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Preparation and analysis of nanocomposites as flame retardants
Abstract
Flame retardants are incorporated into many everyday objects that we use including our
electronics and our furniture. There are different types of flame retardants but to put it
vaguely there are 2 categories: nanocomposites that can act as flame retardants and much
older flame retardants that don’t contain a nanocomposite structure, these flame
retardants have been around for many years and even though can be beneficial to
extinguish a flame, they have been proven to cause more harm than good. For example,
they cause damage to the ozone layer due their components containing halogen atoms such
as chlorine and bromine. The new types of flame retardant include the use of nanomaterials
to enable a fast extinguish time of the flame and a much lower heat release rate. This is
done by the incorporation of the nanocomposite material or polymer into the clay in many
different ways to establish a desired effect on the flame, heat released and any toxic fumes
along with it.
It is important to significantly reduce these effects of using the regular flame retardants as
the degradation can result in harmful toxic gases that are not visible to the naked eye,
meaning that objects we see and may use on a daily basis can contain these harmful
chemicals such as house dust and can be released into the surroundings from burning
waste, especially in electronic parts in computers. The benefits of using nanocomposites for
flame retardants are much greater and significantly outweigh the cons instead of regular
composites.
Product preparation of Flame retardants by Molly Winterbottom
Nanocomposites can take on many different forms when incorporated into the clay, the 3
types we most commonly use may be described as either immiscible (aggregated),
exfoliated or intercalated. The nanocomposite that is the most conventional is the
aggregated structure where the clay doesn’t separate into layers but instead aggregates of
the clay are present. When a single extended polymer chain (or more) is intercalated
between layers of clay forming a well-ordered multilayer structure incorporating alternating
inorganic and polymeric layers containing a repeated distance between each layer, an
intercalated nanocomposite structure is formed. Finally, exfoliated (or delaminated), this
nanocomposite structure is formed when clay layers are well separated from one another
and individually dispersed within the continuous polymer matrix. Registry is maintained, in
an intercalated structure, between the clay layers unlike in the exfoliated structure where it
is lost due to the fact, they have a higher phase homogeneity than that of intercalated
structures. To enhance the nanocomposites properties, the exfoliated structure is the most
desirable structure since it is able to maximize the polymer-clay interactions making the
surface available to the polymer. However, achieving complete exfoliation of clays is not
easy, with the exceptions to a few, most polymer nanocomposites reported were found to
have intercalated nanostructures instead of exfoliated.
Figure 1 – The 3 types of nanocomposite structures; Exfoliated, intercalated and
aggregated (immiscible)
Flame-retardants delay or inhibit the spread of fire by the formation of a protective layer on
the surface of a material or by suppressing the chemical reactions in the flame. They could
be mixed with the base material (flame-retardant additives) or chemically bonded to it
(reactive flame-retardants). Additive flame-retardants don’t bind to the polymer chemically,
instead they are added to the polymer through physical mixing, therefore can be
incorporated into the polymeric mixture at any stage of its manufacturing, whereas Reactive
flame-retardants are added to the polymer via chemical reactions and once incorporated
become a permanent part of the polymeric structure but must be incorporated only during
the early stages of manufacturing. Therefore, additive flame-retardants have an added
advantage over the Reactive flame-retardants.
Figure 2 – Left: Organic Flame-retardant additives for PLA. Right: Inorganic Flame-
retardant additives for PLA
There are 2 methods of making Flame-retardants PLA (polylactic acid) which can be split into
two categories: the first way is copolymerization of reactive comonomers with PLA. And the
second being to incorporate organic or inorganic flame-retardant additives into PLA such as
organohalogen compounds and minerals such as aluminium hydroxide (ATH), magnesium
hydroxide (MDH), various hydrates and boron compounds, mostly borates. This is done
through melt of solution blending. The Flame-retardant additives include organic additives
(small-molecule phosphates, oligomers/hyperbranched polymers) and inorganic fillers
(aluminium hydroxide, hypophosphite salts and expandable graphite) and Mineral flame
retardants are typically additive, while organohalogen and organophosphorus compounds
can be either reactive or additive.1
Figure 3 – The formation of protective layer inhibiting combustion and volatiles.
Through an external heat flux, the additives can form a shield (protective layer) with low
thermal conductivity. This can reduce the heat transfer to the material from the heat
source. It then can reduce the pyrolysis gases from the degradation of the material that feed
the flame and decrease the “fuel flow”. Phosphorus exhibits high efficiency as a flame
quencher, which may be the main reason for the high flame-retardant performance of
phosphorus containing compounds. Their pyrolysis leads to thermally stable pyro- or
polyphosphoric compounds which form a protective vitreous barrier. The same can be
observed if boric acid-based additives are used along with zinc borated or low melting
glasses.
