Structure and properties of cellulose/poly(N‐isopropylacrylamide) hydrogels prepared by IPN strategy

Abstract

Interpenetrating polymer network (IPN) strategy was developed to fabricate novel hydrogels composed of cellulose and poly(N‐isopropylacrylamide) (PNIPAAm) with high mechanical strength and adjustable thermosensitivity. Cellulose hydrogels were prepared by chemically cross‐linking cellulose in NaOH/urea aqueous solution, which were employed as the first network. The second network was subsequently obtained by in situ polymerization/cross‐linking of N‐isopropylacrylamide in the cellulose hydrogels. The results from FTIR and solid 13C NMR indicated that the two networks co‐existed in the IPN hydrogels, which exhibited uniform porous structure, as a result of good compatibility. The mechanical and swelling properties of IPN hydrogels were strongly dependent on the weight ratio of two networks. Their temperature‐sensitive behaviors and deswelling kinetics were also discussed. This work created double network hydrogels, which combined the advantages of natural polymer and synthesized PNIPAAm collectively in one system, leading to the controllable temperature response and improvement in the physical properties. Copyright © 2009 John Wiley & Sons, Ltd.

Enhanced Absorbent Products Incorporating Cellulose and Its Derivatives: A Review

“…Although underivatized cellulose is not nearly as hydrophilic as CMC, several investigators have prepared hydrogels by extensive grafting of other monomers onto cellulose, generally employing suitable organic solvent systems (Yoshinobu et al 1992;Wu et al 2008;Chang et al 2009b;Kim and Mun 2009;Buyanov et al 2010;Feng and et al 2010a;Anirudhan et al 2011;Shu and Zhao 2011;Wu et al 2012). Generally, water absorbency values in the range of 60 to 1800 have been reported for such hydrogels, though Kim and Mun (2009) reported a high value of 2500 g/g.…”

“…In such systems each network relies on a different crosslinking mechanism, and the resulting hydrogels are formed in-situ in such a way that, at least in principle, the two networks can remain intensively entangled. Several reported examples have exhibited high absorption capacity for water (Myung et al 2008;Chang et al 2009b;Chang and Zhang 2011;Varaprasad et al 2011;Liu et al 2013).…”

“…It seems likely that some of the high levels of water uptake reported for SAPs based on interpenetrating networks (e.g. Çaykara et al 2006;Chang et al 2009b) may be due to one network interfering with the crosslinking of the other network during its preparation.…”

“…Some authors have called thermal changes in absorbency a "smart" feature, since they may allow specialized applications of a thermo-sensitive hydrogel (Pourjavadi et al 2007b;Yang et al 2011). Typical temperature-responsive hydrogels exhibit markedly decreased absorbency with increasing temperature (Harsh and Gehrke 1991;Kuwabara and Kubota 1996;Çaykara et al 2006;Chang et al 2009b). Decreases in absorbency as high as a factor of five (Kuwabara and Kubota 1996) or ten (Çaykara et al 2006) have been reported when comparing absorbency at about 20 o C to the correspondding value at about 40 o C. The strongest thermal effects are for SAPs incorporating relatively high proportions of poly(N-isopropylacrylamide); these generally exhibit a strong decrease in absorbency at temperatures near to physiological conditions (Kuwabara and Kubota 1996;Liu et al 2004;Chang et al 2009b;Yang et al 2011).…”

“…Typical temperature-responsive hydrogels exhibit markedly decreased absorbency with increasing temperature (Harsh and Gehrke 1991;Kuwabara and Kubota 1996;Çaykara et al 2006;Chang et al 2009b). Decreases in absorbency as high as a factor of five (Kuwabara and Kubota 1996) or ten (Çaykara et al 2006) have been reported when comparing absorbency at about 20 o C to the correspondding value at about 40 o C. The strongest thermal effects are for SAPs incorporating relatively high proportions of poly(N-isopropylacrylamide); these generally exhibit a strong decrease in absorbency at temperatures near to physiological conditions (Kuwabara and Kubota 1996;Liu et al 2004;Chang et al 2009b;Yang et al 2011). For example, Kuwabara and Kubota (1996) used a two-step procedure to graft a 51/49% acrylic acid/N-isopropylacyrlamide onto CMC at a grafting level of 205%; water absorbency fell from about 14 g/g at 10 o C to 3 g/g at 50 o C. Çaykara et al (2006) prepared semi-interpenetrating networks of poly-[(N-tert-butylacrylamide)-co-acrylamide] with hydroxypropylcellulose; water sorption was observed to fall from as high as 19 g/g at 5 o C down to about 2 g/g at 40 o C and above.…”