxidation.