Aqueous dispersion comprising destructured starch

Abstract

The present invention relates to an aqueous dispersion comprising destructured starch, at least one polymer containing hydrophilic groups in or outside the main chain, at least one polyfunctional compound and at least one non-ionic dispersant additive having a hydrophilic- lipophilic balance (HLB) index of less than 15, use of said dispersion in a coating process and the coating composition obtained from said dispersion.

Description

[0001]AQUEOUS DISPERSION COMPRISING DESTRUCTURED STARCH The present invention relates to an aqueous dispersion comprising destructured starch, at least one polymer containing hydrophilic groups in or outside the main chain, at least one polyfunctional compound and at least one non-ionic dispersant additive with a hydrophilic- lipophilic balance (HLB) index of less than 15, use of said dispersion in a coating process, for example for coating paper or seed, and the coating composition obtained from said dispersion. The use of paper products has become increasingly important in the food packaging sector in recent years. Through the recycling or recovery of paper and cardboard waste, use of these products in fact makes it possible to reduce the problems associated with their disposal, as well as to reduce pollution from incineration. Furthermore, paper products are increasingly replacing plastics products where possible, avoiding the harmful dispersion and accumulation of plastics material in the environment. However, because of the hygroscopic nature of cellulose and the porous structure of its fibres, the mechanical properties of paper products are easily reduced or even lost when exposed to moisture. To be effectively used in packaging, for example food packaging, paper products therefore need a surface coating layer that creates a barrier to water vapour and water. The use of surface coating layers to coat seeds (known as seed dressing) is also increasingly common in agricultural practice to enhance seeds vigor, ensure healthy seedling growth, and protect them from pathogens and pests. Through seed dressing it is in fact possible to influence both the physical properties and the microenvironment in which the seed develops, for example it is possible to favour the rapid formation of root nodules, ensure good seed-soil contact to improve the movement of water towards the seed, and provide compounds that favour seed development and germination such as growth regulators, nutrients, fungicides, etc.. Furthermore, seed coating allows to deliver high levels of efficacy, for the control e.g. of early season insects or diseases, at a much reduced usage rate compared to many foliar or soil applied alternatives, with a minimized impact on the environment and on non-target organisms. Traditionally, chemicals (such as pesticides) are used for treating seeds, and these are either mixed directly with the seeds in a dry state or applied to the seeds in a liquid slurry. Such practices result in significant dispersion of chemicals into the environment and a health risk to the people handling, packaging and planting the seeds. Applying a coating layer to seeds solves the problems outlined above, as well as offering additional benefits such as protecting the seeds from mechanical damage during handling. Although the use of a coating layer is particularly advantageous, its application is nevertheless mainly limited to the seeds of vegetables and a few field crops because of the cost of the synthetic polymer materials currently used to produce the coating compositions. Surface coatings for paper and seed substrates can advantageously be produced using natural polymer-based coating compositions. Despite the growing demand for new coating compositions produced from aqueous dispersions based on natural polymers such as starch, they have nevertheless found few successful applications. In particular, because of the crystalline nature of the amylose and amylopectin molecules, starch-based dispersions have poor filming properties and typically yield inflexible and brittle films. Moreover, such dispersions are often extremely viscous, even when the solids content is low, a characteristic that greatly reduces the possibility of depositing them onto substrates to create a uniform coating layer. Coating layers obtained using such dispersions also have poor barrier properties to water and water vapour on account of the hydrophilic nature of the dispersion components. The effectiveness of using a starch-based aqueous dispersion in coating processes (i.e. deposition of the dispersion onto a substrate to create a coating layer) in fact strongly depends on some intrinsic characteristics of the dispersion itself, such as dry matter concentration, which in the case of industrial paper coating processes is for example preferably between 30 and 50 per cent, dynamic viscosity and the average particle size of the starch. The state of the art includes many attempts to overcome these limitations, for example by modifying the structure of the starch molecule. Patent EP 2 758 465 B1 describes an aqueous dispersion comprising destructured and complexed starch suitable for use in the coating of paper substrates. In the document the viscosity of the aqueous dispersion is reduced by decreasing the molecular weight of the starch through treatments with acids, such as sulfuric acid, bases and enzymes. However, the Applicant has found that, even by reducing the viscosity of the dispersion with the above-mentioned treatments, the use of such a dispersion in a coating process does not result in a sufficiently homogeneous and compact film to ensure good water vapour and water barrier performance. To improve the barrier properties of coating layers produced using starch-based aqueous dispersions, strategies have been developed to increase the hydrophobicity of starch such as, for example, the use of moisture-resistant agents or hydrophobicising components. Examples of moisture-resistant agents used for this purpose are alkyl ketene dimers, styrene-maleic anhydride, acrylic acid-styrene copolymers, styrene acrylate emulsions, citric acid, glyoxal, etc. Examples of hydrophobicising components are organic and inorganic fillers such as amides, waxes, kaolin, mica, talc and hydrophobic silicas. D. Lin et al. (Industrial Crops and Products 100, 2017, 12-18), for example, describes a starch- and polyvinyl alcohol-based dispersion to which glyoxal and styrene-acrylate copolymers are added to increase the moisture resistance of paper products to which this dispersion is applied as a coating layer. The mere addition of moisture resistant agents or hydrophobicising components does not however make it possible to maintain viscosity values in accordance with industrial requirements when a high dry matter content is present, and to ensure the formation of uniform and compact coating layers Document WO 2023 / 026073, for example, describes a composition comprising plasticised starch, polycarboxylic acids and Tween 20 (a non-ionic surfactant with an HLB index of 16.7), which is suitable for application in diluted form as a spray to create a coating layer for plant and fruit materials. The Applicant has however established that the addition of Tween 20 has an aggregating effect and causes an increase in the viscosity of the dispersion itself. Starting from the need to find an aqueous dispersion characterised by low viscosity even when the solids concentration is high and the average particle size is small, the Applicant has surprisingly found that by combining at least one polymer containing hydrophilic groups in or outside the main chain, at least one non-ionic dispersant additive with an HLB index of less than 15 and at least one polyfunctional compound in an aqueous dispersion based on destructured starch, the hydrophobicity of the starch is increased and the average particle size of the starch is reduced. The starch particles are also stabilised and the formation of aggregates is prevented, resulting in a dispersion with a dynamic viscosity of less than 4000 mPa.s, even when the solids content is high. Advantageously this dispersion remains stable over time and does not produce sediment. The specific combination of at least one polyfunctional compound and at least one non-ionic dispersant additive with an HLB index of less than 15 identified by the Applicant in fact has an unexpected synergistic effect, possibly through preventing