Preparation Of Modified Starches In Dry Method Assisted By Kneader And Their Application In Warp Sizing

Starch is a kind of macromolecular compound extracted from grains,roots and tubers,etc.It comes from a wide range of sources,and is cheap,biodegradable and environmentally friendly.However,it is insoluble in cold water and has poor processing performance,which greatly affects the application of starch in food and non-food industries.In order to overcome the performance defects of starch and expand the application field of starch,starch must be modified by physical or chemical methods to meet the application needs of different industries.In a semi-dry or dry process for starch modification no water or a small amount of water（or solvent）is used,so the starch can maintain the granular structure,and the reaction process has the advantages of low energy consumption,simple process,less side reactions,and no waste water discharge,all of which is beneficial to environmental protection,and has significant economic and social benefits.Therefore,it is widely concerned in the starch processing field.In the dry or semi-dry method,however,the agitator is subjected to a great resistance of the reaction medium,so the conventional vertical stirred reactor can not be used.In order to guarantee the uniformity of the mixing reaction,a kneading machine was adopted in this study.The kneading machine is a special kind of horizontal mixing equipment with a pair of differentialΣ-type blade.Its larger stirring power can produce a strong shear,so as to make the mixture mixed evenly.When it is used in the starch modification in the dry or semi-dry method,it can be expected to obtain good quality and uniform reaction product and to improve the production efficiency.Preparation of oxidized starch assisted by kneader was studied in this dissertation.The reaction process parameters included dosages of oxidant（hydrogen peroxide）and catalyst（copper chloride）,moisture content,p H value,and temperature of the system,and time of the reaction.The results showed that 20%water content of the system was favorable to the oxidation reaction,and the carboxyl group content increased with the increase of hydrogen peroxide concentration.The optimal process was obtained through an orthogonal design,as follows:the molar ratio of oxidant hydrogen peroxide to starch glucose unit（AGU）of 0.5,the molar ratio of catalyst copper chloride to AGU of 4.0:1000,the temperature of 85℃,the reaction time of 2hours,the water content of the system of 20%and the p H value of 5.Under these conditions,the carboxyl substitution degree of the oxidized starch was 2.47/100 AGU,and the carbonyl substitution degree was 7.94/100 AGU.The reaction was basically completed after 3 hours with starch oxidation kinetics analysis.Starch oxidation reactants was confirmed by FTIR.SEM photographs showed that the appearance of the starch granules did not significantly change after oxidation.XRD confirmed that the crystallinity was slightly reduced.The content of amylose was decreased with the increase of the oxidation degree.GPC analysis confirmed that the molecular weight of starch decreased and the molecular chain was depolymerized after oxidation.RVA confirmed that the viscosity of starch decreased significantly after oxidation,TG/DTG analysis showed that the thermal stability of starch after oxidation decreased slightly at high temperature.The solubility of starch in cold water and the light transmittance of paste increased after oxidation.At 95℃,the viscosity of the modified starch decreases and the thermal stability of the viscosity increases.Starch with a certain degree of oxidation has better sizing effect on cotton and polyester/cotton yarns.Preparation of carboxymethyl starch（CMS）assisted by kneader was studied using monochloroacetic acid（Cl CH₂COOH）as the etherifying agent and tetrabutyl ammonium bromide（TBAB）as the phase transfer catalyst,and the reaction included two processes:starch alkalization and etherification.The optimum conditions for the reaction:n（TBAB）/n（AGU）was1:1000;the total amount of the solvent isopropanol was 10%based on the starch dry base weight,and it was added twice;the sodium hydroxide dosage,n（Na OH）/n（Cl CH₂COOH）,was 1;alkalization time was 1 hour;and the etherification temperature was 60 ^oC.The etherification reaction of the starch conforms to the second-order reaction kinetics.The carboxymethyl etherification of the starch was confirmed by FTIR and ¹³C NMR.After carboxymethyl etherification,the surface of the starch granule had obvious cracks,uneven surface,and significantly reduced crystallinity.The reaction not only occurred on the surface of the granule in the amorphous region of the starch,but also partly in the interior and the crystalline region of the starch granule.RVA analysis showed that the gelatinization temperature of CMC decreased and the viscosity increased after the carboxymethylation.The solubility of CMC in cold water increased and the paste transparency increased.The viscosity and thermal stability of the CMC paste increased slightly at 95℃.When the CMC was used as textile sizing agent,the paste adhesion on cotton roving and polyester/cotton roving was improved,and good sizing performance of cotton and polyester/cotton yarns was obtained.Preparation of cationic starch assisted by kneader was studied in the study.The etherifying agent was 3-chloro-2-hydroxypropyl trimethyl ammonium chloride（CHPTAC）and the