Light-colored lignin fragment

Abstract

The present invention relates to a method for preparing lignin fragments with a lightness (L*) value of more than 65 comprising a plurality of cycles including a first cycle comprising the steps of a. providing a lignocellulose-containing composition, b. heating the composition of step a) together with an aldehyde or an acetal in the presence of an acidic catalyst and optionally a solvent, c. filtering the reaction to obtain a lignin containing filtrate 1 and a cellulose-rich filter cake 1, a second cycle comprising the steps of d. adding an aldehyde or an acetal, an acidic catalyst and optionally a solvent to the cellulose- rich filter cake 1 obtained in step c), e. heating the composition of step d), f. filtering the reaction to obtain a lignin containing filtrate 2 and a cellulose-rich filter cake 2, one or more further cycles involving g. repeating steps d to f) n times to obtain a cellulose-rich filter cake n+2 and a lignin containing filtrate n+2, wherein n is at least 1, and a separation step including the step of h. isolating the lignin-fragments of the lignin containing filtrate n+2.

Description

[0001] Light-colored lignin fragment

[0002] The present invention relates to a very light-colored lignin fragment, its preparation and use as a color developer.

[0003] Thermal imaging technology, a pivotal innovation in the realm of material science and engineering, has revolutionized the way we visualize and interact with thermal energy in our daily lives. Leveraging the principles of thermography, this technology has found a unique and valuable application in the production of thermal papers - a specialized segment of the paper manufacturing industry that caters to a wide array of commercial printing needs. Thermal papers serve as the medium for instant printing processes that are critical for sectors ranging from retail to transportation, offering a rapid and accurate method of capturing and displaying variable information such as transaction records, travel itineraries, product labeling, and other vital data.

[0004] The quintessential element of thermal imaging technology in the context of thermal paper lies in its ingenious use of heat to induce a chemical reaction that results in a visible representation of information. At the heart of this system are the coated layers applied to the paper substrate. Primarily, thermal papers encompass a support layer, for example a paper layer, that is treated with a colorforming layer. This cover-forming layer comprises color former that remain inert until they are activated by proton transfer from the color developer to the dye upon heating. These color formers, also known as leuco dyes, belong to a class of dyes capable of switching between two states: a colorless (leuco) form and a protonated colored form. When subjected to the localized heat from a thermal printer's print head, color developers transfer one of their hydrogen atoms to the dye. This protonation induces a structural change in the leuco dye, activating its chromophoric (color-producing) properties, therefore producing a sharp and durable color change. This eliminates the need for traditional ink-based printing methods and allows for the delivery of high-quality, on-demand printed content.

[0005] Despite the widespread adoption and numerous advantages offered by thermal imaging technology in commercial printing, there exists a growing concern over the material components used in thermal papers. Historically, chemicals like Bisphenol A (BPA) and Bisphenol S (BPS) have been the primary color developers.

[0006] A24 085WO / 1 9 . 06 . 2025 /

[0007]

[0008] Dye (OBD-2) Bisphenol A

[0009] Colored

[0010] However, their use has raised significant health and environmental alarms. These chemicals, part of the endocrine-disrupting class and derived from petroleum sources, have been identified as toxic and potentially harmful following absorption through the skin. The health implications associated with these developers have led to scrutiny and legislative action, as witnessed in the Ell's stringent restrictions on the acceptable levels of BPA content in thermal papers.

[0011] In WO2023276498, a thermosensitive recording material is disclosed, which utilizes kraft lignin with a significantly lowered odor emission. Dimethyl disulfide, formed during Kraft pulping, was identified as

[0012] A24 085WO / 1 9 . 06 . 2025 the main source of the unpleasant smell emitted during image formation. Itwas found that a Kraft lignin having a dimethyl disulfide content of 2.5 parts per million (ppm) or lower, the malodor could be substantially minimized. However, the use of Kraft lignin, or a similar industrially isolated lignin, within thermal imaging systems results in inadequate delta color density, indicating a deficiency in contrast. This problem arises due to the inherent dark brown hue of Kraft lignin and the modest level of color development attainable with this category of condensed and technical lignin.

[0013] WO2017178513A1 and WO2021074210A1 disclose a method for preparing monomers and fragments from lignocellulose-containing biomass by aldehyde assisted fractionation, involving the addition of an aldehyde under acidic conditions. Despite said fragments possessing a lighter shade compared to industrially isolated lignins, they might still display coloration that is inappropriate for certain uses. Consequently, WO2021074210A1 reveals that a bleaching process may be employed should the fragments exhibit an unfavorable color. Nonetheless, such bleaching procedures carry environmentally detrimental consequences, posing concerns over their ecological impact and sustainability.

[0014] WO2021074211A1 , EP1969175, and TALEBI AMIRI MASOUD ET AL: "Fractionation of lignocellulosic biomass to produce uncondensed aldehyde-stabilized lignin", NATURE PROTOCOLS, NATURE PUBLISHING GROUP, GB, vol. 14, no. 3, 18 February 2019 (2019-02-18), pages 921-954, disclose all aldehyde assisted fractionation of biomass to prepare lignin.

[0015] PAN ZHENYING ET AL: "Fractionation of light-colored lignin via lignin-first strategy and enhancement of cellulose saccharification towards biomass valorization", INDUSTRIAL CROPS AND PRODUCTS, ELSEVIER, NL, vol. 186, 13 June 2022 (2022-06-13) discloses a lignin-first method for extracting lignin from poplar biomass by treating it with dioxane, small amounts of diols like 1 ,4-butanediol, and hydrochloric acid at 80°C. However, it only discloses exclusively with poplar wood. Further, the lignin fragments form large aggregates.

[0016] CN113214706 describes an ink with a fast-drying speed and vibrant colors, designed for use on thermal printing paper to enhance printing efficiency.

[0017] With an ever-expanding market predicted to reach the 6 billion USD mark by the year 2027, the thermal imaging industry is at a crossroads. There is an urgent imperative for innovation in the development

[0018] A24 085WO / 1 9 . 06 . 2025 of safe, effective, and environmentally friendly color developers ensuring the continued success and responsible evolution of thermal imaging technology in commercial paper applications.

[0019] Therefore, the problem of the present invention is to provide a compound, along with its method of preparation, that functions as a color developer, while also being safe, efficient, and environmentally friendly.

[0020] The problem is solved by the process according to claim 1 and the compound according to claim 8. Further preferred embodiments are subject of dependent claims 2 to 15.

[0021] Due to the process according to the present invention it is possible to obtain lignin-based fragments that have an outstanding brightness with a lightness L* value of more than 65, while maintaining high phenolic hydroxyl and carboxylic group content. These fragments can be obtained by a method comprising a plurality of cycles including a first cycle comprising the steps of a. providing a lignocellulose-containing composition, b. heating the composition of step a) together with an aldehyde or an acetal in the presence of an acidic catalyst and optionally a solvent c. filtering the reaction to obtain a lignin containing filtrate 1 and a cellulose-rich filter cake 1 , a second cycle comprising the steps of d. adding an aldehyde or an acetal, an acidic catalyst and optionally a solvent to the cellulose-rich filter cake 1 obtained in step c), e. heating the composition of step d), f. filtering the reaction to obtain a lignin containing filtrate 2 and a cellulose-rich filter cake 2, one or more further cycles involving

[0022] A24 085WO / 1 9 . 06 . 2025 g. repeating steps d to f) n times to obtain a cellulose-rich filter cake n+2 and a lignin containing filtrate n+2, wherein n is at least 1 , and a separation step including the step of h. isolating the lignin-fragments of the lignin containing filtrate n+2.

[0023] Hence, conducting step g) once (n=1) results in the completion of three cycles.

[0024] It was shown that by applying a sequential approach, lignin fragments with very low color intensities can be obtained. In particular, the process according to the present invention allows not only to use softwood materials, whose lignin is always lighter colored. It can be used on both hardwood and softwood material, extracting light-colored material from any lignocellulosic biomass sources.

[0025] The process according to the invention is characterized by its simplicity. With this sequential extraction, the exposed lignins, that are already present at the pore surface, are extracted first. They happened to show high color intensity, due to their shorter molecular weight and higher chromophore content, compared to the lighter and longer lignin polymers extracted later on. In this way, the required color can be achieved without the need for a bleaching procedure. As a result, harsh processing conditions can be avoided. In particular, the lignin fragments of the present invention can be obtained avoiding typical bleaching compounds such as chlorine, sodium hypochlorite, hydrogen peroxide, calcium hypochlorite, chlorine dioxide, peracetic acid, sodium percarbonate, ozone, sodium perborate, and benzoyl peroxide. The avoidance of these compounds makes the method according to the present invention a highly environmentally friendly process, significantly reducing the ecological impact typically associated with traditional bleaching methods, while at the same time ensuring effective results.

