COMBUSTION TEST

To evaluate the fireproof performance of architectural materials such as wood and wood panels, a corn calorimeter is conventionally used[13-14].The flammability characteristics of the Mango wood materials impregnated the fire retarding chemical were measured according to the test method ISO 5660-1(Cone calorimeter method) based on the Building Standard Law of Japan [15]. In the cone calorimeter samples orientation was horizontal. Materials tested in the room test were installed on 3 walls only; ceiling was lined with the paper covered gypsum board. The igniter rod was set just above the samples, and 50 kＷ_/m²of heat was continuously irradiated to the samples under air atmosphere. After ignition, the rod was immediately removed. During the test, oxygen concentration of the exhaust gas and the sample weight were recorded every 2 second on a PC. The heat release rate (HRR) was calculated by the oxygen consumption on a lower heat value (LHV) basis[16]. The HRR is generally described as

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the heat generated rate per heated area (kW/m²) for the fireproof experiment[17]. The standard law is given bellow.

1) The gross calorie value in demand time must be lower than 8 MJ/ m² after it begins to heat.

2) Do not exceed 200 kW/m² as the highest heat release rate continues for 10 seconds in the demand time after it begins to heat it.

3) There must be neither cracks nor damage that gets in the demand time on the reverse harmful on fire prevention after it begin to heat it.

Demand time is 5 minutes in the fire retardant material, 10 minutes in the quasi-noncombustible material, and 20 min in the noncombustible material.

5.4. RESULTS AND DISCUSSION

5.4.1 SEM ANALYSIS

From the Figure. 5. 2 it has been observed that there are significant change occurred during the underwater shock wave modification by inducing micro cracks or micro cavities.

Raw Wood

Shocked Wood Shocked Wood

Raw Wood

Fig.5.2 SEM micrographs of raw and treated wood.

The quantity of cracks depends on the shock pressure. Cracking on the surface increased with the shock pressure increased. A high degree of modification forms different sized

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cracks or cavities in the wood surface especially in the bordered pits of wood.

5.4.2 PERMEABILITY TEST

From the Figure 5.3, it has been investigated that, after chemical injection shock treated wood absorbed more amount of chemical solution than that of controlled. It is due to the micro cracks on the wood surface. Because chemical was penetrated easily into the treated wood though these micro cracks or micro cavities. Impregnation of soft wood timber is largely depending on the movement of preservative through the cavities of the tracheids, passage from the cell to cell being effected through valve like structures, known as bordered pits [18]. Experiment shows that it improves the permeability of wood to break pit membranes by underwater shock wave.

The water uptake of wood is the amount of water contained in the wood after dipping in water. Moisture uptake includes both water absorbed into the cracked wood cell wall and the newly formed hollow center of the cell after shock wave modification, and it is expressed as a weight percentage.

61 62 63 64 65 66 67 68 69 70 71

0 50 100 150 200 250 300

Shock Pressure,MPa

Weight Percentage, %

Fig.5. 3 Effect of underwater shock wave pressure on permeability of wood.

Experimental result shows in the Figure 5.4 that underwater shock wave also improves the water uptake as well as water penetration by the shock modified wood.

４９ 0

10 20 30 40 50 60 70 80 90 100

0 24 48 72 96 120 144

Time , hr

Weight Percentage, %

Treated,200MPa Controlled

Fig.5. 4 Water uptake of controlled and shock modified wood during dipping test.

5.4.3 DRYING TEST

The drying test results were found from the Figure.5.5 it has been evaluated that drying ability was improved in the treated wood sample.

0 10 20 30 40 50 60

0 20 40 60 80 100 120

Time ,hr

Moisture Content,%

Controlled 100MPa,Treated 184MPa,Treated 200MPa,Treated 244MPa,Treated

Fig.5.5 Result of drying test of controlled and shock treated wood samples.

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Compared to the sample unmodified, the shock modified samples were exhibited a large time change on the moisture content. Micro cracks on the wood surface helps to easy evaporation of liquid during the drying. Because, heat energy rapidly penetrates the wood sample and temperature rises much faster than during conventional drying [19].This indicates that the effect of shock wave modification is remarkable.

