The influence of dibutyl sebacate on the sorption properties of a composite superabsorbent based on chitosan

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Composite superabsorbents, combining both acrylate and biodegradable units, are more environmentally friendly products compared to fully synthetic analogues, however, their equilibrium degree of swelling Qe, usually, lower than the latter. Therefore, the search for new approaches to increase this parameter is an urgent task of modern chemistry. A promising way to solve this problem seems to be the use of plasticizers - low-molecular compounds that increase the segmental and molecular mobility of macromolecules. The purpose of this study was investigation of the effect of the presence of dibutyl sebacate on the sorption properties of composite superabsorbents containing chitosan. Dibutyl sebacate is known as a plasticizer for many industrially important polymers, including cellulose derivatives, and is also less toxic than commonly used phthalates. Superabsorbents based on acrylic acid and acrylamide containing 10 wt.% chitosan with different molecular weights: 20, 200, and 600 kDa were obtained by radical precipitation polymerization with substance initiation. The structure of the resulting superabsorbents was confirmed by FTIR spectroscopy, and the morphology of their surfaces was studied by scanning electron microscopy. With an increase in the molecular weight of the polysaccharide used, a decrease in the equilibrium degree of swelling of the resulting composite superabsorbent in distilled water was observed. In the case of swelling in a 0.15 M NaCl solution, a sharp decrease in Qe values occurred. The presence of dibutyl sebacate increased the equilibrium degree of swelling in distilled water of superabsorbents obtained based on chitosan with molecular weights of 200 and 600 kDa. The increase in Qe values correlated with the molecular weight of the polysaccharide: the higher it was, the more pronounced was the effect of the presence of dibutyl sebacate. A study of the swelling kinetics of superabsorbents showed that, regardless of the presence of dibutyl sebacate, the process is two-stage: a stage of fast and slow water sorption was observed. Using mathematical kinetic models, it was shown that swelling was controlled by chemisorption, and at the slow stage of swelling, the diffusion of water molecules inside the superabsorbent phase played a significant role. Thus, the use of dibutyl sebacate is a promising approach to increasing the equilibrium degree of swelling of composite superabsorbents based on chitosan with a molecular weight of more than 200 kDa.