WO2009100878A1

WO2009100878A1 - Salts of dehydroacetic acid as an antimicrobial for plastics

Info

Publication number: WO2009100878A1
Application number: PCT/EP2009/000921
Authority: WO
Inventors: Lei RAO; Joseph Kimler; Larry Kent Hall
Original assignee: Lonza Inc.; Lonza Ltd.
Priority date: 2008-02-12
Filing date: 2009-02-10
Publication date: 2009-08-20

Abstract

The invention relates to a method for imparting an antimicrobial characteristic to plastic material and a process for making a plastic product by processing the material. The material is a polymer composition comprising at least one polymer and 5 to 10,000 ppm of a salt of dehydro-acetic acid (DHA) which is stable at temperatures required for processing polymeric compositions. The method for making a plastic product preferably includes blending and/or extruding the polymer composition in a process which includes a temperature of at least about 170 °C.

Description

Salts of Dehydroacetic Acid as an Antimicrobial for Plastics

[0001] The present invention relates to plastics made of polymeric compositions comprising at least one polymer and additives, and, in particular, to plastics which have an antimicrobial characteristic.

[0002] Modern plastic materials have been in use since the 1930s. Plastics are made of polymers and usually additives. Typical polymers include: synthetic resins, polystyrenes, poly- olefins, polyamides, fluoropolymers, vinyls, acrylics, polyurethanes, cellulosics, polyimides, polyacetals, polycarbonates, and polysulfones. Lacking nutrients required for microbial growth, most pure synthetic polymers have a natural resistance to microbes. However, in order to improve, among other things, physical characteristics of polymers, additives such as plasticizers are often used which can serve as a source of nutrients for microorganisms. [0003] Modern plasticizers include phthalates, adipates, and other esters. In the case of PVC, for example, the addition of plasticizers allows for production of clothing, upholstery, flexible hoses, tubing, flooring, roofing membranes, and electrical cable insulation.

[0004] Plasticizers are particularly susceptible to bacteria and fungi, especially in high moisture areas. Without the addition of antimicrobial agents, plastic materials experience microbial surface growth and development of spores. Microbial growth can result in allergic reactions, unpleasant odors, staining, embrittlement of the plastic, and premature product failure. [0005] Thus, antimicrobials can be used to impart protection against mold, mildew, fungi and bacterial growth. Antimicrobials have been used in commercial products ranging from food to paint to plastic. Several antimicrobial formulations are used within the plastics industry. One of the major biocides used commercially is 10,10'-oxybisphenoxarsine (OBPA) in a phthalate carrier. OBPA, an arsenic containing biocide, has been used in plastic resins, fibers, tapes, and other plastics. See US 3 624 062 and US 4 086 297. And US 4 663 077 also describes the use of OBPA to impart microbiocide properties to polymer compositions.

[0006] The use of OBPA has raised concerns regarding its environmental and human health impact. According to a Kline & Company study of the biocides industry in 2004 and 2005, the U.S. and European markets for biocides are very mature; however the EU's Biocidal Products Directive may convince consumers to reduce the role of OBPA as a biocide. If OBPA is banned, other antimicrobial products will be required to replace it.

[0007] There are certain other antimicrobial compounds in use. US 3 755 224 discloses a polymer containing the biocide 3-isothiazolones. For antimicrobial use in plastic, US 3 890 270 discloses N-(2,6-disubstituted phenyl)maleimides. US 6 495 613 discloses an antimicrobial agent that releases silver, copper, zinc, or ions thereof, incorporated into dental plastics. The antimicrobial agent is preferably copper oxide or zinc silicate.

[0008] Dehydroacetic acid (DHA) has been used as a preservative for cosmetics and food products. It is approved by the FDA (21 CFR 172.130) as a food preservative and is a known antimicrobial, biocide and fungicide. US 5 654 330 discloses use of organic acids, and salts thereof, in combination with 2-bromo-4-hydroxyacetophenone (BHAP). However, the low boiling point of BHAP and its high toxicity, especially when inhaled, make it unsuitable for use at high temperatures, such as those required for processing polyvinyl, polyolefins, and poly- urethanes. Therefore, the composition is unsuitable for use in high temperature processes.

[0009] US 4 348 308 also discloses using a salt of DHA in plastics as one component of an additive composition for improving the color stability of plastic. The composition further contains an ortho-tertiary alkyl-substituted phenyl phosphite. [0010] US 4 252 698 discloses an anti-yellowing composition for PVC wherein an overbased sulfonate or phenolate is combined with a cyclic or open-chained 1,3-diketone, or a metal salt thereof.

