Abstract:
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
