Crosslink density, physicomechanical properties and thermooxidative stability of calcium lignosulfonate filled composites based on NBR and SBR

Abstract Calcium lignosulfonate (CaL) as biopolymer filler was incorporated into rubber matrices based on acrylonitrile-butadiene rubber (NBR) and styrene-butadiene rubber (SBR) in concentration scale ranging from 10 to 60 phr. The work was aimed at investigation of CaL content on crosslink density and mechanical properties of the composites. Subsequently, the composites were kept in hot air chamber for 7 days at 70 °C and 100 °C and the influence of thermooxidative ageing on the change of cross-link density and mechanical properties was investigated. Kinetics of thermal oxidation was studied by non-isothermal differential scanning calorimetry. The achieved results showed that the changes in modulus and elongation at break were in close connection with the changes in crosslink density before ageing as well as after ageing. When compared to the SBR based reference, the crosslink density of the composite with maximum CaL content decreased by about 62%, while the decrease in crosslink density of the corresponding materials based on NBR represented by about 39%. A higher percentage decrease in the crosslink density of composites based on SBR was reflected in a higher proportional decrease of modulus M300 (49%) and a higher increase of the elongation at break (more than 480%) of the corresponding composites in the dependence on CaL content when compared to those based on NBR. The tensile strength of composites based on SBR was found independent of the CaL content while a slight improvement in tensile behavior was recorded for NBR-based composites with higher CaL content (in more than 0,5 MPa for the maximally filled composites when compared to the reference). The experimental outputs revealed that CaL provided some stabilizing effect on the composites during thermooxidative ageing, though this effect was found to be low. Based upon the calculation of the induction periods of thermooxidation it can be concluded that the composites based on NBR exhibit a higher stability than those based on SBR.