Surface morphology of asymmetric latex film prepared from blends of natural rubber and poly(methyl methacrylate) latexes

Colloidally stable latex blends of natural rubber (NR) and poly(methyl methacrylate) (PMMA) latexes containing up to 50 wt.% PMMA can be prepared by mixing commercial NR ammoniated latex concentrate and monodisperse PMMA latex dispersion. The clarity and tackiness of the films obtained depend on the PMMA content; films become opaque and non‐tacky at >30 wt.% PMMA content. The morphology of these films shows asymmetric distribution of the PMMA particles across the thickness of the film. There is preferential enrichment of PMMA particles at both the air/polymer and glass/polymer interfaces and a predominating NR interior. More PMMA particles are accumulated preferentially at the glass/polymer interface than at the air/polymer interface. The accumulation of the PMMA particles at the interface is strongly dependent on the size and concentration of the PMMA particles. The formation of these asymmetric latex films is explained in terms of the surface energetics, compatibility, T g and density of the polymers, stability of the component latex, surface chemistry and particle size of the latex particles used.