ABSTRACT
The effectiveness of alum and potassium sesquicarbonate
was studied by incorporating various concentrations of the flame retardants
into the polyurethane foam sample. The flammability tests were carried out and
the results showed that as the concentration of the flame retardants increased,
the flame propagation rate, after glow time, burn length and flame duration
decreased for both flame retardants, while ignition time, add-on and char
formation increased for both flame retardants. Thermogravimetric analysis shows
that both alum and potassium sesquicarbonate functions as flame retardants on
the foam samples at low percentage concentration but the polyurethane foam
filled with potassium sesquicarbonate required a higher activation energy than
alum for the pyrolysis / combustion of the samples. Also the onset of
degradation time was more delayed in potassium sesquicarbonate than alum.
CHAPTER ONE
1.0 INTRODUCTION
In every day to day activity,
foam materials are all around our homes, vehicles, schools and industries. It
is the cushioning material of choice in almost all furniture and bedding. It is
used as carpet cushions. It is the material used for pillows, roof liners,
sound proofing, car and truck seats. Foam has become such a widely used
material because it provides a unique combination of form and function [1].
Types of foam such as
neoprene, polystyrene, polyethylene, polyurethane, polyether and polyester
based polyurethane are synthetic plastics that have very desirable properties;
easily malleable and shapeable. They are also capable of “giving” and returning
to its original shape [2].
Polyurethane foams which have
been in use for almost 40 years, offer a wide variety of product suitable for
various applications. It appears to be a simple product but actually very
complex. The market place for polyurethane has witnessed innovations and
improvement which have led to great usage. Polyurethane is
a good example of traditional organic polymer system that has useful structural
and mechanical properties in foam but it is limited by its low thermo-oxidative
stability [3].
New technologies , new
processes and new applications introduce new fire hazards (e.g. new ignition
sources such as welding sparks and short circuits) [4]. Modern fire fighting
techniques and equipments have reduced the destruction due to fires. However, a
high fuel load in either a residential or a commercial building can offset even
the best of building construction [5]. Wood, paper, textiles and synthetic
textiles all burn under the right conditions, many burn rigorously and ignite
readily. The ability to control or reduce flammability of materials have
engaged the mind of scientists. Fire hazards may be reduced by either retarding
the fire or initiating a chemical reaction that stops the fire. It has been
observed that some of the fire retardant chemicals have adverse effects on the
properties of materials on which they are imparted [6]. The choice of suitable
polymeric flame retardants is restricted to species that allow the
retention of advantageous properties of the polyurethane.
LITERATURE
REVIEW
1.1 Flame
retardants
Flame retardants are
materials that resist or inhibit the spread of fire. They are chemicals added
to polymeric materials, both natural and synthetic to enhance flame retardant
properties [7]. A fire retardant is a material that is used as a coating on or
incorporated into a combustible product to raise the ignition or to reduce the
rate of burning of product [8].
Chemicals used as flame
retardants can be inorganic, organic, mineral, halogen or phosphorus-containing
compounds. In general, fire retardants reduce the flammability of materials by
either blocking the fire physically or by initiating a chemical reaction that
stops the fire. Flame retardant systems used in synthetic or organic polymers
act in five basic ways [7].
1.
Gas dilution:- This involves using
additives that produce large volumes of non-combustible gases on decomposition.
These gases dilute the oxygen supply to the flame or dilute the fuel
concentration below the flammability limit. Examples are metal salts, metal
hydroxides and some nitrogen compounds.
2.
Thermal quenching:- This is the
result of endothermic decomposition of the flame retardant. Metal hydroxides
and metal salts act to decrease the surface temperature and rate of burning.
3.
Protective coating:- Some flame
retardants form a protective liquid or char barrier which limits the amount of
polymer available to the flame front and also act as an insulating layer to
reduce the heat transfer from the flame to the polymer. This includes
phosphorus compounds.
4.
Physical dilution:- Inert fillers
(glass fibres) and minerals act as thermal sinks to increase the heat capacity
of the polymer or reduce its fuel content.
5.
Chemical interaction:- Some flame
retardants such as halogens and phosphorus compounds dissociate into radicals
species that compete with chain propagating steps in the combustion process.
Flame retardants have faced
renewed attention in recent years, aside from various conventional alternatives
such as antimony or phosphorus based retardants which have toxicological
problems of their own, nanoadditive flame retardants such as carbon nano tubes,
nanographites, layered double hydroxides (LDH) have been shown to enhance a
number of polymer properties, thermal stability, strength, oxidation
resistance, processing, rheology and flammability in polyurethane foams [9].
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