High-Strength and UV-Shielding Transparent Thin Films from Hot-Pressed Sulfonated Wood

Abstract

Wood is a high-strength lightweight material owing to its orthotropic cellular structure and composite-like constitution. In conventional fabrication of wood-derived functional materials, the removal of the potentially beneficial components, such as lignin and hemicellulose, often leads to the disruption of the native hierarchical wood structure. Herein, we developed a facile method of in situ wood sulfonation followed by hot pressing for pine veneers to prepare high-density transparent thin films with preserved wood components and the natural fiber alignment. An optimum lignin content of the hot-pressed films was found to be 20.6% where both mechanical and optical properties were significantly enhanced with a more dense and compact structure. The hot-pressed transparent wood films also showed UV-blocking capability and could be recycled into discrete wood fibers owing to the sulfonate groups endowed by the in situ sulfonation step. The unique combination of properties achieved for thin wood films marks an important step in engineering functional wood-based materials that utilize both the structure of aligned fibers and the complex components of natural wood.

Wood Templated Organic Electronics

“…To introduce wood with new functionalities 36 , wood is usually pre-treated before being modified using other functional materials. Various pretreatment methods including carbonization 44 , sulfonation 40 , delignification 42 , and hot-pressing 96 have been utilized in order to tailor the wood's chemical and structural properties for further applications. In the pursuit of highperformance wood, the importance of these pretreatment techniques has been highlighted in many studies including the preparation of transparent wood 96,97 , conductive wood (CW) 40,42 , or superstrong wood 98 .…”

“…Various pretreatment methods including carbonization 44 , sulfonation 40 , delignification 42 , and hot-pressing 96 have been utilized in order to tailor the wood's chemical and structural properties for further applications. In the pursuit of highperformance wood, the importance of these pretreatment techniques has been highlighted in many studies including the preparation of transparent wood 96,97 , conductive wood (CW) 40,42 , or superstrong wood 98 . In this thesis, the employed two methods, wood sulfonation, and wood delignification, will be discussed with a focus on their contribution to the preparation of CW.…”

“…These rigorous reaction conditions are designed to eliminate non-cellulosic components like lignin and hemicellulose, with the primary goal of producing pulp fibers. Herein, instead of using an acidic, a neutral pH solution was employed in order to partly remove non-cellulosic components from the wood structure while preserving and in-situ sulfonating remained native lignin (Figure 4.4) 40,41,96 . During the sulfonation process, the dissolution of extractives and hemicellulose majorly occurs in the early stages while the deligninifcation gradually happens and is controlled by the reaction time 39, 96, 99 .…”

“…For electronics, typically for energy storage purposes, this is critically important as lignin is a beneficial component that can store electricity via its redox reactions. Furthermore, the removal of other non-cellulosic components induces wood to a higher porosity, which will facilitate the insertion of electroactive materials into the wood microstructure 40,96 . This approach is able to preserve about 17 wt% lignin in CW, which is subsequently utilized in energy storage applications 40 .…”

Preparation of Photochromic Wood Films Comprising Spiropyran-Based Wood Cellulose Scaffold Realized through Grafting and Densification

“…Compression densification is one of the effective methods used to improve wood strength [34]. Further, this method bestows wood with excellent physical properties [35], making it a structural material with high hardness, density, and strength [36][37][38]. Thus, densified wood can replace hardwood as well as other precious wood species.…”