The Degree of Crystallinity in Natural Rubber. III. Correlation between X-Ray and Density Measurements

Abstract In 1925 Katz discovered the crystallization of stretched rubber. In the following years several investigators tried to determine the structure of rubber crystallites. The densities of the rubber crystallites calculated from the results of these investigations varied strongly. The results of x-ray and density measurements on crude rubber carried out by the author can be made to correspond only when the latter are based on the unit cell of Bunn. It is shown by experiment that, to measure the correct degree of crystallization, it is necessary to use monochromatic x-rays.</jats:p

The Degree of Crystallinity in Natural Rubber. V. A Discussion of the X-Ray Results on Natural Rubber in Connection with the Work of Flory, Gee and Wildschut

Abstract A recent theory, developed by Flory, makes it possible to calculate the degree of crystallization from thermodynamical measurements if certain parameters are properly evaluated. Such evaluation is possible by combining Wildschut's thermodynamical measurements with the x-ray results presented in previous papers. Thus the average length of molecule chains between cross-linkages can be derived; it closely corresponds to the results of swelling measurements carried out by Gee. Other parameters are also evaluated in agreement with their physical meaning.</jats:p

The Degree of Crystallinity in Natural Rubber. IV. The Degree of Crystallization in Frozen Raw Rubber and Stretched Vulcanized Rubber

Abstract An improved x-ray technique has been worked out to determine the degree of crystallinity in natural rubber. Inaccuracies which sometimes occur in quantitative x-ray measurements were eliminated, and it has been shown that the amount of crystalline rubber, both in frozen samples of raw rubber and in stretched vulcanized rubber, could be determined fairly accurately. More experiments were carried out and the results are described. These results, which confirm the current views on the problem of crystallization, point to relatively low degress of crystallization, even in highly stretched rubber, and they agree with some other experimental evidence and with a recent theoretical investigation.</jats:p