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What is BPA?BPA, or bisphenol A (see Figure 1), is an organic compound that makes up the backbone of many polycarbonate polymers. It has also been used as a plasticizer in PVCs. BPA adds clarity and toughness to epoxies, coatings, and adhesives.
CERHR has focused on BPA because of its widespread uses and, in some cases, direct exposure to humans. The chemical nature of BPA - specifically its two phenol groups - has lead researchers to believe that it has potential for interaction with biological active sites. Exposure to BPA can occur through inhalation or ingestion. Those formulating or handling BPA directly have the highest inhalation risk. Studies have shown that the release of BPA from products like epoxy liners is dependent upon temperature. Heat and age can both increase BPA migration.
The result of BPA exposure has been actively debated. The National Toxicology Program, an office within the National Institutes of Health, acknowledged in a draft report that the chemical might cause cancer and other serious disorders. However, further studies conducted by the U.S. National Toxicology Program have shown that there is insufficient evidence to state that BPA is carcinogenic or mutagenic. Groups directly related to the manufacture and sale of BPA claim that current exposure levels are well below permissible limits. They also cite reports that refute the claims of the CERHR. Studies by the European Union show that BPA exposure at “realistic” doses does not have any effect on reproduction or development. With the debate over the safety of BPA ongoing, it would be wise to carefully examine applications involving direct contact with food and drink or medical devices.
How Should Manufacturers Respond?So how should a formulator/manufacturer of BPA-containing products respond to these reported hazards? First, a manufacturer should know how much BPA is incorporated into their final products, whether directly or indirectly. This means choosing raw-material suppliers who are forthcoming with their BPA specifications. For example, bisGMA is a commonly used resin in dental adhesives and sealants. With Esstech-supplied bisGMA, average BPA content can be decreased from 180 ppm to 2 ppm (see Table 1). In addition, Esstech also supplies pre-mixed dilutions of bisGMA with triethylene glycol dimethacrylate (TEGDMA).
Glass ionomer cements (GIC) are common BPA-free adhesives used in the dental industry. These cements are two-component systems comprised of a mixture of polymerized acids and specifically designed glass powder. When mixed, the acids begin to partially dissolve the glass particles. The acid polymers then combine chemically with the dissolved glass components to produce a hard matrix material. The final matrix is reasonably translucent, allowing for various formulator manipulations to occur. GICs work well in moist environments, and are good for bonding ceramics to metals. In the dental industry, GICs are also used to bond gold and base metals to resin composites. Their utility allows them to be applied directly to clean substrates without additional preparation.
Research and development has focused on creating resin-modified glass ionomer cements. Resin-modified GICs are still considered BPA-free and add an additional method of curing. Chemists have created an adhesive system with increased toughness that can be chemically cured or photo-cured by introducing resins to GICs.
The ongoing debate over the risks associated with BPA can make it difficult to set a clear course of action. Those handling BPA directly or indirectly should ask themselves the following questions.
- Does my product create a BPA inhalation or ingestion risk?
- Is BPA a crucial component of my system?
- Is there an alternative supplier available whose material is lower in BPA?
- Can the BPA-containing material be replaced with a BPA-free alternative?
About the CompanyEsstech Inc. develops and manufactures advanced materials for the dental, optical, cosmetic, and coating industries. With chemistries that meet medical purity standards, customers worldwide rely on Esstech for technical resins, polymerization initiators, adhesion promoters, surface modifiers, purified monomers and glass nano-fillers.
For more information, contact Esstech Inc., 48 Powhattan Ave., P.O. Box 39, Essington, PA 19029; phone (610) 521-3800 or (800) 245-3800; fax (610) 521-4600; e-mail email@example.com; or visit www.esstechinc.com.