A method for preparing undiscolored lignin, a method for preparing fibrillar cellulose, undiscolored lignin and products comprising undiscolored lignin

Abstract

The present disclosure provides a method for preparing undiscolored lignin, the method comprising providing lignocellulosic plant material (10), combining the lignocellulosic plant material with a reagent solution (12) comprising one or more5 carboxylic acids comprising a thiol group and mixing to obtain a reaction mixture (14), reacting (16) the reaction mixture in heating, preferably at 100–120ºC for 2–4 hours, to release cellulose fibers (20) and to solubilize lignin, and recovering the solubilized lignin as undiscolored lignin (18). The present disclosure also provides undiscolored lignin (18). The present disclosure also provides products such as a0 coating composition, a composite product, a cosmetic product and a medical product comprising the undiscolored lignin (18).

Description

[0001] A method for preparing undiscolored lignin, a method for preparing fibrillar cellulose, undiscolored lignin and products comprising undiscolored lignin

[0002] Field of the application

[0003] The present application relates to a method for preparing undiscolored lignin, and to undiscolored lignin produced by the method. The present application also relates to products comprising undiscolored lignin, such as a coating composition, a composite product, a cosmetic product and a medical product. The present application also relates to a method for preparing fibrillar cellulose.

[0004] Background

[0005] Lignin is the most abundant aromatic compound on Earth and accounts for around 30% of terrestrial non-fossil-based organic carbon. Together with cellulose and hemicellulose, lignin is the main component of lignocellulose biomass, providing structural rigidity to plant cell wall and protection against external influences, such as rotting. As hydrophobic compounds, lignin regulates water in plant cells. Due to the abundance and wide availability, lignin has been broadly investigated as an alternative to fossil-based resources as a source of materials and chemicals.

[0006] It is almost universally acknowledged that the color of lignin is dark red / brown, due to the color of so-called technical lignin (e.g., kraft, alkaline, and organosolv lignin), even so that it is assumed that natural lignin is light colored compound. The dark appearance of technical lignin is attributed to the chemical alterations of lignin structure during the isolation process. During the lignin removal, biomass is subjected to harsh reaction conditions such as temperature well above boiling point of water, high pressure, and extreme pHs. Harsh reaction conditions cause the condensation of lignin molecules, thus increasing the conjugation decree, as well as formation of conjugated carbonyls. Attachment of heteroatoms can also intensify the absorption of light, causing the deeper color. Another downfall of the dark color of lignin is the discoloration of cellulose pulp containing residual lignin, which is more cumbersome to remove, and request use of hazardous bleaching chemicals.

[0007] The dark color of such colored lignin prevents using the lignin in applications, wherein the color and / or appearance of the material is important. Several methods have been investigated to alter the chemical structure, and thus the color of technical lignin. However, the production of lignin with lighter color and very high brightness has so far been elusive.

[0008] There is a need to find methods to produce lignin with light color. Especially there is a need to find methods which are simple, economical and safe. It is also desired to find lignin with properties, that can be used in a variety of applications requiring not only white color but also properties which do not prevent use of the lignin in sensitive applications, such as in medical or cosmetic products.

[0009] Summary

[0010] In the present invention novel lignin isolation methods have been found, which can preserve the natural light color of lignin, i.e. the lignin remains undiscolored. It was shown that lighter colored lignin has high potential in a variety of applications, for example in coatings, sunscreens and cosmetics. It is also significant, that the production of lighter colored lignin is many times accompanied by lower degree of condensation (DoC) and preservation of chemical linkages (mainly p-O-4 bond) of lignin, elevating the potential of the use of lignin in production of platform chemicals.

[0011] The present disclosure provides a method for preparing undiscolored lignin, the method comprising

[0012] -providing lignocellulosic plant material,

[0013] -combining the lignocellulosic plant material with a reagent solution comprising one or more carboxylic acids comprising a thiol group and mixing to obtain a reaction mixture,

[0014] -reacting the reaction mixture in heating, preferably at 100-120°C for 1-4 hours, to release cellulose fibers and to solubilize lignin,

[0015] -recovering the solubilized lignin as undiscolored lignin.

[0016] The present disclosure provides a method for preparing fibrillar cellulose, the method comprising

[0017] -providing lignocellulosic plant material,

[0018] -combining the lignocellulosic plant material with a reagent solution comprising one or more carboxylic acids comprising a thiol group and mixing to obtain a reaction mixture,

[0019] -reacting the reaction mixture in heating, preferably at 100-120°C for 1-4 hours, to release cellulose fibers and to solubilize lignin, -separating the solubilized lignin as undiscolored lignin to obtain cellulose, and -mechanically disintegrating the cellulose to obtain fibrillar / fibrillated cellulose, such as microfibrillar cellulose and / or nanofibril lar cellulose.

[0020] The present disclosure also provides undiscolored lignin having a whiteness index in the range of 91-93, determined by ISO 11475:2004, lightness value (L*) in the range of 94.0-98.0 determined by ISO 11664-4:2008 and / or brightness of more than 80.0, such as in the range of 81.0-83.0, determined by ISO 2470-1 :2016.

[0021] The undiscolored lignin can be obtained with the present method.

[0022] The present disclosure also provides a coating composition comprising the undiscolored lignin.

[0023] The present disclosure also provides a composite product comprising the undiscolored lignin.

[0024] The present disclosure also provides a cosmetic product, such as a sunscreen, comprising the undiscolored lignin.

[0025] The present disclosure also provides a medical product, such as a sunscreen, comprising the undiscolored lignin.

[0026] The main embodiments are characterized in the independent claims. Various embodiments are disclosed in the dependent claims. The embodiments and examples disclosed herein are mutually freely combinable unless otherwise explicitly stated. The embodiments and examples not in the scope of the claims may be considered as embodiments and examples useful for understanding the invention.

[0027] The present method avoids carrying out pretreatment methods which could deteriorate the quality and / or color of lignin and cellulose in the lignocellulosic material used as raw material. Thus, the separated and recovered materials exhibit properties, which enable using them as such in a variety of methods and for preparing a variety of products. For example, the lignin and cellulose maintain an exceptional light color, and the structure and compositions of the lignin and cellulose fibers have not been deteriorated in the same manner as in prior art methods. The present method enables safe, environmentally acceptable and simple process of obtaining lignin with white color and other advantageous properties. Also the separated cellulose exhibits similar properties and can be used for example to prepare fibrillar cellulose and products comprising thereof with simple processes. This is advantageous as one main obstacle for preparing fibrillar celluloses in large scale and cost-efficient way is the high mechanical energy consumption needed for defibrillation of cellulose pulp, and already for pulping raw material. Prior art methods, such as Kraft pulping methods, may not be well suitable for a broad range of lignocellulosic biomasses, especially for softwood, and they produce mainly dark pulp, which needs to be bleached if optically bright fibrillar cellulose is prepared. Also expensive special disintegrating devices and / or several disintegrating runs are needed, which makes the process complex and expensive.

[0028] Unlike in prior art processes, in the present process there is no need to first prepare pulp, which would be subsequently processed into further products, but the present lignin and cellulose can be obtained directly from raw material, such as wood material, thus significantly simplifying the process and saving time and costs. The present process allows a wide variety of different operators to prepare lignin and / or cellulosic products without need for complex and expensive equipment and know-how to operate thereof.

[0029] The present method can provide light-colored cellulose fiber fraction from a variety of wood or other lignocellulosic raw materials without pulping, bleaching, oxidation and / or using other strong chemical modifications, which cellulose can be separated from the soluble lignin fraction and mechanically defibrillated into fibrillar cellulose with significantly lower energy consumption when compared for example to sulfate cellulose fibers or the like prior art fibers. Further, the obtained fibrillar cellulose was found to have good quality, for example the fibrils remained substantially intact, and irreversible agglomeration of fibrils, i.e. hornification, could be avoided. The hornification is not desired as it would deteriorate the quality and desired properties of the fibrillar cellulose, such as by lowering aspect ratio.

[0030] The present processes are scalable and can be implemented on an industrial scale.

[0031] The obtained raw materials and used reagents are biodegradable, so the present processes and products are environmentally friendly. No strongly toxic or otherwise harmful reagents or other materials are used. Especially strong, harmful and expensive reagents, such as halogenated reagents and other reagents used in oxidative processes can be avoided, for example reagents of TEMPO oxidation, which is commonly used process for modifying pulp to facilitate defibrillation thereof.

[0032] Brief description of the figures

[0033] Figure 1 shows a flowchart of the present method for preparing undiscolored lignin.

[0034] Figure 2 shows photographs of a) samples of choline chloride, thiolactic acid, and their 1 :2 molar ratio mixture at room temperature, b) samples of delignification dispersion before and after reaction, scanning electron microscopy images of c) original wood, d) and e) delignified wood, photograph of f) delignified wood, g) bleached kraft fibers, and h) unbleached kraft fibers from softwood, and figure i) shows a graph representing color parameters of delignified wood, bleached kraft fibers, and unbleached kraft fibers (color of bar represents the color of fibers).

[0035] Figure 3 shows visual appearance of kraft lignin (a), and white lignin (b), a graph representing color parameters of kraft and white lignin (color of bar represents the color of lignin) (c), and visual illustration of the color of kraft lignin (d), white lignin (e), and absolute white (f) in 2D color map.

[0036] Figure 4 shows thioacidolysis of lignin by thiolactic acid leading to fragmentation of lignin (a) and reaction of thiolactic acid with conjugated aldehyde group of lignin (b).