[0026] Moreover, the lignin fragment containing filtrates that do not meet the color requirements for a particular application (thus, those obtained in the n+1 cycles) can be utilized for other purposes, such as the production of monomers, for instance. In other words, the lignin fragments containing colored filtrates do not generate waste; rather, they serve as raw materials for different applications.

[0027] The solvent optionally present in the method according to the present invention is preferably a polar aprotic organic solvent, most preferably selected from the group consisting of dioxane, tetrahydrofuran,

[0028] A24 085WO / 1 9 . 06 . 2025 and 1 -methyl THF or a mixture thereof. Preferably, steps b and / or d are conducted at a temperature of 70°C to 100°C, more preferably at 80°C to 90°C, ideally at 85°C as this temperature has been identified to significantly improve the efficiency of extraction. Preferably, the heating conditions are essentially the same in the various cycles.

[0029] Within the context of the present invention, the term "aldehyde" refers to a compound comprising at least one aldehyde group. However, it can also include compounds with multiple aldehyde groups, such as glyoxal. The organic moiety can be very broadly defined and is intended to encompass essentially all aldehydes, including those with alkyl, aryl, heteroaryl, alkenyl, and alkynyl groups. In particular, the organic residue may be hydrogen, a linear or branched-chain C1-C20 alkyl or C1-C20 alkenyl residue (as in propionaldehyde and citral), an aromatic residue such as benzaldehyde, or a heteroaromatic residue containing 1 to 3 heteroatoms selected from the group consisting of oxygen or nitrogen, such as furfural.

[0030] Within the context of the present invention, the term "acetal" refers to a compound comprising an acetal group. An acetal group consists of a central carbon atom bonded to two Ci to C4 alkoxy groups, which may be the same or different. This central carbon atom can be part of a linear or branched Ci to C10 chain that may be optionally substituted with fluoro, chloro, bromo, or iodo groups and may optionally include a carbonyl group or an ester group.

[0031] The aldehyde employed in the various cycles may be identical or distinct. Preferably, the same aldehyde is used in all cycles. Preferably, the aldehyde is selected from the group consisting of formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, valeraldehyde, caproaldehyde, glyoxal, furfural, isobutyraldehyde, isovaleraldehyde, hexanal, heptanal, octanal, nonanal, decanal, undecanal, dodecanal, tridecanal, tetradecanal, pentadecanal, citral, citronellal, benzaldehyde, terephthaldehyde, 2-methylbutyraldehyde, glyoxylic acid, pivaldehyde and glutaraldehyde, preferably formaldehyde, acetaldehyde, propionaldehyde, (iso-)butyraldehyde, valeraldehyde and most preferably propionaldehyde. The use of propionaldehyde and isobutyraldehyde is especially preferred for its balanced reactivity.

[0032] Alternatively, it is also possible to use an acetal instead of the aldehyde. The acetal employed in the various cycles may be identical or distinct. Preferably, the same acetal is used in all cycles. Preferably,

[0033] A24 085WO / 1 9 . 06 . 2025 the acetal is selected from the group consisting of chloroacetaldehyde dimethyl acetal, chloroacetaldehyde diethyl acetal, ethyl formaldehyde acetal, propylal, bromo acetaldehyde diethyl acetal, bromoacetaldehyde dimethyl acetal, ethyl diethoxyacetate ((EtO)2CHCOOCH2CH3), methyl dimethoxyacetate, ethyl diethoxypropanoate, and methyl dimethoxypropanoate.

[0034] These acetal-protected lignin fragments can be synthesized without using any additional solvents, meaning they are produced under neat conditions. The absence of a solvent eliminates the need for its recycling, leading to an exceptionally eco-friendly production process for the acetal-protected lignin fragments. Within the context of the present invention the term acidic catalyst stands for a substance that increases the rate of a chemical reaction by providing an acidic environment. This catalyst can donate protons (H+) or accept electron pairs to facilitate the reaction process. Acidic catalysts can be for example Bronsted acid catalysts such as HCI or H2SO4 or Lewis acids such as FeCh, FeBr3. In a preferred embodiment of the present invention the acidic catalyst is hydrochloric acid, typically at a concentration of 2 to 10 mmol per gram of lignocellulosic material, or 0.1-1 mol / L. HCI is compatible with the aldehydes and acetals used in the fractionation process. This compatibility ensures that the reaction proceeds efficiently without undesirable side reactions. Preferably, the acidic catalysts are essentially the same in the various cycles.

[0035] In a preferred embodiment of the present invention n is 4 to 7, preferably 4 or 5. It has been observed that a direct correlation exists between the number of cycles undertaken and lightness (L*) value of the lignin fragments; with each additional cycle leading to more favorable results. An optimal balance between yield and lightness is achieved after conducting 4 to 5 cycles. Ideally, each cycle ranges from 20 to 40 minutes in duration, with a preference for a 30-minute interval.

[0036] Preferably, the fragments of the lignin containing filtrate n+2 is isolated by removing solvent (if present), acidic catalyst and non-reacted aldehyde or acetal under reduced pressure, and adding dropwise the liquor in diethyl ether or hexane, resulting in the precipitation of lignin as a fine powder. There is no need for additional purification, specifically, a bleaching process is not required.

[0037] In one embodiment of the present invention the lignin fragments are produced from a hardwood material selected from the group consisting of oak (Quercus) - including species like pedunculate oak (Quercus robur) and sessile oak (Quercus petraea), beech (Fagus sylvatica), maple (Acer) - including

[0038] A24 085WO / 1 9 . 06 . 2025 species like Norway maple (Acer platanoides) and sycamore maple (Acer pseudoplatanus), ash (Fraxinus excelsior), elm (Ulmus) - including species like field elm (Ulmus minor) and wych elm (Ulmus glabra), sweet chestnut (Castanea sativa), birch (Betula) - including species like silver birch (Betula pendula) and downy birch (Betula pubescens), alder (Alnus) - including species like black alder (Alnus glutinosa) and grey alder (Alnus incana), linden or lime (Tilia) - including species like large-leaved lime (Tilia platyphyllos) and small-leaved lime (Tilia cordata), walnut (Juglans regia), hornbeam (Carpinus betulus), poplar (Populus) - including species like black poplar (Populus nigra) and white poplar (Populus alba).

[0039] In one embodiment of the present invention the lignin fragments are produced from a softwood material selected from the group consisting of pine (Pinus), cedar (Cedrus), spruce (Picea), fir (Abies), larch (Larix), hemlock (Tsuga), cypress (Cupressus), redwood (Sequoia), yew (Taxus), juniper (Juniperus), and Douglas fir (Pseudotsuga).

[0040] The “Cl ELAB color space”, also known as Lab*, is a color model defined by the International Commission on Illumination (CIE). It consists of three axes: L*, a*, and b*. The L* axis represents lightness, ranging from 0 (black) to 100 (white). The a* axis represents the color position between green and red, with negative values indicating green and positive values indicating red. The b* axis represents the color position between blue and yellow, with negative values indicating blue and positive values indicating yellow. Within the context of the present invention the CIE values are measured according to DIN EN IS0 11664-4 using a CS-10 Colorimeter (CHNSpec, China) operating in the Cl ELAB color space under standard D65 illumination, with a d / 8° geometry, 10° standard observer, and an 8 mm aperture. The device was calibrated prior to each measurement series using the white reference tile provided by the manufacturer. Measurements were conducted at room temperature (approximately 23 ± 1 °C), for unreacted samples, or immediately after thermal activation by heating the sample surface from 50°C to 160 °C for 10 seconds. The device measures colorimetric coordinates (Y, x, y values), with the Y parameter indicating luminance, ranging from 0 to 100. This Y parameter is then converted into color density (C.D.) using the calculation C.D.=-log(K / 100).

