INTUMESCENCE: A CONCEPT FOR THE REACTION AND RESISTANCE TO FIRE OF MATERIALS

Serge BOURBIGOT R2FIRE@UMET-UMR/CNRS 8207

Intumescence?

Formation of heat

barrier

Fire protection of

materials?

Outline

Intumescent PU:

methods for

explaining synergy

Fire protection: jetfuel fire

Fire protection of CFRP

Fire protection of composite: why?

CFRP in aircraft structure has introduced

potential fire threats

engine compartments

(fuel leakage can occur)

fuselage (post-crash

fire)

Jet fuel fire: heat flux

between 150 and 200 kW/m²

Silicone-based intumescent coating

Silicone formulationF1 – High intumescing

coating

F2- Low intumescing

coating

Silicone matrix 56% 56%

Expandable graphite 25% -

Calcium carbonate 12% 37%

Clay 7% 7%

Intumescent paint on CFRP: silicone-based coating

containing expandable graphite* compared to low

intumescing paint

*S. Bourbigot et al. “Protecting substrates against damages by fire”, WO 2013/150121 -

Dow Corning, 2013

Small scale test: Experimental set up

Sample +

holder

(insulative

ceramic)

Burner (200

kW/m² at the

surface –

Tflame ~ 1100°C)

Infrared

pyrometer and

Th. stuck on

composite (T =

f(t))

Protection by intumescence: 1000µm

Time (s)

0 100 200 300 400 500 600 700 800 900

Tem

pe

ratu

re(°

C)

0

100

200

300

400

500

600 Virgin composite

CFRP-F2

CFRP-F1

Effective protection with silicone-based paint

Protection by intumescence

Virgin composite CFRP-F1

Mechanism of protection

F1

F2

T

Time

Heat barrier: high expansion, low k

(0.4 W/m.K@600°C)

Structure: high cohesion thanks to

chemical interactions (SiC, Ca-Si)

Heat barrier: low expansion, low k

(0.4 W/m.K@600°C)

Structure: cohesive porous

structure (highly polymerized Si,

Ca-Si)

Synergy in intumescent polyurethane

Preparation and formulation

⊳ Synthesis of PU:

⊳ Intumescent formulations:

⊳ PU casting

preparation:

APP

OM-POSS

Nano-

gold

Nano-

SiO2

Nano-MgO

PU-APP/NP

@30 wt% load.

(substitution 1

or 2wt% NP)

Fire performance of PU/APP-NP

Time (s)0 100 200 300 400 500

HR

R (

kW

/m²)

0

100

200

300

400

500 Neat PU

LOI = 20% - pHRR = 480 kW/m²

PU-APP

LOI = 35% - pHRR: -63%

PU-APP/1%Nano-gold

LOI = 44% - pHRR: - 64%

PU-APP/2%OM-POSS

LOI = 44% - pHRR: -71%

PU-APP/2%Nano-SiO2

LOI = 47% - pHRR: -65%

PU-APP/2%Nano-MgO

LOI = 52% - pHRR: -83%

Superior performance for

PU/APP-MgO:

synergistic effect

External heat flux = 50 kW/m²

Characteristic times of combustion

Stopping the combustion and taking out the

samples at characteristic times of HRR curves

Tomography of intumescent charsPU-APP PU-APP/2%Nano-MgO

Increasing

HRR

Decreasing

HRR

Final

residue

Tomography of intumescent chars (2)

44 mm

35 mm

82 mm

59 mm

41 mm

42 mm

Increasing

HRR

Decreasing

HRR

Final

residue

Morphology: formation of big cells but higher expansion

and more compact char (at the bottom) with MgO

PU-APP PU-APP/2%Nano-MgO

Summary

PROPERTY PU/APP PU/APP/MgO

Thermal barrier

effect+ ++

Char heat

conductivity0.3 W/m.K Lower (0.15 W/m.K)

Expansion

evolution

≠ behavior to develop the expanded char

between PU/APP and PU/APP/MgO

Final expansion

value1200%

Higher (1700-

2100%)

Morphology ≠, intumescence development

Chemistry

≠, intumescent char but stabilization of

phosphorus at high temperature

(Mg-Phosphate)

Summary and Conclusions

• Identification: careful investigation of the

mechanism must be done for further designing

new systems

• Intumescence: efficient way to fire protect

composite and steel

• Mechanism: formation of cohesive heat barrier

(chemistry) exhibiting relatively high expansion

and low heat conductivity (physics)

Research Group & Acknowledgement