Superabsorbent Hydrogels Based to Polyacrylamide/Cashew Tree Gum for the Controlled Release of Water and Plant Nutrients.

Heldeney Rodrigues Sousa,Lucas Matheus Lima Neris,Ariane Maria Silva Santos Nascimento,Idglan Sá Lima,Leilson Rocha Bezerra,Edson Cavalcanti Silva-Filho,Albert Santos Silva,Francisca Pereira Araújo,Durcilene Alves Silva,Josy Anteveli Osajima,Rafael Felippe Ratke

doi:10.3390/molecules26092680

Heldeney Rodrigues Sousa, Lucas Matheus Lima Neris + Show 9 more

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https://doi.org/10.3390/molecules26092680

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Abstract

Agricultural production is influenced by the water content in the soil and availability of fertilizers. Thus, superabsorbent hydrogels, based on polyacrylamide, natural cashew tree gum (CG) and potassium hydrogen phosphate (PHP), as fertilizer and water releaser were developed. The structure, morphology, thermal stability and chemical composition of samples of polyacrylamide and cashew tree gum hydrogels with the presence of fertilizer (HCGP) and without fertilizer (HCG) were investigated, using X-ray diffractometry (XRD), Fourier Transformed Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Thermogravimetric Analysis (TGA/DTG) and Energy Dispersive Spectroscopy (EDS). Swelling/reswelling tests, textural analysis, effect of pH, release of nutrients and kinetics were determined; the ecotoxicity of the hydrogels was investigated by the Artemia salina test. The results showed that PHP incorporation in the hydrogel favored the crosslinking of chains. This increased the thermal stability in HCGP but decreased the hardness and adhesion properties. The HCGP demonstrated good swelling capacity (~15,000 times) and an excellent potential for reuse after fifty-five consecutive cycles. The swelling was favored in an alkaline pH due to the ionization of hydrophilic groups. The sustained release of phosphorus in HCGP was described by the Korsmeyer–Peppas model, and Fickian diffusion is the main fertilizer release mechanism. Finally, the hydrogels do not demonstrate toxicity, and HCGP has potential for application in agriculture.

Highlights

IntroductionHydrogels are three-dimensional polymeric networks that have the ability to retain a large amount of the water and maintain their structural integrity [1,2,3,4]
Hydrogels are three-dimensional polymeric networks that have the ability to retain a large amount of the water and maintain their structural integrity [1,2,3,4]. These waterdilated networks are usually formed by polymers, which undergo physical or chemical crosslinking [5]. This high swelling capacity of hydrogels is due to the presence of hydrophilic groups, such as -OH, -COOH, and -SO3H, that are connected to the polymeric backbone [6,7,8]
According to X-ray diffractometry (XRD) for cashew tree gum (CG), the broad diffused center at 2θ = 19.5◦ indicates a material with a low degree of structural organization, as reported by the literature [47]

Summary

Introduction

Hydrogels are three-dimensional polymeric networks that have the ability to retain a large amount of the water and maintain their structural integrity [1,2,3,4] These waterdilated networks are usually formed by polymers, which undergo physical or chemical crosslinking [5]. This high swelling capacity of hydrogels is due to the presence of hydrophilic groups, such as -OH, -COOH, and -SO3H, that are connected to the polymeric backbone [6,7,8]. In the case of physical hydrogels, the intercrossing of the chains is formed only by the physical interactions between the macromolecules which can occur in a variety of ways, including hydrophobic association, ionic interaction and hydrogen bonding [1,10]

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