A Polymeric Route to Antimicrobial Functionality

There has been growing interest in new antimicrobial solutions in recent years, driven by a desire to provide longer-lasting protection in products that can be degraded by microbes, or to control or eliminate the undesirable effects created by the presence of microbes, such as odor or discoloration. Historically, these antimicrobial effects have been delivered through conventional active ingredients (AIs) such as fungicides or bactericides. These additives are used in small amounts, and for the most part provide adequate protection to substrates containing them; however, since the additives are typically post-added, they often end up being indiscriminately distributed onto the surface. In addition, these additives can be lost over time due to leaching or degradation caused by exposure to light, heat and the environment.

In recent years, driven by the European Biocides Directive, many of these traditional AIs are coming under greater scrutiny regarding their potential affects on the environment. There is also concern regarding the ability of microorganisms to adapt easily to the additives used and build resistance over time. The result is a growing need for alternative solutions that provide sustainable antimicrobial protection while minimizing many of the potential issues related to the use of conventional additives.

Introduction

Dow Reichhold Specialty Latex has recently developed antimicrobial technology that offers unique ways to mitigate the effects of microbes on products. Unlike conventional active ingredients, the technology relies on antimicrobial polymers that either have inherent antimicrobial characteristics, or incorporate a conventional antimicrobial additive encapsulated or embedded into a polymer.

Since the AI, or part of the molecule that is primarily responsible for the antimicrobial action, is attached to a polymer or uniformly embedded into the polymer at a nanoscopic level, these materials provide a more sustained and effective antimicrobial action over time.

In addition to the antimicrobial action, these same materials can provide polymer-related attributes such as binding, adhesion, barrier and bonding properties that conventional antimicrobial additives cannot. This multifunctional aspect may be of value where an ingredient is required to perform more than one function and thereby help in delivering a simpler and cost-effective solution. The intention for these new materials is thus not a direct replacement of the active ingredients used today but to provide additional benefits that cannot be provided in terms of durability, uniformity, consistency and greater functionality.

Work to date by Dow Reichhold shows that this polymeric route to antimicrobial functionality may be well suited for applications in textiles, nonwovens, medical products, hygiene and personal care products, building materials and a variety of formulated products including coatings, saturants and adhesives. The requirements of a specific application will determine which of the two approaches described below would provide the best combination of antimicrobial and polymer properties.

Inherent Antimicrobial Polymer Approach

The inherent approach to antimicrobial functionality relies on the fact that the active site is part of the polymer and is tightly bound to the polymer backbone. The polymers are waterborne, easy to handle and environmentally favorable. Also, unlike conventional antimicrobial additives, these polymers are high-molecular-weight materials and therefore less likely to be of concern regarding potential toxicology. These polymers can be designed to provide additional attributes as mentioned before such as static control, permeability, barrier and strengthening properties, and can be tailored to suit a given application need.

These materials would also be of interest in areas where a conventional AI may not be desirable. Such applications could include hygiene products, medical devices and products or personal care products where the additional multifunctional aspects of this polymer approach may be of greater value.

Unlike conventional antimicrobial additives that function by disrupting a biochemical pathway, these polymers function by breaching the integrity of the cell wall of the microbe. It is therefore believed that they are less likely to contribute to development of resistance in the targeted microbes. A variety of active sites and polymer backbones can be designed to suit a given application. Since they are waterborne they can easily be deposited on surfaces by well-known processes such as coating, spraying, saturation or wet end deposition.

Active Ingredient Carrier Polymer Approach

The active ingredient approach involves the incorporation of active ingredients into a polymer whether it is inherently antimicrobial, as in the case above, or if the polymer is inert. The AI is typically incorporated during the polymerization process in such a way that it is uniformly distributed into the polymer at a nanoscopic level.

This embedding of the AI into the polymer matrix provides complete additive coverage of the surface in a more uniform and consistent manner, thus increasing the longevity of the antimicrobial effect. In this way it is possible to get increased efficacy and sustainability from an AI while providing the benefits of a polymer in terms of ease of handling and durability.

It is also possible to use this approach to deliver a concentrated dose of the AI into a given formulation or application (coatings for example) where the AI is finely distributed into a polymeric carrier used only to deliver the AI. This is possible only because the method of incorporation allows high levels of the AI to be suspended into a polymer at a nanoscopic level without affecting the clarity of the polymer film.

This approach also makes it possible to enhance the inherently antimicrobial polymer with AI by creating a “tunable” antimicrobial polymer where the activity can be selectively controlled using either the additive or the polymer as the situation demands.

Polymers containing the AI are waterborne and will have the performance properties associated with waterborne technology. Waterborne polymers containing AI are useful in applications where an additive is desirable, and would allow formulators to design sustainable solutions without many of the handling and durability issues related to the conventional additive approach. The choice of polymers and AIs that can be used to provide a solution is varied and can be tailored to meet specific needs.

Conclusion

Dow Reichhold has developed antimicrobial technologies that include inherently antimicrobial polymers as well as polymers that have encapsulated active ingredients. These technologies provide a comprehensive approach to providing antimicrobial benefits across a wide variety of applications where sustainable antimicrobial functionality is needed, combined with the stated benefits of a polymeric offering. These technologies present real value to customers interested in providing the multifunctional benefits derived from a polymer that has inherent or embedded antimicrobial characteristics.

For more information, visit www.dowreichhold.com/AMPolymers, or call Patrick Delaney, business development manager, 630/836.1590.