WO2020094927A1 - Cellulosic spun fibres comprising noble metal nanoparticles - Google Patents

Abstract

According to an aspect of the present invention, there is provided a method of preparing a noble metal nanoparticle coated spun fiber. The method comprises the steps of providing a solution of noble metal ions, providing an aqueous dispersion of a cellulosic pulp, contacting the dispersion of cellulosic pulp with the solution of noble metal ions and mixing to provide a slurry, heat treating the slurry in a hydrothermal treatment at a temperature in the range of 80 to 140 °C, for a period in the range of 60 to 180 minutes for reducing noble metal ions to noble metal nanoparticles on the surface of the cellulosic pulp, recovering a noble metal nanoparticle coated pulp, dissolving the noble metal nanoparticle coated pulp in an solvent to form a dope, and spinning fibers comprising noble metal nanoparticles from the dope.

Description

CELLULOSIC SPUN FIBRES COMPRISING NOBLE METAL NANOPARTICLES

FIELD

[0001] The present invention relates to lyocell fibers. In particular the present invention relates to lyocell fibers coated with noble metal nanoparticles. Methods or producing noble metal nanoparticles-coated lyocell fibers, as well as uses of the fibers are also disclosed.

BACKGROUND

[0002] Noble metal nanoparticles have gained much attention in recent years because of their diverse chemical, physical, optical, magnetic properties. They show excellent properties concerning optics due to a phenomenon called surface plasmon resonance. This phenomenon can lead to strong light absorption and scattering, thereby offering various interesting applications including surface-enhanced Raman scattering, and biological sensing. For example, gold nanoparticles are able to display vivid colors by tuning their aspect ratio. This phenomenon was discovered and applied by our ancestors. A wide range of metal nanoparticles have been utilized as pigments for coloring window glass and for dyeing ceramics. Recently, gold nanoparticles as pigments for dyeing textile materials have re-emerged as a topic of interest. Besides coloring, they extend the functionality of textiles enabling anti-bacterial properties, UV protection, and catalysis.

[0003] Traditionally, noble metal nanoparticles are prepared through the addition of reduction chemicals to reduce a salt/ acid precursor such as chloroauric acid or silver nitrate into noble metal nanoparticles in an aqueous solution. As noble metal nanoparticles easily aggregate into large particles, stabilizers have to be added into the aqueous solution. As a result, textiles are usually dipped into the resulting solution and the noble metal nanoparticles are coated onto the surface of the textiles due to electrostatic effects. It is evident that this conventional approach is complicated and time-consuming. Furthermore, reduction and stabilization chemicals could be transferred to the textile and cause toxic effects. In addition, as stated previously, the gold nanoparticles are coated onto the textile through electrostatic effects, which are relatively weak bonding forces, so that the attached gold nanoparticles might not be stable enough to fulfill a commercial use.

[0004] Therefore, combining noble metal nanoparticles with textiles in a more sustainable pathway has gained much interest recently. Cellulose shows the ability to reduce metal ions and to embed noble metals into its matrix under certain conditions. So far, gold nanoparticles have been successfully synthesized from unbleached pulp, wood or, Ramie using a one-pot reaction. In these approaches, cellulose serves a mini-reactor, in which hydroxyl and hemiacetal groups function as reducing agents and stabilizers, respectively, instead of additional chemicals.

[0005] However, these studies still have some limitations. First of all, they used unbleached wood pulp or wool as raw materials. These raw materials have their own color, which by interference with the original colors can create obstacles in matching the final color of a fabric. In addition, none of these studies continued to use the coated pulp for dry-jet wet spinning to produce cellulose fibers and to make real fabrics by yam spinning and knitting, which has also not been introduced to industry yet.

SUMMARY OF THE INVENTION

[0006] The invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

[0007] According to a first aspect of the present invention, there is provided a method of preparing a noble metal nanoparticle coated spun fiber comprising the steps of providing a solution of noble metal ions, providing a dispersion of a cellulosic pulp, contacting the dispersion of cellulosic pulp with the solution of noble metal ions and mixing to provide a slurry, heat treating the slurry in a hydrothermal treatment at a temperature in the range of 80 to 140 °C, for a period in the range of 60 to 180 minutes for reducing noble metal ions to noble metal nanoparticles on the surface of the cellulosic pulp, recovering a noble metal nanoparticle coated pulp, dissolving the noble metal nanoparticle coated pulp in an solvent to form a dope, and spinning fibers comprising noble metal nanoparticles from the dope.

[0008] According to a second aspect of the present invention, there is provided a modified pulp coated with noble metal nanoparticles.

[0009] According to a third aspect of the present invention, there is provided spun fibers comprising noble metal nanoparticles having a linear density in the range of 0.5 dtex to 3 dtex.

[0010] According to a fourth aspect of the present invention, there is provided yam spun from fibers according to the third aspect of the invention and yam spun from fibers obtainable by the first aspect of the invention.

[0011] A fifth aspect of the present invention provides a knitted fabric comprising the yam of the fourth aspect of the present invention. [0012] Considerable benefits are gained with the aid of the present invention. Pulp coated with noble metal fibers provides fibers for spinning into cellulose fibers from which real fabrics can be made. The cellulose fibers of embodiments of the invention are suitable for yarn spinning and knitting and weaving into fabrics in further embodiments.

[0013] Other features and advantages will become apparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Next, embodiments will be examined more closely with the aid of a detailed description and with reference to the attached drawings in which

[0015] FIGURE 1 shows photographs of bleached pulp treated with gold nanoparticles in various percentages by weight ranging from the highest gold nanoparticle (AuNP) weight percentage (0.59 wt %) on the left to the lowest gold nanoparticle weight percentage on the right (0.02 wt %);

[0016] FIGURE 2 shows absorbance spectra of Enocell pulp treated with with different amounts of gold nano particles (AuNP) ( ranging from 0.02 wt % to 0.59 wt % as well as an absorbance spectrum of untreated Enocell pulp.

[0017] FIGURE 3 shows absorbance spectra of AuNPs-Enocell pulp under different pH conditions. The pH ranges from 2.03 to 12.02. The AuNPs-Enocell pulp comprises Au³⁺ 0.06 wt%; l.5pmol.

[0018] FIGURE 4 shows absorbance spectra of silver nanoparticle (AgNP) - Enocell pulp at different concentrations.

[0019] FIGURE 5 shows photographs of pulp coated with silver and or gold nanoparticles. To the left is pulp coated with silver ions only. The ratio of silver to gold ions decreases moving from left to right.

[0020] FIGURE 6 shows absorbance spectra of AgNPs-AuNPs Enocell pulp with different molar ratios. The total mass of metals on pulp for each recipe, meaning each pulp sample is the same, which is l.5pmol.

