1. What Is the Glass Transition Temperature (Tg) of PEEK?

The glass transition temperature (Tg) represents the point where amorphous regions of PEEK change from a rigid, glassy state to a softer, rubber-like state.

• Typical Tg of Unfilled PEEK: 143°C ~ 150°C

• This range varies slightly depending on:

• Molecular weight

• Polymer purity and crystallinity

• Manufacturer formulation

Because PEEK is a semi-crystalline polymer, Tg is always lower than its melting temperature (Tm ≈ 343°C). Even above Tg, PEEK still retains mechanical strength due to its crystalline structure.

2. Typical Tg Values from Major PEEK Manufacturers

Key point:
ARKPEEK-1000 maintains a Tg of ≈145°C, comparable to leading global brands, ensuring reliability across high-temperature applications.

3. What Factors Influence the Tg of PEEK?

Several intrinsic and processing-related factors impact PEEK's Tg:

3.1. Molecular Weight

Higher molecular weight → slightly higher Tg
Lower molecular weight → slightly lower Tg

3.2. Crystallinity Level

• Higher crystallinity increases dimensional stability, but Tg is mainly determined by amorphous regions.

• Annealing can indirectly affect Tg by optimizing crystallinity.

3.3. Thermal History

Poor drying, improper cooling, or rapid quenching during processing can alter amorphous structure and shift Tg by 1-2°C.

3.4. Additives, Fillers & Reinforcements

Fillers can restrict polymer chain mobility → increasing Tg.
Details below.

3.5. Composite Structures

Blends and alloys (e.g., PEEK-carbon composites) can introduce significant Tg changes depending on filler type and content.

4. Effects of GF, CF & Composite Materials on PEEK Tg

4.1. Glass Fiber Reinforced PEEK (PEEK-GF)

Typical Tg increase: +2°C to +7°C

Glass fiber restricts chain mobility, so PEEK-GF30 grades typically show Tg around 147–152°C.

4.2. Carbon Fiber Reinforced PEEK (PEEK-CF)

Typical Tg increase: +3°C to +10°C

Carbon fiber has a stronger interfacial bonding effect, causing higher Tg improvement.
PEEK-CF30 grades may reach 150–155°C depending on manufacturer.

4.3. High-Performance Composites (CF + PTFE, CF + Graphite, etc.)

Composite modifications further influence Tg:

• CF + Graphite: Slight Tg increase due to crystalline changes

• CF + PTFE: Tg may stay similar or decrease slightly because PTFE reduces chain-chain interaction

4.4. ARKPEEK Composite Materials

ARKPEEK offers multiple reinforced grades:

5. Why PEEK Tg Matters in Real Applications

5.1. Heat-Resistant Mechanical Parts

Above Tg, amorphous regions soften, so Tg defines upper service temperature for mechanical precision components.

5.2. Semiconductor & Electronics

Tg affects dimensional stability during:

• Reflow processes

• Wafer handling

• High-temperature fixturing

5.3. Medical & Sterilization

PEEK's high Tg allows:

• Autoclave sterilization

• Gamma and e-beam stability

• Long-term body-temperature endurance

5.4. Oil & Gas / Aerospace

Tg is critical for sealing parts exposed to:

• Continuous high pressure

• High temperature

• Thermal cycling

PEEK's stable Tg is one major reason it dominates harsh-environment applications.

Conclusion

PEEK's glass transition temperature (Tg) is a key thermal parameter that directly affects processing, dimensional stability, and long-term performance.
While manufacturers show slight variations, unfilled PEEK typically ranges from 143–150°C, and reinforced grades (GF/CF) can reach 152–155°C.

ARKPEEK maintains Tg values equivalent to top global PEEK brands while delivering strong cost-performance advantages—making it a reliable alternative for industrial, scientific, and high-tech applications.