A method for hydrophobization of a cellulose ether

Abstract

According to an example aspect of the present invention, there is provided a method for hydrophobization of a cellulose ether, the method comprising: providing a suspension comprising a cellulose ether, lignin and water; foaming the suspension; drying the foamed suspension.

Description

A method for hydrophobization of a cellulose etherFIELD

[0001] The present disclosure relates to hydrophobization of bio-based foams, such as cellulose-based and other plant-based foams.BACKGROUND

[0002] Biodegradable materials often don’t perform well in wet / humid conditions. This can be observed in the deterioration of the structural integrity of e.g. food packaging. Cellulose absorbs water. Dangerous chemicals, plastics and other harmful substances are used to make cellulose based products waterproof.

[0003] Currently hydrophobicity can be achieved by post-processing the end products with a wide variety of coatings.

[0004] Cellulose foams are archetypal examples of plant-based materials to mimic wood’s cellular structure and chemical composition. Cellulose foams are biodegradable and can function as plastics substitutes and aid in reducing our dependence on nonrenewable resources. However, such cellulose foams lack resistance to wetting, thus limiting their commercial use in single-use goods and packaging.

[0005] Thus far, lignin has not been exploited in hydrophobization of cellulose- based materials, because isolated lignin undergoes drastic structural changes compared to its native chemistry when present in wood. Although commercial lignin is available in large amounts as a by-product of wood pulping, it exhibits a complex chemical structure that challenges its valorisation.SUMMARY OF THE INVENTION

[0006] The invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

[0007] According to a first aspect of the present invention, there is provided a method for hydrophobization of a cellulose ether, the method comprising: providing asuspension comprising a cellulose ether, lignin and water; foaming the suspension; drying the foamed suspension.

[0008] According to a second aspect of the present invention, there is provided a hydrophobic cellulose ether foam obtainable by the method according to the first aspect.

[0009] According to a third aspect of the present invention, there is provided use of the hydrophobic cellulose ether foam according to the second aspect as a carbon sink material or in packaging, for example as a material of a container for storing or transporting consumer electronics or hot or cold food or beverage.

[0010] Various embodiments of the first aspect may comprise one or more features from the following bulleted list:• The cellulose ether is selected from the following group: methyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose, hydroxypropyl ethyl cellulose, ethyl cellulose, and derivatives thereof.• The cellulose ether is methyl cellulose.• The cellulose ether is methyl cellulose which has such a degree of substitution for CH3 that the methyl cellulose is soluble in water.• The cellulose ether is methyl cellulose which has a degree of substitution for CH3 in the range of 1.0 - 3.0, such as 1.5 - 2.0, for example about 1.87.• The cellulose ether, preferably methyl cellulose, has a polydispersity index in the range of 1.0 - 2.0, such as 1.2 - 1.8, for example about 1.5.• The cellulose ether, preferably methyl cellulose, has weight average molecular weight Mw in the range of 10 000 - 600 000 g / mol, such as 500 000 - 600 000 g / mol, for example about 534 000 g / mol.• The lignin is in the form of powdered particles.• The average particle size of the lignin is in the range 0.1 - 1000 pm.The lignin originates from an organosolv pulping process.• The lignin comprises crop-derived or wood-derived lignin originating from an organosolv pulping process.• The lignin comprises hydrophobic functional groups, such as carbonyl groups, nonpolar groups, alkyl groups, ester bonds, or any combinations thereof.• The weight average molecular weight Mw of the lignin is in the range of 1000 to 8000 g / mol, such as 2500 to 8000 g / mol, such as about 3100 g / mol or about 5650 g / mol.• The suspension comprises lignin in an amount of 0.1 to 5 wt-%, such as 0.2 to 2 wt- %, such as 0.5 to 1.5 wt-%, such as 1.0 to 1.5 wt-%, for example about 1 wt-%, calculated from the total weight of the suspension.• The suspension comprises the cellulose ether in an amount of 0.1 to 10 wt-%, such as 0.5 to 2 wt-%, such as 1.5 to 2 wt-%, calculated from the total weight of the suspension.• The suspension comprises lignin and the cellulose ether in a weight ratio of 1 :100 to 100:1, such as about 1 :2 to 2:1, for example about 1 :1.• The suspension comprises lignin and cellulose ether in a weight ratio which is higher than 1 :2.• The suspension comprises at least 85 wt-%, such as at least 90 wt-%, such as at least 95 wt-% water, calculated from the total weight of the suspension.• The suspension comprises methyl cellulose in an amount of 0.1 to 2.0 wt-%, calculated from the total weight of the suspension.• The suspension comprises lignin in an amount of 1.0 to 5.0 wt-%, calculated from the total weight of the suspension.• The suspension comprises water in an amount of at least 95 wt-%, calculated from the total weight of the suspension.During the drying step, the temperature inside the foam is below 100 °C, such as 50 to 90 °C.• The drying comprises radiation heating.• During the drying step, the temperature is high enough to induce chemical crosslinking of the cellulose ether and the lignin.• The drying step produces a hydrophobic cellulose ether foam in the form of a two- dimensional film or a three-dimensional article, such as a three-dimensional porous soft solid.• The density of the foam is in the range of 5 to 100 kg / m3, such as 10 to 50 kg / m3.• The water contact angle of the film or the article is at least 90°, such as about 100°.• The water absorption rate Ka of the film or the article is less than 20 ml / (m2s), such as about 5 ml / (m2s).