[0021] FIGURE 7 is two transmission electron micrographs showing AuNPs on AuNPs- Enocell pulp, the first electron micrograph (a) having 0.06 wt % Au and the second electron micrograph (b) having 0.39 wt % Au. [0022] FIGURE 8 is a graph illustrating complex viscos ityf | h * ) and dynamic moduli (G\ G’’) of the nanoparticle spinning solutions in comparison with a standard spinning dope.

[0023] FIGURE 9 is a graph illustrating stress-strain curves of different fibers under conditioned state. AuNPs-Ioncell(0.06%wt Au³⁺); Au/AgNPs- Ioncell(molar ratios of Au³⁺/Ag⁺: 1/1, total amount metals 0.06%), standard Ioncell(without additives).

[0024] FIGURE 10 is a scanning electron micrograph showing distribution of AuNPs on the surface of Ioncell- fibers (0.06 wt % Au³⁺).

[0025] FIGURE 11 is a graph showing the molar mass distribution of coated and virgin pulp.

[0026] FIGURE 12 is a graph showing absorption spectra from from AuNPs-pulp (0.06%wt Au3+); Au/AgNPs-pulp (molar ratios of Au3+/Ag+: 1/1, total amount of metals, l.5pmol) and corresponding spun fibers.

EMBODIMENTS

[0027] The present invention relates to modifying cellulosic pulps with noble metal ions to provide a modified, nanometal coated pulp for spinning modified cellulosic fibres to be spun into a yam to provide functional textiles having various properties such as improved colorfastness, antibacterial and antimicrobial properties as well as providing e.g. UV protection.

DETAILED DESCRIPTION

[0028] In an embodiment of the present invention a method of preparing a noble metal nanoparticle coated spun fiber is provided. In one embodiment the method comprises the steps of providing a solution of noble metal ions, providing a dispersion of a cellulosic pulp, contacting the dispersion of cellulosic pulp with the solution of noble metal ions and mixing to provide a slurry, heat treating the slurry in a hydrothermal treatment at a temperature in the range of 80 to 140 °C, for a period in the range of 60 to 180 minutes for reducing noble metal ions to noble metal nanoparticles on the surface of the cellulosic pulp, recovering a noble metal nanoparticle coated pulp, dissolving the noble metal nanoparticle coated pulp in an solvent to form a dope, and spinning fibers comprising noble metal nanoparticles from the dope.

[0029] In a further embodiment the solution of noble metal ions comprises ions of noble metals selected from the group consisting of gold, platinum, iridium, osmium, silver, palladium, rhodium, ruthenium, copper and a mixture thereof.

[0030] In an embodiment the solution has a concentration of noble metal ions in the range of 10 - 100 mM, preferably 20 - 80 mM, particularly 30 - 70 mM, typically 40 - 60 mM, most suitably 50 mM.

[0031] In a further embodiment the solution has a pH in the range of 2.0 - 12.2, preferably a pH in the range of 2.8, to 10.5, suitably in the range of 5.0 to 10.0 and most suitably a pH of

7.0.

[0032] In a preferred embodiment the solution comprises noble metal salts selected from the group consisting of HAuCfr, NaAuC^’U, AuCl₃,PdCl₂, Na₂PdCl4, Pd(N0_{3 )2}, [Pd(NH ) ] Cf. H₂PtCl₆, PtCL,, H₂PtCl₆, AgN0₃, Cu(OH)₂-4NH₃, Cu(OAc)₂, CuCl₂, CuS0₄ and a mixture thereof.

[0033] In a particular embodiment the cellulosic pulp is selected from the group consisting of paper pulp, dissolving pulp, bleached cellulosic pulp, recycled cotton pulp, and cellulose (I) pulp, acid sulphite dissolving pulp, preferably a prehydrolysis Kraft pulp, suitably a hardwood prehydrolysis Kraft pulp. Bleached pulps, provide e.g. the advantage that they do not provide an uneven influence in dying of the pulp provided by the nanometal particles, i.e. an even coloration is achieved throughout the pulp.

[0034] As mentioned above some embodiments are apt for the recycling of various cellulosic materials. In one embodiment the recycled cotton pulp is obtained from textiles comprising cotton, optionally from mixed textiles comprising cotton and non-cotton materials.

[0035] Further embodiments relate to the solvent used for dissolving the noble metal nanoparticle coated pulp. In one embodiment the solvent for dissolving the noble metal nanoparticle coated pulp is NMMO. In a further embodiment the solvent for dissolving the noble metal nanoparticle coated pulp is an ionic liquid.

[0036] In a preferred embodiment the solvent for dissolving the noble metal nanoparticle coated pulp is a direct solvent such as NMMO monohydrate or cellulose dissolving ionic liquids. In one embodiment the ionic liquid is selected from the group consisting of imidazolium based ionic liquids with anions selected from the group consisting of acetate, formate, DEP, halides and other suitable anions with a high H-bond basicity. In a preferred embodiment the ionic liquid is a super-base based ionic liquid, preferably comprising a DBNH⁺cation or a TBDH⁺ cation, with acetate or dialkyl phosphate (e.g. diethyl or dimethyl) as an anion.

[0037] Each of the solvents mentioned here provides spinning dope with various properties, e.g. [DBNH] [OAc] has a melting point of 63 °C, Kamlet Taft Paramaters of ET(30) = 52.6, p* =1.04, a = 0.64 and b = 1.11 at 70 °C

[0038] In embodiments, a dope is prepared . In one embodiment dope preparation comprises oven drying the recovered noble metal nanoparticle coated pulp, grinding the oven- dried pulp, adding the ground pulp to the solvent to provide a mixture having a cellulose concentration in the range of 10 to 15 wt %, preferably 13 wt %, dissolving the pulp in the solvent at a temperature in the range of 60 °C to 100 °C, preferably 80 °C for a period of 10 to 90 minutes, preferably 60 minutes to provide a dope, and filtering the dope at a temperature of 60 °C to 90 °C to remove any undissolved cellulose particles. In a further embodiment, the dope is solidified by refrigerating, preferably by refrigerating at a temperature in the range of 5 °C to 7 °C, suitably for a period of 1 to 3 days.

[0039] Further embodiments relate to the spinning of fibers. In an embodiment spinning comprises spinning filaments through a spinneret through an air-gap into a water coagulation bath in a dry-jet wet spinning process.

[0040] The present invention further relates to a modified pulp. In one embodiment a modified pulp coated with noble metal nanoparticles is provided. In a further embodiment the metal nanoparticles are present in an amount in the range of 0.02 wt % of dry weight of cellulose to 3.0 wt% of dry weight of cellulose. The range of 0.02 wt % - 3.0 wt % has been found to be optimal, since above 3.0 wt %, no coloration of the pulp is observed.

