Dual cross-linking of XNBR latex with epoxy-functional calcium silicate particles for the production of accelerator-free medical gloves

In this work, an innovative dual cross-linking strategy for carboxylated nitrile butadiene rubber (XNBR) latex using epoxy-modified calcium silicate particles is presented. In their role as dual cross-linker, the particles are able to form covalent bonds (nucleophilic ring opening of epoxy moieties) as well as ionic cross-links (calcium ions of the inorganic core) across the carboxylic acid groups of the rubber. To characterize the curing efficiency, thin elastomer films are prepared by using a conventional coagulant dipping process and their cross-link densities, curing kinetics, and tensile properties are investigated as a function of the concentration of the cross-linker and curing time. The results show that latex films containing 5 phr of epoxy-functional particles give the highest tensile strength, which is further improved by pre-vulcanizing the liquid latex compound at 60°C for 30 min. The latex formulations are stable over 3 days and the pre-cured films exhibit a high resistance against gamma sterilization and subsequent accelerated aging. Moreover, sterile films do not cause any skin irritation or skin sensitization reactions, showing the high potential of epoxy-functional particles in the production of accelerator-free hypoallergenic gloves.