Composites of covalently linked lignin and cellulose from one feedstock

Composites of covalently linked lignin and cellulose from one feedstock | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Composites of covalently linked lignin and cellulose from one feedstock Joseph Samec, Shida Zuo, Lars Schick, Suthawan Muangmeesri, Saranya Chitsomkhuan, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8194130/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted You are reading this latest preprint version Abstract Future biorefineries must upgrade all constituents of lignocellulosic feedstocks to high-value products. To curb land-use pressure, technologies that upgrade existing side streams from forestry and agriculture into substitutes for high-impact, fossil-derived materials are urgently needed. Prevailing biomass valorization typically prioritizes either cellulose pulp or lignin; true co-valorization remains uncommon. Here we report a metal-free, ambient-pressure reactive fractionation that concurrently yields high-quality cellulose and a functionalized lignin. The isolated lignin is etherified and subsequently covalently coupled to cellulose via epoxide ring-opening, producing a composite. The materials display mechanical performance equivalent of common packaging materials, with retention under wet conditions, overcoming the intrinsic limitations of hydrogen-bonded cellulose networks. By integrating mild fractionation with chemical upgrading, this strategy simplifies processing, broadens the product slate accessible from residual biomass side streams and advances the substitution of problematic packaging materials. These findings establish a scalable route to whole-biomass co-valorization and wet-tolerant bio-based packaging from residual streams. Scientific community and society/Forestry Scientific community and society/Agriculture Physical sciences/Chemistry/Organic chemistry/Carbohydrate chemistry Physical sciences/Materials science/Techniques and instrumentation/Characterization and analytical techniques Physical sciences/Materials science/Structural materials/Composites Fractionation bio-based composite reactive lignin holistic biomass utilization Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Introduction Global growth in population and increasing living standards continue to drive demand for materials; notably, the packaging market is expected to 1.33 trillion dollar by 2028 1 . These materials are sourced from both forestry and fossil feedstocks 1 , 2 . While projections indicate that conventional crude oil extraction will become economically constrained within the next 40 years due to exhaustion of resources; concerns are simultaneously rising over deforestation and the conversion of natural forests to plantations with low biodiversity 3 . Current forestry value chains remain inefficient: typically, less than half of harvested biomass is upgraded into high-value products, with the remainder left on site or diverted to low-value energy 4 – 6 . Although a portion of residual streams should be retained in forests to support soil re-carbonization and re-mineralization, a substantial fraction can be removed sustainably 7 . However, such streams are frequently contaminated during handling and exhibit elevated ash contents 8 , 9 . Similar challenges are seen in agricultural residues, which can contain up to 10 wt% ash 10–12 . High ash loads—rich in alkali and alkaline-earth metals—complicate thermochemical processing and deactivate or foul metal catalysts, limiting the applicability of many established and emerging upgrading routes 13 – 16 . Addressing ash-related contamination is therefore pivotal for converting forestry and agricultural side streams into higher-value materials, including next-generation packaging 17 . Conventional pulping efficiently generates cellulose-rich pulps, while the remaining biomass is typically used to regenerate process chemicals and provide heat and power to the pulp mill 18 , 19 . Lignin can be precipitated from pulping liquors to afford technical lignins, but their native architecture is severely disrupted: condensation and oxidation deplete ether linkages and increase the fraction of sp²-hybridized aromatic C–C linkages at the expense of sp³-hybridized aliphatic bonds, yielding darker, less reactive, and more rigid materials 20 – 22 . Consequently, materials produced from technical lignins often exhibit limited mechanical performance 23 , 24 . Over the past decade, alternative fractionation methodologies that focus on preserving lignin structure—collectively termed “lignin-first” and defined as “active stabilization approaches that solubilize lignin from native lignocellulosic biomass while avoiding condensation reactions that lead to more recalcitrant lignin polymers”—have emerged 25 – 28 . Despite being developed to raise the value of the entire feedstock, only a handful of studies holistically deliver high-value products from both lignin and cellulose 29 , 30 . Among lignin-first strategies, reductive catalytic fractionation (RCF) is the most extensively investigated: a transition-metal catalyst reduces reactive intermediates generated during lignin depolymerization to give high yields of monophenolic compounds 18 , 26 , 27 , 31 – 35 . A major challenge with implementation of RCF is the ash content of biomass, especially residual streams, that would poison the transition metal catalyst. In addition, identifying scalable applications for RCF monomers remains challenging; with few exceptions 36 , they are dimerized to furnish non-toxic bisphenols for materials applications 37 – 39 . Barta and co-workers recently reported a lignocellulose-derived thermoset in which fractions from both lignin and cellulose were funneled into complementary building blocks and crosslinked with a bio-based epoxy 40 . In this scheme, vanillin was converted to 4,4′-methylenebis(cyclohexylamine) (MBCA), while the cellulose stream was transformed to dimethyl 2,5-furandicarboxylate (DMFD); curing the DMFD-based epoxide with MBCA yielded a high-performance network. The study demonstrated that the two principal biomass fractions can be integrated within a single materials platform and that the constituent building blocks are recoverable, enabling chemical recyclability. Inspired by this approach, it was hypothesized—and subsequently demonstrated—that cellulose and lignin can be used without prior depolymerization to produce a thermoset material. The concept relies on a metal-free reactive fractionation performed at ambient pressure, during which lignin is converted in situ into a white, non-condensed, lipophilic syringolated lignin (SL) (Fig. 1 a). The lipophilic SL is readily separated from the hydrophilic hemicellulose fraction and the solid pulp, then further functionalized by etherification to afford epoxy-functionalized syringolated lignin (ESL). Recombining ESL with cellulose yields a thermoset exhibiting exceptional wet-strength properties attributable to covalent bonding (Fig. 1 b). All reactions proceed at ambient pressure and without metal catalysts, which makes the methodology amenable to scale-up. Moreover, the reaction conditions are insensitive to ash content, enabling the use of residual streams such as forestry tops and branches and agricultural stalks. Consequently, this methodology does not compete with current biomass valorization routes and delivers a material capable of substituting common packaging materials such as kraft liner from virgin forestry or polyethylene terephthalate (PET) from the petroleum industry. Results Reactive fractionation of biomass to obtain lignin with a chemical handle and cellulose with accessible surface area Reactive fractionation was performed on poplar wood ( Populus trichocarpa ) using syringol as the nucleophile and formic acid as the solvent at reflux (Fig. 1a) 41 . The process furnished two isolable streams: a light-colored soluble fraction, vide infra , and a cellulose-rich pulp readily separated by filtration that accounted for 46.9% of the initial biomass. The pulp contained 94.2% cellulose and 1.9% hemicellulose, with 3.3% lignin. By comparison, native poplar comprised 47.5% cellulose, 14.1% hemicellulose, and 25.5% lignin. Together, these results indicate that the reactive fractionation achieves efficient delignification while delivering a functionalized lignin stream alongside exceptionally pure cellulose. Mechanistically, syringol intercepts benzylic carbocation intermediates generated during fractionation, suppressing recondensation and enabling direct formation of syringolated lignin (SL). To elucidate how reactive fractionation alters the microstructure of native biomass, scanning electron microscope (SEM) was used to compare wood fibers before and after treatment (Fig. 1c–d). Native fibers exhibited an intact hierarchical architecture 42 . In contrast, fibers in the fractionated pulp showed pronounced fibrillation, surface roughening, and partial splitting along the fiber axis, indicative of weakened inter-fiber adhesion. These morphological changes are consistent with disruption of the lignin–carbohydrate complex (LCC) linkages, yielding smaller bundles and exposing microfibrils 43 . The resulting increase in accessible surface area is expected to enhance subsequent chemical functionalization and interfacial bonding with a resin in composite fabrication. Functionalizing the lignin fraction The SL was isolated by precipitation in 35.8% yield based on initial