1. Ethylene and polyethylene have different properties

Ethylene is the simplest olefin. The molecular formula CH?=CH?. A small amount of it exists in plants and is a metabolite of plants. It can slow down plant growth and promote leaf fall and fruit ripening. Colorless flammable gas. Melting point -169.4℃, boiling point -103.80℃. Almost insoluble in water, hardly soluble in ethanol, easily soluble in ether and acetone.

Polyethylene molecular formula - [CH?—CH?]? is a white waxy translucent material, flexible and tough, lighter than water, non-toxic, and has superior dielectric properties. Easily flammable and will continue to burn after removal from fire. The transparency of polyethylene decreases with the increase of crystallinity. At a certain degree of crystallinity, the transparency increases with the increase of molecular weight. The melting point range of high-density polyethylene is 132-135°C, while the melting point of low-density polyethylene is lower (112°C) and has a wide range.

2. Ethylene and polyethylene have different structures

Ethylene is a compound composed of two carbon atoms and four hydrogen atoms. Two carbon atoms are connected by a double bond. Ethylene exists in some tissues and organs of plants and is converted from methionine under conditions of sufficient oxygen supply.

Polyethylene (PE for short) is a thermoplastic resin obtained by polymerizing ethylene. In industry, it also includes polymers of ethylene and a small amount of α-olefins.

3. The similarities between ethylene and polyethylene

The monomers of ethylene and polyethylene are both CH?—CH?.

Extended information

Polyethylene resin is a non-toxic, odorless white powder or granule. It has a milky white appearance and a waxy feel. It has a low water absorption rate, less than 0.01%. Polyethylene films are transparent and decrease with increasing crystallinity. Polyethylene film has low water permeability but high air permeability, so it is not suitable for fresh-keeping packaging but suitable for moisture-proof packaging.

It is flammable, with an oxygen index of 17.4. It has low smoke when burning, with a small amount of molten dripping. The upper part of the flame is yellow and the lower part is blue, and there is a paraffin smell. Polyethylene has better water resistance. The surface of the product is non-polar and difficult to bond and print. It has been improved by surface treatment. The more branched chains, the less resistant to photodegradation and oxidation.

The heat resistance of polyethylene is not high, and it improves with the increase of relative molecular weight and crystallinity. It has good low-temperature resistance, and the brittle temperature can generally reach below -50℃; and as the relative molecular weight increases, it can reach as low as -140℃. The linear expansion coefficient of polyethylene is large, up to (20~24)×10-5/K. Thermal conductivity is high.

Reference: Baidu Encyclopedia-Polyethylene

Reference: Baidu Encyclopedia-Ethylene