COMPARISON OF FLAMMABILITY AND FIRE RESISTANCE OF CARBON FIBER REINFORCED THERMOSET AND THERMOPLASTIC COMPOSITE MATERIALS

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1 COMPARISON OF FLAMMABILITY AND FIRE RESISTANCE OF CARBON FIBER REINFORCED THERMOSET AND THERMOPLASTIC COMPOSITE MATERIALS Jianping Zhang, Michael Delichatsios, Talal Fateh, B. Karlsson FireSERT, University of ULSTER

2 FireSERT FIRE SAFETY ENGINEERING RESEARCH AND TECHNOLOGY 2

3 Key research equipments (1) Large-scale 20MW Cone calorimeter Large scale fire resistance furnace (3 3 4m)

4 Key research equipments (2) Intermediate-scale (Cone, UFA, SBI, ISO room, etc) Cone calorimeter Universal flammability apparatus (infra-red)

5 Universal Flammability Apparatus (UFA)

6 Key research equipments (3) Micro- and small- scale for milligram samples (thermal and toxicity analysis) Thermal degradation, specific heat, heat of pyrolysis, toxicity, residue strength mg samples TGA, DSC, MDSC, FTIR, ATR, etc Inputs for modelling large-scale tests

7 Overall design Sampling points Unheated distance 205mm (based on ATS furnaces 28 long with 24 heated length)

8 FireSERT FIRE dynamics and MATERIALS LAB ( FML) NANOCOMPOSITES (XRD, TEM, SEM) UNIQUE: FROM NANOSIZE TO 20 MW FIRES INTRINSIC FLAMM. PROPERTIES (TGA, FTIR, MDSC, UNIV. FLAMM. APPARATUS,) LARGE SCALE (20MW) MATERIAL AND CFD MODELLING FOUR PHD STUDENTS, TWO POSTDOCS AND THREE ENGINEERS Major projects: FIRENET (EU) FAÇADE FIRES (EPSRC, Japan) PREDFIRE NANO (EU) Industrial R&D, HFFRs, AIRCRAFTFIRES

9 AircraftFire Project Fire risks assessment and increase of passenger survivability FP7 EASN Project - EU Grant Agreement n The AircraftFire project Presentation and Main Results Contact: jean-michel.most@ensma.fr

10 AcF Research Objective Evaluation of fire threats and passenger survivability in new generation of aircrafts Characterisation of the fire performance of composite materials (physical/chemical/thermal flammability and burning properties) for aircraft design and fire safety analysis (modelling) Development and validation physical models correlated to the evolution of the fire scenarios, Modelling of the cabin fire growth and passenger evacuation Recommendations for efficient industrial technologies Througlife, March 26th,

11 The fire threat in new generation of aircrafts Aluminium is substituted by flammable composites for decorative panels, hull, wing, cowling, structure, etc. The fire threat can significantly increase due to The flammability of materials in high temperature environment The toxicity of the smokes The total aircraft fuel load With impact on the fire development and the passenger evacuation Higher energy supply for avionics and electronics fire risks (ignition, ) Througlife, CAA, Airbus, EADS March 26th,

12 Outline Introduction Testing for carbon fiber composite materials Comprehensive flammability/toxicity evaluation Conclusions Flammability and toxicity parameters Detailed flammability properties for modeling Pyrolysis model Back surface temperature for fire resistance Towards large scale modelling 12

13 Introduction Manufacturers of polymers or flame retardants or composites are constantly looking for improvements in their formulations for improving people safety and property protection. Flame retardants or intumescent paints or carbon fibers are commonly used to prevent or delay the ignition of polymers and to reduce the intensity of the fire and prevent burn through. Unfortunately, they may also introduce new hazards such as an increase in the toxicity of combustion gases or in smoke production and, over longer periods, create environmental and toxicological hazards owing to disposal (e.g., brominated FRs). Existing test methods (such as LOI, UL-94, burn through tests ) assess the ignition and flame spread of a material without considering any toxicity effects Also, most of these methods ranks materials in groups thus does not differentiate the material behaviour inside a given rank 13

