Sustainable coagulation approaches and their impacts towards the properties of natural rubber: a study related to tyre tread applications

With an objective to produce superior quality natural rubber (NR) for preparing tyre treads, various coagulation techniques were attempted for NR latex such as mechanical stirring and heating, steam-induced, salt-induced and freeze–thaw process, from which their efficiency was compared with formic acid-coagulated natural rubber. The effect of coagulation methods on molecular weight and thermo-oxidative ageing of resulting rubber was evaluated. The processing and cure characteristics, rubber–filler interaction and mechanical properties of NR were also evaluated. Rubber separated by mechanical stirring followed by heating and freeze–thaw coagulation showed better retention of molecular weight coagulated NR field latex. FTIR spectrum detected a high amount of nitrogenous materials in rubber compared to acid-coagulated natural rubber. Gel permeation chromatography (GPC), Mooney viscosity and black incorporation time were used to characterise the rubber separated by different methods. Different coagulation techniques adopted have very little effect on the glass transition temperature (Tg). Technological and morphological properties of rubber obtained by stirring and freeze–thaw processes are superior compared to other processes.