Synthesis and characterization of porous superabsorbents of poly(acrylic acid-co-acrylamide)

Abstract

A series of superabsorbent polymers was synthesized by solution polymerization using a short polymerizing time for acrylic acid(AA) and acrylamide(AM) monomer in a redox initiator (ammonium persulfate(APS)/ N,N,N',N'-tetramethylethylenediamine (TMEDA)) with various types of crosslinker (N,N'-methylene bisacrylamide (N-MBA), ethyleneglycol dimethacrylate (EGDMA) or formaldehyde) in the presence of CO2 gas bubbles formed by the chemical reaction of acrylic acid and NaHCO3 stabilized by PF127 foam with a stirring speed of 250 rpm at the temperature 45 ํC for 30 min. The synthesized copolymers were dewatered by precipitation with excess methanol and drying at 50 ํC in a vacumm oven for 24 h. The absorption kinetic behavior for these hydrogels in distilled water was investigated. In addition, the water absorbencies of the synthesized copolymer in various saline and pH buffered solutions were investigated. The swelling behavior of these absorbents were related to their chemical structures, compositions, and the nature of external salt solutions. The effects of the influential reaction parameters on water absorbency of the synthesized copolymers were investigated from which they were produced from the following recipe: 0.1 mole fraction of Am; 2.3x10(-3) mol dm-3 APS; 1.0x10(-2) mol dm(-3) TMEDA; unneutralizated AA; 4.0x10(-3) mol dm-3 N-MBA; 0.06% w/v PF127; and 2.48x10(-1) mol dm-3 NaHCO3. The highest water absorbency of the synthesized copolymer was 2,196+-14 times its dry weight and can absorp up to 1,628+-14 times its dry weight in 10 min. Complexation of poly(acrylic acid-co-acrylamide) with Al2(SO4)3.8H2O coagulant could take place through the chemical bonding between the metal ion and carboxyl acid groups or amide ligands within the polymer. This complex polymeric flocculant (CPF) is more effective for water treatment than the non CPF