Non-isocyanate polyurethanes (NIPUs) exhibit significantly greater sustainability than conventional polyurethanes (PUs) by adhering to key principles of green chemistry, particularly the elimination of toxic chemicals. In this study, waterborne non-isocyanate polyurethane (WNIPU) latexes, exclusively stabilized by cellulose nanocrystals (CNCs) and partially derived from renewable resources, were synthesized for the first time via suspension polymerization. A polyaddition reaction between a siloxane diamine and 1,6-hexanediol bis(cyclic carbonate) occurred within the monomer-in-water Pickering emulsion droplets effectively stabilized with CNCs. The concentration of the CNCs was optimized for the Pickering emulsion. The CNCs acted as nanoparticle surfactants on the surface of the WNIPU latex particles, as confirmed using rhodamine B-labelled CNCs and confocal laser scanning microscopy. Spherical-shaped monomer droplets and WNIPU latex particles with a median size of 10 mu m were achieved. The effect of the cyclic carbonate-to-amine molar ratio on the amine monomer conversion, molecular weight, and thermal properties of the WNIPU was investigated. The obtained WNIPU suspensions exhibited fluorescence under UV irradiation at 365 nm owing to the clustering of carbamates. Combining the fluorescence properties with low glass transition temperatures, these latexes open various potential applications as functional coatings.

Finite element model updating (FEMU) is an advanced inverse parameter identification method capable of identifying multiple parameters in a material model through one or a few well-designed material tests. The method has become more mature thanks to the widespread use of full-field measurement techniques, such as digital image correlation. Proper application of FEMU requires extensive expertise. This paper offers a review of FEMU and a guide to practice. It also presents FEMU-DIC, an open-source software package. We conclude by discussing the challenges and opportunities in this field with the intent of inspiring future research.

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.

Crab shells, often considered wastes, have the potential to be a valuable source of chitin nanofibrils (ChNFs) for various applications. This study introduces a novel, cost-effective method where NaOH treatment and concrete mechanical vibrator (CMV) produce high-quality ChNFs while maintaining their native properties, such as crystalline structure and higher degree of acetylation. This method, which is the first of its kind, addresses the challenge of developing a scalable approach to ChNF preparation. The crab shells underwent pretreatment with 20% NaOH four times over 2 weeks. Fourier transform infrared spectroscope (FTIR) confirmed preserving the α-chitin intrinsic structure after chemical treatment and mechanical disintegration. The resulting individual ChNFs displayed 82% crystallinity and 86% degree of acetylation, indicating the preservation of their physical properties to a large extent. The ChNFs had a diameter ranging between 10 and 23 nm, as observed under a scanning electron microscope (SEM). Rapid removal of water from the ChNF colloidal suspension using a vacuum pump allowed for forming a ChNF film by drying the resulting wet cake under pressure in an oven. The film exhibited impressive mechanical properties with a tensile strength of 149.9 MPa, Young's modulus of 8.4 GPa, and tensile strain of up to 7.1%. The combination of NaOH and the mechanical vibrator for mechanical disintegration presents an innovative and advantageous approach for scaling up production, especially considering the recyclability of NaOH as an industrial chemical.

This study characterized the anisotropic thermal conductivity of clay/cellulose nanocomposites, an eco-friendly functional flame-retardant material exhibiting excellent mechanical properties, gas barrier properties, and biodegradability. Thermal conductivity anisotropy is important for flame-retardant materials. Low thermal conductivity in the through-thickness direction serves as a thermal barrier, whereas high thermal conductivity in the in-plane direction prevents local heat accumulation. We prepared a series of membranes of nanocomposites of montmorillonite clay platelets and cellulose nanofibrils via vacuum filtration/drying and measured their directional thermal conductivities as a function of the montmorillonite clay/cellulose nanofibril content. The results indicate that the through-thickness and in-plane thermal conductivities depend nonmonotonically on the clay content. The highest in-plane thermal conductivity reached 7.5 W m-1 K-1, exhibiting a maximum anisotropy of 30 for a clay content of 50%. Structural investigation via Raman spectroscopy revealed an enhanced planar alignment of the cellulose nanofibrils and indicated alignment of the clay platelets. The correlation between the degree of alignment and thermal conductivity anisotropy suggests that alignment increases the contact area between the cellulose nanofibrils and clay platelets, which enhances in-plane heat conduction by increasing the phonon transport path and impedes through-thickness heat conduction by enhancing phonon boundary scattering.

