METAL-INSIDE-FIBER-COMPOSITE AND METHOD FOR PRODUCING A METAL-AND-FIBER-COMPOSITE

Abstract

A The metal-inside-fiber-composite including a biopolymer based fiber having a fiber wall and a void space. The fiber wall envelops the void space such that the void space forms a continuous void space inside and along the fiber. A metal microstructure makes the metal-inside-fiber-composite electrically conductive. A method for producing a metal-and-fiber-composite, in particular a metal-inside-fiber composite, is also provided.

Claims

1. A metal-inside-fiber-composite, comprising: a biopolymer based fiber having a fiber wall and a void space, wherein the fiber wall envelops the void space such that the void space is formed as a continuous void space inside and along the fiber; a metal microstructure, wherein the metal microstructure is a microstructure of an elemental metal, fills and extends through and along the continuous void space such that the fiber wall forms a protective layer around the metal microstructure, includes metal particles that are crystalline, has an average particle size of at least 80 nm, that are interconnected to form the metal microstructure, is included in the metal-inside-fiber-composite by at least 60 weight percent of a total weight of the metal-inside-fiber-composite, and is electrically conductive to make the metal-inside-fiber-composite electrically conductive.

2. The composite according to claim 1, wherein the biopolymer based fiber is a cellulose based fiber having the fiber wall and a fiber lumen, the fiber wall envelops the fiber lumen such that the fiber lumen forms the continuous void space inside and along the fiber.

3. The composite according to claim 1, wherein the elemental metal is one of copper, nickel, gold, silver, palladium, platinum and lead.

4. The composite according to claim 1, wherein the metal-inside-fiber-composite includes the metal microstructure having at least 70 weight percent of the total weight of the metal-inside-fiber-composite.

5. The composite according to claim 1, wherein the metal microstructure fills the void space to such a degree that the fiber wall lies against the metal microstructure, the fiber wall is supported by the metal microstructure, and the fiber has a greater outer dimension compared to the fiber being in a state where the void space is empty.

6. The composite according to claim 1, wherein the metal particles (6) have an average particle size between 80 nm and 1000 nm.

7. The composite according to claim 1, wherein the protective layer protects the metal microstructure from at least one of environmental corrosion or abrasion.

8. A fabric comprising the metal-inside-fiber-composite according to claim 1.

9. A method for producing a metal-and-fiber-composite, comprising the steps of: providing a fibrous material; providing a first reactant mixture including a metal salt dissolved in a first alcohol; combining the first reactant mixture with the fibrous material; heating the first reactant mixture being combined with the fibrous material to at least 140? C.; with the first reactant mixture being combined with the fibrous material at the at least 140? C., adding a second reactant mixture to the first reactant mixture being combined with the fibrous material; reacting the reactant mixtures at the at least 140? C. to metallize the fibrous material; wherein the second reactant mixture includes the metal salt dissolved in the first alcohol, and adding the second reactant mixture to the first reactant mixture being combined with the fibrous material is repeated at least once.

10. The method according to claim 9, wherein the metal salt is one of copper metal salt, nickel metal salt, gold metal salt, silver metal salt, palladium metal salt, platinum metal salt and lead metal.

11. The method according to claim 9, wherein the first alcohol is benzyl alcohol or a derivative therefrom.

12. The method according to claim 9, wherein at least one of the first or second reactant mixture includes a second alcohol.

13. The method according to claim 9, further comprising combining the first reactant mixture with the fibrous material at the at least 140? C., and adding a third alcohol to the first reactant mixture being combined with the fibrous material.

14. The method according to claim 9, wherein the first reactant mixture has the metal salt dissolved in the first alcohol at a concentration within the range of 0.2 to 0.5 moles per liter.

15. The method according to claim 9, wherein the method further comprises: the fibrous material being a biopolymer based fiber having a fiber wall and a void space, the fiber wall enveloping the void space such that the void space is formed as a continuous void space inside and along the fiber, and reacting the reactant mixtures at the at least 140? C. to form a metal-inside-fiber-composite.

16. The method of claim 13, wherein a volume ratio of a volume of the first alcohol to a volume of the third alcohol of 3 to 1.

