Preparation And Properties Of Carboxymethyl Starch By Microwave Dry Method

Carboxymethyl starch(CMS) is an anionic starch prepared via reaction of starch with etherifying agent and it has better water solubility, retrogradation, freeze-thaw stability and so on. CMS is produced mainly by wet and dry method. Dry method which possesses the advantages of low cost and environmental protection, combined with microwave heating, can be used to shorten the period of the product.With corn starch as raw material, chloroacetic acid as etherification agent, NaOH as catalyst, CMS was prepared by microwave dry method and crosslinked composite modification. By researching its physicochemical properties, structure and flocculability, conclusions were drawn as follows:(1) The effects of microwave irradiation time, radiation power, moisture content and the amount of NaOH were studied. The best process parameters of microwave dry method which obtained by study were:molar ratio of NaOH and etherification agent was3.10, moisture content of the system was20.54%and average power was320W with radiation time was6.38min. The DS of carboxymethyl starch which prepared under the best parameter was0.2137and reaction efficiency was85.48%. Compared to dry method, the microwave dry method could consummator reaction within5-9minutes with a quite high DS and RE.(2) Compared to corn starch, a great deal of improvement was got on the transmittance, retrogradation, anti-entymolysis ability, freeze-thaw stability and viscosity of carboxymethyl starch. And there was a positive connection between DS and the improvement of starch properties. The starch granules of CMS showed severe damage in the surface and there were some holes on its surface. The infrared spectra showed that carboxyl group was introduced into the starch molecules prepared by microwave radiation in dry process, proving that starch has been carboxymethylationed, and no new peaks were appeared on CMS after crosslinking.(3) Compared with the same degree of substitution of carboxymethyl starch prepared by dry method, the microwave made the retrogradation and anti-entymolysis ability improve, constant on transmittance, freeze-thaw stability and gelatinization temperature. There also a slight decreased on peak viscosity and breakdown viscosity. After crosslinking, CMS has a higher freeze-thaw stability and a lower setback viscosity, which showed that crosslinked carboxymethyl starch can exhibit good properties of the two kinds of starches.(4) Carboxymethyl starch shorted the settlement time of Catinoc dye significantly, and there was a positive connection between DS and settlement time. The addition of carboxymethyl starch was15.00g/L and the pH of cationic dye was4-6, leading the decolorization rate over92.00%. The addition of carboxymethyl starch was0.60g/L and the pH of waste liquid was8-10, leading the removal rate of Zn2+over63.00%.