FR3160714A1 - PROCESS FOR HYDROPHOBATING A POLYSACCHARIDE MATERIAL SUBSTRATE - Google Patents

Abstract

The invention relates to a method for treating the surface of a solid substrate made of polysaccharide material, aimed at hydrophobizing this surface. This method comprises the application, to this surface, of a reagent comprising at least one hydroxylated fatty acid and/or oligomer of this hydroxylated fatty acid and/or an ester of this hydroxylated fatty acid, then the heat treatment of the substrate under conditions causing the performance of esterification reactions between carboxyl groups of the hydroxylated fatty acid, and hydroxyl groups of the polysaccharide and hydroxyl groups of the hydroxylated fatty acid.

Description

PROCESS FOR HYDROPHOBATING A POLYSACCHARIDE MATERIAL SUBSTRATE

The present invention relates to a method for treating a surface of a solid substrate made of polysaccharide-based material, in particular cellulose, in particular for the hydrophobization of this surface, as well as a solid substrate made of polysaccharide-based material obtained at the end of such a method.

Cellulose-based materials, such as paper or cardboard products, or fabrics made from cellulose fibers, are highly valued due to their bio-sourced origin, mechanical properties, low cost, biodegradability, and recyclability. However, a barrier to their use is their sensitivity to water due to the strong hydrophilic nature of cellulose.

Different strategies have been proposed by the prior art for the hydrophobization (also called hydrophobization) of the surface of such articles.

A first of these strategies consists of a simple deposit on this surface of a coating based on a hydrophobic substance, such as a wax. The resistance of such coatings to external conditions, and the durability of their maintenance on the treated surface, are however unsatisfactory. Such solutions are also not compatible with the use of treated substrates for the packaging of food or cosmetic products for example, due to a risk of release of the hydrophobic substance into these products.

In order to overcome these drawbacks, it has been proposed to treat the surfaces of such articles so as to achieve a chemical anchoring of the hydrophobic coating. The main methods developed in this regard by the prior art use synthetic polymers. However, treatment with such substances generates recycling problems, incompatible with current environmental requirements. Solutions using bio-sourced substances, more particularly derivatives of edible or non-edible vegetable oils, such as castor oil, have recently been considered to address the problems stated above. However, these solutions involve chemical modifications of the fatty acids contained in these oils, such as epoxidations and silanizations, which are penalizing both in terms of cost and naturalness and recyclability. In addition, the cultivation of these oilseed plants for non-food applications competes with food production on arable land, which is obviously not desirable.

Thus, there are currently no completely satisfactory bio-sourced solutions for hydrophobizing articles made from cellulose-based materials.

The present invention aims to overcome the drawbacks of the methods proposed by the prior art for hydrophobizing the surface of solid substrates formed from cellulose-based materials, and more generally from polysaccharides, in particular the drawbacks set out above, by proposing such a method which makes it possible to carry out such hydrophobization in an efficient and sustainable manner, by using bio-sourced, biodegradable and recyclable reagents, preferably derived from industrial organic waste, which achieves chemical anchoring of these reagents on the treated surface, and which is easy to implement, and moreover at low cost.

An additional objective of the invention is that the implementation of this method does not significantly affect the mechanical properties of the treated substrate, and even, preferably, improves at least some of these mechanical properties.

It has been discovered by the present inventors that these objectives can be achieved by implementing, within a process for surface treatment of solid substrates formed from polysaccharide, in particular cellulose, one or more hydroxylated fatty acids, in the form of monomers and/or oligomers, or esters of such hydroxylated fatty acids. Such hydroxylated fatty acids, with a long carbon chain, can be extracted from plants, in particular from the cuticles of fruits and vegetables, and more particularly from the cutin used in the composition of these cuticles, so that the process using them constitutes an advantageous route for their recovery.

Thus, according to a first aspect, there is proposed according to the present invention a method for treating a surface of a solid substrate manufactured from a material based on a polysaccharide with free hydroxyl functions, for the hydrophobization of this surface, that is to say to give it water-resistant properties, this resistance also advantageously extending to fatty substances, in particular to oils. This method comprises successive steps of:
- application, on the surface of the substrate, of a reagent comprising:
at least one hydroxylated fatty acid,
and/or at least one oligomer of said hydroxylated fatty acid,
and/or at least one ester of said hydroxylated fatty acid and of an alcohol with a linear or branched, saturated or unsaturated, optionally substituted aliphatic chain, said aliphatic chain comprising from 1 to 18 carbon atoms,
or any mixture thereof,
- and heat treatment of the substrate under conditions causing esterification reactions to occur between carboxyl groups of said hydroxylated fatty acid, and, on the one hand, hydroxyl groups of the polysaccharide and, on the other hand, hydroxyl groups of said hydroxylated fatty acid.

In the present description, the term oligomer is understood to mean, in a conventional manner in itself, a molecule consisting of the repetition of 2 to 10 monomeric units. Thus, the reagent according to the invention may contain one or more oligomers, preferably dimers and/or trimers, comprising a hydroxylated fatty acid as a monomeric unit.

The method according to the invention advantageously leads to the grafting, by polyesterification phenomenon, where appropriate poly-transesterification, of molecules of the hydroxylated fatty acid(s) onto the polysaccharide polymer chain forming part of the substrate, as well as of these molecules between themselves. This chemical anchoring is furthermore advantageously reinforced by the formation of hydrogen bonds involving the hydroxyl functions of the substrate and the hydroxyl functions of molecules of hydroxylated fatty acid(s) not involved in the chemical anchoring by esterification. At the end of the method according to the invention, a coating with hydrophobic properties is obtained on the surface of the substrate, and also forming a barrier to fatty substances, which is chemically bonded to this surface, so that it remains attached there in a stable and durable manner. Depending on the quantity of reagent used, this coating can be continuous on the surface of the treated substrate, or discontinuous, in the sense that it individually coats the polysaccharide fibers forming part of its composition. In this latter configuration, surprisingly, the hydrophobic properties conferred on the surface of the treated substrate are particularly good.

The method according to the invention is also advantageously easy to implement, in few steps and at low cost.

