Realistic 3D microstructure models of wood fiber networks (WFNs, e.g., paper, molded fibers, hot-pressed fibers, etc.) are of interest for numerical modeling of mechanical, optical, and other physical properties. One challenge is to numerically describe 3D high-density WFN (HD-WFN) models with complex fiber shapes without fiber overlapping. An efficient method is proposed to generate 3D HD-WFN microstructures with porosities as low as 21.5% while without fiber overlapping. The HD-WFN microstructures are obtained by compressing an initially sparse structure using a geometrically designed 3D displacement field. The sparse structure can be optimized to obtain a very low-porosity HD-WFN by reducing the local fiber clustering. The method can generate HD-WFNs with designated shapes (e.g., molded shapes) and varied structural parameters, including fiber width, orientation, location, and material thickness. Each interfiber bond and local material axis in the HD-WFN models can be determined for numerical simulation of properties. The optical scattering of transparent HD-WFN models (polymer matrix composites, transparent paper) is numerically studied using ray tracing methods. The open-source code is available on GitHub, and it can be used to obtain a large dataset for deep learning modeling.

Mechanical behavior of high-density oriented spruce and aspen fiber networks from mildly delignified holocellulose fibers is investigated. Such recyclable, eco-friendly fiber networks are of interest for molded fiber materials and biocomposites. The aspen holocellulose fiber network showed excellent mechanical properties comparable to spruce despite much shorter fiber length. This contrasts with lower density “paper” structures from short fibers which show lower strength than spruce fiber networks. Present results are explained by improved interfiber shear strength and reduced critical fiber length. Microstructures and damage mechanisms were analyzed for materials design purposes using FE-SEM, wide-angle X-ray scattering (WAXS) and tensile testing with strain-field measurements using Digital Image Correlation (DIC).

The cradle-to-cradle philosophy is desirable for semi-structural cellulose biocomposites. Selective chemical recycling of a thermoset matrix back to reusable monomers was realized while avoiding cellulose fiber degradation. A fully biosourced, PLA-based (polylactic acid) thermoset polymer was molecularly designed for chemical recycling and for curing in chemically heterogeneous plant fiber networks. Curing was by stepwise polymerization of 4-arm functional prepolymers of PLA in a cellulosic wood fiber network of high fiber content. FT-IR data supported covalent fiber/matrix interface bonding. These eco-friendly biocomposites showed high modulus (24 GPa) and high optical transmittance. The matrix was selectively degraded back to the initial building block, lactic acid monomer, under alkali conditions. This progressed without apparent damage to the cellulosic fibers. The green metrics of the synthesis showed strong potential for this material concept in a circular economy.

Translucent wood fiber composites offer new functions to stiff composites. Most "eco-friendly" thermoset resins are only partially biobased. Poly(limonene acrylate), PLIMA, can be fully biobased and is combined with hot-pressed softwood fibers (WF) by liquid resin impregnation and curing. Fibers are random-in-plane or strongly oriented and have different lignin characteristics. Microstructure-mechanical property relationships are compared for hot-pressed WF networks and WF/PLIMA biocomposites from the same fibers. Stress transfer in WF/PLIMA biocomposites is enhanced with a modulus of up to 16.7 GPa and a tensile strength of up to 139 MPa, compared to transparent plastics like poly(methyl methacrylate) (modulus similar to 3 GPa, tensile strength similar to 70 MPa). Optical transmittance is high, even at 35 vol % fiber content, suggesting translucent panels or lighting applications. Eco-indicators show that the PLIMA matrix accounts for similar to 80% of biocomposite cumulative energy demand (CED, cradle to gate) of 60 MJ/kg, compared to similar to 120 MJ/kg for glass fiber/thermoset composites.

Pharmaceuticals, designed for treating diseases, ironically endanger humans and aquatic ecosystems as pollutants. Adsorption-based wastewater treatment could address this problem, however, creating efficient adsorbents remains a challenge. Recent efforts have shifted towards sustainable bio-based adsorbents. Here, cryogels from lignin-containing cellulose nanofibrils (LCNF) and lignin nanoparticles (LNPs) were explored as pharmaceuticals adsorbents. An enzyme-based approach using laccase was used for crosslinking instead of fossil-based chemical modification. The impact of laccase treatment on LNPs alone produced surface-crosslinked water-insoluble LNPs with preserved morphology and a hemicellulose-rich, water-soluble LNP fraction. The water-insoluble LNPs displayed a significant increase in adsorption capacity, up to 140 % and 400 % for neutral and cationic drugs, respectively. The crosslinked cryogel prepared by one-pot incubation of LNPs, LCNF and laccase showed significantly higher adsorption capacities for various pharmaceuticals in a multi-component system than pure LCNF or unmodified cryogels. The crosslinking minimized the leaching of LNPs in water, signifying enhanced binding between LNPs and LCNF. In real wastewater, the laccase-modified cryogel displayed 8–44 % removal for cationic pharmaceuticals. Overall, laccase treatment facilitated the production of bio-based adsorbents by improving the deposition of LNPs to LCNF. Finally, this work introduces a sustainable approach for engineering adsorbents, while aligning with global sustainability goals.

