Preparation Of Enzymatic Starch Modified By Tempo Oxidation And Its Application On Surface Sizing

The molecules of natural starch have large volume, so the starch paste always has highviscosity and poor rheological properties. Also the membrane is easy to crack. All thesesituations will restrict its applications. α-amylase can cut the main chain of starch effectively. Inthis way, the molecular weight and the viscosity of starch decreased, it will make the starcheasy to filtrate into paper, so the strength of paper is improved. By TEMPO/NaBr/NaClOsystem, primary hydroxyls on C6are oxidized into carboxyl groups selectively. The solubilityand permeability of starch are so improved. This article starts with α-amylase forenzyme-hydrolysis of corn starch, subsequently adopts2,2,6,6-tetramethylpiperidine-1-oxyl(TEMPO)-mediated system for oxidation of enzymatic starch paste. Finally several typicalenzymatic starch and TEMPO oxidized starch are selected for physiochemical analysis andsurface sizing The main works and conclusions were as follows.Design of experiment and single factor experiment can be used for optimizing the reactionconditions in enzymatic hydrolysis of starch. Taking enzymatic efficiency and sizingenhancement into account, the optimum conditions reached as below: reaction time30minutes,pH value6.0, temperature95℃, starch consistency60%, dosages of Calcium acetate5mmol/g,dosages of α-amylase75.0IU/g.Selecting three typical paste samples of enzymatic starch for physiochemical analysis.Infrared Spectroscope,X-ray diffraction patterns,Differential scanning calorimetry andScanning Electron Microscope technology are employed for analysis. The results showed thatmolecules of enzymatic starch cut off by α-amylase with no chemical groups introduced while asmall amount of which turn to recrystallization, besides the starch paste displayed as linedcluster molecules.Make the enzymatic starch paste produced at the optium conditions as raw materials. ThenTEMPO/NaBr/NaClO system was adopted for starch oxidation. A better process proposal wasobtained such as pH9.5, temperature5℃, reaction time2h and dosages of TEMPO0.001mmol/g. The dosages of NaClO could be changed to get various modified starch withdifferent carboxyl content under given conditions.Selecting three typical paste samples of modified starch for physiochemical analysis.Infrared Spectroscope,X-ray diffraction patterns,Differential scanning calorimetry andScanning Electron Microscope technology are employed for analysis. The results showed thatmolecules of modified starch had little degradation. Oxidation accurred to C-6primaryhydroxyl with hydroxyl turned into carboxyl. The study also suggested that modified starch hasa little crystallization and its glass transition temperature and phase transition enthalpy is higher than that of natural corn starch. Modified starch paste also displayed as lined cluster molecules.Furthermore, modified starch had better stability than before.Using enzymatic and modified starch samples for surface sizing. Sizing effect revealedthat with sizing dosages, sizing consistency and sizing temperature increased, starch permeationto paper was improved, tensile strength and surface strength of sized sheet rose while foldingendurance decreased. When the dosage of starch which has5.06%carboxyl groups was4g/m2,the tensile of paper increased by51.64%compared to sizing free paper. Surface morphologysuggested that modified starch were capable to penetrate into sheet to give a smooth film whileenzymatic starch could only produced a thick starch film on sheet surface.Oxidizing starch with traditional oxidant sodium such as hypochlorite and hydrogenperoxide. Then applied oxidized starch paste on surface sizing. The results indicated that tensilestrength increased by33.3%for the most, with the oxidant dosages of4%, surface strength rose212.5%, but its enhancement is worse than traditional oxidized starch, not to mention modifiedstarch.By the way of changing the dosages of α-amylase, the molecular weight of starch could becontrolled in a certain range. The low viscosity of starch paste made more hydroxyl free from aunit mass of starch. Through the selective oxidation of TEMPO/NaBr/NaClO system, thesolubility and permeability were improve even further, so the sizing effect of this kind ofmodified starch was better than ordinary starch.