poplar (theoretical maximum 38%). Running the reactive fractionation at reflux afforded a slightly brownish off-white solid (Fig. 2a), whereas lowering the temperature to 80 °C produced a whiter lignin but led to incomplete syringolation and thereby a lignin with reduced reactivity. Heteronuclear single-quantum coherence (HSQC) NMR indicated successful arylation. Strong correlations at δC/δH = 44.8/4.7 and 53.9/4.2 ppm, characteristic of substituted Cα sites in β–O–4 units formed upon syringolation were observed, and the native Cα signal was absent (Fig. 2a) 41 . Quantitative 31 P NMR further corroborated syringolation, showing a distinct and sharp resonance at δP = 142.85 ppm within the C–5–substituted phenolic region, which is consistent with syringolation at the Cα position (Fig. 2d) 44 . The meta/para ( m/p ) ratio of SL was determined to 2:1 by HSQC. SL displayed a high abundance of phenolic OH groups (3.22 mmol g⁻¹), underscoring its reactive potential following syringolated fractionation. The reactive lignin was then functionalized by reaction with epichlorohydrin, which can be sourced from biomass 45 . Selective etherification of SL at its phenolic hydroxyl groups afforded the corresponding epoxy-functionalized syringolated lignin (ESL) (Fig. 2b). Noteworthily, precipitation of the ESL yielded an off-white material in a quantitative yield starting from the brownish lignin (Fig. 2c). The HSQC spectrum of ESL displayed the additional cross-peaks in the aliphatic region, assignable to epoxy methylene and epoxy methine groups 46 (Fig. 2c). The coexistence of introduced syringyl correlations and these new epoxy signals verifies the introduction of epoxide functionality while retaining the syringolated backbone. In line with this assignment using 31 P NMR, phenolic OH decreased from 3.22 to 0.01 mmol g⁻¹ after epoxy-functionalization, whereas aliphatic OH increased from 1.70 to 2.41 mmol g⁻¹, consistent with cleavage of γ–formyl groups introduced during reactive fractionation and regeneration of aliphatic hydroxyls (Fig. 2d) 47 . Gel permeation chromatography (GPC) revealed concomitant changes in the apparent Mw distribution (Fig. 2e): SL spanned 525–1379 g mol⁻¹, whereas ESL shifted to 629–1938 g mol⁻¹, indicating that epoxy-functionalization broadens and shifts the molecular-weight profile while preserving the syringolated backbone. Fourier transform infrared (FTIR) spectroscopy spectra further corroborated these assignments (Fig. 2f). Relative to SL, ESL shows attenuation of the broad O–H stretch near 3400 cm⁻¹ and emergence of a characteristic epoxide band at 908 cm⁻¹, consistent with epoxide formation and with the concomitant decrease in phenolic hydroxyl content observed by 31 P NMR 48 . The tiny shoulder around 3056 cm⁻¹ represent the C–H vibration of epoxide ring, which support the successfully of epoxy-functionalization as well 49 . A marked reduction in intensity near 1720 cm⁻¹ additionally supports cleavage of γ–formyl groups during epoxy-functionalization 50 . Taken together, the HSQC, 31 P NMR, GPC, and FTIR results indicate that SL retains reactive phenolic functionality after reactive fractionation and that epoxy-functionalization efficiently converts these sites to epoxide groups while only modestly shifting the molecular-weight envelope, yielding a tunable lignin precursor suitable for subsequent composite fabrication. Chemical modification of lignin shifted the principal pyrolytic event to higher temperature. Thermogravimetric analysis (TGA/DTG) provided complementary evidence at the thermal property (Fig. 2g–h). The DTG maximum shifted from 366.58 °C for native poplar to 375.83 °C for SL, and further to 392.04 °C for ESL, establishing ESL as the most thermally stable among the series. Reactive fractionation leads to a seemingly more thermally stable lignin, possibly by preventing degradation at the Cα position, thereby suppressing the phenolic β–O–4 quinone-methide pathway, which requires Cα–OH 51 . Epoxy-functionalization further blocks almost all phenolic sites, which impede radical initiations known for lignin degradation pathways 51,52 . Formation of covalent bond between ESL and cellulose to yield a high strength composite We hypothesized that the C–OH of cellulose reacts with the epoxide of ESL to form new ether linkages (Fig. 3a), to give rise to inter-fiber crosslinking. Filter paper (FP) was used as a cellulose model while screening curing temperatures (80–220 °C) in the presence of 4-dimethylaminopyridine (DMAP). The tensile strength of ESL–filter paper sample (ESLFP) increased with curing temperature, reaching 60.8 MPa at 180 °C and then declining at higher temperatures, consistent with the onset of cellulose thermal degradation (Fig. 3b). At this optimum, the composite was sixfold stronger than FP (11.3 MPa), evidencing robust ESL–cellulose interactions (Fig. 3c). The role of DMAP was demonstrated using a no-catalyst control (ESLFP*). Without DMAP, the ESLFP* sample exhibited much lower strength (18.6 MPa), because unreacted ESL was removed during purification, indicating that physical adsorption alone is insufficient to provide load-bearing interfaces. Stiffness followed the same trend: the tensile modulus rose from 1.3 GPa (FP) to 1.4 GPa (ESLFP*) and to 2.7 GPa (ESLFP), consistent with covalent bonding limits inter-fiber slippage under load (Fig. 3d). Water resistance further differentiates covalently bonded material from the ESLFP* with other weaker physical interactions. ESLFP retained 46.5 MPa wet tensile strength (76.5%), whereas ESLFP* exhibited negligible wet strength of 6.3 MPa (33.9% retention) (Fig. 3f). The wet tensile modulus similarly increased from 0.1 GPa (FP) to 0.3 GPa (ESLFP*) and 1.5 GPa (ESLFP) (Fig. 3g). These improvements are attributed to DMAP-catalyzed epoxide ring-opening at cellulose C–OH, which (i) creates covalent ESL–cellulose bridges that persist in water, (ii) reduces swelling-induced plasticization by anchoring the interphase, and (iii) enhances stress transfer through a stiffer, chemically bonded network. Collectively, the data identify DMAP-catalyzed covalent bond formation at 180 °C as the governing factor underpinning both the sixfold increase in dry strength and the high wet-strength and modulus retention of ESLFP. Macroscopic observations (Fig. 4a–b) corroborate the chemistry: in the presence of DMAP, ESLFP darkened relative to both ESLFP* and the non-heated sample. Additional acetone washing after heating removed excess, unreacted ESL, rendering ESLFP* lighter in color, whereas the appearance of ESLFP was unaffected (Fig. S1a–b). Kinetic FTIR analysis was employed to analyze the reaction process between cellulose and ESL, and the spectra reveal time-dependent changes in the chemical composition of ESLFP and ESLFP* heated for different durations (Fig. 4c–d). As heating proceeded, the epoxy band of ESLFP at 908 cm -1 in the ESLFP sample gradually decreased in intensity and red-shifted towards 898 cm -1 , indicating consumption of epoxy groups and the re-emergence of the β–1,4–glycosidic bond vibration of cellulose. In contrast, the epoxy band in ESLFP* remained essentially unchanged, consistent with the design of a no reaction system in the absence of the catalyst. To probe the interactions underpinning the mechanical enhancement, X-ray photoelectron spectroscopy (XPS) was used to monitor surface functional groups. The high-resolution C 1s spectrum of FP shows the expected dominance of the C2 component (C–O, 286.5 eV), reflecting the abundance of alcohol and ether carbons in the polysaccharide backbone (Fig. 5a). By contrast, ESL exhibits a spectrum dominated by the C1 component (C–C/C–H/C=C, 284.8 eV), consistent with aromatic and aliphatic carbons of lignin (Fig. 5b). A distinct contribution near 286.8 eV is observed for ESL, consistent with the presence of the epoxide functionality and aligning with the HSQC evidence for epoxide formation (Fig. 2c). Upon forming the ESLFP composite, the C1 fraction increases relative to cellulose, while the C2 fraction increases relative to ESL, indicating coexistence and intermixing of ESL and cellulose at the surface level (Fig. 5c). Notably, the epoxide-associated contribution near 286.8 eV diminishes after curing, consistent with ring-opening of the epoxide with cellulose C–OH groups rather than mere physical mixing. Together, the C 1s evolutions support chemical coupling at the interface, corroborating the mechanical gains observed for ESLFP. FTIR was used to assess bulk chemical changes since XPS probes only the near surface chemical compositions. Neat ESL displays the epoxide ring vibration at 908 cm⁻¹, whereas FP, ESLFP*, and ESLFP show a band at 896 cm⁻¹ assigned to the cellulose β–1,4–glycosidic linkages. In the DMAP-cured composite (ESLFP), the disappearance of the 908 cm⁻¹ epoxide band—together with the persistent 896 cm⁻¹ cellulose band—indicates epoxide ring-opening and formation of new ether linkages between ESL and cellulose (Fig. S2). SEM further supported the ESL-cellulose ether bond. FP displays fibers with the characteristic microscale roughness of native cellulose (Fig. 5d). After incorporation of ESL, ESLFP shows fibers with a continuous, conformal coating and smoother inter-fiber interfaces, indicative of an interphase that bridges neighboring fibers (Fig. 5e). In contrast, ESLFP* resembles the native fiber morphology after acetone purification, consistent with removal of unreacted ESL and limited interfacial bonding (Fig. 5f). The morphological evidence—continuous coating in ESLFP versus fiber-like surfaces in ESLFP*—is consistent with the covalent coupling inferred from XPS and FTIR and explains the observed enhancements in mechanical strength, modulus, and wet-strength retention. Fabrication and characterization of pulp–ESL composites To realize co-utilization of both streams from reactive fractionation, a fully biobased composite from a single feedstock was prepared by combining the high-purity cellulose pulp with ESL. Guided by the filter-paper model, the same covalent chemistry was translated to pulp obtained from reactive fractionation of poplar: without additional chemical treatment or bleaching, cellulose pulp, ESL, and DMAP were dispersed in DI water, homogenized, and hot-pressed to drive epoxide ring-opening at cellulose C–OH, forming the ether linkages. The resulting ESLP exhibited a tensile strength of 46.7 MPa and modulus of 2.5 GPa, markedly higher than sheets prepared from neat pulp (8.5 MPa, 0.8 GPa) (Fig. 6a–c). These gains confirm that the covalent-bonding strategy operative in the model system also functions with fractionated pulp, demonstrating concurrent valorization of lignin and cellulose into one material. ESLP maintained 33.9 MPa wet tensile strength and a wet modulus of 2.0 GPa, whereas pure pulp retained only 1.9 MPa and 0.2 GPa (Fig. 6d–f). The high wet tensile property retention of ESLP indicates that chemical coupling, rather than hydrogen bonding alone, governs inter-fiber adhesion and underpins suitability for moist environments. Consistent with ESL–cellulose coupling, SEM images reveals a conformal, micro-crosslinked interphase in ESLP analogous to that observed in ESLFP (Fig. 6g). Relative to filter paper, the fractionated pulp offers greater accessible surface area and porosity; ESL therefore penetrates more deeply into the fiber network prior to curing, yielding continuous coatings and bridging at fiber-fiber contacts. The observed fully coated fibers and densified, crosslinked architecture in ESLP align with the enhanced dry and wet mechanics. By contrast, the pressed pulp exhibits a more natural fiber characteristic, which led to a lower mechanical and wet properties (Fig. 6h). Hot-pressing produced a smoother, denser surface, and ESL incorporation reduced surface wettability. Static water contact angles started from 75.8 ° at 0 s (pure pulp) and rapidly decayed to 17.9 ° at 5 s, whereas ESLP started at 88.4 ° (0 s) and remained 85.0 ° at 60 s (Fig. 6i). The higher and time-stable contact angle indicates suppressed wetting, attributable to the covalently bonded ESL interphase together with surface densification—trends consistent with the improved strength, stiffness, and wet-strength retention. The same fractionation and epoxy-functionalization sequence translated to rapeseed straw, an herbaceous residue typically richer in ash, affording a brownish SL and a paler off-white solid ESL after precipitation (Fig. S3a–b). HSQC spectra showed the expected Cα–arylation correlations for SL and the additional aliphatic cross-peaks attributable to the epoxide motif for ESL, mirroring the poplar case (Fig. S4–5). Despite this compositional challenge, the DMAP-assisted epoxide–cellulose coupling remained effective, yielding substantial improvements in both dry and wet properties (Fig. S6): ESLP reached 40.0 MPa tensile strength and 3.0 GPa modulus versus 11.9 MPa and 1.1 GPa for neat straw pulp; under wet conditions, ESLP retained 21.8 MPa tensile strength and 1.8 GPa modulus compared to 1.5 MPa and 0.1 GPa for neat pulp. These results demonstrate that the chemistry is robust to feedstock variability and tolerant to elevated ash content, supporting co-valorization of lignin and cellulose from different biomass streams. As mentioned above, herbaceous feedstocks (e.g., rapeseed straw) often contain substantial alkali/alkaline-earth ash and silica. In conventional metal-catalyzed fractionation routes—such as RCF—these inorganic species would poison and deactivate metal catalysts and complicate liquor handling, narrowing the usable feedstock window. By contrast, our metal-free DMAP-assisted epoxide–cellulose coupling avoids this limitation and delivers large strength gains on high-ash pulps, underscoring the practical advantage of the approach for agricultural residues. Discussion In conclusion, this work presents a fully bio-based composite material that achieves high mechanical strength and remarkable wet stability enabled through covalent bound formation between lignin and cellulose without prior depolymerization. The key lies in utilizing both major biomass fractions—lignin and cellulose, without extensive downstream processing—to form a composite material. The stabilized epoxy-functionalized syringolated lignin acts as a reactive bridge, forming durable ether linkages with cellulose and transforming hydrogen-bonded fiber networks into chemically crosslinked architectures. This material design was enabled by a mild, metal-free reactive fractionation that yields functional lignin and pure cellulose directly from raw biomass, including ash-rich side streams. The resulting composites demonstrate that biomass-derived polymers can rival fossil-based packaging and kraft liner produced from virgin forestry in strength, durability, and moisture resistance, highlighting a scalable path toward circular, wet-tolerant bio-based materials. This study makes progress in the research field by demonstrating a holistic valorization of both lignin and cellulose streams to produce a composite with good mechanical properties without severe processing. Given the simplicity of the process and the wide tolerance to feedstocks, this study will be of interest to both the packaging industries as well as stakeholders that generate residual biomass streams. Methods Chemicals and Materials Materials and chemical reagents can be found in Supplementary information. Reactive fractionation of biomass Dry poplar biomass (5.00 g, particle size of 0.5 mm) and syringol (2.00 g) with 88 wt% formic acid (50 mL) in a closed reactor at 120 °C for 30 min. After completion, the reaction mixture was filtered to obtain a cellulose-enriched pulp, which was sequentially washed with formic acid, ethanol, and deionized water. The filtrate was concentrated by rotary evaporation and precipitated into deionized water to obtain SL. The SL was collected by centrifugation and then freeze-dried to yield a light-colored powder. The reactive fractionation procedure is readily scalable; a 30 g batch of biomass was successfully processed under identical conditions. The same methodology was also applied to rapeseed straw, demonstrating its versatility across both forestry- and agriculture-derived feedstocks. Etherification of SL to yield an epoxy SL (3.00 g, 9.7 mmol, 1.00 equiv., based on phenolic OH content) and tetrabutylammonium bromide (2.06 g, 6.4 mmol, 0.66 equiv.) were dissolved in 15–20 equiv. of epichlorohydrin (the exact amount adjusted according to the solubility of SL) in a 100 mL round-bottom flask equipped with a magnetic stir bar. After purging with N₂ for 5 min, the reaction mixture was stirred at 60 °C for 2 h, then immediately cooled in an ice bath. Subsequently, 4.00 equiv. of 50 wt% NaOH solution was added dropwise, and the mixture was stirred at 60 °C for another 2 h. Dichloromethane was added and the resulting solution was washed with deionized water until neutral, followed by brine. The resulting organic phase was dried over anhydrous Na 2 SO₄ and the residual epichlorohydrin and solvent were removed via rotary evaporation. The crude product was redissolved in a small amount of acetone and precipitated in water. The resulting precipitate was collected by centrifugation and then freeze-dried to yield an off-white ESL powder. The epoxy-functionalization of SL from rapeseed straw was applied using same method. Fabrication of ESL-cellulose composite The curing process was first optimized using filter paper as a cellulose model. ESL (0.20 g) and DMAP (2 wt% of ESL) were dissolved in acetone (5 mL), in which 0.20 g of filter paper was immersed. After air drying, the impregnated filter paper was heated at 80–220 °C for 1 h. The resulting ESLFP was washed with acetone under sonication for 5 min to remove non-covalently bound ESL. A control group was prepared without DMAP, named as ESLFP*. For composite fabrication, the pulp obtained from reactive fractionation and ESL (1:1) were dispersed in 100 mL of deionized water together with DMAP (2 wt%) to form a suspension. The mixture was homogenized at 10,000 rpm for 1 h and then subjected to vacuum filtration to yield a wet ESLP cake. The cake was hot-pressed at 180 °C under 3.5 MPa for 1 h to obtain the ESLP composite. Characterization of products and materials The characterization details can be found in Supplementary information. Declarations Acknowledgements This work was supported by the Wallenberg Initiative Materials Science for Sustainability (WISE) funded by the Knut and Alice Wallenberg Foundation. We thank Dr. Annelie Moldin at Lantmännen for providing details of available residual streams from agriculture and Albin Gunnarson for providing rapeseed straws as feedstock. References Mudgal, D., Pagone, E. & Salonitis, K. Selecting sustainable packaging materials and strategies: A holistic approach considering whole life cycle and customer preferences. J. Clean. Prod. 481 , 144133 (2024). Dhatt, P. S. et al. Biomimetic layered, ecological, advanced, multi-functional film for sustainable packaging. Nat. Commun. 