Traditional cable insulation materials often show performance degradation under high temperatures or heavy mechanical loads. Crosslinking technology can transform polymers into stable, three-dimensional network structures, greatly improving their durability and offering a practical solution for cable applications.
In cable compounds, crosslinking creates covalent bonds between polymer chains, significantly enhancing heat resistance, mechanical strength, and chemical corrosion resistance. These improvements are critical for ensuring the stable operation of power transmission and data communication cables.
Depending on the application, different crosslinking methods may be used. The following sections explain how crosslinking works in cable materials, introduce common techniques, and focus on the details of peroxide and silane crosslinking processes.
If you are concerned that a cable’s outer sheath may soften under load or at high temperatures, crosslinking can lock the polymer chains into a network structure. This prevents melting, deformation, creep, and chemical attack.
Through crosslinking, thermoplastic plastics are transformed into thermosetting plastics, which no longer melt or flow at elevated temperatures. This significantly boosts their heat resistance, mechanical toughness, and chemical stability—features that are essential for cables used in power systems, industrial settings, and outdoor installations.
Crosslinked compounds can maintain their shape and insulation integrity even at temperatures above their original melting point, and they remain stable under overload conditions. Compared to non-crosslinked materials, they offer markedly better heat resistance, mechanical strength, and chemical resistance.
| Properties | Non-cross-linked polymer cable compound | Cross-linked polymer cable compound |
| Melting point behavior | Softens and exhibits flowability | Does not melt or cast |
| Heat resistance | Can withstand temperatures up to 70℃continuously | Can withstand continuous temperatures up to 150℃ |
| Mechanical strength | Moderate | High |
| Chemical resistance | Limited | Excellent |
When dealing with issues such as cracking of the cable’s outer sheath or detachment of the insulation layer, choosing the right crosslinking method is essential. Each method has its own advantages and disadvantages in terms of cost, performance, and processing complexity.
The most commonly used crosslinking techniques include:
Peroxide crosslinking (silane-free)
Silane moisture-cure crosslinking
EB (electron beam) irradiation crosslinking
Each method uses a different reaction mechanism to create a stable polymer network, making it suitable for applications ranging from high-voltage cables to medium-/low-voltage cables and even specialized products.
In this process, organic peroxides decompose under heat to produce free radicals. These radicals remove hydrogen atoms from the polymer’s main chain, and the resulting macroradicals recombine to form a crosslinked network. Common peroxides include dicumyl peroxide (DCP), benzoyl peroxide, and di-tert-butyl peroxide.
This method produces a uniform crosslink density and excellent heat resistance. It is suitable for XLPE power cables that operate continuously at 90℃and can withstand short-term current surges with peak temperatures exceeding 250°C. However, it also has drawbacks, such as odor, the risk of premature crosslinking (scorch), and the need to manage residual peroxide.
Silane-grafted polymers (PEX-b) undergo hydrolysis and condensation reactions to achieve crosslinking. During extrusion, a silane coupling agent is grafted onto the polymer’s main chain. After extrusion, in a water bath or a humid environment, alkoxy silane groups hydrolyze into silanol groups, which then condense to form siloxane crosslinks.
The main advantages of silane crosslinking are its lower processing temperature, reduced risk of premature crosslinking, and compatibility with standard thermoplastic production lines. It offers good heat and chemical resistance, making it well-suited for medium- and low-voltage cables. However, the curing process is relatively slow and requires strict humidity control.
EB crosslinking uses high-energy electrons to penetrate the insulation layer, generating free radicals that recombine to form a crosslinked network. This method is fast, produces no chemical by-products, and achieves a highly uniform crosslink density. It is ideal for specialty cables, heat-shrink tubing, and medical catheters.
