Self‐Densification of Highly Mesoporous Wood Structure into a Strong and Transparent Film

Abstract

In the native wood cell wall, cellulose microfibrils are highly aligned and organized in the secondary cell wall. A new preparation strategy is developed to achieve individualization of cellulose microfibrils within the wood cell wall structure without introducing mechanical disintegration. The resulting mesoporous wood structure has a high specific surface area of 197 m2 g−1 when prepared by freeze‐drying using liquid nitrogen, and 249 m2 g−1 by supercritical drying. These values are 5 to 7 times higher than conventional delignified wood (36 m2 g−1) dried by supercritical drying. Such highly mesoporous structure with individualized cellulose microfibrils maintaining their natural alignment and organization can be processed into aerogels with high porosity and high compressive strength. In addition, a strong film with a tensile strength of 449.1 ± 21.8 MPa and a Young's modulus of 51.1 ± 5.2 GPa along the fiber direction is obtained simply by air drying owing to the self‐densification of cellulose microfibrils driven by the elastocapillary forces upon water evaporation. The self‐densified film also shows high optical transmittance (80%) and high optical haze (70%) with interesting biaxial light scattering behavior owing to the natural alignment of cellulose microfibrils.

Strong Foam-like Composites from Highly Mesoporous Wood and Metal-Organic Frameworks for Efficient CO2 Capture

“… 34 The BET specific surface area ( S BET ) of the TO-wood was 172 m 2 g –1 (Table S1, Supporting Information ), about 30% lower than that reported in our previous work (249 m 2 g –1 ). 31 This is due to the lack of extensive washing step with water, which limited the separation of individualized cellulose microfibrils and swelling of the cell wall.…”

“…As shown in Scheme 1 , a balsa wood block with a dimension of 10 × 10 × 10 mm 3 was delignified with 1 wt % sodium chlorite in sodium acetate buffer (pH 4.6) at 80 °C for 12 h. The delignified wood was then oxidized with a TEMPO/NaClO 2 /NaClO system at pH 6.8 for 48 h following the method reported in our previous work. 31 After TEMPO-mediated oxidation, the wood blocks were further washed in an ethanol/water mixture (1:1, v/v) to remove residue chemicals and minimize swelling in water, producing the TO-wood.…”

“…In our previous study, a hierarchical 3D network of cellulose microfibrils was prepared from wood through a top-down delignification process, followed by TEMPO-mediated oxidation at neutral conditions. 31 This TEMPO-oxidized wood (TO-wood) showed a highly mesoporous cell wall structure with fibrillated but naturally aligned cellulose microfibrils and demonstrated high mechanical performance. Herein, we report a facile approach to fabricate foam-like cellulose/MOF composites with prominent mechanical properties, good thermal stability, and high CO 2 adsorption capacity using TO-wood structure as the template.…”

Interface tailoring by a versatile functionalization platform for nanostructured wood biocomposites

“…This carboxyl functionality is very interesting, since it has recently been used successfully for strong, wood-based films, where modification is based on a less sustainable TEMPO-oxidation method. 77 In fully sustainable synthetic pathways, the chemicals should be recoverable and reused for further reactions. Overall, the reaction system is indeed designed so that all reactants can be recovered and reused after chemical reaction, without altering the degree of esterification (Fig.…”

Effect of Lignin Content on Properties of Flexible Transparent Poplar Veneer Fabricated by Impregnation with Epoxy Resin

“…The tensile strength of PV was 114 MPa, and the tensile strength of TPV 2 , TPV 4 , TPV 6 , TPV 8 , TPV 10 decreased to 97 MPa, 88 MPa, 81 MPa, 67 MPa, and 54 MPa, respectively. In wood, cellulose existing in the cell wall is the skeleton material of the cell wall, and lignin permeates into the cellulose skeleton as a binder to strengthen the cell wall [41,42]. With the removal of lignin, the location of lignin was occupied by epoxy resin, and the voids of the cell wall were also filled.…”