Sustainable Wood Nanotechnologies for Wood Composites Processed by In-Situ Polymerization

The development of large, multifunctional structures from sustainable wood nanomaterials is challenging. The need to improve mechanical performance, reduce moisture sensitivity, and add new functionalities, provides motivation for nanostructural tailoring. Although existing wood composites are commercially successful, materials development has not targeted nano-structural control of the wood cell wall, which could extend the property range. For sustainable development, non-toxic reactants, green chemistry and processing, lowered cumulative energy requirements, and lowered CO2-emissions are important targets. Here, modified wood substrates in the form of veneer are suggested as nanomaterial components for large, load-bearing structures. Examples include polymerization of bio-based monomers inside the cell wall, green chemistry wood modification, and addition of functional inorganic nanoparticles inside the cell wall. The perspective aims to describe bio-based polymers and green processing concepts for this purpose, along with wood nanoscience challenges.

Wood-Nanotechnology-Based Membrane for the Efficient Purification of Oil-in-Water Emulsions

With increasing amounts of oily water discharged from industrial and domestic sources, purifying oily emulsions using effective and eco-friendly methods is of great significance. Although functional membranes with selective wettabilities have been extensively explored for the efficient purification of oil-in-water emulsions, the development of functional membranes that use green and inexpensive materials, are simple to fabricate, and are easy to scale up remains very challenging. Herein, we report a simple approach that uses biomass to prepare a membrane for the purification of emulsions. A simple top-down approach was used to partially remove lignin and hemicellulose fractions in wood sheets, resulting in a highly porous and flexible wood membrane. The obtained wood membrane shows excellent water-absorbing and underwater anti-oil adhesion properties due to the removal of the hydrophobic lignin. The wood membrane is durable and stable, thereby maintaining its selective wettability in harsh environments. Selective wetting properties along with a porous structure enable the wood membrane to purify surfactant-stabilized oil-in-water emulsions. Such a biomass-derived membrane, which is green, inexpensive, easy to fabricate, and scalable, along with its selective wettability and durability, shows great potential for use as a substitute for existing filter media in diverse industries.

Top-Down Approach Making Anisotropic Cellulose Aerogels as Universal Substrates for Multifunctionalization

Highly porous, strong aerogels with anisotropic structural properties are of great interest for multifunctional materials for applications including insulators in buildings, filters for oil cleanup, electrical storage devices, etc. Contemporary aerogels are mostly extracted from fossil resources and synthesized from bottom-up techniques, often requiring additional strategies to obtain high anisotropy. In this work, a universal approach to prepare porous, strong, anisotropic aerogels is presented through exploiting the natural hierarchical and anisotropic structure of wood. The preparation comprises nanoscale removal of lignin, followed by dissolution-regeneration of nanofibers, leading to enhanced cell wall porosity with nanofibrillated networks occupying the pore space in the cellular wood structure. The aerogels retain structural anisotropy of natural wood, exhibit specific surface areas up to 247 m²/g, and show high compression strength at 95% porosity. This is a record specific area value for wood aerogels/foams and even higher than most cellulose-based aerogels for its assigned strength. The aerogel can serve as a platform for multifunctional composites including scaffolds for catalysis, gas separation, or liquid purification due to its porous matrix or as binder-free electrodes in electronics. To demonstrate the multifunctionality, the aerogels are successfully decorated with metal nanoparticles (Ag) and metal oxide nanoparticles (TiO₂) by in situ synthesis, coated by the conductive polymer (PEDOT:PSS), and carbonized to yield conductive aerogels. This approach is found to be a universal way to prepare highly porous anisotropic aerogels.

Nanostructured Wood Hybrids for Fire-Retardancy Prepared by Clay Impregnation into the Cell Wall

Eco-friendly materials need "green" fire-retardancy treatments, which offer opportunity for new wood nanotechnologies. Balsa wood (Ochroma pyramidale) was delignified to form a hierarchically structured and nanoporous scaffold mainly composed of cellulose nanofibrils. This nanocellulosic wood scaffold was impregnated with colloidal montmorillonite clay to form a nanostructured wood hybrid with high flame-retardancy. The nanoporous scaffold was characterized by scanning electron microscopy and gas adsorption. Flame-retardancy was evaluated by cone calorimetry, whereas thermal and thermo-oxidative stabilities were assessed by thermogravimetry. The location of well-distributed clay nanoplatelets inside the cell walls was confirmed by energy-dispersive X-ray analysis. This unique nanostructure dramatically increased the thermal stability because of thermal insulation, oxygen depletion, and catalytic charring effects. A coherent organic/inorganic charred residue was formed during combustion, leading to a strongly reduced heat release rate peak and reduced smoke generation.