17. The method of claim 14, wherein the second reactant mixture has the metal salt dissolved in the first alcohol at a concentration within the range of 0.2 to 0.5 moles per liter.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0077] The inventive metal-inside-fiber-composite and the inventive method for producing a metal-and-fiber-composite are described below in more detail purely by way of example with the aid of concrete exemplary embodiments illustrated in the figures. Further advantages of the invention are also being examined. In detail, it is shown by:

[0078] FIG. 1 An optical microscopy image of a metal-inside-fiber-composite according to an embodiment of the invention, scale bar 50 micrometers;

[0079] FIG. 2 An optical microscopy image of a metal-inside-fiber-composite according to an embodiment of the invention, scale bar 20 micrometers;

[0080] FIG. 3 An electron microscopy image of a metal-inside-fiber-composite according to an embodiment of the invention revealing a view to a fiber, which has a fiber wall being tight to the metal microstructure, has a supported fiber wall and is bulging, scale bar 10 micrometers;

[0081] FIG. 4 An electron microscopy image of a metal-inside-fiber-composite according to an embodiment of the invention revealing a view to a fiber, which has a fiber wall being tight to the metal microstructure, has a supported fiber wall and is bulging, scale bar 10 micrometers;

[0082] FIG. 5 An electron microscopy image of a metal-inside-fiber-composite according to an embodiment of the invention revealing a view to a fiber, which has a fiber wall being tight to the metal microstructure, has a supported fiber wall and is bulging, scale bar 1 micrometer;

[0083] FIG. 6 An electron microscopy image of a metal-inside-fiber-composite according to an embodiment of the invention revealing a view to a fiber, which has a fiber wall being tight to the metal microstructure, has a supported fiber wall and is bulging, scale bar 1 micrometer;

[0084] FIG. 7 An electron microscopy image of a metal-inside-fiber-composite according to an embodiment of the invention, revealing a view to a cross-section of the fiber as a result of fiber-fracture, scale bar 10 micrometers;

[0085] FIG. 8A fabric including a metal-inside-fiber-composite according to an embodiment of the invention;

[0086] FIG. 9 An optical microscopy image of a fabric, the fabric being yarn, scale bar 20 micrometers; and

[0087] FIG. 10 An optical microscopy image of a metal-inside-fiber-composite, the cellulose based fiber being cotton fiber, scale bar 20 micrometers.

DETAILED DESCRIPTION

[0088] FIGS. 1 and 2 show optical microscopy images of a metal-inside-fiber-composite 1 according to the invention. The elemental metal is copper. The fibers are cellulose based fibers 2. The metal-inside-fiber-composite is synthesized/produced by a method according to the invention. The optical microscopy images demonstrate how bright and shiny the metal-inside-fiber-composite is due to the metal microstructure 5.

[0089] FIGS. 3 to 7 show the metal particles 6 being interconnected to form the metal microstructure 5 inside the cellulose based fibers 2. FIGS. 3 to 7 further show the metal microstructure 5 filling and extending through and along the continuous void space of the fiber such that the fiber wall 3 forms a protective layer around the metal microstructure 5.

[0090] FIG. 7 shows a fractured metal-inside-fiber-composite 1 revealing a view to a cross-section of the cellulose based fiber 2 and to the continuous void space 4/fiber lumen being filled with metal particles 6.

[0091] The average particle size of the metal particles 6 of a metal microstructure 5 can be derived from electron microscopy images, based on measuring a reasonable number of metal particles 6 by determining their expansion into several directions in the image plane. The as derived metal particles' sizes are averaged by the number of measured metal particles 6. A reasonable number of metal particles 6 is, for example 20, 50 or 100. The as derived average particle size for metal-inside-fiber-composites 1 lies within the range of 80 nm to 1000 nm.

[0092] Metal-inside-fiber-composites 1 have been produced including the metal microstructure 5 by 60, 70, 80, 90, 95 or 98 weight percent of the total weight of the metal-inside-fiber-composite.

[0093] FIGS. 3 to 7, show a metal-inside-fiber-composite 1, wherein the metal microstructure 5 fills the void space to such a degree that the fiber wall 3 is tightly fitting to the metal microstructure 5.

[0094] FIGS. 3 to 7 further show, the fiber wall 3 being supported by the metal microstructure 5 such that the fiber wall does not collapse.

[0095] FIGS. 3 to 7 further show, that the fiber is bulging compared to the fiber being in a state where the void space is empty.

[0096] Metal-inside-fiber-composites 1 according to the invention form a versatile starting material for producing fabrics 7 thereof. FIG. 8 shows such a fabric 7 being electrically conductive. The fabric 7 is a paper like structure including and produced from metal-inside-fiber-composites 1 according to the invention. FIG. 8 shows two crocodile clips connect the paper like structure 7 with a 3 V coin cell and a red lighting light emitting diode (LED) 8 (2.5 V, 25 mA, 100?) on a breadboard.

