Preparation Of Ultrafine Starch Particles And Its Application In Paper Coating

In recent years, modified starch has been widespread in the papermaking industry for its recyclable, cheap and environmental protection characteristics. Using the modified starch got by special method to replace traditional petroleum based synthetic latex kind adhesive as the coating adhesive not only conforms to environmental protection requirement but also meets the low-cost control requirement of mills.The paper is aimed at developing a novel adhesive used for coated paper and preparing an ultrafine starch product that exists in particulate form, which is similar to features of Ecosphere bio-latex. This kind of product could be applied in the coating by partial substitution (to a scale of 1:1) of styrene-butadiene latex.To achieve the goal mentioned above, the paper in many ways made an attempt to process the starch. The test tried different abrasive medium, different starch raw materials, different crosslinking treatment ways and gelatinization crosslinking etc.. Through a thorough exploration, it was identified that the method-that is, pre-treating starch with chemical crosslinking first and then grinding, could prepare the target product.First, the paper designated the sodium trimetaphosphate as the cross-linking agent and the phosphate starch as the raw material to conduct a crosslinking treatment under proper situation, the starch after cross-linking was then mechanical polished to the particles with the median diameter of 200 nm around under the 10-15% of solid content and finally prepared to be ultrafine starch. In the coating application, the ultrafine starch product replace petroleum based synthetic latex adhesive to a scale of 1:1 instead of 2 parts, then the water retention value and high shear rheology of the coating is obviously improved. But the strength and optical properties of coated paper are still to be improved.In view of this, another group of test selected the phosphorus oxychloride and corn starch respectively as the cross-linking agent and raw material, which also got ultrafine starch with the median diameter of 200～800 nm around but under the 15-20% of the solid content condition. The ultrafine starch is characterized by small particles, being able to directly disperse and mix with pigment and slight swelling etc.. All of these make it possess with a good adhesion in the coating, and exhibit good coating and coated paper properties. For example, the ultrafine starch product replace petroleum based synthetic latex adhesive to a scale of 1:1 instead of 2 parts in the coating application, then the water retention value (168.1gm-2) of the coating is obviously improved 32.9% more than the whole latex formula (250.6gm-2);in addition, application of ultrafine starch in the bottom coating has excellent properties of paper surface intensity. The surface intensity of the formulation containing ultrafine starch (3.95 m·s-1) is improved 37.6% more than the whole latex formulation (2.87 m·s-1), and 53.1% more than the formulation containing common coating starch (2.58 m·s-1), and 22.3% more than the formulation containing Ecosphere bio-latex (3.23 m·s-1). Ultrafine starch can also be used in top coating, but relatively speaking, the advantages of the ultrafine starch in paper surface intensity of the top coating is not as good as the bottom coating. Other paper properties (Including printing and optical properties) of the top coating also exhibit well. In summary, the ultrafine starch has good application effect in coating, especially in the bottom coating, which has great significance and good potential.