The flame-retardant mechanisms involved in the polymer-clay nano-composites are described.

1. Composites technology 16.12.2008
Flame Retardant
Nanocomposites
Christophe Swistak
Valentin Chapuis
Alexandre Durussel

2. Outline
• Applications
• Introduction
– Fire hazards
– Combustion of polymers
• Flame-Retardant composites
• Nanofillers
• Flame retardancy mechanism
• Processing

3. Applications
• Flame retardant wall panels
• Flame retardant doors
• Airplanes & trains
!
!! Flame retardant ≠ Fireproof
Applications / Introduction / Flame retardant composites / Nanofillers /
Flame retardancy mechanism / Processing

4. Dangers due to fire
• Heat release (HR)
– Control intensity and speed of combustion
• « Black » smokes
– Difficult orientation of rescue squads and
victims
• Toxic gazes released during combustion
– Can lead to death
Applications / Introduction / Flame retardant composites / Nanofillers /
Flame retardancy mechanism / Processing

5. Combustion of polymers
• Process in two stages
1. Thermo-oxidative degradation
• Heat transfer
• Decomposition leading to generation of
flammable volatile products
• Diffusion of gazes through the matrix
2. Normal burning
• Combustion involving volatiles products and
oxygen
Applications / Introduction / Flame retardant composites / Nanofillers /
Flame retardancy mechanism / Processing

6. Flame-retardant composites (I)
• Conventional composites
– Polymer matrix (PP, PE, PA, …)
– Fillers
• Aluminium trihydrate AlH3
• Magnesium hydroxide MgOH
• Organic brominated compounds
– Advantages
 Well known
 No problem of dispersion of the filler
– Drawbacks
X Requires gf ~ 30-60%wt to obtain good flame retardancy
X High density, small flexibility
X Toxicity of flame retardant compounds (e.g. Br)
Applications / Introduction / Flame retardant composites / Nanofillers /
Flame retardancy mechanism / Processing

7. Flame-retardant composites (II)
• Nanocomposites
– Polymer matrix (PP, PE, PA, PS, EVA, epoxy, …)
– Nanofillers
• Layered silicates (mostly Monmorillonite (MMT))
• Spherical nanoparticles of silica
• Carbon nanotube
– Advantages
 Same flame-retardant properties with a smaller volume
fraction of filler (gf~2-10%wt)
 Easier to process (especially in injection)
 Better mechanical properties and smaller density
– Drawbacks
X Compatibility between matrix and filler
X Dispersion
Applications / Introduction / Flame retardant composites / Nanofillers /
Flame retardancy mechanism / Processing

8. Nanofillers (I)
• Structure
– Layered structure with thickness ~1nm
– High ratio length/thickness ~ 1000
– “Agglomerated” structure
MMT structure from wikipedia.org
Applications / Introduction / Flame retardant composites / Nanofillers /
Flame retardancy mechanism / Processing

9. Nanofillers (II)
• Dispersion
– Determine flame-retardant property
Kashiwagi et al., Polymer, 2004
Applications / Introduction / Flame retardant composites / Nanofillers /
Flame retardancy mechanism / Processing

10. Nanofillers (III)
• Dispersion
– Big challenge
Maximization of
Matrix/filler
interaction 
Leads to the
better flame-
retardancy
TEM pictures of PP/clay nanocomposite
Günter Beyer et al, 2002, [1]
S. Bourbigot et al, 2008, [7]
Applications / Introduction / Flame retardant composites / Nanofillers /
Flame retardancy mechanism / Processing

11. Nanofillers (IV)
• Dispersion
– Chemical process
1. Expansion
2. Compatibilization
3. Mixing / Polymerization
– Specific system for
each couple of clay
and polymer matrix
W.S. Wang et al, 2008, [9]
Applications / Introduction / Flame retardant composites / Nanofillers /
Flame retardancy mechanism / Processing

12. Nanofillers (V)
• Dispersion
– Mechanical process (separating the layers with a
high shear stress)
– Directly in the production process
– Addition of a stabilization / compatibilization
agent may be necessary
F. Samyn, S. Bourbigot et al, 2008, [7]
Applications / Introduction / Flame retardant composites / Nanofillers /
Flame retardancy mechanism / Processing

13. Flame retardancy mechanism (I)
• Formation of a thermal insulating and
low permeability char
• The char acts as a physical and
chemical barrier between the polymer
and the burning surface
Less smoke/gazes formation
Heat release rate (HRR) decrease
Applications / Introduction / Flame retardant composites / Nanofillers /
Flame retardancy mechanism / Processing

14. Flame retardancy mechanism (II)
G. Beyer et al, 2002, [1]
Reduction of the HRR of 47%
with only 5%wt of filler
Applications / Introduction / Flame retardant composites / Nanofillers /
Flame retardancy mechanism / Processing

15. Flame retardancy mechanism (III)
F. Laoutid et al. 2008, [5]
Reduction of the HRR up to 70 %
with 10%wt of filler
Applications / Introduction / Flame retardant composites / Nanofillers /
Flame retardancy mechanism / Processing

16. Processing
• In-situ Polymerization
• Polymerization in solvent
• Molten processing
1. Polymer melting
2. Add fillers
3. Physical dispersion
– Allows injection / extrusion
– Industrial process
Applications / Introduction / Flame retardant composites / Nanofillers /
Flame retardancy mechanism / Processing

17. Summary
• Important parameters to control
– Heat release rate
– Thermal and diffusion barrier
• Nanocomposites (layered silicates)
 Same or better flame-retardancy for a lower gf 
better mechanical properties
 Improvements in processability and matrix/filler
interaction
 Fillers that are non-toxic
Problems of dispersion and compatibility

18. References
[1] Nanocomposites : a new class of flame retardants for polymers, in Plastics Additives &
Compounding, October 2002
[2] Nanocomposites offer new way forward for flame retardants, in Plastics Additives &
Compounding, September/October 2005
[3] Flame retardant mechanism of polymer/clay nanocomposites based on polypropylene, H. Qin
and al., Polymer 46 (2005), pp. 8386-8395
[4] Characterization of the dispersion in polymer flame retarded nanocomposites, F. Samyn and
al., European Polymer Journal 44 (2008), pp. 1631-1641
[5] New prospects in flame retardant polymer materials: From fundamentals to nanocomposites,
F.Laoutid, et al., Mater. Sci. Eng. R(2008), doi:10.1016/j.mser.2008.09.002
[6] Flame retardant mechanism of polyamide 6-clay nanocomposites, T. Kashiwagi and al. Polymer
45, 2004, pp. 881-891.
[7] Crossed characterisation of polymer-layered silicat nanocomposite morphology: TEM, X-ray
diffraction, rheology and solid-state nuclear magnetic resonance measurements. F. Samyn,
S. Bourbigot and al. European Polymer Journal 44, 2008, pp. 1642-1653
[8] Synergism between flame retardant and modified layered silicate on thermal stability and
fire behavior of polyurethane nanocomposite foams, M. Modesti and al., Polymer Degradation
and Stability (2008), pp. 1-6
[9] Properties of novel epoxy/clay nanocomposites prepared with reactive phosphorous
containing organoclay, W.S. Wang and al., Polymer (2008), pp. 1-11
[10] A novel phosphorus-containing copolyester/monmorillonite nanocomposites with improved
flame retardancy, X.G. Ge and al., European Polymer Journal 43 (2007), pp. 2882-2890
[11] http://www.epp.goodrich.com/fyreroc/
[12] http://www.cfoam.com/fireproofcore.htm