Graphene oxide as a covalent-crosslinking agent for EVM-g-PA6 thermoplastic elastomeric nanocomposites

Abstract

A novel polyamide 6 grafted ethylene-vinyl acetate rubber copolymer (EVM-g-PA6) was synthesized in the presence of graphene oxide (GO). The reaction mechanisms of a sequential ring-opening polymerisation and ester–amide exchange reaction between caprolactam (CL) monomer and acetate groups of EVM with and without GO were proposed and investigated. Under the reaction conditions, the yield of the copolymer out of the CL/EVM (60/40) mixture was 26.4 wt% at 15% of the conversion of CL. The graft PA6 content was determined to be 4–6 wt%, and the grafting efficiency was further enhanced up to 13.1 wt% with the incorporation of 0.7 wt% of GO. This suggested that the GO accelerated the polymerization reaction of CL, and also acted as a crosslinking agent to bridge homopolymerised PA6 with EVM-g-PA6 copolymer. In addition, GO was thermally reduced in situ during the reaction process, thus significantly enhancing both the volume conductivity and permittivity of the copolymers. The flexibility and tensile strength of the EVM-g-PA6 copolymer were enhanced as compared to the corresponding EVM/PA6 blend. With the addition of 2.3 wt% of GO, the stress at 100% extension of the copolymer was enhanced by 190%, and Young's modulus was improved by 109%. The EVM-g-PA6 copolymer and the GO reinforced copolymeric nanocomposites could be developed to a new type of engineered thermoplastic elastomers.