Wool powder pigments

Abstract

The present invention relates to a process for making wool powder pigments comprising wool fibres that have been chemically treated, dyed and then milled to powder. The wool powder pigments demonstrate high dye loading and can be used in a variety of coating compositions.

Description

[0001] WOOL POWDER PIGMENTS

[0002] 1. FIELD OF THE INVENTION

[0003] The present invention relates to wool powder pigments comprising wool fibres that have been treated, dyed and then milled to powder. The invention also relates to the manufacture and usage of wool powder pigments.

[0004] 2. BACKGROUND TO THE INVENTION

[0005] Growing consumer awareness has greatly increased demand for biobased materials. The demand for biobased materials has also increased as regulatory bodies around the globe impose strict criteria on products regarding their biodegradability, recyclability and sustainability. However, it is not always easy to find biobased materials that meet the environmental standards required, while functioning as well as synthetic materials.

[0006] Wool is natural, renewable and biodegradable. It can be converted into many types of biobased products. The use of wool-based pigments in inks, paints, coatings and bioplastics can help meet the demand for biobased materials.

[0007] A pigment is a coloured, insoluble solid substance that is physically and chemically unaffected by the media in which it is suspended. Inorganic pigments generally comprise metal oxides, sulfides or other salts, while organic pigments are coloured organic compounds.

[0008] Pigments can also be made by reacting a soluble dye with an inert base to form an insoluble, coloured material. Wool powder (made by grinding wool fibres into small particles) is thought to be a potential inert base for pigment manufacture (Guo, et al., 2020).

[0009] Pigments comprising dyed wool powder are non-toxic and environmentally friendly. In addition, such pigments may also retain some of the desirable properties of the original wool fibre including moisture control and flame retardancy.

[0010] Unfortunately, converting wool fibres into a dyed wool powder pigment material involves technical challenges. Wool fibres are difficult to mill to powder because of their softness and elasticity. Milling takes a very long time, using a great deal of energy. Usually, several intermediate milling steps are needed before arriving at a final product of sufficient fineness (Wen, et al., 2009).

[0011] For example, to achieve wool powder of 10pm size from 1 mm wool snippets using the process described in WO 2020026161, wool fibres must be wet milled for 8-9 hours then spray dried. This 10|jm powder can then be milled with a micro mill to achieve a size of 500nm but the total milling time is 10-12hrs. This method of production is long and expensive.

[0012] Wool powder of l-10pm is useful but some applications, for example ink jet printing, require nanometer scale pigments. While particle sizes of less than 100 nm have been achieved by some researchers, it is not generally economically feasible to mill wool fibres down to this size, particularly at large scale.

[0013] Various chemical pre-treatments have been employed to improve milling efficiency, with varying success. These include sodium hypochlorite, hydrogen peroxide, tri-n- butylphosphine, thioglycolic acid, peracetic acid and sodium sulphite / sodium hydroxide (Wen, et al., 2009). Unfortunately, pre-milling treatments tend to utilise dangerous, toxic and / or environmentally unfriendly chemicals.

[0014] The second problem is that wool fibres must be capable of high dye loading to achieve the strength of colour required in a pigment. Pigments are mixed with binders appropriate for their intended usage, which dilutes their colour strength. They must therefore be very strongly coloured.

[0015] Unfortunately, wool fibres do not absorb dye particularly well, with dye loading values of about 13%. This level of dye loading doesn't achieve the strength of colour needed in a commercially viable pigment.

[0016] Wool powder researchers have tried dyeing wool fibres after they have been ground into powder. Because wool powder has a greater surface area, dye may enter the powder particles more easily than the unground wool fibres.

[0017] For example, Wen et al. (Wen, et al., 2009) dyed 2g samples of wool powders that were produced using different milling processes, noting that the % of dye uptake increased as the particle size of the wool powder decreased.

[0018] Guo et al. (Guo, et al., 2020) also describes dyeing small amounts of wool powder and explores the use of dyed wool powder as a pigment. Guo et al. use wool powder produced by milling wool fibres that were pre-treated with 0.5% NaCIO solution at room temperature (Xu, Cui, Li, & Guo, 2004). Han et al. describes dyeing 1g of wool powder produced using the same process (Han, Guo, Wang, Song, & Xu, 2023).

[0019] Some of the pre-treated wool powders described above achieved good dye loading, but it is not feasible to dye wool powder in large-scale processing. The dye process comprises several steps of dyeing and rinsing. Between each of these steps, fresh water must be added and removed. This means that the powder being dyed must be filtered and then retained ready for the next step. However, throughout the process the viscosity of the wool powder / dye slurry must be kept low to facilitate handling, such that a great deal of water must be added and removed at each step. Removal of the water requires an extremely fine filter to prevent loss of the tiny wool powder particles. Therefore, water removal is very slow and uses a lot of energy.

[0020] Also, at each filtration step there are inevitably losses. Wool powder losses are usually much greater than wool fibre losses, due to their relative size difference. In addition, wool powder is more valuable than wool fibre (due to costs associated with milling) and so losses at this stage of the process effect the economics to a greater extent than loss of wool fibre.

[0021] With sustainability in mind, the extra water, energy, time and low yields do not bode well for carbon footprint calculations on dyeing wool powder.

[0022] There is therefore a need for a process of treating wool fibres so as to improve milling efficiency and dye loading that overcomes at least some of the disadvantages of known processes and / or at least to provide the public with a useful choice.

[0023] In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents is not to be construed as an admission that such documents, or such sources of information, in any jurisdiction, are prior art, or form part of the common general knowledge in the art.

[0024] 3. SUMMARY OF THE INVENTION

[0025] In the process of the invention wool fibre is converted into a wool powder pigment by chemically processing and dyeing the fibre, prior to milling to produce a coloured wool powder. The coloured wool powder constitutes a pigment which can be combined with suitable excipients to make inks and other coating compositions.

[0026] In one aspect the invention provides a process for preparing wool powder pigment comprising:

[0027] (a) submerging wool fibres in an about 5 to about 20 wt / v% aqueous solution of strong alkali for about 10 to about 45 minutes to form a wool slurry,

[0028] (b) adding water to the wool slurry and mixing,

[0029] (c) adding a solution of acidified peroxide to the wool slurry while mixing, until the pH of the mixture reaches about 4,

[0030] (d) filtering the wool slurry to remove soluble impurities while retaining the treated wool fibres,

[0031] (e) dyeing the treated wool fibres, and

[0032] (f) milling the dyed, treated wool fibres to produce wool powder pigment. The invention also provides a wool powder pigment with a dye loading of at least 15%, preferably at least 20%. In one embodiment the wool powder pigment comprises at least 15 wt% dye, preferably at least 20 wt% dye.

