Bio-based adhesive composition, process for its production and use as an adhesive

Abstract

The invention relates to an adhesive composition in the form of a suspension in water of a complex of microfibrillated cellulose and at least one branched polysaccharide, with a dry matter content between 10 and 40% by weight. This composition is obtained by a process comprising: an extrusion step in a twin-screw extruder of a mixture of water, cellulose fibers and at least one branched polysaccharide, this mixture containing from 10 to 40% by weight of dry matter, and the ratio of the percentages by weight of branched polysaccharide(s) and cellulose in the mixture being between 5 / 95 and 50 / 50; and, before or during this extrusion step, an enzymatic treatment step of the cellulose fibers using a cellulase.

Description

Title of the invention: Bio-based adhesive composition, process for obtaining it and using it as an adhesive

[0001] The present invention falls within the field of adhesive compositions based on ingredients from renewable resources.

[0002] More particularly, the present invention relates to an adhesive composition in the form of a suspension in water of a complex of microfibrillated cellulose and a polysaccharide, with a high dry matter content. The invention also relates to a method for obtaining such an adhesive composition, an adhesive formulation obtained by diluting such an adhesive composition in water, and their use as an adhesive.

[0003] A particular field of application of the composition according to the invention, for which it proves particularly advantageous, is that of the manufacture of wood particle-based panels, such a field of application being in no way limiting of the invention.

[0004] Compared to other existing assembly techniques, adhesive bonding technology is particularly well-developed, notably due to its versatility, which allows it to easily adapt to all desired configurations. Numerous types of adhesives are currently available on the market, meeting the needs of a wide range of industrial applications. In addition to the traditional sectors of packaging, household products, clothing, construction, wood, and transportation, these adhesives can, for example, be used in more specialized applications such as the biomedical field or electronics.

[0005] Adhesives commonly available on the market are generally derived from fossil resources, which runs counter to the current trend of seeking technologies that align with sustainable development strategies. Furthermore, they can be toxic, particularly due to the release of volatile organic compounds (VOCs) from their constituent ingredients.

[0006] In order to reduce their environmental impact, prior art has sought to develop adhesive compositions based on bio-based ingredients. Among the substances used in these prior art compositions, examples include lignocellulosic biomass, and in particular lignins, condensed and hydrolyzable tannins, proteins, and starch.

[0007] Adhesive compositions with improved mechanical properties, advantageously suited to perform a mechanical reinforcement function in addition to an adhesive function, based on cellulose nanocrystals (CNC) or cellulose nanofibrils (NFC), have also been proposed in the prior art. However, these compositions either also contain components that are not bio-based, or are complex and costly to prepare, or exhibit insufficient adhesive capacity for many applications, with some compositions even exhibiting several of these drawbacks.

[0008] The present invention aims to provide an adhesive composition with improved mechanical properties which remedies the above disadvantages, i.e. which is environmentally friendly, in particular formed solely from bio-based ingredients and devoid of toxicity, and which has a high adhesive power.

[0009] Additional objectives of the invention are that this adhesive composition be simple to prepare, particularly on an industrial scale, and at low cost.

[0010] It has now been discovered by the present inventors that these objectives are achieved by a composition based on microfibrillated cellulose and a branched polysaccharide of specific structure, the main chain of which has glucan 1-4 linkages, this composition being obtained by a particular preparation process including a step of cellulose fibrillation by twin-screw extrusion.

[0011] In this description, microfibrillated cellulose refers to a mixture of cellulose nanofibrils (NFCs) and cellulose microfibrils (MFCs). NFCs and MFCs are conventionally defined, both in themselves and in accordance with ISO 20477:2023, as cellulose nanofibers and microfibers composed of at least one elementary fibril that may contain branches. Microfibrillated cellulose is conventionally obtained from cellulose fibers by an enzymatic or chemical treatment followed by, or concurrent with, a mechanical fibrillation treatment. Cellulose nanofibrils and microfibrils typically have a diameter ranging from 1 to 100 nanometers for the smallest, down to a few tens of micrometers (and typically less than 35 µm), and a length ranging from 0.1 to 1000 micrometers.The nanometric fraction (less than 100 nm) of microfibrillated cellulose is generally between 30 and 60% by weight, depending on the exact operating parameters of the microfibrillation (enzymatic or chemical treatment followed by or concurrent with mechanical fibrillation treatment).

[0012] Thus, according to a first aspect, the present invention proposes an adhesive composition which is in the form of a suspension in water of a microfibrillated cellulose complex and at least one branched polysaccharide comprising a main chain with 1-4 glucan linkages, the dry matter content of this composition being between 10 and 40% by weight relative to the total weight of the composition. This composition is obtained by a process comprising: - an extrusion step in a twin-screw extruder of a mixture of water, cellulose fibers and at least one branched polysaccharide comprising a main chain with 1-4 glucan linkages, this mixture containing from 10 to 40% by weight of dry matter relative to the total weight of the mixture, and the ratio of the % by weight of branched polysaccharide(s) comprising a main chain with 1-4 glucan linkages, and of cellulose, in the mixture being between 5 / 95 and 50 / 50, - and, before or during the extrusion step, an enzymatic treatment step using a cellulase, or an oxidizing chemical treatment, of the cellulose fibers.