Figure 4 – heat release rate plot for polystyrene (PS), a polystyrene nanocomposite
containing iron (MMT) and one in which iron is absent (SMM).
As seen in figure 3 from the heat release plot, the polystyrene has the highest heat release,
showing that it is a poor flame retardant and releases around 1000 kw/m2
of heat. The best
out of the three is the polystyrene nanocomposite containing iron (MMT) as it has a heat
release rate lower than the remaining 2 of around 400 kw/m2
. Giving a difference of around
300 kw/m2
compared to the nanocomposite without iron and around a 600 kw/m2
difference compared to polystyrene.
In the gas phase in the Gas-phase flame-retardant mechanism, Flame-retardants can act as
flame inhibitors which can interrupt the combustion process of a radical’s reaction. This
then causes the exothermic processes to stop, leaving the system to cool down and then the
flammable gases that are being released are then reduced until they will eventually
suppress completely. The high-reactive radicals H.
and HO.
can react with other radicals in
the gas phase, such as halogenated radicals X.
resulted from flame retardant degradation.
Less reactive radicals are created which decrease the kinetic energy of the combustion, the
Gas-phase mechanism is shown below in figure 4.
Figure 5 – mechanism of HO.
and H.
radical reacting with X.
producing less reactive
radicals used to decrease the kinetic energy of the fire.
Many flame-retardant chemicals are used in consumer products and commercial goods,
such as furniture and computers, and many of these flame retardants don’t present many
concerns, however the following types often do such as: halogenated flame retardants
(organo-halogen flame-retardants that contain chlorine or bromine bonded to a carbon) and
organo-phosphorus flame-retardants that contain phosphorus bonded to a carbon. A wide
variety of flame-retardants, while having a certain amount of toxicity themselves can
degrade into other toxic compounds, in some cases, the primary toxic agent may be the
result of the degradation of the product. An example of this would-be halogenated
compounds with aromatic ring, once degraded can form dioxin derivatives, especially when
heated, such as during production, a fire, recycling or just exposure to the sun. 2
There are many different types of Flame-retardants that can release different toxic fumes to
the environment. They are categorised into 5 different types: Brominated flame-retardants,
Polybrominated diphenyl ethers (PBDE’s), Tetrabromobisphenol A (TBBPA),
Hexabromocyclododecane (HBCD) and Organophosphate flame retardants (OPFRs).
Brominated flame-retardants are the most abundantly used flame retardant as they’re used
in electronics, building materials and many consumer goods. PBDE’s are easily released from
the products they are in because they are not chemically bound. PBDE’s are known to lower
birth weight and length in children and impair neurological development. TBBPA is mainly
used in electronics like computer circuit boards but also used in paper and some textiles,
they can also be used as an additive in other flame retardants. HBCD are additives that are
mainly used in polystyrene foam in building materials. OPFRs have been identified as being
the replacement of PBDEs.
These flame-retardants can expose themselves in many forms such as house dust, leaking
out of products into the air and through the waste of burning electronic and electrical
waste. These forms of exposure can cause major health effects especially in younger
children and babies due the underdevelopment of their brains and other organs. Since
children crawl, dust in more likely to get onto their hands and food and then placed into
their mouths. These health effects include affects to the endocrine and thyroid disruption,
reproductive, nervous and immune system. Some research has shown that long exposure to
flame retardants could even lead to cancer.3
Many simple procedures can be done to reduce
the exposure caused by these flame retardants such as keeping the dust levels down in the
house by wet mopping and vacuuming frequently. Also, by washing your hands and
especially your child’s hands to reduce the hand-to-mouth contact. Avoiding purchases that
contain polyurethane foam and buy cotton, wool or polyester filled products.
Figure 6 – Char and intumescence formation
Charring is a result of a Flame retardant causing a layer of carbon to appear on the
polymer’s surface. This is caused by the dehydrating action of the Flame retardant that is
generating double bonds in the polymer. This process will then cause a carbonaceous layer
to form via cyclizing and cross-linking processes cycle.4
This layer/barrier of char acts as a
thermal insulator to heat and can separate the oxygen from the burning materials. Leading
to the amount of flammable volatile gases produced and the heat release rate being
reduced due to the prevention of heat and mass transfer.5
To summarise, all the physical and chemical characteristics produced by flame retardants
due to its nanocomposite structures and methods of preparation are highly beneficial to the
environment and the surroundings they are in, especially causing the dramatic reduction in
heat release rates and reduction of toxic chemicals from degradation.
Nanoflam (nanocomposite as a flame retardant) product analysis by Jacob Scholes
What analysis would be done?
