Synthesis And Properties Of Tertiary Aminoalkylated Starch Ethers

Three etherrifying agents N,N-di-alkylepoxypropylamine (DAEPA) containing different alkyl chain lengths (ethyl,propyl and butyl) were prepared by the reaction of epichlorohydrin with di-n-alkylamine. The final product was received in distillation under reduced pressure. The structures of three etherifying agents were analyzed by means of APCI-MS and’H-NMR spectroscopy. Using DAEPA as the hydrophobic reagent, a series of pH responsive tertiary amine cationic etherifying starches (2-hydroxy-3-N,N-di-n-alkylaminopropyl starch, HDAAPS) were prepared using corn starch with different amylopectin contents (HylonV corn starch, HCS,50%amylopectin; Normal corn starch, NCS,73%amylopectin; Waxy corn starch, WCS,100%amylopectin) as raw materials. The catalyst and solvent of etherification were sodium hydroxide and water respectively. The effects of reaction medium, the amounts of solvent and sodium hydroxide, reaction temperature and reaction time on the molar degree of substitution (MS) and reaction efficiency (RE) were studied through single-factor experiments. When the molar ratio of starch to DAEPA was1, optimum conditions were obtained through orthogonal experiment as follows:the solvent was water, the mass ratio of water to starch was five, the molar ratio of sodium hydroxide to DAEPA was0.46, reaction temperature was90℃, and reaction time was12h. Under the optimum conditions, nine series of HDAAPS (HCS-HDEAP, HCS-HDPAP, HCS-HDBAP, NCS-HDEAP, MSNCS-HDPAP, NCS-HDBAP, WCS-HDEAP, WCS-HDPAP, WCS-HDBAP) with different MS were synthesized by changing the hydrophobic-hydrophilic balance of starch.’H-NMR was used for characterization of HDAAPS and calculation of its MS.The solution property investigated showed these particles had pH responsive properties, the starches with certain MSHDAAP (degree of molecular substitution of N,N-di-alkylamino) made the transmittance of aqueous solutions underwent controllable phase transition in’ response to pH, and the conductivity curve in titration process showed the ionization equilibrium of amino group. It was proved that MSHDAAPp increased with the increase of amino group, but the RE, pH value of phase transition (pHtrans) and the acid dissociation constant (pKa) were decreased. The ranges of pHtrans and pKa were7.55-10.57(HCS-HDAAP:7.88-10.32; NCS-HDAAP:7.82-10.57; WCS-HDAAP:7.55-10.36) and6.69-8.57(HCS-HDAAP:6.69-8.45; NCS-HDAAP:6.71-8.56; WCS-HDAAP:6.72-8.57) respectively. The effects of amylopectin content, the number of hydrophobic chain, MS of hydrophobic group, concentration, temperature, shear rate and salt content on viscosity of HDAAPS were studied. It was found that a small amount of hydrophobic group would contribute to high viscosity of HDAAPS. The more the amylopectin content were, the greater the viscosity was. As the number of hydrophobic chain was increased, the viscosity firstly decreased then increased. As the MS of hydrophobic group increased, the viscosity firstly increased then decreased. The viscosity increased sharply with the increase of concntration, and there existed critical concentration of2%/wt. When the temperature increased, the viscosity decreased at different range, and parts of HDAAPS had temperature resistance. With the increase of shear rate, the characteristics of shearing thinning, shearing resistance and shear recovery exhibited. HDAAPS had no salt tolerance.