Vicat softening temperature (VST) to ISO 306
Vicat softening temperature (VST) provides a value for the temperature at which a thermoplastic material begins to soften rapidly. This temperature is determined using a needle-shaped indenter with a round cross-sectional area of 1 mm2.
The indenter is placed on the plastic specimen and loaded with a defined test weight. The specimen is then heated at a specified rate. The VST is obtained when the needle penetrates to a depth of 1 mm. ISO 306 and ASTM D1525 are identical with regard to the test sequence.
- ISO 306 distinguishes between 2 procedures and 2 different heating rates, totaling 4 different test methods in all:
- Method A = 10 N load, heating rate 50 K/h
- Method A = 10 N load, heating rate 120 K/h
- Method B = 50 N load, heating rate 50 K/h
- Method B = 50 N load, heating rate 120 K/h