WO2021124088A1

WO2021124088A1 - Foam granulation method

Info

Publication number: WO2021124088A1
Application number: PCT/IB2020/061938
Authority: WO
Inventors: Kaj Backfolk; Gisela CUNHA; Isto Heiskanen
Original assignee: Stora Enso Oyj
Priority date: 2019-12-18
Filing date: 2020-12-15
Publication date: 2021-06-24
Also published as: SE1951496A1; CA3159216A1

Abstract

The present disclosure relates to a foam granulation method comprising: a) preparing an aqueous mixture comprising nanocellulose and a foaming agent, b) foaming said mixture to obtain a foam, c) adding solid particles to said foam, d) mixing and drying said foam with added particles to obtain a granulate comprising the solid particles.

Description

FOAM GRANULATION METHOD

Technical field The present disclosure relates to methods for granulation of powdery or solid substances into larger granules.

Background

Granulation is the process of forming grains or granules from a powdery or solid substance, producing a granular material. It is applied in several technological processes in the chemical and pharmaceutical industries. Typically, granulation involves agglomeration or coating of fine particles to form larger granules, typically of size range between 0.2 and 4.0 mm depending on their subsequent use. Granulation is carried out for various reasons, one of which is to prevent the segregation of the constituents of a powder mix. Segregation is due to differences in the size or density of the components of the mix. Normally, the smaller and/or denser particles tend to concentrate at the base of the container with the larger and/or less dense ones on the top. An ideal granulation will contain all the constituents of the mix in the correct proportion in each granule and segregation of granules will not occur. Furthermore, many powders, because of their small size, irregular shape or surface characteristics, are cohesive and do not flow well. Granules produced from such a cohesive system will be larger and more isodiametric, both factors contributing to improved flow properties.

There are two main types of granulation: dry granulation and wet granulation. The main difference between dry and wet granulation is that dry granulation is the formation of granules without using any liquid solution whereas wet granulation is the formation of granules by adding a granulation liquid.

In wet granulation, granules are typically formed by the addition of a granulation liquid onto a powder bed which is under the influence of an impeller (in a high- shear granulator), screws (in a twin screw granulator) or air (in a fluidized bed granulator). The agitation resulting in the system along with the wetting of the components within the formulation results in the aggregation or coating of the primary powder particles to produce wet granules. The granulation liquid contains a liquid carrier which must be volatile so that it can be removed by drying. The liquid carrier can be either aqueous based or solvent-based. Aqueous solutions have the advantage of being safer to deal with than other solvents.

Drying of the granules drives off the liquid but a network of solid bridges and polymeric chains give strength and cohesion to the new granules. Drying and granulating particles is sometimes very difficult since it might lead to uncontrolled agglomeration and formation of lumps. Also, spray drying for example is very sensitive to clogging issues and requires low solids and low viscosity.

These problems may be even more relevant when adding functional additives such as a rheology modifier, reinforcement agent or binder. Drying and granulation of such materials might lead to loss of the performance of the additives or to the formation of very large agglomerates.

Accordingly, there is a need for improved solutions to solve the problems derived from the granulation of materials comprising additives such as a rheology modifier, reinforcement agent or binder.

Description of the invention

It is an object of the present disclosure to provide a granulation method for granulating particles with functional additives such as a rheology modifier, reinforcement agent or binder.

It is another object of the present disclosure to provide a granulation method for granulating particles with nanocellulose, which is cost efficient and requires less water than a conventional wet granulation method.

It is another object of the present disclosure to provide a granulation method for granulating particles with nanocellulose, which enables fast re-dispersion of the granulates formed. The above-mentioned objects, as well as other objects realized by the skilled person in the light of the present disclosure, are achieved by the various aspects of the present disclosure.

