Environmental Engineering Reference
In-Depth Information
Table 12.1
Precursors of the most common polymers used for food packaging materials.
Monomer
Chemical structure monomer
Polymer
O
O
Ethylene
terephthalate
Polyethylene terephthalate
(PET)
O
CH
2
CH
2
C
C
H
H
Ethylene
Low- and high-density
polyethylene
C
C
H
H
H
Cl
Vinyl chloride
Polyvinyl chloride (PVC)
C
C
H
H
CH
3
Propylene
Polypropylene
CH
CH
2
CH
2
Styrene
Polystyrene
CH
For the production of metal packaging, concentrated deposits of aluminum and iron ores
are mined from the ground and used for the construction of packaging material. Unless metals
are recycled after use, they become mixed with low-quality trash and deposited in landfills.
Metals do not disappear from the face of the earth; however, a long-term consumption of vir-
gin metals will lead to the depletion of premium mining sites, leaving mineral exploitation
only available to more difficult and less economical locations.
At the present time, deposits of silica used for glass manufacture are abundant. Typically,
silica is extracted from opened pits or by dredging the bottoms of stream beds. The US
Geological Survey considers that sand mining has “little environmental impact except for
temporarily disturbing the immediate environment while mining operations are active” (Bolen,
1996). But the severity of the impact depends on the area where the mining operation takes
place and the method used. Extraction of sand from riparian environments may cause erosion
and disruption of local ecosystems. The removal of sand from streams using dredges lowers
the stream beds at the point of extraction, which creates a modification of the flow patterns
that eventually alters the stream bed for long distances upstream and downstream from the
point of extraction (Kondolf, 1997).
Impact of renewable feedstocks
In the last decade, polylactate became a model polymer for having two main attributes: it is
biodegradable when exposed to the right conditions and is produced from renewable
sources. There are other renewable materials that have been used for a long time before
