Síntese e caracterização de hidrogeis superabsorventes à base de acrilamida e acrilato de sódio

Abstract

Superabsorbent hydrogels are materials polymeric that present for three-dimensional crosslinked hydrophilic networks that can absorb large amounts of water. Among the several applications, the use of superabsorbent hydrogels as conditioner soil has shown interest by researchers. The objective of this work is to synthesize hydrogels based on acrylamide (AAM) and sodium acrylate (NaAAC) crosslinkeds with N, N'-methylenebisacrylamide (MBA), to study the effect of synthesis parameters such as: molar ratio (AAM/NaAAC), MBA concentration and monomers concentration in the properties of materials synthesized. The hydrogels were synthesized by polymerization in solution using the redox initiation system potassium per sulfate (KPS) and N, N, N’, N' tetramethylethylenediamine (TMEDA). The hydrogels have been characterized by their swelling behaviour, percentage of gel, drying, mechanical analysis, rheology, atomic absorption, scanning electron microscopy (SEM) and spectroscopy analyses infrared spectroscopy (FTIR) and 13C NMR. The average percentage of gel for hydrogels was 94 ± 3% and small amount of soluble do not modify the swelling of materials. When more acrylate (NaAAC) content the bigger equilibrium water absorbencies. When MBA and monomers content increased, the equilibrium water absorbency decreased. Swelling measurements of the hydrogels in the chloride salt solution (Na+, K+, Ca2+ e Al3) decreased compared with gel/water system. IR spectroscopy and atomic absorption showed that the nominal reason AAM/NaAAC is close to the expected value. The experiments revealed the hydrogels are suitable to be used as cation exchangers. Drying experiments indicate there are two different water in hydrogels. The hydrogels with higher concentration of MBA (0,5 e 0,8 mol%) showed higher values of elastic modulus (80.9 and 204 kPa) because of its greater physical resistance. The elastic behavior of the samples exceed the viscous one, then gels are considered strong. The influence of pH on the swelling of the hydrogel based on 55 mol% of AAM, 45 mol% of NaAAC, 0.1 mol% of MBA and 24% of monomer concentration is the value constant (»450 g H2O/g gel) in pHs from 4 to 8. The hydrogel shows reversible behavior of swelling and contraction in alkaline (pH = 10,4) and acid (pH = 10,4) buffer media, respectively. The hydrogel used in methylene blue adsorption experiments showed a quick reduction in the concentration of dye, holding 89 % of the initial concentration. The high capacity of water absorption of these materials 11 provide to them a possible application as soil conditioners. Other results point to the possibility as delivery systems for drugs or agrochemicals and as agents of color removal from effluent water