Neat Polyimide Research Articles

Synthesis of metal-doped covalent triazine frameworks: Incorporation into 6FDA-Durene polyimide for CO2 separation through mixed matrix membranes

The development of advanced mixed matrix membranes (MMMs) is expanding through the design of functionalized materials and efficient hybrid mass transfer mechanisms to meet the growing needs for practical and cost-effective gas separation technologies. Here, a novel series of transition metal-doped covalent triazine frameworks (M2+CTFs) was synthesized and incorporated into a 6FDA-Durene polyimide (PI) matrix in the range of 0–0.5 wt% to prepare cost-effective facilitated transport MMMs with high CO2 separation performance. Qualitative and quantitative analyses including FTIR, XPS, CHN, XRF, BET, XRD, TGA, DLS, FESEM, EDX, and TEM were carried out. The presence of nucleophilic N sites and electron-rich heterocycles in highly porous CTFs (through the π–π-stacking interactions with CO2 molecules), together with transition metal ions (Fe2+, Cu2+, and Zn2+) as the fixed site active carriers (with strong CO2 facilitated transport through the π complexation/decomplexation reaction), improves the affinity for CO2 molecules, facilitates their transport, and subsequently increases the CO2/non-polar gas selectivity of MMMs. The resultant M2+CTF/PI MMMs successfully surpass the 2008 upper bound at filler loading of 0.4 wt% for CO2/CH4 and CO2/N2 separations. Embedding M2+CTFs into the PI matrix improves the mechanical properties of the membranes. The Zn2+CTF/PI MMM represents the best separation performance with a CO2 permeability of 1408 Barrer, a CO2/N2 selectivity of 37, and a CO2/CH4 selectivity of 39, which represents a 120 %, 111 %, and 110 % increase compared to the neat PI membrane at a feed pressure of 2 bar. The excellent results of the present study indicate the high potential of cost-efficient synthesized M2+CTF particles and related facilitated transport MMMs for possible application in industrial processes.

High-temperature semicrystalline/amorphous polymer blends exhibiting enhanced dielectric constant with high breakdown strength

High-temperature polymers with high dielectric constant (K) and breakdown strength are of great interest in many electronic and electric devices and systems. Blending different polymers is a general and highly scalable strategy to improve polymer performance. We investigate two types of semicrystalline polyimide (PI) with different chemical structures blended with amorphous polymer poly (1,4-phenylene ether sulfone) (PES). They formed immiscible polymer blends and exhibited distinctively semicrystalline/amorphous behaviors. The blends of 4,4’-biphthalic anhydride (BPDA)-typed PI with PES form semicrystalline polymer phases and the blend at 50/50 wt% composition exhibits an increased dielectric constant while maintaining the high breakdown field of the neat PI(BPDA) at Eb of 600 MV/m. In contrast, blends of pyromellitic dianhydride (PMDA)-typed PI and PES, which form amorphous phases, show a dielectric increase but a large reduction in Eb. Computational simulations indicate that PI(BPDA) assumes a preferred orientation on PES, which expedites crystallization, while overlaying PI(PMDA) on PES results in more disorder and larger voids. Our finding that the PI(BPDA)/PES blends at 50/50 wt% composition generates enhancement in K without negatively affecting Eb is the first in polymer blends. The results suggest that strategically designing high-temperature polymer blends and exploiting the crystallites within the polymer matrix can achieve an enhanced dielectric constant while maintaining a high breakdown strength. This approach is highly scalable and low cost, thus paving the way for developing practical and high-performance dielectric polymers with high energy density and broad operating temperatures.

Fabrication of High Impact-Resistant Polyimide Nanocomposites with Outstanding Thermomechanical Properties.

