METHOD FOR PRODUCING ANTIMICROBIAL YARNS AND FABRICS BY NANOPARTICLE IMPREGNATION

Abstract

The invention relates to a method for producing an antimicrobial fabric or yarn, said method comprising the steps of immersing a fabric or yarn in an aqueous solution of a metal salt whilst simultaneously subjecting said solution to ultrasonic radiation; and removing the fabric or yarn from said solution and subsequently converting the metal salt in situ in the fabric or yarn into metal oxide nanoparticles, preferably via chemical and heat treatment. Fabrics and yarns obtained or obtainable by such method are also provided. In a further aspect the invention provides an apparatus for performing such method.

Claims

1. A method for producing an antimicrobial fabric or yarn, said method comprising the steps of: (i) immersing a fabric or yarn in an aqueous solution of a metal salt whilst simultaneously subjecting said solution to ultrasonic radiation; and (ii) removing the fabric or yarn from said solution and subsequently converting the metal salt in situ in the fabric or yarn into metal oxide nanoparticles, preferably via chemical and heat treatment.

2. A method according to claim 1, wherein step (ii) comprises exposing the fabric or yarn, whilst still damp, to ammonia or a primary amine (preferably in gaseous form); and heating the fabric or yarn.

3. A method according to claim 1 or claim 2, wherein the metal salt is a salt of a metal whose oxide has antimicrobial properties.

4. A method according to any one of claims 1 to 3, wherein the metal salt is a salt of copper, zinc or magnesium.

5. A method according to any one of claims 1 to 4, wherein the metal salt is a halide, nitrate, nitrite, sulphate, acetate, propanoate or butanoate.

6. A method according to any one of claims 1 to 5, wherein the metal salt is selected from the group consisting of copper (II) sulphate, copper (II) acetate, copper (II) chloride, copper (II) fluoride, copper (II) bromide, copper (II) iodide, copper (II) nitrate, copper (II) nitrite, copper (II) propanoate, copper (II) butanoate, zinc sulphate, zinc acetate, zinc chloride, zinc fluoride, zinc bromide, zinc iodide, zinc nitrate, zinc nitrite, zinc propanoate, zinc butanoate, magnesium sulphate, magnesium acetate, magnesium chloride, magnesium fluoride, magnesium bromide, magnesium iodide, magnesium nitrate, magnesium nitrite, magnesium propanoate, magnesium butanoate, and mixtures thereof.

7. A method according to any one of claims 1 to 6, wherein the aqueous solution contains only a single metal salt.

8. A method according to any one of claims 1 to 6, wherein the aqueous solution contains a plurality of metal salts.

9. A method according to any one of claims 1 to 8, wherein the metal salt(s) is/are present in the aqueous solution in an amount of about 0.001 mol/L to about 0.25 mol/L.

10. A method according to any one of claims 1 to 9, wherein the aqueous solution is substantially free of ammonia.

11. A method according to any one of claims 1 to 10, wherein the duration of ultrasonic radiation is about 15 minutes or less.

12. A method according to any one of claims 1 to 11, wherein step (i) is carried out at a temperature of up to about 60° C.

13. A method according to any one of claims 2 to 12, wherein the duration of exposure of the fabric or yarn to ammonia or a primary amine is about 25 minutes or less.

14. A method according to any one of claims 2 to 13, wherein heating is carried out at a temperature of about 100° C. to about 150° C.

15. A method according to any one of claims 2 to 14, wherein heating is carried out by microwave heating or electrical heating.

16. A method according to any one of the preceding claims further comprising the following steps: (iii) washing the fabric or yarn after step (ii) and, optionally, (vi) drying the fabric or yarn.

17. A method according to any one of the preceding claim, wherein the method is performed as a continuous process.

18. A method according to any one of claims 1 to 16, wherein the method is performed as a batch process.

19. A method according to any one of the preceding claims, wherein the fabric or yarn comprises naturally-occurring or semi-synthetic fibres.

20. A method according to any one of the preceding claims, wherein the fabric or yarn comprises cotton, hemp, or silk.

21. An antimicrobial fabric or yarn obtained or obtainable by the method of any one of claims 1 to 20.

22. An apparatus for performing a method as described in any one of claims 1 to 20, said apparatus comprising: a first vessel for immersing a fabric in a metal salt solution, said vessel being adapted to provide ultrasound radiation to said solution; a second vessel arranged to receive the fabric or yarn from said first vessel, said second vessel being adapted for the exposure of the fabric or yarn to gaseous ammonia; a source of ammonia gas connected to said second vessel; and heating means for heating the fabric or yarn.

