Nanocomposite material made of polyurethane and graphene oxide used in antibacterial fabric

Abstract

There is disclosed in one embodiment a non-woven fibrous nanocomposite material including nanometer diameter fibers including thermoplastic polyurethane (TPU), graphene oxide (GO) and cellulose wherein the fibers are deposited using electrospinning. Disclosed in another embodiment is use of the non-woven fibrous nanocomposite material as an antibacterial fabric. Disclosed in a further embodiment is a nanocomposite solution including thermoplastic polyurethane (TPU), graphene oxide (GO) and cellulose, all in solution, wherein the feedstock for the graphene oxide is graphene oxide nanosheets, and the feedstock for the cellulose is cellulose nanocrystals (CNC). Disclosed in a still further embodiment is a method of forming a nanocomposite including the steps of depositing the nanocomposite solution using electrospinning.

Description

NANOCOMPOSITE MATERIAL MADE OF POLYURETHANE AND GRAPHENE OXIDE USED IN ANTIBACTERIAL FABRICFIELD

[0001] In one of its aspects, the present disclosure relates generally to composite non-woven materials.BACKGROUND

[0002] Microorganisms and bacteria are present in everyday life; some are essential and beneficial to the human body, while others such as pathogenic bacteria are potentially harmful. The use of antibiotics to combat pathogenic bacteria has given rise to drug-resistant bacterial strains [1-3], Due to the threats posed by these bacteria, antibacterial textiles and coatings have gained research interest as an alternative route to combat transmission and help mitigate their harm, especially for applications in the healthcare industry [4-6], Textiles on their own provide a suitable environment for bacterial growth due to their ability to retain moisture in conjunction with large surface area [7,8], The fibers used to create textiles can also become a source of nutrition for bacteria. The fibers are susceptible to degradation and consumption by the bacteria leading to loss in strength and the presence of foul odor [8], To address some of the concerns posed by bacteria, textiles have been modified to have antibacterial properties by methods such as chemical activation or the introduction of inherently antibacterial materials. In terms of inherently antibacterial materials, metal nanoparticles, metal oxides, salts and carbon-based nanoparticles such as silver nanoparticles, zinc oxide, and graphene oxide nanosheets have been shown to improve the antibacterial characteristics of textiles [8-11],

[0003] Electrospinning is a manufacturing method by which nonwoven fibrous materials can be created by subjecting a polymeric solution or melt to a high voltage. When the precursor material passes through a high voltage node or spinneret, electrical charges are accumulated, which deforms the solution into a Taylor cone. With a sufficiently strong electric field, the like charge repulsion of the solution overcomes the surface tension, resulting in the ejection of a charged polymer jet from the Taylor cone. The charged jet travels towards a grounded substrate, subsequently thinning and drying due to electrostatic forces and whipping [12-15], Electrospinning has generated interest in the scientific community due to its compatibility workingwith a wide range of polymers and solvents as well as potential application in multiple fields

[0014] , Electrospinning has been investigated in the fields of filtration, tissue engineering, and sensor application, such as stretchable strain sensors [16-18], The compatibility with a variety of polymers and solvents along with the ability to reliably produce nonwoven fibrous material with nanometer diameter fibers makes electrospinning a strong candidate for the synthesis of advanced textiles and filtration media.

[0004] Graphene oxide (GO), a carbon-based nanomaterial, is a single-atom-thick carbon nanosheet with oxygen containing functional groups, such as carboxyl, epoxy, carbonyl, and hydroxyl groups

[0019] , Graphene and its derivatives such as GO have gained attention thanks to their robust properties, including mechanical strength, electrical and thermal properties, chemical functionalization, and antibacterial behavior. The antibacterial mechanism of GO has been reported as physical interactions with cell membranes along with oxidative and membrane stress interactions, and electron transfer [19,20], Physical interaction between the bacteria cell walls and sharp edges of the nanosheets results in damage and stress to the bacterial membrane compromising the integrity and subsequently leading to cell death. The oxidative stress antibacterial mechanism inactivates vital cellular structures by oxidization. Due to the presence of the oxygen containing functional groups, GO is less electrically conductive than graphene but with the added benefit of better chemical modification, hydrophilicity, and dispersibility in polar solvents [21 ,22], GO has seen increasing use in a variety of applications such as biomedical, electronics, and filtration [23-25], The properties of GO make it a suitable candidate for stronger, lighter, and potentially bacterial-supressing nanocomposites design, manufacturing, and applications. Cellulose nanocrystal (CNC), on the other hand, is a prime example of nanomaterial obtained from natural sources. CNC is a highly crystalline, rod-shaped nanomaterial that can be extracted from natural cellulosic sources such as wood, cotton, hemp, etc.

[0026] , CNC has been researched in the fields of biopolymer reinforcement, food packaging, tissue engineering, and wastewater treatment due to its abundance, biocompatibility, hydrophilicity, and biodegradability [26-28], The electronegativity and hydrophilicity of CNC make it a viable proposition for the novel nanocomposite design in future filtration application.SUMMARY

[0005] The present disclosure in one aspect relates to a non-woven fibrous nanocomposite material including nanometer diameter fibers comprising thermoplastic polyurethane (TPU), graphene oxide (GO) and cellulose. In one aspect, in the non-woven fibrous nanocomposite material, the fibers are deposited using electrospinning. The present disclosure in another aspect relates to use of the non-woven fibrous nanocomposite material described above, as an antibacterial fabric.

[0006] The present disclosure in another aspect relates to a nanocomposite solution including thermoplastic polyurethane (TPU), graphene oxide (GO) and cellulose, all in solution, wherein the feedstock for the graphene oxide is graphene oxide nanosheets, and the feedstock for the cellulose is cellulose nanocrystals (CNC). In one aspect, the cellulose is used as a filler. In one aspect, the thermoplastic polyurethane (TPU) can be a base solution which contains the GO and CNC. In one aspect, in the nanocomposite solution, the GO and the CNC each constitute between 0 wt% and 3 wt. % of the solution. In another aspect, in the nanocomposite solution, the GO nanosheets are 5 - 10 pm in lateral dimensions and 0.8 - 2 nm in thickness. In another aspect, in the nanocomposite solution, the CNC crystals are 40nm to 50nm in diameter and 230nm to 270nm in length.

[0007] The present disclosure in one aspect relates to a method of preparing a nanocomposite solution including the steps of providing a thermoplastic polyurethane (TPU) solution, adding graphene oxide (GO) and cellulose nanocrystals (CNC) to the solution, and homogenizing the solution. In one aspect, in the method, the amount of the GO and the CNC are each added in an amount of between 0 wt% and 3 wt. % of the solution. The present disclosure in one aspect relates to a method of forming a nanocomposite including the steps of depositing a nanocomposite solution according to an aspect of the present disclosure, using electrospinning.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Embodiments of the present invention will be described with reference to the accompanying drawings, wherein like reference numerals denote like parts, and in which:

[0009] FIG. 1 is a first diagram of a design of experiments schematic according to one aspect of the present invention;

[0010] FIG. 2 is a second diagram to accompany FIG. 1 of the design of experiments schematic;

[0011] FIG. 3(a) is a schematic representation of an air filtration apparatus used in testing products of the present invention;

[0012] FIG. 3(b) is a photograph of the physical air filtration apparatus used in testing products of the present invention;

[0013] FIG. 4(a) is a SEM image of a TM material according to an embodiment of the present invention;

[0014] FIG. 4(b) is a SEM image of the TGM material according to an embodiment of the present invention;

[0015] FIG. 4(c) is a SEM image a TCM material according to an embodiment of the present;

