:: Overview of plastics
In this section :- (click below)
What are Plastics?
Plastics are macromolecules, formed by Polymerization and
having the ability to be shaped by the application of reasonable
amount of heat and pressure or some other form of force.
Polymerization is the process
by which individual units of similar or different molecules
("mers") combine together by chemical reactions
to form large or macromolecules in the form of long chain
structures, having altogether different properties than those
of starting molecules ("mers"). Several hundreds,
and even thousands of "mers" combine together to
form the macromolecules, or what we call, Polymers.
Depending upon their nature and properties, the polymers
are classified as Plastics, Rubbers or Elastomers and Fibres.
If the polymer chains are very flexible, the inter molecular
forces of attraction low and the chains do not fit to a regular
lattice structure easily, the material will tend to retract
upon when external tension is released. This is the state
typical for a Rubber or Elastomer.
In the other extreme, if the polymer chains are inherently
rigid, the intermolecular forces intense and the molecules
fit readily into a crystal lattice, then the crystallinity
once induced, will tend to be permanent. Such a material would
be a typical Fibre. In the intermediate case, when the intermolecular
forces of attractions are neither too high nor too low, the
polymer is called Plastic.
Generally speaking, a plastic material should posses sufficient
rigidity, dimensional stability and mechanical strength at
room temperature to serve as a useful household article, gadget
or structural part and still be of such a character that it
may be molded to shape by the application of reasonable temperature
There are no intrinsic differences among Rubbers, Plastics
and Fibres. Any apparent difference is a matter of degree.
Polymers can be classified into two categories : -
Natural Polymers and Synthetic Polymers.
Examples of Natural Polymer: Starch, Natural Rubber, Gelatin,
Protein, Shellac, Cellulose etc.
Examples of Synthetic Polymers :
Polyethylenes - Low Density Polyethylene, High Density polyethylene,
Linear Low Density Polyethylene, Polypropylene, Polystyrene,
Styrene Butadiene Rubber(SBR), Nylon etc.
Polymers may also be sub classified into two categories:
In Organic Polymers, the main constituent is Carbon Atom
along with any one or more of the following constituents:
Hydrogen, Oxygen, Nitrogen, Halogens etc.
Examples : Polyethylene, Polyvinyl Chloride, Nylon etc.
In inorganic Polymers the main constituents are other than
carbon, like Silicon, Boron etc.
Examples : Polysilanes, Polysiloxanes etc.
Types of Plastics:
There are mainly two types of Plastics:
Thermoplastics and Thermosetting Plastics
Thermoplastics are those, which once shaped or formed,
can be softened by the application of heat and can be reshaped
repeatedly, till it looses its property.
Example: Polyethylene, Polypropylene, Nylon , Polycarbonate
Applications are : Polyethylene Buckets, Polystyrene Cups,
Nylon ropes etc.
Thermosetting Plastics are those, which once shaped
or formed, cannot be softened by the application of heat.
Excess heat will char the material.
Example : Phenol formaldehyde, Urea Formaldehyde, Melamine
Formaldehyde, Thermosetting Polyester etc.
Applications are - Backelite Electrical switches, formica
/ sermica table tops, melamine Cutlery etc.
Sources of Plastics
majority of the most commonly used plastics(commodity plastics)
are derived from these chemicals :
These chemicals are intern derived from Natha obtained during
petroleum refining process or from Natural Gas,after procesing.
A flow chat of the sources of commodity plastics and some other
important plastics, rubbers and fibre materials is attached
Why Plastics - The Importance of Plastics in Modern Society
Plastic have moulded the modern world and transformed the
quality of life. There is no human activity where plastics
do not play a key role from clothing to shelter, from transportation
to communication and from entertainment to health care. Plastics,
because of its many attractive properties, such as lightweight,
high strength and ease of processing, meet a large share of
the materials needs of man, and that too at a comparatively
lesser cost and causing lesser environmental implications.
From practically zero during the beginning of the 20th century,
human kind today consumes more than 150 million tons of plastics
Plastics possess a unique combination of properties. Plastics
can be super tough, rigid as well as flexible, transparent
as well as opaque and can allow permeation or act as a barrier
Growing population and material consumption has put severe
pressure on our natural resources and fragile eco-systems.
The material needs of our population are growing and plastics
offer a cost effective alternative.
Plastics are employed in myriad applications where they actually
conserve natural resources. For example, asceptic packaging
of food in barrier packaging films will save refrigeration
cost and saving capital and energy. Edible oils and milk are
packaged in flexible packages eliminating the use of tin and
glass containers. Rigid HDPE barrels are used for bulk chemical
storage instead of steel drums. Apart from conserving natural
resources, use of plastics in these applications saves transportation
fuel as plastics are substantially lighter than tin, glass
Safe drinking water in PET bottles is a very common sight
now-a-days. They provide confidence to consumer on the quality
of water and help reduce water-borne diseases. Advance polymeric
membranes help purify water from viruses and bacteria. They
also provide potable drinking water from sea and blackish
water through a process of desalination.
The fact that plastics are made from hydrocarbons derived
from petroleum, which is non-renewable, has raised questions
concerning its sustainability. Nevertheless, the consumption
of petroleum hydrocarbon for the production of plastics is
less than 5%, the balance being consumed as fuels and energy
source. Consequently, the concerns about sustainability of
plastic material is somewhat exaggerated. On the contrary,
processing of many natural materials (glass, paper, wood,
metals) consume far more energy and thus lead to greater consumption
of fossil fuels. Additionally, research and development work
currently in progress globally will provide future opportunities
to make some of the plastics from biomass and other renewable
sources. Thus, plastic manufacture will become even more sustainable
in the years to come. It is fair to say that plastics replace
several naturals, which are either scarce, consume more energy
for processing or cause damage to the eco-system during their
Thus use of plastics makes positive contribution to the sustainability
of earths resources.
Another issue that is often discussed is whether because
of their non-biodegradability, plastics will cause damage
to our eco-system
The signature of all natural materials made by biological
process is that they are biodegradable and bio-assimilable.
The long life and desirability of plastics, which have made
them, a material of choice for many applications is seemingly
a disadvantage when it comes to their disposal. However, when
handled properly, plastics do little damage to our environment.
Plastics have the advantage that they can be easily reprocessed
Plastics offer the unique advantage that one can recover
the fuel value contained in the hydrocarbon polymer after
its use. Plastics can also be made environmentally degradable,
especially for packaging applications. There are expectations
that in the near future plastics will be made even biodegradable
and compostable so that waste plastics can be handled the
same way as wet food waste and agricultural waste. The overall
eco-friendliness of plastics becomes apparent when one evaluates
the total "life cycle", namely, an analysis of raw
materials, energy, effluents, methods of disposal etc. of
a material from its origin to its final disposal.
History of (Synthetic) Plastics
In 1862, Alexander parkes in Britain modified cellulose nitrate
with camphor to produce the first man made plastic material
The First Thermosetting Plastic material was invented in 1907
when Leo Bakeland, USA, made Phenol Formaldehyde(Backelite)
The list below gives a brief history of invention of various
major Plastics materials and their initial use/applications