16 , 6649 (2025). Brockway, P. E., Owen, A., Brand-Correa, L. I. & Hardt, L. 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Chemicals from lignin: an interplay of lignocellulose fractionation, depolymerisation, and upgrading. Chem. Soc. Rev. 47 , 852–908 (2018). Afanasenko, A. M. et al. Clean Synthetic Strategies to Biologically Active Molecules from Lignin: A Green Path to Drug Discovery. Angew. Chem. Int. Ed. 63 , e202308131 (2023). Trullemans, L. et al. Renewable and safer bisphenol A substitutes enabled by selective zeolite alkylation. Nat. Sustain. 6 , 1693–1704 (2023). Witthayolankowit, K. et al. Use of a fully biobased and non-reprotoxic epoxy polymer and woven hemp fabric to prepare environmentally friendly composite materials with excellent physical properties. Compos. Part B Eng. 258 , 110692 (2023). Koelewijn, S.-F. et al. Promising bulk production of a potentially benign bisphenol A replacement from a hardwood lignin platform. Green Chem. 20 , 1050–1058 (2018). Wu, X. et al. Closed-loop recyclability of a biomass-derived epoxy-amine thermoset by methanolysis. Science 384 , eadj9989 (2024). Li, N. et al. Selective lignin arylation for biomass fractionation and benign bisphenols. Nature 630 , 381–386 (2024). He, M., Yang, G., Chen, J., Ji, X. & Wang, Q. Production and Characterization of Cellulose Nanofibrils from Different Chemical and Mechanical Pulps. J. Wood Chem. Technol. 38 , 149–158 (2018). Li, K. et al. Self-Densification of Highly Mesoporous Wood Structure into a Strong and Transparent Film. Adv. Mater. 32 , 2003653 (2020). Meng, X. et al. Determination of hydroxyl groups in biorefinery resources via quantitative 31P NMR spectroscopy. Nat. Protoc. 14 , 2627–2647 (2019). Lari, G. M., Pastore, G., Mondelli, C. & Pérez-Ramírez, J. Towards sustainable manufacture of epichlorohydrin from glycerol using hydrotalcite-derived basic oxides. Green Chem. 20 , 148–159 (2018). Sanday, D. H., Coelho, H. C. P., Saron, C. & Ferraz, A. Renewable Phenolic Oligomers from Self-Acid Condensation of Vanillyl Alcohol and Vanillyl Alcohol/Lignosulfonate Mixtures for Use in Epoxy/Amine Thermosets. ACS Sustain. Chem. Eng. 13 , 4449–4459 (2025). Kim, S. H. & Hong, S. H. Transfer Hydrogenation of Organic Formates and Cyclic Carbonates: An Alternative Route to Methanol from Carbon Dioxide. ACS Catal. 4 , 3630–3636 (2014). Wang, S., Ruan, K., Guo, Y., Kong, J. & Gu, J. Thermally Conductive Naphthalene Epoxy Resin by Tailoring Flexible Chain Length and Liquid Crystal Structure. Angew. Chem. Int. Ed. 64 , e202501459 (2025). Jaques, N. G. et al. Kinetic investigation of eggshell powders as biobased epoxy catalyzer. Compos. Part B Eng. 183 , 107651 (2020). Giummarella, N., Pu, Y., Ragauskas, A. J. & Lawoko, M. A critical review on the analysis of lignin carbohydrate bonds. Green Chem. 21 , 1573–1595 (2019). Cui, C., Sadeghifar, H., Sen, S. & Argyropoulos, D. S. Toward Thermoplastic Lignin Polymers; Part II: Thermal & Polymer Characteristics of Kraft Lignin & Derivatives. BioResources 8 , (2013). Kawamoto, H., Horigoshi, S. & Saka, S. Effects of side-chain hydroxyl groups on pyrolytic β-ether cleavage of phenolic lignin model dimer. J. Wood Sci. 53 , 268–271 (2007). Additional Declarations There is NO Competing Interest. Supplementary Files JS93NatureCommunSI251124.docx Supplementary information Cite Share Download PDF Status: Under Review Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8194130","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":553277213,"identity":"414d8875-b1cd-4916-b7a5-e7493492f7ad","order_by":0,"name":"Joseph Samec","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA1UlEQVRIiWNgGAWjYBACxgYYAQIfSNbCOIM0q4CAmYcY1czt7Q8fF+5gsOefdvjgZ5s/hxnk2xvwa2HsOWNsPPMMQ+KM22nJ0rlthxkMzhwgoGVGDps0bxtDAsPtHDPm3AagFokEQlrSn/8GarGXv53/jdkC5LD5DwhpSTBjBmph3HA7h42Zge0wA8MN/DrAfpGe2SaRuPF2mrFkb1s6j8EZAg4zBIbY58I2G3u528kPP/z4Yy0n336AgJYGYEAzMEjABQhHjTwDWMsoGAWjYBSMAjwAAP4pQadc/cOKAAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0001-8735-5397","institution":"Stockholm University","correspondingAuthor":true,"prefix":"","firstName":"Joseph","middleName":"","lastName":"Samec","suffix":""},{"id":553277214,"identity":"97134e78-92e5-4b5f-b4a1-c5bb497bfe42","order_by":1,"name":"Shida Zuo","email":"","orcid":"","institution":"Stockholm University","correspondingAuthor":false,"prefix":"","firstName":"Shida","middleName":"","lastName":"Zuo","suffix":""},{"id":553277215,"identity":"16a31eac-c70d-48ab-8c63-094e04841994","order_by":2,"name":"Lars Schick","email":"","orcid":"","institution":"Stockholm University","correspondingAuthor":false,"prefix":"","firstName":"Lars","middleName":"","lastName":"Schick","suffix":""},{"id":553277216,"identity":"d165b56a-0382-4558-8e86-c3a294a6996a","order_by":3,"name":"Suthawan Muangmeesri","email":"","orcid":"","institution":"Stockholm University","correspondingAuthor":false,"prefix":"","firstName":"Suthawan","middleName":"","lastName":"Muangmeesri","suffix":""},{"id":553277217,"identity":"d5e70c4c-9389-400a-a90f-12ea760a9192","order_by":4,"name":"Saranya Chitsomkhuan","email":"","orcid":"","institution":"Stockholm University","correspondingAuthor":false,"prefix":"","firstName":"Saranya","middleName":"","lastName":"Chitsomkhuan","suffix":""},{"id":553277218,"identity":"7fb8c6e5-fbf4-4a66-8ed2-fbae790cf516","order_by":5,"name":"Lenny Haddad","email":"","orcid":"","institution":"Stockholm University","correspondingAuthor":false,"prefix":"","firstName":"Lenny","middleName":"","lastName":"Haddad","suffix":""}],"badges":[],"createdAt":"2025-11-24 13:50:26","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8194130/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8194130/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":98578890,"identity":"70309535-8006-4013-8596-86d6a4c92bac","added_by":"auto","created_at":"2025-12-19 08:06:47","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":39513650,"visible":true,"origin":"","legend":"","description":"","filename":"JS93NatCommun251124.docx","url":"https://assets-eu.researchsquare.com/files/rs-8194130/v1/9b6b96d80da7d0968db6b015.docx"},{"id":98627080,"identity":"f5442e61-2a6f-4ed6-87d5-5d7637038fe5","added_by":"auto","created_at":"2025-12-19 17:10:07","extension":"json","order_by":1,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":7377,"visible":true,"origin":"","legend":"","description":"","filename":"NCOMMS2595062.json","url":"https://assets-eu.researchsquare.com/files/rs-8194130/v1/8656489d0582b2e4861a8eee.json"},{"id":98578884,"identity":"a02ceaec-54a8-4593-8db3-dd71669f46ac","added_by":"auto","created_at":"2025-12-19 08:06:46","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":535615,"visible":true,"origin":"","legend":"","description":"","filename":"JS93NatureCommunSI251124.docx","url":"https://assets-eu.researchsquare.com/files/rs-8194130/v1/29a1f4ee4d55ad5466efb2f8.docx"},{"id":98628511,"identity":"6065f281-2f3d-44eb-9757-f0166242306e","added_by":"auto","created_at":"2025-12-19 17:11:38","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":14865472,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eReactive fractionation process and fabrication of composites.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e Schematic illustration of reactive fractionation and \u003cstrong\u003eb\u003c/strong\u003e covalent bond between cellulose and ESL. SEM images of \u003cstrong\u003ec\u003c/strong\u003e natural poplar and \u003cstrong\u003ed\u003c/strong\u003e pulp obtained from reactive fractionation.\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-8194130/v1/ac23386d16862cccbb872f24.png"},{"id":98578885,"identity":"c20787e4-60da-4c5c-ab89-31762767e7d0","added_by":"auto","created_at":"2025-12-19 08:06:46","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":2428346,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eCharacterizations of SL and ESL.\u003c/strong\u003e HSQC NMR spectra of \u003cstrong\u003ea\u003c/strong\u003e SL and \u003cstrong\u003ec\u003c/strong\u003e ESL, showing syringyl aromatic correlations (red) and new cross-peaks (purple) assigned to epoxy methylene/methine groups. \u003cstrong\u003ec\u003c/strong\u003e Selective epoxy-functionalization of SL on phenolic hydroxyls. \u003cstrong\u003ed\u003c/strong\u003e \u003csup\u003e31\u003c/sup\u003eP NMR spectra of SL and ESL after phosphitylation, highlighting the disappearance of phenolic OH. \u003cstrong\u003ee\u003c/strong\u003e GPC curves of SL and ESL, indicating a shift toward higher molecular weight and broader dispersity after epoxy-functionalization. \u003cstrong\u003ef\u003c/strong\u003e FTIR spectra of SL and ESL, showing the reduction of O–H stretching and the appearance of an epoxy ring absorption at 908 cm⁻¹. \u003cstrong\u003eg\u003c/strong\u003e TG and \u003cstrong\u003eh\u003c/strong\u003e DTG curves of poplar, SL and ESL, represent the thermal stability of samples.\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-8194130/v1/c42637260d905b9abf106c85.png"},{"id":98578883,"identity":"f46a6c4d-4747-41d8-96fd-f7f318a6e72a","added_by":"auto","created_at":"2025-12-19 08:06:46","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":500367,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eMechanical properties of ESLFP. a\u003c/strong\u003e Proposed reaction scheme between cellulose and ESL. \u003cstrong\u003eb\u003c/strong\u003e Tensile stress-strain curves of ESLFP prepared under different temperature. \u003cstrong\u003ec\u003c/strong\u003eTensile strength and \u003cstrong\u003ed\u003c/strong\u003e modulus of FP, ESLFP* and ESLFP. \u003cstrong\u003ee\u003c/strong\u003e Wet tensile stress-strain curves of FP, ESLFP* and ESLFP. \u003cstrong\u003ef\u003c/strong\u003e Wet tensile strength and \u003cstrong\u003eg\u003c/strong\u003e modulus of FP, ESLFP* and ESLFP.