WO2018131055A1 - A simple and economical preparation of antibacterial polyolefins samples with naked-exposed nano-silver particles - Google Patents

Abstract

The preparation of nanocomposites having antibacterial activity, composed from Polyolefins matrix with dispersed metallic silver nanoparticles (AgNPs), and no containing other chemicals then the polyolefin and the silver AgNPs, is per- formed according to an inventive one pot very sustainable procedure starting from a porous and porous covalently functionalized semicrystalline polymer powder suspended in distilled water and AgNPs water suspension, which was produced in situ, by chemical or physical methods or also manufactured separately and added in a short time. The prompt fixation for absorption into the pores and also to polar interactions at the interface, of the metal particles on the polymer maintains their nanometric size without the need of other stabilizing chemical products, as in other cases. The leaching of silver nanoparticles to the environment is hindered by the porosity of the adsorbing support and eventually by the silver binding groups covalently connected to polyolefins. The AgNPs remain then available for the antibacterial activity due to the absence of stabilizers that would act as barriers towards contact Silver-bacteria. These nanocomposites, as such or in mixture with polymer not containing AgNPs can be subjected to melting molding processes by conventional methods maintaining the antibacterial activity. Therefore, the materials thus produced constitute a highly sustainable raw material for the production of plastic products of various types with antibacterial activity.

Description

A simple and economical preparation of antibacterial Polyolefins samples with naked-exposed nano-silver particles.

State of art

One of the major focus of nanotechnology is on the design, development and application of nanomaterials and in particular the nanocomposites where a polymer matrix is filled with a second material whose dimensions range from 1÷100 nm. The reduction of the dimensions of the latter to the nanolevel allows the conferring of new predictable physical, chemical or biological properties to the polymer without altering the original structural properties, thus allowing to maintain the original application with the new functional properties. The acquisition of the new functional properties depends on various aspects. These are the amount of filler in structures whose dimensions range from 1 to 100 nm, the ratio of surface area to weight, and the ratio of the total number of atoms to the surface of the structure ^[1]

Therefore, surface properties, playing an important role, may have considerably modified chemical activity, thermal and electrical conductivity, and tensile strength. Modifications of material properties resulting from changes in the structure's size make nanomaterials very interesting from a commercial point of view. Today nanotechnology is broadly applied in various disciplines, such as biotechnology, biomedicine, molecular medicine, pharmacology, ecotoxicology, electronics, agriculture, veterinary science and food industry. The materials containing nanosilver particles (AgNPs) have recently attained considerable scientific and technical interest for the application as antibacterial products. The profitability margin, is considered one of the most attractive among commercial products from the group of nanomaterials. Indeed liquid suspension of colloidal nanosilver with concentration 50÷500 ppm fetches are on the market to prices going from 200 to 2000€ per litre, which corresponds to a price for silver kilogram much higher than the price of about 600€/ kilogram of metallic silver

The application of silver for medicinal purposes was described as early as in the 8th century, but only very recently AgNPs were introduced thanks to the unique properties and in particular antibacterial activity. However, there are many concerns regarding unlimited confidence in nanosilver due to some evidence about its toxic properties which recommends its use under controlled conditions. This is specifically significant when the AgNPs are used in items for direct human use as in food packaging or in contact with materials and fluids which need to be free from bacterial contamination. As an example the main role of food packaging is to protect food from external influences, but in recent years new techniques "active packaging" were developed where the product maintains the quality and safety through positive interaction between the packaging and the internal environment. Antimicrobial packaging is one of the possible applications of the active packaging, a packaging system that can destroy or inhibit pathogenic microorganisms which can contaminate food. In recent years, the use of antimicrobial polymeric films containing the silver nanoparticles has had a significant growth due to its activity towards a wide range of microorganisms, as well as to its stability at high temperatures¹²¹.

The above films can be obtained by:

• Lamination method: mixing in the melt using a Brabender.

• Casting Method: preparation of the suspension of AgNPs PE and Xylene (ultrasound) deposited on the surface of a PE film and subsequent evaporation of the solvent. • Spray Method: preparation of the suspension of AgNPs PE and Xylene (ultrasonic) and subsequent spray on the surface of the film of PE, with consequent evaporation of residual solvent.

