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Ionic Chain-Reaction and Complex Coordination Polymerization 171

FIGURE 5.4 Space-filling structure of a portion of a linear crystalline polyethylene region.

pipes, bags, conduit, wire and cable coating, foam, insulation for coaxial and communication
cables.
3. Low molecular weight HDPE—spray coatings, emulsions, prinking inks, wax polishes, and
crayons.
4. LDPE—packaging products, bags, industrial sheeting, and piping and tubing, fi lms, garbage
cans, industrial containers, household items.
5. LLDPE—telephone jacketing, wire and cable insulation, piping and tubing, drum liners,
bottles, fi lms.
6. MDPE—shrink film, packaging film, gas pipes and fi ttings.

7. VLDPE—frozen food and ice bags, food packaging, stretch wrap.
Recently, efforts are under way to form ethylene, and hence PE, from green chemistry feed-
stocks—sugarcane-derived ethanol and other natural feedstocks.
Plastomers is the name given to copolymers of ethylene that have a little crystallinity, but are
largely amorphous. They are also called very low-density PE (VLDPE). They are more elastic than

LLDPE but less stiff. They are used as a sealing layer in film applications and controlled permeation
packaging for vegetables and fruits.
Low-density polyethylene, PP, and TPX are more susceptible to oxidation in comparison to
HDPE because the presence of tertiary carbon atoms in the former. The degradation of LDPE, PP,
and TPX is retarded through the use of antioxidants.
General properties of some of the important PEs are given in Table 5.3.
Most shopping bags are made from PE, PP, or paper. Today, there is a move to remove the so-
called nongreen plastic bags. A brief comparison of the two is in order. In comparison to paper bags,
plastic bags are lighter, stronger, low cost, and water and chemical resistant. They cost less energy
to produce (about 70%), offer less of a carbon dioxide foot print (about 50%), transport and recycle.
When disposed of improperly, plastic bags are unsightly and represent a hazard to wildlife and

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