Síntese e caracterização de hidrogéis superabsorventes obtidos a partir da copolimerização de acrilamida, n-isopropilacrilamida e metacrilato de sódio

• Ano de defesa: 2011
• Autor(a) principal: Priscilla Mol Queiroz
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Minas Gerais; UFMG
• Palavras-chave em Português: Engenharia Química; Engenharia quimica
• Link de acesso: http://hdl.handle.net/1843/BUOS-8MREEK

In this work, polymer hydrogels were synthesized, aiming at their use assuperabsorbent polymers SAP, obtained by solution free radical copolymerization reactions of three different main monomers: acrylamide - AA, Nisopropylacrylamide - NIPAM and sodium methacrylate - NMA, and N,N- methylenebisacrylamide - MBA as crosslinking agent. The obtained gels were characterized by their hydration capacity and by their mass transfer mechanism. The influence of the reactants concentration in the hydration capacity of the gels was studied. Factorial planning was used as a tool for the proposed study, with a 2k matrix, being k = 4, and central point. The studied variables had their maximum and minimum levels fixed, resulting in 19 systems (24 + 3), with total monomers concentrations varying from 10 to 15%, crosslinking agent from 1 to 3%, with respect to total monomers, and inonic monomer from 22 to 33%, also with respect to total monomers. The obtained hydrogels showed hydration capacity between 70 and 200g H2O/g dry gel and the results demonstrated the relative importance of the different components in the swelling behavior of the gels. The most important variables, according to statistical analysis of the system, were in order crosslinker concentration MBA, ionic monomer concentration NMA and NIPAM concentration. The AA concentration was not statistically significant in this study. The interactions between concentration of NMA and MBA, and MBA and NIPAM were also significant on superabsorbent polymers swelling capacity. All the results were discussed considering gels thermodynamics. Sodium methacrylate contributes significantly for gels swelling, favoring the ionic component of the mixing free energy variation term. The total monomers present a more significant effect on the elastic contribution, due to polymer chain increasing, resulting in greater entanglement of them, when total monomers concentration increases. The increase of crosslinking agent results in gels significantly more rigid, so with a lower swelling capacity, being the most important contribution to the elastic term. The influence of the gels swelling with temperature was also studied, with temperature varying from 20°C to 50°C. All the gels showed an increase in the degree of swelling, with hydration capacity reaching 350g H2O/g dry gel, at 50°C. Gels synthesized at higher temperatures presented higher swelling capacities. As an example, in one specific studied system, the swelling increased approximately 80%, from 100g H2O/g dry gel, for the gel synthesized at 18°C, to 180g H2O/g drygel, for the same system, synthesized at 55°C. The mass transfer mechanism in these systems was also studied, verifying that these gels follow the mechanism described as Case II, that is, the process is controlled by the polymer network relaxation