Nanomechanical mapping of green and vulcanized natural rubber latex film by AFM PeakForce QNM: Impact of proteins and lipids contents on film quality

Soft polymeric films from natural rubber (NR) latex are crucial for applications requiring exceptional mechanical properties, such as medical gloves. It is known that pre-vulcanization, film formation, and post-vulcanization are three important steps in the manufacturing process of thin latex films that control the quality of the final film products. This study investigates the pivotal role of pre-vulcanization in latex film formation, with a specific emphasis on the inhibitory effects of proteins and lipids on particle coalescence during the film formation process. Using atomic force microscopy (AFM) in PeakForce Quantitative Nanomechanics (QNM) mode, we provide experimental evidence that residual non-rubber components (NRCs), particularly proteins and lipids, form a stabilizing layer around latex particles that impedes rubber chain diffusion and particle coalescence. These effects contribute to surface roughness in unvulcanized latex films and hinder the formation of a smooth, uniform film. Pre-vulcanization facilitates network formation within latex particles, improving chain mobility and enabling smoother film formation. Nanomechanical mapping reveals that reducing NRCs content enhances film uniformity and mechanical strength by promoting rubber chain diffusion and cross-linking. These findings underscore the critical balance between NRCs levels and pre-vulcanization in optimizing latex-dipped product quality, offering new insights into the nanomechanical properties governing latex film formation and performance. • Using AFM PeakForce QNM, this technique revealed a decrease in surface roughness and Young's modulus of unvulcanized film after prolonged storage. • The measured Young's modulus values offer insights into the distribution of the crosslinking network within the rubber particles of pre-vulcanized film. • The tensile strength of latex-dipped films increased with a decrease in protein content in CNR and DPNR latex samples, while it decreased in SPNR samples as lipid content decreased. • Nanomechanical mapping of Young's modulus on ultramicrotome-sectioned samples revealed intra- and interparticle crosslinking in the pre- and post-vulcanized surface films, respectively.