Low Water Uptake Research Articles

MPPE/SEBS Composites with Low Dielectric Loss for High-Frequency Copper Clad Laminates Applications.

Copper clad laminates (CCLs) with low dissipation factor (Df) are urgently needed in the fields of high-frequency communications devices. A novel resin matrix of modified poly (2,6-dimethyl-1,4-phenylene ether) (MPPE) and styrene-ethylene/butylene-styrene (SEBS) was employed in the fabrication of high-frequency copper clad laminates (CCLs). The composites were reinforced by E-glass fabrics, which were modified with phenyltriethoxysilane (PhTES). The composite laminates obtained exhibited impressive dielectric loss of 0.0027 at 10 GHz when the weight ratio of MPPE to SEBS was 5:1. In order to modify the dielectric constant (Dk), coefficient of thermal expansion (CTE) and other performances of laminates, Li2TiO3 (LT) ceramic powders were introduced into the resin matrix. The composite laminates showed low dielectric loss of 0.0026 at 10 GHz and relatively high flexural strength of 125 MPa when the mass ratio of LT fillers to resin is 0.4. Moreover, the composite laminates all maintain low water uptake (<0.5%). The microstructure and thermal properties of composite laminates filled with LT ceramic powders were also tested. These results show that copper clad laminates prepared with modified polyphenylene ether (MPPE)/SEBS and LT ceramic fillers have strong competitiveness to fabricate printed circuit boards (PCBs) for high-frequency and high-speed applications.

Quaternized poly(arylene ether benzonitrile) membranes for vanadium redox flow batteries

A series of quaternized poly (arylene ether benzonitrile)s (QAxCN; x = percent quaternization) were synthesized for the vanadium redox flow battery (VRFB) application. The presence of highly polar nitrile groups incorporated in the quaternized polymer chain provides desirable polymer properties (low water uptake, high dimensional stability and low VO2+ permeability) without compromising ion conductivity. VRFB single cells using the aforementioned membranes showed excellent performance. The cell using a 15 μm-thick QA50CN membrane exhibited superior coulombic efficiency (98.2%) and comparable energy efficiency (86.5%) at 40 mA cm-2 compared to the single cell using Nafion-212 with a coulombic efficiency of 95.5% and an energy efficiency of 86.2%. The cell cycling stability and membrane oxidative stability data confirmed that the QAxCN membranes have the potential to replace Nafion membranes for energy storage in VRFB applications.

Utilization of quinoa flour (Chenopodium quinoa Willd.) in gluten-free pasta formulation: Effects on nutritional and sensory properties.

In this study, raw and germinated quinoa seed flour was utilized in gluten-free pasta formulation. Rice:corn semolina (50:50) blend was used in gluten-free pasta as a control group. Quinoa flours were replaced with rice:corn semolina blend at different (0-30%) ratios in gluten-free pasta formulation. Guar gum (3%) was also used to tolerate structural defects caused by gluten deficiency. Trials were conducted according to (2 × 4) × 2 factorial design. Color values, cooking properties, and chemical and sensory attributes of gluten-free pasta samples were determined. Quinoa flour type and quinoa flour addition ratio factors significantly (p < 0.05) affected the L*, a* color values and all of the cooking properties of the gluten-free pasta samples. Utilization of germinated quinoa flour in gluten-free pasta revealed lower water uptake, volume increase, firmness, and higher cooking loss values than that of raw quinoa flour. Quinoa flour especially improved the mean values of protein, total phenolic content, antioxidant activity from 8.1%, 0.7 mg GAE/g, and 13.4%, up to 12.7%, 1.5 mg GAE/g, and 28.8%, respectively. A significant (p < 0.05) increment was observed in Ca, Fe, K, Mg, P, and Z content of the gluten-free pasta and all addition ratios of quinoa flour. As a result, increasing amount of quinoa flour enriched the nutritional composition of gluten-free pasta but high utilization ratio resulted in slight sensory losses.

