Mobility Of Polymer Chains Research Articles

Facile metal-ion infiltration into polyimide membranes with coordination crosslinking for efficient gas separation

We report a facile metal-ion infiltration method for engineering the properties of 6FDA-DAM:DABA (6FDA: 4,4′-(hexafluoroisopropylidene)diphthalic anhydride, DAM: 2,4,6-trimethyl-1,3-diaminobenzene, DABA: 3,5-diaminobenzoic acid; referred to as 6FDD) polyimide membranes. The 6FDD polyimide membrane samples were simply immersed in metal ion (copper, zinc, and cobalt) solutions of various concentrations (1 and 10 wt%) to obtain metal-ion-infiltrated 6FDD membranes. The metal ions and the carboxylate group of the 6FDD polyimide form a coordination bond, which can increase the d-spacing between the inter-polymer chain distances and reduce polymer chain mobility. The coordination between the metal ion and the carboxylated polymer chain enhances the mechanical properties of the polyimide membranes. The metal ion coordination provides not only increased stiffness but also high resistance to the breaking point under elongation. The metal ions were distributed uniformly across the entire 6FDD membrane without any noticeable defects, which indicated the effectiveness and simplicity of the proposed method, which can be applied to versatile membrane module types and conformations. The metal-ion infiltrated 6FDD membrane exhibited improved gas permeability compared to that of the pure 6FDD membrane because of the enhanced diffusivity coefficient resulting from the increased d-spacing. Particularly, the metal-ion-infiltrated 6FDD membranes exhibited significantly higher plasticization resistance because of a decrease in the normalized CO2 permeability at 750 psi compared to that of the pure 6FDD membrane. For example, the normalized CO2 permeability of the 10 wt% copper-ion-infiltrated 6FDD membrane increased by 120% but that of pure 6FDD membrane increased by 315%. This was because the metal–carboxylate group coordination strongly prevented relaxation of the polymer chain when it was exposed to plasticizing gases at high gas feed pressures.

Stability and Population of Radicals in Electrical Trees in Epoxy Resins Based on Electron Paramagnetic Resonance Spectroscopy

The stability and population of radicals in aged epoxy resins with different electrical trees are investigated by electron paramagnetic resonance. Branch trees and bush trees of various sizes are produced in three types of epoxy resins which are cured by different curing agents. By examining the lifetime of radicals in three epoxies, the mobility of polymer chains is found to act as a vital factor for stability. The recombination of radicals is faster in polymers with higher mobility, leading to a shorter lifetime of radical signals. A distinguishable singlet appears in specimens without visible tree channels, proving that radicals are a precursor of electrical trees. Among spectra from a series of branch trees, two species of radicals are found to be generated successively as tree size increases. By comparing the signal intensity of branch trees and bush trees of similar sizes, bush trees show a much smaller radical population, which is attributed to relatively low electrical stress at branch tips and slow degradation of polymer chains.

Organohydrogels with High‐Speed Lubrication by Confining Polymer Chain Mobility by an Interpenetrated Heteronetwork

AbstractHydrogels with pure hydrophilic network have received much attention due to their excellent low frictional behavior. However, the lubrication performance of hydrogels is not satisfied under high‐speed condition due to the energy dissipation caused by adsorbed polymer chains as well as the failure of lubricating mechanisms accompanied by the transition of lubrication regime. In this work, interpenetrating double‐network organohydrogels were constructed by combining hydrophilic and oleophilic polymer networks to modify the physiochemical properties of surface polymer chains, especially the chain mobility. The oleophilic polymer network spatially restricting the mobility of the swollen hydrophilic network in water, resulted in a low coefficient of friction (ca. 0.01) compared with conventional hydrogels at high speed (0.1 m s−1). Meanwhile, the organohydrogels had superior wear resistance, with almost no wear observed on the sliding track after 5 k cycles of rubbing at high speed. The design concept of organohydrogels can be extended to a variety of low‐wear, highly‐lubricating materials.

Organohydrogels with High-Speed Lubrication by Confining Polymer Chain Mobility by an Interpenetrated Heteronetwork.

