Plastic Fantastic

1
Plastic Fantastic
2
One major group of designer materials that have
had phenomenal success and altered our lifestyle
are plastics. Plastics are everywhere. From an
early age you were surrounded by plasticsplastic
toys, plastic containers, plastic bags, even
non-stick coatings on pans, chewing gum and Lycra
in clothes are made from plastics. Although it
may be difficult to believe, the development of
plastics has occurred only in the last 70 years
or so. In fact they have been used on a massive
scale only over the last 50 years. At this moment
you are probably using a number of
different materials that did not exist even 10
years ago, particularly in electronics technology.
3
It is likely that at least some of your clothing
contains synthetic fi bres. Your pen is made
mainly of plastic, your calculator has a plastic
case and so does your mobile phone and computer.
All the CDs and DVDs you play are made of
plastic and so are their containers. Your sports
shoes alone probably consist of six or
more different kinds of plastic, including the
sole, the padding, the upper, the laces and even
the lace tips. Plastics are amazing materials.
They come in every shape, size and colour
and with every material property you could think
ofstrong, flexible, elastic, hard, ductile,
transparent, slippery, brittle to name a few. As
chemists developed new plastics, the variety of
properties and uses expanded dramatically.
4
The term plastic is applied to a wide range of
materials with a wide range of properties and
applications. Technically, plastic means
deforms permanently when subjected to a force,
but as a general term it has come to be used for
a range of synthetic substances more
appropriately known as polymers. Polymers are
large molecules made up of many repeating units.
Poly is from the Greek for many and meros is
the Greek for part. Common names or brands for
these polymers include rayon, nylon, Lycra,
polyurethane, Teflon, Styrofoam and PVC. All
plastics are polymers, but not all polymers are
plastics. Polymers are also produced in profusion
by nature. Some of the many natural polymers are
cellulose, cotton and rubber (found in plants),
wool, skin and hair (proteins from animals). The
DNA found in all living things is another natural
polymer. Chemists have copied many of these
natural polymers, often making small changes to
them. Many synthetic polymers were originally
created as substitutes for expensive, naturally
occurring materials or to improve on natural
polymers.
teflon
5
Friday 7th?
ACTIVITY 7.1 a Collect a variety of plastic items
from your homeplastic bags, soft drink
bottles, milk bottles, takeaway food containers
and whatever happens to be on hand. The plastics
used to make the items will have different
properties related to their use. You are to test
and compare some of the properties of these
plastics. b Decide on some properties to
investigate, such as colour, fl exibility,
elasticity, hardness, water absorbency, ease of
melting and heat shrinkage. You will need to
devise tests for these properties, being sure to
control as many variables as possible. Warning
Burning polymers give off toxic fumes so do not
expose your sample directly to a flame unless
this is done in a fume cabinet. To determine ease
of melting you could use hot water, or a nail
heated in a Bunsen burner, or place the sample in
an oven. c Draw up a table to record your
results. d Use your test results to identify
items that are made from the same material. e
Compare the properties of the different plastics
and relate their properties to their use.
6
By the 1990s the volume of plastics on the world
market exceeded the total volume of metals.
Plastics production worldwide now exceeds 80
million tonnes a year. Australia contributes
almost 1.3 million tonnes to that totalmore that
71 kg for every person. Packaging is the largest
market for plastics, accounting for over a third
of the consumption of raw plastic
materialsAustralians in 2004 used 50 000 tonnes
of soft-drink bottles, 30 000 tonnes of milk
bottles and 6 billion plastic bags during the
year .Although plastic packaging provides
excellent protection for the product and is
lightweight compared to metal or cardboard, it is
proving to be a major environmental problem. In
the past more than one-third of the plastic
consumed in Australia was destined for landfi ll,
but today many local councils have recycling
facilities for plastic materials.
Six polymeric materials account for 66 of all
plastics used, but currently not all of these can
be recycled. Since most plastics are incompatible
when mixed together, the different types of
plastics need to be separated before they
are recycled. To help identify plastics,
manufacturers use a plastics identifi cation
code, which is normally stamped on all
products. It is represented by a triangle with a
number inside it. People often get this code
confused with the recycling symbol, which is a
triangle made up of three arrows with no number
inside. The plastics identifi cation code does
not mean the plastic container can be recycledit
gives the type of plastic the product is made
from.
phone.wav
7
In 1862 Alexander Parkes produced the first
plasticcellulose nitratewhich could then be
converted to various products. He made the
cellulose nitrate from wood or cotton and
camphor. At the same time an American, John
Hyatt, was also experimenting with cellulose
nitrate in an attempt to find a synthetic
substitute that could replace the ivory
originally used to make billiard balls, and win a
US10 000 prize. He produced a material that he
called celluloid and patented it in
1869. Although it was unsuitable for billiard
balls it was used to make combs, brush handles,
photographic film and table-tennis balls. It had
the major disadvantage of being highly flammable.
Its use boomed until the mid-1920s when other
less flammable materials were synthesised.
8
The first true synthetic polymer, called
Bakelite, was developed by Dr Leo Baekeland in
1907. While celluloid was a natural polymer
modifi ed by humans, Bakelite was produced from
manufactured chemicals and was unlike
anything produced in nature. It is still used to
make electrical fi ttings such as sockets and
plugs. Bakelite is a thermosetting plastic (goes
hard when heated) all of the polymers discussed
in this chapter are thermoplastic (soften when
heated). Baekelands discovery started a
scientific and industrial revolution
using manufactured chemicals to produce new
materials, but it was not until the 1950s that
the most common polymers (nylon, polyethylene,
polystyrene and PVC) were manufactured in
significant quantities for the general publics
use.
9
(No Transcript)
10
The refining of crude oil by fractional
distillation produces an impressive array of
products. As you also learnt in the transport
context, crude oil contains a range of
hydrocarbons that vary in size and structure,
including straight and branched alkanes, alkenes
and cyclic hydrocarbons
Currently the petrochemical industry consumes
about 35 of the total oil used in the world
today. In fact about 95 of all synthetic carbon
compounds are derived from compounds produced
from petroleum and natural gas. Research has
shown that many of the compounds distilled from
crude oil are not ideally suited for the desired
applications. The most useful fractions are the
lighter ones and so there is a great demand for
these. Over half the fractions obtained from
crude oil, however, are the heavier, less useful
ones. Oil refi neries have developed methods in
which fractions containing hydrocarbons of higher
molecular mass can be converted into the lower
molecular mass hydrocarbons, which are more in
demand. The process used is called catalytic
cracking. The most widely used starting substance
for making polymers is ethene or, as it is more
commonly called, ethylene. (The historical name
for ethene is ethylene and this historical name
tends to be the preferred name and so is more
commonly used.) Ethylene is obtained from crude
oil, either as a by-product of petrol refi ning
or by the deliberate decomposition or cracking of
some of the higher boiling point fractions
11
(No Transcript)
12
(No Transcript)