flame retardent polyester
TRANSCRIPT
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Seminar
on
Flame Retardent Synthetic Fibres
By : Raghav Mehra
Mtech 1st year
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Contents
Introduction
Why use of flame retardants?
Burning of fibres
Requirements for flame retardantsFlame Retardant Mechanism
Types of flame retardants
Application Techniques
Thermoplastic fibers
Flame Retardant (FR) Pet Fibers through P-N SynergismFlame Retardancy Testings
Toxicology
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INRODUCTION
Fire is the result of three ingredients:
Heat
Fuel
Oxygen.
Heat produces flammable gases from the pyrolysis of polymer. Then, an
adequate ratio between these gases and oxygen leads to ignition of the
polymer.
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COMBUSTION CYCLE
The combustion leads to a production of heat that is spread out (delta H1) and feed
back (delta H2). This heat feed back pyrolysis the polymer and keeps the combustion
going.
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Air (oxygen)
Ignition source
Fuel
FIRE
Air (oxygen)
Fuel
Ignition source
Fire: when all sides
are connected
No Fire: when any one side
is missing
The FireTriangle
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Why use of Flame Retardants ?
In most cases polymers initiate or propagate fires because,
being organic compounds, they decompose to volatile
combustible products when they are exposed to heat.
In many fields such as electrical, electronic, transport,
building, etc the use of organic polymers is restricted because
of their flammability
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Use of synthetic polymers has greatly increased. In order to
lower the "fire risk" and the "fire hazard of these synthetic
polymers. flame retardants need to be added into the
polymer.
The role of these additives is to :Slow down polymer combustion and degradation (fire
extinction),
Reduce smoke emission,
Avoid dripping
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Fire Dynamics
The goals for fire retardant can be simply stated in the followingitems
1. Prevent the fire or retard its growth and spread i.e. the flash
over :
Control fire properties of combustible items,
Provide for suppression of the fire.
Flash over time vs fire retardant use
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2. Protect occupant from the fire effects :
Provide timely notification of the emergency,
Protect escape routes,
Provide areas of refuge where necessary and possible.
Smoke release vs fire spread
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3. Minimize the impact of fire:
Provide separation by tenant, occupancy, or maximum area.Maintain the structural integrity of property,
Provide for continued operation of shared properties.
4. Support fire service operations:Provide for identification of fire location,
Provide reliable communication with areas of refuge,
Provide for fire department access, control, communication, and
selection.
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5. To increase the escape time of persons.
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Burningoffibers
The burning behavior of the fibers depends on / determined by a
number of thermal transition temperatures and thermodynamic
parameters
Tg - glass transition temperatureTm - transition temperature
(Tp) pyrolysis temperature and
(Tc) the onset of flaming combustion
Lower the Tc (and usually Tp) and hotter the flame, more flammable
is the fiber
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LOI (limiting oxygen index) measures the inherent burning character
of the material.
Fibers that have a LOI values of21 or below ignite easily and burn
rapidly in air (20.8% O2).
LOI values above 21 ignite and burn more slowly.
When LOI values rise above 26-28, fibres and textiles may be
considered to be flame retardant and will pass most of the flame
fabric ignition tests in horizontal and vertical direction.
Limiting OxygenIndex (LO
I)
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Fiber Tg (soften)
oC
Tm (melt)
oC
Tp (pyrolysis)
oC
Tc (ignition)
oC
LOI (%)
Wool - - 245 570-600 25
Cotton - - 350 350 18.4
Viscose - - 350 420 18.9
Nylon 6 50 215 431 450 20-21.5
Nylon 6,6 50 265 403 530 20-21.5
Polyester 80-90 255 420-447 480 20-21
Acrylic 100 >220 290 (with
decomposition)
>250 18.2
Polypropylene -20 165
470 550 1
8.6
Modacrylic 180 >180 450 37-39
PVC 180 >180 450 37-39
meta-Aramid 275 375 410 >500 29-30
para-Aramid 340 560 >590 >550 29
LOI values of different fibers
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Points to be kept in mind while selecting and designing
flam
e pr
otec
tiv
ec
lothi
ng:
The thermal or burning behavior of textile fibers
The influence of fabric structure and garment shape on the burning
behaviour
Selection of non-toxic, smoke free flame retardants additives or
finishes
Design of protective garment depending or its usage with comfortproperties
The intensity of ignition source
The oxygen supply
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Requirements for flame retardants
Fire retardant properties Commence thermal activity before and during the thermal decompositionof the
Polymer
Not generate any toxic gases beyond those produced by the degrading
polymer itself
Not increase the smoke density of the burning polymer
Mechanical properties
Not significantly alter the mechanical properties of the polymer
Be easy to incorporate into the host polymer
Be compatible with the host polymer
Be easy to extract/remove for recyclability of the polymer
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Physical properties Be colourless or at least non-discolouring
Have good light stability
Be resistant towards ageing and hydrolysis
Not cause corrosion
Health and Eenvrionmental properties
Not have harmful health effects
Not have harmful environmental properties
Commercial viability
Be commercially available and cost effective
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Burning and Flame Retardant
Mechanism:
Flame retardants function by their interaction or interference with one of
the three required components of fire:
A combustible substance or fuel.
