Plant fiber mat based on wood fibers

Abstract

The present invention relates to a plant fiber mat (1) characterized in that it comprises wood fibers (2) which are derived from woody plants and are secured to one another by means of heat-bonding fibers, the heat-bonding fibers having a decitex of less than or equal to 1.7 dtex.

Description

DESCRIPTION Title of the invention: Mattress made from plant fibers based on wood fibers.

[0001] The present invention relates to the field of construction materials, and more particularly to construction materials intended to provide thermal and / or acoustic insulation.

[0002] Building materials account for a significant portion of energy consumption and greenhouse gas emissions. Among these building materials, the most energy-intensive insulation material is mineral wool. Manufacturers of building insulation materials are seeking to reduce the environmental impact of insulation materials.

[0003] Insulating blankets made from plant fibers containing wood fibers are known. The forests from which it is possible to harvest wood for the production of these insulating blankets have the advantage of being distributed throughout the country, which makes it possible to install defibering and insulating blanket production plants as close as possible to the forests, thus contributing to a circular economy.

[0004] Furthermore, it is known to bind these plant fibres using thermo-binding fibres, which ensure that the fibres hold together once all of these fibres have been placed in an oven, but the use of these thermo-binding fibres, which contain plastic materials, must be controlled to ensure that the insulating material panels produced are the most bio-sourced products possible.

[0005] The present invention takes into account these notions of circular economy and bio-sourced products, aiming to propose in this dual context an insulating product which presents low thermal conductivity values.

[0006] The present invention relates to a mattress of plant fibers characterized in that it comprises wood fibers from woody plants and joined together by means of thermobinding fibers, the thermobinding fibers having a decitex less than or equal to 1.7 dtex.

[0007] At least a portion of the plant fibers present in the mattress according to the invention, that is to say a mattress intended for the production of insulating panels, and in particular semi-rigid panels intended for the interior insulation of buildings, is formed by a set of wood fibers from woody plants. Unlike a herbaceous plant, a woody plant is a plant that contains a high level of lignins, organic macromolecules giving the plant its solidity. The wood fibers from the wood of such woody plants can in particular be the subject of forestry.

[0008] As mentioned above, wood is a widely available and mobilizable resource due to its production across the entire French metropolitan territory, as well as across Europe. As a result, the production of insulating panels using wood fibers from woody plants is fully in line with a circular economy approach, since it is possible to establish defibering and insulating panel manufacturing plants in scattered areas of the territory and to be as close as possible to potential buyers.

[0009] The wood fibers of the plant fiber mattress according to the invention can be obtained using different woody plants such as, for example, Douglas fir, beech, poplar, willow or even spruce.

[0010] The wood fibers are bonded together using thermobonding fibers. These thermobonding fibers have a rigid core and a more flexible sheath. The core and the sheath have different melting temperatures. More precisely, the core has a melting temperature higher than the melting temperature of the sheath. The mixture of thermobonding fibers and plant fibers is intended to be heated in an oven to a temperature such that the sheath melts and binds with the adjacent plant fibers in contact with the sheath while the structure of the core is not altered. It is understood that the thermobinding fibers ensure on the one hand the joining of the plant fibers with each other by means of the sheath, and on the other hand a mechanical role by providing mechanical resistance to the plant fiber mat by means of the rigid core. These thermobinding fibers are mixed with the plant fibers in a percentage sufficient to obtain suitable adhesion of the plant fibers with each other but sufficiently low so as not to limit the insulating properties of the plant fiber mat.

[0011] The decitex of thermobonding fibers is a known parameter that defines the fineness of said thermobonding fibers. It should be noted that this parameter defines the fineness of the thermobonding fibers before they are placed in an oven and partially melted. The decitex of the thermobonding fibers must therefore be measured before mixing the plant fibers and the thermobonding fibers, or at least before the mixture is placed in an oven.

[0012] More specifically, the inventors have demonstrated that, in a context where it is sought to use a maximum of bio-sourced elements, the thermal binding fibres with a low decitex make it possible to reduce the mass of thermal binding fibres in relation to the mass of the plant fibre mat, without limiting the strength of the plant fibres relative to each other thanks to these thermal binding fibres and therefore ensuring that thermal bridges are not created between the plant fibres and do not degrade the thermal insulation properties.

