PEEK (polyetheretherketone) film is a high-performance semi-crystalline thermoplastic widely used in demanding chemical environments. PEEK film chemical corrosion resistance testing evaluates how the material withstands exposure to acids, alkalis, solvents, and oxidizing agents, providing critical data for material selection in semiconductor, aerospace, medical, and chemical processing applications. This guide covers testing standards, sample preparation, evaluation methods, performance criteria, and practical applications of chemically resistant PEEK films.
Technical Overview
PEEK (polyetheretherketone) is a semi-crystalline aromatic thermoplastic belonging to the polyaryletherketone (PAEK) family. Its molecular structure, consisting of rigid benzene rings linked by ether and ketone groups, delivers an exceptional combination of mechanical strength, thermal stability, and intrinsic chemical inertness. PEEK film retains its physical integrity across a continuous service temperature range of approximately -65°C to 260°C, with a glass transition temperature near 143°C and a melting point near 343°C.
Despite its outstanding resistance profile, PEEK is not universally inert. Concentrated sulfuric acid can sulfonate the polymer backbone, strong oxidizing acids such as concentrated nitric acid can degrade the molecular chain, and certain halogenated solvents at elevated temperatures may cause swelling. For this reason, systematic chemical corrosion resistance testing of PEEK film is essential before deployment in aggressive service environments.
Chemical resistance testing quantifies changes in mass, dimensions, mechanical properties, morphology, and appearance after controlled exposure to liquid or gaseous chemical media under specified temperature and duration conditions. The resulting data support qualification, quality control, comparative material selection, and lifetime prediction.
Testing Samples
Virgin PEEK Film
Unfilled, natural-grade PEEK film is the baseline sample type, typically supplied in thicknesses ranging from 6 μm to 500 μm. Test specimens are die-cut into standardized shapes, such as ASTM D638 Type V dumbbells for tensile evaluation or rectangular coupons (for example, 50 mm × 50 mm) for immersion testing. Sample thickness directly influences diffusion kinetics, so thickness must be documented and held constant within a test series.
Modified and Filled PEEK Film
Reinforced or modified grades, including glass-filled, carbon-filled, mineral-filled, or pigmented PEEK films, may exhibit different chemical uptake behavior than virgin resin. Fillers can create interfacial pathways for media ingress, so each formulation requires independent qualification. Samples should be conditioned at 23°C and 50% relative humidity for a minimum of 40 hours before baseline measurement.
Functional Coated or Treated Film
Surface-treated, metallized, plasma-modified, or coated PEEK films intended for barrier, bonding, or membrane separation applications are tested both before and after treatment. Any coating integrity loss, delamination, or change in surface energy after chemical exposure is recorded as part of the corrosion resistance assessment.
Sample Preparation and Conditioning
- Cut specimens cleanly with sharp dies to avoid edge defects and micro-cracks that accelerate media penetration.
- Measure baseline mass, dimensions, thickness, and tensile properties before exposure.
- Condition all specimens per ISO 291 (23°C/50% RH) to standardize moisture content.
- Retain an unexposed control group for comparative property calculations.
- Prepare a minimum of five specimens per test condition to ensure statistical validity.
Testing Items
A comprehensive PEEK film chemical corrosion resistance test program evaluates the following parameters:
- Mass change: percentage weight gain (absorption or swelling) or weight loss (extraction, leaching, or degradation), measured per ISO 175 and ASTM D543.
- Dimensional stability: changes in length, width, and thickness after exposure, indicating swelling or anisotropic stress relaxation.
- Tensile strength retention: percentage of original tensile strength and tensile modulus retained after exposure, measured per ASTM D882 (thin films) or ISO 527-3.
- Elongation at break retention: a sensitive indicator of embrittlement or chain scission caused by chemical attack.
- Appearance evaluation: discoloration, crazing, cracking, blistering, surface roughening, or loss of transparency, rated visually or with colorimetry (ΔE per ISO 11664).
- Thermal property changes: shifts in glass transition temperature and melting behavior measured by DSC (ISO 11357), revealing plasticization or morphological change.
- Crystallinity change: X-ray diffraction or DSC assessment of crystalline fraction, since chemical media can induce crystallization or erosion of crystalline regions.
- Molecular weight change: intrinsic viscosity or GPC analysis for advanced qualification programs requiring insight into chain scission.
- Water absorption and hydrolysis resistance: per ASTM D570, particularly relevant for steam and hot-water service.
Testing Methods
Immersion Test (ISO 175 / ASTM D543)
The immersion method is the primary procedure for evaluating resistance to liquid chemicals. Specimens are fully submerged in the test medium at a defined temperature (commonly 23°C, 60°C, or 100°C, or at the intended service temperature) for exposure periods of 24 hours, 7 days, 28 days, or up to 12 months for long-term qualification. After each exposure interval, specimens are removed, gently blotted, and immediately weighed; a subset is dried to constant mass to separate reversible absorption from irreversible loss. Mechanical testing is performed either in the wet state or after defined recovery conditioning, and both conditions should be reported.
Test Media Selection
Standard media categories covering the typical PEEK service spectrum include:
- Acids: sulfuric acid (10%, 50%, 98%), hydrochloric acid (10%, 37%), nitric acid (30%, 65%), acetic acid, hydrofluoric acid (with strict safety controls).