Particularly surprisingly, it has been discovered by the present inventors that the use in accordance with the invention of one or more hydroxylated fatty acids and/or their oligomers and/or their esters as defined above, makes it possible, in comparison with a similar process using a non-hydroxylated fatty acid, such as palmitic acid, to obtain a much greater hydrophobation of the surface of the treated substrate, even though the person skilled in the art would have expected an opposite result, due to the hydrophilic nature of the hydroxyl groups present within the hydroxylated fatty acid molecules. Furthermore, still in comparison with the non-hydroxylated fatty acids, it has been discovered by the present inventors that, at an equivalent fatty acid content, the use in the process according to the invention of hydroxylated fatty acid(s) leads to a much greater level of chemical anchoring of the fatty acids to the surface of the substrate. Here again, such a result is surprising, due to the competition created by the presence of hydroxyl groups within the hydroxylated fatty acids, with respect to the hydroxyl groups of the polysaccharide, for the esterification reactions with the carboxylic acid functions of the fatty acids. One would have thought that this competition would on the contrary have had the effect of reducing this rate of chemical anchoring on the polysaccharide.

According to the present invention, the term “solid substrate manufactured from polysaccharide-based material” means a solid substrate from industrial production formed at least in part from one or more polysaccharides, at least part of the hydroxyl groups of the polysaccharide chains being in free form. The polysaccharide chains can form a continuous network or a discontinuous assembly.

The polysaccharide forming the substrate can in particular be cellulose, or a polysaccharide from an algae, such as an alginate.

When the polysaccharide is cellulose, the latter can be present in the substrate alone or in the form of lignocellulose, that is to say a complex structure made up of cellulose, lignin and hemicellulose.

Preferably, the solid substrate made of polysaccharide-based material to which the method according to the invention is applied is such that free hydroxyl groups of the polysaccharide chains are exposed at the surface of the substrate to be treated, and are therefore immediately accessible to react with the molecules of hydroxylated fatty acid(s) and/or their oligomers and/or their ester(s) deposited on this surface.

The solid substrate to which the method according to the invention is applied may, for example, be a paper article, such as a sheet, or a cardboard article. It may otherwise be a fabric or a non-woven fabric made of polysaccharide fibers, in particular cellulosic fibers, for example linen or cotton, or even a cellulose fiber, preferably with a diameter greater than 100 nm and preferably greater than 200 nm, for example intended to be woven or shaped to form a fabric or a non-woven fabric. It may also be a compress, in particular for medical use, for example formed from alginate(s).

When the substrate is a paper article, it may have been prepared by any method conventionally used in the paper industry. In particular, it may be made from chemical paper pulp, in particular kraft pulp or bisulfite pulp. Alternatively, it may be paper from the recycling industry.

The reagent used according to the invention may contain a single constituent, or a plurality of constituents, at least one of which is a hydroxylated fatty acid or one of its oligomers or one of its esters as defined above.

In the present description, the term hydroxylated fatty acid is understood to mean, in a conventional manner in itself, an acid with a linear or branched aliphatic hydrocarbon chain comprising from 7 to 24 carbon atoms, and carrying at least one hydroxyl function.

The hydroxylated fatty acid(s) contained in the reagent may comprise a single acid function, or a plurality of acid functions, for example two acid functions.

The reagent used in the process according to the invention may consist solely of hydroxylated fatty acid(s) and/or oligomer(s) of such hydroxylated fatty acid(s) and/or ester(s) of such hydroxylated fatty acid(s) and alcohol(s) with a linear or branched, saturated or unsaturated, optionally substituted aliphatic chain, said aliphatic chain comprising from 1 to 18 carbon atoms. It may otherwise comprise this or these hydroxylated fatty acid(s) and/or these oligomers and/or these esters in a mixture with other constituents. In such configurations, said reagent then preferably comprises at least 50% by weight, more preferably at least 70% by weight, and preferentially at least 80% by weight, relative to the total weight of the dry matter contained in said reagent, of hydroxylated fatty acid(s) and/or oligomer(s) of such hydroxylated fatty acid(s) and/or ester(s) of such hydroxylated fatty acid(s) and alcohol(s) with a linear or branched, saturated or unsaturated, optionally substituted aliphatic chain, said aliphatic chain comprising from 1 to 18 carbon atoms.

By dry matter, we mean, in a classical manner in itself, the material remaining after lyophilization, that is to say freed from the water and organic solvents which may be contained in the reagent.

When the reagent comprises at least one ester of a hydroxylated fatty acid, preferably, this ester is a methyl or ethyl ester.

The method according to the invention may also meet one or more of the characteristics described below, implemented in isolation or in each of their technically effective combinations.

In preferred embodiments of the invention, at least one hydroxylated fatty acid included in the reagent is a polyhydroxylated fatty acid, i.e. comprising a plurality of hydroxyl groups, and preferably dihydroxylated, i.e. comprising two hydroxyl groups. In such embodiments, the content of polyhydroxylated fatty acid(s), preferably dihydroxylated, and/or oligomers of such hydroxylated fatty acid(s) and/or ester(s) of such hydroxylated fatty acid(s) as defined above, in said reagent is preferably at least 50% by weight, more preferably at least 70% by weight, and preferentially at least 80% by weight, relative to the total weight of the dry matter contained in said reagent. Such a characteristic proves to be particularly advantageous in that it allows, by the presence of numerous free hydroxyl functions within the coating formed on the substrate during the implementation of the method according to the invention, and remaining free at the end of the esterification reactions caused by the heat treatment, to carry out possible subsequent additive treatments of this coating, aimed at giving it additional properties, and in particular implementing esterification or etherification reactions of these free hydroxyl functions.

In particular embodiments of the invention, the reagent contains at least:
- a hydroxylated fatty acid, preferably polyhydroxylated, and preferably dihydroxylated, comprising a hydroxyl group in the ω position,
- and/or an oligomer of such a fatty acid,
- and/or an ester of such a fatty acid and an alcohol with a linear or branched, saturated or unsaturated, optionally substituted aliphatic chain, said aliphatic chain comprising from 1 to 18 carbon atoms.

Such a fatty acid, called ω-hydroxylated, comprises at least one hydroxyl OH group in the ω position, that is to say carried by the last carbon atom of the fatty acid chain, the first carbon atom of the chain being the carbon atom of the carboxyl group of the molecule. It has been noted by the present inventors that such a characteristic improves certain of the mechanical properties of the substrates treated by the method according to the invention, in particular, when these substrates are formed from paper, their Young's modulus and their maximum stress. This improvement is all the more significant when the ω-hydroxylated fatty acid used is of the dihydroxylated type.

The content in said reagent of hydroxylated fatty acid(s), preferably polyhydroxylated, and preferentially dihydroxylated, comprising at least one hydroxyl group in the ω position, and/or oligomer(s) of such hydroxylated fatty acid(s) and/or ester(s) of such hydroxylated fatty acid(s) as defined above, is preferably at least 50% by weight, more preferably at least 70% by weight, and preferentially at least 80% by weight, relative to the total weight of the dry matter contained in said reagent.

