Study of Secondary Crystallization of Isotactic Polypropylene via Pulsed 1H-NMR Method

Study of Secondary Crystallization of Isotactic Polypropylene via Pulsed 1H-NMR Method

Peer-reviewed article not indexed in WoS or Scopus

Application of polymers depends significantly on the ability of their structure to remain unchanged as long as possible. Recrystallization processes as well as changes in amorphous fraction of semicrystalline polymers (such as isotactic polypropylene), induced by ageing, can alter the properties of the initial material. It is well known that the form and the portion of a crystalline phase are responsible for mechanical and physical properties of semicrystalline polymers. In this study, the crystallinity was characterized as a solid phase content (SPC) measured by pulsed 1H-NMR. Advantages of the method consist in a direct measurement, non-destructive character, high accuracy (standard deviation 0.03 %), high speed of analysis (a few minutes), fully automated and easy operation. Time and temperature dependence of SFC and relaxation times (T2s - spin - spin relaxation time of solid phase, T2l - spin - spin relaxation time of liquid phase) were assessed. The measurement was performed on several commercial available isotactic polypropylene materials. The maximum in the speed of the secondary crystallization on time was observed. It was discovered that T2s relaxation times were practically independent on time and temperature. However, T2l relaxation times depend on time and temperature significantly.

Application of polymers depends significantly on the ability of their structure to remain unchanged as long as possible. Recrystallization processes as well as changes in amorphous fraction of semicrystalline polymers (such as isotactic polypropylene), induced by ageing, can alter the properties of the initial material. It is well known that the form and the portion of a crystalline phase are responsible for mechanical and physical properties of semicrystalline polymers. In this study, the crystallinity was characterized as a solid phase content (SPC) measured by pulsed 1H-NMR. Advantages of the method consist in a direct measurement, non-destructive character, high accuracy (standard deviation 0.03 %), high speed of analysis (a few minutes), fully automated and easy operation. Time and temperature dependence of SFC and relaxation times (T2s - spin - spin relaxation time of solid phase, T2l - spin - spin relaxation time of liquid phase) were assessed. The measurement was performed on several commercial available isotactic polypropylene materials. The maximum in the speed of the secondary crystallization on time was observed. It was discovered that T2s relaxation times were practically independent on time and temperature. However, T2l relaxation times depend on time and temperature significantly.

polypropylene, pulsed 1H-NMR, secondary crystallization

polypropylene, pulsed 1H-NMR, secondary crystallization

VILČ, L.; KRATOCHVÍLA, J.

20.09.2005

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