Abstract
This work studied the effects of two flame retardants on the
fire characteristics of flexible polyether foam samples. Various
concentrations of two flame retardants melamine and tri
ammonium orthophosphate have been successfully
incorporated into flexible polyurethane foam. Results of the
analyses carried out on the various foam samples showed that
by appropriate incorporation of the two flame retardants, the
flammability properties (After glow time (AGT), ignition time,
flame duration time, flame propagation time and percentage
char) have been greatly improved through both condensed
(solid) phase and gas phase mechanisms specifically. The After
glow time (AGT), flame duration time and propagation rate
were greatly reduced, while the ignition time and percentage
charring were increased with increase in concentration of the
two flame retardants. However, melamine showed better
impact for reduction of after glow time and flame duration time
while tri ammonium orthophosph
INTRODUCTION
1.1 Background
Fire is a world wild problem which claims lives and causes
significant loss of properties. Most of the immediate
surroundings of man consist of polymeric materials which
are combustible materials. These include clothes, furniture,
construction materials, and interior decorations. Generally,
the interiors of homes, offices, vehicles, and packages are
decorated with foamed plastics. The constitution of foamable
polymeric materials made them liable to easy ignition and
vigorous burning under right conditions. Humans have
always been plagued by unwanted fire, which usually gulfed
life and properties worth of millions of naira.
In addition to immediate fire risk posed by the polymeric
materials while burning, their combustion products often
cause serious threat to human health and environment. In
United States between 1996 and 2005 it was reported that
an average of 3,932 human loss and another 20,919 injuries
were as a result of fire accidents [1].
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Recently, on 9th Oct 2009, along Enugu-Onitsha express
road, over ten vehicles loaded full with humans and property
worth millions of naira were engulfed by fire. Therefore, the
need to seek efficient and affordable ways of reducing the
flammability of polymeric materials in our surroundings is of
primary importance.
A flame is a rapid free radical, chain reaction of volatile
materials with oxygen in the air. It is actually the resultant
flame or fire that consumes life and properties. The term fire
retardant (flame retardant) describes materials that inhibit
or resist flammability of polymers. In the same vein a fire
retardant chemical is used to denote a compound or mixture
of compounds that when added to, or incorporated
chemically into polymers, serve to slow down or hinder the
ignition or growth of fire [2]. In other words, a flame
retardant chemical is therefore a compound or mixture of
compounds which when added to or chemically incorporated
into a polymeric material, substantially suppresses the ease
of ignition and/or flame propagation [3].
The above definitions of flame retardant denote that it
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generally either lower ignition susceptibility or lower the
flame propagation once the ignition has occurred. The
products on which flame retardants can be applied include
apparels, carpets, and rugs, construction materials
(thermal) insulation foams, wall coverings and composites to
meet governmental regulations for buildings, aircraft, auto
mobiles. Flame retardants can be incorporated into a
material either as a reactive component or as an additive
component. As a reactive, such flame retardants are
incorporated into the polymer structure of the plastics,
example, when polyurethane and polyamides are retarded
with red phosphorus.
Flame retardants are usually classified into three types: non
durable, semi durable and durable finishes, based on
durability, or fastness to (laundry) light, heat chemicals etc.
[3].
i. Non- durable finishes. These are used for packaging
materials, paper and furnishings. They include
formulations containing, borax and other borates.
Others are aliphatic amine phosphate (e.g.
triethanolamine phosphate), urea sulphamates,
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ammonium and diammonium phosphate, ammonium
bromide and ammonium polyphosphate.
ii. Semi durable finishes. These include flame retardants
for mattresses, drapes, upholstery and carpets which
can withstand 1-20 washings in water, for example,
precipitate of a mixture of oxides of tungsten and tin in
the soluble salts.
iii. Durable finishes. These retardants are very durable
and can import excellent antimony oxide with durable
functions to cotton fabrics, for example chlorinated
paraffin.
Most flame retardants contain elements from group III A,
(boron and aluminum) group VA (nitrogen, phosphorus,
arsenic and antimony) and group VII A (fluorine, chlorine
and bromine) [4].
Group III: A flame retardant which contain boron or
aluminum work by forming char which acts as a protective
layer that prevents oxygen from reaching the inner layers of
the material and thus sustaining the fire. Chemicals
commonly used for this purpose include borax, boric acid,
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and hydrated aluminum oxide.
The group VA flame retardants work by forming a surface
layer of protective char. These include phosphoric acid,
diammonium orthophosphate and others, which are usually
applied in cellulose, polyester, and polyurethane products.
Arsenic is usually not used as flame retardant owing to its
toxicity, antimony in itself is ineffective as a flame retardant,
and it is used only in combination with halogens, especially
bromine and chlorine.
