Preparation and improved mechanical properties of three-dimensional woven fabrics reinforced thermoplastic composites based on intra-yarn hybrid flax/basalt fibers

Three-dimensional (3D) woven fabric reinforced thermoplastic composites with natural and synthetic hybrid fibers have advantages of high modulus, recyclability, excellent structure integrality and delamination resistance. However, the full penetration of thermoplastic matrix into 3D fabrics and uniform distribution of hybrid fibers are difficult. In this work, to solve those problems, the natural flax (F) fibers and synthetic basalt (B) fibers were combined and enveloped with fine PP filaments to prepare hybrid wrapped yarns, which were referred as intra-yarn hybridization. 3D layer-to-layer angular interlaced (LA) woven fabric and 3D through-thickness orthogonal (TO) woven fabric were fabricated using the hybrid wrapped yarns. The effects of preparation conditions (i.e., PP addition methods and mold thicknesses) on the hot-press molding process and mechanical properties of 3D composites were investigated. The results show that mechanical properties of the composites directly hot-pressed with 3D fabrics woven using wrapped yarns are poor and there are many holes in the composites. The additional PP plates to the composites and the suitable mold thicknesses are beneficial to improve the mechanical properties of hybrid composites. The flexural properties, compressive properties and low-velocity impact resistance of 3D woven hybrid composites increase as the increasing basalt fiber content. Furthermore, the bending strength of TO hybrid composites exhibits a 45.8 % improvement compared to LA hybrid composites. The fracture modes of 3D LA and TO hybrid composites are revealed. The preliminary study on 3D hybrid flax/basalt fiber thermoplastic composites are beneficial for material development in fields of the automotive and furniture industries.