[0041] In a further embodiment the metal is selected from the group consisting of gold, platinum, iridium, osmium, silver, palladium, rhodium, ruthenium, copper and a mixture thereof.

[0042] In a preferred embodiment, the modified pulp has a lightness in the range of 73..0 to 88.0, measured according to CIELab measurements as described hereinafter.

[0043] In a particular embodiment, the modified pulp has values on the red-green axis in the range of (a*) 4.4 to 11.9, measured according to CIELab measurements as described hereinafter.

[0044] In one embodiment, the modified pulp has values on the blue-yellow axis in the range of (b*) -6.6 to 1.9, measured according to CIELab measurements as described hereinafter.

[0045] In an embodiment two noble metals are present in the modified pulp, preferably in a ratio in the range of 4: 1 to 1 :5, optionally in a ratio in the range of 2: 1 to 1 :2, suitably in a ratio of 1 : 1. In a typical embodiment, these noble metals are silver and gold, or gold and silver.

[0046] Spun fibers are also described. In an embodiment spun fibers comprising noble metal nanoparticles have a linear density in the range of 0.5 dtex to 3 dtex, preferably 1.0 - 1.7 dtex, suitably 1.2 dtex to 1.5 dtex, measured as described hereinafter.

[0047] In a further embodiment the spun fibers have conditioned tenacity in the range of 35 cN/tex to 60 cN/tex, preferably 40 cN/tex to 50 cN/tex, suitably 45 cN/tex to 55 cN/tex, measured as described hereinafter.

[0048] In one embodiment the spun fibers have conditioned elongation in the range of 8 % to 18 %, preferably 12 % to 16 %, suitably 10.0 % to 15% measured as described hereinafter.

[0049] In a preferred embodiment the spun fibers have wet tenacity in the range of 30 cN/tex to 55 cN/tex, preferably 35 cN/tex to 45 cN/tex, suitably 42 cN/tex to 50 cN/tex, measured as described hereinafter.

[0050] In a suitable embodiment the spun fibers have wet elongation in the range of 6 % to 20 %, preferably 12 % to 17 %, suitably 13 % to 16 %, measured as described hereinafter.

[0051] In a particular embodiment the spun fibers have a lightness (L) in the range of 65 to 70.

[0052] In a preferred embodiment the spun fibers have values on the red-green axis (a*) in the range of 3 to 6.

[0053] In one embodiment the spun fibers have values on the blue-yellow axis (b*) in the range -2 to 5.

[0054] In embodiments the spun fibers described herein are obtainable from the modified pulp described above.

[0055] In one embodiment modified pulp is dissolved in a solvent to form a dope and fibres comprising noble metal nanoparticles are spun from the dope.

[0056] Yams may be spun from fibers according to embodiments of the invention. In one embodiment. In a further embodiment yam is spun from spun fibers obtainable by the method preparing spun fibers described above.

[0057] One further embodiment relates to a knitted fabric. In an embodiment the knitted fabric comprises the yarn described herein above. The noble metal nano particles in the fibres spun into the yam impart various properties on the fabric as is described in the examples section below. In a further embodiment a woven fabric is described. In an embodiment the woven fabric comprises the yam described herein. The noble metal nano particles in the fibres spun into the yarn impart various properties on the fabric as is described in the examples section below. EXAMPLES

[0058] In this study, we utilized bleached prehydrolysis kraft pulp from birch wood as a substrate for the in-situ synthesis of noble metal nanoparticles using HAuCLi and AgNCh as precursors without the addition of any other chemicals. Subsequently, the coated pulp was dissolved in [DBNH] OAc to prepare a cellulose solution to spin colored staple fibers by dry-jet wet spinning successfully. The staple fibers were processed into yarn and further knitted into real fabrics. The mechanical properties of the staple fibers and yams were measured and their washing fastness and ETV-protection were evaluated.

Materials and Methods

[0059] Materials: Enocell birch prehydrolysis Kraft pulp (PHK), Stora Enso (Finland), (Mw = 274.3 kg mol-1, Mn = 68.2 kg mol-l and PDI = 4), l,5-Diazabicyclo[4.3.0]non-5-ene (DBN, 99 %, Fluorochem, UK), acetic acid (glacial, 100%, Merck, Germany), Hexadecyltrimethylammonium bromide(CTAB, 96%, Sigma, USA), Gold chloride trihydrate (HAuC'U, 99%, Sigma, USA), Silver nitrate(AgN0₃, 99%, Sigma, USA).

[0060] Au or Ag nanoparticle coated pulp (small batch size): A 50 mM solution of either AgN03 or HAuCl4 was prepared prior to the synthesis of noble metal nanoparticles. 0.5g of oven-dried pulp was added to 40mL of water, and the mixture was then mixed vigorously by magnetic stirring for l5mins to ensure the pulp to be completely dispersed. After that, a certain amount of the respective solution (50mM) was dropped into the pulp suspension and mixed for 5mins. The resulting slurry was transferred to wide-neck bottles with caps and was placed into a 122 °C oven for 2h to allow the synthesis of noble metal nanoparticles. After 2h, the previously colorless pulp suspension changed to yellow or purple according to the different recipes. Once the color is stable, the reaction is complete. The bottles were taken out and cooled down in the ice water for suction filtration. The nanoparticle coated pulp was then filtrated with a 200 mesh filter paper and rinsed with deionized water for three times, forming a wet pulp sheet. Then this sheet was collected for CIELab measurement after drying at 45 °C overnight.

[0061] Big batch: When preparing a bigger batch of pulp, the volume of water should be calculated based on the liquor-to-pulp ratio of 80: 1. It is better to choose glassware of lOOOmL with a wide bottom. Otherwise, the slurry cannot boil and achieve the required temperature. To ensure efficient mixing, the slurry has to be stirred by a glass bar every 10 minutes.

[0062] Preparation of [DBNH] OAc: DBN was used to neutralize acetic acid to prepare [DBNHjOAc. An equimolar amount of acetic acid was slowly poured into DBN under permanent cooling due to the exothermic nature of the reaction. Then the resulting solution was stirred for lh at 80 °C. [0063] Dope preparation: To ensure that the AuNPs Enocell pulp could be dissolved in the IL, it had to be ground by a Wiley Mill to become a powder. Oven dry AuNP- pulp and IL were put into a reactor in a ratio to obtain a cellulose concentration in the resulting dope of 13 %. The dissolution takes place for 80 mins at 80 °C under reduced pressure with stirring. After dissolution, a colored dope was obtained and filtrated at 80 °C to remove undissolved cellulose particles and ensure an uniform solution quality. Finally, the filtrated dope was shaped to fit the size of the spinning device, and wrapped by Parafilm to be store at 5-7 °C for a few days for solidification.

