Methyl Phosphine Oxide Research Articles

Stereoselective Synthesis of trans-1,2,4-Trihydrobenzo[d][1,2]azaphosphinine 3-Oxides from In Situ Formed Phosphenes and Formaldimines.

Various trans-1,2,4-trihydrobenzo[d][1,2]azaphosphinine 3-oxides are synthesized highly stereoselectively from in situ generated phosphenes and formaldimines under microwave irradiation. Aryl(diazo)methyl(diaryl)phosphine oxides first undergo the Wolff rearrangement to generate phosphenes. Imines, in situ generated from 1,3,5-triazinanes or paraformaldehyde and primary amines, nucleophilically attack the phosphenes followed by a tandem stereoelectronic effect-controlled intramolecular nucleophilic addition and aromatization to give final trans-1,2,4-trihydrobenzo[d][1,2]azaphosphinine 3-oxides, exhibiting completely different annuloselectivity from linear nonformaldimines.

Electroadsorption of La3+ and Ce3+ from aqueous media with a carbon paste electrode modified with HMS-CMPO

This work deals with the electroadsorption of rare earths cerium and lanthanum in aqueous solution by using a carbon paste electrode modified with a silica mesoporous material functionalized with carbamoyl methyl phosphine oxide (CMPO). This functionalization was carried out in a two-step synthesis, the intermediate product was synthesized by attaching N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (APTMS) to the surface of the HMS by a grafting method synthesis, then this intermediate was modified by CMPO, in a further condensation reaction. The final product CMPO obtained was characterized by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), thermal gravimetric analysis (TGA) and N2 adsorption/desorption isotherms using BJH and BET models. Showing thermal stability, a surface area higher than 450m2g-1 and mesoporous properties. The CMPO material was used to modify the mixture of the carbon paste electrode producing an enhancement in the interaction between the electrode surface and the lanthanides studied, at the same time it produces and improvement in the electroactive area by over two orders of magnitude. The modified carbon paste electrode (CMPO-CPE) developed in this work shows an increase in the conductivity, observed with the electrochemical impedance spectroscopy studies, and an increase in the electroactive area of 47 % was calculated from cyclic voltammetry experiments. CMPO-CPE was used to extract La3+ and Ce3+ from aqueous solution using NaNO3 as support electrolyte, by using a fixed potential program over time, measuring the obtained current by Chronoamperometric method. The adsorption and desorption results were corroborated with Inductively coupled plasma atomic emission spectroscopy (ICP-OES) demonstrated the capacity of extraction of the electrode were 74 μg after ten cycles for La3+ at pH 5.0 and 15 μg after ten cycles for Ce3+ at pH 6.0, using a CMPO modified electrode of small surface (3 mm radius). This electrode was tested for over 50 cycles without losing their electroactive properties under tested electrochemical conditions.

Modified Diglycolamide Resin: Characterization and Potential Application for Rare Earth Element Recovery

Rare earth elements (REEs) are crucial for green energy applications due to their unique properties, but their extraction poses sustainability challenges because the global supply of REEs is concentrated in a few countries, particularly China, which produces 70% of the world’s REEs. To address this, the study investigated TK221, a modified extraction chromatographic resin featuring diglycolamide (DGA) and carbamoyl methyl phosphine oxide (CMPO), as a promising adsorbent for REE recovery. The elemental composition and functional groups of DGA and CMPO on the polystyrene-divinylbenzene (PS-DVB) support of TK221 were confirmed using scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), and X-ray photoelectron spectroscopy (XPS). The adsorption kinetics of neodymium (Nd), yttrium (Y), cerium (Ce), and erbium (Er) followed the pseudo-second-order kinetic model and Langmuir isotherm, indicating monolayer chemisorption. Furthermore, iron (Fe) adsorption reached apparent equilibrium after 360 min, with consistent Fe adsorption observed at both 360 min and 1440 min. The inclusion of Fe in the study is due to its common presence as an impurity in most REE leachate solutions. The Fe adsorption isotherm results are better fitted with the Langmuir isotherm, implying chemisorption. Maximum adsorption capacities (qmax) of the resin were determined as follows: Nd (45.3 mg/g), Ce (43.1 mg/g), Er (35.1 mg/g), Y (15.6 mg/g), and Fe (12.3 mg/g). ATR-FTIR analysis after adsorption suggested that both C=O and P=O bands shifted from 1679 cm−1 to 1618 cm−1 and 1107 cm−1 to 1142 cm−1 for Y, and from 1679 cm−1 to 1607 cm−1 and 1107 cm−1 to 1135 cm−1 for Ce, implying possible coordination with REEs. These results suggest that TK221 has a huge potential as an alternative adsorbent for REE recovery, thus contributing to sustainable REE supply diversification.

