Method for preparing multifunctional cellulose and use thereof for preparing multifunctional nanofibrillated cellulose

Abstract

The present invention relates to a process for the preparation of multifunctional cellulose comprising subjecting cellulose fibers to a first functionalization step for grafting a first organic functional group on the cellulose and a second functionalization step for grafting a second organic functional group on the cellulose simultaneously in a pot in an alkaline reaction medium. These polyfunctionalized cellulose fibers thus obtained and containing at least one carboxyl functional group are particularly suitable for being subjected to a nanofibrillating step to produce polyfunctionalized nanofibrillated cellulose.

Description

[0001] The present invention belongs to the general field of valorizing renewable resources, in particular cellulose.

[0002] More particularly, the present invention relates to a method for preparing multifunctionalized cellulose fibers. The present invention also relates to a more comprehensive method for preparing multifunctionalized nanofibrillated cellulose, as well as multifunctionalized nanofibrillated cellulose obtainable by such a method, and its use in composite materials.

[0003] Cellulose is the most abundant renewable resource on earth, and its value-added is considered one of the most effective ways to achieve sustainability. Due to its high abundance, low cost, and biodegradability, cellulose is indeed a high-value candidate for replacing fossil resources for the preparation of bio-based materials.

[0004] The prior art has proposed many methods to modify cellulose so that its surface properties are adapted to the application for which it is intended to be used. Most of these methods achieve the grafting of a single functional group (e.g., a hydrophobic group) on the cellulose surface. Since many applications require cellulose to have multiple functions, several methods have also been proposed for grafting two different functional groups thereon. One of these methods, including providing cellulose fibers with carboxymethyl functional groups and aldehyde functional groups, is described in, for example, a publication by Sichinga et al., 2022, Cellulose, 29(2): 799-815. However, all methods for preparing multifunctional cellulose developed so far are expensive and time-consuming.

[0005] There is still a need for a method for preparing multifunctionalized cellulose fibers in a short reaction time, at low cost and in high yield. This need is even more important as multifunctionalized cellulose fibers can be used to prepare multifunctionalized nanofibrillated cellulose that finds applications in many fields.

[0006] Nanofibrillated cellulose, also known as cellulose nanofibrils or cellulose nanofibrils (CNF), consists of nanoscale cellulose fibers with a width in the nanometer range, typically between 5 nm and 15 nm, and a length in the micrometer range, which has attracted great scientific and commercial interest due to its high abundance, renewability and recyclability, and its attractive properties such as high aspect ratio, high strength and stiffness, low density, transparency, high surface area and low thermal expansion. These excellent properties have led to the manufacture and use of nanofibrillated cellulose in a wide range of applications, including packaging, paper and paperboard, composite materials, adhesives, absorbents, electronic devices, medical treatment, pharmaceuticals and cosmetics.

[0007] Despite its excellent properties, nanofibrillated cellulose remains underutilized due to several limitations associated with its manufacture. Typically, nanofibrillated cellulose is prepared by breaking down cellulose fibers, typically in the initial form of delignified wood pulp, into fine fragments. However, the mechanical treatment methods implemented for this purpose, typically homogenization or high-pressure microfluidization, involve high energy consumption to break the fibers into nanoscale and tend to destroy the nanofiber structure by reducing its molar mass and crystallinity.

[0008] To facilitate the nanofibrillation process and limit its energy requirements, two main types of strategies for pretreatment of cellulose fibers have been developed: enzymatic and chemical.

[0009] Enzymatic cellulose pretreatment involves the use of endoglucanases or cellulase solutions, whose hydrolytic action destroys the cellulose structure, thus facilitating the subsequent mechanical treatment steps. However, the energy required to shear the fibers is still high and requires multiple passes through homogenizers or high-pressure microfluidizers. In addition, the quality of the nanofibers obtained, in particular their dispersibility, is generally poor.

[0010] Chemical pretreatment of cellulose fibers aims at introducing ionic groups on the surface of the fibers for generating electrostatic repulsion phenomena and thereby improving the colloidal stability of the nanofibril dispersion. Mechanical shearing is thus highly promoted. Two main methods have been proposed for this purpose: oxidation catalyzed by the free radical 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO), and carboxyalkylation, in particular carboxymethylation.

[0011] TEMPO-catalyzed oxidation is considered one of the most promising methods for the production of cellulose nanofibers. In fact, TEMPO converts the primary hydroxyl group at C6 in the cellulose chain into a carboxylate group, which generates electrostatic repulsion and promotes the separation of cellulose nanofibers during subsequent mechanical treatment. The use of TEMPO oxidation reduces the energy cost of the process. However, it leads to large amounts of toxic waste that are difficult to dispose of on an industrial scale, and a significant reduction in the degree of polymerization (DP) on the cellulose chains occurs during the oxidation. In addition, the presence of toxic residual reactive substances in the obtained reaction product limits the use of this reaction product and adversely affects the properties of CNF over time.

[0012] Traditionally, the controlled carboxymethylation developed for the complete dissolution of cellulose fibers can be regarded as a strategy to promote nanofibrillation. For this purpose, cellulose fibers are first impregnated with monochloroacetic acid (MCA), and then their hydroxyls are activated by concentrated sodium hydroxide (NaOH) solution to carry out Williamson etherification to the hydroxyls of the cellulose chains. Degree of substitution (DS) is the average number of functional groups, more particularly carboxymethyl groups introduced in the cellulose polymer, which can be controlled by experimental conditions such as MCA and NaOH ratios, temperature and reaction time. The carboxyl groups introduced into the cellulose chains thus promote fiber breakage and the acquisition of CNF, particularly due to the formation of irreversible hydrogen bonds in the cellulose polymer by replacing hydroxyls with carboxymethyl groups.

[0013] The obstacle of the industrial use of CNF is that it is difficult to adapt its surface characteristics to specific applications. Carboxymethylated CNF is usually sold without any additional modification, which limits its use in applications requiring high compatibility and / or interaction with some other components such as organic components, for example, as a reinforcing material in a hydrophobic polymer matrix in the field of composite materials. Nanofibrillated cellulose, for example, in the field of composite materials, in the packaging industry, in separation technologies such as filtration and purification, as many industrial applications of hydrogels or aerogels, etc., does require the introduction of additional functionality on the cellulose surface, such as additional functional groups, additional characteristics, additional reactivity, etc. For most of such applications, it is currently recommended that nanofibrillated cellulose be functionalized by chemical post-treatment after nanofibrillation, which usually results in an increase in production costs and environmental impact.

[0014] As described in the publication by Kaldéus et al., Cellulose, 2018, 25: 7031-7042, the prior art has proposed the preparation of bifunctional cellulose nanofibrils by a process comprising the one-pot preparation of bifunctional cellulose fibers with carboxymethyl functional groups and additional functional groups, more particularly allyl functional groups or propargyl functional groups, before the nanofibrillation step. To this end, the cellulose fibers are first subjected to a carboxymethylation step and then to an etherification reaction by contacting them with allyl bromide or propargyl bromide in an alkaline medium. However, this method requires a large amount of reactants, a long reaction time and it is not possible to graft more than 0.3-0.5 mmol of carboxymethyl groups per gram of cellulose on the cellulose surface. The document also discloses that the simultaneous addition of allyl bromide or propargyl bromide with monochloroacetic acid results in extremely low total fiber charge values ​​and is therefore abandoned. The present invention aims to propose a method for preparing multifunctional cellulose fibers in a short reaction time, at low cost and preferably with high yield, and a method for preparing multifunctional nanofibrillated cellulose from the multifunctional cellulose fibers.

[0015] The inventors have now found that such an object can be achieved by a specific method that enables two or even more functional groups to be grafted onto a cellulose polymer in the form of a solid fiber by a one-pot simultaneous functionalization reaction. One of these functional groups can be a carboxyl-containing functional group, promoting the subsequent nanofibrillation step when necessary. In the context of a more comprehensive method for preparing multifunctionalized nanofibrillated cellulose, the inventors particularly apply this specific method before subjecting the cellulose fibers to a nanofibrillation treatment for the simultaneous multifunctionalization of the cellulose fibers by carboxyl-containing groups (e.g. carboxymethyl) and one or several additional functional groups. They have found that, unexpectedly and contrary to the teachings of the publication of Kaldéus et al. mentioned above, under specific conditions, more particularly when implementing specific reactant concentrations, multifunctional cellulose fibers can be obtained by implementing this specific method for simultaneously achieving carboxylation (e.g., carboxymethylation) and additional functionalization of cellulose fibers, and this simultaneous additional functionalization does not hinder the carboxylation (e.g., carboxymethylation) so that the total carboxyl (e.g., carboxymethyl) charge grafted on the cellulose fibers is not significantly reduced compared to cellulose fibers that have only undergone carboxylation (e.g., carboxymethylation). This simultaneous additional functionalization of cellulose fibers does not interfere with the subsequent nanofibrillation step of the overall method for producing multifunctional CNFs from cellulose fibers. Compared to the nanofibrillation of non-carboxylated (e.g., non-carboxymethylated) cellulose fibers, this nanofibrillation step is still convenient.

[0016] Thus, according to a first aspect, the present invention relates to a method for preparing multifunctionalized cellulose fibers, the method comprising subjecting cellulose fibers, preferably unmodified (i.e. unfunctionalized) cellulose fibers, to:

[0017] - a first functionalization step for grafting a first organic functional group on the cellulose polymer by reacting the cellulose with a first reactant of organic type, the first reactant comprising a halogen atom and / or a vinyl group and / or a phenyl group, and the first functional group, and the first reactant being free of hydroxyl functional groups,

[0018] - and a second functionalization step for grafting a second organic functional group different from the first functional group on the cellulose polymer by reacting the cellulose with a second reactant of an organic type different from the first reactant, the second reactant comprising a halogen atom and / or a vinyl group and / or a phenyl group as well as the first functional group, and the second reactant does not contain a hydroxyl functional group.

[0019] According to the present invention, the first functionalization step and the second functionalization step are carried out simultaneously in one pot in an alkaline reaction medium, and each of the first reactant and the second reactant is present in the reaction medium in an amount between 0.015 mmol and 10 mmol per gram of cellulose.

[0020] The method of the present invention produces multifunctionalized cellulose fibers much faster than prior art methods in a single step conducted under appropriate conditions for covalently grafting the first functional group and the second functional group to the cellulose polymer.

[0021] The process of the invention makes it possible to functionalize cellulose fibers simultaneously with all combinations of functional groups, even simultaneously with carboxyl functional groups and primary and / or secondary amine functional groups. In the latter case, however, the degree of substitution of the cellulose polymer is rather low.

