FR3053055A1 - PROCESS FOR MARKING NANO-CELLULOSE AND / OR MICRO-FIBRILLEE SEMI-CRYSTALLINE - Google Patents

Abstract

The present invention relates to a method for labeling semicrystalline nano and / or micro-fibrillated cellulose using at least one chomophoric organic molecule, comprising at least the steps of: (i) having a dispersion aqueous nano-cellulose and / or microcrystalline semi-crystalline, supplemented with at least one organic chromophore molecule; and (ii) subjecting said dispersion (i) to microwave irradiation under conditions conducive to attachment of said chromophoric organic molecule to the nano and / or micro-fibrillated cellulose.

Description

The present invention relates to a novel method for marking the semi-crystalline fibrillated nanocellulose in order to enable, via this labeling, the detection of this nanocellulose, especially when it is to be detected in a cellulosic environment.

For several years now, scientists and industrialists have been developing materials derived from plant biomass, or even bio-inspired, as alternatives to petroleum products. As such, nanocellulose proves to be a material of great interest as it is derived from renewable natural resources, is biodegradable, recyclable and carbon neutral.

Coming from cellulose, nanocellulose exists in two forms: semi-crystalline Cellulose MicroFibrils (MFC) and / or Cellulose NanoFibrils (NFC) on the one hand, and crystalline Cellulose NanoCrystals (NCC or CNC). somewhere else. MFCs and / or NFCs, also called NMFCs, are obtained by mechanical treatment, whereas it is a chemical process that leads to the formation of NCCs. Figure 1 illustrates these two types of nanocellulose. They are distinguished in particular by their microstructure, as reported in the article Xuezhu et al. [1],

Advantageously, the nanocellulose, in particular semi-crystalline, makes it possible to provide a property of impermeability, in particular to water, by its crystalline part, and an oxygen barrier property by its amorphous part. These barrier properties are all the more interesting when the amorphous part has little fraction of free volume and a large cohesive density.

These properties of nanocellulose are particularly exploited in the food field. Thus, certain papers and / or films, especially cellulose-based films, dedicated to the field of food, may be covered with a thin layer of nanocellulose to ensure a barrier effect against the diffusion of oxygen for example. Nevertheless, there is the problem of the persistence of this thin layer on the substrate on which it is conventionally deposited. However, when the substrate is of a cellulosic nature, because this thin layer of nanocellulose is composed of the same chemical elements (carbon and oxygen) as the cellulose base substrate, the nanocellulose is not distinguishable with respect to the cellulose, both chemically and in terms of fiber size. Moreover, the fact that nanocellulose sometimes has a nanometric dimension relative to cellulose does not make it distinguishable either by microscopic observation, in particular by scanning electron microscopy (SEM) or electronic transition microscopy (TEM). . Therefore, there is a need to have means for evaluating the persistence of nanocellulose when it is implemented in a cellulosic environment, such as in particular a thin layer of nanocellulose deposited on the surface of a nanocellulose. basic cellulosic substrate.

In particular, there is a need for a micro and / or nano-fibrillated nanocellulose labeling method.

Finally, there is a need for such marking to be stable over time.

The present invention aims precisely to meet these needs.

More particularly, it relates, according to a first of its aspects, to a process for labeling nano-cellulose and / or micro-fibrillated semicrystalline cellulose using at least one chromophoric organic molecule, comprising at least the steps of (i) having an aqueous dispersion of nano and / or microcrystalline semi-crystalline cellulose, supplemented with at least one chromophoric organic molecule; and (ii) subjecting said dispersion (i) to microwave irradiation under conditions conducive to attachment of said chromophoric organic molecule to the nano and / or micro-fibrillated cellulose.

The inventors have thus found that it is possible, via the method of the invention implementing a microwave irradiation, to stably and uniformly immobilize chromophoric organic molecules on the microfibrils and / or nanofibrils of cellulose.

According to an alternative embodiment, the chromophoric organic molecules considered according to the invention are fluorescent compounds. The detection of the labeled cellulosic material according to the method of the invention can thus be carried out by measuring fluorescence (microscopy or spectroscopy) or by fluorescent revelation (UV lamp).