[0013] The combination of the enzymatic or chemical treatment step and the extrusion step in the twin-screw extruder advantageously ensures, in a conventional manner, the transformation of cellulose fibers into microfibrillated cellulose. This transformation, commonly referred to as microfibrillation, is well known to those skilled in the art, and it is within their competence to define the exact operating parameters to be applied to achieve it. Examples of such parameters are detailed below in this description.

[0014] Preferably, the mixture subjected to the extrusion step does not contain any organic solvent.

[0015] The adhesive composition according to the invention advantageously has a high dry matter content, this content being between 10 and 40% by weight, in particular between 15 and 35% by weight, for example between 20 and 25% by weight, relative to the total weight of the composition. This content can easily be adapted to each intended application by simply adjusting the operating parameters of the process used to obtain the composition, thus giving it great versatility.

[0016] The composition according to the invention also exhibits a particularly high adhesive strength. This adhesive strength can, for example, be evaluated by measuring the modulus of rupture and / or the modulus of elasticity of a wood particleboard in which the composition is implemented as an adhesive matrix, in accordance with ANSI A208.1-2016. An example of such an evaluation is described in detail later in this description. The adhesive strength of the composition according to the invention is notably much higher than that of a composition containing cellulose nanocrystals and the same branched polysaccharide, with a similar dry matter content, but obtained by a process without an extrusion step, unlike the process according to the invention, and comprising only the mixing of cellulose nanocrystals and branched polysaccharide in water, then the concentration by heating of the suspension thus obtained.

[0017] As indicated above, it is known in the prior art that combining an extrusion step in a twin-screw extruder with enzymatic treatment by a cellulase or oxidizing chemical transforms cellulose fibers into cellulose nanofibrils and microfibrils. However, nothing in the prior art suggested that the presence of at least one branched polysaccharide comprising a main chain with 1-4 glucan linkages during the extrusion step would result in a composition exhibiting particularly high adhesive power. The mechanisms underlying such adhesive performance of the composition according to the invention will not be discussed here.It can be assumed, however, that within the twin-screw extruder, which, through its mechanical action, achieves intimate mixing of the different components of the blend, and simultaneously with the microfibrillation of the cellulose fibers, specific interactions form between the branched polysaccharide(s) containing a main chain with 1-4 glucan linkages and the cellulose. This results in the resulting "microfibrillated cellulose / branched polysaccharide(s) containing a main chain with 1-4 glucan linkages" complex having a unique chemical structure, distinct from that obtained by other processes that mix microfibrillated cellulose and the branched polysaccharide(s) containing a main chain with 1-4 glucan linkages in different ways. This difference in chemical structure likely stems from the number, type, and locations of the molecular interactions between the cellulose and the polysaccharide(s).This particular chemical structure, which cannot be defined in itself due to the complexity of the mechanisms involved, is associated with specific properties, particularly in terms of adhesive performance.

[0018] The adhesive composition according to the invention is advantageously environmentally friendly in several respects.

[0019] This composition is entirely bio-based, its components being derived from renewable plant resources, and being moreover widely available on an industrial scale.

[0020] It is non-toxic. In particular, it does not generate any emissions of volatile organic compounds (VOCs), either during its preparation or during its use. Adhesion is generated by the physisorption and / or chnisorption of the branched polysaccharide onto the cellulose, i.e., its adsorption involving Van der Waals forces, hydrogen, and / or the formation of chemical bonds, particularly ionic bonds. The resulting complex constitutes the adhesive. The preparation does not require the use of an organic solvent and is preferably carried out entirely aqueous phase, which also enhances the safety of manufacturing and using the composition.

[0021] Furthermore, the preparation of the composition produces no waste. All the components used are incorporated into the final product, and there is no carbon loss during the preparation of the composition. The only effluent produced is water from the dewatering of the cellulose, which may be carried out after the enzymatic treatment, as detailed below.

[0022] The composition according to the invention is entirely biodegradable. In particular, it can be degraded in a targeted manner by enzymatic means, so as to facilitate the recycling of the elements that it has helped to bond.

[0023] In addition to its high adhesive power, the composition according to the invention exhibits good mechanical properties, which are conferred by the ability of cellulose nanofibrils to form networks. It is thus also advantageously suited to serve as a reinforcing additive / mechanical reinforcement.

[0024] The composition according to the invention is also simple to manufacture on an industrial scale. In particular, industrial adhesive manufacturing plants are commonly equipped with twin-screw extruders for manufacturing adhesives by extrusion. The extrusion technique is especially relevant in an industrial context since it can be implemented continuously and can even allow the incorporation of wood powder into the adhesive composition at the end of the extrusion process, so as to obtain directly from the extruder a mixture ready to be shaped by thermopressing for the manufacture of a wood particle board.

[0025] In addition to all these advantages of the composition according to the invention, its production cost is limited, in particular due to the wide availability of the raw materials involved in its preparation.

[0026] The process according to the invention advantageously makes it possible to obtain a composition with a high dry matter content, and whose exact characteristics, for example this dry matter content as well as the weight ratio of branched polysaccharide(s) comprising a main chain with 1,4-glucan linkages / cellulose, can be easily adjusted according to requirements. This great versatility proves particularly advantageous from an industrial standpoint. For example, the morphology of the adhesive joints formed by the composition can be easily controlled by choosing the operating parameters of its production process, which make it possible to manipulate the morphology of the cellulose nanofibrils and microfibrils and the rheology of the composition so as to give it the desired properties.

