Environmental Engineering Reference
In-Depth Information
Styrene is copolymerized with butadiene to obtain SBR rubber and with
acrylonitrile-butadiene to obtain ABS plastics. ABS is a relatively tougher
thermoplastic compared to HIPS. The composition of the latter is typically
60% (
w
/
w
) styrene, 25% acrylonitrile, and 15% buta-1,3-diene.
3.5.4 Poly(vinyl chloride)
PVC is a tough and rigid thermoplastic that is the most-used plastic in the
United States after PE and PP. It is also the most-used plastic in building
applications (extruded profile (~17%), pipe (~24%), and residential siding
are popular uses in the US). Plasticized PVC is used in packaging
applications, medical devices, and wire and cable insulation and conduit.
PVC is a versatile plastic; the polarity of the repeat unit allows a very wide
range of additives to be incorporated at very high levels into the polymer.
This allows a variety of plastic compounds with different characteristics
to be designed. Properly compounded, PVC products are well suited for
outdoor applications stabilized.
Ethylene monomer (from natural gas or other petroleum resources) is
chlorinated in the presence of an iron salt catalyst to obtain the monomer:
Alternatively, ethylene can be oxychlorinated with HCl in the presence of
cupric chloride (CuCl
2
) impregnated on a porous support such as alumina.
Both reactions are exothermic and involve the use of corrosive and toxic
gases:
Heating the dichloroethane yields the vinyl chloride monomer with HCl
generated as a by-product. Where oxychlorination is used to manufacture
theprecursor,someofthisHClcanbeusedon-siteforthepreviousreaction.
Stripping the HCl as well as unreacted dichloroethane yields a
polymerizable grade of monomer:
The monomer is polymerized in aqueous dispersion at 325-350°C at high
pressure (~13 atm) to maintain the monomer in liquid phase. In the
manufacture of PVC, there is potential for environmental hazards, and the
