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- Ultraschall (3)
- Vulkanisation (3)
- Prozesskontrolle (2)
- Kautschuk (1)
- Rheologie (1)
- Schallgeschwindigkeit (1)
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Zusammenfassung
In diesem Beitrag wird zunächst die für die on-line Prozesskontrolle an duroplastischen Formmassen entwickelte Ultraschallmesstechnik vorgestellt. Die Methode basiert auf der Durchschallung des vernetzenden Materials mit Hilfe von in das Werkzeug integrierten druck- und temperaturfesten 4 MHz-Ultraschallsensoren. Die Auswertung von Schalllaufzeit und Signalamplitude erfolgt vollautomatisch und dient der Berechnung von Schallgeschwindigkeit und -dämpfung. Beide Größen repräsentieren die änderung der mechanischen Eigenschaften infolge der Vernetzungsreaktion. Durch Anwendung auf vulkanisierende Materialien sollte die Anwendbarkeit der bewährten Methode erweitert werden. Im Ergebnis wird gezeigt, dass die Größe des Messeffekts von der Menge an Vernetzer (Schwefelkonzentration) abhängt. Bei ausreichend hohem Vernetzungsgrad zeigt die Ultraschallgeschwindigkeit signifikante, gut auswertbare Resultate, die den Ablauf der Vulkanisation on-line zu verfolgen gestatten. Ein Vergleich mit Vulkameterkurven zeigt große ähnlichkeiten und berechtigt zu der Hoffnung, dass die Methode industriellen Einsatz finden kann.
19F-NMR-spektroskopische Untersuchungen über die Photolyse aromatischer Verbindungen in Fluorbenzol
(1975)
NMR is a powerful method for structure elucidation and determination of polymers in solution. Soluble polymers can be studied by high resolution techniques - just äs small molecules - provided there is sufficient segmental motion to average out some of the linebroadening effects. The resonance lines remain broader, however, which can result in peak overlapping, especially for proton spectra. Carbon NMR is favoured in this field because of the larger spectral range and the feasibility of getting single lines by proton broad-band decoupling. One particulariy important use of NMR is the determination ofthe microstructure of the polymer chain.
The application of high resolution NMR to solid polymers was not possible until the development of techniques like magic angle spinning, high power proton decoupling and cross polarization. The linebroadening effects in thermoplastic and duroplastic polymers, however, are only reduced to some extent. The spectra show relatively broad lines, with typical linewidths of 100 - 500 Hz, which are roughly 10 to 100 times larger than in the liquid state. Different from thermoplastic and duroplastic polymers the spectra of elastomers have a much better resolution if the measurements are performed well above the glass transition temperature. This condition is fulfilled at room temperature for many elastomers. Above Tg linebroadening effects are averaged out by segmental motions, comparable to the liquid phase. By raising the temperature the resolution can be increased further which especially improves the spectra of elastomers with relatively high glass transition temperatures.
Filiers can influence the linewidth of the spectra. The effect is twofold. First, the filier particies, e.g. carbon black, introduce microscopic inhohogeneities by susceptibility variations. Second, the molecular mobility ofthe polymer chains is reduced. Both effects can be averaged out to a great extent by magic angle spinning and high power decoupling, however. Therefore the filier has no detrimental influence on the resolution of the solid-state elastomer spectra. As a consequence, no decomposition procedures are necessary prior to the NMR investigation. The sample can be measured in its original molecular state.
This was the starting point for a thorough and comprehensive investigation of filled elastomers using the solid state technique in order to find out the possibilities and limits. The experiment tumed out to be very suecessfül. This lead us to the idea to put all the spectra together in form of a spectra catalogue.The collection contains the most important Standard and special commercial rubber types. In order to complement the solid state NMR part two chapters on blends and thermoplastic elastomers are added. Proton and carbon solution spectra of the raw rubbers are also included. Especially important is the interpretation ofthe spectra, in order not to display only "fingerprints".