Admittedly, it has already been proposed to functionalize nanocellulose with the aid of pigments or fluorescent compounds. However, these functionalizations have been carried out with compounds, such as quantum dots, distinct from the organic chromophoric molecules considered according to the invention and / or use grafting techniques very different from that considered according to the invention based on a treatment of nanocellulose in microwaves.

For example, Xue et al. [2] propose to prepare a transparent and photoluminescent nanocellulose paper loaded with quantum dot ZnSe. Polyethyleneimine (PEI) is added to allow, by forming hydrogen bonds, the retention of quantum dots in nanocellulose.

As for the document Chauhan et al. [3], it reports the preparation of cellulose nanocrystals (NCC) on which is grafted via the establishment of covalent bonds, a pH-sensitive azo dye.

Finally, Dimic-Misic et al. [4], in a problem completely different from that referred to according to the invention, compare the rheological properties of different formulations, implemented as coating colors and comprising nanocellulose nano and / or microfibrillated in substitution for carboxymethylcellulose (CMC) pigments (calcium carbonate and kaolin clay) and a latex binder.

The process of the invention is particularly advantageous in several ways.

First of all, it is very efficient, fast, inexpensive, without constraints or extreme conditions. It induces no chemical and / or structural transformation of nanocellulose after labeling.

Advantageously, the process of the invention makes it possible to immobilize organic chromophore molecules at the level of said cellulose microfibrils or nanofibrils via so-called weak bonds (Van der Waals, hydrogen or electrostatic bridges) and to fix them in a perennial manner. .

In addition, the labeling of nanocellulose by chromophore molecules is stable over time.

The implementation of a microwave treatment according to the method of the invention advantageously makes it possible to increase binding energies ("binding energy").

Without wishing to be bound by the theory, it appears that the cellulose molecule, possessing OH groups on the periphery of the ose structure, allows the retention of organic molecules by establishing weak bonds (Van der Waals, hydrogen or electrostatic bridges). .

Once immobilization stabilized in an aqueous medium, the microwave irradiation step allows permanent attachment of the chromophore molecule to nanocellulose. A 3D nanocellulosic network is formed that traps the chromophore molecules. In this way, the bio-inspired material is marked on the surface and in depth.

As illustrated in the following examples, the inventors have shown that the microwave irradiation step is essential to ensure a permanent grip of the chromophore molecules on the NMFC fibers. The chromophore molecules thus remain indissociable from the nanocellulose. Such fixing of the chromophore molecules to the nanocellulose, on the other hand, is not achieved via a heat treatment, for example by heating the cellulosic suspension enriched in chromophoric molecules, as illustrated in Example 4.

Finally, the labeling method according to the invention does not alter the properties of the chromophore, and in particular in terms of fluorescence when it is a fluorochrome.

The nano and / or micro-fibrillated cellulose labeled according to the method of the invention can be easily detected, visually or optically, by fluorescence or fluorescence detection.

According to a particularly preferred embodiment, the method according to the invention further comprises, subsequent to the irradiation step (ii) with microwaves, an elimination step (iii), for example by dialysis against water , ethanol or tetrahydrofuran (THF), residual chromophore organic molecules, not attached to nanocellulose.

According to yet another of its aspects, the present invention relates to a semicrystalline nano and / or micro-fibrillated cellulose labeled with at least one chromophoric organic molecule, obtained according to the method of the invention defined above.

According to another of its aspects, it also relates to the use of marked nano and / or micro-fibrillated semicrystalline cellulose, obtained according to the process of the invention, for coating substrates such as films, in particular of a nature cellulose. Other features, variants and advantages of the process, the nanocellulose thus marked and its use according to the invention will emerge more clearly on reading the following description, examples and figures, given for illustrative and non-limiting purposes. 'invention.

In the remainder of the text, the expressions "between ... and ...", "ranging from ... to ..." and "varying from ... to ..." are equivalent and mean to mean that terminals are included unless otherwise stated.

Unless otherwise indicated, the expression "comprising / including a" shall be understood as "comprising / including at least one".

MARKING PROCESS

As indicated above, the method of the invention aims at marking the nano-cellulose and / or microfibrillated semi-crystalline (NMFC).

