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Conventional high-density polyethylene (HDPE) pipes soften at ~80°C, limiting their use in hot-water plumbing. Crosslinked polyethylene (PEX) pipes retain mechanical properties at temperatures up to 95°C continuous, 110°C peak, making them the global standard for domestic plumbing, underfloor heating, and industrial pipe systems.
Why Crosslinked PE (PEX) Pipes Outperform Conventional PE
Conventional high-density polyethylene (HDPE) pipes soften at ~80°C, limiting their use in hot-water plumbing. Crosslinked polyethylene (PEX) pipes retain mechanical properties at temperatures up to 95°C continuous, 110°C peak, making them the global standard for domestic plumbing, underfloor heating, and industrial pipe systems.
There are three PEX production methods: PEX-a (peroxide crosslinking), PEX-b (silane crosslinking), and PEX-c (electron-beam crosslinking). This article focuses on PEX-a, where organic peroxides are the crosslinking agent.
PEX-a Production Process
| Process Step | Temperature | Description |
|---|---|---|
| Peroxide compounding | 120–180°C | Peroxide mixed into PE melt in extruder |
| Crosslinking (first oven pass) | 180–220°C | Peroxide decomposes, crosslinks form |
| Cooling & calibration | 20–60°C | Pipe dimension stabilized |
| Optional: Oxygen barrier coating | Ambient | EVOH barrier layer applied |
Peroxide Selection for PEX-a Pipes
1. Dicumyl Peroxide (Perodox DCP)
The standard PEX-a crosslinking peroxide. Its decomposition temperature range (130–190°C) aligns well with typical PEX extrusion and oven crosslinking temperatures.
- Form: Coated on calcium carbonate or silica (dust-free handling)
- Dosage: 1.5–2.5 phr
- Target gel content: >70% (ISO 10147)
2. 2,5-Dimethyl-2,5-di(tert-butylperoxy)hexane (Perodox 101)
A liquid bifunctional peroxide that provides more uniform crosslinking in thick-wall pipes. Its slower decomposition kinetics offer better scorch safety during compounding.
- Form: Liquid (injected directly into extruder)
- Dosage: 1.0–2.0 phr
- Applications: Larger-diameter PEX pipes (>32 mm), multilayer PEX-AL-PEX pipes
PEX-a vs. PEX-b vs. PEX-c: Comparison
| Property | PEX-a (Peroxide) | PEX-b (Silane) | PEX-c (E-beam) |
|---|---|---|---|
| Crosslink uniformity | Excellent (through-wall) | Good (outside-in) | Excellent |
| Processing speed | Moderate | High | Very high |
| Equipment CapEx | Moderate | Low | High (E-beam facility) |
| Heat resistance | Excellent | Good | Excellent |
| Typical markets | Europe, China | Global | Specialty |
Quality Control for PEX Pipes
| Test | Standard | Requirement |
|---|---|---|
| Gel content | ISO 10147 | >70% (plumbing); >80% (industrial) |
| Thermal stability (OIT) | ISO 11357 | >20 min at 200°C |
| Burst pressure (hot) | ISO 15875 | >1.0 MPa at 95°C |
| Creep resistance | ISO 15875 | <1% strain at 10 years, 95°C |
Frequently Asked Questions
Q: What gel content is required for PEX plumbing pipes?
A: ISO 15875 requires >70% gel content for PEX-a pipes used in plumbing. Higher gel content (>80%) is recommended for industrial/high-pressure applications.
Q: Can I use the same peroxide for both PEX-a pipes and XLPE cables?
A: Yes—Perodox DCP is widely used for both. However, PEX-a pipes typically require a second oven pass to ensure through-wall crosslinking, while XLPE cables use a CV tube. Process parameters differ; consult your peroxide supplier.
Q: How do I minimize “fish eyes” (uncrosslinked PE particles) in PEX pipes?
A: Ensure uniform peroxide dispersion during compounding. Use a coated peroxide grade (dust-free) for better dispersion. Optimize oven temperature profile to ensure complete peroxide decomposition.
Do Sender PEX Pipe Solutions
Shandong Do Sender Chemicals Co., Ltd. manufactures Perodox® organic peroxides for PEX-a pipe production. Our technical team assists with peroxide selection, gel content optimization, and oven temperature profile design. All products are REACH-compliant and ISO 9001 certified.
Contact us to optimize your PEX-a crosslinking process and meet ISO 15875 plumbing standards.