Regulations and Trends in In-Can Preservatives

As is known, ensuring healthy and long-term in-container preservation in water-based products is one of the most critical issues. To achieve this, the use of a stable and effective biocide or biocide combination in the finished product formulation is a matter so important for manufacturers that it cannot be left to chance. The most radical change in in-container preservative selection, which was relatively easier in the past, came to the agenda in 2001 when the CIT/MIT mixture was classified as an irritant above 15ppm in the 28th ATP of the Hazardous Substances Directive (DSD) in the European Union. This change required products containing CIT/MIT above 15 ppm to be labeled with "Xi, R43". In subsequent years, the labeling mark was updated to "H 317" under the CLP and our country's SEA regulation, and additionally, in accordance with EUH 208, the necessity of a warning statement "contains CIT/MIT, may cause allergic reaction" emerged for uses above 1.5 ppm, which is 1/10 of this limit. Finally, with EU Regulation 2016/131 dated 1 February 2016, the issue was raised that CIT/MIT would be permitted above 15 ppm only in products intended for professional use, even with labeling requirements. In other words, in paints and similar finished products intended for the general public, the use of CIT/MIT above 15 ppm is prohibited, even with the H 317 label.

(http://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:32016R0131&from=EN) There is no update yet published in Turkey within the scope of harmonization with this regulation. However, we can assume that it will be valid in Turkey in the coming years

Due to the changing labeling requirements of CIT/MIT, the MIT/BIT mixture, which has rapidly become an important in-container preservative alternative, was developed by Thor in 1998 and has been successfully used for approximately 20 years in many sectors for the protection of many different products. The lack of effectiveness of MIT alone against fungi and the high dose requirement of BIT against Pseudomonas-type bacteria were overcome by the synergistic effect between MIT and BIT. You can see the excellent effectiveness of the MIT/BIT mixture against bacteria and fungi and its minimum inhibition concentration (MIC) values in Figure 1.

Figure 1. MIC values showing synergistic effect for BIT, MIT individually and for MIT/BIT

  Although the slower killing rate of MIT/BIT compared to CIT/MIT initially raised questions, the results obtained from laboratory studies and, more importantly, the experience gained from its use in different productions in the field easily resolved this situation. Today, the same situation is considered an advantage because it leads to the stability of MIT/BIT in different formulations and its ability to provide long-term protection. The first clear water-based MIT/BIT mixture launched on the market in 1998, the patented Acticide® MBS, remains one of the most widely used products on the market today.

In MIT/BIT mixtures, it is essential to use high-purity MIT and BIT active substances in production to ensure physical and chemical stability.

In solvent- or water-based MIT/BIT mixtures produced with low-purity active substances, stability problems such as precipitation, phase separation and color change are observed, and in paint-type film-forming products using these types of preservatives, problems such as ghost odor formation are encountered. The technical and commercial success of Acticide® MBS has prompted many suppliers to produce MIT/BIT mixtures, but thanks to 20 years of production and application experience, Acticide® MBS has taken a step ahead in terms of stability. In Table 1, you can see the stability photographs after storage at 65°C of various MIT/BIT mixtures, and in Table 2, you can find the chemical analysis results. While Acticide® MBS 5050 samples are labeled as MBS, explanations for other samples can be found in Table 2. The photographs and analytical data show a marked stability problem for some products. Additionally, it is noteworthy that in some samples there is a significant decrease in MIT, which is considered the most stable of the isothiazolinones. As with other in-container preservatives, the amount of preservative required for effective protection depends on many factors including formulation content and redox values derived from polymers, along with the most critical factor: hygiene in the facility. Acticide® MBS alone is used by many manufacturers. However, manufacturers with hygiene concerns may prefer various mixtures of MIT/BIT with other biocidal active substances under the Acticide® MB family umbrella. For example, the mixture containing Bronopol with MIT/BIT (Acticide® MBL) has proven successful in providing additional effectiveness against microorganisms that have developed adaptation jeopardizing facility hygiene. Bronopol is very effective against adapted bacterial species, but because it releases small amounts of formaldehyde during decomposition, it is not suitable for manufacturers who want to produce formaldehyde-free products.

MIT/BIT, provided it is below the labeling limit explained above, can also be used together with CIT/MIT to provide an enhanced short-term effectiveness protection package.

The rapid bactericidal properties of CIT/MIT against contamination from water and other raw materials, combined with the long-term protective properties of MIT/BIT, can be considered a good combination. In this context, the Acticide® CBM family contains a series of products consisting of CIT, MIT and BIT in different proportions to provide good long-term protection depending on the stability of each biocidal active substance. When this type of preservative is selected, it is recommended to conduct stability studies to confirm that each biocidal active substance in the relevant formulation has the correct stability to perform its desired functions. Some products may contain high amounts of fungal spores in their raw materials or may have characteristics more prone to yeast and mold contamination, requiring additional fungal protection. MIT/BIT mixtures containing specially stabilized zinc pyrithione (ZnP) have been developed under the name Acticide® ICB family with extra fungal effectiveness. These products contain different concentrations of MIT, BIT and ZnP depending on the formulation to be protected, to provide excellent in-container protection and effective protection without requiring any additional labeling. Laboratory studies have shown that the inclusion of ZnP increases effectiveness against adapted bacteria and yeasts and provides maximum in-container protection in finished products. While the addition of ZnP increases effectiveness against yeast and fungi, its addition to the finished product for adequate protection reduces the required levels of BIT and MIT, also providing a labeling advantage. Finally, in sectors where formaldehyde donors are accepted, mixtures of MIT/BIT with a donor called TMAD with low free formaldehyde content (Acticide® MBF family) sterilize the area called "head space" between the finished product and the cap, strengthening protection inside the packaging and allowing long shelf life to be given to products such as paints.

Conclusion

The biocidal active substances MIT and BIT have successfully provided long-term in-container protection against microbial contamination in water-based products for many years with a safe safety margin. Additionally, combinations of the MIT/BIT synergistic mixture with other actives respond to different needs. In specific cases where adapted organisms and extra resistant organisms are observed, MIT/BIT combined with Bronopol has proven successful in both problem-solving and prevention scenarios. The combination of MIT/BIT with CIT/MIT provides both short- and long-term protection by utilizing the advantages of CIT without requiring additional labeling. When extra protection against fungi and/or resistant bacteria is required, the development of MIT/BIT mixtures with stabilized Zinc Pyrithione provides an advanced range of protection that can meet all in-container protection requirements of water-based products. In sectors where formaldehyde donors are tolerated, the use of TMAD together with MIT/BIT, without being impeded by formaldehyde-related labeling in the finished product, provides head space protection, enabling the launch of long shelf-life products to the market.

References

[1] Gillatt J, "Microbial Deterioration and Prevention of Polymer Dispersions", Guide to Micro-killers for Material Protection: Handbook, Paulus, W., Springer 2005. [2] Roden K, "Development of In-container Preservatives", PPCJ. Gül Öztoprak - Chemical Engineer - Manager, Istanbul Branch - Thor Specialties Srl Turkey