A thermomechanical analysis of polymer foaming

A novel technique is described for studying the growth of foam from polymer melts containing thermally-decomposable blowing agents. A simple cylinder and plunger sample holder has been combined with a standard thermomechanical analyzer. This enables the recording of height i.e. volume vs. time or temperature at preselected rates for temperature scan. Demonstrations with foamable polyethylene and plasticized poly(vinyl chloride) have revealed the influences of heating rate, blowing agent type and concentration, blowing agent inhibitor, polymer viscosity and crosslinking agent on foam growth rate and final foam height i.e. foam density.

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Zusammenfassung Eine neue Technik zur Untersuchung der Schaumbildung aus Polymerschmelzen, welche thermisch zerstörbare Schaumbildner enthalten, wird beschrieben. Ein einfacher Zylinder und ein Tauchprobenbehälter wurden mit einem thermomechanischen Standardanalysator gekoppelt. Dies ermöglicht das Registrieren der Höhe, d.h. des Volumens als Funktion der Zeit oder Temperatur, bei vorgewählten Geschwindigkeiten für die Temperaturabtastung. Versuche mit schäumungsfähigem Polyäthylen und plastizisiertem Poly(Vinylchlorid) zeigten die Einflüsse der Aufheizgeschwindigkeit, des Typs und der Konzentration des Schaumbildners, des Inhibitors des Schaumbildners, der Viskosität von Polymer und Quervernetzer auf die Geschwindigkeit der Schaumbildung und auf die Endhöhe des Schaumes, d.h. die Schaumdichte.

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Résumé On décrit une nouvelle technique pour étudier la formation de mousse dans les polymères fondus qui contiennent des agents de soufflage décomposables par voie thermique. On a associé un simple cylindre et un porte-échantillon d'immersion à un analyseur thermomécanique standard. Cela permet d'enregistrer la hauteur, c'est-à-dire le volume, en fonction du temps ou de la température, à des vitesses de montée en température présélectionnées. Des démonstrations avec du polyéthylène et du chlorure de polyvinyle plastifié pouvant mousser ont mis en évidence les influences respectives de la vitesse de chauffage, du type et de la concentration de l'agent de soufflage, de l'inhibiteur de l'agent de soufflage, de la viscosité du polymère et de l'agent de réticulation sur la vitesse de formation de la mousse et sur sa hauteur finale, c'est-à-dire la densité de la mousse.

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On leave from Faculty of Technology & Metallurgy University of Beograd, Beograd, Yugoslavia     

Modulated-temperature thermomechanical analysis

By employing a ‘modulated-temperature’ heating programme composed of a series of heat-isotherm stages, it is possible to separate the change in dimensions of an oriented material during heating into two contributions: a thermally ‘reversing’ component which is due to linear thermal expansion and a ‘non-reversing’ part arising from relaxation to the disordered state on heating aboveT _g. Some preliminary results for biaxially drawn poly(ethylene terephthalate) film are presented. These experiments were carried out at the Thermal Methods & Conservation Science Laboratory, Department of Chemistry, Birkbeck College, University of London.     

Simultaneous light emission—differential thermal analysis of selected coordination compounds

A new apparatus which permits the simultaneous determination of both the light emission (LE) and differential thermal analysis (DTA) curves of a compound is described. LE—DTA curves are reported for a selected number of coordination compounds, each containing vigorous reducing—oxidizing ligands or ions. New LE curve peaks are reported for [Co(NH₃)₆](NO₃)₃, [Ni(en)₃](NO₃)₂, and [Rh(NH₃₅X](NO₃₂) (X = Cl, Br on NO₃) complexes. Multiple LE peaks were found for [Co dien (NO₃)₃], cis-[Co(en)₂(NO₂)₂] NO₂ and [Co dien NH₃(NO₂)₂]Cl. The presence of carbon-containing reducing ligand is not necessary in order to obtain a LE peak during the thermal dissociation process     

Application of zNosetrade mark for the analysis of selected grape aroma compounds

A novel and portable gas chromatograph (GC, zNose™) has been evaluated for the measurement in grape berries of selected six-carbon compounds; namely, hexanal, cis-2-hexen-1-ol, cis-3-hexen-1-ol and trans-2-hexenal. The zNose™ is a handheld GC which uses purge and trap for concentration, and has a surface acoustic wave (SAW) sensor as a detector. Operation of the zNose™ using direct aspiration of the sample failed to detect the compounds at the reported odour threshold values. Pre-concentration by Tenax^® trapping and solid-phase microextraction (SPME) were investigated to improve the zNose™ sensitivity. Use of a Tenax^® pre-trap with the zNose™ allowed detection of the compounds at concentration levels in the order of their threshold values. Excessive bleed from the SPME fibre prevented the use of SPME with zNose™.     

