Low Gas Permeability Research Articles

A Metalgel with Liquid Metal Continuum Immobilized in Polymer Network.

Gels are formed by fluids that expand throughout the whole volume of 3D polymer networks. To unlock unprecedented properties, exploring new fluids immobilized in polymer networks is crucial. Here, a new liquid metal-polymer gel material termed "metalgel" is introduced via fluid replacement strategy, featuring 92.40%vol liquid metal fluid as a continuum immobilized by interconnected nanoscale polymer network. The unique structure endows metalgel with high electrical conductivity (up to 3.18×106 S·m‒1), tissue-like softness (Young's modulus as low as 70kPa), and low gas permeability (4.50×10‒22m2·s‒1·Pa‒1). Besides, metalgel demonstrates electrical stability under extreme deformations, such as being run over by a 4.5-metric-tonne truck, and maintains its integrity in various environments for up to 180 days. The immobilization of high-volume-fraction liquid metal fluid is realized by electrostatic interactions is further revealed. Potential applications for metalgel are diverse and include soft electromagnetic shielding, hermetic sealing, and stimulating/sensing electrodes in implantable bioelectronics, underscoring its broad applicability.

Static expansion fracturing mechanism for enhancing gas permeability in low permeability coal seams

Extraction of gas from low-permeability thick coal seams poses challenges globally, attributed to low extraction efficiency, limited enrichment content, and extraction complexities. Investigating static fracturing in low-permeability thick coal seams holds substantial engineering significance and practical utility. This research delves into the current conditions in the Western region, characterized by low gas permeability and challenging extraction in thick coal seams. Through the utilization of FLAC3D and COMSOL, simulation schemes are devised to analyze the influence of borehole parameters on fracture efficacy, elucidating the mechanisms by which external loads and internal gas pressure impact coal seam permeability. Field monitoring tests are employed to evaluate and model gas extraction enhancement via borehole positioning. The results suggest that the application of a static fracturing agent inducing 40 MPa expansion stress, along with a 75 mm borehole diameter and 0.5 m spacing, effectively fractures low-permeability thick coal seams. The spacing between extraction and fracturing holes adversely affects gas extraction efficiency due to the limited range of static fracturing. Field experiments demonstrate that static fracturing significantly improves gas extraction from low-permeability thick coal seams, resulting in a twofold increase in average gas extraction purity post-fracturing. This study establishes a robust theoretical foundation for optimizing gas extraction and mining activities in challenging low-permeability thick coal seam environments.

Innovative thermal crosslinked polyimide gas separation membrane with highly selective and resistance to physical aging base on phenyl ethynyl

In this study, a high performance phenyl ethynyl thermal crosslinked 6FDA-based polyimide (CR-4ETA-x) was developed, which has high gas permeability and selectivity, resistance to physical aging. By introducing 4,4′-(Acetylene-1,2-diyl) diphthalic anhydride (4ETA) monomer into the polyimide structure, the thermal crosslinking precursor membrane was formed. The precursor membrane was heat treated at 440℃ to obtain CR-4ETA-x. After heat treatment, we detected the olefin radical in the crosslinked membrane by electron paramagnetic resonance, which proved that the polyimide network was formed. This allows the crosslinked membrane to have greater d-spacing, higher rigidity, and BET surface area. The CO2 permeability of CR-4ETA-5% is 4114 barrer and the CO2/CH4 selectivity is 19.22. Compared to 6FDA-DAM, the CO2 permeability increased by 477% while the selectivity decreased by only 17%. CR-4ETA-20% shows the CO2 permeability of 3560 Barrer and CO2/CH4 selectivity of 21.1 in CO2/CH4 mixed-gas. After 60 days of aging the permeability maintenance of CR-4ETA-20% were 88%, 84%, 83% and 91% for O2, N2, CO2 and CH4. In addition, in the long-term stability test of more than 100 h, the separation performance of CR-4ETA-20% did not decrease significantly. However, CR-4ETA-x also has limitations, such as poor stability in alkaline environments and lower gas permeability than some advanced carbon molecular sieve membranes. In general, the method of phenyl ethynyl thermal crosslinking provides an effective way for the development of CO2 separation membranes with possible applications.