[0011] US 5 147 917 discloses a halogen resin composition composed of an overbased alkaline earth metal carboxylate/carbonate complex together with a β-diketone compound or a metal salt of a β-diketone. While DHA is listed as a β-diketone, the disclosure again requires a co-agent, in this case, an overbased alkaline earth metal carboxylate/carbonate.

[0012] Unfortunately, many antimicrobial compounds are not heat stable and degrade at the high temperatures required for molding of plastics. One reason the arsenic-containing antimicrobial OBPA is still one of the major biocides in plastics is its stability at the processing temperatures of flexible PVC, polyolefins and urethane compounds. [0013] More environmentally-acceptable antimicrobial chemicals are desired to replace highly toxic materials. For use in plastics, the antimicrobial should be stable at high temperatures. There are ongoing needs for effective antimicrobial protection, which also maintains surface appearance, prevents contamination, withstands weathering for a long time, and extends the life of the plastic materials. [0014] The present invention relates to a method for imparting antimicrobial characteristics to a plastic or polymeric composition, which includes at least one polymer capable of forming a plastic. The method comprises the step of adding a heat stable salt of dehydroacetic acid (DHA) to the polymer composition. The salt of DHA is present in an of 5 ppm to 10,000 ppm and it does not require the presence of a co-agent. The plastic can be thermoplastic, thermoset, or elastomeric.

[0015] In a preferred embodiment, the polymer is a thermoplastic polymer. [0016] The polymer, which is capable of forming a plastic, can be of natural origin, synthetic, or semi-synthetic. It is preferably selected from the group consisting of polystyrenes, polyolefins such as polyethylene or polypropylene, polyamides, fluoropolymers, vinyls, acrylics, polyurethanes, cellulosics, polyimides, polyacetals, polycarbonates, polysulfones, polymeric resins, and combinations and co-polymers thereof. [0017] More preferably the polymer is a vinyl polymer. [0018] Most preferably the polymer is polyvinyl chloride. [0019] Since salts of DHA can be used at high temperatures in the absence of a co-agent, antimicrobial properties can be achieved in polymers that require high heat processing. [0020] Whereas DHA degrades at about 169 °C, a heat stable salt of DHA remains stable at temperatures of at least about 170 °C and above. The present invention includes all heat stable salts of DHA. The heat stable salt of DHA may be a salt of a monovalent or divalent metal.

[0021] The metal is preferably selected from the group consisting of, sodium, potassium, lithium, magnesium, zinc, copper, barium, calcium, strontium, tin and combinations thereof. [0022] Most preferably, the salt of DHA is a zinc salt. The zinc salt of DHA is stable up to temperatures of about 275 °C. [0023] The salt of DHA is present in an amount sufficient to provide antimicrobial properties to a plastic, which is broadly an amount of 5 ppm to 10,000 ppm, Thus, a preferred embodiment of the invention would use at least 50 ppm of DHA salt, and more preferably at least 100 ppm. While the amount of DHA salt can be as high as 10,000 ppm, it is preferably no more than 8,500 ppm, more preferably no more than 5,000 ppm. However, preferred ranges can also be defined by any combination of the minimum and maximum amounts set forth above.

[0024] Particularly preferred ranges are 50 ppm to 8,500 ppm and more preferably 100 ppm to 5,000 ppm,

[0025] The ability to achieve antimicrobial properties while processing at elevated temperatures does not depend on a co-agent to be included with the DHA salt. No other chemical ingredient (e.g., compound, composition, etc.) is required to co-act, augment, modify, enhance, or otherwise effect the salt of DHA, and, in a preferred embodiment, additional chemical ingredient(s) are not included.

[0026] Antimicrobial properties include any biocidal, fungicidal, pesticidal, sporicidal and virucidal activity. The antimicrobial property can also, for example, include biostatic properties. [0027] In another preferred embodiment the plastic contains a co-antimicrobial agent in an amount of 5 ppm to 10,000 ppm.