[0022] Therefore, in a specific embodiment of the present invention, the first reactant and the second reactant do not simultaneously contain a carboxyl functional group and a primary or secondary amine functional group. Therefore, this means that if the first reactant contains a carboxyl functional group, then both the first reactant and the second reactant do not contain a primary or secondary amine functional group, and if the second reactant contains a carboxyl functional group, then both the first reactant and the second reactant do not contain a primary or secondary amine functional group. Similarly, if the first reactant contains a primary or secondary amine functional group, then both the first reactant and the second reactant do not contain a carboxyl functional group, and if the second reactant contains a primary or secondary amine functional group, then both the first reactant and the second reactant do not contain a carboxyl functional group.

[0023] More generally, in certain embodiments of the process of the invention, the first reactant and the second reactant do not simultaneously contain two or more functional groups that are reactive with each other under the operating conditions so as not to compete with the reaction of those reactants with cellulose.

[0024] As used in this specification, the term carboxyl encompasses both the acid form and the carboxylate ion form.

[0025] Functional groups herein mean groups having at least one functional group of any kind that imparts a specific characteristic / property / ability to them. As used in this specification, the term "functional group" encompasses both the functional group itself and a larger organic chemical moiety containing at least one functional group.

[0026] The functional groups grafted onto the cellulose polymer according to the present invention can be any group showing a function that may be of interest for a given application of the multifunctionalized cellulose fiber. These functional groups are preferably selected so as to broaden the application field of the cellulose fiber to applications requiring specific mechanical properties and / or functions, such as the need to adjust the surface properties of the cellulose, such as polarity and / or charge. The functional groups can, for example, contain polymerization initiating functional groups (such as benzophenone type or α-bromoisobutyryl type, for forming polymer chains on the fiber surface, such as acrylates, styrenes, etc.), chromophores, hydrophobic groups, groups with positive or negative charges, olefins or alkyne groups for click chemistry (such as by azide-alkyne cycloaddition), etc. For example, the functional groups can be selected from the group comprising: carbonyl or carboxylate / carboxyl functional groups, alkyl, allyl, alkanoyl or alkyne chains, aromatic rings, specific functional groups such as benzophenone, etc.

[0027] In a particular embodiment of the invention, one of these functional groups (e.g., the first functional group) is a carboxyl-containing group, particularly a carboxyl (or carboxylate group) or a carboxyalkyl group of the type preferably containing a C1-C6 alkyl group (e.g., a methyl or ethyl group). This feature is highly advantageous in the context of a more comprehensive preparation of multifunctionalized nanofibrillated cellulose. Therefore, the first reactant can be a haloformic acid such as chloroformic acid, or a haloacetic acid such as monochloroacetic acid, or a halopropionic acid such as chloropropionic acid, or more generally an alkyl-haloacetic acid such as alkyl-chloroacetic acid. Therefore, the first functionalization step can be defined as a carboxylation step, more particularly a carboxyalkylation step, such as a carboxymethylation step when a carboxymethyl group is grafted onto a cellulose polymer.

[0028] Carboxyl-containing groups can also be grafted onto cellulose fibers, for example using reactants that do not contain halogen atoms but contain vinyl groups, such as acrylic acid or its salts, for example sodium acrylate, and / or reactants that contain optionally substituted phenyl groups, such as cinnamic acid or its salts.

[0029] In a particular embodiment of the present invention, at least one of the first functional group and the second functional group is hydrophobic. Therefore, the multifunctionalized cellulose fibers obtained by the method of the present invention are advantageously compatible with substrates based on hydrophobic polymers. The hydrophobic groups that can be used in the context of the present invention are, for example, alkyl, allyl or alkyne chains, aromatic rings or polymerization initiators, such as benzophenones that can polymerize acrylate or styrene on the cellulose fiber surface.

[0030] As an example, the second functional group may thus be a dye.

[0031] Examples of functional groups that can be grafted onto cellulose by the process of the invention are:

[0032] - benzophenone derivatives, such as (4-methylphenyl)(4-(prop-2-yn-1-yloxy)phenyl)methanone, which can be grafted onto a cellulose polymer by reacting the cellulose polymer with (4-(bromomethyl)phenyl)(4-(prop-2-yn-1-yloxy)phenyl)methanone) under alkaline conditions;

[0033] - allyl groups, which can be grafted onto cellulose polymers by reacting the cellulose polymers with allyl chloride or allyl bromide under alkaline conditions;

[0034] - alkyl acetates, wherein the alkyl group preferably contains 1 to 20, in particular 1 to 12, carbon atoms, such as ethyl acetate or octyl acetate, which can be grafted onto the cellulosic polymer by reacting the cellulosic polymer with ethyl chloroacetate or ethyl bromoacetate, octyl chloroacetate or octyl bromoacetate, respectively, under alkaline conditions;

[0035] - an alkyl chain, preferably a C1-C20, in particular a C1-C12 alkyl chain, such as decane, which can be grafted onto the cellulose polymer by reacting the cellulose polymer with 1,10-dibromodecane under alkaline conditions;

[0036] - alkanoyl chains, preferably C2-C20, in particular C2-C12 alkanoyl chains, such as lauroyl, which can be grafted onto the cellulose polymer, for example, by reacting the cellulose polymer with lauroyl chloride under alkaline conditions;

[0037] - benzoic acid, which can be grafted onto the cellulose polymer, for example, by reacting the cellulose polymer with 2-iodobenzoic acid under alkaline conditions.

[0038] More generally, in a preferred embodiment of the present invention, the first reactant and / or the second reactant has the general formula (I):

[0039] YR(I)

[0040] in

[0041] Y represents a halogen atom, a vinyl group or an optionally substituted phenyl group,

[0042] And R represents a moiety containing a functional group, provided that R does not contain a hydroxyl group.

[0043] In particular, when Y represents a phenyl group, the phenyl group may be substituted by one or more groups selected from:

[0044] - halogen atoms, such as chlorine or bromine atoms,

[0045] - straight-chain, branched and / or cyclic hydrocarbon radical, which is saturated and / or unsaturated, aromatic or non-aromatic, optionally substituted, optionally interrupted by one or more heteroatoms and / or by one or more groups containing at least one heteroatom or a group containing at least one heteroatom such as -OR 1 , where R 1 represents preferably a C1-C6 alkyl group, such as a methyl group or an ethyl group,

[0046] -NO 2 ,

[0047] -SR 2 O or SO 2 R 2 , where R 2 represents an alkyl group, preferably C1-C6, such as methyl or ethyl.

[0048] In a specific embodiment of the present invention, in formula (I), R represents a linear, branched and / or cyclic C2-C20 hydrocarbon group containing a functional group, which hydrocarbon group is saturated and / or unsaturated, aromatic or non-aromatic, optionally substituted, optionally inserted with one or more heteroatoms and / or inserted with one or more groups containing at least one heteroatom, and R does not contain a hydroxyl group.

[0049] In particular, R may represent a benzophenone derivative such as (4-methylphenyl)(4-(prop-2-yn-1-yloxy)phenyl)methanone, an allyl group, an alkyl acetate group (wherein the alkyl group preferably contains 1 to 20, in particular 1 to 12, carbon atoms), an alkyl chain (preferably C1-C20, in particular C1-C12), an alkanoyl chain (preferably C2-C20, in particular C2-C12), an optionally substituted benzoic acid group, etc.

[0050] The method according to the invention may further respond to one or more of the features described below, which may be implemented individually or in each of their technically operable combinations.

[0051] Both the first functionalization step and the second functionalization step of the process of the present invention preferably consist of a Williamson etherification reaction involving the hydroxyl groups of the cellulose polymer. The functionalization step is carried out by contacting cellulose with reactants in an alkaline reaction medium under conditions capable of causing the hydroxyl groups of the cellulose polymer to undergo an etherification reaction.

[0052] The cellulose fibers used in the process of the invention are preferably wood-derived fibers. They can be obtained by decomposing delignined wood pulp, for example by stirring a dispersion thereof in water.

[0053] In a preferred embodiment of the invention, the method includes a step of dispersing the cellulose fibers in water before subjecting them to a first functionalization step and a second functionalization step. Therefore, preferably there is no intermediate solvent exchange step between the dispersion step and the first and second functionalization steps. The inventors have particularly noted that, in the framework of the inventive method, such intermediate solvent exchange steps from water to ethanol and then from ethanol to isopropanol, which are typically carried out in the methods of carboxymethylating cellulose fibers of the prior art (such as in the methods disclosed in the publications of Kaldéus et al. mentioned above), are not necessary for achieving a successful carboxymethylation, or more generally functionalization, of cellulose polymers. In the context of the present invention, avoiding such steps advantageously reduces the production costs of multifunctionalized cellulose and limits the volume of the organic effluent produced thereby.

[0054] In a preferred embodiment of the invention, after dispersing the cellulose fibers in water, the method comprises separating the cellulose fibers from the water, preferably by filtration, before carrying out the next step of the method.

[0055] Thus, the method of the present invention may optionally comprise a step of separating the cellulose fibers, which step may be performed by any technique known to a person skilled in the art.

[0056] The method of the present invention can be implemented to prepare bifunctionalized cellulose fibers using two reactants, each reactant containing the functional groups to be grafted onto the cellulose polymer. It is also possible to use more such reactants, for example three such reactants, each containing different functional groups, so as to still prepare cellulose fibers having three functional groups or even more functional groups in a one-pot manner.

[0057] In a particular embodiment of the invention, the method comprises at least one additional functionalization step for grafting at least one additional organic functional group (i.e., a functional group different from the first functional group and the second functional group) on the cellulose polymer by reacting the cellulose fiber with at least one additional reactant, the additional reactant comprising a halogen atom and the additional organic functional group and being free of hydroxyl functional groups, the one or more additional functionalization steps being carried out simultaneously with the first functionalization step and the second functionalization step in a basic reaction medium in one pot under suitable conditions to covalently attach the one or more additional functional groups to the cellulose polymer. Thus, such additional reactant is present in the reaction medium in an amount between 0.015 mmol and 10 mmol per gram of cellulose.

[0058] In a particular embodiment of the invention, the first reactant, the second reactant and the one or more further reactants do not simultaneously comprise a carboxyl functional group and a primary or secondary amine functional group, or more generally, do not simultaneously comprise functional groups that are likely to react together under the operating conditions.

[0059] One or more additional functional groups, one or more additional reactants and one or more additional functionalization steps can generally have one or more of the features described above and below for the first and second functional groups, the first and second reactants and the first and second functionalization steps of the method of the present invention, respectively. In particular, the one or more additional reactants can have general formula (I).

