Mika Henrikki Sipponen

• D.Sc. (Tech.)
• Professor (Assistant) at Stockholm University

Invited for this month′s cover is the Review by Mika H. Sipponen and collaborators at Aalto University (Finland), University of Naples Federico II (Italy), and University of Venice Ca’ Foscari (Italy). The image shows the versatility of lignins in the fabrication of carrier materials for various active ingredients in nanomedicine, agricultural chem...

Thin film coating of charged nanoparticles with oppositely charged polymers is an efficient and straightforward way for surface modification, but synthetic polyelectrolytes should be replaced by abundant biopolymers. In this study a thin film of chitosan was adsorbed onto colloidal lignin particles (CLPs) that were then systematically studied for o...

Surface modification of colloidal lignin particles (CLPs), which are obtained from renewable resources, is a plausible route towards novel biomaterials. Here we show that adsorption of cationic lignin onto spherical CLPs produces positively charged particles with tailored properties for the stabilization of Pickering emulsions. The threshold dosing...

Dehydration reactions proceed readily in water-filled biological cells. Development of biocatalysts that mimic such compartmentalized reactions has been cumbersome due to the lack of low-cost nanomaterials and associated technologies. Here we show that cationic lignin nanospheres function as activating anchors for hydrolases, and enable aqueous est...

Hair care products have complex surfactant and stabilizer compositions arising from oleochemicals, raising concerns over sustainability. Here, we show a fully biobased hair conditioner based on micellar lignin gels that stabilize emulsions with triglyceride oils. We demonstrate competitive emulsion stability, rheological properties, and performance...

There is a growing demand for biobased functional materials that can ensure targeted pesticide delivery and minimize active ingredient loss in the agricultural sector. In this work, we demonstrated the use of esterified lignin nanoparticles (ELNPs) as carriers and controlled-release agents of hydrophobic compounds. Curcumin was selected as a hydrop...

Surface protection is essential when using wood as a construction material. However, the industry lacks sustainable alternatives to replace the presently dominant fossil-based synthetic water-resistant coatings. Here, we show a...

Conspectus The increasing demand for polymeric materials derived from petroleum resources, along with rising concerns about climate change and global plastic pollution, has driven the development of biobased polymeric materials. Lignin, which is the second most abundant biomacromolecule after cellulose, represents a promising renewable raw materia...

A powerful toolbox is needed to turn the linear plastic economy into circular. Development of materials designed for mechanical recycling, chemical recycling, and/or biodegradation in targeted end-of-life environment are all necessary puzzle pieces in this process. Polyesters, with reversible ester bonds, are already forerunners in plastic circular...

Activating and controlling chemical reactions by the use of light is becoming increasingly important for the synthesis of nanomaterials. A key challenge is the lack of reactive bio-based particles that can replace fossil-based nano- and microparticles, which are currently essential for creating supraparticle materials. Here we show nanoparticle dis...

Owing to its abundant supply from renewable resources, lignin has emerged as a promising functional filler for the development of sustainable composite materials. However, achieving good interfacial compatibility between lignin and synthetic polymers, particularly poly (lactic acid) (PLA), remains a fundamental challenge. To advance the development...

Lignin has emerged as a sustainable alternative to fossil-based polymers in advanced materials such as photonics. However, current methods for preparing photonic lignin materials are limited by non-benign organic solvents...

Lignin, the second most abundant biopolymer on Earth, has recently emerged as a promising redox-active material for organic batteries. Different types of lignin have been explored but inherent challenges have remained, i.e., the difficulties of processing kraft lignin and the low charge storage capacity retention of lignosulfonate due to its high w...

The inferior thermoplastic properties have limited production of melt-spun fibers from lignin. Here we report on the controlled esterification of softwood kraft lignin (SKL) to enable scalable, solvent-free melt spinning of microfibers using a cotton candy machine. We found that it is crucial to control the esterification process as melt-spun fiber...

There is an urgent need for antimicrobial films based on sustainable resources and production methods. In this study, we present a bio-based nanocomposite film composed of chitosan (∼60 wt %), lignin nanoparticles (LNPs, ∼40 wt %), a small amount of glutaraldehyde (1.5 wt %), and a trace level of silver nanoparticles (AgNPs, 0.072 wt %). The unifor...