In a recent study, two masterbatches (referred to as PEN and PEC) containing silver nanoparticles incorporated in separate vectors (silica, and titanium dioxide) was mixed with low density polyethylene (LDPE) in different compositions and extruded to produce normal films. These films were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Differential Scanning Calorimetry (DSC), thermogravimetric analysis (TGA) and Fourier Transform Infrared Spectroscopy (FTIR). The morphology of the films showed the formation of agglomerates of nanoparticles in both PEN and PEC composite. X-ray analysis confirmed the presence of Si02 and Ti02 in PEN samples PEC samples. Thermal analysis indicated an increase of the thermal stability of the PEC compositions. The antimicrobial efficacy was determined by applying the test strain for Escherichia Coli and Staphylococcus Aureus, according to the Japanese Industrial Standard Method (JIS Z 2801 : 2000). The analyzed films showed antimicrobial properties against the tested microorganisms, presenting a better activity against S. aureus than E. coli. In designing these helpful material for packaging however the possible toxic effects for human ^[3].

Silver nanoparticles (AgNPs) effectively kill bacteria and are therefore biocidal. Many other names such as nanosilver and colloidal silver are common. However, many scientists are still uncertain of AgNP's safety. Due to its enormous surface area and reactivity, nanosilver is already used in everyday consumer products requiring broad spectrum antibiotic performance. This market-based intellectual property (IP) study uses a stage gate search process to examine the current patent landscape of companies using AgNPs in their consumer product development and production.

Several patents are reported about the use of polymers and AgNPs to obtain antibacterial materials these are :

a) US 20080213328 A1 : Nanosilver-containing preservation articles, and the preparation process and the uses thereof A plastic material for the conservation is described that includes antibacterial granules (containing AgNPs) mixed with plastics. The granules blended with the plastic materials are present in the plastic materials in an amount of 0.1 to 0.8 weight percentage based on the weight of the plastic materials. In the patent, the authors said nanosiiver-containing antibacterial granules are produced by the process comprising the following steps: (1 ) cutting the stalk marrow of Jun- cus effusus L into pieces; (2) immersing the cut stalk marrow in a solution containing nanosilver particles to allow the attachment of the nanosilver particles to the cut stalk marrow; (3) after the attachment, optionally washing the cut stalk marrow with hot and cold water; (4) drying the nanosilver particles-attached stalk marrow; and (5) grinding the nanosilver particles-containing stalk marrow to appropriate size to produce the said nanosiiver-containing antibacterial granules.

b) US 20040239004 A1 : Method for producing an injection-molded material with an antibacterial function

A method for producing an injection-molded material with an antibacterial function includes the steps of coating nanosilver particles and pigment onto surfaces of plastic raw materials to make pellets of the mixture; and inserting the mixture pellets into an injection molding machine to form an injection-molding material. A cohesive agent may be mixed with a solution of the nanosilver particles and the pigment prior to the step of coating the nanosilver particles and the pigment onto the surfaces of the plastic raw materials. The step of coating the nanosilver particles and the pigment onto the surfaces of the plastic raw material includes spraying the nanosilver particles and the pigment onto the surfaces of the plas- tic raw materials or immersing the plastic raw material into a solution of the nanosilver particles and the pigment. A method for producing an injection-molding material with an antibacterial function comprising the steps of: coating nanosilver particles and pigment onto surfaces of plastic raw materials to make pellets of the mixture; and inserting the mixture pellets into an injection molding ma- chine to form an injection-molded material.

c) US 20100255281 A1 : Polymeric articles having antimicrobial properties containing nano silver particles The present invention relates to the use of nano silver particles in a polymeric article which provides antimicrobial properties to the article. As it has been discovered that nano silver is much more effective than colloidal silver ions. The claimed product is then a polymeric article having antimicrobial properties in which the polymer article comprises one or more polymers and nano silver particles having a size of between about 1 and 100 nanometers. A polymeric article according to claim 1 wherein the particles comprise from about 0.0001 % to about 0.5% of at least the surface of the polymeric article.

d) US 8273812 B2: Nano-silver infused container arrangements

Nano-silver infused container arrangements are made including: a nanosilver infused container body defining at least one opening; and a nano-silver infused container lid configured to close off the at least one opening. In some embodiments, the arrangement is a composition of a polymeric compound and a concentration of nano-silver particles. In some embodiments, the polymeric com- pound includes polyvinyl-pyrrolidone (PVP), polypropylene (PP) and polycarbonate (PC).