[0041] A further aspect of the present invention relates to lignin fragments having a CIELAB color space (La*b*) measured according to DIN EN IS0 11664-4 with a lightness (L*) value of more than 65. These lignin fragments have preferably a mean particle size between 1 m to 30pm measured using light

[0042] A24 085WO / 1 9 . 06 . 2025 microscopy and Imaged. This unique combination of small mean particle size and a lightness (L*) value of more than 65 provides significant advantages for the dyeing process. Preferably, said lignin fragments have a lightness (L*) value of more than 68, and most preferably more than 70. The lignin fragments according to the present invention exhibit such an exceptional level of brightness that they are suitable for use as a substitute for bisphenol A or bisphenol S, i.e, for example, as a color developer. This brightness is a pivotal attribute that previously hindered the application of conventional lignin fragments in areas where clarity and colorless appearance are crucial. Due to the low mean particle size below 30 pm, these lignin fragments also demonstrate excellent compatibility and dispersion with the binder, further enhancing their application potential. The small particle size greatly increases the surface area relative to volume, enhancing the interaction between the lignin fragments and dyes. This leads to improved dye absorption, resulting in more vibrant and uniform colors. Furthermore, small lignin fragments facilitate faster chemical reactions, as a greater number of dye molecules can interact with the lignin fragments simultaneously. This efficiency allows for rapid and even color development. Additionally, the ability of the lignin fragments according to the present invention to promote homogeneous mixing with dyes ensures that the final product exhibits a consistent and visually appealing color. The use of the lignin fragments according to the present invention not only helps in maintaining the aesthetic and functional qualities demanded in the industry but also ensures a safer and more environmentally friendly option. This combination of properties enhances dyeing efficiency and significantly improves the overall quality and visual perception of the end product.

[0043] Preferably, in a further embodiment, the lignin fragments have a CIELAB color space (Lab*) measured according to DIN EN ISO 11664-4 with a lightness (L*) value of more than 65, accompanied by a* values of 0 to 5, and b* values of less than 25. These fragments can be obtained by the process according to the present invention. Relying solely on the L* value does not comprehensively reflect the benefits offered by the fragments in accordance with the present invention. Notably, the method according to the present invention facilitates a reduction in the red hue, resulting in low positive a* values of less than 5 in the CIELAB color space, signifying diminished redness - a highly desired outcome.

[0044] A24 085WO / 1 9 . 06 . 2025 In a further preferred embodiment of the present invention the lignin fragments have a CIELAB color space (Lab*) measured according to DIN EN ISO 11664-4 with a lightness (L*) value of more than 68, accompanied by a* values of 0 to 3.5, and b* values less than 20. It is particularly remarkable that these values can be attained not only with softwood but also, and notably, with hardwood as feedstock.

[0045] In a further preferred embodiment of the present invention the lignin fragments have a CIELAB color space (Lab*) measured according to DIN EN ISO 11664-4 with a lightness (L*) value of more than 70, preferably accompanied by a* values of 0 to 3.5, and b* values less of than 20. This high level of lightness coupled with low a* and b* values ensures that the fragments exhibit a near-neutral color, which is paramount in applications where color purity and visual clarity are vital.

[0046] A further aspect relates to the use of the lignin fragments according to the present invention as color developer. When applied within the field of thermal imaging technology, the fragments according to the present invention exhibit remarkable results. The high level of lightness results in a high color contrast, leading to high level of precision upon printing. In thermal imaging, the subtle color intensity differences upon heating are translated into clear visual images where precision is paramount. The use of lignin fragments in this context ensures that images are not only precise but are also produced in an environmentally conscious manner. Furthermore, the lignin fragments of the present invention demonstrate outstanding thermal sensitivity for quick and accurate image production. They remain stable for months under normal conditions, safeguarding against unwanted color shifts that might affect the print's legibility or accuracy. Moreover, their solvent resistance enhances the durability of the printed images, ensuring they endure across different conditions.

[0047] A further aspect of the present invention pertains to the use of lignin fragments as a potential replacement for a bisphenol-type compound, preferably selected from the group consisting of bisphenol A (BPA; 4,4'-isopropylidenediphenol), bisphenol F (4,4'-methylenediphenol), bisphenol S (BPS; 4,4'-sulfonyldiphenol), bisphenol B (2,2-bis(4-hydroxyphenyl)butane), bisphenol Z (4,4'- cyclohexylidenediphenol), bisphenol E (4,4'-ethylenediphenol), bisphenol AF (4,4'- (hexafluoroisopropylidene)diphenol), bisphenol AP (4,4'-(1-phenylethylidene)diphenol), and bisphenol M (4,4'-(1,3-phenylene)bis(2-methylphenol)). The term “bisphenol-type compound” stands for a molecule that contains two phenolic (-OH) groups attached to aromatic rings, which are usually connected via a linking group such as a carbon bridge (e.g., methylene, isopropylidene, sulfone,

[0048] A24 085WO / 1 9 . 06 . 2025 etc.). In assessing their endocrine activity, the lignin fragments according to the present invention were subjected to L-YES and ERa-CALUX assays. The comparative analysis with the hormone 17 - estradiol revealed that the fragments exhibit much weaker agonistic estrogenic activity, requiring significantly higher concentrations for a response than BPA and showing a reduced effect. Antagonistic activity was assessed only through the ERa-CALUX assay. Overall, lignin fragments demonstrate a notably lower endocrine-disrupting potential compared to traditional commercial compounds in combination with a higher molecular weight (>300 Da) to limit skin penetration, indicating a promising, less harmful alternative for BPA replacement in various applications.

[0049] A further aspect of the present invention relates to a thermosensitive composition that can be used to coat a support material to obtain thermosensitive recording material. Said thermosensitive composition comprises at least a color former in the form of a leuco dye, a sensitizer, and lignin fragments according to the present invention. The thermosensitive composition applied to the support material for thermal printing generally includes both solid and liquid components. The liquid component is primarily used during the coating process to ensure an even application of the thermosensitive layer onto the support material. Once the coating is applied, the liquid (typically water) evaporates, leaving behind the solid components that form the thermosensitive layer.

[0050] In one embodiment of the present invention, the thermosensitive composition comprises at least the following ingredients:

[0051] - a color former in the form of a leuco dye in an amount of 1-15% by weight of the solid components.

[0052] - Lignin fragments in an amount of 1 -25% by weight of the solid components.

[0053] - At least a sensitizer in an amount of 1 -55% by weight of the solid components. The sensitizer can also act as co-binder.

[0054] Further, the composition can additionally comprise compounds such as binders, fillers, and stabilizers. The binder can be present in an amount of 10-40% by weight of the solid components, and fillers and stabilizers can be present in an amount of 30-50% by weight of the solid components.

[0055] A24 085WO / 1 9 . 06 . 2025 The liquid component typically comprises 50-70% by weight of the total composition during the coating process. Preferred solvents include water or organic solvents such as ethanol, isopropanol, or acetone or mixtures thereof. The solvent facilitates the mixing and application of the solid components onto the support material. After the coating is applied, the solvent evaporates, leaving behind the solid thermosensitive layer.

[0056] Preferred color formers in the form of a leuco dye include but are not limited to: 3-diethylamino-6- methylfluoran, 3-dimethylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-(2,4-dimethylanilino) fluoran, 3-diethylamino-6-methyl-7-chlorofluoran, 3- diethylamino-6-methyl-7-(3-trifluoromethylanilino) fluoran, 3-diethylamino-6-methyl-7-(2-chloroanilino) fluoran, 3-diethylamino-6-methyl-7-(4-chloroanilino) fluoran, 3-diethylamino-6-methyl-7-(2- fluoroanilino) fluoran, 3-diethylamino-6-methyl-7-(4-n-octylanilino) fluoran, 3-diethylamino -7-(4-n- octylanilino) fluoran, 3-diethylamino -7-(n-octylamino) fluoran, 3-diethylamino -7-(dibenzylamino) fluoran, 3-diethylamino-6-methyl-7-(dibenzylamino) fluoran, 3-diethylamino-6-chloro-7-methylfluoran, 3-diethylamino-7-t-butylfluoran, 3-diethylamino -7-carboxyethylfluoran, 3-diethylamino-6-chloro-7- anilinofluoran, 3-diethylamino-6-methyl-7-(3-methylanilino) fluoran, 3-diethylamino-6-methyl-7-(4- methylanilino) fluoran, 3-diethylamino-6-ethoxyethyl-7-anilinofluoran, 3-diethylamino-7-methylfluoran, 3-diethylamino-7-chlorofluoran, 3-diethylamino-7-(3-trifluoromethylanilino) fluoran, 3-diethylamino-7- (2-chloroanilino) fluoran, 3-diethylamino-7-(2-fluoroanilino) fluoran, 3-diethylamino-benzo[a] fluoran, 3-diethylamino-benzo[c] fluoran, 3-dibutylamino-7-dibenzylaminofluoran , 3-dibutylamino-7- anilinofluoran , 3-diethylamino-7-anilinofluoran, 3-dibutylamino-6-methyl fluoran, 3-dibutylamino-6- methyl-7-anilinofluoran, 3-dibutylamino-6-methyl-7-(2,4-dimethylanilino) fluoran, 3-dibutylamino-6- methyl-7-(2-chloroanilino) fluoran, 3-dibutylamino-6-methyl-7-(4-chloroanilino) fluoran, 3- dibutylamino-6-methyl-7-(2-fluoroanilino) fluoran, 3-dibutylamino-6-methyl-7-(3-trifluoromethylanilino) fluoran, 3-dibutylamino-6-ethoxyethyl-7-anilinofluoran, 3-dibutylamino-6-chloro-anilinofluoran, 3- dibutylamino-6-methyl-7-(4-methylanilino) fluoran, 3-dibutylamino-7-(2-chloroanilino) fluoran, 3- dibutylamino-7-(2-fluoroanilino) fluoran, 3-dibutylamino-7-(N-methyl-N-formylamino) fluoran, 3- dipentylamino-6-methyl-7-anilinofluoran, 3-dipentylamino-6-methyl-7-(2-chloroanilino) fluoran, 3- dipentylamino-7-(3-trifluoromethylanilino) fluoran, 3-dipentylamino-6-chloro-7-anilinofluoran, 3- dipentylamino-7-(4-chloroanilino) fluoran, 3-pyrrolidino-6-methyl-7-anilinofluoran, 3-piperidino-6- methyl-7-anilinofluoran, 3-(N-methyl-N-propylamino)-6-methyl-7-anilinofluoran, 3-(N-methyl-N-

