Biaxial orientation of polyamide films: processability and properties

The production of biaxially oriented films can be performed with two techniques: the tenter frame and the double bubble process. The most important difference between the two processes is that in tubular orientation the MD and TD stretching are simultaneous. This event is very important specially in the case of biaxially oriented polyamide films to avoid hydrogen bonding which occur during the first stretching stage of tenter frame process and cause resistance to subsequent transverse direction orientation (1-4). Double bubble process consists in the stretching of a tubular film where the stretching ratios in the machine and transverse directions are determined by inside bubble pressure and the difference in roll speeds between the two sets of nips rolls that contain the bubble. The work presented here reports some results about double bubble polyamide films realised with a laboratory scale system. The study concerns the processability (5-6) of two different polyamides: a nylon 6 (PA6) and a copolymer of the nylon 6 with isophthalic acid and isophorondiamine (PA6 - IPA.IPD) at 5% w/w of comonomer. Two main process arrangements where adopted differing for first bubble cooling technique: a water cooling and a air cooling. The films produced in both conditions were then characterised with a particular regard to mechanical and barrier performances. Morphological analyses were also carried out in order to correlate the process conditions to structure and properties of films.     

Optical properties and orientation in polyethylene blown films

We report structural factors affecting the optical properties of blown polyethylene films. Two types of blown polyethylene films of similar degrees of crystallinity were made from (1) single‐site‐catalyst high‐density polyethylene (HDPE; STAR α) and (2) Ziegler–Natta‐catalyst HDPE (ZN) resins. The STAR α film exhibited high clarity and gloss, whereas the ZN film was turbid. Small‐angle X‐ray scattering (SAXS), small‐angle light scattering (SALS), and optical microscopy gave quantitative and qualitative information regarding structure and orientation in the films. A new approach is described for determining the three‐dimensional lamellar normal orientation from SAXS. Both the clear STAR α and turbid ZN films had similar lamellar crystalline structures and long periods but displayed different degrees of orientation. It is demonstrated that optical haze is related to surface features that seem to be linked to the bulk morphology. The relationship between haze and structural orientation is described. The lamellar orientation is linked to rodlike structures seen in optical microscopy and SALS through a stacked lamellar or cylindrite morphology on a nanometer scale and through a fiberlike morphology on a micrometer scale. The micrometer‐scale, rodlike structures seem directly related to surface roughness in a comparison of index‐matched immersion and surface micrographs. The higher haze and lower gloss of the ZN film was caused by extensive surface roughness not observed in the STAR α film. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2923–2936, 2001     

Effect of orientation extension on the structure and physicomechanical properties of porous polyethylene films

Effects of the degree, velocity, and temperature of repeated extension of porous PE films on their structure and transport and mechanical properties are investigated. The sizes of through-flow channels and the permeability of porous films are determined via filtration porosimetry. A rise in the temperature and the degree of extension in the course of orientation extension noticeably increases the sizes of pores, the overall porosity, the specific surface area, and the permeability of the films and improves their mechanical characteristics.     

Use of modifiers in on-line and off-line supercritical fluid extraction

For many applications using supercritical fluid extraction (SFE), modifiers may be required.This paper will present some findings regarding the use of various modifiers including methanol, hexane, acetone, chloroform, dichloromethane, toluene, and tributylphosphate, in on-line and off-line SFE with cryogenic adsorbent trapping. The specific applications involved the extractions of petroleum hydrocarbons and pesticides from naturally incurred soils.     

Fabrication and characterization of orientation in skew stretched polyethylene terephthalate films

Skew stretched films were prepared by first unaxial stretching and subsequently skew stretching at 30 and 60 angles to various stretch ratios. The films were characterized by refractive index (birefringence), infrared absorption (dichroism) and wide-angle x-ray diffraction measurements. The data are represented in terms of ellipsoids and symmetry axes were determined. The results from the different methods are compared. Biaxial orientation factors are computed based on the experimentally determined axes.     

