ISO 2921 is a specification created by the

International Organization for Standardization The International Organization for Standardization (ISO ; ; ) is an independent, non-governmental, international standard development organization composed of representatives from the national standards organizations of member countries. M ...

for a method in determining the temperature-retraction characteristics of stretched

vulcanized rubber Vulcanization (British English: vulcanisation) is a range of processes for hardening rubbers. The term originally referred exclusively to the treatment of natural rubber with sulfur, which remains the most common practice. It has also grown to ...

. Since many

thermoplastic A thermoplastic, or thermosoftening plastic, is any plastic polymer material that becomes pliable or moldable at a certain elevated temperature and solidifies upon cooling. Most thermoplastics have a high molecular weight. The polymer chains as ...

elastomers have a

yield point In materials science and engineering, the yield point is the point on a stress–strain curve that indicates the limit of elastic behavior and the beginning of plastic behavior. Below the yield point, a material will deform elastically and wi ...

at 5% to 20% elongation, the standard does not cover them. It is based on the principle of applying a tension force to the sample of rubber, then cooling the rubber until it no longer retracts by itself. Then, warming the rubber and recording at what temperature the rubber shrinks back to specific sizes. The rubber is placed in a fluid bath, though gasses may also be used if it doesn't change the result of the experiment.

References

#02921 Rubber {{measurement-stub