[0057] A24 085WO / 1 9 . 06 . 2025 cyclohexylamino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-cyclohexylamino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-p-toluidino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-isoamylamino)-6-methyl-7- anilinofluoran, 3-(N-ethyl-N-isoamylamino)-6-chloro-7-anilinofluoran, 3-(N-ethyl-N- tetrahydrofurfurylamino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-isobutylamino)-6-methyl-7- anilinofluoran, 3-(N-butyl-N-isoamylamino)-6-methyl-7-anilinofluoran, 3-(N-isopropyl-N-3- pentylamino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-ethoxypropylamino)-6-methyl-7-anilinofluoran, 3-cyclohexylamino-6-chlorofluoran, 2-methyl-6-p-(p-dimethylaminophenyl)aminoanilinofluoran, 2- methoxy-6-p-(p-dimethylaminophenyl)-aminoanilinofluoran, 2-chloro-3-methyl-6-p-(p- phenylaminophenyl)aminoanilinofluoran, 2-diethylamino-6-p-(p- dimethylaminophenyl)aminoanilinofluoran, 2-phenyl-6-methyl— 6-p-(p- phenylaminophenyl)aminoanilinofluoran, 2-benzyl-6-p-(p-phenylaminophenyl)amino-anilinofluoran, 3- methyl-6-p-(p-dimethylaminophenyl)aminoanilinofluoran, 3-diethylamino-6-p-(p- diethylaminophenyl)aminoanilinofluoran, 3-diethylamino-6-p-(p-dibutylaminophenyl)- aminoanilinofluoran, 2,4-dimethyl-6-[(4-dimethylamino)-anilino] fluoran, 3-[(4-dimethyl- aminophenyl)amino]-5,7-dimethylfluoran, 3,6,6'-tris(dimethylamino)spiro[fluorene-9,3'-phthalide], 3,6,6'-tris(diethylamino)spiro[fluorene-9,3'-phthalide], 3,3-bis(p-dimethylamino-phenyl)-6- dimethylaminophthalide, 3,3-bis(p-dimethylaminophenyl)phthalide, 3,3-bis-[2-(p- dimethylaminophenyl)-2-(p-methoxyphenyl)ethenyl-4,5,6,7-tetrabromophthalide, 3,3-bis-[2-(p- dimethylaminophenyl)-2-(p-methoxyphenyl)ethenyl-4,5,6,7-tetrachlorophthalide, 3,3-bis[1 ,1 -bis(4- pyrrolidinophenyl)ethylene-2-yl]-4,5,6,7-tetrabromophthalide, 3,3-bis-[1-(4-methoxyphenyl)-1 -(4- pyrridinophenyl)ethylene-2-yl]-4,5,6,7-tetrachlorophthalide, 3-(4-diethylamino-2-ethoxyphenyl)-3-(1- ethyl-2-methylindole-3-yl)-4-azaphthalide, 3-(4-diethylamino-2-ethoxyphenyl)-3-(1-octyl-2- methylindole-3-yl)-4-azaphthalide, 3-(4-cyclohexylethylamino-2-methoxyphenyl)-3-(1 -ethyl-2- methylindole-3-yl)-4-azaphthalide, 3,3-bis(1 -ethyl-2-methylindole-3-yl) phthalide, 3,3-bis(1 -octyl-2- methylindole-3-yl) phthalide, , 3-diethylamino-6,8-dimethylfluoran, 3-diethylamino-7,8-benzofluoran, 3-diethyl-aminofluoran-7-carboxylic acid ethyl ester, 3-[N-(4-methylphenyl)-N-ethylamino]-7- methylfluoran, and mixtures thereof.

[0058] Representative examples of sensitizer are stearamide, methylol stearamide, methylene bisstearamide, ethylene bis-stearamide, amide waxes, p-benzylbiphenyl, m-terphenyl, benzyl-2-naphthyl ether, 4-methoxybiphenyl, dibenzyl oxalate, di(4-methylbenzyl) oxalate, di(4-chlorobenzyl) oxalate,

[0059] A24 085WO / 1 9 . 06 . 2025 diphenyl sulfone, benzalphtalide, dimethyl terephthalate, dibenzyl terephthalate, dibenzyl isophthalate, 1 ,2-diphenoxyethane, 1,2-bis(4-methylphenoxy) ethane, 1 ,2-bis(3-methylphenoxy) ethane, 4,4'- dimethylbiphenyl, phenyl-1-hydroxy-2-naphthoate, 4-methylphenyl biphenyl ether, 1,2-bis(3,4- dimethylphenyl) ethane, 2,3,5,6-4'-methyldiphenyl methane, 1 ,4-diethoxynaphthalene, 1 ,4- diacetoxybenzene, 1 ,4-diproprionoxybenzene, o-xylylene-bis(phenyl ether), 4-(m- methylphenoxymethyl) biphenyl, p-hydroxyacetanilide, p-hydroxybutyranilide, p-hydroxynonananilide, p-hydroxylauranilide, p-hydroxyoctadecananilide, N-phenyl-phenylsulphonamide, acetyl biphenyl compounds (e.g. as described in JP2003 063149A2 ) and 2-phenoxyethyl-N-phenylcarbamate.

[0060] Preferably, the thermosensitive composition comprising the lignin fragments according to the present invention demonstrates an impressive delta color density (ACD) when applied to paper (t16O°C / to) of at least 0.8, with a preferable value of at least 1.0, and even more favorably at 1.3 or greater. In the context of the present invention, ACD serves as a key parameter for assessing the print contrast of thermal paper. ACD is defined as the difference in color density between the thermally treated ligninbased coatings (i.e. paper surface) (heated to 160 °C) and the initial, unreacted lignin-based coating at 23°C (=t0). The thermosensitive composition has a very high ACD value, significantly enhancing the depth and legibility of the black imprint. Due to the small particle size of the lignin fragments, preferably with a mean particle size of less than 30pm, they have a large specific surface area, which leads to higher color density, smoother color distribution, and a stronger color appearance. This characteristic is especially beneficial for applications that require high contrast and readability, such as receipts and barcode labels.

[0061] Preferably, said thermosensitive composition has an absolute delta L* value (AL*) (i.e., the absolute value of the change in lightness measured as the difference between the initial lightness value and the final lightness value after heating, regardless of the sign of the change) when applied to paper (t 160°C / tO) of more than 35, preferably more than 45. tO is the initial temperature, i.e. 23°C.

[0062] Within the context of the present invention, delta L* (AL*) refers to the change in lightness of the thermal paper surface upon heating, measured according to DIN EN IS0 11664-4. The L* value of the lignin fragments is more than 65, preferably more than 68 and even more preferably more than 70, to ensure a bright, clean background prior to imaging. This high initial lightness value supports high visual contrast upon image formation. Upon heating (to 160°C), a reduction in L*, which is expressed as a

[0063] A24 085WO / 1 9 . 06 . 2025 negative delta L* (AL*), indicates the progressive darkening of the thermosensitive layer, corresponding to the development of the image. Preferably, the AL* is less than -35, and more preferably less than -40, which reflects a strong and distinct darkening effect that contributes to excellent print contrast and legibility of the thermally formed image.

[0064] A further aspect of the present invention relates to a recording material for thermal printing comprising a thermosensitive composition including a lignin fragment according to the present invention as color developer. In this context, the support material refers to the substrate or base material used for printing. This support material includes paper, wood-free paper made from non-chlorine bleached pulp, base paper containing waste paper plastic films, and synthetic paper that can be coated with the thermosensitive composition.

