WO2021079073A1

WO2021079073A1 - Composite cellulose material and method for making such a material

Info

Publication number: WO2021079073A1
Application number: PCT/FR2020/051917
Authority: WO
Inventors: Jérémie VIGUIE; Laura CROWTHER-ALWYN; David Guerin; William GOURGEON; Caroline LOCRE; Richard Thalhofer
Original assignee: Centre Technique Du Papier; Cargill, Incorporated
Priority date: 2019-10-23
Filing date: 2020-10-23
Publication date: 2021-04-29
Also published as: US20220389662A1; EP4048838B1; EP4048838A1; FR3102491A1; FR3102491B1

Abstract

The present invention relates to a composite cellulose material, comprising: - a layer of a cellulose material, - a starch-based reinforcement grid which is positioned on at least one surface of the layer of cellulose material, the reinforcement grid comprising a plurality of meshes which are delimited by grid wires, the composite cellulose material having a relief in three dimensions comprising folds in the positioning zones of the reinforcement grid, and relief bumps on either side of the plane of the grid which are delimited by the folds.

Description

CELLULOSIC COMPOSITE MATERIAL AND METHOD FOR MANUFACTURING SUCH MATERIAL

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a cellulosic composite material, various products made from such a material such as packaging for food, cosmetic or pharmaceutical products, papers for bags, sachets and pouches, a core for cellular “sandwich” panels or multi-structure. - paper towels or toilet paper, or even wallpaper, printed papers for promotional purposes such as poster papers, for inserts, inserts or leaflets, papers for household use such as paper tablecloths, stationery articles such as book covers or an envelope for example, as well as a method of manufacturing such a material.

STATE OF THE ART

Grid-type structures or frames are widely present in nature, in particular in the leaves of certain plants where they support the body of the leaves, or else in the wings of certain insects. Man was inspired by it to develop plate or shell structures used in many industrial sectors, particularly in transport (marine, nautical, aeronautics, aerospace) and civil engineering.

These structures consist of a skin and a network of reinforcing ribs extending over a surface of the skin, and are of interest for applications that require rigidity, strength and lightness. This arrangement makes it possible to put the material where it is needed: when such a structure is stressed in torsion or in bending, the skin works essentially in so-called membrane deformation mode, while the network of ribs works mainly in bending / torsion. . It is thus possible to obtain parts, most often in the form of ultralight flat or curved panels with very good specific mechanical properties (that is to say in relation to their density).

The mechanical properties of deformation in bending (curvature of the structure) and in torsion (twisting of the structure), as well as the buckling behavior of the ribbed structures are in particular determined by the geometry of the network of ribs. The optimization of these properties involves the development of geometries adapted to the stresses [1]. For example, specific geometric patterns can confer auxetic behavior [2], i.e. exhibiting a negative Poisson's ratio, to the structures they constitute and significantly improve some of their geometric and mechanical properties.

These ribbed structures find an application in particular in the paper industry. Document FR 2250 853 describes on this subject a process for improving the mechanical properties of a sheet of paper. This process consists in forming in the sheet of paper a reinforcement consisting of a regular network of continuous thin lines of a binder commonly used in the paper industry. The binder, in particular a polyvinyl alcohol or a rubber, penetrates into the sheet of paper, and leads to the formation of a reinforcement at the heart of the sheet of paper. The reinforcement, integrated into the sheet of paper, gives the latter an increased tensile strength, while preserving the flexibility of the sheet, in particular in bending and in torsion. In document FR 2250 853, the frame is formed in the sheet of paper, at the heart of said sheet of paper. The resulting sheet of reinforcing paper exhibits improved mechanical properties in the plane of the sheet, including improved tensile strength. On the other hand, the mechanical properties out of the plane of the sheet, such as the bending and torsional strength, remain unchanged and therefore low since they correspond approximately to those of the initial sheet of paper. The reinforcing sheet of paper is therefore not rigid, and therefore, is not suitable for use in areas where the paper is under high stress, in particular under stresses perpendicular to the plane of the sheet of paper such as bending or twisting. This is particularly the case when the paper is used for the manufacture of packaging, in particular for the transport or storage of food products.

