Polymer chain pinning at interfaces in CaCO3–SBR latex composites

The viscoelastic properties of carbonate-based coatings in ambient and water saturated conditions have been investigated using dynamic mechanical thermal analysis (DMTA). At low frequencies, viscous flow is suggested to be due to the reorientation of polymer chains at particle interfaces. At higher frequencies the composite storage modulus, as normalised to that of the latex, decreases due to the conjoint action of increased heat and decreased molecular chain mobility at the interfaces. Water is found to weaken interfacial pinning of the polymer molecules. Water is able to conduct heat away from the solid component of the microstructure more effectively than air, and reduces the effect of temperature on the softening of latex. Pore space allows greater microstructural mobility and consequently polymer chains at interfaces can orient more easily to the loading direction. The glass transition temperature, the normalised storage modulus and the normalised loss modulus were found to depend on both the latex fraction and on the porosity. This paper highlights and explains particular conditions that may arise during processing by which carbonate-based coatings soften.