Green process for obtaining elementary bast fibres

Abstract

The present invention relates to a green and sustainable process for obtaining elementary flax bast fibers, comprising a step of treating unscutched flax bast fibers with steam at a pressure strictly greater than atmospheric pressure. It also relates to elementary bast fibers obtainable by such a process, their use in the manufacture of a textile article, and a textile article comprising at least one such elementary bast fiber.

Description

Technical field

[0001] The present invention relates to the field of spinning, and in particular to the field of obtaining bast fibers, such as flax fibers, of high quality, exceptional fineness, and suitable for spinning. The process according to the invention is a "green" process in that it does not involve any chemical agents, and is sustainable. Technological background

[0002] Linen is a noble and natural material that can be used in the textile industry. It is a simple and elegant textile that guarantees a feeling of freshness on the skin.

[0003] The flax fibers used in the production of textiles are so-called "technical" fibers, whose diameter is generally around 60 to 150 micrometers, and which comprise a bundle of several elementary flax fibers bound by a pectic cement.

[0004] These technical fibers are obtained by retting, particularly by retting on land, of flax after its cultivation, then by scutching and combing the harvested retted flax. Retting on land (a field process) consists of separating the fibers from the stem by the combined action of humidity and microorganisms.

[0005] However, retting, especially land retting, has the major disadvantage that the conditions to which the fibers are exposed depend on weather conditions, and are therefore difficult to predict or reproduce, which can affect the quality of the flax fibers obtained. Depending on the weather conditions, it is sometimes necessary to harvest the flax before retting is complete. In addition, the dependence on weather conditions limits the geographical areas in which flax can be produced, especially in view of the climate changes linked to current global warming.

[0006] On the other hand, the fineness of textile fibers is an undeniable asset that can improve the nobility and quality of the textiles obtained after spinning. Thus, for example, other noble textiles, such as cashmere or silk, have finer fibers than technical linen fibers. It would be desirable to have linen fibers of greater finesse than technical linen fibers. Finer fibers can also have the advantage of being more easily woven or knitted than thicker fibers that are stiffer, particularly in the case of linen and / or in the case of dry spinning.

[0007] Steam explosion of technical flax fibers after retting and scutching has been described, and allows the elimination of part of the "cement" which binds the elementary fibers in the technical fibers obtained after retting.

[0008] Patent application WO8704194 describes modified flax fibers obtained by a vapor phase hydrolysis treatment of under-retted flax previously cut to lengths of the order of 70 mm. The under-retted flax is scutched before its steam treatment, and can also be treated by impregnation with a soda solution to optimize the yield and / or the quality of the fibers after steam treatment. The vapor phase hydrolysis treatment makes it possible to supplement the action of the bacteriological agents of the retting which was not complete due to the premature collection of the flax.

[0009] The publication Kessler et al. Biomass and Bioenergy 1998 14, 3, p.237 describes a steam explosion process for obtaining flax fibers for textile applications. When the flax is unretted, it is necessary to include an impregnation step with a sodium hydroxide solution before steam explosion to improve refining. However, basic treatment leads to partial degradation of the fiber and a reduction in its mechanical properties (Segovia et al. Waste Biomass Valorization 12, 6255-6260, 2021 , Sauvageon et al. Textile Research Journal 2017, 88 (9), 1047-1055).

[0010] It would be useful to have processes for obtaining high-quality flax fibers, particularly those with improved fineness, suitable for weaving and / or knitting, and eliminating the need for retting and / or scutching. It would also be useful to have processes that do not involve any chemical treatment.

[0011] Some processes have been described to obtain elementary flax fibers. These include enzymatic processes (Akin et al. Industrial Crops and Products 25 (2007) 136-146; Juarez et al. Bioprocess Biosyst Eng (2011) 34:913-921; Alix et al. Carbohydrate Polymers 87 (2012) 177-185), microwave irradiation processes, and ultrasonic irradiation processes (Borsa et al. Cellulose 2016, 23 (3), pp.2117-2128). However, these processes are difficult to industrialize because they are poorly controlled, poorly mastered, and / or expensive. In addition, the fibers obtained are not of sufficient quality. For example, fibers obtained with enzymatic processes exhibit fibrillations.