[0037] Figure 5 shows a) a graph representing infrared spectra of original wood, delignified fibers, and white lignin showing the absence of conjugated carbonyl peak in thiolactic acid treated samples, b) and c) scanning electron microscope images, d) transmission electron microscope image of white lignin, e) and f) scanning electron microscope image of lignin precipitated from aqueous alkaline solution, and g) schematic illustration of scattering of light on the surfaces of white lignin and alkaline lignin

[0038] Figure 6 shows a flowchart of the present method for preparing fibrillar cellulose. Figure 7 shows yield of pulp with precipitated lignin, cellulose fiber and lignin after alkaline washing (yield of the cellulose and lignin is calculated from original wood mass) of pine using TGA (a) and TLA (b) and birch with TGA (c) and TLA (d) with different reaction times and temperatures.

[0039] Figure 8 shows tensile properties of films produced from blended samples.

[0040] Detailed description

[0041] In this specification, percentage values, unless specifically indicated otherwise, are based on weight (w / w, by weight, or wt%). In specific examples the embodiments and examples specified with the open term “comprise” may be further limited with a closed term “consisting of’.

[0042] The diameters disclosed herein, unless specifically indicated otherwise, may refer to the smallest diameter, and may be presented as average or number-average diameter. The diameter may be determined microscopically or by other optical methods, which may comprise using a camera, and / or by sieve analysis. More particularly, the disclosed dimensions or other features may be measured by image analysis of microscope images, such as images from a light microscope, a field emission scanning electron microscope (FE-SEM), a transmission electron microscope (TEM), such as a cryogenic transmission electron microscope (CRYO- TEM), or an atomic force microscope (AFM). A suitable imaging and / or analysis software may be used to determine the dimensions and / or the other features.

[0043] The present disclosure provides a method for preparing undiscolored lignin, such as shown in the flowchart of Figure 1 , the method comprising

[0044] -providing lignocellulosic plant material (10), preferably undiscolored lignocellulosic plant material,

[0045] -combing the lignocellulosic plant material with a reagent solution (12) comprising one or more carboxylic acids comprising a thiol group and mixing to obtain a reaction mixture (14),

[0046] -reacting (16) the reaction mixture in heating and preferably in mixing to release cellulose (20), such as cellulose fibers, and to solubilize lignin,

[0047] -separating and / or recovering (17) the solubilized lignin as undiscolored lignin (18). The cellulose (20), such as cellulose fibers, may be also recovered. The lignocellulosic plant material may comprise wood, such as saw dust. Also other plant material can be used, such as lignocellulosic biomass, agricultural residues, bagasse-based material, sugarcane bagasse, corn-based material, corn stover, straw such as wheat straw or rice straw, woody biomass, woody perennials, vascular plants and the like, or mixtures thereof. The wood, including any wood-based material, may comprise softwood, hardwood or combination thereof. The plant material may be provided as disintegrated, such as chopped, powdered, grinded, sawed, cut and / or the like. However it is not necessary to disintegrate the material into fine powder or for example pulp, as the present treatment is effective even on relatively large pieces, such as sawdust or the like.

[0048] It is not necessary to dry the raw material. The lignocellulosic plant material may be provided as never dried, and / or having a moisture content of 20% by weight or more, such as 30% by weight or more, or 40% by weight or more. The moisture content of wood and other plants in their natural state may be about 50% by weight. Avoiding the drying can provide savings in energy consumption and preventing any irreversible morphological alteration of wood micro- and nanostructures. The lignocellulosic plant material may be added to the reaction / process without pretreatment, such as chemical pretreatment or other pretreatment discussed herein. The lignocellulosic plant material may be provided and / or added directly from the production process of the material, such as directly from disintegrating of the plant material and preferably substantially in the original moisture content (never-dried). The disintegration, such as sawing of wood to produce saw dust or chipping of the plant material, may be practically the only pretreatment of the raw material.

[0049] The present method enables using simple sources of plant material as raw material, which can be provided by a variety of operators, such as sawmills. The raw material may be by-product or waste stream of another process. There is no need to pretreat the raw material in complex and specific industrial processes, such as pulping processes or other chemical processes, which are usually implemented by large industrial operators, such as pulping mills and the like. Thus the raw material is inexpensive and readily available. Little or substantially no industrial waste is produced in the production of the raw material.

[0050] The method may comprise combining the lignocellulosic plant material with the reagent solution in a mass ratio in the range of 0.5:10 to 2:10, such as about 1 :10. Such ratio was found to provide suitable mixture, which could be efficiently mixed and wherein the reactions proceeded efficiently.

[0051] The present method can be carried out by using plant-based raw material, which has not been treated in such processes that would cause darkening or discoloration of the lignin and / or cellulose. Thus, the lignocellulosic plant material is undiscolored. There is also no need to separately bleach or otherwise whiten the lignocellulosic material, or specifically the lignin or the cellulose, so no expensive and hazardous bleaching or dyeing chemicals or other chemicals, or processes using thereof, are needed. Also no complicated process steps such as chemical pulping or other pretreatment, for example Kraft process, alkaline process, organosolv process, isocyanate process or the like, and / or steam explosion process are needed or desired, and these may be excluded from the method and / or pretreatment of the raw material. Also softwood milled wood lignin (MWL) may be excluded. In addition to avoiding darkening, it may be also desired to avoid irreversible deterioration of the lignin and / or cellulose fibers and / or fibrils, such as hornification, which are commonly caused by harsh conditions used in prior art methods. Oxidation, such as in bleaching, would deteriorate and / or alter the lignin and cellulose fibers and / or fibrils, and therefore is not desired. The same may apply to enzymatic hydrolysis. Thus, the present method, especially the acidolysis, may be carried out in absence of bleaching, oxidizing or other lignincoloring and also hornifying conditions, pretreatments and / or processes, such as one or more discussed herein, such as in the absence of alkaline process.

[0052] Preferably the lignin, and / or the raw material, is bleaching free (unbleached), nonoxidized and / or not obtained from Kraft process and / or from steam explosion process, and / or is not Kraft lignin, softwood milled wood lignin, alkaline lignin, organosolv lignin, oxidized lignin, and / or isocyanate-functional ized lignin. Correspondingly the raw material preferably does not comprise, or is not, pulp, such as Kraft pulp, bleached pulp, oxidized pulp, anionized pulp, cationized pulp, and / or other derivatized pulp or other raw material treated with the undesired processes / methods disclosed herein. Thus the raw material may be non-pulped. The raw material, or the cellulose of the raw material, may be chemically and / or enzymatically unmodified. The same applies to the obtained fibrillar celluloses, which preferably is not modified and / or derivatized with such methods and / or derivatizations. The present lignin is undiscolored lignin, which refers to lignin that has not been colored or discolored, such as darkened, in a process causing discoloration of lignin, such as known Kraft processes, steam explosion processes and the like processed discussed herein and / or known to cause coloration / darkening of lignin. Discolored lignin may refer to darkened lignin, and also term colored may be used interchangeably, which terms may refer to lignin having color which has become less attractive color than it was originally and / or to a color that has changed from the original color in an undesirable way. The “undiscolored” indicates that the lignin has maintained its original color, or that the original color of the lignin has not been substantially changed, such as darkened. The undiscolored lignin may be called white lignin, uncolored lignin and / or undarkened lignin, which terms may be used interchangeably. The same applies to cellulose obtained with the present process, which may be similarly called undiscolored cellulose.

[0053] The combining may refer to adding the lignocellulosic plant material to the reagent solution, or to adding the reagent solution to the lignocellulosic plant material. The combining may be carried out in a suitable container, such as a reactor, and / or a mixture may be formed in a reactor. The combining may comprise adding the lignocellulosic plant material to a reagent solution comprising one or more carboxylic acids comprising a thiol group. The carboxylic acid comprising a thiol group may comprise mercapto carboxylic acid, such as thiolactic acid or thioglycolic acid. Such carboxylic acids have a low vapor pressure and thus they are poorly evaporating substances. Further, they are biodegradable. Use of undesired reagents, such as oxidants, bromides, sulfuric acid or hydrochloric acid, can be avoided.

[0054] The reagent solution may also comprise one or more hydrogen bond acceptor, such as choline chloride or trimethyl glycine. These may be provided as eutectic mixture with the carboxylic acid comprising a thiol group. The molar ratio of the hydrogen bond acceptor to the carboxylic acid(s) comprising a thiol group may be 0.5:2 to 1 .5:2, such as about 1 :2. The use of hydrogen bond acceptor enhances reaction efficiency. In an aqueous solution the hydrogen bond acceptor can be replaced with sodium chloride. Also carboxylic acids can act as hydrogen bond acceptors, such as the carboxylic acid comprising a thiol group, especially when provided in excess amount, and / or other carboxylic acids, i.e. without a thiol group, such as formic acid or acetic acid. The reacting is carried out until cellulose fibers are released, at least partly, and / or until lignin is solubilized, at least substantially. The “releasing” may refer to releasing, liberating and / or separating fibers from their original form and / or from other constituents of the cellulosic raw material, wherein separated fibers are obtained. The reacting may be carried out at a temperature of 90°C or more, preferably 100°C or more, such as at a temperature in the range of 100-120°C, or more than 100°C, such as 110-120°C. Also hemicellulose may be released, separated, removed, isolated and / or recovered in the reaction and / or process. The reacting may be carried out for 1 hour or more, or 2 hours or more, such as for 1- 4, 1-2 or 2-4 hours. If lower temperatures are used, such as ranging from 80°C or 90°C, for example 90-100 °C, or 80-100 °C, the reaction time may be longer, such as 3-6 hours, or 4-6 hours. In general, the temperature may be in the range of 80-120°C and the reaction time may be in the range of 1-6 hours or 2-6 hours.

