Search Results (45)

The thermal resistance of carbon fiber–reinforced poly(phenylene sulfide) to harsh oxidative conditions is investigated through thermogravimetric experiments performed in an oxygen atmosphere. While these materials usually show great resistance against thermal decomposition in a nitrogen atmosphere, the experiments in oxygen reveal the total decomposition of both the matrix and the carbon fibers. The Gram–Schmidt signal, obtained by coupling thermogravimetric analysis in standard conditions with Fourier-transform infrared spectroscopy, exhibits multiple events, evidencing that the decomposition proceeds through distinct stages. The first step characterizes the char formation, while the second relates to its oxidative decomposition. A third step, only observed for composites, is interpreted as the signature of the oxidative decomposition of carbon fibers. To mimic the sudden elevation of temperature encountered during a fire, the analyses are performed at rates of up to 500 K min⁻¹. These specific experimental conditions reveal a complex dependence of the thermogravimetric signature on the heating rate. Independent of the atmosphere, nitrogen or oxygen, the characteristic temperature of decomposition follows a bell-shape trend, resulting from the combination of lag effects and thermal-conductivity limitations. Additionally, the increase of the heating rate causes the Gram–Schmidt signal to evolve toward a broad peak with indistinct events. To investigate whether these changes affect the decomposition products, the infrared spectra, continuously recorded to probe the whole decomposition, are compared with those from the database. The char formation is characterized by the production of sulfur dioxide, while carbon dioxide is the main product emitted during both char and fiber oxidative decomposition. Owing to the merging of the decomposition stages, sulfur-dioxide detection is partly supplanted by that of carbon dioxide under fast elevations of temperature. Full article

This study investigates the optimization of polyphenylene oxide (PPO) electrospinning for interlaminar toughening in composites, using sulfonation modification and physical blending with polylactic acid (PLA) and polystyrene (PS). Both strategies showed excellent electrospinning performance, significantly reducing fiber diameter (PPO: 12.1 ± 5.8 μm; sulfonated PPO: 524 ± 42 nm; PPO-PLA: 4.73 ± 0.94 μm; PPO-PS: 3.43 ± 0.34 μm). In addition, the PPO-PS fibers were uniform, while PPO-PLA exhibited a mixture of fine and coarse fibers due to phase separation. Interlaminar fracture toughness testing showed that PPO-PS offered the greatest toughening, with G_ICⁱⁿⁱ and G_IC^pre increasing by 223% and 232%, respectively, compared to the values of the untoughened sample, and by 65% and 61.5% compared to those of the PPO sample. G_IIC of the PPO-PS sample was 196% greater than that of the untoughened sample and 30% higher than that of the PPO sample. Scanning electron microscope (SEM) analysis of fracture morphology revealed that the high-toughness system dissipated energy through fiber bridging, plastic deformation, and multi-scale crack deflection, while the low-toughness samples failed due to interface debonding or cohesive failure. This work demonstrates that PPO-PS veils enhance interlaminar toughness through interface reinforcement and multiple toughening mechanisms, providing an effective approach for high-performance composites. Full article

To understand the effect of the hydroxyl group and processing temperatures on dielectric losses of flame retardants and flame-retardant polymers, the performance difference between 6-methyldibenzo[c,e][1,2]oxaphosphinine 6-oxide (DOPO-Me) and 6-(hydroxymethyl)dibenzo[c,e][1,2]oxaphosphinine 6-oxide (DOPO-HM) has been investigated, respectively, in non-polar and polar polymers at 7–20 GHz. DOPO-HM and DOPO-Me differ by only one OH group. The former demonstrates a lower dissipation factor (Df) than the latter, owing to hydrogen bonds. In polystyrene and crosslinked polyphenylene oxide, both flame retardants increase a dielectric loss of flame-retardant polymers, with DOPO-HM being less detrimental because of its higher crystallizability and lower plasticization. In polar poly(methyl methacrylate) (PMMA), conformational changes in PMMA main chains caused by flame retardants and high processing temperatures lead to an early Df drop of PMMA at low loadings of the flame retardants. At high loadings, a change in the physical form of flame retardants from a primitive crystalline state to an amorphous state increases a dielectric loss of flame retardant PMMA, with DOPO-HM resulting in a slightly higher dielectric loss than DOPO-Me. These results prove that the effect of a hydroxyl group in organophosphorus structures on the dielectric loss of flame-retardant polymers is crucially dependent on its interaction with the polymer matrix. Full article

