Environmental Engineering Reference
In-Depth Information
Plasticizers
Plasticizers make rigid materials flexible. They tend to migrate from
plastic materials into the environment; phthalic acid esters (phthalates) plasticizers
are suspected to have a hormone-like behavior.
Fillers
Fillers are very often inexpensive materials added to substitute for the poly-
mer without changing the properties significantly. Most fillers are inert inorganic
substances such as CaCO
3
, sand, or soot. They only slightly interfere with recycling
processes and removal is often easily achieved.
Stabilizers
Especially for PVC, stabilizers are essential because of its low thermal
stability. Stabilizers in PVC add to double bonds left by HCl and prevent therefore a
faster dehydrochlorination. PVC stabilizers are often based on heavy metals. These
can easily contaminate recyclates and products obtained from chemical recycling.
11.4
Overall Plastic Treatment in Japan
Plastic production and demand increased strongly in the 11980-2000 period and
has since remained at a constant level. The amount of plastic waste has followed
this trend. Today about 10 million t of plastic waste are generated each year, of
which about 77 % was treated in 2010. Most of the plastic waste was used for
energy recovery (32 % for the generation of electricity, another 11 % for heat, and
6 % were used as RDF). Only 27 % of the plastic waste was actually used in differ-
ent recycling techniques: 23 % for material and 4 % for chemical recycling. 10 %
of the plastic waste was incinerated without energy recovery and another 13 %
landfilled.
11.5
PET Recycling
About 40 % of PET is used for plastic bottles, another 40 % for fibers, and the rest
for other applications, mainly PET film. Transparent amorphous PET is mainly used
for the fabrication of bottles, because of the very good barrier properties against
gases such as oxygen and carbon dioxide. The barrier is improved further by at-
taching a layer of silicon dioxide or aluminum oxide to the inner side of the bottle,
making it suitable for carbon dioxide containing soft-drinks. Crystalline PET is very
resistant against both heat and cold. Therefore, it is used for trays that are suitable
for freezing and microwaving. In Japan, PET is collected separately from other
plastics and made available for recycling.
The possibilities for PET recycling are many (Fig.
11.5
). Mechanical recycling
is used for obtaining fiber and sheet grade PET. Advanced methods can even de-
liver bottle grade PET. Chemical recycling is conducted by solvolytic processes
which can be seen as a reversed production process (the process is called glycolysis
when ethylene glycol is used). Mainly oligomers of PET are obtained, which can be
