Urea formaldehyde-based resins have been the standard binders used to glue the particles together in many composite wood products, including particleboard, wheatboard, and medium density fiberboard (MDF). In recent years, however, concerns have been rising about the risks of cancer and bronchial health impacts from formaldehyde. Several market factors are driving major changes in the composition and technology of these resins. Pressure from the green building movement through market selection and certification programs, plus emissions regulations from the California Air Resources Board (CARB), are moving manufacturers to look for ways to reduce formaldehyde emissions or eliminate formaldehyde entirely from formulas.
Manufacturers are currently using or undertaking research and development into four major approaches to reduce the problem of exposure to formaldehyde from composite wood binders:
- Modified urea formaldehyde resins with scavenger additives, such as melamine, to reduce the rate of emissions of formaldehyde;
- Alternate formaldehyde resins, such as phenol formaldehyde, which cure at the factory during manufacture and hence have much lower formaldehyde emissions in use than urea formaldehyde;
- Alternate fossil fuel-based binders containing no added formaldehyde, such as methylene diphenyl diisocyanate (MDI);
- Alternate binders based on renewable resource materials, such as soy flour.
Emerging alternatives: Soy-Based Binders
Columbia Forest Products made headlines in 2006 with announcement of PureBond, its new soy-based resin technology. This was a first break from the industry dependence on resins that use a form of formaldehyde in the resin or as a feedstock, replacing it with a resin based upon a renewable resource (soy fl our). It is first being utilized as a binder in hardwood plywood panels and is currently being tested for use in other composite wood products.
The soy flour component is a renewable resource and, while not studied extensively as a building material
component, it is not expected to have health impacts as significant as the formaldehyde and MDI-based binders. Soy products can cause allergic reactions in some people and contain plant estrogens. The compounds are, however, expected to be completely destroyed in processing and not be present in the proteins used in the adhesive.
PureBond does, however, have another primary component — Kymene — with problematic feedstocks. Kymene is produced using polyamideepichlorohydrin (PAE) resin, which in turn is manufactured from a chemical known as epichlorohydrin, or chloropropyl oxide. Kymene resin is manufactured by Hercules Chemical and previously primarily marketed as a resin in paper manufacturing. Epichlorohydrin is a highly volatile and unstable liquid epoxide. It is prepared from propene, found in coal gas or synthesized by cracking petroleum. The International Agency for Research on Cancer (IARC) classifies epichlorohydrin as a probable human carcinogen. Epichlorohydrin is listed in California’s Proposition 65 as a carcinogen and reproductive toxicant.
Conclusions on alternative binders
In the development of alternatives to urea formaldehyde (UF) resins in particleboard, MDF , and wheatboard products, there has yet to be a product that can replace UF that does not raise some environmental health concerns. Taking into account any potential added costs associated with the production of the alternatives (some alternative products require more curing time, which gets built into the product price), health care institutions
will have to take into account the health risks, alongside the costs and performance characteristics of the
products themselves, to determine which alternatives to use in casework.
Alternatives to formaldehyde, such as MDI or soy-based resins, appear to virtually eliminate the exposures to chemicals in the curing processes that continue after installation in formaldehyde-based products, significantly reducing user exposure to hazardous chemicals. These chemicals do, however, raise occupational health concerns for those making the resin binders.
In summary, the health concerns are as follows:
- Modified urea formaldehyde resins with scavenger additives bind the formaldehyde better in the wood, reducing but not eliminating the formaldehyde emissions from the resin. Like other urea formaldehyde based resins,
they will off gas formaldehyde, exposing occupants for long periods of time, just at lower rates;
- Alternate formaldehyde resins, such as phenol formaldehyde, also have lower formaldehyde emissions in use, but do not eliminate emissions altogether. In addition, they raise occupational health and safety concerns during the production process;
- Alternate fossil fuel-based binders containing no formaldehyde, such as methylene diphenyl diisocyanate (MDI),
do not release formaldehyde during use. They are, however, made from formaldehyde. In addition, MDI raises other significant occupational health and safety concerns during the production and manufacturer of the composite wood products;
- Alternate binders based on renewable resource materials, such as soy flour, do not release formaldehyde during use. What we know of a primary component, epichlorohydrin, currently used in combination with the soyflour in the resin, does raise some concerns for occupational heath and safety. The primary manufacturer of the technology claims that the product is manufactured in such a way as to reduce occupational exposure and eliminate potential user exposure.
Healthy Building Network, 2008: Factsheet Alternative Resin Binders for Particleboard, Medium Density Fiberboard (MDF), and Wheatboard
Source: Healthy Building Network, 2008-05.