Preparation of Ultrafine Starch Particle and its Application in Paper Coating

Despite its biodegradability, adequate cohesive strength and comparatively low cost, the use of cooked starch as a paper coating binder is limited due to its high viscosity and serious negative impact on the gloss. Starch-based bio-latex with size in the nanometer or sub-micrometer range has been developed recently to overcome these shortcomings. In this study, ultrafine starch particle(UFSP) was prepared by mechanical milling using a DYNO mill in combination with light chemical pretreatment. Model coating colors containing different dosages of UFSP were applied to base paper and the properties of the coated papers were evaluated. The results showed that the UFSP was disc-shaped with a median particle diameter of 167 nm. Water retention capacity of the coating colors was improved considerably with the addition of UFSP, i.e., the water retention value decreased by nearly 40% when styrene-butadiene latex was replaced by UFSP at a dosage of 3 pph(per hundred parts of pigment). The high shear rate viscosities of the coating colors containing no more than 2 pph of USFP were similar to that of the control coating color at shear strain rate higher than 2000 s^(-1). The properties and performances of the coated papers were comparable to the control coated paper with single synthesized latex binder. The gloss and the print gloss of paper samples with or without USFP were 59.7% and 58.2%, 79.0% and 78.8%, respectively. Surface strength of paper samples with or without USFP were 0.96 and 0.90 m/s, respectively, while the ink absorptivity values were 34% and 33%. This study demonstrates a promising approach to obtain submicrometer sized starch for paper coating.

Interfacial properties of nano TiO_(2) and cellulose paper coating

This paper examined different kinds of organic functional groups that were introduced onto the surface of nano TiO_(2) by surface modification with different types of zircoaluminate coupling agents.The modified nanoTiO_(2) products with different interfacial properties were obtained,and the impact of the interfacial properties of nanoTiO_(2) on the rheological behavior of paper coating and the properties of coated paper was systematically investigated.The steady shear rheological results showed that the paper coatings containing nano TiO_(2) exhibited a pseudoplastic fluid behavior,characterized as obvious shear thinning.Compared to the hydrophilic unmodified nano TiO_(2),modified nano TiO_(2) could contribute more to the viscosity of paper coatings.The study on the dynamic viscoelasticity revealed that,through the enhancing action among each component in paper coatings,the modified nano TiO_(2) with quaternary amine groups or carboxyl led to a higher dynamic elastic storage modulus and viscous loss modulus of paper coatings.In addition,SEM and AFM analyses indicated that adding modified nano TiO_(2) products in paper coating could improve the coating structure,thus ameliorating the optical properties and printability of coated paper.The results obtained could provide a good reference for the application of nano pigments in paper coating.

MODELING DRYING OF A COATED PAPER

Drying of a coated paper is modeled and simulated.The paper sheet is assumed to form three zones,and each zone has its own drying mechanism.Coupling of energy and mass balances must be used in order to solve differential equations.The simulations are carried out in various drying conditions i.e.,only hot air drying,only radiant drying,and mixed hot air-radiant drying.Also the effect of one side and two side assumption on evaporation is studied.Effect of venting air speed and radiant heat source presence and its distance from the drying surface on the drying of a coated paper has been studied.It is found that both distance and venting air speed are inversely related to drying in mixed hot air-radiant drying.Both surfaces participate in evaporation however,during the last time of drying,no difference between the upper and the bottom surfaces exist.