Quadrant often receives questions like “What’s the minimum service temperature of material X?” or “I’m looking for a plastic material that can handle temperatures as low as -50°C/-60°F in my application.” These questions are difficult to answer since thermoplastics actually have no absolute minimum service temperature.
That’s right. There is no universal test standard or method1 to qualify the minimum service temperature of engineering thermoplastics. When consulting different sources, one might find conflicting values for the same thermoplastic material. Minimum service temperature values found in literature or data sheets are typically based on user experience or manufacturer recommendation.
So, what is minimum service temperature, anyway? In most cases, it can be considered as the temperature at which a material can be used without becoming too brittle. As temperatures decrease, thermoplastic materials generally show higher mechanical strength and stiffness while simultaneously becoming more brittle.
It should be noted that the term “too brittle” is difficult to define since this value will depend on the design of the plastic component and the load conditions (static or dynamic) in any given application. The “brittleness” of various thermoplastic materials should be considered as a relative—rather than an absolute—measure. For example, a particular thermoplastic material may perform well as a component in a structural application with moderate load operating at -50°C/-60°F, but that same material could fail in an application operating at -20°C/-5°F where the plastic component is subjected to impact.
Changing process parameters or including additives like plasticizers, glass fibers, carbon fibers, etc can also modify engineering thermoplastics. This will impact the material’s physical properties and ultimately alter the toughness/ductility of the material.
For harder and more brittle materials to be used in applications involving dynamic loading and/or impact at lower temperatures, the design of the component becomes more important. In cases like these, one should try to eliminate sharp edges and internal corners (by applying proper radiuses), stress points, and threads, in order to improve the cold temperature performance of a plastic component.
Table 1 provides values for the minimum service temperature of some common Quadrant Engineering Plastics. As stated above, these values should not be considered as absolute practical limits. The function of a plastic component, its design, load conditions, and assembly method are equally important when assessing the suitability of a material for use in low-temperature applications. Minimum service temperature is simply one data point to consider.
For help determining which material is best for your low-temperature application, the Quadrant support team is standing by to assist you.
|Minimum Service Temperature
*of Some Common Quadrant Engineering Plastics
|Duratron® CU60 PBI||-50||-60|
|Duratron® D7000 PI||-50||-60|
|Duratron® T4203 PAI||-150||-240|
|Ketron® 1000 PEEK||-60||-75|
|Techtron® 1000 PPS||-30||-20|
|Fluorosint® 207 PTFE||-50||-60|
|Fluorosint® 500 PTFE||-30||-20|
|Quadrant 1000 PSU||-50||-60|
|Duratron® U1000 PEI||-50||-60|
|Nylatron® PA 6||-40||-40|
|Quadrant Nylon 101 PA 66||-30||-20|
|Acetron® GP POM-C||-50||-60|
|*Minimum allowable service temperature is determined by the extent to which the material is subjected to impact. The values given in this table are based on unfavorable impact conditions, and consequently, may not be considered as being absolute practical limits.|
1“Brittleness temperature” is sometimes used as a measure to define the minimum service temperature of a thermoplastic, although it is more applicable to elastomers and flexible plastics. Brittleness temperature is measured by ISO 974 [Plastics — Determination of the brittleness temperature by impact] or ASTM D 746 [Standard Test Method for Brittleness Temperature of Plastics and Elastomers by Impact]. It is described as the temperature at which plastics exhibit a 50% probability of brittle failure under specified impact conditions. Brittleness temperature data may be used to predict the behavior of plastic materials at low temperatures in applications where the conditions of deformation are similar to the test conditions as described in ISO 974 and ASTM D 746. However, these test methods do not necessarily measure the lowest temperature at which plastic materials are suitable for use.
If you enjoyed the article, check out our other Tech Talk on Temperature Resistance of Engineering Plastics.