Patent Application
20200071877
The present invention relates to the field of electrically conductive textile elements and methods of producing same.
With the rapid advancement of flexible and wearable electronic devices there has been a demand for conductors as interconnects, contacts, electrodes and metal wires which can be integrated into conductive textiles/garments. Accordingly, methods for synthesizing fabricated high performance electrically conductive textiles have been developed including synthesizing of yarns by or incorporated with metal wires, metal oxide, intrinsically conducting polymers (ICPs), and carbon nanotubes (CNTs). However, conductive textiles fabricated in accordance with these existing methods are not ideal due to their inflexibility, chemical instability, cost of production, hazards posed to the human body, and most significantly, the difficulties associated with large scale production with compatible technology in the current textile and garment industry.
Another approach to synthesizing conductive textiles involves depositing metal coatings on to textile substrate surfaces utilising various metal particle deposition techniques. However, there are also limitations associated with this approach in terms of the relative amount of investment in technology, advanced instrumentation and specialized workforce expertise involved, as well the relatively precise control parameters required which limit industrialization of this process commercially. Furthermore, adhesion of the deposited metal on the textile surface remains another major concern on the durability and conductivity of such conductive textiles.
Further processes have been developed which involve modifying the surface architecture of textile substrates by grafting of functionalized polymer brushes thereon. In particular, polyelectrolytes that covalently tether one end on a textile substrate surface may not only provide modified functional groups on the textile substrate surface, but also increase the amount of functional groups to be utilized in subsequent chemical reactions. By way of example, Azzaroni et al., demonstrated the grating of positively-charged poly[2-(methacryloyloxy)ethyl]trimethylammonium chloride (PMETAC) polyelectrolytes on to a substrate surface. With the loading of catalytic moieties tetrachloropalladtae(II) anion ([PdCl4]2−) for subsequent metal electroless deposition (ELD), a robust metal layer is able to be selectively deposited with suitable adhesion properties. In 2010, Liu et al. reported a versatile approach to prepare durable conductive cotton yarns also by growing PMETAC brushes on cotton fiber surfaces using surface-initiated atom transfer radical polymerization (SI-ATRP), which was the first ever demonstration on grafting of PMETAC brushes on natural textile fibers. Subsequent metal ELD yielded conductive cotton yarns with high electrical stability that is able to withstand multiple bending, stretching, rubbing and even washing cycles. However, the feasibility of scale production of the SI-ATRP method taught by Liu et al. suffers from various problems. For instance, SI-ATRP is not able to be suitable performed under ambient conditions and requires nitrogen protection. Furthermore, the SI-ATRP reaction involves a relatively long period of time (˜24 hours) which is undesirable and not cost-effective for mass production. Thus, there is a need to modify the synthesizing process to allow for high throughput conductive textile production.
Other attempts have been made to modify the synthesizing approach by preparing electrically conductive fibers, yarns and fabrics by deposition of metals onto various textile substrates which are prior-modified with the same positively-charged polyelectrolytes PMETAC using in-situ free radical polymerization. In-situ free radical polymerization may increase the throughput of the polymerization of polyelectrolytes. Generally, the reaction only takes up ˜1-3 hours to complete and can be carried out under ambient conditions, which is highly advantageous over other polymerization methods such as previously mentioned SI-ATRP. However, this modified approach suffers from a drawback in that as the selection of catalytic moieties highly depends on the properties and nature of polyelectrolyte brush that grafted on the textile surface, cationic PMETAC is restricted to couple with anionic [PdCl4]2− moieties for subsequent electroless metal deposition. Furthermore, the [PdCl4]2− moieties used are relatively expensive (USD159.5 per 2 grams for 97% ammonium tetrachloropalladate(II)). Even though the anionic [PdCl4]2− moieties can be reused, it is still not economical if it is used in the mass production.
The present invention seeks to alleviate at least one of the above-described problems.
The present invention may involve several broad forms. Embodiments of the present invention may include one or any combination of the different broad forms herein described.
In a first broad form, the present invention provides a method of producing an electrically conductive textile element including the steps of:
(i) modifying a surface of a textile element with a negatively-charged polyelectrolyte; and
(ii) coating the modified surface of the textile element with metal particles.
Preferably, the step (i) may include modifying the surface of the textile element with a negatively-charged polyelectrolyte by in-situ free radical polymerisation.
Preferably, the negatively-charged polyelectrolyte may includes at least one of poly(methacrylic acid sodium salt) and poly(acrylic acid sodium salt).