Crosslinked poly(arylene ether sulfone) block copolymers containing quinoxaline crosslinkage and pendant butanesulfonic acid groups as proton exchange membranes

Crosslinkable poly (arylene ether sulfone) block copolymers (bSPAES (x/y)) containing pendant butanesulfonic acid and ethanedione groups were prepared from a new side-chain difluoro aromatic monomer 1-(2,6-difluorophenyl)-2-(3,5-dimethoxyphenyl)-1,2-ethanedione via block copolycondensation, demethylation, and further nucleophilic substitution of 1,4-butane sultone. Meanwhile, quinoxaline-based crosslinked block copolymers (C-bSPAES (x/y)) were obtained via cyclocondensation. The corresponding block copolymer membranes have high mechanical properties and anisotropic membrane swelling for either crosslinked or uncrosslinked ones. bSPAES (5/10) with ion exchange capacity (IEC) of 2.05 mequiv. g−1 has low water uptake (WU) of 59.1% at 80 °C but relatively high conductivity of 225 mS cm−1, which is ascribed to its good microphase separation. Meanwhile, the crosslinked C-bSPAES (5/10) with IEC of 1.76 mequiv. g−1 exhibits a decreased WU by half, an improved oxidative stability by 200% and a reduced membrane swelling by 40% than the uncrosslinked bSPAES (5/10). The results suggest that quinoxaline-based crosslinking can obviously improve properties of bSPAES (x/y). In addition, even though maximum power density of C-bSPAES (5/10) is lower than that of Nafion 212, C-bSPAES (5/10) still has an acceptable good single-cell performance, indicating a possible fuel cell application.

Rigid polyurethane foams modified with borate and oxamide groups – Preparation and properties

In this work the results of the research on modification of rigid polyurethane foams properties by new polyols with borate and oxamide groups have been presented. Propylene glycols — the products of hydroxyalkylation of N,N′-bis(2-hydroxypropyl)oxamide bis(dihydrogenborate) by excess of propylene carbonate (PC) was used as a polyol component. The new polyols have been foamed using polymeric 4,4′-diphenylmethane diisocyanate, water and triethylamine. The modification of the foam structure by oxamide and borate groups guarantees their low water uptake, very good heat-insulating properties, good dimension stability and decreases their flammability, and does not worsen their mechanical properties and thermal stability.

Preparation and Characterization of Semi-alicyclic Polyimides Containing Trifluoromethyl Groups for Optoelectronic Application.

Transparent polyimides (PI) films with outstanding overall performance are attractive for next generation optoelectronic and microelectronic applications. Semi-alicyclic PIs derived from alicyclic dianhydrides and aromatic diamines have proved effective to prepare transparent PIs with high transmittance. To optimize the combined properties of semi-alicyclic PIs, incorporating bulky trifluoromethyl groups into the backbones is regarded as a powerful tool. However, the lack of fundamental understanding of structure–property relationships of fluorinated semi-alicyclic PIs constrains the design and engineering of advanced films for such challenging applications. Herein, a series of semi-alicyclic PIs derived from alicyclic dianhydrides and trifluoromethyl-containing aromatic diamines was synthesized by solution polycondensation at high temperature. The effects of alicyclic structures and bulky trifluoromethyl groups on thermal, dielectric and optical properties of PIs were investigated systematically. These PI films had excellent solubility, low water absorption and good mechanical property. They showed high heat resistance with Tg in the range of 294–390 °C. It is noted that tensile strength and thermal stability were greatly affected by the rigid linkages and alicyclic moieties, respectively. These films exhibited obviously low refractive indices and significantly reduced dielectric constants from 2.61 to 2.76, together with low optical birefringence and dielectric anisotropy. Highly transparent films exhibited cutoff wavelength even as low as 298 nm and transmittance at 500 nm over 85%, displaying almost colorless appearance with yellowness index (b*) below 4.2. The remarkable optical improvement should be mainly ascribed to both weak electron-accepting alicyclic units and bulky electron-withdrawing trifluoromethyl or sulfone groups. The present work provides an effective strategy to design molecular structures of optically transparent PIs for a trade-off between solution-processability, low water uptake, good toughness, high heat resistance, low dielectric constant and excellent optical transparency.