[0055] The present acidolysis is carried out at acidic conditions, such as at pH of about 4 or less, such as pH in the range of 3-4. No base is added, i.e. this part of the method is carried out in the absence of added base and / or alkaline conditions.

[0056] The reacting may be carried out in a container, such as in a reactor, which may be equipped with temperature controlling means, such as heating means, and / or mixing means, which may be controllable.

[0057] It was found out that the used carboxylic acids comprising a thiol group resulted in efficient thioacidolysis of lignin and release of cellulose fibers even from relatively large particles of lignocellulosic plant material. In one example shown in Figure 4a, thioacidolysis of lignin by thiolactic acid leads to fragmentation of lignin. A reaction of thiolactic acid with conjugated aldehyde group of lignin is shown in Figure 4b. The present lignin may be called thioacidolysed lignin. Thioacidolysis can be used in industrial scale production of undiscolored lignin and / or fibrillar cellulose in a simple process.

[0058] The solubilized lignin may be precipitated, such as by adding a suitable solvent, and the lignin may be precipitated on the cellulose fibers and / or on a surface / bottom of a container.

[0059] The method may comprise precipitating the solubilized lignin and resolubilizing the precipitated lignin with a solvent. More particularly the method may comprise precipitating the solubilized lignin, recovering the precipitated lignin and resolubilizing the recovered precipitated lignin with a solvent. The (re)solubilizing can be carried out by using a suitable solvent. The precipitated lignin may be resolubilized completely, substantially completely, or party.

[0060] In one embodiment the method comprises resolubilizing the precipitated lignin with a solvent, such as with ethanol, dimethyl sulphoxide, dihydrolevoglucosenone (cyrene), dimethyl isosorbide and / or aqueous alkali solution. The resolubilizing / removing / washing may be carried out when the lignin is precipitated on cellulose fibers and / or on a surface of an object, such as a container. In one example the precipitated lignin is removed at room temperature by alkaline washing

[0061] The method may comprise washing the reaction mixture after reacting with a solvent, such as with ethanol, separating the washing solution and precipitating undiscolored lignin from the washing solution by adding water or aqueous solution. For example, 3-4-fold volume of water may be sufficient to precipitate the lignin. The precipitating may be carried out with a suitable solution, such as aqueous solution or water, which may also act as a washing solution. The precipitate may be allowed to settle, for example for about 24 h or more.

[0062] The released cellulose fibers 20 may be separated, isolated, removed and / or recovered. Also, the cellulose fibers 20 have a light color and they can be used for preparing further products, such as fibrillar cellulose. It was found out that the released cellulose fibers 20 could be easily defibrillated in a mechanical disintegration step to obtain microfibrillar and / or nanofibrillar cellulose. For example, a single disintegrating run / pass with a suitable disintegrating device, such as a microflu id izer, a disc refiner or even a grinder, could produce nanofibrillar cellulose. The nanofibrillar cellulose can be used to prepare products, such as films or hydrogels.

[0063] Solids, such as cellulose fibers, fibrils and / or precipitates may be separated by using suitable solid-liquid separation process and / or means, such as by filtering, centrifuging or the like, for example by using one or more filters and / or centrifuges.

[0064] Thus, the method may comprise preparing fibrillar / fibrillated cellulose by -separating the solubilized lignin as undiscolored lignin (18), such as an undiscolored lignin fraction, to separate, to isolate, to remove, to recover and / or to obtain cellulose (20), such as a cellulose fraction and / or cellulose fibers, and -mechanically disintegrating (21 ) the cellulose or the cellulose fraction to obtain fibrillar / fibrillated cellulose (22), such as microfibrillar cellulose and / or nanofibrillar cellulose. The method may comprise washing the cellulose, such as the cellulose fraction / fibers, for example with water or other washing solution disclosed herein. The fibrillar cellulose thus refers to mechanically disintegrated, fibrillated or defibrillated cellulose, which terms may be used interchangeably.

[0065] The present disclosure provides fibril cellulose, i.e. fibrillar cellulose, obtained with the method and / or comprising / exhibiting the properties disclosed herein, such as the color, lightness, whiteness and / or brightness, and / or lack of chemical and / or enzymatic modification. The present disclosure also provides a method for preparing products from the fibrillar cellulose. The present disclosure also provides the products and use of the fibrillar cellulose for preparing the products.

[0066] As disclosed in the example of Figure 6, the present disclosure provides a method for preparing fibrillar / fibrillated cellulose, the method comprising -providing lignocellulosic plant material (10),

[0067] -combining the lignocellulosic plant material with a reagent solution (12) comprising one or more carboxylic acids comprising a thiol group and mixing to obtain a reaction mixture (14),

[0068] -reacting (16) the reaction mixture in heating, preferably at 100-120°C and preferably for 1 hour or more, such as for 1-4 hours, to release cellulose (20), such as cellulose fibers, and to solubilize lignin,

[0069] -separating (17), and preferably recovering, the solubilized lignin as undiscolored lignin (18) or as an undiscolored lignin fraction, to obtain cellulose (20), such as a cellulose fraction and / or fibers, preferably also washing the cellulose, and -mechanically disintegrating (21 ) the cellulose (20) or the cellulose fraction and / or fibers, to obtain fibrillar / fibrillated cellulose (22), such as microfibrillar cellulose and / or nanofibrillar cellulose. The fibrillar cellulose may be separated and / or recovered, and further processed, such as washed and / or dewatered.

[0070] The required defibrillating / fibrillating time is short, such as 1 minute or more, 2 minutes of more, 5 minutes or more, up to for example 10, 15 or 30 minutes, such as 1-30 or 1-15 minutes, even when low energy disintegrating devices and / or methods are used. The mechanical disintegrating may comprise using one or more devices selected from a refiner; a grinder; a disperser; a homogenizer; a colloider, such as a Masuko supermass colloider device; a friction grinder; a pin mill; a rotor-rotor disperser; a rotor-stator disperser; an ultrasound sonicator; a fluidizer, such as a microflu id izer; and a fluidizer-type homogenizer. One or more passes with one or more of the devices may be carried out. The selection of device, number of passes, amount of energy and / or operating parameters may be controlled to obtain desired result, such as disintegration / defibrillation / fibrillation degree, as cellulose fibrils are detached from the cellulose fibers or fiber fragments, for example to obtain MFC or NFC with desired fibril diameter and / or rheological properties. In general, the more energy and / or time is used for disintegrating the more fibrillated cellulose is obtained.

[0071] Similar temperatures as were disclosed for reacting may be also used in disintegration of cellulose. High temperatures above 100°C were found desired in certain cases, for example to lower specific energy consumption and / or to increase tensile strength of the obtained material.

[0072] The cellulose or the cellulose fraction and / or fibers may be provided to defibrillating, fibrillating and / or disintegrating treatment at a suitable consistency / concentration, such as at a consistency of 0.5-5.0% by weight or 0.5- 3.0% by weight, such as 0.5-2.0% by weight. About 1 % by weight was used successfully in most tests. Higher consistencies are usually unpractical as the formed fibrillar cellulose exhibits high viscosity already at a relatively low concentration making processing and handling thereof challenging.

[0073] As there is no need to use other chemical pretreatments, such as oxidizing processes, for example commonly used TEMPO oxidation, and / or enzymatic processes, the present process is simple, cost-efficient and environmentally safe. The cellulose part of the raw material is preferably not chemically and / or enzymatically modified in the process, or at least is not modified by said undesired pretreaments. The obtained fibrillar cellulose may therefore be native, i.e. chemically and / or enzymatically unmodified.

[0074] Microfibrillar cellulose (MFC) and / or nanofibrillar cellulose (NFC), have a different average diameter of fibrils and / or fibril bundles, for example at a micrometer range or a nanometer range, although there are variations in the use of terminology. The average lengths and / or diameters disclosed herein may be number-average lengths and / or diameters, Fibrillar celluloses can provide specific properties due to high aspect ratio of the fibrils providing numerous exposed hydroxyl groups. These properties cause strong crosslinking of the hydrophilic fibrils and provide gelforming abilities in aqueous dispersions. “Fibrils” as used herein may be understood as including elemental fibrils and / or fibril bundles. Microfibrillar cellulose may comprise fibers and / or fibrils having an average, such as number average, diameter of fibers and / or fibrils at microscale range, such as in the range of 1-100 micrometers, for example 20-50 micrometers. The average, such as number average, fiber / fibril length may vary, and it may be in the range of hundreds of micrometers, such as 100-800 micrometers, or 100-600 micrometers, however having a fiber / fibril length smaller than untreated cellulose fibers. The average, such as number average, diameter of nanoscale fibrils, such as nanofibrillar cellulose, may be 1000 nm or less, less than 1000 nm, 500 nm or less, preferably 200 nm or less, or more preferably 100 nm or less. An average, such as number average, fibril length may be 10 micrometers or less, such as 5 micrometers or less. In specific examples native nanofibrillar cellulose has a number average fibril diameter in the range of 1-100 nm. In one example said nanofibrillar cellulose has a number average fibril diameter in the range of 1-50 nm, such as 1-20 nm.

