Process for obtaining elementary bast fibers

Abstract

Process for Obtaining Elementary Flax Bast Fibers. The present invention relates to a 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

Title of the invention: Process for obtaining elementary bast fibers 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, of exceptional fineness, and suitable for spinning. 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 notably guarantees a feeling of freshness against the skin.

[0003] The flax fibers used in the production of textiles are so-called "technical" fibers, the diameter of which is generally in the order of 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 field retting, of flax after cultivation, followed by scutching and combing the harvested retted flax. Field retting (a process carried out in the field) consists of separating the fibers from the stem through the combined action of moisture and microorganisms.

[0005] However, retting, particularly retting on land, has the major drawback 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 resulting flax fibers. Depending on the weather, it is sometimes necessary to harvest the flax before retting is complete. Furthermore, this dependence on weather conditions limits the geographical areas in which flax can be produced, especially in light of climate change related to current global warming.

[0006] On the other hand, the fineness of textile fibers is an undeniable advantage for improving the refinement and quality of textiles obtained after spinning. Thus, for example, other fine textiles, such as cashmere or silk, have finer fibers than technical linen fibers. It would be desirable to have linen fibers of greater fineness than technical linen fibers. Finer fibers can also have the advantage of being easier to weave or knit than thicker fibers, which are more rigid, particularly in the case of linen and / or in the case of dry spinning.

[0007] The steam explosion of technical flax fibers after retting and scutching has been described, and makes it possible to eliminate 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 steam hydrolysis of pre-shrunk flax that has been cut to lengths of approximately 70 mm. The pre-shrunk flax is retted before steam treatment and may also be treated by impregnation with a sodium hydroxide solution to optimize the yield and / or quality of the fibers after steam treatment. The steam hydrolysis treatment completes the action of the bacteriological agents of retting, which was not entirely effective due to the premature harvesting 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, the basic treatment leads to partial degradation of the fiber and a decrease in its mechanical properties (Segovia et al. Waste Biomass Valorisation 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 of 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] Several processes have been described for obtaining 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, difficult to master, and / or expensive. Furthermore, the fibers obtained are not of sufficient quality. For example, fibers obtained with enzymatic processes exhibit fibrillation.

[0012] In this context, the Inventors have surprisingly demonstrated that implementing a steam explosion step under specific conditions makes it possible to obtain elementary bast fibers from unretted and preferably unretting 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 greater than atmospheric pressure, then a sudden drop in pressure, said process not comprising any contact of the unscutched flax fibers with a pretreatment solution such as an acidic or basic pretreatment solution.

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

[0015] In one embodiment, the contact of the fibers with water vapor is carried out at a temperature between 150°C and 300°C, preferably around 220°C.

[0016] In one embodiment, the contact of the fibers with water vapor is carried out at a pressure between 5 bars and 50 bars, preferably about 26 bars.

[0017] In one embodiment, the contact of the fibers with water vapor is carried out for a period of between 2 and 20 minutes, preferably about 7 minutes.

[0018] In one embodiment, the process further comprises, after steam treatment, at least one rinse, preferably two rinses, with a rinsing solvent.

[0019] In one embodiment, the rinsing solvent is water, preferably purified water.

[0020] Another object of the present invention is a process for obtaining elementary flax fibers, comprising a step of treating retted flax fibers, possibly in the form of ribbon, wick and / or technical fibers, with steam at a pressure strictly greater than atmospheric pressure, then a sudden drop in pressure, said process not comprising any contact of the flax fibers with a pretreatment solution such as an acidic or basic pretreatment solution.

[0021] Another object of the present invention is an elementary flax fiber that can be obtained, preferably obtained, by a process according to the invention, wherein the elementary flax fiber has a length between 15 and 50 mm, and a diameter between 10 microns and 25 microns.

[0022] Another object 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.

[0023] A final object 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

[0024] Fig. 1 presents an electron microscopy cross-section image of an elementary flax fiber.

[0025] Fig. 2 presents an electron microscopy image of the flax fibers of Example 1 before treatment according to the invention.

[0026] Fig. 3 presents an electron microscopy image of the flax fibers of Example 1 after treatment according to the invention.

[0027] Figure 4 presents an electron microscopy image of an elementary flax fiber obtained in Example 1.

[0028] Fig. 5 shows the flax fibres of example 1 taken as a whole before steam treatment.

[0029] Fig. 6 shows the flax fibres of example 1 taken as a whole after steam treatment.

[0030] Fig. 7 is a histogram representing the distribution of fiber lengths in mm, in reverse cumulative percentage, before steam treatment of the fibers by the process of Example 1.

[0031] Fig. 8 is a histogram representing the distribution of fiber lengths in mm, in reverse cumulative percentage, after steam treatment of the fibers by the process of Example 1.

