ISSN:
0022-3832
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
Polyethylene may be characterized by use of the light scattering technique applied to the solid polymer. The treatment of Debye and Bueche allows one to assign numerical values to this characterization in the form of two parameters, 〈η2〉, the mean square dielectric constant deviation and a size parameter, α, associated with a spacing within the polyethylene microstructure. This spacing has not as yet been definitely identified with regard to the polyethylene crystallites or spherulites. The numerical values obtained of 2000-3000 A. are too large to be crystal edges and too small to be spherulite radii. The magnitude of the mean square dielectric constant deviation from the average should be associated with the amount of inhomogeneity in the solid, that is, the amount of crystallinity. No direct relation has been found in this work, however, between per cent crystallinity as measured by density and the value of ∠η2〉. The study of 〈η2〉 through a melting and cooling cycle shows a hysteresis effect which is dependent on rate of cooling from the molten state. The effect of heating polyethylene on the value of 〈η2〉 parallels a curve of per cent crystallinity vs. temperature. When the sample is cooled there is a point of maximum scattered intensity and maximum 〈η2〉 at about 106.5°C. Study of the value of α in the melting and cooling process shows it is essentially a constant at all temperatures under equilibrium conditions. If α is studied as a function of time after rapid cooling from the melt to 106.5°C., it is found to maximize after about 20 minutes. This implies that there is a definite spacing between crystalline regions in the spherulite and that, once this spacing is reached, further aggregation can occur only by more crystalline material attaching itself to the periphery of the spherulite with the same spacing or consolidation of existing crystalline regions.
Additional Material:
18 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1956.120209509
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