Study Of Synthesis And Characterization Of Polyaspartic Acid Resin

This paper was to study and develop a new process of preparing PASP resin with excellent water-absorbency and gel strength from PSI with the existence of the cross-linking agent, including the cross-linking reaction, hydrolyzing process, drying technology and post-treatment process. In addition, the property and structure, stability, biodegradability and application of PASP resin were also investigated.At the cross linking stage, two-step cross linking method was employed. With feed of PSI, a kind of nice PASP resin obtained by the cross linking process and the following hydrolysis steps. This PASP resin has excellent continuity and a difference or gradient in cross-link density between an inner part and an outer part of each resin particle, and also has a proper proportion and distributing of functional groups. Its water absorbency and strength is superior to that of one step crosslinked product. With a feed of certain molecular weight, the optimum conditions as follows:The concentration of cross linking agent is0.07～0.076g·g-1PSI, the concentration of dispersant agent is8-10ml/g PSI, cross linking temperature is40℃, cross linking time islh, amount of solvent is28-32ml/g PSI, the stirring rotate speed is750rpm.At the hydrolysis stage, the pH of reaction system、the concentration of the dispersant agent, the temperature and degree of hydrolysis were all have effects on the structure and properties of PASP resin. the optimum conditions are:Temperature40℃, terminal pH=12, concentration of NaOH solution27%, and the income of NaOH solution is dropping mode. A method of estimating the hydrolysis end point and controlling degree of hydrolysis has been established.The drying stresses developed during drying can result in cavitation, shrinkage, warp, collapse, or even cracking to the gel body. The experiment results show that drying at the temperature above100℃, spray drying and microwave drying can induce the damage of PASP resin’s cross-linked bonds or side chain portions and backbone basic skeleton badly, and destroy the continuity of PASP resin network. A relatively fast dehydrating rate at lower temperature was in favor of the solid product with loose, uniform and nondestructive porous network structure to be obtained. This kind of product has excellent water-absorbency and gel strength. A vacuum drying at40℃under great vacuum is the most suitable drying condition.Post-treatment of a cross-linked PSI and polyaspartic acid resin can improve the network structure of resin, increase its water-absorbency and gel strength. The ageing treatment can result in physical crosslinking to PASP resin, strengthen the frameworks of network structure, and increase the continuity, crystallinity and gel strength of PASP resin, but an unduly time of the ageing treatment can decrease the water absorbency of PASP resin. Freezing treatment is in favor of increasing crystallinity of PASP resin, but can also induce the damage of PASP resin’s cross-linked bonds or side chain portions, freeze-thaw recycle can strengthen physical crosslinking in PASP resin.The biodegradability of PASP resin was evaluated, and the results show that the activated sludge of one step crosslinked PASP resin could degrade25.9%from BOD, the ratio of BOD/COD was0.561. it illustrated that one step crosslinked PASP resin is easy to be biodegraded. The activated sludge of two step crosslinked PASP resin could degrade13.2%from BOD, the ratio of BOD/COD was0.315, it illustrated that two step crosslinked PASP resin is biodegradable polymer material with some microbial stability.The properties of PASP resin was influence by raw material, preparation technology, shape and structure of PASP resin and environment factor. PASP resin, which was prepared by a novel two step cross-linking method, has excellent comprehensive property, ion-resistance property and pH buffering property. It has been observed that water-absorbency kinetic behavior of PASP resin is very complex, one step crossslinked PASP resin with a loose network structure, and a lower cross-linking degree and crystallinity, displays generally over-shooting. Two step crossslinked PASP resin or one step crossslinked PASP resin with a compact network structure, and a greater cross-linking degree and crystallinity, its water-absorbency kinetic behavior is in conformity with Fick’s law of diffusion. The water-absorbency rate is subject to the diffusion. The fact that PASP gel can shrink at a higher temperature implies that PASP gel is a thermal shrinkable gel.The application of PASP resin has been studied by some preliminary experiments. Water holding experiment shows that the water retention of the soil will increase by blended with PASP resin, and water holding time can reach22days, the water retention of two step cross-linked PASP resin is greater than that of one step cross-linked PASP resin. The fixing sand experiment shows that PASP resin has an excellent fixing sand capacity, and the fixing sand capacity of two step cross-linked PASP resin is greater than that of one step cross-linked PASP resin.The study on the cross-linking reaction and the hydrolysis process shows that the cross-linking reaction between PSI and diamine and the hydrolysis reaction of crosslinked PSI all belong to nucleophilic substitution reaction. In addition, UV treatment can cause free radical cross-linking reaction of PASP and PASP resin.