By "nano cellulose and / or microfibrillated semi-crystalline" is meant the cellulose in the form of nanofibrils and / or microfibrils semicrystalline cellulose.

In the remainder of the text, the semi-crystalline nano and / or microfibrillated cellulose will be more simply referred to as "nanocellulose" or "NMFC".

In the context of the present invention, when the term "cellulose" is used, it is any type of cellulose from any source known to those skilled in the art. In other words, any source of cellulose raw material can be used in the context of the present invention, whether for the preparation of cellulose nanofibers or else cellulose films that can be used as substrate to be coated by a thin layer. of nanocellulose, as explained below. The raw material can come from any plant material that contains cellulose. The plant material can be wood. The wood can come from softwood trees such as spruce, pine, fir, larch, Douglas fir or hemlock, or hardwood tree such as birch, aspen, poplar, alder, eucalyptus or acacia, or a mixture of coniferous and hardwoods. The plant material may also come from agricultural residues, grasses or other plant substances such as straw, leaves, bark, seeds, cockles, flowers, vegetables or cotton fruits, corn , wheat, oats, rye, barley, rice, flax, hemp, hemp, sisal, jute, ramie, kenaf, bagasse, bamboo or reed.

The term "cellulose pulp" refers to cellulose fibers that are isolated from any cellulosic raw material by methods known to those skilled in the art. Typically, the diameter of the fibers before any treatment in the context of the nanocellulose preparation varies between 10 to 30 μm and the length of the fibers exceeds 500 μm.

The semicrystalline cellulose microfibrils and / or the semi-crystalline cellulose nanofibrils (NMFC) considered in the context of the present invention are conventionally obtained by mechanical transformation of the cellulose films, in contrast with the cellulose nanocrystals or crystalline nanocellulose ( NCC), not considered in the context of the present invention, which are obtained by chemical transformation of the cellulose fibers.

The semicrystalline cellulose microfibrils and / or semi-crystalline cellulose nanofibrils (NMFC) considered in the context of the present invention may be obtained by any method known to those skilled in the art.

NMFCs generally have fiber lengths of between 0.5 and 100 μm, in particular between 1 and 50 μm, for example between 5 and 10 μm. In addition, they generally have a diameter of between 1 and 100 nm, in particular between 5 and 50 nm, for example between 10 and 30 nm.

These dimensions are variable and may in particular be a function of the cellulose pulp used or of the disintegration method used.

CHROMOPHORE ORGANIC MOLECULE

As indicated above, according to the process of the invention, the aqueous dispersion of nanocellulose is supplemented with at least one chromophoric organic molecule.

By "organic chromophore molecule" is meant an organic molecule bearing at least one chromophore group. A "chromophore" group is a group of atoms having one or more double bonds, and forming with the rest of the molecule a sequence of conjugated double bonds. Chromophoric groups are responsible for the color appearance of organic dyes. In fact, a chromophore molecule is a molecule whose electronic cloud delocalized on several atoms allows it to absorb energy.

In the rest of the text, the organic chromophoric organic molecule (s) considered according to the invention will be more simply referred to as "chromophores".

The organic chromophore molecules used according to the invention may be fluorescent and / or absorbent.

The organic chromophore molecules may be more particularly chromogens, combining a chromophore group and an auxochromic group. An auxochromic group is a group of ionizable atoms that can change the absorption frequency of a chromophore.

Advantageously, the chromophores that are particularly suitable for the invention are fluorescent organic molecules.

By "fluorescents" is meant that the chromophore molecule is capable of emitting fluorescence light after excitation. These molecules are still called "fluorochromes" or "fluorophores".

The chromophores considered according to the invention as organic molecules are therefore distinct quantum dots.

Fluorescent chromophore molecules are more particularly molecules composed of several conjugated aromatic rings.