Hydrogels with pure hydrophilic network have received much attention due to their excellent low frictional behavior. However, the lubrication performance of hydrogels is not satisfied under high-speed condition due to the energy dissipation caused by adsorbed polymer chains as well as the failure of lubricating mechanisms accompanied by the transition of lubrication regime. In this work, interpenetrating double-network organohydrogels were constructed by combining hydrophilic and oleophilic polymer networks to modify the physiochemical properties of surface polymer chains, especially the chain mobility. The oleophilic polymer network spatially restricting the mobility of the swollen hydrophilic network in water, resulted in a low coefficient of friction (ca. 0.01) compared with conventional hydrogels at high speed (0.1 m s-1 ). Meanwhile, the organohydrogels had superior wear resistance, with almost no wear observed on the sliding track after 5 k cycles of rubbing at high speed. The design concept of organohydrogels can be extended to a variety of low-wear, highly-lubricating materials.

Self-Healing Binder for High-Voltage Batteries.

Lithium-ion batteries are core components of flexible electronic devices. However, deformation types, such as impinging, bending, stretching, folding, and twisting, can cause internal cracks and, eventually, damage these batteries. The cracks separate the active particles from the conductive particles and the binder, as well as the electrode from the collector. Self-healing binders can alleviate this mechanical damage and improve the stress response of active material particles during high rates of charging and discharging of these batteries and the operation at a high voltage, thereby enhancing their cycle performance. In the present study, a thermoplastic intrinsic self-healing polymer (TISP) binder is proposed. The TISP is obtained by polymerization of butanediol (2,3-BDO), propylene glycol (1,3-PDO), succinic acid (SuA), sebacic acid (SeA), and iconic acid (IA). The hydroxyl and ester groups in its structure can form diverse bonds including the hydrogen and ion-dipole with active particles and the current collector, thereby producing elevated adhesion. Its properties, including a low glass transition temperature (-60 °C), amorphous structure, and low cross-link density, improve the mobility of polymer chains at 40 °C, and this facilitates structural recovery and the maintenance of strong adhesions. Owing to its higher occupied molecular orbital (HOMO) level than the electrolyte solvent, the TISP is likely oxidized before the main component of the electrolyte during charging. This decomposition produces a chemical passivation interphase on the cathode which reduces side reactions of LiCoO2 and the electrolyte under high-voltage conditions. Tests reveal that a LiCoO2 electrode battery using the TISP as a binder retains 162.4 mAh g-1 after 349 cycles at 4.5 V, and this represents an 86.5% capacity retention. In addition, heating (40 °C, 1 h) of a scratch-damaged electrode can recover a specific capacity of 156.6 mAh g-1 after 349 cycles at 4.5 V. Relative to a battery without any mechanical scratch, this capacity recovery represents approximately 96%, and this demonstrates the importance of the TISP to the high-voltage damaged electrode.

Dewetting Behavior of PS-ZnO Thin Film Coated on Ultrathin Au Layer Grown on Si Substrate

Electronic packaging by coating device component surfaces with polymer thin film is an important step to protect the components from harsh environments. However, along with the device miniaturization to improve its performance, scaling down the coating film can cause a decrease in film durability. Therefore, the thermal stability of pure polystyrene (PS) and zinc oxide-incorporated polystyrene (PS-ZnO) nano-thin films coated on gold (Au) layer with different nano thicknesses on Si substrate were examined to determine the smallest Au thickness at which the polymer films would exhibit optimal stability, and to investigate the effects of the Au component on film resistance to thermal dewetting. With the requirement of having a transparent and conductive Au electrode, the thickness of 20 nm was identified as the optimal value for the Au layer on which both the PS and PS-ZnO films could withstand environment temperatures at 150oC for up to a few hours while the PS-ZnO film exhibited outstanding thermal stability for over 10 days. Such excellent durability was ascribed to the physio-chemical framework in which the coating film can experience forces from the coated layers which potentially affect the mobility of polymer chains. Considering the increase of Au content and Au film roughness with increasing Au film thickness and realizing the similar surface adhesion forces of these Au layers, several possible influences of the Au material on the stability of PS matrix were discussed. The findings provide an insight into heat-resistant coatings for nano-thin Au layers grown on Si, which may also be of benefit in the design and understanding of relevant electronic protection and functional polymeric coatings.