The time-lag method is commonly used to determine membrane permeability, diffusivity and solubility in a single gas permeation experiment in a constant volume system. An unwritten assumption on which this method relies is that there is no resistance to gas accumulation in the downstream receiver of the system. However, this is not the case, even with the specially designed receiver used in this study when, in addition to tubing, the receiver utilizes an additional accumulation tank. The resistance to gas accumulation originates from a finite diffusivity (Knudsen diffusion) of gases in tubing, which are magnified by “resistance-free” accumulation tank(s). As a result of the resistance to gas accumulation, the time lag of the membrane is underestimated, which leads to an overestimation of gas diffusivity in the membrane. The experimentally predicted resistances in different configurations of the receiver, expressed by the difference in the time lag at two different receiver locations, were several times greater than the theoretically predicted values. A high molecular PPO membrane was used to demonstrate this effect. The time lags measured at different locations differed by as much as 30%. The diffusivity of nitrogen in a PPO of 4.04 × 10⁻¹² m²/s determined at the optimum configuration of the receiver is at least 50% lower than the literature-reported values. Full article

Plant-derived PA10T is regarded as one of the most promising semi-aromatic polyamides; however, shortcomings, including low dimensional accuracy, high moisture absorption, and relatively high dielectric constant and loss, have impeded its extensive utilization. Polymer blending is a versatile and cost-effective method to fabricate new polymeric materials with excellent comprehensive performance. In this study, various ratios of PA10T/PPO blends were fabricated via melt blending with the addition of a SEBS-g-MAH compatibilizer. Molau test and scanning electron microscopy (SEM) were employed to study the influence of SEBS-g-MAH on the compatibility of PA10T and PPO. These studies indicated that SEBS-g-MAH effectively refines the domain size of the dispersed PPO phase and improves the dispersion stability of PPO particles within a hexafluoroisopropanol solvent. This result was attributed to the in situ formation of the SEBS-g-PA10T copolymer, which serves as a compatibilizer. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) results showed that the melting–crystallization behavior and thermal stability of blends closely resembled that of pure PA10T. Dynamic mechanical analysis (DMA) revealed that as the PPO content increased, there was a decrease in the glass transition temperature and storage modulus of PA10T. The water absorption rate, injection molding shrinkage, dielectric properties, and mechanical strength of blends were also systematically investigated. As the PPO content increased from 10% to 40%, the dielectric loss at 2.5 GHz decreased significantly from 0.00866 to 0.00572, while the notched Izod impact strength increased from 7.9 kJ/m² to 13.7 kJ/m². Full article

The use of thermoplastic composites (TPCs) as one of the lightweight solutions will inevitably encounter problems in connection. Resistance welding has the characteristics of high strength, simplicity, and high reliability, and is considered a very potential hot-melt connection technology. The resistance welding technology of unidirectional carbon fiber-reinforced polyphenylene sulfide composites (UCF/PPS) was systematically studied. The experimental results show that the 100-mesh brass mesh has the best resin wetting effect and heating efficiency, and the PPS/oxidized 100-mesh brass mesh composite resistance element (Ox-RE/PPS) has the highest welding strength. The welding failure mode changes from interface failure and RE failure to interlayer structure damage and fiber fracture. The single-factor experimental results show that the maximum welding strength is reached at 310 °C, 1.15 MPa, and 120 kW/m². According to the conclusion of the single-factor experiment, the Box–Behnken method was further used to design a three-factor, three-level experiment, and a quadratic regression model was established according to the test results. The results of variance analysis, fitting curve analysis, and perturbation plot analysis proved that the model had high fitting and prediction abilities. From the 3D surface diagram analysis, the influence of power density is the largest, and the interaction between welding temperature and power density is the most significant. Combined with the analysis of Design Expert 13 software, the optimal range of process parameters was obtained as follows: welding temperature 313–314 °C, welding pressure 1.04–1.2 MPa, and power density 124–128 kW/m². The average strength of resistance welding joints prepared in the optimal range of process parameters was 13.58 MPa. Full article

