WO2018009113A1 - Lotion comprising an emulsion - Google Patents

Abstract

It is disclosed a skin treatment composition comprising an emulsion, which comprises a continuous phase and a dispersed phase. The continuous phase comprises cellulose derivatives (CD), and nanocellulose, preferably cellulose nanocrystals (CNC), and a carrier, and the dispersed phase is an oil containing composition. Said emulsion forms a solid emulsion upon drying, said solid emulsion comprising a matrix of solid continuous phase and a dispersed oil phase.

Description

LOTION COMPRISING AN EMULSION TECHNICAL FIELD

The present disclosure relates to skin treatment composition comprising an emulsion. BACKGROUND Lotions, creams and the like are often used in treatment the human or animal skin, where skin treating agents are readily applied to the skin. Lotions, creams and the like can be divided into two types: oil-in-water emulsions, which are composed of small droplets of oil dispersed in a continuous phase, and water-in-oil emulsions, which are composed of small droplets of water dispersed in a continuous oily phase. Oil-in-water emulsions are comfortable as they are less greasy. Water-in-oil emulsions are more difficult to handle but can be more moisturizing as they provide an oily barrier which reduces water loss from the stratum corneum, the outermost layer of the skin. Repeated application of lotion or cream may be necessary, in order to maintain skin moisture and softness, or other desired skin properties, and different types of lotions or creams may be needed to obtain the desired result. SUMMARY

The present disclosure relates to a skin treatment composition comprising an emulsion, which comprises a continuous phase and a dispersed phase, wherein the continuous phase comprises cellulose derivatives (CD) and nanocellulose, preferably cellulose nanocrystals (CNC), and a carrier, and the dispersed phase is an oil containing composition. Said emulsion forms a solid emulsion upon drying, wherein said solid emulsion comprising a matrix of solid continuous phase and a dispersed oil phase. The cellulose derivatives (CD) are preferably chosen from carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), ethyl hydroxyethyl cellulose (EHEC), or hydroxylpropyl methyl cellulose (HPMC), more preferably CMC or HEC, or combinations of two or more of these cellulose derivatives. The continuous phase of the emulsion preferably comprises 0,5-50 wt% cellulose nanocrystals (CNC), more preferably 3-40 wt%, most preferably 10-30 wt%, based on the weight of cellulose derivatives (CD) comprised in the aqueous continuous phase. The carrier is preferably water or an alcohol, such as ethanol or isopropylalcohol, or combinations thereof. The emulsion preferably comprises 0,1-20 wt% cellulose derivatives (CD) based on the total weight of the emulsion, preferably 0,5-10 wt%, and the weight ratio of the dispersed oil phase to the dry content in the continuous phase of the solid emulsion is preferably 20:80 -99:1 wt/wt.

Release of the dispersed oil phase skin treatment composition is preferably initiated, when a pressure above a critical pressure value is applied to the solid emulsion, wherein the critical pressure value preferably is 0,1 kPa. The skin treatment composition comprises one or more active agents chosen from: skin care agents, odour control agents, antibacterial agents, lubrication agents, enzyme inhibiting agents, surfactants/detergents, medical compositions, pH controlling agents and barrier agents. The continuous phase of the skin treatment composition may advantageously comprise skin care agents, or one or more barrier agent.

Further, the continuous phase and/or the dispersed phase may preferably comprise one or more of anionic, cationic nonionic or zwitterionic surfactants or combination thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 schematica lly illustrates cellulose derivatized into hydroxyethyl cellulose;

Fig. 2 is a schematic illustration of the process of making a solid emulsion through solvent casting of the continuous phase;

Fig. 3 illustrates the magnitude of the initial backscattered light of emulsions with given composition of CDs and CNCs with a dodecane content of 25% wt;

Fig. 4 illustrates the deduced character of emulsions droplets with different CDs;

Fig. 5 shows the compressive stress vs strain relation of solid emulsions made with 0.5% CNCs and four different CDs (2.0%);

Fig. 6 shows the relation between compressive strain and relative mass loss due to compression in solid emulsions made with 2.0% of given CD and 0.5% CNCs;

Fig. 7 shows stress-strain curves for tested emulsion;

Fig. 8 shows mass loss as a function of compressive strain for tested emulsion; Fig. 9 shows the compressive stress vs strain relation for the same type of solid emulsion (2.0% CMC 0.5% CNCs;

Fig. 10 shows CLSM microgra phs of solid emulsions made with 2.5% CMC and 2.0% CMC + 0.5% CNC;

Fig. 11 shows CLSM micrographs of solid emulsions made with 2.0% H EC + 0.5% CNC and 2.0% EH EC + 0.5% CNC;

Fig. 12 shows the cell diameter distribution for solid emulsions with EHEC/CNC and HEC/CNC;

Fig. 13 shows the absorbance of CNC-CMC mixtures as a function of amount of CMC, expressed as mass fraction CMC; Fig. 14 shows the absorbance of CNC-HPMC mixtures at 400 nm as a function of a mount of HPMC, expressed as mass fraction CMC;

Fig. 15 is an illustration of the two possible characteristics of the solid contents in solid emulsions; Fig. 16 is an illustration of hypothetical behavior of solid emulsions with varying CNC/CD-ratio;

Fig. 17a is an ESEM image of a solid emulsion specimen;

Fig. 17b is an enlargement of the center portion of Fig. 17a;

Fig. 17c is an ESEM image of the same specimen as in Fig. 17a after compression;

Fig. 18 is an ESEM image of a foamed emulsion specimen; Fig. 19a-c are ESEM images of a PP nonwoven treated with emulsion;

Fig. 20 is an ESEM image of a PET nonwoven treated with emulsion;

Fig. 21a is an ESEM image of a PUR foam treated with emulsion;

Fig. 21b is an enlargement of a portion of Fig. 21a;.

Fig. 22 is an ESEM image of a tissue treated with emulsion; Fig. 23a-b are ESEM images of a tissue nonwoven treated with emulsion;

Fig. 24 in an ESEM image of a PP nonwoven treated with excess of emulsion.

DETAILED DESCRIPTION

The present disclosure relates to a skin treatment composition, which may be in the form of a lotion, a cream, or gel. All these forms can be applied to the external skin, stratum corneum, of the user. A lotion is typically referred to as a low-viscosity topical preparation intended for application to the skin, whereas creams and gels have higher viscosity. The skin treatment composition can be applied to external skin with bare hands, or by an applicator, such as a brush, cloth, or cotton pad. Encapsulating liquid oil in solid cellulose derivative polymer matrices can be made by forming an oil-in-water emulsion stabilized by cellulose nanocrystals with the water soluble derivative in the continuous phase. The polymer will then form a solid matrix upon drying of the emulsion, in which the liquid oil remains encapsulated. The resulting system is commonly referred to as a solid emulsion or dry emulsions and the general technology associated with the production of this and other types of emulsion-originated materials is called emulsion- templating. Materials produced via this method are inherently influenced by the

characteristics of the original emulsion which can be varied by many means, such as choice of dispersed and continuous phase, type of emulsifier and stabilizer and also processing and preparation method of the original emulsion.

The emulsions can be in the form of a lotion can be used as barrier creams, skin lotions or gels, lotions for wet wipes and lotion templates for wet wipe lotions when they are deposited on the substrate and re-dispersed with the addition of water.

The skin treatment composition comprises an emulsion, comprising a continuous phase and a dispersed phase, where the continuous phase comprises cellulose derivatives (CD), and nanocellulose, preferably, cellulose nanocrystals (CNC), and a carrier, and the dispersed phase is an oil containing composition. Generally, a suitable emulsion is formed according to the current disclosure by firstly dissolving at least one polymeric cellulose derivative (referred to herein as "cellulose derivative", such as HPMC) in water. It will be understood that by "water" it is meant a substantially aqueous system where very small amounts of impurities (for example other water miscible solvents) may be present. In some alternative aspects, alternative water-soluble polymers may be used instead of a polymeric cellulose derivative. Suitable alternative water soluble polymers include synthetic polymers as well as those derived from natural materials. One example of a suitable alternative water soluble polymer is polyvinyl alcohol, PVA. Suitable properties of such alternative polymers may be those described below for cellulose derivatives. The skin treatment composition forms a solid emulsion upon drying, whereby a solid emulsion comprising a matrix of solid continuous phase and a liquid dispersed oil phase is formed on the skin of the user. The oil containing composition is in the form of droplet dispersed in the continuous phase.

