Effect of Modified Natural Filler O-Methylene Phosphonic κ-Carrageenan on Chitosan-Based Polymer Electrolytes

The potential for using O-methylene phosphonic κ-carrageenan (OMPk) as a filler in the chitosan-based polymer electrolyte N-methylene phosphonic chitosan (NMPC) was investigated. OMPk, a derivative of κ-carrageenan, was synthesized via phosphorylation and characterized using infrared spectroscopy (IR) and nuclear magnetic resonance (NMR). Both the IR and NMR results confirmed the phosphorylation of the parent carrageenan. The solid polymer electrolyte (SPE)-based NMPC was prepared by solution casting with different weight percentages of OMPk ranging from 2 to 8 wt %. The tensile strength of the polymer membrane increased from 18.02 to 38.95 MPa as the amount of OMPk increased to 6 wt %. However, the increase in the ionic conductivity did not match the increase in the tensile strength. The highest ionic conductivity was achieved with 4 wt % OMPk, which resulted in 1.43 × 10−5 Scm−1. The κ-carrageenan-based OMPk filler strengthened the SPE while maintaining an acceptable level of ionic conductivity

Synthesis and characterization of modified κ-carrageenan for enhanced proton conductivity as polymer electrolyte membrane.

Polymer electrolyte membranes based on the natural polymer κ-carrageenan were modified and characterized for application in electrochemical devices. In general, pure κ-carrageenan membranes show a low ionic conductivity. New membranes were developed by chemically modifying κ-carrageenan via phosphorylation to produce O-methylene phosphonic κ-carrageenan (OMPC), which showed enhanced membrane conductivity. The membranes were prepared by a solution casting method. The chemical structure of OMPC samples were characterized using Fourier transform infrared spectroscopy (FTIR), 1H nuclear magnetic resonance (1H NMR) spectroscopy and 31P nuclear magnetic resonance (31P NMR) spectroscopy. The conductivity properties of the membranes were investigated by electrochemical impedance spectroscopy (EIS). The characterization demonstrated that the membranes had been successfully produced. The ionic conductivity of κ-carrageenan and OMPC were 2.79 × 10-6 S cm-1 and 1.54 × 10-5 S cm-1, respectively. The hydrated membranes showed a two orders of magnitude higher ionic conductivity than the dried membranes

SEM micrographs for cross sections of (a) κ-carrageenan and (b) OMPC films.

<p>SEM micrographs for cross sections of (a) κ-carrageenan and (b) OMPC films.</p

DSC thermograms of κ-carrageenan and OMPC.

<p>DSC thermograms of κ-carrageenan and OMPC.</p

Impedance spectra of κ-carrageenan in (a) dry and (b) hydrated conditions.

<p>Impedance spectra of κ-carrageenan in (a) dry and (b) hydrated conditions.</p

Ionic conductivity from EIS analysis.

<p>Ionic conductivity from EIS analysis.</p

TG curves of κ-carrageenan and OMPC.

<p>TG curves of κ-carrageenan and OMPC.</p

XRD diffractograms of (a) phosphorous acid, (b) κ-carrageenan and (c) OMPC.

<p>XRD diffractograms of (a) phosphorous acid, (b) κ-carrageenan and (c) OMPC.</p

Molecular structure of (a) κ-carrageenan and (b) O-methylene phosphonic κ-carrageenan.

<p>Molecular structure of (a) κ-carrageenan and (b) O-methylene phosphonic κ-carrageenan.</p

¹H NMR spectra of (a) κ-carrageenan and (b) OMPC.

<p>¹H NMR spectra of (a) κ-carrageenan and (b) OMPC.</p