Plastics -- Thermoplastic materials -- Determination of Vicat softening temperature (VST)
This International Standard specifies four methods for the determination of the Vicat softening temperature (VST) of thermoplastic materials:
- method A50 using a force of 10 N and a heating rate of 50 K/h;
- method B50 using a force of 50 N and a heating rate of 50 K/h;
- method A120 using a force of 10 N and a heating rate of 120 K/h;
- method B120 using a force of 50 N and a heating rate of 120 K/h.
The methods specified are applicable only to thermoplastics, for which they give a measure of the temperature at which the thermoplastics start to soften rapidly.
A test specimen is placed in the testing apparatus so that the penetrating needle rests on its surface at least 1 mm from the edge. A load of 10N or 50N is applied to the specimen. The specimen is then lowered into an oil bath at 23 degrees C. The bath is raised at a rate of 50° or 120° C per hour until the needle penetrates 1 mm.