Fabrication and Analysis of High-Performance Thermochemically Densified Wood

While wood construction may be as ancient as humanity itself, wood remains one of the most utilized structural materials because of it’s availability, low cost, durability, surprisingly high specific mechanical properties, and renewability. Recent research into wood-based materials has focused on strategies for enhancing the strength and stiffness of as-grown materials. We fabricated densified wood by thermochemically treating raw white oak wood in Na2SO3 and NaOH solutions, followed by compressing the treated wood at 5MPa at high temperature. Treating the raw wood in NaOH and Na2SO3 cleaves the alpha-O-4 ether bond and beta-O-4 ether bonds, thus dissolving most of the lignin and hemicellulose, which allows the wood cell walls, vessels, and pits to collapse when compressed. This allows the crystalline cellulose microfibril to align themselves adjacent to the neighboring crystalline cellulose, which increases the strength, crystallinity percentage, and crystallite size. The resulting enhanced wood microstructures were characterized using optical and scanning electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, and mechanical testing. Under optimal processing conditions, the thermochemically densified wood exhibited a maximum strength of 350 MPa – 370 MPa, which is 5-fold higher than the raw wood. This process results in a wood material that is comparatively as strong as some structural aluminum alloys and has potential as a future material for high-performance engineering applications.