e) EP 2687089 A1 : A method for manufacturing of polyethylene regranulate and extruded elements from polyethylene regranulate

A method for manufacturing of polyethylene regranulate, characterized in that to a raw polyethylene regranulate silver nanoparticles are implanted in such a way that the raw regranulate is subject to alternate steps of coating the regranulate with a colloidal solution comprising: a hydrocarbon with a boiling point below 70°C: from 98% to 99.6% by weight, a surfactant reducing surface tension: from 0.1 % to 0.5% by weight; an adhesive agent: from 0.1% to 0.5% by weight; a dispersant: from 0.1 % to 0.5% by weight; a viscosity modifier: from 0.1 % do 0,5% by weight; silver nanoparticles in a paraffin shell having a size from 3 nm to 8 nm and in concentration of 50,000 ppm. The regranulate is coated at a temperature below 70°C, until the silver nanoparticles in the regranulate reaches the concentration of 500 ppm to 1000 ppm by weight.

f) High-Density Polyethylene Composites Filled with Nanosilica Containing Immobilized Nanosilver or Nanocopper: Thermal, Mechanical, and .... with bactericidal properties." Polish Patent Applications 399495, 2012. Silica containing immobilized nanosilver (Ag-SiO2) or nanocopper (Cu-Si02) was used as a filler for high-density polyethylene(HDPE). The HDPE/Ag-SiO2 and HDPE/Cu-SiO2 composites were prepared by melt blending and injection molding. Themicrostructure of the composites was examined using transmis- sion electron microscopy (TEM). The crystallization behavior and

thermal properties were studied using differential scanning calorimetry (DSC) and thermogravimetry (TGA). The mechanical properties were characterized by tensile, flexural, and impact tests as well as dynamic mechanical thermal analysis (DMTA). The ability of silica to give antimicrobial activity to HDPE was also investigated and discussed. The TEM images indicate that Ag-Si02 show lower degree of agglomeration than Cu-SiO2 nanoparticles. The crystallization temperature increased, whereas crystallinity decreased in the composites. The thermal stability of the composites was significantly better compared to HDPE. Improved stiffness indicating very good interfacial adhesion was observed. Ex- cellent activity against different kinds of bacteria was found.

g) US 9371586 B2: A method of manufacturing the silica nanopowders with bio- cidal properties, especially for polymer composites

Silica nanopowders with biocidal properties, especially for polymer composites, are produced by sol-gel method. The silica sol is produced from the aqueous mixture containing tetraalkoxysilane, in which alkoxy group contains from Ci to C4 carbon atoms, an alcohol or the mixture of aliphatic alcohols from Ci to C4, in the mole ratio of 1 :5 to 1 :35, in the presence of ammonium compound, used in an amount of from 0.001 to 0.05 mol per 1 mol of tetralkoxysilane, with introducing, after thorough mixing of components, the silver salt in the form of aqueous solution in an amount from 0.02 to 1 mol per 1 mol of tetralkoxysilane, and subsequently the aqueous solution of alkali metal hydroxide in an amount from 0.02 to 1 mol of hydroxide for 1 mol of tetralkoxysilane.

h) CN 1850924 A: Nano silver antibacterial coating, and its manufacturing method

The invention discloses a nanometer silver antibiotic coating material that is made up from nanometer silver solution, hydroxy acrylic acid resin or acrylic acid compounding emulsion, little solvent, little auxiliary agent and water. The fea- ture is that: the nanometer silver solution, which is mixed by nanometer silver and polyethylene antisettling wax slurry, is 3-5% in the coating material. The polyethylene antisettling wax slurry is the carrier, and the thickness of nanometer silver is 60 thousand ppm, and the nanometer silver is 0.8-1.2wt% in the so- lution.

i) EP1846327: Antimicrobial Properties of a Novel Silver-Silica Nanocomposite Material

Nanotechnology enables development and production of novel silver-based composite materials.

