Food and beverage producers rely on a wide array of equipment to ensure their products are safe and free of contamination. Sealing devices such as gaskets are key components in this equipment, yet do not receive the attention they warrant given the critical importance of their function.
PTFE-based and elastomeric seals have for decades been the products of choice for food and beverage applications. The two most commonly referenced Food and Drug Administration (FDA) standards for sealing products are found in the Code of Federal Regulations under Title 21 (Food and Drugs), part 177 (Indirect Food Additives: Polymers). Section 177.1550 focuses on perfluorocarbons such as PTFE- based products, and Section 177.2600 deals with rubber articles intended for repeated use.
These two standards specify which ingredients used in the production of sealing products are acceptable for applications where contact with food products can occur, as well as how much of the approved ingredients can be released from the polymer/elastomer when extracted with specific media — i.e. water, hexane, etc. — under specified testing conditions.
By identifying the allowable components and test method, the FDA has created an “honor system” for gasket and seal manufacturers to independently validate the suitability of their finished sealing products independently. Therefore, it is incumbent upon food and beverage producers to ask the pertinent questions to ensure the sealing products they are purchasing have been manufactured and tested to the appropriate FDA regulation.
Fiber gaskets with elastomeric binders claiming to be FDA 21CFR177.2600 compliant have recently begun to appear in the marketplace. As noted, Section 177.2600 specifically covers “Rubber Articles Intended for Repeated Use,” including molded items such as diaphragms for pumps and valves, elastomeric boots or sleeves, etc. However, the fiber gasketing with elastomeric binders supposedly in compliance with Section 177.2600 typically consists of less than 20 percent elastomer, with more than 50 percent of the construction made up of clay filler.
The 21 CFR Section 177.2600 does not define the characteristics a product must have to be considered a “rubber article”. At present, no sections of the Federal Register pertaining to articles for food contact deal specifically with those constructed mainly of clay and fiber.
Most would agree that “rubber articles” would include items such as rubber sheet, pump/valve diaphragms, flexible boots, etc. It would also be safe to assume that products that are truly “rubber articles” would have testing and published properties based on ASTM D2000 standards (Standard Classification System for Rubber Products in Automotive Applications), including ASTM D2240 (Standard Test Method for Rubber Property — Durometer Hardness), ASTM D412 (Standard Test Methods for Vulcanized Rubber and Thermoplastic Elastomers-Tension), and ASTM D395B (Standard Test Method for Rubber Property — Compression Set).
However, the products in question have published properties based on test methods outlined in the ASTM F104 (Standard Classification System for Nonmetallic Gasket Materials), which clearly states: “Materials normally classified as rubber compounds are not included, since they are covered in Classification D2000.”
Published properties for the fiber gasketing products in question are based on ASTM F36 (Compressibility and Recovery of Gasket Materials), ASTM F146 (Standard Test Methods for Fluid Resistance of Gasketing Materials), ASTM F152 (Standard Test Methods for Tension Testing of Nonmetallic Gasket Materials). By choosing to publish values based on ASTM F104 methods, and not publishing values based on ASTM D2000, the manufacturers are essentially saying their products are not truly “rubber products.” Therefore, section 177.2600 (Rubber articles intended for repeated use) is not technically applicable.
That being said, the fiber gasketing with elastomeric binder has reportedly been tested utilizing the guidelines in Section 177.2600. This begs the question, if most food-grade gasketing products that are not “rubber articles” are traditionally tested in accordance with Section 177.1550, why not perform the testing in accordance with Section 177.1550?
A review of the two sections reveals that the extraction requirements of Section 177.1550 are much more stringent than Section 177.2600. In fact, Section 177.2600 states that the extraction test media is to be changed out (new extraction media is used) after the first 7-hour test is performed:
|Method||Testing Duration||Maximum Extractables|
|21CFR177.2600 (first extraction)||7 hours*||20 mg/sq.in.|
|21CFR177.2600 (second extraction)||2 hours*||1 mg/sq.in.|
|21CFR177.1550||2 hours||0.2 mg/sq.in.|
This means sealing products in compliance with Section 177.2600 can have extractables (material that can leach into the manufacturing process) 105 times greater than that of a sealing product that is compliant with the extractable limits outlined in Section 177.1550.