[0027] The high dry matter content of the composition according to the invention is also an important advantage, facilitating its transport and thereby further reinforcing its environmental qualities. Once it arrives at its destination of use, it can be easily diluted to the desired concentration before use.

[0028] In the present description, a branched polysaccharide is understood, classically in itself, as a polysaccharide comprising a main polysaccharide chain on which one or more branches are attached.

[0029] The main chain of at least one, preferably of each, branched polysaccharide implemented according to the invention is of the glucan 1-4 linkage type. Preferably, at least one, preferably each, branched polysaccharide comprising a main chain with glucan 1-4 linkages implemented according to the invention comprises a main chain with glucan [3(1—>4) linkages.

[0030] More generally, at least one, preferably each, branched polysaccharide comprising a main chain with 1-4 glucan linkages implemented according to the invention is preferably water-soluble and / or neutral.

[0031] Preferably, at least one, preferably each, branched polysaccharide comprising a main chain with glucan 1-4 linkages comprises, branched on the main chain, xylose branches, preferably xylose branches a( 1 —>6).

[0032] In preferred embodiments of the invention, at least one, preferably each, branched polysaccharide comprising a main chain with 1-4 glucan linkages is a xyloglucan, that is to say a polysaccharide whose main chain is formed of glucose monomer units linked by [3(1—>4) linkages and bears lateral branches mainly of xylose type in α(1—>6) and optionally of galactose and / or fucose type.

[0033] Xyloglucans are polysaccharides found mainly in the cell walls of dicotyledonous plants. They belong to the hemicellulose family, which plays a crucial role in maintaining the structure of plant cells.

[0034] The xyloglucans used according to the invention can be of any plant origin. Xyloglucan derived from tamarind seed is particularly preferred in the context of the invention, as it has the advantage of being readily available industrially.

[0035] Prior to being mixed with water and cellulose fibers, xyloglucan can undergo a degalactosylation step to reduce its galactose content. Such a degalactosylation step can be carried out conventionally by those skilled in the art, enzymatically using a 3-galactosidase. Degalactosylation of xyloglucan notably enhances its heat sensitivity and self-assembly properties, which is particularly advantageous for applications of the adhesive composition according to the invention in areas where it is likely to be subjected to high temperatures.

[0036] Preferably, the branched polysaccharide comprising a main chain with 1-4 glucan linkages, and in particular xyloglucan, is not subjected to any oxidation step prior to its mixing with water and cellulose fibers. In particular, it is preferably not subjected to any treatment with an oxidizing agent or enzyme catalyzing the oxidation of galactose.

[0037] The mass molar mass of at least one, preferably each, branched polysaccharide comprising a main chain with 1-4 glucan linkages, and in particular xyloglucan, implemented within the framework of the invention is preferably between 100 and 800 kg / mol.

[0038] The process for obtaining the adhesive composition according to the invention can employ a single branched polysaccharide comprising a main chain with 1-4 glucan linkages, or a plurality of such different branched polysaccharides, each of which can in particular meet one or more of the characteristics stated above.

[0039] The cellulose fibers used to obtain the adhesive composition according to the invention may be derived from any plant or mixture of plants, for example cotton, flax and / or hemp, or from wood, for example hardwoods, preferably sustainably managed, such as birch and beech, found in temperate countries, or eucalyptus, found particularly in hot countries. Cellulose fibers derived from a plurality of different plants may be used in a mixture within the scope of the invention.

[0040] The cellulose fibers used according to the invention are preferably in the form of cellulose pulp. In the present context, cellulose pulp is understood, in a conventional sense, as a natural material based on cellulose fibers mainly extracted from wood or other plant materials, obtained by separating the cellulose from other plant components, such as lignin, in a generally aqueous vehicle.

[0041] The cellulose pulp used according to the invention may have been obtained from any plant(s), and by any conventional method, whether a chemical process, such as the kraft process, the sulfite process, the bisulfite process, or the organosolv process, or a mechanical process, such as grinding. In particular, cellulose pulp derived from a plurality of different plants may be used within the scope of the invention.

[0042] The cellulose pulp is preferably of the bleached type, that is to say that it comprises, as a component of vegetable origin, only cellulose and hemicellulose, and that it is in particular substantially devoid of lignin.

[0043] The cellulose pulp used in the process according to the invention preferably has a dry matter content of between 17 and 60% by weight.

[0044] Optionally, the cellulose pulp can be subjected to an initial pulping step, carried out in a conventional manner in itself, so as to form cellulose pulp.

[0045] The method for obtaining the adhesive composition according to the invention may also meet one or more of the characteristics described below, implemented individually or in each of their technically operative combinations.

[0046] The enzymatic, or chemical oxidizing, treatment step of the cellulose fibers is preferably carried out before the extrusion step.

[0047] The enzymatic treatment step can be carried out using any cellulase. This cellulase is preferably an endoglucanase, such as that marketed under the name FiberCare® by Novozymes. It can be used alone or in combination with an exoglucanase.