[0016] FIG. 4(d) is a SEM image of the TCGM material according to an embodiment of the present invention;

[0017] FIG. 5 (a) is an SEM image of Tc for a deposition at high humidity according to embodiments of the present invention;

[0018] FIG. 5 (aa) is a graph of fiber diameter size distribution for the deposition of FIG. 5(a);

[0019] FIG. 5 (b) is an SEM image of TGcfor a deposition at high humidity according to embodiments of the present invention;

[0020] FIG. 5 (bb) is a graph of fiber diameter size distribution for the deposition of FIG. 5(b);

[0021] FIG. 5 (c) is an SEM image of TCc for a deposition at high humidity according to embodiments of the present invention;

[0022] FIG. 5 (cc) is a graph of fiber diameter size distribution for the deposition of FIG. 5(c);

[0023] FIG. 5 (d) is an SEM image of TCGcfor a deposition at high humidity according to embodiments of the present invention;

[0024] FIG. 5 (dd) is a graph of fiber diameter size distribution for the deposition of FIG. 5(d);

[0025] FIG. 6 (a) is an SEM image of Tc for a deposition at high humidity according to embodiments of the present invention;

[0026] FIG. 6 (aa) is a graph of fiber diameter size distribution for the deposition of FIG. 6(a);

[0027] FIG. 6 (b) is an SEM image of TGcfor a deposition at high humidity according to embodiments of the present invention;

[0028] FIG. 6 (bb) is a graph of fiber diameter size distribution for the deposition of FIG. 6(b);

[0029] FIG. 6 (c) is an SEM image of TCc for a deposition at high humidity according to embodiments of the present invention;

[0030] FIG. 6 (cc) is a graph of fiber diameter size distribution for the deposition of FIG. 6(c);

[0031] FIG. 6 (d) is an SEM image of TCGcfor a deposition at high humidity according to embodiments of the present invention;

[0032] FIG. 6 (dd) is a graph of fiber diameter size distribution for the deposition of FIG. 6(d);

[0033] FIG. 7 is a collections of SEM images converted to black and white images for porosity measurements according to embodiments of the present invention;

[0034] FIG. 8 is a graph of x-ray diffraction response vs 2 theta angle for electrospun membranes according to embodiments of the present invention;

[0035] FIG. 9 is a graph of stress-strain behavior of electrospun fibers according to embodiments of the present invention;

[0036] FIG. 10 is a graph of storage modulus vs temperature for electrospun fibers according to embodiments of the present invention;

[0037] FIG. 11 is a graph of Tan delta vs temperature for electrospun fibers according to embodiments of the present invention;

[0038] FIG. 12 is a graph of water contact angle vs time for electrospun fibers according to embodiments of the present invention;

[0039] FIG. 13(a) is an image of petri dishes with bacteria culture with serial dilution of TPU samples;

[0040] FIG. 13(b) is an image of petri dishes with bacteria culture with serial dilution of TPLI / GO samples;

[0041] FIG. 14 is an optical microscope image of a fiber network with an overlayed SEM image of a material according to an embodiment of the present invention;

[0042] FIG. 15 is an SEM image of a fiber network with sodium chloride (NaCI) particles according to an embodiment of the present invention;

[0043] FIG. 16 are four graphs (a), (b), (c) and (d) of expected filtration efficiency vs. particle diameter according to embodiments of the present invention;

[0044] FIG. 17 is a SEM image of a nanofiber network on the surface of a microfiber network according to an embodiment of the present invention;

[0045] FIG. 18 is a SEM image with a magnification of a fiber network with filtered sodium chloride of a material according to an embodiment of the present invention;

[0046] FIG. 19 is an enlarged image of an upper portion of the far right column of FIG. 1 ;

[0047] FIG. 20 is an enlarged image of the portion below the image of FIG. 19; and

[0048] FIG. 21 is an enlarged image of the portion below the image of FIG. 19.DETAILED DESCRIPTION

[0049] Various apparatuses or processes will be described below to provide an example of an embodiment of each claimed invention. No embodiment described below limits any claimed invention and any claimed invention may cover processes or apparatuses that differ from those described below. The claimed inventions are not limited to apparatuses or processes having all of the features of any one apparatus or process described below or to features common to multiple or all of the apparatuses described below. It is possible that an apparatus or process described below is not an embodiment of any claimed invention. Any invention disclosed in an apparatus or process described below that is not claimed in this document may be the subject matter of another protective instrument, for example, a continuing patent application, and the applicants, inventors or owners do not intend to abandon, disclaim, or dedicate to the public any such invention by its disclosure in this document.

[0050] In the present invention, in one embodiment, a fundamental approach was taken to design a three-constituent nanocomposite viscous solution of host thermoplastic polyurethane (TPU) with varied GO and CNC (in wt.%) content following a design-of- experiment (DoE) curriculum as shown in Error! Reference source not found, and FIG. 2. A full factorial design of experiments results in a total of 32 combinations based on 5 factors, spinning voltage, solution flowrate, spinning distance, wt.% GO, and wt.% CNC at 2 levels, high and low, for each factor. The present invention, in one embodiment, focuses on a subset of the DoE with specific interest on the material design factors of wt.% GO and wt.% CNC at levels of 0 wt.% and 3 wt.%. A precursor nanocomposite solution was used to deposit membranes and coatings with consistent electrospinning process parameters including spinning voltage, deposit time, and solution (precursor) flow rate, as stated in below, Synthesis of nanocomposites deposited membranes were characterized / tested for fiber spatial distribution, porosity presence, air filtration efficiency, crystal structure analysis, thickness, mechanical stretch, and viscoelasticity using anarray of tools and techniques: 3D optical profilometer, scanning electron microscopy (SEM), in house filtration apparatus, x-ray diffraction (XRD), uniaxial tensile tester, dynamic mechanical analyzer (DMA), and water angle measurement. Finally, the bacterial efficacy of the membranes was investigated using Gram negative Escherichia coli (E. coli) cells.ExperimentalMaterials and methods

[0051] Graphene oxide (GO) nanosheets of 5 - 10 pm in lateral dimensions and 0.8 - 2 nm in thickness with ~99% purity was purchased from Adnano Technologies Pvt. Ltd. (Karnataka, India). Cellulose nanocrystals (CNC) of 40nm to 50nm diameter x 230-270nm length were purchased from Cellulose Lab (Fredericton, NB, Canada). Thermoplastic polyurethane (TPU) solution was obtained from Inovenso Ltd. (Istanbul, Turkey). TBL530LR non-woven polyester fabric was sourced from Sheng Hung Industrial CO., Ltd. (Taiwan).Synthesis of nanocomposites

[0052] TPU solution was prepared by Inovenso Ltd. at a concentration of 14 wt.% (w / w) by dissolving TPU pellets into a solution of dimethylformamide (DMF), ethyl acetate (EA), and lithium chloride (LiCI). Nanocomposite solutions of TPU at different weight percentages of GO and CNC were prepared by the addition of the nanocomposite powder to the TPU solution. The solutions were then homogenized using a Fisher Scientific™ Model 500 ultrasonic dismembrator at an amplitude of 50% for 20 minutes. Each solution was created and sonicated shortly before electrospinning to help ensure a homogenous dispersion of nanoparticles.

