WO2022043679A1

WO2022043679A1 - Additive composition

Info

Publication number: WO2022043679A1
Application number: PCT/GB2021/052200
Authority: WO
Inventors: Radu Baciu
Original assignee: Symphony Environmental Ltd
Current assignee: Symphony Environmental Ltd
Priority date: 2020-08-28
Filing date: 2021-08-24
Publication date: 2022-03-03
Anticipated expiration: 2023-02-28
Also published as: GB2598361A; GB202013513D0

Abstract

The present invention relates to an additive composition for a polymer substrate comprising a polymeric material; a degradation catalyst; and an antimicrobial substance; and a method for making the same.

Description

Additive Composition

The present invention relates to an additive composition for a polymer substrate having combined degradable and antimicrobi al properties and a method of making the same.

Antimicrobial plastics, such as mulch films, are known. In sectors including food, agriculture, medicine, electronics and personal hygiene, often the only safe way to facilitate handling of crops or products, whilst simultaneously preventing cross-contamination and maintaining sterility is to package the crops or products in antimicrobial plastics.

In order to impart an antimicrobial property to plastics, an additive composition or “masterbatch” is typically added to a bulk polymer substrate. An additive composition or masterbatch provides a convenient way of handling small amounts of substituents in higher concentrations than those occurring in bulk mixtures, for subsequent dilution with a base polymer resin. A masterbatch can be supplied as a solid additive, for example, in the form of pellets, or a liquid additive. The use of a masterbatch is advantageous, because it enables uniform dispersion of the components within the base/bulk polymeric resin.

Known plastics cannot be re-purposed after being used to package or protect crops, food or medicines, as they eventually become contaminated by natural processes occurring in the surroundings and from the antimicrobial substances on the products themselves. Therefore, the used plastics often end up in the open environment, contributing to environmental pollution. Burning the plastics is an alternative disposal method, but uncontrolled burning releases toxic chemicals into the atmosphere.

Degradable masterbatches for plastics are known and are described in US 3,935,141, WO 2018/095905 and US 5,854,304.

It is an object of this invention to mitigate problems such as those described above.

The terms “additive composition”, “additive” and “masterbatch” are used interchangeably throughout this specification. According to a first aspect of the invention, there is provided an additive composition for a polymer substrate comprising a polymeric material, a degradation catalyst and an antimicrobial substance. The invention advantageously provides an additive or masterbatch which imparts a dual function to the polymer substrate into which it is eventually incorporated, of being biodegradable (due to the presence of a degradation catalyst) and preventing contamination from microbes and microorganisms (due to the presence of an antimicrobial substance). Thus, only a single additive or masterbatch is necessary to impart both of these favourable properties to a polymer substrate. This reduces manufacturing costs due to the requirement of fewer raw materials and reduces the number of process steps.

The additive composition is particularly useful for incorporation into plastic products which may, in use, facilitate cross-contamination, such as food packaging, medicine packaging, medical utensils, hygiene products, carrier bags, refuse sacks and paint containers. In conjunction with the antimicrobial property, the polymer substrate incorporating the additive composition is biodegradable. Accordingly, this prevents the polymer substrate from persisting in the open environment, thereby reducing pollution of streams, lakes and oceans, thus preventing harm to aquatic life. If collected for disposal, the polymer substrate is recyclable in the normal polymer waste streams. Such polymer substrates are also reusable, which decreases costs. The above properties provide a more environmentally friendly antimicrobial plastic compared with the prior art.

The polymeric material acts as a carrier resin by encapsulating the degradation catalyst and the antimicrobial substance.

Conveniently, the additive composition of the present invention does not interfere with the mechanical, physical , chemical or optical properties of the resulting polymer substrate. Thus, advantageously, the quality and performance of the resulting polymer substrate is maintained. Preferably, the additive composition further comprises a stabiliser.

The stabiliser may be encapsulated in the polymeric material. The stabiliser may be a primary' and/or a secondary stabiliser. A primary stabiliser protects the polymer material into which the additive composition is incorporated during its shelf life and service life against premature degradation. A secondary stabiliser acts to protect the raw materials against degradation during processing by machinery (for example, an extruder or injection moulding machine). Preferably, the stabiliser comprises a heat stabiliser. More preferably, the heat stabiliser is in a range from 0.1wt% to 10wt%. A heat stabiliser present in the composition in this range has been found to protect the composition from heat damage during the manufacturing process and during use of the polymer substrate into which the additive may be eventually incorporated.