[0013] This reduction in the mass of thermobonding fibers is possible through better homogenization of the mixture of plant fibers and thermobonding fibers. In fact, thermobonding fibers with a low decitex are finer, for the same fiber length, than thermobonding fibers with a higher decitex. As a result, thermobonding fibers mixed with wood fibers are better able to insert themselves between wood fibers. neighbors and therefore to be better distributed over the entire volume of the plant fiber mattress. For the same thermal performance, it is in this context possible to reduce the percentage of thermal binding fibers required and to improve the rate of bio-sourced components within the finished product.

[0001] The inventors were able to determine by appropriate tests that the mixture of wood fibers from woody plants and thermobinding fibers with a lower decitex than usual, and in particular less than 1.7, allows the production of a mattress with a high content of bio-sourced products and particularly suitable for the insulation of buildings, and in particular for the interior insulation of these buildings. In particular, the mattress of plant fibers in accordance with the invention has a thermal conductivity of less than 37 mW / m / K at 10°C.

[0015] According to a characteristic of the invention, the thermal bonding fibers have a decitex less than or equal to 1.5 dtex. From this value, the processes to be implemented to obtain such fine thermal bonding fibers are complex, but the inventors were able to note that the thermal conductivity of an insulating material using such fine thermal bonding fibers is reduced and can tend towards thermal conductivity values ​​less than or equal to 37 mW / m / K at 10°C.

[0016] According to a feature of the invention, the wood fibers are derived from resinous woody plants. In particular, the wood fibers may be derived from Douglas fir or spruce.

[0017] According to a characteristic of the invention, the plant fiber mattress comprises at least 50% wood fibers from woody plants.

[0018] According to a characteristic of the invention, the plant fiber mat comprises adjuvant fibers from agriculture. These adjuvant fibers may have a significantly lower lignin content than the lignin content of the wood fibers, in particular to give additional flexibility to the plant fiber mat made up of the wood fibers and the adjuvant fibers. For example, these adjuvant fibers may consist of hemp or flax fibers.

[0019] According to a characteristic of the invention, the plant fiber mattress comprises at least 80% wood fibers and at most 20% adjuvant fibers.

[0020] According to a characteristic of the invention, the plant fiber mat comprises at most 10% of thermobonding fibers. It is understood that here and in the following, the percentage of thermobonding fibers is a mass percentage, that is to say representative of the mass of the thermobonding fibers relative to the mass of the plant fiber mat considered.

[0021] According to a characteristic of the invention, the plant fiber mattress comprises between 2% and 5% of thermo-binding fibers.

[0022] According to a characteristic of the invention, the plant fiber mat comprises at least 95% fibers and at most 5% additives. The additives comprise at least additives characterized by their flame retardant properties. The fibers comprise both wood fibers and thermobonding fibers. According to a characteristic of the invention, in this ratio of at least 95% fibers, at least 95% of the fibers are wood fibers. For example, for a plant fiber mat comprising 4% additives and therefore 96% fibers, the plant fiber mat comprises approximately 92% wood fibers, approximately 4% thermobonding fibers and 4% additives. According to another non-limiting example of this characteristic, for a plant fiber mattress comprising 3% additives and therefore 97% fibers, the plant fiber mattress comprises approximately 93% wood fibers, approximately 4% thermobinding fibers and 3% additives.

[0023] According to a characteristic of the invention, the wood fibers from woody plants have a cellulose content of between 30 and 60 kg. 100 kg 1 of dry matter and a lignin content of between 18 and 30 kg.100 kg 1 of dry matter.

[0024] The lignin and cellulose content of these wood fibers is measured on a dry matter basis. The dry matter considered here is obtained by drying woody plant products, for example wood residues, from which the plant fibers are obtained, in a ventilated oven. In this ventilated oven, the woody plant products are heated to approximately 105°C until a constant mass is obtained in the oven. This constant mass is commonly referred to as the reference mass, and the levels of cellulose, lignin, and other components are expressed from this reference mass. It should be noted that the oven referred to here is a separate oven from the oven used to heat the mixture of thermobonding fibers and wood fibers within the mat.