[0053] The nanocomposite solutions were transferred to a 10 mL plastic syringe and mounted onto a NS starter kit NanoSpinner (Inovenso Ltd., Turkey). The samples were spun using a 21 g blunt tip needle and deposited onto either an aluminum foil orTBL530LR non-woven polyester substrate mounted on a grounded flat plate collector. Nanofibers were deposited onto aluminum foil with a 20 kV applied voltage, 1 mL hr1solutionflowrate, 12 cm deposition distance, and a 1 hr deposition time. Depositions made onto non-woven substrate were done with a 20.4 kV applied voltage, 0.25 mL hr1flowrate, 12 cm deposition distance, and 1 min deposition time. The subsequent depositions onto aluminum were removed from the substrate to create standalone fabric membranes for testing while the coating depositions onto non-woven fabric were tested as is. A summary of the process parameters, composition, and specimen ID can be found in Table 1 , where the membrane depositions are indicated by a subscript m (Tm) and the coating depositions are indicated by a subscript c (Tc). Additionally, electrospun coatings were conducted at different ambient humidity conditions. High humidity conditions observed during the summer months were designated as relative humidities > 50% with a calculated average humidity of 63.5%. Low humidity (<50%) conditions observed during the winter months had an average humidity of 26.7%.Table 1 : Nanocomposite design of experiments (DoE)Sample Applied Flowrate Collector TPU wt.% GO wt.% CNC wt.% SubstrateID Voltage [m|_ hr-1] Distance[kV] [cm]TM 20 1 12 100 0 0 AlTGM 20 1 12 97 3 0 AlTCM 20 1 12 97 0 3 AlTCGM 20 1 12 94 3 3 AlTc 20.4 0.25 12 100 0 0 Non-wovenTGc 20.4 0.25 12 97 3 0 Non-wovenTCc 20.4 0.25 12 97 0 3 Non-wovenTCGc 20.4 0.25 12 94 3 3 Non-wovenCharacterizationScanning electron microscopy (SEM)

[0054] The surface morphology of the electrospun membranes was investigated using a Scios 2 field emission scanning electron microscope (FESEM) with the help of The University of New Brunswick’s microscopy and microanalysis group. The Scios 2 FESEM was operated at an accelerating voltage of 5.00 kV and a working distance of 7 mm. Each sample was fixed to an aluminum mount using double sided conductive carbon tape and subsequently carbon coated, to improve conductivity and image quality. Average fiber diameters were determined using the image analysis software Imaged® (National Institutes of Health, USA) and 90 measurements were taken randomly from the SEM micrographs.Porosity analysis

[0055] Porosity of the nanofiber coatings was determined following the procedure outlined by Ghasemi-Mobarakeh et al.

[0029] using Imaged software. In short, SEM micrographs were converted to binary images based on different threshold values using the mean and standard deviation of the greyscale pixel values. After image processing, the porosity was determined by a comparison of the number of white pixels, which represented the voids in the image, to the total number of pixels in the image.X-ray diffraction (XRD)

[0056] XRD analysis was carried out to confirm the quality of the commercially obtained GO and CNC and to confirm the successful deposition of the nanomaterials in the nanocomposite. The analysis was performed at Dalhousie University (NS, Canada) in their Materials / Mechanical Engineering department. Samples were analyzed between 20 = 4° and 60° with a step size of 0.02° and a copper radiation source (Cu Ka).Tensile properties

[0057] Uniaxial tension tests were performed using a Instron 4465 electromechanical tension / compression apparatus equipped with standard pneumatic pinch type grips and a 100N load cell. Samples were cut using a standard ASTM D412 type D dog bone die producing uniform samples of 3 mm gauge width and 35 mm gauge length. A minimum of 3 measurements for the gauge length thickness were taken for each test using a micrometer and the average thickness was used for the calculation of stress. The tests were performed with a constant extension rate of 5 mm min-1.Dynamic mechanical analysis

[0058] Dynamic mechanical analysis (DMA) was conducted using a TA Instruments DMA Q800 dynamic mechanical analyzer with the help of the University of Prince Edward Island. The measurements were carried out as multi-frequency - stress mode tests set for a constant frequency of 1 Hz and a temperature ramp from -30°C to 70°C at a heating rate of 3°C min-1. Rectangular samples with dimensions of 12.7 mm x 50.8 mm were fixed in tension clamps with a force of 0.56 Nm (5 in-lb) of torque.Water contact angle

[0059] Water contact angles were determined at the Verschuren center (Sydney, Nova Scotia). The tests were performed according to the Sessile drop method onto rectangular samples with dimensions of 20 mm x 55 mm.Antibacterial testing

[0060] Antibacterial testing was accomplished using E. coli strain DH5 (Invitrogen Inc) carrying plasmid pGLO (BioRad Laboratories Inc). Ampicillin resistance and constitutive green fluorescent protein expression imparted by the pGLO plasmid allowed for selection and screening of input and output test bacteria during experiments where it was difficultto maintain sterility of electrospun samples. Initial E. coli cultures were grown in Lysogeny Broth (LB) supplemented with ampicillin (100 pg mL1) at 37°C for 18 h with shaking at 200 rpm. Cells from 1 mL of culture were washed once in 1 mL sterile saline (0.85% NaCI) and resuspended in 1 mL sterile saline. Electrospun samples were cut into 1 cm2square samples for antibacterial testing. To each sample 1 pL of resuspended E. coli cells were added to the surface of the fabric. An additional 1 cm2sample was placed on top of the droplet to distribute the liquid culture between the samples and increase the contact area between the fabric and bacterial cells. After inoculation, the samples were placed on a stand inside a lidded Styrofoam container containing approximately 200 mL water to maintain humidity within the chamber. The container was then sealed to reduce the effects of desiccation and incubated at 22°C for 24 hours. After incubation the inoculated membranes were placed in 10 mL of saline and vortexed periodically over 15 minutes to retrieve surviving bacteria from the surface of the membranes. Using the vortexed solutions, 10-fold serial dilutions were performed and 100 pL volumes of dilutions 10’4to 10’8were plated onto Lysogeny broth (LB) agar supplemented with 1.6% agar and ampicillin (100 pg mL-1). After incubation of plates at 37°C for 24 hours, colony forming units (CFUs) were enumerated for each dilution. The same process was used to enumerate CFUs in the initial input cultures and for each experiment the input CFU titre was compared to the CFU titre after cell exposure to the electrospun samples for 24 hrs.Air filtration efficiency

[0061] A schematic of the filtration setup used can be seen in FIG. 3(a) with the physical setup seen in FIG. 3(b). Air particulate filtration efficiency was determined utilizing an Ambilabs® (Warren, Rl, USA) 2WIN dual-wavelength integrating nephelometer. The 2WIN nephelometer inlet was set up downstream of the filter sample holder. A baseline was measured for each set of tests where an aerosolized solution of sodium chloride (NaCI) (500 mg L-1) was passed through the test apparatus at a rate of 40 L min-1and the scattering coefficient was recorded over a 15-minute period. Afterward, an electrospun filter was mounted into the test apparatus and particulate free air flowed through the system before being challenged with the same sodium chloride particulates.The electrospun filter media were challenged and the scattering coefficient was recorded over a 15-m inute period.Results and DiscussionScanning electron microscopy