[0060] In a particular embodiment of the invention, each of the first reactant and the second reactant, and where appropriate one or more additional reactants, is present in the reaction medium in an amount of between 0.03 mmol and 2 mmol of reactant per gram of cellulose and more preferably between 0.03 mmol and 1 mmol of reactant per gram of cellulose. Within such a concentration range, in the context of the multifunctionalization of the cellulose fibers of the invention, simultaneous grafting of all functional groups on the cellulose polymer is successfully achieved.

[0061] The method of the present invention does not involve first dispersing the cellulose fibers in an alkaline medium to cause them to swell and then adding the reactants for the functionalization step thereto. Multifunctionalized cellulose will then indeed be obtained in a dissolved state, but this is incompatible with the purpose of forming multifunctionalized cellulose fibers of the present invention.

[0062] In order to obtain multifunctionalized cellulose fibers as required by the present invention, i.e. solid cellulose, this pre-dispersion of the cellulose fibers in the alkaline reaction medium is avoided. In such an embodiment, the method of the present invention therefore preferably comprises a step of impregnating the cellulose fibers with a first impregnation solution comprising a first reactant, a second impregnation solution comprising a second reactant, and one or more other impregnation solutions each comprising other reactants, preferably continuously, before the first functionalization step and the second functionalization step, and, if appropriate, one or more further functionalization steps. Then, each of these impregnation steps is preferably carried out for a period of between 10 minutes and 1 hour, preferably between 10 minutes and 40 minutes, more preferably between 20 minutes and 40 minutes, for example about 30 minutes, and preferably at room temperature.

[0063] The volume of each impregnation solution is preferably between 5 ml and 50 ml per gram of cellulose. In these solutions, the reactants may be contained in any suitable solvent thereof, at a concentration required to reach a ratio of between 0.015 mmol and 10 mmol of reactants per gram of cellulose, preferably between 0.03 mmol and 2 mmol of reactants per gram of cellulose, and more preferably between 0.03 mmol and 1 mmol of reactants per gram of cellulose.

[0064] Thus, in a particular embodiment of the invention, the method comprises, prior to the functionalization step, a step of impregnating the cellulose fibers with a first impregnation solution comprising a first reactant, then a step of impregnating the cellulose fibers with a second impregnation solution comprising a second reactant, and then optionally one or more further steps of impregnating the cellulose fibers with one or more further impregnation solutions each comprising a further reactant.

[0065] Each of these impregnation steps is preferably carried out by wetting the cellulosic fibers with the impregnation solution.

[0066] The first functionalization step, the second functionalization step, and, where appropriate, one or more further functionalization steps of the process of the invention are then carried out simultaneously in the same reaction medium, according to any conventional operating scheme. The etherification reaction is preferably initiated by contacting the cellulose fibers with the reactants in the presence of an alkali such as sodium hydroxide, preferably at a ratio of between 4 mmol and 40 mmol of sodium hydroxide per gram of cellulose. In a preferred embodiment of the invention, in which the cellulose fibers have previously been impregnated with the reactants, the fibers are then introduced into a reaction medium containing an alkaline compound such as sodium hydroxide dissolved in a suitable vehicle, and possible remaining impregnation solution that would not have impregnated the fibers during the impregnation step of the process.

[0067] In a particular embodiment of the invention, the reaction medium for the functionalization step is in an alcoholic medium, preferably in a mild alcoholic medium, such as containing or consisting of isopropanol, or a mixture of isopropanol and methanol. Preferably, the reaction medium does not contain methanol.

[0068] The first functionalization step and the second functionalization step, and where appropriate one or more further functionalization steps, are preferably carried out for a period of between 30 minutes and 90 minutes, more preferably between 50 minutes and 70 minutes, for example about 60 minutes. Such a short reaction time is advantageously sufficient to ensure that the cellulose polymer is highly functionalized by all functional groups.

[0069] In a preferred embodiment of the invention, the first functionalization step and the second functionalization step, and where appropriate one or more further functionalization steps, are carried out at a temperature between 60° C. and 82° C., preferably between 65° C. and 82° C. They are preferably carried out at a temperature between 65° C. and 75° C., thereby reducing the energy requirement of the process even further.

[0070] As indicated above, in a particular embodiment of the present invention that is particularly suitable for preparing multifunctional nanofibrillated cellulose by the multifunctional cellulose fibers prepared by the method of the present invention, the first functional group is a carboxylic group, especially a carboxyl group or a carboxyalkyl group preferably containing a C1-C6 alkyl group, such as a carboxymethyl group or a carboxyethyl group. Therefore, the first reactant is preferably an alkyl-haloacetic acid (preferably a C1-C5 alkyl-haloacetic acid, such as a haloacetic acid, such as monochloroacetic acid), or a halopropionic acid such as chloropropionic acid. The first reactant can also be free of halogen atoms and comprise vinyl such as acrylic acid or its salt (e.g. sodium salt), or alternatively substituted phenyl such as cinnamic acid.

[0071] The method according to the invention therefore comprises subjecting the cellulose fibres simultaneously to:

[0072] a carboxylation, e.g. carboxyalkylation, in particular carboxymethylation step, for grafting carboxyl-containing groups, in particular carboxyalkyl functional groups, such as carboxymethyl groups, onto the cellulose polymer, e.g. by reacting the cellulose fibers with an alkyl-haloacetic acid, in particular a haloacetic acid such as monochloroacetic acid,

[0073] - and a second functionalization step for grafting second organic functional groups, i.e. functional groups other than the carboxyl-containing groups, in particular carboxyalkyl groups, of the carboxylation / carboxyalkylation step, onto the cellulose polymer by reacting the cellulose fibers with a second reactant comprising a halogen atom and the second functional group and being free of hydroxyl functional groups and optionally also free of primary and secondary amine functional groups,

[0074] and optionally, one or more further functionalization steps for grafting one or more further organic functional groups on the cellulose polymer, i.e. functional groups other than the carboxyl-containing groups, in particular the carboxyalkyl groups, of the carboxylation / carboxyalkylation step, and other than the second functional group, by reacting the cellulose fibers with one or more further reactants, the one or more further reactants comprising a halogen atom and one or more further functional groups and being free of hydroxyl functional groups and optionally also free of primary and secondary amine functional groups,

[0075] The steps are all carried out in an alkaline reaction medium, in one pot, under conditions suitable for covalently grafting carboxyl-containing groups, particularly carboxyalkyl groups, a second functional group, and, where appropriate, one or more additional functional groups, onto the fiber-forming cellulosic polymer.

[0076] The simultaneous carboxylation / carboxyalkylation, in particular carboxymethylation step, and the second functionalization step of the process of the invention, and optionally one or more further functionalization steps, advantageously obtain in a single step multifunctionalized cellulose fibers, which have both carboxyl-containing groups (in particular carboxyalkyl, such as carboxymethyl) and second functional groups grafted on their surface. The degree of substitution of the cellulose polymer by carboxyl-containing groups, in particular carboxyalkyl (for example carboxymethyl) (which can be measured, for example, by conductivity as described in detail below) is not significantly different from the degree of substitution obtained when only the carboxylation / carboxyalkylation, in particular carboxymethylation step, is carried out on the cellulose fibers. Advantageously, the second functionalization step of the process of the invention has no effect on the carboxylation / carboxyalkylation, in particular carboxymethylation, of the cellulose fibers, nor on their morphology and colloidal stability.

[0077] Thus, the method of the present invention advantageously provides a direct synthetic route to introduce several functional groups, including negative charges derived from carboxyl functional groups, particularly from carboxymethyl groups, on the surface of cellulose fibers through a one-pot simultaneous reaction.

[0078] The carboxyalkylation, in particular carboxymethylation step, is preferably carried out by contacting the cellulose fibers in an alkaline reaction medium under conditions such that an etherification reaction of the hydroxyl groups of the cellulose polymer occurs with a reactant comprising:

[0079] - halogen atoms and carboxyl-containing groups, such as carboxyalkyl, in particular monochloroacetic acid,

[0080] - vinyl and carboxyl or carboxyl-containing groups, such as acrylic acid or its salts,

[0081] - optionally substituted phenyl and carboxyl-containing groups substituted with phenyl, such as the group -CH=CH-COOH.

[0082] Preferably, such reactants, in particular monochloroacetic acid, are applied in a ratio of between 0.1 and 10 mmol per gram of cellulose.

[0083] When the second reactant is used in an amount between 0.015 mmol and 10 mmol per gram of cellulose, preferably between 0.03 mmol and 2 mmol and more preferably between 0.03 mmol and 1 mmol per gram of cellulose, the grafting of the second functional group on the cellulose fibers is successfully achieved without significantly hindering the carboxylation, particularly carboxyalkylation, more particularly carboxymethylation step.

[0084] The impregnation of the cellulose fibers with the impregnation solution containing the reactant for the carboxylation / carboxyalkylation step, especially monochloroacetic acid, and the impregnation of the cellulose fibers with the second impregnation solution containing the second reactant are preferably carried out continuously in any order. Preferably, the cellulose fibers are first impregnated with the reactant for the carboxylation / carboxyalkylation step, especially monochloroacetic acid, and then with the second reactant for the second functionalization step.

[0085] In a specific embodiment of the invention, the method comprises successively:

[0086] - Disperse cellulose fibers in water,

[0087] - separation of cellulose fibers from water by filtration,

[0088] - wetting the cellulose fibers with a first impregnation solution in a suitable solvent, for example in an alcohol solvent, in particular isopropanol, containing a reactant for the carboxylation / carboxyalkylation step, for example monochloroacetic acid (MCA), preferably at a ratio of 0.1 to 10 mmol of reactant per gram of cellulose, and preferably at a ratio of 5 to 50 ml of first impregnation solution per gram of cellulose, and impregnating the cellulose fibers with the reactant, preferably at room temperature, for preferably 20 to 40 minutes,

[0089] - wetting the cellulose fibers with a second impregnation solution containing a second reactant for a second functionalization step in a suitable solvent at a ratio of between 0.015 mmol and 10 mmol, more preferably between 0.03 mmol and 0.1 mmol, of said second reactant per gram of cellulose, and preferably at a ratio of 5 to 50 ml of second impregnation solution per gram of cellulose, and impregnating the cellulose fibers with the second reactant, preferably at room temperature, for preferably 20 to 40 minutes,

[0090] where appropriate, impregnating the cellulose fibres with the remainder of the impregnation solution which has not impregnated them, in a bath of a solution containing a base in a suitable medium, for example sodium hydroxide in a mild alcoholic medium, preferably in isopropanol, preferably at a ratio of between 4 and 40 mmol of sodium hydroxide per gram of cellulose,

[0091] - and allowing the carboxylation / carboxyalkylation, in particular carboxymethylation, and second functionalization reaction to proceed, preferably under gentle stirring, at a temperature of between 60°C and 75°C, preferably between 65°C and 75°C, for example about 70°C, for a period of about 1 hour.

