Synthesis And Properties Of PH-Responsive Starch-Based Surfactants

In this study, starch is used to prepare series of pH responsive tertiary amino starch as for the raw material starch is nontoxic, low price, renewable, and biocompatibile and biodegradabile. So this type of starch ether, is researched to solve the problem that existed widely in the field of the preparation and application of pH responsive polymers, this kind of polymers are often synthesized in difficult method, with quite high cost, the products’ transition pH is difficult to tune and their biocompatibility and biodegradability are poor. In a simple and feasible way, tertiary amino starchs with different molar substitution degree has been prepared, and surfacetension pH was investigated systematically. The tertiary amino starchs were also been used as surfactants in the application of emulsification/demulsification by adjusting pH.In this study, hydroxyethyl starch (HES) was used as raw material, allyl glycidyl ether (AGE) as the hydrophobic reagent,2-hydroxy-3-allyloxypropyl hydroxyethyl starch ethers(HAP-HES)was prepared by controlling the hydrophilic to hydrophobic balance. By orthogonal experimental, we studied solvent dosage, catalyst dosage of NaOH, reaction temperature and reaction time on the influence of the molar substitution degree. The results show that the optimal reaction conditions are as follows:amount of solvent m(H20):m(AGU) =2:1, n(NaOH):n(AGU)=0.7:1, reaction time 5 h, and reaction temperature 70℃. IR and 1H-NMR were used for characterization of HAP-HES and degree of molar substitution (MS) of HAP-HES was also calculated.Then 2-hydroxy-3-(3’-dimethylaminoethylthiopropoxy) propyl hydroxyethyl starch ethers (HDMAEP-HES) were prepared by using 2-hydroxy-3-allyloxypropyl hydroxyethyl starch ethers as the raw material, through thiol-ene click reaction. IR and H-NMR were used for characterization of HDMAEP-HES and calculation of their degree of molar substitution (MS) The pKa of the products was measured by acid-base titration, and pKa decreased with the increase of MS. To study the pH sensitivity of HDMAEP-HES, the light transmittance, particle size and Zeta potential were studied. The results showed that the molar substitution degree was higher than 0.9 the light transmittance of HDMAEP-HES declined significantly with the increase of pH. Particle size decreased with the increase of pH, when MS is higher than 0.7, particle size will rise after pH above 9. Zeta potential decreases with increasing pH, when pH<pKa, Zeta potential kept stable, when the pH>pKa, Zeta potential rapidly reduced.Surface tentions were also investigated at different MS. Under different concentration, the surface tension reduced with the increase of concentration and then flattened out.As the MS increased the MS, the cmc of HDMAEP-HES decreased. However under the same concentration with the increase of pH, surface tention decrease slowly, at a narrow range (pH 6.5 to pH 9.5) decreases rapidly, it has the potential to be controlled. The prepared HDMAEP-HES also has been applied to emulsifying 1-octanol/water and n-dodecane/water. These two oil/water systems are emulsified under the condition of 25℃, pH 10.5, ratio of oil-water of 50/50, HDMAEP-HES concentration of 1.0 wt%, the emulsion is still stable after 24 hours. And the 1-octanol/water emulsion can be emulsificatied/demulsificatied by adjusting pH.