INFLUENCE OF COMPOSITION AND PARTICLE SIZE ON ABSORBANCE CAPACITY POLYACRYLAMIDE HYDROGELS OBTAINED BY MICROEMULSION WITH NONIONIC SURFACTANT

Abstract

The hydrogels are of interest in various branches of science materials applications as high absorption capacity, controlled release product, electrophoretic separations support, among others; it is important to analyze the influence of the main reagents in the copolymerization reaction (between cross-linking N,N’-methylenebisacrylamide and the acrylamide monomer) and the reaction medium to control the shape, size and degree of hydration of hydrogels; especially those obtained by small-scale and that provide a greater surface area for industrial use. In this research the inverse micelles of nonionic surfactant Span 80 (sorbitan monooleate, HLB = 4.3) of an oil microemulsion (WOR = 0.67) were used as minireactor. The experimental design consisted of a single multifactorial random block, consisting of the amount of monomer (1 and 2 g) and cross-linking agent (0.01; 0.02; 0.03 g) for the synthesis and third factor given by the concentration of surfactant (5 to 10 % m/m) to modify the reaction medium. The techniques used in the characterization of the product were: optical microscopy (OM), transmission electron microscopy (TEM) and infrared spectroscopy with Fourier transform (FT-IR). Hydrogels presented spherical shape in a cluster type arrangement structures and a size distribution of polydisperse type particles, within the range of 23 to 97 nm; IR spectra showed characteristic peaks polyacrylamide hydrogels (N-H bonds, C = O and C-N). The average particle diameter decreased significantly with increase in the concentration of crosslinking agent in accordance with the highest degree of crosslinking evidenced by lower water absorption. Swelling tests indicated high absorption capacity, 905-1,750 % in a time of 15 min, more than polyacrylamide hydrogels formulated in aqueous solution (700-1,000 %).