Synthesis Of Sodium Alginate/poly(acrylic Acid) Double-network Superabsorbent

In this paper, a tough double-network superabsorbent was synthesized withCa2+(CaCl2) as ionic cross-linker for one monomer, sodium alginate (SA), N,N-methylenebisacrylamide (BIS) as covalent cross-linker for the other monomer,acrylic acid (AA), ammonium peroxodisulfate as redox initiator, by two-step method.The optimum reaction condition was based on the orthogonal experiment design.Factors influencing the water absorbency of superabsorbent were also investigatedby single factor experiment method. In the study of mechanical properties, theeffects of the composition, such as the amount of SA, CaCl2and solid content insodium alginate/poly(acrylic acid) double-network superabsorbents (SA/PAA DNsuperabsorbents) were studied by an electronic universal testing machine. In addition,various factors influencing the heavy metal ions removal capacity of thesuperabsorbents, such as CaCl2content, SA content, initial pH of the solution,temperature of the solution and treatment time with the solution were investigated.The results were as follows:(1) The optimal conditions on maximum de-ionized water absorbency and onmaximum0.9wt%NaCl solution absorbency were monomer concentration20wt%,weight ratio of SA to (SA+AA)8%, neutralization degree of AA40%, cross-linkerconcentration1wt%and monomer concentration20wt%, weight ratio of SA to(SA+AA)8%, neutralization degree of AA50%, cross-linker concentration1wt%, respectively.(2) The absorbency of superabsorbents in de-ionized water and0.9wt%NaCl solution firstly increased and then decreased with the increasing of monomer concentration, weight ratio of SA to (SA+AA), degree of neutralization of AA and cross-linker concentration.(3) With the increasing of solid content, the tensile strength of superabsorbents was increased and the elongation at break was decreased.(4) With the increasing of SA content, the tensile strength of superabsorbents was increased and then decreased and the elongation at break was decreased all the time. The result showed that slight addition of SA could improve the tensile strength of PAA superabsorbent.(5) With the increasing of CaCl2amount, the tensile strength of superabsorbents was increased and then decreased, and the elongation at break was decreased and then increased. The result showed that the moderate addition of cross-link points destiny could improve the tensile strength of the material.(6) The metal ion removal capacity of superabsorbents was obvious, and the affinity order removal of heavy metal ions of the superabsorbents was found Pb2+> Zn2+.(7) With the increasing of CaCl2amount, the metal ion removal capacity of superabsorbents was decreased. The addition of CaCl2can reduce metal ion removal capacity of superabsorbents.(8) With the increasing of SA content, the metal ion removal capacity of superabsorbents was increased. The addition of SA can truly increase metal ion removal capacity of PAA superabsorbent.(9) The metal ion removal capacity of superabsorbents increased with the increasing of treatment time and almost reached equilibrium within3h. (10) When the temperature was below70℃, the metal ion removal capacity of superabsorbents was increased with the increasing of treatment temperature.(11) The metal ion removal capacity of superabsorbent increased with the increasing of pH. pH4and4.5were found to be the optimal pH value of Pb+and Zn2+for maximum metal removal capacity, respectively.