The nanocellulose stabilizes the matrix of solid continuous phase around the droplets of oil containing composition, so that it can resist compressive pressure to a certain extent, which is explained in more detail below. Thereby, the skin treatment composition can be applied to the skin, while keeping the oil composition droplets intact, and when the droplets are subjected to compressive pressure at a later stage, the continuous sold matrix gradually ruptures, and the oil containing composition is released. The present skin treatment composition can thus have a dual function, in that it initially provides moisturizing due to the application of the hydrophilic continuous phase, and later on releases the hydrophobic oil containing

composition, which can include various one or more active agents, as described in more detail below. The solid emulsion can also function as a barrier layer on the skin.

Nanocellulose can be microfibrillated cellulose (MFC) or cellulose nanocrystals (CNC). The carrier is a hydrophilic substance or composition, preferably water or an alcohol, such as ethanol or isopropylalcohol, or combinations thereof. By drying is meant that any liquid in the carrier contained in the continuous phase has evaporated to such an extent that the liquid/moisture content in the continuous phase is in equilibrium with the ambient air.

Typically, 50-100 wt% of the liquid originally in the carrier has evaporated when the continuous phase of the emulsion has formed a solid matrix. When the continuous phase has dried and become solid, it can still allow skin moisture to pass, due to its hydrophilic character.

The skin treatment composition cellulose derivatives (CD) are preferably chosen from, but not limited to, carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), ethyl hydroxyethyl cellulose (EHEC), or hydroxylpropyl methyl cellulose (HPMC), preferably CMC or HEC, or combinations of two or more of these cellulose derivatives. The continuous phase of the emulsion preferably comprises 0,5-50 wt% cellulose nanocrystals (CNC), more preferably 3-40 wt%, and most preferably 10-30 wt%, based on the weight of cellulose derivatives (CD) comprised in the aqueous continuous phase.

The emulsion preferably comprises 0,1-20 wt% cellulose derivatives (CD) based on the total weight of the emulsion, more preferably 0,5-10 wt%. The properties of the skin treatment composition can be adjusted by combining different CDs as desired. Further, the weight ratio of the dispersed oil phase to the dry content in the continuous phase of the solid emulsion is preferably 20:80 -99:1 wt/wt.

The release of the dispersed oil phase is initiated, when a pressure above a critical pressure value is applied to the solid emulsion, which critical pressure value preferably is 0,1 kPa. The critical pressure value for the solid emulsion can be adjusted according to the requirements for the intended application by selecting combinations of CDs as appropriate. Release of the oil containing composition of the dispersed oil phase is initiated when a pressure above a critical pressure value is applied to the solid emulsion comprised in the article. The critical pressure value is preferably 0,1 kPa, more preferably within the range of 0,5kPa - 1 MPa. The critical pressure value for the solid emulsion can be adjusted according to the requirements for the type of hygiene article by selecting combinations of CDs as appropriate is dependent on product, structure and use of product and several other parameters. The pressure applied during use is normally approximately 2,5kPa-10kPa for baby diapers, 2,5kPa-100kPa for incontinence guards, and 2,5kPa-50kPa for wipes, such as tissue handkerchiefs. As a complementary note it is realized that the critical pressure can also be reached by application of friction and/or shear forces, which is considered to be within the capacity of a man with ordinary skills in the art and not described further in detail here.

As mentioned above the skin treatment composition preferably comprises an oil containing composition comprising one or more active agents chosen from, but not limited to: skin care agents, odour control agents, antibacterial agents, lubrication agents, , enzyme inhibiting I agents, pH controlling agents, oil soluble surfactants/detergents, medical compositions.

The oil containing composition of the liquid dispersed phase preferably comprises one or more active agents, such as, but not limited to, skin care agents, odour control agents, antibacterial agents, wettability agents, detection agents, indication agents, lubrication agents, agents contributing to mechanical properties of the absorbent product, enzyme inhibiting agents, pH controlling agents.

Skin care agents comprised in the emulsion, preferably the oil containing phase can include lipids (including but not limited to fats, oils, waxes), solvents (including but not limited to water), water-soluble substances, surface-active agents (including but not limited to emulsifiers, surfactants), viscosity-regulating substances, pH-regulating substances, preserving agents, complexing agents (e. g. chelate), delivery systems (e. g. liposomes, microcapsules, etc.), pigments, perfumes, and active substances (including pharmaceutical agents). The lipids are usually emulsified in water, known as oil/water emulsion, or water is emulsified in the lipid phase, known as water/oil emulsion.

Lipid skin care agents can be paraffins (alkanes) with 12-35 carbons, such as, but not limited to, paraffin oil (mineral oil) or petrolatum (e.g., VASELINE^®).

Other examples of suitable lipid skin care agents are triglycerides, which may be refined and/or hydrogenated, of animal or vegetable origin, preferably with carbon chain lengths C-18 or less, such as, but not limited to milk fat, coconut oil (Cocous nocifera), palm-kernel oil (Elaeis guineeis), or caprylic triglycerid; animal or vegetable lipids with unsaturated C-18 fatty acids, such as, but not limited to, Japan wax (Rhus succesdanes), tallow fat, soybean oil (Glycerin soya), peanut oil (Arachais hypogaea), maize oil (Zea mays), sunflower oil (Helanthus annus), grapeseed oil (Vitis vinifera), safflower oil (Carthamus tinctorius), sweet almond oil (Prunnus amygdalus dulcis), hazelnut oil (Corylus americana), walnut oil (Juglans regia), olive oil (Olea europasa), avocado oil (Persea gratissima), sesame oil (Sesamum indicum), cottonseed oil (Gopssypium), palm oil (Elaesis guineensis), rice oil (Oryza sativa), rape oil (Canola), apricot-kernel oil (Prunus armeniaca), cocoa butter (Theobroma cao), shea butter (Butyrospermum parkii), wheatseed oil (Triticum vulgare), or Bassia latifola oil; or animal or vegetable lipids with carbon chains over C-18, such as, but not limited to, beeswax Cera alba), seed oil (Limnanthes alba), rapeseed oil (Brassica capmestris), cucumberseed oil (Borago officinalis), linseed oil (Linum usitatissimum), ricin oil (Ricinus communis), veronia oil (Veronia galamensis), jojoba oil (Buxus chinensis), candlewax (Euphorbia cera), or ongokea oil (Ongokea gore).

The skin care agents may also be fatty alcohols with straight or branched carbon chain lengths of 12-32 carbons, for example, cetyl alcohol, stearyl alcohol or a mixture thereof, or fatty acid esters with 12-32 carbons, for example, methyl palmitate, methyl stearate, isopropyl myristate, isopropyl laurate, isopropyl palmitate, isopropyl stearate, octyl palmitate, octyl stearate or octyl laurate.

The skin care agents may also be polyalcohols, for example sugar alcohols or polyglycerols. The skin care agents may also be complex lipids, for example, phospholipids or sphingolipids (ceramides); or waxes, for example of animal origin, for example beeswax or lanolin, or of vegetable origin, for example carnauba or candelilla, or of mineral origin, for example ozocerite or ceresin. The skin care agents may also be polysiloxanes, which may be straight, branched or cyclic. Examples are polydimethyl-siloxane (dimethicone) or polydiethylsiloxane.

Skin care agents can include emulsions, such as, but not limited to, emulsions of one or more fat, with hydrophilic substances, such as, but not limited to, water, glycerol, polyethylene glycol (PEG), propylene glycol, butylene glycol, sorbitol, silicone glycols, or the like, or mixtures thereof.

The skin care agents can include pH-regulating additives, for example organic or inorganic acids, such as, but not limited to, adipic acid, ascorbic acid, benzoic acid, citric acid, malic acid, tartaric acid, lactic acid, phosphoric acid, or hydrochloric acid; or buffers, made for example from said acids with their corresponding salts. The skin care agents can also include polymeric acids, for example polyphosphoric acid or polyacrylic acid. The skin care agents can also include alkaline substances such as ammonium hydroxide or calcium carbonate.

Skin care agents can also include additions of probiotic microorganisms, characterized by being antagonistic towards undesired microorganisms, e. g. skin infection pathogens.