Urushi, an oriental lacquer, is sensitive to light and easily deteriorates upon light exposure, leading to the fading and loss of gloss of its coatings. In this study, we attempted to improve the lightfastness of black urushi by utilizing the UV-absorbing properties of kraft lignin. Oleic acid-esterified kraft lignin was prepared and added to the b...

Photonic crystals are optical materials that are often fabricated by assembly of particles into periodically arranged structures. However, assembly of lignin nanoparticles has been limited due to lacking methods and incomplete understanding of the interparticle forces and packing mechanisms. Here we show a centrifugation-assisted fabrication of pho...

Colloidal lignin nanoparticles are promising building blocks for sustainable functional materials. However, their instability in organic solvents and aqueous alkali limits their applicability. Current stabilization methods require nonrenewable and toxic reagents or tedious workup procedures. Here we show a method to prepare hybrid nanoparticles usi...

Lightweight iron oxide nanoparticle (IONP)/TEMPO-oxidized cellulose nanofibril (TOCNF) hybrid foams with an anisotropic structure and a high IONP content were produced using magnetic field-enhanced unidirectional ice-templating. Coating the IONP with tannic acid (TA) improved the processability, the mechanical performance, and the thermal stability...

Lignin is a remarkable natural polyphenol that provides trees with physical and (bio-)chemical resistance, as well as the ability to reach considerable heights. Lignin is also intrinsically circular with slow biodegradability, thereby serving as a carbon source for soils. There is a growing interest in using industrial lignin as an environmentally...

Nanocellulose has a wide range of applications in the field of functional materials, and it has piqued the interest of researchers for some time. This is because nanocellulose inherits the advantages of environmental friendliness and easy availability of plant cell walls in nature, as well as the unique morphology of nanostructures. This review pre...

Lignin has been, for a long time, treated as a low-value waste product. To change this scenario, high-value applications have been recently pursued, e.g., the preparation of hybrid materials with inorganic components. Although hybrid inorganic-based materials can benefit from the reactive lignin phenolic groups at the interface, often responsible f...

Electrochemical energy storage technologies offer means to transition toward a decarbonized society and carbon neutrality by 2050. Compared to conventional lithium-ion batteries, aqueous zinc-ion chemistries do not require scarce materials or toxic and flammable organic-based electrolytes to function, making them favorable contenders in the scenari...

Lignin nanoparticles (LNPs) are considered as intriguing green, renewable alternative to fossil-based nanomaterials. However, the predisposition of LNPs to dissolve under alkaline conditions has impeded covalent surface functionalisation in the...

The design of stimuli‐responsive lignin nanoparticles (LNPs) for advanced applications has hitherto been limited to the preparation of lignin‐grafted polymers in which usually the lignin content is low (<25 wt.%) and its role is debatable. Here, the preparation of O2‐responsive LNPs exceeding 75 wt.% in lignin content is shown. Softwood Kraft ligni...

Photonic crystals are optical materials that are often fabricated by assembly of particles into periodically arranged structures. However, assembly of lignin nanoparticles (LNPs) into close-packed structures has been limited due to lacking methods and incomplete understanding of the interparticle forces and packing mechanisms. Here we show a centri...

Spherical lignin nanoparticles are emerging biobased nanomaterials, but instability and dissolution in organic solvents and aqueous alkali restrict their applicability. Here, we report the synthesis of hydroxymethylated lignin nanoparticles and their hydrothermal curing to stabilize the particles by internal cross-linking reactions. These colloidal...

Lignin is the most abundant aromatic biopolymer with many promising features but also shortcomings as a filler in polymer blends. The main objective of this work was to improve the processability and compatibility of lignin with poly (lactic acid) (PLA) through etherification of lignin. Commercial kraft lignin (KL) and oxypropylated kraft lignin (O...