[0011] An advantage of some embodiments of the present invention is that lignin can be added directly to the suspension, so no post-processing step is required.

[0012] An advantage of some embodiments of the present invention is that the end product may be fully a biodegradable, hydrophobic, and lightweight foam material.EMBODIMENTS

[0013] DEFINITIONS

[0014] Unless otherwise stated herein or clear from the context, any percentages referred to herein are expressed as percent by weight based on a total weight of the respective composition.

[0015] In the present context, the term “organosolv lignin” refers to lignin obtained as a side-stream from an organosolv pulping process.

[0016] In the present context, the term “kraft lignin” refers to lignin obtained as a side-stream from a kraft (sulphate) pulping process.

[0017] In the present context, the term “dealkaline lignin” refers to a lignin that has been solubilized in an alkaline medium during a pulping process and thereafter its pH has been neutralized by an acid.

[0018] An example of dealkaline lignin (DL) is disclosed in Shu et al. (2016).

[0019] An example of kraft lignin (KL) is disclosed in Henn et al. (2021).

[0020] An example of organosolv lignin (OL) is disclosed in De Wild et al. (2014).

[0021] In principle, cellulose-based foams are three-dimensional porous structures inspired by the cellular architecture of wood; see Fig. la. Cellulose foam manufacture typically follows a liquid templating process during which the foam develops open or closed cell structures.

[0022] Producing foams through liquid templating allows taking advantage of interfacial phenomena in the air-liquid boundaries. In fact, driving particles, such as silica and cellulose fibres, to the air-liquid interface of foams may be applied to modify the properties of cellulose foams, see Figs. Ib-f. Since lignin comprises a combination of hydrophobic and hydrophilic end-groups (e.g., methoxy, phenolic, and hydroxyl moieties), lignin particles can form Pickering systems. In other words, lignin particles ideally can reorder their hydrogen bonds toward the continuous liquid phase and their hydrophobic sides toward the air phase. In addition, by saturating the foam system with lignin particles, they aggregate, giving rise to “lignin bumps” on the foam surface. Those bumps represent surface roughness, thus reducing the solid-liquid contact area of the foam surface (Figs. Ib-e). Both hydrophobic lignin groups and lignin bumps may favour the hydrophobic behaviour of cellulose foams.

[0023] It has been observed that improving the foam surface hydrophobic properties can be inspired via biomimicry of the wood structure, where lignin creates a hydrophobic barrier that protects cellulose. Some embodiments disclosed here show how lignin from different cellulose pulping side streams can contribute to partially hydrophobize cellulose foams. Lignin particles may selectively align their hydrophobic and hydrophilic sites in the foam, modifying its surface chemistry and morphology. Thus, tunable water resistance may be achieved, which property may be crucial for novel biobased materials to break into the plastic replacement market.

[0024] In some embodiments, the invention exploits the lignin that wood contains to imitate the synergy arising from lignin embedded in wood. Lignin may act as a hydrophobic barrier, preventing cellulose degradation and microbial attacks.

[0025] According to some embodiments, this disclosure specifies the characteristics lignin should have in order to hydrophobize cellulose foams based on methyl cellulose (methyl ether of cellulose).