Foam granulation refers to a type of wet granulation, in which the granulation liquid is an aqueous foam. The liquid foam is obtained by foaming an aqueous granulation liquid comprising a foaming agent, e.g. a surfactant, and optionally other additives. Foam granulation typically requires less water than conventional wet granulation. Flowever, foam behavior is complex and additives to the foam liquid may affect foam formation and stability in ways that are difficult to predict.

The present inventors have surprisingly found that the use of a foam granulation technique solves the problems of uncontrolled agglomeration and formation of lumps when drying and granulating particles, especially in the presence of reinforcement agents or binders such as nanocellulose.

According to a first aspect illustrated herein, there is provided a foam granulation method comprising: a) preparing an aqueous mixture comprising nanocellulose and a foaming agent, b) foaming said mixture to obtain a foam, c) adding solid particles to said foam, d) mixing and drying said foam with added particles to obtain a granulate comprising the solid particles.

The term ’’foam granulation” as used herein refers to a type of wet granulation, in which the granulation liquid is in the form of an aqueous foam. The inventive method thus involves first preparing an aqueous foam comprising a mixture of nanocellulose and a foaming agent, followed by adding solid particles in said foam. The foam with added solid particles is then subjected to mixing and drying to obtain a granulate comprising the solid particles. The term foam, as used herein, refers to a substance made by trapping air or gas bubbles inside a solid or liquid. Typically, the volume of gas is much larger than that of the liquid or solid, with thin films separating gas pockets. Three requirements must be met in order for foam to form. Mechanical work is needed to increase the surface area. This can occur by agitation, dispersing a large volume of gas into a liquid, or injecting a gas into a liquid. The second requirement is that a foam forming agent, typically an amphiphilic substance, a surfactant or surface active component, must be present to decrease surface tension. Finally, the foam must form more quickly than it breaks down.

The term solid, as used herein, refers to a material that is not liquid or fluid, but firm and stable in shape. A solid is a sample of matter that retains its shape and density when not confined. The solid may be rigid, or susceptible to plastic and/or elastic deformation. The adjective solid describes the state, or condition, of matter having this property. A solid material may be porous or non-porous. Accordingly, the term solid particles refers to porous or non-porous particles in solid form.

Nanocellulose can be effectively dispersed in the liquid phase of the foam and has been found to bind to the solid particles, for example by adsorption or absorption, upon drying of the foam with added solid particles to obtain a granulate.

In some embodiments, the nanocellulose comprises cellulosic nanofibers having an average diameter in the range of 1 - 1 000 nm. The diameter may for example be determined from environmental scanning electron microscope (ESEM) or scanning electron microscope (SEM) images.

Nanocellulose comprises partly or totally fibrillated cellulose or lignocellulose fibers. The liberated fibrils or bundles of fibrils have a diameter less than 1 000 nm, whereas the actual fibril diameter or particle size distribution and/or aspect ratio (length/width) depends on the source and the manufacturing methods. The smallest fibril is called elementary fibril and has a diameter of approximately 2-4 nm (see e.g. Chinga-Carrasco, G., Cellulose fibres, nanofibrils and microfibrils:

The morphological sequence of MFC components from a plant physiology and fibre technology point of view, Nanoscale research letters 2011, 6:417), while it is common that the aggregated form of the elementary fibrils, also defined as microfibril, is the main product that is obtained when making MFC e.g. by using an extended refining process or pressure-drop disintegration process ( Fengel , D., Ultrastructural behavior of cell wall polysaccharides, Tappi J., March 1970, Vo! 53, No. 3). Depending on the source and the manufacturing process, the length of the fibrils can vary from around 1 to more than 10 micrometers. A coarse nanocellulose grade might contain a substantial fraction of fibrillated fibers, i.e. protruding fibrils from the tracheid (cellulose fiber), and with a certain amount of fibrils liberated from the tracheid (cellulose fiber).

