Effects of film structure on mechanical and adhesion properties of latex films

Abstract

In order to investigate the effect of the particular structure of latex films on mechanical (stress-strain behaviour) and adhesion (measured by peeling) properties, this work compares these characteristics for latex films and corresponding “solution films”. Solution films were obtained by dissolving the latex film in an appropriate solvent and forming a new film by evaporating the solvent. In this way, the latex and solution films have exactly the same composition but different structures. Four different systems were studied, namely a homopolymer of 2-ethyl hexyl methacrylate, a copolymer of styrene and butyl acrylate, a copolymer of butyl acrylate with a zwitterionic monomer, and, finally, an ethyl acrylate-methyl methacrylate copolymer partially grafted onto a hydrophilic polyester. It was shown that latex films have Young's moduli systematically higher than the corresponding solution films. This is due to the fact that the hydrophilic shells of the latex particles form a continuous phase in the latex film which increases the modulus thanks to polar interactions. Modeling was possible using an appropriate equation (Palierne's Model) which allowed the determination of the modulus and volume fraction of the shell phase, without adjustable parameter. On the other hand, adhesion energy for latex films is always smaller than for solution films. This is interpreted in terms of structure of the film-support interface and interface and dissipative processes within the bulk of the film.