A method of extraction of natural fibres

Abstract

The invention relates to a method of extraction of textile fibres from palms. More particularly, the invention relates to extraction of textile fibres and surface wax from palm leaflets, such as textile fibres and wax from date palms. Textile fibres are produced from raw palm material by scraping palm leaflets to remove the non-fibrous surface layer. Extracted fibres are then brushed to remove residual surface impurities; and then washed and dried to a moisture content of less than 20%, preferably less than 15%. Optionally palm leaflets are separated from date palm fronds.

Description

[0001] A METHOD OF EXTRACTION OF NATURAL FIBRES

[0002] Field of the Invention

[0003] This invention relates to a method of extraction of fibres and wax and more particularly, but not exclusively, the invention relates to extraction of textile fibres and surface wax from palm leaflets, such as textile fibres and wax from date palms.

[0004] Background

[0005] Date palms are mainly cultivated in the Middle East and North African regions. Typically, global harvests exceed 1 million hectares. The estimated annual byproducts of pruning date palms globally are around 5 million tons (air dry weight), in the form of frond and fruit stalks, leaflets and leaf sheath. These are often treated as agricultural waste.

[0006] Previous attempts to extract fibres from date palm leaflets were limited to milling them into small particles or manually slitting them into long strands with no attempt to remove the non- cellulosic impurities. These tended to be used traditionally in manufacture of fibre fill for cushioning.

[0007] As for the wax extraction, the majority of the palm wax extracted are from the Brazilian carnauba palm and only one published research article investigated the extraction of date palm leaflet wax using a complex supercritical carbon dioxide extraction method.

[0008] Some of these are described in the documents mentioned below.

[0009] Prior Art

[0010] International patent application W02023007223A1 (NAMA WOMEN ADVANCEMENT ESTAB) discloses a method of fibre extraction from palm, using a biological degumming process employed to loosen the date palm leaves structure. The degumming process comprises the steps of retting in warm using a biological enzyme (Laccase). The degumming process is followed by manual combing process and then the leaves are dried at room temperature.

[0011] United States patent application US 11370953B2 (SAUDI ARABIAN OIL CO) discloses a method of preparation of date tree waste-based lost circulation material (LCM). The date tree waste LCM may include fibres from the date tree waste produced from processing date trees in the production of date fruits. The date tree waste may include fibres from one or more of the following: date tree trunks, date tree rachis, date tree leaflets, date tree panicles, and date tree roots.

[0012] Japanese patent application JP2020532607A discloses a method of making of date palm fibre blend lost circulation material (LCM) comprising a ternary blend of fibres made from date palm. Date palm fibre is mixed LCM and date palm fibre made from date palm trunks, date palm leaves and leaf stem fibres made from date palm leaves and leaf stems, and date palm inflorescence fibres made from date palm inflorescences.

[0013] International patent application W02012108860A1 (BROWN LAURENCE B) discloses a method of making a dental implement made from palm leaflet. The dental implement is usable as dental floss that can be manipulated while held in one hand and includes an elongate body cut from dried palm leaflet.

[0014] International patent application W02020139088A1 (SULTAN QABOOS UNIV) discloses a method for preparing a high performance fibre from natural fibre (date palm) a method for preparation of high performance fibre from natural fibre (date palm). The method includes separating raw fibres from the natural fibre source and dewaxing the separated raw fibres with an alcoholic solution of ethanol and water for a predetermined time at a first predetermined temperature. The method further includes sterilizing the dewaxed fibres with an acidified salt solution at a second predetermined temperature and alkalizing the sterilized fibres with an alkali solution at a third predetermined temperature to generate the high- performance fibres.

[0015] United States patent application US 2013 / 0149512 A1 (ANANAS ANAM LIMITED) discloses a process for preparing a non-woven material comprising a multi layered stack. The multi layered stack comprises discrete interconnected layers. Each of the layers, which may be the same or different, comprises a composite fibre from about 80% to 100% w / w leaf or stem fibre and from about 1 % to 20% w / w of a polymer, wherein the polymer is fusible at a temperature of about 180° C or less.

[0016] Another extraction method is described in a paper by Karima Al Bulushi, Thomas M. Attard, Michael North, Andrew J. Hunt, 2018 entitled “Optimisation and economic evaluation of the supercritical carbon dioxide extraction of waxes from waste date palm (Phoenix dactylifera) leaves” which published in the ‘Journal of Cleaner Production’, volume 186, pages 988-996.

