additives feature | Antimicrobials How antimicrobials for PVC compare – table compiled by Lonza


Antimicrobials based on butyl benzisothiazolinone (BBIT), which Lonza markets under the Vanquish 100 banner, are more soluble in plasticizer than in PVC. BBIT is part of a class of chemicals, isothiazolinones (ITs), of which there are two other variants used in plastics: DCOIT (a dichloro blend with isothiazolinone) and OIT (octylisothiazolinone). They all have similar functional properties and solubilities in plasticizers. When BBIT is blended with zinc pyrithione (ZnP) it provides a dual solubility profile: ZnP, which is not plasticizer-soluble, does not migrate out with the plasticizer at 100%. The patented combination is said to be a good solution for parts with long intended life- times, especially underground and underwater, such as geomembranes and swimming pool liners. There are some key differences between the three isothiazolinone variants though, and these are particu- larly relevant to above-ground applications. Robitaille says that BBIT out-performs DCOIT and OIT in micro- biological tests following QUV accelerated weathering. “PVC containing DCOIT yellows less than BBIT, but its DCOIT’s performance as an antimicrobial disappears after fewer than 20 hours QUV exposure [as measured according to the ASTM G21 test],” he says. OIT lasts for 50 hours, but BBIT only fails after 150 hours. Zinc pyrithione, which Lonza markets as Zinc Omadine, was invented around 75 years ago by Olin Corporation, whose speciality chemicals business was spun off as Arch Chemicals, now part of Lonza. Its main use is in anti-dandruff shampoos. ZnP has a decomposition temperature of 240°C, so


its applications in plastics are limited to materials that process below that temperature: polyethylene and polypropylene, EPDM rubber, PVC, and thermoplastic polyurethanes for example. Lonza is looking at ways to


32 COMPOUNDING WORLD | July 2014


increase the decomposition temperature to around 260°C or possibly even higher. ZnP is extremely effective on its own in polyolefins,


and provides an alternative to tricolosan, another antimicrobial that appears to be on the way out because of toxicity issues. Polyolefins are biologically inert, and do not require antimicrobials, but organic matter that may collect on parts in certain applications can provide a food source for bacteria. Plasticized PVC on the other hand provides good food for microbes. Robitaille points out that ZnP is unique in that in


Europe it is registered for use in plastics product types 9 (polymer preservation) and 2 (disinfecting product surfaces). The only other chemicals that have this dual registration are silver, silyl quats and polyhexamethyl- ene biguanide (PHMB), but none of these is very good at preservation, whereas ZnP is very effective at both. Robitaille also says that the current ASTM E-1428


standard, which is used to test the efficacy of antimicro- bials, may need to be rewritten to properly reflect the properties of OBPA replacements. This is because the standard looks at the formation of pink stains on a plastics sample placed on a layer of agar in a petri dish. OBPA easily passes this test because it leaches out of the PVC and forms a large “zone of inhibition” that prevents pink stains – which are due to metabolites and not the bacteria themselves – reaching the sample through the agar. Robitaille explains that the remaining antimicrobials have much smaller zones of inhibition, allowing migration of the pink stain, even if the sample remains bacteria free. With new alternatives, which leach less from the


PVC, pink stains are more likely to form on the sample, even though the antibacterial effect they provide is just as good, if not better. Robitaille says that a test in which


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