A new insight into the design of robust superhydrophobic and fire retardant wood: Breaking the conflicting requirement on adhesives

As a new star of low carbon footprint material, wood with both superhydrophobic robustness and flame retardancy highly boosts its applications in various fields. However, these individual functionalities have conflicting requirements on the interfacial or bulky properties of its surface coating, especially in flammable organic adhesives (such as epoxy resin (EP) and polydimethylsiloxane (PDMS)) and nanoparticle systems. Therefore, breaking the conflicting requirement on adhesives is a crucial and challenging issue for achieving superhydrophobic robustness without impairing flame retardancy. In this work, a structure of three-dimensional (3D) flower-like hydrotalcite (HT) clusters isolated by hierarchical pores was proposed to resolve the conflicting demand. Such kind of structure was fabricated through a one-step thermally-driven method using HT, EP and perfluorooctyl triethoxysilane (PFOES). Benefitting from the release of gaseous ethanol from the inside of wood and its circulation flow among EP and HT during thermally driven process, the HT particles were bonded with small amount of EP and assembled as robust 3D flower-like HT clusters isolated by micro/nano sized pores, rather than embedded in a thick EP coating. This structure significantly reduced the use of flammable EP and increased the loading of flame retardant HT. Therefore, wood with boosting flame retardancy without compromising its own superhydrophobic robustness was achieved (herein named as HT/EP/PFOES wood). Cone calorimetry test showed that the HT/EP/PFOES wood had a 49.33% reduction in the peak of heat release rate (HRR) and a 34.51% reduction of total heat release (THR), which outperformed most of the existing flame retardants and superhydrophobic lignin-cellulosic materials. Meanwhile, its superhydrophobic robustness was not impaired. Together with a facile one-step thermally driven fabrication process, this structure of 3D flower-like HT clusters provided a new insight into fire retardant and robust superhydrophobic wood.