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  • 1
    Electronic Resource
    Electronic Resource
    Plastic films on the bottom of the Skagerack (1975)
    [s.l.] : Nature Publishing Group
    Nature 255 (1975), S. 622-623 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Some of these films (Fig. 1) have been analysed, using infrared spectroscopy (IR) and gel permeation chromatog-raphy (GPC), (see ref. 1). The films were found at depths varying between 180 and 400m. The analyses show that the films consist of low density polyethylene (LDPE) which shows evidence of ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/255622a0
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  • 2
    Electronic Resource
    Electronic Resource
    A comparison between different ways to obtain molecular weight distributions of PVC and a study on the anomalies of PVC in tetrahydrofuran solutions (1973)
    New York : Wiley-Blackwell
    Die Makromolekulare Chemie 166 (1973), S. 247-264 
    Details
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Klassische Methoden zur Bestimmung der Molekulargewichtvserteilung von PVC wurden mit den Ergebnissen der Gelchromatographie (GPC) verglichen. Zwei PVC-Proben, die in bezug auf die Polydispersität Extrema der Handelsware darstellen, wurden durch GPC und durch Fällungsfraktionierung im System Tetrahydrofuran/H2O charakterisiert. Der Bestimmung der GPC-Daten wurde das Konzept der Universalkalibrierung zugrunde gelegt; für unvollständige Auflösung wurde eine Korrektur eingeführt. Die Grenzviskositäten und die mittleren Molekulargewichte wurden sowohl für die Fraktionen als auch für die ursprünglichen Polymeren ermittelt.Verschiedene Methoden der Berechnung der Molekulargewichtsverteilung von Fraktionen wurden verglichen. Falls sich das Auftreten von Peaks, deren Herkunft nicht auf die Molekulargewichts-Verteilung der Probe zurückgeführt werden kann („spurious peaks“), vermeiden läßt, liefert die modifizierte BEALL-Methode bei Verwendung der SCHULZschen Verteilungsfunktion die besten Werte für die Molekulargewichtsverteilung. Unter den Methoden, die auf einer Verwendung der mittleren Molekulargewichte des gesamten Polymeren in Verbindung mit einer Verteilungsfunktion beruhen, zeigt die Methode, die die SCHULZsche Verteilungsfunktion verwendet, die beste Übereinstimmung mit den Ergebnissen der GPC. Verteilungsfunktionen, denen nur ein Wert für das mittlere Molekulargewicht zugrunde liegt, gaben weniger zufriedenstellende Resultate.Die Assoziation der PVC-Moleküle in Tetrahydrofuran führt bei diesem Polymeren während des Fraktionierungsvorgangs und bei anderen Charakterisierungsmethoden zu einem anormalen Verhalten. Die Assoziation nimmt mit der Syndiotaktizität der Probe zu. Um den uuerwünschten Einfluß solcher übermolekularer Strukturen zu vermeiden, wurde eine Wärmebehandlung der PVC-Lösungen durchgeführt. Die Abweichung der log [η] vs. log Mw-Kurven von der Linearität wurde auf diese Weise auf eine Assoziation und nicht auf eine Kettenverzweigung zurückgeführt.
    Notes: Classical methods for determinations of molecular weight distribution of PVC have been compared with gel permeation chromatography (GPC) measurements. Two PVC samples representing extreme values of polydispersity for common commercial resins, have been characterized by GPC and precipitation fractionation, using the tetrahydrofuran/H2O system. The concept of universal calibration and a correction for incomplete resolution have been applied to GPC data. Intrinsic viscosities and molecular weight averages have been determined both for the fractions and the original polymers.Different ways to calculate molecular weight distributions from the fractions have been compared. It was found that the modified BEALL method using the SCHULZ distribution function for the fractions, gives the most accurate molecular weight distribution if spurious peaks could be eliminated. Among the methods using molecular weight averages for the whole polymer in combination with a distribution function, the SCHULZ distribution function showed the best agreement with GPC. Distribution functions based on one molecular weight average only seemed to give less satisfactory results.Association of PVC molecules in tetrahydrofuran causes anomalous behaviour during the fractionation procedure and with other characterization methods. It was found that the amount of aggregates increases with syndiotacticity. To avoid the undesired influence of such supermolecular structures a heat treatment of the PVC solutions was used. The deviation from linearity in log [η] vs. log Mw plots was thus found to be due to aggregation and not to long chain branching.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1973.021660122
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  • 3
    Electronic Resource
    Electronic Resource