hydrogen bridge interactions between the aggregates formed by the starch particles and those between these particles and the polymer containing hydrophilic groups in or outside the main chain in an aqueous environment. Surprisingly, the same synergistic effect is observed when the polyfunctional compound is generated in situ, e.g. using one or more enzymes capable of partially hydrolysing starch, thus producing polyols such as monosaccharides, disaccharides and oligosaccharides. The object according to the present invention is therefore an aqueous dispersion comprising: a. destructured starch; b. at least one polymer containing hydrophilic groups in or outside the main chain; c. at least one polyfunctional compound selected from a polycarboxylic acid, a salt of a polycarboxylic acid, a hydroxyacid, a salt of a hydroxyacid, a polyol and mixtures thereof; d. at least one non-ionic dispersant additive with an HLB index of less than 15; and e. water. Surprisingly, the aqueous dispersion according to the invention is stable over time and maintains low dynamic viscosity and small particle size, even when the solids content is high. Said aqueous dispersion can advantageously be used with a solids content of 10 to 60 per cent by weight, preferably 30 to 50 per cent by weight. Such a dispersion advantageously has a dynamic viscosity (measured by a Brookfield viscometer with spindle LV-3 (63)) of less than 4000 mPa.s, preferably less than or equal to 3000 mPa.s, more preferably less than or equal to 2800 mPa.s, more preferably less than or equal to 2500 mPa.s, even more preferably less than or equal to 2000 mPa.s, when the solids content is 30-50% by weight. Such a dispersion advantageously has a dynamic viscosity (measured by a Brookfield LV viscometer with spindle LV-3 (63) of more than 400 mPa.s, more preferably more than 500 mPa.s, even more preferably more than or equal to 600 mPa.s, when the solids content is 30-50% by weight. As far as the solids content is concerned, this can be measured gravimetrically by checking the weight when the water has completely evaporated. For this purpose the aqueous dispersion according to the present invention can be placed in a moisture analyser (for example a Mettler Toledo HB-43-S Halogen Moisture Analyser) at 140°C for 30 minutes. The dynamic viscosity of the aqueous dispersion may, for example, be measured at a temperature of 22°C using a Brookfield viscometer (or another viscometer of equal performance) having spindle LV-3 (63), at 6 rpm, with conversion factor 200. The aqueous dispersion according to the invention also has an average particle size (measured by means of a Malvern mastersizer 3000 granulometer) with D4;3 values from 0.5 μm to 20 μm, preferably from 0.9 μm to 10 μm, more preferably from 1 μm to 5 μm, even more preferably from 2 μm to 4 μm. Said aqueous dispersion is advantageously stable over time. In particular, when subjected to accelerated stability testing at 54°C it remains stable for at least 14 days with unchanged dynamic viscosity and mean particle size values (net of experimental error) and no phase separation. According to one aspect of the invention, this aqueous dispersion is advantageously biodegradable according to OECD 301 B. Because of its small particle size, low dynamic viscosity and stability over time, even when a high solids content is present, the aqueous dispersion according to the invention is advantageously suitable for use in processes for coating different types of substrates, such as paper products or vegetable seeds. The use of said aqueous dispersion makes it possible to create homogenous, compact surface coating layers that create a barrier to moisture and water. It is therefore also an object according to the present invention to use the aqueous dispersion in a coating process. A further advantage of the aqueous dispersion according to the invention lies in the fact that its dynamic viscosity can be adjusted by varying the solids content in the above-mentioned range, allowing it to be used without changes in the operating conditions of conventional paper coating machines. The aqueous dispersion according to the invention can therefore advantageously be used to prepare coating compositions for paper substrates or plant seeds. A further aspect of the invention is therefore a coating process comprising the step of applying the aqueous dispersion according to the invention to a substrate preferably selected from seeds and a paper substrate. A further aspect of the invention relates to a coating composition for paper or seed substrates obtained from said aqueous dispersion. Advantageously, said coating composition is biodegradable according to EN ISO 14855-1. Brief description of the figures. FIG.1: Scanning electron microscope (SEM) image of the condition of the coating in Example 6 (11 gsm), obtained by coating the aqueous dispersion in Example 1; FIG. 2: Scanning electron microscope (SEM) image of the condition of the coating in comparative Example 7 (27 gsm), obtained by coating the aqueous dispersion in comparative Example 2; FIG. 3: Scanning electron microscope (SEM) image of the condition of the coating in comparative Example 8 (13 gsm), obtained by coating the aqueous dispersion in comparative Example 3; FIG. 4: Scanning electron microscope (SEM) image of the condition of the coating in comparative Example 9 (30 gsm), obtained by coating the aqueous dispersion in comparative Example 4; FIG. 5: Scanning electron microscope (SEM) image of the condition of the coating in comparative Example 10 (13 gsm), obtained by coating the aqueous dispersion in comparative Example 5. The present invention will be described in more detail below. The aqueous dispersion according to the present invention comprises: a. destructured starch; b. at least one polymer containing hydrophilic groups in or outside the main chain; c. at least one polyfunctional compound selected from a polycarboxylic acid, a salt of a polycarboxylic acid, a hydroxyacid, a salt of a hydroxyacid, a polyol and mixtures thereof; d. at least one non-ionic dispersant additive with an HLB index of less than 15; and e. water. In one embodiment, the aqueous dispersion according to the present invention comprises, with respect to the total dry weight of the dispersion: a. 28-63% by weight of destructured starch b. 16-40, preferably 16-36% by weight of at least one polymer containing hydrophilic groups in or outside the main chain; c. 0.3-39% by weight of at least one polyfunctional compound selected from a polycarboxylic acid, a salt of a polycarboxylic acid, a hydroxyacid, a salt of a hydroxyacid, a polyol and mixtures thereof; d. 1-36% by weight of at least one non-ionic dispersant additive with an HLB index of less than 15. With regard to component a, the aqueous dispersion according to the present invention comprises 28-63% by weight of destructured starch, preferably 29-59% by weight, more preferably 35-55% by weight, even more preferably 38-52% by weight, relative to the total dry weight of the dispersion. According to one aspect, said destructured starch comprises 0-25% by weight, preferably 0- 20% by weight, of at least one plasticiser. Within the meaning of the present invention, by destructured starch is meant starch of any type which has lost its natural granular structure and is substantially devoid of residual granular structure. In one embodiment according to the invention, destructured starch is starch that has completely lost its natural granular structure. In a preferred embodiment according to the invention, destructured starch is a starch that has completely lost its granular structure, also known as "fully destructured starch". As far as the granular structure of the starch is concerned, this may advantageously be identified by means of phase-contrast light microscopy, for example at 400x magnification. Through microscopy it can be seen that natural starch has a clearly distinguishable granular structure, whereas destructured starch lacks both the natural crystallinity and granular structure, and the macromolecules of amylose and amylopectin give rise to a continuous texture. The destructured starch according to the present invention is also different from gelatinised starch, which has no crystalline structure but may still have some individual distinguishable granules that transmit and diffuse light beams differently from the surrounding medium. Starch is advantageously destructured in any apparatus capable