There are different synonyms for nanocellulose such as cellulose microfibrils, fibrillated cellulose, nanofibrillated cellulose (NFC), fibril aggregates, nanoscale cellulose fibrils, cellulose nanofibers, cellulose nanofibrils, nanocrystalline cellulose, cellulose microfibers, cellulose fibrils, cellulose nanofilaments, microfibrillar cellulose, microfibrillated cellulose (MFC), microfibril aggregrates and cellulose microfibril aggregates.

Nanocellulose can also be characterized by various physical or physical-chemical properties such as its large surface area or its ability to form a gel-like material at low solids (1-5 wt%) when dispersed in water. The cellulose fiber is preferably fibrillated to such an extent that the final specific surface area of the formed nanocellulose is from about 1 to about 500 m²/g, such as from about 1 to about 200 m²/g, or more preferably 50-200 m²/g when determined for a solvent exchanged and freeze-dried material with the BET method.

Various methods exist to make nanocellulose, such as single or multiple pass refining, pre-hydrolysis or enzymatic treatment followed by refining or high shear disintegration or liberation of fibrils.

One or several pre-treatment steps are usually required in order to make nanocellulose manufacturing both energy efficient and sustainable. The cellulose fibers of the pulp to be utilized may thus be pre-treated, for example enzymatically or chemically, for example to hydrolyse or swell the fibers or to reduce the quantity of hemicellulose 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 original or native cellulose. Such groups include, among others, carboxymethyl (CM), aldehyde and/or carboxyl groups (cellulose obtained by N-oxyl mediated oxidation, for example "TEMPO"), quaternary ammonium (cationic cellulose) or phosphoryl groups. After being modified or oxidized in one of the above-described methods, it is easier to disintegrate the fibers into nanocellulose or nanofibrillar size fibrils.

The nanocellulose may contain some hemicelluloses, the amount of which is dependent on the plant source and the pulping and bleaching process. Mechanical disintegration of the fibers is carried out with suitable equipment such as a refiner, grinder, homogenizer, colloider, friction grinder, single- or twin-screw extruder, ultrasound sonicator, fluidizer such as microfluidizer, macrofluidizer orfluidizer- type homogenizer. Depending on the nanocellulose manufacturing method, the product might also contain fines, or nanocrystalline cellulose. The product might also contain various amounts of micron size fiber particles that have not been efficiently fibrillated.

Nanocellulose can be produced from wood cellulose fibers, both from hardwood and softwood fibers. It can also be made from microbial 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, chemical and/or thermomechanical pulps. It can also be made from broke or recycled paper. The term nanocellulose includes parenchymal nanocellulose and BNC (bacterial nanocellulose). Nanocellulose can also be obtained from vegetable fibers, e.g. sugar beet or potato based nanocellulose.

The above described definition of nanocellulose includes, but is not limited to, the definition of nanocellulose in the ISO/TS 20477:2017 standard.

The nanocellulose of the aqueous mixture may be unmodified nanocellulose or chemically modified nanocellulose, or a mixture thereof. In some embodiments, the nanocellulose is an unmodified nanocellulose. Unmodified nanocellulose refers to nanocellulose made of unmodified or native cellulose fibers. The unmodified nanocellulose may be a single type of nanocellulose, or it can comprise a mixture of two or more types of nanocellulose, differing e.g. in the choice of cellulose raw material or manufacturing method.

Chemically modified nanocellulose refers to nanocellulose made of cellulose fibers that have undergone chemical modification before, during or after fibrillation. In some embodiments, the nanocellulose is a chemically modified nanocellulose. The chemically modified nanocellulose may be a single type of chemically modified nanocellulose, or it can comprise a mixture of two or more types of chemically modified nanocellulose, differing e.g. in the type of chemical modification, the choice of cellulose raw material or the manufacturing method. In some embodiments, the chemically modified nanocellulose is microfibrillated dialdehyde cellulose (DA-MFC). DA-MFC is a dialdehyde cellulose treated in such way that it is microfibrillated. Dialdehyde cellulose can be obtained by oxidation of cellulose. Microfibrillated dialdehyde cellulose can be obtained by treating dialdehyde cellulose for example by a homogenizer or in any other way such that fibrillation occurs to produce microfibrillated dialdehyde cellulose.

