All-Wood Composite Material by Partial Fiber Surface Dissolution with an Ionic Liquid

Synthetic structural materials of high mechanical performance are typically either of large weight (for example, steels, and alloys) or involve complex manufacturing processes and thus have high cost or cause adverse environmental impact (for example, polymer-based and biomimetic composites). In this perspective, low-cost, abundant and nature-based materials, such as wood, represent particular interest provided they fulfill the requirements for advanced engineering structures and applications, especially when manufactured totally additive-free. Here, we report on a novel all-wood material concept based on delignification, partial surface dissolution using ionic liquid (IL) followed by densification resulting in a high-performance material. A delignification process using sodium chlorite in acetate buffer solution was applied to controllably delignify the entire bulk wooden material while retaining the highly beneficial structural directionality of wood. In a subsequent step, obtained delignified porous wood template was infiltrated with an IL 1-ethyl-3-methylimidazolium acetate, [EMIM]OAc and heat activated at 95 °C to partially dissolve the fiber surface. Afterward, treated wood was washed with water to remove IL and hot-pressed to gain a very compact cellulosic material with fused fibers while retaining unidirectional fiber orientation. The obtained cellulose materials were structurally, chemically, and mechanically characterized revealing superior tensile properties compared to native wood. Furthermore, suggested approach allows almost 8-fold tensile strength improvement in the direction perpendicular to fiber orientation, which is otherwise very challenging to achieve.