Preventing bacterial growth: biocides and antimicrobials

 

Polymers and many additives that are used to provide useful properties in compounds are vulnerable to attack by micro-organisms. However, antimicrobials can be added to plastics to increase their resistance, which will maintain properties and boost product life. Plastics Additives & Compounding rounds up some of the products on the market in this important field.

Antimicrobial additives and fungicides are added to plastics to increase their resistance to micro-organisms such as bacteria, fungi and algae, which can cause black pitting, pink staining or odour, impairment of properties, and reduction of product life. Polymers such as polysulphides and polyester-based polyurethanes are vulnerable, but the main culprits for microbial growth are additives such as plasticizers, starch fillers, lubricants, thickening agents, and oils. A main area is PVC, which is also used in many vulnerable applications.

Plasticized PVC film can be attacked by micro-organisms, especially fungi, which use the plasticizer or other ingredients as a carbon source, producing discoloration, bad odour, tackiness and eventual embrittlement over a period of time. Microbial attack can be prevented by incorporation of a fungistatic agent during processing. Biocides act by interfering with the metabolism of micro-organisms by blocking one or more of the enzyme systems. However, to be effective, the additive should migrate to the surface – a process that is influenced both by its chemistry and compatibility. Also influential is the internal structure of the PVC film (ingredients), as well as the processing conditions.

Many chemicals have antimicrobial properties, but few are suitable for use in plastics, requiring low cost, compatibility, thermal stability during processing, environmental stability, and safe and easy handling. Microbial agents must migrate to the surface of the plastic and prevent bacterial growth.

Troy Corporation offers a number of different types of antimicrobial solutions for plastics under the brand name Micropel. The products are defined by their active ingredients. These include OBPA (10,10’-oxybisphenoxarsine), which is an organometallic compound widely used in the flexible PVC and polyurethane industries. It is a broad spectrum antimicrobial, effective against fungi, pink staining organisms, bacteria and algae. OBPA has excellent heat stability, well within the processing range of flexible PVC, polyolefins and urethane compounds. The company says that products are available to the plastics market as 2% and 5% liquid concentrates or as 5% pelletized formulations.IPBC (3-iodo-2-propynyl butylcarbamate) is an organic compound widely used to prevent the growth of fungi, yeast and other micro-organisms in various industrial and personal care applications. IPBC products are engineered to fit the heat stability requirements of various polymers including PVC, polyolefins and rubber. Products are available to the plastics market in proprietary liquid and solid formulations.DCOIT (dichloro-octyl isothiazolone) is an organic compound used in flexible PVC applications. DCOIT is thermally stable for use in flexible PVC processing where it provides effective fungal control. Products are available to the plastics market as 4% and 12% liquid concentrates or as a 10% pelletized concentrate.Also for use in flexible PVC applications is organic compound OIT (octyl isothiazolone). OIT is thermally stable for use in flexible PVC processing where it provides effective fungal control. Micropel products are available to the plastics market as 4% and 20% liquid concentrates or as a 10% pelletized concentrate.TCPP (trichlorophenoxy phenol) is an organic compound used to provide antibacterial protection to PVC and polyolefins. TCPP is thermally stable under the common processing temperatures for PVC and polyolefins.

Akcros Chemicals has developed the Intercide range of products for PVC and are based on a choice of active biocides contained in a phthalate plasticizer, epoxy co-stabiliser or solid co-polymer. The Intercide ABF products are based on OBPA, while Intercide OBF and Intercide IBF products are arsenic-free alternatives. Akcros says that Intercide ABF-2-ESBO consists of a 2% solution of OBPA in epoxidized soya bean oil (ESBO). The OBPA is claimed to offer good protection against a wide spectrum of fungi and bacteria and the ESBO carrier/solvent contributes to the PVC processing stability. The ESBO will replace some, if not all of the epoxy co-stabilizer, which the processor would normally add to the formulation. Intercide ABF-5-SVC was developed for compounders and manufacturers preferring an antimicrobial in pellet form. The use of pelletized product eliminates the dusting hazards associated with powdered products, as well as the potential for accidental spills that may occur with liquid antimicrobials. It is recommended for use at 0.6-1.0% by weight of the total PVC formulation to provide protection against attack from a wide spectrum of fungi and bacteria. It is also suggested for use in PVC wood composites.