of providing temperature, pressure and shear force conditions suitable for destroying the natural granular structure of starch. Suitable conditions for achieving complete destructuring of starch are, for example, described in patents EP 0118240 and EP 0327505, the contents of which are incorporated herein by reference. Advantageously starch is destructured by an extrusion process at temperatures between 110 and 250°C, preferably 130-210°C, preferably at pressures between 0.1 and 7 MPa, preferably 0.3-6 MPa, and preferably providing a specific energy of more than 0.1 kWh / kg during extrusion. Preferably the starch used for preparation of the destructured starch according to the present invention is natural starch (such as for example corn starch, potato starch, rice starch, tapioca starch, pea starch) Particularly preferred are corn and potato starch and their mixtures. As far as destructured starch plasticisers are concerned, these are preferably selected from polyols with 2 to 22 carbon atoms and mixtures thereof. Among the polyols, those preferred are polyols with 1 to 14 hydroxyl groups containing 2 to 6 carbon atoms, their ethers, thioethers and organic and inorganic esters. Examples of polyols suitable as plasticisers are glycerol, diglycerol, polyglycerol, pentaerythritol, ethoxylated polyglycerol, ethylene glycol, polyethylene glycol, 1,2- propanediol, 1,3-propanediol, 1,4-butanediol, neopentylglycol, sorbitol, mannitol, sorbitol monoacetate, sorbitol diacetate, sorbitol monoethoxylate, sorbitol diethoxylate and mixtures thereof. In a preferred embodiment the plasticisers comprise glycerol or a mixture of plasticisers comprising glycerol, most preferably comprising between 2 and 90 per cent by weight of glycerol to the total weight of plasticisers. The destructured starch (component a) according to the invention is preferably complexed with at least one polymer containing hydrophilic groups in or outside the main chain (component b). According to a preferred aspect, the aqueous dispersion according to the present invention therefore comprises destructured and complexed starch. With respect to component b, the aqueous dispersion according to the present invention comprises 16-36% by weight, preferably 17-34% by weight, more preferably 20-32% by weight, even more preferably 21-30% by weight, relative to the total dry weight of the dispersion, of at least one polymer containing hydrophilic groups in or outside the main chain. Preferably, these polymers are biodegradable. Polymers containing hydrophilic groups outside the main chain are preferred. These polymers are advantageously selected from: - polyvinyl alcohols with a degree of hydrolysis of between 10 and 100%, preferably between 70 and 99%; - vinyl alcohol / vinyl acetate block copolymers; and - ethylene-polyvinyl alcohol copolymers. Mixtures of these polymers may also be used. Polyvinyl alcohols with a degree of hydrolysis from 10 to 100% and vinyl alcohol / vinyl acetate block copolymers and their mixtures are preferred. Particularly preferred among these are polyvinyl alcohols with a degree of hydrolysis between 10 and 100%, even more preferred are polyvinyl alcohols with a degree of hydrolysis between 70 and 99%. With regard to component c, the aqueous dispersion according to the present invention comprises 0.3-39% by weight of at least one polyfunctional compound, preferably 3-36% by weight, more preferably 7-28% by weight, even more preferably 11-25% by weight, relative to the total dry weight of the dispersion. By polyfunctional compound is meant a molecule with two or more functional groups selected from a hydroxyl group and a carboxylic group; said polyfunctional compound is selected from a polycarboxylic acid, a salt of a polycarboxylic acid, a hydroxyacid, a salt of a hydroxyacid, a polyol and mixtures thereof. Preferably, said polyfunctional compound is selected from a polycarboxylic acid, a hydroxyacid, a salt of a hydroxyacid, a mixture of polyols and a mixture of a hydroxyacid or a polycarboxylic acid with a polyol. Even more preferably, said polyfunctional compound is selected from a salt of a hydroxyacid, a hydroxyacid, a mixture thereof with a polyol and a mixture of polyols. According to a preferred embodiment, component c is a hydroxy acid or a salt thereof and is present in the aqueous dispersion in an amount of 0.3-39% by weight, preferably 3-36% by weight, more preferably 7-28% by weight, even more preferably 11-25% by weight, relative to the total dry weight of the dispersion. Among the hydroxy acids, molecules with at least two carboxyl groups and at least one hydroxyl group are preferred. Even more preferred are molecules with at least two carboxyl groups and at least two hydroxyl groups. Suitable hydroxy acids are for example malic, tartaric, citric and isocitric acids. Tartaric acid, malic acid and citric acid are preferred. Tartaric acid is even more preferred. Suitable hydroxy acid salts are for example sodium tartrate and sodium citrate. According to a further embodiment, component c is a polycarboxylic acid or a salt thereof and is present in the aqueous dispersion in an amount of 0.3-39% by weight, preferably 3-36% by weight, more preferably 7-28% by weight, even more preferably 11-25% by weight, relative to the total dry weight of the dispersion. Preferably, said polycarboxylic acids are di- or tricarboxylic acids of variable chain length, preferably C1 to C18, saturated or unsaturated. Preferably, said polycarboxylic acids are dicarboxylic acids. The polycarboxylic acids are selected from, for example, oxalic, malonic, succinic, adipic, azelaic, sebacic, pimelic, hexadecandioic, hexadecendioic, octadecandioic, octadecendioic and itaconic acids. Preferably the polycarboxylic acid is azelaic acid. According to a further embodiment, component c is a mixture of at least one hydroxy acid and at least one polyol. The use of such a mixture advantageously allows the pH of the dispersion to be maintained at values above 3. In the case where the plasticisers in component a and component c are both polyols, the total amount of polyol (corresponding to the sum of component c and the plasticiser in component a, if any) must be at least above 8% w / w, relative to the total dry weight of the dispersion, to achieve the desired viscosity. By polyols are meant chemical compounds that contain at least two, preferably at least 3, hydroxyl groups. The polyols suitable for use as component c are, for example, selected from: neopentylglycol, glycerol, trimethylolpropane, pentaerythritol, 1,4-butanediol, sorbitol, maltitol, monosaccharides (e.g. glucose), disaccharides (e.g. maltose) and oligosaccharides, the latter preferably comprising 3 to 10 saccharide units. Said polyols are added to the dispersion comprising the destructured starch (component a), which may include the above-mentioned plasticisers. Alternatively, the component c. is a polyol or a mixture of polyols derived by the starch component a., e.g. by addition of one or more enzymes capable of hydrolysing the glycosidic bonds in starch molecules, thereby partly converting starch to simpler carbohydrates. Suitable enzymes are selected for example from: amylases, glucoamylases, pullulanases and their combinations. Amylases are preferred and among them alpha amylases are preferred. The said enzyme is conveniently added to an aqueous suspension of component a. or of components a. and b. at suitable temperature and pH conditions for starch conversion (based on the selected enzyme); once the sufficient polyol amount is obtained, the enzyme is deactivated as known in the art. A sufficient polyol amount is for example when the sum of monosaccharides and disaccharides obtained is of 35% by weight or lower, preferably of 30% by weight or lower, more preferably of 25% by weight or less, with respect to the starting amount of starch component a. (i.e. the amount of starch component a. before adding the enzyme). Monosaccharides and disaccharides can be determined e.g. through ionic chromatography with pulsed amperometric detection. According to this embodiment, the polyfunctional compound (component c) comprises a mixture of monosaccharides, disaccharides and oligosaccharides, e.g. a mixture comprising glucose and maltose. Also in this case, component c. is present in the aqueous dispersion in an amount of 0.3-39% by weight, preferably 3-36% by weight, more preferably 7-28% by weight, even more preferably 11-25% by weight, relative