Structure And Sizing Properties Of Starchmodified By Isoamylase/horseradish Peroxidase

With the increase of public awareness on environmental protection,polyvinyl alcohol?PVA?sizing agent has been gradually replaced by starch sizing agent.However,there are lots of drawbacks of starch because of its natural molecular structure,such as brittleness and hardness of starch film and poor adhesion to hydrophobic fibre.In order to improve the starch sizing performance,physical addition and chemical structure modification are usually used.Inthis study,branched limit dextrins?BLD?were prepared by hydrolysis of starch by?-amylaseand ?-amylase and they were used as plasticizers to improve the mechanical properties of starch film;partly debranched starches were produced by isoamylase hydrolysis and their molecular structure,gelatinization properties and adhesion to polyester/cotton yarns were studied;grafted starches were prepared by grafting copolymerization of partly debranched starches with 2-acryloxyethyltrimethylammonium chloride catalyzed by HRP;starches with different molecular structure were grafting with acrylamide,and how starch fine structure affected molecular structure of grafted starch and how grafted starch with different molecular structure affected sizing properties were studied.The main research contents and conclusions are below:Firstly,the effects of low molecular weight dextrin plasticizer branched limit dextrin on the mechanical properties of starch filmand starch gelatinization and retrogradation propertieswere studied.BLDs were prepared by hydrolysis of waxy corn and corn starch by?-amylaseand ?-amylase and subsequent ethanol precipitation intofractions of different molecular structure.The characterization of BLD was done using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry?MALDI-TOF-MS?,high-performance anion exchange chromatography?HPAEC-PAD?and ¹H nuclear magnetic resonance spectroscopy?¹H NMR?.The breaking strength and elongation at break of starch film with and without BLDs were determined.The effect of BLD on starch gelatinization and pasting properties were investigated by differential scanning calorimetry?DSC?and rapid viscosity analyzer?RVA?,respectively.Confocal laser scanning microscopy?CLSM?observation of the BLD/corn starch mixtures was also carried out to explore the possible interaction between corn starch and BLDs.The effect of BLDs on the retrogradation properties of corn starch was investigated using DSC and X-ray diffraction?XRD?.Avrami equation was used to analyze the enthalpies of retrograded corn starch.The results showed that the molecular weights of the six BLDs were in the order:C9<W9<C8<W8<C7<W7,and C7,C8,C9 and W7,W8,W9 represented that the BLDs were derived from corn starch?C?and waxy corn starch?W?and the ethanol concentration was 70%,80%,and 90%,respectively.BLDs could reduce the breaking strength and increase the elongation at break of starch film.BLDs increased the gelatinization temperature?including onset,peak and conclusion temperature?and decreased gelatinization enthalpy of corn starch through entering and interacting with starch molecular.C7,C8and C9 increased the peak viscosity and final viscosity of corn starch paste;the setback value for starch with C7 and C8 increased,while that with C9 declined.The BLD with the lowest molecular weight had the best anti-aging effect on corn starch retrogradation.Secondly,molecular structure and properties of partly debranched starches produced by isoamylase hydrolysis of starch were studied.The reducing sugar method and ¹H NMR were used to measure the DE value and degree of branching of partly debranched starches.The gelatinization properties of partly debranched starch were determined by DSC.The adhesion of starch?partly debranched or not?to polyester/cotton yarns were measured.The results showed that the amylose content and DE value of partly debranched starch were higher than native starch,and increased with debranching time;while the degree of branching decreased with debranching time.The gelatinization temperature?including onset,peak and conclusion temperature?of partly debranched starch was higher than that of native starch,while the gelatinization enthalpy reduced.Partly debranched waxy corn and corn starch had lower adhesion to polyester/cotton yarn than native starch.Thirdly,the modification of partly debranched starch grafting with2-acryloyloxyethyltrimethylammonium chloride?ATAC?catalyzed by HRP was studied.The grafting copolymerization of parly debranched waxy corn starch with ATAC