Microwave-mediated stereocontrolled annulations of diazo(aryl)methyl(diaryl)phosphine oxides with pyridinium 1,4-zwitterionic thiolates.

Chemoselective annulations of phosphoryl carbenes generated from diazo(aryl)methyl(diaryl)phosphine oxides with pyridinium 1,4-zwitterionic thiolates were performed under microwave irradiation, affording 1-diarylphosphoryl-1H-benzo[c]thiopyran derivatives via [3+3] annulation and indolizine derivatives via ([1+5]-1) annulation with P-Cope elimination as the key step. The annuloselectivity was controlled by the steric hindrance of pyridiniums in pyridinium 1,4-zwitterionic thiolates.

Vibro-acoustic characteristics of multifunctional carbon fiber reinforced panel

This paper deals with the assessment of vibro-acoustic properties of a multifunctional carbon fiber reinforced panel manufactured by bulk infusion, a modified resin film infusion process. The components of the epoxy resin were chosen to contrast the electrical insulating property and poor flame resistance of the epoxy resins impregnating carbon woven fabric. To confer electrical conductivity to the resin a percentage of 0.5 wt% of Multi-Wall Carbon Nanotubes (MWCNTs) was dispersed in the resin, whereas to increase flame resistance a percentage of 5 wt% of Glycidil Polyhedral Oligomeric Silsesquioxanes (GPOSS) was solubilized in the epoxy mixture. Furthermore, as hardener agents, a mixture of 4,4’-DiaminoDiphenyl Sulfone (DDS) (53.4 wt%) and Bis(3-Aminophenyl) Methyl Phosphine Oxide (BAMPO) (46.7 wt%) was used. The values of the electrical conductivity were found satisfactory enough, being 4.02 × 10−2 S/m for the multifunctional resin and 1.39 × 104 S/m for the in-plane conductivity of the panel, whereas the Limiting Oxygen Index (LOI) value of the multifunctional resin was found to increase from 27% to 36%. Considering these promising results, an experimental assessment of the vibro-acoustic properties of the manufactured multifunctional panel was also performed. The panel was tested mainly to evaluate its low-frequency vibration damping and sound insulation characteristics. The manufactured panel demonstrated an improved efficiency if compared to a baseline configuration, presenting almost the double modal damping and a gain of 10 dB on the global noise reduction.

Synthesis of β-Phosphinolactams from Phosphenes and Imines.

Various cis-β-phosphinolactams are synthesized stereoselectively for the first time from imines and diazo(aryl)methyl(diaryl)phosphine oxides under microwave irradiation. Diazo(aryl)methyl(diaryl)phosphine oxides first undergo the Wolf rearrangement to generate phosphenes. Imines nucleophilically attack the phosphenes followed by an intramolecular nucleophilic addition via less steric transition states to give final cis-β-phosphinolactams. C-Styrylimines generally give rise to β-phosphinolactams in higher yields than C-arylimines. The stereoselectivity and proposed mechanism are rationalized by DFT theoretical calculation.

Europium(III) permeation through a flat sheet supported liquid membrane containing CMPO with iso-decanol phase modifier: Experimental and modeling studies

The permeation of Eu3+ ion across a microporous polymeric membrane impregnated with n-octyl(phenyl)-N,N-di-isobutylcarbamoyl methyl phosphine oxide (CMPO) was investigated from a nitric acid feed into a receiver phase of distilled water. A combination of 0.2M CMPO in 5% iso-decanol+95% n-dodecane was chosen as the carrier solvent. Here, iso-decanol has a dual role; acts as a phase modifier to avoid third phase formation, and minimizes the acid co-transport. The transport of Eu3+ was mainly driven by its distribution ratio by CMPO at the feed–membrane interface (extraction) and membrane–receiver interface (stripping). The effect of various experimental parameters such as feed acidity, nitrate ion concentration, and ligand concentration on permeation of Eu3+ was investigated. Effect of various stripping solutions was also studied to optimize the permeation efficiency of Eu3+ ions. A mathematical model was derived for predicting the mass transfer from feed phase to the receiver phase through the membrane. The results obtained by the calculations were subsequently validated through the experimental results.