Polymer characterization using thermomechanical analysis

The purpose of the work was to characterize the thermomechanical behaviour of two well-known and widely-used thermoplastic polymers. Both dynamic and constant load measurements were made for high-density polyethylene (HDPE), low-density polyethylene (LDPE) and amorphous polystyrene (PS). The results of these measurements yield valuable information which can aid in both design applications and material processing.

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Zusammenfassung Die Thermomechanische Analyse (TMA) wurde zur Untersuchung der thermoplastischen Polymere HDPE, LDPE und PS angewandt. Die Messungen an HDPE und LDPE wurden dynamisch im Temperaturbereich von –90C bis ca. +140C durchgeführt. PS wurde von –190C bis ca. + 130C statisch gemessen. Die Ergebnisse dieser Messungen zeigen deutlich die hervorragende Eignung der TMA bei der Bestimmung von Glasübergangs- und Schmelztemperaturen, der Charakterisierung der elastischen Eigenschaften sowie der Ausdehnungskoeffizienten. Zur Charakterisierung können weitere thermoanalytische Methoden (z. B. TG, DSC) herangezogen werden, wodurch zusÄtzliche Informationen erhalten und die TMA-Ergebnisse erhÄrtet werden können.

     

Unexpected conversions of selected heteroorganic compounds

A few unexpected conversions of selected heteroorganic compounds are described, including the formation of N‐sulfonyl sulfenamide derivatives and the mixed phosphinyl‐sulfenyl anhydrides in the reactions of sulfinyl chlorides with α‐phenylethylamine or t‐butyl‐phenylphosphine oxide, respectively. Unexpected reactions of the ortho hydroxyalkyl‐substituted diaryl sulfoxides and hypervalent sulfur and selenium derivatives, induced by triphenylphosphine, are also presented. Attempts to rationalize the observed reaction courses are briefly discussed. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:437–442, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10077     

A study of furan compounds

The ethyl esters of N-phenyl-, N-p-tolyl-, and N-ethoxyphenyl--pyrrolecarboxylic acid have been synthesized by the reaction of ethyl 2, 5-dimethoxytetrahydrofuran-2-carboxylate with aniline, ptoluidine, and p-phenetidine in the presence of p-toluenesulfonic acid. The reaction of the same ester with benzylamine gives N-benzylpyrrole--carboxybenzylamine or 2,5-dimethoxytetrahydrofuran-2carboxybenzylamide, depending on the ratio of the reactants.For part XXXIX, see [1].     

A study of furan compounds

[N-(2-Furoyl)-, N-(5-methyl-2-furoyl)-, N-(5-chloro-2-furoyl)-, N-(5-bromo-2-furoyl)-, N-(5-iodo-2-furoyl)-, N-(5-nitro-2-furoyl)-, and N-(tetrahydro-2-furoyl) ureas were obtained by acylation of urea with the corresponding acid chlorides.For part XXXIV, see [23].     

Flow-injection determination of membrane- selected organic compounds

A membrane/flow-injection system was developed and tested for the determination of trace organic compounds in aqueous samples. Organic compounds in the injected sample permeate a tubular silicon-rubber membrane and are collected in an extractant flowing through the bore. The extractat containing the permeated compounds flows through a detector producing a peak response. The critical factors for producing a sharp and sensitive peak, such as membrane size, cell dimensions, extractant composition and carrier flow rate, were studied. Conditions for obtaining selectivity and sensitivity for phenols and neutral compounds were investigated.     

Crystallization in glasses monitored by thermomechanical analysis

Thermomechanical analysis (TMA) can be used as a sensitive tool to follow crystallization behavior in non-crystalline materials. Newly developed method is based on slowing down of sample deformation caused by viscous flow above the glass transition due to macroscopic crystal growth. It is shown that a typical TMA sigmoidal curve reasonably well corresponds to direct measurement of crystal growth kinetics by means of optical microscopy. The method has been used to study crystallization kinetics in Ge₃₈S₆₂ glass. The TMA measurement is able to detect earlier stages of crystallization than obtained by differential scanning calorimetry measurement. The activation energy obtained from the shift of extrapolated end of TMA curve with heating rate (E = 263 ± 7 kJ mol^?1) is similar to the activation energy of ??-GeS₂ crystal growth in Ge₃₈S₆₂ glass (E _G = 247 ± 23 kJ mol^?1) obtained from direct optical microscopy measurements.     

Characterization of polymeric dielectric insulation by thermomechanical analysis

Use of a thermomechanical analyzer, TMA, affords a rapid, precise method for determining linear expansion coefficients and linear expansivities of cross-linked polymeric insulation material. Completed cable samples were dissassembled and insulation specimens were cut longitudinally and examined with repeated temperature cycling: ethylene—propylene copolymer rubbers and filled and unfilled crosslinked polyethylenes. The TMA results indicated that all specimes were oriented, likely incurred from extrusion processing. The facility of TMA for investigating potential anisotropic behavior from prior orientation is illustrated by examples of TMA measurements on radial specimens, similarly free of mechanical constraints.     