Neat polyimide films are known to be dense and rigid. They are therefore not suitable for use in membranes, sensors and sustainable energy storage applications. In this study, a novel technique has been used to simultaneously improve the porosity, rigidity, damping ability and impact resistance of polyimide membranes. It is demonstrated that dispersion of a small amount of polyaniline copolymer-modified clay of about 0.25-0.5 wt.% into the polyimide matrix resulted in an enhanced storage modulus while maintaining high damping ability and glass transition temperature, Tg. Novel polyimide/substituted polyaniline-copolymer-clay nanocomposite membranes containing poly(N-ethyl-aniline-co-aniline-2-sulfonic-acid)-modified-clay (SPNEAC) was successfully prepared and incorporated into the polyimide matrix to form modified clay/polyimide nanocomposites. UV-Vis analysis of the nanocomposite films shows that the optical transparency of the SPNEAC-PI nanocomposite membranes decreased with increasing SPNEAC concentration due to the high UV-Vis absorption of SPNEAC. Transmittance of about 3% was observed in the nanocomposite membrane containing 5 wt.% modified clay at 500 nm wavelength, which is significantly lower than that for the neat PI membrane of about 36%. The dispersion of SPNEAC containing a high concentration of clay (≥40 wt.% clay), in polyimide matrix, resulted in the attainment of a higher degree of imidization than was possible for the organoclay/polyimide nanocomposite. This behavior is believed to be due to the synergistic interaction between PI and SPNEAC. A correlation of the morphology and elastic modulus of the SPNEAC2/PI nanocomposites shows that at low loading of SPNEAC 2 ≤ 0.5 wt.%, the cross-sectional morphology of the composite is an open, spiky, weblike structure with a storage modulus of about 1 GPa, but it progressively evolves into densely packed microspheroids with storage moduli of ≥2 GPa at 10 wt.% SPNEAC2. The impact energy of SPNEAC/PI composites, calculated from the α-transition peak area, increased with increasing SPNEAC loading and were about 4 times that of neat PI at 10 wt.% SPNEAC.

Polyimide/Ionic Liquids Hybrid Membranes with NH3-Philic Channels for Ammonia-Based CO2 Separation Processes.

An efficient separation technology involving ammonia (NH3) and carbon dioxide (CO2) is of great importance for achieving low-carbon economy, environmental protection, and resource utilization. However, directly separating NH3 and CO2 for ammonia-based CO2 capture processes is still a great challenge. Herein, we propose a new strategy for selective separation of NH3 and CO2 by functional hybrid membranes that integrate polyimide (PI) and ionic liquids (ILs). The incorporated protic IL [Bim][NTf2] is confined in the interchain segment of PI, which decreases the fractional free volume and narrows the gas transport channel, benefiting the high separation selectivity of hybrid membranes. At the same time, the confined IL also provides high NH3 affinity for transport channels, promoting NH3 selective and fast transport owing to strong hydrogen bonding interaction between [Bim][NTf2] and NH3 molecules. Thus, the optimal hybrid membrane exhibits an ultrahigh NH3/CO2 ideal selectivity of up to 159 at 30 °C without sacrificing permeability, which is 60 times higher than that of the neat PI membrane and superior to the state-of-the art reported values. Moreover, the introduction of [Bim][NTf2] also reduces the permeation active energy of NH3 and reverses the hybrid membrane toward "NH3 affinity", as understood by studying the effect of temperature. Also, NH3 molecules are much easier to transport at high temperature, showing great application potential in direct NH3/CO2 separation. Overall, this work provides a promising ultraselective membrane material for ammonia-based CO2 capture processes.