[0032] Fig. 9 is a photograph of a sample of non-woven flax obtained with elementary fibers according to the invention (right) and of the reference obtained with unrefined flax (left). Detailed description

[0033] Definitions

[0034] "Base 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 vascular cells of the phloem and provide strength to the stem. In the present invention, the term "base fiber" refers to a flax fiber, unless otherwise specified.

[0035] An “elementary fiber” is a single or unitary fiber, in particular a flax fiber, separated from the other elementary fibers constituting the fiber bundles present in technical fibers, in particular technical flax fibers.

[0036] In the present invention, "pretreatment" refers to a fiber treatment step carried out between flax harvesting and steam treatment. of the process according to the invention. This may include a step of contacting the product with an acidic or basic solution, in particular an impregnation step 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.

[0037] “Retting” is the maceration process applied to textile plants such as flax or hemp to facilitate the separation of the fibrous bark from the stem. Retting of textile plants is carried out by immersion for varying periods (water retting) or by exposing the stalk windrows to heat and moisture on the ground (ground retting).

[0038] Flax is said to be "under-retted" when it is prematurely gathered in the case of ground retting. Flax is said to be "un-retted" when it is gathered without any support of the fibers on the ground.

[0039] "Scutching" is a mechanical step classically carried out after retting the stems, and consisting of separating the fibers from the anas (woody part of the plant) to obtain flax of 70 to 80 cm in length.

[0040] The term "approximately" placed before 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.

[0041] Process for obtaining elementary fibers

[0042] A first object of the invention is a process for obtaining elementary flax fibers, comprising a step of treating flax fibers with steam.

[0043] The bast fibers treated by the process according to the invention are flax fibers.

[0044] In some embodiments, the flax fibers treated by the process according to the invention are derived from textile flax or oilseed flax.

[0045] The process according to the invention can be implemented with flax at different stages of maturity. Indeed, the process according to the invention has made it possible to obtain elementary flax fibers from flax harvested at the flowering stage, flax harvested at the green boll stage, flax harvested at the green boll stage with retting, and flax harvested at the brown boll stage. In one embodiment, the bast fibers are selected from the group consisting of flax fibers harvested at the flowering stage, flax fibers harvested at the green boll stage, flax fibers harvested at the green boll stage with retting, and flax fibers harvested at the brown boll stage. In another embodiment, the bast fibers are selected from the group consisting of flax fibers harvested at the flowering stage, flax fibers harvested at the green boll stage, and flax fibers harvested at the brown capsules. Flax fibers subjected to treatment with steam are preferably green flax fibers.

[0046] The bast fibers subjected to treatment with steam are preferably un-retted or under-retted fibers, in particular un-retted fibers.

[0047] The bast fibers subjected to treatment with steam are preferably unscutched fibers.

[0048] The bast fibers subjected to treatment with steam are preferably fibers that have not undergone any pretreatment, in particular no pretreatment by a chemical agent such as an acid or a base.

[0049] The process for obtaining elementary fibers according to the invention is a "green" process since it avoids the use of pretreatments with chemical agents such as acids and bases. The process is also a sustainable process because, due to its ultra-fastness, it requires little energy input.

[0050] The process 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 processed according to the invention are in elementary form, the other fibers being, for example, in the form of bundles of elementary fibers and / or technical fibers.

[0051] The process for obtaining elementary fibers according to the invention makes it possible to obtain, in addition to the 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 pretreatment, in the process according to the invention, these co-products are not degraded and can be recovered, possibly purified, and then valorized.

[0052] Another object of the invention is thus a process for producing at least one co-product such as lignin and / or pectin, comprising carrying out a process for obtaining elementary fibers according to the invention, and separating the desired at least one 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.

[0053] Another object of the invention is a co-product such as lignin and / or pectin obtained by the process according to the invention.

[0054] The process for obtaining elementary fibers according to the invention is described above starting from unretted bast fibers and preferably unretted, for which it presents undeniable advantages.

[0055] Nevertheless, a person skilled in the art will readily understand from reading the conditions of treatment and the advantages provided by the process according to the present invention that he can be applied in the same way to obtain elementary bast fibers from bast fibers after scutching, such as bast fibers obtained by traditional means, including 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.

[0056] 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, said process not comprising any contact of the flax fibers with a pretreatment solution such as an acidic or basic pretreatment solution.

[0057] Steam treatment

[0058] The process according to the invention comprises treating unscutched and preferably unretting bast fibers with steam at a pressure strictly greater than atmospheric pressure, followed by a sudden drop in pressure.

