Synthesis and Characterization of Cellulose-Based Hydrogels Using Citric Acid as a Crosslinker

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Incorporation of synthetic polymers along with natural polymers to prepare hydrogels can improve the performance of these materials. The objective of this study was to synthesize and evaluate a hydrogel using sodium carboxymethyl cellulose (NaCMC), polyethylene glycol (PEG), and citric acid. The Fourier Transform Infrared analysis of these raw materials confirms that the functional groups involved in the crosslinking reaction are present. The effect of preparation conditions such as polymer composition, reaction temperature (65-95 ℃), reaction time (8-24 hours) and citric acid concentration (10-20%) on the swelling degree was evaluated. The results demonstrated that superabsorbent hydrogels were produced with swelling degree typically ranging from 215% to 5595%. The swelling degree was significantly influenced by the temperature, concentration of crosslinker, time and polymer composition. In addition to their high swelling capacity, Thermogravimetric analysis of NaCMC based hybrids that were prepared by blending with 20 wt.% PEG has shown good stability. Response surface methodology was used to optimize the synthesis process. The optimum hydrogel with swelling degree of 6748% was synthesized at 72.38 ℃ temperature, 8 hours of reaction time, 16.54% citric acid concentration, and 80% NaCMC and 20% PEG composition. Influence of ionic strength and pH of the external solution on the swelling behavior of the hydrogel was investigated. Urea as an agrochemical model was loaded onto the obtained hydrogel to study the slow release of the nutrient. The hydrogel was responsive to the variation of ionic strength and pH of the external solution. Due to its considerable slow urea release and good water retention capacity, it could be used in agricultural application.



Carboxymethyl cellulose, Superabsorbent hydrogel, Slow release, Swelling