Heat, supplied either externally or from the combustion process itself.
An oxidizing gas, primarily oxygen.
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1. Dilution:
Reducing the total quantity of combustible material improves overall
flame retardation.
For example; madding fillers, such as clays, to polymer systems
reduces flammability.
In some cases, such as glass fiber reinforced composites, the glass
fiber stiffens the polymer. On exposure to heat or a flame, the glass may
prevent the polymer from melting away from the flame.
In addition, the glass act as a heat sink so that less energy input is
required to ignite the polymer on a second exposure to heat3.
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Example- calcium carbonate decomposes at 825oC to generate the
solid(calcium oxide), and the gas(carbon dioxide); these products do not
support combustion.
Some materials decompose to produce water vapour as the
noncombustible gas.
Example- Aluminumoxide trihydrate (Al2O
3.3H
2O) begins to decompose
at 230oC with the release of34.5 wt% of its original mass as water vapour.
Typically, 50-100 parts by weight of these compounds are required per
100 parts of polymer to achieve flame retardation.
2. Generationof Noncombustible
gas:
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3. Gas-Phase , Free-Radical inhibition:
On Combustion: hydrocarbons fragments vaporize, react with oxygen andform free radicals.
Free radical formation is highly exothermic,
The process continues unless free-radical formation is interrupted and stable
species are produced.
HO. + CO -> CO2+ H. Highly Exothermic
H.+ O2
-> HO. + O. Chain Branching
O. + HBr -> HO. + Br. Chain Transfer
HO. + HBr -> H2O + Br. Chain Termination
The HBr from the decomposing brominated compound deactivates the free
radicals in the vapor phase.
Chlorinated compounds function in the same manner.
In practice, often twice as much chlorine-containing compound is required as
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Antimony tribromide forms a dense white smoke that snuffs the flame by
excluding oxygen from the front of the flame.
Chlorinated compounds function in the same manner.
Generally, twice as much chlorine-containing compound is required as bromine-containing compound.
Compounds containing fluorine generally exist as functional polymers
Very stable and decompose only at high temperature.
Hydrofluoric acid when liberated is an effective deactivator.
Antimony oxide acts as a synergist with halogens, particularly chlorine and
bromine.
Almost ineffective if used without halogen.
Sb2O3 + 6HBr 2SbBr3 + 3H2O
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4. Solid-PhaseChar Formation
Formation of layer of char from from insulating or minimally
combustible material
reduces volatilization of active fragments and absorbs and dissipatesheat.
The effectiveness of the flame retardant is specific for each polymer
For example, phosphorous based flame retardants are effective in
producing minimally combustible char in phenylene oxide-ether polymers,but are essentially ineffective in styrenic polymers
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5.The formation of a glassy
interface on pyrolysis:
Used mainly for borate-derived finishes
Deprive the flame of the oxidizable substrate and hinder further
flame propogation.
Borax/Boric acid is effective on cotton
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Categories of flame retardants
Reactive type:
Added during the polymerisation process
Become an integral part of the polymer.
The result is a modified polymer with flame retardant
properties and different molecular structure compared to theoriginal polymer molecule.
Are used mainly in thermosets
Additive type:
Incorporated into the polymer prior during or after
polymerisation.Not chemically bonded to the polymer.
