Fabrication of ionic wood crosslinked by Ca2+ with high strength, toughness, and weather resistance

Fast-growing natural poplar wood is not meet with in many requirements such as high strength and flame retardant due to its porous structure and loose materials. In this study, we established a simple and feasible method that includes delignification, ionic bond formation via the crosslinking of carboxyl groups in TEMPO-oxidized wood after delignification with calcium ions, and hot-pressing of stacked veneers to improve the quality, density, strength, toughness, and weather resistance of natural wood (NW). This method has the following advantages: The inner cellulose microfiber is highly aligned, thus closely cross-linking and tightly bonding cellulose microfibers and nanofibers between the interfaces and inner layers of the wood boards via hydrogen bonding and ionic bonding. A laminated densified TEMPO-oxidized ionic wood (IW) showed substantially higher specific strength (∼196.9 MPa cm3 g−1), higher tensile strength (∼246 MPa), higher flexural strength (∼257 MPa), higher flexural modulus (∼36 GPa), higher impact toughness (∼42.34 kJ m−2), and superior fire retardancy, UV resistance, water resistance, and also higher density (∼1.25 g cm−3) than NW. Larger-size laminated densified structural materials with satisfactory thermal stability can also be fabricated using the proposed method.