Superabsorbent hydrogel nanocomposites based on starch-g-poly(sodium acrylate) matrix filled with cellulose nanowhiskers

Abstract

Superabsorbents hydrogel nanocomposites based on starch-g-poly(sodium acrylate) and cellulose nanowhiskers (CNWs) were synthesized. A set of experiments was performed to evaluate the influence of some factors such as NaAc/starch mass ratio, crosslinker, and nanowhiskers amount in the swelling capacity and swelling kinetics. Increasing the NaAc/starch mass ratio up to 7 leads to an increase in the water uptake at a maximum value, however, higher ratios decreased that value due to the increase of crosslinking points. Similarly, the incorporation of CNWs up to 10 wt% provided an improvement in the swelling due to the hydrophilic groups from cellobiose units. Further, the incorporation of CNWs diminishes the water uptake. Besides, the CNWs improved the mechanical properties. SEM images showed that CNWs increase the average porous size of composites. The composites presented good responsive behavior in relation to pH and salt presence allowing those materials suitable for many potential applications.

Enhanced Absorbent Products Incorporating Cellulose and Its Derivatives: A Review

“…Illustration of the concept that a network of macroscopic cellulosic fibers in an absorbent product might tend to constrain the swelling of hydrogel particles. Left: Representation of dry condition; Right: Swollen condition As was noted earlier, when nanocellulose elements are incorporated into hydrogels, the observed result is generally a marked decrease in absorbency, often accompanied by an increase in the mechanical strength of the gel material (Dai et al 2009;Larsson et al 2010Larsson et al , 2011Spagnol et al 2012a). In an analogous manner to the mechanism just described to account for the restraining effects of fluff pulp fibers on SAP swelling, some authors have attributed the effects of nanocellulose on SAP absorbency to a "reinforcement" effect (Larsson et al 2011).…”

“…Spagnol et al (2012a) found that incorporation of cellulose nano-whiskers (i.e. long crystals) tended to increase the pore size of starchacrylic hydrogels.…”

“…Effects of the presence of nanocellulose on the swelling of SAP composites has been considered in several studies (Buyanov et al 2010;Larsson et al 2010Larsson et al , 2011Laftah et al 2011;Spagnol et al 2012a). In the review article by Laftah et al (2011), the findings of such studies were summarized by stating that nanofibers can either increase or decrease absorbency in different cases.…”

“…Anisotropic swelling was observed by Buyanov et al (2010) in nanocellulose-filled hydrogel structures that had been pre-compressed during their formation. Spagnol et al (2012a) reported that although nanocellulose inclusion at relatively high levels decreased absorbent capacity, it also resulted in greater pore size. The increase in pore size was judged to be an important advantage in terms of the absorption rate and the overall performance of the absorbents.…”

“…The viscoelastic properties of various hydrogels, sometimes as a function of their state of swelling, have been studied (Guilherme et al 2005;Feng et al 2006;Chang et al 2009a;Dai and Kadla 2009;Larsson et al 2010). Notably, Larsson et al (2011) and Spagnol et al (2012a) showed that the inclusion of microfibrillated cellulose or cellulose nanocrystals within hydrogels had a strong reinforcing effect, essentially increasing the modulus and limiting the amount of swelling. Yoshinobu et al (1992) and Lionetto et al (2003) showed that there was a relationship between the degree of crosslinking and the elastic modulus of various hydrogels.…”