[0033] In another aspect the invention provides a wool powder pigment with water absorbency of less than 200 ml / lOOg.

[0034] In another aspect the invention provides a wool powder pigment comprising at least 15 wt% dye which has a water absorbency of less than 200 ml / lOOg.

[0035] 4. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The invention will now be described by way of example only and with reference to the drawings in which:

[0037] Figure 1 comprises SEM micrographs (200x) of untreated wool fibre snippets (A), treated wool fibre snippets IW15-30 (B) and treated wool fibre snippets IW120 (C) as described in Example 1.

[0038] Figure 2 comprises a SEM micrograph (1500x) of treated wool powder, as described in Example 2.

[0039] Figure 3 is a diagram showing different milling pathways for treated wool fibres (dyed and undyed). For undyed treated wool powder, the dyeing step is omitted.

[0040] Figure 4 is a series of photographs showing (A) Reactive dye bath solutions (10% dye on weight of wool (oww)) containing dyed IW15 wool powder (left) compared to dyed untreated wool powder (right) and (B) Acid dye bath solutions (20 % dye oww) containing dyed IW15 wool powder (left) compared to dyed untreated wool powder (right); as described in Example 4.

[0041] Figure 5 is a photograph showing a comparison of coatings prepared using the wool powder pigment of the invention and a pigment comprising a dyed untreated wool powder control as discussed in Example 6.

[0042] Figure 6 is a photograph of a masterbatch produced using the wool powder pigment of the invention, as described in Example 9.

[0043] 5. DETAILED DESCRIPTION OF THE INVENTION

[0044] 5.1 Definitions and abbreviations

[0045] As used herein the term "comprising" means "consisting at least in part of". When interpreting each statement in this specification that includes the term "comprising", features other than that or those prefaced by the term may also be present. Related terms such as "comprise" and "comprises" are to be interpreted in the same manner. The term "about" as used herein means a reasonable amount of deviation of the modified term such that the end result is not significantly changed. For example, when applied to a value, the term should be construed as including a deviation of + / - 5% of the value.

[0046] Whenever a range is given in the specification, for example, a temperature range, a time range, or a composition range, all intermediate ranges and subranges, as well as all individual values included in the ranges given are intended to be included in the disclosure. In the disclosure and the claims, "and / or" means additionally or alternatively. Moreover, any use of a term in the singular also encompasses plural forms.

[0047] The term "dye" refers to a soluble, coloured substance which chemically bonds to the material that is being dyed. Unlike pigments, which are coloured, insoluble particles, dyes impart colour to a material by becoming chemically integrated into the material.

[0048] The term "dye exhaustion" refers to the proportion of dye absorbed by the fiber being dyed, in relation to that remaining in the dye bath. It is expressed in terms of a percentage (wt of dye lost to the fibre per weight of the original dye in solution). For example, if the exhaustion of the dye bath is 50% then it means that 50% of the dye in the dye bath has moved from the dye solution into the fiber.

[0049] The term "dye loading" refers to the amount of dye taken up by the fibre. Dye loading depends on the concentration of dye used. Dyes are usually used at 10-20% wt / wt wool. If a dyeing process uses 10% dye and has 100% dye exhaustion then the dye loading will be 10%. A dyeing process using 20% dye with 80% dye exhaustion would give dye loading of 16%.

[0050] The term "volume average diameter" means the diameter of a sphere that has the same volume as a given particle (averaged). References to particle size refer to the volume average diameter of the particles unless otherwise specified. Where a particular size is provided for a powder, the size refers to the D50 (meaning that 50% of the particles are smaller than this size).

[0051] It is intended that reference to a range of numbers disclosed herein (for example, 1 to 10) also incorporates reference to all rational numbers within that range (for example, 1, 1.1, 2, 3, 3.9, 4, 5, 6, 6.5, 7, 8, 9 and 10) and also any range of rational numbers within that range (for example, 2 to 8, 1.5 to 5.5 and 3.1 to 4.7) and, therefore, all sub-ranges of all ranges expressly disclosed herein are hereby expressly disclosed. These are only examples of what is specifically intended and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application in a similar manner. 5.2 The process of the invention

[0052] The process of the invention converts wool fibres into a wool powder pigment (dyed wool powder) with properties that make it ideal for use in a variety of applications, including applications to which wool powders have previously been unsuited, such as ink jet printing. The process can be applied to bulk wool fibres so as to make commercially useful amounts of wool powder pigment in reasonable time with minimal energy expenditure.

[0053] Strong alkali is generally avoided in wool processing because it quickly destroys the structure of the wool fibres. However, the inventors have determined that a fast alkali submersion, followed by neutralisation with acidified peroxide, has a positive effect on wool fibres, with respect to dye loading and downstream milling processes.

[0054] In a first aspect the invention provides a process for preparing wool powder pigment comprising:

[0055] (a) submerging wool fibres in an about 5 to about 20 wt / v% aqueous solution of strong alkali for about 10 to about 45 minutes to form a wool slurry,

[0056] (b) adding water to the wool slurry and mixing,

[0057] (c) adding a solution of acidified peroxide to the wool slurry while mixing, until the pH of the mixture reaches about 4,

[0058] (d) filtering the wool slurry to remove soluble impurities while retaining the treated wool fibres,

[0059] (e) dyeing the treated wool fibres, and

[0060] (f) milling the dyed, treated wool fibres to produce wool powder pigment.

[0061] In the first step of the process of the invention, wool fibres are submersed in an aqueous solution of strong alkali (strong alkali solution). The term "wool fibres" as used herein includes scoured wool fibre obtained from sheep or other mammals including but not limited to goat, camel, alpaca, llama, vicuna, qiviut, rabbit, possum and the like. Scouring is the process by which raw wool is washed to remove grease, dirt and suint (animal perspiration). Suitable wool fibres include but are not limited to merino, cashmere, mohair and angora.

[0062] In one embodiment the wool fibres are about 0.1 to about 5 mm in length, preferably about 0.5 to about 1, 2, 3 or 4 mm, more preferably about 1 mm in length. Wool fibres of this length can be produced using a range of standard dry mills such as rotary, guillotine, hammer, cone and ball / bead mills or any other standard technique. In one embodiment the strong alkali is selected from sodium hydroxide and potassium hydroxide, preferably sodium hydroxide. In one embodiment the pH of the aqueous solution of strong alkali is at least 13.