- Alkalis: sodium hydroxide (10%, 50%), potassium hydroxide, ammonia solution.
- Organic solvents: acetone, methanol, ethanol, toluene, xylene, DMF, DMSO, NMP, THF, ethyl acetate.
- Oxidizing agents: hydrogen peroxide (30%), sodium hypochlorite, peracetic acid.
- Salt solutions: sodium chloride, artificial seawater, and process-specific electrolytes.
- Fuels and oils: gasoline, diesel, aviation kerosene, hydraulic fluid, lubricating oil.
Vapor and Humidity Exposure
For applications exposed to chemical vapors rather than full immersion, specimens are suspended above the liquid surface in sealed vessels, or placed in temperature-humidity chambers with controlled chemical vapor concentration (for example, per ASTM D4756 concepts or custom protocols). This is critical for vapor barrier films and flexible printed circuit substrates.
Elevated Temperature and Pressure Testing
Autoclave exposure simulates hot chemical service, steam sterilization, and downhole oilfield environments. Specimens are exposed at temperatures from 121°C to 200°C under autogenous or applied pressure, with post-exposure evaluation identical to immersion protocols.
Environmental Stress Cracking Evaluation
Bent-strip or constant-strain jig tests (adapted from ASTM D1693 methodology for film geometry) assess whether chemical media and sustained mechanical stress interact to produce stress cracking or crazing, a failure mode not captured by unstressed immersion.
Data Interpretation and Rating Criteria
Results are typically classified on a three-tier rating scale:
- Resistant: mass change within ±3%, tensile strength retention above 85%, no visible attack, negligible dimensional change.
- Conditionally resistant: mass change within ±8%, tensile strength retention of 60–85%, minor discoloration or slight swelling; suitability verified by application-specific margin analysis.
- Non-resistant: mass change exceeding ±8%, tensile strength retention below 60%, visible cracking, embrittlement, or dissolution.
Known exceptions for PEEK include concentrated sulfuric acid above approximately 50% concentration (sulfonation attack), fuming or concentrated nitric acid (oxidative chain scission), bromine, and certain fluorinated or high-boiling polar solvents at temperatures above 150°C.
Applications
Chemical corrosion resistance test data for PEEK film directly enable qualification in the following sectors:
- Semiconductor manufacturing: wet-process carrier films, gasketing, and flexible circuit substrates exposed to acids, plasmas, and stripping solvents.
- Fuel cells and electrochemistry: PEEK-based proton exchange and separator films requiring long-term stability in acidic electrolytes at elevated temperature.
- Chemical processing: corrosion barrier linings, diaphragms, and filtration membranes in contact with aggressive reagents and solvents.
- Aerospace: lightweight films and insulation layers exposed to hydraulic fluids, fuels, and de-icing chemicals.
- Medical and life sciences: sterilizable packaging, biosensor substrates, and membrane materials requiring resistance to disinfectants, peracetic acid, and autoclave steam cycles.
- Oil and gas: downhole sensor encapsulation films exposed to sour gas, brine, and amine chemistries under high temperature and pressure.
- Food and pharmaceutical processing: gasketing and release films in contact with CIP/SIP cleaning solutions such as caustic soda and nitric acid sanitizers.
- Lithium-ion batteries: electrically insulating separator and barrier films exposed to carbonate-based electrolytes.
FAQ
Which chemicals attack PEEK film?
PEEK film exhibits excellent resistance to most acids, alkalis, organic solvents, oils, and salt solutions at moderate temperatures. Notable exceptions include concentrated sulfuric acid, concentrated nitric acid, bromine, bromine water, and certain halogenated or highly polar solvents at sustained elevated temperatures. Testing at the actual service temperature and concentration is always recommended for these media.
What exposure durations are required for qualification?
Screening tests commonly use 24-hour and 7-day immersions at 23°C and an elevated temperature such as 60°C. Full qualification typically requires 28-day, 90-day, or longer exposures at the maximum intended service temperature, sometimes extending to 6 or 12 months for critical long-life components.
How is chemical resistance quantified?
Chemical resistance is quantified through percentage mass change, percentage dimensional change, and retention of tensile strength and elongation at break relative to unexposed controls, supplemented by visual rating, colorimetry, and DSC-based thermal analysis where morphology changes are suspected.
Does temperature significantly affect PEEK film chemical resistance?
Yes. Diffusion rates and reaction kinetics accelerate sharply with temperature. A medium that shows no measurable effect at 23°C may cause significant swelling or degradation at 150°C. Test temperatures must always bracket or match the worst-case service condition.
Which standards govern PEEK film chemical resistance testing?
The principal standards are ISO 175 (determination of effects of liquid chemicals) and ASTM D543 (resistance of plastics to chemical reagents), complemented by ASTM D882 or ISO 527-3 for thin-film tensile testing, ASTM D570 for water absorption, and ISO 11357 for DSC thermal characterization.
How does film thickness influence test results?
Thicker films reach sorption equilibrium more slowly, delaying the onset of measurable property change. Thin films approach equilibrium faster and reveal degradation trends earlier, making them conservative indicators. Equilibrium saturation times should be estimated from diffusion modeling or verified by mass-versus-time profiling during test design.