Saturday 6 April 2024

Design Properties for Engineers: Coefficient of Linear Thermal Expansion (CLTE) of Glass Fiber Reinforced High Performance Polymers as a Function of Temperature

Hello and welcome to a new post in which we discuss the coefficient of linear thermal expansion (CLTE) as an important design data for polymer material selection. In general, CLTE is a performance indicator for the dimensional stability of materials when they are exposed to temperature. In general, plastics expand under the influence of temperature. The expansion is big compared to other materials. Length changes of millimetres at a temperature difference of 10 Kelvin are not unusual.

Furthermore, the effect of thermal expansion is different depending which polymer processing technique is used (injection moulding vs. extrusion). Different values are obtained in polymer flow direction and perpendicular to the flow direction. Thermal expansion is lower in flow direction compared to perpendicular to it.

Altogether, CLTE in flow and perpendicular direction is influenced by: 

-filler type, 

-filler amount, 

-the flow orientation (anisotropy),

-and the temperature.

CLTE (Coefficient of linear thermal expansion) of glass fiber reinforced high performance Polymers as a function of temperature

Knowing the CLTE of reinforced high performance polymers as a function of temperature allows you to better assess the suitability for your application. In case the continuous use temperature of your application is between 150°C and 160°C, the CLTE values in this range are helpful. 

Figure 1 shows the CLTE of glass fiber reinforced Polyphenylene sulfide (PPS), Polyphthalamide (PPA), Polyethersulfone (PESU), and Liquid Crystal Polymer (LCP) in flow direction. LCP has an extremely low CLTE (similar to metals) and it behaves almost linear over the temperature change However, in perpendicular direction, similar to other properties, the CLTE of LCP becomes larger over the temperature due to the anisotropy with glass fiber filling. 

Figure 1: CLTE (Coefficient of linear thermal expansion) of selected high performance polymers as a function of temperature [1]. 

CLTE of metals compared to high performance polymers - Example PEEK-GF 30wt%

Figure 2 compares the CLTE of a Polyether ether ketone (PEEK) with a 30 wt% glass fiber reinforcement to a Zinc alloy, an Aluminum alloy, and a stainless steel [2]. PEEK-GF30 wt% is able to compete in terms of CLTE in flow direction with the aforementioned metals which enable metal replacement or overmoulding of metal structures. A similar case is true for Polyarylamide (PARA; MXd6) with 50 wt% glass fiber reinforcement which has in flow direction a similar CLTE as steel and brass [3]. 

Figure 2: CLTE of PEEK-GF30 wt% as a function of temperature vs. metals [2].

Figure 3 compares the CLTE of PEEK to PEEK-GF 30wt% and PEEK-CF 30wt% as a function of temperature. It can be seen that carbon fibers are more effective in reducing the CLTE. At temperatures of 200°C, the differences between GF and CF are minimal, however compared to PEEK unfilled they are large.
Figure 3: Comparsion CLTE of PEEK vs. PEEK-GF 30wt% and PEEK-CF 30wt% [2].

Additional posts on this topic: 

Plastic Part Design Properties for Engineers - CTE/ CLTE of Polymers, Mineral Fillers and Metals

Design Properties for Engineers: Coefficient of Linear Thermal Expansion (CLTE) of High Performance Polymers

Plastic Multipoint Design Data - CLTE of Polymers as a Function of Temperature

Thanks for reading and #findoutaboutplastics


Herwig Juster 

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[2] Ketaspire KT-820 GF30:


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