With the rapid development of highly integrated electronic devices and high-frequency microwave communication technology, the parasitic resistance–capacitance (RC) delay and propagation loss severely restrict the development of a high-frequency communication system. Benefiting from its low dielectric constants (D_k) and low dielectric loss factor (D_f), polyphenylene oxide (PPO) has attracted widespread attention for its application in the dielectric layers of integrated circuits. However, PPO suffers from a very high melting viscosity, a larger coefficient of thermal expansion than copper wire and poor solvent resistance. Recently, many efforts have focused on the modification of PPO by various means for communication applications. However, review articles focusing on PPO are unexpectedly limited. In this article, the research progress concerning PPO materials in view of the modification of PPO has been summarized. The following aspects are covered: polymerization and design of special chemical structure, low molecular weight PPO and blending with thermosetting resin, hyperbranched PPO, thermosetting PPO and incorporating with fillers. In addition, the advantages and disadvantages of various types of modification methods and their applications are compared, and the possible future development directions are also proposed. It is believed that this review will arouse the interest of the electronics industry because of the detailed summary of the cutting-edge modification technology for PPO. Full article

A set of polyphenylene oxides incorporating DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) functionality, denoted as DOPO−R−PPO, was synthesized by copolymerization of 2,6-dimethylphenol (2,6-DMP) with various DOPO-substituted tetramethyl bisphenol monomers. In the initial step, a Friedel–Crafts acylation reaction was employed to react 2,6-DMP with different acyl chlorides, leading to the formation of ketone derivatives substituted with 2,6-dimethylphenyl groups. Subsequently, the ketones, along with DOPO and 2,6-DMP, underwent a condensation reaction to yield a series of DOPO-substituted bisphenol derivatives. Finally, polymerizations of 2,6-dimethylphenol with these DOPO-substituted bisphenols were carried out in organic solvents using copper(I) bromide/N-butyldimethylamine catalysts (CuBr/DMBA) under a continuous flow of oxygen, yielding telechelic PPO oligomers with DOPO moieties incorporated into the polymer backbone. The chemical structures of the synthesized compounds were characterized using various analytical techniques, including Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (¹H NMR), phosphorus nuclear magnetic resonance (³¹P NMR), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). When compared to conventional poly(2,6-dimethyl-1,4-phenylene oxide)s with a similar molecular weight range, all DOPO−PPOs exhibited higher glass transition temperatures, enhanced thermal degradability, and increased char yield formation at 800 °C without compromising solubility in organic solvents. Full article

As an emerging contaminant, the presence of microplastics is widespread in the environment. However, current research regarding the removal of microplastics by drinking water treatment plants (DWTPs) remains insufficient. This study aims to investigate microplastics in water and sludge in four DWTPs in Zhengzhou; these DWTPs have different water sources. The results revealed that the abundance of microplastics in raw water ranged from 12.80 ± 0.80 to 25.07 ± 1.67 n/L. Overall, fibers and fragments ranging from 10 to 100 μm constituted the primary components. The proportion of white and transparent microplastics was the highest. Among the ten polymer types detected, polyvinyl chloride, polyphenylene oxide, and polyethylene terephthalate were the predominant ones in raw water; polyethylene terephthalate emerged as the prevalent polymer type in treated drinking water, with both polyethylene terephthalate and polyvinyl chloride being primarily present in sludge. The removal rate of microplastics ranged from 45.8% to 74.5%. Furthermore, the removal rates at the sedimentation tank outlet accounted for more than 50.0% of the total removal rate. The abundance of microplastics in sludge was significantly higher than that in water, indicating a concentrated environment for the persistence of microplastics. The proper disposal of sludge has emerged as one of the challenges requiring our attention. Full article