Influence of organically modified nanoclay and TiO2 nanopowder on the properties of Azadirachta indica wood flour-reinforced high-density polyethylene, low-density polyethylene, polypropylene, and polyvinyl chloride nanocomposite

The nanocomposites of high-density polyethylene, low-density polyethylene, polypropylene, and poly(vinyl chloride) reinforced with Azadirachta indica wood flour (WF) and different amounts of the organomodified nanoclay and titanium dioxide (TiO2) nanopowder were produced by melt-blending process followed by compression molding. Polyethylene- co-glycidyl methacrylate (PE- co-GMA) was used as a compatibilizer. TiO2 nanopowder was synthesized by sol–gel method and characterized using transmission electron microscopy (TEM). The average size of the synthesized nano-TiO2 was 17.5 nm, which was confirmed both by TEM and X-ray diffraction (XRD) study. The distribution of nanoparticles in the nanocomposites was also examined by the XRD study. The surface modification of the TiO2 nanoparticles by organic surfactant cetyl trimethyl ammonium bromide and their interaction with the wood and the polymer were studied by Fourier transform infrared spectroscopy. Incorporation of compatibilizer PE- co-GMA, nanoclay, and nano-TiO2 significantly influenced the mechanical and thermal properties of the WF-reinforced composites. Wood polymer composites (WPC) reinforced with nanoclay and nano-TiO2 showed improved tensile strength, tensile modulus, flexural strength, flexural modulus, and hardness. Maximum improvement in mechanical properties was shown by WPC loaded with 40 phr WF, 2 phr nanoclay, and 2 phr of nano-TiO2. On inclusion of organically modified nanoclay and nano-TiO2, the WPC samples showed lower water uptake and higher chemical resistance. The nanocomposites were further examined by TEM study and thermogravimetric analyzer.

Stability of flexible thin-film metallization stimulation electrodes: analysis of explants after first-in-human study and improvement of in vivo performance

Objective. Micro-fabricated neural interfaces based on polyimide (PI) are achieving increasing importance in translational research. The ability to produce well-defined micro-structures with properties that include chemical inertness, mechanical flexibility and low water uptake are key advantages for these devices. Approach. This paper reports the development of the transverse intrafascicular multichannel electrode (TIME) used to deliver intraneural sensory feedback to an upper-limb amputee in combination with a sensorized hand prosthesis. A failure mode analysis on the explanted devices was performed after a first-in-human study limited to 30 d. Main results. About 90% of the stimulation contact sites of the TIMEs maintained electrical functionality and stability during the full implant period. However, optical analysis post-explantation revealed that 62.5% of the stimulation contacts showed signs of delamination at the metallization-PI interface. Such damage likely occurred due to handling during explantation and subsequent analysis, since a significant change in impedance was not observed in vivo. Nevertheless, whereas device integrity is mandatory for long-term functionality in chronic implantation, measures to increase the bonding strength of the metallization-PI interface deserve further investigation. We report here that silicon carbide (SiC) is an effective adhesion-promoting layer resisting heavy electrical stimulation conditions within a rodent animal trial. Optical analysis of the new electrodes revealed that the metallization remained unaltered after delivering over 14 million pulses in vivo without signs of delamination at the metallization-PI interface. Significance. Failure mode analysis guided implant stability optimization. Reliable adhesion of thin-film metallization to substrate has been proven using SiC, improving the potential transfer of micro-fabricated neural electrodes for chronic clinical applications. (Document number of Ethical Committee: P/905/CE/2012; Date of approval: 2012–10-04)

An investigation on hygroscopic properties of 15 black carbon (BC)-containing particles from different carbon sources: roles of organic and inorganic components

