REMOVABLE, WATERPROOF MULTI-LAYER COATING HAVING ANTIBACTERIAL PROPERTIES FOR CONTACT SURFACES AND METHOD FOR THE PREPARATION THEREOF

Abstract

A multi-layer coating with antibacterial and anti-COVID properties which is usable in various environments, including hospitals, and which can be easily deposited by spraying on different surfaces and capable of providing an effective removable barrier against pathogens and bacteria, which waterproof coating is characterized in that it uses graphene nanoparticles as an antibacterial and anti-COVID agent deposited by spraying a polymer material as a host layer on the surface to promote the dispersion and uniform surface distribution thereof, the polymer material being directly adhered by spraying to the surface to be coated or sprayed on a second polymer, in turn sprayed on the surface to be coated, which is used as an element to promote the adhesion of the first polymer forming the antibacterial and anti-COVID coating to the surface to be coated.

Claims

1. A method for manufacturing a removable, waterproof multi-layer coating having antibacterial and anti-C OVID properties which uses, as an antibacterial and anti-COVID agent, graphene nanoparticles and zinc oxide nanorods or graphene nanoparticles decorated with zinc oxide nanorods, the method being applicable by spraying on different contact surfaces, made of metal, fabric, or plastic, said method including the following steps: a) preparing at least one polymer solution based on a first sprayable polymer to be used in the form of a continuous film as a coating on the surface to be treated, serving a first function of host layer to promote the optimal dispersion and surface distribution of said graphene nanoparticles and zinc oxide nanorods or graphene nanoparticles decorated with zinc oxide nanorods which, when sprayed on said coating as an antibacterial and anti-COVID agent, remain partially exposed above the free surface thereof, and a second function of ensuring adhesion to the surface to be coated, thus promoting the formation of said continuous film on said surface to be coated; b) preparing the nanoparticles to be sprayed on said film, by thermally expanding the interdispersed graphene then sonicated for 20 minutes in acetone, by means of a probe sonicator and then sonicating the ZnO nanorods in acetone for 3 minutes, by means of an ultrasonic bath thus obtaining nanostructures based on graphene and zinc oxide; c) spraying the polymer solution obtained in step a) on the surface to be treated to form a continuous film adhered to the same surface acting as a host layer; and d) superficially depositing, again by spraying, the nanostructures based on graphene and zinc oxide, or graphene decorated with zinc oxide nanorods, obtained in step b) on said host layer, to form an antibacterial and anti-COVID barrier on said surface, by virtue of the sharp edges of the nanostructures which, protruding externally, interact directly on the cell membranes; where the polymer forming the host layer is selected from Polyvinylpyrrolidone, or polymer 2, which has excellent adhesion to metal surfaces, and Polycaprolactone, or polymer 1, which is a semi-crystalline polymer with a low melting point of about 60 C. and a glass transition temperature of about 60 C., which has excellent adhesion to polymer resin and fabric surfaces, and a poor solubility in water.

2. The method according to the claim 1, wherein ethanol is used as a solvent for PVP at room temperature using a magnetic stirrer, while PCL is dissolved in acetone at a temperature of 30 C. using a magnetic stirrer.

3. The method according to claim 1, wherein the different polymer concentrations vary between 1% and 15% by weight in the solvent and polymer mixtures.

4. The method according to claim 1, wherein there are three different types of nanostructures dispersed on the surface of the polymer host layer, used in a concentration range between 2 mg and 10 mg on 100 mg of polymer forming the host layer: a) Graphene nanoplatelets, b) Zinc oxide nanorods, where nanorod indicates a morphology of objects on the nanoscale, with a rod shape, wherein the average diameter is between 20 nm and 50 nm and the length is between 100 nm and 1 m; and c) graphene nanoplatelets decorated with zinc oxide nanorods; or as a replacement, to minimize the nanomaterial, GNP and ZNO nanostructure production costs and times.

5. The method according to claim 1, wherein in the nanoparticles used for spraying, the interdispersed graphene has been thermally expanded and then sonicated for 20 minutes in acetone, by means of a probe sonicator, while the ZnO nanorods are sonicated in acetone for 3 minutes, by means of an ultrasonic bath.

6. The method according to claim 1, wherein the polymer film is a multi-layer film in which the constituent elements are arranged on two or more subsequent layers, the different layers being sprayed on the surface to be coated based on the substrate adhesion and water-repellant properties thereof and based on the antibacterial and anti-COVID properties thereof.

7. A removable, waterproof multi-layer coating with antibacterial and anti-COVID properties, comprising at least one polymer film acting as a host layer on which graphene nanoparticles and zinc oxide nanorods are sprayed as an antibacterial agent, which remain partially exposed above the free surface, said polymer film being either directly adhered by spraying to the surface to be coated by spraying to a second polymer film, in turn adhered by spraying to the surface to be coated, and used as an element to promote the adhesion to said surface to be coated of the first polymer film forming the antibacterial and anti-COVID coating, the polymer material used to create the coating consisting of Polycaprolactone, or polymer, which is used individually on fabric or resin surfaces and also acts as a binder for nanoparticles, and which is used in combination with a film made of Polyvinylpyrrolidone, or polymer, on metal surfaces, where the Polyvinylpyrrolidone acts as a coating and as a support for the Polycaprolactone and the Polycaprolactone acts as a binder for the nanoparticles.