[0075] Aqueous dispersions of fibrillar cellulose, especially nanofibrillar cellulose, which may be in the form of hydrogels, exhibit characteristic rheological properties, which can be evaluated for example by monitoring viscosity as a function of shear stress or shear rate. For example, dispersion of highly fibrillar celluloses are highly viscous shear-thinning or pseudoplastic non-Newtonian materials, which may be considered as a special case of thixotropic behaviour, which means that their viscosity depends on the speed or force by which the material is deformed. When measuring the viscosity in a rotational rheometer, the shear-thinning behaviour is seen as a decrease in viscosity with increasing shear rate. At low enough shear rates, shear thinning fluids will show a constant viscosity value, q0, termed the zero shear viscosity or zero shear viscosity plateau. The zero-shear-rate viscosity is a limiting value that cannot be measured directly; rather, it must be estimated by extrapolation from several measurements at different shear rates. The zero shear viscosity value is determined from the constant region of the measured curve and it represents the situation wherein the shear rate approaches zero.

[0076] The rheological properties are usually determined at standard conditions, such as at a standard consistency, for example 0.5 wt% or 0.8 wt% consistency or concentration in aqueous medium, which may be water, such as pure or purified water. The fibrillar cellulose may be therefore dispersed in water and / or concentrated to obtain desired standard consistency for determining one or more rheological property or other property. Rheometers that control the applied shear stress or shear strain are called rotational or shear rheometers, and can be used to measure the way in which a liquid, suspension or slurry flows in response to applied forces. They are used for shear-thinning fluids which cannot be defined by a single value of viscosity. The rheometer may use a rotor with a specific geometry, such as vane or plate geometry. The measurements carried out by vane and plate geometry provide different values, which may not be directly comparable. The measurements may be carried out in pure water at pH 7 at 25±1 °C or 22±1 °C, and at a standard consistency / concentration of the nanofibrillar cellulose of 0.5% by weight.

[0077] Nanofibrillar cellulose may be characterized by average fibril length and / or with rheological properties. In one example the fibrillar / nanofibrillar cellulose has a number-average diameter of fibrils and / or fibril bundles of 100 nm or less, and preferably a storage modulus in the range of 1-40 Pa, such as 8-35 Pa, determined by a rotational rheometer using plate geometry at a consistency of 0.5% by weight in aqueous medium at 22±1 °C and / or a storage modulus in the range of 0.7-20 Pa determined by a rotational rheometer using vane geometry at a consistency of 0.5% by weight in aqueous medium at 22±1 °C. The fibrillar / nanofibrillar cellulose may have a zero-shear viscosity in the range of 350- 3000 Pa s, 370-2100 Pa s, or 750-3000 Pa s, determined by a rotational rheometer using vane geometry at a consistency of 0.5% by weight in aqueous medium at 22±1 °C.

[0078] The fiber and fibril length and / or diameter may be determined with several techniques, such as by microscopy. Suitable imaging software may be used. Fibril thickness and width distribution may be measured by image analysis of microscope images, such as images from a field emission scanning electron microscope (FE-SEM), a transmission electron microscope (TEM), such as a cryogenic transmission electron microscope (CRYO-TEM), or an atomic force microscope (AFM).

[0079] The present disclosure provides fibrillar cellulose obtained with the method. The fibrillar cellulose can be used in a variety of products, especially in products requiring chemically and / or enzymatically unmodified fibrils. The preparation method can be detected from the fibrillar cellulose as the commonly used chemical and / or enzymatic processes as well as bleaching processes are avoided and thus the cellulose remains unaffected by such methods and maintains high aspect ratio. As the fibrils are not hornified, the material exhibits desired properties, such as the high rheological properties, for example high viscosity and shear-thinning propeties. It can be detected that the fibril / fibrillar cellulose is fibrillated cellulose, i.e. obtained from plant cellulose by a fibrillating process producing fibrils and / or fibril bundles. The fibrillar cellulose has a high molar mass, such as molecular weight over 300 kDa.

[0080] Examples of products and applications include medical, scientific and industrial products, such as medical patches, cell culture materials, filters, films, membranes, and additives and / or coatings in other products such as fibrous products, composite products, medical products and / or the like, and applications and / or methods using thereof. The present disclosure provides a product comprising or consisting of the fibrillar cellulose. The products, such as films, membranes, sheets and / or the like exhibit high tensile strength, such as high tensile modulus, which was in the range of 7-11 GPa, such as 8-10 GPa, especially for products obtained from both softwood and hardwood based wood raw materials. Products obtained from softwood exhibited more stiff and brittle structure and having higher tensile modulus, such as 9 GPa or more, for example 9.5-11 GPa, whereas hardwood-based products had a lower tensile modulus, such as less than 9 GPa, for example 7-8.5 GPa.

[0081] It was found out that from the present process undiscolored lignin with properties superior to prior art methods could be directly obtained. Thus the undiscolored lignin may be directly obtained with the method disclosed herein. This means that the lignin has the desired light / original color already when it is obtained from the process, and no further methods or steps to alter the color of the lignin are needed or even desired.

[0082] The present disclosure provides undiscolored lignin having one or more properties discussed herein. The properties can be detected from the recovered undiscolored lignin by using common methods and devices. For example, properties relating to the visual appearance of the undiscolored lignin can be determined with common ISO standard methods. The morphology of the present undiscolored lignin can be detected and characterized microscopically, such as shown in Figures 5 b, c and d. The undiscolored lignin may be present as nanoparticles, such as substantially spherical nanoparticles, which may have an average diameter of a nanoparticle of 1000 nm or less, such as 800 nm or less, preferably 500 nm or less, such as in the range of 100-1000 nm, 100-800 nm or 100-500 nm. The nanoparticles may be present as agglomerates, and / or they may be present as interconnected, such as shown in the figures.

[0083] Whiteness index is an optical index used to quantitatively evaluate the whiteness of a material. It is based on the characteristics of the material's reflected light, and uses a set of standardized calculation formulas to measure how white an object looks, and assigns it a numerical value. In one embodiment the undiscolored lignin has a whiteness index in the range of 91-93, determined by ISO 11475:2004. This is substantially higher than prior art lignin whiteness indexes, which typically remain at about 70 or less. This standard uses a formula: WCIE = Y + 800(xn - x) + 1700(yn - y), where Y is the luminance of the sample (Y tristimulus value), x and y are the chromaticity coordinates of the sample, and xn, yn are the chromaticity coordinates of a perfect diffuser for the CIE 1964 standard colorimetric observer. The method measures the reflectance spectrum of a material under a D65 standard light source (simulated daylight) to reflect its Whiteness under daylight conditions.

[0084] The CIELAB color space, also referred to as L*a*b*, is a color space defined by the International Commission on Illumination (abbreviated CIE) in 1976. It expresses color as three values: L* for perceptual lightness and a* and b* for the four unique colors of human vision: red, green, blue and yellow. The lightness value, L* in CIELAB is calculated using the cube root of the relative luminance with an offset near black. This results in an effective power curve with an exponent of approximately 0.43 which represents the human eye's response to light under daylight (photopic) conditions.

[0085] In one embodiment the undiscolored lignin has a lightness value (L*) in the range of 94.0-98.0 determined by ISO 11664-4:2008. Also these values are substantially higher than prior art lignin lightness values, which typically remain at about 75 or less.

[0086] In one embodiment the undiscolored lignin has a brightness of more than 80.0, such as in the range of 81 .0-83.0, determined by ISO 2470-1 :2016.

[0087] The undiscolored lignin can be also characterized with one or more chemical and / or structural properties, which can be also detected from the recovered white lignin. In one embodiment the undiscolored lignin has a an aliphatic OH group content in the range of 1.3-2.0 mmol / g, such as in the range of 1.4-1 .7 mmol / g. This is substantially lower than in prior art lignins.

[0088] In one embodiment the undiscolored lignin has a phenolic OH group content in the range of 0.2-1 .4 mmol / g, such as in the range of 0.8-1 .2 mmol / g. Also this is substantially lower than in prior art lignins.

[0089] In one embodiment the undiscolored lignin has a p-O-4 linkage content of in the range of 21-35%, such as in the range of 26-30%.

[0090] In one embodiment the undiscolored lignin has a degree of condensation in the range of 45.0-52.0, such as in the range of 46.0-50.0.

[0091] In one embodiment the (released) cellulose, or the fibrillar cellulose, has a brightness of 70 or more, such as 75 or more preferably 78 or 79 or more, determined by ISO 2470-1 :2016.

[0092] In one embodiment the (released) cellulose, or the fibrillar cellulose, has a whiteness index, calculated from L* b* a* color values, of 85 or more, such as 88 or more, preferably 90 or 91 or more.

[0093] In one embodiment the undiscolored lignin has a free carboxylic acid content in the range of 1.5-2.1 mmol / g, such as in the range of 1.7-2.1 mmol / g. This is substantially higher than in prior art lignins.

[0094] The recovered and / or isolated undiscolored lignin can be used in a variety of applications, especially in such applications that can benefit from the specific properties. The undiscolored lignin can be also used in other applications utilizing lignin.

[0095] The present disclosure provides products comprising the undiscolored lignin. The undiscolored lignin may be in combination with one or more other ingredients, such as fillers, binders, structural agents, surface agents, lipids, active agents and / or the like. The undiscolored lignin may act as an active or effective agent in the products. The products may be compositions and / or mixtures of agents, composites, structures, hydrogels, films, adhesives, products having a form, which may be obtained by forming a composition comprising the white lignin into a shape, and / or the like products. The forming may be carried out by molding, by extrusion, by additive manufacturing, by casting and / or by any suitable known methods. The same may apply mutatis mutandis also to products comprising the fibrillar cellulose. For example some of the following lignin-containing products may be implemented also with the fibrillar cellulose.

