Enhanced water absorption in pectin-chitosan hydrogel via modification with deep eutectic solvent: Optimisation and characterisation

• Published in: Journal of Molecular Liquids
• Main Author: Noor Atiyah Md Raffe S.; Yusof R.; Mohamed Hanaphi R.; Amin Wan Chik M.
• Format: Article
• Language: English
• Published: Elsevier B.V. 2024
• Online Access: https://www.scopus.com/inward/record.uri?eid=2-s2.0-85203528018&doi=10.1016%2fj.molliq.2024.125963&partnerID=40&md5=5f864237f098af5328d1d10ec8eeea25

Natural polymers are widely available, nontoxic, and biodegradable but have lower absorption when used to create hydrogels. Thus, a new modification of hydrogel combining pectin and chitosan was developed using choline chloride-based deep eutectic solvents (DESs) with ethylene glycol (DES1), glycerol (DES2), and acetic acid (DES3) called eutectogel. DES was added due to the hydrophilic site, which can increase water absorption. The eutectogel with each DES, including control (without DES), were optimized in their ratio of pectin to chitosan (0.5:1, 1:1, 1.5:1, and 2:1) and DES concentration (10 %, 20 %, and 30 %) to obtain the highest water absorption capacity (WAC). All developed gels showed the highest WAC at a ratio 0.5:1 of pectin to chitosan, with 20 % each of DES1, DES2, and DES3 labeled as E20, G20, and A20 having WAC values of 16.02, 13.50, and 12.50 g/g, respectively, owing to the existence of additional hydrophilic sites from DES within the gel for water binding. While the WAC value for the control was 6.2 g/g, this study proves the ability of DES to increase the WAC of E20, G20, and A20 more than two times compared to the control. E20 showed the highest water sorption because of the shorter and smaller size of ethylene glycol in DES1, with two less hindered hydroxyl groups efficiently binding with water molecules compared to glycerol and acetic acid. The interactions were observed through FTIR analysis, specifically in the amino groups of chitosan and carboxyl groups of pectin at the peak of 1636 to 1642 cm−1, which served as indicators of the electrostatic interaction with the modified DES and peak 3335 to 3350 cm−1 indicated of hydrogen bonding. The hydrogen bonding was also confirmed via DSC thermal analysis at 164.06°C to 188.44 °C. Characterization with FTIR, UV–Vis, and DSC confirmed the successful integration of DES, and it revealed that the new hydrogels had better transparency and thermal stability, with E20 showing the best overall performance in enhanced water absorption. © 2024 Elsevier B.V.