BRIEF DESCRIPTION OF THE INVENTION

An aim of the invention is to provide a cellulosic composite material which makes it possible to overcome the drawbacks described above. The invention aims in particular to provide such a cellulosic composite material comprising a layer of a cellulosic material, which exhibits mechanical properties outside the plane of the sheet, in particular the bending strength and the torsional strength, which are increased with respect to said layer of cellulosic material alone.

The invention aims most particularly to provide such a cellulosic composite material suitable for use in fields where paper is in high demand, very particularly but not exclusively for the manufacture of packaging for food, cosmetic or pharmaceutical products, paper for bags. , sachets and pockets, a core for honeycomb sandwich panels or multi-ply paper towel or toilet paper, or even wallpaper, printed papers for promotional uses such as poster, insert, insert or flyer papers , papers for household use such as paper tablecloths, stationery articles such as book covers or an envelope for example

To this end, the invention provides a cellulose composite material comprising: a layer of a cellulosic material, a starch-based reinforcing grid positioned on at least one surface of the layer of cellulosic material, said reinforcing grid comprising a plurality of meshes delimited by grid wires, the cellulosic composite material having a three-dimensional relief comprising folds at the level of the positioning zones of the reinforcement grid, and raised bumps on either side of the plane of the grid delimited by the folds.

According to other aspects, the cellulosic composite material according to the invention has the following different characteristics taken alone or according to their technically possible combinations: the three-dimensional relief has an overall thickness greater than the sum of the thicknesses of the layer of cellulosic material and the reinforcement grid; the degree of coverage of the reinforcing grid on the surface of the layer of cellulosic material is greater than or equal to 10%, preferably greater than or equal to 20%; the degree of coverage of the reinforcing grid on the surface of the layer of cellulosic material is less than or equal to 60%, preferably less than or equal to 50%; the grid wires form square or rectangular meshes; the grid wires form hexagonal meshes; the grid wires form honeycomb type meshes; the grid threads form bow-tie type stitches; one or more grid wires are sinusoidal; the reinforcing grid is deposited on the layer of paper by screen printing, three-dimensional printing, intaglio, flexography, or spraying via one or more nozzles; the reinforcing grid is positioned on the surface of the layer of cellulosic material in an amount between 2 g / m ² and 50 g / m ² after drying; the grid wires have a width in the plane of the grid of between 0.1 mm and 3 mm, preferably between 0.5 mm and 2.5 mm; the degree of coverage of the reinforcing grid on the surface of the layer of cellulosic material is between 10% and 60%, preferably between 20% and 50%.

The invention also relates to articles made from the cellulosic composite material described above.

Such articles can be in particular, but not exclusively, a flexible packaging, such as a food packaging for example, a wallpaper, a display panel, preferably of the sandwich type, or else an envelope. Another object of the invention relates to a method of manufacturing a cellulosic composite material as described above, from a layer of a cellulosic material. This method is mainly characterized in that it comprises a step consisting in depositing a starch-based reinforcing grid on at least one surface of the cellulosic material, said reinforcing grid comprising a plurality of meshes delimited by grid wires, in order to form a three-dimensional relief comprising folds at the level of the positioning zones of the reinforcing grid, and raised bumps on either side of the plane of the grid delimited by the folds.

According to other aspects, the manufacturing process according to the invention has the following different characteristics taken alone or according to their technically possible combinations: the reinforcing grid deposited on the cellulosic material comprises a starch suspension; the deposition of the grid is carried out by screen printing, three-dimensional printing, intaglio, flexography, or spraying via one or more nozzles; the composition of the reinforcing grid comprises at least one starch suspension having a dry matter content of between 5% and 65% by weight during the deposition of the reinforcing grid DESCRIPTION OF THE FIGURES

Other advantages and characteristics of the invention will become apparent on reading the following description given by way of illustrative and non-limiting example, with reference to the following appended figures:

Figure 1 is a diagram of a reinforcing grid, in which the grid threads form hexagonal honeycomb-type meshes;

