Preparation Of An Instant Type Modified Polyvinyl Alcohol

Polyvinyl alcohol(PVA) is a water-soluble polymer while its unique molecular structure leads to poor solubility. The study focuses on improving the poor solubility of PVA through chemical modification. The ester groups, amide groups and other anionic groups have been introduced to the PVA main chains to improve the water-solubility. Finally, the modified PVA products with good solubility at room temperature are obtained. The main contents and conclusions are as follows:(1) PVA through esterification method.In the aqueous, the carboxyl groups on PVA were esterified by hydroxyl groups on lactic acid(LA) in the absence of catalyst. The effects of the amount of LA, reaction temperature, reaction time, on the solubility and viscosity of modified PVA were systematically studied. The optimum conditions for the esterification method was established: 4g of PVA, 10 m L of LA, 40 m L of deionized water are used, and the reaction temperature is 95 ℃, and the reaction time is 8 hours. The obtained products could dissolve in water quickly at room temperature(dissolution time less than one minute).(2) Modification of PVA through Michael addition reaction.In the aqueous, Michael addition reaction occurs between PVA and acrylamide using sodium hydroxide as catalyst. The influence of the reaction conditions including the amount of acrylamide, reaction temperature, reaction time, on the solubility and viscosity of modified PVA has been systematically studied. The optimum conditions for the Michael addition reaction was established: 4g of PVA, 40 m L of deionized water, 2g of acrylamide, 0.6g of sodium hydroxide are used, and the reaction temperature is 90 ℃and the reaction time is 8 hours. The modified products with good water-solubility at room temperature had been synthesized(dissolution time less than half one minute).(3) Introduction of ester and amide groupsIntroduction of ester and amide groups not only improves the solubility of PVA in water, but also affects the solution viscosity. Here, 9 %(w t %) solution of modified PVA has been prepared to determine the effect of modification ratio on viscosity. Moreover, the solution was also made into thin film by casting method to determine its water solubility. The Fourier transform infrared spectroscopy(FTIR) results suggest that the LA and acrylamide have been grafted onto PVA main chains successfully. X-ray diffraction(XRD) results show the crystallinity of PVA is reduced after being modified by LA and acrylamide, which suggest that the modification methods presented in this study are feasible and effective.