Preparation of zinc borates with different structures and morphologies and their effect on thermal and oxidative stability of polyvinyl alcohol

Zinc borates with different structures and morphologies were selectively prepared starting from zinc sulfate hydroxide (Zn4SO4(OH)6) and boric acid in aqueous solution. When the reaction temperatures were 80 and 90 °C, platelet-like and polyhedral zinc borates with the formula of 2ZnO·3B2O3·3H2O were formed, respectively. When the reaction temperature was less than 80 °C, rod-like heptahydrate zinc borates with the formula of 2ZnO·3B2O3·7H2O were formed. The morphology of zinc borates (2ZnO·3B2O3·3H2O) changed from platelet to polyhedron at the reaction temperature of 90 °C with increasing the water content in the reaction solution. The presence of polyethylene glycol and sodium dodecyl benzene sulfonate in the reaction solution favored the formation of small-sized polyhedral 2ZnO∙3B2O3∙3H2O particles. The presence of citric acid favored the formation of 2ZnO∙3B2O3∙3H2O platelets. The chemical structure and morphology of the zinc borates significantly affected their performances on improving the thermal and oxidative stability of polyvinyl alcohol.