At least one hydroxylated fatty acid used according to the invention can thus in particular correspond to the general formula (I):

in which:
n is an integer between 7 and 21, preferably between 12 and 20, more preferably between 13 and 19, preferentially between 15 and 17,
m is an integer greater than 0, preferably between 1 and 3, and preferably equal to 1,
p represents the number of unsaturations contained in said fatty acid and is an integer between 0 and 3, preferably equal to 0.

The hydroxylated fatty acid esters which can be used according to the invention can in particular correspond to the general formula (II):

in which:
n, m and p are as defined previously,
and R represents a linear or branched, saturated or unsaturated, optionally substituted, aliphatic chain comprising from 1 to 18 carbon atoms, preferably from 1 to 6 carbon atoms, preferentially a methyl radical or an ethyl radical.

In the present description, the term “aliphatic chain” is understood to mean, in a conventional manner in itself, a non-aromatic open carbon chain.

Examples of hydroxy fatty acids that may be included in the reagent are, but are not limited to, 10,16-dihydroxyhexadecanoic acid and 9,10,18-trihydroxyoctadecanoic acid.

At least one hydroxylated fatty acid included in the reagent, in a content preferably greater than or equal to 50% by weight, more preferably greater than or equal to 70% by weight, and preferably greater than or equal to 80% by weight, relative to the total weight of the dry matter contained in said reagent, is preferably 10,16-dihydroxyhexadecanoic acid, of formula (I') below:

Esters particularly suitable for implementing the process according to the invention are the methyl ester and the ethyl ester of 10,16-dihydroxyhexadecanoic acid.

The hydroxylated fatty acid(s), their oligomers and esters as defined above, included in the reagent used in the process according to the invention, can be synthesized chemically. They can also be obtained from plant extracts, for example by depolymerization of suberin extracted from plants such as cork or potato peels.

Preferably, the hydroxylated fatty acid(s) and/or their oligomers included in the reagent are obtained from the cuticle of plants, and more precisely from cutin, by at least partial, preferably total, depolymerization of the latter by enzymatic method or by acid or basic hydrolysis.

Cutin is a polymeric network of hydroxylated fatty acids, mostly C16 and C18, crosslinked by ester bonds, which is involved in waterproofing the leaves and fruits of higher plants. It is the main component of the plant cuticle, the continuous extracellular lipid membrane that covers the aerial parts of plant leaves and fruits.

In particularly preferred embodiments of the invention, the reagent is an extract obtained by at least partial, preferably total, depolymerization of cutin extracted from plants.

Preferably, for use as a reagent in the method according to the invention, this extract has been previously freed from the solvent(s) used for the extraction of the cutin and its depolymerization, so that the reagent is free of such solvents, and contains only the material derived from the cutin. This does not, however, exclude embodiments of the invention in which the extract used as a reagent comprises residual quantities, or even more, of solvent(s) used for the extraction of the cutin from plants and/or its depolymerization, for example water. In such configurations, the reagent concentration values mentioned below in the present description take into account only the material extracted from the cutin, to the exclusion of such solvents. This material extracted from the cutin contained in the extract is referred to herein as “dry matter”.

Preferably, the reagent is an extract obtained by depolymerization of cutin from tomatoes, which has the advantage of a great homogeneity of constitution of the cutin from one tomato species to another, this cutin also having a constituent monomer in a largely majority quantity: 10,16-dihydroxyhexadecanoic acid, which is present there at more than 80% by weight.

Tomato processing waste, called tomato dregs, contains a significant amount of cutin, more precisely 60 to 70% by weight of cutin. It is estimated that 4 to 5 million tonnes of tomato dregs are produced each year worldwide. Thus, the process according to the invention can very advantageously make it possible to recover agricultural and industrial waste such as tomato dregs, which is of great interest from both an environmental and economic point of view.

Alternatively, the reagent used in the method according to the invention may be an extract obtained by depolymerization of cutin from other plants, such as apple ( Malus pumila ), bitter orange ( Citrus aurantium ), broad beans ( Vicia faba ), wild cherry ( Prunus avium ), cranberry ( Vaccinium macrocarpon ), vine fruit ( Vitis vinifera ), pea seed ( Pisum sativum ), gooseberry fruit ( Ribes grossularia ), papaya ( Malabar papaiarnarum ), agave leaves ( Agave americana ), grapefruit seeds ( Citrus paradisi ), lemon ( Citrus limon ), lime ( Citrus aurantifolia ), papaya fruit ( Carica papaya ), onion ( Allium cepa ), cranberries ( Vaccinium vitis idaea ), coffee leaves ( Rubiaceae coffea ), rosehip fruits ( Rosa canina ), squash ( Cucurbita pepo ), etc.

Any method for extracting cutin from plants, in particular the fragmentation of tomato dregs or tomato skins, and any method for depolymerizing this cutin, can be used to obtain the reagent used in the method according to the invention. Schematically, these methods comprise the fragmentation of tomato dregs, or other plant elements, such as apple, to extract the cutin therefrom, then the hydrolysis of the cutin to obtain the constituent monomers and/or oligomers of such monomers. After isolation, by physical separation methods or by liquid-liquid extraction, the cutin is thus chemically hydrolyzed, in particular by alkaline means in an organic and/or aqueous medium, or using specific enzymes, in particular cutinases.

An example of a method that can be implemented for this purpose is described in document WO 2015/028299. This method comprises, schematically, the heat treatment of tomato skins, then their introduction into an alkaline solution, for example potassium hydroxide at a concentration between 0.5 M and 6 M, at a temperature between 20°C and 130°C, for example between 65°C and 130°C. The solution is then filtered, then acidified, in particular with hydrochloric acid at a concentration between 12 M and 6 M. After centrifugation, for example at 10,000 to 14,000 rpm for 15 to 20 minutes, the pellet is washed, for example with demineralized water, then dried if necessary.

A preferred method according to the invention consists, after a step of decanting tomato dregs to recover the skins, and the drying, grinding and defatting of the skins thus recovered, in hydrolyzing them in an alkaline medium in an alcoholic solvent. For example, such hydrolysis can be carried out by immersing the defatting and dehydrated skins in alcoholic potash (for example formed from 5% potash in anhydrous ethanol), at 50°C, for 6 hours to 5 days, preferably for 2 days. The mixture can then be filtered under vacuum, and the ethanol removed using a rotary evaporator. The fatty acids contained in the composition obtained can be precipitated, in particular in water at a pH between 2 and 3, for example in a 37% hydrochloric acid solution, then recovered, in particular by centrifugation, for example at 9000 rpm for 20 minutes. After rinsing(s) the pellet obtained with demineralized water and freeze-drying, an oily composition is obtained, with a yield of between 60 and 70%, containing essentially fatty acids, the vast majority of which is 10,16-dihydroxyhexadecanoic acid, which is particularly advantageous for use as a reagent in the process according to the invention.