Polybenzimidazole-Reinforced Terphenylene Anion Exchange Water Electrolysis Membranes.

Anion exchange membrane water electrolysis (AEMWE) for hydrogen production combines the advantages of proton exchange membrane water electrolysis and alkaline water electrolysis. Several strategies have been adopted to improve the performance of AEMWE and to obtain membranes with high hydroxide ion conductivity, low gas permeation, and high durability. In this work AEMs reinforced with poly[2,2'-(p-oxydiphenylene)-5,5'-benzimidazole] (PBIO) polymer fibres have been developed. A fibre web of PBIO prepared by electrospinning was impregnated into the poly(terphenylene) mTPN ionomer. The membranes are strengthened by the formation of a strong surface interaction between the reinforcement and the ionomer and by the expansion of the reinforcement over the membrane thickness. The hydroxide ion conductivity, thermal stability, dimensional swelling, mechanical properties, and hydrogen crossover of the reinforced membranes were compared with the characteristics of the non-reinforced counterpart. The incorporation of PBIO nanofibre reinforcement into the membrane reduced hydrogen crossover and improved tensile properties, without affecting hydroxide conductivity. PBIO-reinforced mTPN membrane was assessed in a PGM-free 5 cm2 AEMWE single cell using NiFe oxide anode and NiMo cathode catalysts, at a cell temperature of 50 °C and with 1 M KOH fed to the anode. The performance of the cell increased continuously over the 260 hours test period, reaching 2.06 V at 1.0 A cm-2.

Enhancing Impregnability in Reinforced Composite Membrane Using Greener Dispersion

Perfluorosulfonic acid (PFSA) polymer commonly offer high ionic conductivity, chemical and physical properties, and rapid response, making them widely used in energy conversion technologies like fuel cell and water electrolysis. Industrial commercialization of the polymer electrolyte membranes for water electrolysis depends not only on sufficient electrochemical performance but also requires gas barrier properties and high dimensional stability. To improve the properties of these polymer electrolyte membranes selection of an appropriate dispersion solvent and optimization of its composition ratio are very important. However, PFSA polymer limits the types of dispersion solvents due to its unique structure, which consist of combining a hydrophilic perfluorovinyl ether side chain with sulfonate groups onto a hydrophobic tetrafluoroethylene backbone.Here, we have introduced a new greener mixture system for the fabrication of PFSA-reinforced composite membranes for water electrolysis and compared it with conventional solvent systems. Our solvent system not only produced a more densely packed support layer but also relaxed the anisotropy of the reinforced composite membrane. As a result, the compressive strength and tensile strain increased, making it possible to compensate for the shortcomings caused by the support. Also, this increased impregnability resulted in relatively low gas permeability and high ionic conductivity. The water electrolysis performance was comparable with those prepared using an NMP-based solvent. These results demonstrate a method for preparing PFSA dispersions for reinforced composite membrane and their potential to replace hazardous solvents used in fabrication processes.

(Invited) Overview of Ion-Conducting Polymer Membranes and Membrane Separators for Water Electrolysis