[0096] The present disclosure provides a coating composition comprising the undiscolored lignin. The coating composition and / or the coating may be paint or other coating, which may be applied by any suitable means, such as by applying by brushing, by a paint roller, by spraying, by dipping and the like methods and means, which results in a formation of a coating. The coating composition comprises undiscolored lignin and may comprise one or more pigments or dyes, fillers, binders and / or other ingredients commonly or customarily used in the art, such as one or more polymers, which may be and / or be based on thermoplastic and / or thermosetting polymers, for example polyethyleneimine. The undiscolored lignin may act as a filler or part thereof, and / or it may act as a coloring component. The coating composition may be prepared by combining, such as by mixing, the undiscolored lignin with one or more of said ingredients, to obtain a composition in a solvent, such as in an aqueous solvent. For example, one or more of the ingredients may be provided as aqueous solution or dispersion.

[0097] The present disclosure provides a composite product comprising the undiscolored lignin. The composite product comprises one or more other ingredients in addition to the undiscolored lignin, which ingredients may be reinforcing ingredients, fillers, modifiers, such as viscosity modifiers, surface modifiers, and the like. A composite product may be for example a lignin-plastic composite.

[0098] The present disclosure provides a cosmetic product comprising the undiscolored lignin. The cosmetic product may be for example a lotion comprising the undiscolored lignin in combination (mixture) with one or more lotion-forming ingredients. The undiscolored lignin can act as a sunscreen agent blocking UV radiation. The lotion may be a sunscreen, which may comprise one or more further sunscreen compounds, for example inorganic compounds such as zinc oxide and / or titanium dioxide, and / or organic sunscreen compounds. In similar manner creams, foams, gels and ointments may comprise the undiscolored lignin in combination with one or more cream, foam, gel and / or ointment forming ingredients. Active ingredients may be included in any of the cosmetics products discussed herein, such one or more cosmetically effective ingredients. The present disclosure provides a medical product comprising the undiscolored lignin. Lignin exhibits properties, which are useful in medical products, such as antimicrobial properties, rheological properties and the like. In similar manner to the cosmetic products, the medical product may comprise creams, foams, gels, lotions and / or ointments, ingredients thereof and one or more therapeutically active ingredients, such as active pharmaceutical ingredients (API). The medical product may be for topical use, i.e. a medication that is applied to a particular place on or in the body. Many topical medications are epicutaneous, meaning that they are applied directly to the skin. In addition to the formulation discussed in previous, topical medications may also be inhalational, such as asthma medications, or applied to the surface of tissues other than the skin, such as eye drops applied to the conjunctiva, or ear drops placed in the ear, or medications applied to the surface of a tooth. Other dosage forms for medical products that can include undiscolored lignin include patches and dusting powders.

[0099] Examples of other products comprising the undiscolored lignin include adhesives and / or resins, such as lignin-phenol-formaldehyde resin adhesives, 3D printed products, lignin-derived activated carbons, and lignin-derived carbon fibers.

[0100] The present disclosure also provides use of the undiscolored lignin and / or the fibrillar cellulose in products, and / or for forming / preparing / manufacturing products, such as one or more products disclosed herein.

[0101] Examples

[0102] In the Examples, percentage values, unless specifically indicated otherwise, are based on weight.

[0103] Example 1 : White colored lignin by using nucleophilic deep eutectic solvent fractionation

[0104] 1. Aim of the study

[0105] As disclosed in the present examples, a novel solvent system based on thiolactic acid and choline chloride was found as reactive solvent for removal of lignin from wood, such as softwood. It is hypothesized that the nucleophilic properties of thiol group on thiolactic acid can lead to fragmentation of lignin via thioacidolysis. Both solid cellulosic fiber and lignin are characterized for their chemical and morphological structure, as well as color of both fractions. Reference delignifications were performed using lactic acid and glyoxylic acid as counterpart to thiolactic acid. Based on the characteristics and literature review, mechanism of lignin removal and white color is proposed. Application potential of lignin was demonstrated in passive radiative cooling to be utilized for examples as a coating.

[0106] 2. Materials and methods

[0107] 2.1 Materials

[0108] Spruce sawdust used as raw material was kindly provided by Keitele Forests Oy at solid content of 50 wt.%. Sawdust was stored in fridge at -18°C and thawed prior using. Thiolactic acid (>97.0%) was obtained from TCI (Germany), and lactic acid (80%) and glyoxylic acid monohydrate (98%) from Sigma-Aldrich (Germany), choline chloride (99%) from Algry Quimica, S.L. (Spain), and ethanol (96%) from VWR (USA). Deionized water was used for all the experiments. Reference kraft lignin and unbleached kraft pulp from sawdust were obtained from UMP.

[0109] 2.2. Delignification of softwood

[0110] Softwood (spruce) sawdust was used as raw material and was provided by local sawmill. Sawdust comprised divergent sized particles in several micrometer size and no size reduction (e.g., grinding) was performed. Furthermore, sawdust was in non-dried state at its natural humidity (around 50 wt.%) as avoiding the drying can bring about saving in energy consumption and preventing any irreversible morphological alteration of wood micro- and nanostructures.

[0111] For delignification solution, 39.68 g of choline chloride and 49.45 ml of thiolactic acid (molar ration between choline chloride and thiolactic acid was 1 :2) were measured into Scott bottle. Mixture was stirred at room temperature until colorless liquid was obtained, followed by addition of 20 g of non-dried sawdust (10 g of solid). The bottle was then closed tightly with screw cap and placed into oil-bath at 120°C. After two hours, the bottle was removed from oil-bath and 150 ml of ethanol was added and mixture was thoroughly mixed and filtrated. Solid fiber fraction was then washed with around 50 ml of ethanol, collected and dispersed in 200 ml of ethanol. Dispersion was then allowed to stand for 15 min with occasionally stirring manually with plastic rod. After standing, dispersion was filtrated and washed with 100 ml of ethanol. At this point, washing liquor was collected and solid was washed with around 2 I of water.

[0112] Lignin was precipitated from washing liquor by addition of around three-fold time of water. Precipitation was allowed to settle for around 24 h. During this time, most of lignin was accumulated on the walls of vessel. Small amount of lignin in liquid was filtrated trough polyvinylidene fluoride membrane (pore size 0.65 pm). Lignin was then dissolved in minimal amount of ethanol (ethanol was added until all lignin was dissolved). Then around three-fold volume of water was added to precipitate lignin. Precipitated lignin was then filtrated on polyvinylidene fluoride membrane (pore size 0.65 pm) and dried in a desiccator under vacuum.

[0113] Alkaline extraction was performed on both ethanol- and water-washed fibers with precipitated lignin by adding 3 g (as dry matter) of material into 500 ml of a 0.25 M NaOH solution. After mixing for 3 h, the fibers were filtered and washed twice with 50 ml of 0.25 M NaOH, followed by washing with 500 ml of water. The dissolved lignin was precipitated using an equimolar amount of HCI relative to NaOH. Lignin was filtered, washed with water, and dried in a desiccator under vacuum.

[0114] Reference delignifications were performed in similar manner but using choline chloride together with either lactic acid or glyoxylic acid at molar ratio of 1 :2.

[0115] 2.3 Characterization

[0116] Morphology of fibers and lignin were performed using scanning electron microscope (SEM, Zeiss Ultra, Germany) and transmission electron microscopy (TEM, JEOL JEM- 2200FS, Japan). The lignin, carbohydrate, and extractive contents of the original and acidic thiourea-treated softwood were determined using the National Renewable Energy Laboratory method.

[0117] 3. Results

[0118] 3. 1 Delignification of softwood

[0119] The fractionation solvent was prepared by mixing choline chloride and thiolactic acid at molar ratio of 1 :2. The combination become colorless liquid by mixing at room temperature for around 10 minutes, being similar to well-known DES based on choline chloride and lactic acid. Sawdust particles dispersed well in this mixture and around halfway of the reaction (after 1 hour mixing at 120°C), it was observed that particles started to fibrillate, and slightly gel-like, light yellow dispersion was obtained after 2 h reaction time.

[0120] Figure 2 shows photographs of a) choline chloride, lactic acid, and their 1 :2 molar ratio mixture at room temperature, b) delignification dispersion before and after reaction, scanning electron microscopy images of c) original wood, d) and e) delignified wood, photograph of f) delignified wood, g) bleached kraft fibers, and h) unbleached kraft fibers from softwood. Figure 2i) shows a graph representing color parameters of delignified wood, bleached kraft fibers, and unbleached kraft fibers (color of bar represents the color of fibers).

[0121] Liberation of fibers from sawdust particles (i.e., fibrillation / pulping) is visible in SEM images where short, individual fibers can be seen. Some roundish shaped lignin particles were observed on the fibers (e.g., lignin cluster in pit, Figure 3e). The formation of concentrated lignin cluster could indicate that some of the dissolved lignin was precipitated during the ethanol washing. Indeed, when water was used instead of ethanol, large quantity of roundish lignin particles was observed on the fibers surface. In both cases, the precipitated lignin was found to be loosely bound to fibers and after room temperature alkaline washing, no lignin particles were observed. Visual observations of the fibers are backed by the chemical analysis, as lignin content notable dropped from around 30 wt.% of original wood to almost zero in case of alkaline washed fibers. In case of water washed fibers, lignin content surpasses the initial lignin content of wood, which is most likely due to the chemical modification of lignin.

