Environmental Engineering Reference
In-Depth Information
Table 11.1 Examples for the composition of rigid and flexible PVC
Rigid PVC
Additive
% wt.
Function
PVC
82.4
Polymer
MBS a
13.2
Impact modifier
Sn stabilizer
2.47
Stabilizer
Monoglyceride
0.99
Emulsifier
Processing aid
0.82
Processing aid
LDPE
0.082
-
Pigment
0.012
Pigment
Flexible PVC
PVC
36.8
Polymer
CaCO 3
28.3
Filler
DINP b
23.9
Plasticizer
Chlorinated paraffin
6.99
Flame retardant
Alkylbenzene
1.84
-
Pb stabilizer
1.10
Stabilizer
Calcium stearate
0.74
Stabilizer
Wax
0.37
Lubricant
a Methyl methacrylate/butadiene/styrene: 15:70:15
b Diisononylphthalate
impact on the material properties. As an example, rigid and flexible PVC are made
from the same polymer but their properties are clearly different. Rigid PVC is hard,
easy to break, while flexible PVC can bend in any form. Table 11.1 shows typical
compositions of flexible and rigid PVC. It can be seen that that in flexible PVC the
amount of additives exceeds that of the PVC itself. Because of that flame retardant
has also to be added, while in rigid PVC the amount of chlorine in the PVC is suf-
ficient to ensure flame resistance. We will now consider classes of additives and the
effects and obstacles they may cause during recycling.
Flame Retardants Most plastics are hydrocarbons and thus resemble other crude oil
products in structure and combustion behavior. To prevent unintended fires therefore,
compounds are added which interfere with the combustion process in various ways.
Halogenated flame retardants form radicals which interrupt the radical propagation
of combustion. Phosphor-based flame retardants cover the surface of burning plastic
with polyphosphates, preventing the evolution of burnable gases and increase the
amount of char formed. Metal hydroxides release water, which has a cooling effect
on the plastic and a diluting effect on the burnable gas. Halogenated flame retardants
make recycling processes more complicated. They are not completely removed dur-
ing material recycling and remain present in products made from recycled material,
even if they are not intended to be there. During chemical recycling, they interfere
with depolymerization processes and contaminate the product fractions.
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