[0063] In one embodiment the aqueous solution comprises about 8 to about 15 wt / v%, more preferably about 10 wt / v% strong alkali. In one embodiment, the aqueous solution of strong alkali contains no alcohol.

[0064] In the process of the invention, the wool fibres are preferably submerged in the smallest volume of strong alkali solution possible to achieve "wetting out". Wetting out is when the wool fibres are totally saturated. The process of the invention can be carried out at any scale, provided that there is sufficient volume of strong alkali solution to wet out the wool fibres.

[0065] In one embodiment the ratio of wool fibres to the aqueous solution of strong alkali is about 1 kg to about 5 L.

[0066] The timing of exposure to the aqueous solution of strong alkali is crucial. The wool fibres are submerged in the aqueous solution of strong alkali for just enough time to incur surface damage without comprising their structural integrity - between about 10 and about 45 minutes. If left too long, excessive protein hydrolysis will cause the wool fibres to become slimy and unsuitable for the remaining process steps.

[0067] The high concentration of strong alkali encourages lanthionisation rather than hydrolysis. Lathionisation is the process in which the disulfide bonds of the keratin proteins in the wool break and some of the cysteine residues are replaced with lanthionine. When the pH rises (later in the process) and the disulfide bonds rejoin, the crosslinks in the keratin proteins will be less flexible than the original crosslinks. This makes the treated wool fibres brittle and less water absorbing compared to the original wool.

[0068] The ideal submersion time within the 10-45 minute window depends on the scale of the process, with larger scale batches potentially taking longer than smaller batches. The ideal time will also depend on the concentration of the strong alkali solution and the equipment used. For example, differently designed mixing apparatus may impact how quickly the wool fibre is hydrolysed. A person skilled in the art can determine the ideal time for a particular batch by monitoring the colour of the solution, as well as periodic visible light microscopy of the wool fibres. Alternatively, small samples of wool fibre can be removed periodically and assessed using a cold dye test, as described in Example 2.

[0069] In some cases a trial run may be required to establish the ideal submersion time for a particular batch of wool fibres, using particular equipment. In one embodiment the wool fibres are submerged in an aqueous solution of strong alkali for about 10, 11, 12, 13, 14 or 15 to about 20, 25, 30, 35 or 40 minutes, preferably about 15 to 25, 30, 35 or 40 minutes, more preferably about 15 to 20 or 15 to 30 minutes.

[0070] During submersion in the aqueous solution of strong alkali, the wool fibres form a thick wool slurry. Once the wool fibres have been submerged in strong alkali solution for the requisite time, water is added to the wool slurry to dilute it so it can be easily mixed. If the wool fibres have been properly processed in step (a), it will be necessary to dilute the mixture in step (b) in order to stir it. Excess water added in step (b) will necessitate more acid in step (c) and more filtration in step (d), so only the minimum volume of water needed to mix the slurry should be added in step (b).

[0071] In one embodiment the solution of strong alkali is diluted by about 50 w / v% in step (b).

[0072] In step (c), while stirring the wool slurry, a solution of acidified peroxide is added and the combination mixed until the pH of the mixture reaches about 4. As used herein the term "solution of acidified peroxide" refers to a solution comprising aqueous hydrogen peroxide and aqueous weak acid. As used herein the term "weak acid" means an acid chemical that does not dissociate completely in water. Examples of suitable weak acids include, but are not limited to, acetic and formic acid.

[0073] The solution of acidified peroxide should not be made in situ. The aqueous hydrogen peroxide and weak acid should be pre-mixed before being added to the wool slurry.

[0074] In one embodiment the aqueous hydrogen peroxide is about 5-20 w / v%.

[0075] In one embodiment the aqueous weak acid is aqueous formic acid, preferably 85 w / v%.

[0076] In one embodiment the solution of acidified peroxide comprises about 10: 1 to 1: 1 v / v aqueous weak acid mixed with aqueous hydrogen peroxide.

[0077] In one embodiment the solution of acidified peroxide comprises 5 w / v% aqueous hydrogen peroxide mixed with 85 w / v% aqueous formic acid in about a 2: 1 ratio v / v.

[0078] The relative amounts of aqueous hydrogen peroxide and aqueous weak acid used to make the acidified peroxide should be such as to avoid production of performic acid while ensuring an excess of hydrogen peroxide available in the wool slurry to smother the production of toxic hydrogen sulphide. A person skilled in the art would be able to calculate how to ensure an excess of hydrogen peroxide during this step of the process. For example, for 4 kg of wool submerged in 20L of 10 wt / v% NaOH solution, about 3.2L of formic acid (85 w / v%) and about 6L of hydrogen peroxide (5 w / v%) will be needed. It may take several minutes for the pH to change to about 4, after which time the wool slurry is filtered to remove soluble impurities. The wool fibres are retained while the soluble impurities wash out with the water.

[0079] In one embodiment the wool slurry is filtered through a 60 to about 300 pm mesh screen. In one embodiment the wool slurry is filtered through a 150 pm mesh screen. The size of the filter selected balances the need to reduce the yield loss associated with large mesh against the increased processing time caused by a small mesh. As the diameter of wool fibre is about 35 pm, there is a small loss of wool fibres that orient so as to pass through the filter.

[0080] Suitable filtration devices include but are not limited to stationary sieves, vibratory sieves and vacuum filters.

[0081] The wool fibres treated in accordance with steps (a) to (d) above have properties that make them uniquely suited for conversion into pigments, by dyeing and then milling the fibres. Such wool fibres are herein referred to as "treated wool fibres". The term "untreated wool fibres" refers to wool fibres that have not undergone the process of steps (a) to (d).

[0082] The treated wool fibres are dyed in step (e). A dye is a colourant which chemically bonds to the substrate to which it is applied. Dyes are soluble compounds. Any dye with a wool affinity can be used in the process of the invention. Suitable types of dye include, but are not limited to acid, reactive, chrome, pre-metallised, metal complex, vat, azoic, direct, basic, natural and sulphur. In one embodiment the dye is an acid or reactive dye.

[0083] Examples of suitable dyes for use in the process of the invention include but are not limited to C.I Reactive 65, C.I Reactive Red 84, C.I Reactive Blue 69, C.I Reactive Yellow 39, C.I Acid Blue 324, C.I Acid Blue 127, C.I Acid Red 249, C.I Acid Red 111, C.I Acid Black 222, C.I Acid Black 58, C.I Acid Yellow 59, C.I Acid Yellow 235, FDC Red 4, DC Red 6, DC Red 22, DC Red 28, DC Red 30, DC Red 40, CD Orange 4, CD Yellow 5, CD Yellow 6, CD Yellow 8, FDC Green 3, DC Green 5, FDC Blue 1, betanine, carmine, copper chlorophyline, methylene blue, anthocyanins, caramel and riboflavin.

