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  • 1
    Electronic Resource
    Electronic Resource
    Change of mechanical properties of crosslinked polyethylene during its thermo-oxidative aging (1993)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 208 (1993), S. 47-64 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die thermische Alterung von extrudierten Proben von mit Elektronenstrahlen vernetztem linearem Polyethylen wurde im Temperaturbereich von 110-170°C untersucht. Kurz- und langfristige Veränderungen der mechanischen (Dehnungs-)Eigenschaften wurden beobachtet; die entsprechenden Alterungsmechanismen werden auf der Basis ergänzender Sol-Gel-, Dichte-, FTIR- sowie gravimetrischer Messungen und Zugversuche an Mikrotomschnitten diskutiert.Zwei Mechanismen führen zu kurzfristigen Eigenschaftsänderungen: eine Nachvernetzung und eine Änderung der Kristallstruktur (bei Proben oberhalb ihrer Schmelztemperatur). Im vorliegenden Fall wurden die Polymeren im festen Zustand vernetzt, so daß die Änderung der Kristallstruktur zu einer erkennbaren Abnahme der Streckspannung (ca. 5 MPa) führte.Die langfristigen Veränderungen treten nach dem Ende der Oxidationsinduktionsperiode auf. Sie können als Übergang vom zähen in den spröden Zustand interpretiert werden, der durch Strukturänderungen sowohl auf molekularer (durch Kettenspaltung) als auch makroskopischer Ebene (durch diffusionskontrollierte Kinetik der Oxidation verursachte Kern-Schale-Struktur) hervorgerufen wird. Durch IR- und DSC-Analysen wurde festgestellt, daß wahrnehmbare Änderungen in der Dehnung erst kurz vor dem Ende der Induktionsperiode auftreten.
    Notes: The thermal aging of extruded samples of electron beam-crosslinked linear polyethylene has been studied in the 110-170°C temperature range. Short and long term changes of mechanical (tensile) properties were observed, and the corresponding mechanisms are discussed on the basis of complementary sol-gel and gravimetric measurements on whole samples, and density, FTIR and tensile testing on microtome sections.Two mechanisms are involved in short term changes: a post-crosslinking and a change of the crystalline morphology (for samples exposed above the melting point). The latter effect is especially important in the case under study where the polymer was crosslinked in the solid state and leads to a noticeable decrease (∼5 MPa) of the yield stress.The long term changes take place after the end of the induction period of oxidation. They can be interpreted in terms of ductile-brittle transition induced by structural changes occurring on the macromolecular level (chain scission) as well as macroscopically (core-shell structure resulting of the diffusion control of oxidation kinetics). It appears that noticeable changes of ultimate elongation occur just before the end of the induction period as detected by IR or DSC method.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1993.052080105
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  • 2
    Electronic Resource
    Electronic Resource
    Stabilizer consumption and lifetime prediction in ageing of crosslinked polyethylenePaper presented at the “16th International Conference on Advances in the Stabilization and Degradation of Polymers” in Luzern (Switzerland), June 14-17, 1994. (1995)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 232 (1995), S. 1-12 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The thermal oxidation of β ray-crosslinked polyethylene (XLPE) was studied in temperatures ranging from 90 to 180°C. Various analytical methods were used for determination of an end of the induction period on bulk samples: gravimetry, ultimate tensile properties, density and color change. On microtome slices of ∼30 μm thickness the depth distribution of oxidation products, phenolic antioxidant, density and tensile ultimate properties were followed as a function of exposure time by respectively IR and UV spectrophotometry, densitometry and Microfoil Tensile Testing.Depending on the testing method different durations of induction period (DIP) were obtained. They increase in following order:Phenol depletion 〈 Ultimate elongation 〈 Density 〈 Carbonyl build-up ≤ Color change 〈 Weight loss.The difference between phenol depletion DIP and carbonyl build-up DIP can be considered as negligible at temperatures higher than the melting point (about 30%) but it reachs more than 100% at T〈 Tm.Different kinetic regimes of phenol consumption were observed depending on the exposure temperature. A mechanistic interpretation is proposed explaining the role of the stabilizer system in initially homogeneous and later heterogeneous oxidation of the bulk material.The Arrhenius law was applied to different durations of induction period. A discontinuity appeared in the melting point region (120-130°C) which is tentatively interpreted in terms of different stabilizer concentration in amorphous phase of semicrystalline material (T 〈 Tm) and in melt material (T 〉 Tm). On the basis of the presented complex study of polyethylene thermo-oxidation, different aspects of lifetime predictions are discussed.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1995.052320101
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  • 3
    Electronic Resource
    Electronic Resource