[0092] Thus, a bifunctionalized cellulose fiber containing a carboxyl-containing functional group and an additional functional group is obtained through a one-pot simultaneous reaction.

[0093] As an example, the second functionalization step of the process of the present invention can be carried out to simultaneously introduce into the cellulosic polymer, in addition to carboxyl-containing groups, particularly carboxymethyl groups, ethyl acetate groups, allyl groups, decane groups, or benzophenone derivatives such as (4-methylphenyl)(4-(prop-2-yn-1-yloxy)phenyl)methanone, alkanoyl groups, benzoic acid groups, etc.

[0094] In other specific embodiments of the present invention, the method continuously comprises:

[0095] - Disperse cellulose fibers in water,

[0096] - separation of cellulose fibers from water by filtration,

[0097] - wetting the cellulose fibers with a first impregnation solution containing a reactant for the carboxylation / carboxyalkylation step, in particular monochloroacetic acid (MCA), in a suitable solvent, for example in an alcohol solvent, in particular isopropanol, preferably at a ratio of 0.1 to 10 mmol of such reactant per gram of cellulose, and preferably at a ratio of 5 to 50 ml of first impregnation solution per gram of cellulose, and impregnating the cellulose fibers with the reactant, preferably at room temperature, for preferably 20 to 40 minutes,

[0098] - wetting the cellulose fibers with a second impregnation solution of a second reactant for the second functionalization step in a suitable solvent, at a ratio of between 0.015 mmol and 10 mmol, more preferably between 0.03 mmol and 1 mmol and in particular between 0.03 mmol and 0.1 mmol of said second reactant per gram of cellulose, and preferably at a ratio of 5 ml to 50 ml of the second impregnation solution per gram of cellulose, and leaving the cellulose fibers impregnated with the second reactant, preferably at room temperature, for preferably 20 minutes to 40 minutes,

[0099] - wetting the cellulose fibers with a further impregnation solution of a further reactant for a further functionalization step in a suitable solvent, at a ratio of between 0.015 mmol and 10 mmol, preferably between 0.03 mmol and 1 mmol and in particular between 0.03 mmol and 0.1 mmol per gram of cellulose, and preferably at a ratio of 5 to 50 ml of further impregnation solution per gram of cellulose, and leaving the cellulose fibers impregnated with the further reactant, preferably at room temperature, for preferably 20 to 40 minutes,

[0100] where appropriate, impregnating the cellulose fibres together with the remainder of the impregnation solution with which they have not been impregnated, in a bath of a solution containing an alkali in a suitable medium, for example sodium hydroxide in a mild alcoholic medium, preferably in isopropanol, preferably at a ratio of between 4 and 40 mmol of sodium hydroxide per gram of cellulose,

[0101] - and subjecting the carboxylation / carboxyalkylation, in particular carboxymethylation, second functionalization and further functionalization reactions to preferably gentle stirring, preferably at a temperature between 65°C and 75°C, for example about 70°C, for a period of about 1 hour.

[0102] Thus, trifunctional cellulose fibers containing a carboxyl-containing functional group and two additional functional groups are obtained through a one-pot simultaneous reaction.

[0103] The same process can be used to introduce even more functional groups on the cellulosic polymer simply by adding the step of impregnating the cellulosic fibers with additional further reactants prior to impregnating the cellulosic fibers in the alkaline reaction medium.

[0104] As an example, the second functionalization step and further functionalization steps of the process of the invention can be carried out to introduce both ethyl acetate groups and allyl groups, or allyl groups and alkyl groups, into the cellulosic polymer in addition to carboxyl-containing groups, particularly carboxyalkyl groups, such as carboxymethyl groups.

[0105] Another aspect of the present invention relates to multifunctionalized cellulose fibers obtainable by the method according to the present invention. The functional groups carried by such multifunctionalized cellulose fibers may have any of the features or combinations of features described above in connection with the method of the present invention.

[0106] Examples of such multifunctionalized cellulose fibers are functionalized with carboxyl-containing groups, such as carboxyalkyl, particularly containing C1-C6 alkyl groups (e.g. carboxymethyl or carboxyethyl), or alkylcarboxyl, particularly containing C1-C16 alkyl groups (e.g. methylcarboxyl), or phenyl and carboxyl-containing groups such as cinnamoyl, and functionalized with one or more of the following groups:

[0107] - benzophenone derivatives, such as (4-methylphenyl)(4-(prop-2-yn-1-yloxy)phenyl)methanone,

[0108] -allyl,

[0109] - alkyl acetates, wherein the alkyl group preferably contains 1 to 20, in particular 1 to 12, carbon atoms, for example ethyl acetate or octyl acetate,

[0110] - an alkyl chain, preferably a C1-C20, in particular a C1-C12 alkyl chain, such as decane,

[0111] - an alkanoyl chain, preferably a C2-C20, in particular a C2-C12 alkanoyl chain, for example a lauroyl chain,

[0112] -benzoic acid.

[0113] An example of such multifunctional cellulose fibers according to the present invention is a trifunctional cellulose fiber functionalized with a carboxyalkyl group (eg, a carboxymethyl group) particularly containing a C1-C6 alkyl group together with at least two of an ethyl acetate group, an alkyl group, and an allyl group.

[0114] The invention also relates to the use of the multifunctional cellulose fibers according to the invention for preparing composite materials, which can be used in many applications, for example in the textile sector, in the packaging sector, in the pulp and paper industry sector and the like.

[0115] The multifunctionalized cellulose fibers according to the present invention can also be used to prepare microfibrillated multifunctionalized cellulose and / or multifunctionalized nanofibrillated cellulose.

[0116] Another aspect of the present invention is a method for preparing multifunctionalized microfibrillated cellulose, which method comprises subjecting cellulose fibers to the method for preparing multifunctionalized cellulose fibers according to the present invention, preferably comprising a carboxylation / carboxyalkylation step as described above, and then subjecting the multifunctionalized cellulose fibers thus obtained to a microfibrillation step.

[0117] Microfibrillated cellulose is defined in this specification as consisting mainly of micron-sized cellulose fibers with a width typically between 20 nm and 50 nm and a length in the micrometer range. Small amounts of nano-sized cellulose particles mixed with these micron-sized cellulose fibers can also be found in microfibrillated cellulose.

[0118] The microfibrillation step may be carried out in any manner known to those skilled in the art, in particular by gentle agitation of the multifunctionalized cellulose fibers in an aqueous vehicle, for example at ambient temperature, for a period of time of, for example, 12 to 36 hours, in particular about 24 hours.

[0119] Another object of the present invention is a multifunctionalized microfibrillated cellulose obtainable by the process for preparing microfibrillated cellulose according to the present invention, which is functionalized with two or more different functional groups, which functional groups may have any of the features or combinations of features described above in connection with the process for preparing multifunctionalized cellulose fibers according to the present invention, but excluding the combination of tert-butylformamide with any of the following functional groups:

[0120] - methacrylate,

[0121] -pent-4-ynoate,

[0122] - 2-methyl-3-[(prop-2-yn-1-yl)amino]propanoate of the following formula:

[0123]

[0124] - 3-(1-{2-[2-(2-methoxyethoxy)ethoxy]ethyl}-1H-1,2,3-triazol-4-yl)propanoate of the following formula:

[0125]

[0126] - and 3-(5-fluorescein-1H-1,2,3-triazol-4-yl) propionate of the formula:

[0127]

[0128] Examples of such multifunctionalized microfibrillated cellulose are functionalized with carboxyl-containing groups (especially carboxyalkyl groups, especially C1-C6 alkyl-containing groups, such as carboxymethyl or carboxyethyl) and one or more of the following groups:

[0129] - benzophenone derivatives, such as (4-methylphenyl)(4-(prop-2-yn-1-yloxy)phenyl)methanone,

[0130] -allyl,

[0131] - alkyl acetates, wherein the alkyl group preferably contains 1 to 20, in particular 1 to 12, carbon atoms, for example ethyl acetate or octyl acetate,

[0132] - an alkyl chain, preferably a C1-C20, in particular a C1-C12 alkyl chain, such as decane,

[0133] - an alkanoyl chain, preferably a C2-C20, in particular a C2-C12 alkanoyl chain, for example a lauroyl chain;

[0134] -benzoic acid.

[0135] Other examples of multifunctionalized microfibrillated cellulose according to the present invention are trifunctionalized microfibrillated cellulose, which is functionalized with carboxyl-containing groups, in particular carboxyalkyl groups, such as carboxymethyl groups, together with ethyl acetate groups and allyl groups.

[0136] The invention also relates to the use of the multifunctionalized microfibrillated cellulose according to the invention for preparing composite materials, which can be used in many applications, for example in the textile field, the packaging field, the pulp and paper industry field and the like.

[0137] The multifunctionalized microfibrillated cellulose according to the present invention can also be used to prepare multifunctionalized nanofibrillated cellulose.

[0138] Another aspect of the invention is a method for preparing multifunctionalized nanofibrillated cellulose, the method comprising subjecting cellulose fibers to:

[0139] - a method for preparing a multifunctional cellulose according to the present invention, wherein one of the first and second functional groups (e.g. the first functional group) is a carboxyl-containing group, in particular a carboxyalkyl group preferably containing a C1-C6 alkyl group (e.g. carboxymethyl or carboxyethyl), or a carboxyl group containing a C1-C16 alkyl group (e.g. methylcarboxyl), or a group containing a phenyl group and a carboxyl group such as cinnamoyl,

[0140] - Then, the multifunctionalized cellulose fibers obtained are subjected to a step of nanofibrillation by mechanical treatment.

[0141] The large amount of negative charges on the multifunctionalized cellulose fibers originating from the carboxyl groups grafted on the surface thereof promote the fiber to break into nanoscale during the subsequent nanofibrillation step, thereby reducing the energy required for nanofibrillation. Compared with the prior art method of preparing nanofibrillated cellulose by only subjecting cellulose fibers to carboxymethylation, multifunctionalized nanofibrillated cellulose is obtained without any additional steps, with the same nanofibrillation degree and without any additional energy requirements.