\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-8194130/v1/108af49b810285372192b7d9.png"},{"id":98578886,"identity":"6b587370-c83e-4911-893c-a3aa45f72b11","added_by":"auto","created_at":"2025-12-19 08:06:47","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":5377708,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eKinetic experiments of ESLFP* and ESLFP.\u003c/strong\u003e Photographs of \u003cstrong\u003ea\u003c/strong\u003e ESLFP* and \u003cstrong\u003eb\u003c/strong\u003e ESLFP heated for different durations. Kinetic FTIR spectra of \u003cstrong\u003ec\u003c/strong\u003e ESLFP* and \u003cstrong\u003ed\u003c/strong\u003eESLFP heated for different durations.\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-8194130/v1/10ef587c7986de2ebc4d9146.png"},{"id":98627365,"identity":"ee66e4de-a3ae-48bc-8755-685b9c0fa65c","added_by":"auto","created_at":"2025-12-19 17:10:19","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":10220941,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSurface observations of FP, ESLFP* and ESLFP.\u003c/strong\u003e XPS spectra of \u003cstrong\u003ea\u003c/strong\u003e FP, \u003cstrong\u003eb\u003c/strong\u003e ESL, and \u003cstrong\u003ec\u003c/strong\u003eESLFP. SEM images of \u003cstrong\u003ed\u003c/strong\u003e FP, \u003cstrong\u003ee\u003c/strong\u003e ESLFP and \u003cstrong\u003ef\u003c/strong\u003e ESLFP*.\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-8194130/v1/5fa8fdd6c5643dba6d05aebe.png"},{"id":98578889,"identity":"8aa1b260-b4e3-428d-910d-b9a1f211641a","added_by":"auto","created_at":"2025-12-19 08:06:47","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":6021726,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eCharacterizations of ESLP.\u003c/strong\u003e \u003cstrong\u003ea\u003c/strong\u003e Tensile stress-strain curves of ESLP and pulp. \u003cstrong\u003eb\u003c/strong\u003eTensile strength and \u003cstrong\u003ec\u003c/strong\u003e modulus of ESLP and pulp. \u003cstrong\u003ed\u003c/strong\u003e Wet tensile stress-strain curves of ESLP and pulp. \u003cstrong\u003ee\u003c/strong\u003e Wet tensile strength and \u003cstrong\u003ef\u003c/strong\u003emodulus of ESLP and pulp. SEM images of \u003cstrong\u003eg\u003c/strong\u003e ESLP and \u003cstrong\u003eh\u003c/strong\u003e pulp. \u003cstrong\u003ei\u003c/strong\u003eContact angle images of ESLP and pulp after different times.\u003c/p\u003e","description":"","filename":"image6.png","url":"https://assets-eu.researchsquare.com/files/rs-8194130/v1/dd83a55f70f1605ab65d481a.png"},{"id":98632216,"identity":"2fa050fc-2f05-4e07-935b-74f91a6b27ca","added_by":"auto","created_at":"2025-12-19 17:21:38","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":39570468,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8194130/v1/6af19136-2f3d-494d-8099-b343cf56df12.pdf"},{"id":98578881,"identity":"d501715b-fc03-40be-9886-1b704dd0acf6","added_by":"auto","created_at":"2025-12-19 08:06:46","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":535615,"visible":true,"origin":"","legend":"Supplementary information","description":"","filename":"JS93NatureCommunSI251124.docx","url":"https://assets-eu.researchsquare.com/files/rs-8194130/v1/a80b98beadb84b85bc31ded3.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Composites of covalently linked lignin and cellulose from one feedstock","fulltext":[{"header":"Introduction","content":"\u003cp\u003eGlobal growth in population and increasing living standards continue to drive demand for materials; notably, the packaging market is expected to 1.33 trillion dollar by 2028\u003csup\u003e1\u003c/sup\u003e. These materials are sourced from both forestry and fossil feedstocks\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e. While projections indicate that conventional crude oil extraction will become economically constrained within the next 40 years due to exhaustion of resources; concerns are simultaneously rising over deforestation and the conversion of natural forests to plantations with low biodiversity\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e. Current forestry value chains remain inefficient: typically, less than half of harvested biomass is upgraded into high-value products, with the remainder left on site or diverted to low-value energy\u003csup\u003e\u003cspan additionalcitationids=\"CR5\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e. Although a portion of residual streams should be retained in forests to support soil re-carbonization and re-mineralization, a substantial fraction can be removed sustainably\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e. However, such streams are frequently contaminated during handling and exhibit elevated ash contents\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e,\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e. Similar challenges are seen in agricultural residues, which can contain up to 10 wt% ash\u003csup\u003e10\u0026ndash;12\u003c/sup\u003e. High ash loads\u0026mdash;rich in alkali and alkaline-earth metals\u0026mdash;complicate thermochemical processing and deactivate or foul metal catalysts, limiting the applicability of many established and emerging upgrading routes\u003csup\u003e\u003cspan additionalcitationids=\"CR14 CR15\" citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e. Addressing ash-related contamination is therefore pivotal for converting forestry and agricultural side streams into higher-value materials, including next-generation packaging\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eConventional pulping efficiently generates cellulose-rich pulps, while the remaining biomass is typically used to regenerate process chemicals and provide heat and power to the pulp mill\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e,\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e. Lignin can be precipitated from pulping liquors to afford technical lignins, but their native architecture is severely disrupted: condensation and oxidation deplete ether linkages and increase the fraction of sp\u0026sup2;-hybridized aromatic C\u0026ndash;C linkages at the expense of sp\u0026sup3;-hybridized aliphatic bonds, yielding darker, less reactive, and more rigid materials\u003csup\u003e\u003cspan additionalcitationids=\"CR21\" citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e. Consequently, materials produced from technical lignins often exhibit limited mechanical performance\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e,\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e. Over the past decade, alternative fractionation methodologies that focus on preserving lignin structure\u0026mdash;collectively termed \u0026ldquo;lignin-first\u0026rdquo; and defined as \u0026ldquo;active stabilization approaches that solubilize lignin from native lignocellulosic biomass while avoiding condensation reactions that lead to more recalcitrant lignin polymers\u0026rdquo;\u0026mdash;have emerged\u003csup\u003e\u003cspan additionalcitationids=\"CR26 CR27\" citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e. Despite being developed to raise the value of the entire feedstock, only a handful of studies holistically deliver high-value products from both lignin and cellulose \u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e,\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e. Among lignin-first strategies, reductive catalytic fractionation (RCF) is the most extensively investigated: a transition-metal catalyst reduces reactive intermediates generated during lignin depolymerization to give high yields of monophenolic compounds\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e,\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e,\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e,\u003cspan additionalcitationids=\"CR32 CR33 CR34\" citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e. A major challenge with implementation of RCF is the ash content of biomass, especially residual streams, that would poison the transition metal catalyst. In addition, identifying scalable applications for RCF monomers remains challenging; with few exceptions\u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e, they are dimerized to furnish non-toxic bisphenols for materials applications\u003csup\u003e\u003cspan additionalcitationids=\"CR38\" citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eBarta and co-workers recently reported a lignocellulose-derived thermoset in which fractions from both lignin and cellulose were funneled into complementary building blocks and crosslinked with a bio-based epoxy\u003csup\u003e\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e. In this scheme, vanillin was converted to 4,4\u0026prime;-methylenebis(cyclohexylamine) (MBCA), while the cellulose stream was transformed to dimethyl 2,5-furandicarboxylate (DMFD); curing the DMFD-based epoxide with MBCA yielded a high-performance network. The study demonstrated that the two principal biomass fractions can be integrated within a single materials platform and that the constituent building blocks are recoverable, enabling chemical recyclability.