A Raman spectroscopic study of selected natural jarosites

Raman spectroscopy has been used to characterise the jarosite group of minerals of formula Mn(Fe3+)6(SO4)4(OH)12 where M may be K, (NH4)+, Na, Ag or Pb and where n = 2 for monovalent cations and 1 for the divalent cations. Raman spectroscopy proved useful for mineral identification especially where closely related minerals crystallise out from solutions where paragenetic relationships exist between the minerals. The band position of the SO4(2-) symmetric stretching mode proved to be a function of the ionic radius of the cation. The bending modes show a slight dependence. The spectra of the natural samples can be complex. This complexity is attributed to the incorporation of low levels of other cations into the structure.     

Synthesis, structure, and magnetochemical analysis of selected first-row transition-metal anilino- and anisolesquarate compounds

The isomorphous polymeric complexes [M(mu-C(6)H(5)NHC(4)O(3))(2)(CH(3)OH)(2)](n) [M = Mn (1), Co (2), Cu (4), Zn (5)] are produced by reacting the anilinosquarate anion with the appropriate metal nitrates in a methanolic solution. Each of these complexes contains the central metal atom in a slightly distorted octahedral environment, with the coordination polyhedron consisting of four mu-1,2-bridging anilinosquarate ligands and two trans-oriented methanols. The polymer chains propagate to form a two-dimensional net of metal centers, with the conformation of the component sheets in the net being controlled by intramolecular N-H...O and O-H...O hydrogen bonds. Under reaction conditions similar to those used in the synthesis of the polymers 1, 2, 4, and 5, the nickel(II) monomer [Ni(C(6)H(5)NHC(4)O(3))(2)(H(2)O)(4)].2H(2)O (3) is produced in which each nickel center is attached to two cis-coordinated anilinosquarate and four aqua ligands in a distorted octahedral arrangement. The ligand conformation in 3 is stabilized by both intra- and intermolecular hydrogen bonding, which results in the formation of a sheet polymer having distinct hydrophobic and hydrophilic surfaces. Magnetochemical analysis of 1 and 4 reveals normal paramagnetic behavior for 1 and a very weak ferromagnetic interaction in 4; the absence of significant magnetic interactions is attributed to the distortion of the C(4) cycle of the anilinosquarate ligand (lower than C(2)(v) symmetry) in these complexes. Reaction of anisolesquarate with M(NO(3))(2).xH(2)O in acetonitrile produced the set of isomorphous salts [M(H(2)O)(6)][CH(3)OC(6)H(5)C(4)O(3)](2) [M = Mn (6), Co (7), Ni (8), Zn (9)]. The anisolesquarate anions in 6-9 are hydrogen bonded to the [M(H(2)O)(6)](2+) ions to form polymer chains, which are further linked by hydrogen bonds to form complex sheets. Complexation of the anisolesquarate ligand was not observed even when other solvents and reaction conditions were employed.     

Hydrogen absorption properties of selected uranium intermetallic compounds

Some results of an investigation of hydrogen absorption by selected intermetallic compounds of uranium and thorium with nickel, cobalt, manganese and palladium are reported. Of the compounds under consideration, ThNiAl and UNiAl revealed the greatest capability for hydrogen absorption. The basic thermodynamic functions were calculated for hydrides of both these compounds and the lattice constants were determined by an X-ray method.     

Retention behaviour of selected flavonoid compounds in NP-HPLC

Chromatographia - HPLC retention data for a number of flavonoid compounds have been evaluated on normal phase silica and cyano colums according to the Soczewinski-Snyder (S.-S.) model. On the...     

A comparative study of the dimers of selected hydroxybenzenes

Hydroxybenzenes are the parent compounds of large classes of derivatives, many of which exhibit biological activities. This work presents the results of a comparative study of the dimers of selected hydroxybenzenes, considering all the possible mutual geometrical arrangements of the two monomers and comparing their relative stabilities and interaction energies. The OH···OH hydrogen bond between the two monomers is the dominant stabilizing factor, with frequent preference for mutual perpendicularity of the two aromatic rings. C? H···O unconventional H‐bonds, OH···π unconventional H‐bonds, H···π interactions and π··π interactions also may play significant roles. The factors stabilizing individual hydroxybenzenes (presence of intramolecular hydrogen bonds; number, positioning and orientation of the OH groups; symmetry features) have greater influence on the dimers' relative energy than on the interaction energy between monomers. While results from different calculations methods (HF, MP2, and DFT/B3LYP) show consistency for all the features just‐mentioned, they show some relevant differences in the way they take into account different types of interactions between monomers, resulting in some differences in the geometry arrangements of the monomers in the lowest energy dimers and in differences in the relative preferences among higher‐energy dimer geometries. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012