The aqueous mixture may comprise nanocellulose and foaming agent only, or it can comprise nanocellulose and foaming agent combined with other ingredients or additives. Depending of the purpose of the granules, a lower amount of nanocellulose can be used as a foam stabilizing agent, or a higher amount of nanocellulose can be used as a functional additive in the final granules. The aqueous mixture preferably includes nanocellulose as its main component based on the total dry weight of the aqueous mixture. In some embodiments, the aqueous mixture in step a) comprises in the range of 5-99.5 wt%, preferably in the range of 30-99.5 wt%, preferably in the range of 50-99.5 wt%, preferably in the range of 60-99.5 wt%, more preferably in the range of 65-98 wt% of nanocellulose, based on the total dry weight of the aqueous mixture.

The foaming agent is a compound capable of forming and/or stabilizing a foam in an aqueous composition. The foaming agent is typically an amphiphilic substance, i.e. a chemical compound possessing both hydrophilic and hydrophobic (lipophilic) properties. A foaming agent reduces the work needed to create the foam by reducing the surface tension of the liquid and increases the colloidal stability of the foam by inhibiting coalescence of bubbles.

The foaming agent of the solid composite may be any foaming agent suitable for facilitating the formation of a foam in an aqueous nanocellulose dispersion and for stabilizing the formed foam. In other words, the foaming agent should be capable of forming a stable foam in an aqueous nanocellulose dispersion.

In some embodiments, the foaming agent is a non-ionic surfactant.

Certain polymeric foaming agents have been found to be particularly useful in the present invention. In addition to acting as foaming agents, polymeric foaming agents may also improve the stability and mechanical properties of the solid composite formed when the water of the aqueous foam has evaporated. The use of a polymeric foaming agent may therefore reduce or completely dispense with addition of an optional additional polymeric binder. Thus, in some preferred embodiments the foaming agent is a polymeric foaming agent.

The polymeric foaming agent is preferably an amphiphilic polymer, i.e. a polymer possessing both hydrophilic and hydrophobic (lipophilic) properties. In some embodiments, the at least one foaming agent is water-soluble. The polymeric foaming agent may for example be a water-soluble polymer with hydrophobic moieties, such as a hydrophilic polymeric backbone provided with hydrophobic sidechains, or a block copolymer comprised of hydrophilic and hydrophobic sections.

In some embodiments, the at least one foaming agent is selected from the group consisting of optionally hydrophobically modified polysaccharides, proteins, polyvinyl alcohol, polyvinyl acetate and mixtures thereof. The optional hydrophobic modification typically comprises one or more hydrophobic groups, e.g. alkyl groups, covalently attached to the foaming agent. In some embodiments, the at least one foaming agent is an optionally hydrophobically modified polysaccharide selected from the group consisting of optionally hydrophobically modified cellulose, starch, hemicellulose and mixtures thereof.

In some embodiments, the at least one polymeric foaming agent is an optionally hydrophobically modified polysaccharide selected from the group consisting of optionally hydrophobically modified cellulose acetate (CA), ethyl(hydroxyethyl)cellulose (EHEC), methylcellulose (MC), ethylcellulose (EC), hydroxyethylcellulose (HEC), hydroxypropylcellulose (HPC), sodium carboxymethylcellulose (CMC), hydroxypropylmethylcellulose (HPMC), sulfoethylcellulose, starch, and mixtures thereof.