1-Phosphino-1,3-butadiene Derivatives Incorporated with Dibenzobarrelene Skeleton: Synthesis and Photophysical Properties

Abstract An intramolecular [4+2] cycloaddition of 1-(9-anthrylchlorophosphino)-1,4-diphenylbut-1-en-3-yne produced the 1-(chlorophosphino)-1,4-diphenyl-1,3-butadiene derivative incorporated with a dibenzobarrelene skeleton, the following reactions of which gave the corresponding secondary phosphine oxide and phenylphosphine sulfide. The secondary phosphine oxide was deprotonated with butyllithium followed by treatment with methyl iodide to give methylphosphine oxide. The phenylphosphine sulfide was desulfurized with P(NMe2)3 to give the corresponding phenylphosphine, which was converted to the oxide and selenide and AuCl and BH3 complexes. Their structures were determined by X-ray crystallography. These compounds show blue fluorescence in solution (ΦF = 0.49–0.86) and the solid state (ΦF = 0.02–0.72) in a narrow range (λem = 442–463 nm) except the phenylphosphine selenide with a low fluorescence efficiency. Their photophysical properties were considered theoretically. The secondary phosphine oxide and the methylphosphine oxide were optically resolved by means of HPLC equipped with a chiral column, and the chiroptical properties were investigated to show weak circular polarized luminescence (CPL) of |gem| = 2.8–8.8 × 10−4.

Comparative evaluation of extraction of tetra- and hexa-valent neptunium ions by CMPO in a room temperature ionic liquid

ABSTRACT Solvent extraction studies were performed to understand the extraction behavior of Np4+ and NpO2 2+ from acidic feeds with CMPO (octyl (phenyl)-N,N-diisobutyl carbamoyl methyl phosphine oxide) dissolved in 1-butyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide, a water immiscible ionic liquid. Slope analyses on the distribution data revealed the extraction of ML2 type species, where M = Np4+ or NpO2 2+, and L = CMPO. Studies were also carried out with Pu4+ and UO2 2+ under identical conditions. The nature of the extracted species was found to vary with the nature of the ionic species.

Adsorption and separation behavior of strontium and yttrium using a silica-based CMPO adsorbent

To separate Y(III) from a Sr(II)–Y(II) mixture, two silica-based adsorbents, CMPO/SiO2-P and (CMPO + Dodec)/SiO2-P were prepared by impregnating octyl(phenyl)-N,N-diisobutylcarbamoyl methylphosphine oxide (CMPO) extractant and a molecule modifier (1-Dodecanol) into macroporous silica/polymer composite support (SiO2-P). The Adsorbents showed high adsorption affinity to Y(III) and weak adsorption affinity to Sr(II) in HNO3 solution. The amount of adsorbed Y(III) increased with the HNO3 in the solution. The amount of adsorbed Y(III) increased with contact time and reached equilibrium within 30 min. The results showed that a pseudo-second-order kinetic model with a high correlation coefficient described the adsorption process better than other kinetic models. Successful Y(III) separation from Sr(II)–Y(III) mixture in HNO3 solution was achieved.

