Polyethylene is a high molecular weight compound formed by the addition polymerization of ethylene. The actual molecular weight varies from 10000 to several million depending on the polymerization conditions. The first invention of polyethylene was low-density polyethylene obtained by high-pressure method, with a specific gravity of 0.9l0-0.925g/cm3. The specific gravity of polyethylene obtained by low and medium pressure methods is 0.94l-0.965g/cm3, which is called high-density polyethylene. Polyethylene is a white wax like translucent material that is soft and tough, slightly stretchable, non-toxic, flammable, and melts and drips when burned, emitting the odor of paraffin burning. The properties of polyethylene are related to its molecular weight and crystallinity.

    Many mechanical properties of polyethylene are determined by the density and melt index of the material. From low-density polyethylene to high-density polyethylene, its density varies within the range of 0.90-0.96g/cm3. The melt index (melt flow index) of polyethylene varies greatly, ranging from 0.3 to above 25.0. Many important properties of polyethylene vary with density and melt index.   

    Polyethylene is water-resistant and its physical properties remain unchanged in high humidity or water. Concentrated sulfuric acid, concentrated nitric acid, and other oxidants will slowly erode polyethylene. Polyethylene undergoes swelling in fatty hydrocarbons, aromatic hydrocarbons, and chlorinated hydrocarbons, but the swelling agent can recover its original properties after volatilization. Below 60 ℃, polyethylene can withstand most solvents, but when the temperature is above 70 ℃, hydrocarbon solvents will quickly corrode polyethylene. As the temperature continues to rise, polyethylene will dissolve in certain solvents. Polyethylene separated from the solution forms a paste or gel state depending on the temperature after cooling.

    Polyethylene undergoes reactions such as cross-linking, chain breakage, and formation of unsaturated groups when exposed to radiation, but the main reaction is cross-linking. When irradiating polyethylene in inert gas, hydrogen gas will overflow and cause weight loss; When polyethylene is irradiated in the air, its weight increases due to the addition of oxygen. After irradiation, unsaturated groups were added to polyethylene molecules, resulting in a decrease in oxidative stability. The crosslinking reaction of polyethylene under irradiation is superior to the chain breakage and formation of unsaturated groups, and the crosslinking reaction can improve the weather resistance of polyethylene. Therefore, irradiated polyethylene products have better weather resistance than non irradiated polyethylene products.     

    Polyethylene plastic has poor thermal conductivity. In order to quickly transfer heat into the entire volume of plastic powder particles during the rolling process, the particle size of polyethylene powder used for rolling should meet certain requirements. The smaller the particles, the easier it is for heat to be transferred, and the temperature of the material is more likely to reach its melting point. But when the particles are too small, the material is prone to moisture absorption and clumping, which is not conducive to rolling motion inside the mold. Polyethylene plastics purchased in the market are often pellets that need to be ground and sieved to meet the requirements of the rolling molding process.

    Polyethylene is a plastic with high toughness, and when processed using conventional grinding machines, its pellets are torn into shapes that are not conducive to further grinding. The crushing of polyethylene granules requires specialized high-speed shredding equipment.