Thermal tests

Melting temperature, glass transition temperature

The melting temperature of a thermoplastic material is used for material identification and provides information on possible material confusion or polymer degradation due to unsuitable process conditions. The melting temperature is measured according to DIN EN ISO 11357 by means of dynamic differential thermal analysis (DSC). The amount of heat released or absorbed by a material is measured as a function of temperature. In addition to the melting temperature, DSC can be used to measure the enthalpy required for melting. For amorphous polymers, the glass transition temperature is an important parameter.

Softening temperature according to Vicat

The Vicat softening temperature according to DIN EN ISO 306 is a measure of the heat distortion temperature and thus of the temperature resistance of plastics. To measure the softening temperature (VICAT Softening Temperature, VST), a defined tip is pressed onto the surface with constant pressure while simultaneously raising the temperature of the workpiece. The Vicat Softening Temperature is defined as the temperature at which the tip penetrates the surface to a depth of 1mm. The softening temperature gives an indication of the practical continuous use limit of thermoplastics. 

HDT heat deflection temperature

The HDT heat deflection temperature is measured according to DIN EN ISO 75-2. Similar to the Vicat softening temperature, the HDT heat deflection temperature is used to determine the practical continuous use temperature of plastics. In this test, the test specimen is placed on abutments at the ends and loaded in the middle with a punch with constant bending stress according to the three-point bending principle. The test specimen is heated until a specified standard deflection is reached. The standard deflection corresponds to an edge fibre elongation of 0.2 %.

Melt flow index

The melt flow index is often referred to by the abbreviations MFI (melt flow index) or MI (melt index). It is used to characterise the flow behaviour of a thermoplastic and thus its degree of polymerisation. Through comparative measurements, the MFI is suitable for revealing material impurities and processing errors. A distinction is made between the melt volume-flow rate (MVR) and the melt mass-flow rate (MFR). Both are linked via the melt density, the measurement method is described in DIN EN ISO 1133 and is a routine procedure in plastics analysis.

Alexander Grosch
Marketing and project management
+49 6022 81-2674
Andreas Hohm
Marketing and project management
+49 6022 81-2671

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