To properly analyse a flame-retardant nanocomposite, there are many parameters we
should consider; heat release rate, peak of heat release rate, rate of carbon monoxide
production, smoke production rate, total mass loss rate, time of ignition and total peak of
heat release rate. Comparison between materials without nanocomposite incorporation and
materials which do, using these parameters should outline how useful these
nanocomposites are. The main goal for a nanocomposite as a flame retardant is to improve
the parameters listed without causing deterioration of the mechanical properties to the
polymer matrix.6
There are different morphologies concerning nanoparticles and they can
be described in three ways, aggregated, intercalated and exfoliated. The exfoliated structure
is much better in enhancing the properties of the nanocomposites compared to the other
two counterparts. The exfoliated configuration is of particular interest because it maximizes
the polymer-clay interactions making the entire surface of layers available for the polymer,
which should lead to the most significant changes in mechanical and physical properties.7
One study showed that the peak heat release rate was reduced by 40% with the addition of
an exfoliated nano-composite as opposed to without the nano-composite.8
Figure 1 – shows the three different morphologies mentioned.
Also, there are techniques we can use to analyse the nanocomposite itself to display its
physical properties which will be listed later on.
Which techniques would you use?
• Transmission electron microscope
A transmission electron microscope uses an accelerated, concentrated beam of
electrons which is shot at a very thin specimen. Once the electrons have gone
through the sample, they are detected, and this produces an image. These images
are produced with different shades according to the different densities of the
different parts of the specimen being examined. The electrons are produced by an
electron gun facing the specimen and uses an electromagnetic lens which focuses
the electrons into a very fine beam. Transmission electron microscopes are able to
produce much higher resolution images as they are not limited by wavelength such
as a light microscope. Some of the main advantages of TEM include TEMs offer the
most powerful magnification, potentially over one million times, TEM’s provide
information on element and compound structure and images are high-quality and
detailed. However, some disadvantages are the cost, training is required for
someone to operate and images produced are black and white.9
• X-ray diffractometer
XRD irradiates a material with incident X-rays, then it measures the intensities and
the scattering angles of the x-rays that are given off by interacting with the sample.
Once the X-ray beam is focused on the specimen it is diffracted by the specimen’s
crystalline phases according to Bragg’s law (A = 2d sinθ). They are diffracted because
the interaction between the X-rays and the atoms’ electrons. Using the measured
intensities, the orientation will be determined by the peak present at the value 2θ.
An intercalated nanocomposite results in an increase in basal spacing in the XRD
pattern, while the formation of an exfoliated nanocomposite leads to the complete
loss of registry between the layers and so no peak can be observed. A strong peak at
lower values of 2θ = intercalated structure. A broad peak at any 2θ = the possibility
of disorder; this disorder could be caused by exfoliation or it could be a simple
composite which is disordered. Some advantages of XRD are that it is fast and a
powerful technique for identifying structures, the sample sizes can be small and
resulting data is relatively straight forward. Some disadvantages are that the sample
should be homogenous, and samples are best to be crushed into a powder.10
• Nuclear magnetic resonance
When molecules are placed in a strong magnetic field, the nuclei of some atoms will
begin to behave like small magnets. The resonant frequencies of the nuclei are then
measured and converted into an NMR spectrum that displays all of the correct
frequencies as peaks on a graph. The height of each peak represents the number of
nuclei that resonate at each specific frequency. This is known as the intensity of
signal. The more resonating nuclei, the higher the intensity. Advantages are that it is
not invasive, and the radiation is there is not much ionizing radiation. However,
some disadvantages are that it may be too sensitive, and it is extremely expensive to
firstly buy and then keep it running.11
What information would they provide?
Some of the information that the technique TEM could provide include grain lattice type,
crystal structure, size, size distribution and homogeneity, dispersion, and chemical and
physical property of phases such as number, morphology, and structure of the phases at
nano level. 12
Figure 2 – Shows images of cross sections taken by TEM of PLA composites.
XRD can be used as another non-destructive technique and can provide
detailed information about the crystallographic structure, chemical composition, and
physical properties of materials.
One of the major advantages of NMR (solid state) is to allow the analysis of polymer–filler
interfaces due to the sensitivity of the NMR spectra and the relaxation parameters to the
local and segmental molecular motions of polymer chains. Polymer–filler interactions
normally contribute to the formation of an adsorption layer in which chain motions are
more restricted than those in the bulk, and solid-state NMR has been shown to be able to
differentiate the polymer behaviour in the interfacial region from that in the bulk.13
Nanomaterials Potential by James Skerry
The nanomaterial Nanoflam is a nanomaterial which is used mainly as a flame retardant that is effective
due it being able to form either a hydrophobic coating or a thermal barrier coating14
to protect against
heat. There are a variety of uses for this type of flame retardant which include in computer systems and
upholstery.
