WO2015040642A1

WO2015040642A1 - Process for the preparation of an antibacterial polymer material for food application

Info

Publication number: WO2015040642A1
Application number: PCT/IT2013/000254
Authority: WO
Inventors: Sabrina Sangiorgi; Linda Sangiorgi; Norberto Roveri; Marco Marchetti; Marco Lelli; Francesca RINALDI; Rocco MERCURI; Rosanna CAPPARELLI; Chiara MEDAGLIA; Nunzia NOCERINO; Andrea FULGIONE
Original assignee: B.B.S. S.P.A.
Priority date: 2013-09-19
Filing date: 2013-09-19
Publication date: 2015-03-26

Abstract

The present invention relates in general terms to a process for the preparation of an antibacterial polymer material comprising Zn²⁺ ions, and to the use of said material for the manufacture of products for food applications. The present process makes it possible to obtain a material which has antibacterial properties both in bulk and superficially and is stable over time.

Description

PROCESS FOR THE PREPARATION OF AN ANTIBACTERIAL POLYMER MATERIALOR FOOD APPLICATION

The present invention relates in general terms to a process for the preparation of an antibacterial polymer material comprising Zn²⁺ ions, and to the use of said material for the manufacture of products to be used in food applications, for example in the form of plates, glasses and tableware in general.

Prior art

At present there exist a number of technologies for treating polymers in order to render them antibacterial; they mainly use metal nanoparticles, for example silver or copper. Alternatively, use can also be made of bases derived from quaternary ammonium salts, or specific biocides that are mixed with the polymer component in varying proportions and according to different methods in order to render it antibacterial .

Zinc has also long been known as an antibacterial agent and is commonly used both in the pharmaceutical and food industries, for example in food and bone supplements to enhance the body's immune defences. Zinc has industrial application also in the preparation of antibacterial coatings for sanitary and/or medical materials and surfaces.

US5460644 describes the use of zinc ammonium in the preparation of an antibacterial coating for various kinds of manufactured products.

US2002012760 discloses a tray manufactured with a polymer material with antibacterial properties, made by using ceramic materials and, in particular, zeolites functionalized with metal ions, namely: Mg²⁺, Ag⁺, Zn²⁺ and Cu²⁺.

US5102401 describes the use of polymers with antibacterial properties made by using zeolites loaded with silver ions.

Especially in the field of food-related applications, there remains the need to find an antibacterial polymer material that can be used to prepare products for food applications by means of a versatile process that can be easily applied substantially to any polymer material utilizable in food-related applications. In this regard, the Applicants have found that when a starting polymer material is mixed with a source of Zn²⁺ ions comprising at least the zinc salt of pyrrolidone carboxylic acid (ZnPCA), it is possible to obtain, by extrusion, an antibacterial polymer material that is particularly suitable for food-related applications, for example in the manufacture of products such as plates, cutlery and the like. Moreover, the Applicants have found that said mixing can take place both before and after the step of extruding the polymer material, making the present process highly versatile and applicable to a vast range of polymeric materials.

Summary

In a first aspect, the present invention relates to an extrusion process for the preparation of an antibacterial polymer material, which comprises mixing a starting polymer material with a source of Zn²⁺ ions comprising at least ZnPCA, wherein said mixing can take place before or after the extrusion step. In an additional aspect, the invention relates to the use of the material thus obtained for the manufacture of products for food applications.

Therefore, in a further aspect, the invention relates to a product for food applications manufactured from the polymer material obtained, or obtainable, with the process disclosed above. Said product can be manufactured directly by extrusion or also by moulding of the extruded antibacterial polymer material.

Detailed description

As mentioned above, the invention relates to a an extrusion process ("compounding") for the preparation of a polymer material for food applications which comprises an extrusion step that takes place at a temperature preferably comprised from 60° C to 290° C, as described in detail below.

