Field Of The Invention

The invention relates to an antimicrobial non-woven fabric and a method of preparing the antimicrobial non-woven fabric.

Background Of The Invention

Drinking water is an important part of life and according to a survey only 4% of potable water is available on planet earth. Drinking contaminated water can cause fatal diseases such as diarrhea, cholera and typhoid. According to WHO statistics, about 3.8 crore people in India are affected by water-borne diseases each year, in which 75% are children. Therefore, there is a need to provide an efficient water filter to overcome the problems pertaining to access to potable water.

Antimicrobial filter is mostly used for reducing the bacterial concentration in drinking water for safe water filtration and reduce water-borne diseases like diarrhea, dysentery, typhoid etc., and silver has been widely used as antimicrobial agent to inhibit bacterial proliferation in the contaminated water.

Further, the application of nanotechnology for the purpose of purification of water is already known in the art. Application of nanotechnology in antimicrobial filter has potential to kill pathogenic due to higher reactivity and potency of nano-sized particles.

Phong, Nguyen et al. disclosed a polyurethane foam embedded with silver nano-particle for water filtration wherein 12 nm silver nanoparticle was soaked by PU foam within 10 hour. The filter resulted in reduction of the gram negative bacteria and gram-positive bacteria.

Another disclosure in Chen, Shuixia, Jinrong Liu et al. provided application of the silver nanoparticle for water filtration wherein activated carbon fiber with antimicrobial activity, silver nitrate (AgNO3) was mixed with the petroleum pitch and spun into the fiber. The antimicrobial fiber had ability to kill E.coli and S. aureus bacteria in drinking water.

Other than silver nanoparticles, ZnO (zinc oxide) nanoparticles as disclosed in Masoumbaigi, Hossin, et al. can also be used as antimicrobial agent (B. subtilis and E. coli). It disclosed that applicability of ZnO nanoparticles in drinking water and sanitation system can be possible.

Furthermore, the application of textile fabric such as woven fabric, non-woven fabric, knitted fabric, for water filtration is also known in the art. The non-woven fabric has higher filtration capacity than other type of fabrics due to their higher number of pores pertaining to higher filtration velocity than other fabrics. However, water filtration through use of such fabrics is inefficient since bacteria are mostly 1-10 µm in size, hence can easily pass through the filter device and contaminate filtered water.

The above discussed techniques although commercially used, are expensive and have failed to provide effective water filtration. Further, the problem of higher leaching rate with the increase in concentration of antimicrobial agent like silver which is highly toxic to the human body cells, if present in high amounts, still persists and therefore, there is a need of an improved filter having antimicrobial properties which effectively cleans the contaminated water with controlled leaching.

Summary Of The Invention
In one aspect, the present invention relates to an antimicrobial non-woven fabric comprising a non-woven fabric and a combination of nanoparticles comprising of one or more metal and a minimum of two metal oxides.

In another aspect of the invention, a process of preparing an antimicrobial non-woven fabric is disclosed. The process comprises the steps of making a dispersion of nanoparticles of one or more metal and a minimum of two metal oxides. To the dispersion, a non-woven fabric is added and heated.

Brief Description Of The Drawings
Figure 1: Temperature and time curve of High Temperature High Pressure process.

Figure 2: XRD pattern of synthesized ZnO nanoparticles.

Figure 3: XRD pattern of commercial ZnO nanoparticles.

Figure 4: (a) SEM image of synthesized ZnO nanoparticles and (b) TEM image of synthesized ZnO nanoparticles.

Figure 5: (a) XRD pattern of synthesized MgO nanoparticles and (b) TEM image of synthesized MgO nanoparticles.

Figure 6: (a) UV/Visible absorption spectrum of synthesized silver nanoparticles and (b) TEM image of synthesized silver nanoparticles.

Figure 7: (a) TEM image of synthesized copper nanoparticles and (b) DLS results of synthesized copper nanoparticles.

Figure 8: SEM images of polyester woven fabric with ZnO nanoparticles embedded at different concentrations (a) Untreated polyester filament, (b) polyester non-woven fabric treated with ZnO nanoparticles (8 mg/ml), (c) polyester non-woven fabric treated with ZnO nanoparticles (10 mg/ml), (d) polyester non-woven fabric treated with ZnO nanoparticles (12 mg/ml).

Figure 9: SEM images of polyester non-woven fabric with ZnO nanoparticles embedded at different magnification at 12mg/ml (a) Untreated polyester filament, (b) polyester non-woven fabric treated with ZnO nanoparticles (12 mg/ml) at 5000 magnification, (c) Untreated polyester filament, (d) polyester non-woven fabric treated with ZnO nanoparticles (12 mg/ml) at 10000 magnification.

Figure 10: SEM images of polyester non-woven fabric with ZnO nanoparticles embedded at 24 mg/ml (a) Untreated polyester filament at 10000 magnification, (b) polyester non-woven fabric treated with ZnO nanoparticles (24 mg/ml) at 10000 magnification.

Figure 11: FESEM image and EDX analysis of ZnO nanoparticles embedded polyester woven fabric (8mg/ml).

Figure 12: FESEM image and EDX analysis of ZnO nanoparticles embedded polyester woven fabric (10mg/ml).

Figure 13: FESEM image and EDX analysis of ZnO nanoparticles embedded polyester woven fabric (12mg/ml).

Figure 14: Image of bacterial colonies in control sample at 0 minute.