More specifically, this oily composition obtained at the end of the cutin depolymerization operations contains at least 85% by weight of fatty acids. 10,16-Dihydroxyhexadecanoic acid preferably represents at least 88% by weight of these fatty acids. This composition, which also contains phenolic and carotenoid compounds absorbing at 380, 288 and 225 nm, as well as other substances in small quantities, in particular phenolic compounds, can advantageously be directly used in the process according to the invention.

The hydroxylated fatty acid ester(s) that may be included in the reagent according to the invention may be prepared by esterification of the corresponding hydroxylated fatty acid according to any conventional method in itself for those skilled in the art, without catalysis or preferably with acid catalysis. They may otherwise be obtained by transesterification of the hydroxylated fatty acids contained in plant cutins, preferably carried out using acid catalysis or basic catalysis, using a strong base or alcoholates such as sodium methanolate or sodium ethanolate. The alcohol used to carry out the esterification or transesterification reaction of the fatty acid preferably contains from 1 to 18 carbon atoms and preferably from 1 to 8 carbon atoms. It is preferably chosen from methanol, ethanol, propanol, butanol, pentanol, hexanol and its isomers including 2-ethyl-butanol, heptanol and its isomers such as 2-heptanol, octanol and its isomers such as 2-ethyl-hexanol, and also isopropanol, 2-methyl-propanol, 2-methyl-propan-2-ol, butan-2-ol, amyl alcohols, 2-methyl-butanol, 3-methyl-butanol, 2,2-dimethylpropanol, pentan-3-ol, pentan-2-ol, 3-methylbutan-2-ol, 2-methylbutan-2-ol, guerbet alcohols such as 2-propyl-heptanol, 2-butyl-octanol.

For example, a hydroxylated fatty acid ester that can be included in the reagent used in the process according to the invention can be directly produced from tomato skins, by bringing these skins into contact with alcohol, in particular methanol or ethanol, in the presence of an acid, for example 2 to 5% concentrated sulfuric acid, at a temperature of between 50 and 70°C for at least 6 hours. The esters obtained at the end of the transesterification reaction can be purified by adding water to the reaction medium and then centrifuging.

Preferably, when the reagent is an extract obtained by depolymerization of cutin, preferably tomato cutin, or a product obtained by esterification of the fatty acids contained in such an extract by a monoalcohol such as methanol or ethanol, this extract or this product is applied to the surface of the substrate, or introduced into the vehicle of the composition and the latter applied to the surface of the substrate, without this extract or this product being subjected to additional treatment operations, other than purification and/or drying, in particular without being subjected to a heat pretreatment at a temperature of 40°C or more, or 50°C or more.

The use in the process according to the invention of an extract obtained by depolymerization of cutin, preferably tomato cutin, or of a product obtained by esterification of the fatty acids contained in such an extract by a monoalcohol such as methanol or ethanol, advantageously makes it possible to obtain stable hydrophobization of the polysaccharide surface, in particular cellulosic, of the substrate, unlike for example the waxes proposed by the prior art, the coating formed on the surface of the substrate being furthermore biodegradable and recyclable.

The reagent, particularly when it is an oily extract obtained from plant material, in particular by depolymerization of cutin from a plant such as tomato, can be applied alone to the surface of the substrate. In such embodiments, the application is preferably carried out hot, at a temperature ensuring that this extract is in fluid form, for example at 60°C.

In alternative embodiments of the invention, the reagent is applied to the surface of the substrate in a composition containing it in a liquid vehicle. The method then optionally comprises, before the heat treatment step, a step of drying the substrate at a temperature allowing at least partial, preferably total, evaporation of the vehicle from the surface of the substrate.

This liquid vehicle can be of any type, vehicles allowing the reagent to be solubilized being, however, particularly preferred within the framework of the invention.

This vehicle may in particular be a monoalcohol, preferably C1-C4, preferably ethanol, which has the advantage of a biosourced origin. The composition is then preferably in the form of a solution, in which the reagent is completely dissolved in the vehicle. The vehicle may otherwise, for example, be a mixture of water and a monoalcohol, preferably C1-C4, preferably ethanol. This mixture then preferably contains at least 40% by volume of said monoalcohol, preferably ethanol, relative to the total volume of the mixture. The composition is then in the form of an emulsion.

The liquid vehicle used may alternatively consist of water, the composition then being in the form of a water-in-oil or oil-in-water dispersion or emulsion. In such embodiments, it is advantageous for the composition to comprise one or more emulsifying agents/surfactants, which may be of the amphoteric, anionic, cationic or non-ionic type. These emulsifying agents/surfactants are then preferably biosourced, examples being hydrogenated lecithin and monoglycerides. The composition may alternatively be free of such emulsifying agents/surfactants, and contain for example ammonia (NH ₃ ). It has in fact been discovered by the present inventors that it is possible to disperse the hydroxylated fatty acids in ammonia water, in particular at an ammonia concentration in a hydroxylated fatty acids/NH ₄ OH molar ratio greater than 1, in particular at a concentration of 10 to 80% of hydroxylated fatty acids in the ammonia water and at a temperature ranging from 30°C to 80°C. The ammonia is furthermore advantageously removed from the coating formed on the substrate during the heat treatment step of the process according to the invention.

Thus, in particular embodiments of the invention, the vehicle of the composition is water containing ammonia.

In particular embodiments of the invention, the concentration of the reagent (more precisely its dry matter) in the composition is between 25 and 200 g/l. At such concentrations, in particular, hydroxylated fatty acids, their oligomers and their esters are well soluble in monoalcohols, in particular ethanol.

The composition used in the method according to the invention may contain, in addition to the reagent and the vehicle, one or more additives making it possible to confer on the substrate and/or the coating formed on its surface in accordance with the invention, one or more additional desired properties. This or these additives are preferably biosourced, and preferably biodegradable and/or recyclable, to meet the environmental objective of the invention. As such additives, mention may be made, in addition to the emulsifying agents/surfactants mentioned above, of pigments, dyes, thickeners, flame retardants, dispersants, reinforcing agents, anti-slip agents, etc.