[0064] Rheology: The shear rheology of all spin dopes was determined by applying an Anton Paar MCR 300 Rheometer with a plate and plate geometry (1 mm gap size, 25 mm plate diameter). All samples were subjected to a dynamic frequency sweep over an angular velocity range of 0.1-100 s ¹ at relevant temperatures (60-100 °C). Crossover points were also calculated to obtain the dynamic moduli at certain temperatures.

[0065] Dry-jet wet spinning: The solidified dope was first inserted into the cylinder (Foume Polymertechnik, Germany). Multi- filaments were spun from a 200-hole spinneret, hole diameter 0.1 mm, at 83 °C extruded by a piston, passing through a 1 cm air-gap into a water coagulation bath. It should be noted that the immersion depth to the first deflection roller, the deflection angle and the retention distance of the filament bundle were kept constant. The fibers were drawn with a draw ratio (DR) of 12 to reach a titer of 1.3 dtex and a tensile strength above 40 cN/tex to yield fibers suitable for textile applications. The calculation of the DR is shown in the equation below.

D_r = VJV_e

where, V_e represents the extrusion velocity V_tu stands for the take-up velocity of the godet couple.

[0066] Fiber opening, washing, and finishing: After spinning, the fibers were cut into 4 cm staple fibers. These shorter filaments were first opened by hand. The opened filaments were washed in a 80 °C water bath for 2 hours to remove the residual ionic liquid. The staple fibers were spin finished to improve the runability of the yarn spinning by reducing the surface energy. First of all, according to the weight of the fibers, the amount of water and chemicals (Feomin&Afilan, bought from Archroma) required was calculated. Then, the chemicals were added into the 50 °C water and stirred until they dissolved entirely. Followed by that, the fibers were placed in this solution to immerse for 5 mins. Fastly, the fibers were dried at room temperature and fully opened by a Mesdanlab fiber opener.

[0067] Yarn spinning: This process was performed by DirectTwist® (cone-to-cone multifunction twisting machine), Agteks, Istanbul, Turkey. Carding: The opened fibers were aligned parallel to each other to produce a thin web of fiber fleece. As it moves, it can produce a rope-like strand of parallel fibers after passing through a funnel-shaped device. Combing: To ensure that the yam is smoother and finer, the short fibers would be removed from strand. Drawing out: The sliver was first elongated under a series of rollers rotating at different speeds to form a single, more uniform strand. The strand is then fed into large cans with a small amount of twist. Twisting: In this stage, the strands of fiber are further elongated and twisted. These fibers are called the roving. Spinning: The roving is elongated by roller and passed through the eyelet. Then spindle turns the bobbin at a constant speed. This turning of the bobbin and the movement of the traveller twists and winds the yam in one operation.

[0068] Nonwoven samples: In this study, nonwoven samples were prepared by a mechanical web formation process (Automatex, Italy). The opened fibers formed randomly oriented nonwovens with roll cards that convert fibers into the surface. In this step, a Batt drafter was used to increase the delivery speed of the web. The resulting web was then bonded by needle punching, with the aim of consolidating and compacting the webs by repeatedly insertion barbed needles into the web. The prepared samples were utilized for the anti-bacterial measurement.

[0069] Knitted samples: Three similar threads were plied together. The single threads show Z-twist and 700 twist/m. The plying twist was S and 300 twist/m. The yam was knitted by a lab-scale circular knitting machine (L. Degoisey Tricolab ITF DS 34, France). The structure was single jersey.

[0070] CIELAB: After drying overnight, the pulp was collected for measuring reflectance spectra within the range of visible light and the L, a, b values were determined by a GretagMacbeth spectrometer, with a standard illuminant D65 and a CIE10 °C observer. Pulp sheets were pressed by glass plate to make the surface as uniform as possible to avoid interferences caused by the roughness of the surfaces. Each sample was measured for ten times and the mean values were calculated. The same analysis was also conducted for the spun fibers and fabrics before and after washing.

[0071] Transmission electron microscopy (TEM): O.Olg pulp coated with AuNPs was weighed into a 20 mL glass bottle, then 9mL deionized water was added and the mixture was shaken vigorously until the pulp dispersed completely. Then the resulting suspension was treated in an ultrasonic bath for 20 mins in order to break up significant aggregation of the nanoparticles on the pulp surface. Then drops of 5pL of the resulting dispersion were transferred on a copper grid immediately and it was waited for 5 min for the substance to absorb onto the grid surface. Finally, filter paper was used to remove extra water from the edges and the copper grid with the sample was put into a storage box to dry for ten minutes. When doing this, it was crucial to confirm that every tool was clean as already little contamination would ruin the samples. Therefore, for each sample duplicates should be measured. The imaging was performed by JSOL Tencial microscope at l20kV.

[0072] Gel permeation chromatography (GPC): The MMD of the raw material and the spun fibers was determined by gel permeation chromatography (GPC) using a 5 column set up with one precolumn (PLgel Mixed-A, 7.5 x 50 mm) and four analytical columns (4 x PLgel Mixed-A, x 300 mm) equipped with an Rl-detector (Shodex RI-101). The samples were dissolved in a 90 g 1-1 LiCl/N,N-dimethylacetamide (DMAc) solution and diluted with pure DMAc in order to obtain a sample concentration of 1 mg ml-l in 9 g 1-1 LiCl/DMAc. 100 mΐ of the respective solution was injected at a flow rate of 0.750 ml min-l (9 g 1-1 LiCl/DMAc eluent) at 25 °C. The calibration was conducted with pullulan standards (Mw: 343-708,000 Da) based on a direct- standard-calibration model, in which the molar mass distribution was corrected according to the molar masses of cellulose equivalent pullulan standards.

[0073] Tensile testing (fibers): The mechanical properties of noble metal nanoparticles Ioncell fibers were determined, including diameter, tenacity, and elongation at break under conditioned (23 °C, 50% relative humidity) and wet states. Before carrying out this testing, the fibers should be placed in a conditioned room for overnight. This testing was performed by using a Vibroskop 400 and Vibrodyn 400 (Lenzing Instruments GmbH & Co KG, Austria) the gauge length was 20mm, pretension 1 OOmg and the speed 200mm/min

[0074] Tensile testing (yarn): Similar to the filaments, tensile testing was applied to the yam. First of all, the hank composed of 10 skeins was weighed to calculate the Tex value. Then this hank was separated into one by one in the length of 1 meter. Picking up the most homogeneous part with distance of 25CM on skeins after weighing the mass, and marking it for the following measurement. Each one of skeins were attached to one paperboard to avoid twisting and conditioned overnight. In this experiment, the device used was MTS 400 tensile tester using 5 ON load cell, 250mm gauge length and 250mm/min of speed. In order to guarantee the accuracy, this tensile testing of yam was performed for 30 times and use the average value.

