As a high molecular polymer, the arrangement of molecular chains is not disorderly, but basically belongs to two types: one is spatial ordering with both short-range and long-range order, and this aggregate structure is called crystalline state; One that has only short-range order and no long-range order is called amorphous. The crystalline state and the amorphous form are in a state of juxtaposition and coexistence.

(1) amorphous form

Any rubber is agglomerated by long-chain molecules. Usually, the long diameter (thickness) ratio is 50000/1, and there is only short-range order and no long-range order. In addition, the inner rotation of the macromolecule is in a state of constant motion, so that it is impossible for the macromolecule to maintain a linear shape, but it must be gathered in disorder, which is an amorphous state. Glue such as butylbenzene and butyronitrile belong to this form.

(2) Crystalline state

Some rubber species (such as natural rubber) under normal temperature conditions, their basic structure is amorphous, but under low temperature or stretching, the molecular arrangement tends to be long-range local order, and crystallization occurs. At this time, the mechanical strength of the raw rubber is significantly increased, and the level of the vulcanized rubber can be reached (19.6 to 30 MPa). However, not all rubber types are the same. For example, under the same conditions, the rubber feet made of styrene-butadiene rubber will not exhibit performance. Significant improvement. Therefore, the natural rubber belongs to the crystalline rubber type, and the styrene-butadiene rubber belongs to the amorphous rubber type. However, it should be noted that even if the crystalline behavior of the crystalline rubber is far from complete, the amorphous portion of most crystalline rubbers still accounts for 70% to 80%, and can occur under low temperature or tensile conditions. Therefore, even in the crystalline polymer, the crystalline region and the amorphous region coexist at the same time.

Crystallization can’t be done in an instant, but there is a slow process, because it takes a certain amount of time from disorder to order. The speed of the process is also related to temperature. Taking natural rubber as an example, starting from 0 °C, as the temperature drops, the crystallization rate gradually increases, reaching the apex at -20 °C, and the temperature drops again, and gradually slows down.

As mentioned above, in addition to temperature, elongation is another external factor that contributes to the crystallization of rubber, indicating that under the action of the elongation force, the rubber molecular chain will instantaneously appear in the crystal arrangement regardless of the ambient temperature. However, this crystallization and elongation force must be the same. Once the elongation force is released, the crystal structure melts quickly, and the crystallization disappears synchronously and disappears.