Figure 2 is a diagram of a reinforcing grid, in which the grid threads form hexagonal bow-tie type meshes;

Figure 3 is a diagram of a reinforcing grid, in which all of the grid wires constituting the meshes are sinusoidal; Figure 4 is a diagram of a reinforcing grid, in which the grid wires are orthogonal in pairs and form square meshes;

FIG. 5 is a graph illustrating the evolution of the flexural strength of a cellulosic composite material according to the invention, comprising a sheet of paper and a reinforcing grid with square mesh of starch type dextrin, as a function of the coverage rate from the sheet of paper through the grid;

FIG. 6 is a graph illustrating the evolution of the flexural strength of a cellulosic composite material according to the invention, comprising a sheet of paper and a grid of starch square mesh reinforcement of the dextrin and waxy mixture type, depending on the degree of coverage of the sheet of paper by the grid;

FIG. 7 is a graph illustrating the flexural strength of the cellulosic composite material for reinforcing grids having different patterns; FIG. 8 is a graph illustrating the flexural strength of cellulosic composite materials comprising reinforcing grids of different compositions;

Figure 9 is a graph illustrating the overall thickness of composite materials from the graph of Figure 8;

Figure 10 is a graph illustrating the quantity or basis weight of composite materials from the graph of Figure 8;

FIG. 11A is a top photograph of a composite material obtained by depositing a starch reinforcing grid on a layer of Gerstar ™ cellulosic material;

Figure 11B is a top grazing photograph of the composite material of Figure 11A; FIG. 12 is a graph illustrating the flexural strength of composite materials obtained by depositing a starch reinforcing grid on tracing paper and on blotting paper;

Figure 13 is a graph illustrating the overall thickness of composite materials from the graph of Figure 12; Figure 14 is a diagram illustrating the determination of the overall thickness.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The invention relates to a cellulosic composite material comprising a layer of cellulosic material and a reinforcing grid positioned on at least one surface of the layer of cellulosic material. The reinforcing grid can be deposited on the whole of this surface, or on only part of this surface. Such a cellulosic composite material makes it possible to manufacture packaging, most particularly for food products.

It is specified that a “composite material” corresponds to a combination of at least two immiscible components. A synergistic effect is obtained by such a combination, so that a composite material has properties, in particular mechanical properties, that each of the components alone does not have, or has to a lesser degree than the composite material. In this case, the first component of the cellulosic composite material is the layer of a cellulosic material, and the second component is the reinforcing grid. The layer of cellulosic material forms the matrix of the cellulosic composite material. Such a matrix ensures the cohesion of the structure of the cellulose composite material, and transmits the forces exerted on the latter to the reinforcing grid. The reinforcing grid is a reinforcement of the cellulose composite material, and ensures good mechanical strength thereof.

The deposition of the reinforcing layer on the surface of the layer of cellulosic material thus makes it possible to improve the specific mechanical properties out of the plane of said layer of cellulosic material, in particular by increasing its flexural strength as well as its torsional strength.

The layer of cellulosic material is preferably a sheet of paper.

Preferably, the sheet of paper has a basis weight of between 13 g / m ² and 140 g / m ² , preferably between 30 g / m ² and 90 g / m ² . These grammage ranges correspond to a relatively flexible sheet of paper, typically sheets intended for the manufacture of flexible packaging such as pouches, bags and sachets, which are particularly preferred for making the cellulosic composite material of the invention.

The reinforcing grid comprises a plurality of meshes delimited by grid wires.

The reinforcement grid includes starch.

The starch can be native starch or modified starch, for example dextrin.

Starch is a polymer of glucose, usually a mixture of amylopectin (branched) and amylose (linear), naturally present in many plants. In the state of the art, two starch modification strategies are usually implemented industrially: the acidic or enzymatic conversion of starch in order to generate polymers of lower molecular mass, for example dextrins, and chemical modification of starch, by reacting the hydroxyl groups of the starch with functional agents to introduce substitution groups. They are, for example, in particular starches such as hydroxypropyl ethers or hydroxypropyl starch.

