What is Vicat softening temperature?

Vicat softening temperature is the temperature of the thermoplastic when it is put in a liquid heat transfer medium and a 1mm square pressing needle is used to press the sample into a 1mm square under a certain load and a constant heating rate.

The Vicat softening point is used to control the quality of polymers and to find out what their thermal properties are. It does not represent the temperature at which materials can be used.

Uses of the Vicat temperature tester for thermal deformation

Vicat’s thermal deformation is controlled by an intelligent controller, and the high-precision grating dial indicator is used to measure the deformation. This gives a more stable measurement value. When you use a computer, make sure the test curve and test status are shown in real time. So, you can control the temperature, get automatic data on deformation and process control, save the data to make a test report, and have the data automatically recorded and saved.

The change is caused by heat. The Vicat softening point temperature measuring instrument can be used to measure the thermal deformation and Vicat softening point temperature of non-metallic, polymer, thermoplastic, and thermoplastic pipes and fittings. It is a tool for testing non-metallic materials that was made to meet the most recent international standards. The testing machine is used a lot in places like the chemical industry and places that do scientific research.

Factors affecting the determination of Vicat softening point temperature

  • The influence of the sample preparation method on test results

Molded samples made of the same material and the same thickness do better in tests than injection-molded samples made of the same material and the same thickness. This could be because the sample made with injection molding has a lot of stress on the inside. Different ways of preparing samples can be seen to affect the test results.

  • Influence of sample state adjustment on test results

When samples that have been molded or injected are annealed, the temperature is usually about 20 °C below the softening point. The time for annealing is 2-3 H. The test results show that, compared to the original samples, the annealed ones are better in different ways. This may be why some parts of the frozen polymer chain have been changed and more internal stress has been taken away.

  • The effect of sample size

The results of the tests show that the measured values are more likely to be the same when the sample thickness is between 3 and 4 mm. Except for PVC, the dispersion is still within the acceptable range when the thickness is 6 mm. Samples that are too thin can only be measured by stacking them. Now, there are more strict rules about how samples should be the same thickness and how flat their surfaces should be.

In terms of the length and width, the pressing point can’t be more than 2mm from the edge. At this point, it can make sure that the measured value is accurate and won’t change over time.

  • The effect of static load on

When a static load of 5000g is put on the sample, the temperature at which it starts to soften is lower than when a load of 1000g is put on it.

With a heating rate of 5 °C per 6 minutes, the test result is higher than with a heating rate of 12 °C per 6 minutes. This is because the temperature of the solution takes some time to reach the sample. So, the heating rate of 5 °C per minute should only be used when there is a lot of demand or trouble.

The difference between thermal deformation and Vicat softening temperature

There are clear differences between the ways to test for Vicat softening point and thermal deformation temperature. The test of thermal deformation temperature is the temperature at which the spline can be bent to a certain size. Vicat is the temperature at which a needle probe can be inserted into the spline to a certain depth.

The temperature at which a substance starts to melt is called its melting point. It mostly means the temperature at which the amorphous polymer starts to get softer. It has to do with not only how a polymer is made but also how heavy its molecules are. There are many ways to figure something out. Different ways of figuring out the results often give different results. Most of the time, people use the Vicat method and the global method.

Vicat softening temperature (VST for short) is the temperature of polymer samples like engineering plastics and general plastics when pressed to a depth of 1 mm by a 1 mm25 pressing needle in a liquid heat transfer medium under certain load and constant temperature rise conditions.

Thermal deformation temperature: ASTM D648, ISO 75-2, and GB/T 1634.2 figure out the temperature at which the sample deforms (or softens) by a certain amount when put under a certain load. The HDT test uses loads of 1.82 mpa and 0.45 mpa. Most engineering plastics, like nylon, PET, PBT, etc., have a strength of 1.82 mpa. People often use 0.45 mp, PP, PE, PS, etc., because they don’t change much when heated.

What is the relationship between Vicat temperature and glass transition temperature?

Vicat temperature, or Vicat softening temperature, is the temperature of a thermoplastic sample when it is placed in a liquid heat transfer medium and pressed into a 1mm square with a 1mm square pressing needle under a certain load and constant heating rate. The glass transition temperature is the temperature at which an amorphous polymer, or the amorphous part of a crystalline polymer, changes from a glassy state to a high-elasticity state, or from a high-elasticity state to a glassy state.

The glass transition temperature is the lowest temperature at which the macromolecular segments of an amorphous polymer can move freely. It is also used to measure the physical deformation of both amorphous and crystalline polymers. In the business world, Vicat and Martin thermal deformers are often used to measure the temperature at which polymers soften (t s).

For example, t s and t g are similar for amorphous polymers, and t s and t m (melting point) are similar for crystalline polymers. When amorphous polymers are used as plastics, the upper temperature limit is usually 15–30 °C below that, and the lower temperature limit is about 15–30 °C above the temperature at which the polymer starts to break down. Rubber’s service temperature is typically 10–30 °C higher than t f but lower than t g.

