Design, synthesis and characterization of polymeric films and membranes

Abstract

Solid polymer electrolyte membranes play a vital role in polymer electrolyte membrane fuel cells. Although these membranes have been used successfully, there is still a need to improve their proton conductivity, lower their cost and increase their operation temperature. Polybenzimidazole, a high temperature resistant polymer, was synthesized and polymer electrolyte membrane was fabricated with a novel method including ultrasonic generator and ultrasonic nozzle. A computer model was developed by using COMSOL Multiphysics program. Polypropylene (PP) films were fabricated by using single screw extruder in order to find out how the machine parameters affect the mechanical properties of the product. Nanoclay reinforced PP films were produced by using single screw extruder after compatibilizer, nanoclay and PP were mixed in a twin screw extruder. Tensile, tear and burst strength tests were performed on these films. With the increasing temperature and winding speed, the thickness of the films decreases; however, with the increasing screw motor speed film thickness increases. With the increasing temperature tear strength becomes higher in machine direction (MD); however tear strength decreases in cross direction (CD). With the increasing screw motor speed tear strength of the films did not show any specific trend in MD; however, tear strength of the films in CD increases. With the increasing winding speed the tear strength of the films decreases in MD; however, the data did not show any specific trend in CD. When the molecular orientation increases because of lower temperatures, tensile strength should increase according to the literature. However in this iii work, as the temperature increased, tensile strength increased in MD. With increasing screw motor speed tensile strength of the films increases in MD; however, tensile strength of the films decreases in CD. With increasing winding speed the tensile strength of the films increases in MD; however, tensile strength of the films decreases in CD. Nanoclay reinforced films having only 1% nanoclay content have more homogeneous nanoclay dispersion than the films having 3% nanoclay content. The films having 5% nanoclay content have better nanoclay dispersion compared to the other films. Screw speed was increased for the films having 5% nanoclay content. Since the screw speed was increased, shear stress increased. This caused the polymer and the nanoclay mix more homogeneously. According to the differential scanning calorimetry (DSC) results the melting points of the nanoclay reinforced films slightly increase as their nanoclay contents increase from 1% to 5%. Tensile tests showed that as the nanoclay contents increase, the extension of the films decreases. Nanoclay reinforced films having only 1% nanoclay content have higher tensile strength than the films having 3% nanoclay content. No specific result could be obtained about the effect of the compatibilizer content on tensile strength of the nanoclay reinforced films. Nanoclay reinforced films having only 1% nanoclay content have higher tear strength than the films having 3% nanoclay content. Since the screw speed was increased for the films having 5% nanoclay content in order to obtain a film structure, the films, having 5% nanoclay content, gained higher tear strength. Burst strength results show that as the nanoclay content of the nanoclay reinforced films increases from 1% to 5%, the extension of the films decreases. Nanoclay reinforced films having only 1% nanoclay content have higher burst strength than the films having 3% nanoclay content.