Traditional liquid alkaline electrolyzer uses a porous diaphragm to allow diffusion of hydroxide ion from a feed of concentrated KOH solution while separating anode and cathode and suppressing mixing of produced H2 and O2 gases. Although liquid alkaline electrolyzer is considered as a matured technology, recent renaissance of new electrode separators suggests there is significant potential for improvement in efficiency and cost reduction by lowering area specific resistance and increasing operation current density.Ion-conducting polymers (e.g., proton or hydroxide) are used as a key component of polymer electrolyte membranes, such as acidic proton exchange membrane (PEM) and alkaline anion exchange membrane (AEM), in electrochemical energy conversion and storage technologies including water electrolyzers. For example, the state-of-the-art PEM electrolyzers have used Nafion for a PEM and ionomer catalyst binder for decades, though it is not ideal proton-conducting membrane material for those applications. Recent pressure on perfluoroalkyl substrates (PFASs) from government and environmental activist groups due to their environmental and health hazard has attracted the development of alternative polymer electrolyte membranes based on hydrocarbon polymers within electrochemical society. Compared to perfluorosulfonated Nafion, hydrocarbon ion-conducting polymers (both PEMs and AEMs) can offer advantages of flexible synthetic tunability, lower gas permeability, and importantly lower production cost.In this tutorial, an overview of recent progress in the development of advanced porous membrane separators, PEMs and AEMs, their key membrane properties, and the state-of-the-art performance in applications of water electrolyzers will be discussed. Figure 1

Microstructure and Pore Characteristics of a Double-Layered Pore Structure Powder Filter Fabricated by the WPS Process

In order to supply high-purity process gas in the semiconductor manufacturing process, a gas filter is used to remove particles that may be contained in the gas. However, because the gas filters currently in use have simple pore structures, there is a need to increase filtration efficiency through the development of filters with complex pore structures. In this study, a metal powder filter with double-layered pores was manufactured using a Wet Powder Spraying process (WPS) to increase the filtering efficiency of gas filters used in semiconductor manufacturing. The effects of the mixing ratio of spherical-shape and flake-shape powders and the rolling process on the filter’s characteristics were investigated. The filter’s performance, microstructure, and surface roughness were evaluated by measuring porosity and gas permeability. The results showed that as the ratio of flake-shaped powder decreased, the thickness of the coating layer and the porosity of the filter decreased. Additionally, it was observed that as the rolling process progressed, the non-uniform pore structure was oriented parallel to the cross-section of the filter regardless of the mixing ratio. Measurements found that the gas permeability of the uncoated filter support was the highest, and that gas permeability decreased as the proportion of spherical powder increased regardless of the average particle size of the mixed powder. Lower gas permeability was observed in rolled samples. A filtration efficiency of LRV 3 or higher was confirmed.

Bioinspired Robust Gas-Permeable On-Skin Electronics: Armor-Designed Nanoporous Flash Graphene Assembly Enhancing Mechanical Resilience.

Soft on-skin electrodes play an important role in wearable technologies, requiring attributes such as wearing comfort, high conductivity, and gas permeability. However, conventional fabrication methods often compromise simplicity, cost-effectiveness, or mechanical resilience. In this study, a mechanically robust and gas-permeable on-skin electrode is presented that incorporates Flash Graphene (FG) integrated with a bioinspired armor design. FG, synthesized through Flash Joule Heating process, offers a small-sized and turbostratic arrangement that is ideal for the assembly of a conductive network with nanopore structures. Screen-printing is used to embed the FG assembly into the framework of polypropylene melt-blown nonwoven fabrics (PPMF), forming a soft on-skin electrode with low sheet resistance (125.2 ± 4.7 Ω/□) and high gas permeability (≈10.08mg cm⁻2 h⁻¹). The "armor" framework ensures enduring mechanical stability through adhesion, washability, and 10,000 cycles of mechanical contact friction tests. Demonstrating capabilities in electrocardiogram (ECG) and electromyogram (EMG) monitoring, along with serving as a self-powered triboelectric sensor, the FG/PPMF electrode holds promise for scalable, high-performance flexible sensing applications, thereby enriching the landscape of integrated wearable technologies.

