On the absorption kinetics of superabsorbent polymers

Superabsorbent polymers are hydrogels capable of absorbing considerable amounts of water without dissolving, and may have wide application in building materials. This material was initially used in cement-based materials with the purpose of internal curing, which is related with the balance of internal relative humidity during cement hydration. The mechanisms involved in the kinetic change between the hydrogel and water or pore fluid within the cement-based system are not fully understood. This work deals with the absorption kinetics of superabsorbent polymer in synthetic pore fluid medium. The physical state of particles selected from a superabsorbent polymer sample with particle size distribution comprehended between 50 to 500 micrometers was examined by means of optical microscopy and subsequent image analysis. This method showed to be an accurate technique for quantifying the absorption of water or fluid into the cross-linked structure of superabsorbent polymers. It is concluded that the size of the polymers particles have a significant effect on the absorption kinetics of poliacrylate-based polymers. The mechanisms which may affect the kinetic change are discussed and a model based on the well known Fick’s law is proposed.