1. Parameters for the thermal decomposition of epoxy resin/carbon fiber composites in cone calorimeter 4 th ICHS Conference, September 14, 2011 D. Quang Dao J. Luche, F. Richard T. Rogaume C. Bourhy-Weber S. Ruban L. Bustamante Valencia

2. S. Ruban – ICHS2011, Paper No. 182, Sept. 14 th 2011 2 Public Epoxy resin/carbon fiber composite wall (few cm) Context The high-pressure (70 MPa/10.1 kpsi) fully wrapped epoxy resin/carbon fiber composite cylinder is currently the preferred option for fuel cell electric vehicle Epoxy resin/carbon fiber composite cylinder Liner: H 2 tightness (few mm) Cost Gravimetric capacity Volumetric capacity Light weight Excellent mechanical performance High capacity of H 2 storage Good chemical and electrical resistance H 2 vehicle refilling station Cylinder connector Fire safety strategy: preventing the cylinder from bursting Releasing hydrogen through a thermal pressure relief device and/or using a thermal protection

3. S. Ruban – ICHS2011, Paper No. 182, Sept. 14 th 2011 3 Public Objective To optimize the design of the fire protection of the cylinder by improving the understanding of the thermal behavior of the epoxy resin/carbon fiber composites The thermal behavior is influenced by (Pilling et al.) : Decomposition temperature Carbon fiber fraction Nature of carbon fiber Experiments showed: CF fraction & temperature Conductivity & decomp. rate Fire resistance of composite The thermal parameters such as mass loss, mass loss rate, piloted ignition time, thermal response parameter and temperature of ignition are investigated

4. S. Ruban – ICHS2011, Paper No. 182, Sept. 14 th 2011 4 Public Materials studied The epoxy resin/carbon fiber composites are pre-impregnated bands of commercial references Two representative references are tested: 56 vol% Carbon fiber 59 vol% Carbon fiber Results of elementary analysis Thermal properties measured These results are key to understand the fire behavior of the composite samples The carbon fiber fraction [vol%] is determined experimentally by the acid attack method: 1. Density measurement of the virgin composite 2. Resin dissolution in sulfuric acid +H 2 O 2 3. Mass measurement of the fibers (known density)

5. S. Ruban – ICHS2011, Paper No. 182, Sept. 14 th 2011 5 Public HORIBA PG250 IRTF 13 HORIBA PG250 FTIR 13 Cone calorimeter experiments Heat fluxes: 14-75 kW.m -2 Spark ignition was used Atmosphere: air Test procedure: ISO 5660 100 ± 0.5 mm long × 100 ± 0.5 mm wide × 10.1 ± 1.5 mm thick Sample masses Measurements: Mass loss Masse loss rate (MLR) Piloted ignition time (t ig ) In-depth temperature Two k-type thermocouples in-depth Composite samples

6. S. Ruban – ICHS2011, Paper No. 182, Sept. 14 th 2011 6 Public Ignition time and critical heat flux (CHF) Where: q  e : Heat flux [kW.m -2 ] T ig, T  : Ignition and ambient Temp. [K] : Thermal conductivity [kW.m -1.K -1 ]  : Density [g.m -3 ] C p : Thermal capacity [kJ.g -1.K -1 ] The model of Hopkins and Quintiere (1996) for t ig : CF fraction & temperature t ig & critical heat flux Fire resistance of composite t = 0 s is the exposition to external heat flux

7. S. Ruban – ICHS2011, Paper No. 182, Sept. 14 th 2011 7 Public Thermal parameters TRP: Thermal response parameter characterizes the material resistance to generate a gas combustible mixture P: Thermal inertia is a measurement of a material ability to resist to a temperature variation Allows calculation of TRP & P

8. S. Ruban – ICHS2011, Paper No. 182, Sept. 14 th 2011 8 Public In-depth temperature Summary of the thermal parameters The ignition temperatures of samples are between 240 °C and 300 °C 56 vol% 59 vol%

9. S. Ruban – ICHS2011, Paper No. 182, Sept. 14 th 2011 9 Public Mass loss and mass loss rate Heat fluxIgnition timeMass loss 56 vol% 59 vol% 56 vol%

10. S. Ruban – ICHS2011, Paper No. 182, Sept. 14 th 2011 10 Public 1) Resin devolatilization 2) Resin decomposition and production of liquid residue 3) Acceleration of the decomposition rate & combustion of the liquid residue 4) Char pyrolysis and oxidization The four stages are: Heat flux = 50 kW.m -2 Decomposition stages The thermal decomposition of the epoxy resin / carbon fiber composite takes place in four stages

11. S. Ruban – ICHS2011, Paper No. 182, Sept. 14 th 2011 11 Public Stage 1 Stage 2 Stage 3 Stage 4 Sample combustion in cone calorimeter Heat flux = 50 kW.m -2

12. S. Ruban – ICHS2011, Paper No. 182, Sept. 14 th 2011 12 Public Mass loss rate MLR The increase of carbon fiber fraction leads to the MLR peak amplitude decrease at a given external heat flux Heat flux MLR peak width MLR amplitude Thermal resistance In accordance to the observations of Pilling et al. 56 vol% 59 vol%

13. S. Ruban – ICHS2011, Paper No. 182, Sept. 14 th 2011 13 Public Heat of gasification Where: L: Heat of gasification [kJ.g -1 ] q fl : Heat flux of the flame [kW.m -2 ] m  : Specific MLR (SMLR) [g.s -1.m -2 ] T ig, T  : Ignition and ambient Temp. [K]  : Emissivity [-] σ: Stefan-Boltzmann constant [W.m -2.K -4 ] T v : Vaporisation temperature [K] CF vol% TRP (volatile production resist) L (energy to produce volatiles)

14. S. Ruban – ICHS2011, Paper No. 182, Sept. 14 th 2011 14 Public Conclusion The influence of the carbon fiber volume fraction on fire behavior of two epoxy resin (56 and 59 vol% CF) composites was assessed: The increase of the carbon fiber fraction in the composites leads to a lower thermal resistance of the material It was found that all the parameters that characterize the material thermal resistance such as piloted ignition time, thermal response parameter, heat of gasification, thermal inertia and critical heat flux for ignition, decrease when the carbon fiber volume fraction increases from 56 to 59 vol% The thermal decomposition of the composite occurs in four stages: devolatilisation, solid to liquid transition, combustion of liquid residue and char formation The choice of an optimal carbon fiber fraction is critical to maintain simultaneously good mechanical and thermal resistance properties for epoxy resin/carbon fiber composites

15. S. Ruban – ICHS2011, Paper No. 182, Sept. 14 th 2011 15 Public Acknowledgements To OSEO for the funding for this project To all the team of the Pprime Institute for the laboratory work and their scientific support

16. S. Ruban – ICHS2011, Paper No. 182, Sept. 14 th 2011 16 Public Thank you! Sidonie Ruban sidonie.ruban@airliquide.com