Effects of Grafting Azacrown Ether on Thermal and Swelling Properties of Chitosan Films

Abstract

Abstract:The thermal and swelling properties of a series of azacrown ether-crosslinked chitosans prepared with varying molar amounts of N,N-diallyl-7,13-diaza-1,7,10,16-tetraoxa-dibenzo-18-crown-6 (molar equivalents ranging from 0, 0.125, 0.167, 0.25 and 0.5) films were studied with Thermographimetric analysis (TGA), Differential Scanning Calorimetry (DSC), Dynamic Mechanical analysis (DMA) techniques and swelling kinetics. Introducing the azacrown (DAC) as crosslinker into the chitosan matrices (Ch) altered the thermal and swelling properties of the chitosan/crown ether films (Ch-DAC) systematically with respect to molar ratios. At lower DAC content, a depression of T g revealed a dominating internal plasticization effect of DAC on chitosan, while higher DAC molar ratios systematically increased the T g of the network. The films high swelling capacity (as high as 1200%) was reached within three hours in aqueous acidic media and decreased systematically with increasing DAC content. The swelling behavior was highly dependent on pH and followed second order kinetics. Understanding the thermal and swelling properties of this series of azacrown ether-crosslinked chitosans sets the stage to further shed light on their impact for heavy metal adsorption in water remediation applications.

Adsorption of Pb(II), Hg(II) and Cu(II) ions on azacrown ether grafted chitosan films

“…Medium-molecular-weight chitosan (77% deacetylated) was supplied by the Sigma-Aldrich Company (Germany) as pale-white powder. The detailed characteristics of the starting chitosan was reported in detail elsewhere (Toeri et al, , 2017. The azacrown ether (DAC) used in this study was synthesized and characterized according Toeri and Laborie .…”

“…More interesting are the nitrogen rich azacrown ether macrocyclic polyethers known for their prevalence for soft-metal ions over the all-oxygen crown ethers (Izatt et al, 1985;Yang, Wang, & Tang, 1999). Previously, we have reported on the synthesis, physical, chemical and structural properties of N,N′-diallyl-7,16-diaza-1,4,10,13-tetraoxa-dibenzo-18-crown-6 (DAC) and DAC modified chitosan (Ch) films Toeri, Osorio-Madrazo, & Laborie, 2016, 2017. Composition, structure, and morphology of a series of the azacrown ether crosslinked Ch films were systematically characterized.…”