[0097] FIG. 9 shows an optical microscopy image of a fibrous material, the fibrous material being yarn, wherein the fibrous material has been made electrically conductive by a method according to the invention.

[0098] FIG. 10 shows a metal-inside-fiber-composite, the cellulose based fiber being cotton fiber.

[0099] FIGS. 1 to 10 show, that the metal-inside-fiber-composite 1 according to the invention increases the resilience of the composite, because the metal microstructure and metal particles 6 are protected inside the cellulose based fibers 2 and cannot be detached therefrom during further processing as a metal coating on the surface of a cellulose based fiber might be.

[0100] A disadvantage relating to a biopolymer based fiber having a metal coating on the surface is that the coating can be incomplete or the electrical conductivity can be inhibited by cracks in the coating. The metal-inside-fiber-composite 1 according to the invention does not suffer from this disadvantage.

[0101] In the following a method of producing a metal-and-fiber-composite according to the invention is outlined.

[0102] In an exemplary embodiment of the method the following chemicals are used:

[0103] Benzyl alcohol (in particular anhydrous, with a purity of 99.8%) as first alcohol, copper (II) acetylacetonate as metal salt (Cu(acac) 2, in particular with a purity of ?99.99%), and glycerol as third alcohol (in particular with a purity of ?99%), methanol as second alcohol (in particular anhydrous, with a purity of 99.9%) and acetone (in particular being extra dry ?99.8%). All chemicals were used without further purification.

[0104] Instead of benzyl alcohol, alternatively, a derivative therefrom can be used. For example one of methyl benzyl alcohol, methoxy benzyl alcohol etc.

[0105] Instead of glycerol, alternatively, another polyol can be used, for example one of ethylene glycol, diethylene glycol, triethylene glycol etc.

[0106] Instead of methanol, alternatively, one of ethanol and propanol can be used.

[0107] Furthermore, delignified cellulose in the form of pulp was used as fibrous material.

[0108] The delignified cellulose can be obtained, for example, in the form of a 33 weight percent of cellulose in water mixture, wherein the water can be removed by drying the cellulose in an oven with ambient atmosphere at 60? c.

[0109] In this exemplary embodiment Cu(acac)2 is used as metal salt, nevertheless also copperacetate, coppermethoxide, nickelacetylacetonate, nickelacetate, and nickelmethoxide, or one of a gold metal salt, a silver metal salt, a palladium metal salt, a platinum metal salt and a lead metal salt, can be used as metal salt in combination with the chemicals listed above, and in the exemplary embodiment of the method outlined below.

[0110] In this exemplary embodiment delignified cellulose is used as fibrous material, nevertheless also, biopolymer based fibers, cellulose based fibers, and fibrous fabrics, in particular polymeric fibrous fabrics, can be used as fibrous material in combination with the chemicals listed above, and in the exemplary embodiment of the method outlined below.

[0111] For producing, according to an embodiment of the method for producing a metal-and-fiber-composite, metal-inside-fiber-composites according to the invention, 600 mg of Cu(acac)2 are dissolved in 5.2 mL of anhydrous benzyl alcohol (relating to a concentration of 0.44 moles Cu(acac)2 per liter), in particular inside a glove box under argon atmosphere. Alternatively, the concentration can be within the range of 0.2 to 0.5 moles per liter, in particular 0.22 moles per liter.

[0112] Five drops of methanol are added and the mixture is stirred, in particular for several hours. This reactant mixture/solution is transferred to a glass vessel containing 30 mg of loose cellulose fluff, in particular inside the glovebox.

[0113] The reaction vessel is sealed with a Teflon cap, in particular taken out of the glovebox, and transferred into a preheated oil bath set at 160? C. The solution is not stirred and kept at 160? C. for three hours. Nevertheless, stirring is optional, meaning that the solution, alternatively, can be stirred.

[0114] 1.8 ml of glycerol (vol % of total amount of benzyl alcohol:vol % of glycerol=3:1) are dropped on top of the solution.

[0115] During the following hour still at 160? C., the liquid around the now reddish colored cellulose fibers becomes orange and transparent.

