Study On The Synthesis And Swelling Kinetics Of Salt-resistant Superabsorbent Polymers

In this thesis,according to the applications and recent researches on the superabsorbent,a series of superabsorbent composites based on the monomers,acrylic acid,isopropenylphosphonic acid,2-acryloylamino-2-methyl-l-propanesulfonic acid and inorganic materials,diatomite,modified kaolin,attapulgite,were prepared by solution polymerization.On the basis of investigation of the salt-resistant superabsorbent composite synthesis,structure,properties and swelling kinetics,the main results were obtained as follows:(1)A diatomite composite superabsorbent was synthesized by solution polymerization of partially neutralized acrylic acid and diatomite using N,N'-methylenebisacrylamide as a crosslinking agent,and hydrogen peroxide and L-ascorbic acid as a redox initial system.The influences of some reaction conditions,such as diatomite content,neutralization degree of acrylic acid,amount of initiator and crosslinking agent,monomer concentration,and the reaction temperature on swelling characteristic were investigated.The water absorbency of the sample prepared at the optimal conditions was 99 g·g^-1in 0.9 wt%NaCl solution.Moreover,the sample had good swelling rate,hydrogel strength,reswelling ability and water retention.However, the resistance of sample to salt was a little lower than that of polyacrylate.(2)A modified kaolin composite superabsorbent was synthesized by solution polymerization of partially neutralized acrylic acid,isopropenylphosphonic acid(IPPA) and carboxymethyl starch modified kaolin(CMS-kaolin)using trihydroxymethyl propane glycidol ether as a crosslinking agent,and ammonium persulfate as an initiator. The influences of some reaction conditions,such as CMS-kaolin content,neutralization degree of acrylic acid,amount of initiator,amount of crosslinking agent,IPPA content, and the reaction temperature on swelling characteristic were investigated,the water absorbency of the sample prepared at the optimal conditions was 74 g·g^-1in 0.9 wt% NaCl solution. (3)A salt-resistant fast swelling macroporous superabsorbent composite was prepared by copolymerization of partially neutralized acrylic acid, 2-acryloylamino-2-methyl-1-propanesulfonic acid and attapulgite.To enhance the swelling rate of the copolymer,foaming technique was used in the course of copolymerization.Furthermore,for improving the properties of swollen hydrogel,such as strength,resilience and dispersion,the copolymer was surface-crosslinked.And then the surface-crosslinked copolymer was blended with inorganic salt in post treatment process. The influences of some reaction conditions,such as amount of 2-acryloylamino-2-methyl-1-propanesulfonic acid,attapulgite,initiator,N, N'-methylenebisacrylamide,trihydroxymethyl propane glycidol ether,foaming agent, neutralization degree of acrylic acid,and reaction temperature on water absorbency in 0.9 wt%NaCl aqueous solution both under atmospheric pressure and load were investigated. In addition,the effect of them on swelling rate was also studied.After that,an orthogonal design was employed to optimize the reaction conditions.The water absorbency of macroporous superabsorbent composite prepared under optimal conditions in 0.9 wt% NaCl aqueous solution under atmospheric pressure and certain load(P≈2×10³ Pa)were 56 g/g and 9 g/g,respectively,and the swelling rate reached 0.493 mL/(g.s).The excellent hydrogel strength,resilience and dispersion of swollen hydrogel were also observed.In addition,the effects of pH values,ions and their concentration on swelling behavior of sample were investigated.The results showed that the swelling behavior of sample was affected by pH value.However,the supercase IT diffusion was observed in all NaCl solutions with different pH values.It was found that cations,especially multivalent cations in swelling medium,had significant effect on swelling behavior of sample.An overshooting effect appeared in all solutions containing multivalent cations. For anions,it showed little effect on swelling process,and supercaseΠdiffusion was also observed no matter which anions existed in swelling medium.(4)Open circuit potential measurement was introduced to trace the swelling kinetics of superabsorbent.Based on the results and theoretical analysis,the reliability of open circuit potential measurement in tracing the swelling kinetics of superabsorbent was verified.Moreover,the swelling model for the superabsorbent in salting liquid was slightly modified.