Development of NR/CHR rubber blends with carbon black and silica fillers for tyre inner liners

Abstract

Inner liner of a tubeless tyre is currently constructed using a speciality synthetic rubber called chlorobutyl rubber (CIIR). Blending of CIIR with natural rubber (NR) will enable to achieve improvement in physico-mechanical properties with a reduced compound cost. Also, use of CIIR/NR blends for inner liners are best at retaining air pressure and minimizing the temperature dependence of air permeability. The properly increase is enhanced by addition of a mix of carbon black and silica fillers, which are reinforcing fillers. One reason for carrying out this research is to enhance the market opportunities of NR by developing NR/CIIR blends to reach the end product requirements. In this study, different series of compounds were prepared, one with CIIR alone by varying the carbon black to silica ratio at 10 phr intervals, other with CIIR/NR blends by varying the CIIR to NR blend ratio at 20% intervals. Total filler loading was kept constant at 60 phr. Melt viscosity, hardness, tensile strength, modulus at 300 % and tear strength increased with silica loading, while scorch time, abrasion volume loss and air permeability decreased above silica loading of 30 phr.. Cure time did not show any variation with type of filler. When replacing CIIR with NR, cure rate index increased significantly from 40% NR and hence the cure time decreased. Mechanical properties and air permeability varied significantly. Materials used for the inner liner mainly chlorobutyl rubber are very expensive and hence by using the above mentioned blend with the optimum filler loading, the production cost can be minimized. Results in overall showed optimum properties for the 20:80 CIIR/NR blend at 10:50 carbon black /silica filler ratio.