[0084] Wool has a long history of being dyed, and the principles of the dyeing wool are well understood. The treated wool fibres can be dyed using any standard technique known in the art. The treated wool fibres may be dried prior to dyeing or may be dyed directly after filtration, while still wet. In one embodiment treated wool fibres are dried at about 30 to about 50°C using any technique commonly used in the art, prior to dyeing. Generally, the dyeing process involves dissolving the dye in water at a temperature and pH suitable for the dye, adding suitable dye auxiliaries and then mixing in the treated wool fibres, to be left for a set period of time. The exact process will vary depending on the type of dye.

[0085] In one embodiment in step (e) the treated wool fibres are dyed with a loading of about 15 to about 30% dye, preferably about 15 to about 20% dye.

[0086] In one embodiment, step (e) results in a dye exhaustion of about 80, 85 or 90 to about 100%.

[0087] In one embodiment, steps (a) to (e) of the process of the invention increase dye loading of the wool fibres by at least 10, 12, 15, 18, 20, 22, 24, 26, 28 or 30%, compared to untreated wool fibres. The increase in dye loading will depend to some extent on the nature of the dye used.

[0088] Following the dyeing step, the dyed, treated wool fibres of step (e) are milled to produce a wool powder pigment that comprises dyed wool powder.

[0089] In one embodiment, the process provides wool powder pigment, with a % yield of at least 80, 90, 95 or 97%. Such high yields are impossible to obtain where wool fibres are first milled and the resulting wool powder is dyed.

[0090] In one embodiment, step (e) of the first aspect of the invention is omitted.

[0091] Although the treated wool fibres have properties that make them ideal for conversion into pigments, the treated wool fibres, when milled, also have useful applications where a colourless material is required, for example, as in overprint varnish formulations. The treated wool fibres also have advantageous water absorption properties and can be more easily milled than wool fibres treated with other chemical protocols.

[0092] Accordingly, in a second aspect the invention provides a process for preparing treated wool powder comprising:

[0093] (a) submerging wool fibres in an about 5 to about 20 wt / v% aqueous solution of strong alkali for about 10 to about 45 minutes to form a wool slurry,

[0094] (b) adding water to the wool slurry and mixing,

[0095] (c) adding a solution of acidified peroxide to the wool slurry while mixing, until the pH of the mixture reaches about 4,

[0096] (d) filtering the wool slurry to remove soluble impurities while retaining the treated wool fibres, and

[0097] (e) milling the treated wool fibres to produce treated wool powder. The preferred embodiments of the first aspect (steps (a) to (d) also apply to the second aspect.

[0098] The milling process is unaffected by the presence or absence of the dye in the treated wool fibres. Therefore, the statements below also apply to both the first and second aspect of the invention, irrespective of whether the treated wool fibres are referred to as "dyed" or not.

[0099] During the milling process, the dyed, treated wool fibres are reduced in size from about 1 mm length fibres to particles of about 350, 400, 450 or 500 nm to 100 pm size (D50 volume average diameter). Wool particles of this size are described as wool powder.

[0100] A variety of milling apparatus and techniques may be used to achieve the size and shape of wood powder particles required. Particles of 10 pm can be achieved using standard wet milling or dry milling techniques. Wet milled wool powder may be dried following milling, usually by spray drying. Dyed wool powder must be dried prior to dry milling. However, dry milling avoids a post-milling spray drying step.

[0101] Suitable wet milling apparatus include, but are not limited to, attritor mills, horizontal media mills, cascading type ball and / or bead mills and basket or batch mills. In one embodiment, wet milling is carried out in an attritor mill.

[0102] Suitable dry milling apparatus include rotary, guillotine, hammer, cone, ball / bead, air jet and cold / cryogenic mills.

[0103] The brittle nature of the dyed, treated wool fibres allows them to be milled to powder much faster than untreated wool fibres (dyed or undyed), providing economic benefits.

[0104] If very fine wool powder is desired, dyed wool powder of less than about 150 pm average size (achieved via conventional wet or dry milling) can be subjected to micro milling. Micro mills are ball / bead mills that use very fine grinding media, for example, the MicroMedia™ XI agitated bead mill.

[0105] Such micro mills can produce wool powders of less than about 500 nm average size (see Example 7).

[0106] Untreated wool fibre must generally be milled to about 10 pm before it is suitable for micro milling. 10 pm wool powder can be made via wet milling and spray drying etc, but this is a long, slow process, making it uneconomical to produce very fine wool powder.

[0107] In contrast, the treated wool fibre produced by the pre-milling steps of the process of the invention is brittle enough that a larger particle size (for example 150 pm) is acceptable for micro milling, greatly speeding up the process of making very fine wool powder. The brittleness of the dyed, treated wool fibres of the invention also allows air jet milling to be used to obtain 10 m wool powder in relatively little time. Untreated wool fibres need to be milled for much longer to reach this size.

[0108] Figure 3 shows the various options for milling the dyed (and undyed) treated wool fibres to produce wool powder pigment (or treated wool powder) of the invention.

[0109] As shown in Example 7, treated wool fibres (after cone milling to 150 pm) can be introduced directly into the micro mill to produce 500nm particles within 3-4 hours. The process of the invention achieves significant savings with respect to time, power usage and equipment requirements, compared to earlier attempts to produce dyed wool powder pigments.

[0110] In one embodiment the dyed wool fibres are milled to produce wool powder pigment of about 100, 80, 60, 40, 20 or 10 pm or less particle size. In one embodiment the dyed wool fibres are milled to produce wool powder pigment of about 10 pm particle size.

[0111] In one embodiment the wool powder is further milled in a micro mill to produce wool powder pigment of about 500, 400, 300, 250 or 200 nm or less particle size. In one embodiment the wool powder is further milled in a micro mill to produce wool powder pigment of about 500 to about 200 nm particle size.

[0112] In one embodiment the wool powder is further milled in a micro mill to produce wool powder pigment of about 500 to about 350 nm particle size.

[0113] In one embodiment the wool powder is further milled in a micro mill with an ink carrier, with or without an ink dispersant.

