PCTFE (Polychlorotrifluoroethylene): Cryogenic Sealing & Zero-Permeation Barrier Polymer
Published: 2026-05-31
Polychlorotrifluoroethylene (PCTFE) is a distinctive fluoropolymer where one fluorine atom in the PTFE repeat unit is replaced by chlorine — breaking the molecular symmetry and enabling melt-processability with the lowest moisture vapor...
Polychlorotrifluoroethylene (PCTFE) is a distinctive fluoropolymer where one fluorine atom in the PTFE repeat unit is replaced by chlorine — breaking the molecular symmetry and enabling melt-processability with the lowest moisture vapor transmission rate (MVTR) of any clear plastic film. PCTFE's defining characteristic is near-zero permeation to water vapor, oxygen, and most gases — approximately 10-100× lower than FEP or PFA at equal thickness — making it the barrier material of choice for pharmaceutical blister packaging (Aclar film), moisture-sensitive electronic component protection, and cryogenic valve seats and seals for liquid oxygen (LOX), liquid nitrogen (LIN), and liquid natural gas (LNG) service down to -240°C (-400°F).
PCTFE can be processed by compression molding, extrusion, and injection molding at melt temperatures of 270-300°C. It requires corrosion-resistant tooling due to trace HCl release. PCTFE has significantly lower thermal expansion than PTFE (70 vs 120 μm/m·°C) — critical for seal applications where differential expansion between the seal and metal housing would cause leakage. Its mechanical properties are intermediate between PTFE and PEEK: stronger and stiffer than PTFE, but lower strength and temperature rating than PEEK.
Technical Properties
| Density | 2.13 g/cm³ |
|---|---|
| Tensile Strength | 40 MPa |
| Melting Point | 211-216 °C |
| Shrinkage Rate | 1.0% |
| Flexural Modulus | 1.7 GPa |
| Hdt | 125 °C at 1.82 MPa |
| Continuous Service Temp | 180 °C |
Engineering Tool: Shrinkage & Cost Estimator
Calculate part weight, mold cavity dimensions accounting for shrinkage, and material cost — all locally in your browser.
Equivalents & Cross-References
| Equivalent / Alternate | Action |
|---|---|
| Daikin Neoflon PCTFE | |
| Honeywell Aclar | |
| 3M Kel-F |
Frequently Asked Questions
Why is PCTFE specified for cryogenic valve seats instead of PTFE?
Three critical advantages at cryogenic temperatures: (1) PTFE undergoes a crystalline phase transition at 19°C (room temperature) — not a cryogenic problem — but at -80°C PTFE's thermal contraction is sufficient to cause seal leakage in metal-seat valve designs unless the seal is spring-energized. PCTFE's lower CTE reduces this problem; (2) PCTFE has significantly lower cold flow (creep) than PTFE under compressive load at all temperatures — a valve seat that takes a compression set during cryogenic service will leak on warm-up; (3) PCTFE has 10-100× lower helium permeability than PTFE — critical for LOX/LH₂ rocket engine valve seats where helium leakage through the seal material itself (not around the seal) is a failure criterion. Non-fluoropolymer alternative for extreme cryogenic sealing: flexible graphite or metal-to-metal seats.
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References & Industry Standards
- ASTM International. Standard Specifications for Engineering Plastics & Thermoplastics. astm.org
- UL Prospector. Plastics & Elastomers Material Database. ulprospector.com
- MatWeb. Material Property Data for Engineering Thermoplastics. matweb.com
- ISO 1043. Plastics — Symbols and Abbreviated Terms. iso.org