process parameters included solvent,catalyst,Na OH dosage,alkalization time,temperature and reaction time.The cationic etherification reaction was favorable when no solvent was added.The anionic catalyst LF had better effect than the phase transfer catalyst tetrabutylammonium bromide,and the efficiency was higher when the amount of sodium hydroxide n（Na OH）/n（CHPTAC）was 1:1.Considering the appearance of starch and reaction efficiency,the etherification temperature of70℃and etherification time of 4h were more appropriate.The experiments via orthogonal design showed that the order of the experimental parameters affecting the degree of substitution was as follows:n（CHPTAC）/n（AGU）>temperature>n（Na OH）/n（CHPTAC）>time.The optimal experimental conditions were as follows:n（CHPTAC）/n（AGU）=0.1,temperature was 70℃,n（Na OH）/n（CHPTAC）=1.0 and time was 3 hours.The order of the experimental parameters affecting the reaction efficiency was as follows:n（CHPTAC）/n（AGU）>temperature>n（Na OH）/n（CHPTAC）>time.The optimal experimental conditions were as follows:n（CHPTAC）/n（AGU）=0.05,temperature was 70℃,n（Na OH）/n（CHPTAC）=1.0 and time was3 hours.The cationic etherification reaction was confirmed by FTIR and ¹³C NMR,and the appearance and crystal structure of the starch granules did not change significantly,but the crystallinity decreased.The content of amylose was decreased with the increase of substitution degree of the modified starch.RVA analysis showed that the gelatinization temperature of the cationic starch was slightly lower than that of the native starch,the paste viscosity was higher at low temperature,and cationic starch showed good thickening property after modification.The solubility of cationic starch in cold water increased gradually and the light transmittance of paste increased slightly,with increase of degree of substitution.As for sizing properties,the viscosity and thermal stability at 95℃of the paste increased slightly after modification.By analyzing the sizing properties of the starch for 14.6 tex cotton yarns and polyester/cotton yarns,it was found that the sizing properties of cationic starch were better than that of native starch,especially in the index of yarn elongation at break.Preparation of carbamate starch assisted by kneader was studied in the study.The esterification agent was urea,and the process included type and dosage of catalyst,the dosage of urea,temperature and time.The results showed that ammonium chloride was the best catalyst,with the molar ratio of ammonium chloride to starch glucose unit 0.025:1.Considering the reaction efficiency and appearance,the reaction at 110℃was more suitable,and the reaction efficiency reaches the maximum after 4 hours.With the increase of urea dosage,the reaction efficiency decreased gradually.The orthogonal experiment of four factors and three levels showed that the order of the experimental parameters affecting the degree of substitution was n（CH₄N₂O）/n（AGU）>n（NH₄Cl）/n（AGU）>time>temperature.The optimal preparation conditions were as follows:n（CH₄N₂O）/n（AGU）0.5:1,n（NH₄Cl）/n（AGU）0.025:1,time 4 hours and temperature 105℃.The order of the experimental parameters affecting the reaction efficiency was n（CH₄N₂O）/n（AGU）>n（NH₄Cl）/n（AGU）>time>temperature.The optimal experimental conditions were as follows:n（CH₄N₂O）/n（AGU）was 0.3:1,n（NH₄Cl）/n（AGU）was0.03:1,time was 4 hours and temperature was 110℃.The experimental parameters of the best degree of substitution by the response surface were:n（CH₄N₂O）/n（AGU）=0.50,n（NH4Cl）/n（AGU）=0.02,time=4.45h,the degree of substitution could reach 0.296,and the verification accuracy was 97.3%.The effect of carbamate reaction was confirmed by FTIR and¹³C NMR.SEM images showed that the appearance of starch granules had no obvious changes,and only the number of micropores on the surface increased after the modification.There are other changes between starch carbamate and the native starch.For example,crystallinity decreased slightly,and thermal analysis showed that thermal stability decreased slightly.Furthermore,amylose content increased with the increase of substitution degree,and the viscosity average molecular weight decreased gradually.RVA analysis showed that the gelatinization temperature of starch decreased after esterification,and the viscosity,attenuation value and recovery value increased first and then decreased.The solubility of carbamate starch in cold water increased slightly,and the light transmittance of starch paste increased slightly.The sizing experiment showed that the viscosity of the sizing paste at 95℃increased first and then decreased.The adhesive force of the paste measured by roving method was higher than that of the native starch,especially for polyester/cotton roving.For 60s single yarn of Australian wool,the sizing result showed that the sizing performance was better than that of native starch when the degree of substitution of the modified starch was less than 0.2.The experimental results in this study showed that modification of starch via dry or semi-dry process assisted by kneading machine is an effective way to modified starch.In this method,a series of modified starches,such as oxidized starch,carboxymethyl starch,cationic starch and carbamate starch,were prepared,and the optimized modification process conditions were obtained.The structure and properties of these modified starches were studied,and the application of the modified starches in textile sizing process was discussed.