Spray-Dried Alumina Granules Coated with a Novel Nanocomposite of Kaolin and a Synthesized Poly(vinyl alcohol-co-acrylic acid) Copolymer

The production of coated alumina granules by the spray-drying method often requires the incorporation of several additives, leading to complex interactions and potential defects during ceramic sintering. Furthermore, the excessive addition of these additives can significantly affect the fluidity of the granules, posing a critical problem in the manufacturing process. To address these issues and reduce the negative effects of additive competition and excessive fluidity, we introduced the synthesized poly(vinyl alcohol-co-acrylic acid) PVA/PAA copolymer which serves as both dispersant and binder with a plastic character in the granule formation process. To take environmental and economic considerations into account, we incorporated a percentage of kaolin (K) nanofiller to form a PVA/PAA-K nanocomposite, substituting part of the copolymer with an inorganic material. The clay was characterized by X-ray diffraction, X-ray fluorescence, Laser granulometry and BET. The properties of alumina suspensions were analyzed by adsorption isotherm, rheological behavior and electrokinetic measurements, with different PVA/PAA-K ratios. The pulverized alumina granules were then examined by scanning electron microscopy and laser granulometry. The molecular weight of PVA/PAA was estimated at 11,000 g mol(-1). The rheological study of alumina suspensions proved the effectiveness of replacing 4.2 wt% of conventional additives with a combination of 1.8 wt% PVA/PAA and 0.2 wt% K which showed a remarkable reduction in viscosity and improved stability. The granules obtained had a uniform size distribution and exceptional sphericity, in the micro-granule range. These promising properties make them suitable for the production of advanced dense ceramics with a defect-free structure after sintering.