Examples of probiotic microorganisms which can be used are individual strains or mixtures of several strains of lactic acid bacteria taken from the species Lactobacillus acidophilus,

Lactobacillus curvatus, Lactobacillus plantarum or Lactococis lactis.

Skin care agents can also include active substances, such as, but not limited to, antiinflammatory agents, e. g. acetylsalicylic acid, allantoin, azulen, alpha- bisabolol (chamomile), flavonoids, glycyrrhizinic acid, ichthammol (Inotyol)), tannins, or astringents (vasoconstrictors), for example TiO, ZnO (and other Zn compounds), aluminum acetate solution, aluminum tartrate solution (and other Al compounds), ethanol or ethanol-based solutions.

Skin care agents can also include nourishing agents such as, but not limited to, Aloe vera (Aloe barbadensis), alpha-hydroxy acids, for example citric acid, tartaric acid, lactic acid, malic acid, etc.; or algae extract, ascorbic acid (vitamin C), or vitamin A compounds, for example retinol, retinal, tretinoin and isotretinoin, or avocado sterols, betaine (trimethylglycine), ceramides, grapeseed extract, essential fatty acids, flavonoids, phytosphingosine, phytosterols, hyaluronic acid, yeast extract, chitosan, milk protein (Lactis proteinum), pantenol (provitamin B5), polysaccharides, rosemary extract, tocopherol (vitamin E), ubiquinone (coenzyme Q10), urea.

Skin care agents can also include calendula officinalis flower extract, mannitol, ammonium glycyrrhizate, caffeine, zinc gluconate, aesculus hippocastanum extract, tocopheryl acetate. Skin care agents can also consist of ready-made mixtures of skin ointments, creams and lotions, for example, TENA Skin Cream, which include the ingredients: Aqua, Canola Oil, Glycerin, Ethylhexyl Stearate, Glyceryl Stearates, Zea Mays Oil,Polyglyceryl-3 Methylglucose Distearate, Cetearyl Alcohol, Dicaprylyl Carbonate, Hydrogenated Coco-Glycerides, Panthenol, Tocopheryl Acetate, Hydroxyethyl Acrylate/Sodium Acryloyldimethyl Taurate Copolymer,

Betaine, Parfum, Xanthan Gum, Sodium Citrate, Phenoxyethanol, Benzoic Acid, Dehydroacetic Acid, Tocopherol, Citric Acid, Sorbitan Isostearate, Polysorbate 60, Pantolactone; or TENA Skin Cream Perfume free which include the ingredients; Aqua, Canola Oil, Glycerin, Ethylhexyl Stearate, Glyceryl Stearates, Zea Mays Oil,Polyglyceryl-3 Methylglucose Distearate, Cetearyl Alcohol, Dicaprylyl Carbonate, Hydrogenated Coco-Glycerides, Panthenol, Tocopheryl Acetate, Hydroxyethyl Acrylate/Sodium Acryloyldimethyl Taurate Copolymer, Betaine, Xanthan Gum, Sodium Citrate, Phenoxyethanol, Benzoic Acid, Dehydroacetic Acid, Tocopherol, Citric Acid, Sorbitan Isostearate, Polysorbate 60, Pantolactone; or TENA Skin Lotion, which include the ingredients: Aqua, Dicaprylyl Carbonate, Polyglyceryl-3 Methylglucose Distearate, Ethylhexyl Stearate, Glycerin, Glyceryl Stearates , Canola Oil, Cetearyl Alcohol, Tocopheryl Acetate, Hydroxyethyl Acrylate/Sodium Acryloyldimethyl Taurate Copolymer, Panthenol, Parfum, Xanthan Gum, Sodium Citrate, Phenoxyethanol, Benzoic Acid, Dehydroacetic Acid,

Tetrasodium Iminodisuccinate, Tocopherol, Citric Acid, Sorbitan Isostearate, Polysorbate 60, Pantolactone. TENA products are sold commercially by SCA Hygiene Products, Gothenburg, Sweden.

It should be noted that this disclosure is not limited to the skincare agents mentioned above, and that instead these are just examples of skincare agents that could be used.

Odour control agents that can be of use within the scope of the present disclosure include bacteria growth inhibitors and/or moisture-insensitive odour inhibitors. Bacteria growth inhibitors can include, but are not limited to, one or more inhibitors selected from the group that includes: chlorhexidine, quaternary ammonium compounds, cupric salts, silver and silver salts, chelating agents, parabens, e.g. methyl, ethyl, or propyl parabens, chitin, and pH buffered materials.

Other active agents that can be comprised in the oil containing composition are antibacterial agents; such as Barberry, Blueberry, Burdock, Cinnamon, Chamomile, Cranbarry, Dill,

Eucalyptus, Oak, Olive oil. Furthermore, other active agents are suitably wettability agents, such as nonionic, cationic, anionic and zwitterionic surfactants or surface active polymers; detection and indication agents, such as halochromic dyes, alizarin, Phenol Red, Bromothymol Blue or Cresol Red; agents contributing to mechanical properties of the absorbent product, lubricating agents such as fatty acids, dimethicone, triglyceride, fatty esters or fatty alcohols; enzyme inhibiting agents such as potato extract and zinksalizylate; pH controlling agents, organic acids such as lactic acid, citric acid, also inorganic acids or alkaline substances such as ammonium hydroxide or calcium carbonate. When the skin treatment composition is in the form of a lotion, it typically has a viscosity below 30000 cP at 5 rpm and 25°C , whereas it typically has a viscosity above 30000 cP at 5 rpm and 25°C when in the form of a cream, and 10000-70000 cP at 5 rpm and 25°C when in the form of a gel. As skin lotions, creams or gels, the liquid dispersed phase could carry active ingredients and the polymeric continuous phase would fort instance provide a cooling or soothing effect due to the prolonged evaporation rate of the water or other carrier present in the continuous phase. The lotions or gels would also be able to form the protective deposits on skin as for the example above. A cleansing effect could also be attained if oil soluble surfactants/detergents would be dissolved in the liquid dispersed oil phase. The skin treatment composition may be applied on a fibrous layer, so as to form a wet wipe. For wet wipe lotions, all examples mentioned above would be applicable. The wet wipe may be packaged in a liquid impermeable wrapping so as to prevent premature drying, or it can be provided in dry form, i.e. allowing the emulsion to dry and form a solid emulsion. The additional benefit is that the dry solid emulsion deposited on a substrate allows the user to re- emulsify/re-disperse the solid emulsion on the substrate and take advantage of the wet form when adding water, at a point in time decided by the user. The wipe may comprise one or more layers, and the solid emulsion may then be present in an amount of 0.01-20 g/m2 of a layer in the product. The wipe may further comprise one or more intermediate layers, arranged between first and second outer layers, and wherein the solid emulsion is present in one or more of the intermediate layers. Examples of wipe product, in which the emulsion can be incorporated, include but are not limited to dry wipes, such as facial wipes, dry baby wipes, cleaning wipes, dust cloths, or tissue products, such as kitchen paper, paper towels, or table napkins. The oil containing composition of the dispersed oil phase will typically be released when the wipe is squeezed by the hand of the user.

The solid continuous phase of the solid emulsion is hydrophilic and liquid permeable. The oil containing composition of the dispersed phase is hydrophobic, and is preferably defined by a required HLB (hydrophilic-lipophilic balance) value of oil/water emulsion of 6-17. A

hydrophilic substance has an affinity for water; readily absorbing or dissolving in water, and a hydrophobic substance lacks affinity for water; tending to repel and not absorb water;

tending not to dissolve in or mix with or be wetted by water. The contact angle (Θ) is the angle at which the liquid-vapor interface meets the solid-liquid interface. The contact angle is determined by the result between adhesive and cohesive forces. As the tendency of a drop to spread out over a flat, solid surface increases, the contact angle decreases. Thus, the contact angle provides an inverse measure of wettability. A contact angle less than 90° (low contact angle) usually indicates that wetting of the surface is very favorable, and the fluid will spread over a large area of the surface. Contact angles greater than 90° (high contact angle) generally means that wetting of the surface is unfavorable, so the fluid will minimize contact with the surface and form a compact liquid droplet. For water, a wettable surface may also be termed hydrophilic and a non-wettable surface hydrophobic. Table 1 describes varying contact angles and their corresponding solid/liquid and liquid/liquid interactions. Table 1

A material that is homogeneous gives a contact angle, whereas the same material in porous form gives a different contact angle. The contact angle of a fiber or fiber network (nonwoven web) can be measured. The hydrophilic-lipophilic balance of a surfactant is a measure of the degree to which it is hydrophilic or lipophilic, determined by calculating values for the different regions of the molecule. Methods for doing this are available in the art. CNCs function is to aid in the emulsification of the oil within the cellulose derivative polymer matrix, and to provide the matrix with mechanical strength and inherently enhanced encapsulation properties once it has solidified. The enhanced mechanical properties of the solid emulsions is partly influenced by the mechanical properties of the CNCs, which have been found to be within range of other commercial reinforcing agents, such as kevlar, carbon fibers, steel wires and boron nanowhiskers.

