Macro- and Micronutrient Simultaneous Slow Release from Highly Swellable Nanocomposite Hydrogels.

Clay-loaded hydrogels have been arousing great interest from researchers and academics due to their unique properties and broad applicability range. Here we developed hydrogel-based nanocomposites intended for slow/controlled release of macro- and micronutrients into independent or concurrent systems. The produced nanocomposites underwent a hydrolysis treatment that improved their physicochemical properties. We obtained materials capable of absorbing water contents 5000 times greater than their weights, an outcome that makes them promising, particularly if compared with commercially available materials. Though swelling degree was affected by the presence of calcium montmorillonite (MMt), MMt has increased nutrient (urea and boron) loading capacity and, as a consequence of its interaction with the studied nutrients, has led to a slower release behavior. By evaluating the simultaneous release behavior, we observed that both the ionic (sodium octaborate) and the nonionic (urea) sources competed for the same active sites within the nanocomposites as suggested by the decreased loading and release values of both nutrients when administrated simultaneously. Because of its great swelling degree, higher than 2000 times in water, the nanocomposites formulated with high MMt contents (approximately 50.0% wt) as well as featuring high loading capacity and individual (approximately 74.2 g of urea g(-1) of nanocomposite and 7.29 g of boron g(-1) of nanocomposite) and simultaneous release denote interesting materials for agricultural applications (e.g., carriers for nutrient release).

Nanocomposite PAAm/methyl cellulose/montmorillonite hydrogel: evidence of synergistic effects for the slow release of fertilizers.

In this work, we synthesized a novel series of hydrogels composed of polyacrylamide (PAAm), methylcellulose (MC), and calcic montmorillonite (MMt) appropriate for the controlled release of fertilizers, where the components presented a synergistic effect, giving very high fertilizer loading in their structure. The synthesized hydrogel was characterized in relation to morphological, hydrophilic, spectroscopic, structural, thermal, and kinetic properties. After those characterizations, the application potential was verified through sorption and desorption studies of a nitrogenated fertilizer, urea (CO(NH2)2). The swelling degree results showed that the clay loading considerably reduces the water absorption capability; however, the hydrolysis process favored the urea adsorption in the hydrogel nanocomposites, increasing the load content according to the increase of the clay mass. The FTIR spectra indicated that there was incorporation of the clay with the polymeric matrix of the hydrogel and that incorporation increased the water absorption speed (indicated by the kinetic constant k). By an X-ray diffraction technique, good nanodispersion (intercalation) and exfoliation of the clay platelets in the hydrogel matrix were observed. Furthermore, the presence of the montmorillonite in the hydrogel caused the system to liberate the nutrient in a more controlled manner than that with the neat hydrogel in different pH ranges. In conclusion, excellent results were obtained for the controlled desorption of urea, highlighting the hydrolyzed hydrogels containing 50% calcic montmorillonite. This system presented the best desorption results, releasing larger amounts of nutrient and almost 200 times slower than pure urea, i.e., without hydrogel. The total values of nutrients present in the system show that this material is potentially viable for application in agriculture as a nutrient carrier vehicle.