Effect of maleic-anhydride and filler type on XNBR/IIR rubber blend

Abstract

This work addresses the interfacial incompatibility between carboxylated-acrylonitrile-butadiene rubber (XNBR) and isobutylene-isoprene rubber (IIR) blend due to difference in polarities. A melt-blended XNBR and IIR with maleic-anhydride (MA) and fillers (carbon black (CB) and silanized-silica (SiL)) were prepared and carefully investigated. The activation energy (E_a (KJ/mol)) of vulcanization was also studied. It was observed that adding MA into the blends lowered E_a (KJ/mol) compared to those without MA. For example, compound SS1 (XNBR/IIR-2phr MA-40phr SiL) obtained E_a (KJ/mol) of ∼20 KJ/mol while its counterpart SS (XNBR/IIR-40phr CB) and SB (XNBR/IIR-40phr SiL) recorded ∼140 and 130 KJ/mol, respectively. However, SS (XNBR/IIR-40phr CB) exhibited superior mechanical properties than others. With bound rubber (%), SS obtained over 22, 18, and 24% than its counterparts; SB(XNBR/IIR-40phr SiL), SB1(XNBR/IIR-4phr MA-40phr SiL) and SB2(XNBR/IIR-4phr MA-40phr CB), respectively. The SS also recorded 66, 62 and 85% higher tensile strength than SB, SB1, and SB2, respectively. For the fatigue life cycle, SS recorded over 45, 13, and 15 % than SB, SB1 and SB2, respectively. The inferior physico-mechanical properties observed for the other blends were suspected to be due to the observations that the addition of MA into the blends, generally led to high grafting/coupling, resulting in high networks density such as; MA—g—IIR—MA, IIR—g—MA—g—XNBR—CB—S_x—XNBR/IIR, or XNBR—g—MA—g—XNBR/IIR—SiL—S_x etc.,) which resulted in loss of flexibility and viscoelasticity. The current compounds also exhibited better physico-mechanical properties than related blends already reported. Thus, the synergistic balance of properties of XNBR and IIR makes such blend compositions suitable for advanced applications, particularly in automotive, sealing, inner linings, hoses and barrier technologies.