TECHNI CAL FI ELD

The present disclosure relates to a m ethod for producing a stable composition comprising hornificated particles of nanocellulose. BACKGROUND

Plastic m icrobeads have been used for several years as exfoliation agents in personal care products, such as cosm etics, soaps, facial scrubs and toothpastes. However, such m icrobeads are usually small (less than 1 m m ) , and when washed down the drain can pass unfiltered through sewage treatment plants, making their way into rivers and water canals, which culm inates in severe m icroplastic water pollution and endangerm ent of marine ecosystems worldwide. The plastics from which the m icrobeads are form ed are typically from fossil-fuel based sources, e.g. polyethylene, and are typically not biodegradable.

As a consequence, several countries have banned the use of plastic m icrobeads in personal care products, and manufacturers are now seeking more environmentally-friendly alternatives.

Known alternatives to plastic m icrobeads used as for example abrasive com ponents of personal care products include organic materials such as ground fruit/nut kernels, cellulose grains or wax beads (jojoba beads, synthetic wax, carnauba beads, candelilla beads) , and inorganic m aterials such as silica or pum ice stone. However, such abrasive m aterials often have drawbacks. For instance, inorganic materials are typically difficult to grind, are typically highly abrasive and are usually dense, making them difficult to maintain in suspension. Another drawback is that the yield during production is quite low. Also, many fruit or nut kernels have a dark color, which can impact the color of the personal care product. Other abrasive m aterials are difficult to obtain in bulk or can present issues of toxicity or chem ical intolerance when applied to the hum an body.

Various uses of cellulose fibers in skincare or cosm etic applications are provided in WO 2018/030392, W02002/022172, US2013330417, EP3081209 and JP2006240994A.

FR3017291 A1 discloses cellulose exfoliant particles that disintegrate after application to human skin or scalp. A drawback with the use of cellulose particles in the form of cellulose beads is that it could be difficult to evenly disperse them in a composition since they might easily flocculate and/or sedim ent.

There is thus a need, for a new class of abrasive materials for use in personal care products which overcome some or all of the problems with known abrasive materials. First and foremost, the abrasive materials must be biodegradable. I mportantly, the abrasive materials should be skin-friendly (i.e. non-toxic). The abrasive materials should be easy to grind, and allow a range of abrasiveness (provided by both particle size and shape). The abrasive materials should be stable during the lifetime of the product (both physically stable and chemically stable), should provide stable personal care products and be possible to evenly disperse in a composition. Properties such as flavour, odour and colour should be as neutral as possible. Suitably, the abrasive materials should also have some porosity, which promotes uptake and release of chem ical components.

SUMMARY The present technology relates to a method for producing a composition comprising hornificated particles of nanocellulose, said method comprising the steps of: providing a suspension comprising nanocellulose, drying said suspension so as to provide hornificated particles of nanocellulose, adding a stabilizing agent in an amount of 0.1 -50 wt-% based on the amount of particles, to the suspension after drying to form said composition.

A composition comprising hornificated particles of nanocellulose and a stabilizing agent in also provided.

A personal care composition is also provided, comprising the hornificated particles described herein and a stabilizing agent. Further provided is the use of stabilized hornificated particles comprising or consisting of nanocellulose, preferably m icrof ibrillated cellulose (MFC), as described herein, as an abrasive material in a home care or personal care composition. Further aspects of the present technology are provided in the following text, figures and the dependent claims.

DETAI LED DI SCLOSURE

It is an object of the present disclosure to provide an im proved method for the production of a stable com position comprising hornificated nanocellulose particles.

It is known in the forestry and papermaking industries that harsh, extensive drying or dewatering of cellulose fibers or fibrils will cause them to hornificate. Hornification involves coalescence or adhesion of fibers or fibrils to each other as a result of drying or dewatering, leading to lower porosity and poor solvent accessibility. Hornification can also be a property change on the surface of a fiber or fibril, e.g. that the surface becom es more hydrophobic which lead them to be more prone to flocculate. Cellulose fibrils aggregate strongly, and thus become virtually im possible to completely separate them again (also known as co crystallization) . Hornificated particles are thus coalesced fiber aggregates or m icrofibril or elementary fibrils. They are obtained by controlled drying of aggregation of nanofibrils into beads or larger particles. Post-treatment (e.g. post-curing) can increase the extent of hornification.