Novel polyimide-hexagonal boron nitride nanocomposites for synergistic improvement in tribological and radiation shielding properties

Polyimide (PI), a high-performance polymer with a high strength-to-weight ratio, thermal stability up to 330 °C, and chemical resistance, is a candidate material for aerospace and automotive applications. However, the poor tribological performance at elevated temperatures and radiation-induced brittle fracture threaten the durability of PI materials. To counter these challenges, novel hexagonal boron nitride (h-BN) based PI nanocomposites were prepared at 2 wt% and 5 wt% h-BN using direct forming. The dispersion of h-BN in the PI matrix was facilitated using ball milling. The glass transition temperature (Tg) of PI-2 wt% and 5 wt% h-BN increased by 18 °C and 20 °C, respectively, compared to neat PI. Tribological characterization using dry ball-on-disk sliding revealed an improvement in wear rate of ∼56 % and ∼70 % for PI-2 wt% and 5 wt% h-BN compared to neat PI at room and high temperatures (300 °C). PI-hBN nanocomposites were subjected to a neutron radiation source. The linear and mass absorption coefficient of PI-2 wt% and 5 wt% h-BN enhanced significantly by 1.9 and 2.2 times, respectively, compared to neat PI. The developed nanocomposites, with their excellent tribological behavior and neutron shielding capacity, have great potential as multifunctional materials for aerospace applications.

Effects of different amine-functionalized graphene oxide on the mechanical and thermal properties of polyimide composites

The utilization of functionalized graphene oxide as nanofillers has attracted significant attention in the development of high-performance composite materials. In this study, amine-functionalized graphene oxide (AFGO) by different amines, including p-phenylenediamine- (PPD-GO) and 4, 4’-diaminodiphenyl ether (ODA-GO), respectively, was prepared and used to synthesize a series of polyimide (PI) composite membranes via in situ polymerization method. The PPD-GO/PI and ODA-GO/PI composite membranes exhibited much higher mechanical and thermal properties than that of neat PI, owing to the diverse interfacial interaction and the surface architecture behavior. Compared to neat PI, the tensile strengths were enhanced 14.6% and 14.5%, the tensile modulus were enhanced 26.9% and 23.2%, and the Tg increased by 9°C and 17.5°C of the PI composite membrane containing 0.3 wt% PPD-GO or ODA-GO, respectively. This study provides a guidance for the development of high-performance PI composite materials through the regulated interfacial structure via the moderate chain length.

Evaluation of three-component boron-free glass fiber/TiO2/polyimide nanocomposite properties prepared by 3D turbula dispersion and spark plasma sintering method

Interest has grown in recent time on the development of three-component polymer nanocomposite with enhanced properties. However, the study focuses on the effect of TiO2 nanofiller on the mechanical, tribological, dielectric, and corrosion resistance properties of boron-free glass fiber (BGF) reinforced polyimide (PI) composite produced with spark plasma sintering route. Microstructure of the samples was examined using scanning electron microscopy. Mechanical, tribological, dielectric, thermal, and corrosion behaviour of the samples were characterized by nanoindenter, ball-on-disc, LCR meter, TGA, and potentiodynamic polarization test, respectively. The SEM results show that the introduction of the nanoparticles into the BGF/PI composite aids in more uniform distribution of the BGF particles within the PI matrix, and thus good interfacial interaction of the glass fiber and the PI matrix structure. Comparing the BGF/PI composite sample with BGF/TiO2/PI nanocomposite, it was observed that the nanocomposite depicted better hardness, elastic modulus, low friction coefficient and wear rate, dielectric, and enhanced corrosion properties. With TiO2 additions, hardness and modulus of the PI composite was improved by 56.6% and 10.1%, respectively. In addition, PI composites filled with TiO2 depicted a 0.07 coefficient of friction and wear rate of about 67.7% in reduction than that of neat PI and 9.0% in reduction than that of the pristine BGF/PI composites. Improved interactions between the reinforcements and the host matrix are suggested as the possible mechanism resulting to the desirable properties of the three-component PI nanocomposite recorded. Finally, the developed nanocomposite is suggested to be favourable for automobile, aerospace, and microelectronic device applications.

