chee 583 plastic recycling
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CHEE 583PLASTIC RECYCLING
Engr. Lina D. dela Cruz
Chemical Engineering DepartmentTechnological Institute of the
Philippines
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Plastic recycling is the term given to the
processing of waste plastic which turns oldor scrap plastic in to a useable product
which can then re-enter the
manufacturing chain.
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Plastic recyclingis the process of recovering
scrap or wasteplasticand reprocessing thematerial into useful products, sometimes
completely different in form from their
original state.
http://en.wiktionary.org/wiki/recoveryhttp://en.wikipedia.org/wiki/Plastichttp://en.wikipedia.org/wiki/Plastichttp://en.wiktionary.org/wiki/recovery -
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For instance, this could mean melting down
soft drinkbottles and then casting them asplastic chairs and tables. Typically a plastic
is not recycled into the same type of plastic,
and products made from recycled plastics are
often not recyclable.
http://en.wikipedia.org/wiki/Soft_drinkhttp://en.wikipedia.org/wiki/Soft_drink -
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Challenges
When compared to other materials like glass
and metal, plastic polymers require greaterprocessing (heat treating, thermal
depolymerization and monomer recycling) to
be recycled.
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Due to the high molecular weight of their largepolymer chains, plastics have a low entropy of
mixing. A macro molecule interacts with itsenvironment along its entire length, so total energyinvolved in mixing it is large compared to that of anorganic molecule with a similar structure. Heating
alone is not enough to dissolve such a largemolecule, so plastics must often be of nearlyidentical composition to mix efficiently.
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When different types of plastics are melted
together, they tend to phase-separate, like oiland water, and set in these layers.
The phase boundaries cause structural
weakness in the resulting material, meaning
that polymer blends are useful in only limited
applications.
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Yet another barrier to removing large quantities of
plastic from the waste stream and landfills is the
fact that many common but small plastic items lack
the universal triangle recycling symbol and
accompanying number.
A perfect example is the billions of plastic utensilscommonly distributed at fast food restaurants or
sold for use at picnics.
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5 STAGES OF RECYCLING
Stage One
Sorting the Plastic
Firstly the waste plastic needs to be collected by therecycling company, once the plastic arrives at the
recycling plant the first stage is sort the plastic in tothe specific types.
Plastic recycling is more complex than that of metalor glass recycling due to the many different types of
plastic and more importantly mixed plastic cannotbe used in manufacturing without delivering poorquality products.
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Hence, that is why plastic recycling
companies need to be thorough when it
comes to sorting the waste plastic in to the
different forms prior to the next stage in the
recycling process
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Stage Three- Shredding the
Plastic
The shredding stage is when the waste plastic
is taken and loaded on to conveyor belts or
directly in to huge hoppers that funnel the
clean scrap towards rotating metal teeth that
rip the plastic in to small pellets which are
bagged up afterwards ready for testing.
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Stage FourIdentify andClassify the Plastic
Once the shredded plastic has been bagged it
is then chemically tested and labelled as to
its exact specification, this rGrade plastic can
be used as is by adding to a mix of virgin
plastic in a manufacturing run, alternatively
the rGrade plastic can be further recycled.
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Stage Five - Extruding
This is the final stage in recycling plastic.
This involves melting the clean shreddedplastic and extruding in to the form of pellets
which then go on to manufacture the next lot
of plastic products.
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Recycled products are becoming more
popular and are set to continue as oil
exploration moves to ever more hostile and
difficult to reach locations, which will of
course result in prices of products made from
oil will increase.