Monomer and Polymer

Question 1

what is a Polymer

Answer 1

Polymers - plastics - are very large molecules made from many smaller molecules called monomers. Alkenes are able to act as monomers because they contain a double bond. They can join end-to-end in a reaction called addition polymerisation. The polymers they form are called addition polymers. In general:
A lot of monomers → a polymer molecule

Question 2

what is polymerisation

Answer 2

Some small molecules can join together to make very long molecules called polymers. This process is called polymerisation.

Question 3

what is thermosetting

Answer 3

Thermosetting plastics do not melt but break
down and char on heating. In these plastics, the
long chains are also linked together sideways by
carbon-carbon bonds: the material is said to be
cross-linked.

polymers - end to end
thermosetting -end to end and sideways

Question 4

what are thermoplastics

Answer 4

Polymers such as polyethylene, polypropylene and
polystyrene soften and eventually melt at temperatures
in excess of 100-150°C Such materials are
called thermoplastics.

Question 5

fire hazards of polymers

Answer 5

1 Toxic and corrosive gases.

2. smoke
3. burning tar
4. exotherms
5. catylists
6. flammable solvents
7. dusts

Question 6

discuss polymer fire hazards re t toxic and corrosive gases

Answer 6

If plastics only contain the elements carbon and
hydrogen, or carbon, hydrogen and oxygen, the
main toxic gas to be expected is carbon monoxide
(CO) which is formed when all organic materials
are burned in quantity.
CARBON MONOXIDE

Many plastics contain nitrogen in addition to carbon, hydrogen and oxygen The fire products
from these will contain nitrogen-containing
species such as organic nitriles, hydrogen cyanide
and NO2. All of these are toxic. Intense, well ventilated burning will convert most of the original
nitrogen into NO2.
NITOGEN DIOXIDE
HYDROGE CYANIDE

Chlorine is present in polyvinyl chloride in PVC fires, almost all the chlorine goes to form hydrogen chloride (HC1) gas in the fire gases. HC1 is both toxic and corrosive, having a very sharp smell and forming a corrosive solution with water (hydrochloric acid
HYDROGEN CHLORIDE

PTFE (poly-tetrafluoroethylene - ‘Teflon’) and
some related materials, such as ‘Kel-F’ and some
synthetic rubbers, sometimes known as “vitons’.
contain fluorine

Question 7

discuss smoke hazards of polymer fires

Answer 7

Fires involving materials which contain the aromatic
(benzene) ring structure will tend to produce large quantities of smoke.
These include polyurethanes, phenol-formaldehyde
resins, polystyrene , polyesters, epoxy
resins and polycarbonates.

large quantities of thick black smoke causing smoke logging and smoke filled escape routes

Question 8

hazards of tar droplets from polymer fire

Answer 8

Thermoplastics melt on heating and so in a fire may
form burning droplets which could help the fire to
spread.

Question 9

what is th exotherm hazard of polymers

Answer 9

if blocks of
polyurethane foam are stored before the exothermic
curing process is complete, self-heating may
occur, leading to spontaneous combustion
POLYURETHANE

Question 10

what are the hazards of catylists in polymers

Answer 10

Various types of catalyst are used in polymerisation
processes including acids, alkalis, complex organometallic
compounds and organic peroxides
Acids and alkalis present well known hazards. An
organo-metallic catalyst may be in the form of a
slurry in flammable solvents: some of these compounds,
such as aluminium triethyl, react violently
with water. Organic peroxides are oxidising agents
and, therefore, present a considerable fire risk.
Under some conditions such materials can be
explosive.

Question 11

hazards of flammable solvents used in polmerisation

Answer 11

Flammable liquids, such as acetone, methyl ethyl
ketone, toluene, industrial alcohol and methyl
alcohol are widely used as solvents in various
processes and also as cleaning fluids, so may be
present in fires on industrial premises

Question 12

hazards of dust in ploymers

Answer 12

Some processes produce fine plastic dusts. These
may present an explosion hazard if dispersed as
a suspension in air

Question 13

discuss Self-extinguishing plastics

Answer 13

Many plastics are described as “self-extinguishing”.
While PVC and phenol-formaldehyde resins
are naturally so, others may be made self-extinguishing
by chemical changes in the polymer molecule
or by the use of special additives.
The term ‘self-extinguishing’ means that, while a
flame may (or may not) cause the material to burn,
it will not continue to burn if the applied flame is
removed. However, the term refers to the performance
of plastics in a specific small scale test. In a
fire situation, it will burn if surrounded by other
burning materials, or perhaps on its own if a large
enough area of the plastic has been ignited to produce
flames which are self-sustaining

Question 14

what is a momomer and discuss

Answer 14

Monomers by definition are reactive compounds
capable of polymerisation. Some, like ethylene,
do not polymerise very easily and need exactly
the right conditions of temperature and pressure,
perhaps with a catalyst. Others, like styrene, may
polymerise by accident, due to the presence of
impurities, water, heat or other causes, and when
this happens a great deal of heat may be given
out. Some monomers have to be transported with
a polymerisation inhibitor added to prevent the
process occurring spontaneousl
As these monomers are mostly poor conductors
of heat, the heat cannot get away easily, temperatures
may rise and a fire may result
monomers are flammable, and
some are toxic.