[0025] The inventors were able to observe through appropriate tests that wood fibers having lignin contents and cellulose contents as mentioned are particularly suitable for their use within plant fiber mattresses for insulation products. As mentioned above, the plant fiber mattress according to the invention can be obtained using different woody plants such as, for example, Douglas fir, beech, poplar, willow or spruce.

[0026] According to a characteristic of the invention, the wood fibers from woody plants have a cellulose content of between 41.2 and 56.4 kg. 100 kg 1 of dry matter and lignin between 23.7 and 28.1 kg. 100 kg' 1of dry matter. The inventors were able to demonstrate that plant fibers, particularly those from Douglas fir wood, had characteristics, in terms of structure, that were more interesting for obtaining a plant fiber mattress in accordance with the invention with low thermal conductivity.

[0027] According to a characteristic of the invention, the plant fiber mattress is formed from a mixture of wood fibers with at least two types of wood fibers from different woody plants, provided that at least 50% of the fibers present In the plant fiber mattress are wood fibers from woody plants.

[0028] According to a characteristic of the invention, at least 70% of the wood fibers have a diameter less than or equal to 100 pm.

[0029] According to a characteristic of the invention, at least 60% of the wood fibers have a diameter less than 70 (im.

[0030] According to a characteristic of the invention, at least 45% of the wood fibers have a diameter less than 50 (im.

[0031] In each of these three characteristics, the aim is to reduce the quantity of wood fibers whose diameter is considered too large. The aim is to avoid as much as possible the presence, in the plant fiber mattress, of wood fibers whose excessively large diameter penalizes the overall insulation performance of the mattress.

[0032] This distinguishes us from characteristics according to which we aim to define the diameter of the fibres within the mattress by a desired average value, or maximum average value, this average value not preventing a great diversity of values ​​of diameter of the fibres around this average value.

[0033] According to a characteristic of the invention, at least 60% of the wood fibers have a diameter of between 30 μm and 70 μm. In accordance with what has been mentioned above, a plant fiber mattress comprising such a distribution of wood fibers has high insulation performance, insofar as the dispersion of the diameter of the wood fibers is controlled. Here, a distribution of wood fibers is sought whose diameter is centered around a target value, with few wood fibers having a diameter below a low threshold, here 30 μm, to avoid part of the wood fiber being in powder form, in particular due to a production process where excessive cooking and too much pressure from fiberizing discs are applied, and at the same time with few wood fibers which have a diameter greater than a high threshold, here 70pm, for the reasons previously mentioned.

[0034] The inventors were able to observe that the thermal conductivity value of a plant fiber mat according to the invention was all the lower, and therefore of interest in an application to building insulation, when the grain size of the wood fibers present in the mat complied with certain values. In particular, to obtain the desired thermal conductivity values, at least less than 0.037 W / m / K, it is sought to have at least 60% of the wood fibers having a diameter less than or equal to 70 microns. The large quantity of fine wood fibers resulting from this grain size allows good thermal conductivity of the finished product, in particular due to the average fineness of the wood fiber and due to the homogeneity of fineness between the wood fibers and the thermally bonding fibers.

[0035] Having homogeneity between the fineness of the thermobinding fibres, i.e. thermobinding fibres with a low decitex, and the fineness of the wood fibres allows a good mixture of all the fibres, it being understood that a non-homogeneous distribution favours local clusters of thermobinding fibres which implies an absence of these thermobinding fibres in other areas of the mattress and therefore wood fibres likely to be in contact with each other and create a thermal bridge which is bad for the thermal conductivity value of the finished product.

[0036] The grain size as claimed, both the fact that at least a given percentage of wood fibers have a diameter less than a threshold value and the fact that at least 60% of the wood fibers have a diameter between 30 μm and 70 μm, can in particular be ensured by appropriate parameterization of the cooking of the fibers and appropriate parameterization of the pressure of the fiberizing discs used after cooking to give them the appropriate shape.

