Mechanical properties of films cast from alkali soluble resin stabilized latexes

Alkali soluble resins (ASRs) are often combined with polymer latexes in coatings formulations in order to provide stability to the latex as well as to improve the mechanical properties of films cast from the dispersions. In this work, we explore the influence that the alkali soluble resin has on the mechanical properties of films cast from a series of ASR stabilized styrene(St)/butyl acrylate(BA) copolymer latexes. Tensile test results show that in stark contrast to the mechanical properties of most films cast from latexes, the composition of the St/BA phase has virtually no influence on the Young's modulus and is largely dependent on the high Tg ASR phase, leading to very high values, on the order of 108 Pa. When the Tg of the St/BA phase increased, elongation break also increases leading to materials with high toughness, an observation which is again in contrast to the general behavior shown by films cast from homogeneous latexes. These unique mechanical properties, which are reminiscent of those of rubber toughened thermoplastics, are related to the continuous high Tg ASR phase that is formed upon drying. The influence of ethylene glycol and glycerol, common polar additives in coatings formulations, is also explored and it is shown that the polar ASR phase is selectively plasticized, leading to a significant decrease in mechanical performance.