Preparation Of Phosphorylated Oxidized Starch By Microwave And Its Application In Coating Paper

With the development of science and technology, physical methods in the preparation of modified starch are becoming more and more important. Starch modied by physical methods is equipped with some properties, such as non-residual chemicals, physical and chemical properties of their products are significantly improved, product application scope and value are greatly enhanced. Microwave is a physical method that shows fast heating rate, good heating uniformity, easily control, selective absorption and higher frequency heating characteristics, which is a convenience and time saving heating energy and widely applied to the field of food and chemical industries.In this paper, maize starch was used as a raw material and phosphated oxidized starch was prepared by using hydrogen peroxide and phosphate as oxidant and esterification agent respectively by microwave heating medium. Effects of microwave power, catalyst dosage, reaction temperature, reaction time and pH value on properties of oxidized starch were studied; On the basis of experiment above, effects of microwave power, ratio of mixed phosphate, urea dosage, reaction temperature and reaction time on properties of phosphated oxidized starch were investigated and the optimal preparation process parameters of phosphated oxidized starch were determined. Oxidative reaction conditions were: microwave power 500W, catalyst 0.08%, reaction temperature 45℃, oxidation time 30 min, pH value about 3.5; Esterification reaction conditions were: microwave power 800W, NaH 2 PO 4 /Na 2 HPO 4 ratio 2:1, urea 4%, reaction temperature 140℃, reaction time 30min.The molecular structure, crystal structure and particle morphology, paste nature of starch modified before and after were analyzed by fourier transform infrared spectroscopy (FTIR), X-ray diffraction(XRD), differential scanning calorimetry(DSC), polarized light microscopy(PLM), scanning electron microscopy(SEM) and rotational viscometer respectively. The results showed that the final product that were prepared by microwave method was phosphated oxidized starch, oxidation and esterification didn't completely change the crystalline structure of starch granules, but its crystal structure had damaged to some extent, the melting temperature decreased and the melting process lengthened; The granules surface of starch modified after showed a very significant change, not only its edges and corners were blunt, but some holes appeared on its surface. The results indicated that modification happened not only on particle surface and into the particle interior, gelatinization temperature of modified starch had been lower, the past viscosity of phosphated oxidized starch was larger than oxidized starch but its stability was enhanced.In order to substitute starch for some or all latex in coating color, effects of different experimental samples of phosphated oxidized starch and its dosage on coating paper properties were discussed, then rheological properties of coating color and its water retention properties were studied. The results indicated that, when the phosphated oxidied starch prepared in this experiment was added into coating color, coating paper was good, better starch/latex ratio was 4:10 or 3:10 and the best drying temperature should be controlled at 85℃; Phosphated oxidized starch coated paper showed better performance than oxidized starch and commercially available coating starch 3S; Experiments also indicated that the addition of phosphated oxidized starch did not change the coating's shear thinning properties, but the viscosity improved; coating viscoelastic test results showed that the addition of phosphated oxidized starch was beneficial to enhance the interaction between coating components, but the dosage should not be too large; Water Loss of coating added oxidized starch phosphate was smaller significantly than pure latex coating formulations, from 108.32g/m2 to the smallest 63.86g/m2 , down by about 41%, which indicated that water retention properties of coating can be significantly increased by adding a certain amount of phosphated oxidized starch.