[0142] In particular, the inventors have observed that the multifunctionalized cellulose fibers obtained by simultaneously carrying out the first functionalization step (particularly the carboxyalkylation step and more particularly the carboxymethylation step) and the second functionalization step of the process of the invention for grafting carboxyl-containing functional groups on the cellulose fibers have particularly good dispersibility characteristics in an aqueous medium, which can be confirmed by dynamic rheological analysis. After the microfibrillation step achieved by gently stirring the fibers in water, the dispersions of such multifunctionalized cellulose fibers in water show gel-like behavior at least in the concentration range of 0.5% w / w to 4.5% w / w. In the concentration range of 2% w / w to 4.5% w / w, these dispersions do not even flow, which indicates the high dispersibility of the cellulose microfibrils in water. Such a high dispersibility facilitates the subsequent nanofibrillation step of the process of the invention.

[0143] The method for preparing the multifunctionalized nanofibrillated cellulose of the present invention may comprise, after the step of functionalizing the cellulose fibers (e.g. a simultaneous carboxymethylation step and a second functionalization step) and before the nanofibrillation step, a step of purifying the multifunctionalized cellulose fibers, e.g. by filtration, optionally followed by a step of washing them, e.g. with isopropanol and then with water, until a neutral pH is reached.

[0144] It may also optionally include a step of breaking the cellulose fibers to micrometers, i.e. a microfibrillation step, before the nanofibrillation step. Since the fibers are highly substituted with carboxyl groups, such a step is particularly easy to carry out and energy-saving. In particular, it may be carried out by gently agitating the cellulose fibers in an aqueous medium, for example at ambient temperature, for a period of 12 to 36 hours, in particular about 24 hours.

[0145] The nanofibrillation step of the method of the present invention can be carried out by any conventional technique for mechanically breaking the cellulose fibers to the nanoscale. It can be carried out, for example, by homogenization or high-pressure microfluidization. For example, the multifunctional cellulose fibers can be passed through a piston pump applying high pressure and then preferably at, for example, about 350 mL.min -1 The liquid is passed through a Z-shaped interaction chamber with inner diameters of, for example, 400 μm, 200 μm and 100 μm multiple times at a constant flow rate of, for example, 100 bar, 1500 bar and 2000 bar, respectively.

[0146] In this context of preparing multifunctional nanofibrillated cellulose, the second functional group is preferably selected so as to broaden the application field of nanofibrillated cellulose to applications requiring specific mechanical properties and / or functions, in particular to applications requiring adjustment of the surface properties of cellulose (such as polarity and / or charge), such as for filter media, for reinforcing composite materials, as an emulsion stabilizer in water-in-oil (w / o) or oil-in-water (o / w) systems, etc. The second functional group may, for example, contain a polymerization initiating functional group (such as benzophenone type or α-bromoisobutyryl type, for forming polymer chains on the fiber surface, such as acrylates, styrenes, etc.), a chromophore, a hydrophobic group, a group with a positive or negative charge, an olefin or alkyne group for click chemistry (such as by azide-alkyne cycloaddition), etc. For example, the second functional group may be selected from the group comprising: a carbonyl or carboxylate / carboxylic acid functional group, an alkyl, allyl, alkanoyl or alkyne chain, an aromatic ring, a specific functional group such as benzophenone, benzoic acid, etc.

[0147] In a particular embodiment of the present invention, the second functional group is a hydrophobic type. Therefore, the multifunctionalized nanofibrillated cellulose obtained by the method of the present invention is advantageously compatible with a matrix based on a hydrophobic polymer. The hydrophobic group that can be used in the context of the present invention is, for example, an alkyl, allyl or alkyne chain, an aromatic ring or a polymerization initiator, such as a benzophenone that can polymerize acrylate or styrene on the cellulose fiber surface.

[0148] Examples of second functional groups that can be grafted onto the cellulose fibers in the second functionalization step of the process of the invention are: benzophenone derivatives, such as (4-methylphenyl)(4-(prop-2-yn-1-yloxy)phenyl)methanone; allyl groups; alkyl acetates, wherein the alkyl group preferably contains 1 to 20, in particular 1 to 12 carbon atoms, such as ethyl acetate or octyl acetate; alkyl chains, preferably C1-C20, in particular C1-C12 alkyl chains, such as decane; alkanoyl chains, preferably C2-C20, in particular C2-C12, for example, lauroyl chains; benzoic acid groups, etc.

[0149] Another aspect of the present invention relates to multifunctionalized nanofibrillated cellulose, more particularly bifunctionalized nanofibrillated cellulose, obtainable by the process according to the present invention, which nanofibrillated cellulose is functionalized by covalently grafting onto the cellulose polymer a carboxyl-containing group, particularly a carboxyalkyl group, preferably a carboxyalkyl group containing a C1-C6 alkyl group, such as a carboxymethyl or carboxyethyl group, and an additional functional group, which additional functional group is preferably free of hydroxyl functional groups and optionally also free of primary and secondary amine functional groups, excluding allyl, propargyl, methyl-triazole-disperse red 13 groups and methyl 3-ethylthiopropionate groups.

[0150] In a particular embodiment of the present invention, the multifunctionalized nanofibrillated cellulose comprises between 0.5 and 0.8 mmol of carboxyl groups, in particular carboxyalkyl groups, preferably carboxyalkyl groups containing C1-C6 alkyl groups, such as carboxymethyl or carboxyethyl groups, per gram of cellulose.

[0151] The additional functional group may be responsive to any of the characteristics described above in connection with the second functional group.

[0152] In particular, it can be chosen from the group consisting of: benzophenone derivatives, such as (4-methylphenyl)(4-(prop-2-yn-1-yloxy)phenyl)methanone; allyl groups; alkyl acetates, wherein the alkyl group preferably contains 1 to 20, in particular 1 to 12 carbon atoms, such as ethyl acetate or octyl acetate; and alkyl, preferably C1-C20, in particular C1-C12 alkyl, such as decane; alkanoyl chains, preferably C2-C20, in particular C2-C12 alkanoyl chains, for example, lauroyl chains; benzoic acid groups.

[0153] Another aspect of the present invention relates to multifunctionalized nanofibrillated cellulose, in particular trifunctionalized or higher functionalized nanofibrillated cellulose obtainable by the process according to the present invention, which nanofibrillated cellulose is functionalized by covalently grafting onto the cellulose polymer carboxyl-containing groups, in particular carboxyalkyl groups, preferably carboxyalkyl groups containing C1-C6 alkyl groups, such as carboxymethyl or carboxyethyl groups, and at least two additional functional groups, which additional functional groups are preferably free of hydroxyl functional groups and optionally also free of primary and secondary amine functional groups.

[0154] The additional functional groups may be responsive to any of the characteristics described above in relation to the second functional group and the one or more further functional groups.

[0155] The trifunctionalized nanofibrillated cellulose according to the invention may for example carry simultaneously carboxymethyl groups, ethyl acetate groups or alkyl groups, and allyl groups.

[0156] As indicated above, the bi-functionalized, tri-functionalized or even more functionalized multi-functionalized nanofibrillated cellulose of the present invention may have any one or more functional groups required for the desired application.

[0157] For example, it may carry functional groups that modify the nature of its interactions with other compounds, i.e. may involve hydrogen bonds, electrostatic interactions, etc., or that change its polarity from hydrophilic to hydrophobic, in particular in the context of preparing composite materials, so as to favor a better dispersion of the nanofibrillated cellulose in a hydrophobic polymer matrix.

[0158] Another aspect of the invention relates to the use of the multifunctionalized nanofibrillated cellulose, in particular difunctionalized or trifunctionalized nanofibrillated cellulose according to the invention for the preparation of composite materials, in particular for the reinforcement of materials based on a hydrophobic polymer matrix, whereby one of the functional groups grafted on the cellulose polymer is a hydrophobic group such as an alkyl chain, or a polymerization initiator such as a benzophenone-containing group, and the multifunctionalized nanofibrillated cellulose is then treated before use by forming polymer chains such as acrylate chains on its surface.

[0159] The multifunctionalized nanofibrillated cellulose according to the present invention can also be used to manufacture new cellulose-based products intended for use in many applications, in particular in the following fields, the functional group or groups of the nanofibrillated cellulose being appropriately selected according to each specific application:

[0160] - in the paper industry, for the production of speciality papers, for improving the compatibility of nanofibrillated cellulose with synthetic polymers such as acrylates - polymerizing benzophenone functional groups of acrylate polymers, which for example have been grafted onto the cellulose fibers according to the invention;

[0161] - in the packaging sector, for adjusting the permeability and gas barrier properties of materials, and for improving the compatibility of nanofibrillated cellulose with other components of packaging, such as paints, hydrophobic surface coatings, etc. - polymerizing benzophenone functional groups of acrylate polymers, and / or alkyl chains that modify the permeability and gas transmission properties of materials, which, for example, have been grafted onto the cellulose fibers according to the invention;

[0162] - in the manufacture of porous materials such as membranes, foams, aerogels, where the very high specific surface area of ​​the nanofibrillated cellulose can allow the control of the nanoporosity of the material after drying, leading to many applications where porosity and high specific surface area are key parameters, such as filtration membranes, catalyst supports, thermal insulation materials, etc. - charged groups capable of adjusting the water adsorption and porosity properties of the material, such as carboxyalkyl, e.g. carboxyethyl, which for example have been grafted onto the cellulose fibers according to the invention;

[0163] - for stabilizing emulsions: nanofibrillated cellulose functionalized with hydrophobic or chelating groups can be used as stabilizer for hydrophobic phases, for example in paints, varnishes, cosmetics, or for dispersing functional agents such as sunscreens, for example titanium dioxide in the paper industry, or reinforcing agents such as clays - benzophenone functional groups that polymerize the polymer, and / or alkyl chains that change the amphiphilic nature of the nanofibrillated cellulose, which for example has been grafted on the cellulose fibers according to the invention;

[0164] - in the field of nanocomposites, taking advantage of the excellent mechanical properties of nanofibrillated cellulose, the functionalization imparting compatibility with other components such as polystyrene, polyurethane, acrylates, etc. - benzophenone functional groups that polymerize the polymers, and / or alkyl chains that favor interaction with synthetic polymers in the composites, which for example have been grafted on the cellulose fibers according to the invention;

[0165] - In the textile field: Nanofibrillated cellulose can be functionalized with dyes, so chemical grafting can prevent fading.

