Effect of Cross-Linking Density of Powdered Rubber on Gas Barrier Property and CO2 Permselectivity of NR/BR Composites

In this study, a novel cost-effective methodology was developed to enhance the gas barrier properties and permselectivity of unfilled natural rubber (NR)/polybutadiene rubber (BR) composites through the construction of a heterogeneous structure using pre-vulcanized powder rubber to replace traditional fillers. The matrix material is composed of a blend of NR and BR, which is widely used in tire manufacturing. By incorporating pre-vulcanized trans-1,4-poly(isoprene-co-butadiene) (TBIR) rubber powder (pVTPR) with different cross-linking densities and contents, significant improvements in the gas barrier properties and CO₂ permselectivity of the NR/BR/pVTPR composites were observed. The results indicated that compared to NR/BR/TBIR composites prepared through direct blending of NR, BR, and TBIR, the NR/BR/pVTPR composites exhibited markedly superior gas barrier properties. Increasing the cross-linking density of pVTPR resulted in progressive enhancement of the gas barrier properties of the NR/BR/pVTPR composite. For example, the addition of 20 phr pVTPR with a cross-linking density of 346 mol/m³ resulted in a 79% improvement in the oxygen barrier property of NR/BR/pVTPR compared to NR/BR, achieving a value of 5.47×10⁻¹⁴ cm³·cm·cm⁻²·s⁻¹·Pa⁻¹. Similarly, the nitrogen barrier property improved by 76% compared to NR/BR, reaching 2.4×10⁻¹⁴ cm³·cm·cm⁻²·s⁻¹·Pa⁻¹, which is 28 % higher than the conventional inner liner material brominated butyl rubber (BIIR, P_N2=3.32×10⁻¹⁴ cm³·cm·cm⁻²·s⁻¹·Pa⁻¹). Owing to its low cost, exceptional gas barrier properties, superior adhesion to various tire components, and co-vulcanization capabilities, the NR/BR/pVTPR composite has emerged as a promising alternative to butyl rubber in the inner liner of tires. Furthermore, by fine-tuning the cross-linking density of pVTPR, the high-gas-barrier NR/BR/pVTPR composites also demonstrated remarkable CO₂ permselectivity, with a CO₂/N₂ selectivity of 61.4 and a CO₂/O₂ selectivity of 26.12. This innovation provides a novel strategy for CO₂ capture and separation, with potential applications in future environmental and industrial processes. The multifunctional NR/BR/pVTPR composite, with its superior gas barrier properties and CO₂ permselectivity, is expected to contribute to the development of safer, greener, and more cost-effective transportation solutions.