Preferably, the step (i) may include modifying a silanized surface of a textile element with a negatively-charged polyelectrolyte.
Preferably, the step (ii) may include coating the modified surface of the textile element with metal particles by electroless metal deposition.
Preferably, the metal particles may include at least one of copper and nickel particles.
Preferably, the textile element may include at least one of a yarn and a fiber configured for being formed in to a fabric.
Preferably, the textile element may include at least one of a polyester, nylon, cotton and silk yarn or fiber.
In a further broad form, the present invention provides an apparatus for producing an electrically conductive textile element including:
an apparatus for modifying a surface of a textile element with a negatively-charged polyelectrolyte; and
a coating apparatus for coating the modified surface of the textile element with metal particles.
Preferably, the apparatus for modifying the surface of the textile element with the negatively-charged polyelectrolyte may be configured to modify the surface of the textile element with a negatively-charged polyelectrolyte by in-situ free radical polymerisation.
Preferably, the negatively-charged polyelectrolyte may include at least one of poly(methacrylic acid sodium salt) and poly(acrylic acid sodium salt).
Preferably, the apparatus for modifying the surface of the textile element with the negatively-charged polyelectrolyte may be configured to modify a silanized surface of a textile element with a negatively-charged polyelectrolyte.
Preferably, the coating apparatus may be configured to coat the modified surface of the textile element with metal particles by electroless metal deposition.
Preferably, the metal particles may include at least one of copper and nickel particles.
Preferably, the textile element may include at least one of a yarn and a fiber configured for being formed in to a fabric.
Preferably, the textile element may include at least one of a polyester, nylon, cotton and silk yarn or fiber.
In a further broad form, the present invention provides an electrically conductive textile element produced in accordance with the method steps of the first broad form of the present invention.
In a further broad form, the present invention provides a fabric formed from at least one textile element wherein the at least one textile element is produced in accordance with the method steps of the first broad form of the present invention.
The present invention will become more fully understood from the following detailed description of a preferred but non-limiting embodiment thereof, described in connection with the accompanying drawings, wherein:
Exemplary embodiments of the present invention will now be described with referenced to the
Referring firstly to
In performing the process, cotton yarns are first immersed in a solution of 5-20% (v/v) C═C bond bearing silane for approximately 30 minutes so as to allow the hydroxyl groups of cellulose to suitably react with the silane molecules. The cotton yarns are then rinsed thoroughly with fresh deionized (DI) water so as to remove any excess physical adsorbed silane and by-product molecules. This step of silanisation is represented by (100) in
The rinsed cotton yarns are then placed into an oven at 100-120° C. for between approximately 15-30 minutes to complete the condensation reaction. Subsequently, the silane-modified cotton yarns are immersed into approximately 50 mL aqueous solution comprising of 3-7 g of MANa powder and 35-75 mg of K2S2O8 (similarly, AANa powder may be used in respect of PAANa polyelectrolytes). The whole solution mixture with cotton yarns is heated at 60-80° C. in an oven for 0.5-1 hour in order to carry out the free radical polymerization. In the free radical polymerization process, the double bond of silane can be opened by the free radicals resulting in the growth of PMANa polyelectrolyte onto the cotton fiber surface. This step of free radical polymerisation is represented by (110) in
Thereafter, the PMANa-coated cotton yarns are immersed into a 39 g/L copper(II) sulphate pentahydrate solution for 0.5-1 hour, where the Cu2+ ions are immobilized onto the polymer by ion exchange. Followed by reduction in 0.1-1.0 M sodium borohydride solution, Cu2+ will be reduced to Cu particles which act as nucleation sites for the growth of Cu in the subsequent electroless deposition of Cu. This step of ion exchange and reduction is represented by (120) in
The polymer-coated cotton after reduction in sodium borohydride solution is immersed in a copper electroless plating bath consisting of 12 g/L sodium hydroxide, 13 g/L copper(II) sulphate pentahydrate, 29 g/L potassium sodium tartrate, and 9.5 mL/L formaldehyde in water for 60-180 minutes. The as-synthesized Cu-coated yarns are rinsed with deionized (DI) water and blown dry. The step of performing electroless metal deposition is represented by (130) in
The silane-modified cotton and PMANa-grafted cotton are able to be characterized by Fourier transform infrared spectroscopy (FTIR). As shown in
The PMANa-grafted cotton is also able to be characterized by energy-dispersive X-ray spectroscopy (EDX). It is shown in
The conductivity of the copper-coated cotton yarns is able to be characterized by a two-probe electrical testing method. In this regard, linear resistance of the copper-coated yarns in the fabrication is found to be ˜1.4 Ω/cm as shown in
