Bamboo fibers delignification method

Abstract

In a first aspect, the invention relates to a fiber production method comprising the delignification of bamboo fibers. The bamboo fibers comprise or consists of separated bamboo technical fibers, each bamboo technical fiber comprising plural elementary bamboo fibers. In a further aspect, the invention relates to bamboo technical fibers obtained from the method.

Description

[0001] BAMBOO FIBERS DELIGNIFICATION METHOD

[0002] Background of the Invention

[0003]

[0001] The invention generally relates to a method for the treatment of bamboo fibers. More specifically, the invention relates to delignification of bamboo technical fibers. In a further aspect, the invention relates to bamboo technical fibers obtainable from the method.

[0004] [2] Bamboo is a natural composite material known for its impressive mechanical properties, largely attributed to its hierarchical structure. This structure comprises microfibrils, elementary fibers, technical fibers, and culms. Fig. 1 provides a detailed breakdown, starting from an internode section of the culm 10 and going down to the elementary fiber, itself comprising the microfibrils (not shown), illustrating the intricate composition of a bamboo plant.

[0005] [3] The vascular bundles 12 are longitudinally aligned in the culm 10 and embedded in a matrix of parenchyma tissue. The vascular bundles 12 comprise conducting tissue in the form of the phloem 14, protoxylem 16 and metaxylem 18 vessels. The vascular bundles 12 further comprise fiber sheaths 20 (sclerenchyma sheaths), and, in some bamboo species, additional fiber strands. Both the fiber sheaths 20 and the strands comprise elementary fibers 22, each elementary fiber 22 being an individual plant cell. When viewed in cross section, the elementary fibers 22 typically exhibit an (irregular) hexagonal or pentagonal shape and a lumen 24. The layers between neighbouring elementary fibers are called middle lamellae.

[0006] [4] The fiber sheaths and strands constitute technical fibers 26 when extracted from the plant. In the context of the present document, the term “technical fiber” may designate also fragments of the fiber sheaths and strands that comprise plural elementary fibers 22.

[0007] [5] Within the hollow culm, nodes serve to enhance rigidity and prevent Brazier buckling, thanks to reinforcement from the nodal diaphragm. At the fundamental level, m icrofibrils serve as basic building blocks, featuring cellulose nanofibrils arranged in a helical pattern. These microfibrils then combine to form elementary fibers, where several microfibrils align in parallel. [6] Technical fibers, the next level in the hierarchy, result from the aggregation of multiple elementary fibers, constituting the primary structural components of bamboo culms. In botany, technical fibers may be called bundles when they are still in the plant. Extracted technical fibers may thus resemble the original bundles in configuration and / or geometry, but not necessarily (depending on the processing of the extracted technical fibers). Culms, the final stage, consist of layers of technical fibers arranged hierarchically, forming the vascular bundles. These bundles, aligned longitudinally within the culm and surrounded by parenchyma tissue, exhibit increasing density from the inner to the outer culm. This nuanced arrangement contributes to bamboo's functional properties, making it well-suited for specific bending stiffness and strength.

[0008] [7] The length of extracted bamboo technical fibers may be equal to the internodal distance. In the nodes, the fibers are entangled, unlike in the internodes, where the technical fibers run essentially parallel.

[0009] [8] More information about bamboo fibers can be found, e.g., in the article: Osorio L, Trujillo E, Lens F, Ivens J, Verpoest I, Van Vuure A. In-depth study of the microstructure of bamboo fibers and their relation to the mechanical properties. Journal of Reinforced Plastics and Composites. 2018;37(17):1099-1113. doi: 10.1177 / 0731684418783055.

[0010] [9] Bamboo has been proposed as an alternative source of natural fibers due to its fast growth rate and naturally high content of solid cellulose macrofibers. However, the rigid macrofibers bamboo are embedded within a matrix of hollow parenchyma cells, which are strongly adhered together in a natural polymer matrix composed of lignin and hemicelluloses. Different methods have been explored to isolate the long macrofiber from natural bamboo. One of the recent ones, by Hu and coworkers (Nature Sustainability 2022, 5, 235-244), is based on peroxyformic acid as a delignification agent that selectively breaks down the lignin / hemicellulose binder as well as the thinwalled parenchyma cells, allowing the nearly solid cellulosic macrofibers to be separated with little mechanical damage at a large scale.

