Mechanical, Thermal and Performance Evaluation of Hybrid Basalt/Carbon Fibers Reinforced Bio-Based Polyethylene Terephthalate (BioPet) Composites

Looking at the dynamically developing market of engineering materials, there is a need to create newer functional composites. Today's economic situation related to high energy prices and environmental threats force industry to conduct sustainable production. Polymer composites based on plant raw materials are increasingly appearing on global markets, which are light, have good mechanical properties and are also pro-ecological. This work involved the production of hybrid composites based on bio-based poly (ethylene terephthalate) by means of injection molding. Two types of fibers were used simultaneously as the reinforcement phase: basalt fibers and carbon fibers in the amount of 5, 7.5, and 10 wt% of each. The produced materials were subjected to a wide range of mechanical, thermal, and functional characteristics. The experimental data were compared with the theoretical results which were calculated from different micromodels. The studies showed that with the addition of the filler, the mechanical properties of the produced composites increased, but the optimal content was found for composites with 7.5/7.5 wt% addition of fibers, where the improvement was – 81%, 337%, and 25%, for tensile strength, Young's modulus, and impact strength, respectively. In the produced materials, the thermal properties of composites were also improved, where the shrinkage decreased by min. half, and linear coefficient at least 3 times. Sufficient adhesion between the fibers and the matrix was confirmed by SEM images and mechanical micromodels, which confirmed the highest efficiency of reinforcement with a total content of 15 wt% of fibers. To assess the influence of extreme conditions on the behavior of composites, hydrolytic degradation was carried out, which showed that the addition of fibers will not increase water absorption. The mechanical tests of the incubated materials lead to the conclusion that the produced materials could be successfully used in long-term applications because the properties obtained during the tensile test have deteriorated by only max. 5%. The work showed for the first time the modification of bioPET using two types of fibers introduced simultaneously. Hybridization of bioPET with basalt and carbon fibers has shown that it is possible to create very durable composites with a high Young's modulus. The work showed that different fibers are responsible for increasing other parameters – basalt fibers increase strength, while carbon fibers increase Young's modulus. The research may contribute to the popularization of bio-based polymer composites that have high strength for low weight and are a cheaper equivalent than polyamide-based composites.