Study of the distribution of the molecular orientation in thick polyethylene samples by X-ray diffraction, infra-red dichroism and Raman spectroscopy

The molecular orientation in thick polyethylene samples has been studied by wide-angle X-ray diffraction, i.r. dichroism and Raman spectroscopy. The original specimens, with dimensions of the order of a centimetre, were cut to obtain 1 mm thick platelets on which the measurements were made. The mean coefficient of the second-order Legendre polynomial, P₂, was calculated from X-ray diffraction and from the 1894 cm⁻¹ i.r. band for the crystalline phase, from the 909 cm⁻¹ i.r. band for the vinyl end groups and from the 1130 and 1060 cm⁻¹ Raman bands for the all-trans C-C conformers. The fourth-order coefficient, P₄, was also determined from X-ray diffraction and Raman spectroscopy for a series of cylindrical rods of draw ratios (λ) ranging from 6 to 20. An excellent correlation is observed between the P₂ coefficients measured from different X-ray reflections and from the 1894 cm⁻¹ i.r. band. The Raman spectroscopy results show that the all-trans bonds located in the amorphous phase are aligned perpendicular to the extrusion direction for the λ = 6 rod, and gradually reorient towards the fibre axis for λ values up to 20, while the P₂ and P₄ coefficients calculated for the crystalline phase remain constant at λ ≥ 12. The variation of the orientation through the thickness of the samples was investigated for the cylindrical rods and for an H-shaped moulding produced by extrusion and rolling. Minor differences in the degree of molecular orientation were detected between the centre and the surface of the rods, whereas important variations were measured for the H-shaped sample.     

Differential scanning calorimetry and infra-red crystallinity determinations of poly(aryl ether ether ketone)

The differential scanning calorimetry (d.s.c.) heating thermograms of 12 poly(aryl ether ether ketone) (PEEK) samples of varying degrees of crystallinity have been recorded. The relation found between the degree of crystallinity as determined by specific gravity measurements, and the melting enthalpy of the polymer, shows that recrystallization is occurring during a heating scan rate of 10°C min⁻¹. This implies that d.s.c. is not a convenient technique to assess PEEK crystallinity. The infra-red absorbance spectra of the same samples have also been examined in the range from 1030 to 880 cm⁻¹. The 965 cm⁻¹ band, up to now considered as indicative of the PEEK crystallinity, is shown to be practically independent of the degree of crystallinity above 15%. However, there is evidence to support the existence of a true i.r. crystalline band located at 947 cm⁻¹. It is also suggested that the 965 cm⁻¹ band is due to a normal vibration mode of a short segmental conformation, whose presence is favoured in the crystalline phase, but also in the amorphous zones nearest to the crystallite surface.     

In situ FTIR studies on the conversion of methanol over acidic forms of various zeolites

In situ investigations of the interaction of methanol on zeolites of the faujasite, pentasil and mordenite types were performed. We suppose that CH₃)- or (CH₃)₂O… species exist on the surface of the H-ZSM-5 zeolite in the temperature range between 380 and 470 K which desorb above 470 K and form dimethyl ether (DME). The band at 1502 cm⁻¹ represents aromatics being intermediates in the aromatization of methanol. The band at 1595 cm⁻¹ is due to polymeric “coke” which cannot be removed from the zeolite up to 670 K. In the case of the H-Y zeolite no band at 1500 cm⁻¹ assigned to aromatics could be observed.     

Preparation of ultra-high-strength nylon-6 fibre by a multi-step zone-annealing method

A multi-step procedure to improve the zone-annealing method was attempted to prepare a high-modulus and high-strength nylon-6 fibre. By the adoption of this procedure, the dynamic storage modulus at room temperature was markedly increased and reached 15.7 × 10¹⁰ dyne cm⁻² which is 1.5 times that obtained by the previous zone-annealing method. Tensile properties, orientation, crystallinity and mechanical dispersion were also measured. Comparing the multi-step procedure with the previous one-step procedure, the excellent effects of the multi-step procedure on mechanical properties are discussed. Further, in order to prevent selective relaxation of amorphous molecular chains on removing the applied tension after zone-annealing, heat-setting at constant length was subsequently carried out on the as-zone-annealed fibre. The mechanical properties were further improved: for example, the dynamic storage modulus at room temperature of the resulting fibre was raised to 16.9 × 10¹⁰ dyne cm⁻², which was well beyond the highest modulus available in the literature, 14 × 10¹⁰ dyne cm⁻².     