14 Introduction (ctd) This paper presents a simple method to characterize the fire performance and toxicity of polymers using parameters deduced from micro (TGA) and small-scale (Cone calorimeter) tests, namely Fire spread and growth parameter Smoke parameter Toxicity parameter Mass residue Heat release rate for thermally thin materials 14

15 Literature review (Numerical modelling) Two types of methods have been developed for the prediction of fire spread due to pyrolysis/burning of combustible materials: Firstly, purely thermal models for upward flame spread have been used, with input data from the Cone Calorimeter, to predict flame spread in large scale and the resulting heat release rate. Secondly, more fundamental work has been carried out using CFD (computational fluid dynamics) models and pyrolysis models to predict fire growth. 15

16 Flammability and toxicity parameters 16

17 Flammability and toxicity parameters It is desirable and cost effective to be able to assess the flammability of materials by means of small scale-tests before new formulations progress in large-scale production of products made out of these materials; This can be achieved by combining experiments with CFD modelling; but performing CFD modelling including deducing all the required material properties is very time consuming; In this work, we developed, based on measurements, a set of fundamental parameters that can characterize and compare the flammability and toxicity of materials 17

18 Key flammability properties 2 These properties are determined using a combination of: TGA TGA-FTIR MDSC Cone calorimeter Universal flammability apparatus (UFA) Two stage tube furnace A numerical model describing the pyrolysis of materials that form char upon degradation

19 Flammability and toxicity parameters Fire spread and growth parameter Smoke parameter Toxicity parameter Mass residue Heat release rate for thermally thin materials 19

20 Flammability and toxicity parameters Fire spread and growth parameter = square of peak heat release rate divided by time to ignition PHRR 2 t ign This parameter is proportional to FIGRA as measured in SBI FIGRA Q t max max PHRR SBI t ign 2 20

21 Flammability and toxicity parameters Smoke parameter = smoke yield / effective heat of combustion y s / H c The product of the smoke parameter and the fire growth parameter is proportional to the SMOGRA measured in SBI SMOGRA ~ PHRR t ign 2 ys H c ~ Q t max max ys H c 21

22 Flammability and toxicity parameters Toxicity parameter = the ratio of the effective heat of combustion of the fire retarded polymer to the effective heat of combustion of the neat polymer. H 1 H c, FR _ polymer c, neat _ polymer In the case where the polymer weight percentage is different for different formulations, the following should be used 1 wt% of polymer in non FR formulation H c of FR formulation H c of non FR formulation Fraction of mass pyrolysed in non FR formulation wt% of polymer in FR formulation Fraction of mass pyrolysed in FR formulation 22

23 Flammability and toxicity parameters Mass residue = how much of the initial material is left behind as residue after combustion. This is not significant for fire spread and growth but it can provide the amount of total fuel load in a fully developed fire. Values for this parameter are not presented in this paper but are included in other publications for the materials examined in this work. 23

24 Flammability and toxicity parameters Heat release rate for thermally thin materials = maximum mass loss rate in Nitrogen (appropriately normalized by the initial mass and heating rate) In TGA multiplied by the heat of combustion in the Cone Calorimeter 1 m initial dm dt max H c / Heating rate 24

25 Materials and experiments Experiments were performed in a Cone Calorimeter for sample exposed to an external heat flux of 50kW/m 2. In parallel, experiments of the same formulations were performed in TGA /FTIR/ATR/ tube furnace but only results from TGA at 10 C/min in Nitrogen are employed in this paper. We have established the variability (uncertainty) in our apparatus to be a number between 3-5% for individual measurements. 25

26 Materials and experiments ACF1, type 1: epoxy (thermoset) +carbon fiber(~70%) ACF2, type 2 :epoxy ( thermoset) +carbon fiber(~70%) ACF6 PEEK ( thermoplastic) +carbon fiber (~70%) ACF7, type 3 : epoxy (thermoset) +carbon fiber (~70%) NOTE : exact composition has not been provided being prorietary 26