The native or modified starch can be combined with other constituents in the reinforcing grid.

Following the deposition of the starch grid on the surface of the layer of cellulosic material, the starch shrinks when it dries. Surprisingly, the shrinkage forces exerted during the drying of the starch-based formulation previously deposited on the surface of the cellulosic layer lead to a deformation gradient in the thickness of the cellulosic layer. This deformation is favored by the rewetting of the cellulose layer which occurs between the removal of the grid and the end of drying. A fold is then formed, which can also be called a "valley fold" in that a valley is formed in the fold on the face on which the reinforcing grid has been deposited, at the places where the retraction of the grid occurs. starch, that is to say at the level of the deposit zones of the grid. These folds form with the plane of the surface of the cellulosic layer an angle which depends in particular on the width of the grid lines (or wires) and on the quantity deposited. The term "valley fold" is a common term in origami that describes the present situation well. The formation of these folds at the level of the reinforcing grid forms a three-dimensional relief, relatively homogeneous, due to the deformation of the cellulosic material located between the folds to form bumps or "peaks" in relief on either side of the grid plan. This deformation increases the so-called “overall” thickness of the composite material formed, as well as its out-of-plane mechanical properties, in particular the bending and torsional strength.

More precisely, the term “overall thickness” is understood to mean the distance between the planes tangent to the upper and lower rough surfaces of the cellulosic layer, and mutually parallel. The determination of the overall thickness, denoted Ep, is illustrated in Figure 14.

The deposition of the starch grid on the surface of the cellulosic layer thus makes it possible to obtain a synergistic effect: a local increase in thickness, at the level of the deposit zones of the grid, due to the local addition of material. (starch), as well as an additional effect of increasing the overall thickness, which occurs more globally on the cellulosic layer, and more importantly at the level of the deposition zones of the grid, according to the strain gradient in the thickness of said cellulosic layer. In other words, the thickness of the composite material obtained is greater than the sum of the thicknesses of the layer of cellulosic material and of the reinforcing grid.

This increase in overall thickness results in an improvement in the out-of-plane mechanical properties of the composite material, in particular its flexural and torsional strength, which is greater than what was initially expected by the applicant, and which would be obtained by the increase alone. local thickness due to the addition of material.

The overall thickness measurement is performed according to the IS012625-3 standard, as the distance between a fixed reference plate on which the sample rests and a parallel probe which exerts a specified load on the surface under test.

A precision counterbalanced micrometer is used which comprises two parallel and flat horizontal keys, between which a test specimen of the material of interest is placed. The upper circular probe has an upper diameter of (35.7 ± 0.1) mm, i.e. a nominal area of 10.0 cm ² . The pressure between the two micrometer keys is (2.0 ± 0.1) kPa.

A starch grid further offers the advantage of being inexpensive. The starch can be in the form of a starch suspension, which simplifies the deposition of the grid, the starch suspension being in fact relatively simple to use and distributing itself suitably over the surface of the layer. of cellulosic material. The starch suspension can be supplemented with a certain number of products, such as in particular rheology modifiers, pigments, plasticizers, surfactants in order to modulate or improve the properties thereof during the use of the grid or during its use. Materials other than starch can be envisaged, without departing from the scope of the invention. These materials must, however, exhibit a shrinkage similar to starch, in order to be able to lead to an increase in the overall thickness. By shrinkage is meant the dimensional variations and associated phenomena observed during drying [3].

The degree of coverage of the reinforcing grid on the surface of the layer of cellulosic material is greater than or equal to 10%, preferably greater than or equal to 20%.

The coverage rate of the reinforcing grid can be defined as being the ratio between the surface portion of the layer of cellulosic material which is covered by the reinforcing grid, and the portion of said surface which is free, that is to say - say not covered by said reinforcing grid.

With a coverage rate of less than 10%, the amount of reinforcement grid deposited is low and more difficult to measure and repeat. In addition, there is less improvement in the out-of-plane mechanical stiffness properties, including bending and torsional strength.

