Composite Materials Based on Sodium Alginate and Synthetic Powders of Calcium Carbonate

Properties of composite materials with polymer matrix and inorganic filler are affected by preparation methods and starting components’ properties. For example, filler powder particle size distribution, phase composition and presence/absence of dopants can greatly affect properties of resulting composites. The present research attempts to clarify the influence of synthetic CaCO3 powder properties on alginate/CaCO3 composite material preparation process. Composite materials in the form of granules, networks and films were created from suspensions of synthetic powders of calcium carbonates CaCO3 in aqueous solutions of sodium alginate. Powders of calcium carbonates CaCO3 were synthesized from 0.5 M aqueous solutions of calcium chloride CaCl2 and aqueous solutions of potassium K2CO3 (at molar ratio Ca/CO3 = 1), sodium Na2CO3 (at molar ratio Ca/CO3 = 1), and ammonium (NH4)2CO3 (at molar ratios Ca/CO3 = 1 and Ca/CO3 = 0.5) carbonates. Phase composition of powder synthesized from CaCl2 and K2CO3 was presented by calcite. Phase composition of powders synthesized from other soluble carbonates included calcite and vaterite. The powder preparation protocol excluded the stage of synthesized powder washing for by-product removal. This preparation protocol provided preservation of reaction by-product in the synthesized powder at a very low level. The presence of NH4Cl as a reaction by-product even in small quantities can be taken as a reason for visually observed subsequences of cross-linking reaction at the stage of suspensions preparation. Aqueous solution of sodium alginate and suspensions containing powders synthesized from potassium K2CO3 and sodium Na2CO3 carbonates demonstrated similar dependence of viscosities from shear rate. The presence of (NH4)2CO3 in the powder synthesized at molar ratio Ca/CO3 = 0.5 was the reason for the lower viscosity of the suspension in comparison with suspensions loaded with powders containing KCl, NaCl and (NH4)2Cl as reaction by-products due to decomposition of unstable (NH4)2CO3 and gas phase formation. The presence of (NH4)2Cl in the powder synthesized at molar ratio Ca/CO3 = 1 in contrast was a reason for the highest viscosity suspension in comparison with those under investigation. Additionally, (NH4)2Cl presence in synthetic powders shows the ability to facilitate partial dissolution of CaCO3 providing a higher concentration of Ca2+ cations at the stage of suspension preparation, thus aiding the cross-linking process of alginate hydrogel. Granules, meshes and films were created via interaction of suspensions of calcium carbonates CaCO3 in aqueous solutions of sodium alginate with 0.25 M aqueous solutions of calcium chloride CaCl2 to provide the formation of matrix of composites via Ca-crosslinking of sodium alginate followed by washing and freeze drying under deep vacuum. The created composite materials in the form of granules, meshes and films based on Ca-cross-linked alginate and powders of synthetic calcium carbonate can be recommended for skin wound and bone defect treatment and drug delivery carriers.