Application of Silane Coupling Agent in Silane Cross-linked Cable Materials

Silane cross-linked polyethylene is widely used as insulation material for low-voltage power cables in the wire and cable industry. Compared with peroxide crosslinking and irradiation crosslinking, this material has the advantages of simple manufacturing equipment, easy operation and low comprehensive cost, and has become the dominant insulation material for low-voltage cross-linked cables.

Silane cross-linked polyethylene mainly has two processes: grafting and cross-linking

In the grafting process, polymer loses H atoms on the tertiary carbon atoms under the action of free radicals generated by free radical initiators and thermal decomposition, and the free radical reacts with the -CH=CH2 group of vinylsilane to form a grafting polymer containing trioxysilylethyl groups. In the cross-linking process, the grafting polymer first undergoes hydrolysis under the action of water to generate silanols. The silanols condense with adjacent Si-O-H groups to form Si-O-Si bonds, thereby causing cross-linking between polymer macromolecules. The addition of silane coupling agent in the silane crosslinking material can improve the tensile and breaking strength, chemical corrosion resistance, scratch resistance, and memory effect.Silane coupling agent is generally controlled at 1%-2%.

Silane can increase the intermolecular links, making the molecular chains less likely to slide relative to each other

At the same time, the increase in polar groups hinders the movement of chain segments, making it difficult to achieve forced high elasticity, resulting in an increase in tensile strength. However, excessive crosslinking often causes a decrease in the crystallinity of the polymer, or a decrease in the propensity to crystallize, thereby reducing the tensile strength and increasing the elongation at break. Therefore, as the amount of coupling agent increases, the tensile strength gradually increases, but after reaching a certain level, it shows a downward trend. The elongation at break decreases with the increase of the amount of silane coupling agent. When the amount of the coupling agent is too large, the elongation at break increases instead.

After cross-linking, due to the increase in polar groups, the branching degree of the molecular chain increases, the distance between molecules increases, the force decreases, and the impact strength increases. When the crosslinking degree is too high, the polar groups are too dense, hindering the movement of chain segments, making it impossible to achieve forced high elasticity, and the impact strength decreases instead. Therefore, as the amount of coupling agent increases, the impact strength increases. When the amount of coupling agent is too large, the impact strength shows a downward trend. Therefore, the amount of silane coupling agent added in the silane crosslinked cable material is generally controlled at 1%-2% to achieve good results.