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Non-metal materials are used in a variety food contact and non-food contact applications. Plastic, rubber and rubber-like materials, with widespread use, are the largest and most diverse category. Ceramics and/or carbon composites are used in specialized applications due to their hardness and rigidity, inertness, and resistance to high temperatures and chemicals. Ceramics are commonly used in membrane and mechanical seal applications, while carbon composites are used in molded parts, sensor components and mechanical seal applications. The use of certain non-metals (e.g., glass, wood, paper, cloth) is restricted, to certain applications, when necessary and appropriate.
When used in primary product contact, these materials must meet the same hygienic design, fabrication, and cleanability requirements as metals. These materials must be non-toxic and non-contaminating, and meet all current and appropriate US Food and Drug Administration (FDA) indirect food additive regulations, including any restrictions for certain uses and applications. 3-A Sanitary Standards go beyond these requirements and specify that these materials be inert, nontoxic, nonabsorbent, fat-resistant, relatively resistant to scratching, scoring, decomposition, crazing, and chipping under normal use conditions and when exposed to the conditions encountered in the environment of intended use. Providers of components bearing the 3-A Symbol must provide documentation that the equipment meets these requirements and the conditions of acceptable and non- recommended uses.
Plastic and rubber materials are used in food applications ranging from solid to more elastic structures. These materials may have certain desirable physical properties compared to metal and may be preferred for certain functions. However, no plastic/rubber material is directly equivalent to stainless steel in meeting the desirable hygienic design properties. Both metal and plastic/rubber surfaces will degrade over time under stress conditions. However, the chemical mechanisms and the progression of degradation are different. Metal degradation generally occurs at the surface, and is usually visible. Surface degradation may also occur in plastic and rubber, but often degradation may initiate in the interior of the material and migrate toward the surface. Therefore, degradation may not always be visible upon surface examination, until the material has become badly deteriorated.
Deterioration of plastic/rubber materials may occur under various conditions such as water absorption/loss, high temperature, absorption of food components or cleaning chemicals, exposure to corrosive chemicals, and oxidizing chemicals/ultraviolet (UV) light. Since many plastic/materials are not compatible for use in specialized process systems involving ozone and other oxidizing chemicals, and/or UV light, care must be exercised in material selection for such applications.
There is no plastic/rubber (or other non-metal) material that is suitable for all food processing applications. Thus, it is important that care be used in purchasing equipment to be sure that the materials used are appropriate to the processing system and meet the appropriate regulations and desirable properties for the specific intended use. The manufacturer should assure that the materials used have the ability to withstand the stresses associated with the food processing system without cracking, breaking, or deteriorating during continued use.
As with any food equipment purchase, it is recommended that the buyer do a thorough inspection to assure that the surfaces be smooth, impervious, durable, free of cracks and crevices, and that the equipment meets hygienic design criteria. It is the responsibility of the processor to assure that the equipment is properly installed, properly operated, and is maintained in hygienic condition. Special care needs to be exercised in maintenance programs. Such programs should involve frequent evaluation and documentation of wear and deterioration under continued use with replacement as needed. It is important that worn plastic and rubber components (including gaskets) be replaced as soon as possible. A common error made by food processors is to use less expensive, and often inferior, components, which are not of the same material and which may not meet hygienic design requirements. Although there may be a cost savings, using inferior replacement parts will lead to problems with cleanability and ultimately to failure of equipment.
*This article was contributed by Dr. Ronald Schmidt for the August issue of Dairy Foods magazine. Ron passed away on October 12. We publish this to honor the memory of Ron as a dedicated teacher and friend.