[0166] The features and advantages of the present invention will become more apparent from the following examples, which are provided for illustrative purposes only and are by no means limiting of the present invention. Figures 1 to 10 Support, including:

[0167] - Figure 1Shown are photographs (top row) and optical microscope images (bottom row) of cellulose fibers in their native form ("cellulose", a1 / , b1 / ), after functionalization with a moiety derivatized with benzophenone ("cellulose-BP", a2 / , b2 / ), after carboxymethylation ("CMC", a3 / , b3 / ), and after functionalization with a moiety derivatized with benzophenone and carboxymethylation according to the invention ("CMC-BP", a4 / , b4 / );

[0168] - Figure 2 Shown are Fourier transform infrared spectroscopy (FT-IR) spectra of (4-(bromomethyl)phenyl)(4-(prop-2-yn-1-yloxy)phenyl)methanone ("BP"), cellulose fibers in native form ("cellulose"), cellulose fibers partially functionalized with the benzophenone ("cellulose-BP"), cellulose fibers carboxymethylated ("CMC"), and cellulose fibers partially derivatized with the benzophenone and simultaneously functionalized with carboxymethylation ("CMC-BP") according to the present invention;

[0169] - Figure 3 From the bottom spectrum to the top spectrum the solid state of 13 C CP / MAS NMR spectra: (4-(bromomethyl)phenyl)(4-(prop-2-yn-1-yloxy)phenyl)methanone ("BP"), cellulose fibers in natural form ("cellulose"), cellulose fibers partially functionalized with the benzophenone ("cellulose-BP"), cellulose fibers carboxymethylated ("CMC"), and cellulose fibers partially derivatized with the benzophenone and simultaneously functionalized with carboxymethylation according to the present invention ("CMC-BP");

[0170] - Figure 4 shows a graph representing the storage modulus G' (solid marks) and the loss modulus G" (open marks) as a function of frequency of dispersions of bifunctionalized cellulose fibers in water at different concentrations (0.5%, 1%, 2%, 4.5% w / w) measured by dynamic rheology, these bifunctionalized cellulose fibers being obtained according to the invention by simultaneous functionalization with benzophenone moieties and carboxymethylation;

[0171] - Figure 5 The loss tangent (tanδ = G' / G") is shown as Figure 4 A graph showing the concentration variation of a dispersion;

[0172] - Figure 6shows the FT-IR spectra of cellulose fibers obtained according to the invention by simultaneous functionalization with benzophenone-derived moieties and carboxymethylation, before or after grafting thereon polymer chains based on methyl methacrylate ("CMC-BP"), dodecyl methacrylate or styrene monomers;

[0173] - Figure 7 FT-IR spectra of trifunctionalized cellulose fibers obtained by simultaneous functionalization with ethyl acetate groups, functionalization with allyl groups and carboxymethylation according to the present invention ("CMC-EA-allyl") at neutral pH or pH 2, and those trifunctionalized cellulose fibers after post-modification with 3-mercaptopropionic acid ("CMC-EA-PA") at neutral pH or pH 2 are shown;

[0174] - Figure 8 Shown are photographs (top row) and optical microscope images (bottom row) of cellulose fibers in their native form ("Cellulose", a1 / , b1 / ), after carboxymethylation ("CMC", a2 / , b2 / ), and after simultaneous functionalization according to the invention with allyl groups, with decane groups and methylation ("CMC-Allyl-Dec", a3 / , b3 / );

[0175] - Fig. 9 Shown are Fourier transform infrared spectroscopy (FT-IR) spectra of cellulose fibers functionalized with (4-(bromomethyl)phenyl)(4-(prop-2-yn-1-yloxy)phenyl)methanone and sodium acrylate according to the present invention ("cellulose-BP-acryloyl"), and the same difunctionalized cellulose fibers after polymerization with dodecyl methacrylate ("dodecyl methacrylate polymerized CMC-BP-acryloyl");

[0176] -and Fig.10 A photograph of a membrane formed by vacuum filtration after cellulose fibers were functionalized with (4-(bromomethyl)phenyl)(4-(prop-2-yn-1-yloxy)phenyl)methanone and sodium acrylate and subsequently polymerized with dodecyl methacrylate according to the present invention is shown after a drop of water (indicated by the arrow) is deposited on the membrane.

[0177] Material

[0178] Delignified bleached softwood kraft pulp was used as the starting cellulosic material. Monochloroacetic acid (MCA), (4-(bromomethyl)phenyl)(4-(prop-2-yn-1-yloxy)phenyl)methanone, ethyl chloroacetate, allyl bromide, 3-mercaptopropionic acid, 4,4-azobis(4-cyanovaleric acid), methanol, sodium hydroxide, methyl methacrylate, dodecyl methacrylate, styrene, and tetrahydrofuran were purchased from Sigma Aldrich and used without further purification. Isopropyl alcohol and diethyl ether were provided by VWR International.

[0179] General scheme for characterization

[0180] Optical microscopy :The cellulose sample (0.1 g L -1 , in milliQ water) were deposited on a slide, dried at 40°C, and observed by a BX51 polarizing microscope (Olympus France S. AS) with a 4x objective. Images were captured by a U-CMAD3 camera (Olympus Corporation) displayed with a U-TV0.5XC-3 adapter.

[0181] Rheology : Rheological measurements were performed using a stress controlled rheometer AR-2000 (TA Instruments). Plate geometry (40 mm) was selected. All measurements were performed at 20°C. The samples were covered with paraffin oil to prevent evaporation during the measurements. The elastic modulus (G') and the viscous modulus (G") were measured in the linear response range, meaning. The measurements were performed twice and the average values ​​are reported in the graphs.

[0182] Infrared analysis (FT-IR, Fourier transform infrared spectroscopy): Infrared spectra were obtained from potassium bromide (KBr) pellets containing freeze-dried cellulose samples, which were placed directly on the FTIR spectrometer (Thermo Scientific). -1 Up to 4000cm -1 After 200 consecutive scans, the -1 All spectra were collected at 400 nm resolution.

[0183] Conductimetry : The surface charge of cellulose was measured by conductivity titration with 0.01 M NaOH solution using a TIM900 titration manager and a CDM230 conductivity meter equipped with a CDC749 conductivity cell. The degree of substitution (DS) was then calculated using the following equation:

[0184]

[0185] Where n COOH is the equivalent number of -COOH groups calculated by conductometric titration, m 纤维 is the mass of cellulose pulp (dry basis), 162 accounts for the molecular weight of the anhydroglucose units of cellulose, and 58 is the net increase in the weight of the anhydroglucose units of cellulose for each sodium carboxymethyl group replacing a hydrogen atom of a hydroxyl group.

[0186] Solid State 13 C CP / MASNMR (Cross-polarization magic angle spinning nuclear magnetic resonance): Cellulose sample (100 mg) was dissolved in 50 μL H 2 O and excess water was absorbed using an adsorbent. Approximately 80-100 mg of each sample was loaded into a 4 mm NMR rotor. Cross-polarization magic angle (CP / MAS) NMR experiments were collected on a Bruker Avance III 400 spectrometer operating at 100.62 MHz. 13 The CP / MAS was operated at 67.5 kHz and equipped with a double resonant H / X CP / MAS 4 mm probe. The measurements were performed at room temperature with a MAS spin rate of 9 kHz. The CP pulse sequence parameters were: 3.5 μs proton, 90° pulse, 1.75 ms CP contact time and 9 s cycle time at 67.5 kHz. 13 The number of acquisitions of C spectra was typically 5.120 scans. 13 C NMR spectra were referenced to the carbonyl peak of glycine at 176.03 ppm. All spectra were processed with Gaussian multiplication parameters LB = -5 Hz and GB = 0.1. NMR spectra were deconvoluted as described in Villares et al., Sci. Rep., 2017, 7, 40262.

[0187] Example A - Introduction of benzophenone-derived moieties and difunctionalization of carboxymethyl groups into cellulose fibers

[0188] Cellulosic fibers were difunctionalized with carboxymethyl groups and benzophenone-derived moieties carrying benzophenone functional groups according to the following reaction scheme:

[0189]

[0190] R=H,

[0191] Where n is an integer between 200 and 5000.

[0192] A.1 / preparation

[0193] First, cellulose fiber (delignified bleached softwood kraft pulp) (100 mg) was dispersed in water using a blender. The fiber was filtered using a vacuum filtration system and washed with ethanol. The fiber was then impregnated with monochloroacetic acid (10 mg) dissolved in 0.5 mL of isopropanol for 30 min at room temperature. Then, (4-(bromomethyl)phenyl)(4-(prop-2-yn-1-yloxy)phenyl)methanone (10 mg) dissolved in diethyl ether (2 mL) was added to the fiber. The fiber was impregnated with the solution for 30 min at room temperature. After impregnation, the fiber was added to a solution of sodium hydroxide (16 mg) in isopropanol (1 mL) heated to 60 ° C in a two-necked round-bottom flask. 2.5 mL of isopropanol was added to achieve a total isopropanol reaction volume of 5 mL. The reaction was allowed to proceed at 70 ° C under reflux for 60 min. The fiber was purified by filtration and a washing step was performed with isopropanol (×3) and then water (×3) until a neutral pH was reached.

[0194] Fibrillation was achieved by magnetic stirring overnight in water to obtain cellulose microfibrils.

[0195] For comparative purposes, cellulose was impregnated with monochloroacetic acid or (4-(bromomethyl)phenyl)(4-(prop-2-yn-1-yloxy)phenyl)methanone alone to introduce only one functional group (carboxymethyl or benzophenone derivative) and treated as described above.

[0196] A.2 / Characterization

[0197] The appearance and microscopic images of natural cellulose fibers ("cellulose", a1 / , b1 / ), benzophenone derivative functionalized cellulose fibers ("cellulose-BP", a2 / , b2 / ), carboxymethylated cellulose fibers ("CMC", a3 / , b3 / ), and benzophenone derivative functionalized carboxymethylated cellulose fibers ("CMC-BP", a4 / , b4 / ) are shown in Figure 1 It can be observed that the introduction of only the benzophenone derivative part ("cellulose-BP") does not significantly change the fiber morphology compared to the natural fiber ("cellulose"). On the contrary, the visual appearance and microscopic images of the two carboxymethylated samples ("CMC" and "CMC-BP") show a gel-like appearance and fiber breakage. The introduction of negative charges on the cellulose surface by the carboxymethyl group promotes the separation between the fibers and the subsequent fibrillation.

