| In order to solve the problem of poor water solubility and difficult gelatinization of starch at medium temperature,according to the requirement of sizing performance of medium temperature sizing yarn,water-soluble acetate starch sizing at medium temperature was prepared by acid hydrolysis and esterification treatment.The properties of acetate starch sizing were studied and applied in sizing experiment,which laid a foundation for starch sizing at medium temperature.The research contents of this paper are as follows:?1?The acid hydrolysis of corn starch was carried out to prepare acid hydrolyzed starch.The optimum preparation technology was discussed and the properties of acid hydrolyzed starch were tested.The results showed that the optimum process of acid hydrolysis of raw starch was as follows:reaction temperature was 55?,starch slurry mass fraction was 40%,hydrochloric acid dosage was 6%of starch dry weight,and reaction time was 75 min.The slurry viscosity was 4.7s when the solid content of the acid-hydrolyzed starch was 6%.?2?Starch acetate was prepared from acid-hydrolyzed starch with vinyl acetate as esterifying agent and sodium hydroxide as catalyst.The relationship between substitution degree of starch acetate and water solubility at medium temperature was studied,and the properties of starch acetate prepared by the optimum process were tested.The results showed that water-soluble acetate starch began to dissolve at 65?when the degree of substitution of acetate starch was 0.139.The optimum preparation technology of acetate starch are Reaction temperature-25?,reaction time-90 min,reaction pH-9,concentration of starch milk is 40%,dosage of esterifier is 20%of dry weight of starch..Under this reaction condition,the degree of substitution of acetate starch is 0.2047,the conversion is 54.33%,and starch can be gelatinized in medium-temperature water at 65?.When the solid content is 6%,the starch slurry has a viscosity of 5.3 s,high specific adhesion and flexible size film.?3?Infrared spectroscopy?FT-IR?,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,X-ray diffraction?XRD?and differential scanning calorimetry?DSC?were used to characterize and analyze corn starch,corn acidified starch and corn acetate starch.The results showed that:?1?corn starch granules were smooth elliptical or polygonal,acidified starch granules had depressions,acetate starch granules had honeycomb-like meshes and pits on the surface;?2?three kinds of starches had stretching vibration peaks of-OH at 3490 cm-1,2927 cm-1,which belonged to C-H,and all appeared at1649 cm-1,1384 cm-1 and 622 cm-1.The characteristic absorption peaks of starch showed that the three substances were starch size;HS starch had similar absorption peaks with original starch,indicating that acidification did not change the chemical structure of starch and did not produce new groups;acetate starch had obvious carbonyl C=O absorption peaks at 1726 cm-1,indicating that acetyl group was indeed introduced into starch after esterification treatment;?3?raw starch?acid hydrolysis and acetate starch have strong diffraction peaks at 15°,18°and 23°of 2?,indicating that the crystalline structure of the three starches are all type A.After acid hydrolysis and esterification,the crystalline structure of starch has not been changed.The diffraction peaks of acid-hydrolyzed starch and acetate starch were significantly weaker than those of corn starch,indicating that the crystallinity of corn starch,HS and acetate starch was decreased,and the crystallinity of corn starch,HS and acetate starch was 39.43%,35.93%and 26.7%respectively.?4?when acetate starch was dissolved at medium temperature,the molecules were bonded with reticular structure,which was consistent with that of high temperature.?5?The gelatinization temperature of starch esters decreases with the increase of degree of substitution.When degree of substitution is0.139,it begins to gelatinize at medium temperature,and the gelatinization temperature is65.9?.The gelatinization temperature of AS with substitution degree of 0.2047 is 62.5?and the solubility at medium temperature is 91.7%.The solubility of AS is excellent.?4?The sizing experiments of pure cotton and polyester cotton yarns at medium temperature with acetate starch were carried out.The results show that the properties of acetate starch sizing at medium temperature are better than those of SPR,but slightly lower than those of acetate starch sizing at high temperature.?5?Surfactant rapid penetrant T was used to size acetate starch at medium temperature.The results showed that rapid penetrant T could improve sizing performance and achieve high temperature sizing effect.The properties of water soluble acetate starch sizes prepared by wet esterification meet the requirements of mid-temperature sizing and sizing,which lays a theoretical and practical foundation for starch mid-temperature sizing and mid-temperature sizing.Figure 18,table 40,reference 64. |
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