8. A multi-layer coating having antibacterial and anti-COVID properties according to claim 7, wherein there are three different types of nanostructures dispersed in the active suspensions, used in a concentration range between 2 mg and 10 mg: a) Graphene nanoplatelets, b) Zinc oxide nanorods, where nanorod indicates a morphology of objects on the nanoscale, with a rod shape, wherein the average diameter is between 20 nm and 50 nm and the length is between 100 nm and 1 m; and c) graphene nanoplatelets decorated with zinc oxide nanorods; or, as a replacement, GNP and ZNO nanostructures, where the combination of GNP and ZNO is usable in place of the graphene nanoplatelets decorated with zinc oxide nanorods, so as to minimize the nanomaterial production costs and times.

9. The multi-layer coating according to claim 8, wherein, in case of an aluminum surface, the coating consists of a three-layer film, superimposing the aluminum layer first with polymer 2, thus taking advantage of the optimal metal adhesion thereof, even if poorly hydrophobic, and then superimposing polymer 1 used as a binder on this layer of polymer 2, so as to obtain excellent hydrophobicity features and optimal adhesion to the polymer substrate, the GNP and ZNO nanostructures or the combination of the two being then sprayed on said film of polymer 1.

10. The multi-layer coating according to claim 7, wherein, in case of a fabric substrate, the coating consists of a single antimicrobial and anti-COVID film consisting of GNP and GNP+ZnO nanorods distributed on the binder of polymer 1.

11. A kit for manufacturing a removable, waterproof multi-layer antimicrobial coating for contact surfaces in environments to be sanitized according to claim 7, comprising: a dispenser containing a first sprayable polymer solution based on PCL, to be used individually on fabric or resin surfaces and which acts as a coating and as a binder for the nano structures; a dispenser containing active sprayable suspensions of nanostructures; a dispenser containing a second sprayable polymer solution based on PVP for metal surfaces which acts as a coating and as a support to the first polymer solution based on PCL which acts as a binder for the nanoparticles.

12. The method of claim 1, further comprising using a second polymer solution based on a second polymer, in place of or in combined action with the first polymer forming the host layer, so that the creation of the nanoparticle barrier, the adhesion to the surface to be coated, and the creation of a continuous film are simultaneously ensured.

13. The method according to claim 2, wherein the different polymer concentrations vary between 1% and 15% by weight in the solvent and polymer mixtures.

14. The method according to claim 12, wherein the different polymer concentrations vary between 1% and 15% by weight in the solvent and polymer mixtures.

15. The method according to claim 2, wherein there are three different types of nanostructures dispersed on the surface of the polymer host layer, used in a concentration range between 2 mg and 10 mg on 100 mg of polymer forming the host layer: a) Graphene nanoplatelets, b) Zinc oxide nanorods, where nanorod indicates a morphology of objects on the nanoscale, with a rod shape, wherein the average diameter is between 20 nm and 50 nm and the length is between 100 nm and 1 m; and c) graphene nanoplatelets decorated with zinc oxide nanorods; or as a replacement, to minimize the nanomaterial, GNP and ZNO nanostructure production costs and times.

16. The method according to claim 3, wherein there are three different types of nanostructures dispersed on the surface of the polymer host layer, used in a concentration range between 2 mg and 10 mg on 100 mg of polymer forming the host layer: a) Graphene nanoplatelets, b) Zinc oxide nanorods, where nanorod indicates a morphology of objects on the nanoscale, with a rod shape, wherein the average diameter is between 20 nm and 50 nm and the length is between 100 nm and 1 m; and c) graphene nanoplatelets decorated with zinc oxide nanorods; or as a replacement, to minimize the nanomaterial, GNP and ZNO nanostructure production costs and times.

17. The method according to claim 12, wherein there are three different types of nanostructures dispersed on the surface of the polymer host layer, used in a concentration range between 2 mg and 10 mg on 100 mg of polymer forming the host layer: a) Graphene nanoplatelets, b) Zinc oxide nanorods, where nanorod indicates a morphology of objects on the nanoscale, with a rod shape, wherein the average diameter is between 20 nm and 50 nm and the length is between 100 nm and 1 m; and c) graphene nanoplatelets decorated with zinc oxide nanorods; or as a replacement, to minimize the nanomaterial, GNP and ZNO nanostructure production costs and times.

18. The method according to claim 2, wherein in the nanoparticles used for spraying, the interdispersed graphene has been thermally expanded and then sonicated for 20 minutes in acetone, by means of a probe sonicator, while the ZnO nanorods are sonicated in acetone for 3 minutes, by means of an ultrasonic bath.

19. The method according to claim 3, wherein in the nanoparticles used for spraying, the interdispersed graphene has been thermally expanded and then sonicated for 20 minutes in acetone, by means of a probe sonicator, while the ZnO nanorods are sonicated in acetone for 3 minutes, by means of an ultrasonic bath.

20. The method according to claim 4, wherein in the nanoparticles used for spraying, the interdispersed graphene has been thermally expanded and then sonicated for 20 minutes in acetone, by means of a probe sonicator, while the ZnO nanorods are sonicated in acetone for 3 minutes, by means of an ultrasonic bath.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Further features and advantages of the invention will become apparent from the following detailed description, with reference to the accompanying drawings, in which:

[0065] FIG. 1 shows the configuration of the double-layer coating on aluminum substrate without (a) and with (b) nanostructures.

[0066] FIG. 2 shows the antimicrobial and anti-COVID treatment of the present invention, sprayed on a thin layer of PCL deposited on resin and fabric.

[0067] FIG. 3 shows SEM images of the surface of the antimicrobial and anti-COVID material arranged on different substrates.

[0068] FIG. 4 shows the comparison between the viscosity curves obtained for PVP in alcoholic solution in the two minimum and maximum concentrations, c1=9% by weight and c2=15% by weight, considered in this study.