Role of TBP on the extraction of trivalent f-cations with CMPO dissolved in a room temperature ionic liquid

ABSTRACTA detailed study on solvent extraction and optical spectroscopy was performed to understand the extraction of trivalent actinides by the solutions of CMPO (octylphenyl-N,N-diisobutyl-carbamoyl methyl phosphine oxide) in a room temperature ionic liquid (RTIL), viz. 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, [C4mim][NTf2]. Solvent extraction studies of Am(III) from nitric acid solution indicated an ion-exchange extraction mechanism. Slope analyses on the distribution data revealed that the stoichiometry of the extracted complex of Am3+/CMPO changed from 1:3 (Am/CMPO) in the absence of tri-n-butyl phosphate (TBP) to 1:2 in the presence of TBP. The distribution ratio values of Am(III) decreased significantly in the presence of TBP suggesting that the latter has an important role in the complexation of CMPO with the metal ion. The extraction of acid increased many folds in the presence of TBP as compared to the bare CMPO solution. The absorption and emission spectra of the extracted complex in RTIL differ significantly in the presence and absence of TBP, signifying the role of TBP in the CMPO-RTIL solvent.

Extraction of Rare-Earth Elements from Hydrochloric Acid by Carbamoyl Methyl Phosphine Oxides in the Presence of Ionic Liquids

The distribution of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y between aqueous HCl solutions and solutions of carbamoyl methyl phosphine oxides (CMPOs) has been studied in the presence of the 1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ionic liquid (IL). The efficiency and selectivity of REE(III) extraction by CMPO solutions increase considerably in the presence of the ionic liquid in the organic phase. The stoichiometry of the extractable complexes has been determined; the effects of the IL cation, organic solvent, CMPO structure, and aqueous HCl concentration on the efficiency of REE(III) recovery into the organic phase has been considered.

Extraction of actinide ions using three CMPO-functionalized pillar[5]arenes in a room temperature ionic liquid

Abstract Extraction of actinide ions from nitric acid feeds was investigated using solutions of three CMPO (carbamoyl methyl phosphine oxide) functionalized pillar[5]arenes with varying spacer lengths in a room temperature ionic liquid, [C8mim][NTf2]. The extraction of Am3+ was found to decrease with increasing nitric acid concentration suggesting a mechanism analogous to a cation-exchange mechanism. The nature of the extracted species was determined by the conventional slope analysis method to be ML type which was subsequently confirmed by luminescence spectroscopy. Studies carried out to determine the thermodynamic parameters suggested highly exothermic reactions with negative entropy values. The reusability and recycling studies involved stripping and radiolytic stability of the solvent systems which suggested reasonably encouraging results. While a DTPA solution in guanidine carbonate was found to back extract the extracted metal ion from the ionic liquid phase, the radiolytic stability of the CMPO-pillararenes were reasonably good.

Redox and Photophysical Behaviour of Complexes of NpO2+ Ions with Carbomyl methyl phosphine oxide in 1-Hexyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide Ionic Liquid

Room temperature ionic liquids (RTIL) have attracted considerable attention due to their many remarkable properties useful for technological applications not only involving formation of metal ion complexes but also as electrolyte. For understanding the role of ionic liquid in such applications requires the experimental and theoretical studies on the metal ion complexes. Therefore, an electrochemical, theoretical and luminescence studies have been carried out in the present work to correlate redox behavior, complexation, and photophysical characteristics NpO2+ complexes with carbomyl methyl phosphine oxide (CMPO) ligand in ionic liquid, which is important for the actinide partitioning. The electrochemical behavior of NpO2+extracted by CMPO in 1-Hexyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide (HmimNTf2) (IL) was studied at glassy carbon (GC) electrode. The redox reaction of NpO2+ to NpO22+and vice versa in HmimNTf2 is quasi-reversible and controlled by diffusion as well as charge transfer kinetics. The cyclic voltammograms obtained in ionic liquid were much broader with reduced cathodic and anodic peak current densities (jpc and jpa) as compared to the one obtained with aqueous solution. The transport properties and kinetics of Np(V) were deduced from electrochemical calculations. The complexation behaviour of CMPO with Np(V) in aqueous solution as well as in HmimNTf2 was studied using density function theory (DFT). Based on these calculations NpO2+forms [Np(CMPO)2(NO3)2]1− type of complex in aqueous solution whereas [Np(CMPO)2(NO3)2]1−.(IL)2complex in IL. Oxidation state of neptunium was further confirmed using Time resolved fluorescence spectroscopy (TRFS) and UV–vis absorption spectroscopy. Moreover TRFS data depicted the stabilization of Np as NpO2+ in both aqueous as well as in RTIL phases. The emission spectroscopic measurement also pin pointed the fact that emission peaks of Np-CMPO complex in RTIL is blue shifted with respect to aqueous solution, which is attributed to the change in equatorial bonding/coordination of the NpO2+in the basal plane. From Photoluminescence (PL) spectroscopy and its kinetics; it was also observed that emission intensity and average lifetime are more in case of Np-CMPO complex in RTIL as compared to aqueous phase because of presence of relatively higher concentration OH group in aqueous phase which are known to be fluorescence quencher. This is a rare study where electrochemical measurements established the redox behavior, DFT calculations confirms the complexation behavior and TRFS brings out the interesting optical features of NpO2+in aqueous and ionic liquid media.