Adsorption is a relatively simple wastewater treatment method that has the potential to mitigate the impacts of pharmaceutical pollution. This requires the development of reusable adsorbents that can simultaneously remove pharmaceuticals of varying chemical structure and properties. Here, the adsorption potential of nanostructured wood-based adsorbents towards different pharmaceuticals in a multi-component system was investigated. The adsorbents in the form of macroporous cryogels were prepared by anchoring lignin nanoparticles (LNPs) to the nanocellulose network via electrostatic attraction. The naturally anionic LNPs were anchored to cationic cellulose nanofibrils (cCNF) and the cationic LNPs (cLNPs) were combined with anionic TEMPO-oxidized CNF (TCNF), producing two sets of nanocellulose-based cryogels that also differed in their overall surface charge density. The cryogels, prepared by freeze-drying, showed layered cellulosic sheets randomly decorated with spherical lignin on the surface. They exhibited varying selectivity and efficiency in removing pharmaceuticals with differing aromaticity, polarity and ionic characters. Their adsorption potential was also affected by the type (unmodified or cationic), amount and morphology of the lignin nanomaterials, as well as the pH of the pharmaceutical solution. Overall, the findings revealed that LNPs or cLNPs can act as functionalizing and crosslinking agents to nanocellulose-based cryogels. Despite the decrease in the overall positive surface charge, the addition of LNPs to the cCNF-based cryogels showed enhanced adsorption, not only towards the anionic aromatic pharmaceutical diclofenac but also towards the aromatic cationic metoprolol (MPL) and tramadol (TRA) and neutral aromatic carbamazepine. The addition of cLNPs to TCNF-based cryogels improved the adsorption of MPL and TRA despite the decrease in the net negative surface charge. The improved adsorption was attributed to modes of removal other than electrostatic attraction, and they could be 7C-7C aromatic ring or hydrophobic interactions brought by the addition of LNPs or cLNPs. However, significant improvement was only found if the ratio of LNPs or cLNPs to nanocellulose was 0.6:1 or higher and with spherical lignin nanomaterials. As crosslinking agents, the LNPs or cLNPs affected the rheological behavior of the gels, and increased the firmness and decreased the water holding capacity of the corresponding cryogels. The resistance of the cryogels towards disintegration with exposure to water also improved with crosslinking, which eventually enabled the cryogels, especially the TCNF-based one, to be regenerated and reused for five cycles of adsorption-desorption experiment for the model pharmaceutical MPL. Thus, this study opened new opportunities to utilize LNPs in providing nanocellulose-based adsorbents with additional functional groups, which were otherwise often achieved by rigorous chemical modifications, at the same time, crosslinking the nanocellulose network.

Nanocellulose is very hydrophilic, preventing interactions with the oil phase in Pickering emulsions. This limitation is herein addressed by incorporating lignin nanoparticles (LNPs) as co-stabilizers of nanocellulose-based Pickering emulsions. LNP addition decreases the oil droplet size and slows creaming at pH 5 and 8 and with increasing LNP content. Emulsification at pH 3 and LNP cationization lead to droplet flocculation and rapid creaming. LNP application for emulsification, prior or simultaneously with nanocellulose, favors stability given the improved interactions with the oil phase. The Pickering emulsions can be freeze–dried, enabling the recovery of a solid macroporous foam that can act as adsorbent for pharmaceutical pollutants. Overall, the properties of nanocellulose-based Pickering emulsions and foams can be tailored by LNP addition. This strategy offers a unique, green approach to stabilize biphasic systems using bio-based nanomaterials without tedious and costly modification procedures.