\u003c/p\u003e \u003cp\u003eInspired by this approach, it was hypothesized\u0026mdash;and subsequently demonstrated\u0026mdash;that cellulose and lignin can be used without prior depolymerization to produce a thermoset material. The concept relies on a metal-free reactive fractionation performed at ambient pressure, during which lignin is converted in situ into a white, non-condensed, lipophilic syringolated lignin (SL) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). The lipophilic SL is readily separated from the hydrophilic hemicellulose fraction and the solid pulp, then further functionalized by etherification to afford epoxy-functionalized syringolated lignin (ESL). Recombining ESL with cellulose yields a thermoset exhibiting exceptional wet-strength properties attributable to covalent bonding (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). All reactions proceed at ambient pressure and without metal catalysts, which makes the methodology amenable to scale-up. Moreover, the reaction conditions are insensitive to ash content, enabling the use of residual streams such as forestry tops and branches and agricultural stalks. Consequently, this methodology does not compete with current biomass valorization routes and delivers a material capable of substituting common packaging materials such as kraft liner from virgin forestry or polyethylene terephthalate (PET) from the petroleum industry.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003e\u003cstrong\u003eReactive fractionation of biomass to obtain lignin with a chemical handle and cellulose with accessible surface area\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eReactive fractionation was performed on poplar wood (\u003cem\u003ePopulus trichocarpa\u003c/em\u003e) using syringol as the nucleophile and formic acid as the solvent at reflux (Fig. 1a)\u003csup\u003e41\u003c/sup\u003e. The process furnished two isolable streams: a light-colored soluble fraction, \u003cem\u003evide infra\u003c/em\u003e, and a cellulose-rich pulp readily separated by filtration that accounted for 46.9% of the initial biomass. The pulp contained 94.2% cellulose and 1.9% hemicellulose, with 3.3% lignin. By comparison, native poplar comprised 47.5% cellulose, 14.1% hemicellulose, and 25.5% lignin. Together, these results indicate that the reactive fractionation achieves efficient delignification while delivering a functionalized lignin stream alongside exceptionally pure cellulose. Mechanistically, syringol intercepts benzylic carbocation intermediates generated during fractionation, suppressing recondensation and enabling direct formation of syringolated lignin (SL). To elucidate how reactive fractionation alters the microstructure of native biomass, scanning electron microscope (SEM) was used to compare wood fibers before and after treatment (Fig. 1c\u0026ndash;d). Native fibers exhibited an intact hierarchical architecture\u003csup\u003e42\u003c/sup\u003e. In contrast, fibers in the fractionated pulp showed pronounced fibrillation, surface roughening, and partial splitting along the fiber axis, indicative of weakened inter-fiber adhesion. These morphological changes are consistent with disruption of the lignin\u0026ndash;carbohydrate complex (LCC) linkages, yielding smaller bundles and exposing microfibrils\u003csup\u003e43\u003c/sup\u003e. The resulting increase in accessible surface area is expected to enhance subsequent chemical functionalization and interfacial bonding with a resin in composite fabrication.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunctionalizing the lignin fraction\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe SL was isolated by precipitation in 35.8% yield based on initial poplar (theoretical maximum 38%). Running the reactive fractionation at reflux afforded a slightly brownish off-white solid (Fig. 2a), whereas lowering the temperature to 80 \u0026deg;C produced a whiter lignin but led to incomplete syringolation and thereby a lignin with reduced reactivity. Heteronuclear single-quantum coherence (HSQC) NMR indicated successful arylation. Strong correlations at \u0026delta;C/\u0026delta;H = 44.8/4.7 and 53.9/4.2 ppm, characteristic of substituted C\u0026alpha; sites in \u0026beta;\u0026ndash;O\u0026ndash;4 units formed upon syringolation were observed, and the native C\u0026alpha; signal was absent (Fig. 2a)\u003csup\u003e41\u003c/sup\u003e. Quantitative \u003csup\u003e31\u003c/sup\u003eP NMR further corroborated syringolation, showing a distinct and sharp resonance at \u0026delta;P = 142.85 ppm within the C\u0026ndash;5\u0026ndash;substituted phenolic region, which is consistent with syringolation at the C\u0026alpha; position (Fig. 2d)\u003csup\u003e44\u003c/sup\u003e. The \u003cem\u003emeta/para\u003c/em\u003e (\u003cem\u003em/p\u003c/em\u003e) ratio of SL was determined to 2:1 by HSQC. SL displayed a high abundance of phenolic OH groups (3.22 mmol g⁻\u0026sup1;), underscoring its reactive potential following syringolated fractionation.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe reactive lignin was then functionalized by reaction with epichlorohydrin, which can be sourced from biomass\u003csup\u003e45\u003c/sup\u003e. Selective etherification of SL at its phenolic hydroxyl groups afforded the corresponding epoxy-functionalized syringolated lignin (ESL) (Fig. 2b). Noteworthily, precipitation of the ESL yielded an off-white material in a quantitative yield starting from the brownish lignin (Fig. 2c). The HSQC spectrum of ESL displayed the additional cross-peaks in the aliphatic region, assignable to epoxy methylene and epoxy methine groups\u003csup\u003e46\u003c/sup\u003e (Fig. 2c). The coexistence of introduced syringyl correlations and these new epoxy signals verifies the introduction of epoxide functionality while retaining the syringolated backbone. In line with this assignment using \u003csup\u003e31\u003c/sup\u003eP NMR, phenolic OH decreased from 3.22 to 0.01 mmol g⁻\u0026sup1; after epoxy-functionalization, whereas aliphatic OH increased from 1.70 to 2.41 mmol g⁻\u0026sup1;, consistent with cleavage of \u0026gamma;\u0026ndash;formyl groups introduced during reactive fractionation and regeneration of aliphatic hydroxyls (Fig. 2d)\u003csup\u003e47\u003c/sup\u003e. Gel permeation chromatography (GPC) revealed concomitant changes in the apparent Mw distribution (Fig. 2e): SL spanned 525\u0026ndash;1379 g mol⁻\u0026sup1;, whereas ESL shifted to 629\u0026ndash;1938 g mol⁻\u0026sup1;, indicating that epoxy-functionalization broadens and shifts the molecular-weight profile while preserving the syringolated backbone. Fourier transform infrared (FTIR) spectroscopy spectra further corroborated these assignments (Fig. 2f). Relative to SL, ESL shows attenuation of the broad O\u0026ndash;H stretch near 3400 cm⁻\u0026sup1; and emergence of a characteristic epoxide band at 908 cm⁻\u0026sup1;, consistent with epoxide formation and with the concomitant decrease in phenolic hydroxyl content observed by \u003csup\u003e31\u003c/sup\u003eP NMR\u003csup\u003e48\u003c/sup\u003e. The tiny shoulder around 3056 cm⁻\u0026sup1; represent the C\u0026ndash;H vibration of epoxide ring, which support the successfully of epoxy-functionalization as well\u003csup\u003e49\u003c/sup\u003e. A marked reduction in intensity near 1720 cm⁻\u0026sup1; additionally supports cleavage of \u0026gamma;\u0026ndash;formyl groups during epoxy-functionalization\u003csup\u003e50\u003c/sup\u003e. Taken together, the HSQC, \u003csup\u003e31\u003c/sup\u003eP NMR, GPC, and FTIR results indicate that SL retains reactive phenolic functionality after reactive fractionation and that epoxy-functionalization efficiently converts these sites to epoxide groups while only modestly shifting the molecular-weight envelope, yielding a tunable lignin precursor suitable for subsequent composite fabrication. Chemical modification of lignin shifted the principal pyrolytic event to higher temperature. Thermogravimetric analysis (TGA/DTG) provided complementary evidence at the thermal property (Fig. 2g\u0026ndash;h). The DTG maximum shifted from 366.58 \u0026deg;C for native poplar to 375.83 \u0026deg;C for SL, and further to 392.04 \u0026deg;C for ESL, establishing ESL as the most thermally stable among the series. Reactive fractionation leads to a seemingly more thermally stable lignin, possibly by preventing degradation at the C\u0026alpha; position, thereby suppressing the phenolic \u0026beta;\u0026ndash;O\u0026ndash;4 quinone-methide pathway, which requires C\u0026alpha;\u0026ndash;OH\u003csup\u003e51\u003c/sup\u003e. Epoxy-functionalization further blocks almost all phenolic sites, which\u0026nbsp;impede radical initiations known for lignin degradation pathways\u003csup\u003e51,52\u003c/sup\u003e.