Gas permeation, thermal, morphology and mechanical properties of polyimide/clay nanocomposites: Effect of organically modified montmorillonite

Novel polyimide/clay nanocomposites were fabricated by incorporating organically modified clay at different loading percentage of 1–5 wt% within the polyimide (PI) matrix. A novel PI was synthesized through a direct polycondensation reaction between novel 5,5′-((4-methoxyphenyl)azanediyl)bis(isobenzofuran-1,3-dione)and 4,4′-(1,4-phenylenebis(oxy))bis(3-(trifluoromethyl)aniline). The organoclay was prepared from Sodium montmorillonite (Na-clay) and protonated form of diamine (modifier) via ion-exchange reaction. The structural characterization of nanocomposites were made using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), the mechanical properties were obtained by tension tests. The results of XRD, TEM, and FE-SEM indicated that clay could well disperse in the PI matrix and were intercalated by diamine and PI macromolecules. The thermal stability and glass transition temperature of nanocomposite at lower clay loadings are similar to PI but gradually decrease with increase in clay content. The tensile properties of PI/Clay nanocomposites showed the highest values at the optimum clay content of 3 wt%. The gas permeation of PI/clay nanocomposites was increased with the increase in loading percentage of organoclay, whereas the gas selectivity was maintained at par to that of neat PI film until it diminished at 5 wt% percentage of organoclay causing mineral agglomeration. PI/clay 3 wt% MMMs exhibited 245% and 240% increase in CO2 and O2 gas permeability respectively, while showing minimal variation in the selectivity of O2/N2 and CO2/N2 compared to that of neat PI matrix.

Synergism lubrication of graphene and carbon nanotube in polymeric composites under drying sliding condition

The internal lubrication of polyimide (PI) with added graphene oxides (GOs) and carbon nanotubes (MWCNTs), as well as their binary hybrid nano-additives (GCNTs), were contrastively investigated under dry sliding conditions. The friction coefficient of neat PI or its nanocomposites decreases as a stepwise increase of the load fitting a negative exponential equation while growing linearly as a stepwise increase of the velocity. Micromorphological and physicochemical variations occurring at friction interfaces have been analyzed using X-ray photoelectron spectroscopy, Raman spectroscopy, and high-resolution transmission electron microscopy results. Given the structural discrepancy between GOs and MWCNTs, the obtaining results showed that the different microcosmic tribological mechanisms for GCNTs enable to produce a synergistic lubricating effect, resulting in facilitating the complicating interface sliding between nanocomposites and steel balls.

Synthesis and characterization of new nanocomposites-based polyimide/modified montmorillonite and their applications in gas separation

ABSTRACT This study reports synthesis of nanocomposite materials-based polyimide (PI) matrix and reactive modified montmorillonite (m-MMT) as a reinforcing agent. New diamine and PI derived from amino acid (L-phenylalanine) fractions in the structure as pendant group were synthesized. The best dispersion of m-MMT was observed for PI/m-MMT 3% nanocomposites, which resulted in the best mechanical performance with an increase of 56% in tensile modulus and 14% in yield strength, respectively compared to that of pure PI. The maximum ideal selectivity achieved was 15.89 with 3% loading at 4 bar pressure which is 42.52% higher than neat PI membrane.

Mechanical and tribological behaviors of MWCNT/polyimide nanocomposites under drift of glass transition temperature

Herein, the tribological behavior of multi-walled carbon nanotube (MWCNT)/polyimide (PI) composites in water was investigated based on manufacturing optimization using response surface methodology (RSM). Wear surfaces and transfer films were analyzed by SEM, EDS, TEM, and Raman spectroscopy. It indicates that the molding process for neat PI and MWCNT/PI is deeply subjected to a narrow processing temperature window. Depending on the positive drift of the glass transition temperature for MWCNT/PI, the tribological properties in water were significantly affected by molding temperature. Besides, combined with experimental results and simulation analysis, it suggested that MWCNT performs rolling and/or sliding motions in molecular bearings form between frictional pairs for enhanced lubrication.

