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 matrix with tough inclusions) has been investigated. The maximum weight fraction of hard latex particles (ϕmax) which still gives rise to transparent and crack-free films has been used as film-forming ability criterion. It was shown that when the Tg of the soft latex is low (Tg(soft) < 0°C), ϕmax is constant and equal to 0.55 because the film-forming ability is controlled by contacts between hard particles. Nevertheless, the expected effect of Tg(soft) on film-forming ability is observed (i.e., ϕmax decreases when Tg(soft) increases) when Tg(soft) is above 0°C. From the mechanical behavior point of view, it was shown that the two main parameters controlling the mechanical behavior of latex blend films are: the mechanical properties of the soft polymer because it represents the continuous matrix and the weight fraction of hard latex particles since they enhance the local deformation of matrix under load. However, it was also proven that debounding between the Tg latex particles and low Tg matrix occurs rapidly (at an elongation ratio ≈ 30%) during uniaxial strain experiments and has to be taken into account in order to gain a thorough understanding of the mechanical behavior of these biphasic films. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2093–2101, 1997