EB crosslinking avoids the odor and residues associated with peroxides while maintaining excellent mechanical properties. However, due to the high cost of equipment and the need for strict safety measures, this technology is typically limited to specialized facilities.
| Methods | Mechanism | Key Advantages | Key Disadvantages |
| Peroxide crosslinking | Thermal free radical generation | High heat resistance, suitable for HV cables | Scorch, odor, and residue management |
| Silane vapor crosslinking | Hydrolysis/condensation | Low scorch, thermoplastic processing | Long curing time, critical humidity control |
| Electron beam irradiation crosslinking | High-energy electrons | Fast, chemical-free, uniform cross-linking | High capital cost, safety measures |
Silane-XLPE-Production-Equipment
If you're concerned about power cable failure under overload or short-circuit conditions, peroxide cross-linking is a reliable solution. This process imparts excellent heat resistance, elasticity, and mechanical toughness to high- and ultra-high-voltage cables.
Organic peroxides, such as dicumyl peroxide (DCP), undergo homolytic cleavage at high temperatures, generating free radicals that initiate cross-linking reactions between polyethylene chains. The resulting three-dimensional network structure remains stable in long-term operation at 90℃and resists melting even after a short-term temperature shock of 250°C, maintaining excellent dielectric properties even during fault conditions.
During processing, the peroxide must be uniformly dispersed in the polymer matrix. During extrusion, the temperature profile must be precisely controlled to align the melt processing with the peroxide decomposition timing. After extrusion, the cable enters a hot water bath at 160–180℃for subsequent cross-linking and curing. Proper temperature management prevents scorching caused by premature cross-linking and reduces gel particles and surface roughness.
Peroxide-cross-linked polyethylene (PE-Xa) dominates the medium- and high-voltage power cable market due to its mature process and high reliability. The network density of the insulation layer is closely related to thermal and mechanical properties: increasing the peroxide content increases the crosslink density and gel content, but reduces the material's elongation.
Long-term operating data shows that this type of cable retains over 80% of its dielectric strength after 20 years of continuous stress at 90°C. Short-circuit tests also show that it can operate stably at 250℃for 5 seconds. Mechanically, the insulation layer maintains strong adhesion to the conductor and sheath, ensuring overall operational safety.
| Parameters | Typical Values | Test Standard |
| Crosslink Density | Gel Content 70-80% | ASTMD2765 |
| Continuous Temperature Rating | 90°C | IEC60216 |
| Short Circuit Rating | 250℃for 5 seconds | IEC60230 |
| Dielectric Strength Loss | 90℃<20% after 20 years | IEC60811 |
If you're concerned about high production costs or scorch issues with medium and low voltage cables, silane crosslinking technology offers a solution that balances efficiency and quality. This method not only operates under thermoplastic processing conditions but also significantly reduces odor and the risk of premature crosslinking.
During the silane crosslinking process, the polymer is grafted with vinyltrimethoxysilane (VTMS) or vinyltriethoxysilane (VTES) during the extrusion stage. The silane groups then hydrolyze in a water bath to form silanol (Si–OH) groups, which then undergo a polycondensation reaction to form siloxane (Si–O–Si) crosslinks. This moisture cure process typically occurs at temperatures between 40–80℃for several hours, creating a stable three-dimensional network structure.
Silane-crosslinked polyethylene (PE-Xb) offers an excellent balance between performance and cost. Its processing is similar to that of conventional thermoplastic polyethylene, but requires lower extrusion temperatures and avoids the odor issues associated with peroxide methods. Crosslink density and network uniformity depend primarily on the grafting content (0.5–1.5wt%) and the humidity and temperature conditions during curing.
The finished cable can withstand long-term operating temperatures of 90℃and short-term peak temperatures of 200–225°C. With excellent water tree resistance and chemical corrosion resistance, this type of cable is widely used in medium-voltage power distribution and low-voltage building wiring. However, due to the relatively long curing time, sufficient curing space must be reserved at the production site, or forced ventilation drying facilities must be installed to accelerate the curing process.
| Features | Silane crosslinking | Advantages |
| Processing Temperature | 100°C–120°C | Low burnout risk |
| Cure Method | Wet bath/air cure | Compatible with thermoplastic wiring |
| Thermal Rating | 90℃continuous temperature, 200℃peak temperature | Compliant with medium-voltage/low-voltage cable standards |
| Web Uniformity | Medium gel content (30–50%) | Excellent performance at a low cost |
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