Preferably, the stabiliser comprises a UV stabiliser or a combination of a UV stabiliser and a heat stabiliser. The use of a UV stabiliser is particularly advantageous where the product or polymer substrate into which the additive composition is incorporated into is exposed to UV radiation, for example, products which are used outdoors. More preferably, the UV stabiliser is in a range from 0.05wt% to 10wt%. A UV stabiliser present in the composition in this range has been found to prevent the additive composition from undergoing premature photo and/or heat degradation which occurs when UV radiation interacts with chemical bonds within the polymeric material. Preferably, the antimicrobial substance is active against at least one microorganism selected from the group comprising Gram-positive bacteria, Gram -negative bacteria, fungi, algae and/or viruses. Advantageously, the antimicrobial substance of the additive composition is active against many common microorganisms which cause food to spoil or contaminate packaged products and may cause illnesses in humans and animals. For example, the fungi against which the antimicrobial substance may be active against includes, for example, moulds, mildew and yeasts. The viruses against which the antimicrobial substance may be active against include, for example, filamentous, isometric, enveloped, head and tail and coronavirus. Preferably, the antimicrobial substance is in a range from 2wt% to 50wt%. This particular concentration range of antimicrobial substance has been found to be advantageous, from both processing and efficacy perspectives. Preferably, the antimicrobial substance comprises a pyrithione biocide. Pyrithione biocides are powerful antimicrobial agents having a wide spectrum efficacy, in particular against Gram-positive and Gram -negative bacteria, fungi, viruses and algae. More preferably, the pyrithione biocide is selected from the group comprising zinc pyrithione, sodium pyrithione, copper pyrithione, barium pyrithione, cadmium pyrithione, titanium pyrithione and/or zirconium pyrithione.

Preferably, the antimicrobial substance comprises a food preservative. Food preservatives are advantageous because they are cheap and accessible. They also already have safety approval from regulatory bodies. More preferably, the food preservative is selected from the group comprising sodium benzoate, potassium benzoate, potassium sorbate, sodium sorbate, sodium nitrate, sodium nitrite, calcium propionate, ascorbic acid and/or citric acid.

Preferably, the antimicrobial substance comprises a zeolite, wherein the zeolite comprises silver and/or zinc. Preferably, the zeolite comprises silver, zinc and/or copper. These substances are advantageous due to their high chemical stability and high efficacy against bacteria, fungi, viruses and algae. Preferably, the zeolite comprises silver and zinc and sodium, or the zeolite comprises silver and copper and sodium. Preferably, the additive composition comprises a filler. The use of a filler reduces the manufacturing costs of the composition because the quantity of polymeric material required is less than what would be required without a filler. The presence of the filler does not alter the physical or chemical characteristics of the additive composition. More preferably, the filler is in a range from 5wt% to 75wt%. This particular range of filler provides a homogenous additive composition, without adversely affecting the antimicrobial properties and improving the degradable properties.

Preferably, the polymeric material is in a range from 15wt% to 95wt%. The polymeric material acts to encapsulate the components of the additive composition together and allows the incorporation of the non-polymeric materials into the polymeric matrix in a fine dispersion. Preferably, the degradation catalyst is in a range from 0.5wt% to 25wt%. This particular concentration range of degradation catalyst has been found to provide favourable results in terms of rate of degradation, when the additive is incorporated into a polymer substrate. Preferably, the degradation catalyst comprises a transition metal salt of a saturated fatty acid. Transition metal salts of saturated fatty acids are inert and undergo a predictable oxidation degradation mechanism. Therefore, the use of such degradation catalysts means that the rate of degradation of the additive composition can be finely tuned and controlled. Preferably, the transition metal is selected from the group comprising copper, cerium, iron, cobalt and/or manganese and the saturated fatty acid is selected from the group comprising palmitic acid, myristic acid, stearic acid and/or lauric acid. This is advantageous because such transition metals and saturated fatty acids are cheap and widely available and exhibit predictable degradation profiles.