This has important implications for customers that have been successfully using products that meet the Section 177.1550 extractable limits. Switching from these products to ones that comply with Section 177.2600 will not provide equivalent performance. Further investigation into several fiber gasketing materials claiming to be FDA-compliant revealed that all of these products tested had extractable levels that exceeded the limits in Section 177.1550. In fact, extractables from the fiber gasketing products were as much as three times higher than the allowable limit in Section 177.1550.
Immersion testing of the fiber gasket products showed a weight gain of 2 percent to 3.5 percent after being immersed in ambient temperature distilled water for just 22 hours. In addition, the compressed fiber products are constructed of organic materials that can potentially support bacterial growth. Most PTFE-based products with or without inorganic fillers do not support bacterial growth even if the process media permeates them.
Equipment and system conditions must also be factored into the selection of sealing products. Many processing operations use steam to cook, and/or sterilize (commonly referred to Steam-in-Place or SIP). Steam temperatures can be as high as 350ºF (177ºC). well above the temperature range of nitrile binders commonly used in fiber gasketing products.
Section 176.170 (Components of Paper and Paperboard in Contact with Aqueous and Fatty Foods) specifically states that the Condition of Use (COU) A is typically for heat sterilization Use of products containing polymers, such as acrylonitrile polymer (nitrile rubber) above 250ºF (121ºC) could result in the migration of the polymer and/or components into the food process.
Since all of the fiber gasketing materials claiming to be FDA-compliant have acrylonitrile polymer (nitrile rubber) binding agents, the products are technically limited by FDA regulations to 250ºF (121ºC). These products are not suitable for food contact temperatures above 250ºF (121ºC).
Thermal degradation from elevated processing temperatures or SIP operations could also result in chemical compounds that could negatively impact the organoleptic properties (taste and smell) of the product, or toxic byproducts that could be released into the food process stream.
|PTFE Gasketing||Elastomer Gasketing||Fiber Gasketing|
|Process Media Absorption||Natural hydrophobic polymer with inorganic fillers||Solid polymer seals typically are fairly impervious||High clay content (hygroscopic) and higher void content due to construction method|
|Cleanability||Unaffected by Steam-in-Place (SIP) or Clean-in-Place (CIP) chemicals||Verify the suitability of the polymer before use.||Thermally degraded at elevated temperatures and moderate to poor resistance to CIP media|
|Bacterial Growth||All inorganic construction – will not support bacterial growth||Solid polymer seals typically are fairly impervious, but surface growth may occur||Organic fibers and binding agent possible food source for microbial growth|
|Elevated Temperature Capability||Suitable for temperatures up to 500ºF (260ºC)||Limited by the polymer type.||Limited to 250ºF (121ºC) due to acrylonitrile binder (per FDA reg.)|
|Cost||More expensive||Less expensive||Less expensive|
|Ease of Use||Easily cut and installed; releases easily from the flanges with no residual material||Molded or cut parts are easily installed, but may bond to sealing surfaces over time.||Easily cut and installed, but removal can be inhibited if the service is at elevated temperature and the acrylonitrile binder bonds to the flange faces.|
Total cost of ownership (TCO) is defined as the direct and indirect costs associated with an asset over a designated life cycle.
The annual sealing product spend for a typical food and beverage manufacturing plant is likely well below 1 percent of the operating cost. Yet sealing products are one of the first areas targeted for potential cost savings.
The lower cost of fiber gasketing materials can be attractive, but customers should take the time to carefully examine the claims of these products, as well as their potential impact on their operations. A small savings from switching to an unproven product that claims to be FDA-compliant could result in product contamination, product loss due to pathogens or other microorganisms, production downtime to decontaminate and sterilize or, worst case scenario, a complete product recall.
Author: Matt Tones, Senior Applications Engineer, Garlock Sealing Technologies