Investigating the Structure-Related Properties of Cellulose-Based Superabsorbent Hydrogels

Abstract

Superabsorbent hydrogels are macromolecular networks able to absorb and retain large amounts of water solutions within their fine mesh-like structure. More importantly, they are capable of multiple swelling/shrinking transitions in response to specific environmental cues (e.g., pH, ionic strength, temperature, presence of given electrolytes), thus exhibiting a stimuli-sensitive behavior, which makes them appealing for the design of smart devices in a number of technological fields. In particular, in the last two decades, cellulose-based superabsorbent hydrogels have proven to be an environmentally friendly and cost-effective alternative to acrylamide-based products. This chapter reviews the relationship between the molecular structure of cellulose-based hydrogels and their physicochemical properties. First, the network formation through the use of different cellulose derivatives and chemical or physical crosslinking agents is presented. Successively, the smart swelling capability of the hydrogels as a function of composition and structure is thoroughly discussed. Finally, several approaches to the hydrogel characterization are reviewed, with focus on the assessment of key mechanical, thermal and morphological properties.

A Novel Hydrogel Based on Renewable Materials for Agricultural Application

“…However, poor crosslinking efficiency has been reported when only CMCNa is utilized, due to electrostatic repulsion between the charged macromolecules of polyelectrolyte chains [16]. Therefore, HEC, which promotes the formation of intermolecular rather than intramolecular cross-links in hydrogels, was added to the whey/cellulose solution to stabilize the macromolecules in a three-dimensional polymer network [15]. Such swelling capacity can also be enhanced by increasing the content of CMCNa.…”

“…When CMCNa is used alone, though, the resultant hydrogels show poor strength, as intramolecular cross-links are formed instead of intermolecular ones [8]. As a consequence, another cellulose derivative-hydroxyethylcellulose (HEC)-was applied in combination with CMCNa to improve such intermolecular cross-linking and stabilize the polymer structure [2,15]. This type of CMCNa/HEC binary system has been featured in several papers in the literature, wherein swelling properties were reported as similar to conventional acrylate-originating products [8,[16][17][18].…”

“…This drop in thermal stability was a consequence of the decrease in the enthalpy of the system after cross-linking had occurred Wavenumbers (cm -1 ) 1750 cm -1 1710 cm -1 1320 cm -1 2860 cm -1 H5 H3 H10 H0 Figure 9: FTIR spectra for hydrogels prepared from CMCNa and HEC (3% wt) at the weight ratio 3 : 1 at different concentrations of CA. 9 International Journal of Polymer Science [15]. Derivative TGA curves for the H5 and H10 cross-linked samples showed two temperature peaks corresponding to the first and second stages of decomposition.…”

“…The cross-linked samples showed about 24% of disintegration at the temperature of 190°C in all cases, correlating with the degradation temperature of CMCNa [32,39], while only two stages were detected for the cross-linked hydrogels. The first stage of mass loss may be attributable to the evaporation of the bound water [39], whereas the second stage of decomposition could have been due to degradation of the material (related to decomposition of the cross-linker) [15]. It was discerned that the hydrogels prepared in the presence of the cross-linker exhibited a lower thermal decomposition temperature than the initial composition without the cross-linking agent.…”

Investigation the correlation between chemical structure and swelling, thermal and flocculation properties of carboxymethylcellulose hydrogels

“…The second stage (up to 350 C) with the weight loss up to 55% could be attributed to the breaking of the glycosidic linkage, formation of furanic compounds, breaking of amide linkages. 34 Mass loss continues in the third stage due to the furher decomposition of cellulose and copolymer backbone. Hydrogel synthesized with 15 wt% of oxalic acid exhibites slower weightloss due to the higher degree of cross-linking [ Figure 12].…”