Preparation of PBI/PTFE composite membranes from PBI in N,N′-dimethyl acetamide solutions with various concentrations of LiCl
ABSTRACT In this report, properties of 2 mg ml−1 PBI in N,N′-dimethyl acetamide (DMAc) solutions containing LiCl with molar ratios of [LiCl]/[BI] = 3.62–14.51 (where [BI] is the concentration of benzimidazole repeat unit in the solutions) were investigated. We show the solutions properties of PBI in DMAc mixed with LiCl (PBI/DMAc/LiCl) are strongly influenced by the molar ratio of [LiCl]/[BI] in the solutions. Thus, the properties of membranes prepared by solutions castings also depend on the LiCl concentration in the solutions. Both viscosity of PBI/DMAc/LiCl solutions and hydrodynamic radius of PBI in PBI/DMAc/LiCl solutions decrease when the molar ratio of [LiCl]/[BI] is increased from 0.0 to ∼8.0 and then increase when the molar ratio of [LiCl]/[BI] is increased from 8.0 to 14.5. These results suggest a lowest polymer aggregation of PBI in DMAc/LiCl solutions when the [LiCl]/[BI] molar is ∼8.0. Using a dialysis method with conductivity measurements, we found around 2.5 LiCl molecules were bonded on each BI repeat unit when the [LiCl]/[BI] fed molar ratio was 8.0 in PBI/DMAc/LiCl solutions. The value “2.5” of “2.5 LiCl molecules” bonded on each BI was close to the value “2” of “2 –NH groups” and “2 –NC– groups” consisted in the chemical structure of a BI repeat unit. The IR spectra also show the hydrogen bonds between –NH and –NC– of BI structures are dissociated by the presence of LiCl in PBI/DMAC solutions. These results suggest that all the –NH and –NC groups of PBI are bonded by LiCl when the [LiCl]/[BI] fed molar ratio is at ∼8.0. The porous poly(tetrafluoro ethylene) (PTFE) reinforced PBI (PBI/PTFE) composite membranes prepared from PBI/DMAc/LiCl solutions with [LiCl]/[BI] molar ratios of 3.6, 8.0, and 9.0 were used to prepare membrane electrode assemblies (MEA). The fuel cells performances of these MEAs were investigated at 150 °C and revealed a highest fuel cell performance when the composite membrane was prepared from a solution with a [LiCl]/[BI] molar ratio of ∼8.0.
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ABSTRACT: A series of ionically crosslinked composite membranes were prepared from sulfonated poly(arylene ether sulfone) (SPAES) and polybenzimidazole (PBI) via in situ polymerization method. The structure of the pristine polymer and the composite membranes were characterized by FT-IR. The performance of the composite membranes was characterized. The study showed that the introduction of PBI led to the reduction of methanol swelling ratio and the increase of mechanical properties due to the acid–base interaction between the sulfonic acid groups and benzimidazole groups. Moreover, the oxidative stability and thermal stability of the composite membranes were improved greatly. With the increase of PBI content, the methanol permeability coefficient of the composite membranes gradually decreased from 1.59×10−6cm2/s to 1.28×10−8cm2/s at 30°C. Despite the fact that the proton conductivity decreased to some extent as a result of the addition of PBI, the composite membrane with PBI content of 5wt.% still showed a proton conductivity of 0.201S/cm at 80°C which could actually meet the requirement of proton exchange fuel cell application. Furthermore, the composite membranes with PBI content of 2.5–7.5wt.% showed better selectivity than Nafion117 taking into consideration the methanol swelling ratio and proton conductivity comprehensively.Journal of Membrane Science - J MEMBRANE SCI. 01/2010; 346(1):105-112.
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ABSTRACT: We examined the effects of dead space loading (DSL) on ventilation (V˙E), neural respiratory drive (EMGdi%max, diaphragm EMG expressed as a % of maximal EMGdi), contractile respiratory muscle effort (Pes,tidal%P(Imax), tidal esophageal pressure swing expressed as a % of maximal inspiratory Pes) and exertional dyspnea intensity ratings in 11 healthy adults with normal spirometry. Subjects completed, in random order, symptom-limited incremental cycle exercise tests under control (CTRL) and DSL (500 ml) conditions. Compared with CTRL, DSL decreased exercise tolerance by 20-25%; increased exertional dyspnea intensity ratings in direct proportion to concurrent increases in EMGdi%max, Pes,tidal%P(Imax) and V˙E; and had little/no effect on the inter-relationships between EMGdi%max, Pes,tidal%P(Imax) and V˙E during exercise. In conclusion, DSL was associated with an earlier onset of intolerable dyspnea; however, neuro-muscular and neuro-ventilatory coupling of the respiratory system remained relatively preserved during exercise in the presence of an increased external dead space. Under these circumstances, DSL-induced increases in exertional dyspnea intensity ratings reflected, at least in part, the awareness of increased neural respiratory drive, contractile respiratory muscle effort and ventilatory output.Respiratory Physiology & Neurobiology 08/2011; 179(2-3):219-26. · 2.05 Impact Factor
- Polymer International 08/2010; 59(12):1695 - 1700. · 2.13 Impact Factor