PEEK vs PEI vs PPSU Engineering Plastic: Temperature Resistance, Strength and Chemical Compatibility

Overview #

The selection decision between PEEK, PEI, and PPSU is where most procurement engineers lose money — not at the price negotiation stage, but at the specification stage. Buyers routinely over-specify PEEK for applications where PEI performs identically at 40–60% lower material cost, or under-specify PPSU in medical device housings where its hydrolytic stability under repeated steam sterilization cycles is the only parameter that matters. When sourcing these materials as stock shapes from China, the critical risk is not the base polymer — it is whether the supplier is running virgin resin or blended regrind, a distinction that a standard TDS will not reveal without specific incoming test requests.

Material Properties and Temperature Resistance Thresholds #

The single most important parameter separating these three polymers in structural applications is continuous service temperature — and the gap between them is large enough to change the engineering decision entirely.

PEEK (polyether ether ketone) carries a continuous service temperature of 250°C and a short-term peak tolerance up to 310°C. PEI (polyetherimide, commercially Ultem) is rated for continuous service at 170°C, with a glass transition temperature (Tg) of 217°C. PPSU (polyphenylsulfone) sits at 180°C continuous service with a Tg of 220°C. For applications operating above 180°C — aerospace brackets, semiconductor process components, high-temperature fluid manifolds — PEEK is not a premium option, it is the only option in this group.

Mechanical performance follows a similar hierarchy. PEEK stock shapes (unfilled, per ISO Standards ISO 10350) show tensile strength of 100 MPa, flexural modulus of 3.6 GPa, and a notched Izod impact of 50 J/m. PEI delivers tensile strength of 105 MPa and flexural modulus of 3.3 GPa — comparable to PEEK in ambient-temperature structural loading, which is precisely why buyers over-specify PEEK in room-temperature applications. PPSU is the toughest of the three at ambient conditions, with notched Izod impact resistance of 690 J/m, making it the correct choice for thin-wall housings subject to mechanical shock.

Most Western buyers do not realize that SAC China Standards GB/T governing high-performance polymer stock shapes allows dimensional tolerances on rod and plate that are wider than ISO 2768 medium class — which means a Chinese supplier quoting “standard tolerance” may be delivering material that fails your engineering drawing without technically being out of spec on their own documentation. Always specify ISO 2768 fine (f) or tighter explicitly on your purchase order.

Note on PEEK Tg: PEEK’s Tg of 143°C appears lower than PEI and PPSU, but its semi-crystalline structure maintains structural integrity well above Tg — up to its crystalline melt point of 343°C. PEI and PPSU are amorphous; they soften progressively above their Tg. This distinction is critical for applications with thermal excursions above 150°C.

For buyers sourcing engineering plastic stock shapes — rod, plate, tube — from Chinese suppliers, the comparison table above should be treated as a minimum TDS verification checklist, not a marketing reference.

Chemical Compatibility and Sterilization Resistance #

Chemical resistance is where the three materials diverge most sharply in practice, and where sourcing decisions made on temperature ratings alone produce field failures.

PEEK is chemically inert to virtually all organic solvents, hydraulic fluids, and concentrated acids at room temperature. It is attacked by concentrated sulfuric acid (>96%) and halogens at elevated temperature — a narrow exception that rarely affects industrial applications. PEI is resistant to aliphatic hydrocarbons and dilute acids but is attacked by chlorinated solvents, ketones, and concentrated bases. This is not a marginal limitation: in our supplier qualification program, we have seen PEI components specified for solvent-cleaning environments fail within 90 days of installation because the procurement team did not cross-check the cleaning agent chemistry against the polymer’s compatibility data. The failure mode is stress cracking, not bulk dissolution — it is slow, invisible until fracture, and almost always attributed to mechanical overload rather than chemical attack.

PPSU’s defining advantage is hydrolytic stability. It withstands 1,000+ autoclave cycles at 134°C steam sterilization without measurable degradation in tensile strength or dimensional stability — a performance level that neither PEEK nor PEI can match at equivalent cost in thin-wall geometries. For medical device trays, surgical instrument handles, and dental equipment housings, PPSU is the correct specification. PEI (specifically Ultem 1010, the food-contact and sterilization grade) tolerates steam sterilization but shows measurable property degradation after approximately 500 cycles at 134°C, which is acceptable for many applications but must be specified explicitly.

Compliance documentation requirements differ significantly across the three materials. For food contact and medical applications, request FDA Guidelines 21 CFR compliance confirmation for the specific grade — not the base polymer family. For European supply chains, ECHA REACH SVHC declaration is mandatory; Chinese suppliers frequently provide a generic REACH statement that covers the polymer but not the colorants, lubricants, or processing aids in the compound. Request a full substance declaration, not a pass/fail letter.

Sourcing Qualification and Lot Consistency from Chinese Suppliers #

This is where the real procurement risk lives — not in the datasheet comparison, but in what happens between initial sample approval and production volume delivery.

In our qualification program, we require three consecutive production batch COAs before recommending a Chinese supplier for PEEK or PEI stock shapes. The parameter we track most closely is not tensile strength — it is melt flow index (MFI), tested per ASTM International ASTM D1238. For PEEK 450G grade, the MFI at 380°C/5kg load should be 3–5 g/10min. Deviation beyond ±1 g/10min across consecutive batches is a reliable indicator of raw material substitution or regrind blending at the compounder level. A standard COA showing hardness and tensile strength will not catch this — MFI will.

Three out of six Chinese suppliers we evaluated for PEEK rod stock in a recent semiconductor tooling qualification could not produce lot-to-lot MFI data across four months of production. Two of those suppliers had passed initial sample approval with excellent dimensional and mechanical data. The failure mode at production volume was warping during CNC machining — caused by inconsistent crystallinity from variable MFI feedstock, not by machining parameters.