[0114] In one embodiment the process of the invention decreases the time required to mill treated wool fibres from about 1 mm to about 10 pm or less, relative to untreated wool fibres. In one embodiment the time is decreased by about 20, 30, 40, 50, 60 or 70%.

[0115] In one embodiment the process provides a wool powder pigment with a dye loading of about 10 to about 30%, preferably about 10 to 20% and more preferable about 12 to 18%.

[0116] In one embodiment the process of the invention decreases water absorption of the wool powder pigment relative to a dyed wool powder that has not been treated prior to milling. In one embodiment the process of the invention decreases water absorption by about 10, 15, 20 or 25%. In one embodiment the treated wool fibres are dyed. In one embodiment the treated wool fibres are undyed.

[0117] In one aspect the invention provides a process of obtaining wool powder pigment of less than 250 nm by micro milling dyed, treated wool powder of at least 150 pm. A person skilled in the art would understand how to select the appropriate milling technique and apparatus to produce a wool powder pigment of a particular size.

[0118] The process of the invention changes the wool fibre so as to reduce the time required to mill the fibre to a powder. However, it does so while also chemically changing the wool fibre so as to improve dye uptake and decrease water absorbance.

[0119] In Example 1 wool fibre samples were immersed in a solution of strong alkali for times ranging from 15 to 120 min before dilution and neutralisation. It was found in Example 2 that the immersion for 15 to 30 minutes was sufficient to allow the desired chemical changes to occur, without destroying the structural integrity of the wool fibres needed for uptake of dye molecules. In addition, the processing steps (a) to (d) changed the properties of the wool fibres so as to make them easier and faster to mill (see Example 3). Example 4 show that the process of the invention has also affected the properties of the wool fibres with respect to dye loading. The treated wool fibres show a higher dye loading and dye exhaustion than untreated control fibres. Example 5 shows that steps (a) to (d) of the process of the invention affects the dye loading properties of the wool fibres, with treated wool fibres loading more dye than untreated. Example 6 shows that the process of the invention leads to wool powder pigments and treated wool powders with lower water absorption values than comparable dyed wool powders.

[0120] Example 7 shows that the process of the invention can produce very fine wool powder pigments relatively quickly and economically. Example 8 shows that the wool powder pigments of the invention have stronger colour than untreated wool powder. Examples 9 and 10 demonstrate the use of the wool powder pigments in coating compositions. Example 11 shows that the process can be scaled up easily and still obtain the same wool powder pigment. Example 12 demonstrates the process of the invention in which the wool powder is milled with an ink excipient.

[0121] 5.3 Wool powder pigment

[0122] The process of the invention provides wool powder pigments with superior properties. Wool powder pigments are wool powders made from dyed wool particles. The wool powder pigments of the invention have been produced by milling dyed wool fibres, wherein the wool fibres have been chemically pre-treated prior to dyeing and milling. In one aspect the invention provides a wool powder pigment prepared in accordance with the first aspect of the invention.

[0123] In another aspect the invention provides a wool powder pigment of about 10 pm to about 250nm. In one embodiment the wool powder pigment has a size of about 1 to about 10 pm. In one embodiment the wool powder pigment has a size of less than about 1 pm. In one embodiment the wool powder pigment has a size of about 250 to about 1000 nm. In one embodiment the wool powder pigment has a size of about 250 to about 500 nm.

[0124] In another aspect the invention provides a wool powder pigment with a dye loading of at least 15%, preferably at least 20%. In one embodiment the wool powder pigment comprises at least 15 wt% dye, preferably at least 20 wt% dye.

[0125] In another aspect the invention provides a wool powder pigment with water absorbency of less than 200 ml / lOOg.

[0126] In another aspect the invention provides a wool powder pigment comprising at least 15 wt% dye which has a water absorbency of less than about 200 ml / lOOg.

[0127] 5.4 Treated wool powder

[0128] The process of the invention where the dyeing step is omitted produces undyed, treated wool powder. This wool powder also enjoys superior properties, conferred by the premilling treatment steps (a) to (d), such as low water absorbency.

[0129] In one aspect the invention provides a treated wool powder prepared in accordance with the second aspect of the invention.

[0130] In another aspect the invention provides a treated wool powder with water absorbency of less than about 150 ml / lOOg. In one embodiment the treated wool powder is about 10 pm to about 250nm. In one embodiment the treated wool powder has a size of about 1 to about 10 pm. In one embodiment the treated wool powder has a size of less than about 1 pm. In one embodiment the treated wool powder has a size of about 250 to about 1000 nm. In one embodiment the wool powder has a size of about 250 to about 500 nm.

[0131] 5.5 Uses of the wool powder pigments of the invention

[0132] The wool powder pigments of the invention can be used in a variety of applications by combining them with suitable binders and excipients.

[0133] In one aspect the invention provides a composition comprising a wool powder pigment of the invention and one or more binders and / or excipients. Similarly, the invention also provides a composition comprising treated wool powders of the invention and one or more binders and / or excipients.

[0134] For example, a wool powder pigment composition may comprise an ink for use in printing applications such as offset, gravure, flexographic, screen, ink jet and transfer printing. Suitable excipients for inclusion into ink compositions include but are not limited to solvents, resins, lubricants, UV protectors, solubilisers, surfactants, fluorescents, pigment carriers and the like.

[0135] In the process of the invention, the milling step may be carried out in the presence of an ink pigment carrier or resin (such as glycerol, acrylic resin or the like) with or without a dispersant (for example, a polymeric dispersant or a surfactant-based dispersant).

[0136] Direct milling of wool powder pigments into carriers and resins has been performed with and without dispersants at wool powder starting sizes of around 10pm and around 150pm. The resulting product is then combined with other ink excipients to make the final product (see Example 12).

[0137] In one embodiment the composition is an ink comprising about 0.1 to about 40% w / v wool powder pigment, preferably about 0.1 to about 10% w / v, more preferably about 5% w / v. The inks may be used to print surfaces including paper and textiles, replacing inks comprising synthetic pigments or those containing heavy metals such as copper, cobalt or chrome.

[0138] In one embodiment the composition is a biopolymer comprising about 0.1 to about 40% w / v wool powder pigment, preferably about 5 to about 20% w / v, more preferably about 10% w / v. In one embodiment the biopolymer is a PHA (polyhydroxy alkanoate) biopolymer. In one embodiment the PHA is polyhydroxy-butyrate-co-valerate).

