Differential scanning calorimetry studies of the cure of carbon fiber–epoxy composite prepregs

Diaminodiphenyl sulfone (DDS) cured tetraglycidyl-4,4'-diaminodiphenyl methane (TGDDM) epoxies, whose cure reactions are accelerated by BF₃:amine catalysts, are the most common composite matrices utilized in aerospace high performance, fibrous composites. To process reproducible composites requires an understanding of the cure reactions and how these reactions are modified by the BF₃:amine catalysts. In this article we report systematic differential scanning calorimetry (DSC) studies of (i) the constituents of BF₃:NH₂C₂H₅-catalyzed TGDDM–DDS epoxies and their mixtures, (ii) the effect of BF₃:NH₂C₂H₅ concentration on the cure reactions, (iii) the nature of the catalyzed cure reactions, and (iv) the environmental sensitivity of the catalyst. DSC studies are also reported on the cure reaction characteristics and environmental sensitivity of commercial C fiber–TGDDM–DDS epoxy prepregs.     

Thermoinitiated cationic polymerization of epoxy resins by sulfonium salts

Catalytic activities of benzyl sulfonium salts with nonnucleophilic anions (BF₄^?,PF₆^?,AsF₆^?,SbF₆^?) for epoxy polymerization were examined. The order of reactivities correlated well with nonnucleophilicity of anions. Epoxy resins catalyzed by these salts are characterized by longer shelf-life and shorter gel time at high temperature. Some physical properties of cured product were compared with those cured by a commonly used BF₃ amine complex.     

Photopolymerization of 1,2-epoxypropane and 1,2-epoxybutane by arenediazonium salts: evidence for anion dependence of the extent of polymerization

The rates and extents of polymerization of 1,2-epoxypropane and 1,2-epoxybutane, induced by photolysis of dilute concentrations of salts of 2,5-diethoxy-4-tolylthiobenzenediazonium ion with various Lewis acids (SbF^?₆, PF^?₆, BF^?₄ etc.) have been determined by viscosity, ¹H n.m.r. and polymer isolation methods. A clear dependence exists of the degree of conversion on the anion: thus SbF^?₆ salt yields up to 100% high polymer, PF^?₆ salt yields c. 20% high polymer, while BF^?₄ salt yields small conversions (2%, but increasing to 15–18% at high initiator concentrations) which consists almost entirely of oligomers, mainly the cyclic tetramer.     

The Copper (II) Complexes of Phenyl-2 Pyridyl Ketone and the Triple Complexes Obtained by Adding Ethylenediamine

Copper salts of low pH (1.8–2.5) combine with phenyl-2-pyridyl ketone to form a ketone complex [(Py–CO–C₆H₅)₂Cu]²⁺. An electrically uncharged complex is obtained at pH > 9 [(Py–C(OH)(C₆H₅)O^?)₂Cu]⁰, liberating two protons from two molecules of the ligand. The stability constant of this complex is β = 16.05. By mixing the copper salts (except the halide) containing this ligand with ethylenediamine, a charged triple complex is obtained at pH < 7 [Py–C(OH)(C₆H₅) O–Cu–NH₂C₂H₄NH₃⁺]²⁺. At pH > 9.5, an uncharged triple complex is obtained: {[(Py–C(OH)(C₆H₅)O^?)₂Cu}₂ · NH₂C₂H₄NH₂}⁰. The copper halide salts produce only an uncharged triple complex; the halide ions are coordinated with the copper atoms. All of these complexes in their solid state, are bi- or polynuclear. As a result, they are magnetically subnormal.     

Influence of metal salts in reaction medium on performance enhancement of novel aliphatic–aromatic-based polyamide thin-film composite osmosis membranes

In this study, we report an easy and novel way to develop high flux aliphatic–aromatic-based thin-film composite (TFC) polyamide osmosis membranes by addition of inorganic metal salts with amine reactants in the reaction system of polyethylene imine (PEI) and 1,3-benzene dicarbonyl chloride. Inorganic metal salts like CuSO₄, NiSO₄, MgSO₄, and Al₂(SO₄)₃ added to block some of the amine groups of PEI through complexation which in turn changes the polycondensation reaction kinetics of amine acid chloride reaction. The prepared membranes were characterized using water contact angle and atomic force microscopy studies and the performances were evaluated both in reverse osmosis and forward osmosis mode. In presence of metal salts in reaction interface, the performance of TFC membranes was greatly enhanced and the optimum metal salt concentration was identified for individual metal salts for maximum performance enhancement. The effects of different anions for same metal ion and different molecular weight of PEI were evaluated on composite polyamide membrane performances. Water permeability (flux) of 63.48 L m^?2 h^?1 was achieved upon inorganic salt addition compared to the unmodified TFC membranes with flux of 42.1 L m^?2 h^?1 at similar salt rejection of ~95%. Based on the new findings, a conceptual model was proposed to explain the role of metal ion in amine solution on the resulting characteristics of aromatic–aliphatic type polyamide–polysulfone composite membrane.     