Cellulose is a linear homopolymer consisting of -l,4-linked anhydroglucose as the repeating unit, where the individual anhydroglucose units are linked through an oxygen in a β -1,4 configuration. The amount of repeating units varies between 10000 and 15000, depending on the source of the cellulose. The relatively large amount of hydrogen and oxygen present in the polymer renders intermolecular aggregates stable in the sense that both intra- and intermolecular forces gets reinforced by extensive and complex hydrogen bonding. This chemistry also results in characteristic hierarchical structure of cellulose containing materials where cellulose chains packs in sheets and form highly crystalline assemblies known as elementary fibrils. These elementary fibrils further make up the structure of microfibrils which are characterized by multiple elementary fibrils connected through amorphous segments of cellulose.

Ce l l u l ose N a nocrysta ls ( CN C) can be isolated through hydrolysis of the amorphous regions on the microfibrils by using various strong acids. The resulting crystals exhibit characteristic spatial dimensions dependent on the source of cellulose. For CNCs isolated from Microcrystalline Cellulose (MCC) length and width ranges from 35-265 nm and 3-48 nm respectively, whereas crystals, for example, isolated from cotton have a length and width of 70-300 nm and 5-15 nm. MCC, which is the choice of starting material for CNCs in this disclosure is a purified type of cellulose that have been partly depolymerized into a white, odorless crystalline powder that is insoluble in water. MCC is usually made by purifying cellulose using hydrochloric acid in a hydrolysis process, similar to the way CNCs are subsequently made from MCC, but varying in extent of depolymerization.

Ce l l u l ose De rivatives (C D ) exist in many different forms, as a result of the reactivity of the hydroxyl groups on the anhydroglucose unit of cellulose, which serve as functional groups of cellulose in the sense that they are being replaced by appropriate chemical species upon derivatization.

The characteristics of cellulose derivatives are as follows: i) the type(s) of chemical species substituted on the hydroxyl groups of cellulose, ii) The degree of substitution (DS), i.e. the average number of substituted hydroxyl groups per glucose unit. There are three hydroxyl groups per anhydroglucose unit, and hence the maximum degree of substitution possible is 3. iii) The molecular substitution (MS), defined as the average number of functional units present per glucose unit. For etherified celluloses this value has no theoretical limit, since reactants may add in a step-wise manner, resulting in a growing side-chain with a larger amount of functional units, hence a larger MS. iv) The molecular weight of the derivative in terms of number and weight, abbreviated M_n and Mw respectively. Fig. 1 illustrates cha racteristics ii) a nd iii) where cellulose has been derivatized into hydroxyethyl cellulose. The degree of substitution (DS) in this case is 0.5 since there is one substituted hydroxyl group per six tota l in a structure showing two anhydroglucose units (1/6*6/2). The MS of this derivative is 1 since there are two hydroxyethyl groups per two anhydroglucose units; note that the hydroxyethyl groups being attached to the sa me group (at the C₆-position) makes no difference when it comes to the magnitude of MS. A family of CDs, mainly used in this disclosure is that of ether derivatives. Many of the cellulose ether derivatives are water soluble and exhibits significant surface activity, factors which render them appropriate in this disclosure. The reason for this is that they are with increasing surface activity more likely to be involved in the stabilization of phase interfaces, for example in emulsions. Table 2 gives example of various water soluble cellulose ether derivatives, some of which also are used within the frames of this disclosure to produce characteristic materials. Table 2

An emulsion refers to a system of two immiscible liquids where one of the liquids has been dispersed in the other by addition of an emulsifier. The emulsifier is generally a surface active molecule, but Ramsden and Pickering showed in the beginning of the 20th century that particles can also be used as emulsifiers to produce stable emulsions.

Emulsions are categorized either as water-in-oil (w/o) or oil-in-water (o/w) emulsions, which refers to what phases are dispersed and continuous. In the case with o/w-emulsions the oil is dispersed in a continuous phase of water and vice versa for a w/o-emulsion. The character of an emulsion is strongly related to the chemistry of the emulsifier, which if relatively hydrophilic tends to produce o/w-emulsions. One example of such an emulsion is that which is produced if CNCs are used as emulsifier. The relatively hydrophilic character of CNCs makes the o/w-emulsion preferred.

In this disclosure a solid emulsion refers to a system of a solid continuous phase and a liquid dispersed phase. Solid emulsions can be produced from regular emulsions and it is then required that the emulsions do not phase separate when being processed. Processes that can be applied to transform an emulsion into a solid emulsion include solidification of continuous phase through solvent casting and polymerization of continuous phase. The process of making a solid emulsion is as follows: i) dissolution of polymer and emulsifier in aqueous phase ii) emulsification of aqueous phase with oil phase iii) evaporation of polymer solvent (water) in the continuous phase. These three steps puts requirement on the material used : i) the polymer to be used has to be water soluble, ii) The polymer solution cannot be too viscous at appropriate concentrations or it may hinder

emulsification. iii) The polymer solution (with potential added emulsifier) has to be sufficiently surface active for an emulsion to form, iv) the polymer has to form a protective matrix during evaporation of the water to prevent coalescence of oil droplets. Fig. 2 is a schematic illustration of the process of making a solid emulsion through solvent casting of the continuous phase. Oil (white) is emulsified with aqueous polymer solution (black) and added emulsifier (grey), producing oil droplets. The emulsion is dried and the dissolved polymer solidifies upon the evaporation of the solvent; resulting in a solid emulsion. E X P E R I M E N T S

A number of emulsions, prepared according to the method described below, were tested to assess their properties.

The CNC obtained from commercia l sources was cha racterized by means of Atomic Force Microscopy (AFM). Pieces of mica were cut and freshly cleaved using double-sided tape. A few drops of 0.1% (w/w) cationic polyethylenimine (PEI, M_w = 40000 g/mole) were added to the mica plate prior to the addition of CNC to ensure adhesion of the negatively charged specimens to the plate. The mica plate containing PEI were dried with nitrogen after which a few drops of a 0.05% (w/w) CNC-suspension was added a nd dried with nitrogen in a simila r manner. The PEI and CNC-suspension were let to rest only one minute before drying with nitrogen to ensure no aggregation would occur, that if present would make sizing difficult. AFM was performed (NT-MDT Atomic Force

Microscope) using silicon cantilevers with a golden reflective side and a force constant of

1.45-15.1 N/m in a semi-contact mode. Micrographs were analyzed to determine dimensions of the isolated nanocrystals.

E m u l s i o n p r e p a r a t i o n

CDs used for solid emulsions were diluted in Milli-Q (18.2 ΜΩ) to manageable viscosities that wouldn't hinder emulsification, usually corresponding to a solution of 4-7% (w/w), depending on the type of CD. The actual concentration of the CDs was measured gravimetrically after drying solutions in an oven to get a more accurate value of the solid content. Emulsions were prepared by adding CD solution to a plastic vial (50 ml) containing the CNC- suspension. Calcium chloride was then added together with additional Milli-Q (18.2ΜΩ) to meet the desired oil/water ratio. The oil phase was added to the continuous water phase, after which emulsification and homogenization was performed using either a Diax 900 homogenizer (Heidolph Instruments) or an UltraTurrax IKA T25 digital at a speed of 20000- 23000 rpm. Emulsions No. 27-34 were made in a Heidoph Silent Crusher M, dispersion tool 22F. The resulting emulsion was homogenized for 5 minutes, and was then left for 1 week.

The components used for preparation of the emulsions are disclosed in Table 3. 36 samples were prepared, having the compositions shown in Table 4. The emulsions were stored in room temperature and the emulsion stability was evaluated after 1 week. Table 3

Other materials used in experiments were Hexadeca ne Reagentplus >99% (Sigma Aldrich; Fluorescein isothiocyanate isomer I (Sigma Aldrich).