Two-dimensional near-infrared correlation temperature studies of an amorphous polyamide

Near-infrared spectra of a totally amorphous polyamide measured over the temperature range 25–200°C was analyzed using generalized two-dimensional (2D) correlation spectroscopy. At least, five distinct bands at 5690, 5810, 5900, 5980 and 6010 cm⁻¹ were identified in the region of the CH overtones (5200–6200 cm⁻¹). Among them, two bands at 5810 (aliphatic) and 6010 cm⁻¹ (aromatic) are found to be very sensitive to the temperature-induced structural changes of the polyamide under examination. In the ν(NH) overtone region (6300–6800 cm⁻¹), the asynchronicity of the bands assigned to the vibrations of the free and hydrogen-bonded NH groups indicate a complicated dissociation mechanism and the existence of different hydrogen-bonded species in the investigated totally amorphous polyamide sample. Owing to the spectral resolution enhancement in 2D correlation spectra, a splitting of the first overtone of the free NH stretching vibration into two components at 6780 (totally free) and 6740 cm⁻¹ (free-end) can be observed.     

In situ IR and pulse reaction studies on the active oxygen species over SrF2/Nd2O3 catalyst for oxidative coupling of methane

Pulse reaction method and in situ IR spectroscopy were used to characterize the active oxygen species for oxidative coupling of methane (OCM) over SrF₂/Nd₂O₃ catalyst. It was found that OCM activity of the catalyst was very low in the absence of gas phase oxygen, which indicated that lattice oxygen species contributed little to the yield of C₂ hydrocarbons. IR band of superoxide species (O₂⁻) was detected on the O₂-preadsorbed SrF₂/Nd₂O₃. The substitution of ¹⁸O₂ isotope for ¹⁶O₂ caused the IR band of O₂⁻ at 1128 cm⁻¹ to shift to lower wavenumbers (1094 and 1062 cm⁻¹), consistent with the assignment of the spectra to the O₂⁻ species. A good correlation between the rate of disappearance of surface O₂⁻ and the rate of formation of gas phase C₂H₄ was observed upon interaction of CH₄ with O₂-preadsorbed catalyst at 700 °C. The O₂⁻ species was also observed on the catalyst under working condition. These results suggest that O₂⁻ species is the active oxygen species for OCM reaction on SrF₂/Nd₂O₃ catalyst.     

The elastic modulus of the poly(phosphonitrilic chloride) crystal

The Young's modulus for a crystal of poly(phosphonitrilic chloride) (poly-dichlorophosphazene) (NPCl₂)_n has been calculated using force constants derived from spectroscopy. Assuming that the molecule is a uniform helix the value of the modulus is 1.38 × 10⁹ dyne cm⁻² [dyne cm⁻² = 0.1 N m⁻²]; the result is 1.66 × 10¹⁰ dyne cm⁻² if a cis-planar structure is assumed for the molecule. Neither value is close to those obtained experimentally (1.8 × 10⁶ to 6.5 × 10⁶ dyne cm⁻²). This is because experimental values relate to the amorphous polymer whereas the calculated values are those for the crystal. There is good agreement between the values calculated for the (NPCl₂)_n crystal and those for other polymer crystals.     