Figure 15: Images for results of reduction in bacterial colonies at different time and different concentration of the ZnO nanoparticles.(a) CFU/ml at 2 hour for M1, (b) CFU/ml at 2 hour for M2, (c) CFU/ml at 2 hour for M3, (d) CFU/ml at 4 hour for M1, (e) CFU/ml at 4 hour for M2, (f) CFU/ml at 4 hour for M3, (g) CFU/ml at 7 hour for M1, (h) CFU/ml at 7 hour for M2, (i) CFU/ml at 7 hour for M3.

Figure 16: Images for results of reduction in bacterial colonies for tap water at different time at a concentration of 12 mg/ml of ZnO nanoparticles.(a) CFU/ml at 0 hour for control, (b) CFU/ml at 1 hour, (c) CFU/ml at 3 hours, (d) CFU/ml at 4 hours.

Figure 17: Images for results of reduction in bacterial colonies at different time at a concentration of 12 mg/ml of ZnO nanoparticles.(a) CFU/ml at 0 minutes for control, (b) CFU/ml at 10 minutes, (c) CFU/ml at 20 minutes, (d) CFU/ml at 30 minutes, (e) CFU/ml at 40 minutes, (f) CFU/ml at 50 minutes.

Figure 18: Images for results of reduction in bacterial colonies at different time at a concentration of 24 mg/ml of ZnO nanoparticles. (a) CFU/ml at 0 minutes for control, (b) CFU/ml at 10 minutes, (c) CFU/ml at 20 minutes, (d) CFU/ml at 30 minutes, (e) CFU/ml at 40 minutes.

Figure 19: SEM images of polyester non-woven fabric embedded with silver nanoparticles at different magnification. (a) Polyester filament at 80000 magnification, (b) Polyester filament with at 40000 magnification, (c) Polyester filament at 20000 magnification, (d) Polyester with at 10000 magnification.

Figure 20: Images for results of reduction in bacterial colonies in tap water at different time with silver nanoparticles. (a) CFU/ml at 0 minutes for control, (b) CFU/ml at 5 minutes, (c) CFU/ml at 10 minutes, (d) CFU/ml at 20 minutes, (e) CFU/ml at 30 minutes.

Figure 21: SEM images of polyester non-woven fabric embedded with MgO nanoparticles at different concentrations (a) Untreated polyester nonwoven (b) polyester non-woven fabric treated with MgO nanoparticles (16 mg/ml) (c) polyester non-woven fabric treated with MgO nanoparticles (20 mg/ml).

Figure 22: Images for results of reduction in bacterial colonies at different time and different concentration of the MgO nanoparticles (a) CFU/ml at 0 minutes for control, (b) CFU/ml at 1 hour for 20 mg/ml, (c) CFU/ml at 2 hours for 20 mg/ml, (d) CFU/ml at 1 hour for 16 mg/ml and (e) CFU/ml at 2 hours for 16 mg/ml.

Figure 23: SEM images of polyester woven fabric with Copper nanoparticles embedded at different concentrations (a) Untreated polyester nonwoven, (b) polyester non-woven fabric with copper nanoparticles (4 mg/ml), (c) polyester non-woven fabric treated with copper nanoparticles (6 mg/ml).

Figure 24: Images for results of reduction in bacterial colonies at different time and different concentration of copper nanoparticles (a) CFU/ml at 0 minutes for control, (b) CFU/ml at 30 minutes for 4 mg/ml, (c) CFU/ml at 1 hour 4 mg/ml, (d) CFU/ml at 2 hours 4 mg/ml, (e) CFU/ml at 30 minutes for 6 mg/ml, (f) CFU/ml at 1 hour for 6 mg/ml, and (g) CFU/ml at 2 hours for 6 mg/ml.

Figure 25: Gravity filter cartridge modified with anti-bacterial non-woven fabric.

Detailed Description Of The Invention
The present invention relates to an antimicrobial non-woven fabric and a filter made by layering the antimicrobial non-woven fabric preferably used for water filtration. The antimicrobial non-woven fabric is cost-effective and has controlled leaching rate of the antimicrobial agents in water so that the drinking water contains permissible limits of such antimicrobial agents.

The antimicrobial non-woven fabric comprises a non-woven fabric and an antimicrobial agent embedded on said non-woven fabric wherein the antimicrobial agent is a combination of nanoparticles of one or more metal and a minimum of two metal oxides.

The non-woven fabric is a polyester fabric preferably polyethylene terephthalate (PET) and has several advantages over other fiber forming polymer like polypropylene, nylon such as high tensile strength, high operating temperature, resistance against nitric, sulfuric and carbolic acids, high surface to volume ratio and larger pore size distribution and porosity over knitted and woven fabric, easy filter cake release, good dye ability with disperse dyes, lower crystallinity of the fiber and higher amorphous part. Moreover, polyester fabric has a fine fabric diameter which leads to high surface area to volume ratio with appropriate porosity and pore size distribution, which results in availability of more free volume for nanoparticles to diffuse inside the fiber and hence imparts higher filtration capacity to it. Further, polyester has a rigid chain structure due to presence of benzene ring in its chemical structure and it is more rigid chain than polypropylene and nylon. Due to the rigid structure of polyester (PET), the crystallization rate and capacity of polyethylene terephthalate is lower than polypropylene and nylon.

The metal present in a combination of antimicrobial agent is selected from nanoparticles of silver, copper or a combination thereof. The metal oxide is a combination of nanoparticles of zinc oxide (ZnO) and magnesium oxide (MgO).

Silver nanoparticles are fine particles of silver in a size range of 1 nm to 100 nm, possess higher surface area to volume ratio and has unique thermal, electrical and optical properties. It has the capability to penetrate the bacterial cell wall and forming a silver ions, free radicals, anchor the bacterial cell wall so, by their higher toxicity towards the bacteria it can damage cell wall of bacteria, and stop protein synthesis. Thus, silver nanoparticles have good antimicrobial activity.

