Beginner Topic 1029 of 1102 Biochemistry, Environment & Industry

Polyethylene

The most common plastic, in low and high density forms.

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In-depth explanation of Polyethylene

Polyethylene is the most widely produced plastic, made by polymerising ethene, CH2=CH2, into long chains of repeating -CH2-CH2- units. Low-density polyethylene is made by high-pressure radical polymerisation and has many short and long branches, making it flexible and suitable for films and bags. High-density polyethylene is made with Ziegler-Natta or related catalysts that produce mostly linear chains, which pack tightly into rigid containers and pipes. Both forms are chemically inert, waterproof and inexpensive to produce. Recycling codes 2 and 4 identify HDPE and LDPE respectively.

Going deeper: Polyethylene

Key ideas: Made from ethene, n CH2=CH2 gives (CH2CH2)n. Low-density PE (LDPE) uses free radical polymerization at high pressure (1000 to 3000 atm, 200 C), has branches, density about 0.92 and is used for films and bags. High-density PE (HDPE) uses Ziegler-Natta catalyst at low pressure, is linear, density about 0.95 to 0.97, used for bottles and pipes.

Common mistakes and connections: Students say HDPE has more branching, but it has less, which lets chains pack closely. Polyethylene is chemically inert, nonpolar and floats on water. Ziegler and Natta won the 1963 Nobel Prize. Links to addition polymerization and radical mechanisms, and to recycling codes 2 and 4.

Visualization of Polyethylene

A segment of polyethylene, a long chain of repeating CH2-CH2 units made from ethene. Branching or linear packing sets whether it is flexible LDPE or rigid HDPE. The interactive lesson shows this as a live animation or chart.

Worked example and use case

Plastic shopping bags are usually LDPE, while milk jugs are usually HDPE.

Frequently asked questions about Polyethylene

What is Polyethylene?

The most common plastic, in low and high density forms.

Is Polyethylene a beginner, intermediate or advanced topic?

Polyethylene is a beginner topic in Biochemistry, Environment & Industry. It needs no earlier chemistry lessons and is a good starting point.

What should I learn before Polyethylene?

Study these earlier topics in Biochemistry, Environment & Industry first: Cosmetic Chemistry, Plastics, Thermoplastics and Thermosets.

What comes after Polyethylene?

The next topics in Biochemistry, Environment & Industry are PVC and Nylon.

Can I practise Polyethylene with quizzes?

Yes. The interactive lesson includes a self-check question on Polyethylene, and the Biochemistry, Environment & Industry quiz draws on every topic in this area.

Where Polyethylene fits in Biochemistry, Environment & Industry

Polyethylene is topic 54 of 127 in Biochemistry, Environment & Industry.