The degree of coverage of the reinforcing grid on the surface of the layer of cellulosic material is less than or equal to 60%, preferably less than or equal to 50%.

A coverage rate greater than 60% does not further improve the out-of-plane mechanical properties, in addition to significantly stiffening the composite material formed, especially in the plane, which is not necessarily desirable depending on the subsequent application of the composite material. . A coverage rate of less than 60% but greater than 50% improves very little the out-of-plane mechanical properties and stiffens the composite material in the plane.

According to one embodiment, the coverage rate is between 10% and 60%, preferably between 10% and 50%, and more preferably between 20% and 50%. These coverage rates make it possible to have a good compromise between an improvement in the overall thickness and in the bending and torsional strength, and the cost of manufacturing the cellulosic composite material using a moderate amount of reinforcing grid composition. .

With a coverage rate greater than 90%, the area of the areas not covered by the reinforcing grid would be insufficient for the bumps to form in the cellulosic material.

The reinforcing grid is deposited on the layer of paper preferably by screen printing, three-dimensional printing, intaglio, flexography, or spraying via one or more nozzles.

Screen printing is a printing technique using as a printing form a canvas, also called a screen, the meshes of which are sealed on the areas which should not be printed. The ink is deposited on the back of the canvas and a doctor blade system makes it possible to force the passage of the ink through the unblocked mesh of the canvas and come into contact with the material to be printed. This technique is advantageous for the deposition of reinforcing grid, since it uses inks of medium viscosities (viscosities between 500 and 5000 mPa.s) and allows to carry out localized deposits which can range from 5 to 120 pm of ink thickness. before drying.

According to the intaglio technique, hollows are engraved in the printing form (usually a metal plate). The plate is coated with ink and then scraped to leave ink only in the hollows of the printer form. This printing form is pressed onto the paper to allow ink to transfer from the recesses of the printing form to the surface of the sheet. This process is particularly advantageous for depositing ink thicknesses of 10 to 60 μm before drying, but requires a particularly viscous ink (viscosity between 10,000 and 25,000 mPa.s) and exerts a pressure constraint on the transfer reducing the thickness of the cellulose layer.

Flexography makes it possible to print the reinforcing grid using a flexible printing form in relief.

The reinforcing grid preferably represents an increase in basis weight after drying of between 2 and 50 g / m ² , preferably between 5 and 20 g / m ² . In other words, this corresponds to the amount of reinforcing grid that is positioned on the surface of the layer of cellulosic material.

The grid wires preferably have a width in the plane of the grid of between 0.1 mm and 3 mm, preferably between 0.5 mm and 2.5 mm.

The meshes of the reinforcing grid can have various patterns. It can be, for example, a square, rectangular, hexagonal, honeycomb type, bow tie type, or even sinusoidal pattern.

Examples of patterns are shown in Figures 1, 2 and 3. For these various examples, the meshes are sized to have a coverage rate of approximately 30%.

Referring to Figure 1, the reinforcement grid comprises hexagonal pattern meshes. The hexagon has six parallel sides two by two and of the same length, denoted b, equal to 5 mm. The thickness of the threads forming the mesh, denoted e, is equal to 1 mm.

With reference to FIG. 2, the reinforcing grid comprises meshes with a pattern of the bow tie or hourglass type.

According to a first example, the length L of a lateral side of the bow tie is equal to 6 mm, the length H of the base is equal to 12 mm, the angle Q between the base and the lateral side is equal to 45 °, and the thickness e of the wires forming the mesh is equal to 0.8 mm.

According to a second example, the length L of a lateral side of the bow tie is equal to 5 mm, the length H of the base is equal to 10 mm, the angle Q between the base and the lateral side is equal to 60 °, and the thickness e of the wires forming the mesh is equal to 0.8 mm.

With reference to FIG. 3, the reinforcing grid comprises meshes with a sinusoidal type pattern. Each stitch is formed by two warp threads which extend opposite one another on the other in a substantially vertical direction, the curvature of one thread being reversed with respect to that of the other thread, and by two weft threads which extend opposite one another. another in a substantially horizontal direction, the curvature of one wire being reversed with respect to that of the other wire.

