Preforms and composites manufactured by novel flax/polypropylene cowrap spinning method

In the past decade, natural fiber composites with thermoplastic matrices have been embraced by many composite manufactures for its properties such as lightweight and low cost. Reinforced cowrap spinning yarns and thermoplastics offer a potential for low-cost manufacturing of complex-shaped and good, drapable composite parts, due to reduced impregnation times and resin flow distance during processing. In this article, the cowrap spinning yarns were produced by cowrap spinning method with flax and polypropylene (PP) and then woven to fabric preforms. The natural flax fibers were twistless in yarns and preforms, and PP served as a carrier for flax and prevented damage to flax fibers during processing, and became the polymer matrix in the final composites. To get an even distribution of fibers and thermoplastic resins in preforms and different flax fiber content, the main spinning parameters (hollow spindle twist and hollow spindle rotational speed) were analyzed and optimized. Besides fabric structure, the parameters affecting the mechanical properties of flax/PP preforms and composites were investigated. The fabric density, fabric structure (including plain, twill, and basket weave), and yarn tensile orientation (at 0°, 90°, and 45°) had a great influence on the tensile strength and elongation of preforms. Different pretreatments on flax/PP were investigated, and the microstructure and mechanical properties of thermoplastic composites showed improved wettability of impregnation and good adhesion and bonding interface between flax fiber and PP matrix in composites.