[0116] Subsequent to this color change, 2.6 ml of a previously prepared 0.44 moles Cu(acac)2 per liter anhydrous benzyl alcohol solution plus methanol are added (concentration can be within the range of 0.2 to 0.5 moles per liters, in particular 0.22 moles per liter Cu(acac)2). This addition of reactant solution is done twice more and in between the addition steps, the reaction was kept at 160? C. for one and a half hours until the liquid turned orange and transparent again.

[0117] Following the last color change, 2.7 mL of glycerol are dropped on top of the supernatant. The step is optional and can, alternatively, be omitted.

[0118] The reaction is kept at 160? C. for a total of less than 24 hours, in particular less than 12 hours or less than 8 hours. If adding glycerol is omitted (see above) the reaction can be kept at 160? C. for a total of less than 12 hours. Afterwards, the reaction mixture is cooled down to room temperature.

[0119] If stirring is applied (see above) and adding glycerol is omitted (see above), the reaction can be kept at 160? C. for a total of less than 6 h.

[0120] The metal-inside-fiber-composite, wherein the elemental metal is copper, is washed several times with acetone until the supernatant is transparent and colorless and they are dried under vacuum.

[0121] Using a glove-box is optional, because all steps of the method can be performed outside a glove-box under ambient atmospheric conditions.

[0122] Instead of the 160? C., also a temperature of 140? C. or of 180? C. can be used.

[0123] Heating can also be performed by using microwave irradiation.

[0124] The formation of the metal microstructure inside the cellulose based fiber proceeds via the transformation of the metal ionic species of the metal salt to the metal. It has been observed, that the addition of methanol to the first and/or second reactant mixture supports the reduction process such that it proceeds faster and to a more complete degree.

[0125] The first alcohol, in particular benzyl alcohol, acts as solvent and as reducing agent. It has been further observed that using glycerol in addition to the first alcohol and/or the second alcohol further supports the reduction process. It can be advantageous to add glycerol to the reactant mixture/solution after three hours of reaction time to give the metal salt enough time to penetrate into the biopolymer based fibers. It is assumed that the addition of glycerol at the beginning of the synthesis could accelerate the reaction mechanism too much and the metal could form as well in solution and not preferably inside the biopolymer based fiber.

[0126] It has been observed, that without repeating the step of adding the second reactant mixture to the first reactant mixture being combined with the fibrous material not enough amount of the metal microstructure forms inside the biopolymer based fiber to make the metal-inside-fiber-composite electrically conductive.

[0127] Without repeating the step of adding the second reactant mixture to the first reactant mixture being combined with the fibrous material the metal-inside-fiber-composite typically includes the metal microstructure by around 35 weight percent of the total weight of the metal-inside-fiber-composite. The amount of metal microstructure included inside the metal-inside-fiber-composite can, for example, be determined based on weighing the fibrous material before and after the production of the metal-inside-fiber-composite. It could also be determined based on weighing the metal-inside-fiber-composite and weighting the metal-inside-fiber-composite after selectively removing the fibrous material.

[0128] By repeating the step of adding the second reactant mixture to the first reactant mixture being combined with the fibrous material, metal-inside-fiber-composites can be produced including the metal microstructure at desired amounts. For example, the metal microstructure can be included by 60 weight percent, by at least 70 weight percent, by at least 80 weight percent, by at least 90 weight percent, or by at least 95 weight percent of the total weight of the metal-inside-fiber-composite.

[0129] Analysis of as-prepared metal-inside-fiber-composites and fibrous material by x-ray diffraction (not shown) reveal, that the metal microstructure includes crystalline metal particles.

[0130] Further advantages of the method for producing a metal-and-fiber-composite according to the invention are briefly outlined below: [0131] No need for expensive high-vacuum processes like magnetron sputtering, [0132] an easy synthesis using a comparably cheap heating source, in particular an oil bath, microwave irradiation, [0133] No need for a catalyst, only solvent and metal salt, [0134] No need for a pre- or post-treatment of the metal-and-fiber-composite for making it electrically conductive, [0135] Compared to other electroless liquid-phase approaches, method is fast (<24 h), [0136] The method provides for the growth of a large metal microstructure also inside fibrous materials, in particular inside void spaces of fibers, wherein the access to the inside is provided by pores which are drastically smaller that the particles of the formed metal microstructure, [0137] The method can also be used for making biopolymer based, for example cellulose based, fibers or three-dimensional fibrous structures electrically conductive, not only 2D-like structures, [0138] The method is easily scalable, not needing to change the process parameters apart from using more chemicals and longer reaction times, [0139] It will be possible to mix or spin the metal-and-fiber-composite with other natural or synthetic fibers.