[0012] In this context, the Inventors have surprisingly demonstrated that the implementation of a steam explosion step under specific conditions makes it possible to obtain elementary bast fibers from unscutched and preferably unretted flax with a high yield, even in the absence of any chemical treatment. Summary

[0013] Thus, a first object of the present invention is a process for obtaining elementary flax fibers, comprising a step of treating unscutched flax fibers with steam at a pressure strictly higher than atmospheric pressure, then a sudden lowering of the pressure, said process not comprising any contacting of the unscutched flax fibers with a pretreatment solution such as an acid or basic pretreatment solution.

[0014] In one embodiment, the flax fibers are unretted and unscutched flax fibers.

[0015] In one embodiment, the unscutched flax fibers are selected from the group consisting of bloom stage harvested flax fibers, green boll stage harvested flax fibers, green boll stage harvested flax fibers with retting, and brown boll stage harvested flax fibers, preferably the unscutched flax fibers are green flax fibers.

[0016] In one embodiment, the method does not include any post-treatment step with a chemical agent such as an oxidant, an acid and / or a base.

[0017] In one embodiment, the contacting of the fibers with the water vapor is carried out at a temperature between 150°C and 300°C, preferably around 220°C.

[0018] In one embodiment, the contacting of the fibers with the water vapor is carried out at a pressure of between 5 bars and 50 bars, preferably approximately 26 bars.

[0019] In one embodiment, the contacting of the fibers with the water vapor is carried out for a period of between 2 and 20 minutes, preferably approximately 7 minutes.

[0020] In one embodiment, the sudden lowering of the pressure is preferably implemented over a duration of less than 1 second, preferably between 0.1 seconds and 1 second, in particular a duration of approximately 0.3 seconds.

[0021] In one embodiment, the method further comprises, after the steam treatment, at least one rinse, preferably two rinses, with a rinse solvent.

[0022] In one embodiment, the rinse solvent is water, preferably purified water.

[0023] Another subject of the present invention is an elementary flax fiber obtainable, preferably obtained, by a process according to the invention, in which the elementary flax fiber has a length of between 15 and 50 mm, and a diameter of between 10 microns and 25 microns.

[0024] Another subject of the invention is the use of a flax fiber according to the invention or obtained by a process according to the invention, in the manufacture of a textile article and / or a fabric.

[0025] A final subject of the invention is a textile article and / or a fabric comprising at least one elementary flax fiber according to the invention, or obtained by a process according to the invention. Brief description of the drawings

[0026] There figure 1 presents an image of a cross-section by electron microscopy of an elementary flax fiber. The figure 2shows an electron microscopy image of the flax fibers from Example 1 before steam treatment. The figure 3 shows an electron microscopy image of the flax fibers from Example 1 after steam treatment. The figure 4 shows an electron microscopy image of an elementary flax fiber obtained in Example 1. The Figure 5 shows the flax fibers from Example 1 taken as a whole before steam treatment. The figure 6 shows the flax fibers of Example 1 taken as a whole after steam treatment. The figure 7 is a histogram representing the distribution of fiber lengths in mm, in inverse cumulative percentage, before steam treatment of the fibers by the method of Example 1. The figure 8 is a histogram representing the distribution of fiber lengths in mm, in inverse cumulative percentage, after steam treatment of the fibers by the method of Example 1. The figure 9 is an SEM image of the fibers of unretted and unscutched brown flax capsules treated according to the invention. figure 10 is an SEM image of the fibers of unretted and unscutched brown flax capsules treated according to the invention. figure 11 is a histogram representing the distribution of fiber lengths in mm, in inverse cumulative percentage, after steam treatment of unretted and unscutched brown flax capsule fibers by the process according to the invention. figure 12 is a histogram representing the distribution of fiber diameters in microns, in inverse cumulative percentage, after steam treatment of unretted and unscutched flax brown capsule fibers by the process according to the invention. figure 13 is a photograph of a sample of non-woven linen obtained with elementary fibers according to the invention (on the right) and of the reference obtained with unrefined linen (on the left). Detailed description Definitions

[0027] THE " bast fibers ", also called phloem fibers, are plant fibers extracted from the phloem (the inner bark or bast) surrounding the stem of certain dicotyledonous plants. They support the phloem-conducting cells and give strength to the stem. As used herein, the term "bast fiber" refers to a flax fiber unless otherwise specified.

