Today's KNOWLEDGE Share :The difference between HDT and Vicat

Today's KNOWLEDGE Share

Heat deflection temperature (HDT):

HDT is a measure of the stiffness of the material as the temperature increases.

HDT test measures the temperature at which the specimen loses its “load-bearing” capability.

A material can have only “one” HDT.

HDT for material is affected by the addition of reinforcement, fillers, plasticizers, or any other type of additive.

Vicat softening temperature (VST):

The vicat test is used to identify a temperature at which a needle of specified dimensions penetrates a plastic specimen at a specified distance under a given load.

It reveals the temperature at which the specimen loses its “stability-form” and softens.

The vicat point is closer to the actual melting or softening point of the polymer. The Vicat number will typically be higher.

The difference between HDT and Vicat testing:

The main difference between heat deflection temperature testing and Vicat softening point testing is associated with the elements the material being tested is subjected to.  

HDT testing :

HDT testing subjects a standard sized test specimen to stress, while also raising the temperature at a uniform rate. The temperature at which deflection occurs is recorded, which allows you to determine the heat the sample is able to withstand. The result is also dependent on factors such as the load, the speed the temperature is raised and the flexure chosen. This data can be used to compare samples and create an accurate picture of the ways paints and polymer coatings may behave under both heat and stress.  

Vicat softening point testing :

The Vicat softening point method was introduced as a way of determining the softening point of a material or coating. It’s essential because thermoplastic doesn’t have a melting point where solids become liquids, instead they are subject to softening. In Vicat testing, a circular indenter of 1 mm² in section penetrates exactly 1 mm into the specimen under a standardized load of 10 N or 50 N. The indentation is used to calculate how much the specimen has softened.  

 

Meeting industry standards for HDT and Vicat:

HDT testing should be carried out according to testing standards ISO 75 (parts 1, 2 and 3) and ASTM D648 while Vicat testing is ISO 306 and ASTM D1525.  

source:industrialphysics.com/omnexus.specialchem.com

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