[0062] The TPU and nanocomposite nanofibers displayed a bead on string morphology as shown in FIGs 4(a)-(d). TM and TCM, FIG. 4(a) and FIG. 4(c), indicated a high density of beads while TGM and TCGM, FIG. 4(b) and FIG. 4(d), had a lower density of beading. With the process parameters being constant the deviations present in the fiber morphology potentially arose from influences on the solution properties. The presence of nanomaterial in the polymer solution would be expected to result in higher viscosity due to increased intermolecular interactions between polymer chains and either the GO nanoflakes or CNC. The increased solution viscosity would be expected to increase the average fiber diameter due to the greater resistance to deformation during the thinning process. Similarly, the nonconductive nature of GO and CNC would be expected to reduce the conductivity of the solution leading to a reduced charge density and thicker fibers due to the reduced deformation from electrostatic forces. As shown in Table 2, the average fiber diameters were not observed to vary significantly with the addition of a single nanomaterial with diameters of 144.90, 151.97, and 142.50 nm for TM, TGM, and TCM respectively. A larger increase in fiber diameter was observed for TCGM with an average fiber diameter of 164.60 nm. The slight deviation in the average fiber diameters and indicated reduction of beading for TGM and not TCM when compared to TPU notes that CNC had no noticeable change to solution properties while GO was able to reduce beading without effecting the average fiber diameter. The lack of fiber diameter increases with the presence of GO or CNC could also be an indication of poor nanomaterial dispersion. If the nanomaterials were inadequately dispersed, then aggregations of the nanomaterial would have localized viscosity increases and conductivity decreases while the rest of the TPU would remain unaffected resulting in similar deformation and thinning in comparison to TPU. The observed increase to fiber diameter with the introduction ofboth GO and CNC could be attributed to an enhanced interaction between the nanomaterials and potential better dispersion leading to a higher solution viscosity. Nanomaterials on their own tend to agglomerate due to their large surface area to volume ratios and resulting high surface energy. By having both CNC and GO it could lead to reduced agglomeration ascribed to Van der Waals iterations between the nanomaterials resulting in better dispersion.Table 2: Average fiber diameter of electrospun nanofibersSpecimen ID Average Fiber Diameter [nm]TM 144.90 ± 35.56TGM 151.97 ± 49.53TCM 142.50 ± 76.07TCGM 164.60 ± 52.71

[0063] The average fiber diameters for the electrospun coatings ranged from 86.90 nm to 272.90 nm where the smaller fibers were obtained at a lower deposition humidity as seen in Table 3. The average fiber diameters at high humidity were almost double in size in comparison to diameters observed at low humidity for all material designs of Tc, TGc, TCc, and TCGc. For the low humidity depositions, TGc was measured to have the smallest diameter of 86.90 nm while the diameters for TCc and TCGc deviated by a few nanometers, 100.00 nm and 101.90 nm, respectively. In the case of the high humidity depositions, the nanocomposite nanofibers were larger than the TPU nanofibers with the largest increase seen for the addition of both CNC and GO with the average fiber diameter of TCGc being 272.90 nm.Table 3: Average fiber diameter of nanocomposite coatings deposited at high and low humiditySample ID High Humidity [nm] Low Humidity [nm]Tc 188.00 ± 53.81 117.00 ± 41 .21TGc 230.00 ± 61 .83 86.90 ± 22.29TCc 213.00 ± 71.93 100.00 ± 26.14TCGc 272.90 ± 96.32 101.90 ± 37.43

[0064] The surface morphologies for the nanofiber coatings are shown in FIGs 5(a)-(d) for high humidity depositions and FIGs 6(a)-(d) for low humidity depositions. All four high humidity compositions (FIGs 5(a)-(d)) indicated the successful synthesis of nanofibers with an open architecture, minimal fiber coverage, and limited number of fiber layers. With fewer fibers in total covering the given area it could result in a higher porosity and larger pore size contributing to lower differential pressure. Comparatively, the morphology obtained at low relative humidity (FIGs 6(a)-(d)) is seen to have a larger number of fibers along with the presence of nonuniformities such as beads that were not observed for the high humidity deposits. The increased fiber presence could translate into lower porosity, smaller average pore size, an increased filtration efficiency, and a higher expected differential pressure.

[0065] Between high and low humidity, two different trends were observed for the average fiber diameter and the effect of the nanomaterials. In the case of the high humidity, the addition of the nanomaterials increased the sizes of the fibers with the greatest effect seen for the combination of CNC and GO. Since the process parameters were kept constant, aside from relative humidity, the differences could have arisen from changes to the electrospinning solution properties. Changes to the solution properties such as viscosity and electrical conductivity affect the fiber diameter and obtained morphology. An increase in fiber diameter could be attributed to either an increase in solution viscosity resulting in a higher resistance to deformation during the thinning process or a reduction in electrical conductivity and subsequent reduction in the electrostatic force applied. The presence of the nanomaterials may have increased the intramolecular forces between the polymer chains of TPU leading to an increase in viscosity.

[0066] On the other hand, the presence of nanomaterials, namely GO, for the low humidity coatings resulted in smaller average fiber diameters. The presence of the oxygencontaining functional groups in GO may have facilitated better electron motion in the solution leading to an increase in conductivity. The increased conductivity would havemade the solution more susceptible to stretching and thinning due to the electric field resulting in smaller fibers.

[0067] Considering the effect of humidity, it would be generally expected that a lower humidity would result in larger fibers due to an increase in solvent evaporation rate. Due to the nature of the main solvent used, DMF, and its miscibility in water, the nanofiber may solidify faster in an environment with a higher relative humidity due to the increased presence of water. If the nanofibers were to solidify faster, then they would result in larger fiber diameters since they would not have as much time to stretch and thin. Therefore, in a higher humidity environment, the nanomaterials seem to assist in the rapid solidification of the TPU fibers while in a low humidity environment, GO can contribute to increased thinning.Porosity Analysis

[0068] Due to the lack of nanofibrous layers present for the high humidity depositions, as seen in FIGs 6(a)-(d), a multilayered porosity approach as outlined by Ghasemi- Mobarakeh et al.

[0029] could not be taken. Therefore, a single layer porosity analysis was used to determine the coating porosity based on the average gray scale pixel value for each micrograph of interest. An example of the threshold progression according to Ghasemi-Mobarakeh et al.

[0029] utilized for the low humidity micrographs can be seen in FIG. 7. For the majority of the compositions the high humidity coatings displayed a greater porosity than the first layer, the layer that accounts for the minimal number of fibers, of the low humidity coatings as seen from Table 4. As expected, the trend observed for the low humidity coatings showed a decrease in porosity as more layers of nanofibers were included in the calculation. The greatest decrease in porosity observed was a decrease from an initial top layer (layer 1 ) of 77.1 % to combined 3 layers (layer 3) resulting in 8.9% for the TPU deposition.Table 4: Porosity of electrospun nanofiber coatingsHigh Humidity Low Humidity PorositySample IDPorosity Layer 1 Layer 2 Layer 3Tc 82.0% 77.1% 57.2% 8.9%TGc 75.7% 79.0% 50.0% 32.6%TCc 87.0% 75.0% 58.2% 9.2%TCGc 84.4% 77.9% 51.1% 18.9%

[0069] Porosity is seen to decrease with the consideration of more fibers or the addition of more fiber layers for the low humidity depositions. This aligns with the applied method relying on information obtained from SEM micrographs. Since SEM imaging gives topographical information about the samples it is not able to provide insights into the depth or thickness of the filtration media from just a top-view scan. By changing the threshold values in the analysis, the main feature being looked at with respect to porosity is only the through pores. In other words, layers 2 and 3 of the analysis are heavily influenced by what pores can be seen to go all the way through the thickness of the coating or up to the extent indicated by the grayscale values. This however may not be an accurate representation of true porosity with regards to electrospun fibers and their complex interconnected network.