Most procurement teams focus on AQL sampling for dimensional conformance at incoming inspection. For high-performance polymer stock shapes, we recommend adding a spot-check protocol: AQL 2.5 for dimensional inspection per ISO Standards ISO 2859-1, plus MFI verification on 10% of incoming lots as a raw material integrity check. The cost of the MFI test is negligible against the cost of scrapped machined components.

When evaluating Chinese suppliers for specialty polymers and high-performance thermoplastics, the supplier’s ability to provide resin traceability — identifying the original polymer manufacturer (Victrex, Solvay, BASF, or equivalent) — is a stronger qualification signal than any certification document. Suppliers who cannot or will not provide resin origin documentation are almost always running blended or unverified feedstock.

The English technical content available for PEEK and PEI sourcing from China is almost entirely produced by Western resin brand owners — Victrex, Solvay, SABIC. Chinese stock shape converters produce almost no English-language technical documentation. That gap is exactly where specification errors enter the supply chain: buyers apply brand-owner datasheet values to converter-produced stock shapes without verifying that the converter is actually running the branded resin.

Practical Guidance for Buyers #

When sourcing PEEK, PEI, or PPSU stock shapes from China, the first specification to request is not tensile strength — it is resin origin documentation and melt flow index data across the last three production batches. Tensile strength is easy to report correctly on a COA; MFI consistency across batches is the parameter that reveals whether the supplier is running virgin branded resin or blended feedstock.

The most common sourcing mistake we see is specifying PEEK for applications where the operating temperature never exceeds 150°C. At that service condition, PEI delivers equivalent mechanical performance at roughly 40–60% lower material cost. The cost difference compounds significantly in machined-component applications where stock shape cost is a meaningful fraction of finished part cost.

Before committing to volume order, require the following: (1) MFI test report per ASTM D1238 for the specific grade, with results from three consecutive production batches; (2) resin origin declaration identifying the polymer manufacturer by name; (3) dimensional inspection report per ISO 2768 tolerance class, explicitly stated — not “standard tolerance”; (4) for medical or food-contact applications, grade-specific FDA 21 CFR or EU 10/2011 compliance letter, not a generic polymer family statement. Suppliers who cannot provide items 1 and 2 within five business days of request should not advance to qualification.

What to Specify on Your TDS Request #

Use this checklist when requesting technical documentation from Chinese stock shape suppliers:

• Resin grade and manufacturer: Specify by brand name (e.g., Victrex 450G, Solvay KetaSpire KT-820, SABIC Ultem 1010) — not generic “PEEK” or “PEI”
• MFI / MVR: Test method (ASTM D1238 or ISO 1133), load and temperature conditions, and acceptable range (e.g., PEEK 450G: 3–5 g/10min at 380°C/5kg)
• Tensile strength: Test method (ISO 527 or ASTM D638), specimen type, and minimum acceptable value
• Flexural modulus: Test method and minimum value
• Dimensional tolerance class: Explicitly state ISO 2768 fine (f) or medium (m) — do not accept “standard tolerance”
• Crystallinity (PEEK only): Request DSC confirmation of semi-crystalline structure; amorphous PEEK has significantly lower chemical resistance
• Lot traceability: Resin batch number traceable to the polymer manufacturer
• Sterilization compatibility (if applicable): Number of autoclave cycles tested, temperature and pressure conditions, and property retention data
• Compliance documentation: FDA 21 CFR grade designation (if food/medical), REACH SVHC full substance declaration, RoHS status per EU RoHS Directive
• Incoming inspection AQL level: Confirm supplier’s outgoing QC AQL level — request AQL 2.5 as minimum for dimensional inspection

Frequently Asked Questions #

Q1: What is the most important test to run at incoming inspection for PEEK stock shapes from China?

A: Melt flow index per ASTM D1238 at 380°C/5kg load. A result outside the 3–5 g/10min range for PEEK 450G is a reliable indicator of regrind blending or raw material substitution that a standard COA will not catch.

Q2: When does PEI make more sense than PEEK for structural components?

A: When continuous service temperature stays below 170°C and chemical exposure is limited to aliphatic hydrocarbons and dilute acids, PEI delivers comparable tensile strength (105 MPa vs. 100 MPa for PEEK) at roughly 40–60% lower material cost. The decision should be driven by the temperature and chemical compatibility data in the comparison table above, not by a preference for the “premium” material. Verify the specific grade against ISO Standards ISO 10350 property data before finalizing the specification.

Q3: What is the most common quality failure when sourcing PEEK rod from Chinese converters?

A: Warping during CNC machining caused by inconsistent crystallinity — which traces back to variable MFI feedstock, not machining parameters. This is where most sourcing decisions go wrong. The threshold is ±1 g/10min MFI deviation across consecutive batches; beyond that, crystallinity uniformity cannot be guaranteed.

Q4: What compliance documentation should I require for PPSU components used in medical device applications?

A: Request grade-specific FDA Guidelines 21 CFR compliance confirmation — not a generic polymer family letter — plus a full ECHA REACH substance declaration covering colorants and processing aids, not just the base polymer. For sterilization applications, also request autoclave cycle test data showing property retention after a minimum of 500 cycles at 134°C.

Q5: Is Chinese-sourced PEEK equivalent to Victrex-branded PEEK in machined component applications?

A: Only if the Chinese converter is running Victrex or equivalent virgin resin and can document it. “PEEK” as a generic descriptor covers a wide range of compound quality. Without resin origin documentation and MFI lot consistency data, you are not buying equivalent material — you are buying a label.

Published by sinoraw.com Technical Team | Request a sourcing consultation