[0011]

[0010] Document US 2023 / 160141 A1 discloses a chemical process for extracting cellulose-based fibers from natural plant material, in particular bamboo. In a first step, the natural plant material, such as an internode section of a bamboo stem, is treated with an alkali solution of one or more chemicals in order to partially remove lignin and hemicellulose from the plant material. In a second step, the partially-delignified plant material can be treated with a different solution of one or more chemicals in order to further remove lignin and hemicellulose. Alternatively, the fabrication method may comprise a single-step delignification process using a single solution of one or more chemicals. In either case, the delignified plant material can be rinsed and agitated, resulting in release of the cellulose-based macrofibers from each other. Subsequent drying of the released macrofibers can result in self-densification, which can further improve the mechanical properties of the macrofibers.

[0012] Summary of the invention

[0013]

[0011] In a first aspect, the invention relates to a fiber production method comprising the delignification of bamboo fibers. The bamboo fibers comprise or consists of separated bamboo technical fibers, each bamboo technical fiber comprising plural elementary bamboo fibers.

[0014]

[0012] The delignification of the separated bamboo technical fibers may be performed in a buffer solution at a pH in the range from 4 to 6 (preferably from 4.5 to 5.5, more preferably from 4.5 to 5), the buffer solution containing one or more delignification agents. The one or more delignification agents may include O2, O3, CIO2, H2O2, NaCIO2, NaCIO, Ca(CIO)2 or any combination of the foregoing. Preferably, the one or more delignification agents comprise or consist of NaCICh.

[0015]

[0013] According to embodiments of the method, the buffer solution may comprise at least one of acetate, propanoate, butanoate, and citrate anions.

[0016]

[0014] The separated bamboo technical fibers may, preferably, comprise or consist of mechanically separated bamboo technical fibers.

[0017]

[0015] The separated bamboo technical fibers may, preferably, have lengths of at least 5 cm, more preferably of at least 10 cm, still more preferably of at least 15 cm. According to certain embodiments, the separated bamboo technical fibers may have a length of at most 75 cm, preferably of at most 60 cm and more preferably of at most 50 cm.

[0018]

[0016] The separated bamboo technical fibers may, preferably, have diameters in the range from 40 pm to 700 pm, preferably in the range from 50 pm to 500 pm.

[0019]

[0017] According to an embodiment, the delignification is performed in a 0.05 M to 0.5 M (0.05 mol / L to 0.5 mol / L) sodium acetate solution with 1 to 5 wt.% NaCICh brought to a pH in the range from 4.25 to 5.5 by addition of acetic acid. The duration of the delignification treatment may be 3 to 5 hours at a temperature from 70°C to 90°C. According to a specific embodiment, the delignification of the separated bamboo technical fibers may be performed during 3.5 to 4.5 hours at a temperature from 75°C to 85°C in a 0.09 M to 0.2 M (0.09 mol / L to 0.2 mol / L) sodium acetate solution with 2.5 to 3.5 wt.% NaCICh brought to a pH in the range from 4.5 to 5 by addition of acetic acid.

[0020]

[0018] Preferably, the delignification is performed under preservation of the structural integrity of the elementary bamboo fibers (in particular of the microstructure of cellulose fibers).

[0021]

[0019] According to a preferred embodiment, the method comprises rinsing the delignified bamboo technical fibers with water.

[0022]

[0020] The method may further comprise drying the delignified and rinsed bamboo technical fibers thereby causing void spaces therein (such as, e.g., lumens and spaces previously occupied by middle lamellae) to collapse and thereby causing densification of the bamboo technical fibers. The drying may include conductive, convective, and / or radiative heating processes, e.g., an air-drying process, a vacuum-assisted drying process, an oven drying process, a freeze-drying process, a critical point drying process, a microwave drying process, or any combination of the above. An air-drying process may, e.g., start at room temperature (e.g., 20°C - 25°C) and then increase the temperature of static air or an airflow stepwise or continuously to a higher temperature, e.g., up to 80°C . A vacuum-assisted drying process may include subjecting the delignified bamboo technical fibers to reduced pressure, e.g., less than 1 bar, e.g., in a vacuum chamber or vacuum oven. The drying preferably induces capillary effects that cause the void spaces to collapse and the microfibrils to move closer together so that the bamboo technical fibers are densified. An air-drying process may be preferred in the context of the invention.