[0059] Steam treatment can be carried out under any suitable conditions to achieve the desired fiber individualization. Those skilled in the art are able to adapt the steam treatment conditions, in particular the treatment duration, pressure, and temperature of the steam, to achieve fiber individualization. These conditions can be adapted, in particular, according to the nature of the fibers (origin of the flax), their degree of maturity, any pretreatments carried out, the characteristics of the fibers (dimensions), and / or the quantity of fibers to be treated.

[0060] Preferably, the steam treatment is carried out by bringing the fibers into contact with pressurized steam, that is, at a pressure strictly greater than atmospheric pressure and at a high temperature, and then by abruptly reducing the pressure. Such a treatment is known as "steam blasting." Without wishing to be bound by any particular theory, the Inventors believe that the abrupt drop in pressure can induce shearing, which contributes to mechanically breaking the pectin cement that binds the individual fibers.

[0061] The abrupt reduction (or sudden drop) in pressure is preferably implemented over very short periods of time. Thus, the time to bring the reactor (and its contents) from a pressure strictly greater 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 about 0.3 seconds.

[0062] The pressure, strictly greater than atmospheric pressure at the point of contact with water vapor, can be adjusted by a person skilled in the art. In particular, the pressure can be greater than 5 bar, preferably greater than 8 bar.

[0063] The final pressure (after a sudden drop in pressure) can be any pressure lower than the pressure above atmospheric pressure as defined above. In a preferred embodiment, the final pressure is atmospheric pressure. In some other embodiments, the final pressure is a pressure lower than atmospheric pressure.

[0064] 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 abrupt pressure reduction is at least 5 bars, preferably at least 8 bars, more preferably at least 15 bars, and in particular at least 25 bars.

[0065] Steam treatment is preferably carried out by bringing the bast fibers into contact with steam in a suitable reactor.

[0066] In one embodiment, the duration of the contact is between 30 seconds and 20 minutes. In particular, it may be approximately 7 minutes.

[0067] In one embodiment, the temperature at the time of contact is between 150°C and 300°C. In particular, it can be approximately 220°C.

[0068] In one embodiment, the pressure at the point of contact is between 5 bar and 50 bar. In particular, it may be approximately 26 bar.

[0069] Steam treatment combines the action of heat from steam and pressure to wet the material and initiate the hydrolysis of the pectin cement that binds the elementary fibers.

[0070] The water that is brought into contact with the basal fibers in the form of vapor can be of any quality, including purified water or tap water. Therefore, the pH of this water is not necessarily exactly neutral, depending on the water source. In some embodiments, the pH of the water used is between 6.5 and 8.

[0071] Other steps

[0072] The process for obtaining elementary fibers may further include, before or after 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.

[0073] In some embodiments, the process for obtaining elementary fibers further comprises, after 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, especially purified water. The temperature of the solvent for each rinsing step can be independently lower than, equal to, or higher than ambient temperature, preferably higher than ambient temperature. The temperature of the rinsing solvent, in particular water, can be approximately 70°C.

[0074] In some embodiments, the process for obtaining elementary fibers further includes, after the steam explosion and, where appropriate, after the rinsing step(s), at least one mechanical processing step of the fibers such as a carding step.

[0075] After steam treatment and any subsequent steps such as rinsing, the flax is obtained in the form of elementary fibers in a humid environment, which untangle easily.

[0076] In some embodiments, the process includes, prior to steam treatment, a mechanical dehulling step. This step separates the technical fibers and the wood (also called shives) from the stem and optimizes the production of technical fibers.

[0077] In certain embodiments, the process includes, prior to steam treatment, a processing step that refines and / or shortens the length of the technical fibers to improve the quality of the fibers obtained during treatment. After this process, the presence of elementary fibers is minimal.

[0078] The process according to the invention preferably does not include a scutching step of the fibers prior to their treatment with steam.

[0079] Elementary basal fibers

[0080] Another object of the invention is an elementary flax fiber that can be obtained, preferably obtained, by a process of obtaining according to the present invention.

[0081] The elementary bast fibers according to the invention have an exceptional fineness, which can be similar to that of cashmere and / or silk fibers. In one embodiment, the elementary flax fibers according to the invention have a diameter between 10 microns and 25 microns, preferably between 10 microns and 20 microns, in particular a diameter of about 20 microns.

[0082] 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.

[0083] The basic bast fibers according to the invention are particularly well-suited for textile applications. In particular, they are suitable for short-staple spinning, unlike conventional bast fibers such as technical flax fibers, which are suited to long-staple spinning. Furthermore, the bast fibers according to the invention are suitable for carding.

[0084] Utilization of elementary basal fibers

[0085] 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.

[0086] 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.

[0087] Another object of the invention is a textile article and / or fabric comprising at least one elementary bast fiber according to the invention. The textile article and / or fabric may, in particular, be a ribbon, a yarn, a knit, a mesh, a roving, a woven material, or a non-woven material. In some embodiments, the textile article and / or 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 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 fabric are, in this embodiment, elementary bast fibers according to the invention.

