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Combination of Ultrasound Spectroscopy and Dilatometry to Analyse the Structure Formation during Crystallization of Polymers under Pressure

Isothermal crystallization experiments of isotactic polypropylene at moderate pressure have been carried out using a new measuring cell. By a combination of pressure dilatometry and ultrasound spectroscopy it was able to measure simultaneously specific volume, longitudinal ultrasound velocity and excess attenuation coefficient during glass transition or crystallization. It was shown, that pressure dilatometry as well as ultrasound spectroscopy can be applied to analyse the crystallization process in polymers. Both methods allow detection of fast and very slow crystallization mechanisms and yield comparable results. By means of Hoffman-Lauritzen theory it was shown, that acceleration of crystal growth under the influence of pressure can be attributed to the shift of the characteristic transition temperatures. In addition to the systematic crystallization experiments the excess attenuation coefficient, which was measured during crystallization from the melt up to the semicrystalline solid state, was analyzed. It was found, that ultrasound excess attenuation mainly arises from sound scattering at the boundaries of spherulites and because of molecular relaxation processes, which might lead back to the rigid amorphous fraction in between the crystal lamellae.

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Author
 Alexander Ohneiser

Alexander Ohneiser
Deutsches Kunststoff-Institut Darmstadt
Technische Universität Darmstadt

Information

Free keywords: semicrystalline polymers, ultrasonic spectroscopy
Institute / chair: Fachbereich Physik der Technischen Universität Darmstadt
Language: German
Technical consultant for expert services: Priv.-Doz. Dr. I. Alig (Betreuer), Prof. Dr. B. Stühn
Publication year: 2011
Provider: Wissenschaftlicher Arbeitskreis Kunststofftechnik (WAK) / Kunststoffe.de

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