What are the chemical properties of XLPE insulating materials?
Crosslinked polyethylene (XLPE) is a new type of polymer insulating material developed on the basis of polyethylene. Generally, heat shrinkable pipes and heat shrinkable sleeves are made of XLPE insulating materials. The molecular structure of polyethylene is changed from straight chain to three-dimensional network by crosslinking, i.e. chemical or physical methods.
Physical crosslinking method is to irradiate polyethylene with high-energy particle radiation, so that polyethylene can be combined into three-dimensional network structure of cross-linked polyethylene. At present, the crosslinked polyethylene overhead insulating wire, which is commonly used in our country, is produced by this method.
The chemical method is to mix chemical crosslinking agent into polyethylene material. In the chemical reaction, the independent polyethylene molecule becomes crosslinked polyethylene through new molecular combination. The crosslinking process is shown in Fig. 2-13.
After crosslinking, the mechanical, heat resistance, creep resistance and environmental cracking resistance of polyethylene are greatly improved, as shown in Table 2-13. It can be seen from the table that the above properties of cross-linked polyethylene are superior to polyethylene, and it basically maintains the electrical properties of polyethylene. The existence of cross-linking makes cross-linked polyethylene not dissolve like PE, but decompose and carbonize after a long time when the temperature exceeds 300 C.