In some embodiments, the at least one polymeric foaming agent is selected from the group consisting of ethyl(hydroxyethyl)cellulose, hydrophobically modified ethyl(hydroxyethyl)cellulose (HM-EHEC), hydroxyethylcellulose, hydrophobically modified hydroxyethyl cellulose (HM-HEC), methylcellulose (MC), hydrophobically modified methylcellulose (HM-MC), hydrophobically modified carboxymethylcellulose (HM-CMC), and hydrophobically modified starch (HM- starch). Examples of useful hydrophobically modified starch derivatives include, but are not limited to dialdehyde starch, hydroxypropylated starch, octenyl succinic anhydride (OSA) starch, and dodecyl succinic anhydride (DDSA) starch.

In some embodiments, the at least one polymeric foaming agent is an optionally hydrophobically modified methyl cellulose.

In some embodiments, the at least one polymeric foaming agent is a hydrophobically modified polyvinyl alcohol (PVOH), such as ethylene modified PVOH. In some embodiments, the polymeric foaming agent is a polyvinyl alcohol containing at least 2% acetate groups, more preferably at least 10% acetate groups, and even more preferably at least 15% acetate groups. The at least one polymeric foaming agent may also be a charged amphiphilic polymer. The charge may facilitate the retention of the polymer.

The at least one polymeric foaming agent may also be a mixture of different amphiphilic polymers or derivatives of the above-mentioned amphiphilic polymers.

In some embodiments, the polymeric foaming agent has a molecular weight above 5 000 g/mol, preferably above 10000 g/mol, more preferably above 25000 g/mol, and more preferably above 50000 g/mol. The molecular weight refers to the weight average molecular weight M _.

In some embodiments, the aqueous mixture in step a) comprises in the range of 0.1-80 wt%, preferably in the range of 0.5-50 wt%, preferably in the range of 0.5- 10 wt%, preferably in the range of 0.5-5 wt%, more preferably in the range of 2-5 wt% of foaming agent, based on the total dry weight of the aqueous mixture.

In some applications, such as in materials intended for contact with foodstuff, low molecular components which could potentially migrate or be leached from the material, are preferably avoided. Thus, in some embodiments the aqueous mixture and the resulting granulate is free from surface active chemicals having a molecular weight below 1 000 g/mol. Instead the foaming agent is comprised of polymeric foaming agent(s) less prone to migration or leaching.

The foaming agent may optionally be combined with one or more polymeric dispersing and/or rheology modifying agents. The inventors have found that the addition of a polymeric dispersing and/or rheology modifying agent can further improve the foam formation and the stability of the formed aqueous foam. A polymeric dispersing and/or rheology modifying agent may also improve the stability and mechanical properties of the granulate formed when the water of the aqueous foam has evaporated.

A polymeric dispersing and/or rheology modifying agent may be especially useful when the foaming agent is not a polymeric foaming agent. However, a polymeric dispersing and/or rheology modifying agent may also be useful when the foaming agent is a polymeric foaming agent, but additional modification of the foam properties is desired. The polymeric dispersing and/or rheology modifying agent may be a dispersing agent, a rheology modifying agent or a combination of both.

Examples of dispersing agents useful in the aqueous mixture include, but are not limited to, polycarboxylates such as polyacrylates or carboxylated polysaccharides, and polyphosphates, and salts, e.g. metal salts, thereof.

Examples of rheology modifying agents useful in the aqueous mixture include, but are not limited to, cellulosic polymers, starch, alginate, proteins, polyacrylates and other acrylic polymers and ethoxylated polyurethanes.

Examples of polymeric dispersing and/or rheology modifying agents useful in the aqueous mixture include, but are not limited to, polycarboxylates such as polyacrylates or carboxylated polysaccharides.

In some embodiments, the polymeric dispersing and/or rheology modifying agent is a carboxymethyl cellulose (CMC).

The concentration of the polymeric dispersing and/or rheology modifying agent is suitably selected depending on the type and molecular weight of the polymer. In some embodiments, the aqueous mixture comprises in the range of 0.1-20 wt%, preferably in the range of 0.3-10 wt%, more preferably in the range of 0.5-5 wt% of the polymeric dispersing and/or rheology modifying agent, based on the total dry weight of the aqueous mixture.

