Environmentally Benign Polyelectrolyte Complex That Renders Wood Flame Retardant and Mechanically Strengthened

Abstract

Home structure fires are responsible for a majority of fire deaths and injuries. Wood is a key component of home construction due to its excellent mechanical properties and renewability, but it is inherently flammable. This study demonstrates the ability of a waterborne polyelectrolyte complex (PEC) to significantly increase wood's time to ignition, while decreasing peak heat release rate and total heat release. The PEC treatment, comprised of polyethylenimine and sodium hexametaphosphate, preserves the visual aesthetic of the wood and adds little additional weight (ca. 6%), while concurrently increasing flexural modulus and flexural strength. Scanning electron microscope images after torch testing provide evidence of a microintumescent flame retardant mechanism. This unique water‐based coating provides an environmentally benign means to render wood construction much safer.

Innovative Polyelectrolyte Treatment to Flame-Retard Wood

“…Reduced-pressure surface impregnation occurs mostly by the small intervascular pits in the birch wood surface [ 59 ]. Weight gain is low (6% reported for whitewood stud) compared to that of similar treatment reported in the literature [ 19 ]. Weight gain variability in wood is strongly dependent on the wood species and is related to density variation, the proportion of sapwood/heartwood, and the presence of rings, among other factors [ 60 , 61 , 62 , 63 ].…”

“…Promising one-pot alternatives to LbL coatings are currently in development, notably polyelectrolyte complexes (PECs) in water-based solutions [19]. PECs are versatile species consisting of a polyanion and a polycation [20].…”

“…Wood has also been impregnated with phytic acid to improve fire retardancy [ 33 , 34 , 35 ]. In 2019, a PEC of polyethyleneimine and sodium hexametaphosphate was used to treat softwood samples [ 19 ]. Samples were first soaked in a water-soluble PEC solution at a basic pH and then treated with an acid to make the PEC water-insoluble by protonation of polyethyleneimine’s (PEI’s) amine groups, leading to complexation between the two polyelectrolytes.…”

Transforming wood as next‐generation structural and functional materials for a sustainable future

“…Several other strategies, for example, metal-assisted layered double hydroxide coating, Polyelectrolyte complex deposition, h-BN deposition, hydrothermal modification along with carbon nanoparticle impregnation, and bioinspired struvite mineralization of wood, have been proven effective in improving the fire safety of wood. [203][204][205][206][207] Along with fire resistance, weather resistance is also essential for wood as structural materials because hydrous or acidic/alkaline environment leads to degradation and swelling. Wood can absorb a remarkable amount of water even after high-pressure densification.…”

One‐step treated wood by using natural source phytic acid and uracil for enhanced mechanical properties and flame retardancy

“…It is widely used in building materials, energy consumption, transportation, furniture, and decoration due to its lightweight, high strength and low cost 2‐4 . However, the flammable wood limits its application in the field of building materials and furniture, especially in densely populated areas 5‐8 . Fire protection of wood can be obtained by depositing flame retardant (FR) additives as coatings, but coatings will gradually fail over time and need renewed application.…”