ISO 75 and ISO 306: HDT and VST Tests on High Temperature Polymers
Traditionally silicone oil has been the most popular medium for performing heat deflection temperature (HDT) and vicat softening temperature (VST) tests on polymers. The test principle and procedure are simple, and although silicone oil based test systems are very well established, they can be used safely only up to a maximum temperature of 280°C.
High temperature polymers like Polyether Ether ketone (PEEK) and Polyetherimide (PEI) have an increasing demand in the polymer industry due to their higher mechanical and thermal properties. An alternative medium is required to test these high temperature polymers because they have HDTs and VSTs higher than the temperature at which silicone oil can be used. We used a CEAST HV500, which utilizes an aluminum oxide fluidized bath, to perform a range of HDT and VST tests for both high and low temperature applications according to ISO 75-1 & 2 and ISO 306 Method B, respectively. We tested different grades of PEEK, Polystyrene (PS), Polycarbonate (PC), Polyamide (PA), Polyphenylene Sulphide (PPS-40 % glass fillers), Polypropylene (PP-15 % glass fillers) at temperature ramps of 50ºC/h and 120ºC/h in compliance with the aforementioned ISO standards.
We compared the results obtained from the aluminum oxide system with those obtained from the traditional silicone oil systems for materials with HDT values less than 280°C. With a sample size of 12 specimens per batch, statistical analysis on HDT tests showed a very repeatable and reproducible result with a maximum difference of 5% between the two mediums. We recommend the aluminum oxide fluidized bath system to be used for high temperature polymers which have HDTs or VSTs higher than 280°C. Lower temperature polymers can also be tested with the aluminum oxide fluidized bath system as testing has shown good agreement with results obtained from traditional silicone oil systems.
The effect of temperature on the mechanical properties of plastic materials has a fundamental role in the design of components, especially in the selection of materials. Unlike metals and ceramics, plastics are extremely sensitive to the slightest changes in temperature. The selection of plastics for applications under different temperatures is a complex task. The material must be able to support a stress under operating conditions without losing its strength and without critical distortion. The effect of temperature on geometrical stability and mechanical properties in general can be studied following different procedures and methods like at constant temperature or with a temperature ramp.
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