Thermal stability of natural fibers via thermoset coating for application in engineering thermoplastics

An effective integration of natural fibers into engineering thermoplastics requires sufficient thermal stability of natural fibers during processing, since melting temperature of engineering thermoplastics lies above 200 °C. The aim of the work was to protect natural fibers from the heat of the molten thermoplastic via coating with a modified epoxy resin, thus enabling manufacture of natural fiber-reinforced engineering thermoplastic composites with minimized thermal degradation of the fibers. Processing temperature comprised the range of engineering thermoplastic polyamide 6 (PA6), which was 225 °C. Flax fabrics were spray coated with partially bio-based epoxy resin and incorporated via hot press technique into a PA6 matrix. The composite samples including spray coated flax fibers as well as the reference flax fibers without coating were characterized with regard to their mechanical properties, namely bending and tensile tests, thermal properties with differential scanning calorimetry (DSC) as well as thermogravimetric analysis (TGA) and optical via scanning electron microscopy (SEM) and computer tomography (CT). The results show that this approach enables manufacture of composites with reproducible mechanical properties, i.e. bending and tensile properties as well as enhanced thermal stabilities.