| Chitosan graft acrylic acid and acrylamide superabsorbents(CPAAM) are prepared by solution polymerization and soaked in ethanol-NaOH solution using chitosan, acrylic acid(AA) and acrylamide(AM) as raw materials(monomers), potassium peroxydisulfate(KPS) as initiator. N,N'-methylene-bis-acrylamide(NMBA) as crosslinker. The effect of the reaction conditions on the absorbencies of the CPAAM is studied. It is found that the optimization condition to synthesize CPAAM with the highest absorbency is as follows:the mass concentrations of monomers, mM=8.6%(wt%, the same as follow; relative to tall the tall of water); mCTS/mM=1:6; mAA/mAM=5:1; the mass concentrations of the initiator and the crosslinker are 2.5% and 0.16%(relative to tall AA-AM monomers concentration), respectively; the reaction temperature and time are 60℃and 5 h, respectively. The CPAAM synthesized at this condition can absorb 1315 g/g in distilled water and 66 g/g in 0.9% NaCl aqueous solution.The effects of solutions temperature and pH on the absorbencies are studied systemically. The results have shown that CPAAM absorption rate decreased in distilled water and increased in 0.9%NaCl solution with increasing temperature; CPAAM absorption rate remained almost constant with the increase of pH from 4.5 to about 10 in distilled water, and were nearly platform-like. When the pH is gradually increasing from 10 to 14, the absorption rate declined sharply; and when the pH decreased from 4.5 to 2, absorption rate also decreased rapidly.The effects of various salts solutions and concentrations on the absorbencies are studied. The results have shown that the hydration of ion is the primary affecting factor for the absorbency of the CPAAM among univalent salt solution under the same concentration. As the concentrations of the salt solutions increase, the equilibrium absorbencies decrease rapidly. When the concentrations of the salt solutions are greater than 6mmol/L, the effect of the concentrations of the salt solutions on the equilibrium absorbencies tends to constant values. And in various salt solutions, the difference of the absorbencies becomes very small and the absorbencies are nearly equal. In 2mmol/L concentrations of the salt solutions, the order of absorbency is LiCl>NaCl>KCl, MgCl2>CaCl2>BaCl2, KBr>KCl>KF, NaCl>CuCl2>FeCl3, ZnCl2>CuCl2>CoCl2>FeCl3, Na2CO3> NaCl>Na3PO4>Na2SO4. In high cation solutions, the absorbencies increased rapidly before 50min; after about 50min the absorbencies started to decline obviously; The effect of high cations are greater than the monovalent cations for absorbency of the CPAAM.The adsorption properties of CPAAM in various salt solutions are investigated and the factors that influence the adsorption such as the time and the concentration are discussed. In the solution concentrations of 2 mmol/L salt solution, the adsorption increases gradually when the time increased; the adsorptions reached constant values after about 150min. The order of the equilibrium adsorption capacities of Ba2+, Ca2+, Mg2+ is Ba2+>Ca2+>Mg2+, and the equilibrium adsorption capacities are 2.6 mmol/g.2.0mmol/g.1.3mmol/g, respectively. In Cl--salt solutions, the equilibrium adsorption capacities of Cu2+, Zn2+, Co2+, Fe3+are 3.9 mmol/g,3.2 mmol/g,2.8 mmol/g,2.1 mmol/g, respectively. In NO3--salt solutions, the equilibrium adsorption capacities of Cu2+,Ni2+,Pb2+,Cr3+ are 4.5 mmol/g,4.1 mmol/g,4.0 mmol/g,2.1 mmol/g, respectively. With the increase of concentration, the adsorption capacities increase rapidly. When the solution concentrations increase to 10mmol/L, the equilibrium adsorption capacities of Cu2+, Zn2+, Co2+ Fe3+ reach 8.2 mmol/g,8.1 mmol/g,5.3 mmol/g,3.8 mmol/g respectively; and that of Cu2+, Ni2+ Pb2+, Cr1+ reached 8.3 mmol/g,4.9 mmol/g,5.3 mmol/g,2.7 mmol/g respectively.In Cl--salt solution the adsorption capacities of CAAM are less than that in NO3--salt solutions. But in high concentration solutions, the equilibrium adsorption capacity tend to nearly equal. |
PDF Full Text Request