AO-resistant properties of polyimide fibers containing phosphorous groups in main chains

A series of polyimide fibers containing phosphorus element derived from (3-aminophenyl) methyl phosphine oxide (DAMPO) diamine was exposed to an artificial atomic oxygen environment which simulated the space environment in low earth orbit (LEO). The mass loss, surface morphology, chemical composition, and mechanical properties of the fibers before and after atomic oxygen (AO) exposure were compared in detail with a blank sample. Results showed that the phosphor-containing fibers demonstrated lower mass change and less tensile strength reduction. SEM results showed that the fibers with phosphorous element had relatively dense surface after AO exposure. Meanwhile, XPS results indicated that a passivated phosphate layer, which could protect the following under-layer from attacking by AO, was formed on the surface of the fibers. These results indicated that the incorporation of diamine (DAMPO) into the main chains could protect the fibers for avoiding further erosion from AO exposure. Hence, the phosphor-containing PI fibers exhibits potential application in space fields.

Effect of phase modifiers TBP and iso-decanol on the extraction and complexation of Eu3+ with CMPO

ABSTRACTThe effect of tri-n-butyl phosphate (TBP) and iso-decanol as phase modifiers on the complexation of Eu3+ with octyl-phenyl N,N-diisobutyl carbamoyl methyl phosphine oxide (CMPO) was studied. On an increase of iso-decanol the extraction efficiency of Eu3+ decreases. The metal–ligand stoichiometry was found to be 1:3. The Eu complex of CMPO–TBP was more symmetric compared to CMPO–iso-decanol. The Eu3+ complex exhibited D3h and C3h symmetry for 30% and 5% iso-decanol, while that for TBP was C6v. The radiative, non-radiative life time, electric and magnetic dipole transition probabilities, branching ratio, quantum efficiency etc. were evaluated. The covalency between Eu3+ and CMPO is as follows: CMPO–TBP < CMPO-5% iso-decanol < CMPO-30% iso-decanol.

Understanding the complexation of the Eu3+ ion with TODGA, CMPO, TOPO and DMDBTDMA: Extraction, luminescence and theoretical investigation

A comparative study was carried out to understand the complexation behavior of the Eu3+ ion with important reagents, namely TODGA (N,N,N′,N′ tetraoctyl diglycolamide), CMPO (octyl (phenyl)-N, N-diisobutyl carbamoyl methyl phosphine oxide), DMDBTDMA (dimethyl dibutyl tetradecyl malonamide) and TOPO (tri-n-octyl phosphine oxide) in dodecane, used for the separation of actinides and lanthanides from lab and nuclear high-level wastes, by experimental (extraction and luminescent) and theoretical means. A solvent extraction study revealed the metal–ligand stoichiometry as 1:3 for all the systems with the extraction efficiency TOPO>CMPO>TODGA>DMDBTDMA at 1M HNO3, while TODGA>CMPO>DMDBTDMA>TOPO at 3M HNO3. A luminescence investigation revealed the presence of single species in the extracted complex for all the systems, with no inner sphere water molecules for all the systems except for DMDBTDMA which had one inner sphere water molecule. The high intensity of the 5D0–7F2 transition revealed the presence of Eu3+ ions in an asymmetric environment with the local point group symmetry C3v for the TODGA and DMDBTDMA complexes, compared to C3h symmetry for the CMPO and TOPO complexes. Judd–Offelt parameters, radiative, non-radiative lifetimes, branching ratio, transition probabilities and quantum efficiencies for all the complexes were estimated and compared. Three O-donor atoms from each TODGA molecule coordinated to the Eu3+ ion in the first coordination sphere, while three CMPO units were found to be coordinated in a monodentate fashion. For the Eu-TOPO complex, three O donor atoms from each of the three TOPO molecules and six O donor atoms from three nitrate ions were coordinated. Out of three DMDBTDMA ligands, one was found to be coordinated in a bidentate mode, whereas two were in a monodentate mode, along with three nitrate ligands bonding in a monodentate fashion.