[0026] Some embodiments relate to the wettability of methyl cellulose coatings containing different lignins: dealkaline lignin (DL), Kraft lignin (KL), and organosolv lignin (OL).

[0027] Some embodiments relate to the wetting behaviour of several foam biocomposites made by liquid foam templating methyl cellulose aqueous suspensions with varying lignin content.

[0028] In some embodiments, the amphiphilicity of lignin without further chemical modification is exploited. It has been observed that the colloidal behaviour of lignin will drive its partially-hydrophobic regions to the air-liquid interfaces. Depending on the number of hydrophobic groups, lignin will aggregate, modifying the surface chemistry and roughness of the foam surface.

[0029] Some embodiments of the present invention correlate the water surface contact angle of methyl cellulose / lignin foams with their surface roughness, as estimated from scanning electron microscopy (SEM) with an image recognition and tracking algorithm.

[0030] We have observed that adding tunable water resistance properties to a naturally hydrophilic and biodegradeable material may enable its use in various applications. An example of an application area of the present invention is a carbon sink like building insulation which requires water and moisture resistance for tens of years. Another example is a replacement for a single use styrofoam cup, which has to not only hold coffee but disintegrate in cardboard recycling. Further examples include packaging applications ranging from B2B frozen salmon transport (wet) to consumer electronics (dry).

[0031] In an aspect, the present invention provides a method for hydrophobization of a cellulose ether, the method comprising: providing a suspension comprising a cellulose ether, lignin and water; foaming the suspension; drying the foamed suspension.

[0032] Said providing step may comprise mixing dry cellulose ether powder, dry lignin and water.

[0033] In some embodiments, the cellulose ether is selected from the following group: methyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose, hydroxypropyl ethyl cellulose, ethyl cellulose, and derivatives thereof. Preferably the cellulose ether is methyl cellulose.

[0034] In some embodiments, the cellulose ether has such a degree of substitution, for example by alkyl and / or hydroxyalkyl groups, that the cellulose ether is soluble in water.

[0035] In some embodiments, the cellulose ether is methyl cellulose which has such a degree of substitution for CH3 that the methyl cellulose is soluble in water.

[0036] In some embodiments, the cellulose ether is methyl cellulose which has a degree of substitution for CH3 in the range of 1.0 - 3.0, such as 1.2 - 2.5, such as 1.5 - 2.0, for example about 1.87. An advantage is that within these substitution degree ranges the methyl cellulose may be water-soluble.

[0037] In some embodiments, the cellulose ether is methyl cellulose which has a polydispersity index not larger than 2.0, such as in the range of 1.0 - 2.0, such as 1.2 - 1.8, for example about 1.5. An advantage of these PDI ranges is that the quality of the polymer is good, i.e. the structure of the polymer is not too heterogenous.

[0038] In some embodiments, the cellulose ether is methyl cellulose which has weight average molecular weight Mw in the range of 10 000 - 600 000 g / mol, such as 500 000 to 600 000 g / mol, for example about 534 000 g / mol. These Mw ranges provide a suitable viscosity for processing the suspension. A higher molecular weight implies a higher viscosity, which may advantageously enable the wet foam to maintain its structure during drying.

[0039] In some embodiments, the lignin is in the form of powdered particles, wherein the average particle size of the lignin is in the range 0.1 to 1000 pm.

[0040] In some embodiments, the lignin originates from an organosolv pulping process.

[0041] Organosolv is a pulping technique that uses an organic solvent or a biosolvent to solubilise lignin and hemicellulose. Organosolv pulping involves contacting a lignocellulosic feedstock such as chipped wood with the solvent (and water) at temperatures ranging from 140 to 220 °C. This causes lignin to break down by hydrolytic cleavage of alpha aryl-ether links into fragments that are soluble in the solvent system. The solvent may be selected from the group acetone, methanol, ethanol, butanol, ethylene glycol, formic acid, and acetic acid. The concentration of the solvent in water ranges from 40 to 80%. The lignocellulosic feedstock may comprise wood or an annual plant such as straw or bagasse.

[0042] In an example, the organosolv pulping process utilizes wood as the lignocellulosic feedstock.