[0023]

[0021] After (preferably immediately after) drying and / or densification, the bamboo technical fibers may be subjected to a plasma activation treatment. One may consider the plasma activation treatment as a second part of the drying process. The plasma activation treatment is preferably effective to make the surface of the bamboo technical fibers hydrophilic for efficient water migration, accelerating and finalizing internal drying and improving densification. The plasma activation treatment preferably is or includes an air plasma activation treatment (e.g., with a power density from 0.05 to 10 W / cm2, preferably from 0.5 to 1 W / cm2, with a frequency in the range from 0.5 to 100 kHz, preferably from 5 to 10 kHz, and, e.g., at 20 L / min of an N2 / O2 mixture of 80 / 20 (vol. / vol.)). It has been found that by making the fiber surface hydrophilic, this treatment facilitates efficient drying and densification, increasing mechanical properties (such as, ultimate tensile strength and Young’s modulus) by up to 10% compared to untreated fibers.

[0024]

[0022] The delignified bamboo technical fibers may be subjected to a plasma coating process, wherein the bamboo technical fibers are coated with a plasma-polymer, e.g., a polymerized organosilicon coating. The plasma coating process is preferably carried out after the plasma activation treatment, since it may restore thermal stability of the fibers and reduce moisture sorption (even below the initial value). According to an embodiment, the plasma coating process includes depositing a solution (0.5 to 3 % wt. / wt. of an organosilicon, e.g., p-aminophenyltrimethoxysilane, in 95% ethanol) using a combination of N2 and O2 (preferably 80 / 20 vol. / vol.) Preferably, the organosilicon compound used in the plasma coating process has the formula X-Si-Rs, where R is alkoxy, acyloxy, halogen or amine, and the X functional group is any one of amino, phenyl, aminophenyl, chloromethyl, epoxy, glycidoxy, isocyanate, methacryloxy, etc. Preferred examples of organosilicons include p-aminophenyltrimethoxysilane, p- chloromethylphenyltrimethoxysilane, and others members of the phenyltrimethoxysilane family.

[0025]

[0023] According to a specific embodiment, the fiber production method comprises delignification of mechanically separated bamboo fibers, each bamboo technical fiber comprising plural elementary bamboo fibers. The separated bamboo fibers have a length of at least 5 cm, preferably of at least 10 cm, more preferably of at least 15 cm. The separated bamboo technical fibers have a length of at most 75 cm, preferably of at most 60 cm and more preferably of at most 50 cm. The separated bamboo technical fibers have diameters in the range from 40 pm to 700 pm, preferably in the range from 50 pm to 500 pm. The delignification of the separated bamboo technical fibers of the given lengths and diameters is performed during 3.5 to 4.5 hours at a temperature from 75°C to 85°C in a 0.09 M to 0.2 M sodium acetate solution with 2.5 to 3.5 wt.% NaCICh brought to a pH of 4.5 to 5 by addition of acetic acid, under preservation of the structural integrity of the elementary bamboo fibers. The delignified bamboo technical fibers are then rinsed with water and dried so that void spaces therein collapse and cause densification of the bamboo technical fibers. The dried bamboo technical fibers are subjected to a plasma activation treatment and then to a plasma coating process, wherein the bamboo technical fibers are coated with a plasma-polymer coating, preferably a plasma-polymerized organosilicon coating.

[0026]

[0024] In a further aspect, the invention relates to bamboo technical fibers obtained from the method as described herein.

[0027]

[0025] The bamboo technical fibers preferably have an ultimate tensile strength of at least 1 GPa, preferably at least 1.5 GPa, and more preferably of at least 2 GPa. The bamboo technical fibers preferably have a Young’s modulus of at least 60 GPa, more preferably of at least 100 GPa, and still more preferably of at least 150 GPa.