Abstract. The hygroscopic behavior of black carbon (BC)-containing particles (BCPs) has a significant impact on global and regional climate change. However, the mechanism and factors controlling the hygroscopicity of BCPs from different carbon sources are not well understood. Here, we systematically measured the equilibrium and kinetics of water uptake by 15 different BCPs (10 herb-derived BCPs, 2 wood-derived BCPs, and 3 soot-type BCPs) using a gravimetric water vapor sorption method combined with in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). In the gravimetric analysis, the sorption–desorption equilibrium isotherms were measured under continuous-stepwise water vapor pressure conditions, while the kinetics was measured at a variety of humidity levels obtained by different saturated aqueous salt solutions. The equilibrium water uptake of the tested group of BCPs at high relative humidity (&gt;80 %) positively correlated to the dissolved mineral content (0.01–13.0 wt %) (R2=0.86, P=0.0001), the content of the thermogravimetrically analyzed organic carbon (OCTGA, 4.48–15.25 wt %) (R2=0.52, P=0.002), and the content of the alkali-extracted organic carbon (OCAE, 0.14–8.39 wt %) (R2=0.80, P=0.0001). In contrast, no positive correlation was obtained with the content of total organic carbon or elemental carbon. Among the major soluble ionic constituents, chloride and ammonium were each correlated with the equilibrium water uptake at high relative humidity. Compared with the herbal BCPs and soot, the woody BCPs had much lower equilibrium water uptake, especially at high relative humidity, likely due to the very low dissolved mineral content and OC content. The DRIFTS analysis provided generally consistent results at low relative humidity. The kinetics of water uptake (measured by pseudo-second-order rate constant) correlated to the content of OCTGA and OCAE as well as the content of chloride and ammonium at low relative humidity (33 %) but to the porosity of BCPs at high relative humidity (94 %). This was the first study to show that BCPs of different types and sources had greatly varying hygroscopic properties.

Anion Exchange Membranes Prepared from Quaternized Polyepichlorohydrin Cross-Linked with 1-(3-aminopropyl)imidazole Grafted Poly(arylene ether ketone) for Enhancement of Toughness and Conductivity.

A novel anion exchange membrane was synthesized via crosslinking of the quaternized polyepichlorohydrin (QPECH) by 1-(3-aminopropyl) imidazole grafted poly(arylene ether ketone) (PAEK-API). While the QPECH provided an excellent ion conductive property, the rigid rod-structured PAEK-API played a reinforcing role, along with providing the high conductivity associated with the pendant API group. The chemical structure of QPECH/PAEK-API membranes was identified by 1H nuclear magnetic resonace spectroscopy. A variety of membrane properties, such as anion conductivity, water uptake, length swelling percentage, and thermal, mechanical and chemical stability, were investigated. The QPECH/PAEK-API1 membrane showed quite high hydroxide ion conductivity, from 0.022 S cm−1 (30 °C) to 0.033 S cm−1 (80 °C), and excellent mechanical strength, associated with the low water uptake of less than 40%, even at 80 °C. Such high conductivity at relatively low water uptake is attributed to the concentrated cationic groups, in a cross-linked structure, facilitating feasible ion transport. Further, the QPECH/PAEK-API membranes showed thermal stability up to 250 °C, and chemical stability for 30 days in a 4 NaOH solution, without significant loss of ion exchange capacity.

Sulfonated co‐poly(ether imide)s with alkyne groups: Fabrication of crosslinked membranes and studies on PEM properties including MFC performance

AbstractA new diamine monomer having alkyne side‐groups (DADAF) has been successfully synthesized, and it was used to prepare a series of sulfonated co‐polyimides (DFN‐XX) when reacted with 1,4,5,8‐naphthalenetetracarboxylic dianhydride along with different mole% of 4,4′‐diaminostilbene‐2,2′‐disulfonic acid. The membrane was made from the copolymers by solution casting route, and one of the copolymers DFN‐70 was used to prepare crosslinked membranes by adding a different amount of 1,6‐hexanediazide during solution casting step. The morphological transformation from non‐crosslinked S‐coPI to crosslinked S‐coPI was observed by employing transmission electron microscopy, atomic force microscopy, and small‐angle X‐ray scattering analyses. Compared to the non‐crosslinked DFN‐XX membranes, crosslinked DFN‐70 copolymer membranes showed low water uptake and improved mechanical and peroxide radical stability. Also, crosslinked DFN‐70 copolymer membranes showed significantly higher proton conductivities (0.004‐0.06 S cm−1) compared to those of DFN‐70 (0.003‐0.05 S cm−1) particularly, at 80°C when the relative humidity increased from 40% to 98%. Furthermore, crosslinked DFN‐70 copolymer membranes exhibited significantly enhanced performance in a microbial fuel cell (MFC) as compared to those of non‐crosslinked DFN‐70 membrane.