Table 4

Sample CD CD CNC CaCI Water Oil Oil wt% Solid Emulsion No. wt% wt% wt% wt% Content Stability

Wt% after 1

week

1 EHEC 2 0.5 0.033 72.5 2-ethylhexyl 25 2,5/27,5 Ok

palmitate

2 HPMC 2 0.5 0.033 72.5 2-ethylhexyl 25 2,5/27,5 Ok

palmitate

3 HEC 2 0.5 0.033 72.5 2-ethylhexyl 25 2,5/27,5 Ok

palmitate

4 CMC 2 0.5 0.033 72.5 2-ethylhexyl 25 2,5/27,5 Ok

palmitate

5 Na- 2 0.5 0.033 72.5 2-ethylhexyl 25 2,5/27,5 Ok

CMC palmitate

6 HEC 0.5 2 0,033 72.5 2-ethylhexyl 25 2,5/27,5 Ok

palmitate

7 HPMC 0.5 2 0,033 72.5 2-ethylhexyl 25 2,5/27,5 Ok

palmitate

8 EHEC 2 0.5 0.033 72.5 Dodecane 25 2,5/27,5 Ok 9 EHEC 2.5 - 72.5 Dodecane 25 2,5/27,5 Ok

10 HPMC 2 0.5 0.033 72.5 Dodecane 25 2,5/27,5 Ok

11 HPMC 2.5 - 72.5 Dodecane 25 2,5/27,5 Ok

12 HEC 2 0.5 0.033 72.5 Dodecane 25 2,5/27,5 Ok

13 HEC 2.5 - 72.5 Dodecane 25 2,5/27,5 Not Ok

14 CMC 2 0.5 0.033 72.5 Dodecane 25 2,5/27,5 Ok

15 CMC 2.5 - 0.033 72.5 Dodecane 25 2,5/27,5 Ok

16 HEC 2 0.5 72.5 Olive oil 25 2,5/27,5 Ok

17 HPMC 2 0.5 82.5 Olive oil 15 2,5/17,5 Not Ok

18 HPMC 2 0.5 62.5 Olive oil 35 2,5/37,5 Ok

19 HPMC 2 0.5 72.5 Liquid 25 2,5/27,5 Ok

Paraffin

20 HEC 2 0.5 82.5 Liquid 15 2,5/17,5 Ok

Paraffin

21 HEC 2 0.5 62.5 Liquid 35 2,5/37,5 Ok

Paraffin

22 HEC 1 0,25 0,033 73,75 Isopropyl 25 1,25/26,25 Ok

Palmitate

23 HPMC 1 0,25 0,033 73,75 Isopropyl 25 1,25/26,25 Not Ok

Palmitate

24 EHEC 1 0,25 0,033 73,75 Isopropyl 25 1,25/26,25 Not Ok

Palmitate

25 CMC 1 0,25 0,033 73,75 Isopropyl 25 1,25/26,25 Ok

Palmitate

26 Na- 1 0.25 0.033 73,75 Isopropyl 25 1,25/26,25 Ok

CMC Palmitate

27 CMC 2 0.5 77,5 Liquid 20 2,5/22,5 Ok

Paraffin

28 HPMC 2 0.5 77,5 Liquid 20 2,5/22,5 Ok

paraffin

29 HEC 2 0.5 77,5 Liquid 20 2,5/22,5 Not Ok

Paraffin

30 H EC/HP 2 0.5 77,5 Liquid 20 2,5/22,5 Ok

MC paraffin

31 CMC 2 0.5 77,5 Silicone Oil 20 2,5/22,5 Not Ok

32 HPMC 2 0.5 77,5 Silicone Oil 20 2,5/22,5 Ok

33 HEC 2 0.5 77,5 Silicone Oil 20 2,5/22,5 Not Ok

34 H EC/HP 2 0.5 77,5 Silicone Oil 20 2,5/22,5 Ok

MC

Emulsions No. 1-5 were applied to five different substrates, with the emulsion in wet condition, by placing the emulsion prepared as described above between two rollers, and then pull rollers over the substrate twice. The substrates were round pieces having a diameter of 60 mm, samples were punched out using an Atom S.p.A from the materials disclosed in Table 5. Table 5

The wet uptake, i.e. the weight of emulsion held by the substrate before drying of the emulsion was determined by weighing the substrate before and after application of the emulsion was according to Table 6 (three samples per formulation).

Table 6

Fig. 17-23 show ESEM (Environmental Scanning Electron Microscope) images of solid emulsions a nd substrates ca rrying solid emulsion, where the emulsion has been allowed to dry and form a solid continuous phase with liquid phase dispersed therein. The drying was done at room temperature at 23C and 50% RH. Fig. 17a shows a solid emulsion specimen of emulsion No.2, before compression, having a thickness of 900 μιη . Fig. X.lb is an enlargement of the center portion of Fig. X.la, in which oil phase drops are highlighted by means of white lines. Fig. X.lc is the same specimen after compression to a thickness of 600 μιη. No oil phase drops can be seen, since the oil phase has been released.

Fig. 18 shows a foamed specimen of the sa me solid em ulsion (No.2). Air filled pores are highlighted by mea ns of arrows. Fig. 19a-c are images of a PP nonwoven (Table 5) treated with solid emulsion (SE), where the wet uptake is 0,48 g SE/g substrate. It can be seen that the solid emulsion is incorporated in the structure, on fibers, at fiber crossings and/or at the binding points. Fig. 19c shows how the solid emulsion is holding oil. Fig. 20 is an image of a PET nonwoven (Table 5) treated with solid emulsion (No.2), where the wet uptake is 0,03 g SE/g substrate.

Fig. 21a is an image of a PUR foam (Table 5) treated with solid em ulsion (No.2), where the wet uptake is 0,17 g SE/g substrate. The enlarged image in Fig. 21b shows how there is solid em ulsion present of the cell wall. Fig. 22 is an image of a tissue (Table 5) treated with solid em ulsion (No.2), where the wet uptake is 0,24 g SE/g substrate.

Fig. 23a-b are images of a tissue nonwoven (Table 5) treated with solid emulsion (No.2), where the wet uptake is 0,39 g SE/g substrate.

Fig. 24 is an image of a PP nonwoven (Table 5) treated with an excess of solid em ulsion (No.2).

Emulsions No. 8-15 were analyzed by means of various methods described below.

Light microscopy was performed by adding a few drops of fresh emulsion into a plastic vial, after which the emulsion was diluted with appropriate amount of distilled water. The amount of water used was determined visually based on the turbidity so that the emulsion droplets would be distinguishable whilst still showing a statistically relevant amount of droplets. The size of the emulsion droplets was determined using a shape recognizing software which was tuned to identify the majority of the droplets present in each micrograph. No requirements on perfect recognizing was made, instead it was made sure that the program didn't identify random non-droplet artifacts as droplets.

The choice of cellulose derivatives was based on their performances as additives in emulsion formulations with CNCs. A summary of studied CDs can be seen in table 7 where their grade and viscosity indicated what CD it was. Performances were based on visual observation where an unstable or unsuitable emulsion simply was referred to as Some emulsions were seemingly stable in the wet state but not during drying and was therefore also referred to as "-" or "+" in the solid emulsion column. Table 7

*viscosity measured in a 1% solution. **viscosity measured in a 4% solution Emulsions No. 8-15 were analyzed Multiple Light Scattering within 10 minutes of production by pouring fresh polymer pickering emulsions in customized tubes that were then inserted in a Turbiscan MA2000. The magnitude of backscattered light, both initial and time dependent, were collected over a specific length interval in the tube

corresponding to data points ranging from 600 to 1400 out of 1800 total points. The length interval was chosen to make sure variations in light intensity were meaned over a suitable set of data points. Initial magnitude of backscattered light was collected to get information regarding the average relative droplet size in the emulsions, whereas time dependent (over 24 hours) were means to assess the relative stability of the emulsions. Solid emulsions were prepared from emulsions No. 8-15, by pouring the emulsions into petri dishes and allowing them to dry. The amount of time required for an emulsion to dry was tracked gravimetrically where a steady state occurred where then all of the water had been assumed to have left the emulsion since the mass ratio did not change as a function of time. Solid emulsions assumed to be ready for characterization when the mass ratio in the petri dish did not change as a function of time. The mass of the individual emulsions were always 20 grams.