Hornification is most often an undesirable feature. At the end of a fiber dewatering or drying process the tem perature of the material starts to increase, because there is no more water to evaporate. Hornification of fibers in e.g. a paper sheet generally leads to the strength properties of the paper sheet being reduced.

The present disclosure is based on the inventive realization that it is possible to produce a more stable com position, including both a more stable interm ediate com position according to the invention and a more stable final com position, such as a personal care or homecare product, paint or other final com position, com prising hornificated nanocellulose particles by addition of a stabilizing agent already after the form ation of the hornificated particles, and the production of the composition according to the invention. The com position according to the invention is an interm ediate com position to be m ixed with additional additives, chem icals or com positions to form the final end product or final com position. The composition can be in either wet or dry state. Normally stabilizing agents would be added later during the formation of the final composition to be used. It was now found that by adding the stabilizing agent already directly after the formation of the particles, a more dispersible composition is obtained, and it can be used to produce a more stable final com position. Also, it has been found that it will be easier to evenly disperse the com position, or the hornificated particles in the com position, in the final product. Also, it would be possible to provide a com position that would com prise the optim um amount of stabilizing agent for that amount and type of hornificated nanocellulose particles present in the composition, which facilitates the m ixing of the com position with other ingredients in order to produce the final product, e.g. a coating, a personal care or home care product or a paint. The stabilizing agent can be added and m ixed with hornificated particles that are still in wet form or with dried hornificated particles.

Hornification is a result of harsh drying conditions. The hornificated particles therefore have a dry content of 61 % or more. Suitably, hornificated particles have a dry content of 70% or more, and preferably 80% or more, more preferably 90% or more, most preferably 95% or more. Dry content can be determ ined by an oven-drying method, e.g. ISO/CD 638- 1 “Paper, board and pulps — Determination of dry matter content”.

The extent of hornification may also be characterised by the water absorption capacity of the nanocellulose particles, defined as g water uptake/g m aterial. Water absorption capacity can be determ ined by EDANA method NWSP 240.0. R2 in which saline solution is replaced by deionized water. Hornificated particles have a water absorption capacity of less than 10 g water/g m aterial; preferably less than 5 g water/g material; more preferably 1 - 5 g water/g material.

The present disclosure relates to a m ethod for producing a com position comprising hornificated particles of nanocellulose, said method comprising the steps of: providing a suspension com prising nanocellulose, drying the suspension so as to provide hornificated particles of said nanocellulose, adding a stabilizing agent in an amount of 0.1 -50 wt-% based on the amount of particles, to the suspension after drying to form said composition. The amount of stabilizing agent is preferably between 1 -30 wt-% , preferably between 5-25wt-% based on the total amount of particles. The amount of stabilizing agent may depend on the type of stabilizing agent used as well as on the amount and kind of particles used in the com position. If more than one stabilizing agent is used, the amount of stabilizing agent mentioned is the total amount of the different stabilizing agents.

With a more stable com position is meant a composition that has improved colloidal stability, and which is less prone to sedimentation and inter-particle flocculation. The composition can be left for at least one week and no sedim entation occurs. The composition also has improved stability at higher electrolyte concentrations, such as mono-, di- or m ultivalent ions, at a broader tem perature interval and is more stable during transportation, i.e. it is more resistant against vibration motions and tem perature fluctuations, which occur during transportation. Hornification is a result of harsh drying or dewatering conditions, which is achieved by the drying step according to the present invention. With drying is also meant dewatering. The drying step provides hornificated particles, which preferably have a dryness level of 70% or more, and preferably 80% or more, more preferably 90% or more, most preferably 95% or more. The drying step suitably takes place for a time of 1 -1800 seconds, 10- 1000 preferably 15-500 seconds, and more preferably 30-120 seconds. The drying step may - depending on the drying method - take place at a temperature of 70-350°C, preferably 80-185 °C, and more preferably 100-150 °C.

The drying step preferably takes place in an inert atmosphere. Drying in an inert atmosphere reduces the formation of oxidised material with an off-white color, thereby maintaining the brightness of the hornificated particles closest to white. The nanocellulose could also be dispersed in a co-solvent such as an alcohol solvent prior to drying.

