Assistant Professor Mika H. Sipponen leads the Sustainable Materials Chemistry (SUSMATCHEM) research group at the Department of Materials and Environmental Chemistry (MMK) at Stockholm University. Sipponen earned his M.Sc. (Tech.) degree in Chemical Technology from Aalto University (Finland) in 2010, and his D.Sc. (Tech.) degree in the same subject area in 2015. He was awarded an Academy of Finland postdoctoral researcher grant in 2016, and has been recognized twice as an Outstanding Reviewer of the RSC journal Green Chemistry (in 2018 and 2021). In 2020, he was awarded the Nouryon Nordic Prize in surface and colloid science. He has also received prestigious grants from the Swedish Foundation of Strategic Research (SSF, FFL8) and European Research Council (ERC-StG-2022). Sipponen has been working on topics related to lignin chemistry and biomass processing since 2008, engaging in industrially aligned applied research while also taking a keen interest in associated fundamental phenomena. He is a co-founder of the startup company Lignoflow, and has served as an expert evaluator and coordinator of European projects. His current research program focuses on the development of lignin-based functional materials, including their structure, properties, and performance.
Examiner for Chemistry of Renewable Materials (KZ8022), course in the MSc programme in Sustainable Chemistry.
Lecturer in Introduction to Sustainable Chemistry (KZ7012), course in the MSc programme in Sustainable Chemistry.
Examiner in Advanced Materials Chemistry (KZ44019), PhD level course.
The group develops lignin-based functional materials for sustainable energy and environmental applications. In addition, we are interested in transformation of other industrial sidestreams to value-added materials following the principles of green chemistry. Our research also involves fundamental studies on the formation and structure of renewable nanomaterials, as well as their chemical and biological functions.
We are working on the following research areas and projects:
Materials for a sustainable society
Materials for energy
C1Bio - Kolfixering genom grön kemi för en C1-baserad bioekonomi (Vinnova 2020-2023)
Materials for environment
COATLIG: Development of environmentally friendly lignin-based coatings (MMK)
LIFAGRO: (Research projects for early-career researchers, Formas 2021-2025)
Synthesis and processing methods for sustainable materials
Green material synthesis
LIGNOMEMB: Biocatalytic membranes based on lignin nanoparticles (Starting Grant, Vetenskapsrådet, 2021-2025)
LIGNOVITRI: Lignin-based reprocessable polymer materials (Carl Trygger Stiftelse, 2021-2023)
SUSLIG: Lignin-based functional mateirals for a sustainable future
CIRCULIG: Circular lignin materials from well-defined functional building blocks
Biobased materials processing
BarkBuild: Tree bark as a renewable source of wood protection materials for building applications (ERA-NET ForestValue, 2022-2025)
UPSIDEHYB: Upcycling food industry side streams into functional organic-inorganic hybrid materials
Research Group members
Mika Sipponen, PI
Ievgen Pylypchuk, Researcher
Jinrong Liu, PhD Student
Mohammad Morsali, PhD Student
Unnimaya Thalakkale Veettil, PhD Student
Matilda Andersson, PhD Student
Fengyang Wang, PhD Student
Liyang Liu, Postdoctoral Fellow
Mirva Eriksson, Researcher
Miguel Angel Postigo Pelaez, Research Assistant
Sukaina Ben, Trainee
Former group members
Adrian Moreno Guerra, Postdoctoral Fellow
Esakkiammal Sudha Esakkimuthu, Guest Researcher, MSCA-IF
Federica Maria Camilla Ferruti, Visiting PhD student
Letizia Anna Maria Rossato, Visiting PhD student
Morsali, M., Moreno, A., Loukovitou, A., Pylypchuk, I., Sipponen, M.H.* Stabilized Lignin Nanoparticles for Versatile Hybrid and Functional Nanomaterials. Biomacromolecules 23, 2022, 4597–4606.
Liu, J., Moreno, A., Chang, J., Morsali, M., Yuan, J., Sipponen, M.H.⁂ Fully Biobased Photothermal Films and Coatings for Indoor Ultraviolet Radiation and Heat Management. ACS Appl. Mat. Interf. 14, 2022, 12693-12702.
Moreno, A.,* Morsali, M., Sipponen, M.H.* Catalyst-Free Synthesis of Lignin Vitrimers with Tunable Mechanical Properties: Circular Polymers and Recoverable Adhesives. ACS Appl. Mat. Interf. 13, 2021, 57952-57961.