The chromophores used according to the invention may be more particularly chosen from: cyanines and derivatives thereof, such as carbocyanine or phthalocyanine derivatives; rhodamines and their derivatives; - coumarin and its derivatives; pyrene derivatives; naphthalene derivatives; porphyrin derivatives; benzophenoxazine derivatives; acridine and its derivatives, for example hydroxyacridines, 9-methylacridine, DDAO (7-hydroxy-9H (1,3-dichloro-9,9-dimethylacridin-2-one), CAS nbr: 118290-05 -4), DAO (7-hydroxy-9H (9,9-dimethylacridin-2-one), hydroxystilbenes, quinoline derivatives, such as 6-hydroxyquinoline, erythrosine and its derivatives such as hydroxy-erythrosins - resorufme and its derivatives such as hydroxyrorufmes - fluorescein and its derivatives - rhodols and their derivatives - eosin and its derivatives - benzopyran derivatives - benzothiazole derivatives - the nitrobenzoxadiazole and its derivatives; azo derivatives (containing the azo functional group (-N = N-)). As cyanine derivatives, the following chromophores may be more particularly mentioned: Propyl Astra Blue Iodide (CAS RN: 199620-18-3)

. IR-140 (5,5'-dichloro-11-diphenylamino-3,3'-diethyl-10,12-ethylenethiatricarbocyanine perchlorate, CAS No. 53655-17-7)

. IR-676 iodide (1,1,3,3,3 ', 3'-hexamethyl-4,5,4', 5'-dibenzoindodicarbocyanine, CAS RN: 66289-64-6)

Green Indocyanine, also known as "Cardiogreen" (4,5-benzoindotricarbocyanine, CAS No. 3599-32-4)

By way of rhodamine derivatives, the following chromophores can in particular be mentioned:

Rhodamine 6G perchlorate (9- [2- (ethoxycarbonyl) phenyl] -3,6-bis (ethylamino) -2,7-dimethylxanthylium perchlorate, CAS No. 13161-28-9)

Rhodamine perchlorate (9- (2-carboxyphenyl) -3,6-bis (ethylamino) -2,7-dimethylxanthylium perchlorate; CAS No. 62669-66-3)

As a coumarin derivative, perhaps, for example, the chromophore 7-amino-4- (trifluoromethyl) coumarin (CAS No. 53518-15-3)

As a derivative of pyrene, perhaps for example cited 1-aminopyrene (CAS No: 1606-67-3)

By way of naphthalene derivative, mention may in particular be made of the chromophore known under the name Dansylcadaverine (A- (5-Aminopentyl) -5-di-methyl-amino-naphthalene-1-sulfonamide, CAS No. 10121-91- 2).

As a porphyrin derivative, mention may be made of the chromophore known under the name "TMPyP" (5,10,15,20-Tetrakis (1-methyl-4-pyridinio) porphyrin tetra (p-toluenesulfonate), CAS No. : 36951-72-1)

As a benzophenoxazine derivative, mention may be made of Nile Blue A perchlorate ([9- (diethylamino) benzo [a] phenoxazin-5-ylidene] azane perchlorate, CAS No. 53340-16-2).

As non-fluorescent chromophoric molecules, mention may be made of azo derivatives, such as, for example, DNAF (10- (2 ', 4'-dinitrophenylazo) -9-phenanthrol, CAS No. 54261-71-1).

According to a particular embodiment, the chromophoric molecules used according to the invention are chosen from: cyanines and their derivatives, such as carbocyanine or phthalocyanine derivatives; rhodamines and their derivatives; - coumarin and its derivatives; pyrene derivatives; naphthalene derivatives; porphyrin derivatives; benzophenoxazine derivatives; and - azo derivatives.

According to a particular embodiment, the chromophores used according to the invention are chosen from: Propyl Astra Blue Iodide, IR-140, IR-676 iodide, Green Indocyanine, Rhodamine 6G perchlorate, 7-amino-4- (trifluoromethyl) coumarin, Nile Blue A perchlorate, Dansylcadaverine, Rhodamine 19 perchlorate, TMPyP, 1-aminopyrene and DNAF.

According to a particular embodiment, the chromophore used according to the invention is TMPyP. In fact, this chromophore makes it possible to obtain, under UV irradiation at 365 nm, a high fluorescence intensity.

According to another particular embodiment variant, the fluorescent chromophore according to the invention is chosen from compounds of white color in visible light, such as derivatives of pyrene or dansylcadaverine.