According to a second aspect of the present invention, there is provided a polymer product comprising the additive composition. Examples of the polymer substrate to which the additive composition may be added include polyolefins such as polyethylene (e.g. low- density polyethylene (LDPE), linear low-density polyethylene (LLDPE), medium-density polyethylene (MDPE), high-density polyethylene (HDPE); polypropylene (PP), e.g. monopolymer, random co-polytner; a multi-layer combination of PE and PP; thermoplastic elastomers; ionomers; ethylene-vinyl acetate (EVA) and EVA combined with PE or PP; polyvinyl alcohol (PVOH); PVOH combined with at least one of PE, PP, or EVA; polystyrene (e.g. general purpose polystyrene (GPPS), or high impact polystyrene (HIPS) or a combination thereof); styrene-acrylo-nitrile (SAN), or acrylonitrile butadiene styrene (ABS).

Preferably, the polymer product is plastic packaging. The packaging may be for food, medicines, medical utensils or personal hygiene products. Preferably, the polymer product is a face mask. Advantageously, a face mask having antimicrobial properties provides additional protection to the wearer against pathogens and protection to individuals in the vicinity of the wearer. Furthermore, the surfaces of the face mask are kept free of microbes due to the presence of the antimicrobial substance within the material. Accordingly, cross-contamination between the mask and, for example, surfaces touched by the wearer after touching the mask is avoided. The antimicrobial substance in the additive composition acts to decontaminate the air exhaled by the wearer and thus provides further protection to individuals in the vicinity of the wearer.

The presence of the antimicrobial substance also acts to prevent the wearer from inhaling pathogens, such as bacteria, fungi, algae, and viruses.

Due to the antimicrobial property of the face mask, the face mask is safe to wear for a longer period of time compared with face masks which do not incorporate an antimicrobial substance. In view of the degradable property imparted to the face mask, if the face mask is disposed of in the open environment, it wall biodegrade through mechanisms initiated by naturally-occurring microorganisms, therefore preventing the accumulation of plastic in the environment.

According to a third aspect of the present invention, there is provided a method of making an additive composition comprising the steps of

(a) mixing and heating a polymeric material, a degradation catalyst and an antimicrobial substance to form a homogenous mixture, and

(b) processing the homogenous mixture to form at least one pellet of additive composition.

The additive composition according to the present invention may be prepared by mixing the individual components of the composition, i.e. a polymeric material, a degradation catalyst and an antimicrobial substance, until a homogenous mixture is formed. In an alternative embodiment, the degradation catalyst and the antimicrobial substance are mixed to form a homogenous mixture prior to addition of the polymeric material. One the mixture is homogenised, it is extruded to form at least one pellet of additive composition.

The additive composition may be incorporated into a bulk polymer material by a processing technique such as extrusion, injection moulding, rotational moulding, nonwoven, woven, woven coated or extrusion and thermoforming. The skilled person would understand that other suitable processing techniques may be used. The resulting polymer material incorporating the additive may be formed into a film or sheet by extrusion. Thermoforming of the formed sheet may be performed subsequent to extrusion, in order to form shaped objects, such as cups, bowls and plates.

In some embodiments, the final polymer product incorporating the additive composition is a film or sheet having a thickness between 5 pm to 300 pm, and more typically between 10 pm to 100 pm. In some polymer products, specifically plastic membranes, the thickness may be between 800 pm to 900 pm.

In alternative embodiments, the resulting polymer products have a multi-layer structure which can be achieved by, for example, a co-extrusion or lamination process, using heat or adhesives as sealants. The additive may be incorporated into at least one of the layers of the multi-layered structure.

Preferred additive compositions for a polymer substrate may have the following formulations:

Table 1 Bacterial and fungal growth studies were performed on an LLDPE film incorporating the antimicrobial and biodegradable additive composition. The bacterial growth studies were performed in accordance with ISO 22196-2011 and the fungal growth studies were performed in accordance with ASTM E2180-07. The antimicrobial substance present in the masterbatch was a silver/zinc zeolite at a concentration of 25wt%. The film was shown to exhibit the following behaviour against the bacteria Staphylococcus aureus (Gram (+) bacteria), Escherichia coli (Gram (-) bacteria) and Aspergillus niger (fungus):

Table 2

Wherein:

CFU= Colony forming unit

# = When the number of viable bacteria “A_t” is less than or equal to 1.0, it shall be taken as

“A_t” and the average of logarithm numbers shall be calculated

Percent reduction (%) = (a-b)/a x 100%

Table 3

With reference to Table 2, the R values for S. aureus (Gram (+) bacteria) and E. coli (Gram (-) bacteria) are >4.91 and >4.90, respectively. For comparison purposes, an R value of 5 indicates a bacterium kill rate of 99.999%. Therefore, the R values as set out in Table 2 show that the bacterium kill rate for the LLDPE film incorporating the antimicrobial and biodegradable additive composition is between 99.99% and 99.999%. Further, the results tabulated in Table 2 indicate that the antimicrobial agent (i.e. silver/zinc zeolite) has bactericidal activity, meaning that the film continuously kills bacteria on its surface.