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFormation of covalent bond between ESL and cellulose to yield a high strength composite\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe hypothesized that the C\u0026ndash;OH of cellulose reacts with the epoxide of ESL to form new ether linkages (Fig. 3a), to give rise to inter-fiber crosslinking. Filter paper (FP) was used as a cellulose model while screening curing temperatures (80\u0026ndash;220 \u0026deg;C) in the presence of 4-dimethylaminopyridine (DMAP). The tensile strength of ESL\u0026ndash;filter paper sample (ESLFP) increased with curing temperature, reaching 60.8 MPa at 180 \u0026deg;C and then declining at higher temperatures, consistent with the onset of cellulose thermal degradation (Fig. 3b). At this optimum, the composite was sixfold stronger than FP (11.3 MPa), evidencing robust ESL\u0026ndash;cellulose interactions (Fig. 3c). The role of DMAP was demonstrated using a no-catalyst control (ESLFP*). Without DMAP, the ESLFP* sample exhibited much lower strength (18.6 MPa), because unreacted ESL was removed during purification, indicating that physical adsorption alone is insufficient to provide load-bearing interfaces. Stiffness followed the same trend: the tensile modulus rose from 1.3 GPa (FP) to 1.4 GPa (ESLFP*) and to 2.7 GPa (ESLFP), consistent with covalent bonding limits inter-fiber slippage under load (Fig. 3d). Water resistance further differentiates covalently bonded material from the ESLFP* with other weaker physical interactions. ESLFP retained 46.5 MPa wet tensile strength (76.5%), whereas ESLFP* exhibited negligible wet strength of 6.3 MPa (33.9% retention) (Fig. 3f). The wet tensile modulus similarly increased from 0.1 GPa (FP) to 0.3 GPa (ESLFP*) and 1.5 GPa (ESLFP) (Fig. 3g). These improvements are attributed to DMAP-catalyzed epoxide ring-opening at cellulose C\u0026ndash;OH, which (i) creates covalent ESL\u0026ndash;cellulose bridges that persist in water, (ii) reduces swelling-induced plasticization by anchoring the interphase, and (iii) enhances stress transfer through a stiffer, chemically bonded network. Collectively, the data identify DMAP-catalyzed covalent bond formation at 180 \u0026deg;C as the governing factor underpinning both the sixfold increase in dry strength and the high wet-strength and modulus retention of ESLFP.\u003c/p\u003e\n\u003cp\u003eMacroscopic observations (Fig. 4a\u0026ndash;b) corroborate the chemistry: in the presence of DMAP, ESLFP darkened relative to both ESLFP* and the non-heated sample. Additional acetone washing after heating removed excess, unreacted ESL, rendering ESLFP* lighter in color, whereas the appearance of ESLFP was unaffected (Fig. S1a\u0026ndash;b). Kinetic FTIR analysis was employed to analyze the reaction process between cellulose and ESL, and the spectra reveal time-dependent changes in the chemical composition of ESLFP and ESLFP* heated for different durations (Fig. 4c\u0026ndash;d). As heating proceeded, the epoxy band of ESLFP at 908 cm\u003csup\u003e-1\u003c/sup\u003e in the ESLFP sample gradually decreased in intensity and red-shifted towards 898 cm\u003csup\u003e-1\u003c/sup\u003e, indicating consumption of epoxy groups and the re-emergence of the \u0026beta;\u0026ndash;1,4\u0026ndash;glycosidic bond vibration of cellulose. In contrast, the epoxy band in ESLFP* remained essentially unchanged, consistent with the design of a no reaction system in the absence of the catalyst.\u003c/p\u003e\n\u003cp\u003eTo probe the interactions underpinning the mechanical enhancement, X-ray photoelectron spectroscopy (XPS) was used to monitor surface functional groups. The high-resolution C 1s spectrum of FP shows the expected dominance of the C2 component (C\u0026ndash;O, 286.5 eV), reflecting the abundance of alcohol and ether carbons in the polysaccharide backbone (Fig. 5a). By contrast, ESL exhibits a spectrum dominated by the C1 component (C\u0026ndash;C/C\u0026ndash;H/C=C, 284.8 eV), consistent with aromatic and aliphatic carbons of lignin (Fig. 5b). A distinct contribution near 286.8 eV is observed for ESL, consistent with the presence of the epoxide functionality and aligning with the HSQC evidence for epoxide formation (Fig. 2c). Upon forming the ESLFP composite, the C1 fraction increases relative to cellulose, while the C2 fraction increases relative to ESL, indicating coexistence and intermixing of ESL and cellulose at the surface level (Fig. 5c). Notably, the epoxide-associated contribution near 286.8 eV diminishes after curing, consistent with ring-opening of the epoxide with cellulose C\u0026ndash;OH groups rather than mere physical mixing. Together, the C 1s evolutions support chemical coupling at the interface, corroborating the mechanical gains observed for ESLFP.\u003c/p\u003e\n\u003cp\u003eFTIR was used to assess bulk chemical changes since XPS probes only the near surface chemical compositions. Neat ESL displays the epoxide ring vibration at 908 cm⁻\u0026sup1;, whereas FP, ESLFP*, and ESLFP show a band at 896 cm⁻\u0026sup1; assigned to the cellulose \u0026beta;\u0026ndash;1,4\u0026ndash;glycosidic linkages. In the DMAP-cured composite (ESLFP), the disappearance of the 908 cm⁻\u0026sup1; epoxide band\u0026mdash;together with the persistent 896 cm⁻\u0026sup1; cellulose band\u0026mdash;indicates epoxide ring-opening and formation of new ether linkages between ESL and cellulose (Fig. S2).\u003c/p\u003e\n\u003cp\u003eSEM further supported the ESL-cellulose ether bond. FP displays fibers with the characteristic microscale roughness of native cellulose (Fig. 5d). After incorporation of ESL, ESLFP shows fibers with a continuous, conformal coating and smoother inter-fiber interfaces, indicative of an interphase that bridges neighboring fibers (Fig. 5e). In contrast, ESLFP* resembles the native fiber morphology after acetone purification, consistent with removal of unreacted ESL and limited interfacial bonding (Fig. 5f). The morphological evidence\u0026mdash;continuous coating in ESLFP versus fiber-like surfaces in ESLFP*\u0026mdash;is consistent with the covalent coupling inferred from XPS and FTIR and explains the observed enhancements in mechanical strength, modulus, and wet-strength retention.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFabrication and characterization of pulp\u0026ndash;ESL composites\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo realize co-utilization of both streams from reactive fractionation, a fully biobased composite from a single feedstock was prepared by combining the high-purity cellulose pulp with ESL. Guided by the filter-paper model, the same covalent chemistry was translated to pulp obtained from reactive fractionation of poplar: without additional chemical treatment or bleaching, cellulose pulp, ESL, and DMAP were dispersed in DI water, homogenized, and hot-pressed to drive epoxide ring-opening at cellulose C\u0026ndash;OH, forming the ether linkages. The resulting ESLP exhibited a tensile strength of 46.7 MPa and modulus of 2.5 GPa, markedly higher than sheets prepared from neat pulp (8.5 MPa, 0.8 GPa) (Fig. 6a\u0026ndash;c). These gains confirm that the covalent-bonding strategy operative in the model system also functions with fractionated pulp, demonstrating concurrent valorization of lignin and cellulose into one material. ESLP maintained 33.9 MPa wet tensile strength and a wet modulus of 2.0 GPa, whereas pure pulp retained only 1.9 MPa and 0.2 GPa (Fig. 6d\u0026ndash;f). The high wet tensile property retention of ESLP indicates that chemical coupling, rather than hydrogen bonding alone, governs inter-fiber adhesion and underpins suitability for moist environments.\u003c/p\u003e\n\u003cp\u003eConsistent with ESL\u0026ndash;cellulose coupling, SEM images reveals a conformal, micro-crosslinked interphase in ESLP analogous to that observed in ESLFP (Fig. 6g). Relative to filter paper, the fractionated pulp offers greater accessible surface area and porosity; ESL therefore penetrates more deeply into the fiber network prior to curing, yielding continuous coatings and bridging at fiber-fiber contacts. The observed fully coated fibers and densified, crosslinked architecture in ESLP align with the enhanced dry and wet mechanics. By contrast, the pressed pulp exhibits a more natural fiber characteristic, which led to a lower mechanical and wet properties (Fig. 6h).\u003c/p\u003e\n\u003cp\u003eHot-pressing produced a smoother, denser surface, and ESL incorporation reduced surface wettability. Static water contact angles started from 75.8 \u0026deg; at 0 s (pure pulp) and rapidly decayed to 17.9 \u0026deg; at 5 s, whereas ESLP started at 88.4 \u0026deg; (0 s) and remained 85.0 \u0026deg; at 60 s (Fig. 6i). The higher and time-stable contact angle indicates suppressed wetting, attributable to the covalently bonded ESL interphase together with surface densification\u0026mdash;trends consistent with the improved strength, stiffness, and wet-strength retention.\u003c/p\u003e\n\u003cp\u003eThe same fractionation and epoxy-functionalization sequence translated to rapeseed straw, an herbaceous residue typically richer in ash, affording a brownish SL and a paler off-white solid ESL after precipitation (Fig. S3a\u0026ndash;b). HSQC spectra showed the expected C\u0026alpha;\u0026ndash;arylation correlations for SL and the additional aliphatic cross-peaks attributable to the epoxide motif for ESL, mirroring the poplar case (Fig. S4\u0026ndash;5). Despite this compositional challenge, the DMAP-assisted epoxide\u0026ndash;cellulose coupling remained effective, yielding substantial improvements in both dry and wet properties (Fig. S6): ESLP reached 40.0 MPa tensile strength and 3.0 GPa modulus versus 11.9 MPa and 1.1 GPa for neat straw pulp; under wet conditions, ESLP retained 21.8 MPa tensile strength and 1.8 GPa modulus compared to 1.5 MPa and 0.1 GPa for neat pulp. These results demonstrate that the chemistry is robust to feedstock variability and tolerant to elevated ash content, supporting co-valorization of lignin and cellulose from different biomass streams. As mentioned above, herbaceous feedstocks (e.g., rapeseed straw) often contain substantial alkali/alkaline-earth ash and silica. In conventional metal-catalyzed fractionation routes\u0026mdash;such as RCF\u0026mdash;these inorganic species would poison and deactivate metal catalysts and complicate liquor handling, narrowing the usable feedstock window. By contrast, our metal-free DMAP-assisted epoxide\u0026ndash;cellulose coupling avoids this limitation and delivers large strength gains on high-ash pulps, underscoring the practical advantage of the approach for agricultural residues.