[0028] A " elementary fiber » is a fiber, in particular a linen fiber, single or unitary, separated from the other elementary fibers constituting the bundles of fibers present in technical fibers, in particular technical linen fibers.

[0029] By " pretreatment" in the present invention we mean a fiber treatment step which is carried out between the harvesting of the flax and the steam treatment of the process according to the invention. This may in particular be a step of contacting with an acidic or basic solution, in particular a step of impregnation with a basic solution such as a sodium hydroxide solution. A basic pretreatment solution preferably has a pH greater than 8, preferably greater than 12. An acidic pretreatment solution preferably has a pH less than 6, preferably less than 4.

[0030] THE " retting » is the maceration that textile plants such as flax or hemp undergo, to facilitate the separation of the filamentous bark from the stem. Retting of textile plants is carried out by more or less prolonged immersion (water retting) or by exposure to heat and humidity on the ground of the stem windrows (ground retting).

[0031] A linen is said to be " under-rotted » when the flax is prematurely picked in the case of retting on the ground. Flax is said to be “unretted” when it is picked without any retention of the fibers on the ground.

[0032] THE " scutching » is a mechanical step classically carried out after retting the stems, and consisting of separating the fibers from the shives (woody part of the plant) to obtain tow 700 to 800 mm long.

[0033] Scutching thus refers to the classic operation of first industrial transformation of retted flax straw: it is the mechanical separation of the fibers from the wood of the plant by beating the material. The successive stages are: ginning (removal of the seeds), drawing (alignment of the stems with each other), grinding (breaking the wood) and beating (separation of the technical fibers). The fibers obtained are classified into two categories: the long fibers strictly speaking resulting from scutching, otherwise called the long strand or tow (200-600mm); and the short fibers, called tow (10-200mm).

[0034] L' " working» is the breaking of the stems between notched rollers to separate the wood (inner part of the stem also called shives for flax stems) from the fibers found in the cortex (outer part) of the stem. Following this separation, the technical fibers of the flax are mechanically processed using cylinders fitted with inclined points which allow the technical fiber bundles to be separated from each other and the length of the strands to be shortened. The fibers obtained are rather semi-long (40-200 mm) and are similar to tow. The major points differentiating the processing from scutching are the absence of drawing, therefore the absence of alignment and the absence of beating.

[0035] THE " diameter" of a fiber is the average dimension of the fiber's cross-section, even if it is not exactly circular. When dealing with a set of fibers, the "average" diameter is a number average of the diameter of each of the fibers in the set.

[0036] A " pre-treatment » is a treatment of fibers before their exposure to water vapor.

[0037] A " post-processing » is a treatment of fibers after their exposure to water vapor and the sudden lowering of pressure.

[0038] The term " approximately » placed in front of a numerical value designates an interval between plus and minus ten percent of the numerical value, preferably between plus and minus five percent of the numerical value, in particular between plus and minus one percent of the numerical value. Process for obtaining elementary fibers

[0039] A first object of the invention is a process for obtaining elementary flax fibers, comprising a step of treating flax fibers with water vapor.

[0040] The bast fibers treated by the process according to the invention are flax fibers.

[0041] In certain embodiments, the flax fibers treated by the method according to the invention are derived from textile flax or oilseed flax.