To further test the adhesion of the copper on the cotton yarn surface and the washing durability, the copper-coated cotton yarns are first woven into a fabric first. As-synthesized copper-coated cotton yarns shown in
It should be noted that according to the testing standard, 1 washing cycle is equivalent to approximately 5 commercial machine laundering cycles. In total, 6 washing cycles are conducted, which accordingly, is considered to equate to approximately 30 commercial machine laundering cycles. Changes in the electrical resistance of the washed fabrics are able to be evaluated using a four-probe method whereby the sheet resistances of the fabrics produced in accordance with this embodiment are measured to be 0.9±0.2 ohm/sq (unwashed), and 73.8±13.4 ohm/sq after the fourth wash which is equivalent to approximately 20 commercial machine laundering cycles as shown in
The surface morphology of the washed copper-coated cotton yarns are able to be characterized by unraveled the washed copper-coated cotton yarns from the fabric and examined under an SEM. As shown in the SEM images of
It is also noted that during application of the standard washing cycle to the produced fabric, 50 pieces of steel balls are added into the washing canisters in seeking to simulate vigorous rubbing and stretching forces of a laundering machine. The abrasion of the steel balls on the fabric impacts substantially upon the fiber structure. As the copper-coated cotton fibers are no longer held in a tightened manner it is perceived that they lose contact with each other so as to reduce conductive pathways available for the movement of electrons. Accordingly, the sheet resistance increases upon repeated washing cycles notwithstanding, the SEM images in
In alternate embodiments of the present invention, rather than coating the cotton fibers with copper particles, nickel metal particles may instead be electrolessly plated on to the textile surface by using the same approach described above. Same experimental procedures and testing may be conducted however the source of nickel that may be utilised is 120 g/L nickel(II) sulphate solution in the ion exchange procedure. Subsequently an electroless nickel plating bath is utilised consisting of 40 g/L nickel sulphate hexahydrate, 20 g/L sodium citrate, 10 g/L lactic acid, and 1 g/L dimethylamine borane (DMAB) in water for 60-180 minutes. The sheet resistance of the resulting nickel-coated cotton fabric is found to exhibit substantially similar results as that of the copper coated fiber yarns as shown in
It will be appreciated that other embodiments of the present invention may involve the use of substrates other than cotton and could be suitably applied to various textile materials such as silk, nylon and polyester. In this regard, an exemplary PAANa-assisted copper-coated yarn produced in accordance with an embodiment of the present invention is shown represented by (400) in
It will be appreciated from the preceding summary of the broad forms of the invention that various advantages may be conveniently provided including electrically conductive textile elements may be produced which may be suitably flexible, wearable, durable and/or washable for integration into a textile/fabric. Moreover, such high performance electrically conductive textile elements (fibers, yarns and fabrics) may be produced utilising relatively low-cost technology cost-effectively on a mass scale based upon the chemical reaction of in-situ free radical polymerization to grow negatively-charged polyelectrolytes such as PMANa or PAANa on textile substrates which may conveniently provide an improved negatively-charged polyelectrolyte layer bridging the electrolessly deposited metal and textile elements and substrates. Notably, the adhesion of conductive metal to textile substrates may be greatly improved by such surface modification of a layer of negatively-charged polyelectrolyte PMANa or PAANa, in which the electrical performance of such conductive textiles may be more reliable, robust and durable under repeated cycles of rubbing, stretching, and washing. Also, the in-situ free radical polymerization method used to prepare the negatively-charged polyelectrolyte may be performed under ambient and aqueous conditions without using any strong chemicals.
Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described without departing from the scope of the invention. All such variations and modification which become apparent to persons skilled in the art, should be considered to fall within the spirit and scope of the invention as broadly hereinbefore described. It is to be understood that the invention includes all such variations and modifications. The invention also includes all of the steps and features, referred or indicated in the specification, individually or collectively, and any and all combinations of any two or more of said steps or features.
The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge.
| Number | Date | Country | Kind |
|---|---|---|---|
| 15102150.5 | Mar 2015 | HK | national |
This application is a continuation of U.S. patent application Ser. No. 15/554,695, filed Aug. 30, 2017, which is incorporated herein by reference in its entirety for all purposes.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 15554695 | Aug 2017 | US |
| Child | 16593885 | US |
