Volume 61 Issue 2 (2011) - Годишник на ТУ - София - Технически ...

Charring rate decreases with increasing density according to the power law –Douglas fir wood belong to the class of high density woods (678 kg/m 3 ), i.e. itscharing rate is about 1 mm/min. Charring rate is not generally much influenced byfire retardants. However, the char yield is usually increased quite a lot, that mightcontribute to the protection of the wood core, [12].DTA Signal, μV6040200346309431421433451455300IP0 200 303 353 400 600 800 1000 12003131234-20Temperature T, 0 C-40-60153158190265159a)Heat Flow q, mJ/min3002502001234515037610034750Exothermic Effects-50-1002770IP0 200 271 400 600 800 1000 1200Endothermic EffectsTemperature T, 0 CFig. 4. Thermal analysis – DTA (a) and DSC (b) curves, of bare Douglas fir wood (1), flame retardedwood by capillary FRIS impregnation with 2 vol. % of anionic surfactant (2) and flame retarded wood byplasma-aided capillary impregnation at different operating rate of DBD pre-treatment: 3 – low frequency(50 Hz) DBD at 10 kV; 4 - low frequency (50 Hz) DBD at 15 kV, and 5 - high frequency (10 kHz) DBD at10 kV (at heating rate of 50 0 C/min).b)90