One concern that comes up very frequently about plastics is their resistance when exposed to heat; that is, the notion of heat resistance of plastics. How does a plastic withstand high temperatures without degradation of its properties? When replacing our traditional materials with high-performance plastics, it is essential to consider a number of factors. In this article, we will discuss about the heat resistance of plastic materials. To select the best plastic that suits to our needs, we must determine if our plastic part will be in continuous use at high temperatures. If that is the case, it is essential to know at what specific temperatures the plastic part will be used. This will allow us to make an informed choice in order to find the best heat resistant plastic for these applications.
When a plastic is being exposed to heat, it will reach a point where its properties will start to degrade and its molecular structure will be modified. However, before degradation of its molecular structure happens, the plastic is still thermally stable, which will vary greatly depending on the plastic materials targeted. This stability refers to the ability of a plastic to resist degradation when being used at high temperatures and to maintain all its properties, molecular structure and mechanical resistance. It is called the thermal stability of the material.
When the plastic reaches its melting temperature, it will start a phase transition from solid to liquid. However, it is important to remember that its molecular structure can change even if the plastic has not yet reached its melting temperature. In other words, even if the plastic has not started to melt, that does not mean that its properties have not been modified. Prior to reach the melting temperature, the plastic will reach a point of temperature range that will significantly reduce its mechanical resistance (glass transition temperature). Above this temperature, the molecular linkage of the plastic will be weakened, which means that the plastic will no longer be able to withstand the stresses that it normally resists.
Contrary to what many people think, plastic materials perform very well in environments at high temperatures. When selecting a material that will be in continuous use at high temperatures, high-performance plastics can meet these requirements without changing their molecular structure. These plastics will be able to maintain their properties and robustness even in the most demanding environments. Plastics resistant to high temperatures (with high thermal stability) are materials that resist degradation of their properties when used at temperatures higher than 149 °C (300 °F) for extended periods of time. Some of theses plastics with very high thermal stability are:
• PAI (POLYAMIDE-IMIDE)Can withstand temperatures up to 270 °C (518 °F).
High chemical and mechanical resistance.
Can withstand temperatures up to 300 °C (572 °F).
Good wear resistance, unaffected by chemicals and radiation; well adapted to high demanding environments.
Good thermostability up to 177 °C (350 °F).
Resistant to steam sterilization, compliant with FDA standards,excellent electrical insulator.
Can withstand temperatures up to 170 °C (338 °F).
Excellent machinability.