[0028]

[0026] The bamboo technical fibers obtained according to the method preferably have a soluble lignin content of 5 % by weight or less (e.g., 4.2 % by weight or less) and an insoluble lignin content of 4 % by weight or less (e.g., 3 % by weight or less).

[0029]

[0027] In yet a further aspect, the invention relates to delignified bamboo technical fibers having a lignin content of at most 4 wt.% and coated with a plasma-polymerized organosilicon coating.

[0030]

[0028] In the present document, the verb “to comprise” and the expression “to be comprised of’ are used as open transitional phrases meaning “to include” or “to consist at least of”, not excluding the presence of further features or components. Unless otherwise implied by context, the use of singular word form is intended to encompass the plural, except when the cardinal number “one” is used: “one” herein means “exactly one”. Ordinal numbers (“first”, “second”, etc.) are used herein to differentiate between different instances of a generic object; no particular order, importance or hierarchy is intended to be implied by the use of these expressions. Furthermore, when plural instances of an object are referred to by ordinal numbers, this does not necessarily mean that no other instances of that object are present (unless this follows clearly from context). When this description refers to “an embodiment”, “one embodiment”, “embodiments”, etc., this means that the features of those embodiments can be used in the combination explicitly presented but also that the features can be combined across embodiments without departing from the invention, unless it follows from context that features cannot be combined. Brief Description of the Drawings

[0031]

[0029] By way of example, preferred, non-limiting embodiments of the invention will now be described in detail with reference to the accompanying drawings, in which:

[0032] Fig. 1 : is a schematic illustration of the hierarchical structure of the internode section of a bamboo plant;

[0033] Fig. 2: is a diagram plotting stress as a function of strain for samples of densified delignified bamboo technical fibers that have been subjected to delignification treatments of 3, 4 and 5 hours, respectively;

[0034] Fig. 3: is a diagram of the maximum strain measured on densified delignified bamboo technical fibers as a function of the duration of the delignification treatment;

[0035] Fig. 4: is a diagram of the maximum stress measured on densified delignified bamboo technical fibers as a function of the duration of the delignification treatment.

[0036] Detailed Description of a Preferred Embodiment

[0037]

[0030] According to a preferred embodiment, mechanically extracted (separated) technical bamboo fibers are delignified, then densified and finally subjected to plasma treatment.

[0038]

[0031] The starting material of the process is mechanically extracted technical bamboo fibers (e.g., with lengths from 20 to 40 cm and diameters from 50 pm to 500 pm).

[0039]

[0032] The separate technical bamboo fibers are subjected to a delignification treatment to selectively remove, in particular, the lignin-rich middle lamellae, while preserving the structural integrity of cellulose elementary fibers.

[0040]

[0033] The delignification process based on peroxyformic acid used by Hu and coworkers (Nature Sustainability 2022, 5, 235-244) is effective for delignification of a bamboo stem section, but it may be considered too aggressive for separated bamboo fibers, as the lignin and cellulose are both cleaved and degraded, leading to thin delignified fibers with poor mechanical strength.

[0041]

[0034] Therefore, a more convenient method for the delignification of separated bamboo technical fibers, selective for the lignin cleavage while preserving the chemical structure of cellulose, was developed. Cellulose is cleaved at low pH via the hydrolysis of ester bonds. Increasing the pH of the reaction medium may thus reduce or prevent degradation of cellulose.

[0042]

[0035] A delignification process using sodium chlorite and acetic acid / acetate as oxidant was devised for selective lignin extraction. NaCICh has been selected as the oxidant: it was found that the ideal concentration is 3 wt.%. However, the concentration of NaCICh can be selected in the range from 1 to 5 wt.% if the reaction time and / or the temperature of the solution is adapted. In tests, the approximative time of reaction for 1 wt.% was 6 h and 2 h at 5 wt.%. It was found that the temperature could be varied from 60°C to 90°C.

[0043]

[0036] Trials wherein separated bamboo technical fibers were immersed in a 1 wt.% NaCICh solution and 0.1 M sodium acetate during 2 h at 80°C indicated a partial delignification of bamboo fibers (coloured) after 2h of reaction time. When the concentration of NaCICh was increased to 3 wt.%, a reaction time of 2 h was sufficient.