The effect of water, methanol, and hexane vapors on gas permeability was studied in a hybrid membrane containing 5 wt% copolyimide brushes with poly(methyl methacrylate) side chains (PI-g-PMMA) in a poly(phenylene oxide) (PPO) matrix, and in a pristine PPO membrane. These membranes in the form of dense nonporous films were further examined by atomic force microscopy (AFM) and scanning electron microscopy (SEM), as well as by measuring their mechanical and gas transport properties. A gas separation study of the membranes in a dry state and the membranes saturated with water, methanol, and hexane vapors was performed to estimate the effect of each vapor on the H₂, CO₂, N₂ permeability and selectivity in the separation of H₂/N₂ and CO₂/N₂ pairs. In general, saturation with water, methanol, and hexane vapors caused a decrease in the gas permeability of both membranes. The hybrid membrane containing copolyimide brushes demonstrated enhanced selectivity in the separation of H₂/N₂ and CO₂/N₂ pairs. It was found that a special effect of the vapors used for membrane saturation is associated with their molar volume. The solubility and diffusion coefficients of N₂ and CO₂ were obtained by Grand Canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations. Full article

In this study, carbon nanotubes (CNTs) are functionalized through diazonium salt reaction to introduce polar groups onto their surfaces. These functionalized CNTs (FCNTs) are added into PPO solutions at different loadings (0 wt%, 0.5 wt%, 1 wt%, 1.5 wt%) and used for electrospinning. The results show that the addition of FCNTs facilitate the production of PPO veils having small fiber diameters. The veils are used as interleaves in CF/EP composite laminates. The Mode I and Mode II interlaminar fracture toughness tests reveal that PPO veils containing 0.5 wt% FCNTs exhibit the optimal toughening. G_ICⁱⁿⁱ and G_IIC have an improvement of approximately 120% and 180% over the untoughened samples, respectively, which is 15% and 26% higher than that of PPO veils containing no CNTs, respectively. The toughening mechanism is also analyzed using scanning electron microscopy (SEM). Full article

Nano zinc oxide-decorated graphene (G-ZnO) was blended with polyphenylene sulfide (PPS) to improve its tensile, thermal, crystalline, and barrier properties. The properties of neat PPS and PPS/G-ZnO nanocomposites were characterized and compared using various tests, including tensile tests, scanning electron microscopy, X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis, evaluation of Escherichia coli inhibition, and barrier performance. The results demonstrated that G-ZnO played a crucial role in heterogeneous nucleation and reinforcement. When the concentration of G-ZnO was 0.3%, the tensile strength, elongation at break, thermostability, crystallinity, and water vapor permeability coefficients (WVPC) approached their maximum values, and the microscopic morphology changed from the original brittle fracture to a relatively tough fracture. In addition, when G-ZnO was added to PPS at a ratio of 0.3%, the tensile strength, elongation at break, and WVPC of PPS were increased by 129%, 150%, and 283%, respectively, compared to pure PPS. G-ZnO endowed the nanocomposites with antibacterial properties. The improvement in barrier performance can be attributed to three reasons: (1) the presence of G-ZnO extended the penetration path of molecules; (2) the coordination and hydrogen bonds between PPS polymer matrix and G-ZnO nanofiller narrowed the H₂O transmission path; and (3) due to its more hydrophobic surface, water molecules were less likely to enter the interior of PPS/G-ZnO nanocomposites. This study provides valuable insights for developing high-performance PPS-based nanocomposites for various applications. Full article