The amount of water evaporated from emulsions during transformation to solid emulsions was tracked gravimetrically. Redispersion of stable solid emulsions was done by adding the same amount of water that had evaporated to a plastic vial containing the solid emulsion (broken up in pieces). The vial was left for a day to make sure redispersion of the solid emulsion to an emulsion was fully complete and not influenced by energy input which would create new interfaces rather than maintaining the original ones. The emulsion was after complete redispersion (determined visually) poured into a petri dish and left to dry. The solid emulsions thus obtained were characterized by means of Confocal Laser

Scanning Microscopy (CLSM) and Mechanical Testing. The solid emulsions used in the CLSM were as described above, but with addition of 10-100 ppm Fluorescein

isothiocyanate (FITC) to the water phase prior to emulsification. The addition of FITC was performed to make the solid structure of the solid emulsion fluoresce and hence become more easily visible and distinguished from the oil in the emulsion. Emulsions that were analyzed in CLSM were dried on the glass plates that were used during microscopy. This was done to not affect the microstructure by cutting or compressing during sample preparation. A small amount of emulsion was analyzed during CLSM so drying was not required to be continued by the same amount of time as with the emulsions in petri dishes.

For mechanical testing, solid emulsion samples were punched from casted films to produce circular discs with a diameter of 16 mm and characteristic height according to that of the solid emulsion, generally varying between l-2mm. The height of the solid emulsion samples were determined by quadruple measurements using a digital caliper. The fresh circular discs were wiped gently to remove any oil that leaked during sample preparation and then weighted. The discs were then inserted in a universal testing machine (I nstron). Compression was done with a loading cell of 5kN . The tested sample was compressed between two flat steel surfaces, which were moved towards each other at a rate of (compression rate) of 0.1% of the initial distance between the plates per second. Multiple discs (>3) were punched from one emulsion to give multiple

measurements for each type of emulsion to ensure statistical accuracy. The solid emulsion discs were thoroughly wiped after compression before weighting to get a rough, yet sufficient estimation of the oil content. To later correlate oil leakage to volume fraction of oil in the initial solid emulsion equation 3.1 was used, which required the density of dispersed and continuous phase and the mass fraction of leached oil.

3.1

The pressure measurements (mechanical compression testing) were performed using a INSTRON instrument model/serial No: 5565AK7508 and the static load cell used for the experiments had a serial No: 66822. The "upper punch" (max load lOkN) used for the compression had the number T1223-1021 and the "lower punch" (max load lOOkN) had the number of T489-74. The sample punch had a defined geometry which gave the samples a certain area which the software used to calculate pressure from the applied load. The thickness was determined since the experiments were run to compress a certain % of the thickness over time, independent on the measured thickness of the sample. The test result is shown in Fig. 5 and Table 10. This mechanical testing can be done with the solid emulsion incorporated in a substrate and for sake of simplicity the critical pressure value is taken as 0.1 kPa.

Characterization of CNC-CD interactions for by means of UV/VIS-spectroscopy was performed (Spectrophotometer HP8453) by adding 2000μΙ_ CNC 0.3% or 0.6%

suspension to qua rtz cuvettes. CDs were then added from a solution with similar concentration as that of the CNC suspension. Measurements were done after

each incremental addition of derivative until the final ratio of CD to CNC was 0.5.

Distilled water was used as blank for all measurements. Concentrations of the species in the cuvettes were kept low to hinder viscous effects that would result in dispersion of air bubbles in the cuvettes which would give rise to inaccurate absorbance values.

Surface tension of relevant CDs were measured using the Du Noijy ring method (Sigma 60 tensiometer) on solutions containing 0.3 wt % CDs. Final values of surface tensions were automatically calculated through the mean value of five measurements in series per CD.

Accuracy of obtained values were furthermore determined through earlier measurements on pure water which was compared with theoretical values.

In a characterization of nanocellulose, microfibrillated cellulose (MFC) was used as a substitute or alternative to CNCs as Pickering emulsifier in the emulsions in this disclosure MFC was for these reasons analyzed with AFM and compared with CNCs. Results visualized the hierarchical structure of cellulose, where elementary fibrils with amorphous and crystalline regions, approximately 40 nm wide, were found to originate from larger microfibrils approximately 150 nm wide. Also notable were the extremely long fibrils of MFC (relative to CNCs), which can affect the applicability as emulsion stabilizers.

The studied emulsions contain 2.5% solid content: 2.0% CD + 0.5% CNC or 2.5% CD. This specific concentration was based on the choice of CD, where it was found that appropriate CD were not too viscous during emulsification whilst still estimated to be able to form a solid emulsions with sufficient amount of solid content.

Assessment of em ulsion stability using Multiple Light Scattering (MLS) reveals significant differences in initial oil droplet size amongst the emulsions with varying type of CDs. Emulsions produced with EHEC (No. 8-9) and H PMC (No. 10-11) exhibited smaller droplet sizes compared to those with HEC (No. 12-13) and CMC (No. 14-15), whereas EHEC and H PMC relative to each other were quite simila r (68-70% Backscattered light (BS)). These emulsions only showed minor oil droplet size change (decline) with the addition of CNCs; indicating that the polymers played a major role in characteristic oil droplet size. For emulsions with H EC and CMC the trend was the opposite, though minor in the case of CMC; indicating that the CNCs were to a greater extent involved in the oil droplet character. Fig. 3 shows the magnitude of the initial backscattered light of emulsions with given composition of CDs and CNCs with a dodecane content of 25% wt. Also shown is the backscattered light of a redispersed CMC/CNC emulsion. Data was collected less than 10 minutes after emulsification. In order to characterize the relative stability of emulsions with varying CDs with and without CNCs, MLS was performed over 24 hours. Stability in this section refers to small amount of coalescence as indicated by small decrease in intensity of backscattered light over time. The relative stability of emulsions solely made with CDs ranked in the following order (see table 4.1), from the most stable to the least;

CMC(1.1%)>EHEC(2.8%)>H PMC(4.1%)>HEC(46.3%). Emulsions with H EC showed to be largely phase separated after 24 hours; an observation which was not found in any of the other emulsions. The phase separation of emulsions solely stabilized with HEC in relation to the stability of the ones with HEC + CNCs shows interesting contrasts, which points on the role of the CNCs; to be active at the oil/water interface. It has from this stability test been shown that HEC is an extremely poor emulsifier and that the polymer is in no way involved in the character of the oil droplets for emulsions with HEC and CNCs.

With the addition of CNCs (keeping the solid content constant) the stability ranking changed to CMC(0.6%)>HEC(1.9%)>EHEC(2.9%)>HPMC(5.6%). The stability of CMC and HEC emulsions were found to be enhanced by the addition of CNCs, though the relative enhancement of CMC emulsions was insignificant in comparison to HEC emulsions. HEC went from being completely unstable (46% decrease in BS) to one of the most stable (2% decrease in BS) with the addition of CNCs. The stability of EHEC was unaffected by the addition of CNCs with its minor change of 0.1% BS, whereas the one with HPMC decreased as indicated by the increase in difference from 4.1% to 5.6%. The most stable emulsions were produced with CMC, and although CMC on its own produced extremely stable emulsions (2nd in stability rankings) it was shown that CNCs could enhance the stability even further (from 1.1% BS to 0.6% BS). I n the case of CMC, electrostatic interactions have be acknowledged and credited for the unique stability. These aspects become even more interesting in the case of CMC and CNCs, given that the CNCs are negatively charged just as the polymeric part of CMC, and the stability that emulsions with these components show is on another level relative to other emulsions in this disclosure. Table 8 shows the difference in BS light over a time period of 24 hours for emulsions with given composition of CDs and CNCs. All these emulsions were made with 25% dodecane. A large value in difference in BS over measured time period corresponds to a relatively unstable emulsion. Table 8

The usage of HPMC and EHEC were found to form small droplets. This character persisted after the substitution of 20% of the CDs with CNCs, resulting in no significant influence of CNCs for emulsions with HPMC and EHEC. Emulsions with only CMC and HEC exhibited a character of large droplets. These large droplets were affected by the substitution of 20% of the CDs with CNCs in the sense that smaller droplets were obtained, resulting in significant influence of CNCs for emulsions with CMC and HEC. For these reasons it must be that CNCs were always responsible for the droplet character if they were present in emulsions with CMC and/or HEC. The contrast in character between emulsions containing EHEC/HPM and CMC/HEC, respectively is illustrated in Fig. 4, which is an illustration of the deduced character of emulsions droplets with different CDs.

