Polypropylene (PP)

The material. Polypropylene, or PP, first produced commercially in 1958, is the younger brother of polyethylene, a very similar molecule with similar price, processing methods, and application. Like PE it is produced in very large quantities (more than 30 million tons per year in 2000), growing at nearly 10% per year, and like PE its molecule lengths and side branches can be tailored by clever catalysis, giving precise control of impact strength, and of the properties that influence molding and drawing. In its pure form poly­propylene is flammable and degrades in sunlight. Fire retardants make it slow to burn and stabilizers give it extreme stability, both to UV radiation and to fresh and saltwater and most aqueous solutions.

Composition

(CH2-CH(CHs))n

General properties

Density

890

– 910

kg/m3

Price

*2.1

– 2.35

USD/kg

Mechanical properties

Young’s modulus

0.9

– 1.55

GPa

Yield strength (elastic limit)

21

– 37

MPa

Tensile strength

28

– 41

MPa

Elongation

100

– 600

%

Hardnes s – Vickers

6.2

– 11

HV

Fatigue strength at 107 cycles

11

– 17

MPa

Fracture toughness

3

– 4.5

MPa. m1/2

Thermal properties

Melting point

150

– 175

°C

Maximum service temperature

100

– 115

°C

Thermal conductor or insulator?

Good insulator

Thermal conductivity

0.11

– 0.17

W/m. K

Specific heat capacity

1870

– 1960

J/kg. K

Thermal expansion coefficient

122

– 180

p, strain/°C

Electrical properties

Electrical conductor or insulator?

Good insulator

Electrical resistivity

3.3 X 1022

– 3X 1023

pohm. cm

Dielectric constant

2.1

– 2.3

Dissipation factor

3 X 10~4

– 7 X 10~4

Dielectric strength

22.7

– 24.6 X 106

V/m

Polypropylene is widely used in household products.

Ecoproperties: material

Annual world production

43 X 106

– 44 X 106

tonne/yr

Reserves

*1.2 X 109

– 1.3 X 109

tonne

Embodied energy, primary production

85

– 1.10

MJ/kg

CO2 footprint, primary production

2.6

– 2.8

kg/kg

Water usage

*50

– 150

l/kg

Ecoproperties: processing

Polymer molding energy

*8.2

– 9

MJ/kg

Polymer molding CO2 footprint

*0.65

– 0.72

kg/kg

Polymer extrusion energy

*3.2

– 3.5

MJ/kg

Polymer extrusion CO2 footprint

*0.25

– 0.28

kg/kg

Recycling

Embodied energy, recycling

36

– 44

MJ/kg

CO2 footprint, recycling

1.1

– 1.2

kg/kg

Recycle fraction in current supply Recycle mark

5.1

5

PP

– 6

%

Typical uses. Ropes, general polymer engineering, automobile air ducting, parcel shelving and air-cleaners, garden furniture, washing machine tank, wet-cell battery cases, pipes and pipe fittings, beer bottle crates, chair shells, capacitor dielectrics, cable insulation, kitchen kettles, car bumpers, shatter proof glasses, crates, suitcases, artificial turf, thermal underwear.