was catalyzed by HRP.Qualitative characterization of grafted starch was done by fourier transform infrared spectroscopy?FT-IR?.The molar degree of substitution and grafting ratio of grafted starches were measured by ¹H NMR analysis.Thermogravimetric?TGA?and DSC were used to determine the thermal properties of starches.The adhesion of waxy corn starch and grafted starch to polyester/cotton yarns was determined.The results showed that the molar degree of substitution and grafting ratio of grafted starch increased with debranching time.Grafted starches showed poorer thermal stability than native starch.The adhesion of the grafted starch,which was produced from the partly debranched starch debranched for 10 min before grafting copolymerization with ATAC,to polyester/cotton yarn was 91.72 N,which was 7%higher than that of waxy corn starch?98.20 N?.Fourthly,how starch fine structure affected the molecular structure of grafted starch was studied.Grafted starches were prepared by the grafting copolymerization of fifteen starches with acrylamide?AM?catalyzed by HRP.The raw starches included six different types:two corn starches?CS and WCS?,three rice starches?RS1,RS2 and RS3?,four wheat starches?WS1,WS2,WS3 and WS4?,two tapioca starches?TS1 and TS2?,three potato starches?PS1,PS2 and PS3?,and one mung bean starch?MS?.The molar degree of substitution and grafting ratio of grafted starches were measured by ¹H NMR analysis.The molecular size and amylose content of starch were determined by size exclusion chromatography?SEC?.The correlation between the structural parameters of native starch and grafted starch was analyzed.Two starch biosynthesis models were used to fit amylose and amylopectin chain length distribution of native starches,and four structural parameters of amylopectin( ?_Ap,i, ?_Ap,iii,h_Ap,i,and h_Ap,iii)and six structural parameters of amylose( ?_Am,i, ?_Am,ii, ?_Am,iii,h_Am,i,h_Am,ii and h_Am,iii)were achieved.Correlation analysis was performed between the structural parameters of wheat starches and their grafted starches.The results showed that RS1-g-PAM had the highest degree of branching?4.3%?,and TS2-g-PAM had the lowest molar degree of substitution?0.021?and grafting ratio?0.9%?and WS4-g-PAM has the highest molar degree of substitution?0.139?and grafting ratio?6.1%?.There was a positive correlation between the grafting ratio of grafted starches and the amylose content of native starches.Higher amylose content of native starch resulted in higher grafting ratio of grafted starch.Both amylose and amylopectin affected grafting reaction.The parameter ?_Am,Im,I and ?_Ap,Ip,I displayed relatively strong correlation with grafting ratio,indicating that grafting copolymerization of starch with acrylamide easily occured on the amylose chain with low degree of polymerization and the outer chains of amylopectin.Finally,the effect of grafted starch molecular structure on sizing properties was studied.Grafted starches were prepared by the grafting copolymerization of four different kinds of starches?corn,waxy corn,potato and tapioca starch?with AM catalyzed by HRP.Qualitative characterization of the grafted starch was done by FT-IR analysis.The degree of branching,molar degree of substitution and grafting ratio of grafted starch were calculated by ¹H NMR analysis.The sizing properties,including viscosity,adhesion to cotton yarns and film mechanical properties of starches?grafted or not grafted?were measured.The correlation between the structural parameters and sizing properties of grafted starches was analyzed.The results showed that the hydrophilic monomers AM successfully grafted onto the molecular chains of all the four starches.The grafted starch derived from waxy corn starch had the lowest degree of branching?3.30%?,and the highest molar degree of substitution?0.0686?and grafting ratio?3.01%?.For all the four starches,grafted starches had higher viscosity and adhesion to cotton yarns.Compared with native starch film,the grafted starch film had higher elongation at break and lower breaking strength.There was a positive correlation between the viscosity and grafting ratio of grafted starch.The adhesion of grafted starch to cotton yarn had a significantly positive correlation with grafting ratio.Higher grafting ratio resulted in larger viscosity andtensile strength of sized cotton yarns.The elongation at break of grafted starch film had a negative correlation with the degree of branching of grafted starch.Higher degree of branching resulted in lower elongation at break of grafted starch film.