[0017] None of the above techniques were capable of extracting long textile grade fibres from date palm leaflets or were able to extract surface wax.

[0018] An object of the present invention is to solve the aforementioned problems.

[0019] Another object is to valorize large quantities of agricultural residues generated by palm, particularly date palm plantations and to extract long textile fibres from the leaflets and to extract the surface wax.

[0020] Summary of the Invention

[0021] According to a first aspect of the invention there is provided a method for producing textile fibres from raw palm material comprising the steps of: a) scraping palm leaflets to remove the non-fibrous surface layer; b) brushing the extracted fibres from step a) to remove residual surface impurities; and c) washing and drying the fibres from step b) to a moisture content of less than 20%, preferably less than 15%. In some embodiments the method includes the initial step of separating palm leaflets from the date palm fronds.

[0022] In some embodiments of the method the initial step before step a) includes pre-soaking the palm leaflets.

[0023] In some embodiments of the method the pre-soaking step comprises pre- soaking in water from 1 to 5 days at ambient temperature.

[0024] In some embodiments of the method the pre-soaking step comprises boiling or heating the leaflets in a liquid between 80°C to 100°C.

[0025] In some embodiments of the method, the scraping is performed by using a reciprocating blunt scraper along the length of the leaflets.

[0026] In some embodiments of the method the scraping step is performed using a rotating drum or decorticator having one or more rotating blunt scraping blades thereon.

[0027] In some embodiments of the method the scraping step includes the palm leaflets being fed between the scraping blades and a stationary element such as a beater.

[0028] In some embodiments of the method the clearance between the rotating scraping blades and the stationary beater is between 0.1 to 0.4 mm.

[0029] In some embodiments of the method the scraping is performed by using a rotating cylinder with saw tooth wire, in which the leaflets are being fed using two feed rollers.

[0030] In some embodiments of the method the rotating cylinder with a saw tooth wire, has a tooth pitch between 6 - 16 teeth per inch, tooth angle between 40° - 60°, tooth height 1.5 - 5 mm, and wire thickness 0.4 - 1 mm. In some embodiments of the method the drying step in c) includes roll squeezing or centrifugal dewatering.

[0031] In some embodiments of the method the drying step c) involves air drying the fibres in open air or in an oven.

[0032] In some embodiments of the method step of d), preferably after step b), of removing gum from intra and / or inter fibre bundles.

[0033] In some embodiments of the method step d) includes treating with one or more enzyme solutions.

[0034] In some embodiments of the method the solutions include one or more of: pectinase, laccase and acid xylanase.

[0035] In some embodiments of the method step d) includes treating fibres with an enzyme solution before pretreating the fibres with an acidic solution, preferably at a temperature of least 50°C and more preferably at a temperature of at least 100°C for a duration of at least 0.5 hour, preferably at least 3 hours.

[0036] In some embodiments of the method the acidic solution is a diluted sulfuric acid, or phosphoric acid, or a sodium phosphate buffer.

[0037] In some embodiments of the method the acidic solution is less than pH 4, preferably less than pH 3 and preferably around pH 2.

[0038] In some embodiments of the method a rinsing step is applied after treating with an acidic buffer.

[0039] In some embodiments the method includes a step of soaking the fibres in a pectinase solution. In some embodiments the method includes an additional step of soaking the fibres in a solution of laccase, and / or xylanase.

[0040] In some embodiments the method includes soaking the fibres in a solution of pectinase, laccase and acid xylanase.

[0041] In some embodiments the method the includes a step of enzyme soaking and subsequent to enzyme soaking, scouring the fibres with alkaline solution.

[0042] In some embodiments of the method that include step d) the method further includes treating the fibres with a surfactant. Preferably the surfactant is a constituent of the soaking solutions.

[0043] In some embodiments of the method, after the scouring step, the fibres are beaten, for example by using rotary serrated rollers, a hammer, a mallet or any combination thereof.

[0044] In some embodiments of the method the fibres are neutralized in a solution of acetic acid for at least 15 minutes preferably 30 mins and then rinsed with water.

[0045] In some embodiments of the method the fibres are boiled, preferably for around 2 to 3 hours in an alkaline solution.

[0046] Preferably the alkaline solution includes sodium hydroxide and optionally hydrogen peroxide, optionally sodium silicate or sodium sulfite and optionally ethylenediaminetetraacetic acid.