A novel approach in wood waste utilization for manufacturing of catalyst-free polyurethane-wood composites (PU-WC)

In recent decades, due to the increase in environmental awareness and noticeable environmental degradation, the area of wood waste management has attracted increasing attention. The purpose of this study is to develop a new type of highly filled polyurethane wood-composite (PU-WC) by the utilization of large amount of wood wastes without addition of a catalyst. Although wood-plastic composites (WPCs) are widely known, there is still a lack of knowledge about WPCs with a polyurethane matrix. Obtained results showed that composites with a wood content of up to 80% show mechanical properties to commonly used MDF boards. This may be caused proper adhesion between polyurethane matrix and the wooden filler which was confirmed by scanning electron microscopy. The flexural strength of the manufactured composites varied between 19.25 and 25.11 MPa, while the flexural modulus varied between 966 and 1255 MPa. Dynamic mechanical analysis (DMA) of the composites showed a shift of Tgβ (from −70.3 to −52.3 °C) and Tgα (from 94.9 to 117.8 °C) to higher temperatures with increasing filler amount. The observed shift could be interpreted as a reduction of polymer chain mobility and an increase in cross-linking density of composites with a higher amount of wood. This is caused by chemical reactions between isocyanates and reactive hydroxyl groups on the wood surface. Thermogravimetric analysis has shown that PU-WC degrades in one step with Tmax at around 360 °C and T2% significantly reduce with greater addition of wood. Water absorption tests that water absorption strongly depends on wood content and varies between 13 and 80%. Moreover, cyclic water absorption tests showed no considerable difference between the water adsorption of samples after each cycle. Our work suggests that PU-WC can be used successfully as a potential substitute for wood or different types of wood-plastic composites (WPC).

Highly conductive polyacrylonitrile-based hybrid aqueous/ionic liquid solid polymer electrolytes with tunable passivation for Li-ion batteries

The rapid growth in demand for lithium-ion batteries that can deliver more energy and power has generated concerns over safety. Aqueous electrolytes are a strong candidate to alleviate this apprehension, however their ability to overcome the “cathodic challenge” is limited due to anion-dominated passivation at the anode. In this work, the recently developed “hybrid aqueous/nonaqueous” electrolyte (HANE) strategy was employed to tune the degree of passivation at the anode in solid polymer electrolytes (SPEs) by using various ionic liquids as the nonaqueous component. Whereas common HANE systems sacrifice ionic conductivity to create a more robust passivation layer at the cathodic limit, the “hybrid aqueous/ionic liquid” SPEs (HAILSPEs) investigated in this work do not. Two HAILSPE systems (H1, H2.5) were fabricated from a blend of polyacrylonitrile (PAN), water, lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), and either triethylsulfonium-TFSI (S2,2,2) or N-methyl-N-propylpyrrolidinium-TFSI (Pyr1,3). These HAILSPE systems demonstrated a remarkable improvement in transport properties compared to their predecessors, achieving room temperature ionic conductivities of up to 5.39 mS/cm. A reduction in apparent activation energy and nearly complete decoupling of ionic transport from polymer chain mobility were found to contribute to this increase. Stable and complete growth of a passivating layer at 2 V vs. Li/Li+ was also observed, which was tuned by changing the ionic liquid. The work presented here provides a potential route for overcoming the “cathodic challenge” in aqueous SPEs.

The Interaction Effect of the Design Parameters on the Water Absorption of the Hemp-Reinforced Biocarbon-Filled Bio-Epoxy Composites.