According to a first example, the curved deviation, denoted a, of each wire with respect to an equivalent straight wire is equal to 1.5 mm, the space I between two opposite sides of the equivalent square is equal to 5 mm, and the thickness e of the wires forming the mesh is equal to 0.8 mm.

According to a second example, the curved deviation, denoted a, of each wire with respect to an equivalent straight wire is equal to 1.8 mm, the space I between two opposite sides of the equivalent square is equal to 6 mm, and the thickness e of the wires forming the mesh is equal to 1 mm.

The invention also relates to a process for manufacturing a cellulosic composite material as described above.

The method comprises a step consisting in depositing the reinforcing grid on at least one surface of the cellulosic material.

According to a preferred embodiment, the deposition of the grid is carried out by screen printing, three-dimensional printing, intaglio, flexography, or spraying via one or more nozzles.

Preferably, the composition of the reinforcing grid comprises at least one starch suspension having a dry matter content of between 5% and 65% by weight during the deposition of the reinforcing grid.

EXAMPLES

Example 1: determination of the flexural strength of cellulosic composite materials comprising reinforcing grids at different coverage rates

A rectangular mesh reinforcement grid was printed by screen printing on a paper of 55 g / m ² of dry basis weight, to obtain the corresponding cellulosic composite material. The grid is shown in Figure 4.

The thickness of the grid is 20 μm for a line width, denoted a, between 0.25 mm and 2.5 mm depending on the percentage of coverage between 20% and 75%. The medians of the lines are spaced from each other by 5 mm. The grid has a dimension of 300 mm by 200 mm.

Two formulations were tested for the reinforcing grid: a dextrin, a mixture based on 90% dextrin and 10% waxy starch (rich in amylopectin).

The obtained cellulose composite material was dried in an oven at a temperature of 60 ° C for 1 minute and 30 seconds. The results obtained with the reinforcing grid based on low molecular weight dextrin are illustrated in FIG. 5. The graph of FIG. 5 shows the flexural strength (mNm) at 15 ° as a function of the degree of coverage (%). Photographs illustrate the surface appearance of the composite material obtained. The flexural strength of the material, measured according to the ISO 2493-1: 2010 standard, goes from 0.07 mNm (zero coverage rate, no reinforcement grid) in the running direction, also known as the machine direction and noted MD, at 0.22 mNm for the cellulosic composite material exhibiting a coverage rate of 50%.

In the transverse direction, the flexural strength increases from 0.04 mNm to 0.12 mNm. The results obtained with the reinforcing grid based on the mixture of 90% dextrin and 10% waxy-type starch are illustrated in FIG. 6, and are similar to those of FIG. 5. The graph of FIG. 6 shows the resistance in flexion (mNm) at 15 ° depending on the coverage rate (%).

The flexural strength of the material, measured according to the ISO 2493-1: 2010 standard, goes from 0.07 mNm (zero coverage rate, no reinforcement grid) in the MD travel direction, to 0.21 mNm for the cellulose composite material with a coverage rate of 50%.

In the transverse direction, the flexural strength increases from 0.04 mNm to 0.13 mNm. Example 2: determination of the flexural strength of cellulosic composite materials comprising reinforcing grids having different patterns

Eight cellulosic composite materials comprising grids made from the same composition, and having meshes of different patterns, were tested to determine their flexural strength. They are compared to the material (a) not comprising a grid, which is a flexible wrapping paper marketed by the company Ahlstrom-Munksjo. The coverage rate is approximately 30% for all eight materials except material (c).

The cellulose composite materials are as follows: material (a): Gerstar ™ material without grid, - material (b): rectangular grid, material (c): rectangular grid with a coverage rate of 51%, material (d): honeycomb type hexagonal grid, material (e): bowtie type hexagonal grid, the angle Q between the base and the side side is 45 °, - material (f): bowtie type hexagonal grid, the angle Q between the base and the lateral side is equal to 60 °, and the thickness e of the wire is 1 mm, material (g): hexagonal bow-tie type grid, the angle Q between the base and the side lateral is equal to 60 °, and the thickness e of the wire is 0.8 mm, material (h): sinusoidal grid, the thickness e of the wire is 1 mm, material (i): sinusoidal grid, the thickness e of the wire is 0.8 mm The results are represented in the form of a graph on the figure 7. The graph of figure 7 shows the flexural strength (mNm) as a function of the different materials. The measurements are carried out in the MD machine direction as well as in the transverse direction

CD. Photographs illustrate the surface appearance of the various composite materials.