Poly(ethylene oxide)–LiX rubbery electrolytes with X–X disulfonamide anions having two or three ether groups in their structures

This work deals with poly(ethylene oxide), PEO–MX (M=Li, K and Cs) amorphous electrolytes with ⁻X–X⁻, [CF₃SO₂NCH₂(CH₂OCH₂)₂CH₂NSO₂CF₃]²⁻ (EDSA) and [CF₃SO₂NCH₂CH₂(CH₂OCH₂)₃CH₂CH₂NSO₂CF₃]²⁻ (TTSA) disulfonamide anions. These dianions have X⁻ end-groups identical to anions [CF₃SO₂N(CH₂)₂OCH₃]⁻ (MESA) and [CF₃SO₂N(CH₂)₃OCH₃]⁻ (MPSA), one of which (MPSA) was reported to yield chelate-like associated species (presumably LiX₂⁻ triplets) at concentrations above EO/Li=20 in PEO. This feature of LiMPSA, evidenced through glass transition temperature (T_g) measurements, does not apply to Li₂EDSA and Li₂TTSA. Though none of these lithium salts form crystalline intermediate compounds with PEO, the limit of solubility of LiMESA (EO/Li=16) does not allow a clarification of this point for this salt. At lower concentrations, however, a conductivity comparison with the potassium and caesium salts shows that the apparent degree of dissociation (=C_Li+/C_Li) of LiMESA is comparable to that of LiMPSA. As opposed to both these salts and to some extent to Li₂EDSA, a much greater dissociation takes place for Li₂TTSA, the anion of which contains an inner, third ether group in its structure.     

Identification of copper(II) and copper(I) and their interconversion in Cu/ZSM-5 De-NOx catalysts

A combined Fourier transform IR (FT-IR) and electron paramagnetic resonance (EPR) study shows that copper in ‘excessively exchanged’ Cu/ZSM-5 is initially present as OH bridged Cu²⁺ dimers, besides isolated Cu²⁺ ions. Upon heating, the dimers lose water and become oxygen bridged [Cu---O---Cu]²⁺ complexes. These are ‘EPR-silent’, presumably as a consequence of antiferromagnetic coupling of the unpaired electrons in each Cu²⁺; they are, however, detectable by their perturbation of the lattice vibrations, detected by a FT-IR band at 918–923 cm⁻¹. Reduction by hydrogen or carbon monoxide converts the [Cu---O---Cu]²⁺ complexes to pairs of Cu⁺ ions, while the color changes from green to grey. Reductive adsorption of nitrogen monoxide on Cu²⁺ results in the formation of Cu⁺---NO⁺. Destructive thermal desorption of nitrogen monoxide at 100°C not only restores the Cu²⁺ ions, but also appears to regenerate the [Cu---O---Cu]²⁺ complex. The results suggest that pairs of copper ions are instrumental in the catalytic decomposition of nitrogen monoxide.     

Mn/MFI catalyzed reduction of NOx with alkanes

Mn/MFI catalysts were prepared by different methods and probed as catalysts for the catalytic reduction of NO_x with CH₄ or iso-butane in a gas flow containing excess O₂. Mn/MFI with high manganese loading was obtained by solid state ion exchange (SSI). The intensity of an IR band at 957 cm⁻¹, which is due to the perturbation of zeolite lattice vibrations by Mn ions attached to cage walls is proportional to the Mn content of the catalysts. Conversely, the intensity of the 3610 cm⁻¹ band, assigned to Brønsted acid sites decreases linearly with the Mn loading. A catalyst obtained by exchanging Na/MFI with an aqueous solution of Mn acetate is found most active for NO_x reduction with methane. Transport by surface diffusion of Mn ions from MnI₂ to exchange positions in MFI is more efficient than their transport through the gas phase. High NO conversion over proton-free catalysts indicates that protons are not instrumental in NO_x reduction over Mn/MFI.     

Thermal and cation influence on ir vibrations of modified natural clinoptilolite

The study of IR spectra in the range of 400 to 1700 cm⁻¹ of cation exchanged natural clinoptilolite-heulandite samples has shown the influence of the characteristics of cations and their content in the frequency and transmittance of vibration modes of zeolite. The 450 cm⁻¹ band assigned to T-O internal bending, 1205 cm⁻¹ band of T-O internal asymmetric stretching, and 1640 cm⁻¹ band of OH bending, were most affected by the cation exchange and thermal history of the sample.     