The drying step is preferably done by thermal, radiation and/or mechanical drying. The drying step preferably comprises spray drying, ring drying, flash drying, TurboRotor m ill drying, oven drying, or a combination thereof, preferably flash drying or spray drying.

The extent of hornification may also be characterized by the water absorption capacity of the particles, defined as g water uptake/g material. Water absorption capacity can be determined by EDANA method NWSP 240.0.R2, in which saline solution is replaced by deionized water. Hornificated particles may therefore have a water absorption capacity of less than 10 g water/g material; preferably less than 5 g water/g material; more preferably 1 - 5 g water/g material. The water absorption capacity of the composition may be more than 10g water/g material, preferably more than 15 g water/g material and most preferably more than 20 g water/ g material.

The degree of hornification may also be characterized by the amount of fibrils released by the particles upon wetting. For the hornificated particles according to the present invention the percentage of loose fibrils upon wetting is < 5% . Dispersibility in aqueous media can be determ ined via e.g. Canadian standard CAN/CSA-Z5100-17 5.3.10.

The hornificated particles that comprises or consists of nanocellulose, preferably comprises or consists of m icrof i b r i 11 at ed cellulose (MFC), preferably unmodified native m icrof ibrillated cellulose (MFC). The MFC particles may comprise at least 20 wt% MFC, preferably at least 30 wt% MFC, more preferably at least 50 wt% MFC, even more preferably at least 70 wt% MFC, or 100 wt% MFC. Typically, the particles solely comprise cellulosic fibres. The particles may however - apart from the nanocellulose- additionally comprise cellulosic fibres such as e.g. pulp fibers or chem ically modified nanocellulose. It has been found that when m icrof ibrillated cellulose is dried at harsh conditions to a dryness level above 61 % , hornificated m icrof ibrillated cellulose particles are formed. Suitably, the hornificated particles have a dryness level of 70% or more, and preferably 80% or more, more preferably 90% or more, most preferably 95% or more. Dryness level can be determ ined by an oven-drying method, e.g. I SO/CD 638- 1 “Paper, board and pulps — Determination of dry matter content”.

The MFC of the composition to form the hornificated particles m ay be unmodified MFC (native MFC) or chem ically modified MFC, or a m ixture thereof. I n some em bodim ents, the MFC is an unmodified MFC. Unmodified MFC refers to MFC m ade of unmodified or native cellulose fibers. The unmodified MFC m ay be a single type of MFC, or it can comprise a m ixture of two or more types of MFC, differing e.g. in the choice of cellulose raw m aterial or m anufacturing method. Chem ically modified MFC refers to MFC m ade of cellulose fibers that have undergone chem ical modification before, during or after fibrillation. I n some embodiments, the MFC is a chem ically modified MFC. The chem ically modified MFC m ay be a single type of chem ically modified MFC, or it can com prise a m ixture of two or more types of chem ically modified MFC, differing e.g. in the type of chem ical modification, the choice of cellulose raw material or the manufacturing m ethod. The modified MFC m ay be carboxym ethylated cellulose, preferably with a degree of substitution ( DS) less than 0.4, more preferably with a DS between 0.05- 0.35.

By nanocellulose is m eant any one of m icrof ibrillated cellulose (MFC) , bacterial cellulose and/or nanocrystalline cellulose.

Microfibrillated cellulose (MFC) shall in the context of the patent application be understood to mean a nano scale cellulose particle fiber or fibril with an average diam eter of less than 1000 nm . MFC comprises partly or totally f ibrillated cellulose or lignocellulose fibers. The liberated fibrils have an average diameter less than 1000 nm , whereas the actual fibril diameter or particle size distribution and/or aspect ratio (length/width) depends on the source and the manufacturing m ethods.

Depending on the source and the manufacturing process, the length of the fibrils can vary from around 1 to more than 100 m icrometers. A coarse MFC grade m ight contain a substantial fraction of f ibrillated fibers, i.e. protruding fibrils from the tracheid (cellulose fiber) , and with a certain amount of fibrils liberated from the tracheid (cellulose fiber) .