With reference to Table 3, the sample film was incubated at 25 °C for 120 hours. The LLDPE film incorporating the silver/zinc zeolite had reduced the number of Aspergillus niger fungi by >99.99% after 120 hours.

In use, the additive composition is incorporated into a polymer product, thereby imparting antimicrobial and degradable properties to the polymer product. The polymer product may be used in many applications such as food packaging, including bread bags and coated paper inserts for food trays; food utensils; tableware; medicines packaging; medical utensils; agricultural applications; mattress covers and in other products used in the hygiene and/or medical sectors. The resulting polymer product may be incorporated into a woven structure, for example, as a coating. Conversely, the resulting polymer product may be incorporated into a non-woven structure, for example in personal protective equipment such as coveralls and hair nets, and shopping bags.

The additive composition may be incorporated into non-woven polypropylene fibre and formed into a face mask. The face mask is of the type for protecting the user and those in the vicinity of the user from pathogens. The face mask incorporating the additive composition may comprise three layers: an outer layer, an inner layer and a central layer, wherein the central layer is positioned in between the outer layer and the inner layer. In use, the inner layer is the layer in closest proximity to the wearer’s mouth and nose and the outer layer is the layer which is exposed to the external atmosphere. The additive composition is contained in all three of the layers and is therefore effective at minimising contamination of persons near the wearer by exhaled microorganisms, as well as providing protection from contaminants which may otherwise be inhaled from other individuals in the vicinity of the wearer.

Claims

1. An additive composition for a polymer substrate comprising: a polymeric material; a degradation catalyst; and an antimicrobial substance.

2. The additive composition of claim 1, further comprising a stabiliser.

3. The additive composition of any preceding claim, wherein the antimicrobial substance is active against at least one microorganism selected from the group comprising Gram-positive bacteria, Gram-negative bacteria, fungi, algae and/or viruses.

4. The additive composition of any preceding claim, wherein the antimicrobial substance is in a range from 2wt% to 50wt%.

5. The additive composition of any preceding claim, wherein the antimicrobial substance comprises a pyrithione biocide.

6. The additive composition of claim 4, wherein the pyrithione biocide is selected from the group comprising zinc pyrithione, sodium pyrithione, copper pyrithione, barium pyrithione, cadmium pyrithione, titanium pyrithione, and/or zirconium pyrithione.

7. The additive composition according to any preceding claim, wherein the antimicrobial substance comprises a food preservative.

8. The additive composition according to claim 7, wherein the food preservative is selected from the group comprising sodium benzoate, potassium benzoate, potassium sorbate, sodium sorbate, sodium nitrate, sodium nitrite, calcium propionate, ascorbic acid and/or citric acid.

9. The additive composition according to any preceding claim, wherein the antimicrobial substance comprises a zeolite, wherein the zeolite comprises silver and/or zinc, or wherein the zeolite comprises silver, zinc and/or copper.

10. The additive composition according to any preceding claim, further comprising a filler.

11. The additive composition according to any preceding claim, wherein the degradation catalyst is in a range from 0.5wt% to 25wt%.

12. The additive composition according to any preceding claim, wherein the degradation catalyst comprises a transition metal salt of a saturated fatty acid.

13. The additive composition according to claim 12, wherein the transition metal is selected from the group comprising copper, cerium, iron, cobalt and/or manganese and the saturated fatty acid is selected from the group comprising palmitic acid, myristic acid, stearic acid and/or lauric acid.

14. A polymer product comprising the additive composition of any preceding claim.

15. A polymer product according to claim 14, wherein the polymer product is plastic packaging.

16. A polymer product according to claim 14, wherein the polymer product is a face mask.

17. A method of making an additive composition according to any of claims 1 to 13 comprising the steps of:

(a) mixing and heating a polymeric material, a degradation catalyst and an antimicrobial substance to form a homogenous mixture; and