Study On Salt-resisting Superabsorbent Composite Based On Organic Bentonite And Acrylic Acid Copolymer

Superabsorbent polymers are a kind of lightly crosslinked functionalpolymer materials with different kinds of hydrophilic groups, such as–COOH,-CONH2,-OH etc. Because of its excellent water absorptionproperties, superabsorbent materials have received considerableattentions. In order to improve the integrated performance of traditionalsynthesis superabsorbent materials, organic-inorganic superabsorbentcomposites become a hot research project in the field of superabsorbentmaterials. In this thesis, a novel superabsorbent composite was preparedby free radical polymerization in aqueous solution, using organicbentonie as inorganic component, acrylic acid copolymer as matrixpolymer. The structure of the synthesis superabsorbent composite wascharacterized by Fourier transform infrared spectroscope （FTIR）,Scanning electronic microscope （SEM） and X-ray diffraction （XRD）,the thermal property was also measured by Thermogravimetic analysis（TGA）.Bentonite was firstly purified, and then modified with hexadecyltrimethyl ammonium chloride（CTAC）. The influences of content ofCTAC, reaction temperature and reaction time on organic degree werediscussed. The optimal experiment conditions were obtained. The bestorganic bentonite sample was characterized by Fourier transforminfrared spectroscope （FTIR）, X-ray diffraction （XRD） andThermogravimetic analysis （TGA）. The results show that the CTACcations were successfully absorbed in the layers of bentonite clay andthe layers’ distance were obviously expanded （from1.244nm to2.185nm）, and the modification effect was well.Organic bentonite/poly（acrylic acid-co-acrylamide-co-vinyl acetate）composites were prepared in aqueous solution, using organic bentonite, acrylic acid, acrylamide, and vinyl acetate as raw materials. The variousfactors that affected water absorbency of the superabsorbent compositewere investigated. The best experiment conditions were as follows:polymerization temperature was70℃, mass fraction of acrylic acid was80%（weight percent relative to monomer, the same below）, massfraction of acryliamide to vinyl acetate, mass fraction of initiator, massfraction of cross linker, neutralization degree of acrylic acid, massfraction of organic bentonite was1.5,0.5%,0.03%,70%,5%respectively. The water absorbency of the superabsorbent compositesynthesized under this condition reached up to695g/g and113g/g inpure water and0.9%saline solution, respectively. FTIR result, SEMobservation, XRD and TGA analysis confirmed that organic bentoniteuniformly dispersed in acrylic acid copolymerization, and thehomogeneous superabsorbent composite was formed. In addition, thethermal stability of the composite was higher than pure organicsynthesis material.Swelling rate, water retention properties, reswelling performance ofthe superabsorbent composite were tested. The results showed that thewater absorbency of the superabsorbent composite nearly reached alimiting value within60min. At room temperature, water retention ratioof composite was53%, and that of pure organic synthesis material wasonly36%, after10days. For the first time, water absorbency was695g/g, but water absorbency could reach302g/g after five reswellingtimes.Absorbency properties in diverse salt solutions and concentrationswere studied. In10mmol/L concentrations of salt solutions, Theequilibrium absorbency of the superabsorbent composite increasedgradually in univalent cation solutions, and first increased and thendecreased in divalent cation solutions. The order of absorbency wasLiCl>NaCl>KCl, NaCl>MgCl₂>FeCl₃, Na₂CO₃>NaCl>Na₂SO₄. Indifferent concentration solutions, with the concentrations of saltsolutions increased, the equilibrium absorbency decreased. When theconcentrations of salt solutions were smaller than40mmol/L, the equilibrium absorbency decreased rapidly, when the concentrations ofsalt solutions were greater than40mmol/L, the equilibrium absorbencydecreased slowly. The results showed that the equilibrium absorbencyof the superabsorbent composite in various salt solutions andconcentrations was influenced by ion radius, and ion hydrolysis andcomplexation reaction.Practical application in soil demonstrated the superabsorbentcomposite could effectively keep moisture content absorbed in soil, andcould be used as a water-saving material in practice.