Structure and mechanical properties of natural rubber vulcanized with various zinc oxide nanoparticles

Abstract Effect of zinc oxide (ZnO) nanoparticles on vulcanization mechanism of natural rubber and crosslinking structure of its vulcanizate was investigated by rubber‐state NMR spectroscopy. Natural rubber was compounded with various ZnO nanoparticles (c‐ZnO, NC105, NC205, NC23, NC234(STA), and AZ12N), stearic acid, N ‐ tert ‐butyl‐2‐benzothiazole sulfonamide (TBBS), N ‐(1,3‐dimethylbutyl)‐ N ′‐phenylenediamine (6PPD), and sulfur. Vulcanization of the compounded natural rubber was analyzed with a moving die rheometer. The resulting natural rubber vulcanizates were characterized by swelling method, rubber‐state NMR spectroscopy, and tensile test. The rubber‐state NMR measurements revealed that natural rubber was efficiently vulcanized with NC205 and AZ12N but not with c‐ZnO, NC234, and NC234(STA). A relationship between the structure of vulcanized natural rubber and surface activity, surface structure, and particle size of the ZnO nanoparticles was investigated in this study. The mechanical properties of vulcanized natural rubber were found to depend on not only strain‐induced crystallization but also amount of effective CS linkages.