[0122] The liberation of individual fibers can be attributed to the dissolution of middle lamella of wood fibers. Together with outer layers of cell wall, middle lamella forms region binding adjacent fibers together, and by removal of this layer, individual fibers can be liberated. Furthermore, surface of fibers showed coarse appearance with nanometric sized fibrils protruding from the surface (e.g., web-like structure of nanofibril with diameter of 20-50 nm can be seen in surface of alkaline washed fibers). In the inner part of fibers (notable in secondary cell wall), cellulose microfibers are bound together with nanometric network of lignin and hemicellulose, and by removal of lignin (and hemicellulose), these microfibrils can be liberated. High yield of fibers after delignification (around 60 wt.%) indicates that in addition to removal of lignin, minor amount of cellulose is removed, being contradict to the kraft process, where yield of pulp is generally around 50 wt.%. Reference unbleached sawdust kraft pulp exhibited notable smoother surface morphology, which can be attributed to the degradation of nanometric sized cellulose bundles as well as irreversible aggregation of nanofibrils (hornification) due to the use of high pressure and temperature. Loose structure of thiolactic acid delignified fibers, i.e. lack of hornification, was demonstrated by easy of disintegration of fibers into cellulose nanofibrils with only one pass through microflu id izer. Cellulose nanofibrils were further converted to film with high mechanical strength (193 MPa). Furthermore, all the fiber fractions exhibited relatively high molar mass (Mw over 300 kDa).

[0123] The notable feature of the fiber fraction is white appearance, being in stark contrast to brown color of unbleached kraft pulp, wherein the lignin has been colored. ISO brightness, commonly used for analysis of industrial cellulose pulp, of solid fraction was 79, being almost three times higher than reference kraft sawdust. Furthermore, whiteness index of solid fraction, calculated from L* b* a* color values, was 91 . Bleached softwood kraft pulp, used as second reference, showed only slightly higher ISO brightness (88%) and whiteness index (95). Although the exact bleaching sequences of kraft pulp is not known, in kraft process, high brightness requires several bleaching steps and, in most cases, chloride-based bleaching chemicals. Therefore, it can be envisioned that solid fraction obtained by thiolactic acid possess high application potential as bleaching- free pulp in applications where high brightness is desired.

[0124] 3.2 White lignin

[0125] Even though white colored fiber fraction has for long been produced in industrial scale (albeit with hazardous bleaching chemical), lignin with high lightness (L* value over 80) and whiteness index (~90) has so far only been reported by chemical functionalization of isolated lignin with large extent of hazardous isocyanates. Therefore, as was surprisingly found out, dried lignin precipitated from ethanolic washing liquor exhibited white appearance with L* value and whiteness index of 96 and 92, respectively. Interestingly, ISO brightness of white lignin was 82 (brightness of kraft lignin is 3). Color parameters of lignin were found to be very close to the fiber fraction, yet the carbohydrate content of lignin fraction was 5 wt.%. The undiscolored lignin obtained with the present methods was called “white lignin”. Figure 3 shows visual appearance of kraft (a), and undiscolored white lignin (b), a graph representing color parameters of kraft and undiscolored white lignin (color of bar represents the color of lignin) (c), and visual illustration of the color of kraft lignin (d), undiscolored white lignin (e), and absolute white (f) in 2D color map.

[0126] The color of lignin can be described as off-white as absolute white compound would have L*, a*, and b* color parameter values of 100, 0, and 0, respectively. However, as visualized in 2D color space, color of white lignin is very close to absolute white (center of space) and AMS Standard 595A color of white lignin is White 506. Comparison of color values with those reported in literature were compared to the present undiscolored lignin, and it was concluded that based on the best knowledge, lignin isolated by the present thiolactic acid-based delignification exhibits whitest color and notable high brightness. Furthermore, the yield of white lignin is superior compared to literature values.

[0127] 3.3 Chemical characteristics of white lignin

[0128] The amount of lignin monomeric units and functional groups are presented in Table 1 together with results of kraft lignin and softwood milled wood lignin (MWL) reported in literature. Due to the minimal variations on the chemical properties of different softwood lignin, comparison between literature values of pine MWL and white lignin (spruce) can be made. The p-O-4 linkages of lignin are generally assumed to be the main cleavage sites of lignin and white lignin possessed lower amount of these linkages (28 vs. 43%) compared to MWL. However, the decrease in the p-O-4 linkage content can be seen only minor when comparing to kraft lignin (the 3-0-4 linkage content of 5), indicating that despite the high delignification efficiency, thiolactic acid-based system causes less severe alteration of main linkage of lignin, maintaining around two third of the 3-0-4 linkages. Furthermore, methoxy group content of white lignin were similar to MWL.

[0129] Table 1 . Comparison of main chemical group, linkage, and degree of condensation of white lignin, kraft lignin, and milled wood lignin.

[0130] Most notable difference between white lignin and MWL is the lower number of hydroxy groups, especially aliphatic groups, in white lignin. Furthermore, white lignin contained 1.90 mmol / g of carboxylic acid groups, whereas in MWL, there were only 0.33 mmol / g of carboxylic acid groups. The high content of carboxylic acid groups indicates that thiolactic acid moiety is attached to lignin structure, which is supported by the large peak at the aliphatic region of1H NMR spectrum, originating from methyl group of thiolactic acid moiety.

[0131] 3.4 Delignification mechanism

[0132] Thiolactic acid is dual functional molecule with carboxylic acid and thiol groups. Thiol can participate in several reactions with lignin, including formation of thioacetals with carbonyl moieties of lignin. Importantly, thiol can cleavage the p- 0-4 linkage of lignin, as well as other ether-based linkages, resulting fragmentation of lignin.

[0133] As discussed in previous, white lignin contained notable higher amount of carboxylic acid and lesser number of hydroxy groups as well as lower content of the p-O-4 linkage compared to MWL. Based on this observation and mechanism of thioacidolysis presented in literature, reaction mechanism of cleavage of the p- 0-4 linkage is proposed. Acidic thiolactic acid (pKa of 3.74) protonates the oxygen attached to a carbon, followed by nucleophilic addition of thiolactic acid to lignin. Protonation of ether bond results in fragmentation of lignin by intermolecular episulfide ring formation. Episulfide ring is then opened by reaction with thiolactic acid, which can then be followed by replacement of primary hydroxy group at y position by thiolactic acid moiety.

[0134] In the literature, preservation of linkages between lignin monomers are usually desired, as it is generally accompanied with the low DoC and enables the more efficient fragmentation of lignin into monomeric units. To preserve linkages of lignin, several lignin stabilization methods, most notable use of aldehydes and alcohols (e.g., diols) have been introduced. Aldehydes can react with diol structure of p-O-4 linkage, preventing the dehydration. Alcohols can react with carbocation formed by acidic dehydration of lignin, forming etherified p-O-4, being more stable compared to original bond. However, preservation of linkage of lignin is many times in trade-off with yield, especially with more complex biomass, such as softwood. For example, use of citric acid and 1 ,4-butanediol facilitated both chemical stabilization and spatial confinement of lignin, resulting in isolation of light-colored lignin (L* value of 74) and well preserved 3-0-4 linkages compared to MWL (around half of the 3-0-4 were converted to 1 ,4-butanediol ethers).10 However, the yield of precipitated lignin calculated from original Klason lignin was 16 %. The increase of temperature from 110 to 180 °C showed notable increase of lignin yield to around 70%, however, amount of original and etherified 3-0-4 decreased to around one-third of the MWL values. In same time, color of lignin slightly darkened to L* value of 60.

[0135] Interestingly, when using lactic acid instead of thiolactic acid, lignin was obtained with much lower yield and darker color. Lactic acid is oxygen analogue of thiolactic acid with hydroxy functional group instead of thiol. Due to the higher electronegativity of oxygen compared to sulfur, electrons of oxygen are less available for reacting with electrophiles, making hydroxy groups less nucleophile compared to thiol. Furthermore, etherification has been proposed to prevent cleavage of 3-0-4 bond, thus, despite the potential chemical modification of lignin, use of lactic acid-choline chloride system leads poor isolation lignin from softwood. In addition, use of glyoxylic acid instead of thiolactic acid resulting in similarly low yield of dark lignin like in case of lactic acid. In the literature, glyoxylic acid has shown to act as lignin protection compound, preventing the cleavage of 3-0-4 bond (and by that, condensation of lignin). By this definition, glyoxylic acid does not lead to extent of fragmentation of lignin and although glyoxylic acid has shown as efficient method for delignification of other lignocellulose biomass, softwood lignin, with more complicated structure rich in carbon-carbon bond, is poorly dissolved.