[0069] FIG. 5 shows the comparison between the viscosity curves obtained for samples consisting of PCL acetone solutions with increasing concentrations, from the minimum to the maximum considered in this study: 3% by weight, 5% by weight and 7% by weight.

[0070] FIG. 6 shows the viscosity curves measured on the same PCL sample with a maximum concentration of 7% by weight, in successive time intervals. 3200 s elapse between the first and last test.

[0071] FIG. 7 shows a detail of the SEM image of the surface of the bi-layer polymer coating with GNP and ZnO nanoparticles.

[0072] FIG. 8 is a graphic depiction of the contact angles on different surfaces.

[0073] FIG. 9 is a SEM image of the antimicrobial and anti-COVID PCL+ nanorod surface of ZnO and GNP.

[0074] FIG. 10 shows contact angle values for various antimicrobial and anti-COVID surfaces with PCL on fabric.

[0075] FIG. 11 shows an image and technical features of 3M #600 adhesive tape used for the adhesion tests.

[0076] FIG. 12 shows an AFM image (left) and surface profile (right) of the PCL polymer binder on a fabric substrate.

[0077] FIG. 13 shows an AFM image (left) and surface profile (right) of the PCL polymer binder on a resin substrate.

[0078] FIG. 14 shows an AFM image (left) and surface profile (right) of the PVP+PCL polymer binder on a metal substrate.

[0079] FIG. 15 shows SEM images on aluminum substrate before the test (a) and after the test (b).

[0080] FIG. 16 shows SEM images on resin substrate before the test (a) and after the test (b).

[0081] FIG. 17 shows SEM images on fabric substrate before the test (a) and after the test (b).

[0082] FIG. 18 shows the antimicrobial tests of the polymer binder of the present invention on a metal surface contaminated by two different types of bacteria. The image shows the microbial load of each sample considering as 100% the value of the surface coated only by the polymer binder at time zero.

[0083] FIG. 19 reports the survival of S. aureus cells exposed to fabric surfaces coated with the product of the present patent, using different nanomaterials mixed with the polymer binder at different times. In the image, the microbial load of each sample is shown considering as 100% the value of the fabric substrate coated only by the polymer binder at time zero.

[0084] FIG. 20 reports the antimicrobial tests of the binder of the present invention on a resin substrate contaminated by two different types of bacteria. In the image the microbial load of each sample is shown considering as 100% the value of the substrate coated by the polymer binder free of nanomaterials at time zero.

[0085] FIG. 21 reports the evaluation of the antimicrobial effect of the treatment of the invention deposited on the surface of fabric (left) and resin (right) specimens in a closed environment. The data are expressed considering substrates with only polymer as control. P value <0.05.

[0086] FIG. 22 reports the evaluation of the antimicrobial effect of the treatment of the invention deposited on the surface of fabric (left) and resin (right) specimens in the pediatric odontostomatology unit. The data are expressed considering substrates with only polymer as control. P value <0.05.

DETAILED DESCRIPTION

[0087] As already mentioned, the invention consists of an innovative coating consisting of a polymer coating on which graphene nanoparticles are deposited by spraying and which has antibacterial and anti-COVID properties. The following description discloses, by way of example, the application of the invention to three different types of surfaces.

[0088] Specifically, the degree of bacterial inhibition was evaluated due to graphene nanoplatelets and zinc oxide nanorodsa particular ZnO nanostructure characterized by rod shape and diameter between 25 nm and 40 nm and length between 100 nm and 1 m sprayed onto a host polymer which is in turn deposited on a substrate of a different nature: metal, plastic and fabric. The suspensions were applied to the substrates by a spraying technique.

[0089] The main antimicrobial mechanism exhibited by such nanostructures is based on the perforation of the bacterial wall. This damage mechanism is typical of graphene nanoplatelets and zinc oxide nanowires.

[0090] The antimicrobial activity of the coating was evaluated in relation to Gram-positive (Staphylococcus aureus) and Gram-negative (Pseudomonas aeruginosa) bacteria, which represent the main pathogens associated with nosocomial infections.

[0091] The results obtained from the test carried out using the colony forming units count (CFU) method show an excellent antimicrobial behavior of the coatings of the present patent.

[0092] In general, the coating of the present invention consists of a host polymer the main function of which is to promote the partial dispersion of the nanoparticles, without allowing the total incorporation thereof in the polymer matrix.

[0093] A second function of the polymer is to ensure adhesion to the surface to be coated, promoting the formation of a continuous film.

[0094] Depending on the surface on which it is applied, it may be necessary to use a second polymer, in place of or in combined action with the host polymer, so that the creation of the nanoparticle barrier, the adhesion to the surface to be coated, and the creation of a continuous film are simultaneously ensured.

[0095] Production of colloidal suspensions and antimicrobial nanomaterial coatings.

[0096] The following carriers were used for the production of suspensions of nanostructures with antimicrobial propertiesantibiofilm, without fixed residue: [0097] 1. Ethanol [0098] 2. Isopropanol [0099] 3. Hydroalcoholic solutions

[0100] The first step of the study was aimed at the choice of polymers.

[0101] For the creation of the antimicrobial and anti-COVID coating, two different commercial polymers were used, the choice of which depends on the type of surface on which the antibacterial and anti-COVID coating must adhere, i.e., whether a metal surface or a resin or a fabric; said polymers are both biocompatible and non-toxic, and are used as binder for the GNP and ZnO nanoparticles, so as to ensure good adhesion to the substrate.

[0102] The first polymer used, hereinafter referred to as polymer 1 or POL1, is Polycaprolactone (PCL), a semi-crystalline polymer with a low melting point of about 60 C. and a glass transition temperature of about 60 C. and which has excellent adhesion to resin and fabric surfaces.

