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Formulation of Matt Wood Varnish using Rice Husk Ash as a Flatting Agent

Igwebike-Ossi Clementina Dilim

This study investigated the applicability of rice husk ash (RHA) as a flatting (gloss-reducing) agent in wood varnish and compared its flatting effect with those of two commercial extenders; fumed silica (the standard flatting agent) and silica flour. RHA was obtained by first heating rice husks in a gas stove to obtain rice husk char, which was then subjected to controlled incineration in a muffle furnace at a temperature of 650oC and duration of 4 hrs. The creamy-white granular ash was ground and sieved to obtain RHA powder with a particle size of ~32 microns (μm), which was used in the formulation of matt wood varnish. Silica flour was also sieved to the same particle size as RHA. Wood varnish produced with fumed silica of 20 μm-particle size was used as the reference standard while that produced with 0% flatting agent served as the Control. The gloss values of the wood varnish dry films were measured with a gloss meter at 60o angle of reflectance and their matt values calculated from their gloss values. The results showed that although the three flatting agents displayed varied degrees of flatting effect, they all substantially reduced the gloss levels of the wood varnish samples with a resultant corresponding increase in their matt values. Fumed silica was highest in flatting performance, followed closely by RHA while silica flour ranked third. This trend was evident in the matt values (%) of 95.8 ± 0.08, 88.9 ± 0.14 and 68.55 ± 0.34 obtained for wood varnish produced with fumed silica, RHA and silica flour, respectively. The control had the highest gloss and lowest matt value of 34.4% ± 0.42. These values correspond to increases in matt values (%) higher than that of the control by 178.49, 153.43 and 99.27 for fumed silica, RHA and silica flour wood varnishes, respectively.