[0037] It should be noted that the characteristic of the diameter of the wood fibres is particularly considered but that it is possible that these characteristics are combined with other characteristics relating to the dimension of the wood fibres, such as their length.

[0038] According to a characteristic of the invention, at least 85% of the wood fibers have a length less than or equal to 5000 pm.

[0039] According to a characteristic of the invention, at least 40% of the wood fibers have a length of less than 2000 pm.

[0040] According to a characteristic of the invention, the plant fiber mattress has a thickness greater than 20 mm.

[0041] According to a characteristic of the invention, the plant fiber mattress has a thickness of at least 40 mm.

[0042] The thickness of the plant fibre mattress which is to be considered here is the nominal thickness of the mattress, that is to say the thickness which can be observed by the user when using the product for the purposes of insulating a building in particular.

[0043] In accordance with known practices of the prior art, the mat of plant fibers according to the invention is obtained by passing through an oven, configured at a determined cooking temperature, a mat of plant fibers, constituted beforehand, if necessary on a conveyor device directing the mat of plant fibers towards the oven, by a mixture of wood fibers entangled with each other, and binding elements intended to bind the wood fibers together during passage through the oven.

[0044] The nominal thickness may in particular be measured after packaging, for example when purchasing the product. For example, the nominal thickness as mentioned above is observed after various successive stages of the industrial manufacturing process during the implementation of the product, these stages may include, after the wood fiber mat has been placed in an oven, cutting, for example example, in panels of suitable dimensions, the subsequent compression of the plant fibre mattress obtained after passing through the oven during packaging, packaging and storage before marketing.

[0045] According to a characteristic of the invention, the plant fiber mattress has a volume density of between 20 kg.m' 3 and 80kg.m' 3 . More specifically, the plant fiber mattress has a volume density of between 40kg.m' 3 and 60kg.m' 3 .

[0046] According to a characteristic of the invention, the thermobonding fibers have a length less than or equal to 6 mm.

[0047] According to a characteristic of the invention, the thermally bonding fibers comprise at least polyethylene.

[0048] According to a characteristic of the invention, the plant fiber mattress has a thermal conductivity less than or equal to 37 mW / m / K at 10°C. Thus, assembled into panels intended to provide insulation, particularly in construction, the straw has an interesting thermal conductivity to make it a construction material intended for insulation.

[0049] Other characteristics, details and advantages of the invention will emerge more clearly on reading the description which follows on the one hand, and examples of embodiments given for informational and non-limiting purposes of the invention with reference to the appended schematic drawings on the other hand, in which:

[0050] [Fig.l] schematically represents a general view of a mattress of plant fibers in accordance with the present invention;

[0051] [Fig.2] represents a table illustrating a distribution of wood fibers, in the mattress of plant fibers according to their length;

[0052] [Fig.3] represents a table illustrating the distribution of wood fibers in the plant fiber mattress according to their diameter;

[0053] [Fig.4] represents a local view of the wood fibers and thermobinding fibers present within the plant fiber mat represented by figure 1.

[0054] It should first be noted that while the figures set out the invention in detail for its implementation, these figures can of course be used to better define the invention, where appropriate. It should also be noted that these figures only set out examples of embodiments of the invention.

[0055] The features, variants and different embodiments of the invention may be combined with each other in various combinations, provided that they are not incompatible or mutually exclusive. In particular, variants of the invention may be conceived comprising only a selection of features described below in isolation from the other features described, if this selection of features is sufficient to confer a technical advantage or to differentiate the invention from the state of the art.

[0056] In the figures, elements common to several figures retain the same reference.

[0057] Figure 1 represents a plant fiber mat 1 according to the present invention. The plant fiber mat 1 is formed from a plurality of plant fibers entangled with each other and from thermobonding fibers allowing the plant fibers to be held in the final product. According to the invention, these plant fibers are wood fibers 2 from woody plants, for example produced by forestry.