In particular, according to one embodiment, the present process comprises the steps of:

- mixing a starting polymer material with a source of Zn²⁺ ions comprising at least ZnPCA, at a temperature comprised from about 80° C to about 290° C, and

- extruding the mixture obtained,

or else

- extruding a starting polymer material at a temperature comprised from about 80° C to about 220° C, and

- mixing the extruded material with a source of Zn²⁺ ions comprising at least ZnPCA. Advantageously, since the mixing of the polymer material with the source of ions zinc can take place either before or after the extrusion step, the present process is extremely versatile, as it can be applied substantially to any type of polymer for food applications, depending, for example, on melt temperature. According to the latter, in fact, it is possible to opt for a pre-mixing of the component, or, alternatively, for mixing after the extrusion step.

In this regard, when the mixing takes place prior to extrusion, the temperature is preferably comprised from about 80° C to about 290° C, more preferably from about 100° C to about 240° C. Practically speaking, the polymer, for example in granular or powder form, is mixed with the source of ZnPCA and heated until reaching the melt temperature necessary for extrusion with a simultaneous addition of the zinc source. In a preferred embodiment, the zinc source and the polymer material are pre-mixed dry, and the material thus obtained undergoes the extrusion process at the specified temperatures. Alternatively, it is also possible to pre-mix the polymer and ZnPCA source in a wet state, for example by preparing an aqueous solution of ZnPCA and mixing said solution with the selected polymer. In both cases, the two components (polymer and zinc source) will be intimately blended together, at the melt temperature of the polymer, leading to the formation by extrusion of the antibacterial polymer material for food applications of the invention.

When the mixing instead takes place after the extrusion step, the source of zinc ions is added at a temperature preferably comprised from about 80° C to about 220° C. In this respect, it should be noted that mixing after extrusion is particularly convenient in the event that the selected polymer has a melting point falling within the specified temperature interval.

It follows that irrespective of whether the mixing takes place before or after extrusion, it is possible to adapt the present process to traditional extrusion processes without there being any need to make substantial modifications to the extrusion equipment used. The extrusion, in fact, can be either direct or reverse, and can be carried using apparatus used in the art, such as, for example single-screw extruders, twin screw extruders or the like.

Mixing takes place for a time generally comprised from 3 to 50 minutes, so as to allow the two components to interact and blend together in a homogeneous manner. In one embodiment of the present invention, the polymer material is selected from among: polyvinylchloride (PVC), polycarbonate (PC), polyethylene (PE), polypropylene (PP), polystyrene (PS), polyamide (PA), acrylonitrile butadiene styrene copolymer (ABS) , nylon, styrene acrylonitrile (SAN) , styrene butadiene (SB) , thermoplastic polyurethane (TPU) and melamine.

Even more preferably, said material is selected from among: polyethylene (PE) , polypropylene (PP) , high- density polystyrene or transparent polystyrene, and polyamide (PA) .

In the present process, when the mixing takes place prior to extrusion, the polymer material is preferably selected from among: polyvinylchloride (PVC) , polycarbonate (PC), polypropylene (PP) , polystyrene (PS), polyamide (PA), acrylonitrile butadiene styrene copolymer (ABS) , nylon, and styrene acrylonitrile (SAN) .

Unlike some antibacterial materials known in the art, the polymer material obtained with the process of the invention has an amount of zinc ions such that it can be used as is, without there being any need to add other virgin polymer material. The antibacterial material obtained with the process of the invention is in fact characterized in that it contains an amount of zinc ions comprised from about 5 ppm to 500 ppm, preferably comprised from about 20 ppm to 300 ppm. Such intervals make it possible, in practice, to use the material as obtained at the end of the present process or, optionally, as a master batch or additive to be added to another polymer for the production of a final antibacterial polymer.