[0065] The recording material according to the present invention can be prepared by coating a support layer as mentioned above with a thermosensitive composition. This composition generally includes a color former in the form of a leuco dye, a color developer, and other additives to enhance the stability and performance of the thermal paper. The lignin fragments serve as the color developer. When heat is applied to the thermal paper via the thermal print head, the lignin fragment reacts with the color former. This chemical reaction results in a visible color change, producing the printed image. During printing, the thermal print head selectively heats specific areas of the paper. The heat causes the color former and the lignin fragments to interact, leading to the formation of a colored image.

[0066] The support material must be compatible with the thermal printing process, possessing appropriate thermal sensitivity, durability, and surface properties to ensure high-quality printing. The incorporation of the lignin fragments into the thermosensitive composition enhances the paper's ability to produce clear, sharp images when heated. Therefore, the recording material for thermal printing described in this invention features a composition that includes the lignin fragments as a color developer, playing a crucial role in producing visible images through the thermal printing process.

[0067] Figures

[0068] Figure 1 shows an overview of the Sequential Aldehyde Assisted Fractionation (SAAF) Procedure which yields several batches of lignin following increasing time of Aldehyde Assisted Fractionation (AAF) extraction.

[0069] A24 085WO / 1 9 . 06 . 2025 Figure 2 shows CIE L*ab value of Lignin Powders as compared to bisphenol A (BPA) as reference sample.

[0070] Figures 3A to 3C show the color of of a) Kraft and Lineo Lignin, b) AAF lignins extracted from birch or pine wood and protected with either isobutyraldehyde (IBA) or propionaldehyde (PA), c) SAAF lignins extracted from birch or pine wood and protected with either isobutyraldehyde (IBA) or propionaldehyde (PA)

[0071] Figure 4A shows the evolution of extracted lignin color during the SAAF process. From left to right, lignin extracted after 1 cycle (30min), 2 cycles (2x 30 min), after 3 cycles (3x 30 min) from the cellulose- rich solids.

[0072] Figure 4B shows the characterization of the extracted lignin chromophores (alpha-beta unsaturated ketones) with Fourier Transform Infra-Red (FT-IR), observed at 1668-1685 cm-1.

[0073] Figures 5A / 5B shows pictures and color density measurements illustrating the color change of the dye in an octadodecanol matrix, when in contact with SAAF lignins. The samples containing the dye (OBD-2, 1 mol eq. or 1 mass eq.) and the developers (SAAF lignin, 1 mol eq. or 2 mass eq.) in an octadodecanol matrix (100 mg) were heated to 100°C, followed by a rapid cool down to room temperature. Figure 5A represents the use of 1 :2 mass ratio between the dye and the developer. Figure 5B represents the use of 1 :1 molar ratio between the dye and the developer. The color density was measured with a colorimeter (CS-10 Colorimeter, CHNSpec, China). It relates to the visual intensity and richness of a color, primarily used in the context of printing, painting, and imaging. The device measures colorimetric coordinates (Y, x, y values), with the Y parameter indicating luminance, ranging from 0 to 100. This Y parameter was then converted into color density (C.D.) using the calculation C. D.=-log(K / 100). Upper pictures were taken at room temperature, prior to heating. Lower pictures show color development once cooled down.

[0074] Figures 6A / 6B show the static sensitivity evolution of coating color density upon heating using benzalphtalide as a sensitizer. Conditions: PVA, OBD-2, CaCO3, Zn Stearate, lignin as developer, benzalphtalide as sensitizer.

[0075] A24 085WO / 1 9 . 06 . 2025 Figure 7A / 7B show a real life application, EPFL logo, with as developers the SAAF-Pine lignin with red (a) and black (b) fluoran dye.

[0076] Figure 8A / 8B / 8C shows an ERa-CALUX plot ERa-CALUX plot of lignin-based developers (PA Pine, PA Birch, IBA Pine) compared to commercial BPA, BPS and estradiol reference.

[0077] Figure 9A shows the evolution of extracted lignin color during the SAAF process after dilution in dioxane (10 mg / mL). From left to right: 1 cycle (30min), 2 cycles (2 x 30 min), 3 cycles (3 x 30 min), 4 cycles (4 x 30 min) of total extraction time from the cellulose-rich solids.

[0078] Figure 9B shows UV-Vis data of SAAF lignin solution extracted 1 cycle (30min), 2 cycles (2 x 30 min), 3 cycles (3 x 30 min) hours. The solutions were prepared with iso massic concentrations in dioxane as the solvent. The data are corrected for the dioxane background.

[0079] Figure 10A shows the evolution of extracted lignin color during a Sequential Trans-Acetalisation Assisted Fractionation STAAF process using chloroacetaldehyde dimethylacetal. From left to right: 1 cycle (30min), 2 cycles (2 x 30 min), 3 cycles (2 x 30 min + 1 x 1 h), 4 cycles (2 x 30 min + 2 x 1 h) of total extraction time from the cellulose-rich solids.

[0080] Figure 10B shows UV-Vis data of STAAF lignin solution extracted for 1 cycle (30min), 2 cycles (2 x 30 min), 3 cycles (2 x 30 min + 1 x 1 h), 4 cycles (2 x 30 min + 2 x 1 h). The solutions were prepared with iso massic concentrations in dioxane (10mg / mL) as the solvent. The data are corrected for the dioxane background.

[0081] Figure 11 shows the coating stability at room temperature under natural light conditions using benzalphtalide as a sensitizer. Conditions: PVA, OBD-2, CaCO3, Zn Stearate, lignin as developer, benzalphtalide as sensitizer.

[0082] Figure 12 shows L* of different samples (comparative examples and samples of the present invention).

[0083] Figure 13 shows C.D. of different samples (comparative examples and samples of the present invention).

[0084] A24 085WO / 1 9 . 06 . 2025 Figure 14 shows delta CD of different samples (comparative examples and samples of the present invention).

[0085] Figures 15A to 15D shows images of the particles of different samples.

[0086] Examples

[0087] Example 1A:

[0088] Sequential aldehyde-assisted biomass fractionation (Figure 1)

[0089] 4.5 grams of the extracted and dried biomass (birch wood) was weighed and transferred into a 100- mL round-bottom flask, which contained an oval PTFE-coated stir bar. Into the flask, 4.8 mL of propionaldehyde (67 mmol, 6.6 equivalents), 25 mL of 1,4-dioxane, and 0.85 mL of 37% (wt / wt) hydrochloric acid (10 mmol, 1.0 equivalent) were sequentially added. A condenser was then attached to the flask, connected to a source of cooling water, and a gas bubbler was fitted at the top of the reflux condenser to create an air lock. The mixture was heated to 85 degrees Celsius under stirring for 30 minutes and thereafter allowed to cool to room temperature.

[0090] A filtration apparatus, consisting of a 250-mL filter flask, a neoprene adapter, and a Buchner funnel with a ground-glass frit of porosity grade 3, was assembled. The reaction was filtered to collect the cellulose-rich solid, which was then washed with dioxane in two portions of 10 mL each, resulting in liquor number 1 . This liquor was concentrated using a rotary evaporator at a 40 degrees Celsius bath temperature and a final pressure of 60 mbar, removing the hydrochloric acid, aldehyde, and dioxane.

[0091] To the resulting dark-brown oil, 10 mL of ethyl acetate was added. The solution was then added dropwise with a pipette, rinsing with an additional 5 mL of ethyl acetate, into a 500-mL Erlenmeyer flask containing 250 mL of hexanes that was being stirred at 700 rpm by a bar-type PTFE-coated stir bar. Upon addition, a dark purple precipitate formed. The hexanes solution was filtered through a filtration apparatus and washed with more hexanes. To the filter cake, 50 mL of diethyl ether was added and the mixture was sonicated for 5 minutes. The diethyl ether solution was then filtered, the filter cake was recovered and dried overnight in a vacuum oven to yield Lignin number 1 .

[0092] A24 085WO / 1 9 . 06 . 2025 The solutions of hexanes and diethyl ether that had been filtered were concentrated with vacuum using a rotary evaporator at a 40 degrees Celsius bath temperature and a final pressure of 25 mbar; this yielded the Propylated C5-sugar collection number 1.

[0093] Following the protocol, the mass of the cellulose-rich solid recovered from the filtration step was weighted and placed into a 100-mL round-bottom flask containing an oval PTFE-coated stir bar. Appropriate amounts of propionaldehyde, 1 ,4-dioxane, and hydrochloric acid were added to the flask, with the quantities adjusted based on the recovered mass of cellulose-rich solid. A condenser equipped with a cooling water source and a gas bubbler was then fitted onto the flask.

