By Dr. Burkhard Ledig, CPI Global Technical Manager, Busak+Shamban
Specifying the right seal material when CIP and SIP are used is not a simple matter. CIP-cleaning in place-uses chemicals lethal to the majority of elastomer seals, while SIP-sterilization in place-employs superheated steam (up to 140°C) with an even greater deteriorating effect. In addition to this, for some applications, the seals must meet the strict requirements for FDA approval. In fact, test results proved that some elastomer types recommended in DIN 11864 and DIN 11851, applying to fittings for connections in process equipment usually subject to CIP and SIP, were unsuitable or not wholly suitable for sealing with these cleaning regimes. And perfluoroelastomer (FFKM), not given as a recommended material for sealing within the standards, was universally suitable even at elevated temperatures. New research has shown, however, that by matching the right sealing compound to a specific application, seal life can be extended and downtime reduced (see Fig. 1).
Figure 1. Process equipment sealing compounds must match industry CIP applications. Photo courtesy of Busak+Shamban.
Automated CIP or SIP systems ensure safe and efficient processing, prevent toxic contamination of products and minimize recontamination of the process. To achieve cleaning efficiency and effectiveness, a complex mixture of chemicals is required.
CIP cleaning media include the following:
- Alkaline CIP mixtures based on sodium hydroxide and surfactants used to remove organic and fatty contamination, emulsions and gels.
- Acid CIP mixtures based on nitric acid and phosphoric acid or sulfuric acid used to remove inorganic sediments in tanks, tubes, fermentation or similar equipment.
- Alkaline CIP disinfecting mixtures based on sodium hypochlorite and active chlorine.
- Acid CIP disinfecting mixture based on peracetic acid and hydrogen peroxide used on surfaces based on activated oxygen.
- Intensive disinfecting media based on hydrogen peroxide and surfactants added to alkaline CIP media to remove those residues requiring an oxidation stage.
These chemical media do not affect processing equipment manufactured from stainless steel, but severe damage may be caused to elastomeric seals, especially in applications where thermal load and pressure are involved.
Seal materials must be chemically resistant to the product processed, CIP media used and also the harsh SIP sterilization process using superheated steam up to 140°C. They need to withstand abrasion by any solids contained in the product and have a low level of extractables. Seal surfaces must be easy to clean and sterilize and, if required, the material should have FDA approval and, in many cases, also 3A approval.
Standards applying to seals
Standards do not really help in deciding which materials to specify for seals. They only offer general information and refer just to groups of elastomeric materials and their compliance with FDA Standard 21 CFR 177.2600. No specific characteristics are defined, such as vulcanizing system or shore hardness, nor are indications given regarding chemical resistance to common CIP media or performance in steam sterilization at temperatures up to 140°C.
The standards DIN 11864 and DIN 11851, pertaining to covering fittings for the food, chemical and pharmaceutical industry on aseptic and stainless-steel connections, recommend ethylene propylene diene rubber (EPDM), hydrogenated acrylonitrile butadiene rubber (HNBR), silicone rubber (VMQ) and fluoroelastomer (FKM) as materials for elastomeric seals used in sterilizing technology. For some applications, these materials must also comply with the relevant FDA regulation under 21 CFR 177.2600.
Summary of test results
- Silicone rubber (VMQ) is not suitable for most CIP and SIP applications, including alkaline media or under hot steam sterilization conditions.
- Generally, HNBR is not suitable in many CIP media.
- The FDA-compliant FKM materials showed significant weaknesses in alkaline-based media and acidic media, including the peracetic acid and hydrogen peroxide mix, due to their polar nature.
- EPDM was established as an excellent sealing material for aseptic technology, but some formulations are less suited to “intensive” CIP additives.
- FFKM showed the most resistance in CIP media, especially at elevated temperatures. It is universally suited for CIP applications and SIP sterilization processes.
Performance in SIP sterilization
After CIP cleaning, many process plants employ a sterilization stage with steam, typically in the range of 125°C up to 140°C, and for this reason, the steam resistance of the elastomers used must always be considered.
The performance of elastomer materials in steam:
- At 125°C up to 140°C, FKM and HNBR are already beyond their performance limits.
- In the presence of atmospheric oxygen and steam, EPDM is resistant up to 150°C, whereas without oxygen, temperatures of up to 200°C are achievable.
- FFKM, perfluoroelastomer, offers the best temperature resistance, with some grades capable of operating in temperatures up to 230°C.
- Steam temperatures are increasing up to and beyond 150°C. Under these operating conditions, EPDM may reach its natural limit and, in these cases, perfluoroelastomer is the best material.
Selecting for chemical compatibility
Research results demonstrate that it is not simple to select the optimum seal material for a CIP or SIP application. Even materials that may appear similar react differently in chemical media. To ensure seal life is maximized, it is vital to work with a sealing supplier that can offer a range of tested and proven materials (see Fig. 2).
Figure 2. The manufacture of seals, within the Busak+Shamban cleanroom environment, for semiconductor applications. Photo courtesy of Busak+Shamban.
The following seal materials were tested:
- Two types of peroxide, cross-linked EPDM
- Two types of FKM, cross-linked with bisphenol
- HNBR, cross-linked with peroxide
- A FFKM Isolast® perfluoroelastomer, which conforms to FDA 21 CFR 177.2400 (d) and 21 CFR 177.2600 (e, f) guidelines
Silicone rubber (VMQ) was not tested, as initial experiments showed it to be insufficiently resistant in alkaline media and under conditions of live steam sterilization (see Table 1).
Table 1: Summary of testing results
The material test specimens were immersed in the following CIP media concentrations at given temperatures for one week in accordance with DIN 53521:
- Alkaline CIP formulations based on caustic soda liquor and surfactants; concentration of 4%, temperature 80°C (see Table 2)
Table 2: Alkaline CIP formulations based on caustic soda liquor and surfactants
- Acidic CIP formulations based on nitric acid or sulfuric acid; concentration of 2%, temperature 80°C (see Table 3)
Table 3: Acidic CIP formulations based on nitric acid or sulfuric acid
- Disinfectant alkaline CIP formulations based on sodium hypochlorite and active chlorine; concentration of 3%, temperature 80°C (see Table 4)
Table 4: Disinfectant alkaline CIP formulations based on sodium hypochlorite and active chlorine
- Disinfectant acidic CIP formulation based on peracetic acid and hydrogen peroxide; concentration of 2%, temperature 80°C (see Table 5)
Table 5: Disinfectant acidic CIP formulation based on peracetic acid and hydrogen peroxide
- Disinfectant spray injection media based on hydrogen peroxide with a concentration of 1%, temperature 80°C (see Table 6)
Table 6: Disinfectant spray injection media based on hydrogen peroxide
After the test period, the hardness (shore A) and percentage weight change were measured, along with the most important parameter-volume change.
Because of the dead-space-free instal-lation of seals in sterile technology, narrow limits are set on volume change of the seal-ing material.
Recommendations for use dependent on volume change:
- Less than 5%: material suitable for sealing
- More than 5% but 10% or less: material can only be used for sealing with reservations
- More than 10%: material not suitable for sealing.
Dr. Burkhard Ledig is CPI Global Technical Manager at Busak+Shamban. He studied chemistry at Marburg, and has worked for Busak+Shamban since 1997. He has held various positions, including European Technical Manager-Isolast®. He conducts market projects for the company’s Pharmaceuticals, Food and Chemicals, and Process Technology divisions.