Linear and nonlinear viscoelasticity of chemically modified ground tire rubber/NBR blends

GTR was surface-treated with sulfuric acid, nitric acid, and potassium permanganate, and an oil-extracted GTR (GTR-OE) powder was also prepared to evaluate the effect of process oil. Surface modification of GTRs was assessed using ATR-FTIR spectroscopy and contact angle measurements. NBR blends containing 10, 20, 40 phr treated and untreated GTR were prepared and characterized using stress relaxation, dynamic mechanical thermal analysis (DMTA), scanning electron microscopy (SEM), and small- and large-amplitude oscillatory shear (SAOS and LAOS) rheology at 120 °C. Contact angle measurements indicated enhanced surface wettability after treatment, while SEM suggested improved interfacial adhesion, particularly for KMnO₄-treated GTR. DMTA showed reduced damping with increasing GTR content and a small secondary relaxation for untreated and oil-extracted GTR blends, indicating limited compatibility with the NBR matrix. SAOS results showed increased storage and loss moduli, pronounced solid-like response, enhanced elasticity, and reduced damping particularly for KMnO₄-treated GTR blends, suggesting strengthened interfacial interactions and network formation. Lissajous–Bowditch curves (LAOS measurements) revealed that NBR/GTR blends, particularly NBR/KMnO₄-treated GTR and NBR/GTR-OE, exhibited stronger strain-stiffening, higher nonlinearity, and greater energy dissipation than neat NBR at large strains. These findings demonstrated that appropriate chemical modification of GTR can effectively tailor linear/nonlinear viscoelastic responses, offering a practical route to value-added utilization of GTRs.