[0058] The wood fibers 2 used for the manufacture of the plant fiber mattress 1 are obtained after passing through a defibering unit. For example, these wood fibers can be obtained from residues from the forestry industry or from untreated wood scraps.

[0059] This wood can come from broad-leaved woody plants, for example, poplar (populus sp.), beech (fagus sylvatica L.), or willow (salix sp.), or resinous woody plants such as Douglas fir (pseudo tsuga sp.) or spruce (picea sp.). In the embodiment shown, and in the numerical examples which will be given in the remainder of the description, the wood fibers come from resinous woody plants, and more particularly from Douglas fir wood offcuts.

[0060] Douglas fir, like other woods of interest such as spruce or beech, has a cellulose content of between 30 and 60 kg per 100 kg of dry matter, commonly written as 'kg.100kg'. 1 MS", and a lignin content of between 18 and 30 kg.100kg' 1MS. The inventors were able, by means of suitable tests, to note that the wood fibres from these woody plants of interest have a structure which makes it possible to obtain, in combination with the presence of thermally bonding fibres, and more particularly thermally bonding fibres of a given thickness, mattresses of plant fibres 1 whose insulating properties are optimal.

[0061] More specifically, the inventors were able to determine that woods which have structural characteristics close to Douglas fir were ideal for providing wood fibers capable of forming a plant fiber mattress 1 with optimal insulating properties. These woods have a cellulose content of between 41.2 and 56.4 kg. 100kg' 1 MS and a lignin content between 23.7 and 28.1 kg.100kg 1 MS.

[0062] It should be noted that the plant fiber mattress 1 is, according to the invention, formed from at least 50% wood fibers 2 from woody plants as previously mentioned. In addition, the plant fiber mattress 1 may comprise adjuvant fibers, not shown here. These adjuvant fibers may be fibers from agriculture such as hemp fibers (Cannabis sativa L.), kenaf fibers (Hibiscus cannabinus L.) or flax fibers (Linum usitatissimum).

[0063] These adjuvant fibers have the characteristic of being longer and having a lower lignin content than the fibers plant fibers 2 from forestry in accordance with the present invention. This lower lignin content of the adjuvant fibers compared to the plant fibers makes it possible to provide the plant fiber mat 1 with greater flexibility compared to a plant fiber mat without adjuvant fibers.

[0064] More specifically, with regard to the sole distribution of wood fibers within the plant fiber mat, i.e. without taking into account the thermo-binding fibers, it is possible to have between 70% and 90%, preferably 80%, of wood fibers and between 10% and 30%, preferably 20%, of more flexible fibers, such as flax or hemp, forming an adjuvant. This ratio makes it possible to give the plant fiber mat, on the one hand, flexibility thanks to the low lignin content of the fibers used as an adjuvant and, on the other hand, good thermal conductivity thanks to the interaction between the thermo-binding fibers and the wood fibers, and in particular a thermal conductivity less than or equal to 37 mW / m / K at 10°C.

[0065] As an illustrative and non-limiting example of the invention, the plant fiber mattress 1 comprises 80% Douglas fir wood fibers and 20% hemp fibers.

[0066] The fiberizing unit is a device for forming wood fibers 2 from wood residues obtained, for example in the form of untreated wood scraps in sawmills. As illustrated in Figures 2 and 3, the fiberizing unit is advantageously configured to obtain wood fibers whose median diameter is approximately 55 μm and the median length of the wood fibers is approximately 2500 μm.

[0067] Figures 2 and 3 illustrate the distribution of wood fibers from Douglas fir within a mat of plant fibers 1 in accordance with the invention, for a sample of given dimensions, and for which it has been confirmed that it provides a thermal conductivity of less than 37 mW / m / K.

[0068] More specifically, Figure 2 illustrates the cumulative DC distribution of wood fibers as a function of their length LF.