There are advantages and disadvantages to using Nanoflam. Before Nanoflam, compounds such as
Magnesium Hydroxide, Aluminium Hydroxide and any other compounds that contain halogens such as
chlorine and bromine were used as flame retardants. The reason why these compounds are less effective
is because the amount of heat released from the flame retardants when exposed to fire is much greater
than the amount released for Nanoflam, an effective flame-retardant releases as little heat as possible.
Another advantage of using Nanoflam is contrast to other compounds is that it is safer to handle and use.
Compounds such as Magnesium Hydroxide and Aluminium Hydroxide are alkaline compounds which if
they come into contact with the skin, it can cause irritation and injury. This is the same for any
halogenated compounds as well as the fact that if the compound contains chlorine and it releases a lot of
heat, the flame retardant can break down and potentially produce chlorine which can cause damage to
the ozone layer, which should be taken into consideration as 1 molecule of chlorine can destroy over
100,000 molecules of ozone faster than ozone can be naturally produced.
A disadvantage of using Nanoflam is that it can be expensive due to the manufacturing process and the
cost of the components needed to make it can be highly expensive. Other compounds could be more
expensive than Nanoflam which can be an advantage dependent on if it is more effective than Nanoflam.
Nanoflam has the potential to be more effective in future use in flame retardants. Nanoflam is more
effective because compared to other flame retardants, it releases the least heat compared to other flame
retardants. The graph below shows the graph of 3 different nanocomposite flame retardants with the
rate of heat release over a period of 5 minutes:
PS – Polystyrene
PS-MMT – Polystyrene nanocomposite containing iron
PS-SMM – Polystyrene nanocomposite without iron
The graph above shows that the nanocomposite containing iron was more effective because the iron
particles could absorb the heat and decrease the amount of heat emitted than a nanocomposite
without iron which means the nanoparticles absorb less heat than the nanocomposite that contained
iron.15
There are other forms of nanocomposite flame retardants other than Polymer-MMT nanocomposites
such as polymer-clay nanocomposites16
. These types of nanocomposites are better flame retardants
compared to conventional flame retardants like Magnesium or Aluminium Hydroxide, these types of
flame retardants have superior properties such as: light weight, solvent resistance and increased
thermal stability17
, meaning less heat is released compared to other compounds.
Overall, Nanoflam is a better flame retardant to use than other conventional flame retardants because it
is much safer to use compared to other alkaline flame retardants (e.g., Mg(OH)2), it causes less
environmental damage compared to halogenated flame retardants, and it has overall much more
superior properties even though the manufacturing process can be expensive.
1
D.-Y.Wang, in Novel Fire retardant Polymers and Composite Materials, 2017 (accessed 9/01/2021)
2
Dr.James G. Speight, in Environmental Organic Chemistry for Engineers, 2017 (accessed 12/01/2021)
3
https://www.niehs.nih.gov/health/topics/agents/flame_retardants/index.cfm (accessed 25/01/2021)
4
http://fr.polymerinsights.com/home/mechanisims (accessed 26/01/2021)
5
X. Qiu, Z. Li, X. Li, and Z. Zhang, “Flame retardant coatings prepared using layer by layer assembly: a
review,” Chemical Engineering Journal, vol. 334, pp. 108–122, 2018.
