Studies on acrylonitrile butadiene copolymer (Nitrile Rubber) nano composites

Abstract

Polymer nanocomposites are polymeric materials comprising of particles that have at least one dimension in the nanosize range (1 – 100 nm). These materials have properties superior to conventional microscale composites. Interestingly, the improvement in properties can be achieved with a very small amount of nanofiller. In this work acrylonitrile butadiene copolymer (nitrile rubber) nanocomposites were prepared by a two step process. In the first step, a masterbatch of nanofiller and nitrile rubber (NBR) was prepared in an internal mixer. In the second step, neat NBR was compounded with NBR – nanofiller masterbatch and compounding ingredients and moulded at 150°C and 20 MPa pressure. In NBR – nanoclay (layered silicate) composites addition of nanoclay reduced the cure time and the vulcanization kinetics closely fitted a first order model. Investigation of morphology showed exfoliated and few intercalated structures at low nanoclay content and a tendency to form agglomerates at higher concentrations. Comparisons were made between experimental data and the values predicted using various mechanics – based theoretical models. The tensile strength, modulus and storage modulus increased up to 5 phr nanoclay content and thereafter showed a decline. However there was no change in the glass transition temperature. Addition of nanoclay enhanced thermal stability while decreasing the gas permeability of nanocomposites. The equilibrium solvent uptake, diffusion, sorption and permeation coefficients decreased with nanoclay content with the minimum value at 5 phr nanoclay. The activation energy for diffusion and permeation for the nanocomposites were higher than that of neat NBR. The mechanism of solvent diffusion through the nanocomposites was found to be Fickian. The dependence of various properties on nanoclay content was correlated to the morphology of the nanocomposites. The effect of nanocalcium carbonate (NCC) content, a particulate nanofiller, on the properties of nitrile rubber composites was investigated. The cure time of the compounds showed a decrease on incorporation of NCC up to 5 phr and thereafter increased at higher NCC content. The tensile strength, modulus and storage modulus increased with the nanofiller content and declined after an optimum loading. The solvent uptake and transport coefficients decreased with NCC content, the minimum value being at 7.5 phr. The mechanism of diffusion of toluene solvent through the nanocomposites was found to be Fickian. Thermodynamic constants such as enthalpy and activation energy were also evaluated. The dependence of various properties on NCC content was corroborated with morphological analysis using transmission electron microscopy.