The chromophore thus blends with the naked eye with the cellulosic substrate. Thus, the labeling is not detectable visually but only optically by fluorescence or fluorescence detection. Step (i) of the process of the invention is more particularly carried out by adding, with stirring, the chromophore to an aqueous dispersion of nano and / or micro-fibrillated cellulose.

In fact, the cellulose nanofibrils or microfibrils used are dispersible in water.

The dispersion of nano and / or micro-fibrillated cellulose may be more particularly prepared beforehand by dilution, in particular with stirring, of NMFC in an aqueous medium, in particular in water.

The content of nano and / or microfibrils of cellulose may especially be between 1 and 5% by weight, in particular between 2 and 4% by weight, and even more particularly between 2 and 3% by weight, relative to the weight. total of the aqueous dispersion of step (i) of the process of the invention.

As for the chromophore, it may be more particularly implemented, depending on its nature, in the form of an aqueous solution or dispersion.

Thus, according to a particular embodiment, the dispersion in step (i) is obtained by adding an aqueous solution or dispersion of chromophore, with stirring, to an aqueous dispersion of nano and / or micro-fibrillated cellulose.

Advantageously, the addition of the chromophore to the nanocellulose dispersion is operated with considerable agitation, so as to obtain a good distribution of the chromophore within the network of nano- or micro-fibrils.

According to one particular embodiment, the content of chromophores in the aqueous dispersion of nano and / or micro-fibrillated cellulose of step (i) of the process of the invention is between 0.1 and 5% by weight, in in particular between 0.5 and 3% by weight, and more particularly between 0.8 and 2.6% by weight, relative to the total weight of the aqueous dispersion.

MICROWAVE IRRADIATION

In a second step (ii) of the process of the invention, the semicrystalline nano and / or micro-fibrillated cellulose dispersion enriched with the chromophore of step (i) is subjected to microwave irradiation.

As mentioned above, this irradiation with microwaves is essential to allow to fix the chromophoric organic molecules on NMFC fibers. It also allows a homogeneous distribution of the chromophore molecules on the nanocellulose. Those skilled in the art are able to adjust the conditions of irradiation microwaves to obtain a permanent grip of the chromophore molecules on the nanocellulose fibers. At the end of the microwave irradiation, the chomophoric molecules thus remain indissociable from the nano and / or micro-fibrillated cellulose.

In particular, the irradiation with microwaves may have an energy of between 200 and 1000 W, in particular between 350 and 850 W, for example between 500 and 750 W.

The duration of exposure to microwave irradiation may be in particular between 0.5 and 10 minutes, in particular between 1 and 5 minutes, and more particularly between 1 and 2 minutes.

As mentioned above, at the end of step (ii), a cellulosic material permanently marked on the surface and at depth by the chromophore is obtained.

Dialysis step

As mentioned above, the process of the invention may comprise, after the microwave treatment, a step (iii) of elimination of the residual chromophoric organic molecules which have not been immobilized with nanocellulose at the end of the process. microwave irradiation (ii) of the process of the invention. The elimination of chromophoric organic molecules not fixed to the nanocellulose may for example be carried out by dialysis, in particular by dialysis against deionized water, ethanol or THF.

According to a particular embodiment, the step of eliminating residual organic chromophore molecules is performed by dialysis against deionized water.

Dialysis can be carried out for a period of at least 1 week, in particular of at least 3 days.

APPLICATION

The nano and / or micro-fibrillated cellulose labeled according to the invention can be detected by optical identification of the presence of the chromophoric organic molecule (s).

According to a particular embodiment, the labeled cellulose can be detected visually in ambient light.

In the case of the implementation of a fluorescent molecule, the labeled cellulose may be more particularly detected by fluorescence measurement or by fluorescent revelation.

The measurement of the fluorescence can be performed by microscopy or spectroscopy. The sample is irradiated under a light whose wavelength (abs) corresponds to the absorption maximum of the fluorophore. Detection of light re-emitted at the emission wavelength of the fluorophore is measured or monitored to verify the presence of said fluorophore. The apparatus used for the fluorescence spectra may be, for example, a FLUOROLOG FL3-2ÎHR of the brand HORIBA.