Synthesis and characterization of nanocomposites based on polyimide bearing benzimidazole side groups filled with titania nanoparticles

ABSTRACT This study reports on the fabrication and property investigation of nanocomposites based on polyimide (PI) containing benzimidazole pendant groups reinforced with titania nanoparticles (TiO2 NPs) via the in-situ thermal imidization approach. This method involves the formation of poly(amic acid) (PAA), as the precursor of PI, by polycondensation of an equimolar amount of dianhydride, pyromellitic dianhydride (PMDA), with a benzimidazole-containing diamine monomer, 5-(2-benzimidazole)-1,3-bis(4-aminophenoxy)benzene (BIDA), in dimethylacetamide (DMAc) solvent, followed by embedding various weight percentages (3, 5, and 8 wt%) of amine-functionalized titania nanoparticles (NH2-TiO2 NPs) in PAA media, and subsequent thermal imidization to be converted to PI/TiO2 nanocomposite films. The structural, morphological, and thermal properties of the obtained neat PI and its nanocomposite films were studied by various methods, such as FT-IR spectroscopy, X-ray diffraction (XRD) analysis, thermal gravimetric analysis (TGA), and scanning electron microscopy (SEM). The data resulted from TGA analysis indicated that the incorporation of NH2-TiO2 NPs into the PI matrix show higher thermal stability when compared to the neat PI. The SEM images revealed that the dispersion of titania NPs was uniformly done in PI matrix, with a particle size of around 42 nm.

Effect of Polymer Matrix on Inelastic Strain Development in PI- and PEI-Based Composites Reinforced with Short Carbon Fibers under Low-Cyclic Fatigue

Since the inelastic strain development plays an important role in the low-cycle fatigue (LCF) of High-Performance Polymers (HPPs), the goal of the research was to study the effect of an amorphous polymer matrix type on the resistance to cyclic loading for both polyimide (PI)- and polyetherimide (PEI)-based composites, identically loaded with short carbon fibers (SCFs) of various lengths, in the LCF mode. The fracture of the PI and PEI, as well as their particulate composites loaded with SCFs at an aspect ratio (AR) of 10, occurred with a significant role played by cyclic creep processes. Unlike PEI, PI was less prone to the development of creep processes, probably because of the greater rigidity of the polymer molecules. This increased the stage duration of the accumulation of scattered damage in the PI-based composites loaded with SCFs at AR = 20 and AR = 200, causing their greater cyclic durability. In the case of SCFs 2000 µm long, the length of the SCFs was comparable to the specimen thickness, causing the formation of a spatial framework of unattached SCFs at AR = 200. The higher rigidity of the PI polymer matrix provided more effective resistance to the accumulation of scattered damage with the simultaneously higher fatigue creep resistance. Under such conditions, the adhesion factor exerted a lesser effect. As shown, the fatigue life of the composites was determined both by the chemical structure of the polymer matrix and the offset yield stresses. The essential role of the cyclic damage accumulation in both neat PI and PEI, as well as their composites reinforced with SCFs, was confirmed by the results of XRD spectra analysis. The research holds the potential to solve problems related to the fatigue life monitoring of particulate polymer composites.

Scalable in-situ surface-coated polymer dielectrics with significantly enhanced high-temperature breakdown strength

Wide bandgap inorganic layers exhibit the effect to improve the insulating properties as charge barrier layers between the electrode and polymer dielectrics. However, their influence mechanisms on the high-temperature breakdown behavior still need to be further revealed. Herein, the in-situ grown strontium oxide (SrO) layers were coated on the surfaces of polyimide (PI) film to conduct this research. Compared with neat PI, the breakdown strength and discharge energy density (efficiency >90%) of the coated film was significantly elevated up 45% and 1000% at 200 °C, respectively. The experimental results show that SrO greatly reduces the entropy of surface molecular conformations and increases the energy level of localized states of PI film. The SrO coating effectively improves the injection barrier and interface trap levels simultaneously, undertakes a higher electric field, and hinders the destruction of PI film's surface molecules by high-energy electrons, thus reducing the conduction loss and constraining the generation and development of electrical trees at high fields. This work not only provides a comprehensive insight into the in-situ oxide coating on the insulating properties in polymer dielectrics but also offers a paradigm for developing scalable dielectric materials with high breakdown strength used in harsh-condition electrification.