[0047] In some embodiments of the method the subsequent step of neutralizing the fibres is preferably performed in an acetic acid solution.

[0048] Embodiments of the invention will now be described by way of examples only and with reference to the Figures in which: Brief Description of the Drawings

[0049] Figure 1 is a process flow diagram illustrating steps of extraction of textile fibres and surface wax from palm leaflets;

[0050] Figure 2 is a photograph of leaflet fibre morphology before degumming (left) and after degumming (right);

[0051] Figure 3 shows an image of palm leaflet fibres after scraping;

[0052] Figure 4 shows an image of palm leaflet fibres after degumming;

[0053] Figure 5 shows an image following wax extraction from a date palm leaflet; and

[0054] Figure 6 is an FTIR spectra of the resulting wax after the extraction method which indicates the quality of the extracted wax.

[0055] The FTIR provides information about the functional groups present in a sample based on the absorption of infrared light at different wavelengths. The leaflets wax, a natural wax, is composed mainly of fatty acids, and esters. The peaks around 2912 cm-1, 2848 cm-1, 1730 cm-1, and 1169 cm-1are particularly indicative of the wax's long-chain hydrocarbon structure and ester linkages. Some of the peaks at 2219 cm-1and 2132 cm-1could be due to impurities.

[0056] Detailed Description of Preferred Embodiments of the Invention

[0057] Referring to Figure 1 , there is shown a process flow diagram for extraction of textile fibres and surface wax from palm leaflets.

[0058] Initial Preparation The leaflets are separated from the date palm fronds either manually by hand, knife, or by using a mechanized system with blades to peel off the leaflets, which are then collected for further processing.

[0059] Pre-Soaking

[0060] Fresh green leaflets may be used directly for fibre extraction; however, pre-soaking may enhance the quality of the extracted fibres. Whereas, for dry leaflets they must be presoaked in water for 1 -5 days at room temperature or they might be boiled between 80°C to 100 °C to shorten the pre-soaking time and also enable the extraction of the surface wax.

[0061] Scraping

[0062] Palm leaflets are then scraped to remove the non-fibrous surface layer and facilitate the fibre extraction. The scraping action can be performed using a reciprocating blunt scraper along the length of the leaflets. It can also be performed using a rotating drum (decorticator) with multiple blunt scraping blades rotating against a stationary beater. In this case the leaflets are fed into the clearance 0.1 to 0.4 mm between the rotating scraping blades and the stationary beater, in one or multiple strokes from one or both ends. It is important that the scraping is performed while the leaflets are still moist.

[0063] In other embodiments, the scraping method includes feeding the leaflets between two feed rollers into a rotating cylinder with a saw tooth wire that has a tooth pitch between 6 - 16 teeth per inch, a tooth angle between 40° - 60°, a tooth height 1.5 - 5 mm, and a wire thickness 0.4 - 1 mm.

[0064] Brushing

[0065] After scraping, the extracted fibres can be then brushed for further refinement and remove residual surface impurities. Brushing is performed by a rotating drum with multiple blunt blades or short metal combs, in which the fibres are held from one end and fed into the clearance between the rotating drum and a flat metal surface, in one or multiple strokes from one or both ends.

[0066] Degumming

[0067] The degumming is an optional step used to further remove intra and inter fibre bundles gum and fibrillate the bundles into smaller bundles and / or individual fibrils with less than 25pm diameter.

[0068] This can be achieved by using an enzyme degumming process or chemical degumming process or a combination of both.

[0069] During the degumming process, an acidic pretreatment of the fibres is required. In embodiments, the fibres are heated in diluted sulfuric acid, or 0.2% phosphoric acid solution, or 0.1 M sodium phosphate buffer with pH ranging between 2 - 3 and the temperature ranging between 50 - 100°C and duration 0.5 - 3 hours.

