Chitosan-calcium carbonate composites by a biomimetic process

The crystal growth of calcium carbonate on a chitosan substrate was achieved using a supersaturated calcium carbonate solution, by using various additives, such as 6-aminocaproic acid (6AA) and polyacrylic acid (PAA). Polyacrylic acid modified the chitosan-film surface and promoted the nucleation of calcium carbonate crystals. In the absence of polyacrylic acid, sporadic nucleation and crystallization was observed via optical microscopy. By introducing polyacrylic acid into the systems, positively charged protonated nitrogen and negatively charged carboxylate ions were produced by reaction between the amino group in the chitosan and carboxyl group in polyacrylic acid, which were detected by ATR-IR and XPS techniques. These charges induced the nucleation of the calcium carbonate crystals, calcite and vaterite, on the chitosan-film surface. In this case, the crystals showed spherical morphology, which consisted of a large number of small particles with a diameter of about 0.2 μm. The calcium carbonate crystals growing on the rigid chitosan-film surfaces are uniform.