Preparation And Swelling Properties Of PEG/CSt-g-PAAm Hydrogels

Since the first superabsorbent polymer (SAP)—starch-grafted acrylonitrile superabsorbent reported by the U.S. Department of Agriculture in 1966, SAP has being developed greatly. New kinds of SAP have come out continually, in which polyacrylate superabsorbent is the most popular and applied in various fields owing to their simply preparation, good water absorbency and innoxious. In this study, a novel cassava starch(CSt)-graft copolymerization on acrylamide(AM) and acrylic acid (AA) hydrogel (PEG/CSt-g-PAAm) was prepared by solution copolymerization, using ceric ammonium nitrate(CAN) and ammonium persulfate (APS) as initiators, N,N'-methylenebis- acrylamide(MBA) as a crosslinker, and PEG6000 as pore- forming agents. PEG/CSt-g-PAAm hydrogels have more simply preparation, low cost, high gel strength and good comprehensive properties.In this dissertation, we focused on the factors mostly influence the swell performance of the PEG/CSt-g-PAAm hydrogels, such as neutralization degree of acrylic acid, dosages of CAN, crosslinker, CSt, PEG6000 and acrylamide, and the reaction temperature. The impacts of these various factors were particularly investigated by single factor experiment and uniform method. A mathematical model was gained by regression analysis, which could dope out the brine absorbent ratio of the hydrogels correctly. Crude material cost analyse gave a linear relationship between the cost and CSt content, and illuminated that high CSt content hydrogels had the price advantage compared with the low CSt content hydrogels. By comparing the swelling properties of PEG/CSt-g-PAAm and CSt-g-PAAm hydrogels, the swelling mechanisms of PEG/CSt-g-PAAm hydrogels was also discussed.1,The infrared spectrums showed that cassava starch had grafted with AM and AA, and the SEM showed that there were micropores appeared in the PEG/CSt-g-PAAm hydrogels. X-ray diffraction technique was used to detect the starch crystallization changes. From the XRD patterns, we could conclud that the crystal structure of cassava starch was destroyed in the PEG/CSt-g-PAAm and CSt-g-PAAm hydrogels, although there was no pasting process to deal with the cassava starch. The amorphous structure makes the hydrogels more easily be degradated in the natural environment.2,Single factor experiment results showed that ceric ammonium nitrate and ammonium persulfate as complex initiators could play the same role in the graft reaction as only using a great deal of ceric ammonium nitrate, which is very costly. Acrylamide no only could affect the swelling ratio of the hydrogels, but also impacted on the reaction time, gel strength and other performances of the gel. The best dosages of AA, CAN, AM, and CSt were 23g, 4ml, 4.6g, 27.6g, respectively. The neutralization degree was 70%, and the best reaction temperature was 55℃.3,Matlab6.5 software was used to analyse the uniform experiment results, and an equation was gained by multiple linear regression analysis and stepwise regression analysis, which showed the order of the factors effect on the brine absorptance of the gel was: PEG > AM > CSt > CAN > crosslinker > neutralization degree. The influences of AM, CSt, crosslinker and neutralization degree were negative, by contraries, the influence of PEG and CAN were active. So we can conclude that PEG can increase the swelling ability of the hydrogels. The max brine absorptance calculated by the equation was very close to the experimental value. While the dosages of AA, CAN, AM, CSt, crosslinker, PEG, and NaOH respectively were 23g, 5.7ml, 4.6g, 9.2g, 2.3ml, 2.3g, 28.1g, the max brine absorptance was 34g/g.4,It was found that increasing cassava starch could reduce the raw material cost. There was a linear relationship between the total cost and the dosage of CSt (more CSt, less cost). While CSt content in hydrogels was half of the total weight of the desiccated resin, the hydrogel cost that 1t brine demand was the least.5,The effect of PEG on the hydrogel strength, swelling rate and reusability of the gel was discussed. The results showed that the hydrogel strength was raised by 3 times when the PEG content of the hydrogel was 1%. At the same time, PEG could speed up the swelling rate and significantly improve the reusability through the swelling comparison of the PEG/CSt-g-PAAm and CSt-g-PAAm hydrogels. The study of swelling kinetics at different temperature showed that the hydrogen bond between PEG and hydrogel molecular could decrease the swelling rate, but the effect declined at high temperature and high swelling ratio. The influence of PEG to water-loss rate was not obvious, although there were micropores in the PEG/CSt-g-PAAm hydrogels.