Unveiling the Hierarchical Microstructure of Prevulcanized Natural Rubber Latex Film and Its Impact on Mechanical Properties

Despite the widespread application of prevulcanized natural rubber latex film (VNRL), its microstructure of VNRL has not been fully elucidated, and the impact of the microstructure on strain-induced crystallization (SIC) and mechanical properties remains largely unexplored. Herein, the hierarchical microstructure of VNRL was unraveled, and the results were compared with those of a vulcanized natural rubber sheet (VNR) prepared by mechanical mixing and compression molding. With identical total cross-linking density, VNRL exhibits a more homogeneous network with higher entanglement content than VNR. Upon deformation, these entanglements can disentangle or slide along the chain backbones, reducing the constraining effect of cross-links on the molecular chains under moderate strains. Therefore, VNRL exhibits slightly delayed SIC and lower crystallization index (CI) in the strain range from 3.4 to 6 compared to VNR. However, at strains >= 4.5, the crystallization rate of VNRL surpasses that of VNR due to the formation of larger crystals, leading to a higher crystallization index of VNRL at strains >= 6. Meanwhile, the homogeneous structure enables the extension of the VNRL network to larger strains, ultimately resulting in superior fracture strain and strength compared to VNR. In addition, the nonrubber components of VNRL form a microscopic skeleton within the matrix, which can distribute stress and prevent crack growth, thereby enhancing the tear resistance and toughness of VNRL. This work provides new insights into the structure-property relationship of VNRL.