[0028] This co-antimicrobial agent can be any heat stable antimicrobial agent suitable for use in plastics, in particular any heat-stable biostatic, biocidal, fungicidal, pesticidal, sporicidal or virucidal agent. [0029] The co-antimicrobial agent is preferably selected from the group consisting of Zn- pyrithione, isothiazolones, azole fungicides such as tebuconazole, and combinations thereof. This embodiment of the invention would use at least 5 ppm of co-antimicrobial agent, preferably at least 50 ppm, and more preferably at least 100 ppm. The amount of co- antimicrobial agent can be as high as 10,000 ppm, preferably no more than 8,500 ppm, more preferably no more than 5,000 ppm. Thus, the co-antimicrobial agent is particularly preferably present in an amount of 50 ppm to 8,500 ppm and most preferably 100 ppm to 5,000 ppm. [0030] However, suitable ranges for the amount of co-antimicrobial agent can be formed by combining any minimum and any maximum amount set forth above. [0031] The invention further includes a process for the production of a plastic product with an antimicrobial property by processing a polymer composition that has been provided with antimictobial characteristics by the method set forth above.

[0032] The polymer processing can have a temperature profile which includes a temperature of at least 170 °C.

[0033] In a preferred embodiment, the temperature is not less than 170 °C for a significant portion of the processing. Another preferred embodiment has a temperature profile which is predominantly over 170 °C. [0034] The processing is preferably selected from: blending, extruding, fiber spinning, film blowing, filament winding, spin coating, molding, blow molding, injection molding, reaction injection molding, transfer molding, and combinations thereof.

[0035] As a result of the present invention, the polymer can be used to make any product ranging from common building and domestic items to sterile laboratory equipment and medical instruments. [0036] The invention further includes a plastic product obtained by processing a polymer composition as described above.

[0037] Major applications include: flexible roofing membrane, pool liners, shower curtains, electrical appliances, food contact packaging, and automotive parts and accessories. The omission of arsenic containing antimicrobials reduces safety concerns. [0038] The heat stability of a salt of DHA allows the compound to be added to the polymer prior to processing. By permeating the polymer with the salt of DHA, the antimicrobial nature can be maintained even, for example, if internal layers of the plastic become exposed to the environment via erosion of the outer layer, accidental puncture, or incidental wear and tear due to rugged use. [0039] Furthermore, melding the salt of DHA with the polymer can decrease the risk inherent in antimicrobial coatings, that of dissolution of the antimicrobial into the surrounding media. [0040] Another advantage of the present invention is that salts of DHA could replace antimicrobials currently used in manufacturing of plastics, which rely on arsenic-containing antimicrobials. Doing away with arsenic-containing antimicrobials is also better for the environment.

Description of the figures:

Figure 1 depicts an untreated PVC sample with heavy fungal growth. Figure 2 depicts a PVC sample treated with zinc dehydroacetate. There is no fungal growth on the sample and a small zone of inhibition is visible around the sample. Figure 3 depicts a PVC sample treated with zinc dehydroacetate and n-octylisothiazolone. There is no fungal growth on the sample and a large zone of inhibition is visible around the sample.

Figure 4 depicts a PVC sample treated with zinc dehydroacetate and zinc pyrithione. There is no fungal growth on the sample and a large zone of inhibition is visible around the sample.

[0041] The following examples illustrate the present invention and are not intended to limit the invention or its scope in any manner.

Antimicrobial Treated Plastic Sample Preparation for all Examples:

[0042] The antimicrobial compositions containing salts of dehydroacetic acid, with or without additional antimicrobial components, were mixed with a commercial flexible PVC (FPVC) compound. The mixtures were extruded on an intermeshing modular co-rotating twin screw extruder having six temperature zones, and pelletized after cooling. The temperature profile, from feed zone to die zone of the extruder was 140 °C, 170 °C, 175 °C, 175 °C, 175 °C, and 175 °C. The antimicrobial treated FPVC compounds were then cast on a presser at 185 °C to form plastic sheets. Three 5.08x5.08 cm² (2"^χ2") square samples were cut from each plastic sheet as test samples. [0043] An untreated control sample was manufactured without any antimicrobial components.

Example 1: Fungal Resistance Test (ASTM G21):

[0044] A fungal inoculum was prepared. The fungal inoculum consisted of five species (test organisms): Aspergillus niger ATCC 9642, Aureobasidium pullulans ATCC 15233, Chae- tomium globosum ATCC 6205, Penicillium funiculosum ATCC 11797, and Trichoderma virens ATCC 9645.

[0045] Test samples, in triplicate, were placed in Petri dishes on mineral salts agar and inoculated with the fungal inoculum. The samples were then incubated at 28 °C for 4 weeks and examined weekly for the growth of the test organisms.

