Sanitary Gasket Materials Review
Sanitary Gaskets for the food processing and cannabis extraction industry come in a wide variety of materials. From silicone to nitrile to FKM/Viton®, each material offers benefits and drawbacks depending on:
All of these variables will determine the life expectancy of your seals and gaskets which will in turn, affect the operational performance of your equipment . This article will explore a range of materials used in food processing that might also be considered for cannabis extraction. They include:
Silicone is often used for its resistance to extreme temperature ranges (-58˚F to + 450˚F). This temperature range, along with its low leaching characteristics, makes it an industry default. Silicon’s main drawbacks are it’s poor resistance to alkali chemicals and solutions containing more than 10% ethanol. Hence, for any process that involves alcohol or alkali chemicals such as an ethanol, methanol, or isopropyl alcohol extraction, silicone gaskets would degrade over time. For extraction and decarboxylation of cannabis in coconut oil or butter however, silicone seals are moderately priced and highly resistant to vegetable oils and petroleum products. This material is typically Platinum or Peroxide cured. Platinum cured silicone is used in operations where purity is concerned. Peroxide cured silicone generally has more mechanical strength. (Ray, Chris. “So, Which Is Better, Platinum or Peroxide?” TBL Plastic, www.tblplastics.com/platinum-vs-peroxide-silicone-tubing/.)
BUNA®, also known as nitrile, is a synthetic rubber that was originally used in the tire industry for its high tensile strength and resistance to abrasion. It’s a lot tougher than silicone and therefore, popular in mechanically rigorous environments. Like silicone, it has excellent resistance to oils and petroleum products. It’s cheaper than silicone though and also good for processing ethanol and alkali solutions. BUNA’s® major drawback is a limited temperature range (-30˚F to + 200˚F). This precludes its use in applications involving steam. It’s also less resistant to cleaning chemicals than silicone or EPDM and does not meet USP Class IV standards (United States Pharmacopeia testing of plastics for basic safety). However, BUNA® does come in an FDA approved form under the label ‘white nitrile’
EPDM, short for Ethylene Propylene Diene Monomer has excellent water and steam resistance, with a temperature range of -30˚F to +300˚F. Because of its incredible resistance to
ozone, sunlight, severe weather conditions, oxygen, alkalis, and aging, EPDM is excellent for outdoor applications and as a general purpose material in contact with air, hot and cold water and saturated steam. EPDM is also a common gasket material to use with ethanol extraction. It’s poor resistance to oils, fats and most acids however, renders it a poor choice for butter extractions. Its resistance to terpenes and citrus oils is fair though not as high as that of FKM/Viton® (poor resistance to ethanol at greater than 40% concentration) or Kalrez® (Very expensive). This makes EPDM a solid choice for ethanol solvent recovery systems and extraction equipment.
Viton® is the Dupont Brand name for FKM, short for fluoroelastomer. This material is a synthetic rubber commonly used in O-rings. Dupont’s Specific mix of FKM is FDA approved and meets the USP Class VI and 3A codes. Generic brands of FKM are generally cheaper but are not FDA approved. This material has a high temperature range of -20˚F to +400˚F and has excellent resistance to acids, alkalis, fats, and oils. It has poor resistance to ethanol at over 40% concentration as well as bases when used with ketones. Along with PTFE/Teflon on our list, KFM/Viton has the highest resistance to terpenes and citrus oils, making it a good choice for contact with cannabis extracts toward the end process or through refining processes.
Teflon® is the Chemours brand name for PTFE, short for polytetrafluoroethylene. Used in highly corrosive environments, PTFE has a broad temperature range from -100˚F to +450˚F and is highly resistant to acids, alkali, fats, oils, ethanol, and abrasion. PTFE has been known to have problems under great mechanical stress, usually due to very high pressure. As a plastic with a tendency to creep, or deform under such stress, it is widely suggested that PTFE be used with high pressure clamps and are not recommended for processes that involve large temperature fluctuations. (See following paragraph on Tuf-Steel® for more information about clamping).
Tuf-Steel®Tuf-Steel® is a 50/50 blend of PTFE and atomized 316 (low iron content) stainless steel. It essentially has the same chemical resistance as PTFE without the tendency to creep. It’s temperature range is the highest of all the materials on our list, from -325˚F to +550˚F and is the preferred gasket material for steam-in-place systems and water-for-injection applications. On various websites, the manufacturer of Tuf-Steel® recommended that this gasket material be used with the Torque-Rite® Clamp to prevent leaks. They specifically state “Stops leaks when correctly torqued (50 in./lbs with Torque-Rite® TR-50)”. (“Tuf-Steel®.” Tuf Steel | High Temperature Steam Sanitary Gasket | Rubber Fab, www.rubberfab.com/products/sanitary-gaskets/specialty-gaskets/tuf-steel.) Here at Nyborg, we opted to use a regular high pressure clamp because we found the Torque-Rite® clamp to be cost prohibitive. ($17 for a 3” high pressure clamp vs. + $250 for a 3” Torque-Rite Clamp). We torqued our bolts to well beyond 50 in/lbs (more like 50 ft/lbs) with a torque wrench before leakage stopped. This experienced leakage could be due to improper torquing but thus far, it would seem that a great deal more pressure than 50 in/ lbs is required for a full seal using the Tuf-Steel® gasket.
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