Evaluation of the suitability of local dolomite as a replacement for calcite in solid tyre manufacture

Abstract

The mineral calcite is currently used in a wide range of industries and the main use of calcite powder in Sri Lanka is as a non-reinforcing filler in the manufacture of rubber products. The mineral dolomite is more abundantly found in Sri Lanka than calcite and it consists of a mixture of calcium and magnesium carbonates. Dolomite is very similar to calcite, but harder, denser and slightly more acid resistant. The main aim of this study was to evaluate the suitability of dolomite as a replacement for calcite in solid tyre manufacture. A series of 90:10 natural rubber (NR)/polybutadiene rubber (BR) blend compounds was prepared according to a middle layer, solid tyre formulation by varying the calcite to dolomite ratio at 10 phr intervals. Total filler loading was kept constant at 70 phr. Cure characteristics and physico-mechanical properties of all eight blend compounds were evaluated and compared.

The NR/BR blend compound containing 100% dolomite was comparable to the blend compound containing 100% calcite in terms of hardness, modulus at 300% elongation, tensile strength, abrasion weight loss, resilience, compression set and resistance to flex-cracking. The blend compound containing 100% dolomite exhibited a higher scorch safety and lower cure time in comparison to that containing 100% calcite, which are advantages during the moulding operation. However, maximum torque and minimum torque of the blend compound prepared with 100% dolomite were higher than those of the blend compound prepared with 100% calcite. The NR/BR blend compound with 10:60 calcite to dolomite ratio is the best among the blend compounds containing both calcite and dolomite in terms of physico-mechanical properties. Further, the cure characteristics and most of the physico-mechanical properties of the 100% calcite as well as 100% dolomite containing blend compounds were in accordance with the requirements of a middle layer, solid tyre compound. Results in overall indicated that abundantly found dolomite would be a suitable replacement for commonly used calcite in solid tyre manufacture.