[0048] The operating conditions for the enzymatic treatment step, which reduces the degree of polymerization of the cellulosic chains and promotes microfibrillation / nanofibrillation within the extruder, are conventional in themselves and depend on the specific cellulase used. It is within the expertise of those skilled in the art to determine these operating conditions for each given configuration. By way of example, the enzymatic treatment step can be carried out in water and / or at a temperature between 20 and 70 °C and / or for a duration between 30 minutes and 4 hours and / or using a quantity of cellulase, in particular endoglucanase, between 50 and 500 units per gram of cellulose.

[0049] When the enzymatic treatment step of cellulose fibers, particularly cellulose pulp, is carried out before the extrusion step, this step is preferably followed by a water rinsing step of the cellulose fibers, optionally followed by a spinning step. Such a spinning step can be carried out in any conventional manner on its own, for example by centrifugation. It is preferably carried out so as to achieve a dry matter content of the cellulose pulp thus obtained of between 17% and 60% by weight, preferably of about 40% by weight.

[0050] The oxidative chemical treatment step can also be carried out in any conventional manner. For example, it can be carried out by contacting the cellulose fibers with TEMPO (2,2,6,6-Tetramethylpiperidinyloxy), under conditions suitable for causing the conversion of the hydroxyl group at the C-6 carbon atom of the cellulose glucose monomers into carboxylic acid function. It is within the competence of a person skilled in the art to know how to determine the appropriate operating conditions for this purpose.

[0051] The mixture of water, cellulose fibers and branched polysaccharide(s) comprising a main chain with 1-4 glucan linkages, can be formed in any conventional manner in itself, in particular in a mechanical mixer, for example for a period of between 1 and 30 minutes.

[0052] In particular embodiments of the invention, the mixture of water, cellulose pulp and the branched polysaccharide(s) comprising a main chain with 1-4 glucan linkages contains 15 to 35% by weight, preferably 20 to 25% by weight, of dry matter relative to the total weight of the mixture.

[0053] In addition, the ratio of % by weight of branched polysaccharide(s) comprising a main chain with 1-4 glucan linkages, and of cellulose, in the mixture, i.e. the ratio "% by weight of branched polysaccharide(s) comprising a main chain with 1-4 glucan linkages / % by weight of cellulose", is between 10 / 90 and 50 / 50, preferably between 10 / 90 and 40 / 60, preferably between 10 / 90 and 30 / 70, preferably again between 15 / 85 and 25 / 75, for example about 20 / 80.

[0054] Such characteristics advantageously increase the adhesive power of the composition.

[0055] The mixture subjected to the extrusion step preferably contains no other ingredients, in particular no chemical treatment agents other than a possible oxidizing agent. Preferably, only cellulase, when the enzymatic treatment step is carried out during the extrusion step, or the oxidizing agent such as TEMPO, when the oxidizing chemical treatment step is carried out during the extrusion step, are added to the water, cellulose fibers and the branched polysaccharide(s) comprising a main chain with 1-4 glucan linkages.

[0056] The extrusion step is preferably carried out at a temperature between 10 and 50 °C, for example between 10 and 25 °C, and / or with a screw rotation speed between 100 and 500 revolutions per minute, for example about 400 revolutions per minute.

[0057] It may include a single pass, or a plurality of passes, for example 2 to 5 passes, of the material in the twin-screw extruder.

[0058] Any conventional twin-screw extruder can itself be implemented within the scope of the invention. Screw profiles comprising several shear zones are particularly preferred within the scope of the invention.

[0059] In particular embodiments of the invention, each screw of the twin-screw extruder comprises 2 to 6, preferably 3 to 5, fibrillation segments (also called mixing segments).

[0060] In particular embodiments of the invention, the extruder meets one or more of the following characteristics: - at least two fibrillation segments, preferably at least three fibrillation segments, of each screw of the twin-screw extruder can be configured to generate different shear rates and cumulative strains, the shear rates preferably differing from each other by a factor greater than or equal to 2; - each screw of the extruder may include a conveying segment on at least one side of each fibrillation segment, preferably on both sides of each fibrillation segment, each conveying segment preferably having a direct screw pitch and / or each fibrillation segment preferably having a reverse screw pitch; - each fibrillation segment can be configured to induce, on the material in transit in the twin-screw extruder, a deformation approximately ten times greater than the deformation induced by a conveying segment; - at least one fibrillation segment, preferably each fibrillation segment, of at least one of the two screws may include at least one, optionally only one, zone among the direct thread zones and the reverse thread zones; - and / or the two screws of the twin-screw extruder can be identical to each other.

[0061] The term "conveying segment" means a segment of a screw of the twin-screw extruder configured with conveying elements to convey material in a direction oriented from the inlet to the outlet of the twin-screw extruder.

[0062] A direct screw thread zone is defined as a zone of a fibrillation segment of a screw of the twin-screw extruder configured to favor the advancement of material towards the outlet of the twin-screw extruder.

[0063] A reverse thread zone is understood to be a zone of a fibrillation segment of a screw of the twin-screw extruder configured to favor the advancement of material towards the inlet of the twin-screw extruder.

[0064] Each fibrillation segment, as well as a zone within a fibrillation segment, can be composed of a plurality of elements, in particular processing elements such as mixing discs, juxtaposed along the longitudinal axis of the screw to which they belong. Among other things, the angular configuration of the discs relative to each other defines the shear rate induced on the material in transit within the segment or zone.