6
https://www.intechopen.com/books/flame-retardants/flame-retardant-polymer-
nanocomposites-and-interfaces
7
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5445768/#B2-materials-03-04580
8
https://pubs.rsc.org/en/content/articlelanding/2017/nj/c7nj02566a#!divAbstract
9
https://www.microscopemaster.com/transmission-electron-microscope.html
10
https://www.scimed.co.uk/education/what-is-x-ray-diffraction-xrd/
11
https://academic.oup.com/ilarjournal/article/42/3/189/778963
12
https://www.researchgate.net/figure/A-ring-diffraction-pattern-from-a-polycrystalline-
gold-specimen_fig5_267104201
13
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5445768/#B2-materials-03-04580
14
J.M. Lopez-Cuesta, Flame-retardant polymer nanocomposites, p540-566, 15/01/21
15
Huaili Qin, Shimin Zhang, Chungui Zhao, Guangjun Hu, Mingshu Yang, Flame retardant
mechanism of polymer/clay nanocomposites based on polypropylene, Volume 46, 15/01/21
16
Byung-Wan Jo, Seung-Kook Park, Do-Keun Kim, Mechanical properties of nano-MMT
reinforced polymer composite and polymer concrete, Volume 22, 15/01/21
17
T. Periadurai, C.T. Vijayakumar, M. Balasubramanian, Thermal decomposition and flame
retardant behaviour of SiO2-phenolic nanocomposite, Volume 89, 15/01/21

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Group report of nanoflam

  • 1. Preparation and analysis of nanocomposites as flame retardants Abstract Flame retardants are incorporated into many everyday objects that we use including our electronics and our furniture. There are different types of flame retardants but to put it vaguely there are 2 categories: nanocomposites that can act as flame retardants and much older flame retardants that don’t contain a nanocomposite structure, these flame retardants have been around for many years and even though can be beneficial to extinguish a flame, they have been proven to cause more harm than good. For example, they cause damage to the ozone layer due their components containing halogen atoms such as chlorine and bromine. The new types of flame retardant include the use of nanomaterials to enable a fast extinguish time of the flame and a much lower heat release rate. This is done by the incorporation of the nanocomposite material or polymer into the clay in many different ways to establish a desired effect on the flame, heat released and any toxic fumes along with it. It is important to significantly reduce these effects of using the regular flame retardants as the degradation can result in harmful toxic gases that are not visible to the naked eye, meaning that objects we see and may use on a daily basis can contain these harmful chemicals such as house dust and can be released into the surroundings from burning waste, especially in electronic parts in computers. The benefits of using nanocomposites for flame retardants are much greater and significantly outweigh the cons instead of regular composites. Product preparation of Flame retardants by Molly Winterbottom Nanocomposites can take on many different forms when incorporated into the clay, the 3 types we most commonly use may be described as either immiscible (aggregated), exfoliated or intercalated. The nanocomposite that is the most conventional is the aggregated structure where the clay doesn’t separate into layers but instead aggregates of the clay are present. When a single extended polymer chain (or more) is intercalated between layers of clay forming a well-ordered multilayer structure incorporating alternating inorganic and polymeric layers containing a repeated distance between each layer, an intercalated nanocomposite structure is formed. Finally, exfoliated (or delaminated), this nanocomposite structure is formed when clay layers are well separated from one another and individually dispersed within the continuous polymer matrix. Registry is maintained, in an intercalated structure, between the clay layers unlike in the exfoliated structure where it is lost due to the fact, they have a higher phase homogeneity than that of intercalated structures. To enhance the nanocomposites properties, the exfoliated structure is the most desirable structure since it is able to maximize the polymer-clay interactions making the surface available to the polymer. However, achieving complete exfoliation of clays is not easy, with the exceptions to a few, most polymer nanocomposites reported were found to have intercalated nanostructures instead of exfoliated.
  • 2. Figure 1 – The 3 types of nanocomposite structures; Exfoliated, intercalated and aggregated (immiscible) Flame-retardants delay or inhibit the spread of fire by the formation of a protective layer on the surface of a material or by suppressing the chemical reactions in the flame. They could be mixed with the base material (flame-retardant additives) or chemically bonded to it (reactive flame-retardants). Additive flame-retardants don’t bind to the polymer chemically, instead they are added to the polymer through physical mixing, therefore can be incorporated into the polymeric mixture at any stage of its manufacturing, whereas Reactive flame-retardants are added to the polymer via chemical reactions and once incorporated become a permanent part of the polymeric structure but must be incorporated only during the early stages of manufacturing. Therefore, additive flame-retardants have an added advantage over the Reactive flame-retardants. Figure 2 – Left: Organic Flame-retardant additives for PLA. Right: Inorganic Flame- retardant additives for PLA There are 2 methods of making Flame-retardants PLA (polylactic acid) which can be split into two categories: the first way is copolymerization of reactive comonomers with PLA. And the second being to incorporate organic or inorganic flame-retardant additives into PLA such as organohalogen compounds and minerals such as aluminium hydroxide (ATH), magnesium hydroxide (MDH), various hydrates and boron compounds, mostly borates. This is done through melt of solution blending. The Flame-retardant additives include organic additives (small-molecule phosphates, oligomers/hyperbranched polymers) and inorganic fillers (aluminium hydroxide, hypophosphite salts and expandable graphite) and Mineral flame
  • 3. retardants are typically additive, while organohalogen and organophosphorus compounds can be either reactive or additive.1 Figure 3 – The formation of protective layer inhibiting combustion and volatiles. Through an external heat flux, the additives can form a shield (protective layer) with low thermal conductivity. This can reduce the heat transfer to the material from the heat source. It then can reduce the pyrolysis gases from the degradation of the material that feed the flame and decrease the “fuel flow”. Phosphorus exhibits high efficiency as a flame quencher, which may be the main reason for the high flame-retardant performance of phosphorus containing compounds. Their pyrolysis leads to thermally stable pyro- or polyphosphoric compounds which form a protective vitreous barrier. The same can be observed if boric acid-based additives are used along with zinc borated or low melting glasses. Figure 4 – heat release rate plot for polystyrene (PS), a polystyrene nanocomposite containing iron (MMT) and one in which iron is absent (SMM).