[0069] Each cumulative distribution value DC illustrates the percentage of wood fibers, within a given sample, that have a length less than a given dimension. For example, Figure 2 illustrates, in a first box C1, that 5.5% of the wood fibers present in a given sample of a plant fiber mat according to the invention have a length LF less than or equal to 200 pm. And, in a second box C2, it can be seen that 22% of the wood fibers present in this same given sample of a plant fiber mat according to the invention have a length LF less than or equal to 1000 pm. From these two values ​​it can be deduced that 16.5% of the wood fibres present in this sample have an LF length between 200 pm and 1000 pm, the 5.5% of wood fibres whose LF length is less than or equal to 200 pm being part of the 22% of wood fibres whose LF length is less than or equal to 1000 pm.

[0070] Thus, the tests which were able to be carried out by the inventors on this sample show, by studying the values ​​of the cumulative distribution DC, that at least 44% of the wood fibers forming a mat of plant fibers 1 in accordance with the invention have a length of at most 2000 pm. In addition, it should be noted that, as visible in Figure 2, 85.5% of the wood fibers have a length LF of at most 5000 pm.

[0071] By carrying out tests on other types of wood having lignin and cellulose contents in accordance with what has been mentioned previously, and in particular on beech wood, the inventors were able to observe that a mattress of plant fibres in accordance with the invention can comprise at least 60% of wood fibres whose length is less than or equal to 3000 μm.

[0072] Figure 2 also highlights the ranges of wood fiber dimension values, here their length, which are most represented within the plant fiber mattress 1. More specifically, the increase in the cumulative distribution DC between a first given length of wood fibers LF, for example <2000 pm, a second given length of wood fibers LF, for example <3500 pm, and a third given length of wood fibers LF, for example <5000 pm, makes it possible to highlight the fact that there are more wood fibers, here Douglas fir wood, which have a length between 2000 pm and 3500 pm, knowing that they represent approximately 24% of the total mass of plant fibers present in the mattress, than Douglas fir fibers which have a length between 3500 pm and 5000 pm, knowing that they represent approximately 17.5% of the total mass of plant fibers present in the mattress.

[0073] Figure 3 reports the same test as that highlighted in Figure 2, this time taking into account the diameter of the wood fibers DF.

[0074] Each cumulative distribution value DC illustrates the percentage of wood fibers, within a given sample, that have a diameter less than a given dimension. The values ​​combined in Figure 3 successively illustrate that 2.5% of the wood fibers present in a given sample of a plant fiber mat according to the invention have a diameter DF less than or equal to 30 μm, that 22.5% of the wood fibers present in this sample have a diameter DF less than or equal to 40 μm, that 47.5% of the fibers present in a given sample of a plant fiber mat according to the invention have a diameter DF less than or equal to 50 μm, that 64.5% of the wood fibers present in this sample have a diameter DF less than or equal to 70 μm, and that 73.5% of the wood fibers present in this sample have a diameter DF less than or equal to 100 μm.

[0075] Thus, the tests which were able to be carried out by the inventors on this sample show, by studying the values ​​of the cumulative distribution DC, that at least 73.5% of the wood fibers 2, here Douglas wood fibers, have a diameter less than or equal to 100 pm and at least 64.5% of these wood fibers 2 have a diameter DF less than or equal to 70 pm.

[0076] Here again, it should be noted that by carrying out tests on other types of wood having lignite and cellulose contents in accordance with what has been mentioned previously, and in particular on beech wood, the inventors were able to observe that a wood fibre mat in accordance with the invention can comprise at least 60% of fibres whose diameter DF is less than or equal to 70 μm and at least 50% of fibres whose diameter DF is between 50 μm and 55 μm.

[0077] As mentioned above, the wood fiber mat 1 is formed from a tangle of plant fibers, and more particularly wood fibers. These wood fibers 2 are, as seen in Figure 4, joined to each other by means of dry binding elements. These binding elements are more particularly formed by thermobinding fibers 3.

[0078] The plant fiber mattress 1 is obtained by means of a manufacturing installation in which the wood fibers 2 are mixed with the thermobinding fibers 3 so as to obtain a thermobinding fiber content which is less than 10%, preferably between 2% and 5%.

