AbstractThe mechanical properties of clay‐based pigmented coating films bonded with a series of carboxylated styrene–butadiene latex binders have been investigated. The in‐plane tensile strength and the elongation at rupture increased with increasing amount of polymeric binder. It is suggested that this is due to an improvement in stress transfer through the structure. The mechanical behavior of the films was furthermore found to be strongly related to the properties of the polymeric binder at the usage temperature. In torsional pendulum experiments an increase in the glass transition temperature of the polymeric binder was observed when it was incorporated in the coating film. This is interpreted as being the result of a decrease in the segmental mobility of the polymer molecules due to the presence of the clay particles, i.e., due to the interaction between the clay pigments and the binder. The interaction was, however, less noticeable in experiments using an NMR (nuclear magnetic resonance) technique. If the clay was replaced by calcium carbonate, a strong interaction, as measured using NMR, was observed between CaCO3and the styrene–butadiene polymer, although the in‐plane mechanical strength and ductility were reduced. A structural model accounting for some of the observed differences in mechanical behavior between clay‐based and CaCO3‐based coating films
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