[0094] The reaction was again heated to 85 degrees Celsius with stirring for 30 minutes, then cooled to room temperature. The same filtration apparatus was used to filter the reaction and collect the washed cellulose-rich solid, producing liquor number 2. This liquor was concentrated to remove hydrochloric acid, aldehyde, and dioxane using a rotary evaporator set as before. Ethyl acetate was added to the dark-brown oil and the ensuing solution was introduced dropwise into hexanes under stirring, leading to the formation of a precipitate and the creation of Lignin number 2 after filtration and drying.

[0095] Lastly, the mixtures of hexanes and diethyl ether were once again concentrated in vacuo, this time to obtain Propylated C5-sugar collection number 2. The entire procedure was repeated until a total extraction time of 3 hours was achieved.

[0096] Experiment to Measure the CIE Lab* Values

[0097] The color changes were monitored using a colorimeter (CS-10 Colorimeter, CHNSpec, China). The colorimetric properties of the thermochromic samples were described using either the CIE Lab* or CIE Yxy color spaces, which mathematically represent all perceivable colors in three dimensions.

[0098] For the CIE Lab* space:

[0099] • L* value represents perceptual lightness, which is how humans perceive lightness differences, with 0 being the darkest black and 100 being the brightest white.

[0100] • a* axis represents the red-green opponent colors.

[0101] • b* axis represents the yellow-blue opponent colors.

[0102] A24 085WO / 1 9 . 06 . 2025 For the ClE Yxy space:

[0103] • Y represents absolute luminance based on physical measurements of light intensity and ranges from 0 (dark) to 100 (bright). Represents absolute luminance based on physical measurements of light intensity.

[0104] • x (chromaticity coordinate) and y (chromaticity coordinate) represent the color's position in the chromaticity diagram, with values ranging from 0 to 1.

[0105] Color density (C.D.) was obtained using the same colorimeter and relates to the visual intensity and richness of a color, primarily used in the context of printing, painting, and imaging. The device measures colorimetric coordinates (Y, x, y values), with the Y parameter indicating luminance, ranging from 0 to 100. This Y parameter was then converted into color density (C.D.) using the calculation C.D =-log(Y / 100).

[0106] To assess the color characteristics of various lignins, including Kraft lignin, Lineo lignin, AAF lignin, and SAAF lignin, a procedure was carried out wherein 200 mg of each lignin sample was precisely measured and placed into a 5 mL vial. The color values (CIE Lab) of the lignin samples were subsequently determined using a colorimeter (CS-10 Colorimeter, CHNSpec, China).

[0107] As shown in Figures 2, SAAF lignin fragments present a much lighter color than for example traditional Kraft lignin as shown by the parameter L* of the CIE Lab space. As the L* value approaches 100, the color becomes lighter, and as it approaches 0, the color becomes darker.

[0108] In addition, SAAF Lignin was compared with the traditional AAF lignin extraction process (as disclosed in WO 2017 / 178513). SAAF Lignin presents a significant lighter color (L*= hi gher than 68, Figures 2 / 3, Table 1) than AAF lignin (L*=lower than 63, Figure 2 / 3, Table 1).

[0109] However, the L* value alone does not fully capture the color of AAF lignin, which appears pink. This is indicated by a parameter in the Lab space; higher positive values of a* correspond to increased redness (SAAF Birch wood a = 14.36 and 14.49 as compared to AAF Birch wood lignin a= 0.3-1.48, Table 1).

[0110] A24 085WO / 1 9 . 06 . 2025 Table 1 : CIE Lab value of raw Lignin Powders as compared to bisphenol A (BPA) as reference sample measured at room temperature (23°C + / - 1°C). The CD values represent the color characteristics of the ligin powder alone (i.e., neither coated on paper nor mixed with other ingredients).

[0111] Legend:

[0112] - I BA stands for isobutyraldehyde;

[0113] - PA stands for propionaldehyde;

[0114] - SAAF stands for Sequential Aldehyde Assisted Fractionation according to the present invention;

[0115] - AAF for Aldehyde Assisted Fractionation (prior art).

[0116] Thus, the experiment clearly shows that all SAAF lignins can be used as bisphenol A replacement, whereas this is not possible for Kraft or Lineo Lignin due to their low L values.

[0117] Experiment to measure the mean particle size:

[0118] The particle size was measured from microscope images using the software Imaged. The microscope was calibrated using a stage micrometer, and calibration was verified before each measurement session. Measurements were based on the Feret diameter (defined as the maximum distance between two parallel tangents on opposite sides of the particle). Individual particles were manually selected using the measurement tool. Ten isolated particles were randomly selected per image across at least three different images to avoid sampling bias. The magnification used was x 1000. From the recorded diameters, the arithmetic mean particle size and the standard deviation were calculated.

[0119] A24 085WO / 1 9 . 06 . 2025 Example 1 B:

[0120] Sequential Trans-Acetalisation Assisted Fractionation (STAAF)

[0121] 4.5 grams of the extracted and dried biomass (birch wood) was weighted and transferred into a 100- mL round-bottom flask, which contained an oval PTFE-coated stir bar. Into the flask, 34 mL of chloroacetaldehyde dimethyl acetal (CADMA) and 0.85 mL of 37% (wt / wt) hydrochloric acid (10 mmol, 1 .0 equivalent) were sequentially added. A condenser was then attached to the flask, connected to a source of cooling water, and a gas bubbler was fitted at the top of the reflux condenser to create an air lock. The mixture was heated to 85 degrees Celsius with stirring for 30 minutes and thereafter allowed to cool to room temperature.

[0122] A filtration apparatus, consisting of a 250-mL filter flask, a neoprene adapter, and a Buchner funnel with a ground-glass frit of porosity grade 3, was assembled. The reaction was filtered to collect the cellulose-rich solid, which was then washed with dioxane, or CADMA, in two portions of 10 mL each, resulting in liquor number 1. This liquor was concentrated using a rotary evaporator at a 40 degrees Celsius bath temperature and a final pressure of 60 mbar, removing the hydrochloric acid and the acetal.

[0123] To the resulting dark-brown oil, few mL of CADMA or dioxane was added. The solution was then added dropwise with a pipette into a 500-mL Erlenmeyer flask containing 250 mL of diethyl ether that was being stirred at 700 rpm by a bar-type PTFE-coated stir bar. Upon addition, a pink / purple precipitate formed. The diethyl ether solution was filtered through a filtration apparatus and washed with more diethyl ether. The filter cake was recovered and dried overnight in a vacuum oven to yield Lignin number 1.

[0124] The solution of diethyl ether that had been filtered was concentrated using a rotary evaporator at a 40 degrees Celsius bath temperature and a final pressure of 700 mbar; this yielded the chloro-acetalized C5-sugar collection number 1.

[0125] Following the protocol, the mass of the cellulose-rich solid recovered from the filtration step was weighted and placed into a 100-mL round-bottom flask containing an oval PTFE-coated stir bar. Appropriate amounts of CADMA, and hydrochloric acid were added to the flask, with the quantities

[0126] A24 085WO / 1 9 . 06 . 2025 adjusted based on the recovered mass of cellulose-rich solid. A condenser equipped with a cooling water source and a gas bubbler was then fitted onto the flask.

[0127] The reaction was again heated to 85 degrees Celsius with stirring for 30 minutes, then cooled to room temperature. The same filtration apparatus was used to filter the reaction and collect the washed cellulose-rich solid, producing liquor number 2. This liquor was concentrated to remove hydrochloric acid and CADMA using a rotary evaporator set as before. CADMA was added to the dark-brown oil and the ensuing solution was introduced dropwise into diethyl ether under stirring, leading to the formation of a precipitate and the creation of Lignin number 2 after filtration and drying.

[0128] Lastly, the diethyl ether solution was once again concentrated in vacuo, this time to obtain chloro- acetalized C5-sugar collection number 2. The entire procedure was repeated until a total extraction time of 3 hours was achieved.

[0129] Example 2:

[0130] To understand the extraction of these lighter materials, many characterization methods were used. As explained in the literature, many functional groups act as chromophores within the lignin backbone, like unsaturated ketones and carboxylic acid. Fourier-transformed infrared spectroscopy (FT-IR) was used on a powder mix of lignin and KBr (1 :5 ratio, wt%, known concentrations) under air and at room temperature to monitor lignin functional groups. As shown on Figure 4b, a linear decrease of the alphabeta unsaturated ketones peak intensity (1668-1685 cm-1) was observed with increasing extraction time (from one to three cycles). Similarly, higher contents of carboxylic acid were observed within colorful batches, as measured by Phosphorus Nuclear Magnetic Resonance (31 P NMR). As carboxylic groups are mostly found as chain end within the lignin backbone, the shorter molecular weights observed on colored polymers with size exclusion chromatography (SEC) were not surprising.

[0131] Table 2: Characterization of carboxylic acid groups (COOH) and phenolic hydroxyl groups content of extracted lignins with31P NMR, using NHPD as an internal standard and number / weight average molecular weight (Mn / Mw) of extracted lignins measured by SEC (polystyrene internal standard).

