Abstract Proton‐exchange membrane fuel cell vehicles offer a low‐carbon alternative to traditional oil fuel vehicles, but their performances still need improvement to be competitive. Raising their operating temperature to 120 °C will enhance their efficiency but is currently unfeasible due to the poor mechanical properties at high temperatures of the state‐of‐the‐art proton‐exchange membranes consisting of perfluorosulfonic acid (PFSA) ionomers. To address this issue, xx designed composite membranes made of two networks: a mat of hybrid fibers to maintain the mechanical properties filled with a matrix of PFSA‐based ionomer to ensure the proton conductivity. The hybrid fibers obtained by electrospinning are composed of intermixed domains of sulfonated silica and a fluorinated polymer. The inter‐fiber porosity is then filled with a PFSA ionomer to obtain dense composite membranes with a controlled fibers‐to‐ionomer ratio. At 80 °C, these obtained composite membranes show comparable performances to a pure PFSA commercial membrane. At 120 °C however, the tensile strength of the PFSA membrane drastically drop down to 0.2 MPa, while it is maintained at 7.0 MPa for the composite membrane. In addition, the composite membrane shows a good conductivity of up to 0.1 S cm −1 at 120 °C/90% RH, which increases with the ionomer content.
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Melt synthesis of sulfonated EPDM ionomers in batch and continuous processes
Zinc‐neutralized sulfonated EPDM ionomers (Zn‐SEPDM) were prepared by batch and continuous melt sulfonation processes, and the ionomer products were compared with ionomers synthesized by sulfonation of EPDM in homogeneous solution. The efficiency of a batch melt sulfonation using an intensive mixer as a reactor was comparable to that of the solution sulfonation process, but the efficiency of the melt sulfonation in a twin‐screw extruder was considerably lower, which was thought to be a consequence of a relatively short reaction residence time due to limitations of the equipment. Melt neutralization was not complete, which produced a dark colored product. However, the incomplete neutralization and the color of the product did not affect the mechanical properties of the melt sulfonated ionomers, which were comparable to those of ionomers made by conventional solution sulfonation. The metal sulfonate concentration alone determined the mechanical properties of the ionomer. Melt sulfonation of Zn‐SEPDM ionomers by batch or continuous melt processes appears to be a practical alternative to solution sulfonation, but further optimization of the melt sulfonation processes is needed to ensure uniform sulfonation and complete neutralization.
more » « less- NSF-PAR ID:
- 10455263
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Polymer Engineering & Science
- Volume:
- 60
- Issue:
- 12
- ISSN:
- 0032-3888
- Page Range / eLocation ID:
- p. 3216-3230
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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ABSTRACT This study discusses the effect of carboxylated (COOH) and phosphonated (PO3H2) single‐walled carbon nanotubes (SWCNTs) on the transport properties of sulfonated poly(styrene‐isobutylene‐styrene) (SO3H SIBS) as polymer nanocomposite membranes (PNMs) for direct methanol fuel cell (DMFC) and chemical and biological protective clothing (CBPC) applications. The properties were determined as a function of sulfonation level of SIBS, SWCNTs functionalization and loading. A comprehensive materials characterization study was performed to understand the interactions between the nanofillers and the functionalized polymer matrix, and to determine the effect of their incorporation on the resulting nanostructure of the PNMs. Results indicate that the sulfonation level is the variable that dictates nanofiller dispersion, mechanical properties, water absorption capabilities, morphology, and oxidative stability of SO3H SIBS. Meanwhile, the nanofiller loading and functionalization influenced the transport properties. The nanofillers reduced methanol permeation. PO3H2SWCNTs increased the proton conductivity but at a high sulfonation level (i.e.
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Abstract This work discusses the effect of isopropyl phosphate (IP) on the transport properties of sulfonated poly(styrene‐isobutylene‐styrene) (SO3H SIBS) as membranes for direct methanol fuel cell (DMFC) and chemical and biological protective clothing (CBPC) applications. The properties were determined as a function of SIBS sulfonation level (i.e., 24, 34, 49, and 84 mol %) and IP loading (i.e., 1, 3, 5, 11, and 15 wt %). A comprehensive material characterization study (e.g.
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Covalent adaptable networks (CANs) represent a novel class of polymeric materials crosslinked by dynamic covalent bonds. Since their first discovery, CANs have attracted great attention due to their high mechanical strength and stability like conventional thermosets under service conditions and easy reprocessability like thermoplastics under certain external stimuli. Here, we report the first example of ionic covalent adaptable networks (ICANs), a type of crosslinked ionomers, consisting of negatively charged backbone structures. More specifically, two ICANs with different backbone compositions were prepared through spiroborate chemistry. Given the dynamic nature of the spiroborate linkages, the resulting ionomer thermosets display rapid reprocessability and closed-loop recyclability under mild conditions. The materials mechanically broken into smaller pieces can be reprocessed into coherent solids at 120 °C within only 1 min with nearly 100% recovery of the mechanical properties. Upon treating the ICANs with dilute hydrochloric acid at room temperature, the valuable monomers can be easily chemically recycled in almost quantitative yield. This work demonstrates the great potential of spiroborate bonds as a novel dynamic ionic linkage for development of new reprocessable and recyclable ionomer thermosets.more » « less
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Abstract A recent experiment by Kim’s group from the University of Nevada, Las Vegas has demonstrated the possibility of actuating ionomer cilia in salt solution. When these actuators are placed between two external electrodes, across which a small voltage is applied, they move toward the cathode. This is in stark contrast with the case of ionic polymer metal composites, where these ionomers are plated by metal electrodes and bending occurs towards the anode. Here, we seek to unravel the factors underlying the motion of ionomer cilia in salt solution through a physically-based model of actuation. In our model, electrochemistry is described through the Poisson-Nernst-Planck system in terms of concentrations of cations and anions and voltage, which is solved through the finite element method. Based on computer simulations, we establish that Maxwell stress is the main driving force for the motion of the cilia.