Contribution of calcium aluminates to the water resistance of hydrated calcium sulfates

The water sensitivity of calcium sulphate materials has been known for a long time. In a humid atmosphere, plaster elements can become veiled under the action of their own weight because a low water uptake of 3% by mass can cause a drop in compressive strength of 50%. The low water resistance of calcium sulfates limits the applications of these materials to decorative elements or interior coatings despite their strengths compared to other construction materials: good fire resistance, low CO2 emission and low production cost. The objective of our research work is to evaluate the insensitivity of calcium sulfates to water by ettringitic binders containing calcium aluminate cement (CAC). Four types of calcium sulfates have been studied: natural gypsum, hemihydrate-α, hemihydrate-β, and synthetic anhydrite. In this research, only the majority binders of calcium sulfates will be studied: [70%, 80% of Calcium sultates with 30%, 20% of CAC]. The experiments results have shown that in high-calcium sulphate binders (≥ 70%), CAC helps reduce the water sensitivity of binders regardless of the nature of calcium sulphate by decreasing the total porosity, which leads to an increase in mechanical strengths; and reducing the connectivity of the pores, which contributes to reducing the entry of water and its movements into the material and consequently, reducing the degradation of the test pieces during immersion tests in the water.

Surfactant-Free Latex Nanocomposites Stabilized and Reinforced by Hydrophobically Functionalized Cellulose Nanocrystals

Stable poly(styrene-co-2-ethylhexyl acrylate) latex particles with diameter less than 600 nm were prepared by the miniemulsion polymerization of Pickering emulsions stabilized with hexyl-functionalized cellulose nanocrystals (CNC-hexyl-COOHs). Polymer nanocomposites were fabricated by casting of the CNC-stabilized latex particles, and the thermomechanical properties and microstructures of the films were studied and related to the type and amount of stabilizer as well as the processing conditions. Compared to the latex films stabilized with low-molecular-weight sodium dodecyl sulfate (SDS) surfactant, or using a combination of SDS and carboxylic acid CNC-COOHs, films stabilized solely with the alkyl-functionalized CNC-hexyl-COOHs showed much higher storage moduli in the rubbery regime and lower water uptake. Scanning electron microscopy (SEM) revealed a CNC network structure that is formed by excluded volume effects of the latex particles, which concentrates the CNC-hexyl-COOHs into the interstitial space during solvent evaporation. This effect results in the formation of a percolation network at a lower CNC concentration within the latex composite films. The network can be further reinforced by increasing the concentration of CNCs through an “ex situ” process where CNC-hexyl-COOH-stabilized latex particles were mixed with CNC-COOH aqueous dispersions before film casting. The ability to replace low-molecular-weight surfactants in water-based latexes with alkyl-functionalized CNCs that are not only biosourced but also act as reinforcing agents offers an opportunity to expand the property profile of a variety of commercial products such as paints, coatings, and adhesives.

Imidazolium functionalized poly(vinyl alcohol) membranes for direct methanol alkaline fuel cell applications

AbstractIn this study, imidazolium functionalized poly(vinyl alcohol) (PVA) was synthesized by acetalization and direct quaternization reaction. Afterwards, composite anion exchange membranes based on imidazolium‐ and quaternary ammonium‐ functionalized PVA were used for direct methanol alkaline fuel cell applications. 1H NMR and Fourier transform infrared spectroscopy data indicated that imidazole functionalized PVA was successfully synthesized. Inductively coupled plasma mass spectrometry data demonstrated that the imidazolium structure was efficiently obtained by direct quaternization of the imidazole group. Composite anion exchange membranes were fabricated by application of the functionalized PVA solution on the surface of porous polycarbonate (PC) membranes. Fuel cell related properties of all prepared membranes were investigated systematically. The imidazolium functionalized composite membrane (PVA‐Im/PC) exhibited higher ionic conductivity (7.8 mS cm−1 at 30 °C) despite a lower water uptake and ion exchange capacity value compared to that of quaternary ammonium. In addition, PVA‐Im/PC showed the lowest methanol permeation rate and the highest membrane selectivity as well as high alkaline and oxidative stability. Dynamic mechanical analysis results reveal that both composite membranes were mechanically resistant up to 107 Pa at 140 °C. The superior performance of imidazolium functionalized PVA composite membrane compared to quaternary ammonium functionalized membrane makes it a promising candidate for direct methanol alkaline fuel cell applications. © 2020 Society of Chemical Industry