[0079] In one embodiment of the invention, the mixture of wood fibers 2 and thermobonding fibers 3, obtained according to the contents just mentioned, is blown into a manufacturing facility and then sucked against a conveyor to form a carpet of wood fibers. This carpet of wood fibers is then heated in an oven to form the plant fiber mat 1. The plant fiber mat can be cut into insulating panels of different sizes or rolled up and compressed for storage.

[0080] The thermobonding fibers 3 are formed of a core 31 and a sheath 32. The core 31 forms a rigid part of the thermobonding fibers 3 participating in providing the straw fiber mat 1 with mechanical resistance, while the sheath 32 ensures the joining of the plant fibers 2 with each other. For this purpose, the core 31 and the sheath 32 have different melting temperatures, and more precisely the sheath 32 has a lower melting temperature than the core 31.

[0081] Thus, when the wood fiber mat passes through an oven to obtain a plant fiber mattress according to the invention, the temperature within the oven is such that the sheath 32 melts to bathe the adjacent wood fibers, the whole solidifying as it cools at the outlet of the oven so as to join these wood fibers together. It should be noted that the melting temperature of the core 31 is designed so that, despite the passage through the oven of a wood fiber mat consisting of the mixture of wood fibers and binder, the core 31 retains its rigid property helping to ensure mechanical strength to the plant fiber mattress 1 after the oven.

[0082] It is understood that within the oven, the wood fibers 2 and the thermobonding fibers 3 are heated so that the wood fibers 2 become solid with each other. At least the passage in the oven, and if necessary a subsequent compression and cutting before packaging, transforms the carpet of wood fibers into a mattress of plant fibers in accordance with the invention.

[0083] The plant fiber mat has a thickness of at least 20 mm and preferably greater than 40 mm. This thickness is considered after the wood fiber mat has passed through the oven.

[0084] In the embodiment shown, the sheath 32 of the thermobonding fibers 3 is formed of polyethylene and the core 31 is also formed of polyethylene. It should be noted that in an alternative embodiment the core 31 of the thermobonding fibers can be formed of a polyester, and more precisely of polyethylene terephthalate. Polyethylene has the advantage of easily bonding to plant fibers, which makes it a good candidate for forming the sheath 32 of the thermobonding fibers.

[0085] It should be noted that this is only an example of an embodiment, the plant fiber mattress 1 being able to be obtained by a manufacturing installation different, for example a manufacturing facility in which the wood fibers 2 and the binding elements are mechanically deposited on a conveyor and then directed towards an oven so as to form the mat of plant fibers 1. However, the content of the plant fiber mattress 1 in thermobinding fibers 3 and the structure of said thermobinding fibers 3 remain identical.

[0086] The thermobonding fibers are characterized in particular by their fineness. This fineness is expressed in decitex, commonly defined by the mass in grams of ten thousand meters of this thermobonding fiber 3. According to the invention, the thermobonding fibers 3 have a fineness less than or equal to 1.7dtex, preferably less than or equal to 1.5dtex. Such fineness of the thermobonding fibers 3 allows a better distribution of these thermobonding fibers within the mattress, between the wood fibers, which is more effective for gluing and fixing the position of the wood fibers relative to each other.

[0087] It is understood that it is thus easier to ensure that the wood fibres do not come into contact and do not form thermal bridges. The better distribution of the thermally bonding fibres, resulting from the fineness of these fibres as highlighted according to the invention, makes it possible to limit the mass or volume ratio of thermally bonding elements in the overall mass or volume of the insulating product formed by the mat of plant fibres.

[0088] Furthermore, the thermobonding fibers 3 have a length, taking into account manufacturing tolerances, of approximately 6 mm, which can allow, in addition to the previously mentioned fineness, a better distribution of the thermobonding fibers within the plant fiber mat 1. It should be noted that this length of the thermobonding fibers can more particularly be less than or equal to 6 mm.

[0089] The fineness of the thermobonding fibres is particularly interesting here insofar as it is complementary to the fineness of the wood fibres, evoked by the fact that at least 60% of the plant fibres have a diameter of less than 70 microns, which makes it possible to obtain a good mixture of the two types of fibres. present in the mattress and a homogeneous distribution of the thermo-binding fibers between the wood fibers, which allows good fixation of the wood fibers and the regular formation of air pockets allowing the thermal conductivity value to be lowered to the desired values ​​for application to building insulation.