The composition may further contain one or more polyols, such as glycerol. Alternatively, the process may not use any polyols. This means that no polyol is added to the composition, or brought into contact with the substrate during the process. The polysaccharides forming the substrate, and the polyols that may be contained in the reagent, when the latter is a plant extract or derived from a plant extract, are then not considered herein as polyols used by the process.

The composition may also contain one or more esterification reaction catalysts and/or crosslinking agents. Alternatively, the process may not use any esterification reaction catalysts and/or any crosslinking agents.

The application of the reagent to the surface of the substrate can be carried out in any conventional manner allowing the deposit on a substrate of a substantially homogeneous layer of a reagent in fluid form or contained in a liquid composition. This application can in particular be carried out by coating, for example by roller, blade, spraying, centrifugation or even by immersion of the substrate in a bath of the composition.

The application of the reagent to the surface of the substrate is carried out in such a way as to deposit the desired quantity of reagent on this surface, this quantity depending on the properties expected for the treated substrate. For example, in the case of a substrate made of cellulose fiber fabric, for example linen, smaller quantities of reagent will give it aerated and hydrophobic (“water-repellent”) properties, while larger quantities will give it the appearance of leather or the appearance (and properties) of oilcloth.

In particular embodiments of the invention, the application of the composition to the surface of the substrate is carried out so as to deposit on this surface at least 2.5 g of reagent/m ² of said surface, for example from 2.5 to 60 g/m ² , in particular from 3 to 50 g/m ² , this quantity however being able to be much greater, and amounting to 1500 g/m ² for example, or even more. Such quantities make it possible to form on the surface of the substrate a coating (continuous or formed individually on the polysaccharide fibers, depending on the quantity of reagent deposited) giving it a strong hydrophobic character, but also a barrier to oils, and furthermore having improved mechanical properties compared to the initial substrate.

Depending on the substrate and the applications for which it is intended, it may be advantageous within the framework of the invention for the quantity of reagent deposited on the surface of the substrate to be greater than or equal to 30 g/m ² . At such quantities, the mechanical property that is elongation at break is advantageously not penalized compared to the initial substrate, this property may even be improved.

The heat treatment step of the process according to the invention is preferably carried out in an oven, by simply heating the substrate bearing the coating, without applying pressure to the latter, in particular by heat pressing.

It is within the skill of the person skilled in the art to determine the conditions of the heat treatment step that are suitable for carrying out the esterification reactions between carboxyl groups of the hydroxylated fatty acid, and hydroxyl groups of the polysaccharide and hydroxyl groups of the hydroxylated fatty acid, depending on the particular characteristics, on the one hand, of the substrate, on the other hand, of the reagent, and, finally, of the presence or absence within the composition containing the latter of additional polyols and/or catalysts and/or crosslinking agents.

The heat treatment is preferably carried out at atmospheric pressure, preferably at a temperature between 100 and 250°C, preferably between 100 and 200°C, or between 100 and 150°C, for example at approximately 150°C.

The heat treatment is further preferably carried out for a period of between 30 seconds and 24 hours, preferably for approximately 24 hours in the absence of an esterification reaction catalyst.

Such temperature and duration conditions advantageously ensure optimal grafting of the hydroxylated fatty acid molecules onto the polysaccharide polymer, by esterification reaction, as well as the formation of numerous ester bonds between the hydroxylated fatty acid molecules themselves, the whole leading to the formation on the surface of the substrate of a continuous or discontinuous network with hydrophobic properties, constituting an effective barrier to water but also to fatty substances, and improving the mechanical properties of the substrate.

As explained above, the method according to the invention finds particularly advantageous application in the fields of papermaking, in particular for the manufacture of special papers with high added value, packaging and textiles, in particular for the manufacture of technical fabrics, for example for applications in the form of clothing, as well as in the medical field, more particularly compresses.

Another aspect of the invention relates to a solid substrate manufactured from a polysaccharide-based material that can be obtained, in particular being obtained, at the end of a process according to the invention. This substrate comprises, on at least one surface, molecules of at least one hydroxylated fatty acid covalently linked to the polysaccharide, more particularly by ester bond between their carboxylic acid function and hydroxyl functions of the polysaccharide.

This substrate and this coating, in particular concerning its components, may meet one or more of the characteristics described above with reference to the method according to the invention.

In particular, the polysaccharide can be cellulose or an alginate.

The substrate may be a paper article, such as a sheet, or a cardboard article. It may otherwise be a fabric or a non-woven fabric made of polysaccharide fibers, in particular cellulosic fibers, for example linen or cotton, or even a cellulose fiber, with a diameter preferably greater than 100 nm, and preferably greater than 200 nm, for example intended to be woven or shaped to form a fabric or a non-woven fabric. It may also be a compress, in particular for medical use, for example formed from alginate(s).

Preferably, the majority component of the coating formed on the surface of the substrate is 10,16-dihydroxyhexadecanoic acid, which is preferably present therein in a content greater than or equal to 70% by weight, and preferably greater than or equal to 80% by weight, relative to the total weight of the coating, and the carboxylic acid groups of which are involved in ester bonds with, on the one hand, hydroxyl groups of the polysaccharide polymer forming part of the substrate, and on the other hand, hydroxyl groups of other molecules of hydroxylated fatty acid(s) or their oligomers or their esters as defined above, contained in the coating.

The characteristics and advantages of the invention will appear more clearly in light of the examples of implementation below, provided for purely illustrative purposes and in no way limiting the invention, with the support of figures 1 to 6, in which:

FIG. 1 There FIG. 1 shows spectra obtained by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) for, respectively, a paper substrate alone (“P”), and the same substrate after treatment by a method according to the invention involving the application to the substrate of a solution containing a tomato cutin extract based essentially on hydroxylated fatty acids, in ethanol at a concentration of 0.2 g/ml (“0.2”), 0.1 g/ml (“0.1”) or 0.025 g/ml (“0.025”).

FIG. 2 There FIG. 2 shows spectra obtained by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) for, respectively, a paper substrate alone (“P”), the same substrate after treatment by a method according to the invention involving the application to the substrate of a solution containing a tomato cutin extract based essentially on hydroxylated fatty acids, in ethanol at a concentration of 0.2 g/ml (“0.2”), 0.1 g/ml (“0.1”) or 0.025 g/ml (“0.025”), and the same substrate after treatment by a method according to the invention involving the application to the substrate of a solution containing palmitic acid in ethanol at a concentration of 0.2 g/ml (“AcP”).

FIG. 3 There FIG. 3 shows photographs of paper substrates treated by a method according to the invention, implementing the application to the substrate of a solution containing a tomato cutin extract based essentially on hydroxylated fatty acids in ethanol, for % by weight of coating formed on the substrate at the end of the method, relative to the weight of the substrate, of, respectively, in a/ 1.8%, in b/ 8.8%, in c/ 13.9%, after depositing a drop of water on their surface; the respective drops are designated by arrows in the figure.