    On the effect of mechanical energy on the degradation of polyethylene in the solid state and in the melt (1977)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 17 (1977), S. 728-732 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    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 influence of mechanical forces on structural changes in commercial grades of high and low density polyethylenes was investigated by using extremely high shear rates (〉2 × 104S-1) during processing in a special injection molding machine and by long-term loading at ambient temperature. Changes in molecular weight distribution (MWD) and the degree of long-chain branching (LCB) were followed by gel permeation chromatography and viscometry. No effect of the mechanical forces was observed either in the long-term loading or in the processing. At temperatures exceeding 280°C the small changes noted in MWD and LCB wrere found to be entirely due to thermal de radation.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760171006
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  • 4
    Electronic Resource
    Electronic Resource
    Thereto-oxidative degradation of polyethylene. IV. Blends containing poly(vinyl chloride) and chlorinated polyethylene as models for polyethylene recycle qualities (1977)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 17 (1977), S. 700-705 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    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: In order to study the changes in mechanical and structural properties of low density polyethylene (LDPE) during recycling of PE film wastes from industrial and commercial sources, mixtures of LDPE with 5 percent poly(vinyl chloride) PVC were processed, recycled and heated in air. The effect of added chlorinated high-density polyethylene (CPE), carbon black, antioxidants and heat stabilizers were also investigated. Compounding and recycling were performed in a twin screw extruder equipped with granulating device. Films were blown in an adiabatic vertical extruder. The thermo-oxidative treatments were carried out in a forced-air oven at 107°C. Tensile strength, elongation to break and film impact strength were determined according to ASTM standards. Structural changes were determined by gel chromatography, solution viscometry, melt indexing, differential scanning calorimetry and infrared spectroscopy. Even 5 percent PVC adversely affects the proeessability and mechanical properties of LDPE films. Addition, of the same amount of CPE gives marginal improvements in the mechanical properties, possibly due to a compatibilizing action. PVC and CPE also adversely affect the thermooxidative stability of LDPE. When unstabilized, PVC and CPE evolve large amounts of HCl during processing. Minor degradation of the LDPE also occurs. Stabilization of the LDPE may be achieved by phenolic antioxidants.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760170908
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  • 5
    Electronic Resource
    Electronic Resource
    Thermal degradation of polyethylene in a nitrogen atmosphere of low oxygen content. III. Structural changes occuring in low-density polyethylene at oxygen contents below 1.2% (1974)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 18 (1974), S. 779-804 
    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: Samples of low-density polyethylene, free from additives, were kept at temperatures between 284° and 355°C under nitrogen containing 1.16% oxygen or less. Changes in molecular weight distribution (MWD) and degree of long-chain branching (LCB) were followed by gel chromatography (GPC) and viscosity measurements. Other structural changes were investigated by infrared spectroscopy and differential scanning calorimetry (DSC). Both chain scission and molecular enlargement occur simultaneously. Chain scission accounts for the formation of low molecular weight material and volatiles. Molecular enlargement reactions cause an increase in LCB and ultimately the formation of insoluble material. At lower temperatures (284°C) an increase in the high molecular weight end of the MWD is observed. The amount of olefinic unsaturation, carbonyl, and ether groups increase with degradation. Conjugated systems are formed. The formation of thin discolored and insoluble surface layers indicate that the attack of oxygen is diffusion controlled. The DSC thermograms undergo large changes at 333° and 355°C, increasing with time and oxygen content. A reaction scheme for the thermo-oxidative degradation of polyethylene is discussed. Both inter- and intramolecular hydrogen abstractions by peroxy radicals are suggested to occur. Thus, the formation of trans-vinylene and ether groups results from intramolecular abstraction, while internal carbonyl groups are formed by intermolecular abstraction. Chain scission will be accomplished by both routes and together with “back-biting” is suggested to accoun for the formation of volatiles. The formation of conjugated sequences causing discoloration is correlated with the formation of trans-vinylene groups. Because of the restricted accessability of oxygen under our conditions, the reactions discussed previously for pure thermal degradation1 are also considered to be important. The molecular enlargement observed is thus proposed to be mainly due to the combination of alkyl radicals even when oxygen is present.