[0075] UV-protection: The UV-b locking properties of uncoated and Au-NPs coated fibers were measured according to the standard SFS-EN 13758-1 :2001. After assembling the knitted samples on a holder, the transmittance between 290nm and 400nm was recorded. The measurements were conducted ten times and the mean value was used as the final result. The ultraviolet protection factor UPF; was obtained from the following equation:

where E(/l) denotes the solar spectral irradiance (W m ²nm^_1), e(/1) the relative erythemal effectiveness, Al the wavelength interval (nm) within a fixed number of measurement points, and T the spectral transmittance of a specimen i at a wavelength l.

[0076] Washing fastness: The washing fastness of the AuNP-Inocell fabric samples was evaluated according to the ISO 105-006:2010 standard. The fabric was cut into one specimen measuring l00mm*40mm and was attached to a multifiber adjacent fabric next to the face side. Then the prepared sample was put into a stainless steel container containing l50mL detergent solution (1/250 g/mL) and 10 steel balls were added under 40 °C. After the washing machine was warmed up to 40 °C, the containers with the samples were inserted and the machine was operated for 40 mins at the same temperature. Followed by that, the composite specimen were rinsed by two separate lOOmL portions of water at 40 °C extracting the excess water from the composite specimen. Finally, the specimen were dried in air below 60 °C. The ClEFab value was measured before and after washing to indicate the stability of color against washing.

Results and discussion

Functionalization of pulp with noble metal nanoparticles:

[0077] Au nanoparticles: This work was the first one to use bleached birch pulp as a raw material to prepare Au nanoparticles. After the addition of 50Mm of chloroauric acid to a pulp slurry, the color of the pulp changed progressively from white to pink or purple depending on the concentration of Au³⁺. This color was caused by the localized plasmon resonance of the gold nanoparticles originating from the reduction of Au(lll) to Au(0), implying a direct synthesis of gold nanoparticles. A series of different concentrations is shown in Figure 1. And the LTV absorption spectra are plotted in Figure 2.

[0078] To verify the formation of AuNPs, AuNPs coated pulp and a blank pulp sample were characterized by a UV-Vis spectrometer to obtain a reflectance spectrum. As shown in Figure 2, there was a plasmon resonance band produced at 520-550nm, which proves the presence of AuNPs on the pulp surface under this procedure. With an increasing amount of CA, the position of peak rose gradually and the resolution of the signal became better. This implies that the yield of gold nanoparticles with a narrow size distribution increases with an increasing amount of CA. Interestingly, the spectrum showed a blue shift inferring that the average size of AuNPs synthesized on the pulp became smaller with an increasing concentration. In addition, when the wt% of Au/pulp was higher than 2.95wt%, the pulp maintained its white color and implying that there was no formation of gold nanoparticles on the pulp. Assumingly, adding an excessive amount of Au³⁺ compared to the number of activation sites on the pulp results in a reaction of Au³⁺ with the prepared AuNPs converting them into Au¹⁺ (colorless).

[0079] AuNPs are chromophores due to the LSPR effect. Reflectance values L, a, b were hence measured to prove the formation of gold nanoparticles (s. Table 1 . Here, L denotes lightness, positive and negative a values describe the redness and greenness of the samples, positive and negative b values represent the yellowness and blueness attributes. As described in Table 1, the color of the uncoated pulp was white, with a comparatively high brightness L value and nearly zero a and b values. The L value of all pulps treated with AuNPs decreased and the a value increased in proportion to the addition amount of CA, compared with the untreated one. These changes complementally implied the formation of AuNPs with purple color.

Au³⁺/pulp 0.59 wt% 0.39 wt% 0.30 wt% 0.20 wt% 0.16 wt% 0.1 wt% 0.06 wt% 0.02 wt% Blank

L 52.781 52.968 55.407 59.961 65.37 72.702 74.284 82.468 92.92 a* 6.766 6.498 6.203 9.542 11.856 11.353 11.893 6.543 -0.958 b* -5.462 -5.661 -6.606 -4.393 -2.35 1.852 1.558 1.282 2.797

Table 1 : Reflectance value of samples with different wt% Au(III)

[0080] pH dependence: It is generally known that the reactivity of cellulose is pH- dependent, as the charge of its functional groups, including hydroxyl groups and phenol groups from the residual lignin or extractives, are affected by different pH conditions. Hence, it is crucial and necessary to explore this parameter in this research. As illustrated in Figure 3 and Table 2, experimental conditions with a pH ranging from 2 to 12 have been studied. The overall trend showed a normal distribution, a maximum absorption was achieved under neutral pH. Under acidic or alkaline conditions, the peak value of the plasmon resonance band displayed a decreasing trend until reaching a minimum value at pH2 and pH 12.2, respectively. This indicates that a neutral pH represents the optimum condition for preparing Au-cellulose hybrids using bleached birch pulp as substrate.

pH q3 75 54)7 <k57 94)2 10.53 12.02

L 79.363 76.399 74.362 74.284 74.589 74.939 77.037

a* 4.498 5.279 11.193 11.893 7.586 9.459 5.928

b* -1.811 -3.269 0.529 1.558 -2.081 -1.308 -2.458

Table 2: Reflectance value of samples prepared under different pH condition, (Au 0.06 wt %; l.5pmol).

[0081] Addition of silver ions: Furthermore, we could show that this in- situ reduction could be applied to silver ions on bleached pulp. After the same procedure and reaction for 2h at 122 °C, the color of the pulp changed from white to yellow, indicating the formation of AgNPs on the pulp surface. In the absorbance spectrum, the LSPR band caused by AgNPs was detected at around 450nm, which is similar to literature. Besides, the colors and reflectance spectra produced by two different concentrations of AgN0₃ (0.2wt%,l.5q?wo/;0.32wt%, 2.5 mhioΐ) were almost the same, suggesting that the addition amount did not significantly affect the formation of AgNPs in terms of yield and size. The respective results are summarized in Figure 4.

[0082] In order to obtain different colors and to induce more functionality into the final Ioncell fibers, silver and gold ions were combined with birch pulp to prepare new composites using the same green reduction method as described above. A series of colors is displayed in Figure 5.

