flame retardant pp
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8/2/2019 Flame Retardant Pp
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ByHarshini Tammareddy
09120018
8/2/2019 Flame Retardant Pp
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Polypropylene was the first synthetic stereo-
regular polymer to achieve industrial
importance and it is presently the fastest
growing fibre for technical end-uses. Polypropylene fibres have been widely used
in apparel, upholstery, floor coverings,
hygiene medical, geotextiles, car industry,
automotive textiles, various home textiles,wall-coverings and so on .
8/2/2019 Flame Retardant Pp
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The crystalline melting point of isotacticpolypropylene with a crystallinity of around45% and containing 90–95% isotactic materialis quoted as 165 °C.
Because of its wholly aliphatic hydrocarbonstructure, polypropylene by itself burns veryrapidly with a relatively smoke-free flameand without leaving a char residue. It has a
high self-ignition temperature (570 °C) and arapid decomposition rate compared withwood and other cellulosic materials andhence has a high flammability.
8/2/2019 Flame Retardant Pp
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While polypropylene fibres may be treated
with flame retardant finishes and back-
coatings in textile form with varying and
limited success, the ideal flame retardantsolution for achieving fibres with good
overall performance demands that the
property is inherent within the fibre.
8/2/2019 Flame Retardant Pp
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By inhibiting the initiating radicals in the pre-flame andflame zones; typically, antimony–halogen based
additives are effective here; By adding some hydrated inorganic additives which
decompose endothermically and release water, andhence withdraw heat from the substrate and dilute thecombustible volatiles;
By modifying the chemical structure of the polymer tochange its decomposition procedure and/or to improvethe compatibility with other flame retardants;
By addition of char-forming additives preferably having
an intumescent property.
8/2/2019 Flame Retardant Pp
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Most flame retardants act either in the
vapour phase or the condensed phase
through a chemical and/or physical
mechanism to interfere with the combustionprocess during heating, pyrolysis, ignition or
flame spread stages
8/2/2019 Flame Retardant Pp
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There are two main types of flame retardants
for polypropylene: namely the additive and
the reactive types.
Additive type flame retardants, generallyincorporated into the polymer by physical
means, have been widely used and include
many of the commonly used antimony–
bromine, intumescent and hydrated fillerformulations available
Disadvantage :Poor compatibility, leaching,
and a reduction in mechanical properties.
8/2/2019 Flame Retardant Pp
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Reactive flame retardants : Involves either thedesign of new, intrinsically flame-retardingpolymers or modification of existing polymersthrough copolymerisation with a flame-retarding
unit either in the chain or as a pendant group. Inthis the incorporation of even a few weightpercent of the unit into the polymer chains canlead to remarkable improvements in the overallflame retardency of the polymer .
Disadvantages :This lacks sufficient versatility inmanufacturing, processing and is uneconomical,due to the expense associated with developing anew material for use.
8/2/2019 Flame Retardant Pp
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Five principal types of generic flame retardant
systems for inclusion in polypropylene fibers
have been identified .
1. phosphorus-containing
2. halogen-containing
3. silicon-containing
4. metal hydroxide and oxide and5. Nanocomposite flame retardant formulations.
8/2/2019 Flame Retardant Pp
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The range of phosphorus-containing flame
retardants is extremely wide since the
element exists in several oxidation states.
Phosphines, phosphine oxides, phosphoniumcompounds, phosphonates, elemental red
phosphorus, phosphites and phosphate are all
used as flame retardants in polymers in
general, although, only few of these are
applicable to polyolefins and especially
polypropylene.
8/2/2019 Flame Retardant Pp
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Ammonium polyphosphate (APP) is a very
commonly used flame retardant in PP often
combined with cyclic urea–formaldehyde
resins, hydroxyethylcyanuarates orpiperazine-base species which usually
demonstrate phosphorus–nitrogen synergism.
8/2/2019 Flame Retardant Pp
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Phosphorus-containing species typically act
in the condensed phase promoting char
formation on the surface initially, which
functions as a barrier to inhibit furtherdegradation and hence starve the flame of
fuel and protect the polymer surface from
heat and air.
8/2/2019 Flame Retardant Pp
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Halogen-containing species, often in
combination with some phosphorus and
antimony-containing flame retardants,
usually act in the vapour phase by capturingthe radicals to interrupt the exothermic
oxidative flame chemical processes and thus
suppress combustion.
8/2/2019 Flame Retardant Pp
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Considerable research has shown that theaddition of relatively small amounts of silicon compounds, especially when added tointumescent formulations to pp can
significantly improve their flame retardency,through both char formation in thecondensed phase and the trapping of activeradicals in the vapour phase. Silicone-
containing flame retardants are consideredto be ‘environmentally friendly’ additivesbecause their use is claimed to lead to areduction in the harmful impact onenvironment
8/2/2019 Flame Retardant Pp
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Other advantages of the silicone-based
additives are that they can improve the
impact resistance dramatically and add the
conventional silicone properties of improved
mouldability , processibility , gloss and
electric insulating properties
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Solid phase reaction.
The incorporation of silicones often produces
slight intumescent char formation in
polypropylene, while the polymer itself burnswithout a char .
8/2/2019 Flame Retardant Pp
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The main interest for metal hydroxide flame
retardants for polypropylene lies in their low
toxicity, corrosion properties and emission of
smoke during processing and burning.
These compounds offer an attractive
alternative to halogenated formulations for
flame-retarding polypropylene. These metal
hydroxides decompose endothermically andrelease water during burning and thus reduce
the heat and temperature from the substrate
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However, very high metal hydroxide
concentrations are usually required to
achieve an acceptable degree of flame
retardancy and tend to be poor in
mechanical strength .
Typical metal hydroxide flame retardants are
Al(OH)3 and Mg(OH)2.
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During the last six years or so, nanocompositeshave been considered to be a new class of flameretardant system for polymers.
In particular, organic–inorganic nanocomposites,
comprising organically modified clay dispersed inselected polymer matrices have attractedconsiderable attention with the advantage thatthey are efficient at concentrations of 5% w/wor less . Several kinds of nanocompounds can be
used to enhance the flame retardancy of polymers in general and polypropylenespecifically, such as modified montmorillonites ,TiO2, Sb2O3 and boroxosiloxanes .
8/2/2019 Flame Retardant Pp
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Typical nanocomposites are usually prepared
by a blending process or by bulk
polymerisation and they may exist in either
an intercalated form, in which interlaminar
contact is maintained between the
aluminosilicate layers, or in an exfoliated
form, in which such registry is lost and the
layers are completely delaminated by the
incoming material and hence result with the
silicate layers fully dispersed throughout the
matrix
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Building/Construction applications as pipes,
lamp holders, stadium seats, fiber spinning
etc.
Temperature resistant tubes,pipes, etc. Textile industry.
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