27 GLOBAL FLAMMABILITY PARAMETERS FOR THE COMPOSITE MATERIALS 27

28 FLAME SPREAD AND SMOKE 28

29 ACF7 29

30 Materials and experiments Materials PHHR tig Fire growth parameter smoke yield CO yield CO2 yield THRR TML HoC Initial mass Final mass Residu e kw/m Units 2 s kw 2 /m 4 -s g/g g/g g/g MJ/m 2 g kj/g g/kj g g % ACF ACF ACF ACF1- AVE ACF ACF ACF2- AVE ACF ACF ACF6- AVE ACF ACF ACF7- AVE

31 Materials and experiments Flame spread parameter versus smoke yield PHRR 2 /t ig (kw 2 /m 4 -s) ACF1 ACF2 ACF6 ACF7 ACF1-Pprime ACF3 ACF9-1 ACF9-2 ACF1 (2mm) y s (g/g) 31

32 Materials and experiments Flame spread parameter versus smoke parameter PHRR 2 /t ig (kw 2 /m 4 -s) ACF1 ACF2 ACF6 ACF7 ACF1-Pprime ACF3 ACF9-1 ACF9-2 ACF1 (2mm) y s /HoC (g/kj) 32

33 COMPARISON WITH OTHER POLYMERS 33

34 THERMALLY THIN PARAMETER 34

35 TGA and DTG curves at 10 o C/min for ACF1,ACF2,ACF7 ( different epoxy thermoset carbon fiber composites) and ACF6 ( PEEK thermoplastic carbon fiber composite) Weight (%) Weight loss rate (%/min) ACF1 ACF2 ACF6 ACF Temperature ( o C) 35

36 10000 Thermally thin parameter PHRR 2 /t ig (kw 2 /m 4 -s) ACF1 ACF2 ACF6 ACF7 ACF1-Pprime ACF3 ACF9-1 ACF9-2 ACF1 (2mm) 1 ( max m m initial t ) H heating rate eff y s /HoC (g/kj) 36

37 DETAILED FLAMMABILITY PROPERTIES AND PYROLYSIS MODEL 37

38 Deduced effective ignition and thermal properties of ACF1, ACF2, ACF6 and ACF7. Material s Thickness Critical heat flux Diffusivity Conductivity Density Specific heat Ignition temperature HoC Heat pyrolysis mm kw/m 2 m 2 /s W/m-K kg/m 3 J/kg-K K kj/g kj/g ACF X =0.2 ACF X = 0.2 ACF X =1 ACF X = 0.2 of Material s y s y co Residue Average MLR Average HRR Stoichio. Ratio, S a Smoke point height b Activation energy, E a Pre-expon. Factor, Ln(A) g/g g/g % g/m 2 -s kw/m 2 mm kj/mol s -1 ACF Fcn( ) c Fcn( ) c ACF ACF ACF Reaction order, n 38

39 PYROLYSIS MODELS FOR DIFFERENT FORMULATIONS 39

40 One of the objectives of this paper is to develop a simple model that can be incorporated in CFD models for full scale modelling. In this work, it is found that the heat flux ratio between the heat flux assuming that there is no carbon fibre layer ( q flux between the carbon fibre layer and the virgin layer ( the material pyrolysed in the following three cases: q int erface 4 ext T ign ) and the actual heat ) can be related to the depth of a) Heat flux ratio increases linearly with the pyrolysed depth (ACF1) independent of the heat flux, as found for typical charring materials b) Heat flux ratio increases non-linearly with the pyrolysed depth independent of the heat flux (ACF2 and ACF7) c) Heat flux ratio initially increases linearly the pyrolysed depth but then remain nearly constant independent of the heat flux (ACF6) 40