[0136] 3.5 Color of the lignin

[0137] Color of compounds is complicated phenomenon related both to chemical and physical properties of materials. In organic molecules, conjugated double bonds are responsible for color as electrons in pi-orbital can absorb photons. Compounds with low DoC can only absorb high energy photons (i.e., ultraviolet radiation), however, when DoC increases, lower energy photons are absorbed due to the decrease in the energy difference between HOMO and LIIMO orbitals, eventually leading to absorption of visible light. When certain visible light radiation is absorbed by molecule, rest of radiation is reflected (or transmitted), which is then observed as color. Based on the chemical structure of softwood MWL, DoC of lignin is relatively low as aromatic conjugation is interrupted by ether linkages between sub-units. Nevertheless, DoC can significantly increase during the delignification processes giving rise to high absorption of visible light (DoC of kraft lignin was 82%). It was shown that condensation degree of the white lignin (48%) was only slightly higher compared to MWL (43%), indicating only minor increases in DoC. Importantly, most notable color-giving groups of lignin, conjugated carbonyl can be eliminated with thiolactic acids by formation of stable thioacetals with aldehydes and ketones, as well as by interrupting the conjugation by reaction with carbon-carbon double bond (such as those on cinnamic aldehyde groups) (Figure 5). Compared to DRIFT spectrum of original wood, DRIFT spectra of fiber and lignin fractions after thiolactic acid treatment lacked to peak around 1660 cm’1, associated to the conjugated carbonyls. Furthermore, elimination of conjugated carbonyl functionalities is evident in disappearance of peak around 380 nm in UV spectrum of thiolactic acid-choline chloride treated Kraft lignin. The absorption maximum of lignin closes to the visible light region is generally assumed to originate from the conjugated carbonyl and double bond structures

[0138] Figure 5 shows a) a graph representing infrared spectra of original wood, delignified fibers, and white lignin showing the absence of conjugated carbonyl peak in thiolactic acid treated samples, b) and c) scanning electron microscope images, d) transmission electron microscope image of white lignin, e) and f) scanning electron microscope image of lignin precipitated from aqueous alkaline solution, and g) schematic illustration of scattering of light on the surfaces of white lignin and alkaline lignin

[0139] Morphology is another aspect having effect on the visual appearance (i.e., color) of compounds. For example, dark colored Kraft lignin can be converted into uniform sized lignin nanoparticles and various colors can be produced by varying the size of the nanoparticles. Here, when lignin was precipitated from ethanolic washing liquor, white undiscolored lignin was obtained, yet lignin precipitated from alkaline aqueous solution exhibited more yellowish color (although color of alkaline lignin was notable brighter compared to Kraft lignin and comparable with those reported in literature). Chemical properties of two lignin samples were similar, however, they showed notable different morphology. In SEM images, white lignin showed uneven surface morphology with presence of various sized, roundish nanoparticles (Figure 5b, c). Presence of nanoparticles was confirmed also from TEM images (Figure 5d). On the other hand, alkaline lignin showed solid and relatively smooth surface (Figure 5e,f). The rough surface of white lignin with nanometric sized fine structure most likely shatter the visible light in random directions (i.e., by diffusion reflectance), causing whiter visual appearance compared to alkaline lignin (Figure 5g).

[0140] 3.6 Lignin as surface active compound

[0141] Due to the abundance and green aspects, lignin has been proposed as functional filler, for example in coatings. Strong UV-blocking ability of lignin could serve as UV-protecting agent, yet the strong absorption of visible light causes both esthetic (dark color) and more importantly, heating of the coating in outdoor applications. For example, building coated with dark coating can heat up under sunlight and extra cooling might be needed, ultimately leading to increase in energy consumption (and in CO2 emission when energy is produced from fossil-based sources).

[0142] To demonstrate the potential of white lignin as surface active compound, five films with white lignin content ranging from 33 to 92 wt.% were made together with CNF. Under the solar simulator irritation white lignin samples showed only around 15°C increase in temperature compared to ambient, whereas Kraft lignin sample exhibited almost 20°C higher temperature than white lignin sample. This is well account to the notable absorption of the visible light by Kraft lignin sample. On the contrary, white lignin exhibited high reflectance (around 80 %) at almost whole visible light region. White lignin showed notable increased in absorption only at the end of visible light region and peaked at UV region around wavelength of 350 nm. As the UVA region is around 315-400 nm, white lignin can provide good protection against UV radiation that is not absorbed by ozone layer.

[0143] Solar sky simulation results indicates that both white and kraft lignin samples could provide cooling to the surface. These results agree with absorptance studies. At atmospheric transparent window wavelength range (8-14 pm), both white lignin and kraft lignin samples exhibited similar absorptance results, which by Kirchhoff’s Law of thermal radiation equals to emissivity. Thus, both samples are expected to emit radiation efficiently due to radiative cooling effect, as was seen in sky simulation studies. Based on these results, white lignin exhibits notable higher potential as cooling surface coating compared to kraft lignin, due to the lower absorption of solar radiation (i.e., less heating of the surface under sunlight), however, several aspects, such as optimization of the composition of surface and possible hydrophilization (to prevent the damage on the surface due to the rain and atmospheric humidity) should be investigated in future studies.

[0144] 4. Discussion

[0145] Safety and environmental aspect of solvent systems is utmost important when evaluating novel chemical processes. Most notable hazard of the thiolactic acid is the inhalation and oral toxicity with LD50 value of 730 mg / g orally for rat, being around five times more toxic compared to lactic acid. However, dermal toxicity of the two chemicals is similarly low (> 2000 mg / kg). Conversely, industrially used pulping chemical, sodium sulfide, exhibit lower oral LD50 value (208 mg / g) compared to thiolactic acid and is notable more dermal toxic. Furthermore, thiolactic acid is biodegradable, therefore poses no bioaccumulation hazard if accidentally leaked into environment. It should be noted that like most of thiols, thiolactic acid has pungent odor. Nevertheless, due to the high vapor pressure, odor is less detectable compared to most thiols. However, use of good ventilation (e.g., fume hood) is always recommended when working with thiolactic acid and similar chemicals.

[0146] Unlike lactic acid, thiolactic acid cannot be directly obtained from nature (lactic acid is produced by fermentation of sugars), however, thiolactic acid can be produced from natural occurring propionic acid or alanine via 2-chloropropionic acid pathway. The second compound in delignification mixture, choline chloride, is widely described as green chemical as it is natural occurring, biodegradable compounds with low toxicity. Although choline chloride is in industrial scale produced from oil-based compounds, potential biobased pathway has been proposed via ethanol, produced for example by fermentation.

[0147] 5. Conclusions

[0148] In this study, white colored lignin was isolated for the first time by thiolactic acidbased delignification solvent. Due to the mild thioacidolysis, around two thirds of original lignin linkages were preserved, which is notable as around 70% of original lignin from softwood was isolated in single step. Rest of the lignin could be removed from solid fiber fraction by alkaline dissolution at room temperature. Lignin surface exhibit high reflectance at visible light region and good emissivity at atmospheric window, and together with UV-absorbing properties, white lignin has high potential as UV-shielding radiative cooling material for coating and paints. In addition to the white lignin, cellulosic fiber fraction was obtained with brightness similar to the bleached kraft pulp, thus eliminating the need for the use of hazardous and expensive bleaching chemicals.

[0149] Example 2: Novel delignification chemistry for low-energy production of fibrillated cellulose

[0150] Materials

[0151] Pine sawdust with a moisture content around 90 wt.% and birch wood chips with a moisture content around 50% were kindly provided by a local saw- and papermill and used as raw material. Birch wood chips were dried in the oven at 100°C over night and milled with Rapid mill. Thiolactic acid (>97.0%) was obtained from TCI (Germany), thioglycolic from Sigma-Aldrich (Germany), choline chloride (99%) from Algry Quimica, S.L. (Spain), and 0.25 M NaOH and 1 M HCI from VWR (USA). Deionized water was used in all the experiments.

[0152] Fractionation of sawdust

[0153] Prior fractionation, both pine sawdust and milled birch were soaked in water for 24 h. After soaking, the wood material was filtrated, and dry matter content was determined using a dry-matter analyzer.

[0154] To prepare the fractionation solution, choline chloride and thiolactic acid or thioglycolic acid with a molar ratio of 1 :2 were measured in a Scott bottle. The mixture was stirred at room temperature until a colorless liquid was obtained, followed by addition of 10 g (dry matter) wood. The bottle was then closed tightly with a screw cap, placed into an oil bath at 100°C or 120°C, and allowed to react under mixing with a magnetic stirrer for 1 , 1.5, or 2 h. The bottle was removed from oil bath and allowed to cool for 15 min at room temperature. Then, 200 ml of water was added to precipitate lignin. The mixture was then thoroughly mixed, filtered, and washed with 2000 ml of water. The cellulosic pulp with precipitated lignin was collected and stored at 4°C in an undried state. Alkaline extraction of lignin was performed at room temperature by mixing 3 g (dry matter) cellulosic pulp with precipitated lignin with 150 ml of 0.25 M NaOH for 3h. Solid cellulose fibers were filtrated, washed twice with 50 ml of 0.25 M NaOH followed by washing with 1000 ml of water. Cellulose fibers were collected and stored at 4°C in an undried state.

[0155] Lignin was precipitated from alkaline washing liquor by addition of an equimolar amount of 1 M HCI compared to used alkali (NaOH). Precipitation was filtrated, washed with 1000 ml of water, and dried at room temperature in a fume hood under laminar air flow.

[0156] Low-energy production of fibrillated cellulose

[0157] Commercial kitchen blender was used to fibrillate cellulose fibers. Prior blending, 400 ml of 1 % cellulose fiber dispersion was prepared. Maximum blending time of 15 min was used and blending was stopped if viscose gel was produced prior to reaching the time limit. Blended sample was collected and stored at 4°C in an undried state.

[0158] The power consumption of disc grinding was recorded with an energy meter (iEM3250 Schneider Electric. France) and specific energy consumption (SEC, kWh / kg =MWh / t) was calculated using Eq. 1 : where, P is the total power consumption (kW), Po is the power consumption of the blender under idle load (kW), m is the mass of material processed (kg), and t is the time of (micro )fibrillation (h).

[0159] Fabrication of cellulose nanofibril films

[0160] Sheets from non-blended and blended fibers were produced using vacuum filtration method by filtering 0.3 wt.% dispersion (0.33 g as dry matter) on a polyvinylidene fluoride (PVDF) membrane (pore size 0.65 pm). After removing visible water, the film was covered with another PVDF membrane between two paper sheets for 9 min at 93°C under a vacuum at about 70 mbar of pressure.

[0161] Mechanical properties of films Prior to the tensile test, the sheets were conditioned at 23°C in 50% RH for 48 h. The tensile test was conducted in the same conditions. The tensile properties of the films were analyzed using a universal material testing machine (Zwick D0724587, Switzerland) with a 100 N load cell. Before the measurement, the thicknesses of the films were measured with a precision thickness gauge (Hanatek FT3, UK) at five different locations (the average of the thickness values was used) followed by cut into 5 mm wide strips. During the tensile test a gauge length of 40 mm and strain rate of 4 mm / min were used and five strips in total were analyzed for each film.

