Research On 2-bromoisobutyl Starch Initiator For Preparation Of Grafted Starch By ARGET ATRP Technology

Natural starch is a kind of natural carbohydrat polymer with the structure that contains a lot of polyhydroxy groups.Its special chemical structure makes starch show stronger polarity and greater hydrophilicity.Therefore,natural starch has a certain adhesion to hydrophilic natural fibers in the field of textile sizing,but it shows a poor adhesion to hydrophobic synthetic fibers.After the gelatinization of natural starch in an aqueous meduim under high temperature,the paste formed has the defects of high apparent viscosity,low viscosity stability and forming a brittle film.In order to make starch have good performance in field of warp sizing,in this paper,2-bromoisobutyrylbromide(BIBB)was used as esterifying agent to react with starch.The effect of various reaction conditions on the esterification was discussed to find out the most suitable synthesis process parameters.At the same time,a series of 2-bromoisobutyl esterified starches(BBES)with different degrees of substitution(DS)were synthesized,and effect of the 2-bromoisobutyl esterification on the properties of starch paste and mechanical properties of starch film were evaluated for being expected to overcome the above problems by the introduction of the 2-bromoisobutyl substituents into starch molecules.Firstly,in this work,the acid-converted starch(ACS)prepared,tetrahydrofuran(THF),BIBB,4-dimethylaminopyridine(DMAP)and triethylamine(TEA)were used as raw material,reaction medium,esterifying reagent,catalytic reagent and acid binding agent,respectively.The BBES samples with different DS were successfully prepared by changing the amounts the synthesis process parameters(the amount of BIBB,reaction temperature,amount of DMAP and reaction time).The effects of synthetic process parameters on the DS of BBES were studied for finding out the most suitable synthetic parameters.The experiments showed that BIBB had successfully modified starch by FTIR analysis.As the molar ratios of BIBB to ACS increased from 0.35 to 2.80,the reaction temperature raised from 20? to 60?,and reaction time from 3h to 24h,the DS gradually increased,and then showed a slight increase.In addition,with the amount of the DMAP,the DS exhibited a trend of increasing at first and then decreasing.Based on the above data analysis,the most suitable synthesis process parameters for BBES are:reaction temperature 40?,reaction time 24h,DMAP to BIBB molar ratio 0.23.Secondly,under the most suitable synthesis process conditions,BBES with different DS were synthesized by changing the amount of BIBB to ACS.Influences of 2-bromoisobutyl esterification on the apparent viscosity,stability of viscosity,adhesion and film properties were studied.The results showed that apparent viscosity of cooked BBES paste had certain increase,and its viscosity stability was higher in comparison with those of the ACS paste.The adhesion of BBES to polyester and polylactic acid fibers was superior to ACS.And with the increase in the DS,bonding forces of BBES to both fibers increased,reached its highest value at DS=0.016,and then gradually decreased.In addition,degree of crystallinity as well as tensile strength of BBES film were lower than those of ACS one,and its breaking elongation much higher than that of ACS one,indicating 2-bromoisobutyl esterification was able to reduce brittleness of starch film,enhancing its toughness.The surfaces of the cross-sections of BBES and ACS films were analyzed by SEM technique for proving the esterification could show a toughness effect on the film.As the DS increased,the strength of the BBES film gradually decreased,and the elongation at break increased.When the DS was 0.016,it obtained the maximum the elongation of 3.6%,and then the elongation decreased.Considering the experimental results and various factors,BBES with the DS of 0.016 was suitable for sizing polyester and polylactic acid warps.This work could not only provide a suitable modification range of BBES used as sizing agent,but also could lay a foundation for preparing starch grafted copolymer applied as sizing agent under ARGET ATRP technology by adopting the suitable BBES.