Page 184 - Materials Chemistry, Second Edition

Ch005-P373623.qxd 3/22/07 5:34 PM Page 163
163
Sustainability of Municipal Solid Waste Management
the system proved to be highly effective in producing quality paper and the
focus of the research has turned to optimize the paper recycling process.
Different raw materials were tested to optimize the mixing ratio for better
product quality.

5.4 Recycling of Plastic Waste

“Plastic recycling is still a relatively new and developing field of recycling.
The post consumer items made from PET and HDPE resins have found reli-
able markets within the US and in ASIA” (Connecticut Metal Industries
Inc., 2005). Applications for recycled plastics are growing every day. Plastics
can be blended with virgin plastic to reduce cost without sacrificing proper-
ties. Recycled plastics are used to make polymeric timbers for use in picnic
tables, fences, outdoor toys, etc., thus saving natural resources.
The problem of plastics wastes has increased tremendously since the
use of plastics increased in most industrial, commercial, and residential
applications. Households and industry produce huge amounts of plastic
waste. Plastic waste causes severe environmental problems when incinerated
or open burned on roadsides or in illegal dumpsites. Also plastic bags are a
major source of littering residential areas, parks, and even protected areas.
About 50% of the total volume of plastic wastes consists of household
plastic refuse, which are mainly in the form of packaging wastes. Once
rejected, plastic packages get contaminated and when reusing them a more
serious problem appears, which is the so-called commingled plastics, affecting
in return the properties of the new recycled products (Wogrolly et al., 1995).
The recycling of thermoplastics, or plastics, can be accomplished easily
with high revenue. Each type of plastic must go through a different process
before being recycled. Hundreds of different types of plastic exist, but
80–90% of the plastics used in consumer products are (1) PET (polyethylene
terephthalate), (2) HDPE (high-density polyethylene), (3) V (vinyl), (4) LDPE
(low-density polyethylene), (5) PP (polypropylene), (6) PS (polystyrene), and
(7) PVC (poly-vinyl chloride). The most common items produced from post-
consumer HDPE are milk and detergent bottles and motor oil containers.
Soda, mineral water, and cooking oil bottles are made of PET.
Mechanical recycling involves cleaning, sorting, cutting, shredding,
agglomeration, pelletizing, and finally reprocessing by injection molding, blow-
ing or extrusion according to the required products. A simplified schematic
diagram for the plastic recycling process is shown in Figure 5.11.
Recycled PET has many uses and there are well-established markets for
this useful resin. By far the largest usage is in textiles. Carpet manufacturing
companies can often use 100% recycled resin to manufacture polyester carpets
in a variety of colors and textures. PET is also spun like cotton candy to
make fiber filling for pillows, quilts, and jackets. PET can also be rolled into
clear sheets or ribbon for audio cassettes. In addition a substantial quantity