    Additional Material: 17 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1974.070180315
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  • 6
    Electronic Resource
    Electronic Resource
    Thermal degradation of polyethylene in a nitrogen atmosphere of low oxygen content. II. Structural changes occuring in low-density polyethylene at an oxygen content less than 0.0005% (1974)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 18 (1974), S. 761-778 
    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: Samples of low-density polyethylene, free from additives, were heated at temperatures between 284° and 355°C under high-purity nitrogen. Changes in molecular weight distribution (MWD), molecular weight averages, and degree of long-chain branching (LCB) were followed by gel chromatography (GPC) and viscosity measurements. Other structural changes were investigated by infrared spectroscopy and differential scanning calorimetry (DSC). At 284° and 315°C, the MWD's were shifted toward higher molecular weights and the M̄w values increased. At 333° and 355°C, the MWD's shift toward lower molecular weight, but the high molecular weight, tail is largely retained. M̄w decreases slowly at 333°C. At 355°C, M̄w undergoes a rapid initial drop which levels off. M̄w/M̄n and the degree of LCB increase with heating time and temperature. Olefinic unsaturation increases. The vinyl groups show a larger relative increase than do the trans-vinylene and vinylidene groups. At 355°C, the peak of the unimodal DSC thermogram is shifted to ∼3°C higher temperature. A lower melting peak then develops, and after 72 and 90 min the two peaks are about equal in size. The density increases from 0.922 g/cm3 to 0.930 g/cm3 for samples heated at 355°C, and the weight loss was 1.5% after 90 min. A reaction scheme for the thermal degradation of polyethylene is discussed. Initiation is suggested to be accomplished by scission of allylic C—C bonds. Propagation proceeds by both intra- and intermolecular hydrogen abstraction, followed by β-scission. Termination can occur by both combination and disproportionation. Combination reactions are suggested to account for the observed formation of LCB and high molecular weight material. Due to changes in the degree of LCB during the degradation, viscometry alone will not give a proper measure of the changes in molecular weight.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1974.070180314
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  • 7
    Electronic Resource
    Electronic Resource
    Thermal degradation of polyethylene in a nitrogen atmosphere of low oxygen content. II. Structural changes occurring in low-density polyethylene at an oxygen content less than 0.0005% (1974)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 18 (1974), S. 3179-3179 
    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
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1974.070181023
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  • 8
    Electronic Resource
    Electronic Resource
    Thermal degradation of polyethylene in a nitrogen atmosphere of low oxygen content. III. Structural changes occurring in low-density polyethylene at oxygen contents below 1.2%In its original printing, this paper was unfortunately not in correct sequence. It is being republished here in its entirety. (1974)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 18 (1974), S. 3153-3178 
    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: Samples of low-density polyethylene, free from additives, were kept at temperatures between 284° and 355°C under nitrogen containing 1.16% oxygen or less. Changes in molecular weight distribution (MWD) and degree of long-chain branching (LCB) were followed by gel chromatography (GPC) and viscosity measurements. Other structural changes were investigated by infrared spectroscopy and differential scanning calorimetry (DSC). Both chain scission and molecular enlargement occur simultaneously. Chain scission accounts for the formation of low molecular weight material and volatiles. Molecular enlargement reactions cause an increase in LCB and ultimately the formation of insoluble material. At lower temperatures (284°C) an increase in the high molecular weight end of the MWD is observed. The amount of olefinic unsaturation, carbonyl, and ether groups increase with degradation. Conjugated systems are formed. The formation of thin discolored and insoluble surface layers indicate that the attack of oxygen is diffusion controlled. The DSC thermograms undergo large changes at 3333° and 355°C, increasing with time and oxygen content. A reaction scheme for the thermo-oxidative degradation of polyethylene is discussed. Both inter- and intramolecular hydrogen abstractions by peroxy radicals are suggested to occur. Thus, the formation of trans-vinylene and ether groups results from intramolecular abstraction, while internal carbonyl groups are formed by intermolecular abstraction. Chain scission will be accomplished by both routes and together with “back-biting” is suggested to account for the formation of volatiles. The formation of conjugated sequences causing discoloration is correlated with the formation of trans-vinylene groups. Because of the restricted accessability of oxygen under our conditions, the reactions discussed previously for pure thermal degradation1 are also considered to be important. The molecular enlargement observed is thus proposed to be mainly due to the combination of alkyl radicals even when oxygen is present.
    Additional Material: 17 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1974.070181022
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  • 9
    Electronic Resource
    Electronic Resource
    Thermooxidative degradation of polyethylene. I and II. Structural changes occurring in low-density polyethylene, high-density polyethylene, and tetratetracontane heated in air (1978)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 16 (1978), S. 2555-2586 
    Details
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Samples of low-density polyethylene (LDPE), high-density polyethylene (HDPE), and tetratetracontane (n-C44H90) free from additives were heated in air at temperatures between 120 and 180°C. As a comparison, “as received” HDPE containing unspecified additives has also been included.The structural changes have been studied with gel chromatography, viscometry, infrared spectroscopy, differential scanning calorimetry, and gravimetric measurements.LDPE, HDPE, and n-C44H90 follow the same course of thermooxidative degradation when they are free from additives and present in the molten state. Both molecular-diminishing and enlargement reactions occur. At temperatures below 150°C molecular enlargement is not observed until after rather long exposure times, whereas at higher temperatures enlargement occurs immediately. The difference is because “peroxide curing” becomes increasingly important above 150°C, whereas ester formation is operating at all temperature levels. Degradation below Tm is restricted to the amorphous phase that results in a different degradation pattern.In accelerated testing work extrapolations of the Arrhenius type in the prediction of structural change are thus not justified, even within the actual narrow temperature range. Neither are changes in commonly used standards like carbonyl content justified as a measure of the changes; for example, in mechanical properties.The stabilizer in the unpurified HDPE not only influences the induction period but also the course of the thermooxidative degradation.
    Additional Material: 28 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1978.170161012
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