[0198] FT-IR spectra were collected for natural cellulose fibers ("cellulose"), benzophenone derivative functionalized cellulose fibers ("cellulose-BP"), carboxymethylated cellulose fibers ("CMC"), carboxymethylated cellulose fibers functionalized with benzophenone derivatives ("CMC-BP"), and (4-(bromomethyl)phenyl)(4-(prop-2-yn-1-yloxy)phenyl)methanone ("BP"). These spectra are shown in Figure 2 Except for the "BP" spectrum, they all show the characteristic curve of cellulose fibers. -1 When the area is carefully examined, it is clear that functionalization has resulted in the appearance of new peaks. The carboxymethylation is indicated by the presence of a peak at 1736 cm -1 The appearance of a new band at 1640 cm-1 indicated that the band corresponded to the C=O stretching of the carboxylic acid group. This band was clearly detected in both CMC and CMC-BP samples. -1 There is a strong band at 1600 cm-1 (attributed to the ketone C=O, which is a unique band belonging to benzophenone) and -1 These benzophenone bands were detected in both samples functionalized with benzophenone derivatives (cellulose-BP and CMC-BP). -1 Not very clear, because it is different from 1635cm -1 However, the 1600 cm-1 bands of cellulose-BP and CMC-BP samples overlap with the symmetric deformation vibration bands of water molecules adsorbed at 1600 cm-1. -1 The presence of the band at 1400 nm clearly demonstrates the successful grafting of the benzophenone derivative moiety. Thus, the introduction of two functional groups in the CMC-BP sample is demonstrated by the bands corresponding to the carboxymethyl and benzophenone groups in the CMC-BP spectrum. In addition, the intensity of the carboxyl groups is similar for both CMC and CMC-BP samples, which shows that the degree of substitution of the carboxymethylation reaction is not affected by the simultaneous reaction with the benzophenone derivative.

[0199] The carboxymethylated samples CMC and CMC-BP were analyzed by conductometric titration to determine the carboxyl content after carboxymethylation. The total charge of CMC was 0.745 ± 0.019 mmol.g -1 , which corresponds to a degree of substitution (DS) of 0.13 ± 0.01. When the fiber is simultaneously carboxymethylated and functionalized with a benzophenone derivative (CMC-BP), the total charge is 0.709 ± 0.037 mmol.g -1 , and the corresponding DS is 0.12 ± 0.01. Therefore, no significant decrease in the total charge was observed when the two reactions occurred simultaneously, indicating that both functional groups, carboxylmethyl and benzophenone, were successfully grafted.

[0200] Solid-state 13C CP / MAS NMR experiments were performed to demonstrate the covalent grafting of carboxymethyl and benzophenone derivative functional groups onto cellulose fibers. The spectra obtained are shown in Figure 3 The spectrum of the unmodified fiber (cellulose) shows the characteristic resonances of cellulose between 110 ppm and 55 ppm: C1 at δ 100-108 ppm, C4 at δ 79-90 ppm, C2, 3, 5 at δ 68-78 ppm and C6 at δ 58-67 ppm. Carboxymethylated cellulose (CMC and CMC-BP) presents the same peaks as well as a peak at 174 ppm attributed to the carboxymethyl group, which proves that the carboxymethylation of the cellulose fiber has fully occurred.

[0201] As indicated above, the presence of charges from the carboxymethyl groups on the cellulose fibers affects their mechanical and viscoelastic properties and imparts them with gel-like behavior. Dynamic rheology was used to evaluate the properties of dispersions of CMC-BP in water at different concentrations (0.5%, 1%, 2%, 4.5% w / w) and to characterize the gel behavior of these carboxymethylated bifunctional cellulose fibers. The results are shown in Figure 4 It is observed that G'>G'' over the entire concentration range between 0.5% and 4.5% w / w, which is characteristic of gel-like behavior. The values ​​obtained are consistent with those observed for microfibrillated cellulose, as described in Paakko et al., Biomacromolecules, 2007, 8, 1934-1941.

[0202] Calculate the loss tangent (tanδ = G' / G"). The result is Figure 5 For all concentrations tested, the loss tangent is below 1, which is characteristic of gel behavior, and even below 0.3, clearly demonstrating the formation of an entangled network structure.

[0203] A.3 / Aggregate analysis

[0204] Benzophenone is one of the most famous free radical polymerization photoinitiators. Benzophenone abstracts hydrogen from H donors such as monomers and forms two types of free radicals: ketyl radicals on the benzophenone moiety and alkyl radicals generated on the H donor, thereby starting polymerization. Therefore, the benzophenone functional group grafted at the cellulose surface can act as an initiator to graft the polymer chain onto the cellulose surface. Therefore, the resulting polymer is tethered to the benzophenone moiety on the cellulose surface through one chain end and can adopt various configurations depending on the grafting density.

[0205] Three different monomers were used, namely methyl methacrylate, dodecyl methacrylate or styrene, and polymerization was achieved by UV irradiation. The bifunctional fiber CMC-BP was impregnated with the monomers (20 mmol per gram of cellulose). -2 After irradiation at 40 °C for 30 min, the fibers were washed with tetrahydrofuran to remove excess monomers.

[0206] The growth of hydrophobic uncharged polymer chains on cellulose fibers was monitored by FT-IR. The spectra obtained for each monomer as well as the spectrum of the initial bifunctionalized cellulose fibers ("CMC-BP") are shown in Figure 6 Compared to the latter, the spectrum obtained after incubation of cellulose with the monomers shows the presence of new bands corresponding to polymer growth. Since the sample was not acidified, the carboxylic acid groups (COO - ) appears at 1600cm -1 For polymethacrylates (methyl and dodecyl), at 1730 cm -1 The new band at 1450, 1490 and 1585 cm -1 The presence of bands corresponding to CH aromatic stretching at 147° at 40° confirms the polymerization of styrene.

[0207] On the contrary, as a comparative example, when native cellulose fibers were incubated with the monomers, after washing with THF and water, the FT-IR spectrum did not show any trace of any monomers, which ruled out the hypothesis that the monomers were adsorbed on the fiber surface.

[0208] Example B -Introduction of dual functionalization of allyl and carboxymethyl groups

[0209] The same protocol as described in Example A was followed using allyl bromide (11 μL, dissolved in 0.5 mL isopropanol) instead of the benzophenone derivative as the reactant for the functionalization of cellulose fibers.

[0210] Dual-functionalized cellulose fibers containing carboxymethyl and allyl groups were obtained.

[0211] They were analyzed by conductometric titration to determine their carboxyl content. The total charge was 0.53 ± 0.04 mmol.g -1 , which corresponds to a degree of substitution (DS) of 0.09 ± 0.01.

[0212] Example C - Dual functionalization by introducing ethyl acetate groups and carboxyl groups

[0213] The same protocol as described in Example A was followed using ethyl acetate (11 μL, dissolved in 0.5 mL isopropanol) instead of benzophenone derivative as reactant for cellulose fiber functionalization.

[0214] Bifunctionalized cellulose fibers containing carboxymethyl and ethyl acetate groups were obtained.

[0215] They were analyzed by conductometric titration to determine their carboxyl content. The total charge was 0.71 ± 0.09 mmol.g -1 , which corresponds to a degree of substitution (DS) of 0.12 ± 0.02.

[0216] Similar results were obtained using ethyl bromoacetate instead of ethyl chloroacetate, demonstrating that the nature of the halide does not significantly affect the grafting.

[0217] Similar results were obtained using octyl chloroacetate instead of ethyl chloroacetate, demonstrating that the alkyl chain length has no effect on the grafting.

[0218] Example D -Introduction of dual functionalization of decane groups and carboxymethyl groups

[0219] The same protocol as described in Example A was followed using dibromodecane (20 μL, dissolved in 0.5 mL isopropanol) instead of the benzophenone derivative as the reactant for the functionalization of cellulose fibers.

[0220] Bifunctionalized cellulose fibers containing carboxymethyl and decane groups were obtained.

[0221] They were analyzed by conductometric titration to determine their carboxyl content. The total charge was 0.53 ± 0.04 mmol.g -1 , which corresponds to a degree of substitution (DS) of 0.09 ± 0.01.

[0222] Example E - Trifunctionalization by introducing carboxymethyl, ethyl acetate and allyl groups

[0223] Cellulosic fibers were trifunctionalized with carboxymethyl, ethyl acetate, and allyl groups according to the following reaction scheme:

[0224]

[0225] R=H, Where n is an integer between 200 and 5000.

[0226] The trifunctionalization was carried out by a similar procedure to the difunctionalization described above in Example A, but the cellulose fibers (100 mg) were impregnated with monochloroacetic acid (10 mg) dissolved in 0.5 mL isopropanol, then ethyl chloroacetate (11 μL) in 0.5 mL isopropanol, and then allyl bromide (11 μL) in 0.5 mL isopropanol for three consecutive 30-min impregnations. The impregnated fibers were then added to a sodium hydroxide solution and the same procedure as for the difunctionalization was followed.

[0227] The surface charge of the obtained trifunctionalized fiber ("CMC-EA-allyl") determined by conductometric titration was 0.227±0.045 mmol.g -1 .

[0228] These trifunctionalized fibers were analyzed by FT-IR at neutral pH and pH 2 (to obtain a pH equal to 2, the sample was acidified with some drops of 0.01 M HCl). The spectra obtained are shown in Figure 7 They confirm the presence of carboxymethyl groups in both samples. At neutral pH, the spectrum (“CMC-EA-allyl”) actually shows a peak at 1600 cm -1 Corresponding to COO - The shoulder of the root, at pH 2 (“CMC-EA-allyl pH 2”), shifts to 1733 cm due to protonation to COOH. -1 At neutral pH, a peak at 1733 cm -1 The peak at 1195-1210 cm indicates the presence of ethyl acetate functional groups on the cellulose surface. No allyl groups were detected in the FT-IR spectrum because the stretching or bending vibrations of olefins (1195-1210 cm -1 、1410-1442cm -1 、3011-3100cm -1 ) overlaps with the cellulose band.

[0229] To detect the presence of allyl groups on the fiber surface, post-modification was performed by thiol-ene coupling with 3-mercaptopropionic acid. To this end, 100 mg of trifunctionalized fiber was solvent exchanged from water (100 mL), ethanol (100 mL, 99%) and then methanol (100 mL). The fiber was then dispersed in methanol (10 mL) and stirred for 60 min. Then, 4 μL of methyl 3-mercaptopropionate and 400 μg of 4,4'-azobis-(4-cyanovaleric acid) were added. The reaction was carried out at 60 ° C for 18 h. The fiber was then washed with methanol.