[0083] With a rising proportion of Au ions, the color became increasingly stronger and changed from yellow to pink. This phenomenon implies that the color caused by AuNPs takes the predominant role in the mixture of Ag and Au nanoparticles. The reason is that the LSPR effect of AuNPs is stronger than the corresponding impact caused by AgNPs. This hypothesis is also confirmed by the UV reflectance spectrum, in which the PLSR bands resulting from AuNPs were dramatically stronger than the bands from AgNPs. Only for the pure Ag samples, the SPB can be observed, but the signal was quite weak, while for Au samples, each sample containing AuNPs shows a SPB, although these peaks turned into quite flat and weak when the ratio of Ag/Au was higher than 1 : 1. In comparison, when the ratio of Ag/Au was lower than 1 :1, the peak becomes increasingly stronger and sharper, even better than the reference sample of pure 0.06%wt AuNPs. This fact indicates that the addition of Ag ions is able to enhance the effect of PLSR and to control the size distribution of AuNPs to some extent. As to why the SPB of AgNPs becomes weaker in the presence of AuNPs, we assume that there are some intercoupling reactions between AgNPs and AuNPs, thereby reducing the PLSR effect of AgNPs. In addition, the roughness of the pulp sheets is another factor that affects the reflectance spectrum, as the roughness can cause light scattering that makes the absorption uneven.

[0084] In a similar manner, the absorbance spectrum and CIE L, a, b value were shown in Figure 6 and Table 3 to verify the change of color. The higher L value and nearly zero of a and b values indicated that the untreated sample was white. The change of L, a and b values proved the formation of AgNPs and AuNPs, as these nanoparticles would create colors due to the LSPR phenomenon. Molar Ratios(Ag⁺/Au³⁺) 4:1 2:1 1:1 1:2 1:5 0:3 Blank

^~L 74.33 73.32 75.51 87.17 80.18 74.284 92.92 a* 15.44 16.12 13.53 -0.14 9.64 11.893 -0.96

b* 6.40 4.65 8.13 19.51 10.61 1.558 2.80

Table 3: Reflectance values of AgNPs-AuNPs Enocell pulp of various ratios (total molar mass of metals on pulp for each recipe is the same, which is 0.15iimol ).

[0085] Transmission electron microscopy (TEM) of the NPs on the pulp: As shown in images below (Figure 7), the shape of the obtained AuNPs varies, including cubic and round shaped. In addition, we observed that with an increase in wt% of gold ions, the amount of AuNPs formed increased, leading to a high density, while their size decreased slightly. On the contrary, lower wt% yielded less AuNPs, which however showed larger sizes. As far as the size distribution is concerned, although only a few large AuNPs were formed, the gold nanoparticles have a similar size on average and do not produce large aggregates. These facts also correspond to the results of the UV reflectance spectra.

[0086] Spinning solution and dry-jet wet spinning The spinnability of cellulose solutions strongly depends on their rheological properties. According to previous studies, optimum spinning conditions in the Ioncell-F process require a zero shear viscosity of around 30000 Pas and a crossover point of the dynamic moduli ranging between 3000-4000 Pa for standard solutions.¹⁴ Figure 8 depicts the oscillatory shear rheology measurements of Au and Au/Ag cellulose spinning solutions in comparison with uncoated pulp.

[0087] Both nanoparticle dopes show a slightly increased viscosity indicating that the generated nanoparticles potentially serve as fillers in the cellulose matrix thereby influencing the viscoelastic behavior of the resulting solution. Moreover, the nanoparticles present also caused a shift of the crossover point to higher moduli and higher shear rates implying a decrease of the molar mass average of cellulose. One reason for this behavior could be a possible degradation of the cellulose during the coating process, which was further investigated in the GPC section below. Despite this shift, the optimum spinning conditions for the nanoparticle dopes resulted in a about 5-lO°C higher spinning temperatures compared to standard solutions due to their increased viscosity.

[0088] Tensile properties of the spun fibers: In this study, the Au-Ioncell fibers spun from 13% cellulose concentration were studied for their mechanical properties (s. Table 4).

Table 4 Mechanical properties of AuNPs-Ioncell(0.06%wt Au3+); Au/AgNPs-Ioncell(molar ratios of Au³⁺/Ag⁺: 1/1), standard Ioncell(without additives).

[0089] As it can be seen in Table 4 and Figure 9, AuNPs-Ioncell fibers and Au/AgNPs- Ioncell fibers have similar or even superior tenacities to standard Ioncell fibers. It could be explained as follows: Gold nanoparticles tend to fill into‘gaps’ in the cellulose structure, and the free volume within cellulose chains is reduced. More polymer molecules are then interconnected by AuNPs, which greatly increases the cross-linking density of cellulose chains. AuNPs with a high inherent modulus also behave as rigid modifier particles, which can contribute to the improvement of strength and modulus. Finally, the presence of nanoparticles between the voids of the molecular chains limit the segmental chain movements, which increases the flexibility and thus the stiffness of fibers. ⁶ In a word: gold nanoparticles, which act as a bridge function, make it possible to strengthen the bonding forces between the fiber matrix and improve the mechanical properties of the Au-Ioncell fiber. Under wet condition, the tensile strength shows a similar trend. However, the strength is gently weaker than in the conditioned state, since the hydrogen bond network in the amorphous regions is partially destroyed after water absorption and swelling. Hence, the proportion of available hydrogen bonds in the amorphous sections could be estimated with the ratio of wet-to-dry tenacity. Swelling should be responsible for the reduction of the bonds in the crystalline region, as it affects the surface area of ordered regions.¹⁷

[0090] Scanning electron microscopy (SEM) of the spun fibers: In order to detect the distribution of the nanoparticles on the Ioncell fibers, SEM with back scattered mode was employed. In the image below, light spots should be AuNPs, as relatively heavier atoms display brighter colors compared to atoms with smaller relative atomic mass under the back scattered mode of SEM. According to the SEM images (Figure 10), the AuNPs are homogeneously distributed on the fiber surface. [0091] Gel permeation chromatography (GPC) of the spun fibers: In order to verify whether the coating process affects the degree of polymerization, the molecular mass distribution of pulp before coating and after coating was measured by gel permeation chromatography (GPC). Figure 11 illustrates that Enocell pulp treated with Au degrades only slightly. The results show that the in-situ reduction method hardly affects the molecular chain length of cellulose, and the macromolecular properties of the fibers spun from AuNPs-Enocell did not deviate from fibers produced from virgin material.

[0092] CIELAB evaluation on the effect of the spinning process on the generated NPs:

The absorption spectra were measured to study the effect of the spinning process on the AuNPs. From these spectra, the absorption bands become higher and wider after spinning than before spinning, indicating that the AuNP size distribution became broader during spinning (s. Table 5 and Figure 12).

[0093] With regard to the increased f absorption peak, there are two explanations. One is that spinning conditions such as high temperature and high pressure continue the reduction reaction of AuNPs and form more AuNPs. The other is that the presence of the ionic liquid and the mechanical process itself reshape the AuNPs to yield other shapes which possess a stronger plasmon resonance effect.