Stereoselectivity of Michael Addition of P(X)-H-Type Nucleophiles to Cyclohexen-1-ylphosphine Oxide: The Case of Base-Selective Transformation.

Michael addition of phosphorus nucleophiles to the unsymmetrically substituted tert-butyl(1,4-cyclohexadien-3-yl)phosphine oxide and its derivatives has been described. The addition proceeds with the formation of the mixture of two isomeric products with good yield and diastereoselectivity. The reaction of tert-butyl(cyclohexen-1-yl)methylphosphine oxide with phosphorus nucleophiles is base sensitive and might afford two epimers which differ at one chirality center. The absolute configuration of the products has been assigned on the basis of conformational and (1)H NMR analysis, and the mechanism of the reaction has been discussed. The Michael addition of phosphorus nucleophiles is postulated to proceed with or without consecutive epimerization of two α-carbanions.

Complexation of amidocarbamoyl phosphine oxides with Ln+3 (Ln = La, Nd, Pm, Sm and Eu) cation series: structural and thermodynamical features

Abstract In the present study, we have mainly investigated the nature of interactions in Ln3+ (Ln = La, Nd, Pm, Sm, Eu) complexes with amidocarbamoyl methyl phosphine oxide (CMPO) and amidocarbamoyl propyl phosphine oxide (CPPO) ligands based on density functional theory (DFT) approaches. In the first step, thermodynamical properties for complexation of CMPO and CPPO ligands with Ln3+ cation series have been determined in the gas phase and with the presence of three solvents: n-hexane, chloroform and toluene, via polarized continuum model (PCM) computations. The trend of metal-ligand interaction strength has been analyzed and compared with the trend of ionic hardness within the series of lanthanide cations and different size of alkyl chain of amidocarbamoyl phosphine oxide ligand. The calculated thermochemical results in the gas and solution phases reveals that there is a consistency between increasing trend in the hardness of Ln3+ cation series and also electron-donating property of alkyl chain with increasing in thermodynamical stability of [Ln–CMPO]3+ and [Ln–CPPO]3+ complex series. We have also demonstrated that in the complexation reaction of all complex series, using n-hexane as solvent is more favorable thermodynamically than chloroform and toluene. It should be stated that this issue has been observed in many experiments. Finally, analysis of calculated deformation energies and also the variation in bond order of some selected key bonds in CMPO and CPPO ligands and their corresponded Ln+3 complexes series show a similar trend with increasing in the hardness of Ln3+ cation series and electron-donating of alkyl chain of amidocarbamoyl phosphine oxide ligand.

Physical and thermal properties of poly(ethylene terephthalate) fabric coated with electrospun polyimide fibers

Two analogous polyimides (PIs) containing flexible isopropylidene units were prepared. One was based on 4,4′-oxydiphthalic anhydride and 4,4′-(4,4′-isopropylidenediphenyl-1,1′-diyldioxy) dianiline and the other was based on 4,4′-(4,4′-isopropylidenediphenoxy) bis(phthalic anhydride) and bis(3-aminophenyl) methyl phosphine oxide. The ability of these two PIs to form uniform nanoscaled fibers was investigated by electrospinning technique. At optimal spinning conditions, PI fibers were electrospun onto the surface of woven poly(ethylene terephthalate) (PET) support to form a bilayer composite structure. These new fabric systems were analyzed regarding morphology, air permeability, wetting properties, and thermal stability. It was expected that the new PET/PI mats would possess enhanced properties compared with the initial woven PET fibers due to the excellent properties of PIs. Experimental results showed that PET woven substrate coated with electrospun PI fibers had improved values of air permeability, water contact angle and thermal stability when compared with the initial woven PET fibers.