PVC, a versatile polymer, is often mistakenly perceived as inherently antimicrobial. This misconception likely stems from historical practices and the release of certain chemicals during processing and while antimicrobial PVC is certainly feasible, a deeper understanding reveals a more nuanced picture.
Historical Practices and Their Impact
Traditionally, PVC was stabilized with lead compounds. Upon thermal degradation, these compounds released certain chemicals with potential antimicrobial properties. Nevertheless, due to significant health and environmental concerns, lead stabilizers have been phased out in recent years.
Additionally, the thermal processing of PVC releases hydrogen chloride (HCl), a gas with known antimicrobial properties. However, this effect is transient and diminishes rapidly, leaving the PVC surface susceptible to microbial colonization. With this in mind any PVC material being tested using an antimicrobial test such as ISO-22196 needs to be carried out against samples that are known to have off gassed all traces of hydrogen chloride or any other volatile compound that could influence the test. Both antimicrobial treated samples and samples used as controls should be moulded at the same time as the treated samples and need to be aged to a point that the controls demonstrate no antimicrobial efficacy.
The Role of Phthalates in Microbial Growth
Phthalates, commonly used as plasticizers in flexible PVC, can inadvertently contribute to microbial growth. These compounds can be metabolized by some microorganisms, leading to material degradation and the creation of a favorable environment for further microbial colonization. The main deteriogenic organism of pPVC objects that contain phthalate plasticisers such as DOA is Aureobasidium Pullulans, a yeast like fungus which can rapidly colonise the surface of pPVC causing surface defects, discolouration, embrittlement and eventual failure.
Another organism that causes degradation of flexible PVC products is a gram negative bacteria called Serratia marcescens, this phenomenon is particularly evident in household items such as shower curtains, shower head nozzles and door sealing strips, which often become unsightly due to microbial growth that results in bright pink or orange staining that is impossible to remove.
Healthcare Implications
In healthcare settings, the use of phthalate-containing PVC products, such as PVC tubing and PVC pipes, can pose a significant risk of microbial contamination and subsequent infection. The proliferation of bacteria and fungi on these surfaces can contribute to the development of healthcare-associated infections (HAIs) and the formation of biofilms, which can harbor antibiotic-resistant microorganisms. Serratia Marcesens is an opportunistic human pathogen that can infect open wounds, causes eye infections such as conjunctivitis, tear duct infections and can even cause chest infections.
The Challenge of Incorporating Antimicrobial Additives
The incorporation of antimicrobial masterbatches into thermally processed PVC is challenging. Suitable carrier materials are limited, and many negatively impact the host material’s properties. Maintaining clarity in transparent plasticised PVC is particularly difficult due to the incompatibility of most polymer additives. Phase separation and lamination around areas of high shear such as gates on injection moulded parts is very common with carriers that are not fully miscible with the host material.
Silver-ion Based Antimicrobials: A Promising Solution
Silver ion based antimicrobials offer a promising solution. These additives can be effectively incorporated into both rigid and plasticized PVC. They are non-migratory, compliant with global biocide regulations, and suitable for healthcare and food contact applications. For antimicrobial PVC used in food contact applications there really is no option other than to use a silver ion technology as silver is the only non migratory biocide supported in product type 4 (food and feed area disinfectants) in the European and GB article 95 list that is suitable for thermal processing and provides long term efficacy.
Advanced Carrier Technologies
Recent advancements in our proprietary carrier material have enabled the development of fully miscible carrier systems for PVC. These systems allow for the very effective dispersion of antimicrobial additives, even at high concentrations, without compromising clarity or other material properties. By utilizing these innovative carrier systems, it is possible to achieve high levels of antimicrobial efficacy while maintaining the desired aesthetic and functional properties of PVC products.
The Future of Antimicrobial PVC
To ensure optimal hygiene and infection control, it is crucial to choose antimicrobial PVC products that are equipped with effective an antimicrobial technology that is proven to provide robust and effective efficacy against the organisms that the end product might be exposed to, for instance, antimicrobial PVC used inside a refrigerator should be tested against food borne mold and bacteria at refrigeration temperatures whereas, an antimicrobial PVC tarp would need to be tested against mold and mildew and over a longer period of time.
By understanding the complexities of antimicrobial PVC and the challenges associated with incorporating antimicrobial agents, we can develop more effective and sustainable solutions for a wide range of applications. As technology continues to advance, we can expect to see further innovations in antimicrobial PVC, leading to safer, more hygienic and long lasting products for healthcare, food service, and other industries.
