BIOCIDES IN EVERY DAY PLASTICS

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 temperatures
Non damaging effects on the polymer end-properties: sensorial, mechanical, electrical, 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.
Active bases, very diversified, can be sliced in:
Organic antimicrobials that can be synthesized or derived from naturally occurring sources. Examples of organic antimicrobial technologies include triclosan, quaternary ammonium compounds, Octyl-4-isothiazolin-3-one (OIT)
Inorganic antimicrobials based on alkali, alkaline, transition block and metalloid elements. Examples of inorganic antimicrobial technologies include silver and copper.
Organometallic antimicrobials containing both organic and inorganic components in their structures. Oxybisphenoxyarsine (OBPA), zinc pyrithione are examples.
The liquid carriers include plasticizers such as phthalates, epoxidized soybean oil (ESBO) and epoxidized ester (Lankroflex by Akcros); and water or chemicals such as glycolic solutions (dipropylene glycol etc.), alkaline solutions.
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, odor and polymer degradation, fouling etc. Biocides used to fight these microorganisms have two main roles:

To stop bacteria or fungi degrading the polymer's physical and sensorial properties, reduce microbe populations both within the material and at the surface. The growth of microorganisms can lead to unpleasant odors, surface and bulk degradations. Reducing odors 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 ('Kline & Company')
Non-arsenic based formulations rising at 10-20% per year
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, fiber 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), acetals (POM), polyesters (PET and PBT), ABS, rubbers, thermoset resins. The patent registration concerning antimicrobials shows the increasing interest for antimicrobial fight. The linear increase leads to more than a tripling between 1990 and 2010 as we can see on Figure 'Antimicrobial-Patents'.

Natural Sourced Biocides
Cu+, Ag+, Zn2+ and Ba2+ Boost Antimicrobial Activity of PA66
C. Citterio, L. Mercante, M. Rodighiero, K. Brocchini; Lati Industria Termoplastici S.p.A., (INNOVATIVE ANTIMICROBIAL THERMOPLASTIC COMPOSITIONS) study the effects of several natural microbiocides on a 50% glass reinforced polyamide 66 (PA 66). Involved bacterial species are Staphylococcus aureus and Escherichia coli.

Antimicrobials are based on:
Cu+
Silver, Ag+, a well-known antimicrobial agent acting on the cell wall
Zinc salt
Barium salts
Bismuth
Wood flour
Sorbic acid derivatives
For the four strongest biocides, Table 2 displays the actual concentrations (inferior to 1%), the antimicrobial activity (expressed in log values) and the percent of impact strength versus impact strength of the blank.

Silver is confirmed effective in PA. The used commercial preparation is found successful even at low Ag+ concentration due to its dispersion on the support and the synergistic effect of zinc.

Additives based on Copper (I) were found valid alternative to Silver based ones in polyamides, with the advantage to have a better cost/performance ratio. Copper as antimicrobial agent is recognized by the US Environmental Protection Agency. Furthermore, Cu (I) is listed in Directive 2002 ⁄ 72 ⁄ EC and following amendments to be safely used in food contact applications.

Where Copper and Silver cannot be exploited, other valid alternatives such as Zinc and Barium salts can be used without detrimental effect on the main features of the thermoplastics, although a higher loading level is necessary. Further investigations should be conducted on the duration of the antimicrobial action, although the duration of in-mass additives is much longer than a surface treatment.
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, and 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.


Figure 6: Antifungal Activity


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 fibers can prevent the development of bacteria and the resulting odors.


Keep in Mind the Whole Array of Traditional and Recent Solutions
Arsenic derivatives
Oxybisphenoxyarsine (OBPA) is the most used (more than 50% of the total)
Calcium orthoarsenate
Metal derivatives
Zirconium phosphate-based ceramic ion-exchange resin containing silver
Nanosilver
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 stabilized 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
Cationic siloxane
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
Stabilized 1.5% metal-salts free active solution of chlor-methyl and methyl-isothiazolinones
Stabilized 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
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

TAKEN FROM SPECIALCHEM PUBLICATIONS