Inverse solubility of chitin/chitosan in aqueous alkali solvents at low temperature. (15th February 2019)

• Record Type: Journal Article
• Authors: Ru, Geying; Wu, Shuaishuai; Yan, Xiaoshuang; Liu, Biaolan; Gong, Pei; Wang, Liying; Feng, Jiwen
• Is Part Of: Carbohydrate polymers. Volume 206(2019)
• Page Start: 487
• Page End: 492
• Publication Date: 2019-02-15
• Subjects: Chitin -- Chitosan -- Dissolution -- Cation effect -- NMR; Polysaccharides -- Periodicals; Polysaccharides -- Periodicals; Polysaccharides -- Périodiques; Electronic journals; 547.78
• DOI: 10.1016/j.carbpol.2018.11.016
• Languages: English
• ISSNs: 0144-8617

Abstract

Highlights: Aqueous alkali exhibits fully different dissolving power for deacetylated chitin, i.e., KOH > NaOH >> LiOH for chitin (DA = 0.94–0.74), KOH ≈ LiOH ≈ NaOH for chitosan I (DA = 0.53–0.25), and inverse LiOH >> KOH > NaOH for chitosan II (DA < 0.25). It is the first time to find the dissolution behavior of chitosan I and chitosan II in aqueous NaOH and KOH solvents are different. In the two alkali mixed solvent, NaOH or KOH can destroy the interaction of LiOH with D9 (chitosan II region) in the order of NaOH >> KOH, but LiOH cannot destroy the interaction of KOH with raw chitin. Metal cations is the determining factor to the inverse solubility of chitin/chitosan in alkali solvent rather than OH − ion and low temperature. Abstract: The low-temperature dissolving mechanism of chitin/chitosan in the alkali (LiOH, NaOH and KOH) aqueous solvents has not been well established yet. As revealed by our XRD and NMR methods, the prepared deacetylated chitins can be categorized as chitin (DA = 0.94–0.74), chitosan I (DA = 0.53–0.25) and chitosan II (DA < 0.25). Aqueous alkali exhibits fully different dissolving power in the above three regions, i.e., KOH > NaOH >> LiOH for chitin, KOH ≈ LiOH ≈ NaOH for chitosan I, and inverse LiOH >> KOH > NaOH for chitosan II. While in the two-alkali mixed solvent, NaOH or KOH can destroy the interaction of LiOH with D9 (chitosan II region) in the order of NaOH >> KOH, but LiOH cannot destroy the interaction of KOH with raw chitin. The varied solubility of chitin/chitosan in alkali solvent is suggested to be from the cation's preferential interaction rather than OH − ion and low temperature.