| Polybenzimidazole is a linear polymer with a very high glass transition temperature. It has exceptional properties at elevated temperature such as stability, retention of stiffness, and toughness. PBI containing phosphoric acid has high proton conductivity and low water vapor permeability.; A new way of direct film casting of PBI containing phosphoric acid, has been found. The use of trifluoroacetic acid as a solvent resulted in a new and quick way to prepare PBI film containing phosphoric acid which showed about four times more conductivity at a given doping level than PBI doped with phosphoric acid from DMAc solution.; Mechanical property studies of different molecular weight PBI films {dollar}rmetasb{lcub}inh{rcub} = 0.91{dollar} to 142 dl/g) have shown that increasing molecular weight linearly improved mechanical properties of PBI films with pronounced effect on toughness.; As PBI film was doped with sulfuric acid, mechanical properties decreased with very sharp drop in toughness. More reduction in mechanical properties was observed as the concentration of sulfuric acid in the film increased.; Doping PBI film with low concentrations of phosphoric acid improved modulus and strength at break while lowering the toughness. Increasing the concentration of acid in these films lowered the strength and modulus of PBI film. However, toughness first increased up to concentration of 200-300M% phosphoric acid and then decreased.; Comparison of phosphoric acid doped PBI film and PBI film cast from {dollar}rm PBI/TFA/Hsb3POsb4{dollar} solution reveals that phosphoric acid doped PBI film has at least three times better mechanical properties: toughness, modulus, and strength.; X-ray photographs of PBI film cast from {dollar}rm PBI/TFA/Hsb3POsb4{dollar} solution shows a crystalline pattern with a monoclinic unit cell of dimensions: {dollar}a = 15.8{dollar} A, b = 13.23 A, c = 16.83 A, and {dollar}gamma = 79.1sp0.{dollar} On the other hand, phosphoric acid doped PBI film has relatively low crystallinity.; PBI can cocrystallize with some complexing agent like trifluoroacetic acid, phosphoric acid, {dollar}rm TFA/Hsb3POsb4, TFA/Hsb2O,{dollar} and phenol-water and form different crystal structures. The crystalline structure varies depending on the doping procedure.; Employment of PBI doped with phosphoric acid as polymer electrolyte membranes in fuel cells opened a new prospect in PEM fuel cell applications. It shows promising properties from the polymer point of view. |
