Properties of rice husk ash silica filled natural rubber and acrylonitrile-butadiene rubber blends

Abstract

Purpose: Rice husk is burnt and discarded without effective use; however, it is a reliable resource that can be used to extract silica from its ash (RHAS) and can be incorporated in rubber blends as filler. The effect of Natural rubber (NR) and Acrylonitrile-butadiene rubber (NBR) ratio of NR/NBR blends filled with RHAS on physico-mechanical, and swelling percentage in specific oils (brake oil, hydraulic oil, engine oil) and toluene were studied since these blends have potential applications like fluid sealing. Method: RHAS was extracted via sol-gel method and characterized using X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopic (FTIR), and Scanning Electron Microscopic (SEM) analyses. NR/NBR blends with different NR to NBR ratios (100:0, 80:20, 60:40, 40:60, 20:80, 0:100) were prepared by incorporating 25 parts per hundred parts of rubber and curing characteristics, physico-mechanical and swelling properties were evaluated. Findings: The XRD, FTIR, and SEM analyses confirmed that the RHAS contains silica with a combination of nanoparticles and large agglomerates. The blends showed preferable curing characteristics while the hardness, compression set, and tear strength of blends ranged from 60-70 International Rubber Hardness Degrees, 0.5-6%, and 10-20 N/mm, respectively. Although the tensile properties (before ageing) were low, the retention of tensile strength after ageing was better in NR/NBR blends. Blends with high NBR proportion showed tolerable swelling against toluene, hydraulic oil, and engine oil while blends with low NBR proportion showed better swelling resistance to brake oil. Limitation: Time was limited to evaluate the properties of blends with different loading levels of RHAS. Value: There is a potential to use these NR/NBR blends in applications like fluid seals which require oil resistance and toluene resistance, where 0.5-6% and about 60-100% swellings are tolerable, respectively, compromising the physico-mechanical properties meanwhile replacing carbon black in respective applications.