[0065] An example of a twin-screw extruder that can be used in the process of obtaining the adhesive composition according to the invention is described in document WO / 2020 / 221934 Al.

[0066] Another aspect of the invention relates to a method for obtaining an adhesive composition according to the invention. This method comprises: - an extrusion step in a twin-screw extruder of a mixture of water, cellulose fibers and at least one branched polysaccharide comprising a main chain with 1-4 glucan linkages, this mixture containing from 10 to 40% by weight of dry matter relative to the total weight of the mixture, and the ratio of the % by weight of branched polysaccharide(s) comprising a main chain with 1-4 glucan linkages, and of cellulose, in the mixture being between 5 / 95 and 50 / 50, - and, before or during the extrusion step, an enzymatic treatment step using a cellulase, or an oxidizing chemical treatment, of the cellulose fibers.

[0067] This process can meet one or more of the characteristics described above with reference to the process for obtaining the adhesive composition according to the invention.

[0068] In particular, the enzymatic treatment step using a cellulase, or the oxidizing chemical treatment step, of the cellulose fibers is preferably carried out before the extrusion step.

[0069] The adhesive composition according to the invention can be used as is, or in diluted form in water.

[0070] Thus, an additional object of the invention is an adhesive formulation obtained by diluting an adhesive composition according to the invention in water. This adhesive formulation preferably has a dry matter content of between 2 and 20% by weight relative to the total weight of the formulation.

[0071] Another aspect of the invention relates to the use of an adhesive composition according to the invention, or an adhesive formulation according to the invention, as an adhesive.

[0072] In this context, the fields of application of the adhesive composition and adhesive formulation according to the invention are numerous. Examples include the fields of paper or cardboard packaging, household products, clothing, construction, wood, transport, biomedical or electronics, such a list being by no means exhaustive, all of these fields of application benefiting from the high adhesive performance of the composition / formulation, and its good mechanical properties.

[0073] A particular field of application of the adhesive composition and adhesive formulation according to the invention is that of the manufacture of wood particle-based panels, in which the composition or formulation is used for bonding wood particles to form such a panel.

[0074] The adhesive composition and adhesive formulation according to the invention can also, for example, be used for bonding fabric, paper, glass, etc.

[0075] Another aspect of the invention relates to a method of bonding two elements, comprising the application of an adhesive composition according to the invention or an adhesive formulation according to the invention between said elements.

[0076] The elements can for example be formed from fabric, paper, glass, etc.

[0077] The invention also relates to a method of manufacturing a wood particle board, comprising gluing wood particles together by means of an adhesive composition according to the invention or an adhesive formulation according to the invention.

[0078] The features and advantages of the invention will become more apparent in the light of the following implementation examples, provided by way of illustration only and in no way limiting the invention, with the support of Figures 1 to 4, in which:

[0079] [Fig-1] [Fig.1] shows photographs of joints glued between two blades of glass, in the dry state, for: a) an adhesive composition based on xyloglucan and cellulose nanocrystals not in accordance with the invention, and b) an adhesive formulation in accordance with the invention, based on xyloglucan and microfibrillated cellulose.

[0080] [Fig.2] Fig.2 shows graphs representing the measured values, in a / of the modulus at break (MOR) and in b / of the modulus of elasticity (MOE), as a function of the density of the panel, for panels made of wood particles and different adhesive compositions: panels with 9% by weight of dry adhesive made from aqueous compositions with low dry matter content obtained by mixing xyloglucan and cellulose nanocrystals by stirring (“9%w / w CompA”); panels with 16 to 23% by weight of dry adhesive made from aqueous compositions with 20% by weight of dry matter obtained by mixing xyloglucan and cellulose nanocrystals by stirring and then oven drying (“16-23%w / w CompB”); panels with 23% by weight of dry adhesive made from formulations according to the invention with a dry matter content of 10% by weight (“23%w / w Inv.”).

[0081] [Fig.3] Fig.3 represents a graph showing the modulus at break (MOR) of panels formed from wood particles and different adhesive compositions, as a function of the weight proportion of xyloglucan in the initial "xyloglucan / cellulose" mixture, for: panels with 23% by weight of dry adhesive formed from formulations according to the invention with a dry matter content of 10% by weight ("23%w / w Inv."); panels with 23% by weight of dry adhesive formed from aqueous compositions with 10% by weight of dry matter obtained by stirring xyloglucan and enzymatically pretreated cellulose nanocrystals, then oven-dried ("23%w / w CompC"); panels with 23% by weight of dry adhesive formed from aqueous compositions with 20% by weight of dry matter obtained by stirring xyloglucan and cellulose nanocrystals then oven-dried ("23%w / w CompB"); and panels with 9% by weight of dry adhesive formed from aqueous compositions with low dry matter content obtained by stirring xyloglucan and cellulose nanocrystals ("9%w / w CompA").

