4 th ICHS Conference, September 14, 2011

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

2. Context Gravimetric capacity Cost Volumetric capacity 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 • Light weight • Excellent mechanical performance • High capacity of H2 storage • Good chemical and electrical resistance Cylinder connector H2 vehicle refilling station Fire safety strategy: preventing the cylinder from bursting Releasing hydrogen through a thermal pressure relief device and/or using a thermal protection Epoxy resin/carbon fiber composite wall (few cm) Liner: H2 tightness (few mm)

3. Objective Experiments showed: CF fraction & temperature Conductivity & decomp. rate Fire resistance of composite To optimize the design of the fire protection of the cylinder by improving the understanding of the thermalbehavior 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 The thermal parameters such as mass loss, mass loss rate, piloted ignition time, thermal response parameter and temperature of ignition are investigated

4. Materials studied Two representative references are tested: • 56 vol% Carbon fiber • 59 vol% Carbon fiber The epoxy resin/carbon fiber composites are pre-impregnated bands of commercial references Results of elementary analysis 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: • Density measurement of the virgin composite • Resin dissolution in sulfuric acid +H2O2 • Mass measurement of the fibers (known density) Thermal properties measured

5. Cone calorimeter experiments 13 13 HORIBA HORIBA IRTF FTIR PG250 PG250 Composite samples Two k-type thermocouples in-depth 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 (tig) • In-depth temperature Heat fluxes: 14-75 kW.m-2 Spark ignition was used Atmosphere: air Test procedure: ISO 5660

6. Ignition time and critical heat flux (CHF) CF fraction & temperature tig & critical heat flux Fire resistance of composite t = 0 s is the exposition to external heat flux Where: • qe: Heat flux [kW.m-2] • Tig, T: Ignition and ambient Temp. [K] • : Thermal conductivity [kW.m-1.K-1] • : Density [g.m-3] • Cp: Thermal capacity [kJ.g-1.K-1] The model of Hopkins and Quintiere (1996) for tig:

7. 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. In-depth temperature 59 vol% 56 vol% The ignition temperatures of samples are between 240 °C and 300 °C Summary of the thermal parameters

9. Mass loss and mass loss rate 56 vol% 59 vol% Heat flux Ignition time Mass loss 56 vol% 59 vol%

10. Decomposition stages The thermal decomposition of the epoxy resin / carbon fiber composite takes place in four stages The four stages are: 1) Resin devolatilization 2) Resin decomposition and production of liquidresidue 3) Acceleration of the decomposition rate & combustion of the liquid residue 4) Char pyrolysis and oxidization Heat flux = 50 kW.m-2

11. Sample combustion in cone calorimeter Stage 2 Stage 1 Stage 3 Stage 4 Heat flux = 50 kW.m-2

12. Mass loss rate MLR 56 vol% 59 vol% MLR amplitude Heat flux Thermal resistance MLR peak width In accordance to the observations of Pilling et al. The increase of carbon fiber fraction leads to the MLR peak amplitude decrease at a given external heat flux

13. Heat of gasification TRP (volatile production resist) L (energy to produce volatiles) CF vol% Where: • L: Heat of gasification [kJ.g-1] • qfl: Heat flux of the flame [kW.m-2] • m: Specific MLR (SMLR) [g.s-1.m-2] • Tig, T: Ignition and ambient Temp. [K] • : Emissivity [-] • σ: Stefan-Boltzmann constant [W.m-2.K-4] • Tv: Vaporisation temperature [K]

14. 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. 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. Thank you! Sidonie Ruban sidonie.ruban@airliquide.com