Effect of waste clay brick powder on microstructure and properties in blended oil well cement pastes at HTHP conditions

The use of waste materials to improve the thermal stability of oil well cement (OWC) at high temperature and high pressure (HTHP) conditions has received increasing attention. This study investigated the performance of sustainable blended OWC pastes by recycling waste clay brick powder (CBP) as a partial substitute for commercial high temperature resistant additives (silica flour, SF). The main objective was to assess the impact of these substitutions on the hydration, microstructure and mechanical properties of blended OWC. CBP was incorporated at substitution rates of 25 wt%, 50 wt%, 75 wt% and 100 wt% by weight of SF. These pastes were firstly precured at 50 °C for 7 days (to simulate the primary cementing operation prior to steam injection), and then thermally cycling cured at 300 °C/13.0 MPa (to simulate the steam injection process). The study conducted comprehensive tests and analyses, including compressive strength, gas permeability, hydration products and microstructural analyses. The results showed that the suitable substitution rate of CBP in this study was 25 wt%-50 wt%. At these substitution levels, the blended OWC pastes had good compressive strength (18.5 MPa and 17.9 MPa) and low gas permeability (3.1 × 10−3 mD and 4.51 × 10−3 mD). From the environmental and economic analyses, the energy intensity and CO2 emissions of all blended OWCs were significantly lower compared to those of conventional OWC. Meanwhile, the cost of blended OWC in this study was significantly lower compared to that of the commercial SF-OWC system. Overall, this study highlighted the potential of recycling waste materials to promote raw material sustainability and improve the performance of OWC pastes at HTHP conditions.

Exploring the effects of montmorillonite and halloysite nanotubes on mechanical, optical and barrier properties of poly (butylene adipate‐co‐terephthalate) blown films: Implications for sustainable packaging and food storage

AbstractBiodegradable packaging plastics combining good mechanical properties and low gas permeability is required to avoid environmental and food safety concerns. This study explores the impact of montmorillonite (MMT) and halloysite nanotubes (HNT), on the mechanical, optical, and oxygen permeability of blown film poly (butylene adipate‐co‐terephthalate) (PBAT) composites. The morphology of the films was evaluated by x‐ray diffraction (XRD), differential scanning calorimetry and scanning electron microscopy. Good distribution/dispersion of clays is found in the PBAT‐MMT films. Besides, there is an increase in the crystallinity of PBAT due to the nucleating effect of HNT. Improvement in the tensile strength and elongation at break in the machine direction is obtained up to a clay content of 1.5 vol%. The incorporation of 1.5 vol% of MMT and 1 vol% of HNT leads to a reduction in the oxygen permeability of the PBAT film by 29% and 38% respectively. Furthermore, the films remain transparent regardless of clay content. Finally, the feasibility of the films for food storage is tested in grapes, obtaining extended shelf life. The favorable mechanical, barrier and optical properties of the biodegradable films, along with the scalable production process, make them attractive for application in the storage and preservation of food products.

Functionalized pectin/alginate food packaging films based on metal-phenol networks

It was focused on development a film with excellent properties. The pectin/sodium alginate (PS) composite films were developed by a casting technology, incorporating with tannic acid and Fe3+ for double cross-linking, and the effects of the film thickness, optical, mechanical, barrier, and antioxidant properties were investigated. This results displayed the inclusion of tannic acid (TA) and Fe3+ considerably increased the physical aspects, and they were very compatible with the matrix of the PS, exhibiting higher UV barrier capacity and lower gas permeability. On the other hand, the more compact structure observed by SEM as well as the hydrogen bonding interactions between the film components revealed by FTIR spectroscopy and XRD diffraction analyses further confirmed the significant enhancement of the properties. The functionalized coating of TA-Fe3+ demonstrated an improved adhesion and barrier properties, thereby effectively retarding the ageing process of golden passion fruit and this encompassed a decrease in the weight loss and a significant enhancement in water retention capability.

