Effects of Silica Morphology on Emulsion Paint Properties Using Rice Husk Ash and Silica Flour as Pigment Extenders
This study investigated the effects of silica (SiO2) morphology on emulsion paint properties by comparing the physical properties of emulsion paints produced with amorphous silica ( rice husk ash) with those of crystalline silica (silica flour) used as pigment extenders in the paint. Calcium carbonate was used as the reference standard in the study. Rice husk ash (RHA) was obtained by heating rice husks on a gas stove to obtain rice husk char which was subjected to controlled incineration in a muffle furnace at a temperature of 6500C and duration of 4hrs. The granular RHA obtained was ground to obtain powdery RHA of smaller particle size. The RHA powder, silica flour (SF) and CaCO3 were then sieved to obtain the same particle size range of 32-63microns (μm) used in the formulation of the emulsion paints. The extender levels in the formulations were varied from 2-12% by weight and the physical properties of the emulsion paint variants were determined. The results revealed that RHA-filled white emulsion paints (RHAWEP) had higher viscosities than those of silica flour due to the amorphous nature of silica in RHA which conferred on it, a thickening effect superior to that of crystalline silica. RHAWEPs had higher pigment volume concentration (PVC) values than those of silica flour and CaCO3 due to its lower specific gravity and this resulted in the flat (non-glossy) appearance of the RHAWEP dry films but semi-gloss appearance of those of SF and CaCO3.