Photocatalytic properties of visible-light enabling layered titanium oxide/tin indium oxide films

Visible-light enabling titanium oxide/tin indium oxide (TiO₂/ITO) thin films deposited on unheated glass slides with prolonged deposition duration were investigated in this study. Structural properties characterized by X-ray diffraction (XRD), Raman spectra and scanning electron microscopy (SEM) showed typical polycrystalline structure with primary anatase phase along with elongated pyramid-like grains lying on the film surface and densely packed columnar structure from cross-sectional profile. The XRD preferential peak of (2 1 1) and the Raman peak intensity at 640 cm⁻¹ dramatically increased without noticeable broadening and shift as the deposition time was prolonged beyond 2 h. This implies that more perfectly crystalline structure, less internal stress, and comparatively larger grains were obtained by this technique. The Ti2p_3/2 and O1s XPS peaks shifted toward higher binding energy suggest that the local chemical state was influenced by the prolonged deposition duration in the film, which resulted in red shift of absorption threshold into visible-light region. Under ultra-violet (UV) and visible-light illumination, the visible-light enabling film exhibited the best photocatalytic activity on MB degradation with the rate-constant of about 0.231 h⁻¹. Hydrophilic conversion rate was estimated to be 8.14 × 10⁻³ deg⁻¹ min⁻¹ and long-term UV-induced hydrophilicity of 10° in the dark storage up to 72 h was observed. In addition to its inherent characteristics of the layered TiO₂/ITO structure on hole/electron separation, all these could be attributed to more perfectly formed crystalline structure, densely packed columnar crystals and the surface roughness along with its enlarged surface area.     

Grazing incidence reflection absorption Fourier transform infrared (GIRA-FTIR) spectroscopic studies on the ferroelectric behavior of poly(vinylidene fluoride–trifluoroethylene) ultrathin films

Grazing incidence reflection absorption Fourier transform infrared (GIRA-FTIR) spectroscopy was used to characterize the ferroelectric behavior of a thin poly(vinylidene fluoride–trifluoroethylene) P(VDF–TrFE) copolymer. The lab-built GIRA-FTIR apparatus allowed the heating and corona poling process to be carried out whilst collecting the GIRA spectra of the thin polymer film. The Curie transition from the ferroelectric to paraelectric phase was confirmed from the abrupt change in intensity of the 849 cm⁻¹ band in the RA-FTIR spectrum. It was found that the Curie temperature dropped dramatically when the film thickness was lowered to below a certain critical value of approximately 100 nm. The switching of the CF₂ dipoles in the ferroelectric crystals after applying the external electric field could be determined by monitoring the change in the 849 cm⁻¹ band intensity. For the 600 nm thick P(VDF–TrFE) film, the switching of the dipoles appears to occur almost instantaneously, while the kinetics of dipole switching of the 75 nm thick film were significantly retarded. The repeated switchability of the CF₂ dipoles upon the application of a bipolar cyclic electric field was also confirmed. The bistability of the film due to remnant polarization was also confirmed from the absorbance of the 849 cm⁻¹ band after removing the applied voltage during corona poling.     

In situ FT-IR study of NH3 formation during the reduction of NOx with propane on H/Cu-ZSM-5 in excess oxygen

IR experiments under flow of NO and propane on H/Cu-ZSM-5 evidence at 623 K the appearance of bands at 2248, 2157 and 2047 cm⁻¹ tentatively assigned through the use of ¹⁵NO to nitrile, carbonyl (CO---Cu⁺) and isocyano species respectively. Addition of O₂ suggests conversion of isocyano to isocyanato species (2208 cm⁻¹) which by hydrolysis leads to NH₃ formation, revealed by IR bands at 3366, 3290, 3192 and 1610 cm⁻¹.     