“Levulinic acid may be the missing part of the puzzle to “unzip” lignin…” This and more about the story behind the research that inspired the Cover image is presented in the Cover Profile. Read the full text of the corresponding research at 10.1002/cssc.202200718. View the Front Cover here: 10.1002/cssc.202201247. image

The Front Cover shows tree trunks as potential sources of lignin, an underutilized industrial feedstock, which can undergo reductive electrochemical depolymerization. By using levulinic acid as solvent, which can be obtained via hydrothermal processing of lignocellulosic biomass or paper waste, and a cheap and abundant metal as the electrocatalyst,...

Spherical lignin nanoparticles are emerging biobased nanomaterials, but instability and dissolution in organic solvents and aqueous alkali restricts their applicability. Here we report synthesis of hydroxymethylated lignin nanoparticles and their hydrothermal curing to stabilize the particles by internal crosslinking reactions. These colloidally st...

The successive breakdown of the lignin macromolecule into smaller units is the key to generate high value-added products from this complex plant polyphenol. Obtaining well-defined aromatic compounds is, therefore, an important step towards the production of biobased chemicals for the fuel, coating and lubricant industries. Nevertheless, processes r...

Sustainable materials are needed to mitigate against the increase in energy consumption resulting from population growth and urbanization. Here, we report fully biobased nanocomposite films and coatings that display efficient photothermal activity and selective absorption of ultraviolet (UV) radiation. The nanocomposites with 20 wt % of lignin nano...

Lignin nanoparticles (LNPs) are attractive materials to a broad range of applications. These colloidal submicrometer particles can be used directly in many applications such as composites and hydrogels; however, some end uses require or benefit from modification or functionalization of LNPs. Examples include noncovalent adsorption of enzymes on LNP...

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,...

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 carboniz...

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 was extracted with aqueous acetone, yielding two fractions enriched in lignin and cellulose, respectively. The soluble hydrolysis lignin was conver...

The commercial breakthrough of Li‐ion batteries (LIBs) in the 1990s irrevocably shaped today's energy storage landscape, but the disposed batteries represent a growing hazard to the environment. One may initially assume that recycling processes are commendable technologies to ensure a counterbalance to LIBs manufacturing. However, the question rema...

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 polymeriza...

The Cover Feature shows lignin–inorganic hybrid and composite materials as an emerging type of materials with soft/hard interface and attractive properties to applications such as adsorption, catalysis, and energy storage. The cover artwork was proposed and designed by Jinrong Liu. More information can be found in the Minireview by T. M. Budnyak et...

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 polymeriza...

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 r...

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 faci...

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 (C...

Three-dimensional (3D) printing has been an emerging technique to fabricate precise scaffolds for biomedical applications. Cellulose nanofibril (CNF) hydrogels have attracted considerable attention as a material for 3D printing due to their shear-thinning properties. Combining cellulose nanofibrils hydrogels with alginate is an effective method to...

Biorefineries need cost-efficient pretreatment processes that overcome the recalcitrance of plant biomass, while providing feasible valorization routes for lignin. Here we assessed aqueous ammonia for the separation of lignin from hydrothermally pretreated wheat straw prior to enzymatic saccharification. A combined severity parameter was used to de...

The Front Cover shows versatility of lignin as a material towards fabrication of carrier systems for active ingredients in nanomedicine, agricultural chemistry, and biocatalysis. In this critical review, Mika H. Sipponen and co‐workers discuss 180 articles on the recent advancements and future opportunities for lignin‐based nano‐ and microscaled ca...

To liberate society from its dependence on fossil‐based fuels and materials it is pivotal to explore components of renewable plant biomass in applications that benefit from their intrinsic biodegradability, safety, and sustainability. Lignin, a byproduct of the pulp and paper industry, is a plausible material for carrying various types of cargo in...

The surface modification of nanoparticles (NPs) using different ligands is a common strategy to increase NP−cell interactions. Here, dentin phosphophoryn‐derived peptide (DSS) lignin nanoparticles (LNPs) are prepared and characterized, the cellular internalization of the DSS‐functionalized LNPs (LNPs‐DSS) into three different cancer cell lines is e...

Brittleness has hindered commercialization of cellulose nanofibril (CNF) films. The use of synthetic polymers and plasticizers is a known detour that impairs biodegradability and carbon footprint of the product. Herein, we utilize a variety of softwood Kraft lignin morphologies to obtain strong and ductile CNF nanocomposite films. An optimum 10 wt...

