为什么 PEEK 的 CTI 很低，而 PES 的 CTI 却很高？

Many materials engineers often question the CTI values when choosing between PEEK and PES: Are these figures correct? Could there be typographical errors?

不少材料工程师们在PEEK和PES之间做选择时，经常会对两者的CTI值发出疑问：这些数据对吗？是不是写错了？

To answer these questions, the author attempts to provide the following explanation:

为了解答这些疑问，笔者尝试做如下解释：

Prerequisites for relevant explanations:

相关解释的前提：

  • Baseline data (neat resin, IEC60112)

    基础数据对照（纯树脂，IEC60112）

  • PEEK (Victrex 450G): CTI ≈150 V

  • PES (Solvay 2010): CTI ≈500‑550 V

Core principle: 核心原理：

  • CTI does not reflect bulk insulation resistance or dielectric strength. 

    CTI 不看本体绝缘电阻、不看介电强度；

  • It characterizes the tendency to form continuous conductive carbon tracks under arc erosion. 

    看电弧灼烧下，材料表面是否容易生成连续导电炭层。

  • Arc micro‑discharge degrades polymer. If substantial carbon residue accumulates, conductive carbon tracks form and CTI decreases. If degradation products volatilize as gas with minimal carbon residue, CTI remains high.

    电弧微放电把高分子降解，若大量残留炭，炭痕导电，CTI 就低；降解产物尽量挥发成气体、少留残炭，CTI 就高。


1. Fundamental differences in molecular structure

1. 分子结构差异（根本原因）

  • PEEK: ‑[O‑Ph‑O‑Ph‑CO‑Ph]‑ₙ, polyether‑ether‑ketone;

    PEEK：‑[O‑Ph‑O‑Ph‑CO‑Ph]‑ₙ，聚醚醚酮；

    Functional groups: ether ‑O‑, ketone carbonyl ‑CO‑

    官能团：醚键‑O‑、酮羰基‑CO‑

  • PES: ‑[O‑Ph‑SO₂‑Ph]‑ₙ, polyethersulfone; 

    PES：‑[O‑Ph‑SO₂‑Ph]‑ₙ，聚醚砜；

    Functional groups: ether ‑O‑, sulfone ‑SO₂‑

    官能团：醚键‑O‑、砜基‑SO₂‑


1）Sulfone group (‑SO₂‑) vs Ketone carbonyl (‑CO‑)

1）砜基 (‑SO₂‑) vs 酮基 (‑CO‑)

PES sulfone group (‑SO₂‑) contains sulfur and oxygen. Under arc thermal decomposition, gaseous species such as SO₂ are released and volatilize, removing carbon and suppressing carbon‑layer build‑up. Continuous conductive carbon tracks are difficult to form.

PES 的砜基‑SO₂‑含硫、氧：电弧热分解时，会生成 SO₂等气态小分子直接挥发，带走碳元素，抑制炭层累积，不容易形成连续导电炭迹。

PEEK ketone carbonyl (‑CO‑): upon thermo‑oxidative cleavage, aromatic‑ketone structures readily undergo aromatic cross‑linking, tending to dehydrogenate and form carbon‑rich char in‑situ. Without abundant volatile heteroatoms to remove carbon, conductive carbon pathways raPIdly develop on the surface, lowering CTI.

PEEK 的酮羰基‑CO‑：热氧裂解，芳环‑酮结构很容易发生芳环交联，倾向于脱氢富碳、就地生成炭残渣；没有大量可挥发杂原子带走碳，表面快速形成黑色导电炭通路，CTI 被拉低。

2）Critical influence of crystallization behavior

2）结晶行为带来巨大差异（非常关键）

PEEK is semi‑crystalline, crystallinity 25‑35%: co‑existing crystalline and amorphous phases. Arc degradation preferentially occurs at phase boundaries. Grain boundaries serve as propagation paths for carbonized conductive channels, accelerating tracking development.

PEEK 是半结晶树脂，结晶度 25‑35%：结晶区与无定形区两相共存。电弧优先在两相界面处发生降解，界面容易形成连续的炭化导电通道，炭痕顺着晶界扩展，加速漏电起痕发展。

PES is fully amorphous: uniform morphology without grain boundaries. Arc erosion causes homogeneous surface degradation. Oriented continuous carbonized pathways hardly propagate between electrodes, leading to much higher CTI.

PES 是完全无定形树脂：没有晶界，结构均匀；放电烧蚀为均匀面降解，不容易产生定向连续炭化通路，炭迹很难贯通两极，CTI 显著更高。

Counter‑intuitive fact: PEEK possesses good bulk insulation (volume resistivity, dielectric strength). Its weakness is char formation under arc. PES has decent bulk insulation; its decomposition products mostly vaporize and leave little char residue.

这是很反常识：PEEK 本体绝缘性能（电阻率、介电强度）其实很好，但一烧就出炭；PES 本体绝缘不差，分解产物大量气化，不容易留炭。

2. Comparative table

2. 补充对比表

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3. Practical engineering implications

3. 工程上的现实启示

  • For high‑voltage creepage and humid / polluted environments: PEEK is not preferred; PES / PSU are better candidates. Even neat PEEK delivers low CTI. CTI drops further to 80‑100 V with glass‑fiber or carbon‑fiber filling. Filled PEEK shall be avoided for high‑voltage electrical components.

    高压爬电、污染潮湿工况：PEEK 不适合，优先 PES / PSU；PEEK 哪怕纯料 CTI 也很低，加玻纤 / 碳纤后 CTI 进一步掉到 80‑100 V，高压电气严禁直接使用。

  • PEEK strengths: high‑temperature bulk insulation, chemical resistance, wear resistance. Limitation: poor resistance to tracking. Larger creepage distance must be designed for compensation.

    PEEK 优势：高温本体绝缘、耐化学、耐磨；短板是耐漏电起痕差，必须加大爬电距离做补偿。

  • PES strengths: high‑CTI amorphous specialty polymer. Limitations: lower heat‑resistance compared with PEEK, HDT ≈203 ℃, significantly inferior chemical resistance versus PEEK.

    PES 优势：高 CTI 无定形特种料；短板：耐热比 PEEK 低，HDT 约 203℃，耐化学远弱于 PEEK。

  • Modification note: It is very difficult to raise PEEK CTI above 400 V via compounding. Most fillers degrade CTI further. No mature commercial high‑CTI modified‑PEEK grades are widely available.

    改性手段：PEEK 几乎很难通过改性把 CTI 做到 400V 以上；填料大多会继续恶化 CTI；市场没有高 CTI 改性 PEEK 成熟牌号。

Other aromatic polymers，PPS CTI ≈125 V (prone to charring due to high aromatic content). 

同样是芳香族，PPS CTI≈125V，也是芳环多、易成炭；

Sulfone‑containing amorphous polymer, PSU CTI ≈450‑500 V，same mechanism as PES.

同样是砜基无定形，PSU CTI≈450‑500 V，和 PES 逻辑一致。