Table 5 Reflectance values of samples of AuNPs-pulp (l .5pmol;0.06%wt Au^+); Au/AgNPs- pulp (molar ratio of Au³⁺/Ag⁺: 1/1, total amount of metals is l .5pmol) and corresponding spun fibers.

[0094] Tensile properties of the spun yarn: For commercial use, the mechanical property of yam is the most important indicator, which has been summarized in Table 6. The mechanical properties of yam depend on a couple of factors: length, fineness, strength, and extension of the fibers. As for yam count, it is estimated by dividing the linear density of the yam by the linear density of the single fibers. The reason to double the linear density of a yarn is to take the resistance force to tension applied in the yam weaving process into consideration. The coefficient of variation (CV,%) represents the anomaly of spun yam. The smaller this value is, the more homogeneous the spun yam. Flowever, it is challenging to calculate the CV of different yams due to the varying fiber counts. Hence, the equation below is introduced for a better comparison.

CV_lim = 1 * 100%

n

Where CVii_m stands for the limit coefficient of variation and n represents the fiber count.

[0095] The higher CV value can be explained by the higher fiber fineness originating from this experiment. And the other reason is the deviation of the fiber length since the cutting of the filaments was carried out by hand and not on a standardized machine.

Table 6 Mechanical properties of AuNPs-Ioncell yarnfl .5pmol,0.06%wt Au³⁺) and Standard- Ioncell yam(Without the contents of Au³⁺).

[0096] Washing fastness of the knitted fabrics: We measured the washing fastness of the fibers before and washing with a certain detergent. Along with the basis of the gray scale, the difference of colors was quantified as in the equations below. DE represents the total color difference of the fabric before and after washing. In these formulas, L is the lightness dimension, a and b are the color-opponent dimensions. The subscripts 0 and 1 represent the samples before and after washing, respectively.

where AE denotes the total color difference in the CIELAB space before and after washing, &L * the difference in lightness, Aa * the difference in the red-green axis, and &h ΐ the difference in the yellow-blue axis.

[0097] Table 7 summarizes the result before and after testing. The very small DE value implies that the color difference is quite small. This result proves that Ioncell fabrics treated with AuNPs have excellent colorfastness properties against washing in contrast the direct coating method as reported. In addition, as reported by the master thesis from our group, the color difference of textiles dyed by vat and reactive dyes varied ranging 4-32 according to various dyes. This indicated that the stability of color from AuNPs are stronger than the conventional dyes.

Before washing After washing

5T6 56.81

a* 5.284 4.646

b* 0.319 0.487

DE 1.032

Table 7 Reflectance values of before and after washing with detergent (AuNPs-Ioncell fibers, 0.06wt% AU³⁺).

The degree to which human skin can be protected from exposure to sunlight by a fabric without any damage is defined by the fabric’s UV protection factor (UPF). UPF values below 15 are low, 15 to 24 are described as good, 24 to 39 are very good and values above 40 are excellent. With values above 40, more than 97.5% of LTV light is absorbed. Knitted and woven fabrics comprising fibres coated with noble metal nanoparticles provide good and very good protection from both UVA and UVB light as is shown in Table 8.

Sample Cover factor T(UVA) / % T(UYB) / % UPF

Knited fabric Uncoated 3.4 25.8±2.7 19.6±2.6 4.9±0.7

Au 3.2 22.9±1.9 19.8±1.9 4.9±0.5

AgAu 3.3 23.2±2.2 19.9±2.2 4.9±0.5

Ag 3.3 23.3±2.3 2l .3±l .7 4.6±0.4

Woven fabric Uncoated 19.9 8.8±0.6 3.7±0.4 22.5±2.1

(24

threads/cm) Au 18.8 4.2±1.0 2.1±0.7 43.2±14.6

AgAu 19.4 3.6±1.1 1.8±0.6 49.6±12.4

Ag 19.6 5.7±2.7 3.5±1.1 26.8±8.2

Table 8. Transmittance ofUVA light T(UVA) (%, 315-400 nm), transmittance ofUVB light /%, 290-315 nm), as well as the UV protection factor of knitted and woven samples containing Au, AgAu, and AgNPs. Uncoated samples were added as a reference. The cover factor is calculated as tightness factor = V(tex/stich length in mm) for knitted fabrics and the cover factor is calculated as weft yam cover factor = (threads per cm x Vt ex) for woven fabrics.

Conclusion

[0098] AuNPs were prepared by the reduction of chloroauric acid (CA) in situ on bleached birch pulp to form cellulose- AuNPs hybrids. The pulp was colored by the AuNPs due to their localized surface plasmon resonance (LSPR) properties. After dissolving in [DBNH] OAc, these coloured pulps were processed into fibres by dry-jet wet spinning. During this process, factors such as the amount of CA solution added, the pH, and the combination with silver ions were studied. Among the relatively low wt%(weight percentage) of CA, the yield of AuNPs increased but showed decreasing sizes. As soon as the wt% were above the threshold, the color of the pulp began to fade until it became colorless. With regard to the pH, the results showed that either acidic or alkaline conditions negatively affect the yield of AuNPs, while accelerating the reaction rate. This method can also be applied to silver ions.

[0099] We were able to produce AgNPs on bleached pulp, which displayed a yellow color due to a different LSPR. The fabrics prepared by cellulose-AuNPs showed excellent stability of the AuNPs to the pulp after the color fastness tests. Furthermore, the addition of AuNPs or/and AgNPs can improve the mechanical properties of spun fibers.

[00100] It is to be understood that the embodiments of the invention disclosed are not limited to the particular structures, process steps, or materials disclosed herein, but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting.

[00101] Reference throughout this specification to one embodiment or an embodiment means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases“in one embodiment” or“in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Where reference is made to a numerical value using a term such as, for example, about or substantially, the exact numerical value is also disclosed.

[00102] As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as de facto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.

[00103] Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, such as examples of lengths, widths, shapes, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well- known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.

[00104] While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

[00105] The verbs“to comprise” and“to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", that is, a singular form, throughout this document does not exclude a plurality.

INDUSTRIAL APPLICABILITY

[00106] At least some embodiments of the present invention find industrial application in the manufacture of textiles, in particular in providing washfast colored functional textiles having e.g. anti-bacterial properties, and protecting against ultraviolet light.