to the total dry weight of the dispersion. With respect to component d, the aqueous dispersion according to the present invention comprises 1-36% by weight, preferably 2-35% by weight, more preferably 3-27% by weight, even more preferably 4-23% by weight, with respect to the total dry weight of the dispersion, of at least one non-ionic dispersant additive having an HLB (hydrophilic-lipophilic balance) index of less than 15. Said non-ionic dispersant additive preferably has an HLB index between 1 and 15, more preferably between 1 and 10. Said dispersant additive is advantageously selected from non-ethoxylated sorbitan esters, A-B- A or random block polymer dispersants, alkoxylated alcohols and their combinations. Non- ethoxylated sorbitan esters, ethoxylated alcohols and fatty alcohol alkoxylates are preferred. Alkoxylated alcohols based on vegetable raw materials are particularly preferred. Examples of non-ethoxylated sorbitan esters are those known as Span®, including for example: sorbitan monolaurate (known as Span 20), sorbitan monopalmitate (known as Span 40), sorbitan monostearate (known as Span 60), sorbitan tristearate (known as Span 65), sorbitan oleate (known as Span 80), sorbitan trioleate (known as Span 85) and combinations thereof. Examples of block polymer dispersants are ATLOX 4912 and ATLOX 4914 from Croda. Examples of alkoxylated alcohols are DISPERBYK 195 from BYK and Synative® AC EP 5 LV from BASF. The aqueous dispersion according to the present invention may optionally comprise further additives selected from: inorganic fillers and hydrophobicising organic fillers, anti-foaming agents, suspension agents, densifiers, preservatives, surface modifiers, pigments, dyes, pH modifiers and combinations thereof. When present, these additives are contained in quantities from 0.01 to 30% by weight, relative to the dry weight of the dispersion. Where the dispersion according to the present invention is used for seed dressing, such dispersion may advantageously comprise one or more further components selected from among: pesticides (e.g. fungicides, insecticides, nematicides), preferably biopesticides, nutrients, plant growth regulators, biostimulants, such as biostimulants based on protein hydrolysates, and combinations thereof. The aqueous dispersion according to the invention is preferably prepared from destructured starch complexed with at least one polymer containing hydrophilic groups in or outside the main chain. Within the meaning according to the present invention, destructured starch complexed with at least one polymer containing hydrophilic groups means a destructured starch that has formed one or more supramolecular structures that can be determined using an X-ray spectrometer (Cu Kα X-ray radiation with λ=1.5416 Å), in the form of one or more crystalline forms with which one or more diffraction peaks from those listed below can be associated. It is known that crystalline forms of complexed starch can change from one form to another over time, due to their different thermodynamic stabilities. The present invention also relates to a process for preparing the aqueous dispersion described above, wherein the aqueous dispersion comprises an added polyfunctional compound as component c. said process comprising the steps of: i. preparing a composition comprising destructured starch (component a) and at least one polymer containing hydrophilic groups in or outside the main chain (component b); ii. adding the composition obtained in step i. to an aqueous solution containing at least one polyfunctional compound (component c) and optionally at least one non-ionic dispersant additive having an HLB index of less than 15 (component d), resulting in a pre-dispersion. Maintaining this pre-dispersion at a temperature preferably from 80 to 95°C, more preferably from 90 to 95°C, for at least 1 hour, preferably at least 2 hours, while stirring; iii. feeding the pre-dispersion in step ii. to a dispersing machine, for example equipped with a mixing vessel and a mixing system comprising at least one rotor and at least one stator, and vigorously shaking (preferably by means of a crown disperser) at temperatures above 80°C, preferably above 90°C for longer than 30 minutes, preferably at least 90 minutes, or until the dispersion is homogeneous and reaches a constant dynamic viscosity value; iv. optionally adding at least one dispersant additive (component d) to the dispersing machine in step iii. and mixing vigorously at temperatures above 80°C, preferably above 90°C for at least 60 minutes, or until the dispersion is homogeneous and reaches a constant dynamic viscosity value; v. optionally adjusting the solids content of the aqueous dispersion by adding or removing the appropriate amount of water (for example by evaporation) to achieve a solids content of 10 to 60% by weight, preferably 30 to 50% by weight, wherein component d. is added at least in step ii and / or in step iv. In the process according to the invention, components c and d of the aqueous dispersion may be added in the same process step (i.e. in step ii.) or in two separate process steps (i.e. component c is added in step ii. and component d in step iv.). According to one embodiment, components c and d of the aqueous dispersion are both added in step ii. of the process. The composition obtained in step i. is therefore added to an aqueous solution comprising 0.3-39% by weight, preferably 3-36% by weight, more preferably 7-28% by weight, and even more preferably 11-25% by weight, with respect to the total dry weight of the dispersion, of at least one polyfunctional compound and 1-36% by weight, preferably 2- 35% by weight, more preferably 3-27% by weight, even more preferably 4-23% by weight, with respect to the total dry weight of the dispersion, of at least one non-ionic dispersant additive with an HLB index of less than 15. According to a preferred embodiment, components c and d of the aqueous dispersion are added in two separate process steps. The composition obtained in step i. is therefore added to an aqueous solution containing 0.3-39% by weight, preferably 3-36% by weight, more preferably 7-28% by weight, and even more preferably 11-25% by weight, with respect to the total dry weight of the dispersion, of at least one polyfunctional compound, while the non-ionic dispersant additive with an HLB index of less than 15 is added subsequently in step iv. in an amount of 1-36% by weight, preferably 2-35% by weight, more preferably 3-27% by weight, even more preferably 4-23% by weight, to the total dry weight of the dispersion. The dispersant additive is preferably added in step iv. in pre-dispersion or solid form. The Applicant has in fact unexpectedly found that addition of the dispersant additive at a later stage than addition of the polyfunctional compound results in a further improvement in viscosity and particle size. According to a preferred embodiment, the process for preparing the aqueous dispersion therefore comprises the steps of: i(a). preparing a composition comprising destructured starch (component a) and at least one polymer containing hydrophilic groups in or outside the main chain (component b); ii(a). adding the composition obtained in step i(a). to an aqueous solution containing at least one polyfunctional compound (component c), resulting in a pre-dispersion. Holding this pre-dispersion at a temperature of 80 to 95°C, preferably 90 to 95°C for at least 1 hour, preferably at least 2 hours, while stirring; iii(a). feeding said pre-dispersion containing at least one polyfunctional compound to a dispersing machine, equipped for example with a vessel and a stirring system comprising at least one rotor and at least one stator, and vigorously mixing (preferably by means of a crown disperser) at temperatures above 80°C, preferably above 90°C, for a time of at least 90 minutes; iv(a). adding in the same machine as step iii(a). at least one non-ionic dispersant additive having an HLB index of less than 15 (component d) and vigorously mixing at temperatures above 80°C, preferably above 90°C, for at least 90 minutes or until the dispersion is homogeneous and reaches a constant dynamic viscosity value. According to an alternative embodiment wherein the component c. is derived from the starch component a., the process for preparing the aqueous dispersion of the invention, comprises for example the steps of: i. preparing a composition comprising destructured starch (component a) and at least