From the graph, it is observed that the improvement in flexural strength of the cellulosic composite material is generally greater with the honeycomb-type grid (d), bowtie-type hexagonal grid (f) grid materials of thickness 1 mm, and with a sinusoidal grid (h) of thickness 1 mm, compared to materials with orthogonal grid.

Example 3: determination of the flexural strength of cellulosic composite materials comprising reinforcing grids of different materials

Eight cellulosic composite materials comprising grids made from several different compositions, and having meshes of an identical pattern to sinusoidal hexagonal meshes, were tested to determine their flexural strength. The coverage rate is approximately 30% for the eight materials. All eight composite materials include the same cellulosic material: Gerstar ™ flexible packaging material.

The compositions of the different grids are as follows: material (a): Gerstar ™ material without grid, material (b): polyvinyl alcohol grid (PVOH), material (c): water grid, material (d): starch grid hydroxypropyl, material (e): grid mixture 90% dextrin and 10% waxy starch, material (f): grid mixture 85% dextrin and 15% waxy starch, material (g): grid mixture 80% dextrin and 20% waxy starch, material (h): dextrin grid.

The results are shown as a graph in Figure 8. The graph in Figure 8 shows the flexural strength (mNm) as a function of the different materials.

The overall thickness (mm) of the different cellulosic materials is shown in Figure 9, and the basis weight (g / m ² ) of the different cellulosic materials is shown in Figure 10.

The measurements are made in the MD machine direction as well as in the CD cross direction.

From the graph of Figure 8, it is observed that the five starch grids result in a very significant gain in flexural strength compared to the reference. This is explained by the synergy effect obtained both by a local increase in the thickness of the material, at the level of the deposit zones of the grids due to the local addition of starch, and by an additional effect of increase in overall thickness.

A photograph of the composite material obtained by depositing the starch grid is shown in Figure 11A. A grazing view photograph of this same material is shown in Figure 11B.

The PVOH and water grids give poorer results than starches: the gain in flexural strength compared to the reference is relatively low. This is because the synergistic effect observed for the starch grids does not occur. There is only a local increase in material thickness at the deposition areas of the grids due to the deposition of material.

A starch grid was also placed on other cellulosic materials: slap paper and blotting paper. The results are shown in the graphs of Figures 12 and 13. The graph of Figure 12 shows the flexural strength (mNm) as a function of the different materials. The graph in Figure 13 shows the overall thickness (mm) depending on the different materials.

In these figures, (a) Clq and (e) Clq correspond to the uncoated tracing paper (a) and covered with the grid in a mixture of 90% dextrin and 10% waxy starch (e) respectively, and (a) Bvd and (e) Bvd correspond to the blotting paper not covered with the grid (a) and covered with the grid in a mixture of 90% dextrin and 10% waxy starch (e) respectively.

It is observed that the gain in flexural strength is similar to that obtained with the flexible Gerstar ™ wrapping paper of the graph of figure 8. This effect is surprising for the blotting paper insofar as, taking into account the absorbent properties of this paper. material, the starch suspension partially penetrates into the thickness of the sheet. One would therefore have expected that the folds observed with Gerstar ™ paper (which is not absorbent) would not form on blotting paper.

REFERENCES [1]: D. Wang M. M. Abdallan & W. Zhang. Buckling optimization design of curved stiffeners for grid-stiffened composite structures. Composite Structures, vol. 159, p. 656-666, 2017.

