Polyethylene film is a high molecular organic compound with a simple structure. It is a widely used high molecular material in the world today. It is polymerized by ethylene. It is divided into high density polyethylene, medium density polyethylene and low density polyethylene according to the density. Low-density polyethylene is relatively soft, and it is mostly used for high-pressure polymerization. High-density polyethylene has the characteristics of rigidity, hardness and mechanical strength, and it is mostly used for low-pressure polymerization. High-density polyethylene can be used for containers, pipes, and high-frequency electrical insulating materials for radar and television. Low density (high pressure) polyethylene is often used in large quantities. Polyethylene is waxy and has a smooth feel like wax. When not dyed, low-density polyethylene is transparent, while high-density polyethylene is opaque.
Polyethylene is a highly polymerized chain connected by repeating -CH2-units through the addition reaction and polymerization reaction of ethylene (CH2=CH2). The performance of polyethylene depends on its polymerization method; high-density polyethylene (HDPE) is obtained by Ziegler-Natta polymerization under medium pressure (15-30 atmospheres) organic compound catalytic conditions. Under this condition, the polymerized polyethylene molecule is linear, and the molecular chain is very long, and the molecular weight is as high as hundreds of thousands. If it is under high pressure (100-300MPa), high temperature (190-210 C), and peroxide catalyzed by free radical polymerization, low density polyethylene (LDPE) is produced, which has a branched structure. Polyethylene is insoluble in water and has very little water absorption. Even for some chemical solvents, such as toluene and acetic acid, it only slightly dissolves at temperatures above 70°C. However, particulate polyethylene can be melted or solidified with temperature changes between 15°C and 40°C. When the temperature rises, it melts and absorbs heat; when the temperature decreases, it solidifies and releases heat. And because it absorbs very little water, is not easy to get wet, and has insulation properties, it is a good building material.