Natural fiber-reinforced composites perform poorly when exposed to moisture. Biocarbon has been proven to improve the water-absorbing behavior of natural fiber composites. However, the interaction effect of the design parameters on the biocarbon-filled hemp fiber-reinforced bio-epoxy composites has not been studied. In this study, the effects of the design parameters (pyrolysis temperature, biocarbon particle size, and filler loading) on the water absorptivity and water diffusivity of hemp-reinforced biopolymer composites have been investigated. Biocarbon from the pyrolysis of hemp and switchgrass was produced at 450, 550, and 650 °C. Composite samples with 10 wt.%, 15 wt.%, and 20 wt.% of biocarbon fillers of sizes below 50, 75, and 100 microns were used. The hemp fiber in polymer composites showed a significant influence in its water uptake behavior with the value of water absorptivity 2.41 × 10-6 g/m2.s1/2. The incorporation of biocarbon fillers in the hemp biopolymer composites reduces the average water absorptivity by 44.17% and diffusivity by 42.02%. At the optimized conditions, the value of water absorptivity with hemp biocarbon and switchgrass biocarbon fillers was found to be 0.72 × 10-6 g/m2.s1/2 and 0.73 × 10-6 g/m2.s1/2, respectively. The biocarbon at 650 °C showed the least composite thickness swelling due to its higher porosity and lower surface area. Biocarbon-filled hemp composites showed higher flexural strength and energy at the break due to the enhanced mechanical interlocking between the filler particles and the matrix materials. Smaller filler particle size lowered the composite's water diffusivity, whereas the larger particle size of the biocarbon fillers in composites minimizes the water absorption. Additionally, higher filler loading results in weaker composite tensile energy at the break due to the filler agglomeration, reduced polymer-filler interactions, reduced polymer chain mobility, and inadequate dispersion of the filler.

Mechanical Properties and Synergistic Interfacial Interactions of ZnO Nanorod-Reinforced Polyamide–Imide Composites

Metal oxide nanoparticle -reinforced polymers have received considerable attention due to their favorable mechanical properties compared to neat materials. However, the effect of nanoscale reinforcements of the interface on the composites' mechanical properties has not been investigated in-depth to reach their optimal performance in structural applications. Aiming at revealing the effect of synergistic interfacial interactions on the mechanical properties of polymer composites, using a nanoscale reinforcement, herein, a series of zinc oxide nanorod-reinforced polyamide-imide (PAI)/ZnO) composites were fabricated and their mechanical properties and viscoelastic responses were investigated. The composite prepared by reinforcing them with 5 wt % ZnO nanorods resulted in improved elastic modulus, stiffness, and hardness values by 32%, 14% and 35%, respectively, compared to neat polymer thin films. The viscoelastic dynamics of the composites revealed that there was an 11% increase in elastic wave speed in the composite, containing 5 wt % ZnO nanorods, indicating better response to high impacts. Delayed viscoelastic response decreased by 67% spatially and 51% temporally, with a corresponding decrease in the creep rate, for the 5 wt % ZnO nanorod- containing composite, evidencing its potential applicability in high strength lightweight structures. The improved mechanical properties with respect to the filler concentration evidence strong particle-polymer interfacial interactions, creating "chain-bound" clusters, providing clear reinforcement and polymer chain mobility retardation. However, hypervelocity impact testing revealed that all the composites' films were vulnerable to hypervelocity impact, but the spallation region of the composite films reinforced with 2.5 wt % and 5 wt % ZnO nanorods exhibited a cellular-like matrix with shock-induced voids compared to a rather hardened spallation region with cracks in the neat film.

Dynamic diffusion of water inside graphene-reinforced PU/PTFE coatings: A molecular dynamics approach

Polymers are extensively used in various applications due to their excellent properties. Recently, graphene-based polymer composites have gotten significant attention due to their superior barrier properties to corrosive media. Although there are lots of experimental studies on graphene-based composites, there are very few works available at the atomistic level using molecular dynamics. The present work investigates the role of temperature on the diffusion of water and the effect of graphene-reinforcement in the polyurethane (PU) and polytetrafluoroethylene (PTFE). The results showed an increase in the diffusion at higher temperatures due to an increase in the mobility of polymeric chains at higher temperatures and hence a smooth path for the travel of water molecules. There is a significant decrease in the diffusion of water molecules in the graphene-reinforced systems when compared with neat PU and PTFE systems. The decrement in the diffusion of water in the range of 273 K to 350 K was around 79–93% for graphene-reinforce PU systems and around 58–62% in the case of graphene-reinforced PTFE systems.

