Vicat Softening Point Tester evaluates the heat deformation resistance of resins.

Overview

The Vicat Softening Point Tester is a commonly used device to evaluate the ability of resin materials to withstand heat deformation. The working principle is based on a standardized heating rate and constant load, measuring the temperature of a specific shape of a resin specimen when it reaches a specified amount of deformation during heating, which is the Vicat Softening Temperature (VST). This index has important reference value for predicting the dimensional stability and applicable temperature range of resin materials in high temperature environments.

Test Principle:

During the test, a flat-tipped needle-like needle with a cross-sectional area of no less than 1 square millimeter is placed vertically on the surface of the specimen and a specified constant load (usually 10 N or 50 N) is applied. Under uniform heating conditions (usually 50°C/h or 120°C/h), when the needle penetrates the specimen to a depth of 1 mm, the temperature at this time is recorded, which is the Vicat softening point. This process reflects the material's transformation from rigid to viscoelastic under a combination of thermal and mechanical loads.

Commonly used international and domestic standards include ISO 306, ASTM D1525, and GB/T 1633. These standards uniformly stipulate the specimen size, heating rate, load size, and result presentation method, ensuring the reliability and comparability of test results. The test conditions corresponding to different standards are different, so the standard code and test conditions used must be indicated when reporting the results.

Test parameters

The test results are mainly affected by two parameters: the heating rate and the applied load. The faster the heating rate, the higher the measured Vicat softening point; The greater the load, the lower the measured softening point. This relationship can be described qualitatively by the following empirical formula:

VST ∝ (heating rate)^α / (Load)^β

where α and β are positive coefficients related to material properties. Therefore, when comparing the heat resistance of different resin materials, it must be done under exactly the same test conditions.

Application:

Through the Vicat softening point test, the heat resistance of different types or formulations of resins can be quantitatively compared and graded. This test is widely used in quality control, new product development, and process optimization of thermoplastic resins such as polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polyamide (PA), and acrylonitrile-butadiene-styrene copolymer (ABS).

The test results help predict the risk of dimensional changes or functional failure due to heat exposure to subsequent processing (e.g., thermoforming, welding) or end-use environments. For example, resins with higher Vicat softening points are generally better suited for applications where shape stability is required at higher temperatures.

Notes:

During the test, it is necessary to ensure that the sample preparation is standardized, the surface is flat, and the pressing needle is in good contact with the specimen. Environmental conditions such as laboratory temperature and humidity should also be controlled according to standard requirements. It is important to recognize that the Vicat softening point is a conditional test value, not an inherent physical constant of the material. It mainly reflects the softening behavior of the material under specific conditions, and cannot be directly equivalent to the upper limit of the long-term service temperature of the material or the thermal deformation temperature (HDT). For some highly elastic or highly crystallinity materials, the applicability of this test method may be limited.

Vicat softening point reference range

Note: The above data are typical ranges under common standard conditions (such as 50°C/h, 10 N), and the specific values are affected by the material grade, formulation and test conditions.

Conclusion

The Vicat Softening Point Tester provides a relatively fast, easy, and standardized method for evaluating the heat resistance of resin materials. By tightly controlling the test parameters and understanding their correlation with the actual properties of the material, this test provides effective thermal performance data support for material selection, quality control, and product design. In practical applications, it is recommended to conduct comprehensive evaluation in combination with other thermal performance testing methods (such as thermal deflection temperature testing, thermogravimetric analysis, etc.) to obtain more comprehensive information on the heat resistance of materials.

References

ISO 306:2022, Plastics — Thermoplastic materials — Determination of Vicat softening temperature (VST).

ASTM D1525-17, Standard Test Method for Vicat Softening Temperature of Plastics.

GB/T 1633-2000, Determination of Vicat softening temperature (VST) of thermoplastics.

Plastic Testing Technical Handbook, Chemical Industry Press.