Crystalline orientation and molecular transport properties in nanoporous syndiotactic polystyrene films

The orientation of the crystalline δ nanoporous phase in syndiotactic polystyrene films, obtained by different procedures, have been characterized. For both solution cast and biaxially stretched films a high degree of uniplanar orientation, corresponding to the tendency of the ac crystallographic planes, to be parallel to the film plane has been observed and rationalized. According to molecular dynamics simulations of diffusion of small molecules into the δ nanoporous phase, this uniplanar orientation would minimize the molecular diffusivity through the nanoporous crystalline phase.     

Development of off-line and on-line capillary electrophoresis methods for the screening and characterization of adenosine kinase inhibitors and substrates

Fast and convenient CE assays were developed for the screening of adenosine kinase (AK) inhibitors and substrates. In the first method, the enzymatic reaction was performed in a test tube and the samples were subsequently injected into the capillary by pressure and detected by their UV absorbance at 260 nm. An MEKC method using borate buffer (pH 9.5) containing 100 mM SDS (method A) was suitable for separating alternative substrates (nucleosides). For the CE determination of AMP formed as a product of the AK reaction, a phosphate buffer (pH 7.5 or 8.5) was used and a constant current (95 microA) was applied (method B). The methods employing a fused-silica capillary and normal polarity mode provided good resolution of substrates and products of the enzymatic reaction and a short analysis time of less than 10 min. To further optimize and miniaturize the AK assays, the enzymatic reaction was performed directly in the capillary, prior to separation and quantitation of the product employing electrophoretically mediated microanalysis (EMMA, method C). After hydrodynamic injection of a plug of reaction buffer (20 mM Tris-HCl, 0.2 mM MgCl2, pH 7.4), followed by a plug containing the enzyme, and subsequent injection of a plug of reaction buffer containing 1 mM ATP, 100 microM adenosine, and 20 microM UMP as an internal standard (I.S.), as well as various concentrations of an inhibitor, the reaction was initiated by the application of 5 kV separation voltage (negative polarity) for 0.20 min to let the plugs interpenetrate. The voltage was turned off for 5 min (zero-potential amplification) and again turned on at a constant current of -60 microA to elute the products within 7 min. The method employing a polyacrylamide-coated capillary of 20 cm effective length and reverse polarity mode provided good resolution of substrates and products. Dose-response curves and calculated K(i) values for standard antagonists obtained by CE were in excellent agreement with data obtained by the standard radioactive assay.     

Raman characterization of orientation in poly(lactic acid) films

Poly(lactic acid) is a new biopolymer material which is marketed by Cargill Dow Polymers under the tradename Nature Works*. One major application for this material is biaxially oriented films for food packaging because it possesses excellent barrier for flavor constituents, deadfold and heat sealability. Shrinkage must be minimized when the film is heat sealed for these applications and, therefore, characterization of the orientation of the amorphous phase of PLA films is necessary. Raman spectroscopy methodology has been developed to quantify orientation in PLA films. Bands were assigned to crystalline and amorphous phases of PLA such that orientation in both phases could be monitored. Raman depolarization ratios were used to characterize uniaxial systems but were insufficient for most biaxial draws. A new phenomenon for oriented films involving Raman band shifts was observed in these systems, and was shown to be capable of determining orientation, even for symmetrical biaxially drawn films. The origin of these shifts, as well as their use for the quantification of orientation will be discussed. Further, since the line widths of the bands could be used to quantify crystallinity, both crystallinity and orientation could be determined with one measurement.     

Molecular structure and thickness dependence of chain orientation in aromatic polyimide films

Degrees of orientation of main chains and imide rings were quantitatively estimated for spin‐coated films of six kinds of aromatic polyimides (PIs) using polarized attenuated total reflection (ATR)/Fourier transform infrared (FT‐IR) spectroscopy. The degrees of chain orientation parallel to the film planes are significantly larger for the PIs having rigid structures than those having flexible structures, and the introduction of side groups decrease the degrees of chain orientation. In contrast, the rotational orientations of imide rings are almost isotropic for all PI films. Moreover, the film thickness dependences of the degrees of orientation were investigated for two kinds of rigid‐rod PIs having bulky trifluoromethyl ( CF₃) side groups in their diamine moieties. The degrees of chain orientation slightly decrease as the film thickness increases, whereas the rotational orientation of imide rings is independent of the film thickness. The degrees of chain orientation on the substrate sides significantly differ from the atmospheric sides of PI films. This difference was generated during thermal imidization because of tensile stress originated from the mismatch in thermal expansion coefficients between the substrates and the PI films. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2109–2120, 2005     

