Civil Engineering Reference
In-Depth Information
energy consumption for all plastics is high and they are also energy polluting.
Extraction and refining of crude oil also has a considerable impact on the envi-
ronment. The different plastics have the following properties.
Polyethylene (PE)
Polyethylene is produced 99.5 per cent from polyethylene, which is polymerized
from ethylene (ethene) and to which 0.5 per cent antioxidant, light-stabilizer and
pigment is added. The antioxidant is usually a phenol compound and the ultra-
violet stabilizer consists of amines or carbon black. Other additives are also used
in larger or smaller proportions. Exposure to ethylene (ethene) may occur in the
workplace. The finished product probably does not emit anything. As waste it is
difficult to decompose, but it can be burned without giving off dangerous fumes.
Polypropylene (PP)
This is produced through polymerization of propylene. Ultraviolet stabilizers,
anti-oxidants and colouring are usually added. Phenol compounds are used as
antioxidants and amines as ultaviolet stabilizers, to a total of about 0.5 per cent.
Other additives are used in variable proportions.
Exposure to propylene during its manufacture can be damaging. There are no
dangerous emissions from the finished product. As waste it is difficult to decom-
pose.
Polystyrene (PS)
Polystyrene is produced by the polymerization of styrene to two different prod-
ucts: foamed-up expanded polystyrene (EPS) and extruded polystyrene (XPS).
The end product for both is insulation, but the latter is also vapour-proof. EPS
comprises 98 per cent styrene; in XPS only 91 per cent is used. Additives include
an antioxidant, an ultraviolet stabilizer and even a fire retardant. Phenol propi-
onate in a proportion of 0.1 per cent is usually the antioxidant, amines are the
ultraviolet stabilizer and the flame retardant is organic bromine compounds with
or without antimony salts, up to one per cent in EPS and two per cent in XPS. An
inhibitor can also be included in the product to prevent spontaneous polymer-
ization; this is usually hydrochinon in a proportion of about 3 per cent. EPS is
then foamed up with pentane and XPS with chlorofluorocarbons.
During production emissions of benzene, ethyl benzene, styrene, pentane and
chlorofluorocarbons are quite likely. In production plants the effects of benzene,
ethylene and styrene have been registered.
The finished product can have some unstable residues of monomers of styrene
(less than 0.05 per cent) which may be released into the air, depending upon how
the material has been installed in the building. XPS can also release smaller amounts
of chlorofluorocarbons. As a waste product it can be environmentally damaging
through the leakage of certain additives. It is also difficult to decompose.
