Abstract
Wood-based multifunctional materials with excellent mechanical performance are increasingly considered for sustainable advanced applications due to their unique hierarchical structure and inherent reinforcing cellulose phase orientation. Nonetheless, a wider multipurpose utilization of wood materials is so far hampered because of constraints arising from scalable functionalization, efficient processing, facile shaping as well asnatural heterogeneity and durability. This study introduces a multifunctional all-wood material fabrication method relying on delignification, ionic liquid (IL) treatment, and pressure-assisted consolidation of wood. Structure-retaining controlled delignification of wood was performed to enable direct access to the hierarchical cellulose assembly, while preserving the highly aligned and thus beneficial wood structural directionality. As a following step, the obtained biobased scaffold with an increased porosity was infiltrated with an IL and heat-activated to partially dissolve and soften the cellulose fiber surface. Samples washed with water to remove IL exhibited pronounced isotropic flexibility, which upon combined compression and lateral shear allowed the fabrication of various 3D shapes with adjustable fiber architecture. The obtained very compact and totally additive-free all-wood materials were extensively characterized, revealing superior mechanical performance, and gained multifunctionality compared to native wood.
Highlights
Multifunctional high-performance lightweight structural materials of exceptional mechanical properties are in high demand in our technologized society
Protocol established in our previous investigation was employed, which showed that lignin content was partly reduced in natural wood upon delignification, whereas only minor reduction in hemicellulose contents was observed.[35]
The delignification process leads to a higher porosity of the wood, facilitating the chemicals assess to the cellulose fibers
Summary
Multifunctional high-performance lightweight structural materials of exceptional mechanical properties are in high demand in our technologized society. The top-down approach that allows the utilization and modification of the inherent hierarchical structure of wood has recently become an appealing alternative to add novel specific functionalities to broaden the application areas of wood, while preserving its sophisticated structure These include transparency,[8] electrical properties,[9−11] magnetism,[12,13] biosorption,[14] stimuli-responsiveness,[15] supercapacitance,[16] and oil− water separation features.[17,18] Transformation of wood into a high-performance engineering material has recently been demonstrated involving structure-preserving delignification followed by densification steps.[19,20] An interconnected cellulose phase with an impressive stress transfer even without the addition of a matrix was achieved after full delignification and drying of wood, which facilitated neighboring fibers to come into close contact with each other.[21] transparent and anisotropic films with aligned cellulose fibers were manufactured directly from wood following a similar method.[22] Alternatively, excellent mechanical performance was achieved by Song et al after densification of partially delignified wood (DLW) by hot pressing, where the remaining lignin acted as a matrix.[23] Delignification of carefully preselected wood followed by phenolic resin infiltration and densification resulted in very stiff, strong, and moisture-stable wood-based composites.[24] relatively long infiltration times combined with the need of raw material preselection reduce scalability of such approach. Five parallel measurements with periodic image scanning were carried out for 136 h
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