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  • 1
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Fracture mechanics analysis at high speed and low temperature has been carried out on polypropylene samples of various molecular weights, obtained under different crystallization conditions. In addition differential scanning calorimetry measurements and morphological observations by scanning electron microscopy have been also performed. It has been found that the fracture mechanics parametersG c andK c increase markedly with enhancing the molecular weight, whereas an opposite trend is observed with increasing the crystallization temperature. Furthermore it has been seen that an annealing procedure, on the already solidified samples, strongly enhances the fracture toughness parameters. The above findings have been confirmed by fracture surface observations showing that crazing is the dominant feature of deformation in such materials. Possible underlying molecular mechanisms, which can explain the overall properties and the morphological characteristics, are discussed as well.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 170 (1989), S. 137-143 
    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 vorliegende Arbeit untersucht das linear-elastische Bruchverhalten von (PMMA) mit Poly(ethylen-co-vinylacetat) (EVA) oder EVA  -  g-Bernsteinsäureanhydrid (EVA-g-SA) mittels Kerbschlagzähigkeitsmessungen nach Charpy. Rasterelektronenmikroskopaufnahmen zeigen, daß in Blends, die durch „in situ“-Polymerisation des acrylischen Monomeren in Gegenwart des Elastomeren hergestellt wurden, eine IPN-Morphologie vorliegt, während ein Blend, das durch Mischung der Polymerkomponenten im Schmelzezustand gebildet wurde, die typische zweiphasige Struktur von dispergierten Elastomerdomänen in einer glasartigen Matrix zeigt.Die Ergebnisse der mechanischen Messungen stimmen gut mit den beobachteten Morphologien überein.
    Notes: In the present work blends between poly(methylmethacrylate) (PMMA) and poly(ethylene-co-vinylacetate) (EVA) or its derivative EVA-g-succinic anhydride (EVA-g-SA) have been investigated by linear elastic fracture mechanics (LEFM) with Charpy impact tests and by scanning electron microscopy (SEM). Blends prepared by “insitu” radical polymerization of the acrylic monomer in the presence of the rubbers have an IPN morphology, while a blend prepared by melt-mixing the polymer components shows the typical biphasic structure of rubbery domains dispersed in a glassy matrix.Furthermore, a different behaviour is found when using EVA-g-SA instead of EVA. A fair agreement is found between the response of the LEFM analysis applied to the results of Charpy impact tests and the observed morphologies.
    Additional Material: 4 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 217 (1994), S. 159-190 
    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: Mit einer Reihe unterschiedlicher Methoden wurde versucht, die Zähigkeit tri- und tetrafunktioneller Epoxid- sowie ungesättigter Polyesterharze zu erhöhen. Die Epoxidharze wurden durch harte, thermisch stabile Konstruktionskunststoffe, ein Bisphenol-A Polycarbonat bzw. ein thermoplastisches Polyetherimid (Ultem 1000), modifiziert. Bei den ungesättigten Polyesterharzen wurde ein anderes Verfahren angewendet: Zwei handelsübliche flüssige Kautschuke wurden chemisch modifiziert, um ihre Reaktivität gegenüber den funktionellen Gruppen der Matrix zu steigern: Ein hydroxyterminiertes Polybutadien und ein aminoterminiertes Butadien-Acrylnitril-Copolymeres wurden zu Polymeren mit Isocyanat- bzw. Maleimidendgruppen umgesetzt. Ein weiteres hier beschriebenes System zielt darauf ab, die rasch abnehmende Steifheit der Polyestermatrix bei Temperaturen oberhalb Raumtemperatur zu verringern. Dazu wurde ein hitzehärtbares Bismaleimidharz als zweite co-reaktive Komponente in den Polyester eingebracht.
    Notes: A number of different approaches were used to enhance the toughness of tri- and tetrafunctional epoxies and of unsaturated polyester resins. In the case of epoxies, tough, thermally stable, engineering thermoplastics, namely a bisphenol-A polycarbonate and a thermoplastic poly(ether imide) (Ultem 1000) were employed as modifiers. For unsaturated polyesters a different approach was adopted: two commercial liquid rubbers were chemically modified to enhance their reactivity towards the matrix functionalities. In particular, a hydroxy-terminated polybutadiene and an aminoterminated butadiene-acrylonitrile copolymer were transformed into isocyanate-terminated and maleimide-terminated rubbers, respectively. A further system which is described in the present contribution is aimed at mitigating another deficiency of the polyester matrix, namely its rapidly decreasing rigidity at temperatures above room temperature. In this case, a thermosetting bismaleimide was incorporated into the resin as a co-reactive second component.
    Additional Material: 28 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 241 (1996), S. 11-29 
    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: Das Fließ- und Bruchverhalten eines durch das gleichzeitige Härten eines ungesättigten Polyesters (UP) und eines wärmehärtbaren Bismaleimidharzes (BMI) erhaltenen quervernetzten Polymernetzwerkes wurde über einen weiten Temperatur- und Beanspruchungsbereich untersucht. Die Fließspannung σy und der Youngsche Elastizitätsmodul E steigen bei Zunahme der Spannungsbeanspruchung bzw. bei Absinken der Temperatur. Zudem steigen bei ansonsten gleichen Testbedingungen σy und E mit zunehmendem BMI-Gehalt im Blend. Andererseits wurde eine Beeinflussung des Bruch-Parameters Kc durch die Gegenwart des BMI nicht beobachtet. Der Fließprozess wurde sowohl mit Hilfe der Theorie von Argon als auch mit der von Bowden untersucht; die daraus abgeleiteten Molekül-Parameter wurden mit der bei der Härtung gebildeten Molekularstruktur in Beziehung gesetzt.