[0088] 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.

[0089] The invention will be better understood through the following examples, which should be considered illustrative and not limiting of the scope of the invention. Examples

[0090] Example 1: Method according to the invention

[0091] Technical flax fibers in ribbon form (untwisted roving, dry spinning), 100% natural combed flax, were subjected to a steam explosion at 220°C and 26 bar for 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. The flax fibers untangle easily to obtain elementary fibers in a humid environment.

[0092] Figures 2 and 3 show the fibers before and after steam treatment, respectively. Figure 4 shows an isolated elementary fiber obtained after steam treatment. Measurements of the diameter of this elementary fiber at different locations yielded the following values: 20.46 micrometers and 19.06 micrometers. Measurements performed on another fiber also provided a value of 13.17 micrometers.

[0093] Figures 5 and 6 show the flax fibers as a whole before and after steam treatment. Before treatment, numerous technical fibers with a diameter of approximately 60 to 80 micrometers are observed. After treatment, the sample contains almost exclusively elementary fibers with a diameter of approximately 19 to 23 micrometers, and very few technical fibers.

[0094] Example 2: Characterization of the elementary fibers obtained according to the invention

[0095] The length of the flax fibers was compared before and after steam treatment according to the invention. The histograms in [Fig. 7] and [Fig. 8] represent the distribution of fiber lengths in mm, as an inverse cumulative percentage, respectively before and after steam treatment of the fibers by the process of Example 1. The technical flax fibers (before treatment) have a size distribution ranging from 60 to 120 mm, making them suitable for spinning into long fibers. Conversely, the size distribution of the fibers after treatment, which only reaches 30 to 50 mm, makes them suitable for spinning into short fibers.

[0096] Table 1 below presents 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. Furthermore, maintaining the values ​​of the strength and elongation indicators demonstrates that the elementary fibers according to the invention are compatible with spinning.

[0097] [Tables 1] Fiber Area (pm²) Diameter (pm) Tensile Strength (MPa) Modulus of Elasticity (GPa) Elongation at Break (%) Lin before treatment 2598 57.5 794+269 45+27 2.66 Lin after treatment 419 23.1 849+626 16.2+0.7 1.9+0.9

[0098] Example 3: Implementation of the process with flax of different maturity levels

[0099] The process according to the invention was implemented with flax stems harvested at different stages of maturity on 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.

[0100] After mechanical defibration and processing, the fibers were subjected to steam treatment such as that described in Example 1.

[0101] 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. Furthermore, these mechanical properties are similar to those of fibers obtained by the traditional method (column 3, green capsules with retting). Implementing the process without retting and scutching therefore makes it possible to obtain fibers with mechanical properties as good as those of fibers obtained by the traditional method.

[0102] [Tables2] Maturity 1: Flowering 2: Green capsules 3: Green capsules with retting 4: Brown capsules 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

[0103] 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 (needle punching).

[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 aggregates and / or fiber knots. They were then opened with the first module of the Laroche opener at 800 rpm. The fibers were then conveyed by the Bobino loader to the carding machine and carded to parallelize them. The final density was achieved with a web spreader. The nonwoven fabric was consolidated by needle punching.

[0107] The resulting non-woven fabric had a final thickness of 3 to 4 mm, and a final density of 300 g / m2.

[0108] The 100% linen non-woven fabric obtained from elementary linen fibers according to the invention had a visual and tactile fineness clearly superior to that of a non-woven fabric obtained from technical fibers, which is visible in the photo of [Fig.9].

Claims

Demands

1. A process for obtaining elementary flax fibers, comprising a step of treating unscutched flax fibers with steam at a pressure strictly greater than atmospheric pressure, followed by a sudden drop in pressure, said process not comprising any contact of the unscutched flax fibers with a pretreatment solution such as an acidic or basic pretreatment solution.

2. A process for obtaining elementary flax fibers according to claim 1, wherein the flax fibers are unretted and unretting flax fibers.

3. A process for obtaining elementary flax fibers according to claim 1 or claim 2, wherein the contact of the fibers with water vapor is carried out at a temperature between 150°C and 300°C, preferably about 220°C.

4. A process for obtaining elementary flax fibers according to any one of claims 1 to 3, wherein the contact of the fibers with steam is carried out at a pressure between 5 bars and 50 bars, preferably about 26 bars.

5. A process for obtaining elementary flax fibers according to any one of claims 1 to 4, wherein the fibers are brought into contact with water vapor for a period of between 2 and 20 minutes, preferably about 7 minutes.

6. A process for obtaining elementary flax fibers according to any one of claims 1 to 4, wherein the process further comprises, after steam treatment, at least one rinsing, preferably two rinsings, with a rinsing solvent, preferably water.

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