Moreno, A.,* Liu, J., Gueret, R., Hadi, S.E., Bergström, L., Slabon, A., Sipponen, M.H.* Unravelling the Hydration Barrier of Lignin Oleate Nanoparticles for Acid‐and Base‐Catalyzed Functionalization in Dispersion State. Angewandte Chemie Int. Ed. 60, 2021, 20897-20905 (Hot Paper)
A. Moreno, M. Morsali, J. Liu, M. H. Sipponen,* Access to Tough and Transparent Nanocomposites via Pickering Emulsion Polymerization using Biocatalytic Hybrid Lignin Nanoparticles as Functional Surfactants. Green Chemistry 23, 2021, 3001-3014.
A. Moreno,* M. H. Sipponen,* Biocatalytic Nanoparticles for the Stabilization of Degassed Single Electron Transfer Living Radical Pickering Emulsion Polymerizations. Nature Communications 11, 2020: 5599.
A. Moreno, M. H. Sipponen,* Lignin-based smart materials: a roadmap to processing and synthesis for current and future applications. Materials Horizons 7, 2020, 2237.
A selection from Stockholm University publication database
Access to tough and transparent nanocomposites via Pickering emulsion polymerization using biocatalytic hybrid lignin nanoparticles as functional surfactants dagger
2021. Adrian Moreno (et al.). Green Chemistry 23 (8), 3001-3014Article
Weak interfacial binding of lignin within synthetic polymer composites results in unsatisfactory mechanical properties that limit their application prospects. In the present work, polystyrene (PS) and poly(butyl methacrylate) (PBMA) nanocomposites containing lignin nanoparticles (LNPs) are produced by simple melting of polymeric latex dispersions obtained from free radical polymerization of oil-in-water Pickering emulsions stabilized by hybrid LNPs coated with chitosan and glucose oxidase. Owing to the formation of viscous polymer melts, the hybrid LNPs ended up uniformly dispersed within the polymeric matrices, which gave the polymeric nanocomposites markedly improved tensile strength without sacrificing their elasticity in comparison to pure PS and PBMA. Consequently, the composites reinforced with 15 wt% of the hybrid particles showed improvement in toughness by a factor of 3.5 and 15 compared to those of the corresponding pristine PS and PBMA. In addition, the presence of the hybrid particles conferred the nanocomposites with commendable UV-blocking and antioxidant properties which are relevant for protective packaging and coating applications. Overall, our results show a new and green route with excellent material economy (overall mass yield up to 91%) to obtain strong and transparent polymeric nanocomposites reinforced with up to 30 wt% of LNPs, which is expected to attract renewed interest in lignin-polymer composites for a broad range of applications.
Multifunctional lignin-based nanocomposites and nanohybrids
2021. Erlantz Lizundia (et al.). Green Chemistry 23 (18), 6698-6760Article
Significant progress in lignins valorization and development of high-performance sustainable materials have been achieved in recent years. Reports related to lignin utilization indicate excellent prospects considering green chemistry, chemical engineering, energy, materials and polymer science, physical chemistry, biochemistry, among others. To fully realize such potential, one of the most promising routes involves lignin uses in nanocomposites and nanohybrid assemblies, where synergistic interactions are highly beneficial. This review first discusses the interfacial assembly of lignins with polysaccharides, proteins and other biopolymers, for instance, in the synthesis of nanocomposites. To give a wide perspective, we consider the subject of hybridization with metal and metal oxide nanoparticles, as well as uses as precursor of carbon materials and the assembly with other biobased nanoparticles, for instance to form nanohybrids. We provide cues to understand the fundamental aspects related to lignins, their self-assembly and supramolecular organization, all of which are critical in nanocomposites and nanohybrids. We highlight the possibilities of lignin in the fields of flame retardancy, food packaging, plant protection, electroactive materials, energy storage and health sciences. The most recent outcomes are evaluated given the importance of lignin extraction, within established and emerging biorefineries. We consider the benefit of lignin compared to synthetic counterparts. Bridging the gap between fundamental and application-driven research, this account offers critical insights as far as the potential of lignin as one of the frontrunners in the uptake of bioeconomy concepts and its application in value-added products.
