Improving the optical performance of the nanostructured starch-calcium carbonate hybrid pigments

This work presents a method to produce hybrid pigments from unmodified starch and precipitated calcium carbonate (PCC) to be used as a papermaking additive. The hybrid pigments are composed of a layer of 20-200 nm PCC crystallites on top of a starch granule which has been partially dissolved. The preparation procedure consists of starch activation, co-precipitation i.e. encapsulation of starch granules with PCC followed by heating to hydrate and dissolve the starch. In this article, the effects of starch origin, activation temperature and content as well as the precipitation variables are examined to optimize the properties of the hybrid pigments when applied in paper. The proper activation of the granules was a key variable for successful encapsulation and determined the retention of starch in the pigment structure after cooking. Different crystal structures could be precipitated on top of the granules and the hybrid pigment size could be decreased by changing from corn to rice starch. The starch content, origin of starch and precipitation conditions were found to be crucial for the paper properties.