[0042] The method according to the invention can be implemented with flax of different maturities. Indeed, the method according to the invention made it possible to obtain elementary flax fibers with flax harvested at the flowering stage, flax harvested at the green capsule stage, flax harvested at the green capsule stage with retting, and flax harvested at the brown capsule stage. In one embodiment, the bast fibers are chosen from the group consisting of flax fibers harvested at the flowering stage, flax fibers harvested at the green capsule stage, flax fibers harvested at the green capsule stage with retting, and flax fibers harvested at the brown capsule stage. In one embodiment, the bast fibers are chosen from the group consisting of flax fibers harvested at the flowering stage, flax fibers harvested at the green capsule stage, and flax fibers harvested at the brown capsule stage.Flax fibers subjected to steam treatment are preferably green flax fibers.

[0043] The bast fibers subjected to treatment with water vapor are preferably unretted or under-retted fibers, especially un-retted fibers.

[0044] Bast fibers subjected to treatment with water vapor are preferably unscutched fibers.

[0045] The bast fibers subjected to treatment with water vapor are preferably fibers that have not undergone any pretreatment, in particular no pretreatment with a chemical agent such as an acid or a base.

[0046] The process for obtaining elementary fibers according to the invention is a "green" process since it avoids the use of pre-treatments with chemical agents such as acids and bases. It also avoids the use of pre-treatments involving other chemical agents potentially toxic to humans and / or the environment, such as ion-chelating agents, in particular metal ions. Preferably, the process also does not include any post-treatment step with chemical agents such as oxidants, hydrazine, sodium sulfide, acids and bases. The process is also a sustainable process, because due to its ultra-speed it requires little energy input.

[0047] The method for obtaining elementary fibers according to the invention makes it possible to obtain a high yield of elementary fibers, in particular a yield greater than 50%, greater than 60%, greater than 70%, greater than 80%, greater than 90%, or even greater than 95%. A yield greater than 95% of elementary fibers means that more than 95% of the fibers in a sample treated in accordance with the invention are in elementary form, the other fibers being able to be, for example, in the form of a bundle of elementary fibers and / or technical fibers.

[0048] The process for obtaining elementary fibers according to the invention makes it possible to obtain, in addition to elementary fibers, co-products such as lignin and / or pectin. Due to the absence of chemical treatment, in particular the absence of acid or basic pre-treatment and / or oxidizing, acid or basic post-treatment, in the process according to the invention, these co-products are not degraded and can be recovered, possibly purified, and then recovered.

[0049] Another subject of the invention is thus a process for producing at least one co-product such as lignin and / or pectin, comprising the implementation of a process for obtaining elementary fibers according to the invention, and the separation of the at least one desired co-product from the elementary fibers obtained at the end of the process. In certain embodiments, the co-product is a polysaccharide or comprises at least one polysaccharide or a mixture of polysaccharides.

[0050] Another subject of the invention is a co-product such as lignin and / or pectin obtained by the process according to the invention.

[0051] The process for obtaining elementary fibers according to the invention is described above starting from unscutched and preferably unretted bast fibers, for which it has undeniable advantages.

[0052] Nevertheless, a person skilled in the art will easily understand from reading the treatment conditions and the advantages provided by the method according to the present invention that it can be applied in the same way to obtain elementary bast fibers from bast fibers after scutching, such as bast fibers obtained by the traditional route, in particular flax bast fibers in the form of spinning sliver, or from spinning processes, more simply referred to as "sliver" in the remainder of the application, roving, and / or technical fiber.

[0053] Another object of the invention is thus a process for obtaining elementary flax fibers, comprising a step of treating flax fibers after scutching with steam at a pressure strictly higher than atmospheric pressure, then a sudden lowering of the pressure, said process not comprising any contacting of the flax fibers with a pretreatment solution such as an acid or basic pretreatment solution. The scutched fibers may optionally be in the form of ribbon, roving and / or technical fibers. Preferably, the process does not comprise any post-treatment such as post-treatment with an oxidizing, acid or basic solution. Steam treatment

[0054] The process according to the invention comprises the treatment of unscutched and preferably unretted bast fibers with water vapor at a pressure strictly higher than atmospheric pressure, then a sudden reduction in pressure.