Procedures for Db chemical characterization in off-line experiments

A new procedure to isolate carrier-free isotopes of Nb and Ta after a 12-MeV proton bombardment of a natural Hf foil has been considered. The cross section of the corresponding ^natHf(p,x)¹⁷⁹Ta reaction has been estimated for the first time as 5.4?±?0.5 mb. The isotopes that were produced were subsequently used for development of procedures for the chemical characterization of element 105 (Db). HF/HNO₃ and HNO₃/H₂O₂ media have been chosen and the parameters of the experiments have been optimized. Based on the results obtained in this work, off-line experimental procedures have been proposed for the evaluation of the chemical behavior of Db.     

Optical properties and structure of drawn polyethyleneterephtalate-polyethylene films

Films made by coextrusion of polyethyleneterephtalate and low density polyethylene exhibit specular reflection of light when stretched. Unlike the behaviour of films made of pure PET, where specular reflection is rare and does occur at extremely high stretching rates only, PET/LDPE films show specular reflection independent of the stretching rate.A film, containing 70% PET and 30% LDPE, prepared by coextrusion of the two components, has been investigated by scanning electron microscopy, light microscopy and by measuring the optical properties with a spectrophotometer. The (unstretched) as prepared sample has been compared with a sample stretched to =4.The optical measurements show as a result of the stretching a strong decrease of the transmittance and an increase of the remittance. While there is no drastic change of the dispersion (which is only slight), the increase of the refractive index indicates some straininduced crystallization.The scanning electron micrographs show long, needlelike voids and indicate a fractionation of the two components as a result of the stretching. This fractionation has been investigated by heating the samples up under the light microscope: while the stretched sample shows a separation of the components, the unstretched sample does not.Dedicated to Prof. Dr. F. H. Müller.     

Chain orientation and anisotropies in optical and dielectric properties in thin films of stiff polyimides

Thin films of poly(p-phenylene biphenyltetracarboximide) (BPDA-PDA), prepared by thermal imidization of the precursor poly(amic acid) on substrates, have been investigated by optical waveguide, ultraviolet-visible (UV-VIS), infrared (IR), and dielectric spectroscopies. The polyimide films exhibit an extraordinarily large anisotropy in the refractive indices with the in-plane index n_∥ = 1.806 and the out-of-plane index n_⊥ = 1.589 at 1064 nm wavelength. No discernible effect of the film thickness on this optical anisotropy is found between films of ca. 2.1 and ca. 7.8 μm thickness. This large birefringence is attributed to the preferential orientation of the biphenyltetracarboximide moieties with their planes parallel to the film surface, coupled with the strong preference of BPDA-PDA chains to align along the film plane. The frequency dispersion of the in-plane refractive index n_∥ is consistent with the results calculated by the Lorentz–Lorenz equation from the UV-visible spectrum exhibiting several absorption bands in the 170–500 nm region. The contribution from the IR absorption in the range 7000–400 cm,^?1 computed by the Spitzer-Kleinmann dispersion relations from the measured spectra, adds ca. 0.046 to the in-plane refractive index n_∥. Tilt-angle–dependent polarized IR results indicate nearly the same increase for the out-of-plane index n_⊥. Application of the Maxwell relation then leads to the out-of-plane dielectric constant ε^⊥ ? 2.7 at 1.2 × 10¹³ Hz, as compared with the measured value of ca. 3.0 at 10⁶ Hz. Assuming this small difference to remain the same for the in-plane dielectric constants ε_∥, we obtain a very large anisotropy in the dielectric properties of these polyimide films with the estimated in-plane dielectric constant ε_∥ ? 3.4 at 1.2 × 10¹³ Hz, and ε_∥ ? 3.7 at 10⁶ Hz. © 1992 John Wiley & Sons, Inc.     

