Also known as the peroxide method, in the manufacturing process, a cross-linking medium peroxide is used to form chemical bonds between the long molecular chains of polyethylene through high temperature and high pressure, which is the so-called cross-linking. This cross-linking method is named PX-a.
Silane Method
During the extrusion process, the silane is mixed into the raw materials. The combination of polyethylene chain and silicon molecule is classified as PX-b; the amount of antioxidant in the material is one of the most important factors affecting the life of the pipe.
Radiation method
Use gamma or beta rays to irradiate polyethylene to form physical crosslinks, called PX-c;
Azo method
Crosslinks formed by azo media, called PX-d, are not currently produced commercially.
Commercialized PEX pipes are currently the first three types. The performance of the three types of PEX pipes is not completely the same, mainly in heat resistance (thermal strength), creep resistance and stress crack resistance. Generally speaking, in the macromolecular structure, the thermal motion of the macromolecule with the two-dimensional network structure is relatively easy, and the thermal motion of the macromolecule with the three-dimensional structure is slightly difficult. The macromolecules of PEXa are mainly two-dimensional network structures, while the macromolecules of PEXb and PEXc are mainly three-dimensional body structures. Therefore, when the same kind of polyethylene is used as the basic raw material, when the degree of cross-linking is the same, the heat resistance, creep resistance and stress crack resistance of PEXb and PEXc are higher than that of PEXa. Increase the degree of cross-linking of PEXa, and this difference between them will be reduced.