Strain-induced Crystallization of Natural Rubber

Introduction

In addition to evaluation of crystal structure, X-ray diffractometry enables evaluation of periodic structure called "long-period structure." For this long-period structure, it is necessary to observe a period a few times to a few tens of times longer than the periodic structure of atoms or molecules in ordinary crystals, and thus evaluation using small-angle scattering measurement becomes important. Structural changes due to heating, stretching, magnetic fields and other external factors are often seen, particularly in samples such as polymers and rubber which have both a crystal structure (micro structure) and long-period structure (macro structure). New findings can be obtained by evaluating both crystal structure and long-period structure while varying these external factors. 

Measurements and results

Micro structure and macro structure were observed while varying the elongation factor of natural rubber. Figure 1 shows 2-dimensional images of natural rubber with no stretching, 4x elongation, 5x elongation, and 6x elongation. The part with high scattering intensity near the center of each diagram is called the small-angle region, and it shows the macro structure of the natural rubber measurement sample. With no stretching, the observed refraction lines have a ring shape, and thus both the micro structure and macro structure can be regarded as being in a non-oriented state. With 4x elongation, on the other hand, a change was evident in the macro structure (small-angle region), and it was found that, with 5x elongation, change also begins in the micro structure (high-angle region).