[0139] In one embodiment the composition is an over print varnish comprising about 0.1 to about 15% w / v wool powder pigment or treated wool powder, preferably about 0.1 to about 10% w / v, more preferably about 3% w / v. In one embodiment the over print varnish comprises urethane acrylate, preferably aliphatic urethane acrylate. In one embodiment the overprint varnish comprises wool powder pigment. In another embodiment the overprint varnish comprises treated wool powder.

[0140] In one embodiment the invention provides a method of making an ink comprising:

[0141] (a) submerging wool fibres in an about 5 to about 20 wt / v% aqueous solution of strong alkali for about 10 to about 45 minutes to form a wool slurry,

[0142] (b) adding water to the wool slurry and mixing, (c) adding a solution of acidified peroxide to the wool slurry while mixing, until the pH of the mixture reaches about 4,

[0143] (d) filtering the wool slurry to remove soluble impurities while retaining the treated wool fibres,

[0144] (e) dyeing the treated wool fibres, and

[0145] (f) milling the dyed, treated wool fibres in a cone mill to about 150 pm size;

[0146] (g) milling the wool powder pigment in a micro media mill with one or more ink carriers and optionally on or more ink dispersants;

[0147] (h) combining the wool powder pigment and carrier / dispersant composition with ink excipients to produce an ink.

[0148] In the above aspects, in one embodiment the wool powder pigment comprises at least 15 wt% dye and has a water absorbency of less than about 200 ml / lOOg.

[0149] 6. EXAMPLES

[0150] Example 1: Treating wool fibres (steps (a) to (d) process of the invention)

[0151] Treated wool fibres (IW"X") were prepared using the following method, where "X" refers to the duration time that the wool fibres were submerged in the aqueous solution of strong alkali in step (a) before dilution in step (b). The recipe and method are shown below.

[0152] Table 1: Recipe

[0153] Method

[0154] 1. Add 5.4 L water to a 10 L bucket. Slowly add 600 mL 50% hydrogen peroxide to the bucket.

[0155] 2. Slowly add 3.2 L 85% formic acid to the bucket while stirring. Put the lid on and leave in the fume hood.

[0156] 3. Add 15 L water and 5 L 40% sodium hydroxide to a 25 L bucket and set aside.

[0157] 4. Add 4 kg 1 mm wool to the tank. Ensure the drain valve is closed.

[0158] 5. Add the 10% sodium hydroxide to the tank and mix to wet out with the large plastic paddle.

[0159] 6. Once the wool is wet out, start the timer, and continue to mix manually for 15 minutes. 7. After X minutes have elapsed, add 20 L water to the tank and mix with the paddle until the mixture becomes a uniform consistency.

[0160] 8. Lower the lid onto the tank.

[0161] 9. Start the agitator and adjust the speed until the slurry begins mixing well (around 15-20). The stirring will need to be adjusted as the slurry thins out.

[0162] 10. Slowly add the acidified peroxide prepared in the 10L bucket. The addition should take around 25 minutes. The final pH should be 4.0.

[0163] 11. Turn down the agitation and sieve through a 150 pm screen.

[0164] 12. Neutralise the waste solution to pH 6-10 using 40% sodium hydroxide.

[0165] 13. Evenly crumble the sieved IW15 onto perforated tray dryer trays lined with tray dryer fabric.

[0166] 14. Tray dry at 50 °C for approximately 5 hours, until the IWX is dry and not discoloured.

[0167] Treated wool fibre products IW15, IW30, IW55 and IW120 were prepared by immersing wool fibres in strong alkali solution for 15, 30, 55 and 120 minutes, respectively.

[0168] Example 2: Structural integrity of treated wool fibres

[0169] Wool fibres were treated in accordance with steps (a) to (d) of the process of the invention, as exemplified in Example 1, with changes to the concentration of sodium hydroxide solution and time of submersion. As discussed above, the concentration of the strong alkali solution and submersion time determine the level of structural change. Monitoring the loss of structural integrity and chemical decomposition is important to ensure that the wool characteristics are not lost in their entirety and only modified to deliver favourable and novel properties.

[0170] One indication of excessive chemical breakdown is the dissolution of the protein during the alkali step of the IW process described in Example 1. A simple test for this to note the colour of the solution. The less coloured the solution, the lower the concentration of protein in solution.

[0171] Table 2 shows the concentration and times tested.

[0172] Table 2: Results of varying alkali exposure time in process of the invention

[0173] In tests A to D, the agents used in steps (a) and (c) of the process of the invention remain constant, while the duration of the alkaline submersion increases. Tests A and B show that submersion for 55 or 120 min results in undesirable loss of structural integrity. Tests C and D show that 15 and 30 min are appropriate digestion times. Tests E to G show that strong acid cannot be used to in step (c) as this causes yellowing of the wool fibres. Test H shows that a sodium hydroxide concentration of 40% is too high, leading to loss of structural integrity. Tests I to K show that the wool fibres must be submerged in an aqueous solution of strong alkali of the requisite concentration. Ethanolic potassium hydroxide did not produce the chemical change needed in the fibre while sodium hypochlorite produced too much yellowing to be useful.

[0174] A definitive indication of excessive breakdown is the structural change to the fibre. Figure 1 compares SEM micrographs (200x) of treated and untreated wool fibre snippets indicating that the recommended time range for the alkali step at this scale is 15-30 min. Another means of assessing the end point for step (a) is by using a cold stain test run at intervals throughout the step. Small samples of wool fibres can be removed periodically from the solution of strong alkali and then stained with Ig / L Acid Red 40 solution, at pH 2 for two minutes. The colour of each sample is assessed using the L*a*b* system, with a decrease in L* indicating a darker colour and an increase in a* indicating a redder colour. The end point is found through colour progression as L* decreases every 5 minutes and a* increases every 5 minutes. The starting L* is about 80 and finishes at about 50, while a* starts at about 10 and finishes at about 40.

[0175] Example 3: Milling treated, wool fibres to produce wool powder

[0176] The change in structure of the wool fibres after steps (a) to (d) of the process of the invention halves the time required to mill the treated wool fibres into a powder.

[0177] Untreated, scoured control wool fibres (1 mm) mill down to 10pm powder size in 8 hours using the following process: Attritor ball mill (wet mill), 6mm balls, 10% solids content. The slurry is spray dried to achieve a 10pm powder.

[0178] In comparison, IW15 (see Example 1) is milled to 10pm powder size in 4 hours under the same process conditions.

[0179] Dyeing makes no difference to the process. Dyed IW15 mills down to the same size in the same time as undyed IW15.

[0180] Figure 2 shows 10pm wool powder produced by wet milling and spray drying IW15 wool fibres.