Inventors used in vitro tests to demonstrate the antimicrobial activity of a silver- silica nanocomposite compared to the activities of conventional materials, such as silver nitrate and silver zeolite. A silver-silica containing polystyrene material was manufactured and shown to possess strong antimicrobial properties. In this study, a silver-silica nanocomposite material with a novel structure and compo- sition was investigated to determine its antimicrobial properties. The material exhibited very good antimicrobial activity against a wide range of microorganisms. The inhibition of microbial growth due to surface contact with the silver- silica nanocomposite-containing polystyrene demonstrated that materials func- tionalized with the silver nanocomposite have excellent antimicrobial properties. Also a certain number of papents is devoted to the production of antibacterial FIBER and Textiles which are of minor interest as they have different objectives than the present applications .main examples are indicated with their title, j) US2006278534 WO2006135128: Mass production method of nanosilver

Disclosed herein are a method of mass-producing nanosilver, a method of manufacturing nanosilver-coated antibacterial fiber, and antibacterial fiber manufactured thereby. Nanosilver having a size of 5 nm or less can be produced on a mass scale by applying an electric field of 10,000 to 300,000 volts (DC) across two Ag electrode plates equipped in a water electrolysis system. The nanosilver-coated, antibacterial fiber is manufactured by applying a aqueous so- lution of the nanosilver to the surface of the synthetic fibers, adsorbing the nanosilver onto the cloth using a process selected from the group consisting of thermal fixation, high frequency radiation, bubbling, and combinations thereof; and conducting a post-finishing at 160 to 200°C. And thus, an antibacterial fiber manufactured thereby may be a fundamental solution to the synthetic fiber's problems, whic possess perspiration functionality limited and to generate statistic electricity.

k) Sonochemical coating of silver nanoparticles on textile fabrics (nylon ...). For example, a polv(ethylene terepthlate) fabric (meadox double velor) was coated with metallic silver using a patented ion-beam-assisted .

These interesting antibacterial products based on silver nanoparticles have arised some health concern. Several studies were reported where the toxic ef- fects of nanosilver have also been observed. Indeed nanosilver may accumulate in the food chain, which creates the risk of a direct effect on living organisms and may cause necrosis in human tissues and distort the activity of elementary components in human cells.

In a very recent work^[51 it is reported that Silver nanoparticles (nanosilver) and copper nanoparticles (nanocopper) exhibit antimicrobial activity and have been incorporated into polymers to create antimicrobial packaging materials. Their use in conjunction with food has caused concerns regarding the potential risk of particle migration, resulting in human exposure to nanoparticles. A migration experiment was carried out to investigate the effect of time and temperature on the migration of nanosilver and nanocopper particles from polyethylene (PE) nanocomposites to boneless chicken breasts. Migration of silver ranged from 0.003 to 0.005 mg/dm², while migration of copper ranged from 0.024 to 0.049 mg/dm², for a set of four different scenarios representing typical storage conditions. Effects of time and temperature were not significant (p > 0.1 ). A migration and exposure model was developed on the basis of mathematical relationships defining migration by Williams-Landel-Ferry equation for time-temperature superposition. The results of the model accurately predicted the nanosilver levels detected in the laboratory migration tests (R values ranging from 0.43 to 0.99); however, the model was less accurate in predicting nanocopper levels (R val- ues ranging from 0.65 to 0.99), probably because of the highly variable background levels of copper observed in the real food matrix. The 95th percentile of the simulated human exposure to nanosilver based on laboratory experimental results of four scenarios ranged from 5.89 * 1 0^-5 to 8.9 * 1 0^-5 mg kgbw^-1 day^-1. For the measured migration of copper under the same storage conditions, the exposure ranged from 2.26 * 1 0^-5 to 1 .1 7 χ 10^-4 mg kgbw^-1 day^-1. This study highlights the potential migration of nanoparticles from PE composite packaging to a food material and the potential for simulation models to accurately capture this migration potential; however, variable background levels of copper in the food matrix can make prediction more difficult for trace migration of nanocopper. From the selected examples described in the previous pages it appears how in the very broad area of many materials decorated with silver nanoparticles de- voted to different products and applications, the space left available for invention could appear very limited. Certainly the concept of materials displaying antibacterial activity conferred to different materials by these Agnp is quite a known art, but inventions to economical simple production of low price clean and well defined materials for a broader production and control of the stability to help preventing negative health effect are still possible. Some new ideas in this context are the bais of the invention presented in the present proposal.