[0103] The second polymer used, hereinafter referred to as polymer 2 or POL2, is Polyvinylpyrrolidone (PVP) which has excellent adhesion to metal surfaces.

[0104] PCL has poor water solubility.

[0105] Polymer 2 (i.e., PVP) was dissolved in ethanol at room temperature (25 C.) using a magnetic stirrer, while polymer 1 (i.e., PCL) was dissolved in acetone at a controlled temperature of 30 C. using a magnetic stirrer.

[0106] The choice of solvents such as ethanol and acetone was suggested by the rapid evaporation at room temperature which characterizes them and by the excellent rheological behavior of the two polymers towards such solvents, as verified by specific rheological tests. This last aspect ensures excellent sprayability properties of the obtained mixtures.

[0107] Nanostructures used for producing the treatments

[0108] The second step of the study concerned the selection of the nanostructures used for producing the treatments and obtaining the antimicrobial and anti-COVID properties.

[0109] Four different types of nanostructures were dispersed in the active suspensions, and are used in a concentration range between 2 mg and 10 mg with respect to 100 mg of solvent.

[0110] Said Nanostructures are: [0111] (i) Graphene nanoplatelets (GNP); [0112] (ii) Zinc oxide nanorods (ZNO), where nanorod indicates a morphology of objects on the nanoscale with a rod shape, in which the average diameter is between 20 nm and 50 nm and the length is between 100 nm and 1 m; [0113] (iii) GNPs decorated with zinc oxide nanorods (ZNG); [0114] (iv) GNP+ZNO.

[0115] The combination of GNP and ZNO was considered as a replacement for graphene nanoplatelets decorated with zinc oxide nanorods, so as to minimize the nanomaterial production costs and times.

[0116] Treatment Production Method and SEM Characterization

[0117] The next step involved the treatment production method and the characterization thereof through SEM microscopy (scanning electron microscope), AFM microscopy (Atomic Force Microscopy) and functional tests (adhesion and antimicrobial).

[0118] As regards the preparation of the nanoparticles for spraying, in a first moment, the interdispersed graphene was thermally expanded and then sonicated for 20 minutes in acetone, by means of a probe sonicator; the ZnO nanorods were then sonicated in acetone for 3 minutes, by means of an ultrasonic bath.

[0119] As already mentioned, the surfaces (otherwise indicated as substrates hereinafter) on which the antibacterial and anti-COVID coatings were sprayed consist of materials which best represent the objects/devices commonly used in hospitals: metal, fabric and plastic or polymer resin.

[0120] As regards fabric and polymer resin, samples of substrates actually used in a hospital environment were used; aluminum was used for metals.

[0121] In fact, the adhesion problems arising on the metal substrate, by thin nanoparticle coatings even with polymer binder, are very different from those which arise on a plastic substrate (such as synthetic fabrics and polymer resin substrates).

[0122] Therefore, in order to develop and test a coating with adequate adhesion features for metal substrates, it was decided to carry out tests on aluminum-based metal film, as they are sufficiently representative for the purpose of solving adhesion problems.

[0123] Different mixtures of solvent and polymer were made with different concentrations of polymer, between 1% and 15% by weight, in order to identify the optimal composition which with the minimum polymer content would allow the creation of a continuous film, with good adhesion properties on the substrate and good water-repellant features.

[0124] Excellent adhesion properties of polymer 1 were obtained on the polymer-type substrates (the synthetic fabric and the resin substrate) also exhibiting excellent water-repellant properties.

[0125] Furthermore, polymer 2 obtained excellent adhesion properties on aluminum, but the water-repellent properties were not as good.

[0126] Therefore, as regards metal surfaces, it was decided to operate by exploiting the two polymers in a combined manner, thus enhancing the properties of both. A two-layer film was thus created, first overlapping the aluminum layer with polymer 2, exploiting the excellent adhesion thereof on metal, even if poorly hydrophobic, and then overlapping this layer of polymer 2 with polymer 1 used as a binder, in order to obtain excellent hydrophobicity features and excellent adhesion on the polymer substrate.

[0127] The nanostructures (GNP, ZNO or the combination of the two, or ZNG) were then sprayed on the polymer film 1 which thus acts as an adhesive coating for the nanoparticles.

[0128] FIG. 1 shows the optimized configuration of the polymer 1 and polymer 2 bilayer with nanostructures on an aluminum substrate.

[0129] In particular, while polymer 1 has good adhesion only on fabric and resin and has such features and properties that it can be used as an antimicrobial and anti-COVID agent (being able to incorporate GNP and ZnO nanorods on the surface), polymer 2 has a good adhesion to steel but has very poor adhesion to resin and fabric. Therefore, it was decided to use a coating formed by a first layer consisting of polymer 2 in direct contact with the aluminum (to ensure adhesion to the substrate) and a second layer consisting of polymer 1, used as a binder, on which the GNP and ZnO nanoparticles were then applied.

[0130] As regards coating resin or fabric surfaces, given the excellent adhesion and hydrophobic properties of polymer 2 towards these surfaces, it was not considered necessary to use a second polymer.

[0131] Thus polymer 1, which has excellent adhesion to both fabric and resin, was used as a binder and was deposited directly onto the substrate. The spraying operation of polymer 1 was carried out so as to ensure the creation of a homogeneous surface and ensure good adhesion of the nanoparticles thereto. The GNP and ZnO nanoparticles were then sprayed (FIG. 2).

