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R. Ścigała, A. Włochowicz


Studies of supermolecular structure of polytetrafluoroethylene


Polimery 1988, No 6, 224


DOI: dx.doi.org/10.14314/polimery.1988.224

Summary

The type of crystallographic system, dimensions of unit cell, degree of crystallinity and average size of crystallites in polytetrafluoroethylene (PTFE) samples differing in molecular mass (M) in the range of 5.3—127.8 x 106 and subjected to various cycles of thermal treatment, have been characterized. It has been found that both the dimensions of unit cell, values of lattice constants, a and c, and the type of crystallographic system are invariant to M-values. The M-values do not exert any effect also on the size of PTFE crystallites in the form of suspension powders — they are in the range of 30—50 nm. It has been found that the degree of crystallinity of sintered samples decreases with an increase in the cooling rate after sintering and under defined conditions of cooling it in general increases with an increase in M. It has also been ascertained that the average size of crystallites in sinters increases with M in cases of a rapid cooling and decreases under conditions of a slow cooling. It is possible by an appropriate selection of M-value of PTFE and of cooling conditions of articles made of PTFE to change their degree of crystallinity in the range from 45 to 80% and the size of crystallites in the range from 40 to 170 nm.



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