Sulfur and peroxide curing of NBR based rubber compounds filled with kraft lignin and calcium lignosulfonate

Abstract

AbstractRubber compounds based on acrylonitrile‐butadiene rubber were filled with biopolymer fillers, namely kraft lignin, and calcium lignosulfonate. For cross‐linking of rubber compounds, sulfur curing system, dicumyl peroxide, and combination of dicumyl peroxide with trimethylolpropane trimethacrylate were used. The main objective of the work was to investigate the influence of biopolymer fillers content and curing system composition on vulcanization process of rubber compounds, cross‐link density, morphology, and physical‐mechanical properties of vulcanizates. The results revealed that rubber compounds filled with calcium lignosulfonate can be efficiently cured with sulfur as well as peroxide curing systems. Modulus, hardness, and elongation at break were strongly dependent on cross‐link density. Vulcanizates filled with high content of lignosulfonate exhibited comparable values of tensile strength, regardless of the curing system applied. The application of kraft lignin into peroxide systems cured rubber compounds resulted in undesirable reactions between functional groups of the biopolymer and peroxide radicals. Depletion of peroxide radicals resulted in significant deceleration of curing process and decrease in cross‐link density of vulcanizates. This was reflected in typical change of physical‐mechanical characteristics, decrease in modulus and hardness, and increase in elongation at break. Very good adhesion and compatibility between the kraft lignin and the rubber matrix resulted in enhancement of tensile behavior of vulcanizates cured with sulfur system.