The formulation of the aqueous mixture may vary depending on the intended use for the granulate. The aqueous mixture may include a wide range of ingredients in varying quantities to improve the end performance of the granulation process or the formed granulate.

The aqueous mixture may further comprise additives such as starch, a filler, retention aids, flocculation additives, deflocculating additives, dry strength additives, softeners, humectants, antistatic agents, or mixtures thereof. In some embodiments, the aqueous mixture further comprises a polymeric binder. In some preferred embodiments, the aqueous mixture further comprises PVOH. The PVOH may be a single type of PVOH, or it can comprise a mixture of two or more types of PVOH, differing e.g. in degree of hydrolysis or viscosity. The PVOH may for example have a degree of hydrolysis in the range of 80-99 mol%, preferably in the range of 88-99 mol%. Furthermore, the PVOH may preferably have a viscosity above 5 mPaxs in a 4 % aqueous solution at 20 °C DIN 53015 / JIS K 6726.

In some embodiments, the aqueous mixture further comprises a pigment. The pigment may for example comprise inorganic particles of talcum, silicates, carbonates, alkaline earth metal carbonates and ammonium carbonate, or oxides, such as transition metal oxides and other metal oxides. The pigment may also comprise nano-size pigments such as nanoclays and nanoparticles of layered mineral silicates, for instance selected from the group comprising montmorillonite, bentonite, kaolinite, hectorite and hallyosite.

In some embodiments, the pigment is selected from the group consisting of nanoclays and nanoparticles of layered mineral silicates, more preferably bentonite.

In some embodiments, the total solid content of the aqueous mixture prior to foaming is preferably in the range of 1-50 wt%.

In some embodiments, the foaming in step b) is achieved by high speed mixing.

In some embodiments, the amount of solid particles added to the foam in step c) is above 20 wt%, preferably above 30 wt%, and more preferably above 40 wt%, based on the total weight of the foam with added particles.

In some embodiments, the amount of solid particles added to the foam in step c) is in the range of 20-95 wt%, preferably in the range of 30-90 wt%, and more preferably in the range of 40-80 wt%, based on the total weight of the foam with added particles.

In order to facilitate the granulation process, the solid particles preferably have low or zero solubility in water. More preferably, the solid low-density particles are insoluble in water at 25°C. This allows for mixing of the particles in the aqueous foam without any substantial dissolution of the particles occurring during preparation of the granulate. Low solubility in the context of this disclosure means that less than 20%, preferably less than 10%, more preferably less than 5%, most preferably less than 1%, of the dry weight of the particles is lost into solution (i.e. into the aqueous mixture) during preparation of the granulate.

The solid particles may for example comprise cork, wood, other biomass or Styrofoam. Preferably however, the particulate material is a bio-based material, such as cork, wood or other biomass. In some embodiments, the solid particles comprise a particulate material selected from the group consisting of cork particles and wood particles.

In preferred embodiments, the solid particles are bio-based and/or renewable and/or compostable particles. Using bio-based and/or renewable and/or compostable particles allows for preparation of a granulate which is based entirely or at least mainly on renewable and/or compostable materials.

In some embodiments, the solid particles are selected from the group consisting of polysaccharide, lignin and protein based particles.

In some embodiments, the solid particles are polysaccharide particles selected from the group consisting of starch, hemicellulose or cellulose based particles, or mixtures thereof.

In some embodiments, the solid particles are polysaccharide particles selected from the group consisting of hornificated cellulose beads, microcrystalline cellulose (MCC) particles, starch granules, chemically modified starch particles or chemically modified cellulose particles. In some embodiments, the solid particles comprise a superabsorbent polymer (SAP).

The solid particles may be chemically and/or physically crosslinked in order to reduce their solubility in water.

In some embodiments, the solid particles are hydrophobized.

The formation of a foam allows for low-density particles, more specifically particles having a density of less than 1 .2 kg/dm³, to be effectively dispersed in liquid mixture comprising nanocellulose and a foaming agent.

