Influence of molecular weight on the microhardness of poly(ethylene terephthalate) |
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Authors: | C Vanderdonckt M Krumova F J Baltá Calleja H G Zachmann S Fakirov |
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Institution: | (1) Institute für Technische and Makromolekulare Chemie University of Hamburg Bundestrasse 45 20146 Hamburg Germany, DE;(2) Instituto de Estructura de la Materia CSIC, Serrano 119 28006 Madrid Spain, ES |
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Abstract: | Poly(ethylene terephthalate) (PET) was annealed in vacuum at different temperatures (190–260 °C) for different times (10 min–24 h)
in order to examine the mechanical properties (microhardness) of PET samples with a wide range of molecular weights (10 000–120 000).
Short annealing times result in a twofold decrease in mol. wt. due to hydrolytic decomposition. However, long annealing times
give rise to a substantial molecular weight increase. It is found that microhardness (H) rises linearly with the degree of crystallinity obtained during up-grading of mol. wt. and its extrapolation leads to H-values of completely crystalline PET, H
PET
c=405 MPa for samples with conventional mol. wt. and of 426 MPa for samples with mol. wt. higher than 30 000. It is shown that
the increase of mol. wt. for each set of samples with a given range of degree of crystallinity also causes a slight increase
of H. The influence of mol. wt. upon hardness is discussed in the light of the changes in the physical structure (crystallinity,
crystal thickness) which is formed at given heat treatment conditions.
Received: 29 April 1997 Accepted: 23 September 1997 |
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Keywords: | Poly(ethylene terephthalate) microhardness crystallinity high molecular weight |
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