Influence of mixed layer of proteins and phospholipids on the unique film formation behavior of Hevea natural rubber latex

• More insight into the role of the mixed layer on latex film formation was acquired.
• The mixed layer was responsible for the particle shape during film formation.
• The flattening rate of the film increased after the removal of the mixed layer.
• A mechanism of film formation for NR latex was proposed.

This work is an extension on the study of the influence of the mixed surface layer of proteins and phospholipids on latex particles with respect to the film formation behavior of natural rubber (NR) latex. The film formation of untreated fresh NR (FNR) latex was compared with that of deproteinized NR (DPNR) and saponified NR (SPNR) latexes in an attempt to understand the role of the non-rubbers covering the surface of latex particles in film formation process. Atomic force microscopy (AFM) was used to investigate the film formation behavior of these latexes by monitoring the surface morphology and roughness as a function of aging. All NR latexes showed the spherical contour of individual latex particles at the nascent stage of film formation as revealed by AFM. The surface profile subsequently smoothened out and became flattened with aging time. However, the flattened feature of the untreated FNR film was different from those of the DPNR and SPNR films since the mixed layer of proteins and phospholipids had been removed in the former. A mechanism of film formation for NR latex (fresh and untreated) was proposed. The ability of NR latex to form mechanically strong, homogeneous and continuous film has an important impact on its industrial application such as medical gloves.

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