[0082] [Fig.4] Fig.4 represents a graph showing the modulus of elasticity (MOE) of panels formed from wood particles and different adhesive compositions, depending on the proportion by weight of xyloglucan in the initial "xyloglucan / cellulose" mixture, for: panels with 23% by weight of dry adhesive formed from formulations according to the invention with a dry matter content of 10% by weight ("23%w / w Inv."); panels with 23% by weight of dry adhesive formed from aqueous compositions with 10% by weight of dry matter obtained by stirring xyloglucan and enzymatically pretreated cellulose nanocrystals, then oven-dried ("23%w / w CompC"); panels with 23% by weight of dry adhesive formed from aqueous compositions with 20% by weight of dry matter obtained by stirring xyloglucan and cellulose nanocrystals then oven-dried ("23%w / w CompB"); and panels with 9% by weight of dry adhesive formed from aqueous compositions with low dry matter content obtained by stirring xyloglucan and cellulose nanocrystals ("9%w / w CompA").

[0083] 1 / Example 1 - Preparation of adhesive compositions according to the invention

[0084] Adhesive compositions according to the invention are prepared according to the general operating protocol below.

[0085] A cotton cellulose pulp (cotton linter pulp marketed by Southern Cellulose Products Inc., under the name Cotton Linters Pulp, CEL-U-COT, CAS: 65996-61-4) is used in this example.

[0086] This cellulose pulp, with an initial dry matter content between 2% w / w and 99% w / w, is mixed with water for 15 minutes in a pulper to form a cellulose fiber pulp with a concentration of 2% w / w. It is then subjected to enzymatic pretreatment using Novozymes FiberCare® endoglucanase, at a rate of 300 units of endoglucanase / g of cellulose, for 2 hours at 55°C and a controlled pH between 5 and 5.5. This treatment is carried out directly in the pulper. The pH is adjusted by adding approximately 1 L of a buffer solution per 10 L of cellulose pulp to be treated. The buffer solution is a 1 mol / L sodium acetate solution buffered with a few drops of acetic acid to achieve a pH of approximately 4.8.

[0087] The enzyme is thermally deactivated at the end of the treatment by heating it at 80°C for 10 minutes. The treated pulp is then placed in a cloth to drain and rinsed with water using a rinse volume twice the volume of pulp treated. It is then spun dry by centrifugation at 3000 ± 500 rpm until the water flow stops. The cellulose pulp thus obtained has a dry matter content of 40% by weight.

[0088] The necessary quantities of xyloglucan from Tamarind seed, in the form of a dry powder, with a molar mass of approximately 800 kg / mol, non-degalactosylated, and water are then added to this cellulose pulp to form a mixture with the following characteristics: - the desired ratio of the % by weight of xyloglucan and cellulose in the mixture, this ratio varying between 5 / 95 and 50 / 50; - and the desired % by weight of dry matter in the mixture, this % by weight being between 10 and 40%.

[0089] The mixture is formed in a mechanical dough mixer with a bowl diameter of approximately 24 cm, for 5 min at 150 + 30 rpm, at room temperature.

[0090] The mixture thus obtained, in the form of an aqueous suspension, is passed 5 times through a twin-screw extruder with a screw diameter of 16 mm, at a temperature of 10 °C, the rotation speed of the screws being fixed at 400 rpm and the inlet flow rate at 5 kg / h. The twin-screw extruder comprises 6 fibrillation segments with reverse screw pitch zones. The profile of these successive fibrillation segments is more specifically as follows, each of these segments being preceded and followed by a conveying segment: 7 mixing elements at 30° and 6 mixing elements with reverse pitch at 30° / 9 mixing elements with reverse pitch at 30° / 11 mixing elements with reverse pitch at 30° / 9 mixing elements with reverse pitch at 30° / 9 mixing elements with reverse pitch at 30° / 7 mixing elements with reverse pitch at 60°.

[0091] The adhesive compositions conforming to the invention referred to are obtained at the output of the extruder.

[0092] 2 / Example 2 - Comparative composition at low dry matter content

[0093] A comparative adhesive composition Mil is obtained by mixing in water: - xyloglucan (XG) from tamarind seed, with a molar mass of 100 kg / mol, which had not undergone prior degalactosylation treatment, - and cellulose nanocrystals (CNC). These cellulose nanocrystals were obtained from CelluForce as a dried, spray-ready powder. They were produced from Kraft pulp bleached with sulfuric acid and hydrolyzed. According to the supplier's specifications, they have: cross-sectional dimensions of 2.3 to 4.5 nm and lengths of 44 to 108 nm (as measured by atomic force microscopy, AFM); a crystalline fraction of 0.88 (measured by X-ray diffraction); and a surface charge density of 0.023 mmol.g⁻¹ (measured by conductimetric titration).

[0094] The dry ratio of the % by weight of xyloglucan and cellulose in the mixture is equal to 1.5 (60% w / w of xyloglucan / 40% w / w of cellulose).

[0095] The mixture is prepared by simultaneously adding a solution of XG and a solution of CNC in water to a container at a rate of 1 ml.min⁻¹, using a syringe pump. During the addition time, the solutions are thoroughly mixed with a rotor- stator. Once the addition is complete, the resulting mixture is shaken manually for a few seconds and vortexed before being placed in a cold room at 4°C.

[0096] The dry matter content of composition Ml 1 is equal to 3.5% w / w.

[0097] 3 / Example 3 - Evaluation of the adhesive capacity of compositions

[0098] In this example, the adhesive capacity is evaluated for an adhesive composition according to the invention, named Cl, which corresponds to the mixture in weight proportion "20% xyloglucan / 80% cellulose", prepared as described in Example 1. This adhesive composition is diluted in water, at 10 ktr / min for 90 s, using a Dispermat® mixer, to obtain an adhesive formulation Fl according to the invention, having a dry matter content of 3% w / w.

