Polybenzimidazole blends conductivity

Polymer blends leading to high-end polymers, e.g. from sulfonated polymers (sPEEK - sulfonated polyether-etherketone, sPPSU - sulfonated polyphenyl-sulfone) combined with alkaline components (amine, imidazole, polybenzimidazole) The combination results in ionic cross-linked phases. Commercially available polymers can be modified by different sulfonation reagents. Another possibility is to combine different monomers based on block co-polymers. The conductivity can be controlled by the number of S03H groups due to the dependence of the water uptake from the number of groups ([23] and references cited therein). 

One of the frequently advertised advantages of the phosphoric acid imbibed polybenzimidazole systems is their zero water drag coefficient and their possibihty to operate with dry hydrogen and oxygen. However, a vast literature has been devoted to the study of the proton conduction and the effect of relative humidity on the conductivity of the PBl-phosphoric acid system. The promoting effect and the physicochemical interactions of water vapors with the polymer electrolyte and on the fuel cell performance have been explicitly shown for the PBl/PPy(50)coPSF 50/50 polymer blend imbibed with phosphoric acid under fuel cell conditions. ... 

The second section covers the largest and most comprehensive hydrocarbon flash fire burn series ever conducted at an independent lab. This testing ran for 4 years atthe University of Alberta, and involved several hundred flash fires. An instrumented manikin predicted extent, severity and location of any resultant body burn injury, allowing detailed analysis of protective performance. Most major FR fabric types and weights were examined at multiple exposure levels, including meta-aramids, meta-aramid/rayon blends, FR cottons, FR cotton/polyamide blends. Polybenzimidazole and its blends with para-aramid and para-aramid/rayon, disposables, outerwear, and more. Extensive video coverage accompanies the data, and post-exposure garment samples will be shown as well. 

Membrane prepared by blending sulfonated polybenzimidazole (PBI) with Nafion polymer showed a conductivity of 0.032 S cm The methanol permeability of the composite membrane was found to be 0.82 x 10 cm s as compared to Nafion, which is around 2.21 x 10 cm s [22]. Addressing the problem of methanol permeation, a composite membrane of Nafion with polyvinyl alcohol (PVA) for direct methanol fuel cell has been reported. It is concluded that at the weight ratio of 1 1 in PVA and Nafion, the thin film-coated Nafion membrane exhibited low methanol crossover, and the membrane protonic conductivity could be improved by the sulfonation treatment [23]. Recently, Zaidi et al. [24] prepared composite membranes of PFSA ionomer with boron phosphate and showed the conductivity of 6.2 X 10-2 S cm-i at 120°C. 

Composites of zirconium tricarboxybutylphosphonate and polybenzimidazole were prepared by Jang and Yamagnchi [56]. The membranes were thermally stable and the conductivities measured for composites with 50 wt% phosphate were about 3.8 mS cm" at 200°C. Zaidi [57] and Zaidi et al. [58] introdnced boron phosphate to improve the conductivity of SPEEK membranes. By adding polybenzimidazole again the compatibility between the phosphate and the polymer matrix conld be improved. Up to 40% phosphate was added to the polymer matrix. The boron phosphate was synthesized from orthophosphoric and boric acid and added as a solid powder to blends of SPEEK and PBl. 

Savinell and co-workers, [105-107], who have principally studied phosphoric acid doped polybenzimidazole (PBl). Similar systems have been reported by He and co-workers [108], who in addition report the conductivities of PBl based membranes doped with PTA and zirconium hydrogen phosphate [108], Acid-base interactions in entirely polymeric systems have been reported by Kerres and co-workers [102], who prepared and stndied several membranes prepared by blending polymers with acidic (snlfonated-PEEK, sulfonated polyethersulfone) and basic (polybenzimidazole, poly-vinylpyridine) characteristics. Selected acid-base polymer systems are discnssed in the following. 

Abstract There have been numerous studies on modifying DuPont s Nafion (a perfluorosulfonic acid polymer) in order to improve the performance of this membrane material in a direct methanol fuel cell. Modifications focused on making Nafion a better methanol barrier, without sacrificing proton conductivity, so that methanol crossover during fuel cell operation is minimized. In this chapter, a brief literature survey of such modifications is presented, along with recent experimental results (membrane properties and fuel cell performance curves) for (1) thick Nafion films, (2) Nafion blended with Teflon-FEP or Teflon-PFA, and (3) Nafion doped with polybenzimidazole. 

