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.

This article studied the applicability of poly(-acrylamide) and methylcellulose (PAAm-MC) hydrogels as potential delivery vehicle for the controlled-extended release of ammonium sulfate (NH 4 ) 2 SO 4 and potassium phosphate (KH 2 PO 4 ) fertilizers. PAAm-MC hydrogels with different acrylamide (AAm) and MC concentrations were prepared by a free radical polymerization method. The adsorption and desorption kinetics of fertilizers were determined using conductivity measurements based on previously built analytical curve. The addition of MC in the PAAm chains increased the quantities of (NH 4 ) 2 SO 4 and KH 2 PO 4 loaded and extended the time and quantities of fertilizers released. Coherently, both loading and releasing processes were strongly influenced by hydrophilic properties of hydrogels (AAm/MC mass proportion). The best sorption (124.0 mg KH 2 PO 4 /g hydrogel and 58.0 mg (NH 4 ) 2 SO 4 /g hydrogel) and desorption (54.9 mg KH 2 PO 4 /g hydrogel and 49.5 mg (NH 4 ) 2 SO 4 /g hydrogel) properties were observed for 6.0% AAm-1.0% MC hydrogels (AAm/MC mass proportion equal 6), indicating that these hydrogels are potentially viable to be used in controlled-extended release of fertilizers systems.

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).

The correct use of hydrogels in some situations can increase seedling survival rates, plant growth, and the water-retention capacity of the growing medium. A technique for the production of a nanocomposite hydrogel using calcium montmorillonite (NC-MMt) was recently developed. However, additional research is necessary in order to validate this innovative input, particularly for the production of vegetable crops seedlings. In this context, the main objective of the present study was to evaluate the growth and development of seedlings, tomato hybrid ‘BRS Nagai’, in substrates containing different amendments of hydrogel NC-MMt. The trial was conducted in a 3x3 factorial arranged in a complete randomized blocks design, with three replications. Three substrates (peat moss, pine bark, and coconut peat) corresponded to the first factor and three rates of the NC-MMt hydrogel (0%= R1, 1.5%= R2 and 2.0%= R3, on a w/w basis) corresponded to the second factor. Each plot was composed of 16 plants that were assessed after three weeks. Overall, peat moss-based and pine bark-based substrates resulted in higher values for most of the analyzed traits: plant emergency percentage, plant height, stem diameter, leaf area, plant height/shoot dry weight ratio, root dry weight, shoot dry weight/root dry weight ratio and the Dickinson Quality Index. Rates of NC-MMt hydrogel displayed significant responses only to root superficial area and root volume. NC-MMt hydrogel amendment (mainly 1.5%) combined with specific substrates (mainly peat moss-based substrate) was able to improve the growth of ‘BRS Nagai’ tomato seedlings, with no observed toxic effects.

Neste trabalho foi reportada a caracterização de hidrogéis constituídos por metilcelulose (MC) e poliacrilamida (PAAm) preparados pelo processo de reticulação cruzada. As propriedades espectroscópicas e morfológicas foram investigadas por espectroscopia no infravermelho com transformada de Fourier e microscopia eletrônica de varredura, respectivamente. O efeito da carga iônica, presença de sais, concentrações de monômero AAm e polissacarídeo MC na absorção de água e nas propriedades cinéticas dos hidrogéis foi detalhadamente investigado. Os resultados indicaram que o decréscimo da concentração de MC ou aumento da concentração de AAm, carga iônica do contra-íon do sal de cloreto e a presença de fertilizante no meio externo de intumescimento provocaram diminuição significativa na absorção de água dos hidrogéis. O mecanismo de absorção de água dos hidrogéis de PAAm-MC em água seguiu o modelo de difusão Fickiana; já o mecanismo dos hidrogéis intumescidos em sais (cloreto ou fertilizante) seguiu o modelo de transporte anômalo. Pela alta e rápida absorção de água, as matrizes porosas e tridimensionais compostas por PAAm e MC podem em potencial ser aplicadas na agricultura como veículos carreadores.

No abstract

The use of fertilizer and water availability are essential factors limiting the agricultural production. The controlled release technology is very promising because it allows the maintenance of fertilizer concentrations within an ideal range avoiding inefficiency and toxicity problems, minimizing the environmental impacts and improving their efficiency. In this context, the nanostructured hydrogels appear as a possible carrier vehicle for these controlled release systems due to their inherent properties, such as biodegradability, low toxicity, and cost, rapid absorption and desorption controlled capacity of water and solutes. In this work, we performed the synthesis of nanostructured hydrogels based on poly(methacrylic acid) (PMAA)/Cloisite-Na ? via free radical polymerization. SEM images indicated a similarity in the basic structure of all nanocomposites. The porous diameter of the hydrogels increased with increasing of nanoclay content. EDS analysis showed the ions belonging to nanoclay present in the nanocomposites, confirming the formation of true nanocomposites. TG-DTG and DSC techniques confirmed an improvement in the thermal stability of nanocomposites caused by the addition of nanoclay. For instance, the degradation initial temperature of the hydrogel was increased from 198.5 to 203.5 °C, and inversely, the degradation rate of the 2°thermal event was decreased from 0.694 to 0.472% min °C-1 , when the nanoclay was increased from 0 to 20 mass/%. Moreover, the controlled release investigation showed an improvement in the release time and quantity of the fertilizer released with nanoclay content. This result is very required for this specific application.