Lignin-Based Porous Supraparticles for Carbon Capture
2021. Bin Zhao (et al.). ACS Nano 15 (4), 6774-6786Article
Multiscale carbon supraparticles (SPs) are synthesized by soft-templating lignin nano- and microbeads bound with cellulose nanofibrils (CNFs). The interparticle connectivity and nanoscale network in the SPs are studied after oxidative thermostabilization of the lignin/CNF constructs. The carbon SPs are formed by controlled sintering during carbonization and develop high mechanical strength (58 N.mm(-3)) and surface area (1152 m(2). g(-1)). Given their features, the carbon SPs offer hierarchical access to adsorption sites that are well suited for CO2 capture (77 mg CO2.g(-1)), while presenting a relatively low pressure drop (similar to 33 kPa.m(-1) calculated for a packed fixed-bed column). The introduced lignin-derived SPs address the limitations associated with mass transport (diffusion of adsorbates within channels) and kinetics of systems that are otherwise based on nanoparticles. Moreover, the carbon SPs do not require doping with heteroatoms (as tested for N) for effective CO2 uptake (at 1 bar CO2 and 40 degrees C) and are suitable for regeneration, following multiple adsorption/desorption cycles. Overall, we demonstrate porous SP carbon systems of low cost (precursor, fabrication, and processing) and superior activity (gas sorption and capture).
Primary interactions of biomass components during fast pyrolysis
2021. David O. Usino (et al.). Journal of Analytical and Applied Pyrolysis 159Article
Fast pyrolysis is an industrially attractive method to produce fuels and chemicals from biomass; however, to gain better control over the process, the reactions and interactions between the components and decomposition products need elucidation. This study investigated primary reactions during fast pyrolysis of biomass. Pyrolysis of the three main biomass components (cellulose, hemicellulose and lignin) and their blends was carried out with a micro-pyrolyser connected to a Gas Chromatograph-Mass Spectrometer/Flame Ionisation Detector (GC–MS/FID). The blends of the individual components were prepared in similar proportions to that of native biomass (birchwood) and were pyrolysed at 600 °C for 2 s. The results showed that the two-component blends decrease the production of saccharides to a large extent. This was especially noticeable for levoglucosan when cellulose was mixed with either hemicellulose or lignin. Similarly, in the presence of cellulose, the formation of phenolic compounds from lignin was inhibited by 62 %. However, no differences were found in yields of the main products for the xylan-lignin blend compared to those from the individual components. The yields of volatile products from the cellulose-xylan blend were promoted for a majority of the product categories and were most pronounced for the aldehydes. Furthermore, while the formation of the phenols and saccharides was slightly inhibited for the three-component blend, the aldehydes, ketones and furans showed an increased production compared to the weighed sum of products expected, based on the pyrolysis of the individual components. The native biomass showed a similar trend as the three-component blend in all product categories except for the saccharides, which were inhibited to a large extent. This study provides a better understanding of the interactions occurring between different components during fast pyrolysis of biomass.
Solvent-Resistant Lignin-Epoxy Hybrid Nanoparticles for Covalent Surface Modification and High-Strength Particulate Adhesives
2021. Tao Zou (et al.). ACS Nano 15 (3), 4811-4823Article
Fabrication of spherical lignin nanoparticles (LNPs) is opening more application opportunities for lignin. However, dissolution of LNPs at a strongly alkaline pH or in common organic solvent systems has prevented their surface functionalization in a dispersion state as well as processing and applications that require maintaining the particle morphology under harsh conditions. Here, we report a simple method to stabilize LNPs through intraparticle cross-linking. Bisphenol A diglycidyl ether (BADGE), a cross-linker that, like lignin, contains substituted benzene rings, is coprecipitated with softwood Kraft lignin to form hybrid LNPs (hy-LNPs). The hy-LNPs with a BADGE content <= 20 wt % could be intraparticle cross-linked in the dispersion state without altering their colloidal stability. Atomic force microscopy and quartz crystal microbalance with dissipation monitoring were used to show that the internally crosslinked particles were resistant to dissolution under strongly alkaline conditions and in acetone-water binary solvent that dissolved unmodified LNPs entirely. We further demonstrated covalent surface functionalization of the internally cross-linked particles at pH 12 through an epoxy ring-opening reaction to obtain particles with pH-switchable surface charge. Moreover, the hy-LNPs with BADGE content >= 30% allowed both inter- and intraparticle cross-linking at >150 degrees C, which enabled their application as waterborne wood adhesives with competitive dry/wet adhesive strength (5.4/3.5 MPa).