Five types of emulsions that produced stable solid emulsions were in the following sections subjected to mechanical and structural characterization, to distinguish them in relation to varying CDs. One series of the top performing solid emulsion was also mechanically tested with a varied ratio of CNC/CD.

Four solid emulsions with a theoretical (ideal) constant solid content of 9.1% and CD/CNC mass ratio of 4 with variable type of CDs were mechanically compressed. The one emulsion without CNCs (2.5% CMC, 9.1% Solids) was also added in the compression tests. Large contrasts between mechanical properties (expressed as E-moduli and compressive strength) were found between HPMC/EHEC and HEC/CMC emulsions. The compressive E-modulus was for all emulsions calculated as the slope between compressive stress and strain at 10% strain. Chosen strain of 10% was based on the observation that tested emulsions exhibited a rather linear stress-strain relation within that interval. The physical quantity defined as "compressive strength" or "energy required to compress" was calculated as the area under the stress-strain curve. Emulsions No. 27-34 were also mechanically tested. Table 9

Fig. 7 shows stress-strain curves and Fig. 8 shows mass loss (oil leakage), as a function of compressive strain. The solid emulsion with a mixture of HEC/HPMC is significantly softer than the rest, whilst containing around equal amounts of oil, which is a good indication on mechanical diversity. Each curve was obtained from a mean-value from eight different samples.

E-moduli for solid emulsions made with EH EC/CNCs and HPMC/CNCs were found to range between 1 and 4 MPa, whereas those with CMC/CNCs and HEC/CNCs had E- moduli of 30 and 10 MPa respectively. The E-modulus for solid emulsions solely made with CMC was found to have approximately the same va lue as HEC/CNCs on 10 MPa. The required energy to compress given emulsions 50% ranged from 0.2 and 0.6 MPa for EHEC and HPMC to 1.4 and 1.3 MPa for CMC and H EC. See table 10 and Fig. 5 for values and stress-strain curves for solid em ulsions. E-modulus is a measure of stiffness and as such it can be perceived that the (com pressive) stiffness of the solid em ulsions ra nked in the following order: CMC/CNCs > > CMC HEC/CNCs > > HPMC/CNCs > EHEC/CNCs.

Energy required to compress the solid emulsions (strength) is directly related to the inherent mechanical force of which the solids emulsions are able to resist compressive deformation. This capacity ranked in the following order: CMC/CNCs > HEC/CNCs > CMC > HPMC/CNCs > EHEC/CNCs. A difference can be observed when comparing stiffness and strength. It can be seen that HEC/CNCs had a similar capacity to resist deformation as CMC/CNCs despite only having a stiffness similar to that of CMC, both of which had a significantly lower stiffness relative to CMC/CNCs. This difference can be understood by looking at the stress-strain curve for HEC/CNCs (Fig. 5) where it is apparent that said solid emulsion do not exhibit a sudden "dip" in compressive stress at a certain strain value (see curve at strain values between 0.1 and 0.2), causing them to be able to absorb larger amount of energy despite being less stiff. This "dip" is referred to as (compressive) yield strength and was only exhibited by solid emulsions with CMC/CNCs. The apparent yielding of the CMC/CNC-solid emulsion was not seen as an indication of material failure as the rate of oil leakage from the emulsion in relation to strain remained constant. The stress-strain curves for HPMC/CNCs and EHEC/CNCs show their relatively poor mechanical properties; they are neither stiff nor strong. Stress only goes up upon passing strain values at 0.4-0.5 and this is just confirmed as a consequence of the crushing of the material at which point the solid emulsions show increased stress response due to the close packing of the solids in the material. This increase in stress at large strain values was not seen as a material property, and is the reason why strain value above 50% were not included in this part. Fig. 5shows the compressive stress vs strain relation of solid emulsions made with 0.5% CNCs and four different CDs (2.0%). Data for one CMC- emulsion without CNCs (2.5% CMC) also shown. Standard deviations are plotted as dashed lines. Notable features are the low amount of stress required to induce given strain in solid emulsions made with HPMC/CNC and EHEC/CNC relative to the other solid emulsions.

Table 10 Compressive E-modulus and energy required to compress given specimen by 50%. Specimen denoted by their respective composition prior to drying.* Energy calculated relative to the unitless compressive strain that ranged from 0 to 0.5.

The solid emulsions also varied in amount of oil leaked upon compressive strain.

EHEC/CNCs and HPMC/CNCs emulsion exhibited similar behaviour where only a small quantity of oil leaked during early stage compression whereas CMC/CNCs and HEC/CNCs emulsions exhibited a rather linear relation between oil leakage and strain, see Fig. 6. The behaviour of EHEC and HPMC emulsions was due to their poor performances as solid emulsions where some of the encapsulated dodecane had evaporated during storing, leaving behind a somewhat porous, weak material. The linear relation exhibited by CMC/CNCs and HEC/CNCs solid emulsions further showed characteristics of the solid emulsions where material failure due to compression is continuous rather than brittle, something which points on the inherent toughness of the solid emulsions. I nitial dispersed volume fractions in the solid emulsions were also calculated from the relative mass fraction at maximum compression (Fig. 6). The volume of HPMC/CNC, EHEC/CNC, HEC/CNC and CMC/CNC solid emulsions were composed of at least (in the same order) 54%, 74%, 82% and 83% Dodecane. Not shown is also the volume fraction of pure CMC solid emulsions which contained at least 72% dodecane. The solid emulsion may have contained larger amount of oil since the calculation was based on the strain value at 90- 95% and may as a result not have been completely drained during compression. Fig. 6 shows the relation between compressive strain and relative mass loss due to compression in solid emulsions made with 2.0% of given CD and 0.5% CNCs. Note the relatively linear relation for solid emulsions with HEC/CNCs and CMC/CNCs.

Solid emulsions consisting of CMC and CNCs were found to be the strongest and most robust material, so additional compression tests were conducted to look at the influence of CNCs on the strength of the material. Results (see table 11) indicate a decrease in strength and compressive E-modulus when keeping the solid content constant upon increasing CNC content. Both material strength and compressive E-modulus decreased for specimen with more than 0.5% CNCs, see table 11, showing the role of the matrix forming CD which cannot be substituted by CNCs if better mechanical properties is desired. The observation of superior mechanical properties for solid CMC-emulsions with 0.5% CNCs is furthermore interesting as this corresponds to the closest value of 100% coverage of CNCs of the oil droplets in the original emulsions. Both stiffness and material strength declined significantly after this point, something which points on the reinforcing effect of CNCs, but only up to the point of oil droplet coverage, after which the role of the CNCs change. Table 11 shows compressive E-modulus and energy required to compress given CMC-specimen by 50%. Specimen denoted by their respective

composition prior to drying.

Table 11

*Energy calculated relative to the unitless compressive strain that ranges from 0 to 0.5.

The result of decline in mechanical properties upon increasing CNC-content can also be understood by looking at the structure of CMC and CNCs respectively. CMC is a polymer that prior to drying is completely dissolved in the continuous phase, upon drying it will form a molecular homogeneous solid throughout the material and around the oil structures. CNCs on the contrary are colloids and will as such exhibit relatively large inhomogeneities in the dry state, corresponding to the crystals individual dimensions. Though CNCs are acknowledged to exhibit extremely good mechanical properties it should be pointed on that these properties refer to individual CNCs and not bulk of CNCs. When comparing CNCs and CMC as a bulk material it is obvious that the polymer is far superior in terms of mechanical properties.

From table 11 it is also apparent that data for solid emulsions solely made with CNCs are lacking. The reason for this is that such emulsions were shown to become unstable during drying, even with similar solid content as earlier mentioned solid emulsions. This was viewed as a result of lack of encapsulating material. For a liquid such as dodecane to be encapsulated from an emulsion, the solid material must form a dense film around the droplets of the oil. CNCs were obviously unsuitable for this as they were not dense enough in relation to dodecane which is a low viscous liquid (/]=1.34 mPas) consisting of only 12 carbon atoms. The resulting leaking of dodecane from the CNC-solid material was inevitable.

