ISSN:
0025-116X
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
The linear thermal coefficient of expansion for high density polyethylene, extended to draw ratios λ = 8 to 16 is α = -24·10-6 K-1 at 20°C. This value results from the orientation of crystallites with an expansion coefficient αc = -12·10-6 K-1 and from stresses in the amorphous phase. Using the model of series coupling of crystalline and amorphous parts the value αam ≤ -50·10-6 K-1 is calculated for a crystallinity xv = 70%. From measurements of Young's modulus the fraction of tie-molecules χtie = 0,4% of the sample is assessed and the expansion coefficient αtie = -90·10-6 K-1. Annealing of the samples leads to shrinkage while the density ρ increases slightly and the expansion coefficient α increases considerably. Samples annealed at temperatures closely below the melting point show a slight decrease of the density at 20°C but a value of α exceeding that of isotropic samples. This effect can be explained by preferred orientation of the crystal a-axis in fibre direction as soon as orientation starts to break down.
Additional Material:
8 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/macp.1981.021820619