[0181] Example 4: Dyeing treated wool fibres

[0182] Due to the chemical and structural modification to the treated wool fibre, dye molecules can penetrate and bind more efficiently. A deeper colour can also be produced as the fibre carries a higher percentage of the dye.

[0183] An improvement in dye exhaustion not only imparts a better colour to the fibres but also results in a lower colour waste discharge, ensuring expensive dyes are not wasted.

[0184] Untreated scoured wool and IW15 (see Example 1) were each dyed with Acid Dye (Red) and Reactive Dye (Red) using standard dyeing techniques.

[0185] Figure 4 shows photographs of the bath solutions of untreated and IW15 wool fibres after dyeing. In each case more of the dye has been taken up by the IW15 wool fibre, leaving less dye in the bath solution. The untreated wool fibres have a dye exhaustion of 70-75% while the IW15 wool fibre has a 90-100% dye exhaustion. Dye exhaustion is related to dye loading but the latter factors in the relative amount of dye used.

[0186] For a 20% oww (on weight of wool) dye process, dye is added to the dye bath at 20% of the weight of the wool. Therefore 200 g dye would be added to 1 kg of wool fibres. Dye exhaustion at 70% would correspond to 140 g dye uptake, giving 14% dye loading for the untreated wool. Dye exhaustion of 90% would correspond to 180g dye uptake, giving 18% dye loading for the IW15 wool fibres.

[0187] Example 5: Colour analysis of dyed, treated wool fibres

[0188] Further IW15 wool fibre was dyed as per Example 4 and its colour properties measured using the L*a*b* system as shown in Table 3.

[0189] Table 3: L*a*b* values for treated vs untreated wool fibres

[0190] L* indicates the black and white component, with 0 being black and 100 being white. Movement towards 0 shows that the colour is darker. All of the IW15 wool fibres were darker than their untreated counterparts. a* indicates the red / green component, with + being more red and - being more green. The higher the + value, the redder the colour is. All red IW15 treated wool fibres are redder than their untreated wool fibre counterparts. b* indicates the yellow / blue component with + being more yellow and - being bluer. The improvement in the blue and yellow of each of the IW wool fibres can also be seen in Table 3.

[0191] Example 6: Lower water absorption in wool powder pigments of the invention The process of the invention provides wool powder pigments and treated wool powder with lower water absorption values than its untreated counterparts. This characteristic allows the products of the invention to be used in applications that otherwise might not be possible for wool powder due to its hydrophilic tendency and the sensitivity of the coating process to a high moisture content. These areas include bioplastics, inks, paints and coatings where absorption of water into the wool powder would change the viscosity.

[0192] The water absorption of untreated, spray dried wool powder and wool powder made from IW15 (see Example 1) were compared. Both wool fibre samples were wet milled before spray drying to make wool powder. Both dyed and undyed wool fibres were converted to wool powder. The dyes used were acid dye and reactive dye.

[0193] The water absorption test was run according to DIN 55608 (International Standard for Pigments and extenders - Determination of water absorption value). In this test, water is added dropwise to a known amount of powder until a paste is achieved. The results are shown Table 4 below.

[0194] Table 4: Water absorption results ml / 100g

[0195] The process of dyeing the wool fibre increases its water absorption. However, whether dyed or undyed, the wool powder treated in accordance with steps (a) to (d) and then milled had lower water absorption than the untreated wool powder. The wool powder pigments (ie, dyed, treated wool powder) have a water absorption of less than about 200 ml / lOOg while the treated wool powder (undyed) has a water absorption of less than about 150 ml / lOOg.

[0196] Example 7: Particle size of treated wool powders

[0197] Two samples (dyed with Reactive dye Lanasol™ Red b and undyed) of treated IW15 wool fibres (see Example 1) were milled in a cone mill to about 150 pm. They were then ground in a Buhler MicroMedia™ XI wet mill with a grind media size of 0.3mm.

[0198] Following pre-grinding at 300 kWh per ton (300 kWh / t) to disperse the material, the powder was milled for increasing time periods, reflected in the increasing total power used in the milling process. Table 5 shows the results for wool powder pigment of the invention comprising Lanasol™ Red b dyed, treated wool fibres (IW15). Table 5: Particle sizes following micro milling

[0199] Table 5 shows the size parameters of the wool powder pigment as it is progressively milled. Sample 6.8 achieves sizes of 128 nm DIO. DIO means that 10% of the material is smaller than the value given.

[0200] Example 8: Use of wool powder pigments

[0201] The wool powder pigments of the invention were combined with the following aqueous and non-aqueous binder materials giving improved coverage and colour.

[0202] • 5% inclusion in Colormaker Permaset Print Paste.

[0203] • 10% inclusion in Stahl RC 78-236 Resin

[0204] • 10% inclusion in Rutland Soft hand Plastisol

[0205] • 30% inclusion in oil-based paint emulsions (linseed oil and beeswax)

[0206] A comparison was carried out between wool powder pigment of the invention and dyed untreated wool powder.

[0207] The process outlined in Example 1 was used to make treated wool fibres (IW15) which were then dyed with reactive dye (red) and wet milled using an attritor mill to 10pm average size. Dyed, untreated wool powder was prepared by dyeing then wet milling 1 mm wool fibres. Both pigments were mixed with Stahl RC 78-236 resin (a leather coating resin).

[0208] An example of improved depth of colour and coverage is seen in Figure 5. The wool powder pigment of the invention has a stronger colour than that of the untreated wool powder, and therefore is a superior pigment. Example 9: Biopolymer masterbatch

[0209] A masterbatch is a concentrated mixture of pigments in a carrier matrix which can be added to a plastic product to impart colour. A masterbatch must be strongly coloured because it will be greatly diluted in the final plastic product.

[0210] A masterbatch was produced using IW15 (see Example 1) dyed with Acid dye Red NRB in accordance with Example 4 and milled in accordance with Example 3. The wool pigment of the invention (10 wt%) was combined with 90% PHA (Helian Biopolymers® PHBV (Y1000 ~ 1-2% HVO)) in an extruder (Haake®, 16 mm co-rotating twin screw) using standard techniques. The PHA was fed via a dedicated feeder in the feed zone while the wool pigment was introduced at Zone 4 using a side feeder. The PHA feeder was set at 1.8 kg / hr. The side feeder was set at 0.2 kg / hr. A photograph of the masterbatch is shown in Figure 6.

