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What's New in Biocides?

Introduction
Bacteria, fungi and algae can affect the aesthetic and physical properties of a plastic or a rubber by causing black spotting or discoloration, pink staining, odour and polymer degradation, fouling etc. Biocides used to fight these microorganisms have two main roles:
-To stop bacteria or fungi degrading the polymer physical and sensorial properties, reduce microbe populations both within the material and at the surface. The growth of microorganisms can lead to unpleasant odours, surface and bulk degradations. Reducing odours is a goal for applications such as clothing, shoes, waste containers etc.
- To prevent the build-up of harmful bacteria increasing the risk of contamination and transmission of infections for humans. Biocides act as a complementary technique for cleaning, which is also simplified and less costly. After 'Research and Markets' the market for biocides in plastics had soared to $145m (€113m) in 2005 that is to say a significant rise of 40% since 1995. Traditional biocides are being replaced by more environment-friendly biocides also more expensive. For example, European sales of biocidal additives for the plastics and resins market are expected to grow by 5% over the next five years, with:

-Silver-based actives growing by 10% annually after 'Kline & Company'.
- Non-arsenic based formulations rising at 10-20% per year. The following figure 'Biocide-Use-and-Constraints' schematizes the constraints and reasons to use biocides.
Biocide-Use-and-Constraints Most demanding sectors are food processing plants, hospitals, care homes offering an ideal environment for microbes, and the incorporation of biocides in plastics and rubbers helping reduce time and money consuming cleaning.
The rich panel of active biocides and their combinations allow their use in all the polymers such as, for example emulsions, solutions, dispersions, latices, solid polymers processed by injection moulding, dip moulding, blow moulding, rotational moulding, profile and tube extrusion, film, blown films, extruded films, sheets, calendering, fibre spinning, gel-coats and powder coatings, WPC, adhesives, low-VOC water-based paints and coatings... After PVC, the biocides now concern all the commodities and other polymers such as, for example, ultra high molecular weight polyethylene (UHMWPE), high density polyethylene (HDPE), polypropylene (PP), PTFE, polyurethane, polystyrene (PS), Nylons (PA), polycarbonate (PC), polyesters (PET and PBT). ABS, rubbers, thermoset resins...

What are Biocides?
Commercial biocides are composed, necessarily of one or several active chemical(s), and possibly a liquid, pasty or solid carrier, leading to a solution, dispersion or masterbatch. Biocides must achieve a tricky balance of:

- Bio-activity (of course) versus bacteria, fungi, algae
- Controlled compatibility with the polymer host leading to suitable migration and leachability
- Suitable thermal stability allowing to withstand processing and service life
- Non damaging effects on the polymer end-properties: sensorial, mechanical, ageing, failure behaviour, light and heat stability
- Human safety: absence of toxic, allergenic and irritating reactions of the skin
- Environment safety
- Cost effectiveness
- If relevant, US FDA, US EPA, Eu-BPD, REACH, US FIFRA (Federal Insecticide, Fungicide and Rodenticide Act), NSF (US National Science Foundation) etc. registered, notified and/or compliant. The liquid carriers include plasticizers such as phthalates (DIDP, di-heptyl nonyl undecyl etc.), epoxidized soybean oil (ESBO) and epoxidized ester (Lankroflex ED6); and water or chemicals such as glycolic solutions (dipropylene glycol...), alkaline solutions...
Active bases are very diversified from organic to mineral species, for example:

- Arsenic derivatives
- Oxybisphenoxyarsine (OBPA) is the most used (about 70% of the total)
- Calcium orthoarsenate
-Metal derivatives
-Zirconium phosphate-based ceramic ion-exchange resin containing silver.
- Zinc Pyrithione (AlphaSan)
- Titanium Dioxide Nanoparticles
- Zinc pyrithione and N-Butyl-1,2-benzisothiazolin-3-one
- Magnesium metaborate
- Copper sulphate
-Halogen and aromatic derivatives
-Triclosan (2,2,4-dicholoro-2-hydroxydiphenyl ether)
- 2,4,4'-trichloro-2'-hydroxy diphenyl ether
- trichlorophenoxy phenol TCPP
- Ortho benzyl para chloro phenol (Chlorophen)
- Di chloro meta xylenoI (DCMX)
- Ortho phenyl phenate (OPP)
- Para chloro meta cresol(PCMC)
- Para chIoro meta xylenol (PCMX)
- Chlorinated xylenols
- 2,2-MethyIene-bis (4 chlorophenol) {Dichlorophen}
- Sodium salt of Ortho phenyl phenate (SOPP)
-Other halogenated compounds
-N-Haloalkylthio Compounds
- Iodo-Propylbutyl Carbamate (IPBC)
-Sulphur derivatives
-Octyl-4-isothiazolin-3-one (OIT).
- DCOIT dichloro-octyl isothiazolone
- N-(trichloromethyl-thio)phthalamide (Folpet)
- Thiazole derivatives
-Thiazines, thiazolinones
-Bethoxazin (3-Benzo(b)thien-2-yl-5,6-dihydro-1,4,2-oxathiazine 4-oxide)
- Isothiazolinones
- Benzisothiazolinone
- Butyl-benzisothiazolinone (butyl-BIT)
- chlor-methyl and methyl-isothiazolinones
- Copper stabilised chlor-methyl and methyl-isothiazolinones
-Nitrogen derivatives
-1,3,5-Triethylhexahydro-1,3,5-triazine
- Hexahydro-1,3,5-tris (hydroxyethyl)-s-triazine
- 1,3,5-Triethylhexahydro-1,3,5-triazine
- Furazoline
- Furazolidone
- Bromonitropropanediol
- Cetylpyridinium chloride
-Miscellaneous
-Quaternary ammonium compounds
- Carbendazim (N-benzimidazol-2-ylcarbamic acid methylester)
- Bronopol
- Carbendazim
- Carboxylic acids
- Benzoic acid and salts
- Tetrahydro-3,5-dimethyl-1,3,5-thiadiazine-2-thione (Dazomet)
- N-3,4-dichlorophenyl-N,N-dimethyl urea (Diuron)
- 1,6-dihydroxy-2,5-dioxahexane
- 3-Iodo-2-propynyl butyl carbamate
- Methylene-bis-morpholine
- pyrithione
- 2-(Thiocyanomethylthio) benzothiazole
- Tetramethyldithiooxamide
-Mixtures
-Chlor-methyl isothiazolinones, 1,6-Dihydroxy-2.5-dioxahexane and n-Octyl isothiazolinone
- Chlor-methyl isothiazolinones, 1,6-Dihydroxy-2.5-dioxahexane and n-Octyl isothiazolinone and bronopol
- Isothiazolinone and bromonitropropanediol
- 1,6-dihydroxy-2,5-dioxahexane, sodium pyrithione and surfactants
- N-(trichloromethyl-thio)phthalamide (Folpet) and isothiazolin
- Isothiazolinones and other species such as aldehydes, triazines or quaternary ammonium compounds
- Chlor-methyl and methyl-isothiazolinones and 1,6-dihydroxy-2,5-dioxahexane
- 1,6-dihydroxy-2,5-dioxahexane and chlor-methyl and methyl-isothiazolinones
- 1,6-dihydroxy-2,5-dioxahexane and isothiazolinones
- Sodium salt stabilised aqueous solution of chlor-methyl and methyl-isothiazolinones
- Stabilised 1.5% metal-salts free active solution of chlor-methyl and methyl-isothiazolinones
- Stabilised 3.0% active solution of chlor-methyl and methyl-isothiazolinones
- Benzisothiazolinone, chlor-methyl and methyl-isothiazolinones and dibromo-dicyanobutane
- Isothiazolinone and bromonitropropanediol
- Hexahydro- 1 3,5-tris (hydroxyethyl)-s-triazine and sodium pyridine thiol-1-oxide
- Hexahydro- 1 3,5-tris (hydroxyethyl)-s-triazine and sodium pyridine thiol-1-oxide plus EDTA
- Bronopol and chlor-methyl and methyl-isothiazolinones
- Benzisothiazolinone and chlor-methyl and methyl-isothiazolinones
- Benzisothiazolinone and chlor-methyl and methyl-isothiazolinones
- benzimidazole carbamate and n-Octyl isothiazolinone
- 3-Iodo-2-propynyl butyl carbamate, n-OctyI isothiazolinone and N-3,4-dichlorophenyl- N,N-dimethyl urea
- Benzisothiazolinone and Para chloro meta cresol (PCMC) solution
- Alkaline solution of Benzisothiazolinone and hexahydrotriazine
- Chlor-methyl and methyl-isothiazolinones and bronopol
- Benzisothiazolinone and Ortho phenyl phenate solution
- Sustainable Antimicrobial Polymers (Degussa)
- Certain biocides can be members of several families, for example sulphur and nitrogen derivatives, halogen and sulphur derivatives etc. Regulations and trends
Biocides are subjected to numerous regulations varying according to the countries, for example:

- European REACH (Registration Evaluation Authorisation and Restriction of CHemicals)
-European Biocide Product Directive (BPD)
-US Federal Insecticide, Fungicide and Rodenticide Act (FIFRA)
-US Food and Drug Administration (FDA)
-Environmental Protection Agency (EPA) (for food use)
-Pest Management Regulatory Agency (PMRA)
-American National Standards Institute (ANSI)
-US National Science Foundation (NSF).
-ANSI/NSF Standard 51 New ways for old issues
The main technical problems are related to the persistence of the anti-microbial effect by using persistent additives such as silver or nano-sized mineral derivatives, organic oligomers, grafted polymers.
Application of silver derivatives into rubber goods Effective biocides based on silver ion-exchange resins are deactivated by reaction of silver ions with the sulphur or sulphur-based accelerators. To avoid this drawback G.R. HAAS and ALL (ACS Rubber Division, October 2001, paper 28) study the behaviour of two silver ion-exchange resins (Ag1 and Ag2) in EPDM cured with peroxides. After exposure up to 30 days at Aspergillus Niger (AN) or a mixture (Mixt) of fungi, the growth varies from traces (rating 0) for the compounds containing silver up to more than 60% (rating 4) for the controls without biocide.

Antifungal-Actinity Nano-sized Titanium dioxide Nano-sized titanium dioxide leads to photo-catalytic reactions preventing the build-up of harmful bacteria and killing existing microorganisms on the surface of polymer parts and goods. Titanium dioxide, mineral and chemically stable, does not deteriorate and it shows a long-term anti-bacterial effect. Nano-sized particles are particularly active justifying their use in coatings.
Self-spreading ionic silicone oligomers R.R. PANT and ALL (J. of Applied Polymer Science, 104, 2007, p. 2954) study ionic silicone oligomers functionalized with alkylammonium chloride groups assuming two functions:

-A more persistent anti-microbial effect thanks to a higher molecular weight
-A self-spreading behaviour and a good wetting of a variety of materials allowing to penetrate inaccessible locations For example, after 1 minute, the diameter of a drop laid on a given surface is about 4 times bigger than that of a low-viscosity oil and the growth of Staphylococcus Aureus is divided by several times after some days.
Functionalized polymers O. IGUERB (thesis, Louvain Univ., 2006) photo-graft an acrylate layer on oxidized polyethylene films to obtain an antibacterial effect. The antibacterial activity could be improved by using poly(4-vinylbenzyl chloride) (PVBC) incorporated into poly(n-butyl acryloyloxy ethyl urethane) matrix. Another possibility to obtain antibacterial materials could be the grafting of acrylate monomers containing both acrylic groups and hydrophilic positively charged tertiary amine groups.
Nano-sized silver compounds Nanoco Cy has developed a new biocide called NanoSilver that increases the bactericidal properties of silver thanks to the much larger active surface of nanoparticles. Many food products can have longer use-by dates if they are stored in packaging containing NanoSilver. For example, lettuce stays fresh up to four weeks if wrapped in NanoSilver foil, just like meat, bakery and confectionery goods. In restaurants, biocidal plastic can be used for work surfaces, chopping boards, disposable packaging and dishes. NanoSilver opens up also opportunities for the clothing industry. Garments made with NanoSilver modified fibres can prevent the development of bacteria and the resulting odours.