Low hydrogen permeability and high durability proton exchange membrane with three-dimensional acid-base crosslink structure for water electrolysis

Introducing a acid–base cross-linked network structure and reinforcement layer into a proton exchange membrane (PEM) can effectively improve its performance, durability, and hydrogen permeability for high-pressure PEM water electrolysis (PEMWE). Here, a hyperbranched polymer containing imidazole terminal groups (HBP-MZ) is designed and prepared, then is used to form a novel PEM possessing a cross-linked network structure consisting of HBP-MZ, perfluorosulfonic acid (PFSA) and reinforced with a poly(ether-ether-ketone) (PEEK) mesh. The microstructure of the PEM is characterized using thermal performance analysis. Benefiting from the acid–base crosslinked structure, the obtained PEM has a more compact structure, induces a drastic increase in dimensional stability, mechanical properties, proton conductivity and stability in water. The HBP-MZ/PFSA@PEEK membrane exhibits excellent water electrolysis performance, low high-frequency impedance, and superior stability: the HBP-MZ/PFSA@PEEK membrane provides an electrolytic performance of up to 1.76 V at 2.0 A cm−2 and 1.84 V at 3.0A cm−2 (60 °C, with an IrO2 loading of 1.0 mg cm−2), and exhibits a 6.2 μV h−1 average voltage degradation rate during durability testing. Benefiting from the characteristics of HBP and the existing cross-linked structures, the obtained HBP-MZ/PFSA@PEEK membrane exhibits a lower hydrogen crossover current density of 1.06 mA cm−2 and maintains a lower hydrogen content in oxygen under conditions of high current density and high pressure. This work provides a promising way to prepare a PEM with high durability and low gas permeability that could be applied in high-pressure water electrolysis.

Transformation from Knudsen diffusion to facilitated diffusion for CO2 in confined mass transfer channels of polyimide mixed matrix membranes

Incorporation of porous materials in a polymeric membrane is an effective strategy for improving the gas permeability of the resulting mixed matrix membranes (MMMs). However, effective improvement of selectivity of membrane toward CO2 separation is still a significant challenge due to the insufficient CO2 capture performance of porous materials. In this study, polyimide (PI)-based MMMs with enhanced CO2 capture performance were prepared for CO2 separation. First, an ionic liquid (IL) with a high affinity for CO2 was immobilized in the inner pore structures of two types of mesoporous silica (SiO2) molecules to form IL@SiO2 composites. These composites were used as nanofillers to construct the MMMs. The stable immobilization of IL inside the pores of the mesoporous SiO2 indicated that the IL@SiO2 and MMMs both exhibited higher adsorption selectivity for CO2. The gas solubility coefficient of the MMMs was positively proportional to their maximum gas adsorption capacity, which was determined by the gas adsorption capacity of the PI polymer and nanofillers. More interestingly, the diffusion coefficients of different gases in the MMMs were closely related to the confined mass transfer channels introduced by the nanofillers. The diffusion of CO2 in the confined mass transfer channels of MMMs was facilitated and N2 diffusion was slightly inhibited, which increased the diffusion selectivity of the resulting MMMs for CO2. Combined with Maxwell–Wagner–Sillar model calculations for gas permeation, it was confirmed that IL immobilization transformed the diffusion mode of CO2 in the confined mass transfer channels of the MMMs from Knudsen diffusion to facilitated diffusion. However, the immobilization of excessive ILs in the mesopores blocked the mass transfer channels of the MMMs, resulting in lower gas permeability and decreased CO2 separation selectivity.