[0070] In the enzyme degumming process, in preferred embodiments, the fibres are soaked for 6 hours in an acid pectinase enzyme solution, 4 g pectinase powder / 100 g dry fibres, in a treatment solution ratio of 1 :20, with enzyme activity 30,000 U / g at pH 4 and 50 °C while maintaining continuous agitation, for removing the pectin. In other embodiments, the fibres are boiled at 80 °C in 0.1 M sodium phosphate buffer pH 2:3 for at least one hour. After boiling, the fibres may be soaked for 24 hours in the sodium phosphate buffer at room temperature. The fibres are thoroughly rinsed with tap water after removing the fibres from the phosphate buffers. Afterwards, the fibres are soaked for 6 hours in an acid pectinase enzyme solution, 4 g pectinase powder / 100 g dry fibres, in a treatment solution ratio of 1 :20, with enzyme activity 30,000 U / g at pH 4 and 50 °C while maintaining continuous agitation, for removing the pectin.

[0071] Then the fibres are soaked in an enzyme solution of laccase and acid xylanase using 4 g enzyme powder / 100 g dry fibres, in a treatment solution ratio of 1 :20, with laccase activity 2,000 U / g and xylanase activity 100,000 U / g, at pH 4.8 for 10 hours with continuous agitation at 50 °C for first 2 hours, then raised to 60 °C for the remaining 8 hours, for removing the lignin and hemicellulose. The enzyme treatment can also be conducted in an enzyme mix containing all 3 enzymes; pectinase, laccase, and xylanase. After completing the enzyme treatment, the fibres are scoured in an alkaline solution of 2% including soda ash, sodium hydroxide, potassium hydroxide, or lye concentrate at temperature 80 °C for 2 hours.

[0072] In any of the previous steps the treatment may include surfactant such as Triton X-100 and / or chelating agent such as Ethylenediaminetetraacetic acid (EDTA). After the scouring process, the fibres are beaten using rotary serrated rollers, steel or wooden mallet or any combination thereof.

[0073] Finally, the fibres are neutralized in a solution of 5% acetic acid for 30 mins at room temperature, then rinsed with tap water.

[0074] In the chemical degumming process, in preferred embodiments, the fibres are initially treated in a rich mix of alkaline pectinases enzyme solution, that may include but not limited to, polygalacturonases, pectin esterases, pectin lyases, pectate lyases, and rhamnogalacturonan lyases, at pH 8 - 9 and temperature 45°C - 80°C, for a duration of 2 - 48 hours depending on the treatment temperature.

[0075] Afterwards, the fibres are boiled at 90 - 100 °C for 2 to 3 hours in a solution containing 0.5 - 1% Sodium hydroxide, 0.1 - 0.5% hydrogen peroxide, 0.3% Ethylenediaminetetraacetic acid, in addition to, 0.3% sodium silicate or 1% sodium sulfite, while maintaining continuous agitation. After completing the chemical treatment, the fibres are neutralized in a 5% acetic acid solution and then rinsed in water.

[0076] The fibres morphology before and after degumming is illustrated in Figure 2.

[0077] Drying

[0078] After washing, the fibres are dried to a moisture content of less than 20%, preferably less than 15%. The first step in the drying is either roll squeezing to remove as much water as possible or centrifugal dewatering using a mechanized drying system.

[0079] In embodiments, the second drying step involves air drying the fibres in open air for several days depending on the ambient conditions or oven drying at temperature 80°C until the moisture content drops below 15%.

[0080] The resulting fibres at the end of the scraping method is shown in Figure 3, while the resulting fibres after the degumming method are shown in Figures 4.

[0081] Below is a Table which shows properties of the materials obtained using the abovementioned method steps.

[0082] Technical Data

[0083] Table 1 shows average properties of long textile fibres extracted from date palm leaflets after scraping and after degumming using the above methods.

[0084] It will be appreciated that variation may be made to the aforementioned embodiments, without departing from the scope of protection as defined by the claims.

[0085] For example, the method can also be used to extract long textile fibres from the leaflets of other palm species, including but not limited to washingtonia palm, oil palm, coconut palm, and sugar palm.

[0086] According to another aspect of the invention, there is provided a fibrous product derived using the aforementioned method of the first aspect of the invention. Fibrous products produced according to the method may be used to make or incorporated in, a myriad different items or products, including: an item of clothing or footwear: a sheet of flexible material; items for use in automotive or construction, (such as boards or insulation panels) or rope or twine.

[0087] Methodology for Wax Extraction

[0088] The method is shown diagrammatically as a series of steps in Figure 1 initial preparation.

[0089] The leaflets are separated from the date palm fronds either manually by hand, knife, or by using a mechanized system with blades to peel off the leaflets, which are then bundled for further processing.

