Environmental Engineering Reference
In-Depth Information
Waste
Blending
Operation
Polybutadiene
1
st
Molding Operation:
Polybutadiene/Waste
Stabilization
2
nd
Molding Operation:
Polyethylene
Macroencapsulation
FIGURE 5.1
The conceptual design of a polybutadiene encapsulation system. Based on
reference 7.
Additional details on polyethylene macroencapsulation are provided in Section 5.3.2.
Rather than conventional macroencapsulation by extrusion, this process uses a jack-
eted clamshell heater to melt the polyethylene and form the macroencapsulated layer.
The conceptual design of a polybutadiene encapsulation system is pictured in Figure
5.1. This process has yet to achieve wide-scale acceptance or use in the industry.
5.2.3
P
OLYESTER
R
ESINS
Polyesters are a class of thermosetting resins that can be combined with a cross-
linking agent (e.g., styrene monomer) and reacted to form a monolithic solid waste
form. Unlike condensation polymerization, cross-linking of the polyester with sty-
rene is accomplished by the breaking of double bonds, which form free radicals
connecting individual chains. Several forms of polyester resin are available including
orthophthalic (the largest group of polyester resins), isopthalic, vinyl ester, and water-
extendible polyester.
8
Typically, a mixture of thermosetting resin and styrene mono-
mer is reacted in the presence of a catalytic agent to form a cross-linked polymer,
as shown in Figure 5.2.
9
The catalyst is usually organic peroxide such as methyl ethyl ketone peroxide
(MEKP)
or benzoyl peroxide, which decompose to form free radicals that drive the
cross-linking process. Decomposition of the catalyst can be accomplished by heating,
but since the reaction is exothermic, it is difficult to control and is more commonly
achieved by using a chemical promoter such as metallic salts (e.g., cobalt naphth-
enate), anilines (diethyl or dimethyl aniline), and mercaptane (i.e., dodecyl mercap-
tan). Conversely, premature gelling and setting of the monomers caused by heat,
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