A tough double-network ion gel membrane based on poly (ionic liquid) for efficient carbon capture

Ion gel membranes show great potential for carbon capture due to their excellent solubility selectivity for CO2. However, poor mechanical properties and limited stability as well as low gas permeability limit their application. Here, we report a environmentally friendly and simple strategy for preparing double-network(DN) ion gel membranes with both high strength and excellent gas separation performance. We use a “one-pot method” that the first network(FN) and the second network(SN) with ionic liquid were mixed evenly, and the DN membrane was prepared under heating and UV light. Wherein the FN was obtained by a ring-opening reaction between O, O-bis(2-aminopropyl) polypropylene glycol-block-polyethylene glycol-block-polypropylene glycol and a trimethylolpropane triglycidyl ether. And the SN was obtained by free radical polymerisation between 1 and vinyl-3-ethylimidazole bis(trifluoromethanesulfonyl)imide and a p-divinylbenzene (DVB) crosslinker. The crosslinking density of FN and SN, the mass ratio of the FN to the SN, as well as the content and type of free ionic liquid were optimized to improve the mechanical and gas separation properties of the DN membrane. When the crosslinking groups reacted quantitatively, the tensile strength of DN membranes is 1.5 MPa and the elongation at break is 120 %. With the increase of free ILs content, the crystallinity as well as the glass transformation temperature of the DN membrane decreases and the CO2 permeability increases (PCO2:866 Barrer α (CO2/N2):31). When 1-ethyl-3-methylimidazolium dicyanamide was used, the CO2/N2 separation performance can surpass the 2008 upper bound (PCO2:464 Barrer α (CO2/N2):63). The DN membrane has better gas separation and mechanical properties than the SN membrane and shows superior combination of the permeability and selectivity. This research provides a new approach designing a tough ion gel membrane which shows great potential for practical application in carbon capture.

Fractal Characteristics of the Low-Gas Permeability Area of a Fully Mechanized Up-Dip Working Face under Different Dip Angles of Rock Strata

The low-gas permeability area of a fully mechanized up-dip working face was quantitatively studied using a physical similarity simulation test and theoretical analysis under varying dip angles of rock strata. Based on the theory of fractal geometry, this study obtained the fractal dimensions of the low-gas permeability area, the boundary area of the low-gas permeability region, and various layer areas of the low-gas permeability area by increasing the dip angle of rock strata. The findings reveal that the goaf’s high penetration area moved from a symmetrical shape to an asymmetrical one as the dip angle of rock strata increased. The high penetration area on the open-off cut side is notably larger than that on the working face side, due to the effects of advancement at the working face. In the goaf, the lateral length of the cavity decreases as the rock strata’s dip angle increases, while the longitudinal width expands and then contracts until it vanishes because of sliding. In the goaf, the lateral length of the cavity decreases as the rock strata’s dip angle increases, while the longitudinal width expands and then contracts until it vanishes because of sliding. In the goaf, the lateral length of the cavity decreases as the rock strata’s dip angle increases, while the longitudinal width expands and then contracts until it vanishes because of sliding. Moreover, the low-gas permeability area has a larger fractal dimension. The fractal dimension of the area with low gas permeability steadily decreased as periodic weighting emerged, ultimately reaching values of 1.24, 1.27, and 1.34. Moreover, the area’s fractal dimension was greater on the open-off cut side in comparison to the working face side. As the distance from the rock strata floor decreased, the fractal dimension of the area with low gas permeability increased. According to the gradient evolution law, the low-gas permeability area may be divided from bottom to top into three areas: strongly disturbed, moderately disturbed, and lowly disturbed. Based on the theory of mining fissure elliptic paraboloid zones and experimental findings, a mathematical model has been developed to analyze the fractal characteristics of low-gas permeability areas that are influenced by the rock strata’s dip angle. Finally, this study established a dependable theoretical foundation for precisely examining the development of cracks in the area of low gas permeability and identifying the storage and transportation region of pressure relief gas, which is affected by various dip angles of rock strata. It also offered assistance in constructing a precise gas extraction mechanism for pressure relief.