Effects of chemical structure and precursor on optical properties,thermo-mechanical properties,and molecular orientation and order of thin films of stiff aromatic polyimides

Thin films of rigid poly(p-phenylene pyromellitimide) (PMDA-PDA) and semi-rigid poly(p-phenylene biphenyltetracarboximide) (BPDA-PDA), prepared by thermal imidization of the respective poly(amic acid) and poly(amic ethyl ester) precursors, were characterized with respect to their optical, thermomechanical and structural properties. Both polyimides exhibit an unusually large anisotropy between the in-plane and out-of-plane refractive indices, with n ranging from 0.198 to 0.216 for PMDA-PDA and from 0.230 to 0.242 for BPDA-PDA, nearly independent of the nature of the initial polyimide precursor, film thickness, and film preparation method. PMDA-PDA films exhibit low coefficients of thermal expansion (CTE's) of 6.5 and 8.2 ppm/C for the acid-derived and the ester-derived polyimides, respectively. In comparison, the BPDA-PDA films show CTE values of 4.3 and 18.0 for the acid-derived and ester-derived samples, respectively, despite the small differences in their optical anisotropies. Wide-angle x-ray diffraction patterns obtained in reflection and transmission for the various samples reveal a strong in-plane chain orientation for both PMDA-PDA and BPDA-PDA polyimides, with somewhat better intermolecular packing order for the ester-derived polyimide films. These effects of chemical structure and precursor on properties and structures of the polyimide films are discussed in light of recent theoretical considerations of semiflexible polymers.Dedicated to Prof E. W. Fischer on the occasion of his 65th birthday     

Retention system, thermodynamic properties and structure correlations of environmental analytes

Summary A composite chromatographic retention index system has been developed for identifying polycyclic aromatic hydrocarbons, polychlorinated biphenyls and polychlorinated pesticides. When retention indices and thermodynamic data of polycyclic aromatic hydrocarbons on 5% phenylmethylsiloxane stationary phase were compared with those obtained on polydimethylsiloxane a correlation was found between retention and electronic properties. Determination and quantitation of individual contaminants in water and sediment samples from Lake Mecoacán were achieved by capillary gas chromatography with flame ionization and electrocapture detection.     

Thermodynamic properties and structure of water films in flotation processes

The thermodynamic properties of water layers on barite and marble samples covered with various amounts of tetradecylammonium chloride (TDAHCl) after flotation processes were investigated by thermal analysis. The relation between the activation energy, the enthalpy and the entropy of the bonded water and the amount of TDAHCl previously deposited on the bare mineral surfaces was determined. An interpretation of the changes in these parameters, the water structure and the flotability is described.

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Zusammenfassung Mittels Thermoanalyse wurden nach Schwimmaufbereitungsverfahren die thermodynamischen Eigenschaften der Wasserschichten über Baryt- und Marmorproben mit verschiedenem Gehalt an Tetradecylammoniumchlorid (TDACl) untersucht. Es wurde die Beziehung zwischen der Aktivierungsenergie, der Enthalpie und der Entropie des gebundenen Wassers und der Menge an zuvor an der Oberfläche des bloßen Minerals festgesetzen TDACl festgestellt. Die Veränderlichkeit dieser Parameter sowie die bindung des Wassers und di Flotierbarkeit werden interpretiert.

