FILM-FORMING ABILITY AND MECHANICAL-PROPERTIES OF COALESCED LATEX BLENDS

The film-forming ability of latex blends (hard latex + soft latex) and the mechanical behavior at finite strain of latex blend films (soft m atrix with tough inclusions) has been investigated. The maximum weight fraction of hard latex particles (phi(max)) which still gives rise to transparent and crack-free films has been used as film-forming abilit y criterion. It was shown that when the T-g of the soft latex is low ( T-g(soft) < 0 degrees C), phi(max) is constant and equal to 0.55 becau se the film-forming ability is controlled by contacts between hard par ticles. Nevertheless, the expected effect of T-g(soft) on film-forming ability is observed (i.e., phi(max) decreases when T-g(soft) increase s) when T-g(soft) is above 0 degrees C. From the mechanical behavior p oint of view, it was shown that the two main parameters controlling th e mechanical behavior of latex blend films are: the mechanical propert ies of the soft polymer because it represents the continuous matrix an d the weight fraction of hard latex particles since they enhance the l ocal deformation of matrix under load. However, it was also proven tha t debounding between the high T-g latex particles and low T-g matrix o ccurs rapidly (at an elongation ratio approximate to 30%) during uniax ial strain experiments and has to be taken into account in order to ga in a thorough understanding of the mechanical behavior of these biphas ic films. (C) 1997 John Wiley & Sons, Inc.