23. An apparatus according to claim 22 further comprising a recirculation circuit adapted to allow a metal salt solution to be continuously circulated through the first vessel whereby to maintain a substantially constant metal salt concentration in the metal salt solution located in the first vessel.

Description

[0071] The invention will now be described in more detail in the following non-limiting Examples and Figures, in which:

[0072] FIG. 1 shows an apparatus according to the invention;

[0073] FIG. 2 shows a suitable arrangement of feeding tanks and topping up tanks suitable for recirculation and replenishment of the metal salt soaking solution;

[0074] FIG. 3 shows the results of a test comparing metal salt loading into a fabric with and without sonication; and

[0075] FIGS. 4 and 5 show SEM pictures of a cotton fabric treated according to the method of the invention using CuCl.sub.2 as the metal salt.

EXAMPLE 1: SOAKING EXPERIMENTS WITH AND WITHOUT SONICATION

[0076] Small samples of a cotton fabric were each soaked in a solution of a copper salt. Three different copper salt solutions were employed, each at a concentration of 0.1 moles/L: CuSO.sub.4.5H.sub.2O, CuCl.sub.2.2H.sub.2O, and Cu(OAc).sub.2.H.sub.2O.

[0077] Samples were soaked in the copper salt solutions in the following combinations: [0078] 1. CuSO.sub.4.5H.sub.2O, 5 minutes' “silent” soaking (no ultrasonication) [0079] 2. CuSO.sub.4.5H.sub.2O, 5 minutes' soaking with simultaneous ultrasonication [0080] 3. CuCl.sub.2.2H.sub.2O, 5 minutes' “silent” soaking [0081] 4. CuCl.sub.2.2H.sub.2O, 5 minutes' soaking with simultaneous ultrasonication [0082] 5. Cu(OAc).sub.2.H.sub.2O, 5 minutes' “silent” soaking [0083] 6. Cu(OAc).sub.2.H.sub.2O, 5 minutes' soaking with simultaneous ultrasonication [0084] 7. Cu(OAc).sub.2.H.sub.2O, continuous “silent” soaking for 2.5 minutes [0085] 8. Cu(OAc).sub.2.H.sub.2O, continuous soaking with simultaneous ultrasonication for 2.5 minutes

[0086] Ultrasonic radiation was provided by an ultrasonic bath, working at 40 kHz and 180 watts power. 2.5 L of salt solution were employed, resulting in an ultrasonic power density of 0.072 W/cm.sup.3.

[0087] After the end of the soaking period, the samples were removed and dried and the copper content was determined using ICP (inductively coupled plasma atomic absorption spectroscopy).

[0088] The results are shown in FIG. 3. For all copper salts tested, it was found that soaking with ultrasonication yielded a copper loading between 3 and 5 times greater than “silent” soaking. Of the samples soaked for 5 minutes, which is representative of a typical industrial soaking time, copper acetate demonstrated the greatest loading both under silent and under ultrasonic conditions. This is indicative of the affinity of this salt for natural fibres.

EXAMPLE 2: TREATMENT OF COTTON FABRIC

[0089] A sample of cotton fabric was treated using CuCl.sub.2 solution and 5 minutes ultrasonication as described above in Example 1. Following this treatment, and whilst still damp, the fabric was exposed to ammonia gas and then heated using microwave radiation of about 2.45 GHz frequency and about 800 W power for about 2 minutes in order to form copper oxide nanoparticles.

[0090] The resulting nanoparticle-impregnated fabric was studied using scanning electron microscopy (SEM), with exemplary results shown in FIGS. 4 and 5. Approximately spherical nanoparticles with a diameter of about 150-200 nm were produced, giving substantially uniform coverage of the fabric.

EXAMPLE 3: ANTIMICROBIAL TEST

[0091] Samples of cotton fabrics treated according to the method of the invention were tested against E. coli using a simplified absorption test. The samples contained either copper oxide, a copper/zinc oxide combination or zinc oxide nanoparticles. Fabric samples were incubated overnight at 37° C. with a small volume of bacterial suspension containing approx. 2×10.sup.4 bacteria. After incubation bacteria were washed out of fabrics and plated on nutrient agar plates for overnight incubation and subsequent colony counting. Each live bacterium would result in the growth of one colony.

[0092] All of the samples produced>99.9% reduction in cell numbers overnight and zero live bacteria were recovered after incubation, compared to many thousands of bacteria recovered from a plain cotton (untreated) control sample.