Lennart Bergström

Hydrogen bonds govern the structure, dynamics, and mechanical properties of biopolymers, yet experimental insights into their temperature-dependent behavior remain limited. Here, we used inelastic neutron scattering (INS) to probe hydrogen-bond dynamics in cellulose nanocrystals derived from softwood that possess the cellulose Iβ crystal structure. Preferential particle alignment enabled investigation of motions along and transverse to the polymer chains. Temperature-dependent phonon density of states (GDOS) revealed transient redistribution of vibrational spectral weight between 300 and 340 K, consistent with hydroxymethyl conformational rearrangements and hydrogen bond reorganization. Directional measurements further revealed that motions along the cellulose chains are more sensitive to conformational rearrangements than transverse motions. The INS and GDOS measurements are consistent with temperature-induced hydrogen bond rearrangements in cellulose, offering a mechanistic framework relevant to hydrogen bonded, anisotropic polymers. Insights from this work may guide the design of nanocellulose-based and other polymeric materials with tailored heat transport and mechanical properties.

Disposable diapers pose a significant environmental challenge due to their complex composition and persistent accumulation in landfills. This work presents an efficient recycling approach that achieves full-range recycling of all diaper components, transforming more than 95 wt % of urine-contaminated diapers into useful materials with near-zero secondary waste generation. Using a NaOH/urea solution system, cellulose, superabsorbent polymers (SAP), and nonwoven fabrics (NWF) were efficiently separated under mild conditions. The cellulose was directly converted into anisotropic cellulose nanoparticles (CNP) of high quality and long-term colloidal stability, without any complex post-treatment. SAP could function as mechanical modifier that evidently enhances the viscoelastic properties of CNP-based foams. The NWF were dissolved in recyclable n-octadecane and utilized as a polymer source to form performance-enhancing coatings, which effectively improve the water resiliency and mechanical robustness of foams. All remaining residues produced during the recycling process were further upcycled into porous foams with tunable microstructure and mechanical performance. This study demonstrates a practical and scalable approach to valorizing an otherwise challenging waste stream and provides a model for recycling complex multicomponent materials.

Nanocellulose is a promising alternative to fossil‐derived materials, but its development is hindered by a limited understanding of cellulose–water interactions. Herein, quasielastic neutron scattering (QENS) is used to investigate how hydration and temperature affect the localized rotations in cellulose nanocrystals (CNC) and the diffusion of mobile water. QENS reveals that the C6 hydrogens and the C6 OH in the surface regions of CNC exhibit an isotropic rotation. The extracted mean square displacement shows that hydration enhances the overall hydrogen mobility in the cellulose chains. The mobile water diffusion at 270 K is unaffected by cellulose and consistent with diffusion of supercooled bulk water. At 310 K, the diffusion slows compared to bulk water, consistent with water diffusing on the CNC surface. Decoupling of the translational and rotational motion provides insight into the local cellulose–water motions. The localized motions of the nondiffusing water are found to be coupled with cellulose at 310 K, indicating a more complex dynamics at higher temperature. These findings provide new insights into how hydration modulates hydrogen mobility in cellulose, highlighting the interplay between water diffusion and molecular motion.

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% D ₂ O, 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.

Solvent vapor-responsive Ti₃C₂T_x-based actuators with a gradient microstructure in their composite active layer are prepared. The actuation behavior is understood by wide angle scattering, density functional theory and molecular dynamics.

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.

Textile cellulose nanocrystals and wood cellulose nanofibrils are used to prepare foams by freeze drying or supercritical drying. The drying route impacts the foam structure and properties paving the way to tailor foams depending on the application.