Low-Temperature Compounding of Flax Fibers with Polyamide 6 via Solid-State Shear Pulverization (SSSP): Towards Viable Engineering Thermoplastic/Natural Fiber Composites

Low-temperature compounding of natural fiber/thermoplastic composites via solid-state shear pulverization (SSSP) is explored for the first time, with a goal of processing temperature-sensitive natural fibers with high temperature-melting engineering thermoplastics without fiber degradation. The model study was based on polyamide 6 (PA6) as the matrix material and short flax fibers as the filler materials; flax fiber type was varied to provide a range of comparison. Composite structural characterization was conducted using computer tomography, optical microscopy, and scanning electron microscopy, while mechanical property measurements were performed on injection molded specimens in both tension and bending. SSSP demonstrated robust and effective processing results in model PA6/flax composites, especially when compared with conventional extrusion. SSSP was able to isolate unmodified scutched fibers into individual elementary fibers with minimal scission, and effectively distribute them in the polymer matrix in situ. The dispersed and distributed filler morphology led to mechanical property enhancements, including 230% and 40% increases in Young’s modulus and tensile strength, respectively, compared with neat PA6, at a 20 vol% fiber content