High-performance flame-retardant, waterproof, and abrasion-resistant waterborne polyurethane-based transparent coatings for wood protection

Due to the wide application of wood furniture in interior environment, waterborne polyurethane (WPU) coating was widely employed for its excellent properties such as environmental friendliness and transparency, which could maintain wood nature grain and color. In order to solve its disadvantages of WPU coating, such as flammability, hygroscopicity, and lack of abrasion resistance, in this paper based on chitosan (CS) and phytate (PA-Al) the core-shell ammonia polyphosphate (APP) was prepared. And then it was incorporated with layered double hydroxides (LDH) into the WPU coatings on oak (Quercus mongolica Fisch. et Turcz.) wood. Further more, for the purpose to improve the waterproof property of WPU coating, polydimethylsiloxane (PDMS) were applied to assemble into hierarchical structure. The LOI of the oak veneer coated with modified WPU was increased to 32 %, and the pHRR and THR were reduced by 55.6 % and 58.6 %, respectively. Meanwhile, the addition of LDH greatly reduced the smoke release, and particularly the TSP decreased by 66.0 %. Further more, the addition of hard units (APP@CS@PA-Al and LDH) not only did not affect the transparency of the WPU coating (transmittance ≥92 %) but also increased the hardness (pencil hardness up to 4 H) and abrasion resistance (abrasion rate reduced by 37.33 %) of the WPU coating. The WPU coating presented higher hydrophobicity with a water contact angle of 114°. This study provided environmentally friendly and efficient approach for preparing biomass-derived core-shell APP flame retardants for high-performance flame-retardant, waterproof, abrasion-resistant, and transparent WPU coatings suitable for wooden products applications.