Applications: Hazardous media, intensive service, consumer goods, marine media
Biocide applications are well growing when the media is particularly favourable to micro-organism proliferation such as food processing plants or hospitals, consumer goods such as clothing or phones, etc.

- Food processing devices: conveyor rollers, ice-making machines, chopping boards, kitchen wear
- Hospitals: implants such as catheters, and external devices such as short-term use stethoscope diaphragms, medical gloves, floor and wall coverings, switches, toilet seats and door handles, waste bags and refuse containers, healthcare furnishings, soap and tissue dispensers, electronic handsets, water filter housings, pharmaceutical packaging...
- Fibres: hosiery, carpets, clothing, bedding and upholstery, workwear, sportswear, shoes, boots
- Home furniture Shower and bathroom equipment, sinks, tubs, shower-curtains, vanity tops, children's chairs, mattress pads, countertops, bed linens, smooth floors, table cloths
- Garden furniture.
- Films for waste bags, mattress covers, packaging
-Aquatic media: PVC pool and pond-liners, tarpaulins and marine upholstery, antifouling coatings for waterborne craft
- Adhesives & Sealants A broad choice of suppliers and grades
Table 1 shows some examples without claiming to be exhaustive. Suppliers Trade names AddMaster BioMaster AgIon Technologies AgION Akcros Chemicals Intercide Argus Chemical Amical BioCote BioCote Biosignal Biosignal BYK Chemie Preventol Ciba Specialty Chemicals Irgaguard
Biosignal (anti biofilm) Clariant Nipacide
Nipaclean Degussa Sustainable Antimicrobial Polymers Dow Chemical Dowicide DSM ComfortCoat Ferro Micro-Chek Johnson Matthey JMAC biocides Microban Products Microban Milliken Chemical Specialty Alphasan Nanoco NanoSilver Neste Maxguard AB polyester gelcoat based on Microban Perstorp Polygiene PolyChem Alloy PolySept Masterbatch, Rohm and Haas Vinyzene
Rocima RTP Sanitized AG Sanitized Silver Thor Acticide Troy Corp Micropel Victor International Plastics Neutrabac masterbatch
Royalite sheet Wells Plastics I, J, Ionpure masterbatches Wright Corporation
Table 1. Examples of marketed biocides Conclusion
Biocides are additives able to kill and stop bacteria or fungi proliferation, to prevent degradation of polymer physical and sensorial properties, both within the material and at its surface. They act as a complementary technique for cleaning, which is also simplified and less costly. The growth of micro-organisms can lead to unpleasant odours, surface and bulk degradations.
Biocides can be mineral such as silver compounds or organic with a multitude of molecules containing halogens, aromatic rings, arsenic, sulphur, nitrogen etc. Considering their chemical structure and their bio-activity, they are concerned by several regulations differing according to the countries.
Traditional biocides are being replaced by more persistent grades and by more environment-friendly biocides also more expensive. Silver based biocides benefit from those trends but other tracks are exciting, for example nano-titanium oxide or nano-silver, modified silicone oligomers and, of course, directly grafting or molecular modification of polymers themselves.

References
Technical books and guides, papers, websites: AddMaster, AgIon Technologies, Akcros Chemicals, Argus Chemical, BioCote
SpecialChem Bacteria, fungi and algae can affect the aesthetic and physical properties of a plastic or a rubber by causing black spotting or discoloration, pink staining, odour and polymer degradation, fouling etc. Biocides are used to fight these microorganisms. After 'Research and Markets' the market for biocides in plastics had soared to $145m (€113m) in 2005 that is to say a significant rise of 40% since 1995.

Fuente: Special Chem-Article of the week

Tecnologas:
/Materiales/Aditivos y cargas/Biocidas

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