one polymer containing hydrophilic groups in or outside the main chain (component b); ii. adding the composition obtained in step i. to an aqueous solution, resulting in a pre- dispersion, at a temperature preferably from 60 to 95°C; iii. adding to said pre-dispersion an enzyme capable of partially hydrolysing starch, e.g. in amounts of 10-100 enzyme units for gram of starch, and holding this pre- dispersion at a suitable temperature for the enzyme, e.g. from 65 to 75°C up to 30 minutes, while stirring, thus obtaining a total amount of monosaccharides and disaccharides up to 35 % by weight with respect to the dry weight of the starch component a. used in step i.; iv. feeding the pre-dispersion in step iii. to a dispersing machine, for example equipped with a mixing vessel and a mixing system comprising at least one rotor and at least one stator, and vigorously shaking (preferably by means of a crown disperser) at temperatures above 85°C, preferably above 90°C, for at least 15 minutes, or until the dispersion is homogeneous and reaches a constant dynamic viscosity value; v. adding at least one dispersant additive (component d) to the dispersing machine in step iv. and mixing vigorously, e.g. at temperatures above 80°C, preferably above 85°C for at least 15 minutes, preferably for 90 min or until the dispersion is homogeneous and reaches a constant dynamic viscosity value; vi. optionally adjusting the solids content of the aqueous dispersion by adding or removing the appropriate amount of water (for example by evaporation) to achieve a solids content of 10 to 60% by weight, preferably 30 to 50% by weight. In order to obtain a destructured and complexed starch composition, steps i. and i(a). of the process are preferably conducted by feeding said composition comprising starch and at least one polymer containing hydrophilic groups in or outside the main chain to a process for the extrusion of a molten mixture having a specific energy input of more than 0.1 kWh / kg during said extrusion. Such preparation by extrusion takes place for example at temperatures between 110 and 250°C, preferably between 130 and 210°C, more preferably between 140 and 190°C. Suitable extruders for use in preparing the composition are single-screw and twin-screw extruders. Twin-screw extruders are preferable. Twin-screw extruders with screws having mixing zones with highly workable elements are most preferred. The composition comprising starch can be fed to the dispersion system in step ii. in the form of pellets or powder. The powder may be obtained by grinding the pellets. Examples of the dispersing machines in step iii. are high shear mixers, homogenisers such as IKA Ultra-Turrax T25, IKA PILOT 2000 / 4 and IKA DR2000 / 1. In step iii. and iii(a). of the process, vigorous mixing means stirring at 10000 rpm or more, preferably between 10000 and 24000 rpm. The process for preparing the aqueous dispersion described above can be carried out in batch mode or continuously. The aqueous dispersion according to the present invention is therefore preferably obtained by the process described above. The aqueous dispersion according to the present invention may be used to prepare coating compositions for paper substrates. A further aspect according to the invention is therefore a coating process comprising the step of applying the aqueous dispersion according to the invention to a substrate preferably selected from seeds and a paper substrate. A further aspect according to the invention relates to a coating composition for paper substrates obtained from said aqueous dispersion. For the purposes according to the present invention, the term “paper substrate” encompasses all materials made from vegetable fibre raw materials, for example cellulose fibres. Suitable examples are sheets of paper and cardboard of between 10 and 1000 g / m2. The composition according to the present invention may be applied to paper substrates according to any of the processes known to those skilled in the art. Preferably, the composition is applied in the form of an aqueous dispersion using paper coating methods such as blade or film processes. Said coating processes include the steps of: A. depositing a layer of the coating composition according to the present invention on at least one face of a paper substrate; B. drying the paper substrate comprising at least one layer of the coating composition according to the present invention. With regard to deposition step A, application systems with one or more applicator rollers (for example size presses, film presses), with jets (for example jet flow), with offset printing or any combination thereof may advantageously be used. Between steps A and B the coating process may also advantageously include partial removal of the applied coating composition from the paper substrate, thus allowing for adjustment of the weight per unit area and at the same time equalising the thickness of the coating layer (known as levelling). Said removal may advantageously be performed by means of one or more metal blades, by one or more air jets (known as air-blade technology) or by one or more air blades (known as air- knife technology) or any combination thereof. As far as step B of drying the paper substrate is concerned, systems using radiation, preferably infrared, convection, preferably of hot air, or contact, preferably with drying rollers, or any combination of these, may be advantageously used. The present invention also relates to the coating composition that can be obtained from the aqueous dispersion claimed, for example by the process described above. On account of the characteristics of the aqueous dispersion according to the invention, this coating composition has a uniform coating layer and high barrier properties against water and water vapour, making it particularly useful for the manufacture of products for the food industry. The barrier property against water may, for example, be assessed by means of the COBB60 test, according to UNI EN ISO 535:2014, which allows surface water absorption by a paper or board sample over a certain period of time (for example 30, 60, 180 and 1800 seconds, depending on the material) to be determined. The substrate coated with said coating composition may also advantageously be subjected to further extrusion coating and / or extrusion lamination treatments with biodegradable polymer materials such as the polyesters described in patent application WO 2009 / 118377, to form a particularly effective water barrier layer that also makes it suitable for packaging liquids and various types of foodstuffs such as, inter alia, meat, ice cream, yoghurt and foodstuffs particularly sensitive to oxidation and / or moisture such as toast, coffee and potato crisps. In a preferred embodiment, this coating composition is biodegradable and therefore particularly suitable for coating biodegradable paper for composting according to EN ISO 14855-1. The aqueous dispersion according to the invention may also advantageously be used for seed dressing. For the purpose of this application, said dispersion (and consequently also the resulting coating composition) may also include pesticides, fungicides, insecticides, nematicides, biopesticides, biological products, plant growth regulators, biostimulants such as protein hydrolysate products, micronutrients, dyes or other additives. The seed dressing is carried out e.g. through film coating process. The aqueous dispersion of the invention is sprayed onto the seeds to give a thin shell or coating around each seed. The said process must allow enough time for the film to dry out so that the coated seeds do not clump together. The overall size of the seed is not changed, but seeds with a rough surface can be made smoother by film coating, and thereby improve their drilling properties. The addition of a coating typically adds no more than 1-10% of the weight of the seed. The skilled in the art knows that the exact formulation requirements for the use for seed dressing will depend on the products being applied, the target seed and the equipment used for the application. The aqueous dispersion according to the present invention may also advantageously be used as a film-forming component for paints, for example, those which allow water vapour to pass through. It may also be advantageously used as a vehicle (called a carrier) or microencapsulant for active ingredients, fragrances, pigments or labile substances (for example hydroperoxides) in