[0055] Steam treatment can be carried out under any suitable conditions to obtain the desired individualization of the fibers. A person skilled in the art is able to adapt the conditions of the steam treatment, in particular the duration of the treatment, the pressure and the temperature of the steam, to obtain the individualization of the fibers. The conditions can be adapted in particular according to the nature of the fibers (origin of the flax), their degree of maturity, any pretreatments used, the characteristics of the fibers (dimensions), and / or the quantity of fibers to be treated.

[0056] Preferably, the steam treatment is carried out by bringing the fibers into contact with pressurized steam, i.e. at a pressure strictly higher than atmospheric pressure, and at a high temperature, then by abruptly lowering the pressure. Such a treatment is known as "steam explosion." Without wishing to be bound by any theory, the Inventors believe that the sudden drop in pressure can induce shearing which contributes to mechanically bursting the pectin cement which binds the elementary fibers.

[0057] The abrupt lowering (or abrupt drop) of pressure is preferably implemented over very short periods of time. Thus, the time to bring the reactor (and its contents) from a pressure strictly higher than atmospheric pressure to the final pressure is typically less than 5 seconds, preferably less than 1 second, preferably between 0.1 seconds and 1 second, in particular it is approximately 0.3 seconds.

[0058] The pressure strictly higher than atmospheric pressure of contact with water vapor can be adapted by a person skilled in the art. The pressure can in particular be higher than 5 bars, preferably higher than 8 bars.

[0059] The final pressure (after abrupt pressure reduction) may be any pressure below the superatmospheric pressure as defined above. In a preferred embodiment, the final pressure is atmospheric pressure. In certain other embodiments, the final pressure is a subatmospheric pressure.

[0060] Preferably, the difference between the pressure above atmospheric pressure at which the water vapor is brought into contact with the fibers and the final pressure after sudden lowering of the pressure is at least 5 bars, preferably at least 8 bars, more preferably at least 15 bars, and in particular at least 25 bars.

[0061] Steam treatment is preferably carried out by contacting the bast fibers with steam in a suitable reactor.

[0062] In one embodiment, the duration of the contacting is between 30 seconds and 20 minutes. In particular, it may be approximately 7 minutes.

[0063] In one embodiment, the temperature during contacting is between 150°C and 300°C. In particular, it may be approximately 220°C.

[0064] In one embodiment, the pressure during contacting is between 5 bars and 50 bars. In particular, it may be approximately 26 bars.

[0065] Steam treatment combines the action of heat from steam and pressure to wet the material and initiate the hydrolysis of the pectin cement which binds the elementary fibers.

[0066] The water that is brought into contact with the bast fibers in the form of steam can be of any quality, in particular it can be purified water or so-called "tap" water. Thus, the pH of this water is not necessarily exactly neutral, depending on the source of the water used. In certain embodiments, the pH of the water used is between 6.5 and 8. Other steps

[0067] The process for obtaining elementary fibers may further comprise, before or after the steam treatment, any other step known in the art for the treatment and / or individualization of bast fibers, with the exception of steps involving chemical agents, such as acids and bases.

[0068] In some embodiments, the method for obtaining elementary fibers further comprises, after the steam explosion, at least one rinsing step, preferably two rinsing steps. Each rinsing step can be carried out with any suitable rinsing solvent, in particular water, in particular purified water. The temperature of the solvent of each rinse can be independently lower, equal to or higher than room temperature, preferably higher than room temperature. The temperature of the rinsing solvent, in particular water, can be approximately 70°C.

[0069] In certain embodiments, the method for obtaining elementary fibers further comprises, after the steam explosion and, where appropriate, after the rinsing step(s), at least one step of mechanical treatment of the fibers such as a carding step.

[0070] After steam treatment and any subsequent steps such as rinsing, the flax is obtained in the form of elementary fibres in a humid environment, which unravel easily.

[0071] In some embodiments, the method comprises, before the steam treatment, a mechanical decortication step. This step makes it possible to separate the technical fibers and the wood (also called shives) from the stem and to optimize the production of technical fibers.