Infrared spectroscopic study of the acid properties of dealuminated BEA zeolites

A series of HBEA samples were prepared by dealumination through three different methods (steaming, treatments with hydrochloric acid and ammonium hexafluorosilicate (HFS) solutions) of a parent sample with total and framework Si:Al ratios of 12.5 and 33, respectively, constituted of 20 nm crystallites. The samples were characterized by XRD, nitrogen adsorption and pyridine adsorption–desorption followed by IR spectroscopy. Whereas the three dealumination treatments have practically no effect on crystallinity and nitrogen adsorption properties, they cause large changes in the ranges of the O–H bond stretching modes (3300–3800 cm⁻¹) and of the most intense IR absorption of pyridine (1400–1700 cm⁻¹). Treatments with HCl or HFS cause the most significant changes: disappearance of the 3662 and 3782 cm⁻¹ bands corresponding to extraframework Al species and to tricoordinated Al species partially connected to the framework, respectively, appearance of additional bands at 1603 and 1446 cm⁻¹ ascribed to a new type of pyridine species coordinated to Lewis sites (PyL₂) and for desorption temperatures above 350 °C, of a band at 1462 cm⁻¹ generally ascribed to iminium ions, apparently at the expense of the PyL₂ band. In agreement with this formation of iminium ions, desorption at high temperatures causes the complete disappearance of pyridinium ions without complete restoration of the acidic bridging hydroxyl band. PyL₂ species are proposed to be pyridine molecules coordinated to Lewis sites and interacting through hydrogen bond with protonic sites.     

Reverse osmosis of diluted skim milk: Comparison of results obtained from vibratory and rotating disk modules

This paper investigates the reduction of ionic concentration and carbon oxygen demand (COD) in dairy process waters modelled by one volume of skim milk diluted with two volumes of water using shear-enhanced reverse osmosis. Initial COD and conductivity were, respectively, 36,000 mg O₂ L⁻¹ and 2000 μS cm⁻¹. We have compared the performances of a VSEP vibratory pilot and of a single rotating disk-stationary membrane module equipped with the same Desal AG membrane (Osmonics). Membrane shear rates were varied by changing the vibration frequency in the VSEP and the disk rotation speed or adding radial vanes in the other module. In all tests the permeate COD was reduced below 15 mg O₂ L⁻¹. Permeate fluxes reached a maximum of 180 L h⁻¹ m⁻² at a transmembrane pressure (TMP) of 4 MPa at initial concentration with the VSEP at its resonant frequency and with the disk equipped with 6 mm high vanes rotating at 2000 rpm. Permeate conductivity fell from 60 μS cm⁻¹ at 1 MPa to about 18 μS cm⁻¹ at 4 MPa. In concentration tests, corresponding permeate fluxes at the maximum volume reduction ratio reached (VRR = 8), were 55 L h⁻¹ m⁻² for the VSEP and 60 L h⁻¹ m⁻² for the rotating disk at a TMP of 4 MPa. Permeate conductivities increased exponentially with VRR from 18 to 210 μS cm⁻¹ for the rotating disk and to 250 μS cm⁻¹ for the VSEP. However the mean conductivity of collected permeate varied from 38 μS cm⁻¹at highest shear rate to 60 at lower shear rates. This study shows that these filtration systems permit to obtain reusable water from this high initial COD model effluent with one single reverse osmosis step.     

Analysis of Fe species in zeolites by UV–VIS–NIR, IR spectra and voltammetry. Effect of preparation, Fe loading and zeolite type

Three procedures were employed for the preparation of Fe-zeolites with ZSM-5 (MFI), ferrierite (FER) and beta (BEA) structures: ion exchange from FeCl₃ solution in acetyl acetonate and solid-state ion exchange from FeCl₂ using an oxygen or nitrogen stream. A combination of UV–VIS–NIR spectra, IR spectra of skeletal vibrations and of adsorbed NO, as well as voltammetry provided information on the type of Fe species introduced. Single Fe(III) ion complexes (Fe(H₂O)_6−xOH_x) in hydrated zeolites were reflected in the charge-transfer bands at 33 100, 37 300 and 45 600 cm⁻¹. The single Fe(II) ions at cationic sites in evacuated zeolites yielded (through perturbation of framework T–O bonds) characteristic bands (910–950 cm⁻¹) in the region of the skeletal window. These Fe(II) ions with adsorbed NO were also reflected in vibrations at 1880 cm⁻¹. Dinuclear Fe–oxo complexes yielded the Vis band at 28 200 cm⁻¹. Voltammetry indicated the presence of Fe oxides (hematite) through the reduction peak at −0.7 V. Such oxide-like species were also reflected in the absorption edge at 19 800 cm⁻¹, and a doublet at 11 000 and 11 800 cm⁻¹ in the Vis spectra. Fe(II)–NO vibrations at 1840, 1810 and 1760 cm⁻¹ belonged to the undefined exposed Fe cations, probably originating from supported oxides. Using an ion exchange procedure, employing FeCl₃ in acetyl acetonate, exclusively Fe ions at cationic sites could be introduced at low concentrations (Fe/Al < 0.1). At higher Fe loadings, dinuclear Fe–oxo complexes were formed preferably in Fe-ZSM-5, but were absent in Fe-beta. Exclusively single Fe species could not be prepared at Fe concentrations above Fe/Al > 0.2; all three types of Fe species, single Fe ions, dinuclear Fe–oxo complexes and Fe oxides were formed.     