various fields such as pharmaceuticals (medicinal products), agriculture (insecticides and herbicides), cosmetics, biotechnology (fixing of enzymes or other forms of catalysts or microorganisms) or in the food industry. In particular, the aqueous dispersion according to the invention is particularly effective when used to encapsulate essential oils, fragrances and lipophilic substances, acting as a carrier of these substances and also allowing their controlled release over time. The following examples illustrate the present invention for non-limiting purposes. Methods used in the examples. Measurement of dynamic viscosity A Brookfield viscometer with spindle LV-3 (63), at 6 rpm with conversion factor 200 or at 60 rpm with conversion factor 20, was used to measure dynamic viscosity. Measurements were made at a temperature of 22°C. Determination of dry matter Dry matter was determined using a Mettler Toledo HB-43-S halogen moisture analyser by placing the sample at 140°C for 30 minutes. Determination of D 4;3 particle size D4;3 particle size (the average particle diameter versus volume) was measured using the Malvern Mastersizer 3000 analyser. Determination of surface water absorption by paper or cardboard Water absorption was determined by means of the COBB60 test according to UNI EN ISO 535:2014. Scanning electron microscopy The quality of films obtained from dispersions made according to the present invention was checked by scanning electron microscopy. A Zeiss brand microscope, model Supra 40, was used for this purpose. Each section of cardboard analysed was coated with a conductive material such as gold and analysed by SEM at a minimum magnification of 50x. Determination of monosaccharides and disaccharides The glucose and maltose contents were measured by ionic chromatography (manufactured by Metrohm AG) under the following conditions: - Column: Metrosep Carb 2 - 250 / 4.0 (manufactured by Metrohm AG) - Mobile phase: water solution of sodium hydroxide 40 mM and sodium acetate 40 mM - Flow rate: 0.7 mL / min - Detection method: Pulsed Amperometric Detection (PAD) - Column temperature: 30°C. The pre-dispersion sample was diluted in a proper amount of ultrapure water type 1 and filtered with a 0.2 ^m PVDF filter before injection. EXAMPLES EXAMPLE 1: Preparation of a destructured and complexed starch composition (components a and b) 49.5 parts of natural maize starch (containing 12% water by weight), 32.2 parts polyvinyl alcohol with a degree of hydrolysis of 88%, 7 parts glycerol and 11.2 parts water were fed to a TSA twin-screw extruder with the following operating conditions: thermal profile feed zone (°C): 60 extrusion zone (°C): 120-200x4-110-90 flow rate (kg / h) = 3 SME (specific energy) (kWh / kg) = 0.267. The resulting composition was ground up at 25°C and sieved to a particle size < 250 µ and analysed in a Philips X'Pert Θ / 2Θ X-ray spectrometer with Bragg-Brentano geometry using KαX Cu-ray radiation with λ = 1.5416 A and a power of 1.6 kW. The angular range used was from 5 to 60° (2Θ) with steps of 0.03° (2Θ) and an acquisition time of 2 seconds per step. Spectral analysis revealed the presence of diffraction peaks at 2Θ = 12.7-16.5-18.2-19.4-22.0 indicating formation of the complex between starch and polyvinyl alcohol (VHform). Composition was analysed using a Leitz Wetzlar Orthoplan model phase-contrast optical microscope set to the following parameters: Magnification x400 Objective EF 40 / 0.65 PHACO 2 Phase ring No.5 The composition showed that no residual granular structure attributable to starch was present, thus revealing the destructured nature of starch. Preparation of an aqueous dispersion in the presence of a polyfunctional compound (c) and dispersant additive (d). The composition of destructured and complexed starch prepared as described above was added to an aqueous solution comprising 20.5% by weight of tartaric acid (component c) with respect to the total dry weight of the dispersion in an amount equal to 72.7% by weight with respect to the dry weight of the dispersion, yielding a pre-dispersion. This pre-dispersion was mixed for about 120 minutes at 95°C and then processed at high shear (13789 rpm) inside a mixer of the IKA PILOT 2000 / 4 type equipped with a three-stage DISPAX-REACTOR® DR module and thermostated at temperatures between 85-95°C. When the mixture was completely homogeneous, 6.8% by weight of the sorbitan additive SPAN40 (component d) in relation to the total dry weight of the dispersion was added and processing was continued to ensure complete diffusion of the additive into the mixture. Processing was continued until a total dry matter percentage in the dispersion of between 30% and 37% was reached. The dispersion obtained was evaluated in terms of solids content, dynamic viscosity and D 4;3 particle size. The results obtained are shown in Table 1. COMPARATIVE EXAMPLE 2: Preparation of an aqueous dispersion in the absence of a polyfunctional compound (c) and dispersant additive (d). An aqueous dispersion was prepared using a complexed destructured starch composition prepared as described in Example 1, without the addition of the polyfunctional compound and dispersant additive. In particular, the composition of destructured and complexed starch was dispersed within the aqueous phase so as to obtain a final ratio of 30 / 70 w / w between the dispersed and dispersant phases. This mixture was subsequently processed in an IKA PILOT 2000 / 4 type mixer equipped with a DISPAX-REACTOR® DR three-stage module and thermostated at temperatures between 85-95°C. However, the processing carried out at these temperatures caused a marked deterioration in the rheology of the dispersion, which was found to have such a high viscosity that it could not be measured using a Brookfield viscometer with n=63 geometry and prevented the dispersion from being used to prepare a coating layer. Preparation of the dispersion was therefore repeated by processing the mixture in an IKA PILOT 2000 / 4 type mixer equipped with a three-stage DISPAX-REACTOR® DR non- thermostated module set at a speed of 13789 rpm. The resulting dispersion was evaluated in terms of solids content, dynamic viscosity and D 4;3 particle size. The results obtained are shown in Table 1. COMPARATIVE EXAMPLE 3: Preparation of an aqueous dispersion in the presence of a polyfunctional compound (c) but in the absence of a dispersant additive (d). A composition of destructured and complexed starch prepared as in Example 1 was added to an aqueous solution comprising 22% by weight of tartaric acid with respect to the total dry weight of the dispersion in an amount of 78% by weight with respect to the dry weight of the dispersion, resulting in a pre-dispersion. This pre-dispersion was mixed for about 120 min at 95°C and then processed at high shear (13789 rpm) inside an IKA PILOT 2000 / 4 type mixer equipped with a DISPAX-REACTOR® DR three-stage module and thermostated at temperatures between 85-95°C. Processing was continued until a percentage of total dry matter in the dispersion between 30% and 37% was reached. The dispersion obtained was evaluated in terms of solids content, dynamic viscosity and D 4;3 particle size. The results obtained are shown in Table 1. COMPARATIVE EXAMPLE 4: Preparation of a dispersion in the presence of dispersant additive (d) and in the absence of polyfunctional compound (c). An aqueous dispersion was prepared using a complexed destructured starch composition prepared as in Example 1, without addition of the polyfunctional compound. Specifically, the destructured and complexed starch composition was dispersed within an aqueous phase in an amount equal to 91.4% by weight with respect to the dry weight of the dispersion and thermostated at between 85 and 95°C.8.6% by weight of SPAN40 with respect to the total dry weight of the dispersion was added to the dispersion obtained and the dispersion was processed at high shear (13789 rpm) inside an IKA PILOT 2000 / 4 type mixer equipped with a three-stage DISPAX-REACTOR® DR module and thermostated at temperatures between 85-95°C until the additive was completely diffused in the mixture. Processing was continued until a percentage of total dry matter in the dispersion of between 30% and 37% was reached. The resulting dispersion was evaluated in terms of solids content, dynamic viscosity and particle size. The results obtained are shown in Table 1. COMPARATIVE EXAMPLE 5: Preparation of a dispersion in the