CITATION LIST

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Claims

CLAIMS:

1. A method of preparing a noble metal nanoparticle coated spun fiber comprising the steps of

• providing a solution of noble metal ions,

• providing an aqueous dispersion of a cellulosic pulp,

• contacting the dispersion of cellulosic pulp with the solution of noble metal ions and

mixing to provide a slurry,

· heat treating the slurry in a hydrothermal treatment at a temperature in the range of 80 to 140 °C, for a period in the range of 60 to 180 minutes for reducing noble metal ions to noble metal nanoparticles on the surface of the cellulosic pulp,

• recovering a noble metal nanoparticle coated pulp,

• dissolving the noble metal nanoparticle coated pulp in an solvent to form a dope, and· spinning fibers comprising noble metal nanoparticles from the dope.

2. The method according to claim 1, wherein the solution of noble metal ions comprises ions of noble metals selected from the group consisting of gold, platinum, iridium, osmium, silver, palladium, rhodium, ruthenium, copper and a mixture thereof.

3. The method according to claim 1 or 2, wherein the solution has a concentration of noble metal ions in the range of 10 - 100 mM, preferably 20 - 80 mM, particularly 30 - 70 mM, typically 40 - 60 mM, most suitably 50 mM.

4. The method according to any of claims 1 to 3, wherein the solution has a pH in the range of 2.0 - 12.2, preferably a pH in the range of 2.8, to 10.5, suitably in the range of 5.0 to 10.0 and most suitably a pH of 7.0.

5. The method according to any of the preceding claims, wherein the solution comprises noble metal salts selected from the group consisting of HAuCfi, NaAuCb, AuCl₃,PdCl_2,

Na₂PdCl4, Pd(N0₃) , [Pd(NH₃)₄] -Cl₂, H₂PtCl₆, PtCb, H₂PtCl₆, AgN0₃, Cu(OH)₂-4NH₃, Cu(OAc)₂, CuCl₂, CuSCTi and a mixture thereof.

6. The method according to any of the preceding claims, wherein the cellulosic pulp is selected from the group consisting of paper pulp, dissolving pulp, bleached cellulosic pulp, acid sulphite pulp, recycled cotton pulp, and cellulose (I) pulp, preferably a prehydrolysis Kraft pulp, suitably ahardwood prehydrolysis Kraft pulp.

7. The method according to claim 6, wherein the recycled cotton pulp is obtained from textiles comprising cotton, optionally from mixed textiles comprising cotton and non cotton materials.

8. The method according to any of the preceding claims, wherein the solvent for dissolving the noble metal nanoparticle coated pulp is a direct solvent such as NMMO monohydrate or cellulose dissolving ionic liquid.

9. The method according to any of claims 1 to 7, wherein the solvent for dissolving the noble metal nanoparticle coated pulp is an ionic liquid, preferably selected from the group consisting of imidazolium based ionic liquids with anions selected from the group consisting of acetate, formate, DEP, halides and other suitable anions with a high H-bond basicity.

10. The method according to any of claims 9, wherein the solvent for dissolving the noble metal nanoparticle coated pulp is a super-base based ionic liquid, preferably comprising a DBNH⁺cation or a TBDH⁺ cation, suitably with acetate or dialkyl phosphate as an anion.

11. The method according to any of the preceding claims, wherein dope preparation comprises

• oven drying the recovered noble metal nanoparticle coated pulp,

• grinding the oven-dried pulp,

• adding the ground pulp to the solvent to provide a mixture having a cellulose

concentration in the range of 10 to 15 wt %, preferably 13 wt %,

· dissolving the pulp in the solvent at a temperature in the range of 60 °C to 100 °C, preferably 80 °C for a period of 10 to 90 minutes, preferably 60 minutes to provide a dope, and • filtering the dope at a temperature of 60 °C to 90 °C to remove any undissolved cellulose particles.

12. The method according to any of the preceding claims, wherein spinning comprises spinning filaments through a spinneret through an air-gap into a water coagulation bath in a dry-jet wet spinning process.

13. A modified pulp coated with noble metal nanoparticles.

14. The modified pulp according to claim 13, wherein the metal nanoparticles are present in an amount in the range of 0.02 wt % of dry weight of cellulose to 3.0 wt% of dry weight of cellulose.

15. The modified pulp according to claim 13 or 14, wherein the metal is selected from the group consisting of gold, platinum, iridium, osmium, silver, palladium, rhodium, ruthenium, copper and a mixture thereof.

16. The modified pulp according to any of claims 13 to 15, having a lightness in the range of 73.32 to 87.17.

17. The modified pulp according to any of claim 13 to 16, having values on the red-green axis in the range of (a*) 4.4 to 11.9.

18. The modified pulp according to any of claims 13 to 17, having values on the blue- yellow axis in the range of (b*) -6.6 to 1.9.

19. The modified pulp according to any of claim 13 to 18, wherein two noble metals are present, preferably in a ratio in the range of 4: 1 to 1 :5, optionally in a ratio in the range of 2: 1 to 1 :2, suitably in a ratio of 1 : 1.

20. Spun fibers comprising noble metal nanoparticles having a linear density in the range of 0.5 dtex to 3 dtex, preferably 1.0 - 1.7 dtex, suitably 1.2 dtex to 1.5 dtex.

21. Spun fibers according to claim 20, having conditioned tenacity in the range of 35 cN/tex to 60 cN/tex, preferably 40 cN/tex to 50 cN/tex, suitably 45 cN/tex to

55 cN/tex.

22. Spun fibers according to claim 20 or 21 , having conditioned elongation in the range of

8 % to 18 %, preferably 12 % to 16 %, suitably 10.0 % to 15%.

23. Spun fibers according to any of claims 20 to 22, having wet tenacity in the range of 30 cN/tex to 55 cN/tex, preferably 35 cN/tex to 45 cN/tex, suitably 42 cN/tex to 50 cN/tex.

24. Spun fibers according to any of claims 20 to 23, having wet elongation in the range of 6 % to 20 %, preferably 12 % to 17 %, suitably 13 % to 16 %.

25. Spun fibers according to any of claims 20 to 24 having a lightness in the range of 65 to 70.

26. Spun fibers according to any of claims 20 to 25 having values on the red-green axis (a*) in the range of 3 to 6.

27. Spun fibers according to any of claims 20 to 26 having values on the blue-yellow axis

(b*) in the range -2 to 5.

28. Spun fibers according to any of claims 20 to 27, obtainable from the modified pulp according to any of claims 13 to 19.

29. Spun fibers according to claim 28, wherein the modified pulp is dissolved in a solvent to form a dope and fibres comprising noble metal nanoparticles are spun from the dope.

30. Yam spun from spun fibers according to any of claims 20 to 39.

31. Yam spun from spun fibers obtainable by the method according to any of claims 1 to 12.

32. Knitted fabric comprising the yam according to any of claims 30 to 31.

33. Woven fabric comprising the yam according to any of claims 30 to 31.