[0043] In an example, the organosolv pulping process utilizes a biosolvent consisting of formic acid, acetic acid and water as the solvent.

[0044] In some embodiments, the lignin comprises crop-derived or wood-derived lignin originating from an organosolv pulping process.

[0045] In some embodiments, the lignin comprises hydrophobic functional groups, such as carbonyl groups, non-polar groups, alkyl groups, ester bonds, or any combinations thereof. Inclusion of carbonyl groups is particularly advantageous.

[0046] In some embodiments, the weight average molecular weight Mw of the lignin is in the range of 1000 to 8000 g / mol, such as 2500 to 8000 g / mol, such as about 3100 g / mol or about 5650 g / mol.

[0047] The suspension may comprise lignin in an amount of 0.1 to 5 wt-%, such as 0.2 to 2 wt-%, such as 0.5 to 1.5 wt-%, such as 1.0 to 1.5 wt-%, for example about 1 wt-%, calculated from the total weight of the suspension.

[0048] The suspension may comprise the cellulose ether in an amount of 0.1 to 10 wt-%, such as 0.5 to 2 wt-%, such as 1.5 to 2 wt-%, or for example about 1 wt-%, calculated from the total weight of the suspension.

[0049] For example, the suspension may comprise lignin and the cellulose ether in a weight ratio of 1 :100 to 100:1, such as 1 :20 to 20:1, such as 1 :2 to 2:1, for example about 1 :1.

[0050] For example, the suspension may comprise lignin and cellulose ether in a weight ratio which is higher than 1 :2.

[0051] Preferably, the suspension comprises at least 85 wt-%, such as at least 90 wt- %, such as at least 95 wt-% water, calculated from the total weight of the suspension.

[0052] In some embodiments, the suspension comprises- cellulose ether, such as methyl cellulose, in an amount of 1.5 to 2.0 wt-%;- lignin in an amount of 0.1 to 1.0 wt-%; and- water in an amount of 97.0 to 98.4 wt-%, calculated from the total weight of the suspension.

[0053] In some embodiments, the suspension comprises- cellulose ether, such as methyl cellulose, preferably in an amount of 1.5 to 2.0 wt-%;- lignin in an amount of 1.0 to 1.5 wt-%; and- water in an amount of at least 95 wt-%, calculated from the total weight of the suspension, wherein the suspension comprises the lignin and the cellulose ether in a weight ratio which is higher than 1 :2.

[0054] The foaming step may be carried out by the Tessari method, which is described for example in Miranda- Valdez et al. (2023).

[0055] During the drying step, the temperature of the suspension, particularly the temperature inside the foam is below 100 °C, such as 50 to 90 °C. In these temperature ranges, the aqueous medium of the suspension will not start to boil.

[0056] In some embodiments, the drying comprises radiation heating, for example in an oven.

[0057] During the drying step, the temperature is preferably high enough to induce chemical cross-linking of the cellulose ether and the lignin. For example, the temperatureis at least 50 °C, such as at least 60 °C, such as at least 70 °C, such as at least 80 °C, such as at least 90 °C.

[0058] The drying step may produce a hydrophobic cellulose ether foam in the form of a two-dimensional film or a three-dimensional article, such as a three-dimensional porous soft solid.

[0059] The density of the foam may be in the range of 5 to 100 kg / m3, such as 10 to 50 kg / m3.

[0060] The water contact angle of the film or the article may be at least 90° (i.e. equal to or higher than 90°), such as about 100°.

[0061] The water absorption rate Ka of the film or the article may be less than 20 ml / (m2s), such as about 5 ml / (m2s).

[0062] In a further aspect, the present invention provides a hydrophobic cellulose ether foam obtainable by the above disclosed method.

[0063] In a yet further aspect, the present invention provides use of the hydrophobic cellulose ether foam as a carbon sink material or in packaging, for example as a material of a container for storing or transporting consumer electronics or hot or cold food or beverage.

[0064] Examples

[0065] For all the experiments, we employed food-grade MC purchased from Ashland Specialties, Belgium. The MC had a degree of substitution for CEE of 1.87, polydispersity index of 1.50, and weight average molecular weight of 534 kg / mol. We used three lignins: KL, OL, and DL. Softwood KL called BioPiva™ 100 (molecular weight MW = 5000 g / mol) was provided by UPM Biochemicals (Finland). Wheat-straw-derived OF (MW = 5650 g / mol) came from a pilot plant that extracts lignin from agricultural crops. DE was a commercial hardwood lignin purchased from Biosynth® Carbosynth (United Kingdom).