As a source of Zn²⁺ ions the present process comprises the preferred use of a mixture comprising ZnPCA (zinc salt of pyrrolidone carboxylic acid) and at least one organic or inorganic zinc salt. Preferably, said salt is selected from among: zinc acetate, zinc carbonate, zinc borate, zinc nitrate, zinc chloride, zinc hydroxide, zinc borate and zinc oxalate, or preferably mixtures thereof. Preferably, the zinc source comprises at least ZnPCA and zinc acetate, even more preferably in a percentage ratio by weight of 50:50.

ZnPCA is a compound that is widely used, for example, in the cosmetic industry and is readily available in the market in its dihydrate form, having the following general formula:

ZnPCA dihydrate

The applicants have noted that ZnPCA enables a substantially non-toxic antibacterial polymer material to be obtained without interfering with the physicochemical structure of the initial polymer. In fact, both the chemical and physical behaviour of the starting polymer, for example in relation to possible phenomena of swelling or the like, remain substantially unchanged at the end of the present process. In one embodiment, ZnPCA is present in the zinc source in amounts comprised from about 1% to 80% by weight, relative to the total weight, amounts comprised from about 5% to 50% being particularly preferred.

The zinc source can be added to the starting polymer material by wet mixing or, preferably, dry mixing. In one embodiment, the zinc source is added dry to the selected polymer material, for example in granular form, and the material obtained is subjected to extrusion, so that the two components are mixed hot and the formation of the antibacterial polymer material of the invention is thus obtained.

Alternatively, the zinc source is preferably added dry, for example in powder form, to the extruded material, even more preferably at a temperature comprised from 10 to 100 °C.

Advantageously, the zinc source can also be added in the form of an aqueous solution, prepared by dissolving the ZnPCA and the selected zinc salt(s) in an aqueous solvent, preferably distilled water. The source of zinc ions in the form of an aqueous solution can thus be added to the polymer material during or after extrusion, using, for example, apparatus and methods known in the art. The use of an aqueous solution is convenient in that it makes it possible to obtain an antibacterial material with a high degree of homogeneity of the components.

Said aqueous solution can have a total concentration of Zn²⁺ ions preferably comprised from 10 to 15g/l, calculated considering the total weight of zinc salts relative to a litre of aqueous solution.

As mentioned above, the present process makes it possible to obtain an antibacterial polymer material that is particularly suitable for the manufacture of products that can be used in food-related applications, for example in the form of plates, glasses, cutlery, tableware and the like.

In a preferred embodiment, the product obtained is a plate, an item of cutlery or a film. Said product, moreover, can be made to take on the desired form both by means of extrusion steps, or, alternatively, it can be shaped for example by moulding.

In this manner it will be possible to obtain both a ready-to-use final product and a material for example in the form of sheets or flat surfaces, which can be stored and used for subsequent processing, for example moulding, for the manufacture of products of different shapes and sizes for food applications. In any case, in addition to having antibacterial properties essentially due to the presence of zinc ions, the antibacterial polymer material obtained at the end of the present process also shows high stability, so that the release over time of said zinc ions, or of other radicals or toxic by-products, is substantially avoided. Furthermore, thanks to the mixing steps, the polymer material obtained exhibits antibacterial properties both in bulk and superficially. This is particularly advantageous above all in the event that the product must perform its action at a surface level or its surface comes into contact with bacterial forms.

The present invention will now be described with the following experimental part, but without limiting the scope hereof.

Experimental part Example 1 : preparation of the source of Zn²⁺ ions in the form of aqueous solutions la-lc.

The following aqueous solutions la-lc are prepared by dissolving, in distilled water, under stirring at a temperature of about 25° C, for about 1 hour respectively:

- ZnPCA 50% (solution la) ,

- ZnPCA in a mixture with Zn acetate in a % ratio by weight of 50:50 (solution lb);

- the following salts in the percentages by weight indicated (solution lc) :

ZnPCA, 15%

Zn acetate, 3% Zn carbonate, 32%

Zn nitrate, 10%

chloride 20%

Zn hydroxide, 2%

Zn oxalate, 10%

Zn borate, 10%

The aqueous solutions obtained have a weight ratio of 12g of zinc salts per litre of distilled water.