[0090] Treatment

[0091] Fresh or dry leaflets may be boiled between 80°C to 100°C, preferably 80°C to 90°C, from 1 hour to 5 hours, either in water only or in a chemical solution which may include but is not limited to alkaline solutions, surfactants, or acidic buffers.

[0092] Drying

[0093] In embodiments, the leaflets are then air died in the sun for 1 -4 days or inside an oven at 80 °C until the moisture level drops below 15%, other drying techniques can be applied such as using microwave. In other embodiments, the leaflets are then air dried in the shade for 1 -4 days then sun dried for 2 - 4 days, or inside an oven at 80 °C until the moisture level drops below 15%, other drying techniques can be applied such as using microwave.

[0094] Beating

[0095] After the leaflets become fully dry, they are then beaten to release the crude wax. Beating may be done manually by hand or mechanically by passing the dry leaflets against a rotating wooden or metal beating blade.

[0096] Leaflets chopping (optional)

[0097] Leaflets may be chopped to loosen more wax. The chopping may be performed using a rotary cutter, pulverizer, or grinder.

[0098] Separation

[0099] A separation method is then applied to separate wax from any other residual vegetable matter or impurities. The separation method may include but is not limited to manual screening, centrifugal air flotation separations, or both.

[0100] Crude wax refinement

[0101] Refinement of the crude wax is done to purify the wax from the residual vegetable matter. This process may include but is not limited to 1 ) simply heating the crude wax over the melting point with continuous stirring to melt the wax 2) heating the crude wax powder in a solvent such as but is not limited to petroleum ether, xylene, toluene, alkanes, alkaline hydrogen peroxide, ethyl acetate, acetone, benzene, naphthas, alcohols or any other nonpolar organic solvent. The solvent extraction is performed using, but not limited to, a Soxhlet extractor, distiller, or CO2 extractor. In other embodiments, refinement of the crude wax is done to purify the wax from the residual vegetable matter. This process may include but is not limited to 1 ) simply heating the crude wax over the melting point with continuous stirring to melt the wax 2) dissolving and heating the wax within continuous stirring in a solvent such as, but is not limited to xylene, toluene, alkanes, alkaline hydrogen peroxide, ethyl acetate, acetone, benzene, naphthas, alcohols or any other non-polar organic solvent.

[0102] Bleaching (optional)

[0103] Bleaching may be carried out if needed to give a better appearance to the extracted wax. Chemical or other bleaching methods can be used such as hydrogen peroxide, sodium hypochlorite, acids such as but not only hydrochloric acid, chromo-sulphuric acid, phosphoric acid, Ozon bleaching or clays such as fullers earth bleaching.

[0104] Purification

[0105] After wax melting the melt or wax solvent mixture is purified by any purifying technique such as but not limited to 1 ) addition of adsorbents like active carbon, silica gel, activated clay, or any other adsorbent. 2) filtration by passing the wax solution through paper, cloth, or membrane. 3) centrifugation. Any of those techniques may be used separately or combined.

[0106] Mixing (optional)

[0107] Palm leaflets wax can be mixed with other additives or waxes to improve its properties like color, hardness, gloss, melting point, or any other needed properties to serve the final application. This process can be done after or before the cooling of the purified wax.

[0108] Cooling

[0109] Cooling of the wax may be done by any of the following methods but not limited to 1 ) air cooling by letting the wax air dry at room temperature or lower temperature, 2) cooling in a mold to produce well-shaped products, and 3) water cooling by exposing the wax melt to cold water. Formation

[0110] Solidified wax can be formed into any required shape such as but not limited to powder, pellets, flakes, and blocks. The resulting wax at the end of the extraction method is shown in Figure 5. The FTIR spectra of the resulting wax after the extraction method is shown in Figure 6.

[0111] Below is a Table which shows properties of a material obtained using the abovementioned method steps.

[0112] Technical Data

[0113] Table 2 Properties of surface wax extracted from date palm leaflets using the above method. It will be appreciated that variation may be made to the aforementioned embodiments, without departing from the scope of protection as defined by the claims.

[0114] For example, the method can also be used to extract surface wax from the leaflets of other palm species, including but not limited to washingtonia palm, oil palm, coconut palm, and sugar palm.

[0115] Wax products produced according to the method may be used to make or incorporated in, a myriad different items or products, including use in food, cosmetics, automobiles and furniture wax and as a coating for dental floss.