    Notes: The yielding and the fracture behaviour of an intercrosslinked polymer network obtained by the simultaneous curing of an unsaturated polyester (UP) and a thermosetting bismaleimide resin (BMI) was investigated in a wide range of temperatures and testing rates. The yield stress σy and the Young's modulus E increase by increasing the testing rate and decreasing temperature. Moreover, under the same testing conditions, σy and E increased as the BMI content in the blend was enhanced. On the other hand, it was found that the fracture parameter Kc was not affected by the presence of BMI. The yielding process was analyzed using the theories both of Argon and Bowden and the molecular parameters derived there were related to the molecular structure of the network developed upon curing.
    Additional Material: 13 Ill.
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  • 5
    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 thermischen und dynamisch-mechanischen Eigenschaften einiger linearer kautschukelastischer Polyurethane mit chemisch unterschiedlichen starren Segmenten wurden untersucht und zur chemischen Zusammensetzung in Beziehung gesetzt. Interessante Zusammenhänge wurden zwischen der Kristallinität der elastischen Polyurethanharnstoffe und der aromatischen oder cycloaliphatischen Natur der Diisocyanat-Komponenten gefunden. Darüber hinaus scheinen die Ergebnisse bei einem bestimmten Verhältnis zwischen starren und flexiblen Segmenten und bei gegebener Zusammensetzung der flexiblen Gruppen auf eine bessere Phasenseparation bei den Polyurethanharnstoffen mit cycloaliphatischen starren Segmenten als bei solchen mit aromatischen, starren Einheiten hinzuweisen.
    Notes: Experimental batches of linear rubber-like polyurethanes characterized by the presence of chemically different hard segments are studied and their thermal and dynamic-mechanical properties are related to the differences in chemical compositions. Interesting correlations are found between the development of crystallinity in such elastomeric poly(urethaneurea)s and the aromatic or alicyclic nature of the diisocyanate. Moreover, for a fixed ratio between hard and soft segments, and for a given composition of the soft segment, the results seem to indicate a better degree of phase separation in cycloaliphatic-based hard segment poly(urethaneurea)s than in aromatic-based hard segment poly(urethaneurea)s.
    Additional Material: 7 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Basel : Wiley-Blackwell
    Die Makromolekulare Chemie, Rapid Communications 9 (1988), S. 91-95 
    ISSN: 0173-2803
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 5 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Basel : Wiley-Blackwell
    Die Makromolekulare Chemie, Rapid Communications 9 (1988), S. 129-134 
    ISSN: 0173-2803
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 4 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 181 (1980), S. 957-967 
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The crystallization behavior of high density polyethylene/isotactic polypropylene blends (HDPE/PP) was investigated. The overall kinetics of crystallization of HDPE may be strongly influenced by the addition of a small fraction of PP. At 398 K the half crystallization time of the blend containing 10% by weight of PP is around three times larger than for pure polyethylene. This effect may be accounted for by an increase in the melt viscosity of liquid HDPE caused by PP molecules. For crystallization temperatures high enough to prevent HDPE crystallization (Tc 〉 400 K), the presence in the melted blends of liquid HDPE influences the crystallization of PP. In fact, the half time of crystallization of PP increases with increasing the fraction of HDPE in the blend. The kinetics show a minimum at a well defined composition (around 60% in PP) before phase inversion. The same trend is observed when the surface free energy of folding and the lamellar thickness of crystals are reported as function of composition.
    Additional Material: 9 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 188 (1987), S. 2231-2239 
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The morphology and the texture of thin films of ethylene/propylene copolymers with crystallizable polypropylene blocks was investigated by optical and electron microscopy as a function of both molecular composition and crystallization conditions. The thermal and melting behaviour was also studied. It was found that variables such as the observed melting point as well as the enthalpy and the entropy of fusion are composition dependent. Contrary, the equilibrium melting temperature seems to be invariant with composition in agreement with the block type of the investigated copolymers.
    Additional Material: 10 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Polymers for Advanced Technologies 7 (1996), S. 519-528 
    ISSN: 1042-7147
    Keywords: Unsaturated polyesters ; bismaleimide resins ; FTIR spectroscopy ; mechanical properties ; 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
    Notes: An unsaturated polyester resin has been modified by adding a thermosetting bismaleimide (BMI) as second co-reactive monomer. The bismaleimide resin was readily dissolved in the uncured polyester matrix up to a concentration of about 20%. Fourier transform infrared spectroscopy was employed to monitor the cure kinetics of this complex system. The available spectroscopic evidence indicated that both the mechanism and the kinetics of the crosslinking process were strongly affected by the presence of the bismaleimide in the system. The molecular structure of this intercrosslinked network is discussed. The dynamic - mechanical behavior of a typical blend composition was found to be in agreement with the proposed molecular structure. The yield stress and Young's modulus were found to increase by increasing the BMI content in the blend, while the fracture parameter Kc was not affected by the presence of BMI.
    Additional Material: 17 Ill.
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