Thursday 27 August 2020

Design Properties for Engineers: Transition Temperatures (Tg, Tm, CUT) of High Performance Polymers

Today we discuss the major thermal transition temperatures of high performance polymers. Details on alpha, beta, gamma and delta transitions are explained in this blog post. Amorphous thermoplastics show a linear behavior up to the glass transition temperature. Semi-crystalline polymers have a two-step behavior: the first drop in mechanical values can be observed at the Tg, followed by the second drop at the crystal melt temperature. The structural crystal elements can resist much more the temperature increases. 

In the graph below, the glass transition and crystal melt temperature of different high performance polymers are shown. It can be seen that polyimides (PI, PAI, PBI) outperform other polymers. Checking the glass transition temperature is important during the material selection when you decide on the suitability of the polymer to fulfill the application service temperature. Thermoplastics show already a drop in mechanical performance at the glass transition area. 

Transition Temperatures of High Performance Polymers

PTFE, PAI, PBI, and PI are not melting when the glass transition or crystal melt temperature is reached. These polymers show a particular molecular structure (thermoset-like). Nevertheless, using such polymers above their continuous use temperature is not good since thermal-oxidative degradation starts.

Thank you for reading and #findoutaboutplastics

Herwig Juster

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