Used especially in thermoplastics.
If they are compatible with the plastic they act as
plasticizers, otherwise they are considered as fillers.
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Inorganic flame retardants
Organophosphorus flame retardants
Nitrogen-based flame retardants
Halogenated flame retardants
Barrier technologies i.e intumescent systems
Flame retardents cam also be
classified as:
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1. Inorganic flame retardants
Generally are metal hydroxides
Functionas smoke suppressants.
Widely used as substitutes tobrominated flame retardants.
Added as fillers into the polymer
Considered as immobile
Types of inorganic flame retardents:-
Aluminium hydroxide
Magnesium hydroxideAmmonium polyphosphate
Red phosphorus
Antimony trioxides
Zinc borate
Zinc hydroxystannate (ZHS) and Zinc stannate (ZS)
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1.Aluminium hydroxide (ATH)
Available in a variety of particle sizesheat sink effect
Due to the dilution of combustible gases by the water formed as a result of
dehydroxylation.
Alumina formed as a result of thermal degradation of ATH slightly above
200
C high loading levels
2 Magnesium hydroxide
Acts, in the same way as ATH,Thermally decompose sat slightly higher temperatures around 325 C.
Combinations of ATH and magnesiumhydroxide function as very efficient
smoke suppressants in PVC.
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E
fficient as a flame retardant in oxygen containing polymers such aspolycarbonates, polyethylene terephatalate (PET), polyamide and phenolic
resins.
Flame retardancy takes place due to formation of phosphorus-oxygenbonds
that reduces the ester linkages into cross linking aromatic structures with
lesservolatility.
Drawbacks:-
The red colour that could lead to discoloration of polymers
The formation of toxicphosphine gas during combustion and long termstorage
3. Red phosphorus
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4. Ammonium polyphosphate (APP)
Used as an acid source in intumescent systems
Effective in polyamides
5. Antimony trioxideAlone does not function as a flame retardant
But in combination with halogenated flame retardants it functions as a
synergist.
Advantage:addition ofantimony trioxide is to reduce the amount of halogenated
flame retardants applied to thepolymer.
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6. Zinc borate
Used mainly in PVC
Cannot be used alone acts as synergist together with brominated
compounds.
Used as alternative non-toxic synergists to Antimony trioxide in PVC
and other halogen-containing polymer systems.
Acts as fillers
7. Zinc hydroxystannate (ZHS)and Zinc stannate (ZS)
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2. Organophosphorus Flame Retardants
Are primarily phosphate esters
Manly used for cellulose fibres
Types of Organophosphorus Flame Retardants:-
Triethyl phosphate
Aryl phosphates
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Tri
ethyl phospha
teCan be used alone or together with a bromine synergist, such as antimony
trioxide
Used for unsaturated polyester resins
Arylphosphates
Include triphenyl-, isopropyl-, andt-butyl-substitutedtriaryl and cresylphosphates.
Used for phthalate plasticized PVC
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3.Nitrogen-based flame retardants
Inhibit the formation of flammable gases
Used in polymers containing nitrogen such as polyurethane andpolyamide
Examples:
melamines and melamine derivatives
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4.Halogenated flame retardants
Primarily based on chlorine and bromine
React with flammable gases to slow or prevent the burning process
Polybrominateddiphenylethers (PBDEs) form an important class of
halogenated flame retardents
Halogenated flame retardants can be divided into three classes:
Aromatic, including PBDEs in general and PentaBDE in particular.
Cycloaliphatic, including hexabromocyclododecane (HBCDD).
Aliphatic
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5. Barrier technologies
(Intumescent system)
Involve layers of materials that provide fire resistance.(
Examples-
boric acid-treated cotton material sused in mattresses , blends of
natural and synthetic fibers used in furniture and mattresseshigh performance synthetic materials used in fire fighter uniforms
and space suits.
Almost all intumescent systems comprise, in general, of three basic
components
a dehydrating component, such as APP a charring component, such as pentaerythritol (PER)
a gas source, often a nitrogen component such as melamine
The main function of APP is to catalyse the dehydration reaction of
other components in theI
ntumescent system
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Other intumescent systems :
Expandable graphite and silica-based and metal hydroxide compounds,
incorporated as nanocomposites
Extended nanoparticles of clay as char-forming fillers for good fire
protection.
