Effect of Brown Crepe Rubber Content on Cure Characteristics and Physical Properties of Tire Retreading Compound
Natural Rubber (NR) based products manufacturing is one of the main industries in Sri Lanka. Due to high demand of petroleum-based synthetic rubbers, the price and demand for NR have also augmented. Therefore, local rubber industries practice replacement of Ribbed Smoked Sheets (RSS) grade rubber partly with brown crepe (BC) grade of NR in their rubber compounds. Since BC rubber is contaminated with foreign particles such as dust, soil and sand, it is regarded as a low-in-quality cheaper grade. It is reported that certain local rubber industries do not concentrate on the quality aspects of rubber products in adding BC into compounds, since their primary aim is to attract higher profits. This is a problematic situation, today. Since retreading of worn-out tires is a leading sector of the local rubber industry, the local rubber landscape is considerably affected with this problematic development. In this study, the tire retreading compound s based on 70/30, 80/20 and 90/10 ratios of RSS / BC rubber were investigated to identify the most suitable and economical amalgamation. BC content could not be increased more than 70/30, due to non-uniform blending of two grades. Cure characteristics, tensile strength, percent elongation at break, modulus at 300% elongation and physical properties such as hardness, resilience, compression set, age resistance, abrasion resistance and flex cracking resistance were tested for all these compounds with the control compound benchmarked with RSS grade. The best properties were shown for the control compound, and all test properties were gradually reduced with increase of BC percentage. Most of the test properties of the compound with RSS/BC ratio at 70/30 were unacceptable while other compounds were at acceptable levels. Thus, RSS/BC at 80/20 is the optimum ratio for formulating tire retreading compounds with a suitable balance of cost and technical properties.
KEYWORDS: optimum percentage, ribbed smoked sheets, brown crepe rubber, technical properties, tire retreading compounds