     

Interfacial structure and properties in polystyrene/epoxy bilayer films

The interfacial structure and properties of immiscible deuterated polystyrene (dPS)/epoxy bilayer films were investigated with neutron reflectivity as functions of the composition of the epoxy layer, the thickness of the dPS layer, and the annealing time. We have found that the interfacial width and its growth rate depend strongly on the compositions of the epoxy layer but only weakly on the thickness of the dPS layer. The effect of the resin/crosslinker composition on the interfacial width and its growth rate is likely due to the different near‐surface structures that result for different epoxy stoichiometries. For an ultra‐thin dPS film (thickness = 2R_g), the data suggest a slight suppression of the growth of the interfacial width that could be due to confinement effects for the long‐chain molecules such as have been previously reported for a thickness of less than approximately 4R_g, where R_g is the radius of gyration of polymer molecules. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2653–2660, 2002     

Depth-resolved molecular structure and orientation of polymer thin films by synchrotron X-ray diffraction

An exemplary system suitable for optoelectronics applications, i.e. poly(3-hexylthiophene), hereinafter P3HT, deposited by spin casting onto silicon substrates functionalised by three selected molecules and then properly annealed, has been examined. Grazing Incidence X-ray Scattering (GIXS) measurements have been performed with 4-circle diffractometer, allowing for a fine control of sample axes movement.By choosing different grazing incident angles, diffraction patterns from different layers of polymeric thin films have been recorded. Both in-plane and out-of-plane geometries have been combined in order to obtain complementary structural information. In this way structural and orientational differences of the polymer along with the film thickness (?50 nm) have been highlighted. For all P3HT films spun on functionalized Si wafer, macromolecular layers close to the substrate surface give some evidence of higher order and orientation than those outmost the surface, and this behaviour is pronounced to a different extent depending on the functionalized molecules used. Contrariwise P3HT layers deposited onto bare Si wafer display reduced orientation and decreased crystallite size, especially at buried interface.     

Combined extraction chromatography and scintillation detection for off-line and on-line monitoring of strontium in aqueous solutions

This paper presents the application of a new sensor materials, whichcombine extraction chromatography and scintillation detection. The resultantsensor embodies the simultaneous dual functionality of selective extractionand radiation detection, which has been applied towards off-line and on-linemonitoring of radiostrontium in aqueous solutions. The sensor materials are(1) a mixture of commercially available Sr-selective extraction chromatographicresin and granular scintillator, (2) bis-4,4'(5')-tert-butylcyclohexano-18-crown-6(DtBuCH18C6) in 1-octanol coated on the surface of a scintillating glass and(3) inert chromatographic resin impregnated with the organic fluors, 2,5 diphenyloxazole,(PPO) and 1-4 bis(4- methyl-5-phenyloxazol-2-yl) benzene, (DM-POPOP) and eitherDtBuCH18C6 in 1-octanol or a proprietary extractant. For off-line measurements,the sensor materials are used in the same manner as the commercially availableextraction chromatographic resin, but rather than eluting the activity fromthe column, the scintillating extraction column is placed in a scintillationvial and counted without the introduction of liquid scintillation cocktail.For on-line measurements, the sensor materials are used in conjunction witha flow-cell scintillation detection system to assess the activity retainedby the extractant in real-time. Characterization of the detection efficiencyand regeneration capability of the extractive scintillator materials is evaluated.     

Reversed migration micellar electrokinetic chromatography with off-line and on-line concentration analysis of phenylurea herbicides

Three environmentally important phenylurea herbicides (monuron, isoproturon, diuron) were separated in reversed migration micellar electrokinetic chromatography (RM-MEKC) using 50 mM sodium dodecyl sulfate, 50 mM phosphoric acid, and 15 mM gamma-cyclodextrin. Three on-line concentration techniques are then evaluated to increase the detection sensitivity of the RM-MEKC system. Stacking with reverse migrating micelles (SRMM, water as the sample solvent) provided the best results among the focusing techniques studied. Using a z-shaped detection cell, more than 500-fold increase in peak height is obtained. As a sample preparation and off-line concentration method, solid-phase extraction (SPE) that further improved detection sensitivity was used in the analysis of spiked tap and pond water. For example, 1 parts per billion of each herbicide spiked in tap or pond water was detected by MEKC after SPE and SRMM.     

Investigation of structure and properties of divinylbenzene-styrene copolymer films

A method for preparation of divinylbenzene-styrene copolymer porous layer on the inner wall of a fused silica capillary was developed. Capillary gas chromatography was used to investigate the sorption capacity of copolymer film toward substances of various classes.