ZnO nanoparticles are bio-safe material which has the photo-oxidizing and photo-catalysis effect on biological species. Antibacterial activity of the ZnO nanoparticles can be attributed by the formation of reactive oxygen species (ROS), electrostatic interaction, penetration of ZnO nanoparticles in bacterial cell wall and formation of the Zn2+ion.

MgO nanoparticles also have antibacterial activity attributed to Mg2+ ion formation, internalization of MgO nanoparticles and electrostatic attraction leading to death of bacteria.
Copper nanoparticles have antimicrobial activity by formation of the Reactive oxygen species (ROS), Cu2+ ion formation, lipid peroxidation, protein oxidation and DNA degradation.

Th nanoparticles preferably have a particle size in range from 5-100 nm.

Combination of nanoparticles of metal and metal oxide provides the following advantages.
1. Cost of preparation is low.
2. Copper, zinc and magnesium are essential elements for the human body.
3. To lower the leaching rate problem, combination of nanoparticles is used.

The nanoparticles synthesized by chemical reduction route are incorporated in non-woven fabric by high temperature high pressure (HTHP) infusion.

The process for preparing an antimicrobial non-woven fabric comprises of making a dispersion of nanoparticles comprising of one or more metal and a minimum of two metal oxides. Subsequently, a non-woven fabric is added in the dispersion followed by heating the dispersion.

In this process, a dispersion of the nanoparticles and the non-woven fabric in a desired ratio are taken in a vessel and subjected to a high temperature and high pressure conditions for a pre-defined time.

HTHP process helps to swell the filament of the fabric to some extent and heating increases the energy of nanoparticles that assist in penetration of nanoparticles in microstructure of fabric. Absorption of nanoparticles on surface of the fiber also increases which aids to give large surface to volume ratio for antimicrobial agent for good antimicrobial activity and some of the nanoparticles get diffused which are held with Van der Waal’s forces.

The fabric used in the invention has higher amorphous part and its glass transition temperature (Tg) is 80?, above the Tg, higher mobility of polymer chains occurs at that condition. Nanoparticles get absorbed on the surface and penetrate inside the fiber structure which gives higher capability to remove bacteria from infected water and lesser possibility of leaching into water.

The non-woven fabric is preferably polyester. The non-woven fabric and the nanoparticle dispersion is taken in a ratio of 1:60 in a vessel and heated to a temperature of 80°C-130°C and kept at a pressure in a range of 0-170 kPa for up to 100 minutes.

The invention also encompasses a filter made by layering the antimicrobial non-woven fabrics comprising a combination of nanoparticles of one or more metal and a minimum of two metal oxides.

The filter is made by layering in no particular order the antimicrobial non-woven fabrics. The non-woven fabric comprises preferably a polyester such as polyethylene terephthalate embedded with antimicrobial agents such as silver, copper, ZnO and MgO nanoparticles.

The invention also includes a filter comprising layers of antimicrobial non-woven fabric each embedded with silver, ZnO and MgO nanoparticles.

The invention also includes a filter comprising layers of antimicrobial non-woven fabric each embedded with copper, ZnO and MgO nanoparticles.

The filter is preferably used for filtering water.

The filter having polyester non-woven fabrics embedded with a combination of nanoparticles of antimicrobial agents inhibits the waterborne pathogenic bacteria and microbial proliferation due to their antimicrobial activity.

Filtration through fabric depends upon the pore size. Particles above the pore size are unable to pass through fabric so, separation of particles occurs from liquid during filtration process. The filtration takes place in three ways, first screening of particle so particle trap in the fabric, second, Van der Waal force and electrostatic attraction between particles and the fabric fiber so, it is able to stop particles less than the pore size, third, cake formed also helps in the filtration process by bridging effect with the porous part.

The fabric of the invention is found to have the following characteristics:
1. Filtration throughput rate is nearly equal to initial rate, generally rate of throughput goes down because cake is deposited on fabric so, there is less space for the liquid to pass and by the less space some pressure drop is created.
2. Fabric has high level of resistance to blinding, blinding is related to resistance by fabric after cake release due to their solid particles embedded on fabric.
3. Filter fabric has easy filter cake releasing capacity.
4. Filter fabric has same size of the pores, at time of pressure or when no pressure applied so, filter fabric has resistance to stretch and fatigue.
5. Resistance to abrasive force is high, that provides a longer life of the filter fabric.

The layers of antimicrobial non-woven fabric play a major role in inhibiting the bacteria and shows bactericidal and bacteriostatic properties at time of usage of the fabric. Non-woven fabric has different pore size and distribution which does not permit large particle size to pass during water filtration, but bacteria are in micron size, so it easily passes through the filter device, and gets adhered on the fabric itself. Therefore, it is necessary to kill the pathogenic bacteria at time of filtration using an antimicrobial agent.
Non-woven fabric has higher filtration capacity than woven or knitted fabrics due to the larger number of pores which also govern higher filtration velocity than other fabrics, Filtration efficiency of non-woven can be increased by the increase in the surface area per unit volume Few techniques which can increase surface area such as multi lobeled-shape of cross-section, peanut shape cross-section, irregular shape cross-section can be used.

Heat setting increases the stability of the thermoplastic fabric so; it can be used at higher temperature than that without heat setting and thus possess higher level of stability of pore giving higher filtration efficiency. Singing and calendaring is also done for improving rate of releasing cake which occur by removing the protruding end of fiber outside of fabric. Increased smoothness of fabric by calendaring process increases the packing coefficient of fabric so that the size of pore may be reduced giving a better filtration efficiency, raising can also be used to increase the fibrous surface of fabric which help to improve the filtration efficiency.

