Polypropylene is manufactured by the polymerisation of propylene. The structure of propylene is given in figure 2.

The structure of polypropylene is said to be 'partially crystalline'. This means that within the macromolecules there are both crystalline and amorphous regions. The crystalline structure gives rise to high strength whilst the amorphous regions retain greater mobility. Therefore polypropylene is one of a number of thermoplastics that have a relatively high strength and stiffness, even at reasonably high temperatures.

Figure 2

Structure of Propylene

By varying the molar mass and modifying the type of polymer (homopolymer, copolymer, elastomer blend) a range of grades suitable for many applications can be produced.

Homopolymers have high hardness, stiffness and tensile strength and satisfactory toughness. By copolymerisation with lower olefins - preferably ethylene - toughness is increased, particularly at low temperature. Hardness, stiffness and tensile strength thereby decrease.

The cylinders of Chem Resist vessels are extrusion wound in copolymer polypropylene.

This Beige Grey material, RAL 7032, exhibits excellent corrosion resistance to a wide range of inorganic and organic acids and bases.

The copolymer type of material has very good resistance to mechanical impact even at low temperatures.

Properties of Polypropylene

Property

Test Method

Units

Value

Nominal Density

DIN 53479

g/cm3

.091

Breaking Strength

DIN 53455

N/mm2

30

E-Modulus through bending (60s – value)

DIN 53457

N/mm2

900

Impact Strength

DIN 53453

kJ/m2

25

Hardness

DIN 53505

Shore D

67

Linear Coefficient of Thermal Expansion

ASTM D696-44

1/K

1.6…1.8 x 10^-4

Thermal Conductivity

DIN 52612

W/m K

0.22

Working Temperature without Mechanical Pressure

DIN 53446

ºC

-20 TO +120