Natural cellulose fiber‐reinforced polyamide 6 thermoplastic composites prepared via in situ anionic ring‐opening polymerization

Thermoplastic polyamide 6 composites reinforced with flax fiber fabric and kraft pulp cellulose mat were prepared by anionic in situ ring‐opening polymerization (ROP) using a special vacuum‐assisted resin infusion process. The effects of the polymerization initiator, fiber alkali pre‐treatment, fiber type, polymerization temperature, and surface modification of fibers with organosilane coupling agents on the ROP reaction, polymer conversion and the physical and mechanical properties of the composites were investigated. The results showed that a combination of alkali pre‐treatment and the use of relatively less reactive magnesium bromide based anionic initiator gave a successful ROP reaction and high polymer conversion. Analysis of the physical and mechanical properties of the composite panels showed that optimal mechanical properties could be achieved by using a polymerization temperature of 150°C while polymerization at higher temperatures lowered both the flexural and tensile properties due to generation of more internal microvoids, as well as, decreased crystallinity of the matrix. In addition, it was found that optimal mechanical properties of the composites could be obtained using 2 wt% aminopropyltriethoxysilane (APS) coupling agent while higher APS concentrations negatively impacted the interfacial adhesion, resulting in lower mechanical properties. POLYM. COMPOS., 40:1104–1116, 2019. © 2018 Society of Plastics Engineers