    Oxidation kinetics of poly(4-methylpentene) (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 247 (1997), S. 73-89 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The thermal oxidation (in air between 70 and 150°C) of unstabilised camples of poly(4-methylpentene) (PMP) were studied by infrared spectrometry and by gravimetry. The behaviour was compared to PP exposed in the same conditions.The thermal oxidation was found to exhibit two well differentiated kinetic regimes both for PP as for PMP. The first regime predominates at temperature higher than 90°C. It is characterized by an activation energy of the pseudo induction period of about 100 kJ mol-1. The induction period of mass gain is about 1,8 time shorter than the induction period of carbonyl gain. These characteristics, and the fact that induction periods are of the same order for both polymers, are consistent with a «close loop mechanistic» scheme with unimolecular POOH decomposition. The advantages of this hypothesis compared to other proposed hypothesis (bimolecular POOH decomposition, heterogeneous oxidation...) are discussed. The main theoretical difficulty is that of explaining why the unimolecular process predominates, whereas POOH are obviously hydrogen bonded, even at very low conversions of the oxidation process. This point remains to be explained.The second kinetic regime predominates at temperature lower than 90°C. It is characterized by a considerably lower activation energy. We have examined many hypothesis to explain the existence of a transition at that temperature (where neither PMP nor PP display a physical transition). A first hypothesis is that unimolecular POOH decomposition is replaced by a bimolecular one, which can explain a decrease of the apparent activation energy of about 50%. The bimolecular initiation creates pairs of radicals (POO·+ PO·). It can be imagined that a part of them desactivate mutually by termination after rearrangement of PO· by β scission. In this case, the transition at 90°C could be also a result of the temperature induced change in molecular mobility. Above 90°C, the radicals would diffuse almost freely out of the cage. In contrast, below 90°C, termination would become competitive with diffusion. A supplementary research is needed to fully elucidate the cause of this transition at 90°C.The eventuality of the existence of spatial heterogeneity of the oxidation process has been discussed. It is well known that oxidation is heterogeneous at the morphological scale, but there is no evidence of heterogeneity at smaller scale, where the chemical kinetic would not be applicable.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1997.052470106
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  • 4
    Electronic Resource
    Electronic Resource
    “Close loop” mechanistic schemes for hydrocarbon polymer oxidation (1995)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 33 (1995), S. 921-927 
    Details
    ISSN: 0887-624X
    Keywords: thermo-oxidation kinetics ; hydrocarbon polymers ; monomolecular and bimolecular hydroperoxide initiation ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Mechanistic schemes of radical oxidation of hydrocarbon polymers in which initiation is only due to unimolecular or bimolecular hydroperoxide decomposition have been studied. The results of their kinetic analysis have been compared with literature data relative to the thermal oxidation of polypropylene in solid state (60-160°C). These data are in remarkably good agreement with the “unimolecular” scheme whose main characteristics are: (1) the quasi-independence of the kinetic behavior with initial conditions (for low initial content of thermolabile structures), and (2) the fact that an arbitrarily defined induction period depends only on the rate constant of unimolecular hydroperoxide decomposition. © 1995 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1995.080330605
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  • 5
    Electronic Resource
    Electronic Resource
    Chemiluminescence of anhydride-cured epoxy networks: Influence of the anhydride structure (1993)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 31 (1993), S. 683-690 
    Details
    ISSN: 0887-624X
    Keywords: anhydride-cured epoxy ; thermal oxidation ; chemiluminescence ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The chemiluminescence of three epoxy networks based on diglycidyl ether of biphenol A (DGEBA) crosslinked by respectively the phthalic anhydride (PA), hexahydrophthalic anhydride (HHPA), and methyl tetrahydrophthalic anhydride (MTHPA), was studied in the 180-240°C temperature range. Isothermal stationary and nonstationary (perturbed) experiments revealed that the behavior depends sharply on the anhydride structure. The higher emissivity of cycloaliphatic systems (MTHPA and HHPA) is explained in terms of hydrogen abstractibility on the hardener's moiety. The main difference between MTHPA and HHPA (intensity initially decreases for the former, increases for the latter) is explained by the consumption of the MTHPA double bonds in oxidative crosslinking processes. The results of perturbed experiments were essentially attributed to changes of alkyl radical concentration during the exposure under nitrogen. These changes can be modelled by a simple kinetic model taking into account the observed differences between the systems under study. © 1993 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pola.1993.080310312
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  • 6
    Electronic Resource
    Electronic Resource
    Chemiluminescence of diglycidyl ether of bisphenol A  -  Norbornene anhydride networks (1993)
    New York : Wiley-Blackwell
    Journal of Bioluminescence and Chemiluminescence 8 (1993), S. 315-323 
    Details
    ISSN: 0884-3996