The antimicrobial non-woven fabric can also be used for making air filtration mask, geo-textile, sanitary napkins, diapers, packaging bags, surgical gowns, surgical mask, gloves, bath wipes, wound dressings, drug delivery, shoe covers, medical packaging etc.

Examples:
Synthesis of ZnO nanoparticles:
Zinc sulfate monohydrate (ZnSO4.H2O) and sodium hydroxide (NaOH) were taken at molar ratio 1:2. Zinc sulfate monohydrate was dissolved in deionized (DI) water and sodium hydroxide was added slowly dropwise by pipette under vigorous stirring. The stirring was continued for 12 hours and after this washing by DI water was done 5 times by using centrifuge (Sigma 2K15) at 9000 rpm for time 10 minutes. The zinc hydroxide formed was dried at 100? and was crushed by mortar to make a fine powder and calcined at 700? for 2 hours to extract ZnO nanoparticles.

Synthesis of the MgO nanoparticles:
Magnesium nitrate [Mg(NO3)2] and sodium hydroxide were used at molar ratio 1:1. Magnesium nitrate was dissolved in DI water, sodium hydroxide was added slowly dropwise by pipette under stirring, addition was continued up to 2 hours and after this washing by DI water was done 5 times and once with ethanol by using centrifuge (Sigma 2K15) at 9000 rpm, 10 minutes and dried at 80? for 4 hours. The resulting product was crushed by mortar to make a fine powder and calcined at 400? for 3 hours and finally MgO nanoparticles were obtained.

Synthesis of copper nanoparticles:
Copper nanoparticles were synthesized through wet chemical route using a copper precursor salt selected from copper nitrate copper sulphate and copper chloride or any salt of copper and a reducing agent selected from sodium borohydride, hydrazine hydrate, irradiation (Ultraviolet or Microwave).

The colour of the copper nitrate solution changed from sea blue to green indicating reduction of copper nanoparticles. The beaker was kept overnight at room temperature for aging. The copper nanoparticle solution was purified by repeated centrifugation at 12,000 RPM for 15 minutes. The copper nanoparticles were dried in an oven at 80°C to form a dried powder. The dried powder was further calcinated in muffle furnace at 400°C (380-420°C) for 3 hours (2-6 hours).

Synthesis of silver nanoparticles:
0.001M of silver nitrate (AgNO3) was taken in distilled water and 0.002M sodium borohydride (NaBH4) was taken in another beaker with distilled water, 30 ml 0.0020 M sodium borohydride was shifted to a 100 ml conical flask. The conical flask was placed into an ice bath and allowed to cool at 3? for about 20 minutes.
A magnetic bead was placed in the conical flask, which was mounted on a magnetic stirrer and mixed continuously by stirring for 25 minutes. Then 10 ml 0.0010 M of silver nitrate was added by 1ml syringe into the sodium borohydride solution, at a rate of 1 drop/second.

Method of preparation of antimicrobial non-woven fabric embedded with nanoparticles
ZnO nanoparticles were taken in three concentrations in distilled water (8 mg/ml, 10 mg/ml, 12 mg/ml) and further sonicated for 1 hour to deagglomerate the physical attraction between nanoparticles by ultrasonic wave. Nano plates of ZnO were delaminated during this process and a fine dispersion was obtained which was stable for 5 minutes and zeta potential of dispersion was – 0.85 mv. Therefore, the dispersion was sonicated for 5 minutes before the process of loading on the non-woven fabric.

IR dyeing machine (DaeLim starlet-7000 lab. testing machine) was used to for embedding the nanoparticles on filament surface of the fabric.

The fabric used in the present invention was a Needle punch polyester fabric with micro denier fiber (0.9 denier) as it had a higher surface to volume ratio, large number of pores, lower pressure drop, good filtration velocity compared to woven.

The ratio of the non-woven fabric material (M) to the liquid dispersion (L) such as the dispersion of ZnO nanoparticles as described above (M: L ratio) was taken as 1:60. Eight minutes were required to increase the temperature from 30? to 85? and then temperature was increased to 130? in 10 minutes. The temperature was kept constant at 130? for 60 minutes and then cooled to 80? in 10 minutes. The time-temperature graph is outlined in Figure 1. Finally, the fabric was washed with water twice to remove superficially deposited nanoparticles and dried in vacuum oven.
The antimicrobial non-woven fabric embedded with silver nanoparticles, copper nanoparticles, zinc oxide and magnesium oxide nanoparticles were prepared in the same manner as described in the above method.

The invention also discloses a filter comprising
a layer of a non-woven fabric embedded with nanoparticles of silver, copper or a combination thereof;
a layer of a non-woven fabric embedded with nanoparticles of zinc oxide; and
a layer of a non-woven fabric embedded with nanoparticles of magnesium oxide.

The layers are present over one another in any order.

The antimicrobial non-woven fabrics embedded with nanoparticles were layered over one another to make a filter.

Preferably, the filter was made by layering in no particular order the antimicrobial non-woven fabrics preferably polyester comprising a combination of silver nanoparticles, copper nanoparticles, ZnO nanoparticles and MgO nanoparticles.

Preferably, the filter was made by layering in no particular order the antimicrobial non-woven fabrics preferably polyester comprising a combination of silver nanoparticles or copper nanoparticles, ZnO nanoparticles and MgO nanoparticles.

More preferably, the filter was prepared by layering a nonwoven fabric embedded with ZnO as a first layer (outer layer), a non-woven fabric embedded with MgO as a second layer (middle layer) and a non-woven fabric embedded with copper nanoparticles as a third layer (inner layer).