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eIn conclusion, this work presents a fully bio-based composite material that achieves high mechanical strength and remarkable wet stability enabled through covalent bound formation between lignin and cellulose without prior depolymerization. The key lies in utilizing both major biomass fractions\u0026mdash;lignin and cellulose, without extensive downstream processing\u0026mdash;to form a composite material. The stabilized epoxy-functionalized syringolated lignin acts as a reactive bridge, forming durable ether linkages with cellulose and transforming hydrogen-bonded fiber networks into chemically crosslinked architectures. This material design was enabled by a mild, metal-free reactive fractionation that yields functional lignin and pure cellulose directly from raw biomass, including ash-rich side streams. The resulting composites demonstrate that biomass-derived polymers can rival fossil-based packaging and kraft liner produced from virgin forestry in strength, durability, and moisture resistance, highlighting a scalable path toward circular, wet-tolerant bio-based materials. This study makes progress in the research field by demonstrating a holistic valorization of both lignin and cellulose streams to produce a composite with good mechanical properties without severe processing. Given the simplicity of the process and the wide tolerance to feedstocks, this study will be of interest to both the packaging industries as well as stakeholders that generate residual biomass streams.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003e\u003cstrong\u003eChemicals and Materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eMaterials and chemical reagents can be found in Supplementary information. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eReactive fractionation of biomass\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eDry poplar biomass (5.00 g, particle size of 0.5 mm) and syringol (2.00 g) with 88 wt% formic acid (50 mL) in a closed reactor at 120 \u0026deg;C for 30 min. After completion, the reaction mixture was filtered to obtain a cellulose-enriched pulp, which was sequentially washed with formic acid, ethanol, and deionized water. The filtrate was concentrated by rotary evaporation and precipitated into deionized water to obtain SL. The SL was collected by centrifugation and then freeze-dried to yield a light-colored powder. The reactive fractionation procedure is readily scalable; a 30 g batch of biomass was successfully processed under identical conditions. The same methodology was also applied to rapeseed straw, demonstrating its versatility across both forestry- and agriculture-derived feedstocks.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEtherification of SL to yield an epoxy\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSL (3.00 g, 9.7 mmol, 1.00 equiv., based on phenolic OH content) and tetrabutylammonium bromide (2.06 g, 6.4 mmol, 0.66 equiv.) were dissolved in 15\u0026ndash;20 equiv. of epichlorohydrin (the exact amount adjusted according to the solubility of SL) in a 100 mL round-bottom flask equipped with a magnetic stir bar. After purging with N₂ for 5 min, the reaction mixture was stirred at 60 \u0026deg;C for 2 h, then immediately cooled in an ice bath. Subsequently, 4.00 equiv. of 50 wt% NaOH solution was added dropwise, and the mixture was stirred at 60 \u0026deg;C for another 2 h. Dichloromethane was added and the resulting solution was washed with deionized water until neutral, followed by brine. The resulting organic phase was dried over anhydrous Na\u003csub\u003e2\u003c/sub\u003eSO₄ and the residual epichlorohydrin and solvent were removed via rotary evaporation. The crude product was redissolved in a small amount of acetone and precipitated in water. The resulting precipitate was collected by centrifugation and then freeze-dried to yield an off-white ESL powder. The epoxy-functionalization of SL from rapeseed straw was applied using same method.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFabrication of ESL-cellulose composite\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe curing process was first optimized using filter paper as a cellulose model. ESL (0.20 g) and DMAP (2 wt% of ESL) were dissolved in acetone (5 mL), in which 0.20 g of filter paper was immersed. After air drying, the impregnated filter paper was heated at 80\u0026ndash;220 \u0026deg;C for 1 h. The resulting ESLFP was washed with acetone under sonication for 5 min to remove non-covalently bound ESL. A control group was prepared without DMAP, named as ESLFP*.\u003c/p\u003e\n\u003cp\u003eFor composite fabrication, the pulp obtained from reactive fractionation and ESL (1:1) were dispersed in 100 mL of deionized water together with DMAP (2 wt%) to form a suspension. The mixture was homogenized at 10,000 rpm for 1 h and then subjected to vacuum filtration to yield a wet ESLP cake. The cake was hot-pressed at 180 \u0026deg;C under 3.5 MPa for 1 h to obtain the ESLP composite.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCharacterization of products and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe characterization details can be found in Supplementary information.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eThis work was supported by the Wallenberg Initiative Materials Science for Sustainability (WISE) funded by the Knut and Alice Wallenberg Foundation. We thank Dr. Annelie Moldin at Lantm\u0026auml;nnen for providing details of available residual streams from agriculture and Albin Gunnarson for providing rapeseed straws as feedstock.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eMudgal, D., Pagone, E. \u0026amp; Salonitis, K. 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Wood Sci.\u003c/em\u003e \u003cstrong\u003e53\u003c/strong\u003e, 268\u0026ndash;271 (2007).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Fractionation, bio-based composite, reactive lignin, holistic biomass utilization","lastPublishedDoi":"10.21203/rs.3.rs-8194130/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8194130/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eFuture biorefineries must upgrade all constituents of lignocellulosic feedstocks to high-value products. To curb land-use pressure, technologies that upgrade existing side streams from forestry and agriculture into substitutes for high-impact, fossil-derived materials are urgently needed. Prevailing biomass valorization typically prioritizes either cellulose pulp or lignin; true co-valorization remains uncommon. Here we report a metal-free, ambient-pressure reactive fractionation that concurrently yields high-quality cellulose and a functionalized lignin. The isolated lignin is etherified and subsequently covalently coupled to cellulose via epoxide ring-opening, producing a composite. The materials display mechanical performance equivalent of common packaging materials, with retention under wet conditions, overcoming the intrinsic limitations of hydrogen-bonded cellulose networks. By integrating mild fractionation with chemical upgrading, this strategy simplifies processing, broadens the product slate accessible from residual biomass side streams and advances the substitution of problematic packaging materials. These findings establish a scalable route to whole-biomass co-valorization and wet-tolerant bio-based packaging from residual streams.\u003c/p\u003e","manuscriptTitle":"Composites of covalently linked lignin and cellulose from one feedstock","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-12-19 08:06:42","doi":"10.21203/rs.3.rs-8194130/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-communications","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"NCOMMS","sideBox":"Learn more about [Nature Communications](http://www.nature.com/ncomms/)","snPcode":"","submissionUrl":"https://mts-ncomms.nature.com/","title":"Nature Communications","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Communications","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"a47c1b91-ba7f-4475-b8dc-776273ae6520","owner":[],"postedDate":"December 19th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":58867275,"name":"Scientific community and society/Forestry"},{"id":58867276,"name":"Scientific community and society/Agriculture"},{"id":58867277,"name":"Physical sciences/Chemistry/Organic chemistry/Carbohydrate chemistry"},{"id":58867278,"name":"Physical sciences/Materials science/Techniques and instrumentation/Characterization and analytical techniques"},{"id":58867279,"name":"Physical sciences/Materials science/Structural materials/Composites"}],"tags":[],"updatedAt":"2025-12-19T08:06:42+00:00","versionOfRecord":[],"versionCreatedAt":"2025-12-19 08:06:42","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8194130","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8194130","identity":"rs-8194130","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}