Synthesis And Characterization Of A Super-absorbent Resin Based On Acrylic Acid Grafted With Tea Polyphenol

Super-absorbent resin(SAR) is a new type of functional polymer material, which can absorb and hold a large amount of water. It has a wide prospect of application in various fields, such as medical and hygienic products, horticulture, daily necessities, food storage, petrochemical industry, etc. In order to develop new raw material, enhance performance of products and improve biodegradation, a new kind of super-absorbent resin with acrylic acid and tea polyphenol was prepared. Its preparation, properties, structure characteristics and application in soil improvement were studied.Tea polyphenol-graft-poly(acrylic acid)(TP-g-PAA) super-absorbent resin was synthesized by aqueous solution polymerization using acrylic acid as monomer, potassium persulfate as initiator, N, N’-Methylenebisacrylamideas cross-linker and tea polyphenol as additive. The influence of the neutralization degree of monomer, the amount of initiator and cross-linker, the ratio of TP and monomer, reaction temperature and other factors on the water absorbent capacity of the resin was investigated. The results showed that the optimal preparation conditions were as follows: the neutralization degree of 80%, the amount of initiator, cross-linker and TP of 0.12%, 0.04% and 0.08% respectively based on the weight of AA, reaction temperature of 80 ℃and granule size of 0.83 mm ~ 1.70 mm. Under such conditions, the absorbency of the obtained TP-g-PAA resin in distilled water and saline solution was 1087.1 m L/g and 116.1 m L/g respectively.The structure, surface morphology and thermal property of the obtained resins were characterized by Fourier transform infrared spectroscopy(FTIR), scanning electron microscopy(SEM) and thermo-gravimetric analysis(TGA), respectively. The FTIR spectra indicated that the TP-g-PAA resin was rich in not only hydroxyl and carboxyl groups, but also new ester group, which confirmed that the graft copolymerization between TP and AA had been taken place. The SEM image showed that the TP-g-PAA resin had a rough surface with compact channels which favored the water absorption. And the TGA results indicated that the TP-g-PAA resin had good thermal stability.In this study, the properties of the resins were studied. The results indicated that the TP-g-PAA resin could rapidly absorb lots of water and the adsorption reached saturation in 6 h ~ 8 h. The study on salt resistance of the resins showed that the TP-g-PAA resin had better salt resistance than pure resin, and the valence and concentration of cation in solution significantly affected on the absorption capacity of resin. We found that the absorbency of the resins in different salt solution was Na Cl > Mg Cl2 > Al Cl3 and Na Cl > Na2CO3 ≈ Na2SO3 > Na3PO4. Besides, the TP-g-PAA resin had significantly better water retention capacity than pure one under various conditions. In addition, the TP-g-PAA resin showed good repeating and moisture absorption capacity, the moisture content of which was 103.7% after 90 h.The application of super-absorbent resin in soil improvement was investigated and the results showed the resins could significantly increase the water-holding capacity, swelling degree and water retention capacity of soil, and thus improve structure and ventilation of soil. When 0.75% TP-g-PAA resins were added into the soil, the total water-holding capacity of soil was 146.0% and 154% higher than that of the blank group. Besides, the swelling degree of soil containing 0.75% TP-g-PAA resins was 49.5% and 872% higher than that of the blank group. Moreover, the water retention capacity of soil also significantly increased adding 0.75% resins. Under certain conditions of temperature and humidity, the water retention of soil containing TP-g-PAA resins was 39.3% after 8 d, while that of the blank group was below 10%. As a consequence, TP-g-PAA resin can be applied in drought and water-deficient area and improve availability of soil resources.The biodegradation property of TP-g-PAA resin was evaluated by microorganism erosion and soil burying. The results showed that tea polyphenol significantly improved biodegradation of the resin which could be biodegraded by Aspergillus niger, Bacillus subtilis, and even in soil. Furthermore, under the same conditions, biodegradation degrees of TP-g-PAA resin were significantly higher than that of pure AA resin. It could be seen that TP-g-PAA resin was friendly to environment.