ZnO nanoparticles provided good antimicrobial properties and more controlled leaching of metal ions as ZnO nanoparticles have high adhesive properties, to have large surface area and more residence time. Therefore, non-woven fabric embedded with ZnO nanoparticles was preferred as a first layer.

Non-woven fabric embedded with MgO nanoparticles provided mineral rich water, but MgO nanoparticles had lower antimicrobial properties than ZnO nanoparticles. Hence, it was less preferred to have non-woven fabric embedded with MgO nanoparticles as the first layer.

Copper nanoparticles have very high antimicrobial properties.

Characterization methods
Morphological analysis of synthesized nanoparticles was done with Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), X-ray diffraction (XRD) and UV-visible spectroscopy which gave information about shape and size of nanoparticles and XRD showed perfection of crystal and impurities present in zinc oxide nanoparticles.

Deposition of nanoparticles on surface of fiber/ filament of the fabric was characterized using SEM and Field Emission Scanning Electron Microscopy with Energy Dispersive X-Ray Spectroscopy (FESEM-EDX) which helped to understand how much nanoparticles were deposited on surface and manner in which nanoparticles were deposited on surface of fiber/filaments.

SEM analysis of nanoparticles and fabric surface was done on Zeiss EVO 18 Electron Microscope. Sample was mounted in a sample holder and coated with thin layer of gold coating so that it became conductive. The magnification was varied from ×2000 to ×40000 to obtain information on the sample surface topography. SEM analysis was done for ZnO nanoparticles, silver nanoparticles and non-woven fabric embedded with ZnO nanoparticles, silver nanoparticles on filament surface of the fabric.

FESEM-EDX was used to identify the percentage of the nanoparticles on fabric/ filament surface and done by Environmental Scanning Electron Microscope model FEI Quanta 200F with Oxford-EDS system IE 250 X Max 80. Energy-dispersive X-ray spectroscopy used X-rays to identify the element and atom present at surface. EDX was done to identify percentage of fabric with embedded nanoparticles.

TEM analysis typically uses high energy electron beams which is transmitted through very thin sample for analyze the microstructure of the sample. Electrons are accelerated to the several hundred kV, which is resulting in wavelengths smaller than light, and TEM is fitted with electromagnetic lenses for good image which is recorded in digital camera.

UV-visible spectroscopy by UV-2450 Shimadzu spectrophotometer was performed to identify the silver nanoparticles.

Dynamic light scattering (DLS) technique was used to determine the size distribution profile of copper nanoparticles.

XRD patterns of nanoparticles were recorded by a PANalytical X’PertPro diffractometer Cu Ka radiations (? = 1.5418 Å) and were helpful to identify the crystallinity and materials which were manufactured.

Characterization of ZnO nanoparticles
XRD was used for the characterization of the crystal size and their crystallinity, perfection of the crystal, impurities present in the zinc oxide, XRD pattern of synthesized nanoparticles was same as in standard ZnO nanoparticles as shown in Figures 2 and 3 and that the synthesized ZnO nanoparticles had no impurities and pattern gave a sharp peak therefore, acceptable perfection of crystal was obtained.
SEM and TEM analysis

The synthesized nanoparticles were in shape of platelets with thickness of 50-100 nm. It was called Nano plates and were confirmed by the SEM image analysis as shown in Figure 4(a). Nano plates have higher surface to volume ratio than spherical particle and therefore have more antimicrobial activity. Shape of nanoparticles was governed by calcination temperature and time, in the present invention powder was kept at 700? for two hours and was taken out after 12 hours of gradual cooling. TEM micrograph of nanoparticles showed the particle size and shape as shown in Figure 4(b). The nanoparticles looked polyhedral in shape and size was approximately 100 nm, particles were seen to agglomerate.

Characterization of MgO nanoparticles
TEM and XRD were used for the characterization of the particle size and crystallinity, perfection of the crystal, impurities present in the magnesium oxide.

XRD pattern of synthesized nanoparticles (red line) (Figure 5(a)) was same as in standard MgO nanoparticles (black line), average particle size by TEM was 16.43 nm with a deviation of 5.12 nm (Figure 5(b)). Size of the nanoparticles was helpful to show antimicrobial activity towards the pathogenic bacteria.

Characterization of silver nanoparticles
In silver nanoparticles the conduction band and valence band lie very close to each other in which electrons move freely. Free electrons help to rise to a Surface Plasmon resonance (SPR) absorption band occurring because of collective oscillation of electrons of silver nano particles in resonance with UV-light and as shown in Figure 6(a), the maximum absorbance was at approximately 410 nm which was due to silver nanoparticles.

The shape and size of the silver nanoparticles were examined with the help of TEM (Figure 6(b)). Liquid drop of silver nanoparticle solution was placed on a carbon-coated copper grid with the help of micropipette and dried under vacuum dryer at 60?, TEM analysis were recorded. The TEM micrographs showed that the sizes of the nanoparticles were approximately 5 nm to 12.5 nm with spherical shape.

Characterization of copper nanoparticles
TEM image (Figure 7(a)) of the copper nanoparticles showed that nanoparticles had a size of less than 50 nm.

The particle size distribution of the copper nanoparticles dispersed in ethanol was determined by DLS as showed in Figure 7 (b) and the average particle size was 32 nm.

Antimicrobial non-woven fabric embedded with ZnO nanoparticles
SEM images provided information about the surface characteristics of filament and gave information about amount of ZnO nanoparticles embedded on surface of the polyester filament. It was observed from SEM image analysis that control fabric fiber (untreated fiber) had smooth surface (Figure 8(a)) and with increase of nanoparticle concentration, deposition of ZnO nanoparticles increased as shown in Figures 8(b)-(d).

