ZUSAMMENFASSUNG:Das Vernetzen von LDPE mittels Peroxiden hat neben einer Abnahme der Kristallinitat eine Veranderung der iibermolekularen Struktur zur Folge. Mit steigender Vernetzung nimmt der Durchmesser der Spharolithe bzw. der garbenfdrmigen Oberstrukturen ab. Dieses Ergebnis ist auf eine rucklaufige Kristallwachstumsgeschwindigkeit zuruckzufuhren, bedingt durch eine fallende Kristallisationstemperatur und einen Anstieg der Schmelzviskositat infolge zunehmender Vernetzungsdichte. Durch die Vernetzung entstehen zusatzliche konstitutionelle Stdrungen in der PE-Kettenstruktur, wodurch die Abmessungen der Lamellenkristalle und die Grdfie der Mosaikbldcke beeinflufit werden.
SUMMARY:The crosslinking of LDPE with peroxides results in both reduction of crystallinity and change of the supermolecular structure. The diameter of the spherulites and the sheaf-shaped superstructures decrease with increasing network. This result can be referred to a decreased crystal growth rate due to an increase of the melt viscosity owing to an increasing network density and a decreasing crystallization temperature. Additional constitutional disorder in the PE chain structure arises through crosslinking; this influences the size of the lamellar crystals and the ideally imperfect crystal block.
The X-ray long periods from high molecular weight injection molded polyethylene (PE) with a shish-kebab structure have been compared with values derived f'rom electron micrographs. It is shown that while small angle X-ray scattering (SAXS) presents two long periods, the direct measurements from transmission electron microscopy (TEM) furnish only the lower SAXS periodicity. In an attempt to clarify this discrepancy of results, laser light diffraction and Fourier transformation of electron micrographs have been undertaken. Using this method two long periods are found in all regions investigated. Results are discussed in terms of the role played by the structured or "weakly crystalline" interlamellar parts, containing a lower electron density, which are neglected by the small angle scattering of X-rays and which give rise in particular regions to larger scattering periodicities.
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