Ethylene, a gaseous product consisting of carbon atoms and hydrogen, is a raw material for producing polyethylene. Ethylene CH2 = CH2 is, under normal conditions, a colorless gas with a boiling point of -103.8 ° C.
Polyethylene is formed by the polymerization of ethylene: the result is a partially crystallized material. PES has high density zones in which molecules are straightened, and zones with a disordered structure. In this form, polyethylene retains its strength up to temperatures of 110–130 ° C.
The cross-linking of polyethylene foam is understood as the process of binding the links of molecules into a wide cellular three-dimensional network due to the formation of cross-links. When crosslinking in molecular chains containing atoms of carbon and hydrogen, under the influence of a crosslinking agent, separate atoms of hydrogen are detached from the links of polyethylene molecules. The resulting free bond is used to connect hydrocarbon chains to each other.
In chemical crosslinking, hydrogen atoms in polyethylene molecules are replaced by chemical substances.
Raw materials for production are:
- low density polyethylene (granules);
- azodicarbonamide (foaming agent);
- peroxide (crosslinking agent);
After mixing in the established proportions, the raw materials are granulated and sent to an extruder, on which a parent sheet is formed by heating and pressing.
The formed mother sheet is fed into the foaming chamber: in the first part foaming occurs at a temperature of 180 ° C, and in the second - the process of chemical crosslinking at 220 ° C. The gas mixture forms the porous structure of the insulating material.
Then the sheets of polyethylene foam are cooled and cut to the required width during the winding process.
Subsequent processing may include both duplication - welding with protective or functional materials (aluminum foil, film, paper, etc.), and the formation of pipe and extruded products.