[0044]

[0037] The NaCICh salt may be directly dissolved in a 0.1 M sodium acetate solution. Acetic acid may be added to the solution to reduce the pH (buffer solution). Preferably, the quantity of acetic acid is chosen in such a way to bring the pH into the range from 4.5 to 5.5, preferably into the range from 4.5 to 5. In the tests, bamboo technical fibers (approximately 0.10 g) were immersed in 100 mL of 0.1 M sodium acetate with the dissolved NaCICh salt at a pH of 5 (after addition of 600 pL of acetic acid), contained in a test tube. The tube was then immersed in a heated oil bath at 80°C. The colourless and clear solution turned yellowish after the reaction time (from 2 - 5 h).

[0045]

[0038] The delignified bamboo technical fibers were then rinsed in water and dried at room temperature before tensile testing analysis.

[0046]

[0039] Capillary pressure brings together elementary fibers, resulting in densification of the technical fibers. Capillary action is the ability of a liquid to flow in narrow spaces against the force of gravity. In the context of natural fibers, lumens and the internal spaces left by the removal of the middle lamella act as capillaries. When bamboo technical fibers are in contact with water (during the rinsing step following delignification), they absorb water into their lumens through capillary action. Water is drawn into the narrow spaces within and between the elementary fibers.

[0047]

[0040] Capillary pressure is the pressure exerted by a meniscus in a capillary tube or porous material. In the case of saturated bamboo fibers, the water within the extracted middle lamella and lumens creates a meniscus, and capillary pressure is established. The capillary pressure generated by water within the fiber structure voids leads to the collapse or compression of the lumens and spaces between elementary fibers previously occupied by the middle lamellae when the bamboo technical fibers are dried, resulting in the densification of the technical fiber structure. As the lumens and middle lamellae empty spaces collapse under capillary pressure, the fibers come closer together, reducing the void spaces between them.

[0048]

[0041] Preferably, the delignified and rinsed bamboo technical fibers are subjected to a controlled drying process. The drying may, e.g., be initiated at room temperature, and the temperature may then be increased gradually or by steps to a maximum temperature preferably between 60°C and 90°, e.g., 80°C.

[0049]

[0042] With the middle lamellae removed, individual cellulose elementary fibers unify, forming a continuous macromolecular structure. The cohesive bonding (van der Waals as well as hydrogen bonding) enhances the resulting strength (1400 - 2400 MPa), dimensional stability, and Young’s modulus (40 - 150 GPa) of the bamboo technical fibers.

[0050]

[0043] The dried technical bamboo fibers obtained in the trials were stiff and white. The delignification process yielded delignified bamboo technical fibers with a tensile strength of 2.4±0.9 GPa after densification. The soluble lignin content of the resulting technical bamboo fibers was 4.03 wt.% and the insoluble lignin content was 2.8 wt.%.

[0051]

[0044] Tensile testing was conducted using densified delignified bamboo technical fibers that had been exposed to the delignification agent for different times. For a 0.1 M sodium acetate solution with 3 wt.% NaCIO2 brought to a pH of 5 by addition of acetic acid, and a temperature of 80°C, it was found that the optimal reaction time was 4 h. Tensile test analysis (Figs. 2-4) indicated an improvement of the strength and stress when increasing the time of reaction with the maximum stress at 4 h. Increasing the time of reaction to 5 h resulted in a decrease of both stress and strain.

[0052]

[0045] The exposure time (reaction time) thus has an important impact on the mechanical strength of the obtained fibers.

[0053]

[0046] Due to the removal of lignin, the resulting highly robust fibers exhibit compromised thermal stability. This poses a challenge for utilizing the fibers in advanced composites, since processing temperatures for advanced thermoplastics often exceed 200°C.