Mechanical, thermal properties and stability of high renewable content liquefied residual biomass derived bio-polyurethane wood adhesives

Bio-polyurethane adhesives (bio-PU) of high renewable content (up to 87%) were produced using biomass biopolyols obtained previously via crude-glycerol mediated solvothermal liquefaction of three industrial biomass residue feedstocks: digested sewage sludge, hemp stalk hurds and sugar beet pulp, and commercial pentamethylene diisocyanate. The produced adhesives were capable of exhibiting tensile strength values within the threshold of two commercially available polyurethane (PU) wood adhesives (5.77–11.03 MPa). Varying biomass feedstock particle size and dry matter content, adhesive formulation isocyanate to hydroxyl group ratios and biomass biopolyol blending with blank crude glycerol biopolyol showed varying effects on the adhesives produced. Although bio-PU adhesives exhibited lower thermal stability, the non-flame retarded adhesives showed lower potential for fire spread and nearly identical flammability with lower heat release rates in the cone calorimeter. In terms of fire toxicity, biopolyol adhesives were found to be less toxic in well-ventilated flaming fire scenarios, with significantly lower smoke and CO production than the commercial formulation. However, both commercial and biopolyol adhesives yielded significant quantities of CO and HCN toxicants when tested in under-ventilated and post-flashover fire scenarios. Here, the tested bio-PU bound wood system exhibited 25–30% higher fractional effective doses compared to the commercial PU adhesive analogue. The biopolyol adhesives were much more hydrophilic (water uptake of up to 119%), less stable dimensionally (max. elongation of 3%), contained significantly more water soluble components (up to 43%), and biodegraded at higher rates (up to 0.89%/month), compared to commercial PU. They were, nonetheless, hydrolytically stable as their tensile strengths did not decrease below levels after water soaking and drying. Overall, the adhesives produced show promise as sustainable alternatives in applications where high thermal stability and low water uptake are not crucial parameters.

Reinforcement of Nafion Membranes with Electrospun PVDF-HFP Fibers for PEM Water Electrolyzers

