Polyethene

1. Overview1.1 Chemical structure2. properties2.1 physical properties2.2 chemical properties3. Processes3.1 Monomer3.2 Polymerization 3.3 Manufacture 4. Uses5. Groups of polyethylene 6. Advantages7. Disadvantages

The most common plastic

global production is ca. 80 million tones

chemical formula: (C2H4)nH2

» Very simple structure, the simplest of all commercial polymers.

» carbon atoms + two hydrogen atoms.

» thermoplastic polymer

» consists of long hydrocarbon chains

» white waxy

» the melting point is typically in the range 120 to 180 °C

» May or may not be observableDepending on:

- crystallinity - molecular weight- melting point

» excellent chemical resistance

not attacked by strong acids or strong bases

» resistant to gentle oxidants and reducing agents

» burns slowly with a blue flame having a yellow tip

giving off an odour of paraffin» can be dissolved in hydrocarbons

» insoluble in water and most organic solvents

» does not conduct electricity

» can be dissolved at elevated temperatures

» ingredient of monomer is ethylene.

gaseous hydrocarbon with the formula C2H4

» ethylene must be of high purity

» Ethylene is generated by dehydration of ethanol.

» highly exothermic.

» metal chlorides or metal oxides are used.

» common catalysts consist of titanium(III) chloride.

» cracking/decomposing petroleum

small, reactive ethane molecules

can be rearranged

» Ethene molecules polymerize to long chains of polyethylene

chains close to each other by weak bonds

forming a material, comparable with the fibers of a felt

» children's toys

» bullet proof vests

» Packaging

- Plastic bag, e.g. grocery bags

- Plastic films

- Containers

- Bottles, e.g. shampoo bottles

- Geomembranes: (HDPE) and (LDPE)

» two types of polyethylene:

1. HDPE: high density poly ethene ---> low pressure

2. LDPE: low density poly ethene --> high pressure

» LDPE : soft thus suitable for manufacture of packaging, films soft tubes and hoses

» HDPE: for piping

1. Polyethylene film most lightweight and durable packaging mediums available

2. Plastic packaging contributes to reducing food spoilage rates.

3. Polyethylene ducting is compatible with most fans, heaters, air conditioners, air handling units, etc

4. Polyethylene Bags use less energy and resources to create than glass or paper.

5. Clear polyethylene allows recipients to view the contents (such as a magazine cover)

1. Polyethylene is not biodegradable, it accumulates if dumped in the soil

2. Polyethylene threatens the life in the water bodies.

3. Polyethylene is likely to clog the drains problems in the water flow of the pipes

4. Polyethylene is harmful for animals if swallowed.

5. If polyethylene is burnt in open air Hydrogen cyanide is released