FIG. 4 There FIG. 4 shows photographs of substrates treated or not by a process in accordance with the invention, implementing the application to the substrate of a solution containing an extract of tomato cutin based essentially on hydroxylated fatty acids in ethanol, after depositing drops of water on their surface, for, in a/ an untreated paper substrate, in b/ the same substrate in treated paper, and in c/ a treated linen fabric substrate.

FIG. 5 There FIG. 5 shows photographs obtained by scanning electron microscopy of substrates treated or not by a method in accordance with the invention, implementing the application to the substrate of a solution containing an extract of tomato cutin based essentially on hydroxylated fatty acids in ethanol, for, in a/ an untreated linen fabric substrate, and in b/ the same substrate in treated linen fabric – in this last photograph, examples of coating formed on the fibers are highlighted by arrows.

FIG. 6 there FIG. 6 shows photographs of cotton fabric substrates treated by a process according to the invention, implementing the hot application to the substrate, at a rate of, in A/ 1481 g/m ² , and in B/ 617 g/m ² of a solution containing a tomato cutin extract based essentially on hydroxylated fatty acids.

A/ Example 1 - Obtaining an extract of tomato cutin E0

A.1/ Preparation of the extract

A process for extracting hydroxylated fatty acids from tomato cutin is carried out as follows.

Tomato skins are isolated by decantation from tomato dregs. These skins are dried, ground, and defatted by reflux in a Soxhlet extractor using an acetone:ethanol mixture (1:1) for 2 days. They are then dehydrated.

200 g of previously dewaxed and dehydrated tomato skins are suspended in 1 l of a 5% potassium hydroxide KOH solution prepared in anhydrous ethanol. The mixture is heated at 50°C for 16 h. The suspension is then vacuum filtered through an A0 size frit (160-250 µm), the volume of ethanol is reduced by evaporation, then the filtrate is diluted with water and acidified to pH 3-4 using a 37% hydrochloric acid HCl solution. The suspension thus formed is centrifuged at 8000 rpm for 15 min at 20°C, then the centrifugation pellet is recovered, washed with water and then dried under vacuum. 150 g of an oily extract consisting mainly of fatty acids (more than 85% by weight) are thus obtained.

This extract, reddish-brown in color, is referred to herein as “E0”.

A.2/ Analysis of the fatty acid composition of the extract

An analysis of the E0 extract by gas chromatography coupled with GC-MS/FID mass spectrometry, compared to an external standard range of C17, shows that the fatty acid fraction of this oily extract has an ω-hydroxylated fatty acid content of more than 90%. The percent mass composition of the fatty acid fraction of this oily extract thus obtained is shown in Table 1 below.

Constituent Content in the extract (%w/w) Hexadecanoic acid 2.04 Linoleic acid 0.46 Oleic acid 0.28 Stearic acid 0.05 16-Hydroxyhexadecanoic acid 3.6 1,16-Hexadecanedioic acid 0.61 10,16-Dihydroxyhexadecanoic acid 89.66 1,16-Hydroxyhexadecandioic acid 2.12 Dihydroxyoctanoic acid 0.28

Table 1 - Mass percentage composition of the fatty acid fraction of tomato cutin extract

10,16-Dihydroxyhexadecanoic acid is the largely predominant constituent of this oily extract, representing almost 90% of the weight of the majority fraction.

B/ Example 2 – Process for treating cellulosic substrates

The experiments are carried out with, as reagent:
- the E0 extract on the one hand,
- and, for some of them, for comparison purposes not in accordance with the invention, palmitic acid, that is to say a non-hydroxylated fatty acid of the same chain length as 10,16-dihydroxyhexadecanoic acid.

Two substrates are used:
- Whatman® grade 1 cellulose filter paper, 180 µm thick and weighing 87 g/m ² , hereinafter referred to as “Paper”,
- linen fabric, weight 98 g/m ² , hereinafter referred to as “Fabric”.

The process implemented includes the following 3 or 4 steps.

B.1/ Step 1 – Preparation of compositions containing the reagents

The vehicle used is ethanol.

Compositions based respectively on each of the reagents are obtained by introducing the desired quantity of the reagent into the desired volume of the vehicle. The following concentrations of reagent in the vehicle are more precisely implemented in the experiments below: 0.2 g/ml; 0.1 g/ml; 0.025 g/ml.

B.2 / Steps 2 and 3 – Coating the substrate and drying

A coating is formed on the substrate surface by soaking for 30 s in ethanolic solutions of E0 at different concentrations (0.2 g/mL, 0.1 g/mL, 0.025 g/mL), then draining for 1 min.

The amount of reagent deposited is controlled by adjusting its concentration in the vehicle.

The coating step is followed by a drying step at 40°C for 2 hours, to ensure the evaporation of the ethanol.

The mass of coating deposited on the substrate is determined by weighing, and is equal to the mass of the substrate obtained after coating and evaporation of the ethanol, minus the initial mass of the substrate.

B.3/ Step 4 – Heat treatment

The coated substrates are heated in an oven at 150°C at atmospheric pressure for 24 hours, in the absence of any other substance, in particular in the absence of catalyst, crosslinking agent and additional polyol.

Such conditions induce esterification/polymerization reactions within the molecules forming the coating and between these molecules and the substrate.

At the end of this step, the coated substrate is weighed. The mass of the discontinuous polymer coating formed on its surface is equal to the mass of the substrate obtained after heat treatment minus the initial mass of the substrate.

C/ Example 3 – Structure and stability of polymer coatings

These experiments are carried out on the Paper substrate, with solutions of reagent E0 in ethanol, or of palmitic acid in propanol, at 0.2 g/ml, 0.1 g/ml and 0.025 g/ml.

C.1/ Analysis by infrared spectroscopy

Before and after implementing the method as described in Example 2, the substrate is analyzed by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) on a TFI 550 infrared thermometer spectrometer (Thermo Fisher Scientific) continuously purged with dry air. The spectra are obtained by attenuated total reflectance (ATR) using a single reflection accessory equipped with a diamond crystal with a light incidence angle of 45°. All spectra are acquired in the range of 4000 to 700 cm ^-1 with a resolution of 2 cm ^-1 and by accumulating 30 scans.

The obtained spectra are shown on the FIG. 1 .

