Influences of reaction parameters on water sorption of neutralized poly(Acrylic acid-co-acrylamide) synthesized by inverse suspension polmerization

Abstract

Sytheses of highly water-absorbing polymers of poly(potassium acrylate-co-acrylamide) were carried out by an imverse suspension cololymerization, Acrylamide and potassium acrylate were used as comonomers and N,N’–methylenebisacrylamide as a cross-linker. They were polymerized by ammonium persulphate, a thermal initiator, in n-hexane emulsified by sorbitan monooleate (Span 80) surfactant at the temperature of 60 ℃ for 2 h. The synthesized beads were collected by precipitation with excess methanol. The water absorption of synthesized copolymers were determined in distilled water. The effects of the influential reaction parameters on water absorption of the synthesized copolymers were investigated from which they were produced with 5 molar of total monomer concentration, 1.4 g/l of initiator, 1:1.5 volume ratio of the aqueous phase to the organic phase, a cross-linking agent, 0.025%mole of monomer and a stirring speed of 200 rpm. The water absorption ability of the synthesized copolymer, at 40:60 molar ratio of potassium acrylate to acrylamide was as high as 775 times the weight of dry polymer and having a high liquid absorption time (21.41 sec) but with a rather low gel strength when swollen. The synthesized copolymer was soluble in water in the absence of the cross-linking agent. The water retention capability of the copolymers decreased with increasing the cross-linking agent and salt concentrations because of the osmotic pressure differential between the inside and outside of the swollen gel. The water absorption depended largely on the pH of buffer solution, type and concentration of the salt solutions, which were used for liquid absorption capability of the copolymer, type and concentration of the suspending agent, concentration of the initiator, degree of neutralization of acrylic acid, total comonomer concentration and molar ratio of the comonomer. In addition, The synthetic copolymers were investigated for the ration of polymerization, functional groups, thermal properties, and surface morphology by EA, FTIR, DSC and SEM, respectively.