[0132] The samples were prepared by spraying different combinations of polymers and nanostructures on the three substrates. SEM characterizations, rheological measurements, wettability tests and bacterial viability tests were carried out on the samples prepared at different concentrations of nanomaterials in the range 2-10 mg (polymer only, polymer+GNP, polymer+GNP+ZNO).

[0133] Some tests carried out with a concentration of nanostructures equal to 5 mg are reported below, merely by way of example.

[0134] The images obtained from the SEM analysis for the various samples prepared show the morphological surface of the modified substrate by the insertion of nanoparticles for antimicrobial and anti-COVID purposes.

[0135] Images a) and b) in FIG. 3 show the morphology of polymer 2 applied to the aluminum substrate: as shown by said images, polymer 2 is applied homogeneously and uniformly on the metal substrate, covering the entire surface thereof. Again from the images it can be seen that polymer 2 has a smooth surface suitable for spraying the subsequent layer (polymer 1).

[0136] Images c) and d) in FIG. 3 show the morphological surface of polymer 1 relative to the multi-layer configuration (POL2+POL1+GNP+ZNO) on an aluminum substrate.

[0137] To confirm the hypotheses made, the analysis showed that polymer 1 homogeneously covers the entire surface and the deposited nanoparticles are well adhered thereto.

[0138] Furthermore, based on what can be seen from the SEM images, the GNP and ZnO nanoparticles were homogeneously sprayed over the entire surface.

[0139] Images e) and f) in FIG. 4 show the surface of polymer 2 with GNP+ZNO nanoparticles on the fabric substrate.

[0140] The entire surface of the fabric was homogeneously covered with polymer 1. The GNP and ZnO nanoparticles were also uniformly sprayed on polymer 2 and perfectly adhered thereto.

[0141] A visual investigation of the coatings produced shows that both types have excellent adhesion features to the substrate. The color is transparent white. The presence of graphene nanostructures gives a slight gray tint.

[0142] Rheological Characterizations of the Colloidal Suspensions

[0143] The rheological measurements were performed in rotational regime and in shear rate control, using an Anton Paar MCR 302 rotational rheometer, provided with concentric cylinder geometry, available at the SNN-Lab of the La Sapienza University of Rome.

[0144] The peculiar measurement system used allows studying the rheological behavior of the solutions/suspensions carried out in a very high velocity gradient range, so as to simulate the shear rate values corresponding to the spraying method used.

[0145] The measurements were performed on a minimum of three samples for each type, in the shear rate range between 0.1 and 45000 s1. All the measurements were performed at 23 C., controlling the temperature via a Peltier cell integrated in the lower geometry of the measurement system.

[0146] Polymer 1 Dissolved in Ethanol

[0147] The measurements carried out on PVP solubilized in ethanol at the minimum concentration of 9% by weight, which made it possible to obtain a uniform film on the metal substrate with excellent adhesion features, showed a behavior of the pseudo-Newtonian type (viscosity independent of the shear rate) in the range of velocity gradients investigated.

[0148] In particular, the viscosity of the solution was found to vary between 4.78 mPa.Math.s, for the lowest shear rates, to slightly rise to 5.77 mPa.Math.s, for the highest shear rates (45000 s1), thus highlighting the almost virtual independence of viscosity from shear rate.

[0149] Polymer 1 Dissolved in Ethanol and Loaded with GNP

[0150] The rheological measurements carried out on PVP solubilized in ethanol with a higher concentration (equal to 15% by weight), showed an almost perfectly Newtonian behavior in the range of velocity gradients investigated.

[0151] In particular, the viscosity of the solution was found to vary between 4.78 mPa.Math.s for the lowest shear rates, to slightly rise to 5.77 mPa.Math.s for the highest shear rates (45000 s1), thus highlighting the almost virtual independence of viscosity from shear rate.

[0152] The measurements carried out on PVP solubilized in ethanol with a higher concentration (equal to 15% by weight), showed an almost perfectly Newtonian behavior in the range of velocity gradients investigated.

[0153] In particular, the viscosity of the solution was found to vary between 6.52 mPa.Math.s and for the lowest shear rates, to slightly rise to 6.77 mPa.Math.s at the maximum imposed shear rate (45000s1).

[0154] FIG. 4 shows a comparison between the viscosity curves of PVP solubilized in ethanol at the two concentrations considered (the minimum and the maximum compatible with the creation of a uniform film which dries in a few seconds).

[0155] The measurements performed on PCL solubilized in acetone at the minimum concentration of 3% by weight considered in this study and sufficient to generate a uniform film with good adhesion properties on a polymer substrate showed a behavior far from the Newtonian regime: in particular, as the shear rate increases, an increase in viscosity is first observed which then decreases for higher shear rates, after reaching a maximum at 32000 s1.

[0156] The viscosity of the solution varies between 3.22 mPa.Math.s at the beginning of the test to rise up to a maximum of 14.08 mPa.Math.s at 32000 s1, up to then decrease to 4.48 mPa.Math.s at 45000 s1. The increase in viscosity found for the intermediate shear rates is due to the formation of a polymer film by separation from the organic solvent, as shown in FIG. 4.

[0157] A new sample was then produced in which polymer 1 (PCL) is solubilized in acetone at a higher concentration equal to 5% by weight.

[0158] From the analyses carried out on this sample, a consistent increase in the initial viscosity is observed which reaches the value of 12.94 mPa.Math.s at 0.1 s1. Also in this case, as the shear rate increases, an increase in viscosity is observed, which reaches a first maximum of 19.23 mPa.Math.s at 33000 s1; the viscosity then decreases and then increases again and reaches a second maximum, of lower intensity with respect to the previous one and corresponding to 17.85 mPa.Math.s at 39800 s1; lastly the viscosity decreases to the final value of 15.87 mPa.Math.s at 45000 s1.