[0070] The greatest porosity drops from layer 1 to layer 3 were seen for Tc and TCc and they were also observed to have similar average fiber diameters. This is an indication that the addition of CNC into the polymer solution did not significantly alter the solution properties, resulting in similar obtained fiber morphologies and structure with regards to low humidity depositions. The same trend was observed for the high humidity depositions of Tc and TCc, although there was a slightly higher deviation in the average fiber diameter and porosity. In terms of the low humidity deposits TGc started with the highest porosity at layer 1 and ended with the highest porosity at layer 3. Considering that TGc also had the smallest fiber diameter the increase in porosity could be seen as an effect of decreased diameter. The opposite relation was also observed for the high humidity case. TGc had a larger fiber diameter than Tc and a lower porosity. TCGc also showed a similar trend for porosity and fiber diameter for the low humidity case. The connection between fiber diameter and porosity was not reflected for the high humidity TCGc with the observed larger fibers and higher porosity. It could be said that average fiber diameter may havean inversely proportional relationship to through pore porosity. The smaller fiber sizes allow for a higher number of fibers to be present contributing to a higher through porosity and potential smaller average pore size.X-ray diffraction (XRD)

[0071] XRD analysis of the commercial GO, as seen in FIG. 8, was observed to have a peak at 20 = 12.1 ° corresponding to the (001 ) plane. The 20 for GO aligns well with available literature and the provided technical information from the manufacturer [30-32], No distinct peak shifts or changes were observed when comparing the XRD responses of TM and TGM in FIG. 8 around 12.1 °. This could be a result of inadequate dispersion of the nanomaterial in TPU or a lower-than-expected concentration present. If GO was not dispersed well, then the agglomerations would cause strong responses in only select areas while the remaining nanofibers would respond as if they were unaltered. Similarly, if the concentration of GO was low, then the resulting peak shift or alteration may not be noticeable orwell pronounced. The observed peaks for CNC, shown in FIG. 8, were 14.7° and 22.3° aligning with literature values indicating the (110) and (200) planes for cellulose, respectively [33,34], The introduction of CNC into TPU broadened the observed peak of TPU at 21.3° indicating the presence of the nanomaterial. Based on literature, TPU was expected to display a broad amorphous peak around 21 ° [35,36], Lower intensity amorphous peaks can be seen for each TPU and TPU-based nanocomposite; however, other distinct peaks not attributed to GO or CNC can also be seen. With regards to TCGM, a strong narrow peak was observed at 29.6° a long with a few more narrow peaks at diffraction angles above 30°. Seeing as these peaks were not expected from any of the base materials used, they could have arisen from chemical interactions between TPU, CNC, and GO or are indication of possible contamination on the samples. Seeing how these peaks were mainly present for TCGM they are attributed to possible contamination on the surface of the nanofibers with the intensity of their responses potentially overshadowing small responses due to either GO or CNC.Tensile properties

[0072] TM displayed the largest stiffness and strength with values of 7.24 and 2.67 MPa respectively. TGM showed the lowest Young’s modulus, strength, and ductility with values of 5.52 MPa, 1.91 MPa, and 40.27% respectively. The introduction of the nanomaterials seemingly had a negative impact on the tensile properties showing decreases in stiffness, strength, and ductility with the presence of CNC, GO and CNC / GO. Upon further analysis of the tensile results utilizing One-Way ANOVA statistical analysis, the reduction of tensile properties was determined to be not statistically significant (P>0.05). The incorporation of CNC did not adversely affect the stiffness of the nanocomposite, which could be attributed to the homogeneous distribution of CNC in the TPU matrix. The statistically similar Young’s moduli for TM and TGM indicates that the presence of GO neither hindered nor assisted in the relative motion of TPU polymer chains. Similarly, CNC also did not significantly affect (P>0.05) the ductility or ultimate tensile strength of the nanocomposite. This would indicate that the CNC imposed space between the TPU chains while imposing similar intermolecular interactions between CNC and TPU as was already present for the polymer chains. The increased distance would make deformation by chain slippage easier and reduce the amount of polymer entanglement while the motion would be counteracted by the weak Van der Waal forces. Correspondingly the combination of both nanomaterials resulted in neither a significant increase nor decrease to the tensile properties. Contrary to the expectations based on literature, the unaffected tensile properties even with the inclusion of both nanomaterials could be due to an inhomogeneous distribution or improper dispersion of GO and CNC in the nanocomposite. A summary of the tensile properties is displayed in Table 5.Table 5: Tensile properties of electrospun membranesYoung’s Ultimate tensile Precent elongation atSpecimen ID modulus strength break[MPa] [MPa] [%]TM 7.24 ± 3.14a2.67 ± 0.72b54.34 ± 21.98cTGM 5.52 ± 1.59a1.91 ± 0.57b40.27 ± 8.17cTCM 6.34 ± 2.71a2.42 ± 0.86b50.04 ± 14.19°TCGM 5.65 ± 2.15a2.00 ± 0.46b42.51 ± 10.19CValues are means ± standard deviations. Within each column, means with the same superscript letter are not significantly different (P > 0.05).

[0073] As seen in FIG. 9, the stress vs. strain characteristics of each fabric displayed linearly elastic behavior with high elongation under low stress values. TPU is a thermoplastic elastomer, therefore it was expected to have a low elastic modulus with a high precent elongation at break. Little to no necking or plastic deformation is observed with failure occurring immediately after reaching maximum stress.Dynamic mechanical analysis

[0074] As seen in FIG. 10, the storage modulus (at -30°C) are 235.5, 217.7, and 118.3 MPa for TM, TGM, and TCM, respectively. The storage modulus of a viscoelastic material indicates the ability to store energy elastically and is associated with reversible deformation such as bond stretching and chain straightening. Both TM and TGM displayed similar storage moduli values for the entire temperature range with the gap between values narrowing at higher working temperatures, 75.5 and 73.0 MPa for TM and TGM, respectively, at 25°C. Based on the recorded response one would observe slight differences in the elastic properties between the TM and TGM nanofiber membranes when used at temperatures below 25°C and no differences when utilized above 25°C. This would imply that at lower temperatures the presence of GO increased the distance between the molecular chains of TPU reducing the interchain interactions. However, at higher temperatures the increased energy and resulting interchain spacing caused similar molecular motion between the TM and TGM. On the other hand, the TCM had a lower storage modulus for the entire temperature range noting its tendency to be less elastic. TCGM showed a viscoelastic response between the individual nanocomposites of TCM and TGM for the full temperature range. At the lower temperature range the behaviour was closer to TGM but still with a slightly lower storage modulus value indicating that the presence of GO was able to mitigate the reduction in elastic behaviour caused by CNC. At the higher temperature range the response transitions from being closer to TGM to being closer to TCM. This could indicate that with the increased interchain spacing due to temperature the presence of CNC further increased the distance subsequently reducing the intermolecular forces.

[0075] The glass-rubber transition temperature (Tg) can be indicated as the temperature corresponding to the peak value on a tan delta vs temperature curve. As seen in FIG. 11 , the glass transition temperatures were 37.5°C, 40.1 °C, 41.6°C, and 50.9°C for T , TGM, TCM, and TCGM, respectively. The increase of the Tg indicates that the presence of the nanomaterials delay the onset of large-scale motion of the polymer chains resulting in an increased rigidity of TPU at slightly higher temperatures. The increased amount of intermolecular bonding between the nanomaterials and the TPU polymer chains help to restrict the motion at higher temperatures.Water contact angle