[0054]

[0047] Examples of densified delignified bamboo technical fiber produced according to the described methodology has a cellulose content ranging from 96 to 100 wt.% and a lignin content between 1 and 4 wt.%. By removing lignin from the fiber structure, the fiber gains significantly improved mechanical properties. However, this process also reduces thermal stability, as the exposed cellulose is now more susceptible to thermal degradation. Consequently, the onset temperature for typical technical bamboo fibers was found to decrease from 210°C to 150°C after delignification and densification treatment. Additionally, the removal of lignin was found to result in increased sensitivity to humidity and swelling, leading to a 12% increase in equilibrium moisture content (EMC, at 75% RH and 20°C) compared to untreated bamboo fibers. This means that the delignification process, which is part of the densification process, enhances mechanical properties but significantly reduces thermal stability and increases moisture sensitivity, which may be critical factors for industrial applications. To determine the onset temperature of thermal degradation, the samples were initially heated to 100°C and maintained at this temperature for two hours to eliminate all moisture content. Following this isothermal step, the thermogravimetric analysis was performed in a nitrogen atmosphere with a heating rate of 10°C / min and the TGA curve was plotted. The onset temperature was determined by thermogravimetric analysis (TGA), in accordance with standard ISO 11358-1 , as the point of intersection of (a) the baseline (plateau) of the TGA curve at the beginning of the measurement and (b) the tangent to the TGA curve at the point of maximum gradient (the inflection point of the TGA curve).

[0055]

[0048] The thermal stability of densified technical bamboo fibers may, however, be improved. Such a process, may, e.g., comprise subjecting the bamboo technical fibers to a plasma activation treatment (immediately) after the densification. This step activates the surface of the fibers, making them more receptive to subsequent modifications, and also more hydrophobic, which improves water removal and disinfection of the fibers. The plasma activation treatment is, preferably, an air plasma activation treatment (e.g., with a power density in the range from 0.05 to 10 W / cm2more preferably of 0.64 W / cm2, at a frequency in the range from 0.5 to 100 kHz, preferably of 6 kHz, and at an air flow rate of 20 L / min). By making the fiber surface hydrophilic, this treatment facilitates efficient drying and densification, increasing ultimate tensile strength and Young’s modulus by up to 10 % and 20 %, respectively, compared to technical bamboo fibers dried but not subjected to any plasma activation treatment.

[0056]

[0049] Then, plasma-polymerized organosilicons with an appropriate organic / inorganic and polymer crosslinking using an aerosol assisted atmospheric plasma device can help improving the thermal stability of densified technical bamboo fibers. This technique is considered as an environmentally friendly dry technique to surface-treat the bamboo technical fibers. Such plasma-polymerized organosilicons are preferably applied by a second plasma treatment step subsequently to the plasma activation treatment. The plasma coating step may, e.g., include depositing a solution (0.5 to 3 % wt. / wt. of an organosilicon, e.g., 1 % wt. / wt. p-aminophenyltrimethoxysilane, p-chloromethylphenyltrimethoxysilane, or another member of the phenyltrimethoxysilane family, in 95% ethanol) using a combination of N2 / O2 (80% / 20% (vol. / vol.)). It was found that thanks to this plasma coating step, thermal stability could be increased to its initial value (onset temperature of 210°C) and EMC could be reduced by 32% with respect to the plasma-activated delignified fibers, and by 20% with respect to the untreated bamboo technical fibers.

[0057]

[0050] Thanks to the plasma treatment steps, densified technical bamboo fibers with improved mechanical properties, without side effects, and enhanced physical properties can thus be prepared.

[0058]

[0051] While specific embodiments and examples have been described herein in detail, those skilled in the art will appreciate that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention, which is to be given the full breadth of the appended claims and any and all equivalents thereof.

Claims

Claims1. A fiber production method comprising delignification of bamboo fibers, wherein the bamboo fibers comprise separated bamboo technical fibers, each bamboo technical fiber comprising plural elementary bamboo fibers.

2. The method as claimed in claim 1 , wherein the delignification of the separated bamboo technical fibers is performed in a buffer solution at a pH in the range from 4 to 6, the buffer solution containing one or more delignification agents.

3. The method as claimed in claim 2, wherein the one or more delignification agents include O2, O3, CIO2, H2O2 , NaCICh, NaCIO, Ca(CIO)2 or any combination of the foregoing.

4. The method as claimed in claim 2 or 3, wherein the buffer solution comprises at least one of acetate, propanoate, butanoate, and citrate.

5. The method as claimed in any one of claims 1 to 4, wherein the separated bamboo technical fibers comprise or consist of mechanically separated bamboo technical fibers.