Description of the method

Synthetic description

The technical field to which the present invention refers, concerns thermoplastic materials containing nanoparticles of Silver Metal (AgNPs) and then developing antibacterial properties. As shown in the previous section, the prior art contains several patents dealing with polyolefins nanosilver composites with antibacterial activity but all are based on the distinct preparation of AgNPs using several stabilizers to maintain the nanosize of the silver particles: this stabilizer can limit the antibacterial efficiency and the dispersion in the polymer .

Here we presents an inventive process dealing with similar materials but obtained by a simple and highly sustainable procedure. The inventive nature is represented the simplicity of the proposed preparative process with much less critical steps of the preparation procedure described in the known art and the elimination or minimization of additives giving an active material consisting only of the polymer and AgNPs. These last are obtained in the presence of the sup- port according to the pot technology, thus avoiding their possible dispersion in the environment.

In particular, the procedure counts of:

Use of fine PE powder (Low Density PolyEthylene LDPE, High Density Poly- Ethylene HDPE, Linear Low Density PolyEthylene LLDPE and another Ethylene copolymer where Ethylene is the dominant monomer or ethylene polymers containing from 0,1 to 3% by weight of grafted polar monomer);

Ag-nanoparticles produced in situ by various chemical and physical methods from low costs silver melts.

None or only 1-10 ppm of stabilizer; the drive process is possible as the silver nanoparticles are produced in the one pot process in the presence of a water suspension of the fine powdered polyethylene and are immediately trapped by the fine porosity of the solid with a possible contribution of the moderating charged surface attracting the polarized metal nanoparticles.

Complete lack of metal leaching after moulding from polymer to environment thanks to the adsorption of the silver nanoparticles to the polymer internal surface.

The final product is then characterized by low cost due to the one pot production process, the lack of special additives , the very good time and chemical stability, the good contact exposure to bacteria and granted purity. Also the process is very suitable for preparing masterbatches with variable amount of AgNPs loading (1-1 ,000 mg/kg) which can successively be mixed with variable amount of virgin PE to obtain large quantity of antibacterial material which can be moulded into various items.

Detailed Description

The invention presented here refers to the whole process of preparing a PE loaded with only 1 to 10 ppm of nanosilver particles, sufficient to grant a rapid abatement of the present bacteria. As the basic materials is polyethylene or other ethylene polymers, which have low price and very large diffusion, the in- vention is suitable for being considered for a broad variety of applications. Indeed the invention first objective is to provide a simple and economical way to an antibacterial plastic material of broad use. Also the substantial absence of chemicals different from the two basic components, polymer and AgNPs, make these material of low environmental impact and easy recyclability. Finally, the possible leaching of AgNPs environment is avoided as the preparation process involves a deep absorption of AgNPs in the polymer.

In order to experimentally validate the invention the following materials were used:

• Polyethylene (LDPE, HDPE, LLDPE) and/or other polymers where Ethylene is the dominant monomer or ethylene polymers containing from 0,1 to 3% by weight of grafted polar monomer;

· Nanosilver particles in aqueous solution with a concentration of 20 to 100 mg/l [n-Ag-ACQ] produced in situ.

• Nanosilver particles in glycol solution with a concentration of 20 to 100 mg/l [n-Ag-G] produced in situ.

• PE powder containing absorbed silver derivatives (precursors of AgNPs) In order to prepare masterbatches with AgNPs concentration from 1 to 1 ,000 mg/Kg of PE, the nanosilver was produced by chemical reduction of silver salts (AgNO3 and AgCHsCOO) or oxide of metallic silver (Ag₂O) by NaBhU o H₂. This reduction was performed under stirring for 2 hours in the same reactor which before was added a water suspension of powdered polyethylene (ratio by weight from 1 to 0,1 ).

Then, the suspension was filtered and the filtrate was analyzed by UV-VIS spectroscopy, and the resulting spectrum compared with the spectra of pristine nanosilver suspensions.

In the second case the water suspension of PE was added of Silver derivate and then the reduction was performed for added of reduction agent in the same reactor.

In a third process of preparation the AgNPs suspension was produced in a separate reactor in the absence of PE by one of the above described methods, and the AgNPs suspension successively added to the PE suspension in water in a second pot.