[0072] In some embodiments, the method comprises, before the steam treatment, a working step which makes it possible to refine and / or shorten the length of the technical fibers, to improve the quality of the fibers obtained during the treatment. After this process, the presence of elementary fibers is minimal.

[0073] The method according to the invention preferably does not include a step of scutching the fibers prior to their treatment with water vapor. Elementary bast fibers

[0074] Another subject of the invention is an elementary flax fiber capable of being obtained, preferably obtained, by a production process according to the present invention.

[0075] The elementary bast fibers according to the invention have an exceptional fineness, which may be similar to that of cashmere and / or silk fibers. In one embodiment, the elementary flax fibers according to the invention have a diameter of between 10 microns and 25 microns, preferably between 10 microns and 20 microns, in particular a diameter of approximately 20 microns.

[0076] The elementary bast fibers according to the invention are typically shorter than conventional bast fibers. In one embodiment, the elementary flax fibers according to the invention have a length of between 15 and 50 mm.

[0077] The elementary bast fibers according to the invention are particularly suitable for textile applications. In particular, they are suitable for short-fiber spinning, unlike conventional bast fibers such as technical flax fibers, which are suitable for long-fiber spinning. In addition, the bast fibers according to the invention are suitable for carding. Use of elementary bast fibers

[0078] The elementary bast fibers according to the invention are particularly suitable for use in the textile field. Indeed, their mechanical properties and their dimensions (length / diameter) are perfectly suited for use in textiles.

[0079] Thus, another object of the present invention is the use of an elementary bast fiber according to the invention, or obtained by a process according to the invention, in the manufacture of a textile article and / or a fabric.

[0080] Another subject of the invention is a textile article and / or a fabric comprising at least one elementary bast fiber according to the invention. The textile article and / or a fabric may in particular be a ribbon, a yarn, a knit, a mesh, a roving, a woven or a non-woven. In certain embodiments, the textile article and / or the fabric according to the invention comprises elementary bast fibers according to the invention and other types of fibers. In other embodiments, the textile article and / or the fabric according to the invention comprises only elementary bast fibers according to the invention. In other words, 100% of the fibers of the textile article and / or the fabric are in this embodiment elementary bast fibers according to the invention.

[0081] The textile article and / or fabric according to the invention can be obtained by a dry process or by a wet process, preferably a dry process.

[0082] The invention will be better understood by means of the following examples, which should be considered as illustrative and not limiting of the scope of the invention. Examples

[0083] Method of measuring the diameter and / or fineness of fibers

[0084] In order to determine the morphology of the fibers, two parameters must be measured: length and diameter.

[0085] To measure the length, a fiber mass is defined and then taken from the fibers in at least three times to ensure a representative sample of the material is recovered. Using precision tweezers and picks, the fibers are extracted from the sample one by one, then placed on a glass plate where tap water has been previously placed (method inspired by textile standards). The fiber is then untwisted and straightened using tweezers, then is measured with a laboratory ruler. The measurement is entered into a spreadsheet.

[0086] This operation is repeated until all the fibers in the sample taken are measured, which provides a distribution of all the fibers.

[0087] Once all the measurements are entered into the spreadsheet, a graph representing the percentage distribution of lengths can be drawn.

[0088] To measure the diameter, fiber samples are grouped into bundles of about 100 fibers and then cut crosswise using a sharp blade specifically used for cutting thin samples. These cut bundles are then prepared and observed under a scanning electron microscope (SEM) in the direction of their cross section.

[0089] The images recovered from the SEM are transferred into image processing software to measure each fiber quickly and accurately.

[0090] The software allows for the measurement of complex shapes by giving a minimum, maximum, and average diameter, as well as the cross-sectional area of ​​each individual fiber.

[0091] All of this data is sent to a spreadsheet to create a percentage distribution graph of fiber diameter. Example 1: Method according to the invention

[0092] Technical flax fibers in ribbon form (untwisted roving, dry spinning), 100% combed natural flax, were subjected to a steam explosion at 220°C and 26 bars for a period of 7 minutes. Two rinses with purified water at 70°C were then carried out. The appearance of the flax fibers was clearly modified by this steam treatment. Flax fibers disentangle well to obtain elementary fibers in a humid environment.