Intercide ABF-5-DIDP consists of a 5% solution of OBPA in DIDP. The company says that the more concentrated material means that less primary plasticizer is needed in a formulation. It is recommended for use at 0.6-1.0% by weight of the total PVC formulation to provide attack from a wide spectrum of fungi and bacteria.
Intercide OBF-8-DINP is an 8% solution of OIT in DINP. According to the company, it gives good protection to plasticized PVC film and sheeting, extruded profiles, plastisols, moulded goods and fabric coatings, and can also be used in polyurethane foams and shoe soles. The Intercide OBF-8-DINP can be readily incorporated into the formulation at the mixing or compounding stage, and will not affect the processing or heat stability characteristics. Intercide ABF2DIDP-LO consists of a 2% solution of OBPA in DIDP, giving good protection to plasticized PVC against a wide spectrum of fungi and bacteria. The liquid form is particularly advantageous for both paste PVC formulations and for flexible compounds based on suspension grade PVC. Akcros adds that Intercide OBF-20-DINP is suitable for use in products manufactured from both suspension and emulsion PVC. Typical applications include roofing membranes, pool liners, tarpaulins, floor coverings, wall coverings and protective clothing. Intercide DBF-4-DINP is suitable for use in products manufactured from both suspension and emulsion PVC. Typical applications include roofing membranes, pool liners, tarpaulins, floor coverings, wall coverings and protective clothing.

Micro-Chek® antimicrobials from Ferro Corporation are claimed to prevent premature product failure by inhibiting micro-organisms that stain and degrade polymeric materials. Micro-Chek is formulated effectively to provide protection in the most stressful of outdoor environments like roofing membranes, awnings and automotive trim. The company adds that Micro-Chek also provides superior performance in less severe applications such as wall coverings and appliance gasketing.

Specifically, Micro-Chek® 11 antimicrobial is an EPA/PMRA registered, low toxicity industrial mildewcide formulated for the protection of PVC, polyurethane and other polymer compositions susceptible to attack by micro-organisms. Micro-Chek 11 is a 4 % solution of the active ingredient 2-n-octyl-4-isothiazolin-3-one dispersed in an epoxidized soybean oil carrier, and contains no heavy metals.

Thor Group is primarily a manufacturer of biocides based on isothiazolinones, however, the company also produces an extensive range of standard and customized biocides containing other active ingredients such as aldehydes, triazines and quaternary ammonium compounds. Acticide® biocides prevent the biodeterioration of products both in their wet/fluid, dry/cured and intermediate states.

For example, Acticide PDA is DCOIT in polypropylene glycol alkylphenylether and is to protect plasticized PVC sealants and similar products from microbial growth and associated colour changes, while Acticide PDE is DCOIT in epoxidized soya bean oil is a phthalate-free product to protect plasticized PVC. Also for the protection of plasticized PVC are Acticide PDN - DCOIT in diisononyl phthalate –and Acticide PDP, which is DCOIT in diisodecyl phthalate.

Acticide PDR is DCOIT in PVC resin powder – a general purpose PVC resin powder with biostabilizer adsorbed, for ease of incorporation in a wide variety of PVC and similar applications. Acticide® PDS is DCOIT in solvesso, while Acticide PLE is OIT in epoxidized soya bean oil – a phthalate-free product to protect plasticized PVC. Other products include Acticide PLN (OIT in diisononyl phthalate), Acticide PLP (OIT in diisodecyl phthalate) and Acticide PLR (OIT in PVC resin powder).

PolyChem Alloy®, Inc. has developed PolySept® to provide continuous antimicrobial product protection. The company says that PolySept masterbatches typically contain 10-50% of an antimicrobial agent formulated into a plastic resin such as PE, PP, PS, ABS, PA, PBT and PC. Applications for PolySept antimicrobial products include hotel bedding, hospital beds, carpet (including sub-flooring and adhesives), kitchen and bath items susceptible to mould and mildew such as refrigerator and shower door seals, mops, brooms, sponges, and paint and coatings. When incorporated into plastics, PolySept inhibits the growth of bacteria and fungi. The company says that the net result is an aesthetically clean part with no acrid or undesirable smell. Further advantages include meeting GSA requirements, good odour control. The antimicrobial is said to improve air quality in buildings and aircraft, for example. Cosmetic and structural advantages are also claimed.

