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  • 1
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 33 (1995), S. 1455-1460 
    ISSN: 0887-624X
    Schlagwort(e): γ-oxidation ; polyethylene ; FTIR ; molecular weight ; elongation at break ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: γ-Oxidation of linear low-density polyethylene based on hexene and butene was investigated. Irradiation was performed at different dose rates in air (from 2 rad/s to 100 rad/s). Degraded samples were analyzed with IR combined with NO and SF4 derivatizations. Our results showed that the lower the dose rate, the higher the degree of oxidation in terms of γ-product formation. Ketone species appeared to be the dominant γ-products. The G values of γ-product formation were very dependent on the dose rate of initiation. Comparison of the G value ratio of different γ-products revealed stoechiometry differences. The complex appearance and disappearance of unsaturations was tentatively explained. The modifications of elongation at break induced by γ-irradiation were monitored by molecular changes in weight. This was not conclusive because changes in elongation at break are inconsistent with changes in Mw/Mn. © 1995 John Wiley & Sons, Inc.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 31 (1993), S. 603-609 
    ISSN: 0887-624X
    Schlagwort(e): γ-oxidation ; polyethylenes ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Different linear low density polyethylenes (LLDPEs) based on hexene and butene comonomer were irradiated with γ-rays under air. The oxidation products have been quantified using NO and SF4 treatments by IR spectroscopy. An FTIR examination displayed unexpected products such as free hydroperoxides and trans-vinylenes. It was found that the type of α-olefin used to process LLDPE films may influence the mechanism of oxidation. Parameters such as the melt index and the density seem to affect the γ-oxidation rate. © 1993 John Wiley & Sons, Inc.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 47 (1993), S. 211-216 
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: The photoaging of different linear low-density polyethylenes (LLDPEs), namely, ethylene-butene (EB) and ethylene-hexene (EH), has been studied. Experiments have been carried out under natural and accelerated UV exposure. We focused our investigation on the changes of elongation at break and the modifications in the chemical structure (measured by the IR technique) occurring over the photoaging process. Our results showed that the changes of elongation at break were different under the two modes of irradiation from the very beginning of UV exposure; in contrast, the comparison of stoichiometry displayed a small difference in the later stage of UV irradiation. That pointed out the difficulty of establishing a relationship between the buildup of carbonyl groups and the mechanical changes due to UV irradiation, which has been usually attempted. In addition, it appeared that the density, oxygen permeability, and the type of α-olefin of the polymer might have an effect upon the elongation-at-break changes. From our data, it can be suggested that the prediction of weathering resistance of polymers can be based on both mechanical changes and modifications in chemical structure to minimize erroneous prediction. © 1993 John Wiley & Sons, Inc.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 60 (1996), S. 1839-1845 
    ISSN: 0021-8995
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau , Physik
    Notizen: Polypropylene PP (high and low crystallinity) was λ-oxidized, in the presence of air, using different dose rates (from 2 to 100 rad/s). Oxidation outcomes were identified and quantified by FTIR spectroscopy coupled with derivatization reactions (NO and SF4). The difficulty to separate secondary and tertiary hydroperoxides from FTIR measurements after NO treatment was addressed. Polymer physical degradation was also monitored during the λ-irradiation process. GPC was used to follow molecular weight changes and tensile tests for elongation at break modifications. Comparison of the extent of oxidation product for-mation over λ-irradiation allowed us to investigate the importance of λ-dose rate on chemical and physical changes of PP. From this, different mechanisms of ketone and ester formation were examined; relationship between the molecular weight changes and the elongation at break modifications was also investigated. © 1996 John Wiley & Sons, Inc.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 212 (1993), S. 35-43 
    ISSN: 0003-3146
    Schlagwort(e): Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Beschreibung / Inhaltsverzeichnis: Photoabbau und UV-Stabilisatorverbrauch von stabilisiertem linearem Polyethylen niedriger Dichte (LLDPE) durch natürliche und künstliche Alterung wurden mittels spektroskopischer Methoden untersucht. Dabei wurde festgestellt, daß sich die mit dem Stabilisatorverbrauch einhergehenden Abbauprozesse der beiden Alterungsmethoden unterscheiden. Das zeigt, daß auf den Verbrauch von Additiven gestützte Aussagen zur Lebenserwartung eines Polymeren vermieden werden sollten. Für eine große Zahl stabilisierter LLDPE-Proben wurden Alterungsbeschleunigungsfaktoren nach verschiedenen Kriterien ermittelt. Die Untersuchung des natürlichen Photoabbaus von stabilisiertem LLDPE durch Verfolgung der Änderung mechanischer Eigenschaften zeigt, daß sich die Bruchdehnung von LLDPE zu dem Zeitpunkt drastisch verschlechtert, zu dem sich die Carbonylbande im Infrarotspektrum zu entwickeln beginnt.
    Notizen: Photodegradation and loss of UV stabilizer resulting from natural and accelerated exposure in stabilized linear low density polyethylene (LLDPE) are investigated by spectroscopic techniques. It is found that the processes governing the loss of UV stabilizer are quite different under the two modes of UV exposure. This result clearly demonstrates that predictions concerning polymer lifetime based on the disappearance of additives must be avoided. For a large number of stabilized samples, acceleration factors according to different criteria have been estimated. Examination of the natural photodegradation process of stabilized LLDPE through mechanical property changes establishes that stabilized LLDPE undergoes catastrophic breakdown of the elongation at break the instant the carbonyl IR band begins to develop.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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