[0093] There figure 2 and the figure 3 show the fibers before and after steam treatment respectively. figure 4presents an isolated elementary fiber obtained after steam treatment. Measurement of the diameter of this elementary fiber at different locations gave the following values: 20.46 micrometers and 19.06 micrometers. Measurements made on another fiber also provided a value of 13.17 micrometers.

[0094] There Figure 5 and the figure 6 show the flax fibers taken as a whole before and after steam treatment. Before treatment, numerous technical fibers with a diameter of about 60 to 80 micrometers are observed. After treatment, the sample contains almost only elementary fibers with a diameter of about 19 to 23 micrometers, and very few technical fibers. Example 2: Characterization of the elementary fibers obtained according to the invention

[0095] The length of flax fibers was compared before and after steam treatment according to the invention. The histograms of the figure 7 and of the figure 8represent the fiber length distribution in mm, in inverse cumulative percentage, respectively before and after steam treatment of the fibers by the process of Example 1. Technical flax fibers (before treatment) have a size distribution that goes up to 60 to 120 mm, which makes them suitable for spinning into long fibers. In contrast, the fiber size distribution after treatment, which goes up to only 30 to 50 mm, makes them suitable for spinning into short fibers.

[0096] Table 1 below shows the characterization of the elementary fibers obtained in Example 1. The elementary fibers obtained according to the invention have mechanical properties similar to those of technical fibers. In addition, the maintenance of the values ​​of the resistance and elongation indicators demonstrates that the elementary fibers according to the invention are compatible with spinning. Table 1 Fiber Area (µm 2< ) Diameter (µm) Tensile strength (MPa) Modulus of elasticity (GPa) Elongation at break (%) Flax before treatment 2598 57,5 794±269 45±27 2,66 Flax after treatment 419 23,1 849±626 16,2±0,7 1,9±0,9 Example 3: Implementation of the process with flax of different maturities

[0097] The method according to the invention was implemented with flax stems harvested at different stages of maturity from flax of the same variety and from the same plot: flax harvested at the flowering stage, flax harvested at the green capsule stage, flax harvested at the green capsule stage with retting, and flax harvested at the brown capsule stage.

[0098] After mechanical defibration and working, the fibers were subjected to a steam treatment such as that described in Example 1.

[0099] The characteristics of the fibers obtained are summarized in Table 2 below. As in Example 1, the mechanical properties of the elementary fibers obtained are compatible with spinning, both for fibers with and without retting. In addition, these mechanical properties are similar to those of fibers obtained by the traditional route (column 3, green capsules with retting). Implementing the process in the absence of retting and scutching therefore makes it possible to obtain fibers with mechanical properties as good as those of fibers obtained by the traditional route. Table 2 Maturity 1: Flowering without retting 2: Green capsules without retting 3: Green capsules with retting 4: Brown capsules without retting Elementary fibers Number of samples 17 15 24 17 Diameter (microns) 21±3,6 22±1,9 21,8±2,3 21,1±2,7 Tensile strength (MPa) 307,2±95,1 459±194,4 526,3±170,5 546,6±181,5 Elongation (%) 1,1±0,8 1,2±0,4 1,19±0,5 1,3±0,6

[0100] THE figures 9 And 10 are SEM images after steam explosion according to the method according to the invention on flax from the 4th column of table 2 (brown capsules, without scutching and without retting).

[0101] The images are similar to those obtained in Example 1 on a linen ribbon. This confirms that the process according to the invention can be implemented effectively on unretted and unscutched linen. As can be seen in these images, the sample comprises a large majority of elementary fibers and almost no more technical fibers. This confirms the very good efficiency of the process.