[2]: A. Rafsanjani, D. Pasini. Bistable auxetic mechanical metamaterials inspired by ancient geometry patterns. Extreme Mechanics Letters, vol. 9 p. 291-296, 2016. [3]: G. M. Laudone, G. P. Matthews and P. A. C. Gane, “Coating Shrinkage during

Evaporation: Observation, Measurement and Modeling within a Network Structure, ”Tappi 8th Advanced Coating Fundamentals Symposium, Chicago, 8-10 May 2003, pp. 116-129.

Claims

1. Cellulose composite material including:

- a layer of cellulosic material,

a starch-based reinforcing grid positioned on at least one surface of the layer of cellulosic material, said reinforcing grid comprising a plurality of meshes delimited by grid wires, the cellulosic composite material having a three-dimensional relief comprising folds at the level of the positioning zones of the reinforcing grid, and raised bumps on either side of the plane of the grid delimited by the folds.

2. Cellulose composite material according to claim 1, wherein the three-dimensional relief has an overall thickness greater than the sum of the thicknesses of the layer of cellulose material and of the reinforcing grid.

3. Cellulosic composite material according to claim 1 or claim 2, wherein the coverage rate of the reinforcing grid on the surface of the layer of cellulosic material is greater than or equal to 10%, preferably greater than or equal to 20%. .

4. Cellulose composite material according to any one of the preceding claims, in which the coverage rate of the reinforcing grid on the surface of the layer of cellulose material is less than or equal to 60%, preferably less than or equal to 50%. .

5. Cellulose composite material according to any one of the preceding claims, wherein the grid wires form square or rectangular meshes.

6. A cellulose composite material according to any one of claims 1 to 4, wherein the grid wires form hexagonal meshes.

7. A cellulosic composite material according to claim 6, wherein the grid wires form honeycomb-type meshes.

8. A cellulosic composite material according to claim 6, wherein the grid son forms bow tie type meshes.

9. A cellulose composite material according to any preceding claim, wherein one or more grid wires are sinusoidal.

10. Cellulose composite material according to any one of the preceding claims, wherein the reinforcing grid is deposited on the layer of paper by screen printing, three-dimensional printing, intaglio, flexography, or spraying via one or more nozzles.

11. Cellulosic composite material according to any one of the preceding claims, in which the reinforcing grid is positioned on the surface of the layer of cellulosic material in an amount between 2 g / m ² and 50 g / m ² after drying.

12. Cellulose composite material according to any one of the preceding claims, in which the grid wires have a width in the plane of the grid of between 0.1 mm and 3 mm, preferably between 0.5 mm and 2.5 mm. .

13. Cellulosic composite material according to any one of the preceding claims, in which the degree of coverage of the reinforcing grid on the surface of the layer of cellulosic material is between 10% and 60%, preferably between 20% and 50%. %.

14. Flexible packaging characterized in that it comprises a cellulose composite material according to any one of claims 1 to 13.

15. Wallpaper characterized in that it comprises a cellulose composite material according to any one of claims 1 to 13.

16. Display panel, preferably of the sandwich type, characterized in that it comprises a cellulose composite material according to any one of claims 1 to 13.

17. Envelope characterized in that it comprises a cellulose composite material according to any one of claims 1 to 13.

18. A method of manufacturing a cellulosic composite material according to any one of claims 1 to 13 from a layer of a cellulosic material, characterized in that it comprises a step of depositing a reinforcing grid to starch based on at least one surface of the material cellulosic, said reinforcing grid comprising a plurality of meshes delimited by grid wires, in order to form a three-dimensional relief comprising folds at the level of the positioning zones of the reinforcing grid, and raised bumps on both sides other of the plane of the grid delimited by the folds.

19. The manufacturing method according to claim 18, wherein the reinforcing grid deposited on the cellulosic material comprises a starch suspension.

20. The manufacturing method according to claim 18 or claim 19, wherein the deposition of the grid is carried out by screen printing, three-dimensional printing, intaglio, flexography, or spraying via one or more nozzles.

21. The manufacturing method according to any one of claims 18 to 20, wherein the composition of the reinforcing grid comprises at least one starch suspension having a dry matter content of between 5% and 65% by weight during the production. deposit of the reinforcement grid.