Blends of sulfonated PS and sulfonated PPO have been described in several papers as offering a combination of high proton conductivity and low methanol permeability [104, 105]. Optimum conductivity was obtained with a 50/50 blend of the sulfonated polymers, with each having an identical ion exchange capacity [104]. The miscibility of the PS/PPO system appeared to be maintained with the blend of the sulfonated polymers. Polybenzimidazole (PBI) and polysulfone (PSF) are immiscible however, sulfonated PSF is miscible with PBI and showed utility in phosphoric acid based fuel cells operated upto200°C[106]. PEMs comprised of Nafion and a vinylidene fluoride-hexafluoropropylene copolymer blend were evaluated... 

Arrieta et al. [47] conducted hydrolytic and photochemical aging studies for a Kevlar-Polybenzimidazole (PBI) blend in yam form. UV irradiation was conducted at X, = 340 nm and four different temperatures (50, 60, 70 and 80 °C) between 4 and 31 days. The PBI stracture is given in Fig. 5 [47] (reproduced with kind permission from Elsevier—License no. 3890161358622). 

Perfluorinated sulfonic acid polymers, such as Nafion membranes, were the most commonly used materials in practical systems for their high proton conductivity and extremely high oxidative stability. However, due to the poor dimensional stability, low mechanical properties of Nafion at high humidity and high temperature, and high cost, an essential need for cost-effective and reinforced substitutes with improved performance arises [193-195]. Nafion blended with the second component could not only reduce the cost, but also improve the mechanical properties and the dimensional stability. Recently, the reinforced composite membranes based on semi-interpenetrating polymer network (semi-IPN) structures of Nafion , polyimidazole (PI) [196-198], polybenzimidazole (PBI) [199], and poly(vinyIidene fluoride) (PVDF) [200] were reported. As shown in Fig. 2.35, the composite membranes with... 

Current research activities are focused on the identification of membrane materials and structures with high proton conductivity and low methanol permeability. Ultimately, one would tike membranes that work well in a DMFC at 10-20 M methanol, but the focus of most research is on much lower methanol feed concentrations (0.5 and 1.0 M). Since DMFCs are designed primarily for the portable power/electronics market, operating temperatures in the 25-80°C range are usually considered. Extensive data is available in the literature on new membrane materials with reduced methanol permeability, including sulfonated or phosphonated copolymers, phosphoric-acid-doped polybenzimidazole, and various blends and composites (see Table 29.6 for a listing of DMFC properties). 

Poiyphosphazene Biends Blends of sulfonated polyphosphazene, for example, sulfonated poly[bis(3-methylphenoxy)phosphazene] or poly[(bisphenoxy)phosphazene] (see Fig. 29.14) with either an inert organic polymer such as poly(vinylidene fluoride) (Pintauro and Wycisk, 2004 Wycisk et al., 2002) or polyacrylonitrile (Carter et al., 2002) or a reactive polymer (e.g., polybenzimidazole) (Wycisk et al., 2005) have been investigated. The resultant membranes had conductivities of 0.01-0.06 S/cm (in water at 25°C) and equilibrium water swelling from 20 to 60% (at 25°C). Blends of poly[(bisphe-noxy)phosphazene] and polybenzimidazole (where acid-base complexation occurred between the sulfonic acid and the imidazole nitrogen) exhibited good mechanical properties and low methanol permeability. MEAs with this membrane material outperformed Nafion 117 in a DMFC at 60°C with concentrated (5-10 M) methanol feeds. With 1.0 M methanol and 0.5 L/min ambient air at 60°C, the maximum power density was 97 mW/cm and the methanol crossover was 2.5 times lower than that with Nafion 117 (Wycisk et al., 2005). 

Attractive blends for PEMs with high proton conductivity have been made from sulfonated PES, PSU, polyetherketone (PEK), PEEK or poly(2,6-dimethyl 1,4-phenylene ether) (PPE) blended with polybenzimidazole (PBI) or polyetherimide (PEI). To preserve the desired PEM performance, the blends are often crosslinked by radiation, chemical reaction of ionic interactions. For long-term PEM applications it is important that membranes resistance to mechanical, chemical and thermal degradation is maximized. Accelerated aging tests should follow several membrane functionalities, for example conductivity, membrane integrity and permeability. The tests should also identify a possible cross-correlation of effects, namely stress on thermal and/or chemical degradation. 

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