Hydrogenation of carboxylated nitrile butadiene rubber using diimide for crosslinker-free gloves

Abstract

The glove industry is currently focused on innovatively exploring sustainable and efficient methods to enhance the mechanical and chemical properties of Carboxylated Nitrile Butadiene Rubber (XNBR), with hydrogenation showing significant potential for the enhancement of rubber material properties. This breakthrough research significantly enhanced the rubber qualities for application in glove production. The limitations of the current hydrogenation process, which include the expensive equipment to handle high-pressure hydrogen gas, costly metal catalysts, complex procedures, and the use of organic solvents that pose potential environmental risks, were addressed through the diimide-mediated hydrogenation process. It demonstrated significant enhancements in mechanical properties as well as improved heat, chemical, and mechanical stability despite challenges associated with gel formation as a side reaction. Diimide generated from the reaction of hydrazine hydrate (N2H4) and hydrogen peroxide (H2O2) in the presence of boric acid as a promoter was explored for the hydrogenation of XNBR. The structure and hydrogenation degree (HD) were analysed using attenuated total reflectance Fourier-transform infrared (ATR-FTIR). The thermal properties of the resulting Hydrogenated XNBR (HXNBR) were studied through differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), while X-ray diffraction (XRD) was employed to examine rubber crystallinity. The hydrogenation process was optimised using response surface methodology (RSM), involving variations in Total Solid Content (TSC) of XNBR, reaction time, and H2O2:N2H4 mole ratio to gain the minimum gel content percentage. According to the response surface plot, the optimum parameter with a high HD and low gel content was reached at 92% HD with 32% gel content. HXNBR with 92% HD exhibits the highest tensile strength, elongation, and FAB at 5.41 MPa, 373%, and 5.41 N, respectively, demonstrating superior mechanical properties compared to HXNBR with 75% HD at 5.16 MPa, 459%, and 5.16 N, and XNBR at 4.72 MPa, 598%, and 4.72 N. Furthermore, HXNBR with ZnO and crosslinker-free formulation, achieved a tensile strength of 32.0 MPa, a FAB of 7.51 N, and an elongation of 468% for a 0.060 mm thickness glove, outperforming XNBR, which had a tensile strength of 29.9 MPa, a FAB of 6.85 N, and an elongation of 496% with a standard nitrile glove formulation. In addition, HXNBR exhibited improvements in chemical stability (0.0003% coagulum) and mechanical stability (0.0022% coagulum) as compared with XNBR, while maintaining comparable thermal stability with a coagulum content of only 0.0003%. The findings have significant potential in the glove industry, as they provide a promising chance to develop cost-effective formulations with improved glove quality.