GEL FORMATION OF POLYACRYLIC-ACID IN DILUTE AQUEOUS-SOLUTIONS VIA RADIATION CROSS-LINKING

Linear polyacrylic acid was crosslinked in dilute aqueous solution via gamma radiation, and gel formation was investigated as a function of radiation dose, pH, salt concentration and polymer concentration. High gel fractions were found at low pH values whereas above pH similar to 4 no gel was formed. However, the gel content was increased at higher pH by adding salts. The gelation results were explained in terms of i onic interactions. The formation of crosslinks by the combination of c hain-bound radicals was inhibited by interchain electrostatic repulsio n when the polyacrylate chains were charged and the ionic strength was low. The experimental results showed that gel formation in dilute sol ution did not occur when kappa lambda < 1, where lambda is the average distance between neighboring dissociated carboxyl groups on the polya crylate chains and 1/kappa is the Debye-Huckel interaction distance. T hus, we propose kappa lambda > 1 is a necessary, but not sufficient, c riterion for the onset of gelation of charged polymers in dilute solut ion. (C) 1998 Elsevier Science Ltd. All rights reserved.