Effects of Different Particle Sizes of Recycled Acrylonitrile-butadiene Rubber and its Blend Ratios on Mechanical and Morphological Properties and Curing Characteristics of SBR/NBRr Blends

The effects of different particle sizes of recycled NBR (NBRr) on curing characteristics, mechanical, and morphological properties of styrene butadiene rubber/ recycled acrylonitrile butadiene rubber (SBR/NBRr) blends were examined. Three different size ranges of NBRr particles, i.e., 117 - 334 μm, 0.85 -15.0 mm, and 10 -19 cm were used in this study. The SBR/NBRr blends with blend ratios of 95/5, 85/15, 75/25, 65/35, and 50/50 were prepared using a two roll-mill at room temperature. The characterizationresults of the blends show that scorch time, t2, and cure time t90 of the SBR/NBRr blends decreased with increased NBRr content as well as decreasing sizes of NBRr particles due to the existence of cross-linked precursors and unreacted curative in the recycled rubber. Among all blend ratios, the SBR/NBRr blends with smallest size of NBRr particles exhibits lowest minimum torque (ML) compared with the bigger particle sizes of it in SBR/NBRr blends which resulted in more efficient processing. The maximum torque (MH) of all SBR/NBRr blends show the declining trend with increased NBRr content probably due to the poor interactions in SBR/NBRr blends. The SBR/NBRr blends with smallest size of NBRr particles show better mechanical properties (tensile, elongation-at-break, M100, and fatigue) compared with all other blend ratios of bigger sizes of NBRr particles. For physical properties, SBR/NBRr blends with smallest size of NBRr particles exhibited the highest hardness and cross-linking density at all blend ratios whereas resilience decreased, accordingly. As the particle size decreased, the contact surface area increased which provided more efficient interfacial bonds, leading to better properties. The scanning electron microscopy studies showed that the smallest size of NBRr particles in SBR/NBRr blends illustrated a better NBRr-SBR matrix interaction compared with the other NBRr particles in the related SBR/NBRr blends.