[0230] The increase in surface charge due to the presence of propionic acid groups on the cellulose surface was quantified by conductimetry. The total surface charge measured for the modified cellulose fibers was 0.314 ± 0.068 mmol.g -1 The increase in the total surface charge of the propionic acid derivative (“CMC-EA-PA”) compared to the allyl derivative (“CMC-EA-Allyl”) clearly indicated the successful coupling between the allyl groups and 3-mercaptopropionic acid and thus confirmed the allylation of the cellulose fibers.

[0231] FT-IR analysis was performed on the post-modified fibers at both neutral pH and pH 2. The spectra are shown at Figure 7 The FT-IR spectrum shows that at neutral pH the -1 COO - The band increases and shifts to 1733 cm at acidic pH (COOH). -1 Compared with the sample without post-modification, CMC-EA-allyl pH 2 obtained at 1733 cm -1 The band at 1733cm -1 The increase in the intensity of the band at can obviously be attributed to the new propionic acid groups grafted on the allyl functional groups of the cellulose fibers.

[0232] In order to exclude the physical adsorption of 3-mercaptopropionic acid on cellulose fibers, a control reaction between native cellulose fibers and 3-mercaptopropionic acid was performed. Compared with the thiol-ene coupling, the amount adsorbed was very low.

[0233] Example F –Nanofibrillation mechanical treatment

[0234] The bifunctionalized cellulose fibers obtained in Examples A, B, C and D and the trifunctionalized cellulose fibers obtained in Example E may be subjected to nanofibrillation by homogenization.

[0235] To this end, the fiber can be passed through a piston pump at high pressure and then at 350 mL.min. -1 The flow was carried out at a constant flow rate through Z-shaped interaction chambers with inner diameters of 400 μm, 200 μm and 100 μm at pressures of 100 bar, 1500 bar and 2000 bar, respectively.

[0236] For each sample, multifunctionalized nanofibrillated cellulose was thus obtained.

[0237] Example G - Trifunctionalization by introducing carboxymethyl, decane and allyl groups

[0238] The cellulose fibers were trifunctionalized with carboxymethyl, decane and allyl groups.

[0239] The trifunctionalization was carried out by a similar procedure to the difunctionalization described above in Example A, but the cellulose fibers (100 mg) were impregnated with monochloroacetic acid (0.10 mmol) dissolved in 0.5 mL isopropanol, then 1,10-dibromodecane (0.10 mmol) in 0.5 mL isopropanol, and then allyl bromide (0.10 mmol) in 0.5 mL isopropanol for three consecutive 30-min impregnations. The impregnated fibers were then added to a sodium hydroxide solution and the same procedure as for the difunctionalization was followed.

[0240] The introduction of monochloroacetic acid was carried out by reacting with natural cellulose fibers at 0.218 ± 0.024 mmol g -1 Compared with 0.618±0.030mmol.g -1 to prove the surface charge.

[0241] The introduction of the allyl functionality was demonstrated by post-functionalization with 3-mercaptopropionic acid via a thiol-ene coupling reaction as described in Example E. As a result, the surface charge increased to 0.713 ± 0.065 mmol.g -1 , proving the introduction of 3-mercaptopropionic acid group.

[0242] Finally, the cross-linking and plasticity of the fibers confirmed the presence of decane after trifunctionalization, e.g. Figure 8 As shown in the figure. In the figure showing the appearance and microscopic images of natural cellulose fibers ("Cellulose", a1 / , b1 / ), carboxymethylated cellulose fibers ("CMC", a2 / , b2 / ) and allyl and decane functionalized carboxymethylated cellulose fibers ("CMC-allyl-Dec", a3 / , b3 / ), it can be seen that both carboxymethylated samples ("CMC" and "CMC-allyl-Dec") obtain gel-like appearance and fiber breakage. The introduction of negative charges on the cellulose surface by carboxymethyl groups promotes the separation between fibers.

[0243] Example H - Introduction of benzophenone-derived moieties and dual functionalization of acrylate groups into cellulose fibers

[0244] The cellulose fibers were difunctionalized with acrylate groups and benzophenone-derived moieties carrying benzophenone functional groups.

[0245] H.1 / preparation

[0246] First, cellulose fiber (delignified bleached softwood kraft pulp) (100 mg) was dispersed in water using a blender. The fiber was filtered using a vacuum filtration system and washed with ethanol. The fiber was then impregnated with sodium acrylate (0.10 mmol) dissolved in 0.5 mL of water / isopropanol (1 / 4) for 30 min at room temperature. Then, (4-(bromomethyl)phenyl)(4-(prop-2-yn-1-yloxy)phenyl)methanone (0.03 mmol) dissolved in diethyl ether (2 mL) was added to the fiber. The fiber was impregnated with the solution for 30 min at room temperature. After impregnation, the fiber was added to a solution of sodium hydroxide (16 mg) in isopropanol (1 mL) heated to 60 ° C in a two-necked round-bottom flask. 2.5 mL of isopropanol was added to achieve a total isopropanol reaction volume of 5 mL. The reaction was allowed to proceed at 70 ° C under reflux for 60 min. The fibers were purified by filtration and subjected to washing steps with isopropanol (×3) and then water (×3) until a neutral pH was reached.

[0247] Fibrillation was achieved by magnetic stirring overnight in water to obtain cellulose microfibrils.

[0248] H.2 / Characterization

[0249] The presence of acrylate functional groups was confirmed by the surface charge determined by conductometric titration (0.633 ± 0.166 mmol.g -1 ) to prove it.

[0250] The presence of benzophenone functional groups was demonstrated by post-polymerization analysis using dodecyl methacrylate as described in Example A. The results are shown in Fig. 9 , which shows the FT-IR spectra of the bifunctionalized fiber before polymerization ("cellulose-BP-acryl") and after polymerization ("cellulose-BP-acryl poly(dodecyl methacrylate")). The spectrum of the fiber after polymerization shows the FT-IR spectra of the fiber before polymerization ("cellulose-BP-acryl poly(dodecyl methacrylate") and after polymerization ("cellulose-BP-acryl poly(dodecyl methacrylate")). -1 The band at is absent in the spectrum of the unpolymerized fiber, which clearly indicates the presence of polymer.

[0251] Furthermore, the membranes of the obtained bifunctionalized cellulose fibers after polymerization were prepared by vacuum filtration. Inducing water removal favors the interaction between the cellulose fibers, so the obtained dry membrane is free-standing. The presence of the polymer is confirmed by the hydrophobic nature of the membrane: water droplets deposited on the membrane do not penetrate into the membrane, as shown in Fig.10 (water droplets are shown by arrows).

[0252] These results demonstrate the possibility of polyfunctionalizing cellulose fibers according to the present invention using sodium acrylate instead of monochloroacetic acid.

Claims

1. A method for preparing multifunctionalized cellulose fibers, the method comprising subjecting the cellulose fibers to: a first functionalization step for grafting a first organic functional group on the cellulose fiber by reacting the cellulose fiber with a first reactant, wherein the first reactant comprises a halogen atom and / or a vinyl group and / or a phenyl group, and the first functional group, and the first reactant does not contain a hydroxyl functional group, and a second functionalization step for grafting a second organic functional group on the cellulose fiber by reacting the cellulose fiber with a second reactant, the second reactant comprising a halogen atom and / or a vinyl group and / or a phenyl group and the second functional group, and the second reactant does not contain a hydroxyl functional group, It is characterized in that The first functionalization step and the second functionalization step are performed simultaneously in one pot in an alkaline reaction medium, and each of the first reactant and the second reactant is present in the reaction medium in an amount between 0.015 mmol and 10 mmol per gram of cellulose.

2. The method according to claim 1, comprising a step of dispersing the cellulose fibers in water before subjecting the cellulose fibers to the first and second functionalization steps, and there is no intermediate solvent exchange step between the dispersing step and the first and second functionalization steps.

3. The method according to claim 1 or 2, in, The reaction medium is an alcohol medium.

4. The method according to any one of claims 1 to 3, comprising at least one additional functionalization step for grafting at least one additional organic functional group on the cellulose fibers by reacting the cellulose fibers with at least one additional reactant, the additional reactant comprising a halogen atom and / or a vinyl group and / or a phenyl group, as well as the additional functional group, and the additional reactant does not contain a hydroxyl functional group, the additional functionalization step being carried out simultaneously with the first functionalization step and the second functionalization step in one pot in the alkaline reaction medium, the additional reactant being present in the reaction medium in an amount between 0.015 mmol and 10 mmol per gram of cellulose.

5. A method according to any one of claims 1 to 4, comprising the steps of impregnating the cellulose fibers with a first impregnation solution comprising the first reactant, a second impregnation solution comprising the second reactant and, where appropriate, at least one further impregnation solution comprising the further reactant, each impregnation step being carried out for a period of between 10 minutes and 1 hour before the first and second functionalization steps and, where appropriate, the further functionalization steps.

6. The method according to any one of claims 1 to 5, in, The first functionalization step and the second functionalization step, and where appropriate the further functionalization step, are carried out for a period of between 30 minutes and 90 minutes.

7. The method according to any one of claims 1 to 6, in, The first functionalization step and the second functionalization step, and where appropriate the further functionalization step, are carried out at a temperature between 60°C and 82°C.

8. The method according to any one of claims 1 to 7, in, The first reactant and / or the second reactant and / or, where appropriate, the further reactant have the general formula (I): YR(I) in Y represents a halogen atom, a vinyl group or an optionally substituted phenyl group, And R represents a portion containing a functional group, and R does not contain a hydroxyl group.

9. The method according to claim 8, in, In formula (I), R represents a linear, branched and / or cyclic C2-C20 hydrocarbon group containing a functional group, which is saturated and / or unsaturated, aromatic or non-aromatic, optionally substituted, optionally inserted with one or more heteroatoms and / or inserted with one or more groups containing at least one heteroatom, and R does not contain a hydroxyl group.

10. The method according to any one of claims 1 to 9, in, The first functional group is a carboxyl-containing group.

11. A method for preparing multifunctionalized nanofibrillated cellulose, the method comprising subjecting cellulose fibers to: The method for preparing multifunctional cellulose fibers according to claim 10, Then, a nanofibrillation step is performed by mechanical treatment.

12. The method for preparing multifunctional nanofibrillated cellulose according to claim 11, in, The nanofibrillation step is performed by homogenization or high pressure microfluidization.

13. A multifunctional nanofibrillated cellulose, Features The multifunctionalized nanofibrillated cellulose is functionalized by covalently grafting thereon a carboxyl-containing group and at least two additional organic functional groups.

14. Use of the multifunctionalized nanofibrillated cellulose according to claim 13 for preparing a composite material.

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