CMC/Celite Superabsorbent Composites: Effect of Reaction Variables on Saline-absorbency under Load

Aseries of superabsorbent composites were synthesized through graft copolymerizationof acrylic acid (AA) onto carboxymethyl cellulose (CMC) in the presenceof celite powder using N,N -methylenebisacrylamide (MBA) as a cross-linkingagent and ammonium persulphate (APS) as an initiator. The chemical structure andthermal properties of the composite hydrogels were characterized by FTIRspectroscopy and TGA methods, respectively. Morphology of the samples wasexamined by scanning electron microscopy (SEM). In free-state, the swellingconditions and hence the related data are not real, because in all their applications theswelling particles of superabsorbent must absorb aqueous solutions while they areunder pressure. Therefore, the effect of the reaction variables (such as monomer andcross-linker concentrations and CMC/celite weight ratio) on the saline-absorbencyunder load (AUL) application was investigated. The AUL values were estimated usinga simple AUL tester at two different pressures (0.3 and 0.9 psi). Surprisingly, the newsynthesized composite samples exhibited about 86 g/g absorbency in 0.9% NaClsolution under 0.3 psi pressure. The AUL values considerably decreased withincreasing the MBA concentration, 53.4 g/g (CMC/celite = 0.5/1.5 and P = 0.3 psi) vs.42.4 g/g (CMC/celite = 0.5/1.5 and P = 0.3 psi). The ionic monomers increasedsaline-absorbency under load significantly and the effects of parameters such asmonomer and cross-linker concentrations, and CMC/celite weight ratio were notconsiderably different from the free swelling. Therefore, this new synthesized compositemay be considered as an excellent candidate for various industrial applications.