  • 4. As seen in figure 3 from the heat release plot, the polystyrene has the highest heat release, showing that it is a poor flame retardant and releases around 1000 kw/m2 of heat. The best out of the three is the polystyrene nanocomposite containing iron (MMT) as it has a heat release rate lower than the remaining 2 of around 400 kw/m2 . Giving a difference of around 300 kw/m2 compared to the nanocomposite without iron and around a 600 kw/m2 difference compared to polystyrene. In the gas phase in the Gas-phase flame-retardant mechanism, Flame-retardants can act as flame inhibitors which can interrupt the combustion process of a radical’s reaction. This then causes the exothermic processes to stop, leaving the system to cool down and then the flammable gases that are being released are then reduced until they will eventually suppress completely. The high-reactive radicals H. and HO. can react with other radicals in the gas phase, such as halogenated radicals X. resulted from flame retardant degradation. Less reactive radicals are created which decrease the kinetic energy of the combustion, the Gas-phase mechanism is shown below in figure 4. Figure 5 – mechanism of HO. and H. radical reacting with X. producing less reactive radicals used to decrease the kinetic energy of the fire. Many flame-retardant chemicals are used in consumer products and commercial goods, such as furniture and computers, and many of these flame retardants don’t present many concerns, however the following types often do such as: halogenated flame retardants (organo-halogen flame-retardants that contain chlorine or bromine bonded to a carbon) and organo-phosphorus flame-retardants that contain phosphorus bonded to a carbon. A wide variety of flame-retardants, while having a certain amount of toxicity themselves can degrade into other toxic compounds, in some cases, the primary toxic agent may be the result of the degradation of the product. An example of this would-be halogenated compounds with aromatic ring, once degraded can form dioxin derivatives, especially when heated, such as during production, a fire, recycling or just exposure to the sun. 2 There are many different types of Flame-retardants that can release different toxic fumes to the environment. They are categorised into 5 different types: Brominated flame-retardants, Polybrominated diphenyl ethers (PBDE’s), Tetrabromobisphenol A (TBBPA), Hexabromocyclododecane (HBCD) and Organophosphate flame retardants (OPFRs). Brominated flame-retardants are the most abundantly used flame retardant as they’re used in electronics, building materials and many consumer goods. PBDE’s are easily released from the products they are in because they are not chemically bound. PBDE’s are known to lower birth weight and length in children and impair neurological development. TBBPA is mainly used in electronics like computer circuit boards but also used in paper and some textiles, they can also be used as an additive in other flame retardants. HBCD are additives that are
  • 5. mainly used in polystyrene foam in building materials. OPFRs have been identified as being the replacement of PBDEs. These flame-retardants can expose themselves in many forms such as house dust, leaking out of products into the air and through the waste of burning electronic and electrical waste. These forms of exposure can cause major health effects especially in younger children and babies due the underdevelopment of their brains and other organs. Since children crawl, dust in more likely to get onto their hands and food and then placed into their mouths. These health effects include affects to the endocrine and thyroid disruption, reproductive, nervous and immune system. Some research has shown that long exposure to flame retardants could even lead to cancer.3 Many simple procedures can be done to reduce the exposure caused by these flame retardants such as keeping the dust levels down in the house by wet mopping and vacuuming frequently. Also, by washing your hands and especially your child’s hands to reduce the hand-to-mouth contact. Avoiding purchases that contain polyurethane foam and buy cotton, wool or polyester filled products. Figure 6 – Char and intumescence formation Charring is a result of a Flame retardant causing a layer of carbon to appear on the polymer’s surface. This is caused by the dehydrating action of the Flame retardant that is generating double bonds in the polymer. This process will then cause a carbonaceous layer to form via cyclizing and cross-linking processes cycle.4 This layer/barrier of char acts as a thermal insulator to heat and can separate the oxygen from the burning materials. Leading to the amount of flammable volatile gases produced and the heat release rate being reduced due to the prevention of heat and mass transfer.5 To summarise, all the physical and chemical characteristics produced by flame retardants due to its nanocomposite structures and methods of preparation are highly beneficial to the environment and the surroundings they are in, especially causing the dramatic reduction in heat release rates and reduction of toxic chemicals from degradation. Nanoflam (nanocomposite as a flame retardant) product analysis by Jacob Scholes What analysis would be done? To properly analyse a flame-retardant nanocomposite, there are many parameters we should consider; heat release rate, peak of heat release rate, rate of carbon monoxide