Solid CMC/CNC emulsions were redispersed from a solid state to wet before turning into solid emulsions yet again according to the method described above. Compression tests, see Fig.9, shows a decline in strength relative to its original CMC/CNC emulsion (0.75 MPa compared with 1.37 MPa), higher E-modulus than solid emulsions with 2.5% CMC (15.8 MPa compared with 10.6 MPa), and higher strength than both EHEC/CNC and HPMC/CNC solid emulsions (0.75 MPa compared with 0.20 MPa and 0.59 MPa respectively). The appropriate mechanical properties of this redispersed solid emulsion coupled with MLS- data (Fig.3) that showed 47% backscattered light was viewed as sufficient data to justify the claim of a reversible nature of solid CMC/CNC emulsions in relation to solvent addition. MLS did show a decline of roughly 13% backscattered light relative to the original emulsion, but this is clearly to expect considering the stress the material went through before being analysed. Fig.9 shows the compressive stress vs strain relation for the same type of solid emulsion (2.0% CMC 0.5% CNCs) where one (lowermost line) has been redispersed prior to analysis. Standard deviations are plotted as dashed lines.

The bulk homogeneity in the material was verified by simply observing the material at the physical edges. An overview CLSM-micrograph revealed oil containing structures at the very edge of the materials, indicating homogeneity amongst stable solid emulsions. Observed homogeneity amongst stable solid emulsions was seen as a result of the stability of parent emulsions which, unlike for example emulsions solely made with HEC, EHEC or HPMC (i.e. without CNC), did not suffer from instabilities such as creaming or

coalescence. Stability of parent emulsion was for this reason seen as important for the characterization of the solid emulsion. A solid emulsion for example characterized by creaming would for example result in the gathering of oil droplets on top of the solid emulsion as dodecane is less dense than water, resulting in an observed microstructure that would deviate from the one observed in the bulk. The difference between the morphology of the oil containing cells in CMC solid emulsions with and without CNCs is shown Fig. 10 where deformation of oil containing structure is apparent in the case of solid em ulsions with CNCs. The specific deformed character is seen as one of the factors that makes an oil content a bove 74%, by volume, possible as this corresponds to maximal packing of uniform hard spheres; a condition which has been shown to be surpassed as a result of observed structure coupled with the fact that CMC/CNCs solid emulsions contain at least 83% (by volume) dispersed phase. Another property influencing the ca pacity for increased volume fraction dispersed phase is the polydispersity which earlier has been shown to be exhibited by produced em ulsions. Polydisperse objects a re more likely to pack in an efficient manner, as sma ller objects can fit in between larger objects, resulting in higher capacity for dispersed phase increase. Fig. 10 shows CLSM micrographs (one focal pla ne) of solid emulsions made with 2.5% CMC (left) and 2.0% CMC + 0.5% CNCs (right). White feature is the cellulosic matrix with the encapsulated oil shown as black. Note the difference in morphology between the oil containing structures. Sca le ba rs are 40μιη.

The CMC/CNCs solid emulsions features an extent of deformation of the oil containing structures. From Fig. 10 it is apparent that oil cells are connected with one another through flat interfaces made of solid CMC/CNCs, rather than circular interfaces. This flattening is seen as a result of the stability of the oil droplets which could have easily phase separated during drying, but instead it was possible for the droplets to deform into polyhedrons which are packed closely. CD/CNCs emulsions can be compared with emulsions solely stabilized by CNCs because it was deduced earlier that the factor responsible for the oil character in the emulsions was largely CNCs, rather than the CDs (unless the CD was HPMC or EHEC).

Though HEC on its own was unsuitable for emulsions and solid emulsions it was found that substitution of 20% HEC with CNCs made solid emulsions containing at least 82% (by volume) robust and stable. Results (Fig. 11) show the morphology of HEC/CNC solid emulsion. The solid emulsion was found to be similar to that of CMC/CNC, again owing its deformed character to the presence of CNCs. Solid emulsions made with EH EC/CNCs were found to exhibit a different structure, characterized by smaller, less deformed cells. The EHEC/CNC solid emulsions contained at least 74% oil (by volume). I n solid emulsions with HEC/CNCs the effect of CNCs is even more pronounced. Neither CNCs nor H EC produced stable solid emulsions on their own. As previously mentioned the CNCs lacked the encapsulating properties that HEC could provide, but HEC lacked the emulsion stabilizing properties that CNCs could provide. In summary, the HEC/CNCs solid emulsion is a characteristic example of where the roles of CNCs and CDs in solid emulsions are shown. Fig. 11 shows CLSM micrographs (one foca l pla ne) of solid emulsions made with 2.0% H EC + 0.5% CNCs (left) a nd 2.0% EH EC + 0.5% CNCs (right). The EH EC/CNC solid em ulsions contain a large amount smaller oil containing cells relative to both HEC and CMC solid emulsions. Sca le ba rs a re 40/jm.

For EHEC/CNCs the small droplet character is, as earlier deduced, from the fact that the EHEC acts as emulsifier and sta bilizer instead of the CNCs. During the drying of the emulsion the same flat interfaces as observed with CMC/CNCs and HEC/CNCs ca nnot be obtained since the flexibility was seen as a consequence of the CNCs, and if the CNCs are not involved in the interfaces then they cannot provide the solid emulsion with that flexibility during drying. Fig. 12 shows the cell diameter

distribution for solid emulsions with EHEC/CNCs (white) and HEC/CNCs (black).

The volume fraction obtained from data analysis shows that HEC/CNCs solid emulsions contains larger amount of oil than the EHEC/CNCs (66% vs 57%). The oil volume fraction was reported earlier to be 82% for HEC/CNCs and 74% for EHEC/CNCs. Deviations compared to values for the mechanically tested solid emulsions may lie in the fact that emulsions for CLSM were dried to solid emulsions during analysis over a short time (2-4 hours), hence calculated oil content based on the micrographs may not have been representative for the solid emulsions had they been dried longer. Regardless of limitations, CLSM proved to be a suitable method to characterize solid emulsions, and the depth of analysis was dependent on the ability to compensate laser intensity

(increase) as a result of light scattering due to the features the further in the emulsion the scanning laser went. CMC/CNCs solid emulsions were found to be relatively opaque compared to HEC/CNCs and EHEC/CNCs, for this reason multiple focal planes (>10) were never successfully obtained, as the material scattered the light during focal plane change.

It will be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the invention is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein.

Claims

1. A skin treatment composition comprising an emulsion, which comprises a continuous phase and a dispersed phase, characterized in that the continuous phase comprises cellulose derivatives (CD) and nanocellulose, preferably cellulose nanocrystals (CNC), and a carrier, and the dispersed phase is an oil containing composition.

2. The skin treatment composition of claim 1, wherein the cellulose derivatives (CD) are chosen from carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), ethyl hydroxyethyl cellulose (EHEC), or hydroxylpropyl methyl cellulose (HPMC), preferably CMC or HEC, or combinations of two or more of these cellulose derivatives.

3. The skin treatment composition of claim 1 or 2, wherein the continuous phase of the emulsion comprises 0,5-50 wt% cellulose nanocrystals (CNC), preferably 3-40 wt%, more preferably 10-30 wt%, based on the weight of cellulose derivatives (CD) comprised in the aqueous continuous phase.

4. The skin treatment composition of any one of claims 1-3, wherein the carrier is water or an alcohol, such as ethanol or isopropylalcohol, or combinations thereof.

5. The skin treatment composition of any one of claims 1-4, wherein the emulsion comprises 0,1-20 wt% cellulose derivatives (CD) based on the total weight of the emulsion, preferably 0,5-10 wt%.

6. The skin treatment composition of any one of claims 1-5, wherein the weight ratio of the dispersed oil phase to the dry content in the continuous phase of the solid emulsion is 20:80 -

99:1 wt/wt.

7. The skin treatment composition of any one of claims 1-6, wherein release of the dispersed oil phase is initiated, when a pressure above a critical pressure value is applied to the solid emulsion, wherein the critical pressure value preferably is 0,1 kPa.

8. The skin treatment composition of any one of claims 1-7, wherein the skin treatment composition comprises one or more active agents chosen from: skin care agents, odour control agents, antibacterial agents, lubrication agents, enzyme inhibiting agents,

surfactants/detergents, medical compositions, pH controlling agents and barrier agents.