Unveiling the\nHierarchical Microstructure of Prevulcanized\nNatural Rubber Latex Film and Its Impact on Mechanical Properties

Despite the widespread application of prevulcanized natural\nrubber\nlatex film (VNRL), its microstructure of VNRL has not been fully elucidated,\nand the impact of the microstructure on strain-induced crystallization\n(SIC) and mechanical properties remains largely unexplored. Herein,\nthe hierarchical microstructure of VNRL was unraveled, and the results\nwere compared with those of a vulcanized natural rubber sheet (VNR)\nprepared by mechanical mixing and compression molding. With identical\ntotal cross-linking density, VNRL exhibits a more homogeneous network\nwith higher entanglement content than VNR. Upon deformation, these\nentanglements can disentangle or slide along the chain backbones,\nreducing the constraining effect of cross-links on the molecular chains\nunder moderate strains. Therefore, VNRL exhibits slightly delayed\nSIC and lower crystallization index (CI) in the strain range from\n3.4 to 6 compared to VNR. However, at strains ≥4.5, the crystallization\nrate of VNRL surpasses that of VNR due to the formation of larger\ncrystals, leading to a higher crystallization index of VNRL at strains\n≥6. Meanwhile, the homogeneous structure enables the extension\nof the VNRL network to larger strains, ultimately resulting in superior\nfracture strain and strength compared to VNR. In addition, the nonrubber\ncomponents of VNRL form a microscopic skeleton within the matrix,\nwhich can distribute stress and prevent crack growth, thereby enhancing\nthe tear resistance and toughness of VNRL. This work provides new\ninsights into the structure–property relationship of VNRL.