The effect of devulcanized nitrile butadiene rubber (dNBRg) loadings on the rheological and physico-mechanical properties of vNBR/dNBRg blends

The rising demand for disposable protective rubber gloves, particularly nitrile rubber gloves, surged during the COVID-19 pandemic, in addition to their traditional applications in various sectors such as the medical and food industries. However, this rapid growth has intensified environmental concerns due to the increasing volume of discarded nitrile butadiene rubber gloves, improper waste management, and limited research on their potential for reuse in rubber-based products. Devulcanization offers a sustainable and effective solution by converting nitrile rubber glove waste into valuable secondary raw materials. While most existing studies have primarily focused on the devulcanization process itself, there is a paucity of research investigating the properties and applications of devulcanized nitrile rubber gloves (dNBRg) in rubber blends. This research evaluates the effect of varying dNBRg loadings in virgin nitrile butadiene rubber (vNBR) blends on their rheological and physico-mechanical properties. Nine different rubber blends (ranging from 0 to 100 phr) were prepared using a two-roll mill during the compounding process. The results show that increasing dNBRg content leads to a rise in the minimum torque (ML), attributed to the increased viscosity of the blends. Conversely, the maximum torque (MH) and torque difference (∆T) initially decrease up to 40 phr, followed by an increase with further dNBRg incorporation (50 to 80 phr). The scorch time (ts2) remains relatively constant, whereas the cure time (t90) increases at higher dNBRg loadings (70 and 80 phr). FTIR and DSC analysis reveal similar spectral characteristics and a single glass transition temperature (Tg) peak, indicating no significant chemical alterations and good interfacial compatibility within the rubber blends. Nevertheless, increasing the dNBRg content, particularly at 80 phr, leads to reductions of approximately 15.5% in tensile strength, 51% in abrasion resistance index (ARI), 8.5% in density, and 7.2% in compression set up to 70 phr, likely due to non-uniform crosslink distribution and the presence of free radical short polymer chains in dNBRg. Conversely, elongation at break increases by 13.6% up to 50 phr, while the modulus at 100% strain (M100), swelling resistance, volume loss also increased with higher dNBRg loadings, notably, hardness improves by 8.5% at 80 phr. These enhancements are attributed to a higher crosslink density. These findings suggest the potential for dNBRg to partially replace approximately 20 to 30 phr of vNBR in rubber-based products, depending on specific application requirements. This study broadens the utilization of dNBRg as an innovative and sustainable material within the rubber industry, promoting both environmental sustainability and resource efficiency.