Durability parameters of three low-carbon concretes (low clinker, alkali-activated slag and supersulfated cement)

The general transfer properties (water porosity, mercury intrusion porosimetry, water permeability, capillary absorption, gas permeability and resistivity) and chloride penetration resistance (natural chloride diffusion test and rapid chloride permeability test) of three low-carbon concretes C25/30 (low clinker (LCK) concrete, alkali-activated slag with sodium carbonate (Na2CO3-AAS) concrete and supersulfated cement (SSC) concrete) were evaluated and compared, in order to identify the strengths and weaknesses of each technology. The results show that the LCK concrete is characterized by “excellent” transfer properties (low water porosity, gas permeability, water permeability and capillary absorption) but high viscosity in the fresh state and very high chloride permeability. AAS and SSC concretes have similar transfer properties, comparable to classical concretes C25/30, and are extremely resistant to chloride penetration. Finally, the use of traditional protocols for durability tests applied to alternative low-carbon binders is questioned and metrology adaptations are proposed.

The relationship between chemical structure of perfluorinated sulfonic acid ionomers and their membrane properties for PEMEC application

Polymer electrolyte membrane electrolyzer cells (PEMECs) has been confirmed as a prototype electrochemical system that is effective in converting water into hydrogen and oxygen under the application of electricity. Among the core components of PEMEC, the polymer electrolyte membrane (PEM) determines critically an overall electrochemical performance of the PEMEC. Ideally a PEM system should exhibit a complex transport behavior of small molecules (e.g., gases and ions) while mediating flows of ions in the cell; it should exhibit high proton selectivity while serving as a gas barrier to hydrogen and oxygen to increase current efficiency, which are in turn vital factors in determining an effectiveness when the electric energy is used for water electrolysis. Until now, perfluorinated sulfonic acid (PFSA) ionomers have been extensively used as PEM materials in water electrolysis while in generating hydrogen and oxygen gases simultaneously in high purity. In this study we have examined the chemical structure of PEM membranes derived from various types of PFSA ionomers by employing solid-state 19F MAS NMR. Subsequently, a structure-property-performance correlation was sought in accordance with the chemical structure, the dispersion characteristics, and membrane properties of PFSA ionomers. Furthermore, the effects of the membrane morphology as well as the ionomer packing characteristics on proton conduction and hydrogen transportation were investigated. Lastly, the membrane properties exerted by varying the chemical architectures and equivalent weight (EW) values of PFSA ionomers in PEMEC were confirmed. 3 M 725 membrane, which has the highest concentration of sulfonic acid groups in the hydrated state, has the highest proton conductivity. In addition, it showed the best water electrolytic cell performance via the synergistic effect with low gas permeability obtained as a result from the short side chain structure.

Stress and permeability evolution of high-gassy coal seams for repeated mining

Coal bed methane reservoirs in China are generally characterized by high stress and low gas permeability coefficient. Protected layer mining has the effect of unloading pressure and increasing gas permeability coefficient. There are few studies in the case of repeated mining with an orthogonal arrangement of the protected layer. Based on the engineering practice of the high gas coal seams group in Xinjing coal mine, a combination of numerical simulation and field test was used. The distribution law of plastic zone, stress-strain and gas permeability coefficient of the protected layer under the two states of single mining and repeated mining were obtained. The stress and gas permeability coefficient distribution of the protected layer was divided into 5 and 6 zones in plane for single and repeated mining cases. The field test tested the distribution law of stress, gas pressure, deformation, and gas permeability coefficient, and verified the reliability of the numerical simulation results. According to the characteristics of gas permeability coefficient distribution under the condition of repeated mining, a method for accurate gas extraction is proposed. The results of the study have important implications for the design of gas extraction schemes in orthogonal repeated mining situations.

