Modified natural rubber polymer hosts having low transition glass temperatures have been investigated for use in polymer electrolytes. Two types of modified natural rubber, namely 25% epoxidised natural rubber (ENR-25) and 50% epoxidised natural rubber (ENR-50) were employed in conjunction with poly(ethylene oxide), PEO. Results are reported for ionic conductivity and thermal properties for both unplasticized and plasticized polymer electrolyte systems with lithium triflate. The samples were in the form of free standing films with the thickness 0.2-0.5 mm and mixtures of ethylene carbonate (EC) and propylene carbonate (PC) were used as plasticizers. Unplasticized modified natural rubber-based systems exhibit ionic conductivities in the range 10−6 to 10−5 S cm−1 at ambient temperatures. Incorporating 100% of EC/PC by weight fraction of polymer (ENR/PEO) to the systems yielded mechanically stable films and ionic conductivities in the range of 10−4 S cm−1 at ambient temperature.
Epoxidized Natural Rubber (ENR50), lithium imide salt, [LiN(SO2CF3)2] with and without solvent were prepared by solvent casting technique. Non solvated polymer electrolyte showed modest ionic conductivity at ambient temperature. To further enhance ionic conductivity a mixed solvent of ethylene carbonate/propylene carbonate was added into the system. Thermal characterization showed that single transition glass temperature (Tg) for all systems and amorphous phase is dominant. DSC traces of non solvated samples have shown Tg values increased whereas addition of mixed EC/PC solvent into the electrolyte system reduced their values respectively. Impedance measurements for the solvated epoxidized natural rubber (ENR) based electrolyte systems have shown optimal ionic conductivity 10-4 S cm-1 whereas 10-6 S cm-1 for a non solvated one. ENR electrolyte systems showed similar temperature dependence, which suggests that the conductivity is thermally activated.
Polymer electrolytes containing epoxidised natural rubber (ENR50)/poly(vinyl chloride) (PVC) blend as a polymer host, a solvent mixture of ethylene carbonate (EC) and propylene carbonate (PC) as a plasticizer, and lithium imide, LiN (CF 3 SO 2 ) 2 , as a salt were studied. Polymer electrolytes that were obtained by solvent cast yielded solid dry rubbery films with a thickness range of 110-125 μm. Impedance spectroscopy, Fourier transform infra red (FTIR) spectroscopy, differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) were performed on these samples. The prepared solid polymer electrolytes exhibit ionic conductivities in the order 10 −4 S cm −1 at room temperature as expected. However, the physical properties of the electrolytes have improved significantly when optimal composition has been selected.
The present study focuses on preparation of ENR-50/PEMA-NH4CF3SO3 proton conducting polymer electrolytes by solution casting technique. Conductivity increases with NH4CF3SO3 concentration up to 40 wt.% but decreases with further increase in salt content. The temperature dependent conductivity study shows that the conductivity-temperature behaviour of ENR-50/PEMA-NH4CF3SO3 electrolytes follows the VTF rule. DSC studies show that the Tg increases with increase in salt content. This means that the increase in conductivity of ENR-50/PEMA-NH4CF3SO3 is incorrelated to the increase of the segmental motion of the host polymer chains but may be attributed to the increase in the concentration and migration rate of charge carriers.
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