According to the company, PolySept products are effective against a broad spectrum of bacteria, fungi, mould, mildew and MRSA. For example, PolySept® L, made with phosphate ester complex, will inhibit the growth of both gram positive (+ve), gram negative (-ve) bacteria, fungi, mould, mildew, and even dust mites. PolySept products made with phosphate ester complex conform to EPA registration. Significant features include low water solubility, minimal off-gassing, low toxicity, and antistatic properties. PolyChem Alloy adds that significant characteristics of its antimicrobial compounds are their increased levels of Log kill (~3) and large surface area (particle size in microns), which enhances their effectiveness against a wide variety of harmful micro-organisms, mould and mildew. A key benefit of PolySept is the low toxicity of the active biocide. These products are extremely environmentally friendly, containing no arsenic, no heavy metals, no halogens, no phenolics, no formaldehydes, and no insecticides.

The material attributes of the PolySept product line meet a wide range of processing requirements. PCA’s antimicrobial masterbatches are thermally stable from 190°C up to 400°C, which allows use in higher temperature resin systems, such as nylons, polycarbonates and polyesters. The resulting uniform, pelletized concentrate can be used as an additive masterbatch for a variety of moulding and extrusion processes, simplifying or eliminating many handling and feeding issues associated with liquids or powders. The company adds that the PolySept range is effective against gram positive (+ve), gram negative (-ve) bacteria and fungi. The selection of PolySept L, Z or Ag depends on a specific end-use application. For example, PolySept L is an organic based antimicrobial with a broad spectrum of inhibition that produces a renewed active surface due to migration of the active ingredient. It can be processed up to 190°C, with a suggested active content level of 1.5-3.0%. PolySept L is sold as a 100% active liquid or as a masterbatch in polyolefins. PolySept® Z is an organic salt-based, non-migratory antimicrobial with a broad spectrum of inhibition. It can be processed up to 200°C, with a suggested active content level of 0.2-0.5%. PolySept Z is sold as a 100% active powder or as a masterbatch for polyolefins, PVA and styrenics.

PolySept® Ag is an inorganic-based, non-migratory antimicrobial with a broad spectrum of inhibition. Capable of being processed at up to 500°C, the suggested active content level is 0.5-3.0%. PolySept Ag is sold as a 100% active powder or as a masterbatch for polyolefins, styrenics, and engineering resins. Mechanism of action for PolySept biocides is that they act on microbial membranes to eliminate important ion gradient or gradients. Bacteria use these gradients to store energy, while fungi use them as the source of energy for nutrient transport.

Silver-based antimicrobials

Silver antimicrobial additives are also widely used in plastics. The inert nature and antimicrobial efficiency of silver make it an attractive option for the food processing and medical equipment industries. It is not toxic, flammable or corrosive and will not cause bacteria to become resistant to antibiotics. Silver-based antimicrobials work through an ion exchange mechanism that slowly releases silver ions, which interact with the bonding sites on the microbe surface to prevent bacteria from reproducing.

Ciba Specialty Chemicals offers a number of products for antimicrobial applications. The company has submitted a master file to the Center for Devices and Radiological Health of the US Food and Drug Administration (FDA) for its HyGentic™ 4000 silver-based antimicrobial for medical device applications. The master file can be immediately cross-referenced by marketers and developers of devices containing the novel, silver-based technology to support regulatory approvals. The comprehensive data set contained in the master file includes anticipated device applications, chemistry, and toxicology data along with detailed descriptions of manufacturing, labelling, packaging, and distribution processes and practices and the associated quality controls that are in place. Ciba plans to submit additional master files for related products to the FDA in the future. HyGentic™ 4000, a form of elemental silver with unique physical properties was developed by Bio-Gate AG and is distributed globally by Ciba Specialty Chemicals. It is claimed to be particularly well suited for implanted or inserted medical devices where antimicrobial solutions are increasingly in demand. A similar antimicrobial technology developed by Bio-Gate designed for dental fillings is marketed in Europe.