[0102] There figure 11 shows the distribution of fiber lengths in mm, in reverse cumulative percentage, after steam treatment of the fibers in the 4th column of Table 2 (brown capsules, without scutching and without retting). 50% of the fibers have a length of less than 30 mm, and are therefore suitable for use in short fiber spinning.

[0103] There figure 12shows the distribution of fiber diameters in microns, in reversed cumulative percentage, after steam treatment of the fibers in the 4th column of Table 2 (brown capsules, without scutching and without retting). 90% of the fiber diameters are less than 20 microns, which demonstrates the high yield and the reality of obtaining elementary fibers. Example 4: Production of a 100% linen non-woven fabric from the fibers according to the invention

[0104] A roll of non-woven fabric was manufactured from 100% flax fibers obtained by a process according to the invention, by a dry consolidation process (needling).

[0105] The following protocol was implemented:

[0106] The elementary flax fibers obtained according to the invention were dried and conditioned at 20°C and 65% relative humidity. They were quickly opened by hand to remove fiber aggregates and / or knots. They were then opened with the first module of the Laroche opener at 800 rpm. The fibers were then transported by the Bobino loader to the carding machine, then carded to be parallelized. The final density was produced with a lapper. The consolidation of the nonwoven was carried out by needling.

[0107] The resulting nonwoven had a final thickness of 3 to 4 mm, and a final density of 300 g / m 2< .

[0108] The 100% linen non-woven fabric obtained from the elementary linen fibres according to the invention had a visual and tactile fineness significantly superior to that of a non-woven fabric obtained from technical fibres, which is visible in the photo of the figure 13 .

Claims

1. Process for obtaining elementary flax fibers, comprising a step of treating unscutched flax fibers with steam at a pressure strictly higher than atmospheric pressure, then a sudden lowering of the pressure, said process not comprising any contacting of the unscutched flax fibers with a pretreatment solution such as an acid or basic pretreatment solution.

2. Process for obtaining elementary flax fibers according to claim 1, in which the flax fibers are unscutched and unretted flax fibers.

3. A method for obtaining elementary flax fibers according to claim 1 or claim 2, wherein the unscutched flax fibers are selected from the group consisting of flax fibers harvested at the flowering stage, flax fibers harvested at the green capsule stage, flax fibers harvested at the green capsule stage with retting, and flax fibers harvested at the brown capsule stage, preferably the unscutched flax fibers are green flax fibers.

4. Process for obtaining elementary flax fibers according to any one of claims 1 to 3, said process not comprising any post-treatment step with a chemical agent such as an oxidant, an acid and / or a base.

5. Process for obtaining elementary flax fibers according to any one of claims 1 to 4, in which the contacting of the fibers with water vapor is carried out at a temperature between 150°C and 300°C, preferably approximately 220°C.

6. Process for obtaining elementary flax fibers according to any one of claims 1 to 5, in which the contacting of the fibers with water vapor is carried out at a pressure of between 5 bars and 50 bars, preferably approximately 26 bars.

7. Process for obtaining elementary flax fibers according to any one of claims 1 to 6, in which the contacting of the fibers with water vapor is carried out for a period of between 2 and 20 minutes, preferably approximately 7 minutes.

8. Process for obtaining elementary flax fibers according to any one of claims 1 to 7, in which the sudden lowering of the pressure is preferably carried out over a period of less than 1 second, preferably between 0.1 second and 1 second, in particular a period of approximately 0.3 seconds.

9. Process for obtaining elementary flax fibers according to any one of claims 1 to 8, wherein the process further comprises, after the steam treatment, at least one rinsing, preferably two rinsings, with a rinsing solvent, preferably water.

10. Elementary flax fiber obtainable, preferably obtained, by a process according to any one of claims 1 to 9, in which the elementary flax fiber has a length of between 15 and 50 mm, and a diameter of between 10 microns and 25 microns.

11. Use of a flax fiber according to claim 10 or obtained by a process according to any one of claims 1 to 9, in the manufacture of a textile article and / or a fabric.

12. Textile article and / or fabric comprising at least one elementary flax fiber according to claim 10, or obtained by a process according to any one of claims 1 to 11.

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