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How PEEK Handles Extreme Heat Above Tg?

Jul. 16, 2025

How PEEK Handles Extreme Heat Above Tg?cid=7





Why PEEK Can Operate at 260°C Despite a Glass Transition Temperature of Only 143°C


Many are surprised when they see that PEEK (Polyether Ether Ketone) has a glass transition temperature (Tg) of just 143°C, yet it can be used long-term at 260°C. This may seem counterintuitive, but PEEK has been widely applied in many high-temperature environments.

Today, let’s explore PEEK’s molecular structure to understand why it remains stable and reliable far beyond its Tg.




If Tg is So Low, Why Doesn’t PEEK Collapse?

When reviewing the PEEK datasheet, many people raise the question:

“Our product operates continuously above 200°C, but PEEK’s Tg is only 143°C—won’t it have softened long ago?”

This is a valid concern, especially since amorphous materials like PC (Polycarbonate) and PMMA often rely on Tg to define the limit of their dimensional stability.

Once they exceed Tg:

However, PEEK is different—it's a semi-crystalline polymer, which fundamentally alters its high-temperature performance.




Semi-Crystalline vs. Amorphous

In polymers, molecular chains can arrange:

PEEK contains both amorphous and crystalline regions. When reaching its Tg of 143°C, the amorphous regions become active, but the crystalline regions still support the structure.

The crystalline zones remain stable up to PEEK’s melting point (Tm) of around 343°C, acting like steel plates within the polymer, maintaining rigidity and form.




Why Can PEEK Function at 260°C?

Two key reasons:

1. High Crystallinity Supports Structure

2. Extremely Rigid Polymer Backbone

PEEK’s backbone is composed of:

These rigid structures:




Engineering Considerations: Be Careful Under High Loads!

While PEEK can endure 260°C long-term, there's a critical engineering caveat:

Avoid applying excessive mechanical loads at high temperatures.

Above Tg:

Practical Tips for 200~260°C Applications:




Conclusion

Tg marks the transition of the amorphous regions, but it’s the crystalline zones that give PEEK its strength and high-temperature capabilities.

Final Tip:

When selecting high-temperature materials, don’t just look at Tg. Evaluate:

Tg is just the surface—structural robustness is what truly determines high-temperature performance.


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