[0132] A24 085WO / 1 9 . 06 . 2025

[0133] Example 3:

[0134] In a rapid screening procedure known as the "octadodecanol test," the dye (OBD-2) and the developer (light-colored SAAF lignin) undergo a temperature change by heating up the sample to 100°C and subsequently cooling it down to room temperature. This process is employed to assess the developer's capacity to interact with the dye and to induce a color change through proton transfer from the developer to the lactone. Using equimolar ratio of phenol groups, measured by31P NMR, lignin fragments surprisingly overperformed compared to BPA / BPS (bisphenol S), due to their rich phenolic nature as well as the presence of reactive carboxylic groups. Indeed, rapid color change (color density C.D.) in the presence of the OBD-2 dye and heat, was monitored, highlighting the efficiency of this material in transferring the proton to the dye and generating color change (Figure 5).

[0135] In contrast, technical Kraft lignin, whose use is described in JP7163173B2, yielded high background color before development as it a very brown starting powder compared to our SAAF lignin which present a very light beige color (Figure 5a). In addition, after heating, the reactivity of Kraft lignin (color density C.D. below 1) is very low as compared to our SAAF lignin (C.D. above 1 .7). This indicates that our lignin outperformed Kraft lignin by nearly two orders of magnitude, which is crucial for achieving good contrast and fast printing on thermal paper.

[0136] Example 4:

[0137] The static sensitivity of the thermo responsive coating containing light-colored SAAF lignins as developers were compared to the coating containing BPA as developer. This parameter reflects the initial development temperature needed to generate color, and varies depending on the targeted application. Poly(vinyl alcohol)(PVA) solutions containing developer, dye ODB-2, sensitizers benzalphtalide, and additives (calcium carbonate and zinc stearate) were coated on white paper (2:1 weight ratio, average coating thickness of 70 pm), following the procedure described below.

[0138] All the solid ingredients (developer, dye, CaCO3, zinc stearate and sensitizer) were individually ground with a mortar for 5 min to decrease particle size to approximately 1000 pm. Then, an aqueous solution

[0139] A24 085WO / 1 9 . 06 . 2025 of poly vinyl alcohol (PVA) with a solid content of 30 wt% was prepared by dissolving Mowiol(R) 4-88 (Molecular weight « 38,000,300 mg) in distilled water (700 mg) overnight. An aqueous CaCO3solution (used for coating ease) was then prepared by manually mixing CaCO3(80 mg), 30wt% PVA (75 mg) and distilled water (150 mg) for 20 minutes until a homogeneous white solution was formed. Following these preparative steps, developer (50 mg) was mixed with the aqueous 30 wt% PVA solution (80 mg), followed by the addition of distilled water (152 mg), CaCO3solution (300 mg), zinc stearate (20 mg) (for processability), and benzalphtalide (50 mg) (used as sensitizer). This formulation was then mixed for another 5 min. Finally, the dye was incorporated (22 mg, dye:developer mass ratio 1 :2) and the total solid content was maintained to 40 wt%. The final solution was applied to white paper using a U-coater, achieving a coating thickness within the range of 70-80 pm. To investigate the static sensitivity of the coating, the color density was monitored while exposing the paper to increasing temperatures (from room temperature to 140°C, with 20°C incremental, Figure 6) using a temperature- controlled heat gun.

[0140] Table 3: SAAF lignins, extracted from pine or birch, showed slightly lower performance to commercial developer BPA at 120°C with a color density (C.D.) around 1 , regardless of the aldehyde used during lignin fractionation (here propionaldehyde or isobutyraldehyde). Although the achieved C.D. values were below those of BPA, the resultant color development is significant enough to provide substantial color contrast, as evidenced by the coating pictures (Figure 6A).

[0141] A24 085WO / 1 9 . 06 . 2025 Technical lignins, extracted from the Kraft or the Lignosulfonate process, performed poorly. Their initial dark background color (C.D. = 0.5), combined with their limited color development at 140°C (C.D. = 0.7), resulted in notably inadequate color contrast overall (Figure 6).

[0142] Importantly, the coatings remain stable under normal conditions (i.e. at temperatures ranging from 15- 25°C, for a duration of at least 6 months, even when exposed to natural or artificial light) safeguarding against unwanted color shifts that might affect the print's legibility or accuracy as illustrated in Figure 11.

[0143] Example 5:

[0144] PA Pine was selected to illustrate a real-life application. Coatings were formulated using acetalized sugars as sensitizer. The EPFL logo was successfully obtained using a poly(methylmetacrylate) mold and a thermal gun heater. Pleasingly, really good contrast was observed using both a black and a red dye (Figures 7A and 7B). This figure illustrates the variability and adaptability of the SAAF lignin developer with various dyes.

[0145] Example 6: Estrogenicity assessment

[0146] The potential agonistic estrogenic activity of the best performing lignin color developers (PA Pine, PA Birch, I BA Pine) was determined using an estrogen receptor reporter transactivation assay (ERTA) with the human oestrogen receptor (hERa): a human cell line-based assay ERa- Chemical Activated Luciferase gene expression (CALUX®) following ISO 19040-3 (Simon, E. et al., Evaluation of Three ISO Estrogen Receptor Transactivation Assays Applied to 52 Domestic Effluent Samples. Environ. Toxicol. Chem. 2022, 41 (10), 2512-2526).

[0147] In this assay, in short, concentration-effect relationships of compounds are established and compared to the female sex hormone, 17 -estradiol (E2), which serves as the positive control / reference in this assay. From the concentration-effect curves (Figures 8A / 8B / 8C), EC50, PC50 and PC10 values are determined in order to quantify the estrogenic activity of the tested compounds, also compared to the E2 reference; EC50: 50% effect concentration, PC50: 50% effect relative to positive control, PC10: 10% effect relative to positive control, see OECD 455 (Performance-Based Test Guideline for Stably Transfected Transactivation In Vitro Assays to Detect Estrogen Receptor Agonists and Antagonists.

[0148] A24 085WO / 1 9 . 06 . 2025 In OECD Guidelines for the Testing of Chemicals, Section 4; OECD Publishing: Paris, 2021); ISO 23196 (Water Quality - Calculation of Biological Equivalence (BEQ) Concentrations; 2022). Results are shown in figures 8A / 8B / 8C; Data were normalized to the effect of controls (0%) and the maximum modelled effect of E2 (100%).

[0149] Experimentally, ERa-CALUX was performed on 96-well plates along ISO 19040-3. E2 (reference compound) and test compounds were dissolved in DMSO and tested, in duplicate, in dilution series with a final DMSO concentration of 0.8% in all wells. 0.8% DMSO served as negative control. Possible cytotoxicity to the mammalian cell was verified under the microscope. Data were fitted using Prism (8.0.1) to establish concentration-effect relationships (Figures 8A / 8B / 8C) and determine EC50 as well as PC50 and PC10 values (Table 4 below).

[0150] Tests revealed that the lignins exhibit much weaker agonistic estrogenic activity, requiring significantly higher concentrations for induction than BPA / BPS and showing a reduced response (Figures 8A / 8B / 8C + Table 4 below)).

[0151] Table 4: ERa-CALUX® Molar results table:

[0152] 1Average from eight plates

[0153] 2Fitted top of the curve

[0154] 3Highest tested dose was not cytotoxic

[0155] 4Highest induction seen.

[0156] In short, estrogenic toxicity analysis have showed that these extracted-lignin materials are a lot less endocrine disrupting compared to commercial compounds, regardless of the aldehyde chosen to extract them.

[0157] A24 085WO / 1 9 . 06 . 2025 Example 7: Experiment Color variation in solution

[0158] It could also be demonstrated that, when in solution, the distinct color variations of the lignin powders observed during the SAAF process remained evident (Figure 9A). This was confirmed through UV-Vis spectroscopy on lignin samples dissolved in dioxane at a concentration of 10 mg / mL. The spectroscopic analysis revealed that the lignin extracted in 3 cycles (30 minutes each circle) exhibited lower light absorption across the entire visible spectrum (380-700 nm) compared to the lignin extracted in 1 cycle (30 minutes), leading to a lighter-colored solution (Figure 9B). This indicates that the SAAF process and the duration of extraction have a direct impact on the coloration of lignin, not only in its solid form but also when dissolved.

[0159] Example 8: Comparative example

[0160] PAN ZHENYING ET AL: "Fractionation of light-colored lignin via lignin-first strategy and enhancement of cellulose saccharification towards biomass valorization", INDUSTRIAL CROPS AND PRODUCTS, ELSEVIER, NL, vol. 186, 13 June 2022 (2022-06-13). In this example, the lignin fragments of the present invention are compared with those described by Pan et al.