Mechanistic insights into the effect of drug content on adhesive properties of transdermal patch containing lidocaine

This study aims to shed light on the relationship between drug content and adhesive properties in drug-in-adhesive transdermal patch, and to elucidate molecular mechanisms from the perspective of polymer chain mobility. Lidocaine was selected as model drug. Two acrylate pressure sensitive adhesives (PSAs) with different polymer chain mobility were synthesized. Tack adhesion, shear adhesion and peel adhesion of PSAs with 0, 5%, 10%, 15% and 20% w/w lidocaine contents were tested. Polymer chain mobility was determined by rheology and modulated differential scanning calorimetry experiments. Drug-PSA interaction was analyzed by FT-IR. The effect of drug content on free volume of PSA were determined by positron annihilation lifetime spectroscopy and molecular dynamics simulation. It was found that the polymer chain mobility of PSA was increased with increasing drug content. Due to the variation of polymer chain mobility, tack adhesion increased, and shear adhesion decreased. It was proved that interactions between polymer chains were destroyed by drug-PSA interactions, free volume between polymer chains was expanded, resulting in the increase of polymer chain mobility. We can conclude that the effect of drug content on polymer chain mobility should be considered, when designing a transdermal drug delivery system with controlled and satisfactory adhesion.

Formulation Development and Molecular Mechanism Characterization of Long-Acting Patches of Asenapine for Efficient Delivery by Combining API-ILs Strategy and Controlled-Release Polymers

The objective of our study, which combined API-ILs strategy and controlled-release polymers, was to prepare a 72 h long-acting drug-in-adhesive patch for optimum delivery of asenapine (ASE). Special attention was paid to the permeation promotion mechanism and the controlled release behavior of ASE-ILs in pressure sensitive adhesives (PSA). Formulation factors were investigated by ex vivo transdermal experiments. The optimized patch was evaluated by pharmacokinetics study and skin irritation test. The obtained formulation was as follows, 15% w/w ASE-MA (about 1136 μg/cm2 ASE, 413 μg/cm2 MA), AACONH2 (Amide adhesive) as the matrix, 80 μm thickness, backing film of CoTran™ 9733. The optimized patch displayed satisfactory ex vivo and in vivo performance with Q 72 h of 620 ± 44 µg/cm2 and Fabs of 62.4%, which utilization rate (54.6%) was significantly higher than the control group (38.3%). By using the classical shake flask method, 13C NMR, DSC, and FTIR, the physicochemical properties and structure of ILs were characterized. log Do/w, ATR-FTIR, Raman, and molecular dynamics simulation results confirmed that ASE-MA (MA: 3-Methoxypropionic acid) had appropriate lipophilicity, and affected lipid fluidity as well as the conformation of keratin to improve the skin permeation. The FTIR, MDSC, rheology, and molecular docking results revealed that hydrogen bond (H-bond), were formed between ASE-MA and PSA, and the drug increased the molecular mobility of polymer chains. In summary, the 72 h long-acting patch of ASE was successfully prepared and it supplied a reference for the design of long-acting patches with ASE.

Diffusion Behavior of VOC Molecules in Polyvinyl Chloride Investigated by Molecular Dynamics Simulation

Due to the threats posed by many volatile organic compounds (VOCs) to human health in indoor spaces via air, the mass transfer characteristics of VOCs are of critical importance to the study of their mechanism and control. As a significant part of the mass transfer process, diffusion widely exists in emissions from floors (e.g., PVC floors) and in sorption in porous materials. Molecular simulation studies by can provide unparalleled insights into the molecular mechanisms of VOCs. We construct the detailed atomistic structures of PVC blend membranes to investigate the diffusion behavior of VOC molecules (n-hexane) in PVC by molecular dynamics (MD). The variation in the diffusion coefficient of n-hexane in PVC with respect to temperature is in line with Arrhenius' law. The effect of temperature on the diffusion mechanism was investigated from the perspectives of free volume, cavity distribution and polymer chain mobility. It was found that the relationships between the diffusion coefficients of n-hexane in the polymer and the inverse fractional free volume are exponential and agree well with the free volume theory. Hopefully, this study will offer quantitative insights into the mass transport phenomena of VOCs within polymeric materials.

