OTH24

Material description

Material ID: OTH24

Material type: Wood polymer composite (WPC).

Polymer: Cellulose and polyethylene (80%)

Additives (fire retardants, fillers or traces of inorganic elements): Talc (12%), Ferric Oxide (6%), Silicon (1%), Calcium (1%), traces of other elements (<1%)

Core thickness: 23.22mm

Table 1. Estimated mass concentration of compounds.

Compound	Mass Concentration (%)
Cellulose and polyethylene (-)	80
Talc (Mg3Si4O12H2)	12
Ferric Oxide (Fe2O3)	6
Silicon (Si)	1
Calcium (Ca)	1
Traces of aluminium (Al)	<1
Traces of sulfur (S)	<1
Traces of chlorine (Cl)	<1
Traces of potassium (K)	<1
Traces of titanium (Ti)	<1

A. Material composition identification

A.1 Attenuated total reflection – Fourier transform infrared spectroscopy (ATR-FTIR)

Table 2. FTIR compound identification.

Identified Compounds
Cellulose and polyethylene (-)
Talc (Mg3Si4O12H2)
Ferric Oxide (Fe2O3)

Figure 1 . FTIR spectra: Absorbance percentage versus wavenumber from the sample.

Figure 2. FTIR spectra: Absorbance percentage versus wavenumber from the sample and the identified compounds.

A.2 Energy Dispersive X-Ray Fluorescence (EDXRF)

Table 2. Inorganic elements and their mass concentration identified with EDXRF.

Element	Mass Concentration (%)
Fe	6
Si	5
Mg	3
Ca	1
Cl	<1
Al	<1
S	<1
K	<1
Ti	<1
P	<1

Figure 3. EDXRF spectra. Counts vs energy. Identified elements are shown as vertical lines.

B. Thermogravimetric analysis

Table 3. Mass fraction of residue after thermal decomposition.

Condition	Fraction of mass residue at 800°C
Non-oxidative (nitrogen)	0.15
Oxidative (air)	0.07

Table 4. Temperature and amplitude of main peaks in non-oxidative conditions.

Peak ID	Temperature peak (°C)	Amplitude of peak (°C^-1)
Peak 1	372	5.34 x 10^-3
Peak 2	486	8.79 x 10^-3

Table 5. Temperature and amplitude of main peaks in oxidative conditions.

Peak ID	Temperature peak (°C)	Amplitude of peak (°C^-1)
Peak 1	364	5.58 x 10^-3
Peak 2	475	4.59 x 10^-3
Peak 3	512	3.56 x 10^-3

Figure 4. Normalised mass (solid line) and derivative of the normalised mass (dashed line) in 150 ml min^-1 of nitrogen and a heating rate of 20°C min^-1.

Figure 5. Normalised mass (solid line) and derivative of the normalised mass (dashed line) in 150 ml min^-1 of air and a heating rate of 20°C min^-1 .

C. Gross Heat of Combustion

Table 7. Gross Heat of Combustion individual results for sample.

Trial	ΔH_c [kJ g^-1]
Trial 1	27.60
Trial 2	27.07
Trial 3	27.33
Average	27.33
Std dev	0.27

D. Ignition parameters

Table 8. Summary of ignition parameters for sample.

Critical heat flux for ignition	Ignition temperature	Total heat transfer coefficient of losses	Apparent thermal inertia
q̇″_cr [kW m⁻²]	T_ig [°C]	h_r [W m^-2 K^-1]	kρc [kW² m^-4 K^-2 s]
19.50	423	43.50	0.663

Figure 6. Time-to-ignition vs incident radiant heat flux for samples.

E. Burning behaviour

Table 9. Summary of key burning behaviour metrics.

Heat flux	Test	Time to ignition	Fraction of mass residue	Peak heat release rate	Total energy released
q̇″_inc [kW m^-2]		t_ig [s]	m_res [-]	q̇″_p [kW m^-2]	Q_t [MJ m^-2]
35 kW m^-2
	Test 1	100	0.63	201.89	194.26
	Test 2	97	0.72	193.85	186.87
	Avg	98	0.67	197.87	190.56
50 kW m^-2
	Test 1	45	0.62	273.14	240.62
	Test 2	42	0.63	261.03	229.53
	Avg	44	0.63	267.08	235.08
60 kW m^-2
	Test 1	27	0.55	330.29	272.94
	Test 2	27	0.59	301.96	257.32
	Avg	27	0.57	316.13	265.13
80 kW m^-2
	Test 1	-	-	-	-
	Test 2	-	-	-	-
	Avg	-	-	-	-

Figure 7. Normalised mass loss over time for samples tested with 35, 50, 60 and 80 kW m^-2.

Figure 8. Heat release rate per unit area over time for samples tested with 35, 50, 60 and 80 kW m^-2.

Table 10. Effective Heat of Combustion individual results for sample.

Test	ΔH_c [kJ g^-1]
35 kW m^-2 (Test 1)	24.73
35 kW m^-2 (Test 2)	25.30
50 kW m^-2 (Test 1)	25.31
50 kW m^-2 (Test 2)	24.72
60 kW m^-2 (Test 1)	24.82
60 kW m^-2 (Test 2)	25.45
80 kW m^-2 (Test 1)	-
80 kW m^-2 (Test 2)	-
Average	25.06
Std dev	0.33

F. Flame Spread

Table 11. Minimum heat flux for flame spread rate and minimum flame spread rate for sample.

Orientation	q̇″_min.spread [kW m^-2]	V_f.min [mm s^-1]
Horizontal	4.80	-
Vertical	4.20	-

Figure 9. Lateral flame spread rate versus heat flux.

Figure 10. Vertical flame spread rate versus heat flux.

Figure 11. *V_f*^-1/2 as function of *q̇″_ext* in horizontal configuration.

Figure 12. *V_f*^-1/2 as function of *q̇″_ext* in vertical configuration.

Table 12. Flame spread parameter results for sample.

Orientation	Trial	(^kρc_p⁄_Φh²)^¹⁄₂ [m^³⁄₂ s^¹⁄₂ kW^-1]	Φ [kW² m^-3]
Horizontal	1	6.109	9.39
Horizontal	2	5.659	10.94
Vertical	1	1.375	185.30
Vertical	2	1.26	220.85