ZnO nanoparticles were deposited in between interspace of the filament also at higher concentration of 8 mg/ml to 12 mg/ml (Figure 9), therefore at higher concentration, fabric had higher antimicrobial activity because higher amount of ZnO nanoparticles were deposited on surface.

Further, on increasing the concentration of ZnO nanoparticles to 24 mg/ml, SEM analysis showed that nanoparticles were deposited in interspace of fabric and deposited on surface of fiber/ filaments (Figure 10).

Analysis of EDX data showed that the as concentration of ZnO nanoparticles increased, higher deposition of nanoparticles on surface of polyester filament was observed (See Table 1, and Figures 11-13) and at higher concentration some of nanoparticles got embedded in between the interspace of the fabric

Table 1
Sr. No. Sample (mg/ml) Carbon % Oxygen % Zinc %
1 8 52.82 42.4 4.78
2 10 54.05 40.56 5.40
3 12 52.29 40.58 7.13

Antimicrobial activity
Antimicrobial activity of the polyester fabric embedded with ZnO nanoparticles was investigated by Colony Counting Method (AATCC100) and reduction of bacterial concentration at different time scale was determined by reduction in number of bacterial colonies.

A conical flask of 100 ml was used with 20 ml of deionized water and 100 µl of E. coli bacteria. The polyester fabric was put in the conical flask which had water containing morbid E. coli bacteria and the flask was put in a shaker bath at 100 rpm, 37? temperature for set time duration. In case of tap water, 1.5 gram of treated polyester fabric was put in a conical flask and kept outside the shaker and shaken after every 5 minutes by simple hand shaking and reduction of bacteria in water was investigated as CFU/ml at different time scale.


N1 = Number of surviving bacterial colonies from the control sample.
N2 = Number of surviving colonies from test samples

The E. coli was monitored after 2 hours, 4 hours and 7 hours as shown in Table 2.

Table 2

Sample CFU/ml Reduction efficiency (%)
2 hours 4 hours 7 hours 2 hours 4 hours 7 hours
M1 (8 mg/ml) 235× 108 137× 108 22× 108 75.74 85.86 97.72
M2 (10 mg/ml) 115× 108 46× 108 2× 108 88.13 95.25 99.79
M3 (12 mg/ml) 99× 108 14× 108 0 89.78 98.55 100
NOTE: Control sample has 969× 108 CFU/ml

As observed from the above data and Figures 14 and 15, CFU/ml continuously decreased with increase in concentration of nanoparticles from 8 mg/ml to 12 mg/ml at time 2, 4 and 7 hours. This was because of higher concentration of the nanoparticles which resulted in higher amount of ZnO nanoparticles being embedded on filament surface.

Microbiological performance of needle punched non-woven fabric embedded with ZnO nanoparticles was tested with tap water that was taken from the textile chemistry lab of IIT Delhi. 30ml of tap water was taken with 6.5×8 cm2, GSM- 403.84 non-woven fabric (control) and test sample of the fabric measuring the same was immersed and then checked for bacterial reduction with respect to time in tap water, tap water with test sample of the fabric was put in an incubator at 100 rpm, 37? temperature. The sample was tested after 1 hour.

As shown in Figure 16, within 1 hour the growth of bacteria was reduced almost 100% for tap water with non-woven polyester fabric embedded with ZnO nanoparticles at concentration of 12 mg/ml prepared using HTHP technique. As seen in the figure the control sample had 203 x 108 CFU/ml at 0 hour, but the bacterial colonies were reduced to 0 CFU/ml at 1 hour.

The results for less than 1 hour are shown in Figure 17 under same testing conditions. As observed from the figure, significant reduction of bacterial concentration was not achieved within 50 minutes for tap water (Control has 103×109 CFU/ml at 0 minute and at 50 minutes the colony count was 87×109 CFU/ml). This was because the day of testing was different, therefore CFU/ml was higher for control sample than previous one.

When the concentration of ZnO nanoparticles was increased to 24 mg/ml and embedded on the non-woven polyester fabric by the HTHP process described above, the antimicrobial activity within one hour was as shown Figure 18. From the figure it was observed that within 10 minute the bacterial concentration decreased to 42×109 CFU/ml from the 78×109 CFU/ml (at 0 minute) and at 20 minutes petri dish became almost clean (approximately 0 CFU/ml) and at 30, 40 minutes plate became clean (0 CFU/ml). This indicated that the fabric loaded with ZnO nanoparticles was effective in filtering water.

Antimicrobial non-woven fabric embedded with silver nanoparticles
SEM images of fiber surface showed that deposition of silver nanoparticles with size 5 nm to 12.5 nm on fabric were successfully embedded by absorption process using HTHP techniques (Figure 19). Deposition of silver nanoparticles was evenly distributed on surface of fiber which gave a higher surface to volume ratio of nanoparticles than mixing of nanoparticles in melt blend and helped to reduce bacterial concentration at very short span of time which made the filter fabric cheap and efficient to combat waterborne disease.

Antimicrobial activity
Antimicrobial activity was studied by procedure similar to that described for antimicrobial non-woven fabric loaded with ZnO nanoparticles.

Silver nanoparticles have inherent antimicrobial activity because of ion formation, internalization of nanoparticles in bacterial cell wall, mutation of the DNA structure of bacteria by silver nanoparticles. Therefore, approximately 20 minutes were required by the fabric embedded with silver nanoparticles to clean contaminated tap water (Figure 20). The control sample at 0 minute had 272× 109 CFU/ml and the bacterial colony was reduced to approximately at 20 minutes.

