Recycling is the process of making or
manufacturing new products from a product that has
originally served its purpose.
Recycling of plastics should be carried in such a
manner to minimize the pollution level during the
process and as a result to enhance the efficiency of
the process and
conserve the energy.
two general types:
i. Primary recycling involves processing of a
waste/scrap into a product with
characteristics similar to those of original
ii. Secondary recycling involves processing of
waste/scrap plastics into materials that have
characteristics different from those of
original plastics product.
Workers inspect the plastic trash for contaminants
like rock and glass, and for plastics that the plant cannot recycle.
2) Chopping and Washing
The plastic is washed and chopped into flakes.
3) Flotation Tank
If mixed plastics are being recycled, they
are sorted in a flotation tank, where some types
of plastic sink and others float.
The plastic flakes are dried in a tumble dryer.
The dried flakes are fed into an extruder, where
heat and pressure melt the plastic.
Different types of plastics melt at different temperatures.
The molten plastic is forced through a fine screen to
remove any contaminants that slipped through the
washing process. The molten plastic is then formed
The strands are cooled in water, then chopped
into uniform pellets. Manufacturing companies
buy the plastic pellets from recyclers to make
i. Lower labor costs.
ii. Lower transportation costs, hand or ox carts often being used.
iii. Innovative use of scrap machinery often leads to low entry costs
for processing or manufacture.
iv. Existing culture of reuse and recycling, & collection of these
i. Cost: “May not be economical to recycle small quantities of
ii. Training of waste generators will be required, so they can separate
the wastes properly.
It is a change in the properties—tensile
strength, color, shape, etc.—of a polymer or polymer-based
product under the influence of one or more environmental
factors such as heat, light or chemicals such as acids, alkalis
and some salts.
Types of Polymer degradation
• Degradation by irradiation
Most polymers can be degraded by photolysis to give lower
molecular weight molecules. Electromagnetic waves with the
energy of visible light or higher, such as ultraviolet light, X-
rays and gamma rays are usually involved in such reactions.
Chain-growth polymers like poly(methyl methacrylate) can
be degraded by thermolysis at high temperatures to give
monomers, oils, gases and water.
Step-growth polymers like polyesters, polyamides and
polycarbonates can be degraded by solvolysis and mainly
hydrolysis to give lower molecular weight molecules. The
hydrolysis takes place in the presence of water containing an
acid or a base as catalyst.
Cracks can be formed in many different elastomers by
Tiny traces of the gas in the air will attack double bonds in
rubber chains, with Natural rubber, polybutadiene, Styrene-
butadiene rubber being most sensitive to degradation.
The problem of ozone cracking can be prevented by
anti-ozonants to the rubber before vulcanization.
Ozone cracks were commonly seen in automobile tire
Polymers are susceptible to attack by atmospheric
oxygen, especially at elevated temperatures encountered
during processing to shape.
Many process methods such as extrusion and injection
molding involve pumping molten polymer into tools, and the
high temperatures needed for melting may result in oxidation
unless precautions are taken.
Polymer degradation by galvanic action was first
described in the technical literature in 1990.
This was the discovery that "plastics can corrode", i.e.
polymer degradation may occur through galvanic action
similar to that of metals under certain conditions.
Biodegradable plastics can be biologically degraded by
microorganisms to give lower molecular weight molecules.
To degrade properly biodegradable polymers need to be
treated like compost and not just left in a landfill site where
degradation is very difficult due to the lack of oxygen and