There has been a recent surge of interest in biobased foams for applications ranging from building sustainability (insulation) to biomedicine, pharmaceutics, and electronics (scaffolds), with nanocellulose-based foams being particularly promising due to their porous and low-density structure. This study compares the production energy, structure, and properties of foams made from TEMPO-oxidized lignocellulose nanofibers (FTOLCNF) derived from unbleached wood pulp, and TEMPO-oxidized cellulose nanofibers (FTOCNF) from bleached cellulose pulp. Additionally, the incorporation of tannic acid (TA) as a biobased additive is explored for its ability to enhance the mechanical strength of FTOLCNF, contributing to improved performance. This builds upon the inherent advantages of FTOLCNF, which not only demonstrate superior structural integrity and load-bearing capacity (specific Young’s modulus of 37.4 J g–1, compared to 16.4 J g–1 for TOCNF) but also exhibit a higher yield during production due to the minimal processing required for unbleached pulp. Furthermore, FTOLCNF production requires about 18% less cumulative energy than FTOCNF (27 vs 33 MJ kg–1), largely owing to the energy-efficient preparation of TOLCNF from unbleached wood pulp. FTOLCNF also have a significantly lower cumulative energy demand (CED) compared to fossil-based alternatives like expanded polystyrene (EPS) and polyurethane (PU), highlighting their reduced environmental impact. Despite their lightweight nature, FTOLCNF exhibit competitive compressive strength, making them viable candidates for eco-friendly applications across various industries. Overall, this study demonstrates that FTOLCNF are an attractive alternative to other bio- and fossil-based foams, offering a balance of energy efficiency, higher yield, mechanical performance, and sustainability.

Cellulose nanocrystals (CNCs) are widely used in advanced materials due to their unique mechanical and physicochemical properties. However, their interactions with water, particularly in the context of drying, remain poorly understood. The presence of bound water in CNC poses challenges for processing, storage, and applications sensitive to moisture. In this study, we combine molecular simulations and experimental drying investigations to assess the extent of water retention in both native and TEMPO-CNC under different thermodynamic conditions. Our results demonstrate that while native CNCs can be fully dried under low pressure (≤1 mbar) and elevated temperature (110 °C), TEMPO-CNC retain a significant amount of water (1–7 wt%) due to electrostatic interactions between water molecules and the charged surface carboxylic groups and the sodium counter-ions. These findings provide fundamental insights into the drying behavior of functionalized nanocellulose and highlight the importance of considering residual bound water in applications requiring moisture-sensitive performance.

We have produced foams from cellulose nanofibrils from upcycled cotton (upCNF) and wood (wCNF) through unidirectional (UIT) and multidirectional ice-templating (MIT) and investigated the structural humidity response through in-situ WAXS, SAXS, and micro tomography (μCT) between 10 and 95 % relative humidity (RH). The upCNF and wCNF WAXS patterns displayed a shape- and position shift as the RH was increased, with a compression in the (200) direction and an elongation in the (004) direction. The average separation distance extracted from the 1D SAXS patterns revealed no significant change for the upCNF foams regardless of RH and processing route, while a significant increase was observed for the wCNF foams. The μCT measurements of the upCNF foams showed a slight shift in macropore distribution towards larger pores between 50 and 80 % RH which can be attributed to the weakening and partial disintegration of the pore wall as more moisture is introduced. The humidity-induced structural alterations of the upCNF foam were significantly lower compared to the wCNF foams, confirming our claim of upCNF being more moisture resistant than wCNF foams.

Actuators based on electrically conductive and hydrophilic two-dimensional (2D) Ti₃C₂T_X MXene are of interest for fast and specific responses in demanding environments, such as chemical production. Herein, Ti₃C₂T_X-based solvent-responsive bilayer actuators were developed, featuring a gradient polymer-intercalation structure in the active layer. These actuators were assembled using negatively charged pristine Ti₃C₂T_X nanosheets as the passive layer and positively charged polymer-tethered Ti₃C₂T_X as the active layer. 2D wide-angle X-ray scattering and simulations related the gradient polymer intercalated microstructure in the polymer/MXene composite active layer to the counterintuitive actuation behavior. The bending of the bilayer films in solvent vapor is triggered by the gradient polymer-intercalation and the differing diffusion rate of solvent molecules through the MX and MX-polymer layers of the bilayer actuator. With their ease of fabrication, remote light-control capabilities, and excellent actuation performance, the Ti₃C₂T_X-based bilayer actuators reported here may find applications in areas such as sensors for monitoring chemical production, infrared camouflage, smart switches, and excavators in toxic solvent environments.