[0159] Finally, a third sample was produced in which polymer 1 is solubilized in acetone in a concentration equal to 7% by weight. The viscosity curve shows the appearance of a maximum, even if in this case the maximum viscosity is recorded for slightly lower shear rates.

[0160] The initial viscosity value, at a shear rate of 0.1 s1, is equal to 21.44 mPa.Math.s resulting, as expected, higher than samples with lower concentrations of polymer in solution. The maximum of 25.57 mPa.Math.s is found at 30,000 s1, a value slightly lower than the shear rates recorded at the relative maximums of the previous samples, while the final viscosity (at 45,000 s1) is 22.59 mPa.Math.s.

[0161] FIG. 5 shows a comparison between the viscosity curves measured for the three samples made by varying the weight fraction of PCL in acetone.

[0162] As already mentioned, the formation of a polymer film during the rheological measurement was found only in the case of polymer 1 at minimum concentration (3%) on the weight of the solvent (acetone). However, repeated rheological measurements also on the samples with higher concentrations, at 10 intervals from the end of each test, first showed an increase in the viscosity curves (with higher viscosity values over the entire shear rate range) and then, for the last measurement, the formation of a polymer film.

[0163] The viscosity curves measured on the same sample at the maximum concentration of polymer considered (7%), at successive intervals in which each test has a total duration of 200 s, are shown in FIG. 6.

[0164] For the measurement performed at time t0+40 (t0 being the start time of the first test), the formation of the film is indicated by much higher viscosity values than those previously measured. This film formation is clearly visible in the results shown in FIG. 6 and is attributed to the continuous evaporation of solvent during the course of the measurements.

[0165] As regards the wettability of the coatings produced, the results of the measurement of the contact angle on different antimicrobial and anti-COVID coatings, applied on the three substrates described above, are reported below.

[0166] Test on Aluminum Substrate and Aluminum with Polymer 2+Polymer 1 Coating and Nanostructures

[0167] 1st Specimen: Aluminum Substrate Coated with Polymer 2+Polymer 1

[0168] The layer of polymer 2 is first sprayed onto the aluminum sheet and then the layer of polymer 1 is sprayed. The presence of polymer 2 allows good adhesion to the Al substrate.

[0169] Table 1 shows the contact angle values measured on the 5 drops of distilled water.

TABLE-US-00001 TABLE 1 Number of drops Contact angle () 1 70.68 2 73.76 3 72.90 4 73.46 5 74.70 Average 73.10

[0170] 2nd Specimen: Aluminum Substrate Coated with Polymer 2+Polymer 1+GNP

[0171] After having sprayed the two binders (first polymer 2 and then polymer 1) onto the substrate, the GNP is uniformly distributed over the substrate. The average value of the contact angle is slightly higher with respect to the case without GNPs. Also in this case, it is observed how the presence of GNP increases the contact angle value.

[0172] The results are presented in table 2.

TABLE-US-00002 TABLE 2 Number of drops Contact angle () 1 78.36 2 79.92 3 77.08 4 79.31 5 77.04 Average 78.34

[0173] 3rd Specimen: Aluminum Substrate Coated with Polymer 2+Polymer 1+GNP+ZnO Nanorods

[0174] The antimicrobial and anti-COVID surface consists of polymer 2+polymer 1 containing GNP and ZnO nanorods. The surface of polymer 2+polymer 1+GNP and ZNO nanorods is more hydrophobic than that with GNP alone, even if the contact angle is always less than 90. Such an effect is produced by the combination of the two types of nanostructures deposited on the polymer surface, the graphene nanoplatelets which are notoriously hydrophobic and the ZnO nanorods which give a nano-roughness of the surface such as to determine a slight reduction of the surface energy which leads to an increase in hydrophobicity and therefore to a greater value of the contact angle [9,10].

[0175] The results are presented in table 3.

TABLE-US-00003 TABLE 3 Number of drops Contact angle () 1 80.80 2 84.24 3 82.30 4 81.10 5 82.13 Average 82.11

[0176] The morphology of the multi-layer coating observed with SEM (FIG. 7) confirms that GNP and ZnO are well adhered to the polymer binder and thus to the aluminum substrate. The spraying of GNP and ZnO is uniform and homogeneous over the entire surface.

[0177] The results obtained are reported in FIG. 8 and show the excellent hydrophobicity of the coating with the nanomaterials used.

[0178] The results shown above indicate that the ZNO+GNPs are distributed uniformly and homogeneously on the binder of polymer 1 and this involves a decrease in the surface energy as they cover the entire polymer surface. Therefore, the value of the contact angle increases.

Test on a Substrate of Synthetic Fabric and Synthetic Fabric with Coating of Polymer 1 and Nanostructures

[0179] As already stated, polymer 2 does not have good adhesion on fabric and resin substrates, unlike polymer 1, which adheres perfectly thereto. The results of the tests for the measurement of the contact angle carried out on the fabric substrate, with antimicrobial and anti-COVID coating of GNP and GNP+ZnO distributed on the binder in polymer 1 are shown below. [0180] 1st specimen: modified surfacepolymer 1 on fabric substrate

[0181] After the preparation of the solution of polymer 1, it was sprayed onto the fabric substrate. Since fabric is more hydrophobic with respect to aluminum, the contact angle measured in this case is greater.

The results are shown in table 4.