Antimicrobial non-woven fabric embedded with MgO nanoparticles
SEM images provided information about the surface characteristics of filament and gave information about amount of MgO nanoparticles embedded on surface of the polyester filament by HTHP technique. SEM images of fiber surface showed that control (untreated fiber) had a smooth surface (Figure 21 (a)) and with increase of nanoparticles concentration, deposition of MgO nanoparticles on the surface of filament increased as shown Figure 21 (b)-(c).

MgO nanoparticles were deposited between interspace of the filament also at higher concentration of 16 mg/ml and 20mg/ml, therefore at higher concentration, fabric had higher antimicrobial activity because higher amount of MgO nanoparticles are deposited on surface.

Antimicrobial activity
Antimicrobial activity of non-woven fabric embedded with MgO nanoparticles (20-50 nm) was investigated by Colony Counting Method (AATCC100) by procedure similar to that described for antimicrobial non-woven fabric loaded with ZnO nanoparticles.

The non-woven fabric was embedded with MgO nanoparticles at concentration of 16 mg/ml and 20 mg/ml and the bacteria reduction efficiency was determined against E.coli for a contact time (time taken to kill the bacteria E. coli) of 1 hour and 2 hours as shown in Table 3.

Table 3
Sample CFU/ml Reduction efficiency (%)
1 hour 2 hours 1 hour 2 hours
16mg/ml 60× 108 38× 108 85.7 90
20mg/ml 42× 108 28× 108 90 93.3

As observed from the above results and Figure 22 CFU/ml continuous decreased with increase concentration from 16 mg to 20mg/ml at time 1 and 2 hours. The bacteria reduction efficiency increased as concentration of MgO nanoparticles increased and around 90% bacteria reduction efficiency was attained within 2 hours for each sample.

Antimicrobial non-woven fabric embedded with copper nanoparticles
SEM images provided information about the surface characteristics of filament. It was observed from SEM analysis that control (untreated fiber) has smooth surface (Figure 23 (a)) and with increase of nanoparticles concentration, deposition of copper nanoparticles on the surface of filament increased as shown in Figure 23 (b)-(c).

Copper nanoparticles were deposited between interspace of the filament also at higher concentration of 4 mg/ml and 6 mg/ml, therefore at higher concentration fabric had higher antimicrobial activity because higher amount of copper nanoparticles were deposited on surface.

Antimicrobial activity
Antimicrobial activity of non-woven fabric embedded with copper nanoparticles (20-50 nm) was investigated by Colony Counting Method (AATCC100) by procedure similar to that described for antimicrobial non-woven fabric loaded with ZnO nanoparticles.

The non-woven fabric was embedded with copper nanoparticles at concentration of 4 mg/ml and 6 mg/ml and the bacteria reduction efficiency was determined against E.coli for a contact time (time taken to kill the bacteria E. coli) of 30 minutes, 1 hour and 2 hours as shown in Table 4.

Table 4
Sample CFU/ml Reduction efficiency (%)
30 minutes 1 hour 2 hours 30 minutes 1 hour 2 hours
4 mg/ml 25× 108 13× 108 4× 108 90.3 95 98.4
6 mg/ml 15× 108 8× 108 2× 108 94.2 96.9 99.2

As observed from the above results and Figure 24, CFU/ml continuous decreased with increase concentration from 4 mg to 6 mg/ml at 30 minutes, 1 hour and 2 hours. The bacteria reduction efficiency increased as concentration of copper nanoparticles increased and around 90% bacteria reduction efficiency was attained within 2 hours for each sample.

Leaching test
A leaching test was carried out on the antimicrobial non-woven fabrics to determine the concentration of nanoparticles at which the leaching was within the WHO guidelines for safe limit of these metals in filtered water

The leaching test was done by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). This test was capable of detecting metals and several non-metals at concentrations as low as one part in 1015 (part per quadrillion, ppq) on non-interfered low-background isotopes.

Leaching test for filter comprising antimicrobial non-woven fabric embedded with ZnO, MgO and silver nanoparticles
A gravity based filter was bought from a market and its existing cartridge was changed with antimicrobial nonwoven fabric layered filter (ZnO, MgO and Ag) form a modified cartridge as shown in Figure 25 (a).

In this test the modified cartridge was filled by tap water and this water was passed through a pre-filter of non-woven fabric and a treated non-woven fabric of ZnO, MgO, and silver nanoparticles at different concentration of ZnO nanoparticles (22mg/ml, 24mg/ml, 26mg/ml and 28 mg/ml), MgO nanoparticles (8 mg/ml, 10 mg/ml and 12 mg/ml), and silver nanoparticles (2ppm or 0.002 mg/ml). Prefilter was placed above the treated non-woven filter and water was filtered through this setup at flow rate 50 ml/min.

The water filtered through the filter was analysed to determine the leaching of metal particles in water after filtration and to optimize the concentration of nanoparticles applied on non-woven fabric by comparing with the WHO standards i.e. silver = 0.1 ppm, zinc = 5 ppm, magnesium = 30 ppm and copper = 2 ppm.

Table 5 shows the results of leaching of metal particles in water after filtration.