  • 6. production, smoke production rate, total mass loss rate, time of ignition and total peak of heat release rate. Comparison between materials without nanocomposite incorporation and materials which do, using these parameters should outline how useful these nanocomposites are. The main goal for a nanocomposite as a flame retardant is to improve the parameters listed without causing deterioration of the mechanical properties to the polymer matrix.6 There are different morphologies concerning nanoparticles and they can be described in three ways, aggregated, intercalated and exfoliated. The exfoliated structure is much better in enhancing the properties of the nanocomposites compared to the other two counterparts. The exfoliated configuration is of particular interest because it maximizes the polymer-clay interactions making the entire surface of layers available for the polymer, which should lead to the most significant changes in mechanical and physical properties.7 One study showed that the peak heat release rate was reduced by 40% with the addition of an exfoliated nano-composite as opposed to without the nano-composite.8 Figure 1 – shows the three different morphologies mentioned. Also, there are techniques we can use to analyse the nanocomposite itself to display its physical properties which will be listed later on. Which techniques would you use? • Transmission electron microscope A transmission electron microscope uses an accelerated, concentrated beam of electrons which is shot at a very thin specimen. Once the electrons have gone through the sample, they are detected, and this produces an image. These images are produced with different shades according to the different densities of the different parts of the specimen being examined. The electrons are produced by an electron gun facing the specimen and uses an electromagnetic lens which focuses the electrons into a very fine beam. Transmission electron microscopes are able to produce much higher resolution images as they are not limited by wavelength such as a light microscope. Some of the main advantages of TEM include TEMs offer the most powerful magnification, potentially over one million times, TEM’s provide information on element and compound structure and images are high-quality and detailed. However, some disadvantages are the cost, training is required for someone to operate and images produced are black and white.9
  • 7. • X-ray diffractometer XRD irradiates a material with incident X-rays, then it measures the intensities and the scattering angles of the x-rays that are given off by interacting with the sample. Once the X-ray beam is focused on the specimen it is diffracted by the specimen’s crystalline phases according to Bragg’s law (A = 2d sinθ). They are diffracted because the interaction between the X-rays and the atoms’ electrons. Using the measured intensities, the orientation will be determined by the peak present at the value 2θ. An intercalated nanocomposite results in an increase in basal spacing in the XRD pattern, while the formation of an exfoliated nanocomposite leads to the complete loss of registry between the layers and so no peak can be observed. A strong peak at lower values of 2θ = intercalated structure. A broad peak at any 2θ = the possibility of disorder; this disorder could be caused by exfoliation or it could be a simple composite which is disordered. Some advantages of XRD are that it is fast and a powerful technique for identifying structures, the sample sizes can be small and resulting data is relatively straight forward. Some disadvantages are that the sample should be homogenous, and samples are best to be crushed into a powder.10 • Nuclear magnetic resonance When molecules are placed in a strong magnetic field, the nuclei of some atoms will begin to behave like small magnets. The resonant frequencies of the nuclei are then measured and converted into an NMR spectrum that displays all of the correct frequencies as peaks on a graph. The height of each peak represents the number of nuclei that resonate at each specific frequency. This is known as the intensity of signal. The more resonating nuclei, the higher the intensity. Advantages are that it is not invasive, and the radiation is there is not much ionizing radiation. However, some disadvantages are that it may be too sensitive, and it is extremely expensive to firstly buy and then keep it running.11 What information would they provide? Some of the information that the technique TEM could provide include grain lattice type, crystal structure, size, size distribution and homogeneity, dispersion, and chemical and physical property of phases such as number, morphology, and structure of the phases at nano level. 12
