Thermomechanical properties of CaCO₃-latex pigment coatings: impact of modified dispersing agents

The effect of CaCO3 pigment surface modifications on the rheology, microstructure and the thermomechanical properties of porous particle-polymer composites are investigated. The incorporation of (random copolymerised) acrylamido-2-methyl-propane sulphonate (AMPS) and ethylene glycol methyl ether (mPEG) into poly(acrylic acid) dispersant reduced the dispersing efficiency. Similarly, the composite microstructure showed the concentration and size of particle aggregates were strongly dependant on the chemical nature of the dispersing agent. Dynamic mechanical thermal analysis (DMTA) showed that the incorporating of mPEG segments within the dispersant chain improves the dispersant-latex compatibility, which results in better adhesion as was confirmed through SEM imaging. The composite storage modulus of dry and water saturated samples showed a strong dependency on the properties of the latex. Composites made of high glass transition temperature (Tg), styrene acrylate (SA) latex exhibited high stiffness in dry samples. Contrarily, the cross-linking of the styrene butadiene latex (SBR) induced a low drop in stiffness under conditions of water saturation.