Toward waste valorization by converting bioethanol production residues into nanoparticles and nanocomposite films
2021. Guillaume N. Rivière (et al.). Sustainable Materials and Technologies 28Article
A “waste-valorization” approach was developed to transform recalcitrant hydrolysis lignin (HL) from second-generation bioethanol production into multifunctional bio-based products. The hydrolysis lignin (HL) was extracted with aqueous acetone, yielding two fractions enriched in lignin and cellulose, respectively. The soluble hydrolysis lignin (SHL) was converted into anionic and cationic colloidal lignin particles (CLPs and c-CLPs). The insoluble cellulose-rich fraction was transformed into lignocellulosic nanofibrils that were further combined with CLPs or c-CLPs to obtain nanocomposite films with tailored mechanical properties, oxygen permeability and antioxidant properties. To enable prospective applications of lignin in nanocomposite films and beyond, CLPs and c-CLPs were also produced from a soda lignin (SL) and the influence of the lignin type on the particle size and ecotoxicity was evaluated. Finally, the carbon footprint of the entire process from hydrolysis lignin to films was assessed and an integration to industrial scale was considered to reduce the energy consumption. While most previous work utilizes purified lignin and pristine and often purified cellulose fibers to produce nanomaterials, this work provides a proof of concept for utilizing the recalcitrant lignin-rich side stream of the bioethanol process as raw material for functional nanomaterials and renewable composites.
Unravelling the Hydration Barrier of Lignin Oleate Nanoparticles for Acid- and Base-Catalyzed Functionalization in Dispersion State
2021. Adrian Moreno (et al.). Angewandte Chemie International Edition 60 (38), 20897-20905Article
Lignin nanoparticles (LNPs) are promising renewable nanomaterials with applications ranging from biomedicine to water purification. However, the instability of LNPs under acidic and basic conditions severely limits their functionalization for improved performance. Here, we show that controlling the degree of esterification can significantly improve the stability of lignin oleate nanoparticles (OLNPs) in acidic and basic aqueous dispersions. The high stability of OLNPs is attributed to the alkyl chains accumulated in the shell of the particle, which delays protonation/deprotonation of carboxylic acid and phenolic hydroxyl groups. Owing to the enhanced stability, acid- and base-catalyzed functionalization of OLNPs at pH 2.0 and pH 12.0 via oxirane ring-opening reactions were successfully performed. We also demonstrated these new functionalized particles as efficient pH-switchable dye adsorbents and anticorrosive particulate coatings.
Agglomeration of Viruses by Cationic Lignin Particles for Facilitated Water Purification
2020. Guillaume N. Riviere (et al.). acs sustainable chemistry and engineering 8 (10), 4167-4177Article
Virus contamination of water is a threat to human health in many countries. Current solutions for inactivation of viruses mainly rely on environmentally burdensome chemical oxidation or energy-intensive ultraviolet irradiation, which may create toxic secondary products. Here, we show that renewable plant biomass-sourced colloidal lignin particles (CLPs) can be used as agglomeration agents to facilitate removal of viruses from water. We used dynamic light scattering (DLS), electrophoretic mobility shift assay (EMSA), atomic force microscopy and transmission electron microscopy (AFM, TEM), and UV spectrophotometry to quantify and visualize adherence of cowpea chlorotic mottle viruses (CCMVs) on CLPs. Our results show that CCMVs form agglomerated complexes with CLPs that, unlike pristine virus particles, can be easily removed from water either by filtration or centrifugation. Additionally, cationic particles formed by adsorption of quaternary amine-modified softwood kraft lignin on the CLPs were also evaluated to improve the binding interactions with these anionic viruses. We foresee that due to their moderate production cost, and high availability of lignin as a side-stream from biorefineries, CLPs could be an alternative water pretreatment material in a large variety of systems such as filters, packed columns, or flocculants.
Biocatalytic nanoparticles for the stabilization of degassed single electron transfer-living radical pickering emulsion polymerizations
2020. Adrian Moreno, Mika H. Sipponen. Nature Communications 11 (1)Article
Synthetic polymers are indispensable in many different applications, but there is a growing need for green processes and natural surfactants for emulsion polymerization. The use of solid particles to stabilize Pickering emulsions is a particularly attractive avenue, but oxygen sensitivity has remained a formidable challenge in controlled polymerization reactions. Here we show that lignin nanoparticles (LNPs) coated with chitosan and glucose oxidase (GOx) enable efficient stabilization of Pickering emulsion and in situ enzymatic degassing of single electron transfer-living radical polymerization (SET-LRP) without extraneous hydrogen peroxide scavengers. The resulting latex dispersions can be purified by aqueous extraction or used to obtain polymer nanocomposites containing uniformly dispersed LNPs. The polymers exhibit high chain-end fidelity that allows for production of a series of well-defined block copolymers as a viable route to more complex architectures.
