Carbon black and calcium lignosulphonate reinforced rubber composites with applied plasticiser glycerol

Abstract

Rubber compounds based on styrene–butadiene rubber (SBR) and acrylonitrile–butadiene rubber (NBR) were filled with constant amount of carbon black – 25 phr and calcium lignosulphonate – 30 phr. Glycerol as cheap and environmentally friendly softener was added into the rubber compounds in concentration scale from 0 to 20 phr to plasticise the rubber matrix and the biopolymer and to improve the adhesion between the components of rubber compounds. The results revealed that the addition of glycerol resulted in the decrease of rubber compounds viscosity. Based on dynamical-mechanical analysis it can be concluded that glycerol softened lignosulphonate and lowered its glass transition temperature. The softened lignosulphonate was better distributed and dispersed within the rubber matrices, which was clearly demonstrated by performing scanning electron microscopy. Glycerol contributed to better adhesion and compatibility between the rubber and the biopolymer, which was subsequently reflected in improvement of tensile behaviour of composites. Both elongation at break and tensile strength showed increasing trend with increasing amount of glycerol. Due to compatibility in polarity among rubber matrix, biopolymer and plasticiser, higher tensile strength, and higher enhancement of tensile strength in dependence on glycerol content exhibited composites based on NBR. When compared to the reference, the tensile strength increased in more than 5 MPa for composites plasticised with high amount of glycerol. The improvement in tensile strength of SBR-based composites was less evident, though still pointing to a positive effect of glycerol on increasing of adhesion and compatibility on the filler-rubber interface. The main point of the work was to show that improvement of the composites’ properties can be achieved by addition of suitable plasticiser into the rubber compounds with applied biopolymer without additional cost and time-consuming treatment procedures.