I n some em bodiments, the MFC com prises less than 50 wt% , preferably less than 30 wt% , and more preferably less than 20 wt% , of MFC fibers having a diameter above 1000 nm . There are different synonyms for MFC such as cellulose microfibrils, fibrillated cellulose, nanof ibrillated cellulose, fibril aggregates, nanoscale cellulose fibrils, cellulose nanofibers, cellulose nanofibrils, cellulose microfibers, cellulose fibrils, m icrofibrillar cellulose, m icrofibril aggregates and cellulose microfibril aggregates. The cellulose fiber is preferably fibrillated to such an extent that the final specific surface area of the formed MFC is from about 1 to about 400 m ² /g, or more preferably 50-300 m ² /g when determ ined for a solvent exchanged and freeze-dried material with the Nitrogen sorption (BET) method.

Various methods exist to make MFC, such as single or multiple pass refining, pre-hydrolysis followed by refining or high shear disintegration or liberation of fibrils. One or several pre treatment steps are usually required in order to make MFC manufacturing both energy efficient and sustainable. The cellulose fibers of the pulp to be utilized may thus be pre treated, for example enzymatically or chem ically, to hydrolyse or swell the fibers or to reduce the quantity of hem icellu lose or lignin. The cellulose fibers may be chemically modified before fibrillation, such that the cellulose molecules contain other (or more) functional groups than found in the native cellulose. Such groups include, among others, carboxymethyl (CMC), aldehyde and/or carboxyl groups (cellulose obtained by N-oxyl mediated oxidation, for example "TEMPO"), or quaternary am monium (cationic cellulose). After being modified or oxidized in one of the above-described methods, it is easier to disintegrate the fibers into MFC or nanofibrils.

The nanof ibrillar cellulose may contain some hemicelluloses, the amount of which is dependent on the plant source. Mechanical disintegration of the pre-treated fibers, e.g. hydrolysed, pre-swelled, or oxidized cellulose raw material is carried out with suitable equipment such as a refiner, grinder, homogenizer, colloider, friction grinder, ultrasound sonicator, fluidizer such as microfluidizer, m acrofluidizer or fluidizer-type homogenizer. Depending on the MFC manufacturing method, the product might also contain fines, or nanocrystalline cellulose, or other chemicals present in wood fibers or in papermaking process. The product might also contain various amounts of micron size fiber particles that have not been efficiently fibrillated.

MFC is produced from wood cellulose fibers, both from hardwood or softwood fibers. It can also be made from m icrobial sources, agricultural fibers such as wheat straw pulp, bamboo, bagasse, or other non-wood fiber sources. It is preferably made from pulp including pulp from virgin fiber, e.g. mechanical, chem ical and/or thermomechanical pulps. It can also be made from broke or recycled paper.

Hem icellu lose content of the MFC fibers is typically 1 -25% , while it is not lim ited by these values. MFC crystallinity is preferably 35-85% and more pref. 45-75%. Various grades of MFC, including those already com mercially available and currently on the market, can be used as starting material for the preparation of the dry MFC particles of the invention.

The stabilizing agent is preferably nanocellulose and/or a dispersant. The molecular weight of the dispersant is preferably above 5000 g/mol, preferably above 10000 g/mol, preferably above 50000 g/mol, preferably above 100000 g/mol. It is important not to use a dispersant with too low molecular weight since it will then not be possible to achieve the stabilizing properties of the composition. The nanocellulose may be unmodified MFC or a chem ically modified MFC, preferably an anionic MFC. It may be preferred to use phosphorylated nanocellulose or carboxymethylated nanocellulose as a stabilizing agent. The dispersant is preferably an anionic dispersant, preferably carboxymethylated cellulose, anionic starch and/or anionic polyacrylam ide. The stabilizing agent may also be a saccharide, such as a monosaccharide, e.g. glucose, mannose or galactose, oligosaccharides such as sucrose or lactose or polysaccharides or other water-soluble polymer, such as cellulose derivate or hydrophilic polymers such as polyethylene glycol (PEG) or polyvinyl alcohol (PVOH). It may be preferred to use a mixture of different stabilizing agent. One preferred combination is to use a mixture of nanocellulose, preferably m icrof ibrillated cellulose and carboxymethylated cellulose (CMC) with a high molecular weight. The composition may then preferably comprise 1 -30wt-% of nanocellulose and 1 -30wt-% of CMC. The ration between CMC and MFC is preferably 1 : 100 to 100: 1 . If native nanocellulose is added as a stabilizing agent it might be preferred to also add another stabilizing agent, such as CMC, which will both act as a stabilizing agent but also prevent the nanocellulose added from coalescence (hornificate) during eventual final-drying steps. It is preferred not to cause the nanocellulose added as a stabilizing agent to hornificate during future drying steps.

