How does plastics harm the environment?
as they are non-biodegradabe products
Plastic is one of the few new chemical materials which pose
environmental problem. Polyethylene, polyvinyl chloride,
polystyrene is largely used in the manufacture of plastics.
Synthetic polymers are easily molded into complex shapes, have high
chemical resistance, and are more or less elastic. Some can be
formed into fibers or thin transparent films. These properties have
made them popular in many durable or disposable goods and for
packaging materials. These materials have molecular weight ranging
from several thousands to 1,50,000. Excessive molecular size seems
to be mainly responsible for the resistance of these chemicals to
biodegradation and their persistence in soil environment for a long
time. Plastic in the environment is regarded to be more an
aesthetic nuisance than a hazard, since the material is
biologically quite inert. The plastic industry in the US alone is $
50 billion per year and is obviously a tempting market for
biotechnolo gical enterprises. Biotechnological processes are being
developed as an alternative to existing route or to get new
biodegradable biopolymers . 20% of solid municipal wastes in US is
plastic. Non-degradable plastics accumulate at the rate of 25
million tonnes per year. According to an estimate more than 100
million tonnes of plastic is produced every year all over the
world. In India it is only 2 million tonnes. In India use of
plastic is 2 kg per person per year while in European countries it
is 60 kg per pe rson per year while that in US it is 80 kg per
person per year.Plastics are used because they are easy and cheap
to make and they can last a long time. Unfortunately these same
useful qualities can make plastic a huge pollution problem. Because
the plastic is cheap it gets discarded easily and its persistence
in the environment can do great harm. Urbanisation has added to the
plastic pollution in concentrated form in cities. Plastic thrown on
land can enter into drainage lines and chokes them resulting into
floods in local areas in cities as experienced in Mumbai, India in
1998. It was claimed in one of the programmes on TV Channel that
eating plastic bags results in death of 100 cattles per day in U.P.
in India. In stomach of one dead cow, as much as 35 kg of plastic
was found. Because plastic does not decompose, and requires high
energy ultra-violet light to break down, the amount of plastic
waste in our oceans is steadily increasing. More than 90% of the
articles found on the sea beaches contained plastic. The plastic
rubbish found on beaches near urban areas tends to originate from
use on land, such as packaging material used to wrap around other
goods. On remote rural beaches the rubbish tends to have come from
ships, such as fishing equipment used in the fishing industry. This
plastic can affect marine wildlife in two important ways: by
entangling creatures, and by being eaten. Turtles are particularly
badly affected by plastic pollution, and all seven of the world's
turtle species are already either endangered or threatened for a
number of reasons. Turtles get entangled in fishing nets, and many
sea turtles have been found dead with plastic bags in their
stomachs.Turtles mistake floating transperent plastic bags for
jellyfish and eat them. In one dead turtle found off Hawaii in the
Pacific more than 1000 pieces of plastic were found in the stomach.
A recent US report concluded that more than 100000 marine mammals
die each year in the world's oceans by eating or becoming entangled
in plastic rubbish, and the position is worsening World-wide, 75
marine bird species are known to eat plastic articles. This
includes 36 species found off South Africa. A recent study of blue
petrel chicks at South Africa's remote Marion Island showed that
90% of chicks examined had plastic in their stomachs apparently fed
to them accidentally by their parents. South African seabirds are
among the worst affected in the world. Plastics may remain in the
stomachs, blocking digestion and possibly causing
starvation.Presence of nucleating agents (which facilitate
crystallization) or the use of plasticiser shortens the processing
cycles during the moulding operations. There are two main points
about processing of PHBV bioplastics - (i) The limited thermal
stability of the polymer and so it degrades rapidly above 195
degree centi. (ii) The need to optimise conditions to allow a
maximum crystallization rate (which reduces cycle times). The
maximum rate of crystallization is reported to be at about 55-60
degree centi. which is significantly closer to Tg than the Tm.
Processing temperatures should not exceed 180 degree centi. and
duration of time when the material is in melt state should be kept
minimum. At the end of a run the processing equipment should be
purged with polyethylene. When blow moulding the blow-pin and the
mould should be at about 60 degree centi. to optimise
crystallisation rates. Similarly injection moulds are recommended
at 55-65 degree centi. The low-hydroxyvalerate, unplasticised
grades are most critical to process, requiring the higher
processing temperatures. Conditions are slightly less critical with
the higher hydroxyvalerate containing and plasticised grades. In
addition to producing PHAs in dry powder form for melt processing,
Metabolix is also developing PHA latexes. These materials have
unique film forming properties, which are finding application in
higher performance applications as well as in more traditional
commodity uses. Metabolix company supplies PHA samples to companies
under research and development agreements.