Ciba® Irgaguard® B 5000/B7000 series is a silver-based, inorganic antimicrobial range that inhibits the growth of micro-organisms such as bacteria, mould, mildew and fungus that can cause deterioration, unpleasant odour and discoloration on the surface of plastic materials and articles intended to come into contact with food.
Ciba also offers HyGate™ for plastics and fibre applications. These are offered in two different product forms: HyGate™ 4000 and HyGate™ 9000 - the latter is particularly recommended for transparent polymers and microfibres.

According to Ciba, HyGate™ is a good choice when the antimicrobial activity is expected to be highly durable. It can be incorporated into many polymers and man-made fibres. It works as an antimicrobial reservoir. In addition, HyGate™ exhibits its antimicrobial efficacy by preventing the colonization of organisms by being available at the surface of the item.

HyGate™4000 is suitable for thermoplastic polymers, such as PA, PET, TPU and PVC. As well as the general advantages of HyGate, it also contributes to cost savings because polymers and fibres maintain their properties for a long time. HyGate 4000 also keeps its activity even when articles are exposed to harsh cleaning procedures or UV-light. HyGate™9000 is recommended for polymers and fibres, particularly when the articles need to remain transparent and when the diameter of fibres is extremely small.

A recent example of silver-based antimicrobial protection is provided by AgION Technologies for the Logitech® Cordless Desktop® MX 3200 Laser, which is a wireless keyboard-and–mouse combination, against a broad spectrum of bacteria a. According to AgION, the silver-based antimicrobial in the Logitech Cordless Desktop MX 3200 Laser is effective in protecting the product against a broad spectrum of bacteria.

“People are spending more and more time at their computers, and are seeking new ways to keep their environments clean,” says Denis Pavillard, Logitech’s vice-president of product marketing for keyboards and desktops. “The Logitech Cordless Desktop MX 3200 Laser is Logitech’s first product to feature AgION® antimicrobial compound, providing protection against the growth of a broad range of bacteria, mould and mildew.”

The AgION antimicrobial incorporated into the Logitech Cordless Desktop MX 3200 Laser is comprised of naturally occurring silver ions. Silver has long been recognized for its antimicrobial properties and humans have used silver for thousands of years to combat a wide range of microbes.

The AgION antimicrobial provides continuous and long-lasting protection from microbes by releasing silver ions to the surface of the keyboard and mouse at a slow and steady rate. This creates a self-cleaning surface that combats existing micro-organisms as well as any new ones that come along. The patented AgION antimicrobial technology is designed to last throughout the life of the products.
“Computer peripherals such as keyboards and mice can be breeding grounds for microbes because they are not cleaned regularly and when they are cleaned, their small parts and crevices make it difficult to be thorough,” says Stuart R. Patterson, chief executive officer of AgION Technologies. “We are thrilled to work with a great innovator in the peripheral space like Logitech to create antimicrobial protected keyboards and mice. The AgION compound built into the Logitech Cordless Desktop MX 3200 Laser provides safe, long-lasting, and effective protection from the micro-organisms that can linger on the surfaces of our homes and offices.”

AgION’s antimicrobial has been proven effective against a broad range of micro-organisms, including bacteria, algae, and fungi such as mould and yeast, yet is safe enough for human and food contact. AgION’s antimicrobial has been approved for food and water contact by the Environmental Protection Agency and is listed as an indirect food contact substance with the Food and Drug Administration.

Sanitized® Silver is a new-type antimicrobial active ingredient with a broad range of action based on silver, a naturally occurring precious metal. With the use of a unique glass ceramic carrier, Sanitized AG says that it has succeeded in virtually doubling the efficiency yield of this product over other silver-based active ingredients while reducing the necessary application amount by one-half.

According to the company, the result is safety, efficiency and high economy. The active ingredient is incorporated directly into the plastic material. The glass ceramic carrier activates the silver ions only when the surrounding conditions are favourable to the growth of microbes and the active ingredient, based on natural silver, is resistant even at high temperatures of over 350°C. In addition, the transparent glass ceramic carrier has minimal or no effect on the optical properties of clear plastics, unlike other known active ingredients also based on silver. The company adds that Sanitized Silver is exceptionally non-discolouring, and even in direct contact with foods, such as cheese, it causes no discolorations whatsoever. Sanitized Silver is approved by the US FDA.

