Study On Preparation And Characterization Of Composite Super Absorbent Resin Based On Xanthan Gum

Being excellent properties of water-absorbing and water-retention, theability of adsorption micro heavy metal ions, super absorbent resins have beenwidely used in forestry and agriculture, daily chemicals, medical health, sewagetreatment field, etc. However, its high production costs and difficult degradationhave restricted its large-scale promotion and development. Therefore, looking forlow-priced and biodegradable raw material，exploring new environmentallyfriendly synthesis technology and speeding up the foundation research of superabsorbent materials have a very important and realistic significance.In this paper, on the basis of the preliminary researches of our laboratory,inorder to ensure that the products have low-cost raw and high anti-saltperformance, xanthan gum（XG）with biodegradability was used as the modifiedmaterial, acrylic acid（AA）,2-acrylamido-2-methylpropanesulfonic acid（AMPS）or acrylamid（eAM）as monomers, while adding inexpensive bentonite during theprocess of polymerization, the modified XG/Bentonite composite superabsorbent resins with excellent performances were prepared through graftcopolymerization. The various influence factors to the ability of water-absorbingand salt-resistant rate of the resin were discussed, while the water-preservingcapacity, biodegradability, absorbent and heavy metal ions adsorption capacity ofthe resin were studied. Finally, through a variety of modern instrumental analysismethords, the structure of the super absorbent resins were preliminarycharacterized．The main research contents and results were drawn as follows：（1）Using XG and bentonite as raw materials, AA and AM as graftcopolymerization monomers, XG-g-P（AA-co-AM）/Bentonite composite superabsorbent resin with good salt-resistant was prepared by aqueous solutionpolymerization. First, the mechanism of graft copolymerization was discussed.Then, the influence factors on composite super absorbent resin were studied viasingle factor test and orthogonal experiment，while the optimum reactionconditions of preparing composite super absorbent resin were obtained when m （AA）: m（AM）=5:1,w（bentonite）=5%、w（initiator）=1.0%、w（crosslinker）=0.08%based on the quality of monomerˊ, and AAˊneutralizationdegree was75%，while the best water absorption was up to863.8g/g and0.9%NaCl solution up to109.4g/g.Also,the composite resins at the measuredtemperatures of25℃、50℃and75℃had good water-retention capacity.（2）XG-g-P（AA-co-AMPS）/Bentonite composite super absorbent resinwas successfully synthesized via inverse suspension polymerization by using AAand AMPS as monomers, span60and tween80as dispersing agent.The bestsuitable conditions of synthetizing composite resins were optimized by singlefactor tests and orthogonal tests when mass fractions of dispersing agents were3%of the cyclohexanes’，m（AMPS）: m（AA）=1:3, w（initiator）=0.8%ofthe monomer’s, reaction time4hours, polymerization temperature75℃，thesuper absorbent resins under the optimum conditions had good repeatingabsorbability, the highest water absorption up to881.3g/g and0.9%NaClsolution up to120.2g/g.（3）The absorbtion properties of the XG-g-P（AA-co-AMPS）/Bentonitecomposite super absorbent resin in various solutions were investigated. Theresults showed that the absorption of the resins in different liquids arranged asfollows: urine<0.9%saline<tap water<pure water. In the same concentrations ofmetal cation salt solutions, the order of the balance absorbency wasAlCl₃<MgCl₂<NaCl<LiCl, and in the same concentrations of metal anion saltsolutions，the order was Na₃PO₄<Na₂SO₄<NaNO3.（4）The static adsorption behaviors、adsorption kinetics and otheradsorption characteristics of XG-g-P（AA-co-AMPS）/Bentonite composite superabsorbent resins to heavy metal ions Cd²⁺and Ni²⁺were discussed systematicallyunder the different initial concentrations of metal ions、 pH values andtemperatures. The conclusions showed that within the experimental ranges,themaximum adsorption capacities of composite resin for Cd²⁺and Ni²⁺occurswhen pH=7，and the saturated adsorption capacity of Ni²⁺greater than Cd²⁺; theadsorption process was exothermic process; the isothermal adsorption behaviorsof Cd²⁺and Ni²⁺obeyed both Langmuir and Freundlich isotherm equation; theadsorption kinetic behavior could be well described by pseudo-second orderkinetics model; the desorption tests explained that the desorption rate of composite super absorbent resins for Cd²⁺and Ni²⁺gradually increased with theincreases of initial concentrations of HCl and desorption time，but the desorptionrate with the concentrations change was slight.