Unbleached wood fibers and nanofibers are environmentally friendly bio-based candidates for material production, in particular, as reinforcements in polymer matrix biocomposites due to their low density and potential as carbon sink during the materials production phase. However, producing high reinforcement content biocomposites with degradable or chemically recyclable matrices is troublesome. Here, we address this issue with a new concept for facile and scalable in-situ polymerization of polyester matrices based on functionally balanced oligomers in pre-formed lignocellulosic networks. The idea enabled us to create high reinforcement biocomposites with well-dispersed mechanically undamaged fibers or nanocellulose. These degradable biocomposites have much higher mechanical properties than analogs in the literature. Reinforcement geometry (fibers at 30 mu m or fibrils at 10-1000 nm diameter) influenced the polymerization and degradation of the polyester matrix. Overall, this work opens up new pathways toward environmentally benign materials in the context of a circular bioeconomy. Cellulose biocomposites from nanocellulose or plant fibers with polymer matrix are often not degradable and suffer from insufficient mechanical properties to replace established materials. Here, the authors demonstrate the fabrication of hydrolytically degradable polymers through in-situ polymerization of new functionally balanced oligomers within high-content lignocellulose reinforcement networks.

All-lignocellulose composites, meaning densified fiber or fibril materials without added binder, show interesting mechanical properties and can be eco-friendly. Composites based on hot-pressed microfibrillated lignocellulose (MFLC) and lignocellulosic wood fiber (WF) reinforcements are compared with respect to processing, structure, mechanical properties, and eco-indicators. Also, these reinforcements are compared in hot-pressed degradable lignocellulosic crosslinked polycaprolactone (c-PCL) biocomposites based on in-situ polymerization of new caprolactone oligomers.

The intermediate lignin content (≈11%) was favorable for MFLC preparation, although the cumulative energy demand was high for mechanical disintegration from unbleached softwood kraft pulp. The mechanical properties were much better for random-in-plane MFLC compared with WF composites due to lower porosity, better interfiber bonding, and smaller-scale defects. Data for strain-field development during tensile tests was in support of these findings. For c-PCL biocomposites, much higher ultimate strength was obtained for the c-PCL/MFLC composites compared with c-PCL/WF. The most important reason was the strainhardening behavior combined with higher strain to failure, since the scale of developing defects was much smaller with MFLC reinforcement.

Kompositer baserade på enbart lignocellulosa, dvs pressade fiber- eller fibrillmaterial utan tillsatt bindemedel, har intressanta mekaniska egenskaper och är ofta miljövänliga material. Varmpressad mikrofibrillerad lignocellulosa (MFLC) och varmpressade träfibrer (WF) jämförs med avseende på process, struktur, mekaniska egenskaper och ekoindikatorer. De jämförs också i varmpressade nedbrytbara c-PCL-biokompositer baserade på in-situ polymerisation av nya kaprolakton-oligomerer. 

Ett optimum i ligninhalt (≈11%) var gynnsamt för MFLC-framställning, även om det kumulativa energibehovet var högt för mekanisk sönderdelning till MFLC från oblekt barrvedsmassa. De mekaniska egenskaperna var mycket bättre för MFLC jämfört med WF-kompositer för slumpmässig fiberorientering i planet. Orsakerna är lägre porositet, bättre bindning mellan fibrer och att storleken på materialdefekterna är små för MFLC. Data för töjningsfältsutveckling under dragförsök gav stöd för dessa förklaringar. För biokompositer baserade på c-PCL var hållfastheten mycket högre för c-PCL/MFLC-kompositer jämfört med cPCL/WF. Den viktigaste orsaken var starkt töjningshårdnande i kombination med högre töjning till brott, vilket troligen beror på att defekterna som utvecklas under mekanisk belastning av c-PCL/MFLC är mycket mindre än för c-PCL/WF, vid jämförbar töjning.

Hot-pressed, binder-free wood fiber (WF) composites can serve as load-bearing and eco-friendly materials, and the comparison of nanoscale fibril reinforcement with microscale wood fibers is of interest. We investigated property differences and interpreted deformation mechanisms with strain field measurements using digital image correlation combined with orthotropic, elastic–plastic finite element model updating predictions. Random-in-plane microfibrillated lignocellulose (MFLC) composites showed better mechanical properties than WF composites due to stronger strain-hardening from lower porosity and better interfibrillar adhesion, provided by the intrinsic lignin-hemicellulose binder. Axially oriented wood fiber composites (O-WF) achieved comparable mechanical properties to random MFLC, with lower values for eco-indicators. The FEM updating method could successfully determine all 4 independent elastic constants from one 45° off-axis experiment, although the plasticity model required two more experiments.