ISSN:
0098-1273
Keywords:
Physics
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
The annealing behavior of low-density melt-crystallized polyethylene is discussed in terms of an unprecedented lamellar diffusion mechanism. For this purpose a combined small-angle x-ray diffraction (SAXS) and differential scanning calorimetry (DSC) study has been carried out. The presence of an initial double-lamellar population is directly evidenced by electron microscopy of freeze-cut and stained sections. The intercalation of thinner lamellae within the dominant wide-lamella population gives rise to an x-ray periodicity of 220 Å (structure I). The independent stacking of thinner lamellae within the material contributes to a second periodicity at 110 Å (structure II). During annealing at successively higher temperatures TA, the low-molecular-weight components from the thin lamellae progressively diffuse out of the double population, reinforcing the stacks of thinner lamellae. At the melting temperature of the thinner crystals a complete segregation of these lamellae takes place, and a new periodicity (structure III) corresponding to stacks of collapsed thick lamellae emerges. The periodicity of structure III increases further with TA. The thin lamellae of structure II can be extracted by a solvent, removing the corresponding SAXS peak and DSC maxima. The partial removal of thin lamellae from structure I by means of solvent extraction concurrently yields a decrease of the SAXS period. The present results suggest that molecular segregation of a low-molecular-weight fraction, contributing to the population of thinner lamellae, occurs during annealing.
Additional Material:
8 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1984.180221009