The appearance of carbonyl bands (C=O) in esterified form is observed at wavelengths of 1730 cm ^-1 and 1712 cm ^-1 (the wavelength of the acid form of carbonyl being 1703 cm ^-1 ). These bands are higher as the quantity of reagent E0 applied to the substrate was greater. This demonstrates that an esterification reaction of the acid functions of the hydroxylated fatty acids has indeed taken place on the substrate.

A higher amplitude of the bands representative of the _CH2 groups is also observed for the substrates after treatment.

For comparison, the same analysis is carried out after also applying to a substrate a composition comprising the palmitic acid reagent, not in accordance with the invention, at 0.2 g/ml in propanol, according to the same coating method and in the same quantity as the E0 reagent.

The obtained spectra are shown on the FIG. 2 . Surprisingly, the representative bands of esterified C=O carbonyls are much lower when the reagent is palmitic acid ("AcP") than when it is the E0 extract. This indicates less esterification of the acid functions of palmitic acid at the substrate surface. At palmitic acid concentrations in propanol of 0.1 g/ml and 0.025 g/ml, no difference is observed in the spectra compared to the substrate alone.

C.2/ Mass analysis

Samples of the substrate of size 10 cm x 10 cm are weighed, respectively, before and after implementation of the method as described in Example 2, for each of the reagent compositions tested. For each of these compositions, the difference in mass is calculated between the treated substrate and the initial substrate, and the quantity of coating obtained on the surface of the substrate deduced.

The results obtained are shown in Table 2.

Reagent Concentration of reagent in vehicle (g/ml) Initial mass of substrate (g) Final mass of substrate (g) Mass difference (g) Coating obtained (g/m ² ) 0.2 0.8920 1,4925 0.6005 60.05 E0 0.1 0.9087 1,2205 0.3118 31.18 0.025 0.8984 0.9734 0.0750 7.50 0.2 0.8950 0.9174 0.0224 2.24 AcP 0.1 0.8768 0.8776 0.0008 0.08 0.025 0.9120 0.9118 0.0002 0.02

Table 2 – Substrate mass analysis before and after treatment – AcP denotes palmitic acid

Here again, we observe that the esterification, and fixation on the substrate, of the hydroxylated fatty acids of the E0 extract was much greater than that of palmitic acid. The latter was probably removed from the surface of the substrate during the heat treatment step of the process.

C.3/ Ethanol coating resistance test

To test the link between hydroxylated fatty acids and cellulose, an ethanol solubility test (a solvent in which fatty acids, especially hydroxylated ones, are very soluble) is carried out.

For this purpose, substrates are prepared by applying to their surface, respectively, different amounts of a solution of the reagent E0 in ethanol, as described in Example 2. After drying, some of the substrates are subjected to heat treatment step 4, and others are not. The substrates are then rinsed with ethanol by soaking in a 100% ethanol bath for 5 min at room temperature.

The % by weight of reagent present on the substrate, relative to the weight of the substrate, are determined by weighing and comparison with the weight of the initial substrate, before and after rinsing with ethanol.

The results obtained are shown in Table 3.

Substrate Thermal treatment % w/w of reagent on the substrate before rinsing % w/w of reagent on the substrate after rinsing Amount of reagent on the substrate after rinsing (g/m ² ) 1 Yes 13.9 13.8 12 2 Yes 8.8 8.8 7.6 3 Yes 1.8 1.8 1.6 4 No 10.7 1.1 1.0 5 No 4.2 0.9 0.8

Table 3 – Ethanol rinse test of the coating formed on the substrate

It is observed that rinsing with ethanol did not cause any significant loss of mass of the coating for the substrates which were treated by the process according to the invention, this confirming that anchoring by covalent bonding of almost all of the hydroxylated fatty acids on the cellulose and/or between them, by a polyesterification phenomenon, did indeed occur. Conversely, in the absence of heat treatment step 4 of the process, the hydroxylated fatty acids did not react via their carboxylic acid groups with the hydroxyl functions of the cellulose, and did not attach to the latter, so that the loss of mass of the coating was significant during rinsing with ethanol.

Thus, the heat treatment of the process according to the invention does indeed lead to the formation of ester bonds between the hydroxylated fatty acids and the cellulose, which results in anchoring by covalent bonds of the coating formed by the hydroxylated fatty acids on the substrate.

D/ Example 4 - Modification of the surface properties and mechanical properties of the treated substrates

D.1/ Hydrophobic properties

D.1.a/ Experiment 1

A drop of water is placed on each of the substrates 1, 2 and 3 described in Table 3 above. Photographs of these substrates are shown in the FIG. 3 .

It is observed that hydrophobation of the substrate already takes place, although incompletely, from 1.8% by weight of the coating on the substrate (i.e. 1.6 g/m ² ) (sample 3, in a/ in the figure).

At 8.8% by weight (i.e. 7.6 g/m ² ) (sample 2, in b/ in the figure) and 13.9% by weight (i.e. 12.1 g/m ² ) (sample 1, in c/ in the figure) of coating, the hydrophobation of the substrate surface is total: the water droplet does not penetrate the substrate at all. The same result is obtained at a weight content of 4.2% (2.8 g/m ² ) of coating on the substrate.

D.1.b/ Experiment 2

Paper and Fabric substrates are used in this experiment.

These substrates are treated by the process according to the invention of Example 2, using a composition containing the reagent E0 at 0.1 g/mL in ethanol.

Water drops are placed on each of the substrates. For comparison, water drops are also placed on the untreated paper substrate. Photographs of these substrates are shown in the FIG. 4 .

Unlike the untreated paper substrate (in a/ in the figure), it is observed that the surface of the substrates treated in accordance with the invention (in b/ and c/ in the figure) is perfectly hydrophobic and waterproof.

The hydrophobicity properties are evaluated using a TRACKER™ automatic drop tensiometer (Teclis Scientific) in sessile drop configuration. Contact angle measurements are performed on water drops with a volume of 5 µL, 30s after their deposition on Paper substrates treated according to the protocol of Example 2, having coating weight contents, relative to the substrate weight, of 10% and 15% respectively (i.e., coating weight contents of 7.6 and 12.2 g/m ² of substrate, respectively). 7 measurements are performed for each sample. The following drop angle values are obtained:
- at 10% by weight of coating (7.6 g/m ² ): 105.4° (+/-6°),
- at 15% by weight of coating (12.2 g/m ² ): 114.9° (+/-3°).
These values denote significant hydrophobation of the substrate surface.

For comparison, no drop angle is measurable for the same untreated substrate, or treated by the same protocol but using palmitic acid as a reagent, due to the total spreading of the drop on the surface of the substrate and its absorption by the substrate.

