| Autor: |
Pennings, A. J., van der Mark, J. M. A. A. |
| Zdroj: |
Rheologica Acta; June 1971, Vol. 10 Issue: 2 p174-186, 13p |
| Abstrakt: |
Summary This paper deals with a study on the melting behaviour of polyethylene crystals showing a fibrillar morphology. These crystals were prepared by hydrodynamically induced crystallization from xylene solutions. Use was made of several techniques, such as differential scanning calorimetry, polarizing microscopy and infrared dichroism. The experimental observations indicate that the melting process of the fibrous crystals can only partly be related to morphological structures. The infrared dichroism and persistent birefringence up to temperatures of 200 °C are due mainly to the molecular orientation in the melt. The shrinkage on melting was found to depend on the thickness of and fibre orientation in the sample, as well as on the molecular weight of the polyethylene. A maximum shrinkage value of 93% was measured on fibrillar crystals of Marlex (Mw=90 · 103). Calorimetric studies on the fusion of fibrillar crystals of high molecular weight polyethylene (Mw=1.5 · 106) revealed that extendedchain backbones melt at 150 °C and even at 180 °C. The melt of these crystal structures remains partly oriented, as could be inferred from the constant temperature position of the melting peak on repeated crystallizing and melting. |
| Databáze: |
Supplemental Index |
| Externí odkaz: |
|
Full text from SpringerLink