Hydroxyl-Terminated Saponified Natural Rubber Based on the H₂O₂/P25-TiO₂ Powder/UVC-Irradiation System

Abstract

Natural rubber (NR), a long-chain hydrocarbon polymer mostly consisting of cis-1,4-polyisoprene units, has a high molecular weight (MW) and viscosity, enabling it to show excellent physical properties. However, NR has no reactive functional group, making it difficult to react with other molecules, especially in manufacturing processes. The functionalized low-molecular-weight NR (FLNR) is a requirement to disperse ingredients into the rubber adequately. Here, the FLNR was prepared by a photochemical degradation process under UVC-irradiation in the presence of H2O2 using P25-titanium oxide (TiO2) powder as a photocatalyst. The optimum condition for the preparation of FLNR was the use of 2.0 g of TiO2 powder per 100 g of rubber and H2O2 at 20% w/w under UVC-irradiation for 5 h. The hydroxyl groups were found on the NR chains due to the chain-scission of polyisoprene chains and hydroxyl radicals in the system. The weight average MW of NR decreased from 12.6 × 105 to 0.6 × 105 gmol−1, while the number average MW decreased from 3.3 × 105 to 0.1 × 105 gmol−1.

Keywords

• natural rubber
• functionalized low-molecular-weight natural rubber
• photochemical degradation process
• titanium oxide (TiO₂)