D.1.c/ Experiment 3

The Tissue substrate is used in this experiment.

This substrate is treated or not by the process in accordance with the invention of Example 2, using a composition containing the reagent E0 at 0.2 g/mL in ethanol.

Photographs of the substrates observed under the Phenom® Pure® G6 scanning electron microscope (Thermo Scientific®) are shown in the FIG. 5 The system was placed under pressure of 1 Pa, the sample surface was scanned by an electron beam accelerated at a speed of 10 kV, and photographs were obtained in BSD Full mode at a magnification of x290 and x410, respectively.

Unlike the untreated fabric substrate (in a/ in the figure), it is observed that the flax fibers of the substrate treated in accordance with the invention (in b/ in the figure) are coated with a coating.

The hydrophobic properties are evaluated by contact angle measurement as described in Experiment 2 on a Fabric substrate treated according to the protocol of Example 2, having a weight content of the coating, relative to the weight of the substrate, of 51% (equivalent to 48.3 g/m ² of substrate). 10 measurements are carried out for this sample. The following drop angle value is obtained: 148.1° (+/-8°). This value indicates significant hydrophobization of the substrate surface and gives it properties close to superhydrophobicity.

D.2/ Mechanical properties

This experiment is carried out for the Paper substrate, with the reagents E0 and palmitic acid, for different weight contents of the coatings formed from these reagents on the substrate.

The compositions used for the formation of coatings in accordance with the protocol of Example 2 have concentrations between 25 and 200 mg/ml of the reagent.

The mechanical properties of the treated substrates were measured in a tensile test using the MTS Synergie 100 tensile testing machine (MTS Systems Corporation). Specimens of the treated substrate were cut into a dumbbell shape as described in ASTM D412. The test was carried out at a speed of 10 mm/min. The results obtained, in terms of Young's modulus, maximum stress and % elongation at break, are reported in Table 4 below.

Reagent % w/w coating on substrate Quantity of coating deposited (g/m²) Young's modulus (MPa) Maximum stress (MPa) % elongation at break Untreated - - 448 9 4.3 E0 3 2.7 921 14 2 8.3 7.5 795 17 4 17.5 16.0 1250 24 3 34.3 31.2 1250 27 4.2 67 60.1 1166 29 4.6 AcP 1.2 1.1 564 7 2 2.5 2.2 729 8 1.5

Table 4 – Mechanical properties of treated paper substrates – values shown are the averages of five samples – AcP denotes palmitic acid

These results show a strong increase in Young's modulus and maximum stress induced by the process using the E0 reagent in accordance with the invention. The modifications induced by treatment with palmitic acid, a non-hydroxylated fatty acid, are less significant. Treatment of the substrate by the process according to the invention therefore made it possible to improve some of the mechanical properties of the substrate.

Regarding the % elongation at break, a result equivalent to that of the untreated substrate is obtained from a coating content on the substrate greater than or equal to 31.2 g/m ² .

D.3/ Surface appearance

Cotton fabric substrates are used in this experiment.

These substrates are treated by the process according to the invention of Example 2, with the exception of the coating step, which is carried out hot (60°C) using the E0 reagent alone, without vehicle. Quantities of reagent of between 5 and 12 g for a surface area of 81 cm ² , i.e. 617 to 1481 g/m ² of substrate, are respectively deposited on the substrates.

After the heat treatment step, depending on the amount of reagent deposited, substrates with the appearance of leather are obtained, as illustrated in A/ on the FIG. 6 , or oilcloth, as illustrated in B/ on the FIG. 6 .

Claims (18)

Method for treating a surface of a solid substrate manufactured from a material based on a polysaccharide with free hydroxyl functions, characterized in that it comprises successive steps of:
- application, on said surface of the substrate, of a reagent comprising at least one hydroxylated fatty acid and/or oligomer of said hydroxylated fatty acid and/or ester of said hydroxylated fatty acid and an alcohol with a linear or branched, saturated or unsaturated, optionally substituted aliphatic chain, said aliphatic chain comprising from 1 to 18 carbon atoms, or any of their mixtures,
- and heat treatment of said substrate under conditions causing esterification reactions to occur between carboxyl groups of said hydroxylated fatty acid, and hydroxyl groups of said polysaccharide and hydroxyl groups of said hydroxylated fatty acid. The method of claim 1, wherein said polysaccharide is cellulose or an alginate. The method of claim 1 or 2, wherein said hydroxy fatty acid is a polyhydroxy fatty acid. A method according to any one of claims 1 to 3, wherein said hydroxylated fatty acid comprises a hydroxyl group in the ω position. The method of claim 4, wherein said hydroxylated fatty acid is 10,16-dihydroxyhexadecanoic acid. Method according to any one of claims 1 to 5, according to which said reagent is an extract obtained by depolymerization of cutin, preferably tomato or apple cutin. Method according to any one of claims 1 to 6, according to which said reagent is applied to said surface of the substrate in a composition containing it in a liquid vehicle, said method optionally comprising, before said heat treatment step, a step of drying said substrate at a temperature allowing at least partial evaporation of said vehicle from said surface of the substrate. The method of claim 7, wherein said vehicle is a C1-C4 monoalcohol, a mixture of water and a C1-C4 monoalcohol, or water containing ammonia. A method according to claim 7 or 8, wherein the concentration of said reagent in said composition is between 25 and 200 g/l. A method according to any one of claims 7 to 9, wherein said composition further contains one or more additives. A method according to any one of claims 1 to 10, wherein the application of said reagent to said surface of the substrate is carried out so as to deposit on said surface at least 2.5 g of reagent/m ² of said surface. Method according to any one of claims 1 to 11, according to which said heat treatment is carried out at atmospheric pressure at a temperature between 100 and 250°C. Method according to any one of claims 1 to 12, according to which said heat treatment is carried out for a period of between 30 seconds and 24 hours. A method according to any one of claims 1 to 13, wherein the application of said reagent to said surface of the substrate is carried out by coating. A method according to any one of claims 1 to 14, wherein said substrate is a paper or cardboard article, a fabric or non-woven fabric made of polysaccharide fibers, or a cellulose fiber. Solid substrate manufactured from polysaccharide-based material capable of being obtained following a process according to any one of claims 1 to 15, characterized in that it comprises, on a surface, molecules of at least one hydroxylated fatty acid covalently linked to said polysaccharide. The substrate of claim 16, wherein said polysaccharide is cellulose or an alginate. A substrate according to claim 16 or 17, which is a paper or cardboard article, a fabric or non-woven fabric made of polysaccharide fibers, or a cellulose fiber.