Curing,rheology,morphology and properties of lignosulfonate filled rubber compounds with applied low molecular weight plasticizers

Abstract

Calcium lignosulfonate was dosed to acrylonitrile-butadiene rubber in constant amount of 50 phr. Glycerol and ethylene glycol as cheap and highly available low molecular weight substances were used as plasticizers for rubber compounds. They were added into formulations in the amount ranging from 5 to 30 phr. The work was focused on investigation of plasticizers on curing process, rheology, morphology, mechanical and dynamical-mechanical properties of tested formulations. The results revealed that the addition of plasticizers resulted in the decrease in minimum and maximum torques. This points to the decrease in rubber compounds’ viscosity, which was clearly confirmed by rheological measurements. It was demonstrated that plasticizers plasticize both the rubber matrix and the biopolymer. This led to better dispersion and distribution of lignosulfonate and higher adhesion between the rubber and the filler on their interface. Due to its three hydroxyl groups, glycerol possesses a higher polarity than ethylene glycol. This increased polarity enhances its plasticizing efficiency within rubber compounds, particularly regarding the biopolymer, resulting in a more uniform dispersion throughout the rubber matrix. Plasticized lignosulfonate formed small soft domains of high deformability acting as a reinforcing filler contributing to the improved tensile characteristics of vulcanizates. A remarkable increase of tensile strength in more than 6.5 MPa was recorded for the vulcanizate with 20 phr of glycerol when compared to the reference (from 3.7 MPa up to 10.3 MPa). The elongation at break increased by more than 200% at high amounts of both plasticizers, again with higher contribution of glycerol. Dynamic-mechanical analysis indicated the emergence of two peaks in the loss factor temperature dependences, implying the development of the two polymer phases, namely the rubber matrix phase and the lignosulfonate phase, within the vulcanizates due to the application of plasticizers.