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”.

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.

Aggregation-induced quenching often restricts emissive performance of optically active solid materials with embedded fluorescent dyes. Delignified and nanoporous wood readily adsorbs organic dyes and is investigated as a host material for rhodamine 6G (R6G). High concentration of R6G (>35 mM) is achieved in delignified wood without any ground-state dye aggregation. To evaluate emissive performance, a solid-state random dye laser is prepared using the dye-doped wood substrates. The performance in terms of lasing threshold and efficiency was improved with increased dye content due to the ability of delignified wood to disperse R6G.

The preparation of wood substrates modified by charged inorganic nanoparticles (NPs) diffusing into the internal cell wall structure is investigated for generating functional properties. The flammability problem of wood biocomposites is addressed. NPs applied from colloidal sols carry charge to stabilize them against aggregation. The influence of charge on particle diffusion and adsorption should play a role for their spatial distribution and localization in the wood substrate biocomposite. It is hypothesized that improved dispersion, infiltration, and stability of NPs into the wood structure can be achieved by charge control diffusion, also restricting NP agglomeration and limiting distribution to the wood cell wall. Cationic and anionic silica NPs of ≈30 nm are therefore allowed to diffuse into bleached wood. The influence of charge on distribution in wood is investigated as a function of initial sol concentration. Transparent wood is fabricated by in situ polymerization of a thiol­ene in the wood pore space. These biocomposites demonstrate excellent flame retardancy with self­extinguishing characteristics. The approach has potential for commercial fabrication of flame retardant transparent composites for glazing and other building applications.

Transparent wood (TW) biocomposites combines load-bearing properties with high transmittance of light. TW consists of a reinforcing wood substrate that has been infiltrated with a polymer matrix. TW can be combined with additives so that new multifunctional materials are obtained. Functional additives are, however, sensitive to aggregation and the wood structure limits particle infiltration. Dispersion and distribution of additives as well as optical properties were controlled by chemical treatment of the wood substrate. The structure and chemistry of the wood substrate was influenced by delignification or bleaching.

With a thiol-ene polymer matrix, wood was tailored to produce TW with high or low optical scattering. It was possible to dope a delignified wood substrate with a high content of a fluorescent dye to produce TW solid-state dye lasers. Optical scattering enhanced the spectral brightness of the lasers and wave-guiding in TW partially directed the emission, producing a quasi-random laser.

Favourable distribution of nanoparticles (NPs) was obtained by two routes: in-situ synthesis and charge-regulated NP diffusion. With in-situ synthesis, mobile precursors infiltrated the substrate. With charge-regulated diffusion, cationic NPs were dispersed by negative charges in the wood substrate. Structurally coloured TW with wavelength-specific polarization was produced by in-situ synthesis of plasmonic NPs (PNPs). Utilization of wood compounds as reagents and stabilizing ligands produced TW with well-dispersed PNPs. Flame-retardant and self-extinguishing TW with preserved optical transmittance was prepared by charge-regulated diffusion of cationic silica NPs.

In conclusion, functionalization of wood substrates promoted controlled dispersion of additives for TW with new functionalities, such as laser performance, fluorescence, fire-retardant properties and structural colours.

Transparent trä (TW) är biokompositmaterial som kombinerar lastbärande egenskaper med hög ljustransmittans. TW består av träsubstrat som impregnerats med en polymermatris. Genom att tillsätta additiv till TW kan nya multifunktionella material framställas. Additivens funktioner begränsas dock ofta av aggregation och strukturen i trä begränsar partikelimpregnering. Med kemisk behandling av träsubstratet kan additivens dispersion och distribuering samt optiska egenskaper justeras i TW. Strukturen och kemin i träsubstraten påverkades med delignifiering eller blekning.

 Med en thiol-ene-polymermatris kunde TW med hög eller låg ljusspridning framställas genom att justera träsubstratets kemi. Delignifierat trä kunde dopas med stora mängder fluorescerande färgämnen så att en TW-baserad laser framställdes. I lasern förstärktes emissionen av ljusspridning. Dessutom riktade vågledning i TW emissionen så att lasern inte var slumpartad.

Nanopartiklar (NP) distribuerades i trä genom in-situ syntes eller laddningsreglerad diffusion. Med in-situ syntes kan trä impregneras med mobila reaktanter. Med laddningsreglerad diffusion kan katjoniska NP dispergeras av negativa laddningar i träsubstratet. TW med strukturell färg och våglängdsspecifik polarisering framställdes med in-situ syntes av plasmoniska NP (PNP). Träkomponenter reducerade, dispergerade och stabiliserade PNP. TW med flamskyddande och självsläckande egenskaper och med bevarad ljustransmittans framställdes med laddningsreglerad diffusion av kajoniska silika NP.

Sammanfattningsvis så har biokomopsiter med nya egenskaper framställts genom att bleka eller delignifiera träsubstrat så att dispersionen av additiv förbättrades i TW. TW med laserförmåga, fluorescens, flamskyddande egenskaper och strukturell färg har framställts.

Wood is an eco-friendly and abundant substrate and a candidate for functionalization by large-scale nanotechnologies. Infiltration of nanoparticles into wood, however, is hampered by the hierarchically structured and interconnected fibers in wood. In this work, delignified wood is impregnated with gold and silver salts, which are reduced in situ to plasmonic nanoparticles via microwave-assisted synthesis. Transparent biocomposites are produced from nanoparticle-containing wood in the form of load-bearing materials with structural color. The coloration stems from nanoparticle surface plasmons, which require low size dispersity and particle separation. Delignified wood functions as a green reducing agent and a reinforcing scaffold to which the nanoparticles attach, predesigning their distribution on the surface of fibrous "tubes". The nanoscale structure is investigated using scanning transmission electron microscopy (STEM), energy-dispersive spectroscopy (EDS), and Raman microscopy to determine particle size, particle distribution, and structure-property relationships. Optical properties, including response to polarized light, are of particular interest.

Transparent wood (TW) is an interesting polymer biocomposite with potential for buildings and photonics applications. TW materials need to be eco-friendly and readily processed with few defects, for high optical transmittance and low transmission scattering at wide angles (haze). Two wood templates with different lignin-content are impregnated with a new thiol-ene thermoset system. The more eco-friendly bleached wood template results in transparent wood with high optical transmission and much reduced transmission haze, due to strong reduction of interfacial air gaps. Characterization includes template composition, thiol-ene distribution, and polymerization in wood cell wall by EDX and confocal Raman microscopy, also NMR and DSC, tensile testing and FE-SEM fractography for morphology and wood/thiol-ene interface adhesion assessment. The wood template is a true nanocomposite with thiol-ene polymer located inside the nanoporous wood cell wall. Advanced TW applications require not only appropriate wood template modification and careful polymer matrix selection but also tailoring of the process to impregnation and polymerization mechanisms, in order to reduce optical defects.