Identifying the primary reactions and products of fast pyrolysis of alkali lignin
2020. Supriyanto Supriyanto (et al.). Journal of Analytical and Applied Pyrolysis 151Article
This study focused on the effect of temperature and residence time on the primary thermal decomposition reactions during a fast pyrolysis of softwood alkali lignin. The use of Py-GC/MS/FID (Micropyrolyser-Gas Chromatography/Mass Spectrometry/Flame Ionization Detector) allowed for rapid heating of the sample and detailed identification and quantification of the pyrolysis products at a temperature range of 400-600 degrees C, with residence times from 0.5-5 s. The identified primary pyrolysis products were mainly volatile guaiacyl-type compounds. There was a general increase in yield for the majority of the volatile compounds with increased temperature and time. The cleavage of the lignin polymer to linear carbonyl (acetaldehyde) and guaiacyl-type aromatic compounds increased with temperature, while that of catechol and cresol type was mainly favoured at 500 and 600 degrees C. Based on these results, a mechanistic pathway for the pyrolytic process was proposed, drawing a linkage from structural units of lignin to the formed primary products. In summary, our findings suggest that the primary decomposition reactions that occur under the fast pyrolysis conditions can be controlled by varying the process temperature and residence time, and deliver mechanistic insight into the product distribution from structurally complex lignin material.
2020. Tetyana M. Budnyak, Adam Slabon, Mika H. Sipponen. ChemSusChem 13 (17), 4344-4355Article
Lignin is one the most fascinating natural polymers due to its complex aromatic‐aliphatic structure. Phenolic hydroxyl and carboxyl groups along with other functional groups provide technical lignins with reactivity and amphiphilic character. Many different lignins have been used as functional agents to facilitate the synthesis and stabilization of inorganic materials. Herein, the use of lignin in the synthesis and chemistry of inorganic materials in selected applications with relevance to sustainable energy and environmental fields is reviewed. In essence, the combination of lignin and inorganic materials creates an interface between soft and hard materials. In many cases it is either this interface or the external lignin surface that provides functionality to the hybrid and composite materials. This Minireview closes with an overview on future directions for this research field that bridges inorganic and lignin materials for a more sustainable future.
Lignin-based smart materials
2020. Adrian Moreno, Mika H. Sipponen. Materials Horizons 7 (9), 2237-2257Article
Biomass-derived materials are green alternatives to synthetic plastics and other fossil-based materials. Lignin, an aromatic plant polymer, is one of the most appealing renewable material precursors for smart materials capable of responding to different stimuli. Here we review lignin-based smart materials, a research field that has seen a rapid growth during the last five years. We describe the main processing and chemical synthesis routes available for the fabrication of lignin-based smart materials, and focus on their use as sensors, biomedical systems, and shape-programmable materials. In addition to benchmarking their performance to the state of the art fossil counterparts, we identify challenges and future opportunities for the development of lignin-based smart materials towards new high-performance applications.
Lignin-fatty acid hybrid nanocapsules for scalable thermal energy storage in phase-change materials
2020. Mika H. Sipponen (et al.). Chemical Engineering Journal 393Article
Development of affordable thermal energy storage (TES) has been hampered by the lack of environmentally benign and scalable phase-change materials (PCM). Here we show size-controlled colloidal synthesis of fatty acid-lignin hybrid nanocapsules and demonstrate their applicability as PCM in dry and wet states. The one-pot fabrication allowed for facile preparation of hybrid capsules with a predictable concentration of tall oil fatty acid, oleic acid, or lauric acid in core-shell particles stabilized by softwood kraft lignin. Phase-change peaks of capsules containing 40 wt% of lauric acid were observed in aqueous dispersion, indicating a possibility to develop colloidal TES systems. In dry form, the hybrid capsules prevented fragmentation of the phase-change peaks during 290 heating-cooling cycles, while in wet state the capsules appeared stable for 25 cycles. The nanoscaled morphology of the capsules was characterized using thermoporometry-differential scanning calorimetry (tp-DSC), transmission electron microscopy (TEM), atomic force microscopy (AFM), dynamic light scattering (DLS), and small angle X-ray scattering (SAXS). Extraction of lauric acid from the capsules allowed for investigation of the intraparticle space previously occupied by the fatty acid. The fatty acid-deficient nanocapsules were found to contain an internal volume that was 19 times as high as that of lignin nanoparticles. Approximately 20 nm thick lignin shells of the capsules were found to be readily accessible to water, permitting heat transfer across the capsules. The possibility to tailor the hybrid capsules by altering the chain length and saturation degree of the fatty acids opens applications that extend beyond the TES systems.