Synthesis,characterization, and application for addition polymerization of norbornene of novel acetylacetonate bis(anilines) palladium (II) complexes

New acetylacetonate bis(aniline) palladium (II) complexes were synthesized by nitrile substitution of [Pd(acac)(MeCN)₂]BF₄ with L (L = o-toluidine, p-toluidine, 2,6-dimethylaniline, 2,6-diisopropylaniline) which yielded [Pd(acac)(L)₂]BF₄ as a mononuclear species with chelating acac ligand. Preliminary investigations into the polymerization of norbornene in the presence of BF₃·OEt₂ were performed. An X-ray diffraction study of [Pd(acac){NH₂(2,6-Me₂C₆H₃)}₂]BF₄ establishes the presence of hydrogen bonding between the 2,6-dimethylaniline ligand and [BF₄]⁻ anion.     

Cure monitoring of aerospace epoxy resins and prepregs by Fourier transform infrared emission spectroscopy

Spectral analysis of the infrared radiation emitted from thin films of resin transferred from the surface of high performance aerospace carbon fibreepoxy composite prepregs and heated to the cure temperature allows the cure chemistry and kinetics to be monitored in real time. Quantitative spectra with excellent signal-to-noise ratio are obtained by heating a thin resin film on a platinum hotplate fitted to the external optics of a Fourier transform infrared (FTIR) spectrometer and referencing the resulting emission (with the platinum emission subtracted) to a graphite black body at the same temperature. The resulting spectra are identical to absorption spectra and the quantitative features of the analysis are demonstrated by the appearance of isosbestic points during the curing reactions, so indicating that concentration profiles of the reacting species may be obtained. From the initial rate of amine and epoxy consumption, activation energies of 75kJ mol⁻¹ were obtained for both functional groups in the uncatalysed resin 4,4′-tetraglycidyl diamino diphenyl methane (TGDDM) with 27% 4,4′-diaminodiphenylsulfone (DDS), while values of 74 and 89kJ mol⁻¹ were obtained for amine and epoxy consumption from the TGDDM/DDS prepreg catalysed with boron trifluoride monoethylamine (Hercules 3501–6), consistent with homopolymerization occurring in the prepreg as well as amine–epoxy addition. Analysis of the FTIR emission at 177°C of resin from prepreg aged up to 90h at 23°C and 55% relative humidity shows a lowering of epoxy and amine concentration and a higher rate of cure, consistent with the formation of catalytic species. This technique may be used to monitor changes in surface properties such as tack and resin transfer, in addition to changes in the cure profile of the aged epoxy propreg.     

Proposed mechanism for the curing of epoxy resins with amine-lewis acid complexes or salts

The common assumption in the literature is that amine complexes of Lewis acids (particularly boron trifluoride) cure epoxy resins by virtue of their dissociation to liberate the Lewis acid which then functions as the “true” catalyst. Evidence is presented to indicate that this picture of amine–Lewis acid complex curing may be incorrect. Another mechanism is proposed which is consistent with (a) lack of correlation between adduct stability and reactivity, (b) a similarity in reactivity of BF₃ adducts and the corresponding fluoroborate salts, (c) the relationship between reactivity of BF₃ and PF₅ adducts, (d) a correlation between reactivity and structure of the amine in the complex, and (e) the effect of the anion on reactivity of amine salts. The relative reactivity of the catalysts has been equated with the temperature at which gelation occurs on heating at a fairly constant rate.     