Cellulose nanofiber (CNF) aerogels offer excellent thermal insulation properties, but high flammability restricts their application. In this study, CNF aerogels were prepared by incorporating sodium bicarbonate (SBC) that effectively improved the fire retardancy without compromising the thermal conductivity of the aerogels that was only 28 mW m−1 K...

The sustainable synthesis of polymers is a field with growing interest due to the need of modern society to preserve the environment whilst making used products and food sustainable for the future generations. In this work we investigate the possibility of synthesizing aliphatic polyesters derived from various dicarboxylic acid diesters and diols i...

The mechanism of lignin nanoprecipitation and subsequent self-assembly was elucidated by studying generation of lignin nanoparticles (LNPs) from aqueous ethanol. LNP formation was found to follow a kinetically controlled nucleation-growth mechanism in which large lignin molecules formed the initial critical nuclei. Using this information, we demons...

Cross-linked and decolorized lignin nanoparticles (LNPs) were prepared enzymatically and chemically from softwood Kraft lignin. Colloidal lignin particles (CLPs, ca. 200 nm) in a non-malodorous aqueous dispersion could be dried and redispersed in tetrahydrofuran (THF) or in water retaining their stability i.e. spherical shape and size. Two fungal l...

Lignin, an aromatic biopolymer, is the main by-product of pulp manufacture, and has been under intense study, as it offers great promise as an alternative for petrochemical polymers. However due to its heterogeneity, the applications where lignin can be used have been limited, leading to the vast majority of it being burned for fuel. Colloidal lign...

Insects represent a sustainable but under-exploited food resource partly due to the chitin-containing exoskeleton and also the high lipid content that hamper the production of food ingredients. Here we present dry fractionation technology for upgrading house crickets (Acheta domesticus) and yellow mealworm larvae (Tenebrio molitor) by extraction wi...

The main target of a biorefinery pretreatment process is to break down the ligninreinforced plant cell wall structure prior to enzymatic hydrolysis of polysaccharides to fermentable sugars. Various physico-chemical alterations occur in lignin during the biomass pretreatment, but effects of those structural changes on subsequent enzymatic hydrolysis...

There is a paradigm shift going on in lignin utilization. High-volume materials and chemicals, as well as more engineered materials, like carbon fibers or active carriers, are currently being developed. However, in order to enhance lignin utilization in these and other value-added products, there is a need for better understanding of lignin functio...

The main target of a biorefinery pretreatment process is to break down the ligninreinforced plant cell wall structure prior to enzymatic hydrolysis of polysaccharides to fermentable sugars. Various physico-chemical alterations occur in lignin during the biomass pretreatment, but effects of those structural changes on subsequent enzymatic hydrolysis...

Air classification of an industrial barley endosperm fraction with initial protein content of 8.3% mixed with Aerosil 200F flow aid resulted in protein enrichment up to 28.3% with 21.7% protein separation efficiency. By reducing the classifier wheel speed from 21500 rpm to 8000 rpm, the protein separation efficiency increased to 59.4%, whereas the...

A new process is described for the two phase extraction of ergosterol and trehalose from microbial biomass. Baker's yeast was used as a model organism to develop the method, which was then applied for extracting 13 oleaginous microbes. Major findings of the study were that the ergosterol content was not dependent on intracellular oil content and th...

Slow-release fertilizers represent a possible large-scale application for plant polymers. Here we show a facile way to stabilize urea in fertilizer systems by lignin. Chelation of kraft black liquor with calcium acetate at pH 13 precipitated lignin as a calcium complex (Ca-lignin), which offered beneficial effects if compared to those from lignin o...

This work was conducted to determine the effect of oxygen on hydrothermal liquefaction of softwood for the production of valuable chemicals. Softwood was subjected to liquefaction in the presence and absence of either 1.6 g/L sodium carbonate or 5 bar oxygen gas. The oxygen supplementation diverted sugars from dehydration towards oxidation resultin...

This article compares the processes for wheat straw lignocellulose fractionation by percolation, counter-current progressing batch percolation and batch reaction at low NaOH-loadings (3-6% of DM). The flow-through processes were found to improve delignification and subsequent enzymatic saccharification, reduce NaOH-consumption and allow reduction o...

