Scope:

The standard test method Vicat Softening Point of Plastics ASTM D1525, determines the softening temperature of thermoplastic polymers. Retention of mechanical strength and deformation resistance of plastics at elevated temperatures is a desired attribute in applications such as packaging and transport of hot fluids in plastic pipes. The VST is a key property in selecting plastics for elevated temperature applications. While the polymer suppliers’ technical data sheets would include VST data, independent testing is recommended for quality assurance. It may be noted that VST by the ASTM D1525 test method is not recommended for plastics that have a wide softening temperature range such as ethyl cellulose, flexible PVC and PVDC.

Test Procedure:

The ASTM D1525 VST test is performed by applying a specified, constant load onto an indenting needle which is placed upon the surface of the plastic test specimen. The test apparatus has a heating facility which subjects the loaded specimen to a controlled rate of temperature rise. The penetration depth of the needle into the specimen can also be precisely measured. The VST is the temperature at which the indenting needle penetrates to a depth of 1 mm. 

Test equipment may have Oil bath or Dry heating facilities. The dry method mitigates safety concerns due to hot oil, in certain laboratory environments.

Specimen size:

The ASTM D1525 test specimens should be at least 10 mm square and between 3 mm and 6.5 mm thick. Larger sizes and thicknesses are acceptable, depending on the test equipment.

Result:

The Vicat Softening Temperature is reported in ⁰C.