It may be preferred to use the same kind of nanocellulose for the production of the hornificated particles and as the stabilizing agent, preferably native nanocellulose or carboxymethylated nanocellulose is used. It might be preferred to use m icrof ibrillated cellulose (MFC), preferably native MFC or carboxymethylated MFC.

The composition according to the invention preferably comprises 0.1 -20 wt-% , preferably 0.5-10 wt% of hornificated particles.

The degree of abrasiveness of the particles may be related to the particle size and shape, with larger and more angular particles generally providing a more abrasive feel. Depending on the end product, smaller or bigger particles are desirable. Therefore, hornificated particles according to the present technology, may have an average dry particle size (D90) of 1 -2000 pm, preferably 50-1000 pm, and more preferably 150-750 pm. Particle size may be measured by laser diffraction (as per I SO/DI S 13320) or by SEM im aging com bined with particle analysis (as per ISO 13322- 1 :2014) , preferably laser diffraction.

The cellulosic nature of the nanocellulose particles provides a certain level of porosity, e.g. a porosity in the range 0-25% , preferably in the range 5- 15% . Porosity can be determ ined by mercury porosimetry and gas adsorption as per I SO 15901 - 1 : 2016. This is useful when the particles are used in personal care com positions, as it improves uptake of other com ponents of the com position, and the particle's overall com patibility and dispersibility within the com position.

The degree of abrasiveness may be related to the particle hardness. Hornificated particles suitably have a hardness in the range 60-80 Shore D. The abrasiveness of exfoliants depends on their size and shape. The sm allest particles are usually used in facial scrubs, whereas the medium-sized particles are used in body scrubs and finally the biggest particles in foot scrubs.

Another param eter of interest is the surface area. Suitably, the surface area of the nanocellulose particles should be > 1 m ² /g, suitably between 1 - 1000 m ² /g. Calculating the specific surface area of solids can be carried out by the BET method (e.g. using I SO 9277) .

The hornificated particles preferably have a particle size - or are m illed to a particle size - of 1 -2000 pm , preferably 50- 1000 pm , and more preferably 150-750 pm .

The method m ay further com prise addition of wetting agents before, sim ultaneously or after addition of the stabilizing agent. The wetting agent is added before eventual final drying of the com position. The amount of wetting agent in the com position is preferably between 0.1 -5 wt-% based on the amount of particles, preferably between 0.5-2 wt% . The wetting agent is preferably surface-active chem icals with a hydrophilic-lipophilic balance ( HLB) of 1 - 12, preferably between 2- 10 and more preferably between 3-9. The wetting agent can be an anionic, zwitter-ionic, non-ionic or cationic surfactant. The wetting agent is added in order to decrease the hydrophobicity of the particles and to make the com position easier to m ix with an aqueous solution in order to produce aqueous products.

The method according to any the preceding claims, further comprises m illing and/or sieving said hornificated particles either before or after addition of the stabilizing agent.

The method m ay include a step of actively cooling the hornificated particles after the drying step. This is done to prevent the particles from flocculating too m uch. The method may further include a step of drying the composition to a dryness level above 80% after addition of the stabilizing agent, i.e. a final drying step. This is done to provide a dry or almost dry composition that can be sold and easily transported to customer sites where re-dispersion of the composition with additional additives, chem icals, suspensions or compositions is done in order to produce the final composition. This final drying step may be done by any known drying method, preferably by thermal, radiation and/or mechanical drying e.g. spray drying, ring drying, flash drying, TurboRotor mill drying, oven drying, or a combination thereof.

The present disclosure further relates to a composition comprising hornificated particles of nanocellulose and a stabilizing agent. The stabilizing agent is preferably nanocellulose and/or a dispersant with a molecular weight above 5000g/mol. The hornificated particles of the composition preferably has an average dry particle size (D90) of 1 -2000 pm, preferably 50- 1000 pm, and more preferably 150-750 pm , most preferably 400-750 pm .

