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parameter depends on the mechanism of flame-retardant
materials and its performance in combustion process [5, 6].
Nowadays, environmental-friendly phosphorus-based
flame retardants are a major focus. They generate less
smoke, toxic and corrosive gases, and low loading is
enough to show the flame retardancy [7]. Elemental red
phosphorus, phosphine oxides, phosphonates, phosphinates
and phosphonic acid derivatives are some examples of
phosphorus-based flame retardants. Phosphorus containing
flame retardant reduces the heat of combustion by about
70 kcal mol-1, and its flame retardant mechanism depends
on the nature of combustible materials [1, 8, 9]. In the
combustion process, phosphorus-based flame retardants act
both in the gaseous and condensed phases. In gas phase, it
generates free radical scavengers such as P2, PO, PO2
during the combustion and reduces the exothermic reaction
thus suppressing the combustion of materials. In condensed
phase, it modifies the chemical reactions in combustion
processes and forms carbon char rather than producing
pollution gases CO and CO2. The formed char covers the
surface of the materials thus preventing the underlying
materials [7, 8, 10, 11].
also discussed by taking the example of melamine salt of
bis(2,6,7-trioxa-1-phosphabicyclo-[2,2,2]-octane-4-methanol)
phosphate. Chemical reactions responsible for the intu-
mescence process are described in detail by taking
ammonium polyphosphate–pentaerythritol (APP–PER)
system. Allen et al. [18] discussed the salient molecular
features for intumescent behaviour by synthesizing differ-
ent derivatives of pentaerythritol phosphate alcohol using
acid anhydrides, methacryloyl chloride and with excess
diketene.
Li et al. [19] studied the combustion and thermal deg-
radation behaviour of PEPA incorporated diglycidyl ether
of bisphenol-A epoxy resin. The incorporation of PEPA not
only enhances the flame retardancy and thermal stability of
the epoxy resin but also acts as smoke inhibitor. Balabi-
novich [16] studied the volatile and solid decomposition
product of PEPA and its blend with melamine phosphate
(PEPAMP) which is less stable to oxidative degradations.
Gao et al. [20] synthesised the novel phosphorus–nitrogen
intumescent flame retardant by reacting bis (2,6,7-trioxa-1-
phosphabicyclo-[2,2,2]octane-4-methanol)
chlorophos-
phate and diaminodiphenyl methane. An UL-94 test,
thermogravimetry and in situ FT-IR studies reveal that the
presence of P–N intumescent flame retardant along with
poly urethane in poly (butylene terephthalate) increases
flame retardancy and thermal stability.
Phosphorus compounds in combination with carbonifics
(pentaerythritol, mannitol and sorbitol) and spumifics
(urea, dicyandiamide, melamine, polyamides, etc.) show
intumescent behaviour. Intumescence is a phenomenon in
which substrate swells and forms multicellular charred
layer as a result of heating, there by increasing its volume
and decreasing its density. The intumescent char restricts
the mass transfer from combustible material to fire and
entrance of the atmospheric oxygen to substrate. Intumes-
cent process should occur just before the decomposition
temperature of the combustible materials [12]. The main
aim behind the development of the intumescent materials is
thermal protection. Different types of intumescent coating
materials have been produced from time to time, to
increase the escaping time during fire [13]. The mechanism
of intumescent process may be the phosphate ester for-
mation [14]. When the three active ingredients are added
separately to combustible materials, water solubility and
migrations are the main problems associated with this
technique. Those problems are overcome by synthesizing
single compound which provides all the functions neces-
sary for intumescence [15, 16].
The effect of metal chelate on a novel oligomeric intu-
mescent flame retardant, poly(4,40-diaminodiphenylmeth-
ane-o-bicyclicpentaerythritolphosphate-phosphate) (PDB
PP) on flammability of polypropylene was studied by the
Song et al. [21]. It was concluded that the metal chelate
forms cross-linked network with polyphosphoric acid and
enhance the flame retardancy of PP/PDBPP as evidenced
by Raman spectroscopy, IR spectroscopy, SEM, LOI
¨
analysis and cone calorimetry. Gaele et al. [15] studied the
flame retardancy and thermal stability of melamine salt of
both 3,9-dihydroxy-2,4,8,10-tetraoxa-3,9-diphosphaspiro-
[5,5]-undecane-3,9-dioxide and bis(1-oxa-2,6,7-trioxa-1-
phosphabiyclo-[2,2,2]-4yl-methanol) phosphate (PP/NI-FR)
with and without zinc borates using LOI, UL-94 V–O,
cone calorimetry and TG analyses. Phosphorus containing
flame retardant such as 4-(5,5-dimethyl-2-oxo-1,3,2-dioxa-
phosphorinan-2-yloxymethyl)-2,6,7-trioxa-1-phosphabicy-
clo-[2,2,2]-octane-1-oxide (MOPO) was synthesised by
Wang et al. [22]. They prepared intumescent flame retarded
EVA system with different ratios of APP and MOPO. The
addition of intumescent flame retardant additive signifi-
cantly decreases the total heat release rate and increases the
char yield.
Halpern et al. [17] synthesized the intumescent flame
retardant, 2,6,7-trioxa-1-phosphabicyclo-[2,2,2]-octane-4-
methanol phosphate and studied its fire retardancy behav-
iour with thermoplastics, mainly polypropylene. PEPA is a
good environmental-friendly flame retardant suitable for
many purposes. Camino et al. [14] reviewed the formation
of swollen char on heating the intumescent materials.
Earlier development of intumescent coatings and the recent
development of intumescent additives for polymers are
The study of the degradation pattern of the intumescent
materials is an important factor since its applicability can
be assessed only on these grounds. In the present investi-
gation, PEPA was synthesized and its structure was
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