41 Mass loss rate (g/s) PREDICTIONS 0.18 ACF kW/m Time (s) 30kW/m 2 41

42 EXPERIMENTS 42

43 INSULATED BACK SURFACE TEMPERATURE AND NET HEAT FLUX 43

44 700 Back surface temperature ( o C) kW/m 2 ACF1 ACF2 ACF6 ACF Time (s) 44

45 After 100 s, ignition starts and the net heat flux into the solid can be estimated for the slope of temperature histories, the mass remaining ( 45 g over an area of 0.01 m 2 ) and the specific heat of carbon fibers C= 0.5kJ/kg K. This net heat flux is equal to 4.5 *0.5* 300/200 = 3.4 kw/m 2. This heat flux will be imposed on the insulated material behind the fuselage. We expect and have shown ( for heat fluxes up to 75 kw/m 2 ) that same proportional reduction of the imposed heat flux ( by 90 %) occurs at higher imposed heat fluxes and therefore, no flame through or flame spread will occur behind the fuselage. 45

46 APPLICATION TO LARGE SCALE SITUATIONS: BURNING RATE IN THE SBI EXPERIMENT 46

47 HRR (kw) EXP Test 1 EXP Test 2 Burner HRR = 30kW Integral model Time (s) Comparison of the predicted HRR of Flaxboard in SBI by a numerical model and the experimental data using the calculated flammability properties 47

48 CONCLUSIONS Comprehensive flammability/toxicity evaluation Flammability and toxicity parameters Detailed flammability properties for modeling Pyrolysis model Back surface temperature for fire resistance Towards large scale modelling 48

49 Thanks for your attention! Any questions?

50 TOXICITY PARAMETER WHEN IT SHOWS A DIFFERENCE 50

51 Toxicity assesment based on effective Heat of combustion 1.0 Inefficiency of combustion 0.8 PG PG4 0.0 PG1 PG3B

52 Mass left (wt%) Percentage of initial mass left after tests in Cone calorimeter at 30kW/m PG1 PG2 PG3B PG4A

53 Mass left (-GF) Percentage of initial mass left after tests in Cone calorimeter at 30kW/m 2 5 Mass of Glass fibres was substracted 4 PG3B 3 2 PG2 PG4A 1 0 PG1

54 Results and discussions Fire growth and smoke parameters (all formulations) 54

55 Toxicity parameter (all formulations) Results and discussions 55

56 Heat release parameter for thermally thin conditions calculated as ( 1 max m m initial t ) heating rate H eff, where m initial is initial mass of sample (mg), max m t is peak mass loss rate (mg/s) and H eff is effective heat of combustion (kj/g) taken from Cone calorimeter World Rescue Challenge 2012 Page 56

57 Results and discussions Heat Release Rate for thermally thin materials (PBT+GF and PA66+GF) 57

58 Conclusions Five parameters were deduced based on micro- and small-scale tests in order to characterize ignition and flammability behaviours of any material, namely, fire spread and growth parameter, smoke parameter, toxicity parameter, mass residue and heat release rate for thermally thin materials These parameters (except mass residue which is not relevant in this work) were applied to polymers fire retarded with brominated fire retardants (BFRs) or halogen free fire retardants HFFRs) and it is found that: In terms of fire growth and smoke parameters (i) base polymers have the highest fire growth parameter but with minimum production of smoke, (ii) BrFRs reduce the fire growth parameter but increase the smoke production considerably and (iii) HFFRs achieve similar and smaller fire growth parameter but with less smoke production compared to BrFRs. 58

59 Conclusions In terms of the toxicity parameter, BrFRs have highest inefficiency of combustion because of their strong gaseous action, whereas HFFRs have higher combustion efficiency because they mostly act in the solid phase by modifying the char formed on the surface of the polymer. In terms of the heat release rates at thermally thin conditions, PBT+GF and PA66+GF formulations behave differently, where the formulation containing BrFRs has the lowest value for PBT+GF whilst the highest for PA66+GF. The opposite behaviour by PA66+GF is due to the fact that brominated PA66+GF has a maximum mass loss rate about twice that of neat PA66+GF. This result demonstrates the limitation of TGA data which is obtained under thermally thin condition as opposed to real burning conditions where the material behaves as a thermally thick material as typically found in the Cone Calorimeter tests. 59

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62 Acknowledgements The authors acknowledge the EU for financially supporting the ENFIRO project under Grant No and AircraftFire Project under Grant No The authors also thank Mr M McKee and W Veighey for helping with the Cone experiments. 62

63 Thanks for your attention! Any questions?