Amorphous calcium carbonate in form of spherical nanosized particles and its application as fillers for polymers

Abstract

The synthesis of amorphous calcium carbonate (ACC) via a liquid precursor to give spherical particles with monodisperse distribution of diameters in the range of 0.4–1.2 μm has been optimized to the level to obtain multigram yields per batch. The synthesis was achieved by precipitation of ACC from a strongly alkaline solution of calcium chloride (CaCl 2) at ambient temperature using the hydrolysis of water soluble dimethyl carbonate (DMC) as the internal source of CO 2. As ACC produced by this novel method contains a small fraction of bound water a drying process, namely annealing at 200 °C for 6 h was developed. The water free powder was blended with conventional polyolefins (linear low density polyethylene (LLDPE), high density polyethylene (HDPE), polypropylene (PP), polystyrene (PS)) in a melt extrusion process. Blending with poly(lactic acid) (PLA) as a model of a biomedically relevant polymer was also achieved. While a homogenous dispersion of the dried amorphous calcium carbonate (DACC) particles in the polymer composites was easily achieved, the interaction between the polymer continuous phase and particle surface seems to be rather weak. Consequently, the physical properties of the blends having volume fractions from 10 to 40% of the filler behave as expected for non-interacting materials, e.g. the melt viscosity increases as predicted from Einstein's law, the glass transition and melting temperature of the polymer matrices remain largely unaffected. The Young's modulus did increase while tensile strength and elongation at break decrease.