In this work, we present a procedure for the fabrication of Nafion composite membranes reinforced with electrospun PVDF-HFP fibers to enhance the mechanical stability of thin membranes for the PEMWE application. The presented fabrication procedure combines the spray coating with the electrospinning technique by successively depositing thin Nafion layers and PVDF-HFP fiber mats. The fabrication approach allows a high freedom of design in terms of the final membrane thickness, the position of the fiber mat and the fiber to Nafion ratio. Furthermore, the approach enables the integration of a reinforcement layer into the novel direct membrane deposition (DMD) MEA design by depositing the reinforced membrane directly on the cathode electrode.The mechanical properties were analysed by means of a tensile test. Thin unreinforced and reinforced Nafion membranes with a thickness of approximately 60 µm with varying fiber loadings were fabricated. The best mechanical strength was determined for reinforced membranes with a fiber loading of 0.12 mgfiber/cm2. This yielded an average E-modulus of 215 MPa and break strain of 40 % compared to unreinforced membranes with an average E-modulus of 198 MPa and break strain of 18 %. The mechanical strength did not further improve with an increased fiber loading, but instead was found to decrease strongly. By use of confocal light microscopy and Raman microscopy, it was shown that sufficient infiltration of the PVDF-HFP fiber mats with Nafion was limited due to a low material compatibility of the highly hydrophobic fibers with Nafion. Subsequently, insufficient infiltration resulted in the entrapment of air voids inside the porous fiber structure. The percentage of air voids drastically increases with an increasing fiber loading. As a result, non-continuous, defective membranes were obtained which explained the observed decrease of mechanical strength for higher fiber loadings.It was found that an effective method to reduce the number of air voids and thus circumvent infiltration limitations could be achieved by hot pressing the membrane as post-fabrication treatment at a temperature close to or above the glass transition temperature of Nafion. Simultaneously, the mechanical strength of the Membrane is improved. In a tensile test it was shown that the hot pressing of unreinforced membranes improved the mechanical stability with an average E-modulus of 220 MPa and a break strain of 38 %. Using confocal Raman microscopy it was determined that the higher mechanical strength was attributed to a lower water uptake of hot pressed membranes as compared to the untreated membranes. This is likely due to a realignment of the mechanically stable PTFE backbone and the hydrophilic sidechain units during hot pressing.In order to electrochemically characterize composite membranes and test them in their actual application, PEMWE cell tests were conducted. Reinforced DMD MEAs with a membrane thickness of 50 µm and a fiber loading of 0.12 mgfiber/cm2, corresponding to a fiber/Nafion ratio of 1.4 wt.%, were fabricated. In addition to untreated reinforced DMD MEAs, reinforced DMD MEAs were subjected to post-fabrication hot pressing. It was proven that the fiber reinforcement approach presented in this work is applicable to real operating PEMWE systems. Furthermore, it was shown that DMD MEAs can be subjected to post-fabrication treatments without impairing the performance. The robustness and handling of MEAs was found to be improved through both the reinforcement layer and the treatments. Figure 1

Poly(vinyl alcohol) Membranes Cross‐linked with Maleic Anhydride and 2,5‐Furandicarboxylic Acid: Conventional Heating and Microwave Irradiation

AbstractPoly(vinyl alcohol) (PVA) was cross‐linked with maleic anhydride (MA) and 2,5‐furandicarboxylic acid (FDCA) under conventional heating (CH) and microwave irradiation (MW) to obtain different membranes of PVA/MA and PVA/FDCA modified by the cross‐linking agent concentration, reaction time and type of activation method. The influence of the latter parameters, was studied by comparing the swelling degree of the membranes, swelling kinetics, solubility parameter (δ), Flory interaction parameter (χ12), molecular weight between cross‐links (Mc) and the fractional free volume (FFV).Conditions to cross‐link the membranes were chosen from swelling percentage tests and the samples with the lowest water uptake were characterized by means of Fourier transform infrared spectroscopy (FTIR), 13C nuclear magnetic resonance (13C NMR), thermogravimetric analysis (TGA) and atomic force microscopy (AFM). MW activation used from 23 to 30 minutes to cross‐link the membranes, meanwhile, conventionally heated samples were introduced in an oven for 120 min, meaning that MW activation provided high reaction yields in shorter times. For both activation methods, FTIR spectra recorded peaks in an interval of 1706–1713 cm−1, and 13C NMR presented signals from 162 to 171 ppm, meaning that carbonyl groups from esters were formed. AFM images showed that the rise in roughness was not necessarily directly proportional to the increase in the concentration of cross‐linking agent.

Poly(ester imide)s Possessing Low Coefficients of Thermal Expansion and Low Water Absorption (V). Effects of Ester-linked Diamines with Different Lengths and Substituents.