Claims

Claims1 . A method for producing textile fibres from raw palm material comprising the steps of: a) scraping palm leaflets to remove the non-fibrous surface layer; b) brushing the extracted fibres from step a) to remove residual surface impurities; and c) washing and drying the fibres from step b) to a moisture content of less than 20%, preferably less than 15%.

2. A method as claimed in claim 1 including the initial step of separating palm leaflets from the date palm fronds.

3. A method as claimed in claim 2 including the initial step before step a) of presoaking the palm leaflets.

4. A method as claimed in claim 3 therein wherein the pre-soaking step comprises pre- soaking in water from 1 to 5 days at ambient temperature.

5. A method as claimed in claims 3 or 4 where pre-soaking step comprises boiling or heating the leaflets in a liquid between 80°C to 100°C.

6. A method as claimed in claims 1 to 5 wherein the scraping is performed by using a reciprocating blunt scraper along the length of the leaflets.

7. A method as claimed in claim 1 to 6 wherein the scraping is performed using a rotating drum or decorticator having one or more rotating blunt scraping blades thereon.

8. A method as claimed in claim 7 the scraping step includes the palm leaflets being fed between the scraping blades and a stationary element such as a beater.

9. A method as claimed in claim 8 where the clearance between the rotating scraping blades and the stationary beater is between 0.1 to 0.4 mm.

10. A method as claimed in claim 1 to 6 wherein the scraping is performed by using a rotating cylinder with saw tooth wire, in which the leaflets are being fed using two feed rollers.1 1. A method as claimed in claim 10 where the rotating cylinder with saw tooth wire, has a tooth pitch between 6 - 16 teeth per inch, tooth angle between 40° - 60°, tooth height 1.5 - 5 mm, and wire thickness 0.4 - 1 mm.

12. A method as claimed in claim 1 to 11 wherein the drying step in c) includes roll squeezing or centrifugal dewatering.

13. A method as claimed in claim 1 to 11 wherein the drying step c) involves air drying the fibres in open air or in an oven.

14. A method as claimed in claim 1 including the step of d), preferably after step b), of removing gum from intra and / or inter fibre bundles.

15. A method as claimed in claim 14 where step d) includes treating with one or more enzyme solutions.

16. A method as claimed in claim 15 wherein the solutions include one or more of: pectinase, laccase and acid xylanase.

17. A method as claimed in claim 15 or 16 where step d) includes before treating fibres with an enzyme solution, before pretreating the fibres with an acidic solution, preferably at least 50°C, and more preferably at least 100°C, for a duration of at least 0.5 hour, preferably at least 3 hours.

18. A method as claimed in claim 17 wherein the acidic solution is a diluted sulfuric acid, or phosphoric acid, or sodium phosphate buffer.

19. A method as claimed in claim 17 or 18 wherein the acidic solution is less than pH 4, preferably less than pH 3 and preferably around pH 2.

20. A method as claimed in claim 17 to 19 including a rinsing step after treating with an acidic buffer.

21. A method as claimed in claim 17 to 20 including a step of soaking the fibres in a pectinase solution.

22. A method as claimed in claim 21 including an additional step of soaking the fibres in a solution of laccase, and / or xylanase.

23. A method as claimed in claim 15 to 20 including soaking the fibres in a solution of all of pectinase, laccase and acid xylanase.

24. A method as claimed in claim 21 to 23 subsequent to enzyme soaking, scouring the fibres with alkaline solution.

25. A method as claimed in claim 17 to 24 wherein step d) includes treating the fibres with a surfactant; the surfactant preferably being a constituent of the soaking solutions.

26. A method as claimed in claim 24 to 25 including the step of, after the scouring step, beating the fibres; optionally using rotary serrated rollers, hammer, mallet or any combination thereof.

27. A method as claimed in claim 17 to 26 wherein the fibres are neutralized in a solution of acetic acid for at least 15 minutes preferably 30 minutes, and then rinsed with water.

28. A method as claimed in claim 14 comprising boiling the fibres for preferably 2 to 3 hours in an alkaline solution.

29. A method as claimed in claim 28 where the alkaline solution includes sodium hydroxide and optionally hydrogen peroxide, optionally sodium silicate or sodium sulfite and optionally ethylenediaminetetraacetic acid.

30. A method as claimed in either claim 28 or 29 includes the subsequent step of neutralizing the fibres; preferably in an acetic acid solution.

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