A decrease in the plasmonic band gives an indication on the metal transfer into the polymer matrix. Figures 1 and 2 report the UV-Vis spectra of the filtered liq- uid, respectively ethylene glycol and water, compared with the same suspension of silver obtained in the absence of polymer support just after preparation. In both cases, a decrease of the plasmonic resonance band (in terms of decrease of absorbance) can be observed for the liquid suspension prepared in the presence of polymer indicating that the major part of the Ag nanoparticles is dispersed in PE.

(see Figure 1 and 2)

The PE powder containing AgNPs was subsequently converted into a casted film and the ICP-MS analysis provided evidence of the presence and entity of nanosilver particles in the polymer and scanning electron microscopy (SEM) of their size and distribution within the the polymer matrix. The data reported in table 1 indicate that after 10 few hours, the absorption of AgNPs by the polyethylene power is more effective for the suspension of 100 mg of AgNPs in a liter of water than for the same concentration in glycol.

Table 1. ICP-MS analysis

The determination of the AgNPs content in the liquid suspension versus time indicates that the polymer adsorption process is relatively slow as expected ac- cording to the penetration of the Agnp into the polymer pores thus excluding a mere precipitation on the external surface. This grant a good uniform distribution and indicates the general and inventive validity of the proposed preparation method. In order to see how the suspension of nAg-ACQ and PE interact during the preparation of the masterbatch, UV spectra were of the suspension samples were detected at different times. The regular decrease of the plasmonic band of AgNPs confirm the above conclusion as clearly shown in the figure 3.

(see Figure 3) As evidence of the possible transfer of nanosilver on the polymer matrix was carried out a test of "release." The PE powder containing AgNPs has been left for 96 hours in 10ml of water under continuous stirring and were made of samples to measure the absorbance of the solution.

(see Figure 4)

The PE powder loaded with AgNPs (65,4 mg / Kg) was left in water; from Figure 4 shows that no plasmonic band is detectable after 3, 24 and 96 h, thus confirming the stability of the system and the lack of leaching.

It is remarkable that by using PVP stabilized AgNPs for preparing the mas- terbatch with PE powder by the same procedure as above, the nanosilver penetration was less efficient. Indeed two different diluted nAg-PVP suspension (20 and 10 mg/l) show by UV-Vis spectroscopy the plasmonic band of silver (Figure 5), but the intensity decreases more slowly than with naked Ag particles indicating that the transfer of nanosilver particles from the suspension to the polymer occurs at lower extent and with some aggregation,

(see Figure 5)

Examples

I. Preparation of a PE-AgNPs masterbatch by chemical reduction from AgN03 The preparation of a masterbatch consisting of a polyethylene matrix and nano- dispersed silver nanoparticles (AgNPs) having dimensions in the range 4-70 nm, in an amount of 100 ppm was performed by producing Silver nanoparticles in water suspension throught reduction of AgN03 (15,6mg) by NaBH4 (1 ,3mg) in the same reactor containing 100 g of powdered LDPE suspendend in 200 ml of water. At the end of the reaction was obtained and was then filtered to separate the unreacted silver salt and other water soluble by products from the polymer masterbatch.

I. Preparation of a PE-AgNPs masterbatch by chemical reduction from Ag20 The nanosilver particles used in this preparation were prepared by reduction of Silver Oxide in the presence of Polyethylene powder.

To 2 ml of suspension of Ag2O (100mg/100ml) are introduced in the reaction flask containing 100 g of PE suspended in 200 ml of water. Then was hydrogen bubbled for 3 hours. This solution was then centrifuged to separate the unreacted silver oxide from the polymer masterbatch.

III. Kinetic AgNPs of absorption in Polyethylene

In a reactor containing 100 g of polyethylene fine powder suspended in 200 ml of water silver nanoparticles (AgNPs) having dimensions in the range 4-70 nm, were produced in an amount of 100 ppm according to the example 1. The suspension was monitored by taking aliquots of the solution at different times and the UV spectra recorder to detect from the intensity decrease the rate of absorption of AgNPs in the polymer matrix.

IV. Kinetic of leaching of AgNPs from PE

A masterbatch consisting of a polyethylene and nanodispersed silver nanoparticles (AgNPs) having dimensions in the range 4-70 nm, in an amount of 100 ppm obtained according to the example 1 has been left for 96 hours in 10ml of water under continuous stirring . Samples of the liquid phase were collected at different times and the UV-absorbance measured (sea Figure 4).

