Heat Resistance
Wärmeformbeständigkeit | A service provided by |
|---|
|
| Polymer Service GmbH Merseburg |
| Tel.: +49 3461 30889-50 E-Mail: info@psm-merseburg.de Web: https://www.psm-merseburg.de |
| Our further education offers: https://www.psm-merseburg.de/weiterbildung |
| PSM on Wikipedia: https://de.wikipedia.org/wiki/Polymer Service Merseburg |
Heat resistance
Classification
The methods for determining the thermal load-bearing capacity of plastics can be classified in plastics testing together with fire behaviour, component testing and implant testing in the group of technological test methods [1]. In accordance with the physical background, it is also possible without any problems to classify them in the group of thermo-mechanical test methods. However, the material values for heat resistance are not generally valid material properties, such as thermal conductivity.
From the point of view of application technology, the mechanical behaviour of plastics at elevated temperatures is of particular importance.
Definition of terms
Dimensional stability under heat refers to the ability of a test specimen to retain its shape up to a specified temperature under a specified loading condition (see also: stress) or not to exceed a specified amount of deformation at a specified test temperature.
Standard physical-technological or purely technological methods are mostly used to assess the temperature application range.
Theoretical ideas on molecular processes assume that dimensional stability is directly linked to the molecular movement that occurs at higher temperatures. Essentially, two transition areas limit the heat resistance and thus the practical applicability of plastics:
- in the case of amorphous plastics, the glass transition (see glass transition temperature) with the characteristic temperature Tg, and
- in the case of semi-crystalline plastics (see also crystallinity), the crystallite melting range with the melting temperature Tm.
Test methods and characteristics
Heat resistance can be determined by various standardized test methods. The most important are the following:
- Heat deflection temperature according to Martens [2] (based on DIN 53462 [3], [4]).
- Vicat softening temperature (VICAT) according to ISO 306 [5] (based on DIN 53460 [6] and ASTM D 1525 [7])
- Heat distortion temperature (HDT) according to ISO 75-1 to 75-3 [8] (based on DIN 53461 [9]) and ASTM D 648 [10].
All known methods are based on the same measuring principle. A test specimen subjected to a defined load is heated at a constant rate. The heating can take place in a heating bath or in a heating cabinet. The temperature is measured in the liquid or in built-in temperature sensors at the loading location.
In today's practice, heat resistance methods according to VICAT and HDT have gained the greatest importance. For methodological reasons, both test methods lead to different results, which are additionally influenced by the extraordinary processing sensitivity of the plastics.
See also
References
| [1] | Grellmann, W., Seidler, S. (Eds.): Polymer Testing. Carl Hanser Munich (2022) 3rd Edition pp. 569/570, (ISBN 978-1-56990-806-8; see AMK-Library under A 22) |
| [2] | Brown, R. (Eds.): Taschenbuch Kunststoff-Prüftechnik. Carl Hanser Munich Vienna (1984) (ISBN 3-446-14052-2; siehe AMK-Library under C 4) |
| [3] | DIN 53462 (1987-01): Testing of Plastics – Martens Method of Determining the Temperature of Deflection under Abending Stress (withdrawn) |
| [4] | Schmiedel, H. (Eds.): Handbuch der Kunststoffprüfung. Carl Hanser Munich Vienna (1992), pp. 284/285 (ISBN 3-446-16336-0; see AMK-Library under A 3) |
| [5] | ISO 306 (2022-11): Plastics – Thermoplastic Materials – Determination of Vicat Softening Temperature (VST) |
| [6] | DIN 53460 (1976-12): Testing of Plastics – Determination of the Vicat Softening Temperature of Thermoplastics (withdrawn) |
| [7] | ASTM D 1525 (2025): Standard Test Method for Vicat Softening Temperature of Plastics |
| [8] | ISO 75: Plastics – Determination of Temperature of Deflection under Load |
| Part 1 (2020-02): General Test Method | |
| Part 2 (2013-04): Plastics and Ebonite | |
| Part 3 (2025-05): High-strength Thermosetting Laminates and Long-fibre-reinforced Plastics (Draft) | |
| [9] | DIN 53461 (1987-01): Testing of Plastics – Determination of Temperature of Deflection under Load according ISO/R 75 (withdrawn) |
| [10] | ASTM D 648 (2018): Standard Test Method for Deflection Temperature of Plastics under Flexural Load in the Edgewise Position |