[0076] The measured contact angle against distilled water as a polar liquid and ethylene glycol as a non-polar solvent are shown in Table 6. As expected, due to the inherent hydrophobic nature of TPU the initial contact angle was greater than 90° with a measured value of 101.84°. There was a slight increase in angle with the addition of CNC changing the angle from 101.84° to 108.88°. The addition of only GO had no effect on the initial contact angle but the rate of decrease of the contact angle with time changed to a more linear decrease as shown in FIG. 12. The similar linear decrease can be seen for TCGM with the difference being that the initial water contact angle was lower than TPU with a value of 92.98°. The unchanging contact angle with the presence of GO would suggest that 3 wt.% of GO did not change the surface energy characteristic of the TPU, resulting in no effect on the materials hydrophilicity. The increase in angle reported with the addition of CNC would indicate that CNC reduced the surface energy of TPU, resulting in less energy available to overcome the surface tension of water. The decrease in contact angle for TCGM would indicate that the nanomaterials were able to increase the polar surface energy of the TPU nanofibers however they would still be considered hydrophobic because the angle is >90°. Additionally with the observed increase in initial contact angle for ethylene glycol (72.63°) for TCGM it could be said that the polar component of surface energy was increased at the cost of decreasing the dispersive component. The contact angle against ethylene glycol displayed a similar trend with the initial angle for TM being the lowest at 49.68° and the highest being for TCM with 73.36°. The higher initial contact angle for ethylene glycol indicates that the presence of CNC not only made TPU more repellent to polar liquids but also non-polar liquids.Table 6:Water contact angle measurement for electrospun TPU base nanocompositesInitial Static Water Contact Initial Static Ethylene GlycolSpecimen ID Angle average [°] Contact Angle average [°]"T^i 101.84 49.68TGM 101.38 56.58TCM 108.88 73.36TCGM 92.98 72.63Antibacterial testing

[0077] Each antibacterial trial was done with a control electrospun deposit from pure TPU for reference and each inoculation was done in triplicate. E. coli CFUs were enumerated prior to and after exposure to electrospun samples using serial dilution of cells and plating onto selective growth media. Representative CFU enumeration results from 10'6and 10'7output cultures are indicated (FIG. 13(a) and 13(b)). Using the counted CFU from the serial dilution, the antibacterial efficiency was calculated based on a comparison of bacteria added to bacteria retrieved after exposure of cells to fabric samples for 24 hrs. TM had an antibacterial efficacy of 97.79% while the nanocomposite membranes also had similar efficacies above 90% of 98.56% and 98.70% for TGM and TCM, respectively (Table 7).Table 7: Antibacterial efficacy of membranes tested using E. coliBacteria Mean bacteria AntibacterialSpecimen ID added [Logio] recovered [Logio] efficacy [%]TM 7.18 ± 7.04 5.47 ± 5.36 97.79 ± 2.22TGM 7.26 ± 7.15 5.42 ± 5.34 98.56 ± 0.22TCM 7.12 ± 6.98 5.24 ± 4.73 98.70 ± 0.41

[0078] Each of the three compositions was able to reduce the number of bacteria over the 24- hour incubation time by 2 orders of magnitude, resulting in average antibacterial efficacies that are within 1 % of each other. The similar trend reported for both TM and TGM indicates that there was no additional or enhanced antibacterial activity conferred by the presence of GO, contrary to expectations from the literature. This discrepancy could be the result of differing materials and methods used in the present experiments versus previously reported experiments. On the other hand, GO may not be effective in an antibacterial sense with the achieved deposition methodology. The primary antibacterial mechanism for GO is reported as physical interaction of the sharp flake edges with the bacterial cell membrane to compromise cell wall integrity leading to cell death. By introducing the GO into the polymeric solution prior to electrospinning the resulting TPU nanofibers could contain fully encased and embedded GO flakes. Without an exposed GO edge or surface there would be no physical interaction between the nanomaterial and bacteria cells, rendering the GO ineffective. This can be seen from the attained antibacterial efficacy being similar between the two compositions. Fully encased GO flakes were not expected based on the difference between the measured nanofiber diameters and reported lateral dimensions of the nanomaterial being 5 - 10 pm. A single flake of GO could not be fully encased in a single nanofiber; therefore, it was expected to observe exposed sections with SEM imaging, which was not the case. As seen from optical microscopy, in FIG. 14, the black GO flakes can be seen dispersed through the fiber network with similar dimensions to the observed beads, indicating that the flakes could be present within the beads. The lack of clear and defined edge / flake structures for the presence of GO in the SEM images gives strong evidence towards GO being encased. The chosen SEM parameters focused on better surface characteristic detail while sacrificing electron penetration depth. By focusing on the surface detail, GO flakes that are surrounded by TPU would be easily missed since the characteristics of GO would not be seen through the TPU. Another influencing factor may be the hydrophobicity of the electrospun membranes as this could limit interaction of the aqueous bacterial cell suspension with the surface of the membranes. The lack of interaction could lead to fewer opportunities for the bacteria to encounter the GO nanoflakes thus reducing their effectiveness as an antibacterial enhancement. The addition of CNC to the TPU matrix displayed little to no changes in antibacterial behavior in comparison to the pure TPU composition. This was expected due to CNC not being an inherently antibacterial material therefore there should have been change to the antibacterial efficacy, which was observed.Air filtration efficiency

[0079] The experimental filtration efficiency was determined based on the difference between light scattering coefficients measured for a baseline condition and the nanocomposite filter test. Filtration efficiency, E, was calculated using:where <sp_b is the scattering coefficient measured for the baseline and crSp_ris the scattering coefficient measured for the nanocomposite filter. A summary of the experimentally measured filtration efficiency utilizing Equation 1 can be found in Table 8. From Table 8, low humidity coatings resulted in a higher filtration efficiency, 78.70% - 91.83%, in comparison to high humidity coatings, 9.65% - 42.26%. For the low humidity coatings, the highest filtration efficiency was achieved with the addition of CNC of 91.83% and the lowest was the combination of CNC and GO with 78.70%. For the high humidity coatings, the highest filtration efficiency was 42.26% for TPU and the lowest was 9.65% for the addition of CNC and GO.Table 8: Filtration efficiency of electrospun nanofibers at high and low deposition humiditySample ID High Humidity Low HumidityTc 42.26% 84.24%TGc 25.13% 84.80%TCc 29.19% 91.83%TCGc 9.65% 78.70%

[0080] An example of the particulate capture can be seen in FIG. 15, representing the removal of NaCI particulates from the air and their attachment to the nanofibers. NaCI particles were observed to be directly attached to the nanofibers as well as being blockedby other NaCI particles. The buildup of filtered particles could be attributed to a sieving mechanism when the particles were larger than the pores and as well as classical filtration mechanisms for the smaller particles. A sieving mechanism is more feasible based on the buildup of particles and the presence of a filter cake due to the readily clogged pores. Based on micrograph analysis utilizing Imaged software the size distribution of NaCI particulates that were filtered ranged from 0.29 to 0.98 pm (PM2.5).

[0081] According to classical filtration theory air particulate filtration is governed by 5 mechanisms: interception (ER), inertial impaction (£}), Brownian diffusion (ED), the electrostatic effect (Eq), and the gravity effect (EG) [37-39], Since the charge on fibers or particles is difficult to quantify, collection efficiency due to electrostatic effects is generally neglected

[0037] , Different particulate sizes (PM0.1, PM2.5, and PM10) are strongly influenced by different filtration mechanisms

[0040] , Diffusion is the predominant mechanism for ultrafine particles, impaction and interception become more significant as the size increases, and gravity effects and filtration by sedimentation can be assumed negligible for particulates under 0.5 pm

[0040] , Single-fiber-efficiency (SFE) theory has been used to calculate the overall particulate collection efficiency (E) using:and the total SFE (Ez) was calculated by: = ER+ EI+ ED+ EDR+ EG(3) where a is the media solidity (1 - porosity), t is the filter thickness, and df is the fiber diameter

[0037] , The effects due to diffusion (ED and interception (ER) are given by:where Pe is the Peclet number based on the fiber diameter, Ku is the Kuwabara hydrodynamic factor of Ku =parameter given as the ratio of the particle diameter to the fiber diameter R = dp / df. Where dpis theparticle diameter

[0041] , The contribution due to inertial impaction was calculated using: number (Stk) and the variable J calculated by:J = (29.6 - 28°62)7?2- 27.5T?2'8for R < 0.4 (8) where ppis the particle density, Uois the face velocity, Ccis the Cunningham slip correction factor, and p is the dynamic viscosity of the fluid

[0037] ,The enhanced collection efficiency due to the interception of diffusing particles (EDR) and was calculated using

[0037] :

[0082] The results of the filtration calculation using Equation (2) can be seen in FIG. 16 where the filtration efficiency was calculated for both the high and low humidity cases along with the efficiency obtained for each of the 3 layers measured. The filtration efficiencies were calculated against a range of particle diameters from 0.1 to 1 pm.