[0099] For comparison purposes, the adhesion capacity of the Mil composition described in Example 2 is also evaluated (dry matter content of 3.5% w / w).

[0100] The operational protocol implemented is as follows.

[0101] The adhesion capacity is evaluated by a mechanical shear test of a dry bonded joint connecting two microscope slides. 0.12 ± 0.2 ml of each composition / formulation to be tested is deposited on the end of a 25 mm wide glass slide. A second glass slide is placed against the composition / formulation and, if necessary, slight finger pressure is applied to form a bonded joint over a 25 mm x 25 mm area. The bonded joints are placed for 15 to 24 h in an oven at 55 °C and then conditioned in a room controlled at 23 °C and 50% relative humidity for 48 h before the mechanical test is performed.

[0102] For this test, the bonded joint specimens are placed in the jaws of a tensile testing machine on either side of the bonded joints. The resulting shear force of the tensile forces applied to the bonded joints must be coplanar with the bonded joint; therefore, shims or an offset of the machine jaws are applied to compensate for the thickness of the bonded joint formed between the two glass plates. The mechanical test is performed at a speed of 1 mm / min at a frequency of 20 Hz.

[0103] The results obtained, in terms of shear adhesion force between the two glass plates, are as follows: - Fl formulation: 242 N; - Mil composition: 121.10 N.

[0104] The adhesion capacity on glass slide of the formulation Fl according to the invention is thus, at substantially equivalent dry matter content, about twice as high as that of the comparative composition Ml 1, which clearly shows the unequivocal superiority, from a performance and scalability point of view, of the invention compared to the traditional approach consisting of a simple mixing by stirring of the raw materials.

[0105] Photographs of the joints formed between the two glass plates after drying are shown in [Fig. 1], in a) for the comparative composition Mil and in b) for the formulation according to the invention Fl. Morphological differences in these joints are observed. The joint obtained from composition Mil is translucent, while that obtained from formulation Fl is whitish. The joint obtained from composition Mil consists of networks of cellulose and xyloglucan nanocrystals that are not visible under optical observation. The multi-scale cellulose microfibrils and nanofibrils of the joint obtained from formulation Fl are agglomerated and visible to the naked eye.

[0106] 4 / Example 4 - Performance evaluation for the production of panels wood particles

[0107] Three different types of adhesive compositions are tested in this example: - CompA: aqueous compositions not conforming to the invention, obtained by mixing xyloglucan and cellulose nanocrystals according to the protocol described in Example 2, having a dry matter content of 2% by weight; - CompB: aqueous compositions not in accordance with the invention, obtained from aqueous mixtures with low dry content (2% w / w) of xyloglucan and cellulose nanocrystals prepared according to the protocol described in Example 2, these mixtures then being oven-dried at 50°C for a sufficient time so that these compositions have a dry matter content of 20% by weight; - Inv.: adhesive formulations according to the invention, with 10% w / w dry matter, obtained by dilution in water of aqueous compositions according to the invention with a dry matter content of 20% w / w prepared as described in Example 1.

[0108] For each type of composition, several xyloglucan / cellulose weight ratios were tested, including the following: 0% / 100%; 10% / 90%; 20% / 80%; 50% / 50%; 100% / 0%.

[0109] The test protocol is as follows. Each tested adhesive composition / formulation is mechanically mixed with wood particles approximately 1 mm wide and 5 mm long, at a concentration suitable for achieving, after heat pressing, a total dry percentage of between 9 and 23% by weight of adhesive material relative to the total weight of the panel, depending on the compositions tested: 9% w / w for CompA compositions, 16 to 23% w / w for CompB compositions, 23% w / w for Inv formulations. The mixture is placed in a rectangular mold with dimensions of 80x10x10 mm and then hot-pressed in a heat press at 120 °C, 5 MPa, for 20 min. The samples are conditioned at 23 °C and 50% relative humidity before measuring the mechanical flexural performance. The ratio of the span of the flexural support to the thickness of the samples is kept equal to 24 to conform to the American standard ANSI A208.1-2016 and avoid the influence of shear stresses in . The measurement of the modulus of elasticity (MOE) and modulus of rupture (MOR) is performed using a tensile / compression machine equipped with a 3-point bending modulus. The force is measured while applying a displacement to the support centered on the sample at a rate of 2 mm / min. The modulus of rupture (MOR) and modulus of elasticity (MOE) are extracted from the machine's force / displacement response curve according to ANSI A208.1-2016.

[0110] The results obtained are shown in [Fig.2]. The performance of the panels bonded with all the compositions / formulations tested is compared there to the values ​​required by the ANSI A208.1-2016 standard (black lines in the figure) which determines the minimum mechanical properties that must be achieved by panels in terms of modulus at break (MOR) and modulus of elasticity (MOE) (respectively, for MOR: grade Hl 14.9 MPa, grade M-0 7.6 MPa, grade LD-2 2.8 MPa; for MOE: grade Hl 2160 MPa, grade M-0 1380 MPa, grade LD-2 2.8 MPa).