The polymerization mechanism and kinetics of DGEBA with BF3-MEA

The diglycidyl ether of bisphenol-A (DGEBA) and boron trifluoride monoethylamine (BF₃-MEA) were used in a model system to investigate the chemical and physical changes that occur during polymerization. Experiments using ¹⁹F and ¹H nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR) showed that BF₃-MEA breaks down rapidly into HBF₄ and an amine salt at 85°C and above. The HBF₄ complexes with the epoxy groups, producing an activated monomer that reacts with epoxy in an etherification reaction. A mechanism is proposed whereby activated epoxy sites (complexes) continuously add epoxy throughout the reaction, but where unactivated epoxies (monomer molecules) are unable to react with each other. The reaction rate and mode (kinetic vs. diffusion control) therefore are strongly influenced by the BF₃-MEA concentration and the reaction temperature. © 1993 John Wiley & Sons, Inc.     

Solvent Extraction of Au(III) by the Chloride Salt of the Amine Alamine 304 and Its Application to a Solid Supported Liquid Membrane System

Abstract

The extraction of Au(III) by the chloride salt of the amine Alamine 304 (R₃NH⁺Cl^?) in xylene from hydrochloric acid solutions has been investigated. The analysis of metal distribution data by numerical calculations suggested the formation of the species R₃NH⁺AuCl₄ ^? in the organic phase with formation constant log K _ext = 5.44. The results obtained on Au(III) distribution have been implemented in a solid‐supported liquid membrane system, where in NaSCN solutions were found to be the most effective to strip the metal from the organic solution. Influence of membrane composition, metal concentration on gold transport, and the selectivity of the system have also been studied.     

Solid Polymer Electrolyte Complexes of Polyoxyethylene-Containing Star-Shaped Block Copolymers and Copolymers with Uniform Grafts

Ionic conductivities of salt complexes of polyoxyethylene (PEO)-containing star-shaped block copolymers and copolymers with uniform grafts were measured. The results were compared with the thermal characteristics and crystallinity of the complexes obtained from DSC and WAXD analysis. The conductivity increases with PEO content of the copolymers, more noticeably at PEO contents over 50%. For the complexes of the star-shaped block copolymers of styrene (S) and ethylene oxide (EO), conductivity decreases in the following order of salts: KCNS > NH₄CNS > NaCNS. The room temperature conductivity of the KCNS complex with EO/K ratio = 20 can reach a value of 2 × 10^?5 S cm^?1 at 57% PEO content of the copolymer. The complex with FeCl₂ displays a conductivity even higher than that of the NaCNS complex. Addition of γ-butyrolactone reduces the crystallinity and enhances markedly the ionic conductivity. For complexes of the copolymers with uniform PEO grafts the conductivity decreases in the following order of salts: KCNS > LiClO₄ > FeCl₂. Complexes with LiClO₄ exhibit a maximum conductivity at EO/Li = 20. For different kinds of copolymers with uniform PEO grafts, conductivity of the complexes increases in the order: PS-g-PEO < PMMA-g-PEO < polymethyl acrylate-g-PEO.     

emf Studies of zinc halides ln concentrated aqueous NH4NO3CA(NO3)2 solutions

The formation constants of the species ZnC⁺, ZnCl₂, ZnBr⁺ and ZnBr₂ were determined from emf measurements in suitable concentration cells. Mixtures of NH₄NO₃Ca(NO₃)₂ with a molar ratio 0.844/0.156 containing variable amounts of water (from 0 to 1.2 moles per mol of salt) were used as a solvent. The bromide complexes were found to be more stable than the chloride complexes in the anhydrous melt, while the opposite was found in the concentrated aqueous solutions. The results are discussed on the basis of models for chemical equilibria in molten salts and aqueous melts.     

Selective Permeation of Ammonia and Carbon Dioxide by Novel Membranes

Abstract

Experimental results are presented on membranes of novel composition which selectively permeate ammonia and carbon dioxide from mixtures containing hydrogen. The CO₂-selective membrane, which consists of a thin liquid film of the salt hydrate tetramethylammonium fluoride tetrahydrate, exhibits a CO₂ permeance of 4-1 × 10^?5 cm³/cm²·s·cmHg with selectivity, α(CO₂/H₂), ranging from 360-30. The NH₃-selective membrane, poly(vinylammonium thiocyanate), displays a high NH₃ permeance, 5?20 × 10^?5 cm³/cm²·s·cmHg, with α(NH₃/N₂) as high as 3600 and α(NH₃/H₂) as high as 6000. Such membranes, which retain H₂ at pressure in the feed stream, may offer new opportunities in the design of separation processes.     

