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Advanced FKM materials introduced

05 February 2008

FKM materials are ideal for sealing in oily and greasy substances where they are proven to provide extended life. The weakness of standard FKMs is their performance in SIP regimes and aggressive CIP media. Trelleborg Sealing Solutions has engineered two advanced FKM materials, Resifluor 500 and Resifluor V8T41, which have superior high temperature water capabilities and stability in destructive chemicals, especially solvents.

Fluoroelastomer (FKM) material is the optimum choice for sealing when processing greasy or fatty substances. In food and beverage manufacturing, this would be anything with a high butter, milk or fat content. Less obviously, extracts such as lemon aromas have high oil content, and in pharmaceutical production, so do ointments, creams and lotions.

The aim for seals in these hygienic applications is to have a zero dead space installation. This may be compromised if a seal extrudes after expansion, so a critical factor that influences the effectiveness of a seal is volume increase. Tests show that EPDM swells significantly when in contact with process media with a significant oil or fat content, while FKM, with its inherent resistance within non-polar environments, has very low volume change.

However, when greasy and fatty media are processed, there is a higher risk of potential contamination than with most other substances. Dairy produce, for instance, is subject to rapid bacterial and microbial growth. Cleaning regimes for equipment used for such produce are extremely stringent and always include a SIP (Sterilise In Place) regime. The same is true of ointments, creams and lotions in pharmaceutical production.

The long-term performance of standard FKM seals is limited, and they tend to fail in steam at operating temperatures of 100°C / 212°F. This is much lower than steam cleaning temperatures of 130°C / 266°F, so these materials are not suited if there is an SIP phase. In addition, due to their vinylidene-based polymer composition, FKMs are acidic and show significant weaknesses in alkaline-based media.

“The usual option for processors of substances with high fat or oil content is to specify an EPDM seal that will withstand the steam and many aggressive CIP (Cleaning In Place) chemicals,” says Burkhard Ledig, technical manager of CPI Development Europe. “Inevitable deterioration due to fat content is then countered with frequent seal changes. This means the manufacturers suffer a poor MTBM (Meantime Between Maintenance), lowering efficiency of the overall production process and increasing total cost.”

Trelleborg Sealing Solutions therefore investigated the possibility of engineering an FKM material with a higher resistance to CIP and SIP regimes. To do this, two compounds were formulated based on a completely different polymer architecture, which along with an elevated fluorine level meant they had an almost non-polar structure. The resulting materials were Resifluor 500 and V8T41.

Both of the new materials have excellent steam resistance. In tests, Resifluor 500 withstood temperatures up to +150°C / +302°F, while V8T41 proved to have an unsurpassed capability up to +170°C / +338°F. This makes them the ideal choices for high-fat food and beverage applications or in the preparation of oil or grease-based pharmaceutical products.

In addition, Resifluor 500 demonstrated outstanding chemical stability with exceptional performance in both polar and non-polar CIP media including solvents, the most aggressive of all cleaning chemicals. Where solvents are used, different solvent types are required to remove different process media. Depending on the substance, these will be polar or non-polar. Based on the principle that like dissolves like, a non-polar material, such as FKM, is not suited to sealing in non-polar solvents, and the same is true of the polar EPDM in polar solvents. The sealing material must therefore be matched to the type of solvent used in these extreme cleaning processes. This obviously limits the effectiveness of seals in mixed process streams where they may be subject to both solvent types.

Tests confirmed the excellent performance of Resifluor 500 in non-polar solvents such as toluene and hexane and that it is adequate in polar solvents such as methanol, acetone and MEK. A major advantage to processors who have a mixed process stream, this means there is now a cost-effective sealing material that gives extended life in such applications, as long as some volume change is acceptable.

In addition, Resifluor 500 and Resifluor V8T41 have full compliance to the stringent approvals applying to materials used in food, beverage and pharmaceutical production. These standards go from demanding FDA requirements, 3-A Sanitary Standards, USP Class VI and culminate in Cytotoxicity testing where suppliers must prove that products are completely non-toxic.

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