A series of ester-linked diamines, with different lengths and substituents, was synthesized to obtain poly(ester imide)s (PEsIs) having improved properties. A substituent-free ester-linked diamine (AB-HQ) was poorly soluble in N-methyl-2-pyrrolidone at room temperature, which forced the need for polyaddition by adding tetracarboxylic dianhydride solid into a hot diamine solution. This procedure enabled the smooth progress of polymerization, however, accompanied by a significant decrease in the molecular weights of poly(amic acid)s (PAAs), particularly when using hydrolytically less stable pyromellitic dianhydride. On the other hand, the incorporation of various substituents (–CH3, –OCH3, and phenyl groups) to AB-HQ was highly effective in improving diamine solubility, which enabled the application of the simple polymerization process without the initial heating of the diamine solutions, and led to PAAs with sufficiently high molecular weights. The introduction of bulkier phenyl substituent tends to increase the coefficients of thermal expansion (CTE) of the PEsI films, in contrast to that of the small substituents (–CH3, –OCH3). The effects of ester-linked diamines, consisting of longitudinally further extended structures, were also investigated. However, this approach was unsuccessful due to the solubility problems of these diamines. Consequently, the CTE values of the PEsIs, obtained using longitudinally further extended diamines, were not as low as we had expected initially. The effects of substituent bulkiness on the target properties, and the dominant factors for water uptake (WA) and the coefficients of hygroscopic expansion (CHE), are also discussed in this study. The PEsI derived from methoxy-sustituted AB-HQ analog and 3,3′,4,4′-biphenyltetracarboxylic dianhydride achieved well-balanced properties, i.e., a very high Tg (424 °C), a very low CTE (5.6 ppm K−1), a low WA (0.41%), a very low CHE value (3.1 ppm/RH%), and sufficient ductility, although the 26 μm-thick film narrowly missed certification of the V-0 standard in the UL-94V test. This PEsI film also displayed a moderate εr (3.18) and a low tan δ (3.14 × 10−3) at 10 GHz under 50% RH and at 23 °C. Thus, this PEsI system is a promising candidate as a novel dielectric substrate material for use in the next generation of high-performance flexible printed circuit boards operating at higher frequencies (≥10 GHz).

The effect of silk fibroin nanoparticles on the morphology, rheology, dynamic mechanical properties, and toughness of poly(lactic acid)/poly(ε‐caprolactone) nanocomposite

AbstractThe silk fibroin nanoparticles (SFNPs) were extracted from silkworm cocoons and used as a nanofiller in poly(lactic acid) (PLA)/poly(ε‐caprolactone) (PCL) blend. The nanoparticle localization was studied theoretically and experimentally and the effects of SFNP on the morphology, rheology, toughness, and dynamic mechanical properties of the blend were investigated. According to the calculated wetting coefficient, SFNP should be thermodynamically located in the PLA matrix during the melting process. The results of SEM illustrated a common sea‐island structure for the PLA/PCL blend and the incorporation of SFNP reduced the PCL domain sizes from 1.170 ± 92 μm to 794 ± 46 nm. The atomic force microscopy results showed that the nanoparticles are mainly located in the PLA matrix and also, partially at the phase interface with a thickness of layers around 80 nm. The rheological tests displayed the network formation of SFNP in the prepared nanocomposites. The dynamic mechanical analysis revealed that by the addition of SFNP, the storage modulus of neat PLA and PLA/PCL blend were increased by around 57 and 50%, respectively and the glass transition temperatures (Tg) values of PLA and PCL shifted toward each other. Additionally, using SFNP caused a lower water uptake and higher impact strength (~64%) of the blend.

40SiO2–40P2O5–20ZrO2 sol-gel infiltrated sSEBS membranes with improved methanol crossover and cell performance for direct methanol fuel cell applications

Membranes commonly used in direct methanol fuel cell (DMFC) are expensive and show a great permeability to methanol which reduces fuel utilization and leads to mixed potential at the cathode. In this work, sulfonated styrene-ethylene-butylene-styrene (sSEBS) modified membranes with zirconia silica phosphate sol-gel phase are developed and studied in order to evaluate their potential use in DMFC applications. The synthesized hybrid membranes and sSEBS are subjected to an exhaustive physicochemical characterization by liquid uptake, ion exchange capacity, atomic force microscopy, X-ray photoelectron spectroscopy and dynamic mechanical and thermogravimetric analyses. Likewise, the potential use of the prepared membranes in DMFC is evaluated by means of electrochemical characterizations in single cell, determining the limiting methanol crossover current densities, proton conductivities and DMFC performances. The hybrid membranes show lower water and methanol uptakes, higher stiffness, water retention capability, upper power density and lower methanol crossover than sSEBS and Nafion 112.