UK company AddMaster has developed Biomaster that can be supplied as masterbatches, compounds or powder dispersions. The company says that the high concentration of silver in the antimicrobial active agent in Biomaster provides a release of silver ions on demand, which in turn safely inhibits microbial growth. The products are said to exhibit excellent temperature stability (up to 600˚C) and are therefore suitable for incorporation into all thermoplastic and thermoset resin systems with no detrimental effects on the physical properties. Products are available for clear and opaque applications.

The company says that Biomaster antibacterial additives are suitable for use in a wide range of processes such as injection moulding, profile and tube extrusion, synthetic fibres, blow moulding, blown films, extruded films and sheets, calendaring and rotational moulding. Biomaster products contain typically ten times more silver than other silver biocides, and consequently they only need to be used at very low concentrations. According to AddMaster, it has been demonstrated that plastic products incorporating Biomaster at very low addition levels actively inhibit bacterial growth and show a 99.99% reduction within 24 hours. The controlled release of the silver active ingredient provides maximum long term activity. Biomaster additives are powerful broad-spectrum, inorganic, silver-based biocides for use in the preparation of antibacterial plastics. AddMaster says that the Biomaster range has been successfully tested against over 50 common organisms such as MRSA, E.coli, Salmonella, Listeria, Pseudomonas and Aspergillus Niger.

Applications include medical devices, moulded hospital equipment and healthcare furnishings, as well as soap and tissue dispensers, toilet seats and door handles. Biomaster is also suitable for electronic handsets, water filter housings and pharmaceutical packaging.

Milliken Chemical has invested in a new European Microbiology Laboratory, to expand its technical service offering to customers. The company says that this is a result of continued growth and market acceptance for the Alphasan® silver inorganic antimicrobial technology. Located at Milliken’s Technical Centre in Gent, Belgium, the company says that its European customers can now take advantage of faster, more efficient microbiology support.

The Milliken Europe Microbiology Laboratory will provide in-house material and finished part testing facilities to customers active in the plastics, rubber and textile sectors, from compounders and masterbatch producers to OEMs, says the company. Traditionally, European testing activities have been outsourced, with internal support only available to customers using the Microbiology Laboratory at Milliken’s headquarters in South Carolina, USA.

Operating in combination with existing plastics processing and textile facilities and regulatory consultation services, Milliken says that the new microbiology laboratory completes its in-house support infrastructure for those European customers interested in antimicrobial features.

The facility offers standard microbiology equipment such as inoculation and colony counting facilities, sterilization autoclaves, safety cabinets, incubators and microscopy services. In addition to customer test facilities, the laboratory will support research and development activity relating to Milliken’s Alphasan silver inorganic antimicrobial technology.

AlphaSan antimicrobial additive is a zirconium phosphate-based ceramic ion-exchange resin containing silver. According to Milliken, high temperature stability and low colour formation make AlphaSan suited to provide antimicrobial performance in a wide variety of applications including plastics. Silver is well known as being safe for human contact and effective against a broad spectrum of micro-organisms that cause odour, discoloration, biofouling and other aesthetic problems. These antimicrobial properties can bring additional value through product differentiation to a variety of applications. AlphaSan can be added to approved materials at varying levels to impart bacteriostatic, fungistatic, and algistatic properties to the material and the end-use article.

Contacts:
AddMaster
E-mail: info@addmaster.co.uk
Website: www.addmaster.co.uk
AgION Technologies
Website: www.agion-tech.com
Akcros Chemicals
Website: www.akcros.com
Ciba Specialty Chemicals
Website: www.cibasc.com
Ferro Corporation
Website: www.ferro.com
Milliken Chemical
E-mail: Veerle.Dewolf@milliken.com
PolyChem Alloy
Website: www.polychemalloy.com
Sanitized AG
Website: www.sanitized.com
Thor Group
Website: www.thor.com
Troy Corporation
Website: www.micropel.com