Compounding World July 2020 Antimicrobial Additives

The ‘unabridged version of the Article submitted by Wells Plastics Limited to Compounding World July 2020 for their featured piece on Antimicrobial additives’


An interesting consequence of the Covid-19 pandemic has been the focus on surfaces as potential infection sites. The presence of microorganisms on surfaces has been known for a number of decades and is documented in many academic studies, but it has taken the latest pandemic for this to be more widely recognised. The control and reduction of microbe numbers on polymer based surfaces has always been one of the aims of antimicrobial systems such as Bactiglas™, together with odour control, which Wells Plastics has been developing, manufacturing and selling commercially for over 20 years. During this time, Wells Plastics has built up significant expert knowledge and experience with these materials, not just on the manufacture, application and the evaluation of technical performance but also on the regulatory and legislative position and requirements.

Until now, the benefit of antimicrobial properties has been recognised only in certain settings such as healthcare, but with greater public and media awareness of microbes and viruses it has reached a wider audience and interest in the Bactiglas™ range of products has mushroomed. With the requirements for regular hand washing and the disinfecting of surfaces being widely promoted more manufacturers are interested in adding an “in-built” antimicrobial property to their product, be that packaging film, hospital equipment or common touch items such as light switches.

With Covid-19 at the forefront of everyone’s mind, a lot of the interest focuses on anti-viral performance. Such claims should be approached with caution. Viruses are unique organisms and unlike bacteria and fungi they cannot multiple on a surface as they cannot reproduce outside of a host cell. Also, outside of a host cell they undertake no cellular activity and thus do not offer the multiple sites a biocide typically interacts with to produce a biocidal effect. If viruses are present on a surface, they are inactivated by denaturing the capsid protein shell or the glycoprotein envelop. This is readily achieved by the use of surface applied disinfectants. There is limited evidence that encapsulated antimicrobial additives can reduce virus numbers, but typically high concentrations are needed and no-one yet has test data against the Covid-19 virus.

Wells Plastics’ journey with antimicrobials began with a wide portfolio of active materials. Experience and regulatory constraint has resulted in Wells Plastics deciding to concentrate on promoting a single system, based on multiple carriers to the market. Bactiglas™ is designed around a well established and proven silver system.

Although there is always an interest in the “new”, in reality the introduction of new biocides is now difficult in the European Union (EU) due the Biocidal Product Regulation (BPR). The BPR aims to ensure the biocides on the EU market are safe for human health and the environment. Whilst this a desirable aim, an unforeseen consequence is the restriction of innovation. Antimicrobial systems that were on the market prior to the BPR have been able to continue to be used, as long as they appear on the Article 95 list for the relevant product type, while they are waiting to be reviewed and approved. However, brand new antimicrobial systems need to be reviewed first, prior to being placed on the market, a process that can take several years and cost many thousands of Euros. This means companies face an expensive ‘chicken and egg’ situation and need to gain approval before establishing any market position. This makes the introduction of new additives difficult as there is the high hurdle of regulatory approval to be passed before a new system can be widely trialled by customers.

The masterbatch step is crucial in the supply of an active ingredient. It provides a safe and consistent pellet which can be easily stored, handled and dosed by a processor. Importantly, the pre-dispersion of the active substance in a polymer carrier also optimises the performance of these expensive materials in finished articles. The regulatory position for masterbatch companies is complex, as they sit between the active substance supplier and the finished article producer while still having to comply and stay up to date with regulations. Masterbatching companies can only sell in the EU additives which are approved by the BPR or on the Article 95 list.

The other challenge posed by the BPR is the non-approval of additive systems. Interestingly some silver systems, though not that utilised in Bactiglas™, have been “non approved”. This is not due to any health or environmental concerns, but because the Biocidal Product Committee (BPC) ruled “their efficacy is not sufficiently demonstrated”. Thus it is important that any company making antimicrobial claims, be they antibacterial or antifungal (or for that matter antiviral), is able to support such claims with robust data to avoid falling foul of the BPR.

Another additive commonly used in plastics, zinc pyrithione, is also potentially a casualty of the BPR. Zinc pyrithione has been reclassified as Reprotox Cat 1B, and thus it now falls under the exclusion criteria listed in Article 5 of the BPR. This means it should normally not be approved, unless one of the conditions for derogation set in Article 5(2) of the BPR is met. Zinc pyrithione is waiting to be reviewed to determine if it meets these derogation conditions. Even if it does, we still don’t know what risk mitigating measures may be imposed with regards its use.

Nanomaterials, especially those based on silver and zinc, have over recent years been heralded as new technologies for antimicrobial applications, detailed in a growing wealth of academic studies. However, not only are these additives subject to the same regulatory demand as all other antimicrobial systems, but in fact the BPR has additional specific provisions for nanomaterials. The approval of active substances does not cover the nanoform of that material except where explicitly mentioned; meaning a separate dossier with all data requirements is needed. Furthermore, a dedicated risk assessment is needed when the nanoform of the active is used in a biocidal product. Also, the label of the treated article must show the name of each nanomaterial followed by the word “nano” in brackets.
While the regulations are a significant challenge to innovation in this field and the approval of some systems is uncertain, some active substances will survive the BPR process, such as the additive in Bactiglas™.

These proven technologies will continue to offer consumers an added line of defence against the growing concern of bacterial surface contamination.

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