Biocides keep the bugs off your plastics.

Biocides have long been used to protect PVC and PUR foams from attack by microorganisms. Now, biocides are also a growing presence in polyolefins and other plastics, thanks to consumer demand for "germ-free" products.

Use of biocides or antimicrobial additives in plastics traditionally has been limited chiefly to flexible PVC and to polyurethane foams, as they are the most susceptible to attack by fungi, bacteria, and algae that can cause discoloration, odor, and deterioration of mechanical properties. Plasticizers are a key food source for these microorganisms in PVC.

Popular applications for biocides in these two plastics include roof liners, tarpaulins, wall and floor coverings, pool and ditch liners, shower curtains, bath mats, outdoor furniture, marine upholstery, insulation foams, and sports-shoe soles.

In more recent years, increasing public concern about food-borne pathogens and other germs in the environment has been driving consumer demand for antimicrobials in products made of polyolefins and other plastics ranging from housewares such as cutting boards to children's toys. The purpose in these cases is not to protect the plastic from deterioration, but to give the product a perceived benefit from being "germ-resistant."

This consumer-driven demand is expected to continue to grow at a strong pace. However, these newer "value-added" uses of antimicrobials present potential problems as well as opportunities for processors by drawing heat from environmental regulators.

EPA CRACKS DOWN ON CLAIMS

Within the last year, the U.S. Environmental Protection Agency has taken enforcement actions against at least two companies related to their use of antimicrobials in plastics. EPA has jurisdiction over consumer products when they are marketed with claims that they kill germs on inanimate surfaces (see below).

One case involved toymaker Hasbro in Pawtucket, R.I., which was fined $120,000 last year for going too far with antibacterial claims about some of its Playskool-brand products. EPA found that the toys' labels and advertisements suggested that incorporation of the antimicrobial additive would protect children from health risks, when in fact it protects only the plastic in toys.

In December, EPA issued a similar civil administrative complaint against biocide additive supplier Microban Products Co., seeking $160,500 in penalties. The case is not resolved, but EPA's concern is that germ-killing claims on consumer products could lead some people to forego standard hygiene precautions that prevent transmission of harmful germs.

A recent article by Lawrence Culleen, former acting director of EPA's Pesticides Registration Div. and now an attorney in the Washington offices of the law firm Arnold & Porter, provides some insight for makers of products treated with an antimicrobial. The article explains that EPA has jurisdiction over such products under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA-7 USC Sections 136-136y). The Act authorizes EPA to regulate the distribution and sale of "pesticides," which are defined in the Act as including antimicrobial agents used on surfaces such as home countertops and in bathrooms. EPA's authority extends to claims made on labels of such products.

EPA can exempt certain products from its product registration requirements if they contain a registered pesticide for the purpose of protecting the products themselves. These are called treated articles. Culleen advises makers of articles treated with biocides to be very wary when making antimicrobial claims if they wish to take advantage of the "treated-articles exemption." At a minimum, make certain that the pesticide (antimicrobial) used is registered with the EPA and that its label specifically authorizes its use as a treatment for the product (e.g., "for use as a preservative in plastics"). Also, make sure that the label on the treated article does not bear claims that the product controls germs outside of the product itself.

EPA is currently overhauling its registration requirements for antimicrobial products. Proposed changes include amendments to the treated-articles exemption that could give EPA discretion to permit a broader variety of label claims by marketers of such products. [For more information, see "The War on Germs (and Germ-Fighting Products) Heats Up" in the Nov. 21, 1997 issue of the newsletter Analysis & Perspective, published by the Bureau of National Affairs, Inc., Washington, D.C.]

TRENDS IN BIOCIDE USE

Most suppliers of biocides for plastics purchase the active ingredients from chemical producers and then blend them at different concentrations with plasticizers, solvents, or resins. OBPA (oxybisphenoxarsine) is the most widely used active ingredient. It is made by Akzo Nobel in Brazil and formulated into biocide products by Morton International Corp. and Akcros Chemicals. Although newer biocide products tend to be based on other active ingredients (see box), many formulators of biocides still regard OBPA as the most effective overall. "It's hard to beat, both in terms of lower cost and of being the best performer," says Bob Guarino, marketing manager for the leading biocide supplier, Morton International. Although Morton makes biocides based on other active ingredients, Guarino says OBPA has the broadest spectrum of activity against both fungi and bacteria, whereas other chemicals are more effective against one or the other.

OBPA is facing growing competition from biocides that do not contain arsenic. Although OBPA is EPA-registered for biocide use, Guarino concedes that it suffers from the perception that all arsenic is toxic. "Organic arsenic is much less toxic than the more publicly familiar inorganic arsenic," he points out. While new applications are being explored for use of OBPA in a wider range of plastics, suppliers do not believe it has a chance at the food-contact plastics applications that may emerge for biocides.

An up-and-coming competitor for OBPA is triclosan (trichlorophenoxy phenol), a non-metal-containing organic active ingredient that is made by Ciba Specialty Chemicals. It has gotten EPA and FDA approval for commercial use in antibacterial soaps, face creams, shampoos, and more recently toothpaste.

Although triclosan is not new, it is appearing in biocides from a growing range of suppliers - now including Morton International. Ferro also is considering triclosan as a basis for new products.

Sanitized, Inc., an affiliate of Clariant Corp., was the first to register a triclosan-based product for plastics with EPA in 1973. The company pioneered its use in coated fabrics for home furnishings and geomembranes. Company president Stewart Klein says some of the most promising new applications for its Sanitized PLA are molded polyolefin household items such as garbage bins and pails.

