Hidrogéis superabsorventes à base de gelanas desacetilada e altamente acetilada preparados por diferentes métodos

• Autor(a) principal: Souza, Flavio Silva de
• Data de Publicação: 2017
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Biblioteca Digital de Teses e Dissertações da UERJ
• Texto Completo: http://www.bdtd.uerj.br/handle/1/15654
• topic: Hydrogel; deacetylated gellan; highly acetylated gellan; crosslinking mechanism; superabsorbent; thermal properties; compression; Hidrogel; gelana desacetilada; gelana altamente acetilada; mecanismo de reticulação; superabsorvente; propriedades térmicas; compressão; CNPQ::CIENCIAS EXATAS E DA TERRA::QUIMICA::QUIMICA ORGANICA::POLIMEROS E COLOIDES

The objective of this study was to preparation and characterization of hydrogels from gellan gum in the deacetylated and highly acetylated forms. Different methods to prepare the hydrogels were tested, varying the reaction conditions (pH, temperature and crosslinker). The samples were characterized by thermogravimetric analysis (TG), Fourier-transform infrared spectroscopy (FTIR) together with attenuated total reflectance (ATR), scanning electron microscopy (SEM), compression strength tests, solid-state 13C nuclear magnetic resonance (NMR), swelling tests and rheological assays. The swelling results showed that the hydrogels could be classified as superabsorbent, with the largest swelling degrees being obtained with the samples prepared with highly acetylated gellan (HA) at acidic pH and in mixtures that contained the highest proportion of this type of gellan. The hydrogel chosen for the possible application in soil conditioning or controlled release in herbicides was prepared with a mixture of gellans in the proportion of 30:70 (LA:HA), with total polysaccharide concentration of 1.0% (m/v), at pH 4. The SEM images revealed that the morphology of the samples was highly differentiated, according to the variation of pH, temperature and crosslinker. The FTIR spectra presented absorption bands characteristic of each gellan type, and they were shifted according to the formation of intra and intermolecular hydrogen bonds between the gellan chains. The rheological assays showed that all the hydrogels at 25 ºC, irrespective of gellan type and pH, presented hysteresis, typical behavior of thixotropic fluids. Besides this, the viscosity of the samples declined with increasing deformation rate, typical of non-Newtonian pseudoplastic fluids. The results obtained suggest the possibility of using the hydrogels studied in specific applications in the agricultural area, such as irrigation and controlled release of agricultural inputs