| The starch-graft-polyacrylamide (St-g-PAM) attaches the flexible synthetic polymer PAM onto the hydrophilic and semi-rigid starch molecular backbone. It possesses both the characteristics of natural and synthetic polymer, such as mechanical and biological stability and linear extensibility.The degree of gelatinization is an important factor in graft reaction, and high degree of gelatinization is favorable to the graft copolymerization of starch. In addition, the polymerization method (e.g. aqueous polymerization, emulsion polymerization, and suspension polymerization) has also been a focus of the researchers. Although aqueous solution polymerization is a traditional technique in industry, there are still many defects, such as gelation prematurely, low solid content and high chance of cross-linking. Therefore, seeking for a new reaction system is an important approach to improve the performance of the title product.In this study, the raw corn starch was pretreated by water scrubbing, extraced by polar solvents, filtration, drying and sieving. Transmittance of pregelatinized starch vs. extractants and the mesh number was studied. Starch extracted with acetone and sieved through a 200-mesh sieve shows the best solubility and transmittance. St-g-PAM was prepared by using this pretreated starch combined with a new reaction system, i.e., adding an appropriate salt to the traditional aqueous solution.In this study, the optimal technology parameters were obtained by a L18(37) orthogonal experiment, namely mass ratio of AM/Starch 3:1, mass of starch 1.5000g, temperature 60℃, concentration of salt solution 10g/50mL, mass of ammonium persulfate 0.0168g, time 3.5 h, mass of azo initiator 0.0100g. And the outcome under these conditions was as follows, intrinsic viscosity 12.49 dL·g-1, graft efficiency 86.68%, and percentage of grafting 163.91%.The St-g-PAM was identified by Fourier transformed infrared (FTIR) and elemental analysis. The structure and properties of products were studied by X-ray diffraction (XRD)the polarizing microscope, SEM and texture analyser. After the graft reaction, the crystalline structure of starch was completely destroyed, there were many holes with deep depth on the product's structure, showing a spatial network structure, and solution systems before and after reaction were non-Newtonian fluid, the apparent viscosity under each response condition was higher than under no reaction, under most superior condition highest. The type of starch and the choice of solution system were studied through the percentage of grafting (PG), the monomer conversion (MC), the mass of purified product and the intrinsic viscosity; the result showed that the pretreated starch gelatinization effect was better to be more conducive to graft copolymerization than the untreated starch and the combination of the pretreated starch and the salt solution system got the product which had high yield, high monomer conversion and high intrinsic viscosity. The characteristics of the brine polymerization system were studied through the texture analyser, the penetration tester and the visible light spectrophotometer, showing that the salt solution polymerization was more advantageous than the aqueous solution polymerization. Comparing with the traditional aqueous solution copolymerization and the water-in-water emulsion copolymerization, the branched-chain molecular weight synthesised by the salt solution copolymerization was the largest. And it could overcome the flaws of the aqueous polymerization system. |
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