The present disclosure also relates to a composition produced according to the method mentioned herein.

The present disclosure also relates to a personal care composition comprising the composition described herein. The personal care composition may be in the form of a liquid, wherein the hornificated particles are dispersed in said liquid or in the form of a solid, wherein the hornificated particles are dispersed throughout said solid. The definition “liquid” includes sem i-liquids such as gels or creams. The personal care composition preferably comprises 0.1 -20 wt %, preferably 0.5-10 wt % of said hornificated particles. The personal care composition may also comprise one of more surfactants, or other typical additives in personal care products including rheology modifiers, humectants, pigments, etc. Examples of suitable personal care products are toothpastes, face scrubs, body scrubs, foot scrubs, and bath and shower products. As a final step, the method may include a step of formulating the hornificated particles into a personal care composition. Exfoliants are typically added into personal care products during the last formulation step under low shear.

In a further embodiment, the use of hornificated particles comprising or consisting of nanocellulose, described herein as an abrasive material in a personal care composition is provided. Other uses include a papermaking composition, a paint composition, a homecare product, pharmaceuticals or a food product. All details of the particles described above are also relevant for these uses, mutatis m utandis.

The particles according to the present invention are bio-based and biodegradable, and possess light color (white to yellowish). They are also tuneable in terms of their size, shape and hardness/abrasiveness, depending on the drying technology used, temperature of drying (drying rate), grade and initial solids content. The particles are also non-toxic and can be readily produced (upcycled) from by-products of the papermaking and forestry industries.

The particles may comprise one or more additives, which are incorporated within the hornificated particles. Suitable additives include surfactants, solvents, oils, proteins, vitamins, pharmaceuticals, pigments etc.

I n particular, the particles may comprise one or more pigments, which could be incorporated into the particles prior to drying, during the drying process or post-drying. As the particles themselves do not have a strong color, the color of any pigment will be “true”, i.e. not significantly affected by any color of the particles themselves.

Although the invention has been described with reference to a number of aspects, examples and embodiments, these aspects, examples and embodiments may be combined by the person skilled in the art, while remaining within the scope of the present invention.

Examples Example 1 - Fractionation

Highly hornificated MFC particles with a dryness level of 96% were obtained using different drying technologies, and were subsequently fractionated using a set of different sieves, with mesh sizes in the range 40-1000 pm .

Different fractions were obtained through sieving and the percentage of each fraction was determ ined gravim etrically.

Table 1 - Amount (in percentage) of the different hornificated MFC particles' fractions obtained after fractionation.

Note: FBD sam ples were m illed before fractionation

Example 2 - Hornificated MFC particles properties and stability The properties and stability of the hornificated MFC particles were assessed under different conditions.

• Light (Neons - artificial light; Obscurity - reference)

• Temperature (RT, 4°C and 45°C)

• Clim atic chamber (heat and cold cycles) The organoleptic and bacteriological properties and pH of the different samples were analyzed before testing and after 1 , 2 and 3 months under different conditions. Methods:

• Appearance - visual method, observation under natural light

• Color - visual method, observation under natural light

• Odor - Olfactive, scent

• pH -10% of dry MFC particles were dispersed in purified water and the pH of the liquid medium was measured using a pH-meter.

• Mesophilic bacteria - Culture in suitable medium, following NF ISO 21149

• Yeats and moulds - Culture in suitable medium , following NF I SO 16212

All organoleptic and bacterial properties and pH were shown to be conform (not varying significantly with time) and, thus, the stability of the particles was validated.

Table 2 - Organoleptic and bacteriological properties, and physical characteristics of different hornificated MFC particles Exam ple 3 - Performance of hornificated MFC particles in an exfoliating foam ing gel form ulation

The biggest fraction of three different types of hornificated MFC particles was used as exfoliating agent in the form ulation of an exfoliating foam ing gel. The form ulation contained 7% of hornificated MFC particles and 1.1 % of a natural polysaccharide stabilizing agent with a

Mw of 1.850x 10 ⁶ g/mol.

The stability in suspension was assessed visually over time.

Table 3 - Stability of different hornificated MFC particles in a foaming gel formulation