[0066] In the present examples, hydrophobic cellulose foams with different types of lignins and varying lignin content are produced. Initially, three lignins are tested with the same concentration in a methyl cellulose (MC) suspension (0.25 wt-% lignin and 0.9 wt-%MC), as well as a reference without lignin. Such suspensions were deposited on silica wafers via spin-coating. The surface morphology of the coating formed on the silica wafers is tested with SEM and the coating roughness correlated with its wettability (water contact angle). The lignin with the best performance in terms of hydrophobicity (according to contact angle results) is taken and bulk foam blocks made using different concentrations of said lignin. The same imaging and wettability studies were performed on the bulk foams, as with the spin-coated samples. From the exploratory results on the silica wafers, organosolv lignin (OL) showed the best performance, reaching the highest initial water contact angles. OL was chosen to fabricate the bio-composite foam blocks based on the contact angle results on silica wafers.

[0067] The outstanding performance of OL over de-alkaline lignin (DL) and Kraft lignin (KL) arises from the distribution of hydrophobic and hydrophilic groups in the lignin macrostructure. It is well known that isolating lignin via organosolv processing has a very mild influence on the original chemical structure of native lignin, resulting in a structure with more hydrophobic groups. This has been confirmed with Fourier-transform infrared spectroscopy (FTIR). Unlike nuclear magnetic resonance, typically used for elucidating lignin chemical structure, FTIR is a rapid and inexpensive technique for observing the differences between OL, DL, and KL. The FTIR spectrum of OL shows a strong absorption at 1720 cm1, as shown in Fig. If. Such absorption band represents the C=O stretching vibration in unconjugated ketones. Therefore, OL retains more of the hydrophobic interactions characteristic of native lignin than DL and KL. In other words, OL has fewer accessible groups that can form hydrogen bonds with water.

[0068] The sample surface microstructures can be seen in Fig. le. The reference sample shows a smooth-looking surface while adding lignin makes the surfaces rough. This is visible as quasi-spherical “bumps" on the sample surface observed in the SEM images. We conjecture that the portion of each lignin considered partially hydrophobic is driven to form bumps or aggregates due to polymer-polymer interactions (hydrophobic interactions). At the same time, the hydrophilic part is dispersed homogeneously in the methyl cellulose coating formed on the silica wafer. By eye, one can see that the number of bumps varies with the different types of lignins used, OL being the substance with a higher tendency to form bumps. The area fraction phi c|) of the lignin bumps is also tracked from the SEM images and this quantity correlates with the (normalized) height of the FTIR peak at 1720 cm1(normalized by the value at 3030 cm-1), as seen in Fig. If.

[0069] Sessile drop tests are performed to measure the contact angle with water of the foam coated silica wafers. The true static contact angle on absorbing surfaces is not defined since the contact angle continuously shrinks as the liquid gets absorbed from the droplet into the material. This decrease in the contact angle happens at roughly the same rate in all the samples. However, one may see (Fig. If) that the initial contact angle correlates well with the area fraction of lignin and therefore also with the 1720 cm'1FTIR peak.

[0070] Using the best-performing lignin (OL) from the spin-coating tests, bulk foam samples are produced.

[0071] Foam preparation

[0072] MC powder was dispersed in 80 g of tap water at 60 °C. After the MC was fully dispersed in water, lignin was added to the solution. Finally, more tap water was added to ensure the suspension’s total weight reached 100 g. The suspensions were tempered at 3 °C for 24 h. We prepared 11 suspensions with different OL concentrations in the suspension, ranging from 0 to 1.0 wt.%, see Table 1. We foamed the suspension using the Tessari method. We connected two syringes using a plastic tube. One syringe contained 15 ml of the suspension, and the other was adjusted to a free volume of 15 ml. A wet foam was produced by exchanging the suspension from one syringe to another several times until the foam volume was doubled. After this, the wet foam was extruded using a syringe and was continuously dried for 2 h with a heating lamp. The process has been described in more detail in Miranda- Valdez et al. (2023).Table 1. Suspensions for foam samples.

