Morphology and Adhesive Force of Natural Rubber Latex Films by Atomic Force Microscopy

Abstract

Commercial natural rubber latex concentrate is used almost exclusively in the production of rubber-dipped goods, the bulk of which is in the form of gloves. When a 'former' is dipped into the latex, a latex film is formed after the water evaporates and the particles come into contact and fuse together. Any factors that hinder good film formation of the latex would adversely affect the film morphology and hence its application as a barrier material. In view of its low glass transition temperature, natural rubber (NR) latex film is soft and tacky and cannot be used as a glove in its native form. Vulcanization and chemical modification by chlorination of the film surface are additional process steps in glove manufacturing that enable NR latex film to become finally donnable. Basically these processes reduce the surface friction and improve the lubricity of the film surface. A clear understanding of the nature of the surface of the latex film in relation to its performance is pivotal in ensuring product quality. The adhesive force of various NR latex films such as powdered, vulcanized, chlorinated, and polymer-coated was determined from the force-distance curves using atomic force microscopy (AFM) and compared with those of synthetic polymers and commercial glove samples. Distinctive adhesive forces between the AFM probe tip and these materials allow them to be distinguished from one another. Results indicate that the magnitude of the pull-off force is strongly influenced by surface inhomogeneity and topography of the film. The behavior of the pull-off forces agrees with interpretation based on current understanding of this phenomenon. The technique is well-suited for assessing the structure-performance relation of gloves.