[0046] The fungal resistance test results are listed in Table 1 below. While the Positive Control and Untreated Control showed maximum fungal growth (fungal growth rating of 4), Zn-DHA (zinc dehydroacetate), and its blends: Zn-DHA/«-OIT (n-octylisothiazolone), Zn-DHA/Zn-P (zinc-pyrithione), and Zn-DHA/tebuconazole, demonstrate total fungal resist- ance (fungal growth rating of 0).

[0047] For evaluation of the relative resistance of synthetic polymeric materials, a rating scheme as set forth in Footnote 1 of Table 1 was used: Table 1

Rating Scheme:

None 0

Traces of growth (less than 10%) 1

Light growth ( 10-30%) 2

Medium growth (30-60%) 3

Heavy growth (60% to complete coverage) 4

Example 2 : Zone of Inhibition Test (Modified ASTM G21)

[0048] A fungal inoculum was prepared as described in Example 1.

[0049] Test samples, in triplicate, were placed in Petri dishes on Potato Dextrose Agar, and inoculated with the fungal inoculum. The samples were incubated at 28 °C for 4 weeks and the Zone of Inhibition (ZOI) for each sample was examined. The results are compiled in Table 2 below. For evaluation of the ZOI a scheme as set forth in footnote 1 of Table 2 was used. Photos displaying the ZOI are contained in Figures 1 through 4.

Table 2

Zone of Inhibition: None: - Small: + Large: ++

[0050] While the Untreated Control does not provide any Zone of Inhibition (ZOI), Zn-DHA treated FPVC supplies small ZOI, and the blend of Zn-DHA and n-OIT and the blend of the Zn- DHA and Zn-P treated FPVC have a large ZOI.

Claims

1. A method for imparting antimicrobial characteristics to a polymer composition comprising at least one polymer, said method comprising the step of adding to said polymer composition a heat-stable salt of dehydroacetic acid in an amount of 5 to 10,000 ppm.

2. The method of claim 1, wherein said at least one polymer is a thermoplastic polymer.

3. The method of claim 1 or 2, wherein said at least one polymer is selected from the group consisting of polystyrenes, polyolefins, polyamides, fluoropolymers, vinyl polymers, acrylics, cellulosics, polyimides, polyacetals, polycarbonates, polysulfones, and combinations and co-polymers thereof.

4. The method of claim 3, wherein said at least one polymer is a vinyl polymer.

5. The method of claim 4, wherein said vinyl polymer is polyvinyl chloride.

6. The method of any of claims 1 to 5, wherein said heat-stable salt of dehydroacetic acid is a salt of a metal selected from the group consisting of lithium, sodium, potassium, magne- sium, calcium, strontium, barium, zinc, tin and combinations thereof.

7. The method of any of claims 1 to 6, wherein said heat-stable salt of dehydroacetic acid is a salt of a divalent metal.

8. The method of claim 7, wherein said divalent metal is zinc.

9. The method of any of claims 1 to 8, wherein said amount of a heat stable salt of dehydroacetic acid is 50 ppm to 8,500 ppm.

10. The method of claim 9, wherein said amount of a heat stable salt of dehydroacetic acid is 100 ppm to 5,000 ppm.

1 1. The method of any of claims 1 to 10, wherein said polymer further comprises 5 ppm to 10,000 ppm of a co-antimicrobial agent.

12. The method of claim 1 1, wherein said co-antimicrobial agent is selected from the group consisting of zinc pyrithione, isothiazolones, tebuconazole and combinations thereof.

13. The method of claim 1 1 or 12, wherein said co-antimicrobial agent is present in an amount of 50 ppm to 8,500 ppm.

14. The method of claim 13, wherein said co-antimicrobial agent is present in an amount of 100 ppm to 5,000 ppm.

15. A process for the production of a plastic product with an antimicrobial property, comprising the step of processing a polymer composition that has been obtained according to the method any of claims 1 to 14.

16. The process of claim 15, wherein the processing utilizes a temperature profile that includes a temperature of at least 170 °C.

17. The process of claim 15 or 16, wherein said processing is selected from the group consisting of blending, extruding, fiber spinning, film blowing, filament winding, spin coating, molding, blow molding, injection molding, reaction injection molding, transfer molding, and combinations thereof.

18. A plastic product obtained by the process of any of claims 15 to 17.