5.4.4 COMBUSTION TEST

The fire characteristics measured in the cone calorimeter of controlled (not shock treated and not chemical injected), un-shocked, and shock treated wood samples is shown in the Figures 5 .6 -5.9. The gross calorie values are in the Figures 5.9and 5.10, the heat release rate is in the Figures 5.6 and 5.7.The gross calorie value, the main parameter of combustion test measured using cone calorie meter. Figures 5 .6 and 5.7 show the result of gross calorie value. The result of quasi combustible materials was obtained by three samples; all of them were underwater shock wave treated with the shock strength 244 MPa, 200MPa and 184 MPa, and also fire retardant chemical injected. Chemical injected sample (chemical injected but not shock treated) and shock treated with shock strength 100MPa (shock treated and injected) pass the fire retardant material standard. Controlled (Not -injected and un-shock treated) wood sample did not pass even the fire retardant standard.

0 1 2 3 4 5 6 7 8 9 10

0 5 10 15 20

Time (min)

Gross Calorie Value(MJ/m2)

Controlled Unshocked

Fig. 5 .6 The result of gross calorie value for controlled and un-shocked samples.

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0 1 2 3 4 5 6 7 8 9 10

0 5 10 15 20

Time ( min )

Gross Calorie Value ( MJ/ m2 )

Unshocked 100MPa 184MPa 200MPa 244MPa

Fig.5.7 The result gross calorie value for un-shocked and shock treated wood samples.

Some of samples passed the recognition standard about the calorie value by injecting the fire retardant or flame proofing chemicals. The amount of injected chemical is correlates with the calorie value when thicknesses of the wood samples are same. The underwater shock wave loading influence the amount of the injected flame proofing agent by selective destruction of the blocked bordered pit^. Samples shock wave treated with 244, 200 and 184 posses huge amount of micro capillaries, so that its show higher percentage of permeability by absorbing fireproofing or fire retardant chemicals. Due to the significantly higher amount of chemical absorption or impregnation, the above samples exhibit excellent result than that of other samples. The result of passing noncombustible material standard was not obtained by any samples but 200MPa treated sample's result is slightly closed to noncombustible material standard.

The Figures 5.8 and 5.9 show the result of the heat release rate. Heat released in combustion is the driving force of a fire: the larger the heat released by a burning object is, the faster the fire spreads and the hotter the gases and limiting surfaces of the fire enclosure become.

５２ 0

50 100 150 200

0 5 10 15 20

Time (min)

Heate Release Rate (kW/m2 )

Controlled Un-shocked

Fig.5.8 The result of heat release rate for controlled and un- shock treated samples.

0 25 50 75 100

0 5 10 15 20

Time (min) Heat Release Rate (kW/m2 )

Un-shocked 100MPa 184MPa 200MPa 244MPa

Fig. 5.9 Result of heat release rate for un-shock and shock treated samples.

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Thus, one of the most essential quantities describing the burning of materials is the rate of heat release, denoted with Q and expressed in kW or MW. The heat release rate of quasi -noncombustible material is 200KW/m² after passing 9 minutes. Therefore, this standard does not have passed by any sample. Only controlled (un-shocked and non-injected) sampled reached to 145 kW/m² that is near to the standard for quasi-noncombustible material.

5.5 CONCLUSION

The underwater shock wave was loaded to the Mango wood and modified inducing micro cracks or cavities in the surface. From the SEM investigation it has been found clearly. Moderate and high degree of modification crack cell walls require applied shock strength levels between 184 to 200 MPa. Test on 4 samples gave certainty to the fact that any wood species can be underwater shock wave modified for increasing permeability. Changes in the wood structures effects wood properties. The important change is the dramatic increase in wood permeability. Results show from the drying test that drying property of shock wave modified wood can be increased .Moreover, reducing drying time can be improve flexibility of wood processing factories, short term customer demands and trends can be met more easily and, ensuring high quality and keeping rejects low , higher price of wood can be achieved.

The fire retardant injection significantly improves the fire safety of wood by reducing its heat contribution to a fire and prolonging the times for the flame spreading or flashover. Comparison parameter of the flammability parameters for shock wave treated and untreated wood was measured. The shock wave treated samples into which the fire retardant chemical was injected more passed the standard quasi-non combustible standard. The gross calorie value measured in the Cone calorimeter test for controlled, untreated and injected samples were much higher than that of treated and injected samples. The heat release rate was also significantly lower for shock treated and injected materials. Increase recognition of the ability of underwater shock wave treated wood to provide a higher level of fire safety should increase the amount of wood construction.

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