    Keywords: Anhydride (norbornene) cured epoxy ; thermal oxidation ; chemiluminescence ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Networks were prepared by curing diglycidyl ether of bisphenol A (DGEBA) with variable concentrations of norbornene anhydride (NA). Almost completely cured samples with anhydride/epoxide (A/E) inolar ratios of respectively 0.8, 0.9, 1.0 and 1.1, and one incompletely cured sample with A/E = 1.0, were studied by chemiluminescence in the temperature range 135-220°C, using isothermal stationary or non-stationary (atmosphere change) exposures. The comparison of kinetic curves of intensity variation reveals: the importance of unreacted epoxide groups as sources of highly emissive radical species, the lowering effect of oxidation products, and the increasing effect of the decrease of macromolecular mobility due to crosslinking in the case of the incompletely cured sample. Most of the features of kinetic curves obtained in non-stationary experiments are explained in terms of radical formation mechanisms during exposure in inert atmosphere. The results show clearly that chemiluminescence is due to reactions of peroxy radicals rather than hydroperoxide groups.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bio.1170080605
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  • 7
    Electronic Resource
    Electronic Resource
    Chemiluminescence from amine cured epoxy resins modified with halogenated phenylglycidyl ethers (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 53 (1994), S. 1357-1363 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Chemiluminescence from thermooxidized epoxide alone and that modified with phenyl glycidyl ethers has been investigated in isothermal and nonisothermal regime. Isothermal curves are characterized by a monotonous fall of chemiluminescence intensity from some initial value to very low levels of light emission. Nonisothermal curves show a maximum intensity at temperatures above 473 K. The luminescence intensity is influenced by both Tg and thermal stability of epoxide. The higher Tg or higher thermal stability brings about the higher intensity of light emission and vice versa. © 1994 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1994.070531012
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  • 8
    Electronic Resource
    Electronic Resource
    Thermal aging of plasticized PVC. I. Weight loss kinetics in the PVC - didecylphtalate system (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 45 (1992), S. 2091-2096 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Weight-loss kinetics were studied for 10 industrial extruded samples of poly(vinyl chloride) (PVC) plasticized by 20-30% by weight of didecylphtalate at 85, 95, 105, 110, and 120deg;C. For the most unstable samples, which contained a light coplasticizer, the weight-loss rate obeyed Fick's law. In the other cases, it was constant in the early period of exposure. The apparent Arrhenius parameters (i.e., preexponential factor and activation energy) were intercorrelated and varied strongly from one sample to another. This was explained by the existence of two distinct kinetic regimes corresponding, respectively, to diffusion or evaporation, the whole process being controlled by the slowest step, and a transition between both regimes occurring in the temperature range of exposure. In the proposed model, small changes of the preexponential factor of diffusion from one sample to another are sufficient to take into account the observed behavior.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1992.070451204
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  • 9
    Electronic Resource
    Electronic Resource
    Thermal aging of plasticized PVC. II. Effect of plasticizer loss on electrical and mechanical properties (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 45 (1992), S. 2097-2103 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The change of mechanical properties was followed during thermal aging at 85, 95, 105, and 120°C of the 10 PVC-didecylphthalate extrudates studied in the first part of this paper, but also of four new samples differing only by the plasticizer concentration. For these latter samples, the change of dielectric properties was also studied. It appears that the dielectric properties are essentially the function of the plasticizer concentration whatever is the initial concentration or aging conditions. In contrast, the mechanical properties vary in a more complex way and cannot be predicted by a simple physical model. It is suggested that, among other factors, the depth distribution of plasticizer can play an important role.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1992.070451205
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  • 10
    Electronic Resource
    Electronic Resource
    Concentration and temperature dependence of plasticizer diffusion into plasticized PVC (1994)
    Brookfield, Conn. : Wiley-Blackwell
    Journal of Vinyl and Additive Technology 16 (1994), S. 57-61 
    Details
    ISSN: 0193-7197
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The diffusion of a plasticizer S1 from a source made of PVC containing 25 wt% of S1 into a medium made of PVC film containing another plasticizer S2 in 15, 20, 25 and 30 wt%, was studied at temperatures ranging from 70 to 108°C. S1 was generally diphenyl-iso-octyl phosphate (DPIP) and S2 was dioctyl phthalate (DOP) but the reciprocal system was also studied in some cases. Starting from a reference point corresponding to a temperature of 70°C and a DOP concentration of 25 wt%, it was found experimentally that an increase Δv of the DOP volume fraction (v) or an increase ΔT of the temperature, led to the same variation of the diffusion coefficient of DPIP if ΔT/Δv ∼ 139K. A reasonably close value can be obtained from a simple free-volume approach, using the literature data on the plasticizer action of DOP on PVC.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/vnl.730160114
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