[0073] Similarly, to the spin-coated samples, the addition of lignin introduces surface roughness to the samples in form of roughly spherical bumps, seen in the SEM images (Figs. 2a-2k) of the sample surfaces. By eye one can also see that the number of bumps increases as the lignin concentration increases. Tracking the area fraction (|) shows (Fig. 21) that it increases in a linear fashion with the lignin concentration in the suspension C, as predicted by the assumption of uniform dispersion of lignin (black line in Fig. 21).

[0074] The same sessile drop tests are performed for the bulk foam blocks. The droplet used in the tests can be approximated as a spherical cap with volume, defined by the following Equation (1):where r is droplet base radius and theta 0 the contact angle. This can be exploited to determine the water absorption rate Ka = -A1dN / di as a function of lignin concentration C. Here we assume capillary drainage Ka = AP / (RtotA) with area A and total flow resistance Rtot and driving pressure AP, and include a constant evaporation rate K< due to experimental limitations. The flow of water goes through resistive layers of lignin with flow resistance RL and bulk methyl cellulose (RMC) in series. The water absorption rate Ka can be expressed as two flow resistors in series and finally with the help of the Kozeny- Carman equation, the following Equation (2), aswhere AK = Ko - K < and Ko is the absorption rate of pure methyl cellulose form, alpha is a proportionality factor including the hydrophobicity of lignin as well as the geometry of particles and their deposition, and the linear relation c|) = <|>oC is used.

[0075] Figure 3A shows the fit of Eq. 2 to the experimental data. The resulting absorption rate of pure methyl cellulose foam Ko = 11.4 ml / m2s and the asymptotic evaporation rate K,. = 1.8 ml / m2s are shown with dashed lines. The only fit parameter a = 547 is the proportionality constant describing how much water resistance a lignin layer adds compared to pure methyl cellulose. The dotted lines illustrate the sensitivity of the a parameter highlighting the 100-fold improvement in water resistance with the addition of lignin. Even a small amount of lignin, C = 0.5 wt.% in the suspension (highlighted in the figure), dramatically increases the water resistance as the absorption rate has already dropped by (Ko - Ka) / AK = 95 %, indicating a hydrophobic material.

[0076] The addition of lignin increases the initial contact angle Oto, as can be seen in Fig. 3b. Here one can apply the Cassie equation, the following Equation (3), for a surface consisting of lignin (area fraction (|)) and methyl cellulose cos 0 = (f)RLcos 0L+ (1 — < >) cos 0Q where RL and 0L are the roughness ratio and contact angle of a pure lignin surface, and 0o is the contact angle of the surface without lignin. This would indicate that the crossover from initially hydrophilic to initially hydrophobic surfaces 0to = 90° happens around C = 0.5 wt.%. Note that this value also corresponds to the point highlighted in Fig. 3a.

[0077] A more drastic effect is seen in the time evolution of the contact angle. The normalized contact angle 0 / 0to is shown in Fig. 3c and clearly shows that foam blocks with suspension lignin concentrations C < 0.2 wt. % have very rapidly decreasing contact angles. However, with lignin concentrations above this level the decrease in the contact angle during the experiment is only around 5-20 %.

[0078] By combining the Cassie equation (Eq. 3) for the initial state, the spherical cap approximation (Eq. 1), and the Kozeny-Carman capillary drainage model (Eq. 2) for water absorption one can compute the time-evolution of the contact angle. The contact angle 0 at t = 40 s is shown in Fig. 3d as is also the numerical result. The increase in the contact angle with increasing lignin concentration is clear and the numerical approximation is very good.

[0079] In addition to the contact angle tests shown here simpler water column tests are performed to study the performance of lignin foams in wet environments. The water retention of a foam with 0.5 wt.% lignin of was ten times better compared to a reference sample and also significantly better compared to cardboard. The mechanical properties (yield stress and Young’s modulus) of the foam blocks have been tested in a humid environment and seen that the lignin foams show great improvements in retaining their properties.

[0080] The feasibility of producing actual end products has been tested, out of the lab-scale, using the hydrophobization method described here. A replacement for a single use styrofoam cup has been made and it performs as well as other industry alternatives.

[0081] FIGURE 1 presents the biomimicry and lignin migration.