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Application Techniques:
Two-bath process
Suspensions and emulsions:
Solvent suspensions Water-in-oil emulsions
Oil-in-waterEmulsions
Cellulose-ester process:
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Flame retardancy of the synthetic fibers is obtained by
Mechanically building the retardant with the polymer before it is
drawn into a fiber, or
Chemically modifying the polymer itself. Incorporation of
Chemicals in the dope before spinning the fiber fiber has not been
very successful.
Binders are also used
Experimental finishes using graft polymerization, in situ
polymerization of phosphorous-containing vinyl monomers or
surface halogenation of the fibers also have been reported.
Thermoplastic fibers
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Flame Retardant (FR) Pet Fibers
thr
oughP
-N S
yner
gism
Acrylamide-grafted-phosphorylated (AM-g-P) PET fibers
containing just 0.189% phosphorus on-weight-of-fiber (owf).
Methacrylamide-grafted-phosphorylated (MAm-g-P) polyester
fibers at the 0.77% phosphorus content level.
Efficiency of phosphorus in presence of nitrogen that was
achieved was at 263% for acrylamide (AM) system
A very small amount of the FR chemical could impart fire
resistance of very high order to polyester.
This is attributed to P-N synergism in case of the FR polyester
system when the nitrogen is in the amido form present in AM and
MAm monomers.
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Two types of groups of vinyl monomers are used -
N-deficient,
Aacrylic acid (AA) and Methacrylic acid (MAA), and the other
N-containing ones like
Acrylonitrile (AN), Acrylamide (AM), and Mthacrylamide (MAm).
The chemical initiation method
Initiator -benzoyl peroxide(0.125%)
On heating,
The benzoyl peroxide decomposes to give a free radical,
abstracts a H atom from another chain. The free radical formed reacts with the monomer molecules to form a chain
on the backbone
This chain propagates till its termination in the bath at a later stage.
Thus the graft is incorporated in the poly (ethylene terephthalate) chain
molecule.
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P
hosphor
yla
ti
on ofGra
fted P
olyester
Fibres
Carried out by treatment of
phosphorus oxychloride in dry benzene along with
2% pyridine as a catalyst in reflux condenser
for1 6 h at 60 110C.
After completion of the reaction,
samples refluxed with benzene for 4 h,
stored in P2O
5desiccators.
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Synergistic Influence of Amido Nitrogen in P-N
Bond in FRPolyester Fibers
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MoistureAbsorptionofGrafted-Phosphorylated
Polyester Fibers
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Dyeability of Grafted-phosphorylated Polyester
Fibers with Cationic and Acid Dyes
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Flame Retardancy Testing
observations made are:
The ease with which the material ignites
The duration of flaming
The duration of afterglowThe extent of burning and length of char
The duration of flaming and smoldering
Assessment of detectable amounts of smoke
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The Federal test
Test 16 CFR1610
16 CFR1615/1616
The National Firefighters Protection Association (NFPA) ASTM D2863-00
The Room CornerItem Test (ISO 9705)
The Cone Calorimeter Test (ISO 5660)
LIFT apparatus test (ISO 5658)
UL 94 of underwriters laboratory Fire resistance
Flammability:
Variousflame RetardantTestings
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Of greatest concern are those with halogens attached to the
carbon backbone, particularly the halogens: chlorine andbromine.
Brominated flame retardants (BFRs), are widely used
cost effective means
durability
performance of the material.Three most commonly used BFs are penta-, octa- and Deca-
brominated diphenyl ethers.
Collectively they are referred to as polybrominateddiphenyl
ethers, or PBDEs
Chlorinated flame retardants (CFRs ) are used in textiles,
paints and coatings, plastics and insulation foams.
chlorine containing flame retardants persist in the
environment and may accumulate in the tissues of humans
and other animals.
Toxicology
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BFRs are very stable-they do not break down easily in the environment
Attach to particles and accumulate in media such as dust and
sediments.
BFRs also are light enough and are transported long distances through
the atmosphere.
Chemicals are readily absorbed by the body where they accumulate in
fatty tissues.
BFRs disrupt thyroid function , causing hyperactivity and problemswith learning and memory.