Basalt/Wood Hybrid Composites Based on Polypropylene: Morphology, Processing Properties, and Mechanical and Thermal Expansion Performance

The main aim of this study was to investigate the effect of basalt fiber (BF) reinforcement in wood–plastic composites (WPCs). Basalt/wood hybrid composites based on polypropylene (PP) were prepared with different percentages of the reinforcement (the total fiber content was 10 wt%, 15 wt%, and 20 wt%). The BCS17-6.4-KV16 chopped basalt fibers with nominal diameter of 17 μm, cutting length of 6.4 mm, and wood fibers—Lignocel C 120 with the particle size of 70–150 µm—were used as a reinforcement. Composites were produced by the injection molding method. The density of the produced composites and their processing properties such as Vicat softening point and shrinkage were determined. In addition, the thermal expansion behavior of filled plastic composites was investigated. Mechanical tests were subsequently performed to evaluate the tensile, flexural, and impact properties at various temperatures (i.e., at −24 °C, 23 °C, and 80 °C) and after soaking in water. Scanning electron microscopy images were acquired to assess the effects of reinforcement and homogenization of mixtures and to determine the characteristics of the microstructure. The results showed that the hybridization process improved the tensile and flexural properties of reinforced wood composites. Moreover, the incorporation of high-strength basalt fibers into the composite led to increased stiffness. Even a small addition of 10 wt% total fibers led to a significant decrease in shrinkage and coefficient of thermal expansion.