DMTA investigation of solvents effects on viscoelastic properties of porous CaCO₃-SBR latex composites

The impact of water, linseed oil and mineral oil solvents on the viscoelastic properties of calcium carbonate-caboxylated styrene buradiene (CaCO3-SBR) porous coatings has been investigated using a dynamic mechanical thermal analysis (DMTA) technique in single cantilever mode from -30 degrees C to 70 degrees C. Water and oils reduce the glass transition temperature (Tan Delta peak) of pure latex. Oils increase the rubbery storage modulus which may be due to oxidation leading to entangled chains that contribute to resistance to deformation. Scanning electron microscopy (SEM) was used to visualise the porous structure of these composites. Further analysis using Image J software showed that increasing the latex content results in the development of small circular (2D) pores. The effect of solvents on the elastic response of coating depends on the chemical nature of the solvent and its molecular size. Linseed oil and water decreased the composite's storage modulus for 5, 10 and 15 pph coatings, in contrast to mineral oil which had a negative impact at relatively higher latex content (50 pph). The drop in the strength and storage modulus of solvent saturated latex coatings is proportional to the solvent surface tension to viscosity ratio. The low values of storage modulus were interpreted as low adhesion between CaCO3 particles and the carboxylated styrene- butadiene matrix. For low latex content coatings, low storage modulus is due to porosity which forms suitable sites for cracks initiation and propagation through the coatings. At higher latex volume fraction coatings the composite behaviour approaches that of pure latex.