Synthesis and oxygen transport characteristics of dense and porous cerium/gadolinium oxide materials: Interest in membrane reactors

Cerium/gadolinium oxide (CGO)-based ceramic ion conductive membranes (CICMs) have potential uses in catalytic membrane reactors (CMRs) and solid oxide fuel cells (SOFCs). A supercritical CO₂ aided sol–gel process allowed the synthesis of CGO materials with the composition Ce_0.9Gd_0.1O_1.95. The produced nanophase powders were non-agglomerated, with a controlled morphology, a high purity and a high specific surface area (>100 m²/g). The CGO cubic crystalline phase has been obtained at temperatures <300 °C, lower than those of conventional solid state chemistry routes. With respect to ionic oxygen transport, a high conductivity at intermediate temperature (2 × 10⁻² S cm⁻¹ at 600 °C), almost equivalent in dense and porous samples, has been obtained on sintered materials prepared from these powders. In relation to their porosity characteristics, a modelling approach successfully explained the high ionic oxygen transport of some specific porous samples. Future directions for preparing porous conductive ceramics well adapted to CMR or SOFC applications can be anticipated from this model.     

Voltammetric behavior of the C60-γ-cyclodextrin inclusion complex (1:2) on hmde in an aqueous solution

Electrochemical behavior of the water-soluble C₆₀-γ-CD (1:2) inclusion complex has been studied on the hanging mercury drop electrode. A one-electron reversible adsorptive electro-reduction and three irreversible adsorptive electro-reductions were detected by cyclic voltammetry. The amount of C₆₀-γ-CD adsorbed at saturation is 2.50 × 10⁻¹¹ mol cm⁻², the diffusion coefficient is 4.36 × 10⁻⁶cm²s⁻¹ and the standard rate constant of the surface reaction k_s are 0.745 s⁻¹, 0.612 s⁻¹ and 0.513s⁻¹, respectively.     

Investigation of a new reactant for fluorinated polymer surface treatments with atmospheric pressure glow plasma to improve the adhesive strength

Poly(tetrafluoroethylene-co-perfluoro [alkyl vinyl ether]) (PFA) and polytetrafluoroethylene (PTFE) films were treated by three kinds of atmospheric pressure glow plasmas: an untreated sample was treated by He plasma or trimethoxyborane (TMB)/H₂/He plasma, and a TMB-absorbed sample was treated by H₂/He plasma. TMB was a new reactant for the treatment, to increase the films’ adhesive strength with an epoxy glue. These films were also treated by a wet method using a sodium solution (Tetra-Etch compound) and such films were used as the control samples. The peel strength values of the controls of PFA and PTFE were 3.5 and 9.5 N cm⁻¹, respectively. The adhesive strengths of all plasma-treated PFAs were stronger than those of untreated one. Especially, the peel strength of the TMB/H₂/He plasma-treated PFA showed the maximum value of 4.5 N cm⁻¹, which was bigger than that of the control one. The adhesive strength of the TMB/H₂/He plasma-treated PTFE films also showed the maximum peel strength, 7.9 N cm⁻¹, but this value did not exceed that of the control PTFE. Such results suggested that the TMB/H₂/He plasma had the advantage of providing better adhesive improvement of those polymers, especially PFA than the wet method could provide. The results of XPS and SEM indicated that TMB actively removed fluorine atoms from the polymer surface. Therefore, boron compounds are effective for the improvement of the adhesive strength between the fluorinated polymer and the epoxy glue.