[0083] As seen from FIG. 16, the high humidity depositions had calculated efficiencies ranging from 45% to 72% for a particle size of 0.01 pm with TGc having the highest and the TCc having the lowest. As would be expected, an increase in filtration efficiency is shown with increasing particle size with the exception of a drop in efficiency for the high humidity depositions. The drop in efficiency indicates that the most penetrating particle size for the high humidity depositions would be expected in the range of 0.02 to 0.03 pm. Comparatively, the low humidity depositions did not show a notable decrease in filtration efficiency for the given range. Both layers 1 and 2 for the low humidity deposits showed the same trend of increasing filtration efficiency with particle size. Based on the trend it could be assumed that the most penetrating particle size would be smaller than 0.01 pm. In the case of layer 1 the filtration efficiency increases from a range of 89% to 94% to anexpected 100% for all compositions against particles 0.2 pm and larger. As more layers are considered for the porosity, the filtration efficiency for 0.01 pm particles can be seen to increase. Porosity can be seen to have a direct effect on the expected filtration efficiency however since the porosity measured for layers 2 and 3 fall outside the acceptable range of solidity, 0.005 < a < 0.2, that values may deviate from measured values.

[0084] Not only do the experimental results of high humidity and low humidity differ by 50% or more, but the values also differ from the analytical results for all cases. The highest deviations can be seen for the high humidity depositions and low humidity depositions using layers 2 and 3 for calculations using the smallest particle sizes.

[0085] Since the SFE based in Equation (3) only depends on the mechanical mechanism with electrostatic effects often being neglected the electronegativity and enhanced filtration mechanisms due to the incorporation of GO and CNC would not be accurately modeled. Therefore, the total filtration efficiency given in Equation (2), which depends on the solidity, filtration media thickness, and average fiber diameter, would result in differences between the experimental and analytical results. Low humidity depositions considering porosity at layer 1 had the closest agreement with the experimental results indicating that the first layer approach may be closer to the true porosity of the coating. Increased filtration efficiency with the incorporation of CNC could be attributed to morphology-based effects such as lower porosity with similar average fiber diameters. On the other hand, the enhanced filtration could be due to charge characteristics introduced with the electronegativity of CNC. Based on the similar fiber diameters and porosity between Tc and TCc but different filtration efficiency the later mechanisms of CNC are more likely. Similar charge characteristics would be expected from the addition of GO, due to the electronegative oxygen-containing functional groups; however, experimental results indicate that GO had no enhanced filtration behavior. Considering the analytical predictions it would have been expected for TGc to have a lower filtration efficiency than TPU based on the fiber morphology, yet the experimental results indicated no change. The electronegative charge characteristics could be the cause of the lack of change in the filtration efficiency resulting in electrostatic collection efficiency bridging thegap between the morphological differences. The same effects were not observed with the combination of GO and CNC, with TCGc having the lowest filtration efficiency of the high and low humidity deposits. This could have been due to a detrimental interaction between the nanomaterials that was not expected.

[0086] For the high humidity depositions, there is an even greater difference between the analytical and experimental results. Even with the lack of fiber presence seen in the SEM micrographs, SFE theory still predicted a higher than experimentally measured filtration efficiency for the majority of the particle size range. The low filtration efficiency could be attributed to the physical characteristics of the coating rather than the lack of particle capture by impaction, diffusion, or interception. The thinner deposition of fibers could lead to mechanical strength issues of the coating and the potential for fiber failure or incomplete coating of the substrate. FIG. 17 shows a deposition of TCGc deposited at low humidity thus showing a denser more present fiber network with improper fiber coverage or damage being observed. The large gap between the microfibers of the substrate with no nanofibers could allow particles to slip through unimpeded. Since the lack of nanofibers was also observed for the low humidity depositions it could be a more prevalent problem for the higher humidity deposition due to the reduced fiber presence.

[0087] Another consideration is the evolution of damage to the nanofiber web during filtration activities. If the fiber webs were damaged or the substrate was not covered completely then the NaCI particulates would bypass the nanofibers and easily flow through the large non-woven pores without capture. The lack of fiber strength could also lead to mechanical failure during testing depending on the airflow rate and the particles' inertial force. As seen in FIG. 18, NaCI particles are readily filtered by the nanofibers; however, there can still be a section of fiber failure resulting in a way for the flow to bypass the nanofiber entirely.

[0088] Table 9 displays the measured values of pressure drop for the electrospun nanofibers while particulate free air is passed through the media. It can be seen that the low humidity depositions had a higher pressure drop in comparison to the high humidity depositions. The higher differential pressure could be a result of the low humiditydeposition having smaller average fiber diameters and lower porosity. Differential pressure (Ap) was calculated by:0.006 < a < 0.3 (11)As seen from Equation (10), differential pressure is proportional to the thickness and a function of the solidity and inversely proportional to the fiber diameter squared. Considering the relationship between pressure drop and fiber diameter, the expected pressure drop for the low humidity deposits would be 4 times larger than the high humidity deposits. This would be expected based on a comparison of just the average fiber diameters, low humidity being approximately half the size of high humidity, with the assumption that the thicknesses and solidities were consistent.Table 9: Pressure drop of electrospun nanofibers at high and low deposition humidityPressure Drop [kPa]Sample IDHigh Humidity Low HumidityTc 0.10 0.21TGc 0.06 0.27TCc 0.08 0.36TCGc 0.04 0.25

[0089] As seen from Table 10, the calculated pressure drops for the low humidity depositions utilizing Equation (10) and Equation (11 ) are larger than the low humidity depositions which was also observed for the experimental results. The differential pressure can also be seen to increase from the measured layer 1 porosity to layer 3 porosity, which is expected due to the pressure being proportional to the function ofsolidity. However, the measured values for layers 2 and 3 go beyond the applicable range for Equation (11 ), potentially introducing errors into the calculation for pressure drop. Hinds and Zhu

[0037] also mention that values overpredict the differential pressure using Equation (10) because of slip flow for fibers less than 1 pm. Experimental measurements could be up to 30% lower than analytical calculations due to the gas slippage due to the different flow regimes in the smaller fiber range. However, the analytical calculations compared to high humidity and low humidity at layer 1 are 84% - 97% lower than the measured pressure drops.Table 10: Calculated pressure drops of nanofibers at the different measured porosity layersHigh Humidity Low HumiditySample ID Ap Layer 1Ap [kPa] [kPa] Ap Layer 2 [kPa] Ap Layer 3 [kPa]TPU 1.11 6.43 52.92 1321.33TPU / GO 1.93 6.90 133.53 437.02TPU / CNC 0.51 9.62 56.43 1523.54TPU / CNC / GO 0.56 6.71 103.91 907.71

[0090] The experimental differential pressure measured between the high and low humidity depositions is further confirmation of the difference between coating thickness. As previously mentioned, it was expected to have a larger differential pressure for the low humidity deposits based on the smaller fiber diameter. For the majority of the compositions, the difference was greater than a factor of 4, indicating the other observed differences and contributions were due to the thickness and solidity. The high humidity deposits were able to achieve such a low differential pressure due to their larger fibersize, similar porosity, and reduced coating thickness. This also aligns with the trend shown for the analytical predictions of pressure drop although the results do not line up between the experimental and analytical. The equation used to calculate pressure drop works off the general assumption in fluid dynamics that the fluid can be considered a continuum. As the size of fibers decreases and approaches the mean free path of air molecules, 0.066 pm at standard conditions, the air can no longer be analyzed as a continuous fluid

[0037] , This means that the no-slip condition is not valid, and the air is in a slip-flow regime while passing the nanofibers. This leads to the calculation of differential pressure to overpredict for nanofibers which can be seen from the analytical and experimental results.

