An Energy‐Efficient, Wood‐Derived Structural Material Enabled by Pore Structure Engineering towards Building Efficiency

Abstract

Tremendous efforts have been dedicated to developing cost-effective energy efficiency techniques to lower the energy consumption of buildings. [4,5] The low energy cost of energy efficient buildings can substantially lower their carbon footprint and at the same time provide a more uniform temperature throughout the space and a more comfortable and healthy indoor environment. [6] Traditional structural materials including steels, concretes, alloys, and carbon fibers have been widely used in buildings due to their good mechanical properties. However, most of them fail to meet the simultaneous needs of mechanical and thermal insulation properties for advanced energy-efficient buildings because of their relatively high thermal conductivities. Moreover, these materials are nonrenewable, and have high costs and greenhouse gas emissions during their extraction/synthesis processes, which compromises their efficacy in a sustainable society. Compared with conventional building materials, green building materials can enhance indoor environmental quality and thus bring us a more satisfying workplace for the buildings' occupants, and in turn, improve workforce productivity. Wood is a sustainable and versatile building material that stores, rather than emits, carbon dioxide. A reduction of 2432 metric tons of carbon dioxide can be achieved by using wood. [7,8] Recently, the development of using advanced wooden materials for construction has raised substantial interest. [9] Many recent projects such as the tall wood building in Vancouver and the Timber city have used wood as the main constructional material due to its economic and environmental benefits over current constructional materials like steel and concrete, which are nonrenewable and have high embodied energies. [10] Despite the economic and environmental benefits, the current woodbased panels still face many challenges. Natural wood cannot meet the mechanical performance requirements promoted by the Department of Energy (DOE) programs for energy efficient buildings. The mechanical strength of natural wood prevents its applications to mid-rise and high-rise buildings. [11] Developing strong and thermal insulating structural materials is highly desirable for an energy-efficient world. Nonetheless, most of The development of high-performance structural materials for high-rise building applications is critical in achieving the energy conservation goal mandated by the Department of Energy (DOE). However, there is usually a trade-off between the mechanical strength and thermal insulation properties for these materials. Here, the optimization is demonstrated of natural wood to simultaneously improve the mechanical properties and thermal insulation for energy efficient high-rise wood buildings. The improved wood material (strong white wood) features a complete delignification followed by a partial densification process (pore structure control), which enables substantially enhanced mechanical properties (≈3.4× in tensile strength, ≈3.2× in toughness) and reduced thermal conduct...

Delignified Wood from Understanding the Hierarchically Aligned Cellulosic Structures to Creating Novel Functional Materials: A Review

“…The bleached wood pieces were further treated in a 5 wt% NaOH solution at 90 °C for 7 h to remove hemicellulose, followed by two more bleaching steps with acidic NaClO 2 solution (2 wt%). [107] chemicals. The bleaching solution utilized in the preparation of the DW substrate for transparent wood was prepared by mixing deionized water, sodium silicate (3 wt%), sodium hydroxide solution (3 wt%), magnesium sulfate (0.1 wt%), ethylenediaminetetraacetic acid (EDTA) (0.1 wt%), and H 2 O 2 (4 wt%).…”

“…The same research group recently fabricated high quantity and thicker bulk wood materials via the delignification‐densification process. [ 107 ] In this work, wood blocks were first delignified and then stacked and hot‐pressed together to achieve densification. The prepared bulk wood showed a high tensile strength of 161.3 MPa, which is threefold higher than natural wood.…”

Nanoscale Ion Regulation in Wood‐Based Structures and Their Device Applications

“…), chemical modification (only chemical process is involved, for example, oxidation, [ 101 ] acetylation, [ 102 ] furfurylation, [ 103 ] thermal decomposition, [ 104 ] polymerization, [ 105 ] mineralization, [ 106 ] delignification, [ 107 ] surface functionalization, [ 108 ] ionic crosslinking, [ 109 ] counter‐ion exchange, [ 110 ] etc. ), or combined modification (at least two physical and/or chemical processes are involved, for example, delignification combined with densification, [ 79,83,111–113 ] delignification followed by surface patterning, [ 81 ] thermal decomposition followed by mineralization, [ 114 ] delignification followed by polymerization, [ 82,115,116 ] and so on), the wood‐based structures can be readily tuned. For example, pore structure (e.g., pore size, porosity, and pore tortuosity) can be tuned by delignification, densification, stretching, pouching holes, or those combined, offering great opportunity for the regulation of ion and fluid transport and other properties of wood‐based structures.…”

“…Among all structural modification strategies, delignification is considered one of the most popular and powerful methods for tuning the top‐down wood‐based structures, which is capable of modulating the wood structure (e.g., porosity, pore size) down to nanoscale as well as its compositions and surface properties (e.g., surface functional groups, surface charge, and surface wettability). [ 61,63,68,78–85,107,111–113,115,116 ] Delignification can be defined as the removal of lignin component from the woody tissue by enzymatic or chemical processes. In the past few decades, various chemical processes have been developed for wood delignification in delignified wood production (in this case, the hierarchical cellular wood microstructure is maintained) [ 83,107,113,117 ] or paper pulping (in this case, the final product is fibrillated cellulose microfibrils), [ 118,119 ] including enzymatic treatment, [ 120 ] acid treatment, [ 121,122 ] alkaline treatment, [ 117,123–125 ] organic treatment, [ 126–128 ] ionic liquid treatment, [ 129,130 ] and photocatalyst treatment.…”

Effect of Furfurylation on Hierarchical Porous Structure of Poplar Wood

“…Extensive studies have been reported on physical properties, mechanical properties, and modification mechanisms, etc. of wood by furfurylation [ 27 , 28 , 29 , 30 ]. However, little is known about the hierarchical porous structure for furfurylated wood.…”