Dynamic stretching vulcanization: Controlled reorganization of the crosslinked network in natural rubber via mechanical force

The mechanical properties of natural rubber can be enhanced through vulcanization; however, the inherent tradeoff between strength and toughness makes simultaneous improvement of both difficult. Here, we propose a strategy termed dynamic stretching vulcanization, in which a cyclic tensile stress field is applied during vulcanization to regulate the sulfur-crosslinked network and achieve both high strength and high toughness. In this approach, cyclic tensile strains of 100 %–200 % were imposed during sulfur vulcanization, and their effects on sulfur-bond composition, network architecture, and mechanical performance were systematically evaluated. Compared with static vulcanization, dynamic stretching vulcanization significantly reduced the proportion of long, mechanically weak polysulfide bonds and increased the proportion of short, stronger disulfide bonds, while leaving the overall crosslink density nearly unchanged. Dynamic stretching vulcanization resulted in a broader distribution of residual dipolar couplings and two glass transition points, which indicated the formation of coexisting rigid and flexible regions with different degrees of crosslinking. Dynamic stretching vulcanization also advanced the onset of strain-induced crystallization and increased both crystallinity and chain orientation at high strains. The resulting vulcanizate displayed higher tensile strength, fracture energy, and tear strength than the sample prepared by static vulcanization, while the thermal-oxidative aging resistance is significantly improved. Overall, dynamic stretching vulcanization effectively tailors the crosslink distribution and network heterogeneity in natural rubber, yielding substantial mechanical enhancements and offering a mechanochemically guided route for optimized network design. Because it only adds a controllable mechanical field during curing, dynamic stretching vulcanization is readily compatible with scalable rubber manufacturing (e.g., tension-controlled or continuous curing) and is promising for high-durability NR products requiring high tear/crack resistance and thermal-oxidative stability. • Dynamic stretching vulcanization resolves NR’s strength-toughness tradeoff. • Sulfur bond reorganization and network heterogeneity boost mechanical performance. • Dynamic stretching advances strain-induced crystallization. • Scalability potential: dynamic stretching tunes network at near-constant density.