The fluorescent revelation is more particularly carried out via observation of the sample under a UV lamp, for example a mercury vapor lamp.

In particular, in the case of the implementation of a white chromophore in visible light, such as pyrene or dansylcadaverine derivatives, the chromophore is confused with the naked eye with the cellulosic substrate. The labeling is thus not detectable visually but only optically by fluorescence measurement or fluorescence detection. Those skilled in the art are able to adapt the detection means of the labeled nanocellulose obtained according to the process of the invention, in particular with regard to the nature of the chromophore used.

For example, the detection of the nanocellulose labeled with a specific fluorochrome can be advantageously effected by illumination of the fluorochrome at a wavelength corresponding to its absorption maximum to obtain a maximum fluorescence intensity at the wavelength of said fluorophore.

Different light sources for the excitation of the fluorochrome may be used depending on the nature of the fluorochrome used, for example a UV lamp, such as a mercury vapor lamp emitting at a wavelength of 365 nm.

The nano and / or microfibrillated cellulose labeled according to the method of the invention can be implemented in a wide variety of applications. The main use is to implement it as a coating of different substrates. As described above, this use notably benefits from the oxygen and water barrier properties of the nanocellulose.

Thus, according to another of its aspects, the invention relates to the use of nano and / or micro-fibrillated cellulose labeled according to the process of the invention for coating substrates such as films, in particular of cellulosic nature.

According to another of its aspects, the invention relates to an article for the food industry comprising at least one layer consisting of labeled nano and / or micro-fibrillated semicrystalline cellulose obtained according to the method of the invention.

Various deposition techniques may be employed to form such papers or films having an outer layer comprising the nanocellulose (s) according to the invention. Thus, aqueous solutions comprising the nanocellulose (s) can be deposited (s) on a cellulose substrate by any suitable industrial process well known to those skilled in the art.

Among these techniques include bar-coating, screen printing, spin-coating and inkjet.

According to a particular embodiment of the invention, the deposition is carried out by bar-coating.

Because of its nanometric or micrometric size (NMFC), the nano or microfibrillated cellulose labeled according to the present invention has a very good affinity for cellulose during deposition preparations.

The nanocellulose layer according to the present invention may be applied to reach a thickness which may be between 1 and 500 μm, in particular between 10 and 100 μm, in particular between 50 and 100 μm.

More particularly, the labeled nanocelluloses according to the present invention may find utility in the preparation of agrifood films. The invention thus relates, according to yet another of its aspects, a cellulose-based food film comprising at least one outer layer consisting of labeled nano and / or micro-fibrillated semicrystalline cellulose obtained according to the process of the invention.

Since the labeled nanocellulose according to the invention, which can be applied to form a thickness which can be very small, for example of the order of one nanometer, can be of the same nature as the substrate which supports it, the marking allows, through abrasion tests, check the persistence of this outer layer of labeled nanocellulose. Such an abrasion test is described in Example 2 below. The invention will now be described by means of the following examples and figures, given by way of nonlimiting illustration of the invention.

FIGURES

Figure 1: illustration of the two known types of nanocellulose CNC and semi-crystalline NMFC;

2: emission spectra of unlabeled nanocellulose and nanocelluloses labeled with different chromophores prepared according to Example 1;

3: emission spectrum of a nanocellulose film labeled with the chromophore TMPyP, before and after the abrasion test carried out according to Example 2.

EXAMPLES EXAMPLE 1

Marking Fibrillated Nanocellulose by Different Chromophores

Fibrillated nanocellulose samples were labeled with different chromophoric molecules, according to the following general protocol: 5 mL of fibrillated nanocellulose (5 mL at a concentration w / v (%) of 2 g / 100 mL (%), ie 100 mg) are removed and diluted in deionized water (30 mL).

The chromophore is dissolved or dispersed in water (1 mL).

Table 1 below shows the nature and quantity of the different chromophores used. For some chromophores (samples L, K, J and I), a drop of concentrated HCl is added to allow their dissolution or dispersion in water.

The aqueous chromophore solution is then added with vigorous stirring to the nanocellulose suspension.