[0111] It is observed that the strategy according to the invention, which makes it possible to obtain adhesive compositions with a high dry matter content, leads to panels exhibiting better mechanical performance than those obtained from compositions prepared by a more traditional approach, by simply mixing xyloglucan and cellulose nanocrystals. This advantageous result is obtained even when these compositions obtained by traditional means are subjected to oven drying to reduce their moisture content and increase their dry matter content, which was initially low, to a value equivalent to that of the formulation according to the invention.

[0112] These results clearly demonstrate that the adhesive formulations according to the invention exhibit adhesive performance far superior to that of all the comparative adhesive compositions tested.

[0113] Figures 3 and 4 respectively represent the MOR and MOE as a function of the weight content of xyloglucan in the initial xyloglucan / cellulose mixture, for panels obtained as described above, more particularly: - 23% by weight of dry adhesive obtained from formulations according to the invention at 10% w / w of dry matter (“23%w / w Inv.”); - 23% by weight of dry adhesive obtained from CompB compositions with 10% w / w of dry matter (“23%w / w CompB”); - 9% by weight of dry adhesive obtained from CompA compositions with 2% w / w of dry matter (“9%w / w CompA”); as well as for panels with 23% by weight of dry adhesive obtained from compositions with 10% w / w of dry matter prepared like the CompB compositions, except that the cellulose nanocrystals have been pretreated with Novozymes FiberCare® endoglucanase, at a rate of 300 endoglucanase units / g of cellulose, for 2 h at 55 °C and at a controlled pH between 5 and 5.5, before mixing with xyloglucan (“23%w / w CompC”).

[0114] Here again, it is clearly observed that the panels obtained for the adhesive formulations according to the invention (“23% w / w Inv.” in the figures) exhibit mechanical performance far superior to the others.

Claims

Demands

1. An adhesive composition characterized in that it is in the form of a suspension in water of a complex of microfibrillated cellulose and at least one branched polysaccharide comprising a main chain with 1,4-glucan linkages, the dry matter content of said composition being between 10 and 40% by weight relative to the total weight of the composition, and said composition being obtained by a process comprising: - an extrusion step in a twin-screw extruder of a mixture of water, cellulose fibers, and at least one branched polysaccharide comprising a main chain with 1,4-glucan linkages, said mixture containing from 10 to 40% by weight of dry matter relative to the total weight of said mixture, and the ratio of the percentages by weight of branched polysaccharide(s) comprising a main chain with 1,4-glucan linkages and cellulose in said mixture being between 5 / 95 and 50 / 50, - and, before or during said extrusion step,an enzymatic treatment step using cellulase, or an oxidative chemical treatment, of said cellulose fibers.

2. Composition according to claim 1, wherein each screw of the twin-screw extruder comprises 2 to 6 fibrillation segments.

3. Composition according to claim 1 or 2, wherein at least one branched polysaccharide comprising a 1-4 glucan-linked main chain comprises a [3(1^4) glucan-linked main chain.

4. Composition according to any one of claims 1 to 3, wherein at least one branched polysaccharide comprising a 1-4 glucan-linked main chain comprises xylose branches, preferably xylose branches a(1->6).

5. Composition according to any one of claims 1 to 4, wherein at least one branched polysaccharide comprising a main chain with 1-4 glucan linkages is a xyloglucan, preferably of a bulk molar mass between 100 and 800 kg / mol.

6. Composition according to any one of claims 1 to 5, wherein said cellulose fibres are derived from cotton, flax, hemp or wood.

7. Composition according to any one of claims 1 to 6, wherein said mixture of water, cellulose fibers and branched polysaccharide(s) comprising a main chain with 1-4 glucan linkages, contains from 15 to 35% by weight of dry matter relative to the total weight of said mixture.

8. Composition according to any one of claims 1 to 7, wherein the ratio of % by weight of branched polysaccharide(s) comprising a main chain with 1-4 glucan linkages, and of cellulose, in said mixture is between 10 / 90 and 50 / 50.

9. Composition according to any one of claims 1 to 8, wherein said cellulase is an endoglucanase.

10. Composition according to any one of claims 1 to 9, wherein said mixture is free of organic solvent.

11. A method for obtaining an adhesive composition according to any one of claims 1 to 10, characterized in that it comprises: - an extrusion step in a twin-screw extruder of a mixture of water, cellulose fibers and at least one branched polysaccharide comprising a main chain with 1-4 glucan linkages, said mixture containing from 10 to 40% by weight of dry matter relative to the total weight of said mixture, and the ratio of the % by weight of branched polysaccharide(s) comprising a main chain with 1-4 glucan linkages, and of cellulose, in said mixture being between 5 / 95 and 50 / 50, - and, before or during said extrusion step, an enzymatic treatment step using a cellulase, or an oxidizing chemical treatment, of said cellulose fibers.

12. Adhesive formulation obtained by dilution in water of an adhesive composition according to any one of claims 1 to 10

13. IV. Adhesive formulation according to claim 12, having a dry matter content of between 2 and 20% by weight relative to the total weight of the formulation.

14. Use of an adhesive composition according to any one of claims 1 to 10 or of an adhesive formulation according to claim 12 or 13 as an adhesive.

15. Use according to claim 14, for bonding wood particles for the manufacture of a wood particle board.

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