Spherical lignin particles
2020. Monika Österberg (et al.). Green Chemistry 22 (9), 2712-2733Article
There is an increased interest in renewable carbon as a source of materials, where lignin is expected to play a prominent role. This stems, partially, from new regulations aiming to achieve a cleaner and safer environment. Lignin, as a polyaromatic plant-derived biomolecule, is not only abundant but widely accessible in industrial streams. Due to recent developments in production scalability as well as promising application prospects, nanoscaled lignin particles have recently generated interest in the research and industrial communities. This review describes the main routes to prepare spherical lignin particles, highlighting aspects associated to their shape and topology as well as performance. We discuss the use of spherical lignin particles as dispersants and in the formulation of coatings, adhesives and composites, focusing on the advantages of the spherical shape and nanoscaled size. The state of the particles is furthermore compared in terms of their applicability in dry and wet forms. Finally, we discuss the sustainability, stability and degradation of lignin particles, which are issues that are critically important for any prospective use.
Well-Defined Lignin Model Films from Colloidal Lignin Particles
2020. Muhammad Farooq (et al.). Langmuir 36 (51), 15592-15602Article
The transformation of a molecularly complex and irregularly shaped lignin into a nanoscale spherical architecture is anticipated to play a pivotal role in the promotion of lignin valorization. From the standpoint of using colloidal lignin particles (CLPs) as building blocks for a diverse range of applications, it has become essential to study their interactions with soluble compounds of varied origin. However, the lack of model films with well-defined surface properties similar to those of CLPs has hindered fundamental studies using surface-sensitive techniques. Here, we report well-defined and stable thin films prepared from CLPs and demonstrate their suitability for investigation of surface phenomena. Direct adsorption on substrates coated with a cationic anchoring polymer resulted in uniform distribution of CLPs as shown with atomic force microscopy (AFM). Quartz crystal microbalance with dissipation monitoring (QCM-D) experiments revealed higher adsorbed mass of cationic lignin onto the CLP-coated substrate in comparison to the film prepared from dissolved lignin, suggesting preferential adsorption via the carboxylic acid enriched surfaces of CLPs. QCM-D further enabled detection of small changes such as particle swelling or partial dissolution not detectable via bulk methods such as light scattering. The CLP thin films remained stable until pH 8 and displayed only a low degree of swelling. Increasing the pH to 10 led to some instability, but their spherical geometry remained intact until complete dissolution was observed at pH 12. Particles prepared from aqueous acetone or aqueous tetrahydrofuran solution followed similar trends regarding adsorption, pH stability, and wetting, although the particle size affected the magnitude of adsorption. Overall, our results present a practical way to prepare well-defined CLP thin films that will be useful not only for fundamental studies but also as a platform for testing stability and interactions of lignin nanoparticles with materials of technical and biomedical relevance.
Catalyst-Free Synthesis of Lignin Vitrimers with Tunable Mechanical Properties
2021. Adrian Moreno, Mohammad Morsali, Mika H. Sipponen. ACS Applied Materials and Interfaces 13 (48), 57952-57961Article
Biobased circular materials are alternatives to fossil-based engineering plastics, but simple and material-efficient synthetic routes are needed for industrial scalability. Here, a series of lignin-based vitrimers built on dynamic acetal covalent networks with a gel content exceeding 95% were successfully prepared in a one-pot, thermally activated, and catalyst-free “click” addition of softwood kraft lignin (SKL) to poly(ethylene glycol) divinyl ether (PDV). The variation of the content of lignin from 28 to 50 wt % was used to demonstrate that the mechanical properties of the vitrimers can be widely tuned in a facile way. The lowest lignin content (28 wt %) showed a tensile strength of 3.3 MPa with 35% elongation at break, while the corresponding values were 50.9 MPa and 1.0% for the vitrimer containing 50 wt % of lignin. These lignin-based vitrimers also exhibited excellent performance as recoverable adhesives for different substrates such as aluminum and wood, with a lap shear test strength of 6.0 and 2.6 MPa, respectively. In addition, recyclability of the vitrimer adhesives showed preservation of the adhesion performance exceeding 90%, indicating a promising potential for their use in sustainable circular materials.
Show all publications by Mika Sipponen at Stockholm University