[0162] Results

[0163] Fractionation

[0164] The yield of the pulp with cellulose fibers and precipitated lignin were around 80% or higher for both wood samples and with both chemicals (i.e., TLA and TGA) and even exceeded the theoretical maximum of 100% (Figure 7). The over 100% yield is due to the chemical modification of lignin via thioacidolysis. After alkaline washing, the yield of cellulose fibers was in between 47 and 74%, whereas the lignin yield ranged from 6 to 30%, giving high overall yield of fractioned wood.

[0165] The cellulose fiber yield of both wood samples was relatively similar and exhibited no notable difference regarding the used thiol compounds, although the increase in the reaction times and temperature showed decrease in the yield. However, the yield of lignin showed different behavior regarding the wood species. With both chemical, the lignin yield from softwood increased by the increase of reaction time in both studied temperatures. For example, lignin yield from softwood increased from 6 to 14% when reaction time increased from 1 to 2 h at temperature of 100°C with TGA as reagent. On the other hand, at the same temperature and thiol, the lignin yield from birch remained at similar level (11 %) at all reaction times. Generally, slightly higher lignin yields were observed with pine compared to birch, which is in line with higher original lignin content of softwood compared to hardwood.

[0166] Low-energy fibrillation All the cellulose samples were fibrillated in the same 1 % consistency until gel-like viscosity was attained, that prevented the further mixing with blender. In case of pine at temperature of 100°C, no high viscose gel was obtained with TLA at all reactions times and with TGA by using two shortest reaction times. With these samples, blending was stopped after 15 min. Due to the long fibrillation times, these samples exhibited highest energy consumption, ranging from 2.2 to 6.3 MWh / t (Table 2). With other samples, the energy consumption remained lower level, and minimal SEC was obtained with pine at 120°C treated for 1.5 h. With this sample, only after one min, gel was obtained, demonstrating ease of the fibrillation.

[0167] Table 2. Reaction conditions used to produce fiber samples and time and specific energy consumption of blending.

[0168] In the case of birch, all the samples formed gel within seven minutes of blending and the energy consumption remained relatively steady, peaking at 2.2 MWh / t in case of samples produced with TLA at 120°C for 1 ,5h. Minimal SEC of 0.6 MWh / t was obtained with most processed samples in case of birch, being in similar range to the value obtained with pine (0.4 MWh / t). These results demonstrate that birch can more easily be converted into gel-like material with blender even with less severe fraction condition compared to pine, yet similarly, or even slightly lower energy consumption during the blending can be attained with pine when reaction time and temperature during the fraction is increased. This agrees with general assumption of the more recalcitrant structure of softwood compared to hardwood, thus requesting more severe condition during the fractionation. However, with more severe fraction conditions, the difference between two wood species is negligible.

[0169] Mechanical properties of the films produced from blended samples are presented in Figure 8. Highest tensile strength was observed with sample produced with TLA at 120°C for 1.5 h, having tensile strength of 162 MPa. This result is in a good level when compared to literature, especially when considering that SEC below 2 MWh / t was consumed during the mechanical disintegration. With birch, the use of TLA resulted almost similar tensile strength results regardless of the reaction time, yet, around 50 MPa increase in the tensile strength was observed when temperature was increased from 100 to 120°C. In case of TGA, more variation was observed when reaction time was increased. At 100°C, tensile strength values increased from 82 to 144 MPa when reaction time increased from 1 to 2 h.

[0170] Compared to birch, the films prepared from pine samples exhibited more stiff and brittle structure, having the tensile modulus close to 10 GPa at maximum, whereas in case of birch, tensile modulus of 8.1 GPa was obtained. The brittleness of pine samples is evident with low strain values (below 3%) compared to birch. In addition, lower tensile strength values were observed with pine. Interestingly, apart from samples produced with TLA at 100°C for 1 and 1 .5 h, and TGA at 100°C for 1 h, there was minimal difference between tensile properties of all the samples.

Claims

Claims1 . A method for preparing undiscolored lignin, the method comprising -providing lignocellulosic plant material (10),-combining the lignocellulosic plant material with a reagent solution (12) comprising one or more carboxylic acids comprising a thiol group and mixing to obtain a reaction mixture (14),-reacting (16) the reaction mixture in heating, preferably at 100-120°C for 1-4 hours, to release cellulose fibers (20) and to solubilize lignin, and-recovering the solubilized lignin as undiscolored lignin (18).

2. The method of claim 1 , wherein the method is carried out in absence of oxidizing processes and / or alkaline processes3. The method of claim 1 or 2, comprising precipitating the solubilized lignin and resolubilizing the precipitated lignin with a solvent, such as precipitating the solubilized lignin, recovering the precipitated lignin and resolubilizing the recovered precipitated lignin with a solvent.

4. The method of claim 3, comprising resolubilizing precipitated lignin with a solvent, such as with ethanol, dimethyl sulphoxide, dihydrolevogluco- senone, dimethyl isosorbide or aqueous alkali solution, preferably when the lignin is precipitated on cellulose fibers.

5. The method of any of preceding claims, comprising washing the reaction mixture after reacting (16) with a solvent, such as ethanol, separating the washing solution and precipitating undiscolored lignin (18) from the washing solution by adding water.

6. The method of any of preceding claims, wherein the carboxylic acid comprises a thiol group comprises mercapto carboxylic acid, such as thiolactic acid or thioglycolic acid.

7. The method of any of preceding claims, wherein the reagent solution (12) comprises one or more hydrogen bond acceptor, such as choline chloride or trimethyl glycine, preferably as eutectic mixture with the carboxylic acid comprising a thiol group.

8. The method of any of preceding claims, wherein the lignocellulosic plant material (10) comprises wood, such as saw dust.

9. The method of any of preceding claims, comprising adding the lignocellulosic plant (10) material to the reagent solution (12) in a mass ratio in the range of 0.5:10 to 2:10.

10. The method of any of preceding claims, wherein the lignin is unbleached, non-oxidized and / or not obtained from Kraft process and / or from steam explosion process, and / or is not Kraft lignin, softwood milled wood lignin, alkaline lignin, organosolv lignin and / or isocyanate-functionalized lignin.

11. The method of any of preceding claims, comprising preparing fibrillar cellulose by-separating the solubilized lignin as an undiscolored lignin (18) fraction to obtain a cellulose fraction, and-mechanically disintegrating the cellulose fraction to obtain fibrillar cellulose, such as microfibrillar cellulose and / or nanofibrillar cellulose.

12. A method for preparing fibrillar cellulose, the method comprising -providing lignocellulosic plant material (10),-combining the lignocellulosic plant material with a reagent solution (12) comprising one or more carboxylic acids comprising a thiol group and mixing to obtain a reaction mixture (14),-reacting (16) the reaction mixture in heating, preferably at 100-120°C for 1-4 hours, to release cellulose (20), such as cellulose fibers, and to solubilize lignin, -separating the solubilized lignin as undiscolored lignin (18) to obtain cellulose, and-mechanically disintegrating (21 ) the cellulose to obtain fibrillar cellulose (22), such as microfibrillar cellulose and / or nanofibrillar cellulose.

13. The method of claim 12, further comprising carrying out the method of any of claims 1-11.

14. Undiscolored lignin (18) having a lightness value (L*) in the range of 94.0-98.0 determined by ISO 11664-4:2008.

15. The undiscolored lignin of claim 14, having a whiteness index in the range of 91-93, determined by ISO 11475:2004.

16. The undiscolored lignin of claim 14 or 15, having brightness of more than 80.0, such as in the range of 81.0-83.0, determined by ISO 2470-1 :201617. The undiscolored lignin of any of claims 14-16, having an aliphatic OH group content in the range of 1 .3-2.0 mmol / g, such as in the range of 1 .4-1 .7 mmol / g, a phenolic OH group content in the range of 0.2-1 .4 mmol / g, such as in the range of 0.8-1 .2 mmol / g, a p-O-4 linkage content of in the range of 21-35%, such as in the range of 26-30%, a degree of condensation in the range of 45.0- 52.0, such as in the range of 46.0-50.0 and / or a free carboxylic acid content in the range of 1 .5-2.1 mmol / g, such as in the range of 1 .7-2.1 mmol / g.

18. The undiscolored lignin of any of claims 14-17, wherein the lignin is unbleached, non-oxidized and / or not obtained from Kraft process and / or from steam explosion process, and / or is not Kraft lignin, softwood milled wood lignin, alkaline lignin, organosolv lignin and / or isocyanate-functionalized lignin.

19. The undiscolored lignin of any of claims 14-18 obtained with the method of any of claims 1-10.

20. A coating composition comprising the undiscolored lignin (18) of any of claims 14-19.21 . A composite product comprising the undiscolored lignin (18) of any of claims 14-19.

22. A cosmetic product, such as a sunscreen, comprising the undiscolored lignin (18) of any of claims 14-19.

23. A medical product comprising the undiscolored lignin (18) of any of claims 14-19.

24. Fibrillar cellulose obtained with the method of claim 12 or 13.

25. The fibrillar cellulose of claim 24 having a brightness of 75 or more such as 78 or more, determined by ISO 2470-1 :2016.

26. The fibrillar cellulose of claim 24 or 25, having a whiteness index, calculated from L* b* a* color values, of 88 or more, such as 90 or more.

27. A product comprising the fibrillar cellulose of claim 24.

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