The efficiency of non-intumescent and intumescent coatings for fire protection of thermally-modified Scots pine

In this study, the performance of different water-based fire retardant coatings including non-intumescent and intumescent coatings and coating after surface treatment with a mixture of boric acid and borax for improving the fire resistance of thermally-modified Scots pine was investigated before and after accelerated weathering. The modified wood used in this study was produced at 212 ºC for 3 h according to ThermoWood process. The fire resistance test was carried out using the open flame method according to EN ISO 11925-2 standard. The pyrolysis process of the coated specimens was also studied using Thermogravimetric analysis (TGA) under nitrogen atmosphere. The results showed that all three types of coatings were able to improve the fire resistance of the modified wood, especially by reducing the ignition time, but the intumescent coating was more efficient, and after the fire nozzle removal, the flame spread was stopped immediately. The mass loss due to pyrolysis was lower in the non-intumescent coating and the amount of its residual char was higher at the end of the test compared to other coatings. In all three types of coatings, the mass loss occurred in three stages of the TGA curve, and in the middle stage, the mass loss was more pronounced but the third stage of thermal degradation for each coating began at different temperatures. As a result of weathering, the flammability of the thermally-modified wood was increased and the fire protection performance of all coatings was also significantly reduced.