The effect of crepe rubber maturation on properties of raw natural rubber and vulcanizates

Technically Specified Rubber, specifically Standard Thai Rubber (STR), is vital for the tire industry. Crepe rubber has now emerged as a key alternative to traditional cup lump for STR20 production. This study investigates the impact of a 28-day outdoor maturation period on the properties of raw crepe rubber and its carbon black-filled vulcanizates. The study aimed to determine the optimal maturation duration and elucidate how changes in non-rubber components affect rubber properties. Brown crepe samples were matured under outdoor conditions for 28 days, with analyses conducted at intervals of 1, 3, 7, 14, 21, and 28 days. Total solid content (TSC), non-rubber content, plasticity and Mooney viscosity were determined. Furthermore, carbon black-filled compounds were prepared using a sulfur-based curing system to assess vulcanization characteristics, tensile properties, thermal stability via Temperature Scanning Stress Relaxation and dynamic mechanical properties. Results indicated that the progress of maturation led to an increase in TSC, initial plasticity, storage hardening and Mooney viscosity. In contrast, protein and lipid content significantly decreased over the 28-day period. Notably, the vulcanizates achieved peak crosslink density and superior tensile strength and moduli at 14 days of maturation. The same trend was observed in the stress relaxation response and thermal stability. Beyond this maturation, a decline in mechanical performance was observed. In conclusion, 14 days is the optimal maturation period for producing high-quality STR20. These findings have important implications for the production of various NR composites and support optimal pre-treatment of the raw materials before production processes. Effect of crepe maturation on properties of raw and vulcanized rubber • Outdoor maturation significantly impacts crepe rubber and vulcanizate properties. • A 14-day maturation period is optimal for tensile and thermal properties. • Crepe rubber meets STR20 standards within 3–7 days, reducing storage costs. • TSSR analysis reveals structural network changes during rubber maturation. • Maturation optimizes non-rubber components, improving product consistency.