Investigation of effect of type of pigment/extender on the stability of high pigment volume concentration water-based architectural paint

This article elucidates the effect of type of pigment/extenders viz. titanium dioxide (TiO₂), magnesium silicate (steatite), calcium carbonate, dolomite, precipitated sodium magnesium aluminosilicates, hydrated and calcined aluminum silicates (kaolin) when used alone or in combination in the paint dispersions on their sedimentation stability. Accelerated heat age stability test was conducted as per ASTM D 1849. Wettability of pigment extenders were measured in terms of their contact angle using Washburn technique. Rheology viscosity curve and oscillatory amplitude sweep test are carried out to depict the structural properties, more precisely the extent of flocculation in the paint dispersion. From rheology viscosity curve, extent of residual flocculation is determined using Asbeck extrapolation method. Extent of total flocculation in the paint dispersion is estimated from cohesive energy density (E_c) using oscillatory amplitude sweep test. Energy of separation of particles in flocs (E_sep) is also determined using yield point measurement. Attempt was made to correlate extent of flocculation present in paint dispersion with settling and syneresis observed during accelerated heat age stability test. It is observed that, the paint dispersions based on only TiO₂, only hydrous kaolin and only precipitated sodium magnesium aluminosilicates are found to be quite stable whereas the dispersions based on only magnesium silicates and only calcined kaolin are found to be unstable. Paint dispersions based on carbonate extenders show syneresis and soft settling which is easily mixable. From the rheological study, it is identified that E_c is the most crucial parameter that correlates very well with the accelerated heat age stability test results of paint dispersion.