The magnetic nature of iron-containing nanoparticles enables multiple high-end applications. Metal alkoxides are a highly reactive chemical species, which are widely used in ceramics and sol–gel manufacture. However, their use with organic molecules has been mostly limited to catalytic purposes due to their highly reactive nature. Lignin is the sec...

Explaining the reduction of hydrolysis rate during lignocellulose hydrolysis is a challenge for the understanding and modelling of the process. This article reports the changes of cellulose and lignin surface areas, porosity and the residual cellulase activity during the hydrolysis of autohydrolysed wheat straw and delignified wheat straw. The pote...

Recovery of two biotechnologically produced fuel components, butanol and microbial oil, is assessed by absorption of the six shortest 1-alcohols into oleaginous yeast cells. We show an unexpectedly high extent of absorption of >C3 alcohols from water into Rhodosporidium fluviale cells with a lipid content of 69% of cell dry weight (CDW). Increasing...

Regarding the utilization of lignocellulosic solid waste biomass, partial wet oxidation provides an alternative treatment to produce sugars or carboxylic acids. This paper investigates the impact oxygen, temperature and alkali metal catalyst (sodium carbonate) on the partial wet oxidation of wood particles in a single reactor. The experimental data...

The major factors determining enzymatic hydrolyzability of pretreated wheat straw were analyzed and their relative importance quantified. The effects of NaOH-delignification, autohydrolysis and their combination at different severities were analyzed by determining the pore size distribution (DSC-thermoporometry), the cellulose surface area and the...

Partial wet oxidation (PWO) of kraft black liquor (KBL) and wheat straw black liquor (WSBL) was carried out at 170–230 °C. PWO was conducted under oxygen gas only or in the presence of iron catalysts or hydrogen peroxide as an additional oxidant. Unlike the catalysts, increasing temperature enhanced the PWO process in general. Lignin concentration...

Five xylans from hardwood and cereal sources were compared based on grafting reactivity with glycidyl methacrylate (GMA). The structural property that best predicted the reactivities of xylans with GMA was the fraction of 4-O-methylglucuronic acid (MeGlcA) substitution. Comparatively high arabinose substitution was also positively correlated to rea...

A thorough efficacy assessment was performed on three wheat straw saccharification processes including NaOH-delignification, autohydrolysis and their combination, with subsequent enzymatic hydrolysis. Instead of optimizing the process for maximal sugar yield from straw, a novel perspective is provided, allowing optimization of the overall yield aga...

A new colorimetric method for determining the surface-accessible acidic lignin hydroxyl groups in lignocellulose solid fractions was developed. The method is based on selective adsorption of Azure B, a basic dye, onto acidic hydroxyl groups of lignin. Selectivity of adsorption of Azure B on lignin was demonstrated using lignin and cellulose materia...

Enzymatic hydrolysis of cellulose after pretreatment of wheat straw (WS) was investigated for the first time in relation to lignin surface area (SA). Lignin SA in solid residues from WS autohydrolysis (AH) and successive NH3 (aq) extraction was determined using cationic dye adsorption. AH at increasing severity decreased up to 45% and 53% of WS lig...

The objective of this study was to elucidate the impact of autohydrolysis severity on the yield and structure of wheat straw hemicellulose and lignin. The autohydrolysis treatments were carried out at maximum temperatures between 170 °C and 200 °C. The autohydrolysis liquors were separated and the solids were successively extracted with aqueous amm...

In the enzymatic hydrolysis of lignocellulose materials, the recycling of the solid residue has previously been considered within the context of enzyme recycling. In this study, a steady state investigation of a solids-recycling process was made with pretreated wheat straw and compared to sequential and batch hydrolysis at constant reaction times,...

The insertion of oat husk lignin onto chemithermomechanical pulp (CTMP) fibers was studied to increase fiber hydrophobicity. The pretreated pulp samples were subsequently used for preparation of handsheets for characterization. Treatment of CTMP with laccase in the presence of oat husk lignin resulted in a significant increase in hydrophobicity of...