The above-described aqueous solutions la-lc will then be used in the process of extruding the polymer matrix in a temperature interval comprised from 130 to 290° C. The same solutions can be used in the mixing step after extrusion, at a temperature of 80-220° C.

Example 2 : mixing of polymer grains with the Zn source in an amount such that the final amount of Zn varies from 5 to 500 ppm.

Grains of a polymer selected from among: PE, PPE, PET, PP, ABS, PS, SAN, SB, PUR are mixed with the source of zinc 2+ ions in the form of the aqueous solutions la-lc of example 1, or, alternatively, with the source of zinc ions in powder form comprising: ZnPCA, or ZnPCA and Zn acetate 50:50, or the zinc salts of solution lc, mixed dry.

The polymer compositions/source of Zn²⁺ ions then undergo extrusion at the melt temperature of the polymer used, obtaining in each case an antibacterial polymer material which can be used to manufacture products for food applications.

Claims

1. An extrusion process for the preparation of an antibacterial polymer material, which comprises mixing a starting polymer material with a source of Zn²⁺ ions comprising at least ZnPCA, wherein said mixing can take place either before or after the extrusion step.

2. The process according to claim 1 wherein the extrusion temperature is comprised from 60° C to 290° C.

3. The process according to claim 1 or 2, wherein said mixing of a starting polymer material with a source of Zn²⁺ ions comprising at least ZnPCA takes place before the extrusion step, at a temperature comprised from 80° C to 290° C.

4. The process according to claim 1 or 2, wherein said mixing of a starting polymer material with a source of Zn²⁺ ions comprising at least ZnPCA, takes place after the extrusion step, at a temperature comprised from 80° C to 220° C.

5. The process according to any one of the preceding claims, wherein said starting polymer material is selected from among: polyvinylchloride (PVC), polycarbonate (PC), polyethylene (PE), polypropylene (PP), polystyrene (PS), polyamide (PA), acrylonitrile butadiene styrene copolymer (ABS) , nylon, styrene acrylonitrile (SAN), styrene butadiene (SB), thermoplastic polyurethane (TPU) , copolyesters and me1amine .

6. The process according to claims 1-5, wherein said starting polymer material is selected from the group consisting of: polyethylene (PE) , polypropylene (PP) , high-density polystyrene or transparent polystyrene, and polyamide (PA) .

7. The process according to any one of the preceding claims, wherein the source of zinc ions comprises ZnPCA in a mixture with a zinc salt selected from among: zinc acetate, zinc carbonate, zinc borate, zinc nitrate, zinc chloride, zinc hydroxide and zinc oxalate, or preferably mixtures thereof.

8. The process according to claim 7, wherein said zinc source comprises at least ZnPCA and zinc acetate.

9. The process according to any one of the preceding claims, wherein said source of zinc ions is added in the form of an aqueous solution.

10. The process according to claims 1-8, wherein said source of zinc ions is added in solid form, preferably before the extrusion step.

11. The process according to any one of the preceding claims, wherein the ZnPCA is present in the source of zinc ions at a concentration comprised from 1% to 80% by weight.

12. The process according to claim 11, wherein the ZnPCA is present in the source of zinc ions at a concentration comprised from 5% to 50% by weight.

13. A use of the antibacterial polymer material obtained with the process according to the preceding claims for the production of a product for food applications .

14. A product for food applications manufactured from the polymer material obtained from the process according to claims 1-12.

15. The product for food applications according to claim 14, characterized in that it contains an amount of Zn²⁺ ions comprised from 5 ppm to 500 ppm, preferably comprised from 20 ppm to 300 ppm.

16. The product for food applications according to claim 14 or 15, in the form of a plate, glass, item of cutlery, tableware, film or sheets.