Enhanced thermal diffusion in the vertical direction of flexible polyimide composite films with magnetically alignable h-BN platelets via ferrofluids hybridization

A facile approach is proposed to improve the anisotropic heat conduction of polyimide composite films containing hexagonal boron nitride (h-BN), thermally conductive filler with high anisotropy, via surface hybridization with ferrofluids as magnetic carrier source. The surfaces of the h-BNs were decorated with Fe3O4 particles to control their alignment using magnetic field. The h-BNs with hydroxyl groups (f-BN) were mixed with ferrofluids and heated to 130 °C with stirring. A considerable amount of Fe3O4 nanoparticles was attached to the surface of f-BNs, named mf-BNs. Flexible polyimide (PI) composite films were prepared by adding mf-BNs at 1–30 wt.% to investigate the anisotropic alignment of mf-BNs under magnetic field. The thru-plane thermal conductivity of the PI composite film with vertically aligned mf-BN of 30 wt.% is 6 times higher than that of the neat PI film, as increased from 0.212 to 1.246 W/m∙K. This result is attributed to the anisotropic h-BN particles coated with the magnetic fluid arranged within the PI matrix in the vertical direction by using a neodymium magnet with less than 150 mT. This can solve the thermal issues of next-generation electronics by speeding the vertical heat transfer, which can greatly contribute to the improvement of the device reliability.

An Automated Optical Strain Measurement System for Estimating Polymer Degradation under Fatigue Testing.

(1) Background: this study deals with design of an automated laboratory facility based on a servo-hydraulic testing machine for estimating parameters of mechanical hysteresis loops by means of the digital image correlation (DIC) method. (2) Methods: the paper presents a description of the testing facility, describes the grounds for calculating the elastic modulus, the offset yield strength (OYS) and the parameters of the mechanical hysteresis loops by the DIC method. (3) Results: the developed hardware-software facility was tested by studying the fatigue process in neat polyimide (PI) under various amplitude tension-tension loadings. It was found that the damage accumulation was accompanied by the decrease in the loop areas, while failure occurred when it reduced by at least ~5 kJ/m3. (4) Conclusions: it was shown that lowering the loop area along with changing the secant modulus value makes it possible to estimate the level of the scattered damage accumulation (mainly at the stresses above the OYS level). It was revealed that fractography data, namely the pattern and sizes of the fatigue crack initiation and propagation zones, did not correlate well with the dependences of the parameters of the hysteresis loops.

Estimating Low- and High-Cyclic Fatigue of Polyimide-CF-PTFE Composite through Variation of Mechanical Hysteresis Loops.

The fatigue properties of neat polyimide and the “polyimide + 10 wt.% milled carbon fibers + 10 wt.% polytetrafluoroethylene” composite were investigated under various cyclic loading conditions. In contrast to most of the reported studies, constructing of hysteresis loops was performed through the strain assessment using the non-contact 2D Digital Image Correlation method. The accumulation of cyclic damage was analyzed by calculating parameters of mechanical hysteresis loops. They were: (i) the energy losses (hysteresis loop area), (ii) the dynamic modulus (proportional to the compliance/stiffness of the material) and (iii) the damping capacity (calculated through the dissipated and total mechanical energies). On average, the reduction in energy losses reached 10–18% at the onset of fracture, whereas the modulus variation did not exceed 2.5% of the nominal value. The energy losses decreased from 20 down to 18 J/m3 (10%) for the composite, whereas they reduced from 30 down to 25 J/m3 (17%) for neat PI in the low-cycle fatigue mode. For high-cycle fatigue, energy losses decreased from 10 to 9 J/m3 (10%) and from 17 to 14 J/m3 (18%) for neat PI and composite, respectively. For this reason, the changes of the energy losses due to hysteresis are of prospects for the characterization of both neat PI and the reinforced PI-based composites.