A Spectrophotometric Study of Trivalent Actinide Complexes in Solution. IV. Americium with Chloride Ligands

The light absorption spectra of americium(III) in ethanolic and concentrated aqueous lithium chloride solutions, and in long-chain alkylammonium chloride solutions in aromatic diluents were obtained, as well as those of certain solid double salts and complexes. A strong 5f⁶ → 5f⁵6d¹ transition was observed in the aqueous solutions at 235 nm (42,500 cm^?1), and from the dependence of the intensity of this and the 503 nm (19,880 cm^?1) band, on the effective chloride activity, the stability constants of the inner sphere complexes: AmCl²⁺, logβ₁^* = ?2.21± 0.08, and AmCl₂⁺, log β₂^* = ?4.70 ± 0.08, were determined. The spectrum of the long-chain amine extracts is comparable to that of solids of the composition AmCl₃ · 2N(C₄H₉)₄Cl · × LiCl, and the nature of the extracts and of this and similar solids is discussed.     

SORPTION OF PLATINUM,PALLADIUM, IRIDIUM,AND GOLD COMPLEXES ON POLYANILINE

ABSTRACT

Sorption of Pt, Pd, Ir and Au on polyaniline, synthesised by chemical oxidation of aniline in HC1, from HC1, LiC1 and H₂SO₄ solutions in the concentration range 0.1 to 10 mol dm^-3 has been studied. The as-prepared polyaniline (acid-PANI) and the one treated with 1 mol dm^-3 NH₄OH (base-PANl) have been used. Analysis of the data indicate that the AuC1₄ ^? species and negatively charged chloro-complexes of Pt and Pd are involved in the sorption process from HC1 solutions. Sorption of metal species from H₂SO₄ solutions is higher than that from HC1 solutions and negatively charged sulphate complexes of Pt and Pd are involved in the sorption     

Polyaniline Salts and Complexes as Catalyst in Bisindole Synthesis

Polyaniline salts are prepared by doping of polyaniline base with different Bronsted acids (H₂SO₄, HNO₃ and H₃PO₄), organic acid — p-toluene sulfonic acid (PTSA) and Iodine (I₂). Polyaniline complexes are also prepared using Lewis acids (BF₃, AlCl₃ and SnCl₂). Polyaniline salts and polyaniline complexes are characterized by physical, electrical and spectral methods. Polyaniline salts and polyaniline complexes are used as catalyst for the first time in bisindole synthesis. Bisindole (3,3′-bis(indolyl)phenylmethane) is obtained in excellent yields with simple and more environmental benign procedure. The use of polyaniline catalysts are feasible because of their easy preparation, easy handling, stability, easy recovery, reusability, good activity and eco-friendly.     

Compaction of metal salt-urea complexes with triple superphosphate

It has been the experience of the fertilizer industry that urea should not be cogranulated or blended with superphosphate because urea reacts with monocalcium phosphate monohydrate (MCP·H₂O) in superphosphate to form an adduct. This reaction releases the water of hydration and causes the product to become wet and sticky or severely caked during storage. The objectives of this study were [1] to test the feasibility of preventing or retarding the reaction by complexing the urea with various salt hydrates and [2] to measure ammonia volatilization from metal salt-urea complexes on the soil surface.Three metal salt-urea complexes — Al(urea)₆(NO₃)₃, Fe(urea)₆(NO₃)₃, and Mn(urea)₄Cl₂ — were prepared and cogranulated by compaction with pure MCP·H₂O or triple superphosphate (TSP) at a mole ratio of MCP:urea as 1:2. These materials were then compared with the same material without metal salts in terms of changes in free water content during a storage period of 6 weeks. Without metal salts a rapid and significant increase in free water content of the cogranulated MCP·H₂O + urea or TSP + urea was observed. The increases in free water content were found to range from 1.5% to 1.8%, corresponding to approximately 63% and 78% of the added MCP·H₂O that reacted with urea in the cogranulated products. On the other hand, little change or only a slight increase (less than 0.5%) in free water content was observed with the cogranulated metal salt-urea complexes.Ammonia volatilization losses from urea on the soil surface were measured in a period up to 14 d with two soils: Windthorst (pH 7.6) and Savannah (pH 7.0). The fertilizer materials used were granular. In Windthorst soil, the amounts of NH₃-N lost were 25% for prilled urea, 11% for Mn(urea)₄Cl₂, and essentially none for Mn(urea)₄Cl₂ compacted with TSP at a mole ratio of MCP:urea as 1:1 or 1:2. In Savannah soil, the amounts of NH₃-N lost were 39% for prilled urea, 24% for Mn(urea)₄Cl₂, 15% for Fe(urea)₆(NO₃)₃, and less than 6% for each of the two metal salt-urea complexes compacted with TSP. The acidity that resulted from metal complexing of urea reduced NH₃ volatilization from hydrolyzed urea in soils, and additional acidity produced from hydrolysis of MCP·H₂O further reduced NH₃ losses when materials were applied as multicomponent granules (metal salt + urea + TSP).     

