Novel approach in investigation of the poly(acrylic acid) hydrogel swelling kinetics in water

Abstract

The swelling kinetics curves of structurally defined poly(acrylic acid) hydrogel in bidistilled water at temperatures: 25, 30, 35, 40, and 458C were determined. The possibility of kinetically explaining the isothermal swelling process by applying the following models: reaction controlled by diffusion, first order chemical reaction kinetics, and second order chemical reaction kinetics, was investigated. It was found that kinetically explaining the swelling process using these methods was limited to only certain parts of the process. The swelling process in bidistilled water was described in full range assuming that the hydrogel's swelling rate was a kinetically controlled reaction by the rate of the movement of reactive interface of hydrogel. Based on that model, the kinetic parameters, activation energy (E a ) and preexponential factor (A), of the swelling process were determined to be E a 5 35 kJ/mol and lnA 5 8.6. A possible mechanism of the investigated swelling process was discussed.

Removal of heavy metals by homolytically functionalized poly(acrylic acid) with hydroquinone

“…A wide range of their chemical modifications are, but the result of the proneness of these groups to chemical reactions, affording valuable materials with targeted properties. Poly(acrylic acid) (PAA), coined the name ''carbopol'' in pharmaceuticals, is known to be a super absorbent polymer that can absorb and retains a great extent of water, a property that is exploited in hydrogels making for various controlled drug delivery systems [1,2]; a related fact is that the swelling behavior of PAA hydrogels was found to be highly medium pH dependent due to the presence of carboxylic groups [3]. Low molecular weight PAA has been valorized as an efficient salt-scaling inhibitor, chiefly in oilfield operations, via the ability of the carboxylic groups in sequestering metal ions [4].…”

Synthesis and properties of methacrylic acid based hydrogels modified with zeolites

“…Jedne teorije se zasnovaju na zajedničkom kretanju mreže i rastvarača tokom procesa bubrenja, odnosno difuzionom kretanju "adsorpcionog kompleksa" nastalog kao rezultat interakcije između rastvarača i polimerne mreže [58]. Druge teorije predložu model baziran na pretpostavci da se tokom procesa bubrenja odvija fazna transformacija hidrogela iz staklastog u gumoliko stanje, a na osnovu promene deformacije mreže pri smicanju tokom vremena, pod uticajem konstantnog napona koji je posledica interakcije molekula rastvarača i polimerne mreže *58].…”

“…Konvencionalna sinteza navedenih hidrogelova izvedena je korišdenjem modifikovane procedure za sintezu hidrogelova poli(akrilne kiseline) [58] koja se odvija na slededi način. Prvo se 15 cm 3 metakrilne kiseline rastvori u adekvatnoj količini destilovane vode, a zatim neutrališe do željenog stepena neutralizacije 25 mas% rastvorom natrijum hidroksida, uz konstantno mešanje u atmosferi azota.…”

“…Merenja su nastavljena sve do postizanja konstantne mase, odnosno dok se hidrogelovi nisu našli u stanju ravnoteže. Pošto su ispitivani hidrogelovi skloni pucanju pod sopstvenom težinom usled izuzetno velikih količina vode koje apsorbuju, tehnika sa rupičastom mrežicom je korišdena pri merenju [58].…”

“…Primenjen za opis procesa bubrenja hidrogelova, ovaj model ukazuje da je kinetika bubrenja određena pomeranjem sloja formiranog između hidrogela i vode i pokazao se kao veoma dobar za opis bubrenja hidrogelova akrilne kiseline u vodi [58].…”