Effect of tio2 filler on the structural, electrical and tensile properties of hexanoyl chitosan-polystyrene blend polymer electrolyte / Nur Shazlinda Muhammad Hanif

The insolubility of chitosan in aprotic solvents is inadequate to meet the requirements to be used as an electrolyte material in lithium-based electrochemical devices. Acyl modification of chitosan helped to improve its solubility in aprotic solvent. However, hexanoyl chitosan-based polymer electrolytes are of poor mechanical property. A convenient method to improve the mechanical property of hexanoyl chitosan is to blend it with a polymer with good mechanical strength. In this respect, polystyrene was chosen as a blending partner for hexanoyl chitosan. In this work, blends of hexanoyl chitosan and polystyrene are used as the polymer host, LiCF3SO3 and TiO2 are employed as the doping salt and filler, respectively. Surface treatment of TiO2 is done by immersing filler particle in 2 and 4% sulphuric acid (H2SO4) aqueous solutions. Untreated, 2 and 4% H2SO4-treated TiO2 were referred as neutral, weakly acidic and acidic TiO2 respectively. X-Ray diffraction (XRD), Fourier Transform Infrared (FTIR), tensile test, viscometry and impedance spectroscopy (EIS) are used to characterize the prepared samples. Viscometric analysis showed that hexanoyl chitosan and polystyrene are immiscible. Tensile test revealed that blending hexanoyl chitosan with polystyrene increased its mechanical properties, and greater improvement is found with addition of TiO2 fillers. XRD results showed that, polystyrene disrupted the crystalline nature of hexanoyl chitosan. Addition of TiO2 further reduced the crystalline fraction of hexanoyl chitosan/polysyrene based electrolytes. FTIR studies showed that there is no interaction between polystyrene and LiCF3SO3. Hexanoyl chitosan interacted with LiCF3SO3 from the shift of C = O of N(COR)2 and OCOR bands to lower wavenumbers. There is also no interaction between polystyrene and hexanoyl chitosan. Interaction between TiO2 and LiCF3SO3 is indicated by the shift in wavenumber, changes in intensity and shape of peaks of LiCF3SO3. TiO2 did not interact with hexanoyl chitosan nor polystyrene. The conductivity performance of hexanoyl chitosan/polystyrene-LiCF3SO3 polymer electrolytes varied in the order: acidic < weakly acidic < TiO2 free < neutral TiO2. A model based on the interaction between Lewis acid-base sites of TiO2 with ionic species of LiCF3SO3 has been proposed to understand the conductivity mechanism brought about by the different types of fillers. The conductivity enhancement by neutral TiO2 is attributed to the increase in the mobility of Li+ cations. Acidic TiO2 decreased the conductivity by decreasing the anionic contribution. The conductivity variation with filler content is discussed on the basis of the number of free ions. Conductivity of the prepared electrolyte system is also studied as a function of temperature, ranging from 273 to 333 K. The conductivity was found to increase with increasing temperature.