Characteristics of ammonia permeation through porous silica membranes

A sol–gel method was applied for the preparation of silica membranes with different average pore sizes. Ammonia (NH₃) permeation/separation characteristics of the silica membranes were examined in a wide temperature range (50–400°C) by measurement of both single and binary component separation. The order of gas permeance through the silica membranes, which was independent of membrane average pore size, was as follows: He > H₂ > NH₃ > N₂. These results suggest that, for permeation through silica membranes, the molecular size of NH₃ is larger than that of H₂, despite previous reports that the kinetic diameter of NH₃ is smaller than that of H₂. At high temperatures, there was no effect of NH₃ adsorption on H₂ permeation characteristics, and silica membranes were highly stable in NH₃ at 400°C (i.e., gas permeance remained unchanged). On the other hand, at 50°C NH₃ molecules adsorbed on the silica improved NH₃‐permselectivity by blocking permeation of H₂ molecules without decreasing NH₃ permeance. The maximal NH₃/H₂ permeance ratio obtained during binary component separation was ～30 with an NH₃ permeance of ～10^?7 mol m^?2 s^?1 Pa^?1 at an H₂ permeation activation energy of ～6 kJ mol^?1. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Eigenschaften und thermische Reaktionen von Komplexen der Arendiazoniumsalze mit Kronenethern

Properties and Thermal Reactions from Complexes of Arene Diazonium Salts with Crown Ethers In contrast to 18-crown-6, the substituted crown ethers Benzo-18-crown-6, Dibenzo-18-crown-6, and Naphtho-18-crown-6 form in solution complexes with p-CH₃ C₆H₄ N₂⁺BF₄-characterized by a broad charge transfer absorption up to 550 nm. The formation constants lg K_c are 2,32 2,16 and 1,44 for Benzo-, Dibenzo-, and Naphtho-18-crown-6, respectively. Formation enthalpy ΔH = −7,5 kJ/mol and entropy ΔS = +18 J/K mol are measured in the case of p-Cl C₆H₄ N₂⁺BF₄⁻ and Dibenzo-18-crown-6 (20°). K_c depends on substituents in the arene ring of the diazonium salt; ϱ = +0,8. Thermal dediazoniation in the presence of Crown ethers results in high yields of the corresponding arene. This is explained by a fast radical chain reaction between the diazonium salt and the polyether (Meerwein-Reduction).     

Alkyl amine functional dextran macromonomer‐based thin film composite loose nanofiltration membranes for separation of charged and neutral solutes

Thin film composite (TFC) nanofiltration membranes with defined porous structure of the separation layer are desirable for the concentration of neutral solute and separation of salts from a mixture. Herein, we report the formation of TFC membranes composed of polyamide (PA) separation layer by the interfacial polymerization between new dextran‐butyl amine (Dex‐NH₂) macromonomer and trimesoyl chloride on polysulfone support membrane. The membranes prepared with 1%–1.5% (wt/vol) of Dex‐NH₂ exhibited water permeance of 110–116 L m^?2 h^?1 MPa^?1 with 62%–71% rejection of Na₂SO₄ and 12%–14% rejection of MgCl₂. The membranes also showed about 91% rejection of poly(ethylene glycol) of molecular weight 2000 g/mol and about 11% rejection of NaCl. A decrease in permeance and ions selectivity was observed with increasing concentration of Dex‐NH₂. The dextran chains attached to the PA network restrict the diffusion of Dex‐NH₂ toward the interfacial zone and thereby assist the formation of porous and thin PA layer compared to that when free amine (alkyl diamine) was used. These membranes are applicable for the separation of small molecular weight neutral solutes from mixture containing monovalent salts. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45301.