Optimizing Sulfur Vulcanization for Enhanced Mechanical Performance of Hevea Latex-Dipped Film: Insights from AFM PeakForce Quantitative Nanomechanical Mapping

Abstract

This study delves into the pivotal role of sulfur vulcanization in defining the mechanical characteristics of natural rubber (NR) latex-dipped products. Utilizing sulfur vulcanization, known for its operational simplicity and cost-effectiveness, we examine its ability to enhance product elasticity and mechanical strength through various sulfidic bond formations such as mono-, di-, and polysulfidic bonds. Different vulcanization systems and sulfur contents were evaluated for their influence on the mechanical attributes of latex films, employing three types of NR latex, namely concentrated NR (CNR), deproteinized NR (DPNR), and small rubber particle NR (SRP), each representing distinct non-rubber components (NRCs). The study utilized advanced atomic force microscopy (AFM) equipped with PeakForce Quantitative Nanomechanical Mapping (QNM) to visualize and measure Young’s modulus distribution across the film of pre-vulcanized latex. Our findings reveal that films by CNR processed using the conventional vulcanization (CV) system exhibited enhanced tensile strength and elongation at break. It even showed a lower crosslink density than those processed using the efficient vulcanization (EV) system. Interestingly, DPNR films showed a more uniform distribution of Young’s modulus, correlating well with their superior mechanical strength. In contrast, SRP films showed excessive network structure formation in the particles due to accelerated vulcanization rates, hampering subsequent post-vulcanization interparticle crosslinking in film formation and remaining more rigid. The overall results Illustrate clearly that the ultimate mechanical properties of the latex films are strongly dependent on the type of sulfidic bonds formed. This research reveals further the very intricate relationship between the vulcanization methods, sulfur content, and latex type in optimizing the mechanical performance of NR latex products. It provides valuable insights for industry practices aimed at improving the quality and performance of latex-dipped goods.