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  • 1
    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: In dieser Arbeit wurden Veränderungen des verschweisßten Rohr- und Fittingmaterials (isotaktisches Polypropylen Homo- bzw. Copolymer PP-R grau pigmentiert) wührend der für die Praxis relevanten Innendruckversuche untersucht.Bei der technischen Verschweißung von Polyolefinen entstehen charakteristische Gefüigezonen im Schweißnahtbereich, welche vom Fßgematerial und den Fngebedingungen beeinflußt werden. In der vorliegenden Untersuchung wurden sowohl die Materialcbergange im Fiigebereich (mit den Methoden - schichtenweise Differentialkalorimetrie, Polarisations- bzw. Elektronenmikroskopie sowie Fluoreszenzspektroskopie mit extrem hoher Ortsauflösung) als auch die Eigenspannungen hinsichtlich ihrer Verlnderung bei Langzeitpriifung im Innendruckzeitstandversuch bei 95°C bis zu einer Prüfzeit von 18.100h untersucht.Die Abbauvorgänge der Makromoleküle bei der Langzeitprüfung der 364 untersuchten Schweißmuster werden in einer gesonderten Arbeit behandelt (1).Durch die Innendruckversuche bei 950 C findet eine Nachkristallisation und eine Gefügevergrijberung sowohl in der Schweißnaht als auch im Gefüge der Schweißpartner statt. Dabei werden die beim Schweißvorgang eingebrachten Orientierungen und Eigenspannungen unter dem Einfluß von Wärme beim Innendruckversuch weitgehend abgebaut. Durch die unter Druckeinwirkung einsetzenden Flieävorgange jedoch werden neue Eigenspannungen eingebracht.Es konnte gezeigt werden, daß bei guter Verschweißung von PP mit PPCO ein kontinuierlicher Übergang (Mischungsbereich) vom Homopolymeren zum Copolymeren auftritt, der auch beim Langzeiteinsatz im Innendruckversuch erhalten bleibt.
    Notes: The present study deals with changes of welded material of pipes and fittings (isotactic polypropylene homo and copolymer PP-R grey pigmented) during the standardized internal pressure tests, which are commonly used for these products.Technical welding of polyolefines causes characteristic structures, which depend on the natural of the welded material and the welding conditions.In this investigation both the transition of material in the welding seam and the changes of internal stresses during internal pressure tests at 95°C until 18.100h test time were examined. The methods we used were Differential calorimetry of think layers, Polarization- and Electron microscopy, Fluorescence spectroscopy with extreme high local resolution.The effects of decomposition of the macromolecules in the welded samples during the internal pressure tests will be described in a separate paper (1).The internal pressure tests at 95O C cause a recrystallization and an increase of the particle size in the structure of the welding seam and in the structure of the welded parts themselves. Under the above described testing conditions the orientations and internal stresses initiated by the welding procedure will relaxe influenced by heat. However the creep effects that occur in the material when exposed to pressure introduce new internal stresses. It could be shown that in perfectly welded parts a continuous transition from PP to PPCO occurs, which did not change after long time application of internal pressure tests.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Extruded, injection-molded, unoriented crystallized specimens and capillary rheometer efflux strands of commercially stabilized polypropylene without nucleating agents were examined by optical microscopy and x-ray diffraction to determine the conditions for β-form crystallization as a function of the distance from the surface and of the shear rate at commercial processing conditions. Results demonstrate that at all “cooling conditions” ΔT = Tm - Tb (defined as the melt temperature Tm minus the bath temperature Tb) effects of strain flow initiate nucleation of β-form crystals. The shear rate is demonstrated to be important for β-form crystallization. A critical average threshold value for the shear rate of approximately 3 × 102 sec-1 has to be exceeded. The β modification is mostly connected with type-III spherulites and partly to row structures, and it is observed at processing conditions in oriented structures only.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1435-1536
    Keywords: Polypropylene ; Crystallization ; Burst test ; Creep
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Abstract The present study deals with changes in the nature of pipe material (isotactic polypropylene unpigmented, pigmented) during burst tests. In practical operation standardized burst tests are commonly used. The observed recrystallization increases proportionally to the temperature and time of storing and is effective even after 2500 h. Increasing crystallinity effects a rise of the determined Ultra Micro Hardness (UMH) of the pipe material. The application of an internal pressure in the pipe, however, increases the UMH to a remarkably higher extent than the simple influence of crystallinity. The pipes which are exposed to burst tests show creep effects of the material; these effects cause a higher hardness and increasing internal stresses of the pipe material. During the burst tests the original internal stresses are reduced by the influence of heat; on the other hand new internal stresses are introduced by the creep of the material caused by the effects of the internal pressure. The influence of recrystallization and the creep during burst tests of pipes on microscopical visible changes of the material will be shown in a following paper [18].