The phenolic cured butyl rubber reclamation using different de-crosslinking agents

The cured rubber-made bladder used for curing the green tire because, it is thermally stable, and has low gas permeability. The bladder is made with the cured butyl rubber as a base rubber under a phenolic curing system. To save the resources and also, the environmental protection, it should be de-crosslink to gum rubber. A commercial source waste bladder rubber compounded with different de-crosslinking agents, including TMTD, DPDS, DCBS, MBTS, MBT, and TBBS. To do de-crosslinking, the prepared compounds were heated in a laboratory heating oven at different temperatures. The de-crosslinking parameters including the sol fraction and de-crosslinking percent measured using traditional rubber swollen tests. The Fourier transform infrared spectroscopy (FTIR) graphs showed the existence of the phenolic resin in the structure of waste bladder butyl rubber powder. Efficient de-crosslinking was observed for all studied de-crosslinking agents. It evidenced by the scanning electron microscope micrographs and also, the measured crosslink densities of the reclaimed rubbers. The highest and the lowest de-crosslinking percents belonged to the compounds with 4 phr DPDS in recipe at 220 [Formula: see text] and 4 phr DCBS at 180 [Formula: see text], respectively. Based on the obtained de-crosslinking parameters, the DPDS was selected as a suitable de-crosslinking agent for used waste rubber. In accordance with Horikx analysis, the oven heating broke down the crosslinks and rubber main chains simultaneously. Increasing the oven temperature had a positive effect on de-crosslinking process with similar effects on the crosslink and main chain break down.

Nanoclay-Reinforced Nanocomposite Nanofibers—Fundamentals and State-of-the-Art Developments

Nanoclays are layered mineral silicates, i.e., layered silicate nanosheets. Nanoclays such as montmorillonite, bentonite, kaolinite, etc., have been used as reinforcements in the nanofibers. Numerous polymers have been used to fabricate the nanofibers, including poly(vinylidene fluoride), poly(vinyl alcohol), polycaprolactone, nylon, polyurethane, poly(ethylene oxide), and others. To develop better compatibility with polymers, nanoclays have been organo-modified prior to reinforcement in the nanofiber matrices. This state-of-the-art review highlights the fundamentals, design, fabrication, and characteristics of the polymer/nanoclay nanofibers. The nanoclay filled nanocomposite nanofibers have been fabricated using electrospinning and other fiber processing techniques. The electrospinning technique has been preferred to form the nanoclay-filled nanofibers, owing to the better control of processing parameters and resulting nanofiber properties. The electrospun polymer/nanoclay nanofibers usually have fine nanoparticle dispersions, microstructures, smooth textures, and narrow diameters. The physical properties of the designed nanofibers depend upon the processing technology used, solvent, solution/melt concentration, flow rate, spinning speed, voltage, and other process parameters. Hence, this review attempts to assess a literature-driven consequence of embedding nanoclays in the polymeric nanofibers in a broad context of the application of these fibrous materials. Conclusively, to design the polymer/nanoclay nanofibers, montmorillonite nanoclay has been observed as a nanofiller in most of the studies, and, similarly, the electrospinning technique was preferred as a fabrication technique. Almost all the physical properties of the nanofibers studied revealed dependences upon the choice of the polymer matrix for nanofiber formation as well as the nanoclay contents, modification, and dispersion state. Accordingly, the nylon/nanoclay nanofibers have been investigated for nanofiller dispersion, mechanical properties, and thermal profiles. The antibacterial properties were among the prominent features of the poly(vinyl alcohol)/nanoclay nanofibers. The poly(vinylidene fluoride)/nanoclay systems were explored for the microstructure, crystallinity, and piezoelectric properties. The polycaprolactone/nanoclay nanofibers having fine microstructure were capable of forming tissue engineering scaffolds. The drug delivery and sound absorption properties were noticeable for the polyurethane/nanoclay nanofiber systems. Moreover, the poly(lactic acid)/nanoclay nanofibers were found to have prominent biodegradability and low gas permeability features. The resulting polymer/nanoclay nanocomposite nanofiber systems found potential for the technical applications of sensors, packaging, tissue engineering, and wound healing. However, thorough research efforts have been found to be desirable to find the worth of polymer/nanoclay nanofibers in several concealed technological sectors of energy, electronics, aerospace, automotives, and biomedical fields.