Synthesis, characterization and properties of polyimide nanocomposite thin films reinforced with TiO2/Al2O3 hybrid nanoparticles

Highly flexible PI (polyimide) nanocomposite thin films were successfully synthesized incorporating surface functionalized TiO2/Al2O3 hybrid nanoparticles. The as-prepared composite films were characterized by different techniques. The FTIR spectra revealed that the Al2O3/TiO2 hybrid nanoparticles showed characteristic peaks of the individual fillers in a single spectrum. Amino groups grafted on the surface of the hybrid nanoparticles were also confirmed by FTIR. PI composites with 2 wt% TiO2/Al2O3 hybrid nanoparticles showed an increment of T5 (temperature of 5% weight loss) by about 37.2 ℃ compared to the neat PI films. The T10 (temperature of 10% weight loss) of PI composites with 2 wt% TiO2/Al2O3 hybrid nanoparticles was also increased by approximately 36.1 ℃ compared to the neat PI films. The PI composite films with TiO2/Al2O3 hybrid nanoparticles showed an increment of Tg by about 93.1 °C compared to the neat PI films. The tensile strength and tensile modulus of PI nanocomposite films incorporating TiO2/Al2O3 hybrid nanoparticles was improved by approximately 157.2% and 113.7%, respectively compared to the neat PI films.

Mixed Matrix Membranes Loaded with a Porous Organic Polymer Having Bipyridine Moieties.

Mixed matrix membranes (MMMs), derived from three aromatic polyimides (PIs), and an affordable porous organic polymer (POP) having basic bipyridine moieties were prepared. Matrimid and two fluorinated polyimides, which were derived from 4,4′-(hexafluoroisopropylidene)diphthalic anhydride and 2,2′-bis(4-aminophenyl)hexafluoropropane (6F6F) or 2,4,6-trimethyl-m-phenylenediamine (6FTMPD), were employed as polymer matrixes. The used POP was a highly microporous material (surface area of 805 m2 g−1) with excellent thermal and chemical stability. The MMMs showed good compatibility between the PIs and POP, high thermal stabilities and glass transition temperatures superior to those of the neat PI membranes, and good mechanical properties. The addition of POP to the matrix led to an increase in the gas diffusivity and, thus, in permeability, which was associated with an increase in the fractional free volume of MMMs. The increase in permeability was higher for the less permeable matrix. For example, at 30 wt.% of POP, the permeability to CO2 and CH4 of the MMMs increased by 4- and 7-fold for Matrimid and 3- and 4-fold for 6FTMPD. The highest CH4 permeability led to a decrease in CO2/CH4 selectivity. The CO2/N2 separation performance was interesting, as the selectivity remained practically constant. Finally, the POP showed no molecular sieving effect towards the C2H4/C2H6 and C3H6/C3H8 gas pairs, but the permeability increased by about 4-fold and the selectivity was close to that of the matrix. In addition, because the POP can form metal ion bipyridine complexes, modified POP-based MMMs could be employed for olefin/paraffin separations.

Examination on Partial Discharge Characteristics and Frequency Acceleration Equivalence till Breakdown for Nanocomposite Enamel Wire

This paper presents partial discharge characteristics and film thickness wear till dielectric breakdown under bipolar repetitive impulse voltage application to twisted pair enamel wire added with nano-size boehmite to polyimide (PI) resin by comparing with a sample without the addition. The frequency acceleration equivalence of the life time and PD characteristics till breakdown is also examined. As a result, it was found that at frequencies 10 kHz to 30 kHz, a frequency acceleration equivalence held in terms of the total amount of PD charge at an applied voltage Va = 1.5 kV, while it did not at Va = 3.0 kV due to severer heat generated by PD. In addition, it was found that the coating thickness erosion of boehmite PI was less likely to be caused than that of neat PI under the same experimental conditions. Consequently, it is indicated that the total PD charge amount is closely related with the coating erosion speed.