Estimation of Organic Opacifier in Water-Based Architectural Coatings Using Dynamic Mechanical Thermal Analysis

Hollow sphere polymeric pigments prepared from styrene-acrylate copolymer referred to as organic opacifiers (OP) are the primary substitutes of TiO2 in water-based architectural paints. This study describes the method for the quantification of OP in water-based paints using dynamic mechanical thermal analysis (DMTA). The significance of DMTA in visualizing the glass transitions over differential scanning calorimetry (DSC) is showcased. The glass transition temperature (Tg) of OP was found to be ~109°C by DSC method and ~125°C by DMTA method. The peak intensity of tan δ at Tg of OP in paints (tan δ2) is not affected by the curing time and linearly increases as a function of OP concentration in water-based paints, irrespective of the difference in volume solids. DMTA can efficiently quantify OP in paint film if it is ≥3.3% (w/w). Increasing concentration of a coalescing solvent in water-based paints has a detrimental effect on the peak intensity of tan δ2. Two commercially available grades of OP having difference in the core-shell morphology have been studied. Internal morphology of the OP studied by scanning electron microscopy has a significant effect on the peak intensity of tan δ2 thereby affecting its opacity performance in paints. Owing to the limited effect of curing time, volume solids and coalescing solvent on the peak intensity of tan δ2 of paints, this method can be used for the quantification of OP in paints, as it has been validated with seven commercially available paints with known OP contents.