presence of dispersant additive (d) and sulfuric acid. A destructured and complexed starch composition prepared as in Example 1 was added to an aqueous solution of sulfuric acid comprising 8.3% by weight with respect to the total dry weight of the dispersion in an amount equal to 84.7% by weight with respect to the dry weight of the dispersion, yielding a pre-dispersion. This pre-dispersion was mixed for about 120 minutes at 95°C and then processed at high shear (13789 rpm) inside an IKA PILOT 2000 / 4 type mixer equipped with a three-stage DISPAX-REACTOR® DR module and thermostated at temperatures between 85 and 95°C. When the mixture was completely homogeneous, 7% by weight of the sorbitan additive SPAN40 with respect to the total dry weight of the dispersion was added and processing was continued to ensure complete diffusion of the additive into the mixture. The dispersion obtained was evaluated in terms of solids content, dynamic viscosity and D 4;3 particle size. The results obtained are shown in Table 1. EXAMPLES Solids BROOKFIELD D4;3 content (%) Dynamic viscosity (6 rpm; conversion factor 200) 1 35 700 3.4 2 comparative 30 8720 21 3 comparative 32 6400 21.4 4 comparative 30 not measurable 40 5 comparative 30 4000 12.3 Table 1: Characterisation of aqueous dispersions in Example 1 and Comparative Examples 2, 3, 4, 5. The results shown in Table 1 demonstrate that the presence of a combination of a polyfunctional compound and a dispersant additive (Example 1) in the aqueous dispersion based on destructured and complexed starch led to about a 90% reduction in the dynamic viscosity of the dispersion and more than 80% in the D4;3 value compared to Comparative Example 2, which did not include such a combination, despite having a higher solids content. The presence of only the polyfunctional compound (Comparative Example 3) in the aqueous dispersion based on destructured and complexed starch led to a reduction of only 27% in the dynamic viscosity of the dispersion compared to the viscosity of Comparative Example 2, which did not include it, while it did not affect the particle size. On the other hand, the presence of only the dispersant additive (Comparative Example 4) in the aqueous dispersion based on destructured and complexed starch resulted in a dispersion with such a high viscosity that it could not be measured by means of a Brookfield viscometer with n=63 geometry and a D 4;3 value twice as high as in Comparative Example 2. The presence of sulfuric acid and a dispersant additive (Comparative Example 5) in the aqueous dispersion based on destructured and complexed starch resulted in a reduction of only 54% in the dynamic viscosity of the dispersion compared to the viscosity of Comparative Example 2. EXAMPLES 6-10: Coating compositions The aqueous dispersions in Example 1 and Comparative Examples 2 - 5 were used to coat uncoated paper (140 g / m2). Specifically, 65 mL / m2of dispersion was deposited for each example using a manual film spreader bar (KBAR no.14). The wet film was dried for 5 minutes at 105 °C in a previously thermostatted oven and finally left to equilibrate in a controlled environment (23 °C - 50% humidity) for 24 hours. The coating layers obtained were analysed using a scanning electron microscope (Fig.1 - 5) and underwent COBB60 analysis according to UNI EN ISO 535:2014, the results of which are shown in Table 2, in comparison with paperboard without the coating layer. Aqueous dispersion Specimen weight COBB60 Example in example: (g / m2) (g / m2) 6 1 11 17 7 comparative 2 comparative 27 34 8 comparative 3 comparative 13 55 9 comparative 4 comparative 30 16 10 comparative 5 comparative 13 39 Paper board* - 0 40 Table 2. COBB analysis results. *Rismaluce Favini green 140 g / m2The results illustrated in Table 2 show that use of the aqueous dispersion in Example 1 according to the invention produced a thin, uniform coating layer on the paper specimen capable of creating a water barrier. In fact, in Example 6 the amount of water absorbed by the paper specimen (indicated by the COBB value in the last column of Table 2) was about 50% less than in comparative Example 7 (prepared from a dispersion in the absence of components b and c), despite the fact that about 60% less coating was deposited on the specimen. Furthermore, although the amount of water absorbed by the test specimens in Comparative Examples 6 and 9 is comparable, in the case of Comparative Example 9 the coating layer deposited on the test specimen had a thickness of 30 g / m2, which is almost 3 times thicker than that of the test specimen in Example 6 according to the invention (11 g / m2). In fact the viscosity of the dispersion obtained in comparative Example 4 was so high that a larger quantity of dispersion had to be applied in order to obtain a homogeneous coating layer. Finally, the result obtained in Comparative Example 10 shows that merely decreasing the viscosity of the dispersion by depolymerising the starch through the addition of sulfuric acid is not sufficient to produce a homogeneous coating layer with an efficient water barrier using this dispersion. SEM analysis of the coating layers in Example 6 (Fig.1) and comparative Examples 7-10 (Fig. 2-5), moreover, makes it clear that use of the aqueous dispersion according to the invention for coating paper substrates resulted in a uniform and homogeneous coating layer free from irregularities, even when using less material. EXAMPLE 11: Preparation of a dispersion in the presence of an amylase and a dispersant additive (d). 1200 g of a composition of destructured and complexed starch prepared as in Example 1 was added to an aqueous solution (2800 g) comprising 12 g of air-release agent UniqFoam LP2599, resulting in a pre-dispersion. This pre-dispersion was heated to 70°C; 24 g of a-amylase solution (CERELYVE MT 1400 with 1323 enzyme units / g) was added and mixed for 30 min at 70°C. The said pre-dispersion was processed inside an IKA PILOT 2000 / 4 type mixer equipped with a DISPAX-REACTOR® DR three-stage module and thermostatically controlled at temperatures between 90-95°C for 15 minutes. The pre-dispersion contained 5,74 % by weight of glucose and 7,13% maltose with respect to its dry weight. The glucose and maltose contents were measured by ionic chromatography (manufactured by Metrohm AG) under the following conditions: - Column: Metrosep Carb 2 - 250 / 4.0 (manufactured by Metrohm AG) - Mobile phase: water solution of sodium hydroxide 40 mM and sodium acetate 40 mM - Flow rate: 0.7 mL / min - Detection method: Pulsed Amperometric Detection (PAD) - Column temperature: 30°C. The pre-dispersion sample was diluted in a proper amount of ultrapure water type 1 and filtered with a 0.2 ^m PVDF filter before injection. Finally, 50 g (4,8% by weight in relation to the dry matter) of DISPERBYK-195 (HLB<9, component d.) were added in the mixer. Processing was continued for 15 minutes. The dispersion obtained was evaluated in terms of solids content, dynamic viscosity and D 4;3 particle size. The results obtained are shown in Table 3. EXAMPLES Solids content BROOKFIELD D4;3 (%) Dynamic viscosity (spindle n°63, 60 rpm conversion factor 20) 11 38,6 520 9 Table 3: Characterisation of aqueous dispersion EXAMPLE 12: Coating compositions The aqueous dispersions in Example 11 was used to coat uncoated paper (62 g / m2). Specifically, 65mL / m2of dispersion was deposited for each example using a manual film spreader bar (KBAR no.14). The wet film was dried for 5 minutes at 105 °C in a thermostatically controlled oven and finally left to equilibrate in a controlled environment (23 °C - 50% humidity) for 24 hours. The coating layers obtained were analysed using a scanning electron microscope and underwent COBB60 analysis according to UNI EN ISO 535:2014, the results of which are shown in Table 4, in comparison with paperboard without the coating layer. Aqueous dispersion Specimen weight COBB60 Example in example: (g / m2) (g / m2) 12 11 8 8 Paper board** - 0 28 Table 4. COBB analysis results. **Paper UPM Brilliant 62 g / m2The results illustrated in Table 4 show that use of the aqueous dispersion in Example 11 according to the invention produced a thin, uniform coating layer on the paper specimen capable of creating a water barrier. In fact, in Example 11 the amount of water absorbed by the paper specimen (indicated by the COBB value in the last column of Table 4) was about 71% less than paper UPM Brilliant (62 gsm) without coating.