[0090] The different elements presented to participate in the formation of the plant fiber mattress 1 make it possible to obtain such a mattress whose volume density is between 20 kg.m' 3 and 80 kg.m' 3and with, as mentioned above, a thickness of at least 20mm. Such a plant fiber mattress has a thermal conductivity less than or equal to 37 mW / m / K at 10°C, making it possible to provide optimal insulation properties to a construction material.

[0091] The invention as just described achieves the aim it set itself by proposing a mattress of plant fibres whose thermal insulation performance is optimised by means of a composition and a distribution of dimensions of the particular plant fibres, namely wood fibres and for example products from forestry, within the mattress of plant fibres.

Claims

CLAIMS 1. Mattress of plant fibers characterized in that it comprises wood fibers (2) from woody plants and joined together by means of thermobonding fibers (3), the thermobonding fibers (3) having a decitex less than or equal to 1.7 dtex.

2. Mattress of plant fibers (1) according to the preceding claim, characterized in that the thermobonding fibers (3) have a decitex less than or equal to 1.5 dtex.

3. Mattress of plant fibers (1) according to any one of the preceding claims, characterized in that the wood fibers (2) come from resinous woody plants.

4. Mattress of plant fibers (1) according to any one of the preceding claims, characterized in that it comprises at least 50% of wood fibers from woody plants.

5. Mattress of plant fibers (1) according to any one of the preceding claims, characterized in that it comprises adjuvant fibers from agriculture.

6. Mattress of plant fibers (1) according to the preceding claim, characterized in that it comprises at least 80% of wood fibers (2) and at most 20% of adjuvant fibers.

7. Mattress of plant fibers (1) according to any one of the preceding claims, characterized in that it comprises at most 10% of thermobonding fibers (3).

8. Mattress of plant fibers (1) according to the preceding claim, characterized in that it comprises between 2% and 5% of thermobinding fibers (3).

9. Mattress of plant fibers (1) according to any one of the preceding claims, characterized in that it comprises at least 95% of fibers and at most 5% of additives.

10. Mattress of plant fibers (1) according to the preceding claim, characterized in that at least 95% of the fibers are wood fibers.

11. Mattress of plant fibers (1) according to any one of the preceding claims, characterized in that the wood fibers (2) from woody plants have a cellulose content of between 30 and 60 kg.100 kg 1 of dry matter and a lignin content of between 18 and 30 kg.100 kg 1 of dry matter.

12. Mattress of plant fibers (1) according to the preceding claim, characterized in that the wood fibers (2) from woody plants have a cellulose content of between 41.2 and 56.4 kg. 100 kg 1 dry matter and lignin between 23.7 and 28.1 kg. l00kg 1 of dry matter.

13. Mattress of plant fibers according to any one of the preceding claims, characterized in that at least 70% of the wood fibers have a diameter less than or equal to 100 pm.

14. Mattress of plant fibers (1) according to the preceding claim, characterized in that at least 60% of the wood fibers (2) have a diameter of less than 70 μm.

15. Mattress of plant fibers (1) according to any one of the preceding claims, characterized in that at least 60% of the wood fibers (2) have a diameter of between 30 μm and 70 μm.

16. Mattress of plant fibers (1) according to any one of the preceding claims, characterized in that at least 85% of the wood fibers have a length less than or equal to 5000 pm.

17. Mattress of plant fibers (1) according to any one of the preceding claims, characterized in that it has a thickness greater than 20 mm.

18. Mattress of plant fibers (1) according to any one of the preceding claims, characterized in that it has a volume density of between 20 kg.m' 3 and 80kg.m' 3 .

19. Mattress of plant fibers (1) according to any one of the preceding claims, characterized in that the thermobonding fibers (3) comprise at least polyethylene.

20. Mattress of plant fibers (1) according to any one of the preceding claims, characterized in that it has a thermal conductivity less than or equal to 37 mW / m / K at 10°C.

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