Why Crosslinked Polyethylene (XLPE) Dominates Wire & Cable Insulation
Crosslinked polyethylene (XLPE) has largely replaced PVC and conventional PE as the insulation material of choice for low-, medium-, and high-voltage power cables. The crosslinking process transforms thermoplastic PE into a three-dimensional network, delivering superior heat resistance, mechanical strength, chemical resistance, and long-term reliability that uncrosslinked PE cannot match.
Organic peroxides are the industry-standard crosslinking agents for XLPE insulation because they decompose at the extrusion temperature to generate free radicals, which create carbon-carbon crosslinks between PE chains. This article covers peroxide selection, crosslinking kinetics, and application guidelines for wire & cable producers.
XLPE Crosslinking Process Overview
| Process Step | Temperature | Peroxide Role |
|---|---|---|
| Compounding | 90–120°C | Peroxide added (must not decompose) |
| Extrusion (insulation layer) | 120–160°C | Peroxide begins decomposing |
| Curing (CV tube / steam / nitrogen) | 150–200°C | Peroxide fully decomposes, crosslinking completes |
| Cooling | 20–60°C | Gel content verified (>80% target) |
Key Peroxide Grades for XLPE
1. Dicumyl Peroxide (Perodox DCP)
The most widely used XLPE crosslinking peroxide. Its 1-hour half-life temperature of ~171°C aligns well with typical CV (continuous vulcanization) tube temperatures (160–190°C).
- Form: Powder, granular, or coated on inert filler
- Dosage: 1.5–2.5 phr (parts per hundred resin)
- Applications: Low- and medium-voltage power cables (≤35 kV)
2. 2,5-Dimethyl-2,5-di(tert-butylperoxy)hexane (Perodox 101)
A bifunctional dialkyl peroxide with excellent scorch safety. Its symmetrical structure provides two radical sites per molecule, making it highly efficient for thicker insulation walls where deep penetration of crosslinking is required.
- Form: Liquid (easy injection)
- Dosage: 1.0–2.0 phr
- Applications: Medium- and high-voltage cables (≥35 kV); silane-XLPE dual-cure systems
3. tert-Butyl Cumyl Peroxide (Perodox 119)
Lower decomposition temperature (~162°C for 1h t½), suitable for heat-sensitive insulation compounds or lower-temperature CV processes.
Crosslinking Performance Metrics
| Metric | Test Method | Typical XLPE Target |
|---|---|---|
| Gel content | ASTM D2765 | >80% (low voltage); >85% (medium/high voltage) |
| Crosslink density | Swelling ratio (toluene) | Optimized per voltage class |
| Scorch time (ts2) | ASTM D2084 (MDR) | >8 min at processing temp |
| Dielectric strength | IEC 60243 | >20 kV/mm |
| Long-term thermal endurance | IEC 60216 | >90°C continuous rating |
Frequently Asked Questions
Q: What peroxide dosage is optimal for XLPE insulation?
A: Typical dosage is 1.5–2.5 phr active peroxide. Higher voltage cables require higher gel content, which may require slightly higher dosage. Laboratory MDR (moving die rheometer) screening is strongly recommended before full-scale production.
Q: Can I use azo initiators instead of organic peroxides for XLPE?
A: No. Azo initiators decompose at lower temperatures (70–100°C) and leave nitrogen gas by-products, which create voids in the insulation that severely degrade dielectric properties. Organic peroxides are the only industry-approved crosslinking agents for XLPE power cables.
Q: How do I prevent “cable fault” caused by incomplete crosslinking?
A: Monitor gel content per ASTM D2765 for every production batch. Ensure CV tube temperature is uniformly controlled. Use a peroxide with proven decomposition kinetics at your process temperature. Perodox DCP and Perodox 101 are industry-proven for XLPE.
Q: Are peroxide-crosslinked cables recyclable?
A: Thermally crosslinked XLPE is not melt-processable. However, ground XLPE can be used as filler in new compounds or in non-insulation applications. This is an active area of R&D for cable sustainability.
Do Sender XLPE Crosslinking Solutions
Shandong Do Sender Chemicals Co., Ltd. supplies Perodox® brand organic peroxides specifically engineered for XLPE wire & cable insulation. Our technical team provides MDR scorch safety analysis, gel content optimization, and on-site support for cable producers worldwide. All products meet IEC, REACH, and ISO 9001 standards.
Contact our technical team for a customized XLPE crosslinking formulation based on your cable voltage class, insulation thickness, and CV process parameters.