Two-Cycle Strain-Induced Crystallization Behavior of Peroxide Cross-Linked Solid Guayule Natural Rubber

Abstract

Peroxide cross-linked guayule natural rubbers (P-gGR) are prepared from non-acetone-extracted solid green guayule natural rubber (gGR) made by drying latex. Tensile and dynamic mechanical properties of P-gGR samples of three different network chain densities are characterized. All P-gGR samples demonstrate highly reproducible tensile behaviors under two repeated cycles. For the first time, strain-induced crystallization (SIC) behaviors of P-gGR are measured with synchrotron wide-angle X-ray diffraction measurements under two repeated cycles by exposing the incident beam for 70 ms every 3 s. Highly reproducible SIC phenomena are observed, and apparent crystallite sizes, average volumes, indexes of average number, and orientation fluctuations of crystallites are confirmed to not change significantly during cyclic deformation. Non-rubber components such as phospholipids, glycolipids, fatty acids, esters, sterols, and terpenes in gGR barely inhibit the second SIC of the P-gGR and do not cause deterioration of its mechanical properties. The reproducibility of cyclic stress–strain curves and cyclic SIC behavior of the P-gGR sample is ascribed to the thermodynamically stable peroxide cross-linking network. As a viable alternative to Hevea natural rubber in the rubber industry, these findings on gGR provide valuable insights for manufacturing both conventional and high-quality products.