V. Blends preparation

5 g of a masterbatch consisting of a polyethylene and nanodispersed silver nanoparticles (AgNPs) having dimensions in the range 4-70 nm, in an amount of 100 ppm obtained according to the example 1 , is melt mixed with 45 g of pure PE treatment for 10 minutes at 150°C in a brabender to obtain a product containing 10 mg of AgNPs for kg of PE.

VI. Test of bacteria depletion

The reference method allows the quantitative determination of the antibacterial activity of a product, in particular of plastic materials added with antibacterial substances. Each microbial suspension was inoculated (0.4 ml) on the test surface of the test samples and then covered by an inert film. The suspension is left in contact with the material for 24 hr. After the indicated time, the counts are made of the microorganisms present on the media after preparation of subsequent serial dilutions. Finally, the percentage reduction of viability on the test samples compared to the untreated sample is determined.

Inoculums:

• Staphylococcus Aureus (ATCC 6538P) ^• Escherichia Coli (ATCC 8739)

From Table 2 it can see that the prepared PE_nAg/PVP has antibacterial activity. Table 2. Antimicrobial activity result

^*PE_nAg-ACQ masterbatch was prepared according to the example 1 with 100 mg

AgNPs/kg PTFE

**ufc (colony forming units) Reference

1 . Nanocomposites Based on Polyolefins and Functional Thermoplastic Materials. Polymer International, 2008, 57, 805-836

2. Food Packaging with Antibacterial Properties. Scientific Bullettin Series B, 2014, 76, 154-162

3. Review of antimicrobial food packaging. Innovative Food Science & Emerging Technologies, 2002, 3, 1 13-126

4. M. Cushen†, J. Kerry, M. Morris, M. Cruz-Romero, and E. Cummins J.

Agric. Food Chem., 2014, 62 (6), pp 1403-141 1

5. E. Giorgietti, F. Giammanco, P. Marsili A. Giusti "Effect of Picosecond Postirradiation on Colloidal Suspension of Differently Capped AuNPs, J.

Phys. Chem. C, 201 1 , 1 15, 501 1 -5020.

Claims

C L A I M S

1 . Process for the one pot preparation of a masterbatch with antimicrobic activity, having an ethylene polymer matrix (PE) and dispersed metallic Silver nanopartcles (AgNPs), performed in a stirred single reactor by absorption into a fine powder of PE in a 1/1 w/w water suspension, AgNPs produced in situ by reduction of silver derivatives without any stabilizer.

2. A process for the preparation of a masterbatch as in claim 1 , where the AgNPs are produced by chemical reduction of silver derivatives [AgN03, Ag(CH3COO), Ag∑0] by different reduction agents (NaBH4, H2) in the same re- actor.

3. A process for the preparation of a masterbatch as in claims 1-2 where the silver derivative is absorbed on PE powder before the reduction to AgNPs.

4. A process for the preparation of a masterbatch as in claims 1-3 where the AgNPs suspension was produced in a separate reactor in the absence of PE by one of the above described methods, and the AgNPs suspension successively added to the PE suspension in water in a second pot.

5. A process for the preparation of a masterbatch as in claims 1-4 with an AgNPs content from 1 to 1 ,000 mg/kg polymer.

6. A process for the preparation of a masterbatch as in claims 1-5 where the PE powder is formed by either LDPE, or HDPE, or LLDPE or another Ethylene copolymer where Ethylene is the dominant monomer.

7. A process for the preparation of a masterbatch as in claims 1 -6 where the Ethylene polymer contains from 0.1 to 3% by weight of grafted polar monomers.

8. PE-based antibacterial masterbatches containing AgNPs, with particle diameter from 4 to 1 ,000 nm in a quantity from 1 to 1 ,000 ppm, obtained as in claims 1-7 wherein PE may be made up of LDPE, HDPE, LLDPE and another Ethylene copolymer where Ethylene is the dominant monomer or the same functionalized polymers with a content of maleic anhydride in a range from 0.1 to 3% by weight.

9. Blends containing from 1 to 50 mg of AgNPs per kg of PE, obtained by mixing in the melt one of the masterbatches produced as in claims 1-7 with virgin PE.

10. Items and manufactured products prepared by molding or thermo forming the blends prepared as in claim 9 or the masterbatches of claims 1-8.