Polymers 2021 , 13 , 709
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Figure4. Demonstration of the course of burning of oriented strand boards (OSBs) after their ignition by radiant heat ( a ) ignition (100 s); ( b ) burning time of 160 s; and ( c ) 300 s. ( d ) A demonstration of the combustion process by 44 kW.m − 2 . ( e ) A sample selected from the measuring device; specific distance of 12 mm, time of ignition of 57 s and density heat flux of 50 kW.m − 2 . ( f ) Cooled sample 10 min after the experiment; sample thickness of 15 mm and ignition time of 108 s, 44kW.m − 2 .
3.1. Determination of Ignition Temperature and Weight Loss For the purposes of our research, the initial value of the radiant heat flux, to which the selected OSBs were exposed, was experimentally set to 43 kW.m − 2 . This value represented the critical heat flux for the selected samples. Critical heat flux is the heat flux between the minimum incident heat fluxes at which ignition occurs and maximum incident heat flux at which ignition does not occur. It can be used to evaluate the ignition ability. The critical heat flux is obtained experimentally by gradually exposing the samples to decreasing heat flux until ignition ceases [30]. The maximum value of the radiant heat flux, to which selected board materials were exposed, was 50 kW.m − 2 . The heat flux gradually increased by1kW.m − 2 (Table 2). The effect of external heat flux on a sample is the incident energy upon its surface. Part of the energy is reflected (depending on the emissivity of the surface), part is transferred by conduction to deeper layers of the material (depending on its thermal conductivity) and the rest is absorbed by a thin layer on the surface, i.e., heating takes place. As the temperature of the sample increases, pyrolysis and thermal oxidation occur, as a result of which gaseous products are released into the environment [30]. Therefore, the time to ignition of the sample decreases with increasing external heat flux [31], which is confirmed by our results.
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