Influence of Philippine Halloysite on Thermal and Mechanical Performance of Poly(Lactic Acid) Filament for FDM Printing Applications

Additive manufacturing can be utilized to harness developments in polymer research. This study aims to investigate the effect of Philippine halloysite on poly(lactic acid) (PLA) filament for 3D printing using Fused Deposition Modeling (FDM). PLA-based filaments with halloysite powders were prepared by melt-compounding using a twin-screw extruder. The chemical composition and morphology of the halloysite powder was determined using XRD and SEM, respectively. Composite filament with 3% halloysite (PLA/HSC) was developed and characterized. The thermal properties of pure PLA and PLA/HSC were measured using DSC and TGA. CAD files for XRD analysis and tensile tests were generated using SolidWorks computer software (Dassault Systemes). Printability of pure PLA and the composite filament was observed by using Ultimaker S5 3D printer. The effect on chemical composition and mechanical performance of the 3D printed specimens was evaluated using XRD and UTM, respectively. XRD result confirmed the presence of dehydrated halloysite clay mineral. SEM image revealed the spherical morphology of the halloysite powder with average particle size of 72.472 nm. DSC analysis showed that incorporation of halloysite powder filaments had slightly decreased the glass transition of pure PLA matrix. This could be attributed to the enhanced mobility of polymeric chains by plasticization. Moreover, the melting temperature of PLA/HSC composite has slightly higher value than pure PLA filament owing to increased crystallinity imparted by the halloysite particles. With high stability of halloysite at elevated temperatures, the thermal stability of PLA/HSC filament was also enhanced. Mechanical performance of pure PLA was also improved with addition of halloysite. The tensile strength and elastic modulus of pure PLA matrix increased by 180.32% and 143.96%, respectively which could be due to the formation of hydrogen bonds between PLA matrix and halloysite particles. Digital micrographs of the fractured surface reveal that tensile pieces predominantly ruptured by brittle fracture.

Crystallizability of a biodegradable polymer as a criterion for assessing the degree of influence of the aquatic environment on its structure

The work is devoted to the study of the effect of an aqueous medium on a polymeric biodegradable material based on poly-3- hydroxybutyrate (PHB) by differential scanning calorimetry (DSC). To analyze the structural reorganizations of the polymer, we studied the effect of an aqueous medium on the process of polymer crystallization after soaking in distilled water. It is shown that after exposure to water, the forms of crystallization exotherms change, the rate of polymer crystallization decreases, and the heat of the process decreases insignificantly. To analyze the kinetics of non-isothermal crystallization, we used the kinetic crystallization parameter G [deg/min], which characterizes the rate of polymer crystallization in the non-isothermal mode. It has been established that the crystallizability of PHB decreases after exposure of the samples. The observed dependence of the parameter G on the scanning rate indicates a decrease in the mobility of polymer chains, a decrease in their flexibility after exposure to an aqueous medium, which is a consequence of a change in their structure.

Sub‐Nanowires Boost Superior Capacitive Energy Storage Performance of Polymer Composites at High Temperatures

AbstractPolymer dielectrics with high breakdown strength (Eb) and high efficiency are urgently demanded in advanced electrical and electronic systems, yet their energy density (Ue) is limited due to low dielectric constant (εr) and high loss at elevated temperatures. Conventional inorganic fillers with diameters from nano to micrometers can only increase εr at the cost of compromised Eb and Ue due to their poor compatibility with polymer matrix. Herein, hydroxyapatite (HAP) sub‐nanowires with a diameter of ≈0.9 nm are incorporated in polyetherimide (PEI) matrix to form HAP/PEI sub‐nanocomposites. εr and Eb of the composites are concomitantly enhanced with only 0.5 wt.% of HAP sub‐nanowires, leading to high Ue of 5.14 (@150 °C) and 3.1 J cm−3 (@200 °C) with efficiency of 90% and high‐temperature stability up to 3 × 105 charge‐discharge cycles at 200 °C. Microstructural analysis and molecular dynamics simulations indicate that the sub‐nanowires with comparable diameter as polymer chains induce enormous interfacial area, substantially increase mobility of polymer chains and form dense traps for charge carriers. This work extends the current research scope of polymer‐inorganics composite dielectrics to the sub‐nano‐level incorporation and provides a novel strategy for fabricating high performance polymer dielectrics at elevated temperatures.