The upcycling of discarded garments can help to mitigate the environmental impact of the textile industry. Here, we fabricated hybrid anisotropic foams having cellulose nanocrystals (CNCs), which were isolated from discarded cotton textiles and had varied surface chemistries as structural components, in combination with xanthan gum (XG) as a physical crosslinker of the dispersion used for foam preparation. All CNCs had crystallinity indices above 85 %, zeta potential values below -40 mV at 1 mM NaCl, and true densities ranging from 1.61 to 1.67 g center dot cm(-3). Quartz crystal microbalance with dissipation (QCM-D) measurements indicated weak interactions between CNC and XG, while rheology measurements showed that highly charged CNCs caused the XG chains to change from an extended to a helicoidal conformation, resulting in changes the in viscoelastic properties of the dispersions. The inclusion of XG significantly enhanced the compression mechanical properties of the freeze-casted foams without compromising their thermal properties, anisotropy, or degree of alignment. CNC-XG foams maintained structural integrity even after exposure to high humidity (91 %) and temperatures (100 degrees C) and displayed very low radial thermal conductivities. This research provides a viable avenue for upcycling cotton-based clothing waste into high-performance materials.

Anisotropic cellulose nanofiber (CNF) foams represent the state-of-the-art in renewable insulation. These foams consist of large (diameter >10 μm) uniaxially aligned macropores with mesoporous pore-walls and aligned CNF. The foams show anisotropic thermal conduction, where heat transports more efficiently in the axial direction (along the aligned CNF and macropores) than in the radial direction (perpendicular to the aligned CNF and macropores). Here we explore the impact on axial and radial thermal conductivity upon depositing a thin film of reduced graphene oxide (rGO) on the macropore walls in anisotropic CNF foams. To obtain rGO films on the foam walls we developed liquid-phase self-assembly to deposit rGO in a layer-by-layer fashion. Using electron and ion microscopy, we thoroughly characterized the resulting rGO-CNF foams and confirmed the successful deposition of rGO. These hierarchical rGO-CNF foams show lower radial thermal conductivity (λ_r) across a wide range of relative humidity compared to CNF control foams. Our work therefore demonstrates a potential method for improved thermal insulation in anisotropic CNF foams and introduces versatile self-assembly for postmodification of such foams.

Lightweight and mechanically robust hybrid foams based on cellulose nanocrystals (CNC) and multi-walled carbon nanotubes (MWCNT) with an anisotropic structure are prepared by directional ice-templating. The anisotropic hybrid CNC-MWCNT foams displayed a combination of highly anisotropic thermal conductivity and an orientation-dependent electromagnetic interference (EMI) shielding with a maximum EMI shielding efficiency (EMI-SE) of 41–48 dB between 8 and 12 GHz for the hybrid foam with 22 wt% MWCNT. The EMI-SE is dominated by absorption (SE_A) which is important for microwave absorber applications. Modelling of the low radial thermal conductivity highlighted the importance of phonon scattering at the heterogeneous CNC-MWCNT interfaces while the axial thermal conductivity is dominated by the solid conduction along the aligned rod-like particles. The lightweight CNC-MWCNT foams combination of an anisotropic thermal conductivity and EMI shielding efficiency is unusual and can be useful for directional heat transport and EMI shielding. 

Superinsulating nanofibrillar cellulose foams have the potential to replace fossil-based insulating materials, but the development is hampered by the moisture-dependent heat transport and the lack of direct measurements of phonon transport. Here, inelastic neutron scattering is used together with wide angle X-ray scattering (WAXS) and small angle neutron scattering to relate the moisture-dependent structural modifications to the vibrational dynamics and phonon transport and scattering of cellulose nanofibrils from wood and tunicate, and wood cellulose nanocrystals (W-CNC). The moisture interacted primarily with the disordered regions in nanocellulose, and WAXS showed that the crystallinity and coherence length increased as the moisture content increased. The phonon population derived from directional-dependent phonon density of states (GDOS) increased along the cellulose chains in W-CNC between 5 and 8 wt% D₂O, while the phonon population perpendicular to the chains remained relatively unaffected, suggesting that the effect of increased crystallinity and coherence length on phonon transport is compensated by the moisture-induced swelling of the foam walls. Frequency scaling in the low-energy GDOS showed that materials based on hygroscopic and semicrystalline nanocellulose falls in between the predicted behavior for solids and liquids. Phonon-engineering of hygroscopic biopolymer-based insulation materials is promoted by the insights on the moisture-dependent phonon transport.

Biopolymer-based functional materials are essential for reducing the carbon footprint and providing high-quality lightweight materials suitable for packaging and thermal insulation. Here, cellulose nanocrystals (CNCs) were efficiently upcycled from post-consumer cotton clothing by TEMPO-mediated oxidation and HCl hydrolysis with a yield of 62% and combined with wood cellulose nanofibrils (CNFs) to produce anisotropic foams by unidirectional freeze-casting followed by freeze drying (FD) or supercritical-drying (SCD). Unidirectional freeze-casting resulted in foams with aligned macropores irrespective of the drying method, but the particle packing in the foam wall was significantly affected by how the ice was removed. The FD foams showed tightly packed and aligned CNC and CNF particles while the SCD foams displayed a more network-like structure in the foam walls. The SCD compared to FD foams had more pores smaller than 300 nm and higher specific surface area but they were more susceptible to moisture-induced shrinkage, especially at relative humidities (RH) > 50%. The FD and SCD foams displayed low radial thermal conductivity, and the FD foams displayed a higher mechanical strength and stiffness in compression in the direction of the aligned particles. Better understanding how drying influences the structural, thermal, mechanical and moisture-related properties of foams based on repurposed cotton is important for the development of sustainable nanostructured materials for various applications.