Extensively deacetylated high molecular weight chitosan from the multistep ultrasound-assisted deacetylation of beta-chitin

High intensity ultrasound irradiation was used to convert beta-chitin (BCHt) into chitosan (CHs). Typically, beta-chitin was suspended in 40% (w/w) aqueous sodium hydroxide at a ratio 1/10 (g mL(-1)) and then submitted to ultrasound-assisted deacetylation (USAD) during 50 min at 60 degrees C and a fixed irradiation surface intensity (52.6 W cm(-2)). Hydrogen nuclear magnetic resonance spectroscopy and capillary viscometry were used to determine the average degree of acetylation ((DA) over bar) and viscosity average degree of polymerization ((DPv) over bar), respectively, of the parent beta-chitin ((DA) over bar = 80.7%; (DPv) over bar = 6865) and USAD chitosans. A first USAD reaction resulted in chitosan CHs1 ((DA) over bar = 36.7%; (DPv) over bar = 5838). Chitosans CHs2 ((DA) over bar = 15.0%; (DPv) over bar = 5128) and CHs3 ((DA) over bar = 4.3%; (DPv) over bar = 4889) resulted after repeating the USAD procedure to CHs1 consecutively once and twice, respectively. Size-exclusion chromatography analyzes allowed the determination of the weight average molecular weight ((M-w) over bar) and dispersity (D) of CHs1 ((M-w) over bar = 1,260,000 g mol(-1); D =1.4), CHs2 ((M-w) over bar = 1,137,000 g mol(-1); D =1.4) and CHs3 ((M-w) over bar = 912,000 g mol(-1); D = 1.3). Such results revealed that, thanks to the action of high intensity ultrasound irradiation, the USAD process allowed the preparation of unusually high molecular weight, randomly deacetylated chitosan, an important breakthrough to the development of new high grade chitosan-based materials displaying superior mechanical properties. (C) 2016 Elsevier B.V. All rights reserved.