Encapsulation technologies are at the heart of some of today’s most exciting consumer and industrial products, from self-healing paints and coatings to targeted-release agrochemicals. But many of these miracle products are hiding a dirty little secret: formaldehyde.
For most of these products, there is no hard evidence that the levels of formaldehyde they contain present a risk to human health or the environment. However, consumer concerns and regulatory scrutiny are pushing many manufacturers to look for safer alternatives to formaldehyde-based encapsulation technologies. The challenge? Finding replacement encapsulation materials that match the properties that have made formaldehyde resins so popular.
Battelle is working to develop formaldehyde-free alternatives using a process we call “Encapsulation by Design.”
Melamine Formaldehyde Resin: A Tough Material to Beat
Melamine formaldehyde resin is one of the most widely used materials for encapsulation. And for good reason: formaldehyde-based resins are cheap, easy to work with, and have chemical properties that make them highly useful for encapsulated products.
Encapsulation requires materials that combine two important attributes. First, the capsule must provide a stable and effective barrier between an active ingredient and the outside environment or surrounding material. Second, the capsule must be able to break open or dissolve in response to a specific trigger in order to release the active ingredient at the appropriate time. By manipulating the molecular structure of the shell material, chemists can design capsules that respond to different kinds of triggers.
This process has enabled the development of innovative materials and coatings that are able to respond to their environments to deliver an active ingredient exactly when it is needed. These products include shelf-stable formulations that combine reactive chemical components such as bleaches and activators, healing agents and catalysts, or enzymes and substrates. The chemical components are kept safely separated by the protective polymer shell until a selected trigger (e.g. heat, temperature, dilution, pH or other environmental trigger) breaks or dissolves the shell and releases the active agent.
Encapsulation is the technology behind groundbreaking products such as self-healing paints that respond to the presence of corrosion, self-curing resins and time-release personal care products.
Melamine formaldehyde resins have long been used in paints, coatings and laminates because they cure into polymers that are stable, moisture resistant and chemical resistant. These same properties make formaldehyde-based polymers useful for a broad range of encapsulation applications.
Rising Concern Over Formaldehyde Exposure
The National Toxicology Program (NTP), the International Agency for Research on Cancer (IARC) and U.S. Environmental Protection Agency (EPA) have classified formaldehyde as a human carcinogen. People can be exposed to formaldehyde by inhaling gasses emitted by formaldehyde-containing materials or absorbing it through the skin in liquid products.
Melamine formaldehyde resins used in coatings, pressboard and other consumer products and building materials have been shown to outgas formaldehyde over time, generating consumer concerns about exposure risks and prompting many manufactures to look for low- or no-formaldehyde alternatives. The EPA has set formaldehyde emission limits for wood composite products, but has not yet set standards for other products containing melamine formaldehyde resins.
It is unknown whether encapsulated products using melamine formaldehyde-based polymers present a formaldehyde exposure risk. These knowledge gaps make it difficult to determine whether the products truly present a risk to human health or the environment.
However, consumer concerns about formaldehyde exposure make moving to low- or no-formaldehyde formulations a smart move for manufacturers. Finding formaldehyde-free formulations will also help companies prepare for potential regulatory changes in the future.
The Search for Formaldehyde-Free Substitutes
Of course, melamine formaldehyde resin is far from the only material usable for encapsulation. Bio-based polymers like cellulose, gums and alginates are already in wide use for many encapsulated products. These materials are considered more environmentally friendly and safer for consumers.
Unlike petroleum-based plastic microbeads—which have now been banned due to concerns about their environmental persistence and impact on freshwater organisms—bio-based materials break down easily in the environment. Since they are built on natural, Generally Recognized as Safe (GRAS) materials, they are not believed to present risks to human health or the environment.
However, the same qualities that make them so environmentally friendly also make them less effective for many encapsulation applications. Many of the active ingredients and solvents used with formaldehyde-based polymers are not compatible with existing bio-based materials. In addition, bio-based materials may not provide enough protection in environments where moisture and microorganisms are a problem.
More work is needed to expand the range of options for formaldehyde-free encapsulation materials. Battelle is working to develop new encapsulation materials that can be used with a broader range of active materials and can respond to a variety of different triggers.
Encapsulation by Design
There is no “one-size-fits-all” solution for encapsulation. While the properties of melamine formaldehyde resins made them applicable for a broad range of applications, replacing them with formaldehyde-free alternatives is likely to require a suite of different product solutions. These will include variations on existing alginate and cellulose materials, but industry is likely to need other options for applications where these materials do not provide the right chemical properties.
The choice of shell materials for encapsulation depends in several factors, including:
- The physiochemical properties of the active ingredient it will encapsulate
- The chemical and physical properties of the environment surrounding the capsule
- The desired particle size
- The desired release mechanism
Bringing Formaldehyde-Free Encapsulation Products to Market
Battelle has identified GRAS materials that have the potential to replace formaldehyde-based polymers for the encapsulation of wide range of active materials.
Starting with GRAS materials, we can design encapsulation alternatives that will be safer and more environmentally friendly than their formaldehyde-based cousins.
While we cannot claim the new materials are non-toxic without further study, we can surmise that they are likely to be less toxic than materials containing formaldehyde. Battelle is currently conducting toxicology studies on some of the most promising materials for formaldehyde-free encapsulation.
To bring these safer materials to market, more work needs to be done to design materials for specific applications that retain the positive characteristics of melamine formaldehyde resin without the drawbacks. With the right chemistry, the industry will be able to meet the challenge.
About the Author
Ram Lalgudi is a Senior Research Scientist at Battelle.