The suspension obtained is stirred (magnetic bar) for two hours at room temperature, then transferred to a Teflon mini-reactor and subjected to microwave irradiation (1 minute at 700 W).

Dialysis against deionized water (or ethanol or THF), carried out using a Zellu Trans Roth cellulose membrane, of the samples obtained is carried out for 3 days.

TABLE 1

Analysis of the labeled nanocellulose

The fluorescence emission spectra of the various samples of nanocellulose labeled by the different chromophores and of unlabeled nanocellulose (control M) are obtained by visible spectrometry, with excitation wavelengths ranging from 250 to 800 nm obtained at the same time. using a mercury vapor lamp.

The spectra are recorded between 250 and 800 nm.

The spectra obtained are represented in FIG.

The fluorophores A (Propyl Astra Blue Iodide), E (IR-140) and G (Cardiogreen) are not shown in FIG. 2. In fact, these fluorophores emit out of the sensitivity range of the detector, that is to say say in the infra-red. Sample J (DNAF) does not appear since it is not a fluorescent molecule.

It appears from Figure 2 that TMPyP is a particularly interesting chromophore in view of the high intensity of fluorescence. EXAMPLE 2

Formation of a thin layer of nanocellulose

The fibrous nanocelluose suspension (2 mL) enriched in TMPyP (sample H) is then deposited on a cellulose substrate (simulating a paper or food film) by bar-coating (coating on the bar).

After drying at room temperature, abrasion tests simulating a more or less significant friction are then performed to generate a release from the cellulose substrate.

Abrasion protocol

The abrasion tests were carried out in accordance with the NF EN ISO 7784-2 standard. To carry out these tests, the abrasion takes place via a TABER device. It is more specifically a TABER Rotary, Rotary Platform Abraser of TABER INDUSTRIES. The nanocellulose, in liquid form, was deposited on cellulose substrates (any type of cellulosic substrate) by bar-coating. After drying, the abrasions are carried out under controlled atmospheres (temperature, humidity, zero particulate background). Result

The fluorescence emission spectra of the TMPyP-labeled nanocrystalline sample before and after the abrasion test are shown in FIG.

Thus, by fluorescence analysis of the material taken during mechanical loading, it is possible to identify the release of nanocellulose labeled with TMPyP. EXAMPLE 3 (counterexample)

Influence of microwave treatment on the grip of the chromophore to nanocellulose

In order to determine the effectiveness of the microwave treatment with respect to the adhesion of the chromophore molecule to the nanocellulose, an experiment is conducted as follows.

A sample of nanocellulose is treated with TMPyP, as described in Example 1 above, but omitting the microwave irradiation step. At the end of the dialysis purification step, the fluorescence of the nanocellulose is not observed.

However, the fluorescence of TMPyP is found in dialysis waters.

Thus, the microwave treatment makes it possible to hook and fix the fluorophore of interest on the cellulosic matrix. EXAMPLE 4 Against Example)

Effect of a heat treatment on the hooking of the chromophore to the nanocellulose 5 mL of fibrillated nanocellulose (5 mL at a w / v concentration (%) of 2.2 g / 100 mL (%), ie 110 mg) are taken and diluted in deionized water (30 mL). 2 mg of TMPyP chromophore are dissolved in water (1 mL). The chromophore solution is then added with stirring to the nanocellulose suspension as described in Example 1. The sample is then heated to boiling for 15 minutes.

After cooling, the sample is centrifuged (5000 rpm for 5 min x 3 (3 centrifugation sessions) to remove the supernatant as well as most of the unfixed TMPyP on the fibers.

Finally, this sample is dialyzed against deionized water for 3 days. At the end of the dialysis, the nanocellulose sample is analyzed.

It shows no fluorescence.