[0211] Example 10: Overprint varnish

[0212] An overprint varnish is a coating placed over printing to protect the print from moisture, abrasion and other sources of damage. The wool pigments of the invention may be usefully added to overprint varnish in accordance with Table 6 below. Undyed, treated wool powder may also be used in overprint varnish, where no colour tint is desired.

[0213] Table 6: Overprint varnish recipe

[0214] Example 11: Scale up

[0215] The process set out in Example 1 was also repeated on larger scale using 30 kg and 50 kg of wool fibre with the amounts of the other agents increased accordingly.

[0216] In Table 7 below, the bulk density, water absorption and particle size of the 50 kg batch is contrasted with results from a further 4 kg batch prepared as described in Example 1. Table 7: Comparison of 4 kg and 50 kg scale processes of the invention

[0217] Example 12: Preparation of ink formulation by milling with glycerol

[0218] A sample of treated IW15 wool fibres (see Example 1), (dyed with Reactive dye Lanasol™ Red B) was wet milled and spray dried to about 10 pm. It was then ground in a Buhler MicroMedia™ XI wet mill into a carrier of glycerol with a grind media size of 0.8mm. Table 8 shows the milling details and size results for the resulting wool powder pigment.

[0219] Table 8: Milling details and size of wool powder pigment particles

[0220] The resulting magenta wool powder pigment dispersion in glycerol was used to prepare a flexographic ink formulation in accordance with Table 9.

[0221] Table 9: Ingredients for flexographic ink 7. REFERENCES

[0222] Guo, H., Song, H., Gan, L., Xia, L., Sheng, D., Liu, Y., . . . Wang, Y. (2020). Is it feasible to use dyed wool powder as pigment? Advanced Powder Technology, 31, 4632-

[0223] 4641.

[0224] Han, X., Guo, H., Wang, Y., Song, D., & Xu, W. (2023). Physicochemical Behavior of Superfine Wool Powder Dyed with Reactive Dye. Journal of Natural Fibers, 20(1). doi: https: / / doi.org / 10.1080 / 15440478.2022.2131026 Wen, G., Rippon, J., Brady, P., Wang, X., Liu, X., & Cookson, P. (2009). The characterization and chemical reactivity of powdered wool. Powder Technology, 193, 200-207.

[0225] Xu, W., Cui, W., Li, W., & Guo, W. (2004). Development and characterizations of superfine wool powder. Powder Technology, 140, 136-140.

Claims

1. WHAT WE CLAIM:

1. A process for preparing wool powder pigment comprising:(a) submerging wool fibres in a 5 to about 20 wt / v% aqueous solution of strong alkali for about 10 to about 45 minutes to form a wool slurry,(b) adding water to the wool slurry and mixing,(c) adding a solution of acidified peroxide to the wool slurry while mixing, until the pH of the mixture reaches about 4,(d) filtering the wool slurry to remove soluble impurities while retaining the treated wool fibres,(e) dyeing the treated wool fibres, and(f) milling the treated, dyed wool fibres to produce wool powder pigment.

2. A process according to claim 1 wherein step (e) is omitted and step (f) comprises milling treated wool fibres to produce treated wool powder.

3. A process according to claim any preceding claim wherein the strong alkali is selected from sodium hydroxide and potassium hydroxide.

4. A process according to any preceding claim wherein the pH of the aqueous solution of strong alkali is at least 13.

5. A process according to any preceding claim wherein the aqueous solution comprises about 8 to about 15 wt / v%, more preferably about 10 wt / v% strong alkali.

6. A process according to any preceding claim wherein the ratio of wool fibres to the aqueous solution of strong alkali is about 1 kg to about 5 L.

7. A process according to any preceding claim wherein the wool fibres are submerged in an aqueous solution of strong alkali for about 10 to about 20, 25, 30, 35 or 40 minutes, preferably about 15 to 30 minutes.

8. A process according to any preceding claim wherein the solution of strong alkali is diluted by about 50v% in step (b).

9. A process according to any preceding claim wherein the solution of acidified peroxide comprises acetic and / or formic acid.

10. A process according to any preceding claim wherein the solution of acidified peroxide comprises hydrogen peroxide.

11. A process according to any preceding claim wherein the solution of acidified peroxide comprises aqueous hydrogen peroxide of 5-20 w / v% and formic acid, of about 85 w / v%.

12. A process according to any proceeding claim wherein the solution of acidified peroxide comprises about 10: 1 to 1: 1 v / v aqueous weak acid mixed with aqueous hydrogen peroxide.

13. A process according to any preceding claim wherein the solution of acidified peroxide comprises 5 w / v% aqueous hydrogen peroxide mixed with 85 w / v% aqueous formic acid in about a 2: 1 ratio v / v.

14. A process according to claim 1 and any one of claims 2 to 13 wherein the treated wool fibres are dyed with a loading of about 10 to about 30% dye, preferably about 12 to 18 or 15 to about 20% dye.

15. A process according to claim 14 wherein step (e) results in a dye exhaustion of about 80, 85 or 90 to about 100%.

16. A process according to any preceding claim wherein treated wool fibres (dyed or undyed) are cone milled to 150 pm then micro milled to 500nm particles within 3-4 hours.

17. A process according to any preceding claim wherein the treated wool fibres (dyed or undyed) are milled to produce wool powder of about 100, 80, 60, 40, 20 or 10 pm or less.

18. A process according to claim 17 wherein the wool powder (dyed or undyed) is further milled in a micro mill to produce wool powder of average size of about 500, 400, 300, 250 or 200 nm or less.

19. A process according to any preceding claim which decreases water absorption of the wool powder (dyed or undyed) relative to a wool powder that has not been treated.

20. A process according to claim 19 which decreases water absorption of the wool powder (dyed or undyed) by about 10, 15, 20 or 25% relative to an untreated wool powder.

21. A wool powder pigment (dyed wool powder) of size less than 250 nm.

22. A wool powder pigment with a dye loading of at least 15%, preferably at least 20% and / or water absorbency of less than about 200 ml / lOOg.

23. A treated wool powder with water absorbency of less than about 150 ml / lOOg.

24. A process for preparing treated wool powder comprising:(a) submerging wool fibres in an about 5 to about 20 wt / v% aqueous solution of strong alkali for about 10 to about 45 minutes to form a wool slurry,(b) adding water to the wool slurry and mixing,(c) adding a solution of acidified peroxide to the wool slurry while mixing, until the pH of the mixture reaches about 4,(d) filtering the wool slurry to remove soluble impurities while retaining the treated wool fibres, and(e) milling the treated wool fibres to produce treated wool powder.

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