Abstract
The objective of the work was to improve the leaching resistance of fire-retardant (FR) modified wood by the incorporation of a thermoset resin. Here, Scots pine (Pinus sylvestris L.) sapwood was impregnated with melamine formaldehyde (MF) resin and hydrophilic FRs guanyl-urea phosphate/boric acid by a vacuum-pressure treatment. Resistance to leaching of FR-modified wood was evaluated, after conducting an accelerated aging test according to European standard EN 84. Inductively coupled plasma analysis showed that the incorporation of MF resin significantly reduced the leachability of FRs. Scanning electron microscopy/energy-dispersive X-ray spectrometry revealed that the mechanism of water resistance was by doping the FRs into MF resin microspheres. Fourier transform infrared spectra showed the chemical functionality changes of FR-modified wood such as the formation of methylene bridges by drying the modified wood specimens. An increase in the thermal stability of FR-modified wood was confirmed by thermal gravimetric analysis. Excellent fire performance of FR-modified wood after leaching was affirmed by the limiting oxygen index and cone calorimeter tests.
Highlights
Wood as a sustainable biopolymer has been widely used in a range of areas, including building construction panels and furniture
The fire instability property can be improved by introducing salts containing nitrogen and phosphate ions and/or boron compounds into wood structure.[1−3] The former could be di- and monoammonium phosphate, guanyl-urea phosphate (GUP), and melamine phosphate, whereas boric acid (BA) or borax is an example of the latter ones.[1,4−7] The synergistic effect of nitrogen-phosphate salts and boron compounds provides a better fire-retardant property than their individual use.[8,9]
Boron compounds dehydrate at relatively low temperatures and form protective glassy inert layers, which prevent the escape of flammable products, thereby hindering O2 from reaching the wood.[7]
Summary
Wood as a sustainable biopolymer has been widely used in a range of areas, including building construction panels and furniture. The treated wood products are mainly suitable for interior use, where exposure to liquid water is limited. They are not suitable for outdoor uses, additional water-repellent protection layers have been applied on the surfaces of treated wood. These layers minimize moisture migration, which can eventually remove FRs during weathering exposure, which would lead to a product with reduced fire resistance.[12] the design of wood products for exterior purposes requires the fixation of the FRs within the wood structure.[13]
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