Thermal Decomposition and Stability of Hybrid Graphene–Clay/Polyimide Nanocomposites

Polyimide matrix nanocomposites have gained more attention in recent years due to their high thermal stability, good interfacial bonding, light weight, and good wear resistance and corrosion, factors that make them find great applications in the field of aerospace and advanced equipment. Many advancements have been made in improving the thermal, mechanical, and wear properties of polyimide nanocomposites. The use of nanofillers such as carbon nanotubes, graphene, graphene oxide, clay, and alumina has been studied. Some challenges with nanofillers are dispersion in the polymer matrix and interfacial adhesion; this has led to surface modification of the fillers. In this study, the interaction between clay and graphene to enhance the thermal and thermal-oxidative stability of a nanocomposite was studied. A polyimide/graphene nanocomposite containing ~12.48 vol.% graphene was used as the base nanocomposite, into which varying amounts of clay were added (0.45-9 vol.% clay). Thermogravimetric studies of the nitrogen and air atmospheres showed an improvement in thermal decomposition temperature by up to 50 °C. The presence of both fillers leads to increased restriction in the mobility of polymer chains, and thus assists in char formation. It was observed that the presence of clay led to higher decomposition temperatures of the char formed in air atmosphere (up to 80 °C higher). This led to the conclusion that clay interacts with graphene in a synergistic manner, hence improving the overall stability of the polyimide/graphene/clay nanocomposites.

Fracture and mechanical properties of an impact toughened polypropylene composite: modification for automotive dashboard-airbag application.

Thermoplastic olefin (TPO) is the principal material for automotive instrument panels and is prone to fracture especially under heavy airbag deployment, which can prevent the airbag deploying properly. Thus, polyolefin elastomer (POE) was introduced to improve impact properties and fracture resistance. Fundamental methods to characterise TPO with the addition of POE are proposed. The influence of POE content on the mechanical properties was examined. With increasing POE content, the storage modulus and glass transition temperature values decreased, and the damping increased due to the POE increasing the polymer chain mobility. The tensile modulus, ultimate tensile strength and yield stress decreased with increasing POE content, while the ductility of the blends significantly increased. Furthermore, the POE reduced hardness and increased energy absorption during impact. In the fracture analysis, the addition of POE content increased the fracture resistance by increasing the crack energy and decreasing the resistance to crack initiation. Fractographic analysis showed how stretched microfibrils in the blends increase the fracture resistance. These results gave a significant indication of the utility of the elastomer in improving some mechanical properties and impact toughness of the interior automotive material to resist an undesired failure or over-fracture in airbag deployment.

Mixed matrix composite membranes with MOF-protruding structure for efficient CO2 separation

Mixed matrix composite membranes (MMCMs) hold great potential to realize efficient CO2 removal from natural gas. However, the reduction of separation performance arising from the interfacial defects, significant plasticization and aging effect in the thin films severely limit their application. Herein, we fabricated a series of polyimide MMCMs with MOF-protruding structure wherein amino-functionalized ZIF-8 nanocrystals nearly penetrate the thin selective layer. Through engineering the interfacial interactions, e.g., covalent or hydrogen bondings, we successfully fabricated defect-free MMCMs with the thickness ranging from 140 to 280 nm. The stronger interfacial interactions eliminate the interfacial defects and restrict the mobility of polymer chains under high pressure. Accordingly, the MMCM displays a high CO2 permeance of 778 GPU and a CO2/CH4 selectivity of 34 with significantly improved resistance to plasticization and aging. Considering the superior performance, we anticipate our work could provide guidelines on designing advanced MMMs to tackle critical separations.