Preparation And Properties Of Phosphate Carboxymethyl Debranching Waxy Corn Starch

In this paper,phosphate carboxymethyl debranched waxy corn starch（PCDWCS）was prepared using waxy corn starch as a raw material,pullulanase as a debranching agent,chloroacetic acid as an etherifying agent and sodium tripolyphosphate as an esterification agent.The effect of sodium hydroxide dosage,chloroacetic acid dosage,etherification temperature,etherification time and water content of the carboxymethylation of debranched waxy corn starch（DWCS）were investigated.And the effect of esterification temperature,esterification time,amount of sodium tripolyphosphate,p H and amount of catalyst on the esterification of carboxymethyl branched waxy corn starch（CDWCS）were also examined.On this basis,the process parameters of the carboxymethylation of DWCS and the esterification of CDWCS were optimized by response surface methodology.Waxy corn starch and its derivatives were characterized by X-ray diffraction（XRD）,Fourier infrared spectroscopy（FTIR）,scanning electron microscope（SEM）,polarizing microscope（POM）,differential scanning calorimeter（DSC）and thermogravimetric analyzer（TGA）.The freeze-thaw stability,expansion ability,retrogradition,acid and alkali resistance and particle size distribution of waxy corn starch and its derivatives were measured.The effect of zinc ions in simulated wastewater removed by PCDWCS was investigated.The results showed that the optimum conditions for carboxymethylation of DWCS were as follows:etherification temperature 52℃,etherification time 3.4 h,Na OH dosage 64%,chloroacetic acid dosage 79%,water content 7.8%.The carboxymethyl substitution degree could reach 0.933.The optimum conditions for esterification of CDWCS were as follows:esterification temperature 140℃,esterification time 1.6 h,dosage of sodium tripolyphosphate6.0%,p H 5.0.And the phosphate substitution degree could reach 0.125.FTIR results showed that the characteristic peak of carbonyl group was at wave number of 1736.8 cm^-1 and the stretching vibration of P=O bond was at wave number of 1301.2 cm^-1,confirming that carboxymethyl and phosphate groups were successfully introduced into the molecular chain of DWCS.WCS granules were spherical and had obvious polarizing crosses,whereas the polarizing crosses of its derivative disappears.SEM showed that debranching destroyed the original structure of WCS,resulting in small and irregular particles,while the carboxymethylation and esterification led to larg and rough particles of DWCS.XRD showed that the crystalline structure of WCS was C-type.Carboxymethylation and esterification changed the crystalline structure of WCS.The etherification and esterification could increased the particle size of WCS,while debranching decreased the particle size.Debranching,carboxymethylation and esterification reduced the thermal decomposition temperature of WCS and changed the thermal properties of WCS.Debranching,carboxymethylation and esterification significantly reduced the retrogradation of WCS and changed its gelatinization characteristics.Debranching increased the blue value of WCS,while carboxymethylation and esterification significantly reduced the blue value of WCS.PCDWCS could well remove zinc ions in simulated wastewater.