How to measure polymer materials with the Vicat softening point tester

Equipment and materials


In the Vicat softening point temperature testing machine, the length of the pressure needle is 3.5 mm, the cross-sectional area is (1.000 + 0.015) mm2, the flat end of the pressure needle is perpendicular to the load rod, and burrs and other flaws are not allowed. The heating bath chooses a heat transfer medium that doesn’t change the sample, such as silicone oil, transformer oil, liquid paraffin, ethylene glycol, etc. At room temperature, it is not very thick. In this experiment, methyl silicone oil was chosen to move the heat. The constant heating rate can be set to either (5 0.5) °C / 6 min or (12 1.0) °C / 6 min. The static load carried by the sample is given by g = w + R + T, where w is the mass of the weight and R is the mass of the pressure needle and load rod (the load rod and pressure head of the experimental device weigh 95g, and the measuring rod of the displacement sensor weighs 10g), t is the extra force of the device used to measure deformation. The load can be either GA = 1 kg or GB = 5 kg. The device can measure how much something has changed with an accuracy of 0.01 mm.


In the Vicat test, the sample must be between 3 and 6.5 mm thick, and it must be at least 10 mm wide and 10 mm or more long. The sample should have two parallel sides, and the top should be flat and smooth, with no bubbles, sawtooth marks, dents, or cracks. In each group, there are two samples.1) the molded sample has a thickness of 3–4 mm.

2) The thickness of the plate sample is taken as the thickness of the plate, but when the thickness exceeds 6 mm, One side of the sample shall be processed into 3 ~ 4mm. If the thickness is less than 3 mm, it can be stacked with no more than 3 pieces of a thickness greater than 3 mm.

The testing machine can also be used for thermal deformation temperature tests. An axe knife indenter and a long strip sample are selected for the thermal deformation test. The sample length is about 120mm, the width is 3-15mm, and the height is 10-20mm.


1) Turn on the power switch of the equipment according to the startup sequence of “industrial computer” → “computer” → “host”, let the system start and preheat for 10 min.

2) Launch the power test-w computer software and verify that the displacement and temperature sensor values displayed by the software are normal. Under normal conditions, the displayed value of the displacement sensor should be within -1.9-+1.9 and change with the up and down movement of the sensor head.

3) Choose “test” from the main menu. Depending on what the test needs to do, choose the Vicat temperature test test scheme. Choose the method to end the test. The setting for the Vicat test is 1 mm, and the rate of heating is set to 50 °C/h. After you fill it out, press “OK,” and the “experimental curve” interface will show up on the computer. Click “experimental parameters” and “user parameters” in the experimental curve to see if the parameter settings are right.

4) Press the “up” button on the host panel to raise the support. Choose the needle indenter needed for the Vicat test and put it at the bottom of the load rod. When installing, the number on the imprint should match the number on the pressure head, one at a time. Lift the load bar, put the sample in the support, and then lower the load bar so that the indenter is in the middle of the sample and touching it vertically, and the other side of the sample is close to the base of the support.

5) Press the “down” button and carefully immerse the bracket into the oil bath so that the sample is below 35 mm of the liquid level. The starting temperature of the bath should be 50 °C lower than the Vicat softening point of the material.

6) Choose the weight based on the test requirements to make the sample bear a load of 1 kg (10 N) or 5 kg (50 N).In this experiment, a 50N weight is selected, the weight groove is carefully placed on the tray, and a small magnetic steel needle is placed at the center of the upper part.

7) After a 5-minute descent, the bracket of the displacement sensor is moved up and down, and the sensor comes into contact directly with the small steel magnetic needle on the weight. The deformation of each channel on the computer is observed so that it reaches L-+1mm, and then the fine adjustment knob is adjusted so that the display values of all the channels on the computer display screen are between 0 and 1 +0.01mm.

8) Click the “reset” key on each channel to reset the deformation of each channel in the main interface window.

9) To do the experiment, click the “run” button in the “test curve” window. The device heats up at a steady rate, based on the speed that was set. On the computer screen, you can see how each channel has changed. When the pressing needle is pressed into the sample for 1 mm, the experiment ends automatically. The temperature at this point is the Vicat softening point of the sample.

The results of an experiment are saved automatically in the “data” subdirectory with the file name “year month day hour sample number.” The Vicat softening point of the material is given by the arithmetic mean of two samples, and the difference between the measurements of the same group of samples should be less than 2 °C.

10) When the preset deformation or temperature is reached, the experiment will stop automatically, and then turn on the cooling water source for cooling. Then move the displacement sensor bracket upward, remove the weight, raise the sample support, and take out the sample.

11) After the experiment, turn off the power to the host, industrial computer, printer, and computer, in that order.

Data processing

1) Click the data processing icon on the main interface’s menu bar to open the “data processing” window. Then, click open, double-click the required experimental file name, and click “result” to see the Vicat temperature value of the sample, record the Vicat temperature of the sample in different channels, and figure out the average value.

2) Click “report,” and a window called “report generation” will pop up. Check the “fixed column” for the test scheme parameters and the “result column” for information like the sample name, starting temperature, weight, heat transfer medium, etc. To print the experimental report, press the “print” button.