Microban Products has supplied triclosan-based biocides for fibers and plastics since 1983. The company's Microban B product has recently found applications in extruded polyethylene sheet for surgical drapes and in molded PP, silicone, or PUR catheters. Company president Glenn Cueman says the newest and fastest-growing markets are textiles and molded consumer products such as toys, cutting boards, kitchen tools, cutlery, and toothbrush handles. Cueman says the firm has compounded Microban products for use in all of the polyolefins as well as ABS, PS, HIPS, nylon 6, SBR, and some specialty vinyls.

Triclosan is also now being used in thermosets. Microban recently licensed Neste Polyester Inc. to use its additive in a new gelcoat aimed at FRP bathtubs, sinks, countertops, boat hulls, and food containers (see PT, Jan. '98, p. 18).

Triclosan, like all organic biocide active ingredients, has some limitations on thermal stability. These ingredients generally start to decompose at temperatures well below 500 F. However, Luie Vizurraga, president of Allied Resinous Products, says his company has developed compounding technology that increases the heat stability of triclosan up to 530 F. Allied uses triclosan in its own houseware products such as cutting boards and can produce compounds for other processors' use.

Proper mixing is also a must with organic biocides. Says Microban's Cueman, "If not effectively compounded, it will leach out of the product. The way it is encapsulated in the polymer, and ensuring it does not crosslink, are keys to its efficacy."

Some newer inorganic biocides are designed to address both these limitations of organic types. Product manager Robin Kump says DuPont developed its new MicroFree line for engineering thermoplastics because it saw a need for greater heat stability and permanence than were obtained with most organic biocides (PT, Nov. '97, p. 9).

IS FOOD PACKAGING NEXT?

Some additive makers think it's not a question of whether biocides will penetrate food-packaging applications, but how soon. Although OBPA is not considered a candidate here, organic, nonmetal-based biocides like triclosan reportedly have a fighting chance.

In the U.K., through Microban's partnership with Sainsbury Supermarkets, Microban B is already used in polyolefin deli wrap and reheatable food containers. Other items in which it is being incorporated include food-preparation surfaces and food-handling equipment for meat, bakery, and delicatessen counters.

But in the U.S., biocide suppliers are still cautious. Microban's Cueman says there is a lot of interest in plastics biocides from the food-packaging sector, but it is virtually impossible to predict the regulatory outcome. He notes there is overlapping responsibility between EPA and FDA in this arena, which is confusing for manufacturers. "In all likelihood we will be dealing more with FDA in the future. We have customers who have food additive petitions already submitted to the FDA."

Adds Morton's Guarino, "We see potential for areas such as food packaging and food preparation, but FDA approval for food contact would be required. This is something our individual customers would have to seek. We are not pursuing it."

Some suppliers are screening other potential biocides for food packaging that are already FDA registered. Some of these reportedly may prove more cost-effective than triclosan-based additives, which cost up to 10% more than traditional organic/heavy-metal biocides and require higher use levels, too.

RELATED ARTICLE: New Developments in Antimicrobials

Here are the most recent entries in biocides for plastics, as well as new applications for some existing products:

* Intercide ZnP from Akcros is based on zinc pyrithione (an active ingredient made by Olin Corp.) and is supplied in 5% concentrations in various plasticizers. Initial target is flexible PVC. Akcros is working on applications for ZnP and OBPA-based biocides in PUR foams, polyolefins, and PS consumer products.

* Bayer Corp. has just registered with EPA a new organic azole-based fungicide and mildewcide. Tebuconazole is the active ingredient in Preventol A8, which is said to be thermally stable to over 450 F and will be geared to flexible PVC and flexible PUR foams.

* Calgon Corp. supplies Metasol TK-100, a thiabendizole-based mildewcide and fungicide (not bactericide) to masterbatch compounders in Japan for use in PP and PE applications such as air-conditioning ducts. The company is now looking to enter the North American plastics market for a variety of polyolefin and other uses. The product is said to be thermally stable to 572 F.

* DuPont Specialty Chemicals recently entered the biocide field with two MicroFree inorganic antimicrobials. One grade is 98% zinc oxide with a small amount of silver and other inorganics. The other is 98% Ti[O.sub.2] with small amounts of silver, zinc, and copper. Both are off-white powders. They are effective in PP, PE, PET, PBT, ABS, and nylons 6 and 66, says product manager Robin Kump. He says these products are both heat stable and resistant to migration. Potential applications include household articles, appliance components, computer keyboards, phone sets, gymnastic equipment, and fibers for bath mats or carpeting.

* Two new triclosan-based antimicrobials come from Morton International. Morton SB-30 is a polymer concentrate for use in polyolefin applications ranging from solid-waste bags and pails to cutting boards and toys. Polystyrene is another potential application area. Morton 7040 is a liquid version in plasticizer for use in PVC institutional/medical applications.

Morton also has two new isothiazolone-based biocide concentrates - Vinyzene IT-4000 (4% active) and IT-4010 (10% active). They are said to offer long-term protection in flexible PVC and PUR foams. (Isothiazolone is also the active ingredient in biocides from Ferro Corp.)

* Olin Corp. has been selling its Omacide, based on zinc pyrithione (an active ingredient Olin produces), for use in flexible PVC but is currently exploring uses in some niche specialty polyolefin areas.

* A new liquid version of Troysan Polyphase carbamate-based organic biocide is available from Troy Corp. It is said to offer improved thermal stability and is being aimed at PVC refrigerator gaskets and air-conditioning ducts, as well as PUR insulation foams.