[0161] Air-dried poplar wood was first Wiley-milled and sieved to obtain a particle size between 40 and 60 mesh. The prepared biomass was then mixed with a solvent composed of 10% diol (either ethylene glycol or 1 ,4-butanediol) and 90% dioxane by volume, with 0.5 M hydrochloric acid as catalyst. The mixture was adjusted to a solid-to-liquid ratio of 1 :20 g / mL. The reaction was carried out at 80°C for a duration of three hours. After completion, the slurry was filtered to separate the solid cellulose-rich residues from the liquid phase containing dissolved lignin.

[0162] The dissolved lignin was precipitated by adding the filtrate into ten volumes of acidified water adjusted to pH 2. The precipitated lignin was collected by filtration and thoroughly washed with deionized water to remove any remaining acid and solvent residues. The lignin samples were then dried under vacuum conditions. Samples obtained from treatment with ethylene glycol were labeled Li, while those obtained with 1 ,4-butanediol were labeled Ly. The lignin fraction extracted without any diol addition was labeled Lo. Air-dried poplar wood was Wiley-milled to 40-60 mesh and added into known ratio of diol / dioxane (10 / 90, v / v) solvents containing 0.5 M HCI. The solid to liquor ratio was 1 :20 g / mL and the reaction

[0163] A24 085WO / 1 9 . 06 . 2025 was completed in 3 h at 80 °C. After the reaction, the light-colored lignin was obtained by precipitating supernatant in 10 volumes acidic water (pH=2).

[0164] - The lignin fraction obtained without any diol pretreatment was labeled as Lo.

[0165] - The lignin fraction obtained after pretreatment with ethylene glycol was labeled as - The lignin fraction obtained after pretreatment with 1 , 4-butaned iol was labeled as L2.

[0166] A lightening of formulation color from Loto and L2could be observed for the prior art samples (Figure 12); however, the color density of ths lignin-based coating is poor. Poplar L2 showed CD values of 0.36 (to) and 0.78 (t 160°C) exhibited some degree of lightening but failed to maintain a rich color intensity. Similarly, Birch L2displayed CD values of 0.44 (to) and 0.67 (t 160°C), followed this trend of lighter coloration without sufficient density.

[0167] In contrast, the samples according to the invention (SAAF I BA Pine) showed a significantly different behavior. The CD values of 0.19 (to) indicate an initially light color density, which dramatically increased to 1.61 (t 160°C) upon further processing (see also Figure 13). This substantial rise in color density is also reflected in the Delta CD value, which reaches 1.42 for the lignin fragments according to the present invention. In comparison, the prior art samples demonstrate much lower Delta CD values of 0.42 and 0.23, indicating a deficiency in contrast. The CD values represent the color characteristics of the thermosensitive composition (i.e. on paper mixed with other ingredients, see Table 3):

[0168] Table 5 (tO=23°C):

[0169] A24 085WO / 1 9 . 06 . 2025

[0170] However, unlike the lignin fragments according to the invention, which have a very small particle size, the ethylene glycol and 1 ,4-butanediol protection lead to aggregation. This can be seen in the following table 6 as well as in the images in Figures 15a) to d) (a: SAAF IBA Birch; b: Birch L2(Pan); c: Birch Li(Pan); d: Poplar L2(Pan). Table 6:

[0171] Figures 15a shows that lignin according to the present invention disperses very well within a PVA matrix, whereas the lignin from Pan et al. (Figures 15b to 15d) tends to form large aggregates. This aspect is crucial because the particle size significantly influences how materials interact with dyes, impacting color development and the final visual perception of the product. The lignin fragments according to the present invention have a greater surface area in proportion to their volume compared to those of the prior art, which means there is more surface available for the dye to interact with. This enhanced surface area allows for better absorption of the dye, leading to a more intense and uniform color. Additionally, the higher surface area facilitates quicker chemical reactions as more dye molecules can come into contact with the lignin fragments simultaneously. This results in a more efficient dyeing process, allowing the color to develop more rapidly and evenly. Moreover, the lignin fragments according to the present invention create a more homogeneous distribution when mixed with the dye, further ensuring that the final product exhibits a consistent and visually appealing color.

[0172] A24 085WO / 1 9 . 06 . 2025

Claims

Claims1) Method for preparing lignin fragments with a lightness (L*) value of more than 65 comprising a plurality of cycles including a first cycle comprising the steps of a. providing a lignocellulose-containing composition, b. heating the composition of step a) together with an aldehyde or an acetal in the presence of an acidic catalyst and optionally a solvent, c. filtering the reaction to obtain a lignin containing filtrate 1 and a cellulose-rich filter cake 1 , a second cycle comprising the steps of d. adding an aldehyde or an acetal, an acidic catalyst and optionally a solvent to the cellulose-rich filter cake 1 obtained in step c), e. heating the composition of step d), f. filtering the reaction to obtain a lignin containing filtrate 2 and a cellulose-rich filter cake 2, one or more further cycles involving g. repeating steps d to f) n times to obtain a cellulose-rich filter cake n+2 and a lignin containing filtrate n+2, wherein n is an integer of 1 or more, and a separation step including the step of h. isolating the lignin-fragments of the lignin containing filtrate n+2.2) Method according to claim 1 , wherein steps b and / or d are conducted at a temperature of 70°C to 100°C, preferably at 80°C to 90°C, ideally at 85°C.A24 085WO / 1 9 . 06 . 20253) Method according to any of claims 1 to 2, wherein the aldehyde or acetal is selected from the group consisting of formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, valeraldehyde, caproaldehyde, glyoxal, furfural, isobutyraldehyde, isovaleraldehyde, hexanal, heptanal, octanal, nonanal, decanal, undecanal, dodecanal, tridecanal, tetradecanal, pentadecanal, citral, citronellal, benzaldehyde, terephthaldehyde, 2-methylbutyraldehyde, glyoxylic acid, pivaldehyde and glutaraldehyde, preferably formaldehyde, acetaldehyde, propionaldehyde, (iso)butyraldehyde, valeraldehyde, chloroacetaldehyde dimethyl acetal, chloroacetaldehyde diethyl acetal, ethyl formaldehyde acetal, propylal, bromo acetaldehyde diethyl acetal, bromoacetaldehyde dimethyl acetal, ethyl diethoxyacetate, methyl dimethoxyacetate, ethyl diethoxypropanoate, and methyl dimethoxypropanoate and most preferably propionaldehyde and (iso)butyraldehyde.4) Method according to any of the preceding claims, wherein the acidic catalyst is hydrochloric acid.5) Method according to any of the preceding claims, wherein n is 4 to 7, preferably 4 or 5.6) Method according to any of the preceding claims, wherein the lignin of the lignin containing filtrate n+2 is isolated by removing solvent (if present), acidic catalyst and non-reacted aldehyde or acetal under reduced pressure.7) Method according to any of the preceding claims, wherein hardwood trees are used as feedstock, preferably selected from the group consisting of oak, maple, ash, elm, sweet chestnut, birch, alder, linden, walnut, hornbeam and poplar and / or wherein softwood trees are used as feedstock, preferably selected from the group consisting of pine, cedar, spruce, fir, larch, hemlock, cypress, redwood, yew, juniper, and Douglas fir.8) Lignin fragments having a CIELAB color space (Lab*) measured according to DIN EN ISO 11664-4 with a lightness (L*) value of more than 65 having a mean particle size below 0.03 mm measured using light microscopy.9) Lignin fragments according to claim 8, wherein the lightness value (L*) or more than 70.A24 085WO / 1 9 . 06 . 202510) Use of lignin fragments in lignin-based thermo-reactive coatings according to any of claims 8 to 9, as color developer.11 ) Use of lignin fragments in lignin-based thermo-reactive coatings according to any of claims 8 to 9 as replacement for a bisphenol-type compound, preferably selected from the group consisting of bisphenol A, bisphenol F, bisphenol S, bisphenol B, bisphenol Z, bisphenol E, bisphenol AF, bisphenol AP, and bisphenol M.12) Thermosensitive composition comprising at least a color former in the form of a leuco dye, a sensitizer, and a lignin fragment according to any of claims 8 to 9.13) Thermosensitive composition according to claim 12 having a delta color density when applied to paper (t 160°C / tO) of at least 0.8, preferably at least 1 .0 and more preferably at least 1 .3.14) Thermosensitive composition according to claim 13 having an absolute delta L* value when applied to paper (t 160°C / tO) of more than 35, preferably more than 45.15) Recording material for thermal printing, comprising a thermosensitive composition according to any of claims 12 to 14.A24 085WO / 1 9 . 06 . 2025

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