The group VII: A flame retardants which are the halogens
(Bromine, chlorine and fluorine). Bromine works as a flame
retardant in gaseous phase. When Bromine containing
compounds are incorporated into flammable materials, the
bromine dissociates from the material and form a heavy gas,
when the materials is exposed to flame. The dissociation
disperses heat and the bromine gas forms an insulating
layer around the material. The layer prevents flames from
spreading by inhibiting access to oxygen and by slowing the
transfer of heat. The use of these groups of fire retardants is
somehow restricted because of their environmental
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implications. The flame retardants selected for the present
study are from group VA, which is incorporated in flexible
polyurethane form as a reactive not as an additive.
Polyurethanes are in the class of compounds called reaction
polymers, which include epoxies, unsaturated polyesters
and phenolics [5]. A urethane linkage is produced by
reacting an isocyanate group, -N=C=O with a hydroxyl
(alcohol) group, -OH. Polyurethanes are produced by the
poly-addition reaction of a poly-isocyanate with a
polyalcohol (polyol) in the presence of a catalyst and other
additives [6].
During the production, excess isocyanate groups in the
polymer with water or carboxylic acid produce carbon
dioxide that blows the foam. Foaming reactions occur in
three stages; the blow reaction lasts for about 12 seconds
and occurs as soon as isocyanate reacts with polyol to give
polyurethane and the polyurethane reacts further with
isocyanate to produce an allophanate in a reversible
reaction.
R1NHCOOR2 + R3N = CO R1N (CONHR3) COOR2
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The rising time occurs when foam mix starts to rise until it
gets to a full block height. At this stage the isocyanate reacts
with water to generate carbon dioxide which causes the rise.
The formation of the carbon dioxide through the
intermediate carbamic acids gives.
RH = C = O + H – O – H RNH COOH RNH2 + CO2
The curing time is the reaction process that leads to
completion of the polymerization reaction that is usually
greater than 15 hours. Polyurethane can either be flexible or
rigid depending on the nature of the polymer and cross
linking produced. In the production of flexible polyurethane
foam, the polymerization reaction takes place between a
difunctional polyol and tolune diisocyanate. Flexible
polyurethane foams can be classified base on the density:
low density, 16-24 kg/m2, medium density, 32-48kg/m3 and
high density; 48kg/m3 and above [7].
The two basic types of flexible polyurethane foams are
polyester and polyether flexible polyurethane foams.
Polyesters are used mainly for clothing, interlining and
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packaging while polyether are used to produced mattresses,
cushions and general upholstery [8]. Flexible polyurethane
foams can be produced in many grades of flammability,
elongation and load bearing capacities.
The level of flammability of the polyurethane foams is of
great concern both to the foam industries as well as whole
masses. In order to reduce the flammability of these
polyurethane foams, and hereby reducing the destructive
tendencies of fire outbreaks some suitable flame retardants
are incorporated into the foam. This study aims at
producing a flame retarded polyether flexible polyurethane
foam of melamine and tri ammonium orthophosphate in
various formulations.
1.2 Significance of the Research.
Flexible polyurethane foams are used in several applications
in homes, (mattresses, cushions), industries (automobile,
packaging etc); hence decrease in their flammability will
save lots of life and properties in event of fire outbreak in
these areas.
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? Establishing the effects of using different concentration
of the applied fire retardants to the flexible
polyurethane foams will be valuable to commercial
foam manufacturers and researchers in the polymer
industry.
? Statistical establishment of the better fire retardants
out of the two on the fire characteristics of flexible poly
urethane foams will be useful to commercial foam
manufacturers.
? Comparison of the fire characteristics of flame retarded
polyurethane foams with the existing commercial
foams will clear the doubt of whether commercial
manufacturers actually incorporate fire retardants or
not.
1.3 Scope of the Study
* The study was based on only flexible polyether foams.
* The flame retardants incorporated in various
formulations are melamine, (C3H6N6) and triammonium orthophosphate (NH4)3.(P04.3H20).
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* The fire characteristics that were tested include: flame
propagation rate, ignition time, after glow time, % char
formation, and flame duration.
1.4 The objectives of the Study;
* The effects of melamine and triammonium
orthophosphate on the fire characteristics of the
flexible polyurethane foams were investigated.
* The fire characteristics of flexible polyurethane that
was flame retarded with melamine was compared with
that of flame retarded with triammonium
orthophosphate.
* The reduction of the flammability of the flexible
polyurethane foams was verified.
* The extent of the effects of the two flame retardants on
the ignition behaviour of flexible polyurethane foams
was established.