Influence of reprocessing cycles on the morphological, thermal and mechanical properties of flax/basalt hybrid polypropylene composites

Vegetable fibers hybridization with basalt ones is a suitable way to exploit the environmental advantages of vegetable fibers while preserving composites mechanical properties. Nevertheless, there are no studies available on the mechanical recycling of short fiber hybrid reinforced polymer composites. In light of this, the present work addressed the mechanical recycling of flax/basalt hybrid polypropylene composites up to seven reprocessing cycles, evaluating the effect on microstructure, thermal and mechanical behavior and providing a direct comparison with flax composites. The results proved that the interaction of flax and basalt fibers promotes a faster degradation of flax fibers length inducing a significant decrease in hybrid mechanical properties already at the second reprocessing cycle. Despite this, hybrids are able to ensure a higher flexural stiffness and flexural strength by 5.2% and 7.7%, respectively, and an impact strength by 29.8%, 24.0% and 16.6% higher than flax at −50 °C, room temperature and + 50 °C after the second reprocessing cycle, respectively. Considering the easier processability of hybrid composites thanks to a higher Melt Volume Flow Rate (MVR), they can be conveniently repurposed and mechanically recycled to produce components traditionally manufactured with flax fibers.