Presently, water pollution poses a serious threat to the environment; the removal of organic pollutants from resources, especially dyes, is very important. Nanofiltration (NF) is a promising membrane method to carry out this task. In the present work, advanced supported poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) membranes were developed for NF of anionic dyes using bulk (the introduction of graphene oxide (GO) into the polymer matrix) and surface (the deposition of polyelectrolyte (PEL) layers by layer-by-layer (LbL) technique) modifications. The effect of PEL combinations (polydiallyldimethylammonium chloride/polyacrylic acid (PAA), polyethyleneimine (PEI)/PAA, and polyallylamine hydrochloride/PAA) and the number of PEL bilayers deposited by LbL method on properties of PPO-based membranes were studied by scanning electron microscopy (SEM), atomic force microscopy (AFM), and contact angle measurements. Membranes were evaluated in NF of food dye solutions in ethanol (Sunset yellow (SY), Congo red (CR), and Alphazurine (AZ)). The supported PPO membrane, modified with 0.7 wt.% GO and three PEI/PAA bilayers, exhibited optimal transport characteristics: ethanol, SY, CR, and AZ solutions permeability of 0.58, 0.57, 0.50, and 0.44 kg/(m²h atm), respectively, with a high level of rejection coefficients—58% for SY, 63% for CR, and 58% for AZ. It was shown that the combined use of bulk and surface modifications significantly improved the characteristics of the PPO membrane in NF of dyes. Full article

The first commercial hollow fiber and flat sheet gas separation membranes were produced in the late 1970s from the glassy polymers polysulfone and poly(vinyltrimethyl silane), respectively, and the first industrial application was hydrogen recovery from ammonia purge gas in the ammonia synthesis loop. Membranes based on glassy polymers (polysulfone, cellulose acetate, polyimides, substituted polycarbonate, and poly(phenylene oxide)) are currently used in various industrial processes, such as hydrogen purification, nitrogen production, and natural gas treatment. However, the glassy polymers are in a non-equilibrium state; therefore, these polymers undergo a process of physical aging, which is accompanied by the spontaneous reduction of free volume and gas permeability over time. The high free volume glassy polymers, such as poly(1-trimethylgermyl-1-propyne), polymers of intrinsic microporosity PIMs, and fluoropolymers Teflon^® AF and Hyflon^® AD, undergo significant physical aging. Herein, we outline the latest progress in the field of increasing durability and mitigating the physical aging of glassy polymer membrane materials and thin-film composite membranes for gas separation. Special attention is paid to such approaches as the addition of porous nanoparticles (via mixed matrix membranes), polymer crosslinking, and a combination of crosslinking and addition of nanoparticles. Full article

For anion exchange membrane water electrolysis (AEMWE), two types of anion exchange membranes (AEMs) containing crosslinked poly(phenylene oxide) (PPO) and poly(styrene ethylene butylene styrene) (SEBS) were prepared with and without triazole. The impact of triazole was carefully examined. In this work, the PPO was crosslinked with the non-aryl ether-type SEBS to take advantage of its enhanced chemical stability and phase separation under alkaline conditions. Compared to their triazole-free counterpart, the crosslinked membranes made with triazole had better hydroxide-ion conductivity because of the increased phase separation, which was confirmed by X-ray diffraction (XRD) and atomic force microscopy (AFM). Moreover, they displayed improved mechanical and alkaline stability. Under water electrolysis (WE) conditions, a triazole-containing crosslinked PPO–SEBS membrane electrode assembly (MEA) was created using IrO₂ as the anode and a Pt/C catalyst as the cathode. This MEA displayed a current density of 0.7 A/cm² at 1.8 V, which was higher than that of the MEA created with the triazole-free counterpart. Our study indicated that the crosslinked PPO–SEBS membrane containing triazoles had improved chemo-physical and electrical capabilities for WE because of the strong hydrogen bonding between triazole and water/OH⁻. Full article