In some embodiments, the solid particles have a density of less than 1 .2 kg/dm³, preferably less than 1.0 kg/dm³, less than 0.9 kg/dm³, less than 0.8 kg/dm³, less than 0.7 kg/dm³, less than 0.6 kg/dm³, less than 0.5 kg/dm³, less than 0.4 kg/dm³, less than 0.3 kg/dm³ or less than 0.2 kg/dm³.

In some embodiments, the solid particles are porous particles. Porous particles may be of particular interest for their low weight and thermal insulation properties. The porous particles may comprise closed pores, open pores, or a combination of closed and open pores. In some embodiments, the solid particles are porous with closed pores or have a combination of closed pores and open pores. In some embodiments, the solid particles have a specific surface area above 50 m²/g, preferably above 70 m²/g, and more preferably above 100 m²/g.

The average particle size can be analyzed using an air-jet sieve analyzer. Results are then presented as a particle-size distribution and as the particle size at which 50 wt% of the particles were below the given size denoted as the median particle diameter, or d50.

In some embodiments, the solid particles have a d50 average particle size in the range of 5 - 10 000 pm, preferably in the range of 5 - 1 000 pm, preferably in the range of 5 - 800 pm, and more preferably in the range of 5 - 600 pm. In some embodiments, the total solid content of the foam with added particles before drying is at least 30 wt%, preferably at least 40 wt%, and more preferably at least 50 wt%.

In some embodiments, the drying in step d) is performed at a temperature below 240 °C, preferably below 220 °C and more preferably below 200 °C.

In some embodiments, the drying in step d) is performed at a temperature in the range of 40-180 °C, preferably in the range of 60-160 °C.

In some embodiments, the drying in step d) is performed until the total solid content of the granulate is at least 50 wt%, at least 60 wt%, at least 70 wt%, at least 80 wt%, at least 90 wt%, at least 95 wt%, or at least 99 wt%.

In some embodiments, the granulate is further subjected to milling, pulverization, micronization, size classification, screening, and/or blending.

The granulate may also be subjected to further processing, such as compacting, briquetting or pelletizing, to bring it into a suitable form for further use.

According to a second aspect illustrated herein, there is provided a granulate obtainable by the foam granulation method according to the first aspect.

According to another aspect illustrated herein, there is provided a granulate obtained by the foam granulation method according to the first aspect.

The granulate may advantageously be used in pharmaceuticals, food, personal and home care such as cosmetics, composites, papermaking and packaging.

While the invention has been described with reference to various exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims

1. Foam granulation method comprising: a) preparing an aqueous mixture comprising nanocellulose and a foaming agent, b) foaming said mixture to obtain a foam, c) adding solid particles to said foam, d) mixing and drying said foam with added particles to obtain a granulate comprising the solid particles.

2. The method according to claim 1, wherein said nanocellulose comprises cellulosic nanofibers having an average diameter in the range of 1-1000 nm.

3. The method according to claim any one of the preceding claims, wherein the aqueous mixture in step a) comprises in the range of 5-99.5 wt%, preferably in the range of 30-99.5 wt%, preferably in the range of 50-99.5 wt%, preferably in the range of 60-99.5 wt%, more preferably in the range of 65-98 wt% of nanocellulose, based on the total dry weight of the aqueous mixture.

4. The method according to any one of the preceding claims, wherein the at least one foaming agent is a polymeric foaming agent.

5. The method according to any one of the preceding claims, wherein the at least one foaming agent is an amphiphilic polymer.

6. The method according to any one of the preceding claims, wherein the at least one foaming agent is selected from the group consisting of optionally hydrophobically modified polysaccharides, proteins, polyvinyl alcohol, polyvinyl acetate and mixtures thereof.

7. The method according to any one of the preceding claims, wherein the at least one foaming agent is an optionally hydrophobically modified polysaccharide selected from the group consisting of cellulose, starch, hemicellulose and mixtures thereof.