    Notes: Zusammenfassung Es wurden in dieser Arbeit Veränderungen des Rohrmaterials (isotaktisches Polypropylen natur, bzw. pigmentiert) während der für die Praxis relevanten Innendruckversuche untersucht. Die beobachtete Nachkristallisation nimmt sowohl mit steigender Lagertemperatur (Prüftemperatur) als auch mit wachsender Lagerzeit (Prüfzeit) zu und ist selbst noch nach 2500 h Lagerzeit wirksam. Mit zunehmender Kristallinität steigt die ermittelte Ultramikrohärte (UMH) des Rohrgefüges. Das Anwachsen der UMH bei Erreichen eines höheren Kristallinitätsgrades wird durch das Anlegen eines Innendruckes noch zusätzlich verstärkt. Die bei Innendruckprüfung einsetzenden Fließerscheinungen bewirken sowohl einen Härtezuwachs als auch eine Eigenspannungszunahme des Rohrmaterials. Während des Innendruckversuches werden durch den Einfluß von Wärme die im Rohr ursprünglich vorhandenen Eigenspannungen abgebaut; durch den unter Druckeinwirkung einsetzenden Fließvorgang werden jedoch neue Eigenspannungen eingebracht. Der Einfluß der Nachkristallisation sowie der Fließerscheinungen bei Innendruckprüfung von Rohren auf mikroskopisch sichtbare Gefügeänderungen soll in einer späteren Veröffentlichung gezeigt werden [18].
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  • 4
    ISSN: 1435-1536
    Keywords: Polypropylene fibre ; crystallinity ; morphology ; melting behaviour ; mechanical properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Crystallinity measurements were carried out with the help of X-ray diffraction, differential scanning calorimetry (DSC) and density measurements. The results of this study provide a better understanding of the morphology and complex thermal behaviour of polypropylene fibres. Crystallinity studies show that the crystallinity of PP fibres when measured by X-ray and DSC methods as a function of draw-ratios increases with increasing draw-ratios while the crystallinity of the same samples as derived by density measurements shows an inverse trend. These discrepancies are accounted for by the formation of microvoids within the polypropylene fibres due to drawing. In the DSC scan two endothermic peaks were found to occur in some of the samples. This is explained by the presence of two morphological forms i. e. lamellar and fibrillar morphology in the same sample. The crystallinity values obtained from different methods are correlated with mechanical properties, such as tenacity and elongations.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1435-1536
    Keywords: Polyethylene ; Polypropylene ; Crystallization ; DSC ; Avrami exponent
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract This paper presents a new method for a rapid determination of the Avrami exponentn by nonisothermal thermoanalytic analysis (DSC and DTA, resp.). Contrary to conventional techniques this method can be used in the entire temperature range and therefore it is applicable to polymers crystallizing from the melt. The proposed technique is applied to injection moulded low density polyethylene (LDPE), injection moulded high density polyethylene (HDPE), unpigmented extruded polypropylene (PPunpigm.) and pigmented extruded polypropylene (PPpigm.). The resulting values for the Avrami exponentsn LDPE∼2.9,n HDPE∼1.3, $$n_{PP_{unpigm} }$$ ∼2.2 and $$n_{PP_{pigm} }$$ ∼ 2.1 derived by crystallization from the melt were compared with isothermal measurements and with results given by other authors.
    Type of Medium: Electronic Resource
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