TABLE-US-00004 TABLE 4 Number of drops Contact angle () 1 86.03 2 87.44 3 85.92 4 87.69 5 87.80 Average 86.97 [0182] 2nd specimen: fabric substrate coated with polymer 1+GNP

[0183] Polymer 1 acts as a binder for the graphene nanoparticles sprayed onto the fabric. The nanoparticles are thus well adhered and connected to the fabric substrate and this leads to an increase in the contact angle value, with respect to the presence of only polymer 1. The contact angle increases slightly with respect to the presence of only polymer 1. The hydrophobic behavior increases if GNP is incorporated into the polymer binder.

[0184] The results are shown in table 5.

TABLE-US-00005 TABLE 5 Number of drops Contact angle () 1 85.93 2 84.58 3 84.34 4 82.09 5 83.92 Average 84.17 [0185] 3rd specimen: fabric substrate coated with polymer 1+GNP and ZnO nanorods

[0186] Polymer 1 and then the suspension containing GNP and ZnO nanorods was sprayed onto the fabric substrate. The coating thus obtained has a hydrophobic behavior since the measured contact angle is greater than 90 (average value equal to 94.57).

[0187] The results are presented in table 6.

TABLE-US-00006 TABLE 6 Number of drops Contact angle () 1 92.63 2 94.92 3 96.30 4 90.08 5 98.93 Average 94.57

[0188] From the results previously shown, it is apparent that the modified surface consisting of polymer 1+GNP and ZnO nanorods is that with the greatest average contact angle value, which therefore is the surface with the best hydrophobic behavior on the fabric substrate.

[0189] The morphology of the multi-layer coating observed with SEM (FIG. 9) confirms that GNP and ZnO are well adhered to the polymer binder and thus to the fabric substrate. The spraying of GNP and ZNO is uniform and homogeneous over the entire surface.

[0190] The results obtained are reported in FIG. and show the excellent hydrophobicity of the coating with the nanomaterials used.

[0191] To ensure the maintenance of the antimicrobial and anti-COVID properties of the developed coatings over time, it is necessary to verify that they effectively adhere to the substrates on which they are to be applied.

[0192] To verify such features, adhesion tests were carried out on the following coatings, by way of non-limiting example, the data corresponding to 5 mg of nanostructures are reported: [0193] 1) Coating on metal substrate: [0194] a) PVP+PCL [0195] b) PVP+PCL+GNP (5 mg) [0196] c) PVP+PCL+GNP (5 mg)+ZNO (5 mg) [0197] 2) Coating on fabric substrate: [0198] a) PCL [0199] b) PCL+GNP (5 mg) [0200] c) PCL+GNP (10 mg) [0201] d) PCL+GNP (5 mg)+ZNO (5 mg) [0202] 3) Coating on resin substrate: [0203] a) PCL [0204] b) PCL+GNP (5 mg) [0205] c) PCL+GNP (10 mg) [0206] d) PVP+PCL+GNP (5 mg)+ZNO (5 mg)

[0207] To carry out the adhesion tests, the transparent pressure-sensitive adhesive tape number #600 of 3M (ASTM D3359) was used, with a width of 25.4 mm and an adhesion force (on an aluminum substrate) equal to 3.5 N/cm.

[0208] The technical features of the adhesive tape used are summarized in FIG. 11.

[0209] The adhesion test was performed according to the requirements of the AST D3330 standard, which requires, after applying the adhesive tape on the specimen, the removal of the same at a 180 angle with respect to the horizontal plane.

[0210] The following paragraphs show the results of the adhesion tests carried out. In particular, analyses were carried out with an Atomic Force Microscope (AFM) for the quantitative measurement of the degree of adhesion on each substrate of the polymer binder forming the coating and analysis by SEM to determine if the nanostructures detached from the binder itself during the test.

[0211] AFM analyses were carried out to evaluate the adhesion of the polymer matrix to the different substrates.

[0212] FIGS. 12, 13 and 14 depict the morphology of the sample surface at the border between the surface of the coating as is and the surface of the coating on which the adhesion test was carried out, of which the AFM images and the respective graphs are reported related to a single polymer binder for each substrate. The graphs depict the profile of the sample straddling the two areas mentioned above in three different sections.

[0213] Observing such results, it can be said that PCL adheres to both the resin substrate and the fabric substrate, as following the adhesion test the coating was removed for a negligible thickness, equal to about 800 nm. It is further observed that the lighter central part, characteristic of the images in FIG. 12 and FIG. 13, represents the border area between the area subjected to the adhesion test and the area of the coating as is. At this area, a slight lifting of the coating occurs, which occurs during the removal of the adhesive tape.

[0214] The binder consisting of PVP+PCL on an aluminum substrate appears to adhere completely thereto to such an extent that it becomes impossible to clearly observe the separation limit between the two previously mentioned areas.

[0215] In order to determine whether the adhesion test caused a detachment of the nanostructures from the polymer matrix, SEM analyses were carried out, the images of which are shown in the following figures as regards, by way of example, the concentration of 5 mg for the different nanostructures. They show a comparison between the morphology of the coating before and after performing the adhesion test.

[0216] The following samples were analyzed by SEM: [0217] Aluminum substrate (FIG. 15): PVP+PCL+GNP (5 mg)+ZNO (5 mg) [0218] Resin substrate (FIG. 16): PCL+GNP (10 mg) [0219] Synthetic fabric substrate (FIG. 17): PCL+GNP (5 mg)+ZNO (5 mg)

[0220] From FIGS. 15, 16 and 17 it can be seen that, even after the adhesion test was carried out, the nanostructures remain adhered to the polymer binder.

[0221] In conclusion, it can be stated that the polymer coatings loaded with graphene and zinc oxide-based nanostructures adhere to all three substrates on which they have been deposited, showing satisfactory results.