Table 5
Sample Conc. of nanoparticles (mg/ml) Metal conc. (ppm) pH
Zinc Oxide ZnO 22 0.281 7
ZnO 24 0.309 7
ZnO 26 0.325 7
ZnO 28 0.416 7
ZnO, MgO, Ag ZnO-16, MgO-5 and Ag-2 4.51 7
WHO std. WHO std. 5.000 7
Magnesium Oxide MgO 8 12.663 9
MgO 10 14.404 9
MgO 12 16.323 9
ZnO, MgO, Ag ZnO-10, MgO-8 and Ag-2 9.943 7
WHO std. WHO std. 30 7
Silver Ag 0.002 (2 ppm) 0.094 7
WHO std. WHO std. 0.100 7
Note: The tap water used in the test contained 0.15 ppm zinc, 0.048 ppm magnesium, 0.4 ppm copper and 0.009 ppm silver.

The above shows that the antimicrobial non-woven fabric embedded with ZnO, MgO and silver nanoparticles and a filter comprising antimicrobial non-woven fabric embedded with ZnO, MgO and silver nanoparticles provided filtered water that was within the WHO standards of metals allowed in drinking water.

Leaching test for filter comprising antimicrobial non-woven fabric embedded with ZnO, MgO and copper nanoparticles.

In this test gravity based filter was modified antimicrobial nonwoven fabric layered filter (ZnO, MgO and Cu) form a modified cartridge as described above and was filled by tap water and this water is passed through a prefilter and later through the filter comprising non-woven fabric embedded with ZnO, MgO and copper nanoparticles at different concentration such as 22 mg/ml and 24 mg/ml for ZnO nanoparticles, 16 mg/ml and 20 mg/ml for MgO nanoparticles and, 4 mg/ml and 6mg/ml for copper nanoparticles.

Prefilter was placed above the filter and water was filtered through this setup at flow rate 100 ml/min or 1 litre/10min. The tap water contained 16 ppm magnesium, 0.4 ppm zinc and 0.017 ppm copper which was comparatively lower than WHO norms Mg- 30 ppm, Zn- 5 ppm, Cu- 2ppm. The antimicrobial non-woven fabric layers were added into the cartridge and water was passed through the filter such that metal leaching in water was controlled. The results of the test are shown in Table 6.
Table 6
Sample Conc. of nanoparticles (mg/ml) Metal conc. (ppm)
Zn Mg Cu
ZnO 22 0.590
ZnO 24 0.630
MgO 15 18.460
MgO 20 19.520
Copper 4 0.029
Copper 6 0.035
Combination 1 ZnO-22, MgO- 15, Cu-4 0.491 17.325 0.023
Combination 2 ZnO-24, MgO- 20, Cu-6 0.521 18.532 0.03

Thus, the above data shows that leaching of metal ions like Mg, Cu, Zn from the antimicrobial non-woven fabric and the filter was within permissible limit.

Antibacterial testing of water filtered by a filter comprising non-woven fabric and ZnO, MgO and copper nanoparticles.
Dirty Water (tap water) was passed through individual anti-microbial non-woven fabric embedded with ZnO, MgO and copper nanoparticles and through a filter made by layering the three antimicrobial non-woven fabrics at a flow rate of 100 ml/min.

The water before and after filtration was placed in an incubator for growth of ambient bacteria and the number of bacterial colonies after incubation was counted. The results shown in Table 7, indicate that a filter made by combination of non-woven fabric layers embedded with ZnO, MgO and copper nanoparticles reduced bacteria up to 98%.

Table 7
Sample No. of Colonies
Tap water 40
Fabric embedded with ZnO nanoparticles 11
Fabric embedded with MgO nanoparticles 16
Fabric embedded with copper nanoparticles 8
Filter (ZnO + MgO + copper nanoparticles) 2

The foregoing description of specific embodiments of the present invention has been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching.
The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, to thereby enable others, skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated.

We claim:

1. An antimicrobial non-woven fabric comprising
a non-woven fabric; and
a combination of nanoparticles comprising one or more metal and a minimum of two metal oxides.

2. The fabric as claimed in claim 1, wherein the non-woven fabric is polyester.

3. The fabric as claimed in claim 1, wherein the metal is silver nanoparticles.

4. The fabric as claimed in claim 1, wherein the metal is copper nanoparticles.

5. The fabric as claimed in claim 1, wherein the metal is a combination of silver and copper nanoparticles.

6. The fabric as claimed in claim 1, wherein the metal oxides comprise a combination of nanoparticles of zinc oxide and magnesium oxide.

7. The antimicrobial non-woven fabric as claimed in any one of the preceding claims, wherein the particle size of the nanoparticles is in a range from 5-100 nm.

8. A process for preparing an antimicrobial non-woven fabric comprising: -
making a dispersion of nanoparticles comprising of one or more metal and a minimum of two metal oxides;
adding a non-woven fabric in the dispersion; and
heating the dispersion.

9. The process as claimed in claim 8, wherein the ratio of the non-woven fabric to the nanoparticle dispersion is 1: 60.

10. The process as claimed in claim 8, wherein the non-woven fabric is polyester.

11. The process as claimed in any one of the claims 8, wherein the nanoparticle dispersion containing the non-woven fabric is heated at a temperature above the glass transition temperature of the non-woven fabric.

12. The fabric as claimed in any one of the preceding claims 1-7 for manufacturing water filters, air filters, textile, packaging films, sanitary napkins and diapers.

13. The fabric as claimed in claim 12, wherein the filter is prepared by layering a plurality of the antimicrobial non-woven fabric as claimed in any one of the claims 1-7.

14. A filter comprising
a layer of a non-woven fabric embedded with nanoparticles of silver, copper or a combination thereof;
a layer of a non-woven fabric embedded with nanoparticles of zinc oxide; and
a layer of a non-woven fabric embedded with nanoparticles of magnesium oxide.

15. The filter as claimed in claim 14, wherein the layers are arranged over one another in any order.