[0091] According to certain embodiments, nanomaterials such as graphene oxide (GO) and cellulose nanocrystal (CNC) integrated nanocomposite fibrous membrane of thermoplastic polyurethane (TPU) were designed and synthesized following a solutionspecific electrospinning method. GO was chosen to improve the mechanical properties of the membranes and improve antibacterial behaviour. CNC was selected to improve the hydrophilicity and mechanical properties of the membranes. The membranes were deposited with average fiber diameters ranging from 142.50 nm to 164.60 nm. Testing and characterization of the membranes were found to indicate the following: 1 ) neither the presence of GO nor CNC nor combination of CNC and GO significantly affected the tensile properties; 2) dynamic mechanical analysis (DMA) revealed that GO and CNC were able to increase the glass transition temperature of the TPU with the strongest response resulting from the use of both nanomaterials; 3) water contact angle measurements following a Sessile drop methodology indicated that the presence of GO had little effect on the initial contact angle, CNC showed a slightly more hydrophobic initial behaviour, and CNC with GO displayed a more hydrophilic initial behaviour; 4) antibacterial testing showed that neither presence of GO nor CNC improved the antibacterial behavior of the TPU membranes.

[0092] According to certain embodiments, nanocomposites using a TPU matrix with CNC and GO reinforcements were prepared by electrospinning. These nanocomposites were characterized by SEM, tensile testing, DMA, water contact angle testing, and antibacterialtesting. The addition of GO displayed the ability to delay the glass transition temperature and reduce beading of the nanocomposite with no effect on the tensile properties, hydrophilicity, average fiber diameter, or antibacterial behaviour. CNC was able to increase the glass transition temperature and increase the hydrophobicity of the nanocomposite while unaffecting the average fiber diameter, tensile properties and antibacterial properties.

[0093] According to certain embodiments, nanocomposite coating comprised of matrix thermoplastic polyurethane (TPU) and nanofillers graphene oxide (GO) and cellulose nanocrystal (CNC) were designed and synthesized utilizing an electrospinning methodology. The nanofibers were coated onto a non-woven substrate in two different ambient conditions, high and low relative humidity, to determine changes in air filtration efficiency against sodium chloride (NaCI) particulates. The nanocomposites were also investigated to determine the effects of the nanofillers on the filtration properties of the coatings. Through experimental measurements in comparison to single fiber efficiency (SFE) analytical predictions, the coatings were found to indicate the following: 1 ) electrospinning depositions done at low humidity resulted in smaller fiber sizes and superior filtration efficiency for all compositions; 2) GO reduced the average fiber diameter without altering the filtration efficiency when deposited at low humidity; 3) for low humidity deposits, CNC improved the filtration efficiency while not affecting the obtained fiber size; and 4) the combination of GO and CNC reduced the filtration efficiency without altering the fiber size or differential pressure.

[0094] According to certain embodiments, porous non-woven nanofiber coatings of matrix TPU, and nanofillers CNC and GO were successfully electrospun onto a non-woven polyester substrate at two distinct relative humidities. The morphologies of the nanocomposite coatings were analyzed using SEM and the filtration efficiency was determined against NaCI utilizing an in-house apparatus. The following conclusions resulted from the filtration investigation of the nanocomposite coatings:• Nanofiber depositions performed at high humidity resulted in larger fiber diameters and a lower filtration efficiency in comparison to depositions done at low humidity.• Depositions done at low humidity achieved smaller average fibers with a more numerous fiber presence and better coverage.• The presence of GO in low humidity was able to reduce the average fiber diameter and did not negatively affect the differential pressure or filtration efficiency.• The presence of CNC in low humidity was able to improve the filtration efficiency without affecting the fiber size.• The interaction between GO and CNC reduced the filtration efficiency without affecting the fiber size or pressure drop for low humidity depositions.

[0095] While the teaching herein include illustrative embodiments and examples of some aspects of an invention, the description is not intended to be construed in a limiting sense. Thus, various modifications of the illustrative embodiments, as well as other embodiments of the invention, may be apparent to persons skilled in the art upon reference to this description. It is therefore contemplated that the appended claims will cover any such modifications or embodiments.

[0096] All publications, patents, and patent applications referred to herein are incorporated by reference in their entirety to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference in its entirety.

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Claims

AMENDED CLAIMS received by the International Bureau on 28 February 2025 (28.02.2025)

1. A non-woven fibrous nanocomposite material comprising: nanometer diameter fibers comprising thermoplastic polyurethane (TPU), graphene oxide (GO) and cellulose wherein the fibers are deposited using electrospinning.

2. The non-woven fibrous nanocomposite material of claim 1 , wherein the fibers are deposited under conditions of relative humidity of less than 50%.

3. The non-woven fibrous nanocomposite material of claim 1 , wherein the fibers are deposited under conditions of relative humidity of greater than 50%.

4. Use of the non-woven fibrous nanocomposite material of any one of claims 1 to 3 as an antibacterial fabric.

5. A nanocomposite solution comprising: thermoplastic polyurethane (TPU), graphene oxide (GO) and cellulose, all in solution, wherein the feedstock for the graphene oxide is graphene oxide nanosheets, and the feedstock for the cellulose is cellulose nanocrystals (CNC).

6. The nanocomposite solution of claim 5, wherein the thermoplastic polyurethane (TPU) is the base solution which contains the GO and CNC.

7. The nanocomposite solution of claim 6, wherein the GO and the CNC each form between 0 wt% and 3 wt. % of the solution.

8. The nanocomposite solution of claim 6, wherein the CNC crystals are 40nm to 50nm in diameter and 230nm to 270nm in length.

9. A method of preparing a nanocomposite solution comprising the steps of: providing a thermoplastic polyurethane (TPU) solution; adding graphene oxide (GO) and cellulose nanocrystals (CNC) to the solution; and homogenizing the solution, wherein the amount of the GO and the CNC are each added in an amount of between 0 wt.% and 3 wt. % of the solution.

10. The method of claim 9, wherein the amount of TPU is between 94 wt.% and 100 wt.%.AMENDED SHEET (ARTICLE 19)

11. A method of forming a nanocomposite comprising the steps of: depositing the nanocomposite solution of any one of claims 5 to 8 on a substrate using electrospinning.

12. The method of claim 11 , wherein the substrate is a non-woven fabric.

13. The method of claim 11 , wherein the deposition is carried out under conditions of relative humidity less than 50%.

14. The method of claim 11 , wherein the deposition is carried out under conditions of relative humidity greater than 50%.

15. The method of any one of claims 11 to 14, wherein the electrospinning is carried out with the application in the range of 20kv to 20.4kv of voltage, a flowrate for the solution of in the range of 0.25 mL hr— 1 to 1 mL hr— 1 and a collector distance of 12 cm.AMENDED SHEET (ARTICLE 19)

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