Undesirable effects of heating on hydrogels

Abstract

Heating is the most conventional drying method for removing water from as-synthesized hydrogels in laboratory and industry. In this article, the effects of the heating temperature (60-2008C) and time (10 min-24 h) on swelling properties of highly absorbent hydrogels based on 2-acrylamido-2-methylpropane sulfonic acid (AMPS), acrylic acid (AA), potassium acrylate (KA), and acrylamide (AM) were studied. Crosslinkers methylene bisacrylamide (MBA) and poly(ethyleneglycol) dimethacrylate (PEGDMA) were used in the syntheses. Depending on the hydrogel structural composition and its drying temperature and time, the swelling capacities were extremely changed. Generally, AA-, KA-, and AM-based hydrogels showed more hydrolytic-thermal stability than the corresponding AMPSbased hydrogels. MBA-crosslinked hydrogels generally exhibited higher vulnerability against heating. Swelling of PEGDMA-crosslinked poly(AM-KA-AA) hydrogel was greatly increased after heating, whereas its analogous AM-free sample exhibited huge loss of swelling. PEGDMAcrosslinked poly(AMPS) samples also exhibited swelling reduction after drying. Rheological studies showed that the storage modulus was highly reduced ($ 5200 Pa) after heating of MBA-crosslinked poly(AMPS) hydrogels, which reconfirmed the crosslink cleavage. Mechanistic discussions were proposed for the thermal-induced swelling changes. It was concluded that the chemical nature of both crosslinker and monomer must be taken into consideration to choose the temperature and time of the hydrogel drying.

Novel Micro/nanostructures from a Double Network Gel

“…In 1973, Jhon and Andrade 14 proposed that there were three states of water in hydrogels, including free water, intermediate water and bound water. Free water was not associated with the polar groups of polymer chains.…”

Nanocomposite super‐swelling hydrogels with nanorod bentonite

“…14,15 Clays such as montmorillonite and bentonite have negative surface charges in their layers; they are mostly intercalated with using cationic materials such as alkyl ammonium salts. 16 Monomeric and polymeric materials such as chitosan 17,18 can also be used as intercalant. In comparison with conventional hydrogels, the nanocomposites have several advantages such as reducing cost and improving thermal, 14,19 mechanical, 15,19 or optical 18 properties.…”

Converting date seed biomass into highly absorbing hydrogel

“…The date seed modified by poly(AA-SA-AM-AMPS) had AMPS in its structure and its sulfonic groups were susceptible to degradation which caused less IDT for the modified date seed compared with the unmodified one. It has been reported before that an AMPS-containing hydrogel is very sensitive to heating, which is the reason for its low thermal stability [28,29].…”