  • 8. Figure 2 – Shows images of cross sections taken by TEM of PLA composites. XRD can be used as another non-destructive technique and can provide detailed information about the crystallographic structure, chemical composition, and physical properties of materials. One of the major advantages of NMR (solid state) is to allow the analysis of polymer–filler interfaces due to the sensitivity of the NMR spectra and the relaxation parameters to the local and segmental molecular motions of polymer chains. Polymer–filler interactions normally contribute to the formation of an adsorption layer in which chain motions are more restricted than those in the bulk, and solid-state NMR has been shown to be able to differentiate the polymer behaviour in the interfacial region from that in the bulk.13 Nanomaterials Potential by James Skerry The nanomaterial Nanoflam is a nanomaterial which is used mainly as a flame retardant that is effective due it being able to form either a hydrophobic coating or a thermal barrier coating14 to protect against heat. There are a variety of uses for this type of flame retardant which include in computer systems and upholstery. There are advantages and disadvantages to using Nanoflam. Before Nanoflam, compounds such as Magnesium Hydroxide, Aluminium Hydroxide and any other compounds that contain halogens such as chlorine and bromine were used as flame retardants. The reason why these compounds are less effective is because the amount of heat released from the flame retardants when exposed to fire is much greater than the amount released for Nanoflam, an effective flame-retardant releases as little heat as possible. Another advantage of using Nanoflam is contrast to other compounds is that it is safer to handle and use. Compounds such as Magnesium Hydroxide and Aluminium Hydroxide are alkaline compounds which if they come into contact with the skin, it can cause irritation and injury. This is the same for any halogenated compounds as well as the fact that if the compound contains chlorine and it releases a lot of heat, the flame retardant can break down and potentially produce chlorine which can cause damage to the ozone layer, which should be taken into consideration as 1 molecule of chlorine can destroy over 100,000 molecules of ozone faster than ozone can be naturally produced. A disadvantage of using Nanoflam is that it can be expensive due to the manufacturing process and the cost of the components needed to make it can be highly expensive. Other compounds could be more expensive than Nanoflam which can be an advantage dependent on if it is more effective than Nanoflam. Nanoflam has the potential to be more effective in future use in flame retardants. Nanoflam is more effective because compared to other flame retardants, it releases the least heat compared to other flame retardants. The graph below shows the graph of 3 different nanocomposite flame retardants with the rate of heat release over a period of 5 minutes: PS – Polystyrene PS-MMT – Polystyrene nanocomposite containing iron PS-SMM – Polystyrene nanocomposite without iron
  • 9. The graph above shows that the nanocomposite containing iron was more effective because the iron particles could absorb the heat and decrease the amount of heat emitted than a nanocomposite without iron which means the nanoparticles absorb less heat than the nanocomposite that contained iron.15 There are other forms of nanocomposite flame retardants other than Polymer-MMT nanocomposites such as polymer-clay nanocomposites16 . These types of nanocomposites are better flame retardants compared to conventional flame retardants like Magnesium or Aluminium Hydroxide, these types of flame retardants have superior properties such as: light weight, solvent resistance and increased thermal stability17 , meaning less heat is released compared to other compounds. Overall, Nanoflam is a better flame retardant to use than other conventional flame retardants because it is much safer to use compared to other alkaline flame retardants (e.g., Mg(OH)2), it causes less environmental damage compared to halogenated flame retardants, and it has overall much more superior properties even though the manufacturing process can be expensive. 1 D.-Y.Wang, in Novel Fire retardant Polymers and Composite Materials, 2017 (accessed 9/01/2021) 2 Dr.James G. Speight, in Environmental Organic Chemistry for Engineers, 2017 (accessed 12/01/2021) 3 https://www.niehs.nih.gov/health/topics/agents/flame_retardants/index.cfm (accessed 25/01/2021) 4 http://fr.polymerinsights.com/home/mechanisims (accessed 26/01/2021) 5 X. Qiu, Z. Li, X. Li, and Z. Zhang, “Flame retardant coatings prepared using layer by layer assembly: a review,” Chemical Engineering Journal, vol. 334, pp. 108–122, 2018. 6 https://www.intechopen.com/books/flame-retardants/flame-retardant-polymer- nanocomposites-and-interfaces 7 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5445768/#B2-materials-03-04580 8 https://pubs.rsc.org/en/content/articlelanding/2017/nj/c7nj02566a#!divAbstract 9 https://www.microscopemaster.com/transmission-electron-microscope.html 10 https://www.scimed.co.uk/education/what-is-x-ray-diffraction-xrd/ 11 https://academic.oup.com/ilarjournal/article/42/3/189/778963 12 https://www.researchgate.net/figure/A-ring-diffraction-pattern-from-a-polycrystalline- gold-specimen_fig5_267104201
  • 10. 13 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5445768/#B2-materials-03-04580 14 J.M. Lopez-Cuesta, Flame-retardant polymer nanocomposites, p540-566, 15/01/21 15 Huaili Qin, Shimin Zhang, Chungui Zhao, Guangjun Hu, Mingshu Yang, Flame retardant mechanism of polymer/clay nanocomposites based on polypropylene, Volume 46, 15/01/21 16 Byung-Wan Jo, Seung-Kook Park, Do-Keun Kim, Mechanical properties of nano-MMT reinforced polymer composite and polymer concrete, Volume 22, 15/01/21 17 T. Periadurai, C.T. Vijayakumar, M. Balasubramanian, Thermal decomposition and flame retardant behaviour of SiO2-phenolic nanocomposite, Volume 89, 15/01/21