Simultaneous enhanced mechanical properties, processability and flame retardancy of thermoplastic vulcanizate composites by a binary block copolymer with morphology adaptability

Abstract

The micro-morphology of flame retardant particles in the polymer matrix is a critical determinant for its flame retardancy efficiency, dispersion, compatibility, and mechanical properties. In this thesis, a binary block copolymer flame retardant (PAPO-MP), possessing the capability to undergo morphology changes during processing, was incorporated into the thermoplastic vulcanizate (TPV) composites. Compared to the intumescent flame retardants consisting of piperazine pyrophosphate and melamine polyphosphate (IFR), the addition of PAPO-MP significantly enhanced the mechanical properties, while also further increased the flame retardancy. In terms of mechanical properties, 26 %PAPO-MP/TPV composite demonstrated a remarkable improvement with 48.2 % higher tensile strength (TS) and 20.7 % higher elongation at break (EB) than the 26 %IFR/TPV composite. The reason for the enhancement and toughening was that PAPO-MP exhibited thermoplasticity and morphology adaptability, which can disperse as water droplets particles in the TPV matrix after thermal processing, demonstrating exceptional dispersibility, processability, and robust interfacial interactions. In terms of flame retardancy, PAPO-MP also demonstrates superior flame retardancy than IFR compounds. The addition of 26 % PAPO-MP in TPV achieved UL 94 V-0 rating, and increased the limiting oxygen index from 17.9 % to 25.4 % (higher than 24.2 % of 26 %IFR/TPV). During combustion, PAPO-MP primarily inhibited combustion intensity and exerted its flame-retardant effect in the condensed phase, particularly by promoting the formation of a char layer that exhibits excellent resistance to thermal oxidative degradation. In summary, this binary block copolymer with morphology adaptability enhanced both the mechanical properties, processability and flame retardancy of TPV composites.