Transparent wood (TW) is a sustainable composite material with high optical transmittance and excellent mechanical properties. Nanoparticles, dyes and quantum dots can be added in a controlled manner for new functionalities relying on the light scattering properties of the composite. The scattering properties of 3D TW models of cellular microstructure are investigated numerically using geometrical optics. A group of 3D TW material models with controlled microstructural parameters are generated based on an analytical method. A ray tracing approach is adopted to model scattering in these complex materials. Effects from different material parameters on ray scattering are analyzed. A virtual camera or virtual eye to render images positioned behind a TW plate is simulated using backward ray tracing. The blurred impression in human eyes of real objects viewed through a TW “window” can then be mimicked.

Transparent wood biocomposite (TW) is a sustainable optical material that combines high transmittance with mechanical strength but also exhibits pronounced haze. This haze limits applications where high optical transparency is required, and its physical origin remains insufficiently understood. In this study, photon transport in TW and related wood-based scaffolds at different stages of chemical modification, including delignified wood (DW), native wood (NW) and bleached wood (BW) templates is investigated. Time- and space-resolved transmission measurements are used to extract direction-dependent scattering and absorption coefficients. DW, BW, and NW samples exhibit anisotropic light propagation while TW both suppresses scattering and alters the scattering anisotropy, flipping 90° the dominant transport orientation relative to the fibers. Extracted optical parameters confirm low scattering coefficients, up to 2 orders of magnitude lower than the NW, BW, or DW. The main scattering mechanism for TW is identified as in-plane refraction, leading to predominant forward transmission or “snake-like” photon trajectories, marking a transition from diffusive to quasi-ballistic transport. These insights advance the fundamental understanding of light transport in hierarchical biocomposites and offer a framework for designing sustainable optical composites with broad haze control, increasing the functional potential of TW toward “wood glass”.

Incorporating biobased nanofillers including cellulose nanocrystals (CNCs) and chitin nanocrystals (ChNCs) into nonisocyanate polyurethane (NIPU) offers a multifunctional approach to improving mechanical and thermal properties while promoting sustainability and green chemistry. Nanocomposites of segmented thermoplastic polyhydroxyurethane (PHU) from vanillyl alcohol bis(cyclocarbonate) (VABC), poly(tetramethylene oxide) diamine (PTMODA), and bis(aminomethyl) norbornane (NORB) reinforced with a low amount of CNCs and partially deacetylated ChNCs were prepared and characterized. Fourier transform infrared spectroscopy, atomic force microscopy, and small-angle X-ray scattering revealed that partially deacetylated ChNCs were covalently grafted to the PHU through aminolysis of carbonate end groups in the hard segment, while CNCs were mixed with the PHU without interfacial covalent bonding. Consequently, the PHU/ChNC nanocomposites showed nanophase separation with smaller hard domains compared to neat PHU, while the PHU/CNC nanocomposites exhibited a phase-mixed system with broader interface regions. Dynamic mechanical analysis and tensile tests further revealed that the PHU/ChNC nanocomposites demonstrated a 49-fold increase in Young's modulus, a 20-fold increase in ultimate tensile strength, and a three-order-of-magnitude enhancement in storage modulus in the rubbery state compared to the PHU/CNC nanocomposites, highlighting the profound influence of interfacial covalent linkages in enhancing the thermal mechanical performance of segmented PHU.

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.

Passive radiative cooling is emerging as a sustainable strategy to reduce energy consumption by emitting heat directly through Earth’s atmospheric transparency window. Here, we demonstrate transparent wood-based biocomposite coatings as an eco-friendly solution for passive radiative cooling under direct sunlight. We fabricated freestanding, micron-thick coatings using wood scaffolds functionalized with ZnO nanoparticles, followed by thiol–ene in situ polymerization to improve transparency and mechanical resilience. These coatings exhibit high visible transparency combined with exceptionally strong mid-infrared emissivity (∼0.95). When applied onto silicon substrates exposed to direct sunlight, ZnO-functionalized coatings effectively lowered the substrate temperature by ∼6–7 °C. This was primarily attributed to enhanced thermal radiation, highlighting their potential for mitigating overheating in solar cells and other sunlight-exposed structures. Additionally, the enhanced mechanical properties of these biocomposites provide versatility for structural and optical applications, positioning them as a cost-effective, bio-based alternative to traditional cooling technologies.