[0082] FIG. la: The structure of wood is mimicked in laboratory: In the lightweight cellular structure the cellulose gives strength and lignin protection.

[0083] FIG. lb: During the drying process the water (blue) is removed, leaving methyl cellulose (MC) film (purple) doped with lignin particles (OL, DL and KL).

[0084] FIG. 1c: Depending on the surface chemistry, particles are in different parts of the film.

[0085] FIG. Id: A water-resistant layer is created, if the lignin particles migrate to the surface of the bubble films.

[0086] FIG. le: SEM images of spin-coated films illustrate that DL grade lignin stays inside the methyl cellulose while KL and OL lignin are seen more on the surface.

[0087] FIG. If: Lignin FTIR spectrum absorbance value at 1720 cm1(square symbols; normalized by the value at 3030 cm ' ) as a measure of hydrophobic groups, correlates with the contact angle measurement 0o (circle symbols) and the observed coverage of lignin at the surface (f> for materials seen in panel le.

[0088] FIGURE 2 presents the effect of lignin concentration on the sample surfaces.

[0089] FIGS. 2a-k: SEM images of the samples with increasing lignin concentration and equal MC concentration.

[0090] FIG. 21: The area fractionas a function of the lignin concentration C. The black line is the prediction based on uniformly distributed lignin.

[0091] FIGURE 3 presents the effect of lignin concentration on the water absorption and the contact angle.

[0092] FIG. 3a: The average water absorption rate as a function of the lignin concentration in the suspension. The brown line represents a fit to Eq. 2 and the dashed lines show the effect of changing the a parameter. The horizontal dashed lines correspond to the water absorption rates Ko without lignin and the Kxasymptotic value. The value C = 0.5 wt.% corresponding to initially hydrophobic behaviour is highlighted by a vertical line.

[0093] FIG. 3b: The average initial contact angle Oto as a function of the lignin concentration C. The black line corresponds to a fit to Eq. 3.

[0094] FIG. 3c shows the normalized contact angle 0 / 0to.

[0095] FIG. 3d: The (normalized) contact angle 0 / 0to as a function of time, where the colour of the curves represents the lignin concentration C.

[0096] FIG. 3e: The contact angle as a function of the lignin concentration at one point in time (t = 40 s), as well as the result of numerically computing the time evolution from Eqs. 1-3.

[0097] It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but areextended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

[0098] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment.

[0099] As used herein, a plurality of items, structural elements, compositional elements, and / or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.

[0100] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

[0101] While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the inventionbe limited, except as by the claims set forth below.

[0102] The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of “a” or “an”, i.e. a singular form, throughout this document does not exclude a plurality.INDUSTRIAL APPLICABILITY

[0103] The present invention is industrially applicable at least in the manufacturing of hydrophobic cellulosic foam materials.ACRONYMS LISTDL dealkaline ligninKL Kraft ligninOL organosolv ligninMC methyl celluloseSEM scanning electron microscopyFTIR Fourier-transform infrared spectroscopyCITATION LISTNon Patent LiteratureI. Y. Miranda-Valdez, S. Coffeng, Y. Zhou, L. Viitanen, X. Hu, L. Jannuzzi, A. Puisto, M.A. Kostiainen, T. Makinen, J. Koivisto, M. J. Alava, Cellulose 2023, 30(4), 2253-2266.R. Shu, J. Fong, Y. Xu, E. Ma, Q. Zhang, T. Wang, C. Wang, Z. Yuan, Q. Wu, Bioresource Technology 2016, 200, 14-22.K. A. Henn, N. Forsman, T. Zou, M. Osterberg, ACS Applied Materials & Interfaces 2021, 13, 29, 34793-34806.P. J. De Wild, W. J. Huijgen, R. J. Gosselink, Biofuels, Bioproducts and Biorefining 2014, 8, 5, 645-657.

Claims

CLAIMS:

1. A method for hydrophobization of a cellulose ether, the method comprising:- providing a suspension comprising a cellulose ether, lignin and water;- foaming the suspension;- drying the foamed suspension.

2. The method according to any of the preceding claims, wherein the cellulose ether is selected from the following group: methyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose, hydroxypropyl ethyl cellulose, ethyl cellulose, and derivatives thereof.