[0222] As for the polymer binders, PCL adheres to both resin and fabric well, while the binder consisting of PVP+PCL ensures good adhesion of the coating to the metal substrate.

[0223] The SEM analyses also show that even the nanostructures are well adhered to the polymer and therefore remain anchored to the substrate.

[0224] The measurement of the thicknesses of each coating was obtained as the difference between the total measurement of the substrate+coating thickness and the measurement of the thickness of the substrate as is. To this end, the specimens were previously prepared by covering a portion of the total surface thereof with Kapton, which was then removed after the coating was deposited.

[0225] The measurement of the coating thicknesses was carried out by means of an analog micrometer from Mitutoyo, with an accuracy level of 1 m.

[0226] The two following tables summarize the thickness values of each coating deposited on a fabric and plastic substrate (Table 7) and on a metal substrate (Table 8)

TABLE-US-00007 TABLE 7 SUBSTRATE: Fabric and resin Thickness Standard COATING Thickness [m] average [m] dev. PCL 11.00 1 10.00 1 9.00 1 10.00 1 1.00 PCL + GNP (5 mg) 15.00 1 16.00 1 14.00 1 15.00 1 1.00 PCL + GNP (10 mg) 15.00 1 16.00 1 14.00 1 15.00 1 1.00 PCL + GNP + ZNO 15.00 1 16.00 1 18.00 1 16.33 1 1.53

TABLE-US-00008 TABLE 8 SUBSTRATE: Metal Thickness Standard COATING Thickness [m] average [m] dev. PVP + PCL 10.00 1 11.00 1 10.00 1 10.33 1 0.58 PVP + PCL + GNP (5 mg) 12.00 1 11.00 1 14.00 1 12.33 1 1.53 PVP + PCL + GNP + ZNO 15.00 1 17.00 1 16.00 1 16.00 1 1.00

[0227] To evaluate the antimicrobial efficacy of the multi-layer treatments of the different surfaces, tests were carried out with different bacteria, the results reported below were obtained using, by way of non-limiting example, the 5 mg concentration for the nanostructures used. Once treated, the surfaces were first sterilized by UV rays and then contaminated with different types of pathogenic bacteria, by way of non-limiting example, the data on the Staphylococcus aureus bacterium for Gram-positive and the bacterium Pseudomonas aeruginosa for Gram-negative are reported here.

[0228] In this regard, an aqueous suspension of bacteria was applied on both the material treated only with polymer binder, and with the mixture of binders and nanomaterials of the present invention. The inoculated materials were then incubated in environmental temperature and humidity conditions at different times. The extraction of the bacterial load from the tested surfaces, whether metal, plastic or textile, was carried out by making some changes to the IS022196 standard, which defines the standard method for evaluating the effectiveness of antibacterial treatments on porous and non-porous materials.

[0229] After the established incubation period, the residual bacterial load was recovered from the surfaces of the specimens by rubbing with a sterile swab, which was in turn immersed in a physiological solution. The number of colony forming units (CFUs) present in the resulting suspension was then obtained using standard techniques for the determination of colony forming units. The survival of the single bacterial species on the surfaces of the materials coated with the polymer alone at the exposure time zero was evaluated as 100%, to which the viability obtained in the samples covered by the nanostructures with or without ZnO nanorods mixed with the polymer at different treatment times was compared.

[0230] FIG. 18 shows the survival trends of the two bacteria taken from metal substrates coated by the polymer binder: the decrease in microbial load at the level of the surfaces treated with nanomaterials with respect to those without is apparent already from the first hour of exposure in both types of bacteria, a result which appears more marked in the case of P. aeruginosa, having a vitality percentage of 60% from the initial contamination time.

[0231] The antimicrobial tests instead conducted on fabric substrates coated by the binder with or without the nanomaterials show how the treatment of the present invention has a marked antibacterial effect against the Gram-positive S. aureus with respect to the control with only polymer already after only one hour of exposure (with about 60% mortality), continuing to increase with the passage of time (FIG. 19). Less significant differences are obtained with the Gram-negative P. aeruginosa, where the trend of the survival curves is almost similar (data not shown).

[0232] From the bacterial contamination of resin surfaces bearing the polymer matrix under examination supplemented or not with the nanostructures, a significantly lower recovery of still viable cells is obtained from the treated resin substrates with respect to the control samples, already from the first instants of contact. As shown in FIG. 20, this result is observed for both types of bacteria tested.

[0233] The ability to control and limit the biological risk which may be present on the types of surfaces previously analyzed and present in indoor environments was also assessed. Plastic and fabric samples covered by the binder of such an invention were analyzed by evaluating the total microbial load present on the surfaces after 15 days of exposure. By way of non-exhaustive example, we report data regarding graphene nanoplatelets as a nanostructural base. The samples of material coated with only the polymer or binder of the present invention were sterilized and then placed on a support surface inside a room and exposed to air for 15 days. After this period of time, they were processed as described above and the relative microbial counts are shown in FIG. 21. A high antimicrobial effect of the treatment of the present invention is apparent, both at the fabric and resin level, which proves to be valid even after two weeks of exposure.

[0234] Similar experiments were carried out in a hospital environment as well. In particular, the monitoring of the antimicrobial capacity of the treatment of the present invention occurred in two different environments of the UOC of Pediatric Dentistry of Policlinico Umberto I, which has intense outpatient activity, with more than 15,000 visits per year.

[0235] In this case, the results of the tests carried out on the treatment deposited on a plastic substrate in the two different environments of the clinic, reported by way of non-exhaustive example, also show a high antimicrobial capacity of the treatment of the present invention towards the microorganisms present in the environment (FIG. 22).