Advances in antimicrobial additive technology

Originally employed as biostabilizers to preserve plastic articles and extend shelf-life, the use of antimicrobials as active ingredients to provide additional benefits to the user have dramatically increased in recent years. When antimicrobials are used as active ingredients in plastics, they provide the ability of plastic products to maintain surfaces in a sanitary/hygienic state and/or to provide additional protection, such as against odor development.
Antimicrobials are used in plastics for two major purposes, as a biostabilizer (i.e. preservative) and as an antimicrobial active agent. The main difference between the two groups is in the necessary antimicrobial activity profile. Antimicrobial biostabilizers (biocides) or preservatives are added to plastics to protect the material by acting against microorganisms such as bacteria, fungi and algae that can attack the plastic, resulting in unwanted changes in chemical or physical properties, or in the appearance of the plastic product. The risk of microbial growth and subsequent damage to plastic materials is particularly prevalent in wet or damp environments (e.g. bathrooms, kitchens) and for outdoor applications (e.g. pond liners, greenhouses, awnings). Bio deterioration of plastics by microorganisms can occur by three different modes of action:
* Direct degradation by microorganisms using plastic ingredients as a nutrient source
* Indirect degradation or change in appearance via microbial metabolites (e.g., acids, enzymes, pigments)
* Surface effect by settlement of microorganisms on the plastic without degradation
Plastics are often initially attacked by fungi which cause the greatest degradation, though bacteria can also feed on additives in plastics. Once biodegradation of additives such as plasticizers is started and converted to smaller organic compounds, other microorganisms can gain access, resulting in increased bio deterioration. Bio deterioration often results in reduced durability and life-span of the plastic products. The main effects caused by microbial activities are:
* Staining: From intracellular pigments (e.g. a pink-stain caused by pigmented molds such as penicillium) or extracellular dyestuffs (microorganism release of colored metabolites such as white and black discoloration through production of ferric sulfide, FeS ).
* Change in Electrical Properties: Electrical properties, especially insulation can change as a result of microbial attack. This can occur through the settlement of microbes on the plastic surface, without deterioration of the material. The deterioration of electrical properties can also be exacerbated if the microbes produce polymeric materials such as exo-polysaccharides.
* Deterioration of Mechanical Properties: Metabolization of the plasticizers by bacteria and/or fungi may cause brittleness, shrinkage, and eventually loss of tensile strength and integrity. The breakdown of plasticizers into smaller molecules also enables microorganisms that are not capable of metabolizing the intact plasticizer to grow.
*Enhanced Dirt Uptake: Colonization of the surface by microorganisms can cause increased roughness allowing dirt to accumulate more readily. This often is the result of surface changes caused by plasticizer degradation.
* Permeability of Solvents and Gases: Deterioration of the plastic's mechanical properties can also result in increased permeability of solvents and gases
* Odor: Unpleasant odors can form from the production of amines, ammonia, or hydrogen sulfide as a result of microbial metabolism.
8 PVC: Additives commonly used in plastics such as plasticizers, starch fillers, thickeners, lubricants, and oils are particularly vulnerable to microbial growth. The plasticizer in plasticized PVC is particularly vulnerable to fungi, which use the plasticizer and other ingredients as a carbon source, producing discoloration, bad odor, tackiness and ultimately embitterment.
* Polyurethanes (PUR): Blown PURs are particularly susceptible to microbial attack as their open cell structure contributes to the deposition of soil, dust, and fungal/bacterial spores promoting microbial growth on the PUR surfaces. PUR based on esters are more susceptible to microbial deterioration than are polyether polyurethanes.
* PE: PE is generally less susceptible to microbial deterioration than plasticized PVC and polyurethanes. The risk for microbial attack is higher in low molecular weight PE (<10,000) and polymers with relatively little branching.
* Polyesters: Polyesters, usually resistant to microbial degradation, can be susceptible in special cases, such as polyesters from e-caprolactone.