3. The method according to any of the preceding claims, wherein the cellulose ether is methyl cellulose.

4. The method according to any of the preceding claims, wherein the cellulose ether is methyl cellulose which has such a degree of substitution for CH3 that the methyl cellulose is soluble in water.

5. The method according to any of the preceding claims, wherein the cellulose ether is methyl cellulose which has a degree of substitution for CH3 in the range of 1.0 - 3.0, such as 1.5 - 2.0, for example about 1.87.

6. The method according to any of the preceding claims, wherein the cellulose ether is methyl cellulose which has a polydispersity index in the range of 1.0 - 2.0, such as 1.2 - 1.8, for example about 1.5.

7. The method according to any of the preceding claims, wherein the cellulose ether is methyl cellulose which has weight average molecular weight Mw in the range of 10 000 - 600 000 g / mol, such as 500 000 - 600 000 g / mol, for example about 534 000 g / mol.

8. The method according to any of the preceding claims, wherein the lignin is in the form of powdered particles, wherein the average particle size of the lignin is in the range 0.1 - 1000 pm.

9. The method according to any of the preceding claims, wherein the lignin originates from an organosolv pulping process.

10. The method according to any of the preceding claims, wherein the lignin comprises crop-derived or wood-derived lignin originating from an organosolv pulping process.

11. The method according to any of the preceding claims, wherein the lignin comprises hydrophobic functional groups, such as carbonyl groups, non-polar groups, alkyl groups, ester bonds, or any combinations thereof.

12. The method according to any of the preceding claims, wherein the weight average molecular weight Mw of the lignin is in the range of 1000 to 8000 g / mol, such as 2500 to 8000 g / mol, such as about 3100 g / mol or about 5650 g / mol.

13. The method according to any of the preceding claims, wherein the suspension comprises lignin in an amount of 0.1 to 5 wt-%, such as 0.2 to 2 wt-%, such as 0.5 to 1.5 wt-%, such as 1.0 to 1.5 wt-%, for example about 1 wt-%, calculated from the total weight of the suspension.

14. The method according to any of the preceding claims, wherein the suspension comprises the cellulose ether in an amount of 0.1 to 10 wt-%, such as 0.5 to 2 wt-%, such as 1.5 to 2 wt-%, calculated from the total weight of the suspension.

15. The method according to any of the preceding claims, wherein the suspension comprises lignin and the cellulose ether in a weight ratio of 1 :100 to 100:1, such as about 1 :2 to 2 : 1 , for example about 1 :1.

16. The method according to any of the preceding claims, wherein the suspension comprises lignin and cellulose ether in a weight ratio which is higher than 1 :2.

17. The method according to any of the preceding claims, wherein the suspension comprises at least 85 wt-%, such as at least 90 wt-%, such as at least 95 wt-% water, calculated from the total weight of the suspension.

18. The method according to any of the preceding claims, wherein the suspension comprises:- methyl cellulose in an amount of 0.1 to 2.0 wt-%;- lignin in an amount of 1.0 to 5.0 wt-%; and- water in an amount of at least 95 wt-% calculated from the total weight of the suspension.

19. The method according to any of the preceding claims, wherein during the drying step, the temperature inside the foam is below 100 °C, such as 50 to 90 °C.

20. The method according to any of the preceding claims, wherein the drying comprises radiation heating.

21. The method according to any of the preceding claims, wherein during the drying step, the temperature is high enough to induce chemical cross-linking of the cellulose ether and the lignin.

22. The method according to any of the preceding claims, wherein the drying step produces a hydrophobic cellulose ether foam in the form of a two-dimensional film or a three- dimensional article, such as a three-dimensional porous soft solid.

23. The method according to any of the preceding claims, wherein the density of the foam is in the range of 5 to 100 kg / m3, such as 10 to 50 kg / m3.

24. The method according to any of the preceding claims, wherein the water contact angle of the film or the article is at least 90°, such as about 100°.

25. The method according to any of the preceding claims, wherein the water absorption rate Ka of the film or the article is less than 20 ml / (m2s), such as about 5 ml / (m2s).

26. A hydrophobic cellulose ether foam obtainable by the method according to any of the preceding claims.

27. Use of the hydrophobic cellulose ether foam according to claim 26 as a carbon sink material or in packaging, for example as a material of a container for storing or transporting consumer electronics or hot or cold food or beverage.

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