8. The method according to any one of the preceding claims, wherein the at least one foaming agent is an optionally hydrophobically modified polysaccharide selected from the group consisting of optionally hydrophobically modified cellulose acetate (CA), ethyl(hydroxyethyl)cellulose (EHEC), methylcellulose (MC), ethylcellulose (EC), hydroxyethylcellulose (HEC), hydroxypropylcellulose (HPC), sodium carboxymethylcellulose (CMC), hydroxypropylmethylcellulose (HPMC), sulfoethylcellulose, starch, and mixtures thereof.

9. The method according to any one of the preceding claims, wherein the at least one foaming agent is an optionally hydrophobically modified methyl cellulose.

10. The method according to any one of the preceding claims, wherein the foaming agent has a molecular weight above 5000 g/mol, preferably above 10 000 g/mol.

11. The method according to any one of the preceding claims, wherein the aqueous mixture in step a) comprises in the range of 0.1-80 wt%, preferably in the range of 0.5-50 wt%, preferably in the range of 0.5-10 wt%, preferably in the range of 0.5-5 wt%, more preferably in the range of 2-5 wt% of foaming agent, based on the total dry weight of the aqueous mixture.

12. The method according to any one of the preceding claims, wherein the granulate is free from surface active chemicals having a molecular weight below 1 000 g/mol.

13. The method according to any one of the preceding claims, wherein the aqueous mixture in step a) further comprises a polymeric binder.

14. The method according to any one of the preceding claims, wherein the amount of solid particles added in step c) is above 20 wt%, preferably above 30 wt%, and more preferably above 40 wt%, based on the total weight of the foam with added particles.

15. The method according to any one of the preceding claims, wherein the solid particles have a d50 average particle size in the range of 5 - 10000 pm, preferably in the range of 5 - 1 000 pm, preferably in the range of 5 - 800 pm, and more preferably in the range of 5 - 600 pm.

16. The method according to any one of the preceding claims, wherein the solid particles have low or zero solubility in water.

17. The method according to any one of the preceding claims, wherein the solid particles are bio-based and/or renewable and/or compostable particles.

18. The method according to any one of the preceding claims, wherein the solid particles are selected from the group consisting of polysaccharide, lignin and protein based particles.

19. The method according to claim 18, wherein the solid particles are polysaccharide particles selected from the group consisting of starch, hemicellulose or cellulose based particles, or mixtures thereof.

20. The method according to claim 19, wherein the solid particles are polysaccharide particles selected from the group consisting of hornificated cellulose beads, microcrystalline cellulose (MCC) particles, starch granules, chemically modified starch particles and chemically modified cellulose particles.

21. The method according to any one of the preceding claims, wherein the solid particles are porous particles.

22. The method according to any one of the preceding claims, wherein the solid particles have a density of less than 1.2 kg/dm³, preferably less than 1.0 kg/dm³, less than 0.8 kg/dm³, less than 0.6 kg/dm³, or less than 0.4 kg/dm³.

23. The method according to any one of the preceding claims, wherein the total solid content of the foam with added particles before drying is at least 30 wt%, preferably at least 40 wt%, and more preferably at least 50 wt%.

24. The method according to any one of the preceding claims, wherein the drying in step d) is performed at a temperature below 240 °C, preferably below

220 °C and more preferably below 200 °C.

25. The method according to any one of the preceding claims, wherein the drying in step d) is performed at a temperature in the range of 40-180 °C, preferably in the range of 60-160 °C.

26. The method according to any one of the preceding claims, wherein the drying in step d) is performed until the total solid content of the granulate is at least 50 wt%, at least 60 wt%, at least 70 wt%, at least 80 wt%, at least 90 wt%, at least 95 wt%, or at least 99 wt%.

27. A granulate obtainable by the foam granulation method according to any one of the preceding claims.