Civil Engineering Reference
In-Depth Information
solvents. Naphtha is also the most important raw material for the production
of plastics from intermediary substances such as propylene, ethylene and
acetylene. Styrene, benzene, toluene and xylene are also necessary chemicals
for the plastics industry and the latter two are used in the production of
organic pigments. Benzene is the initial source of creosote, which is mixed
with coal tar to make the impregnating poison carbolineum.
Chlorinated hydrocarbons
These are formed when hydrocarbons react with hydrochloric acid. They include
important solvents such as trichloroethane, trichloromethane, trichloroethene,
dichloroethane and dichloromethane. These substances are used mainly in var-
nishes, paints and paint removers. Dichloroethane is also an important solvent for
synthetic rubber and is often used in mastics with a bituminous base.
Polychlorobiphenyls (PCBs) have been used widely in the past as fire retardants
in electrical cables and as softeners in mastics, but are no longer used because of
their high toxicity. The chloroparaffins are very common in plastic products as
flame retardants and secondary softeners, in PVC floor coverings, as softeners
and binding agents in putty and mastics and as fire retardants in synthetic rubber.
Chlorofluorocarbons
Chlorofluorocarbons are produced by replacing hydrogen with fluorine in chlo-
rine compounds and are used for foaming plastic-based mastics and insulation
materials. Chlorofluorocarbons that contain bromine are used as fire retardants
in a range of plastics. These substances are very stable in the lower part of the
Earth's atmosphere. When they reach the stratosphere the sunlight is strong
Table 9.3:
The relative effect of the different chlorofluorocarbons on the ozone
layer
Chlorofluorocarbon
Destruction factor
CFC 11 — (Trichlorofluoromethane)
1
CFC 12 — (Dichlorodifluoromethane)
1
CFC 22 — (Chlorodifluoromethane)
0.05
CFC 113 — (Trichlorofluoromethane)
0.8
CFC 114 — (Dichlorotetrafluoroethane)
1
CFC 115 — (Chloropentafluoroethane)
0.6
CFC 132b — (Dichlorodifluoroethane)
Less than 0.02
CFC 134a — (Tetrafluoroethane)
0
CFC 142b — (Chlorodifluoroethane)
0.05
Halon 2111 — (Bromochlorodifluoromethane)
3
Halon 1301 — (Bromotrifluoromethane)
10
Halon 2402 — (Dibromotetrafluoroethane)
6.2
