1. silane crosslinking method is to add silane agent to polyethylene and complete the three-dimensional network crosslinking process in the hydrolysis process after molding. This crosslinking method requires low conditions, and can be completed as long as there is water and a certain temperature. Even in use, it can continue to crosslink until it reaches saturation crosslinking, and the formed PE-X has a three-dimensional network structure. Silane crosslinking can be divided into one-step method and two-step method, which requires high storage and packaging of raw materials, otherwise raw materials may be pre-crosslinked and scrapped during storage, and the storage period of raw materials is very short (6 months). Silane crosslinking method is a process of forming first and then crosslinking. Its product is characterized by high surface strength and tensile strength, but poor water resistance, and the crosslinking degree of the product will swim with time, and the formed product is called PE-Xb.

2. Peroxide crosslinking method is to add peroxide crosslinking agent to polyethylene, and gradually complete the planar network crosslinking process at a certain temperature (230℃). This cross-linking method requires high cross-linking conditions, and the degree of cross-linking will not change once it is molded. It is a process of crosslinking first and then molding. Its products are characterized by good surface smoothness and flexibility, but poor acid resistance. The formed product is called PE-Xa.

3. Irradiation crosslinking method is a physical crosslinking method. Compared with before, no compound is needed in the cross-linking process. It is a pipe formed by irradiating high-density polyethylene with α β γ rays or electron beams, so that the main chain of polyethylene macromolecules forms new free radicals, and the free radicals recombine to form crosslinking. This cross-linking method requires extremely high conditions, and the cross-linking is very stable, but it has one characteristic: the cross-linking degree of the product skin is high, and the cross-linking degree is lower and lower with the increase of depth. This method is not suitable for producing products with excessive wall thickness. The formed product is called PE-Xc.