6. The method as claimed in any one of claims 1 to 4, wherein the separated bamboo technical fibers have a length of at least 5 cm, preferably of at least 10 cm, more preferably of at least 15 cm.

7. The method as claimed in claim 6, wherein the separated bamboo technical fibers have a length of at most 75 cm, preferably of at most 60 cm and more preferably of at most 50 cm.

8. The method as claimed in any one of claims 1 to 7, wherein the separated bamboo technical fibers have diameters in the range from 40 pm to 700 pm, preferably in the range from 50 pm to 500 pm.

9. The method as claimed in any one of claims 1 to 8, wherein the delignification is performed in a 0.05 M to 0.5 M sodium acetate solution with 1 to 5 wt.% NaCICh brought to a pH in the range from 4.25 to 5.5 by addition of acetic acid, for a duration of 3 to 5 hours at a temperature from 70°C to 90°C.

10. The method as claimed in any one of claims 1 to 8, wherein the delignification of the separated bamboo technical fibers is performed in a 0.09 M to 0.2 M sodium acetate solution with 2.5 to 3.5 wt.% NaCICh brought to a pH in the range from4.5 to 5 by addition of acetic acid, for a duration of 3.5 to 4.5 hours at a temperature from 75°C to 85°C.11 . The method as claimed in any one of claims 1 to 10, wherein the delignification is performed under preservation of the structural integrity of the elementary bamboo fibers.

12. The method as claimed in any one of claims 1 to 11 , comprising rinsing the delignified bamboo technical fibers with water.

13. The method as claimed in claim 12, comprising drying the rinsed bamboo technical fibers thereby causing void spaces therein to collapse and causing densification of the bamboo technical fibers.

14. The method as claimed in claim 13, wherein the bamboo technical fibers are subjected to a plasma activation treatment after densification of the bamboo technical fibers.

15. The method as claimed in claim 13 or 14, wherein the bamboo technical fibers are subjected to a plasma coating process, wherein the bamboo technical fibers are coated with a plasma-polymerized organosilicon coating.

16. The method as claimed in any one of claims 1 to 4, wherein the separated bamboo technical fibers comprise or consist of mechanically separated bamboo technical fibers; wherein the separated bamboo technical fibers have a length of at least 5 cm, preferably of at least 10 cm, more preferably of at least 15 cm; wherein the separated bamboo technical fibers have a length of at most 75 cm, preferably of at most 60 cm and more preferably of at most 50 cm; wherein the separated bamboo technical fibers have diameters in the range from 40 pm to 700 pm, preferably in the range from 50 pm to 500 pm; wherein the delignification of the separated bamboo technical fibers is performed in a 0.09 M to 0.2 M sodium acetate solution with 2.5 to 3.5 wt.% NaCICh brought to a pH in the range from 4.5 to 5 by addition of acetic acid, for a duration of 3.5 to 4.5 hours at a temperature from 75°C to 85°C; wherein the delignification is performed under preservation of the structural integrity of the elementary bamboo fibers; wherein the delignified bamboo technical fibers are rinsed with water;wherein the rinsed bamboo technical fibers are dried, thereby causing void spaces therein to collapse and causing densification of the bamboo technical fibers; wherein the bamboo technical fibers are subjected to a plasma activation treatment after densification of the bamboo technical fibers; and wherein the bamboo technical fibers are subjected to a plasma coating process, wherein the bamboo technical fibers are coated with a plasma- polymerized organosilicon coating.

17. Bamboo technical fibers obtained from the method as claimed in any one of claims 1 to 16.

18. The bamboo technical fibers as claimed in claim 17, having an ultimate tensile strength of at least 1 GPa, preferably at least 1 .5 GPa, and more preferably of at least 2 GPa.

19. The bamboo technical fibers as claimed in claim 17 or 18, having a Young’s modulus of at least 60 GPa, preferably of at least 100 GPa, and more preferably of at least 150 GPa.

20. The bamboo technical fibers as claimed in any one of claims 17 to 19, having a soluble lignin content of 5 % by weight or less and an insoluble lignin content of 4 % by weight or less.21 . Delignified bamboo technical fibers having a lignin content of at most 4 wt.% and coated with a plasma-polymerized organosilicon coating, preferably as claimed in any one of claims 17 to 20.

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