Wood fire performance is a great concern in interior finishing due to the high risk of flame spread. To increase the use of wood in high building while ensuring the safety of building occupants, fire retardant (FR) treatments are required. Traditionally, two fireproofing strategies are employed: impregnation and coatings. They have been widely studied but they, respectively, are time and chemicals consuming and have poor aging resistance. Polyelectrolyte complexes (PEC) impregnation has shown a great potential in surface impregnation. PECs treatments are versatile, eco-friendly and economical. In this study, yellow birch (Betula alleghaniensis) was treated with polyethyleneimine (PEI) and sodium phytate (SPA) PECs. Fire-retardancy performance was evaluated using cone calorimeter and results have shown that it is strongly related to PECs weight gain. A minimal weight gain of 2 wt.-% was found to be necessary to achieve a significative fire-retardancy. To increase the weight gain and ensure a reproductible fire-retardancy, two commercial wetting agents (SCHWEGO wett 6292 and SCHWEGO wett 6237) were added at 0.1 wt.-% and 0.5 wt.-% to the PECs solutions. Surface tensions were measured using the Wilhelmy plate method. Effect on the wood wettability was also studied by dynamic contact angle. An increase of the weight gain was obtained by adding SCHWEGO wett 6237, whereas SCHWEGO wett 6292 has no significant effect. Finally, PECs with SCHWEGO wett 6237 were surface impregnated on yellow birch to study the impact on wood fire-retardancy.

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