Novel method for preparation of spherical starch ester pigment with excellent optical properties in paper coatings

The preparation of highly porous starch acetate particles suitable for filler for paper was studied using solution precipitation techniques. Chemically cleaved starch acetate with a DS value of 2 to 3 and glass transition temperature of +158-160 °C was used as starting material for the preparation of ideally spherical particles in diameter as one half of the wave length of the visible light.Particle shape and size take form spontaneously when solvated (e.g., acetone-ethanol mixture) starch polymer is mixed with non-solvent (e.g., water).The refractive index of the starch pigment is 1.47 and an ISO brightness value as high as 94 has been measured.The preparation of starch pigment dispersion of 20-30% solid contents has been carried out on a semi-industrial scale by using 0.25 m3 DRAISS reactor in combination with 0.2 micron cut-off continuous filtering unit.Starch pigment has improved affinity to paper surface and it can be used as such or mixed with other pigments to enhance optical or printing properties of paper