Claims

CLAIMS 1. Aqueous dispersion comprising: a. destructured starch; b. at least one polymer containing hydrophilic groups in or outside the main chain; c. at least one polyfunctional compound selected from a polycarboxylic acid, a salt of a polycarboxylic acid, a hydroxyacid, a salt of a hydroxyacid, a polyol and mixtures thereof; d. at least one non-ionic dispersant additive having an HLB index of less than 15; and e. water, and having a dynamic viscosity of less than 4000 mPa.s, measured by a Brookfield viscometer with n=63 geometry, when the solids content is 30-50% by weight.

2. Aqueous dispersion according to claim 1 having a D 4;3 particle size of 0.5 to 20 µm.

3. Aqueous dispersion according to one or more of claims 1-2 comprising, compared to the dry weight of the dispersion: f. 28-63% by weight of destructured starch; g. 16-40% by weight of at least one polymer containing hydrophilic groups in or outside the main chain; h. 0.3-39% by weight of at least one polyfunctional compound selected from a polycarboxylic acid, a salt of a polycarboxylic acid, a hydroxyacid, a salt of a hydroxyacid, a polyol and mixtures thereof; i. 1-36% by weight of at least one non-ionic dispersant additive with an HLB index of less than 15.

4. Aqueous dispersion according to one or more of claims 1-3, in which said polymers containing hydrophilic groups are selected from: - polyvinyl alcohols with a degree of hydrolysis between 10 and 100%, preferably between 70 and 99%; - vinyl alcohol / vinyl acetate block copolymers; and - ethylene-polyvinyl alcohol copolymers.

5. Aqueous dispersion according to one or more of claims 1-4, in which said polyfunctional compound is selected from a polycarboxylic acid, a hydroxyacid, a salt of a hydroxyacid, a mixture of polyols and a mixture of a hydroxyacid or a polycarboxylic acid with a polyol.

6. Aqueous dispersion according claim 5 wherein the polyfunctional compound c. is a mixture of polyols derived from the starch component a., preferably obtained by addition of one or more enzymes selected from amylases, glucoamylases, pullulanases and their combinations.

7. Aqueous dispersion according to one or more of claims 1-6, in which said dispersant additive is selected from non-ethoxylated sorbitan esters, alkoxylated alcohols, A-B-A block or random polymer dispersants and combinations thereof.

8. Process for preparing the aqueous dispersion according to one or more of claims 1-5 or 7, comprising the steps of: i. preparing a composition comprising destructured starch (component a) and at least one polymer containing hydrophilic groups in or outside the main chain (component b); ii. adding the composition obtained in step i. to an aqueous solution containing at least one polyfunctional compound (component c) and optionally at least one non-ionic dispersant additive with an HLB index of less than 15 (component d), obtaining a pre-dispersion and maintaining this pre-dispersion at a temperature of 80 to 95°C, preferably 90 to 95°C, for at least 1 hour, preferably at least 2 hours, while stirring; iii. feeding the pre-dispersion in step ii. to a dispersing machine, for example equipped with a mixing vessel and a mixing system comprising at least one rotor and at least one stator, and shaking vigorously, preferably by means of a crown disperser, at temperatures above 80°C, preferably above 90°C, for longer than 30 minutes, preferably at least 90 minutes or until the dispersion is homogeneous and reaches a constant dynamic viscosity value; iv. optionally adding at least one dispersant additive (component d) to the step iii. dispersing machine and mixing vigorously at temperatures above 80°C, preferably above 90°C, for at least 60 minutes or until the dispersion is homogeneous and reaches a constant dynamic viscosity value; v. optionally adjusting the solids content of the aqueous dispersion by adding or removing (for example by evaporation) the appropriate amount of water to achieve a solids content of 10 to 60% by weight, preferably 30 to 50% by weight, wherein component d is added at least in step ii. and / or in step iv..

9. Process for preparing the aqueous dispersion according to claim 6, comprising the steps of:i. preparing a composition comprising destructured starch (component a) and at least one polymer containing hydrophilic groups in or outside the main chain (component b); ii. adding the composition obtained in step i. to an aqueous solution, resulting in a pre- dispersion, at a temperature preferably from 60 to 95°C; iii. adding to said pre-dispersion an enzyme capable of partially hydrolysing starch and holding this pre-dispersion at a suitable temperature for the enzyme while stirring, thus obtaining a total amount of monosaccharides and disaccharides up to 35 % by weight with respect to the dry weight of the starch component a. used in step i.; iv. feeding the pre-dispersion in step iii. to a dispersing machine and vigorously shaking at temperatures above 85°C, preferably above 90°C, for at least 15 minutes, or until the dispersion is homogeneous and reaches a constant dynamic viscosity value; v. adding at least one dispersant additive (component d) to the dispersing machine in step iv. and mixing vigorously, at temperatures above 80°C, preferably above 85°C, for at least 15 minutes or until the dispersion is homogeneous and reaches a constant dynamic viscosity value; vi. optionally adjusting the solids content of the aqueous dispersion by adding or removing the appropriate amount of water (for example by evaporation) to achieve a solids content of 10 to 60% by weight, preferably 30 to 50% by weight.

10. Coating process comprising the step of applying the aqueous dispersion according to one or more of claims 1-7 to a substrate preferably chosen from seeds or a paper substrate.

11. Coating composition obtained from an aqueous dispersion according to one or more of claims 1-7.

12. Coating composition for paper or seed substrates obtained from the aqueous dispersion in one or more of claims 1-7.

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