Microbial degradation can be thwarted by incorporating an antimicrobial additive during processing. Biocides (antimicrobial biostabilizers) interfere with the metabolism of micro-organisms by blocking one or more of the enzyme systems. However, to be effective, most additives must migrate to the surface of the plastic, a process that is influenced both by its chemistry and compatibility with the matrix polymer. 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/easy handling. The proliferation of microorganisms that are resistant to pharmaceutical therapy is of increasing concern to those responsible for patient care in hospitals and elsewhere and is one factor contributing to the growing use of antimicrobial active agents. Beyond reducing infection risk in hospitals, antimicrobial-containing plastics with activity on the surface can improve hygiene in institutional/industrial areas. Allergic reactions to spores of molds that can proliferate in the ideal environment provided by PUR foams in cushions and mattresses, have also gained attention. The trend to use antimicrobial active agents in plastic products to maintain surfaces in a sanitary/hygienic state has thus moved into other settings including homes and offices, resulting in antimicrobial- treated garbage bins, kitchen utensils, bathtubs, sinks, air filters, mattresses, etc. Because antimicrobial active ingredients are incorporated into plastic articles in the same way as biostabilizers many requirements are the same, though antimicrobials used for plastics in contact with food have additional special requirements. Antimicrobial substances are regulated as an indirect food additive in many countries (e.g., FDA registration in USA; EC registration in Europe). The basic requirements for antimicrobials used as either biostabilizers or active ingredients are:
•	Low toxicity to humans, animals, and the environment (during manufacture and under conditions of use)
•	Easy application
•	Compatibility with processing aids, other additives
•	No negative impact on properties or appearance of the plastic article, its storage stability, or useful life
The growing concern over bacterial contamination has led to various new emerging plastic technology developments. The fast growing wood-plastic composites market (WPC) is also a high growth area for microbial biostabilizers. Two vinyzene DCOIT (Dichlorooctylisothiazolinone) based formulations (solid, high concentration liquid) from Rohm and Haas Co. are designed to protect against surface damage from fungi in WPCs. TEK Deck Pro, the first biocide-containing color masterbatch for WPC decks and other building applications was recently launched by Teknor Apex to enable manufacturers to enhance the appearance/longevity of their products while saving additive costs. The masterbatch incorporates Vinyzene biocide with color and UV absorber into one additive package. The biocide advances WPC deck aesthetics by controlling/eliminating fungal growth that otherwise stain and makes deck cleaning difficult. Biosafe Inc.'s new polymeric solid antimicrobial Biosafe HM-4100 is a nontoxic, environmentally sustainable silane-based cationic quarternary ammonium salt not previously used in plastics as its liquid form made it difficult to incorporate. The crystalline powder based on patented polymer technology is suitable for a wide range of thermoplastics. HM-4100 protects plastic products from staining/damage caused by bacteria, mildew, and fungi. It is thermally stable in injection molding and extrusion, will not discolor, or migrate out of the plastic and can be used with optically clear resins without compromising their optical properties. The antimicrobial functions by puncturing and rupturing cell walls, eliminating the possibility to mutate and become resistant to the antimicrobial. Biosafe Inc. has partnered with compounder RTP Co. to make the antimicrobial available in masterbatch form. Biosafe's chemistry is listed by FDA as a modifier for medical devices. Ticona's new Anti-Crobe Antimicrobial Polymers is a family of antimicrobial acetal copolymers for injection molding and extrusion manufacture. The line targets high performance polymer applications where nutrients in warm, moisture environments promote bacterial and fungal growth. Evaluation of two Anti-Crobe acetals against Japan's JIS Z 2801 standard for microbe proliferation, demonstrate that they significantly inhibit microbial growth relative to traditional acetal. The antimicrobial polymers meet FDA direct food contact regulations, the NSF 61 Potable Water standard and pertinent EPA regulations. Earlier this year, Bayer MaterialScience launched two developmental grades of polycarbonate (PC) DP1-1868 and DP1-1869, with antimicrobial properties for medical devices. Bayer is using an inorganic silver nanoadditive to control growth of bacteria on the surface of medical devices. The nanoparticles' high surface area makes the silver additive highly efficient. The company says the additive can potentially control the generation of Gram-positive (bacillus, listeria, staphylococcus) and Gram-negative (e-coli, salmonella) bacteria. Stain testing shows that bacteria on untreated PC grow unabated, while bacteria growth on the antimicrobial PC is virtually nonexistent. Potential applications are IV and urological systems, and housings for diagnostic/hospital equipment. AgION Technologies Inc. entered into an exclusive partnership with BASF to develop and commercialize styrene copolymers featuring Agion antimicrobial technology. The AgION patented technology provides life-time protection from microbial growth on product surfaces by releasing silver ions to the surface at a slow, fixed rate. AgION achieves this controlled release by binding silver ions with zeolite, an inert powder that can be incorporated into materials during production or used as a coating. The silver is released by moisture contacting the treated surface. The technology is approved for food and water contact by both the EPA (U.S. Environmental Protection Agency) and the EFSA (European Food Safety Association). New StatSil elastomer developed by Momentive Performance Materials provides antimicrobial protection using patent pending technology to incorporate a silver-based antimicrobial additive into the base silicone elastomer. The StatSil elastomer was developed in response to growing medical industry concerns over bacterial contamination on critical device surfaces. The material allows product designers to incorporate anti-microbial protection directly into medical devices such as catheters and wound drains to control microbes in or on the human body.
	Antimicrobial Suppliers Company Tradename AgION Technologies LLC Agion Akros Chemicals Intercide Arch Chemicals Omadine; Vanquish Bayer MaterialScience Makrolon Antimicrobial BASF Antimicrobial Styrene Biosafe, Inc. Biosafe Ciba Specialty Chemicals Irgaguard Ferro Corporation Micro-Chek International Specialty Products (ISP) PlastiGuard Lanxess Metasol; Preventol Microban International Ltd. Microban Milliken Chemical Alphasan Momentive Performance Materials StatSil Elastomer Polychem Alloy Inc. Polysept Rohm & Haas Vinyzene Teknor Apex TEK Deck Pro Thor Group Ltd Acticide Troy Corporation Micropel
	(Source : SpecialChem)