The influence of gamma radiation on the mechanical performance, anisotropy, and oil resistance of NBR and HNBR composites reinforced with silica and lignin fillers

In the present work, at room temperature via a mechanical rotary mill, various composites based on Acrylonitrile butadiene rubber (NBR) and Hydrogenated acrylonitrile butadiene rubber (HNBR) have been prepared. As a comparative behavior in both types of rubber, different types of composites were fabricated based on different ratios of silica (S) and lignin (L). After that, all composites were subjected to gamma radiation at different doses to study the effect of ionizing radiation on the prepared composites. The anisotropy comparisons were performed for fabricated composites derived from NBR and HNBR. The prepared composites were investigated by Fourier transform infrared (FTIR), X-ray diffraction (XRD), Thermogravimetric analysis (TGA), and mechanical parameters, swelling in brake oil, and mechanical properties after immersion in oil. In general, the presence of silica and lignin in the rubber matrix improved the properties of the composites and revealed anisotropy behavior towards the two kinds of rubber. Significances moreover show that when 10 phr of silica is substituted by lignin, the mass loss temperatures for composites are decreased because lignin has a lower thermal degradation temperature than silica filler. Furthermore, the mechanical properties after brake oil immersion reveal that HNBR is more oil-resistant than NBR. Also, the studied parameters insured a strong coordination interaction occurred between Zn²⁺ of ZnCl₂ particles and CN groups of NBR or HNBR matrix during heat pressing, which resulting in an enhancement of mechanical and thermal properties.