Selecting Seals for Global Food-Contact Applications
It is not unusual today for sealing components to be used halfway around the world from where they were manufactured. There are certain commonalities in global food-contact regulations, but also significant variations. While U.S. and E.U. predominate, more than 30 countries have such regulations—all of which prohibit the sale of food-contact articles and materials that transfer chemicals to foods in concentrations hazardous to health or that adversely affect the sensory (organoleptic) properties of food. In addition they all specify the use of manufacturing Practices (GMPs) in the production of these products.[1]
The consequences of noncompliance can be draconian—fines, imprisonment or both. Therefore, it’s important to select the right sealing component for where it will be ultimately used.[2] Compliance with the applicable regulations does not necessarily mean a seal is appropriate for its intended use. Selecting a sealing component for a food-contact application is done in the same manner as selecting a seal for any application, taking into account the forces acting on it.[3] For a static seal, this begins with defining the gasket stress and system pressure. The stress must be sufficient to provide an adequate seal, but not so high as to crush or extrude the gasket into the process media. For a dynamic seal, this involves not only the system pressure, but also surface speeds, mating surface conditions and run-out.
For both static and dynamic applications, the typical and maximum temperatures involved and the media being sealed must be identified. Suitable sealing performance might be achieved at these temperatures, but a substance in the sealing material could thermally degrade, producing undesirable by-products. This is of particular concern with regard to fiber sheet compositions, which are often rated for temperatures that can severely degrade their binders, generating potentially toxic decomposition products.
It is also important to determine if there are any cleaning procedures involved, such as clean-in-place or steam-in-place regimes, and whether the surface morphology of the sealing material will permit adequate cleaning.[4,5] Global regulations concerning food contact materials focus largely on chemical substances that can leach out and migrate into the food.
Another issue is the sealing component physically entering the food. For a static seal this may result from intrusion of the gasket into the process stream. For a dynamic seal it may be the result of excessive wear. For both static and dynamic seals, thermal or chemical degradation may cause fragmentation. While the risk of this occurring can be minimized by proper material selection and seal design, it cannot be totally eliminated. There are also instances where the entire sealing component may enter the food due to mishandling or improper installation.
The U.S. Food and Drug Administration’s (FDA’s) Food Safety Modernization Act Preventive Controls for Human Food rule is now final, and compliance for some businesses began in September 2016. Covered facilities must establish and implement a food safety system that includes an analysis of hazards and risk-based preventive controls. As part of these controls, many facilities utilize metal or X-ray detection systems. Sealing components are available that can be detected by one or both techniques.[6,7]
U.S. Regulations
In the U.S., sealing products for food applications are regulated by FDA, who considers them to be food-contact articles made of food-contact materials (FCM). These typically consist of a mixture of Food-contact Substances (FCS). An FCS is considered an indirect additive if it comes into contact with food as part of the packaging, holding or processing. However, it is not intended to be added to, become a component of, or have a technical effect on it.
Regulations regarding indirect additives are found in Title 21 of the U.S. Code of Federal Regulations (21 C.F.R.). The two most common regulations pertaining to sealing products are 21 C.F.R. 177.2600 (rubber articles intended for repeated use) and 21 C.F.R. 177.1550 (perfluorocarbon resins).[8,9] 21 C.F.R. 177.2600 is essentially a list of permitted base elastomers, vulcanization materials, accelerators, retardants, activators, antioxidants, plasticizers, fillers, emulsifiers and other additives. The list also recognizes some materials as inherently safe, which are classified as Generally Recognized as Safe.
21 C.F.R. 177.2600 also includes restrictions on the level of substances permitted. The permitted level of some substances is linked to the type of food. For instance, the level of channel or furnace carbon black is less than 50 percent for nonmilk/edible oil contact. However furnace black content for milk and edible oils is limited to less than 10 percent.
In addition, 21 C.F.R. 177.2600 sets product extraction limits for both aqueous and fatty foods. Extractables in fatty foods must be less than 175 mg/sq. in. after the sample has been refluxed with n-hexane for 7 hours, and just 4 mg/sq. in. for the next 2 hours. For aqueous foods, the limit is 20 mg/sq. in. of extractables when refluxed with water for 7 hours and 1 mg/sq. in. for the next two.
21 C.F.R. 177.1550 applies to polytetrafluorethylene (PTFE) based sealing products, specifying polymer properties, permitted additives and extraction requirements.