Calcium carbonate crystallization in the presence of modified polysaccharides and linear polymeric additives

Crystallization of calcium carbonate was performed in the presence of grafted polysaccharides, polyacrylamide (PAM) and polyacrylic acid (PAA). The grafted polysaccharides gave crystal morphologies that were different from the unmodified polysaccharides but similar to the ones given by homopolymers of the grafted chains. PAM-grafted α-cellulose gave rectangular platelets that aggregated to form ‘spherical’ crystals on the surface of the fiber, whereas PAA grafted α-cellulose gave spherical crystals on the surface of the fiber. X-ray diffraction (XRD) spectroscopy showed that PAM-grafted α-cellulose, PAM as well as the control (no polymeric additive) gave calcite crystals at both 25 and 80 °C. However, the PAA-grafted α-cellulose and PAA homopolymer gave calcite and vaterite crystals at 25 °C with calcite and aragonite crystals along with traces of vaterite being formed at 80 °C. The fiber surface coverage by these crystals was more on the acrylic- and acrylamide-grafted cellulose than on the ungrafted α-cellulose. The evolution of CaCO3 polymorphs as well as crystal morphology in PAA-grafted starch was similar to that of PAA-grafted α-cellulose at the two temperatures employed.