Young's modulus of semicrystalline polymers

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Abstract
The measurement of crystallinity and Young's modulus for two widely different polyethylenes at temperatures between 30 and 140°C. are reported. A theory is presented which accounts fairly well for the observed values of the modulus. By comparing the theory with experiment it is found that the crystallite sizes in slowly cooled polyethylene vary from about 250 to 400 angstrom units depending upon the linearity of the constituent molecules. The theory is also applied to the data of Leitner for natural rubber. It is found that in this material the crystallites were about 4300 A. long. An observed discrepancy between theory and experiment indicates that the amorphous regions between the crystallites are somewhat ordered.