Thermoplastic polyurethane-polyaniline (TPU-PANI) composite membranes for electrochemical & electrodiaylsis application synthesis & characterization /

Abstract

Intrinsically conducting polymers (ICPs) based composite ion exchange membranes have gained the attention of researchers and industry because of their unique properties which include high electrochemical, optical and electrical conductivity properties. Their ease of processing, low production cost and thermal and mechanical stability make them a valuable choice for various applications. In the present study, PSS/DVB incorporated polymer matrix (Thermoplastic polyurethane, TPU) membrane has been modified with polyaniline (PANI) as a conducting component of membrane, using in-house built two-compartment permeation cell technique. The deposition of PNAI in bulk on ion exchange membranes using two-compartment permeation cell is performed for the first time in this study. The intercalation of PANI in membrane matrix was controlled by varying time of polymerization (2, 4 and 8 hours). Pristine (TPU-PSS/DVB) and PANI modified heterogeneous cation exchange membranes (TPU-PANI) were characterized for their surface morphology, physical, structural and electrochemical properties by using scanning electron microscopy (SEM), measurement of water uptake and ion exchange capacity, electrical conductivity and transport number measurements, Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) and electrodialysis. Membrane surface morphology was studied by using scanning electron microscopy (SEM) whereas the gravimetric method was used to evaluate PANI intercalation levels in the composite membranes. Increase in the values of intercalation levels with increased polymerization times show the deposition of PANI in the bulk of the membrane as high as 24% (w/w). Increased PANI coating on membrane matrix resulted in lower water uptake and lower ion exchange capacity values with increased aniline polymerization time. Excessive PANI layering resulted in loss of hydrophilic ion exchange particles because of hydrogen bonding between PANI and sulfonic acid functionality of the resin (–SO3–). Reduction in ion exchange capacity values occurred due to the replacement of H+ ions with secondary amine group in PANI. Increased values of electronic conductivities with prolonged polymerization times showed the presence of PANI in emeraldine salt form as it is the only conducting form of PANI. TGA curves showed the V overall decrease in the thermal stability of PANI modified membranes. Electrochemical study in a two-compartment permeation cell showed a decreasing trend of transport numbers with increased polymerization time for monovalent ion and increasing trend of transport numbers for divalent ions. The transport number of Ca+2 found significant lower as compared to Na+ ions. This trend can be attributed to the smaller radius of sodium ions as compared to calcium ions. Hence, membranes are more permselective for Na+ at 2 hour polymerization time. Trends of % salt rejection of composite membranes using electrodialysis were also in accordance with trends of transport number. Membrane with high transport number showed the maximum increasing trend of % salt rejection that decreased with increased deposition time.