Processability and Crosslink Density: Role of Peptizers in Natural Rubber and Chlorobutyl Rubber

ABSTRACT This study investigates the effects of chemical and physical peptizers on the mastication behavior, molecular weight, vulcanization kinetics, and crosslink density of natural rubber (NR) and chlorobutyl rubber (CIIR). Mastication reduces the number‐average molecular weight (Mn) of NR by approximately 40%, decreasing from 219 × 103 to 131 × 103 g mol − 1 . The addition of a chemical peptizer further decreases Mn to 106 × 103 g mol − 1 , corresponding to ~50% reduction relative to the unmasticated NR. A similar reduction (∼50%) is observed with the physical peptizer. In contrast, mastication leads to an approximately 20% increase in the Mn of CIIR, indicating chain recombination, with negligible influence of peptizers. Rheometric analysis shows that chemical and physical, reduce the minimum torque of NR by approximately 30% and 5% respectively. The chemical peptizer decreases the scorch time of NR by about 40%, without significantly affecting the cure rate index. For CIIR, the physical peptizer reduces the scorch time by approximately 35% and increases the cure rate index about 35%, from 3.4 to 5.8, whereas the chemical peptizer delays the onset of vulcanization. Swelling and DSC analyses confirm a decrease in crosslink density. Overall, peptizers improve processability but may compromise crosslink density, particularly in CIIR.