High Density PE (PE-HD, HDPE)

Strengths

Very cheap, good chemical and hydrolysis resistance, high impact strength at low temperatures, excellent electrical properties, good friction and wear behavior. Better machinability, higher tensile strength (the yield strength increases roughly linearly with density), and lower gas and aroma permeability than LDPE. Accepts a wide range of colors, has a pleasant, slightly waxy feel.

Limitations

Lower stiffness compared with PP. Burns very easily, poor UV resistance, susceptible to environmental stress cracking (including in surfactants), worse resistance to gamma radiation than LDPE. High mold shrinkage. Low maximum operating and heat distortion temperatures.

Designation

Polythene, Polyethene, Poly(methylene) – IUPAC Commission on Macromolecular Nomenclature.

Typical uses

Pipes, toys, bowls, buckets, milk bottles, crates, tanks, containers, film for packaging, blown bottles for food.

Compositional summary

(CH2-CH2)n, typical n=10,000-20,000.

Material family	Plastic (thermoplastic, semi-crystalline)
Base material	PE-HD (Polyethylene, high density)
CAS number	9002-88-4

Effect of composition

UV resistant grades have lower tensile strength and elongation at break.

Processing properties

First commercial production

1955

Forming

Excellent for blow-molding, extrusion, and rotational molding. Very good for injection molding and structural foam-molding. Vacuum-forming possible. Similar processability to LDPE but higher melt viscosity and melt temperatures (by 20-40 °C (36-72°F)).

Machining

Easy to machine. Care must be taken not to let the material get too hot as it is likely to become tacky due to frictional heating. Easy to stamp (when thin walled).

Joining

Easier to bond than LDPE. Very suitable for friction, hot plate, and hot gas welding, ultrasonic welding easier than for LDPE and radio freq. not possible, suitable for friction stir welding, and microwave welding is possible when polyaniline is added.