Properties of Plastic
The growth of the production of plastic since its initial creation in 1868 has been
a series of unsteady increases. These increases are usually a response to a series
of worldly events. Early on the popularity of plastics spread at a constant rate
as knowledge of making them increased. An observable trend before plastics first
initial boom is seen around the Great Depression. When the Great Depression occurred
there was more of a demand for cheaper ways of production
for an overall economic
However, plastic's negative trend during this period outweighed its demand
because there was more of a demand in the public necessity and less of a demand
in entertainment such as plastic toys and lavish accouterments. Another reason why
plastics sales were down during this period was because of a reduced production
of plastic packaging since export rates were down.
Another contingent catalyst on the growth of plastics was the boost in production during World War II.
WWII got America out
of the depression it was experiencing and spread the technology of plastic via weaponry
causing a three fold increase
in plastics production from 1940 to 1945.
Being in recessions and depressions always causes a lack of production to happen.
In every recession
a slight percentage decrease in growth is
observed, as shown in the late 1900s for plastics which caused a sort of plateau effect
. This in coordination with new scientific
discoveries of plastics' harmful effects on people in society and the environment
has spawned this trend. The graph to the right shows our plot of the previously
Types of Plastic
seven major categories
of plastics, all with different physical and chemical
Polyethelyn terephthalate (
PET) is plastic that is used for bottling soft drinks,water, and the like. It's
major uses are in the textile business. It is nicknamed polyester.
High density polyethelyn (HDPE)
is another plastic of considerable reknown. It is used for packaging as well, but
it's major use is for injection molding applications.
is known for it's stable physical properties, which then leads to the application
we all know it as: piping.
Low density polyethelyn ( LDPE)
is generally used for things such as shrink wrap/stretch wrap and is even used for
the plastic coating on paper milk cartons or juice boxes.
Polypropylene (PP) is
used mostly in fibers, appliances, and general consumer products.
Polystyrene (PS) is
one of the most versatile and common plastics. It can be either rigid or foamed,
though we all know it most commonly in its foamed state as packing peanuts.
The "other" category
consists of packages or other things that are made with a plastic resin other than
the previously stated plastics, or has multiple types of plastic resins in it.
As shown below, most plastics have a density hovering between 0.8-1.5 g/cm3
This image is courtesy of Evan I.
All of the plastics listed above are recyclable and have many different uses even
after being recycled. Most of these plastics are also used for some sort of packaging,
whether it be bottles, or packing peanuts to protect a package. Unfortunately, all
of these plastics eventually find their way into the ocean or a landfill because
the recycling process isn't 100% efficient. This means that we cannot completely
reuse all of the results of the recycling process.
Plastic Decomposition is the ability of plastic to separate or resolve into constituent
parts or elements over time. It is unfortunate that plastics take such a long time
to decompose, if they do at all. The table below shows the average time for
certain plastics to decompose compared with other degradable objects.
Again, unfortunately, plastic takes a very long time to degrade and decompose. This
has inspired quite a bit of research but the person to find the best results with
their experiments was a boy, a junior in high school, named
, who discovered microbes that could completely breakdown and decompose
a plastic bag in three months.
There are plastics that take, from what we can guess, over a million years
to degrade; but do they ever really go away? Plastic, when broken down
, just gets smaller and smaller. It never actually
goes away. These little tiny bits and pieces of plastic whose diameter is less than
twenty microns, are the true danger to our oceans. The phytoplankton and zooplankton
are being outnumbered by the enormous amounts of plastic within our oceans. Our
fish are dying from yet to be processed nurdles. In the last few years though, there
has been promise in the research. There are now compostable/biodegradable plastics.
There are companies
that have recently begun mass producing an additive
to put into your compost that assists the microbes in their task of breaking down
the plastic. Most of these "biodegradable" plastics however, are just claimed to
be biodegradable, but really, they just break down into very very small particles
that we talked about earlier. There are now corn starch based plastics that has
been certified as compostable.
The recycling of plastics can be
into industrial scrap recycling and post-use plastics. Industrial scrap
reprocessing is the collection of scraps from the assembly line to be injected back
into the beginning of the process. Everything else is referred to as
post use recycling
. It includes the collection of waste plastics from industries,
retailers, and consumers. Of the 69 million pounds of plastic recycled in 2008,
35.8 million was post industrial, 28.5 million was post commercial, and 5.1 million
was post consumer.
After the plastics are collected, they are organized based on a resin coding system
familiar symbol of a number surrounded by a triangle of arrows – designed by the
Society of the Plastics Industry
range from one to seven and represent the inherent difficulty in recycling
that particular type of plastic. Plastics are cleaned, its labels are removed, and
then it is sent to the main arc of the recycling process where it is recycled
either chemically or mechanically.
mechanically recycle plastics
, the plastics are shredded, cleaned, seperated,
melted, and either converted to pellets - nurdles - or directly remade into new
products. If it is
, the plastic is treated with heat and other chemicals to
break down the plastic on a molecular level, resulting in the basic constituents
of the original plastic. Eventually, the plastics are put back on the market
in such various products
as water bottles, pipes, and egg cartons. If the plastic is melted down without
being previously separated, it is sold as a lumber substitute due to its wood-like
are pre-production plastic resin pellets; these are essentially the
building blocks of all plastic products. They are about the size of fish eggs making
it very easy for marine life to mistake them for food. Ingestion of these pellets
can lead to intestine blockage and starvation as well as the possibility of poisoning.
Over 250-billion pounds of nurdles
are shipped out each year,
and during transport is when most pellets become airborn and travel into the ocean.
Unfortunately nurdles represent about 10% of the litter counted on beaches world