Consequently, the heat treatment operated does not make it possible to fix the chromophore on the cellulosic matrix contrary to the procedure according to the invention which implements a microwave irradiation. References [1] Xuezhu et al., "Cellulose Nanocrystals Vs. Nanofibrils Cellulose: A Comparative Study on Their Microstructures and Effects as Polymer Reinforcement Agents, AC S Appl. Mater. Interfaces 2013, 5, 2999-3009; [2] Juan Xue et al., ACS Applied Materials & Interfaces 2015, 7, 10076-10079, "Let it shine: A transparent and photoluminescent foldable nanocellulose / quantum dot paper"; [3] Chauhan et al., Chem. Commun., 2014, 50, 9493-9496; [4] Dimic-Misic et al., Nordic Pulp & paper research journal 2014, 29, 253-270, "Comparing the rheological properties of novel nanofibrillar cellulose-formulated pigment coating colors with those using traditional thickener".

Claims (14)

A method for marking the semi-crystalline nano and / or micro-fibrillated cellulose using at least one chromophoric organic molecule, comprising at least the steps of: (i) providing an aqueous dispersion of cellulose nano and / or microcrystalline semicrystalline, supplemented with at least one organic chromophore molecule; and (ii) subjecting said dispersion (i) to microwave irradiation under conditions conducive to attachment of said chromophoric organic molecule to the nano and / or micro-fibrillated cellulose. 2. Method according to claim 1, wherein the chromophoric organic molecule is fluorescent and / or absorbent, in particular fluorescent. 3. The method of claim 1 or 2, wherein the chromophore organic molecule is selected from: - cyanines and derivatives thereof, such as carbocyanine or phthalocyanine derivatives; rhodamines and their derivatives; - coumarin and its derivatives; pyrene derivatives; naphthalene derivatives; porphyrin derivatives; benzophenoxazine derivatives; and - azo derivatives. A process according to any one of the preceding claims wherein the chromophoric organic molecule is selected from: Propyl Astra Blue Iodide, IR-140, IR-676 iodide, Green Indocyanine, Rhodamine 6G perchlorate, 7-amino-4- ( trifluoromethyl) coumarin, Nile Blue A perchlorate, Dansylcadaverine, Rhodamine 19 perchlorate, TMPyP, 1-aminopyrene and DNAF. 5. Process according to any one of the preceding claims, in which the content of organic chromophore molecules is between 0.1 and 5% by weight, in particular between 0.5 and 3% by weight, and more particularly between 0, 8 and 2.6% by weight, relative to the total weight of the aqueous dispersion of step (i). 6. Method according to any one of the preceding claims, wherein the aqueous dispersion of nano and / or micro-fibrillated cellulose in step (i) is prepared by addition, with stirring, of the chromophore molecule, in particular implemented under solution form or aqueous dispersion, a dispersion of nano cellulose and / or micro-fibrillated. 7. Process according to any one of the preceding claims, in which the content of nano and / or microfibrils of cellulose is between 1 and 5% by weight, in particular between 2 and 4% by weight, and more particularly between 2 and 3% by weight, relative to the total weight of the aqueous dispersion of step (i). 8. Method according to any one of the preceding claims, wherein the microwave irradiation has an energy of between 200 and 1000 W, in particular between 350 and 850 W, for example between 500 and 750 W. 9. Process according to any one of the preceding claims, in which the duration of submittance to microwave irradiation is between 0.5 and 10 minutes, in particular between 1 and 5 minutes, and more particularly between 1 and 5 minutes. 2 minutes. 10. A method according to any one of the preceding claims, further comprising a subsequent step (iii) elimination of chromophoric organic molecules not fixed to the nanocellulose, in particular by dialysis, and more particularly by dialysis against deionized water. , ethanol or THF. 11. labeled nano-crystalline and / or micro-fibrillated semicrystalline cellulose obtained according to the process as defined in any one of the preceding claims. 12. Use of labeled nano-crystalline and / or micro-fibrillated semicrystalline cellulose, obtained according to the process as defined in any one of claims 1 to 10, for coating substrates such as films, in particular of cellulosic nature. 13. Article for the food industry comprising at least one layer made of labeled nano-crystalline and / or micro-fibrillated semicrystalline cellulose obtained according to the process as defined in any one of claims 1 to 10. 14. Cellulose-based food film comprising at least one outer layer made of labeled nano-crystalline and / or micro-fibrillated semicrystalline cellulose, obtained according to the process as defined according to any one of Claims 1 to 10.