Abstract
In dealing with elasticity and with swelling, we have thus far considered rubber to be composed of a loose network of randomly-kinked long-chain molecules. This simple picture does not fully represent the structure of rubber under all conditions, and gives no explanation of many of the remarkable physical properties of raw rubber. For a more adequate representation we are forced to include the effects of crystallization. In this Part we shall examine some of these effects, and see what light they throw on the mechanism of the process of crystallization and on the structure of rubber generally. At the outset we may find some difficulty in accepting the theory that rubber may contain a crystalline phase. This is because we are accustomed to think of a crystal as possessing a precise geometrical shape. We cannot identify such geometrical forms in rubber. But, on consideration, we see that the essential attribute of a crystal is the internal regularity of the spacing of its constituent atoms. The external geometrical regularity, where it exists, is derived from this more fundamental internal structural regularity. It is frequently found, however, that the internal regularity is not accompanied by external regularity. This is true, for example, of the metals, which are invariably crystalline. The absence of external regularity is due to the small size of the individual crystallites. The same considerations apply to rubbers.
Long-Chain Polyhydroxyesters from Natural Occurring Aleuritic Acid as Potential Material for Food Packaging
