How to choose the right sealing compound
‘Seal materials must be chemically resistant to the product processed, CIP media used, and the harsh SIP sterilization process using superheated steam up to 140°C.’‘Even materials that may appear similar react differently in chemical media.’ By Dr. Burkhard Ledig
The acronyms may be short in the chemical processing, food and pharmaceutical industries, but they pose big sealing challenges. 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 affect. In addition to this, for some applications, the seals must meet the strict requirements for FDA, Food and Drug Administration, approval.
Busak+Shamban, by working closely with major customers in the chemical industry, saw and responded to the trend for increasingly aggressive chemicals and processes. To extend seal life and reduce downtime, they tested existing materials and developed new compounds to cost—effectively meet performance requirements and approvals. The main conclusion of the Busak+Shamban research, the first of its kind within the industry, was that by matching the right sealing compound to a specific application, this could be achieved. Specifying the right material when CIP and SIP is used is not a simple matter. 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 FFKM, perfluoroelastomer, not given as a recommended material for sealing within the standards, was universally suitable, even at elevated temperatures.
CIP chemicals
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 includes 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 sulphuric 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 per—acetic 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 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.
Standards applying to seals
Standards do not really aid 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, 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 sterilising technology. For some applications, these materials must also comply with the relevant FDA regulation under 21 CFR 177.2600.
Summary of Busak+Shamban test results
However, the Busak+Shamban tests showed the following: •Silicon rubber (VMQ) is not suitable for most CIP and SIP applications including alkaline media or under hot steam sterilisation conditions. •Generally, HNBR is not suitable in any CIP media. •The FDA compliant FKM materials showed significant weaknesses in alkaline—based media, as well as acidic media, including the per—acetic 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, Perfluoroelastomer, showed most resistance in CIP media, especially at elevated temperatures. It is universally suited for CIP applications and SIP sterilization processes.
Performance in SIP sterilization processes
After CIP cleaning, many process plants employ a sterilization stage with steam, typically in the range 125°C to 140°C, and for this reason, the steam resistance of the elastomers used must always be considered. The conclusions of Busak+Shamban on performance of elastomer materials in steam: •At 125°C 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
The results of Busak+Shamban research 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 who can offer a range of tested and proven materials.
Busak+Shamban publish a chemical compatibility chart to help equipment manufacturers and processors select the right seal for an application. This gives details of the resistance of different materials in a variety of chemical media, and offers an effective guide to initial compound selection.
Details of Busak+Shamban tests
The following seal materials were tested: •Two types of peroxide cross linked Ethylene Propylene Diene Rubber (EPDM) •Two types of Fluoroelastomer (FKM), cross-linked with bisphenol •A Hydrogenated Acrylonitrile Butadiene Rubber (HNBR), cross-linked with peroxide •An FFKM Isolast perfluoroelastomer which conforms to FDA Guidelines 21 CFR 177.2400 (d) and 21 CFR 177.2600 (e, f) 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. The material test specimens were immersed in the following CIP media concentrations, at the temperatures given for one week in accordance to DIN 53521: •Alkaline CIP formulations based on caustic soda liquor and surfactants; concentration of 4 percent, temperature 80°C. •Acidic CIP formulations based on nitric acid or sulphuric acid; concentration of 2 percent, temperature 80°C. •Disinfectant alkaline CIP formulations based on sodium hypochlorite and active chlorine; concentration of 3 percent, temperature 80°C. •Disinfectant acidic CIP formulation based on per-acetic acid and hydrogen peroxide; concentration of 2 percent, temperature 80°C. •Disinfectant spray injection media based on hydrogen peroxide; concentration of 1 percent, temperature 80°C.
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 installation of seals in sterile technology, narrow limits are set on the volume change of the sealing material.
Recommendations for use dependent on volume change: •Less than 5 percent — material suitable for sealing. •More than 5 percent but less than 10 percent — material can only be used for sealing with reservations. •More than 10 percent — material not suitable for sealing.
Table of results:
EPDM 1EPDM 2FKM 1FKM 2HNBRFFKMAlkaline CIP formulations414431Acidic CIP formulations114441Disinfectant alkaline CIP113141Disinfectant acidic CIP414441Disinfectant spray injection444442 Key: ד —Strongly recommended ה —Recommended ו —Recommended with reserves ז —Unsuitable
Details of test results by material and media:
Alkaline CIP formulations based on caustic soda liquor and surfactants; concentration of 4 percent, temperature 80°C
EPDM1Not recommended8 percent shrinkage due to surfactants, which extracted constituents from the sealEPDM2Strongly recommendedVolume change minimalFKM1&2UnsuitableDestroyed by sodium hydroxideHNBRWith reserves5 percent volume change but other results in alkali show limited performanceFFKMStrongly recommendedBest sealing material in this media on all three parameters — practically unchanged
Acidic CIP formulations based on nitric acid or sulphuric acid; concentration of 2 percent, temperature 80°C
EPDM1&2Strongly recommendedPractically no volume changeFKM1&2UnsuitableExtreme volume increaseHNBRUnsuitableSwelled by almost 100 percentFFKMStrongly recommendedPractically no volume change
Disinfectant alkaline CIP formulations based on sodium hypochlorite and active chlorine; concentration of 3 percent, temperature 80°C
EPDM1&2Strongly recommendedMinimal volume changeFKM1With reservesVolume change of 6 percentFKM2Strongly recommendedMinimal volume changeHNBRUnsuitableVolume change significantly higher than other materialsFFKMStrongly recommendedMinimal volume change
Disinfectant acidic CIP formulation based on per-acetic acid and hydrogen peroxide; concentration of 2 percent, temperature 80°C
EPDM1Unsuitable8 percent volume increaseEPDM2Strongly recommendedFully inert, the most cost—effective material for this mediaFKM1&2UnsuitableVolume change exceeded 65 percent, probably due to absorption of acetic acidHNBRUnsuitableSignificant volume changeFFKMStrongly recommendedMinimal volume change
Disinfectant spray injection media based on hydrogen peroxide; concentration of 1 percent, temperature 80°C
EPDM1&2UnsuitableVolume increase of 20 percent and surfaces became sootyFKM1&2UnsuitableVolume change of between 15 and 22 percentHNBRUnsuitableHigh volume increaseFFKMStrongly recommendedFully inert, the only sealing material suitable for this media Dr. Burkhard Ledig is CPI Global Technical Manager at Busak+Shamban. He has a qualification in polymer science and 13 years experience in the field of polymer products. He studied chemistry at Marburg, and since 1997, he has worked for Busak+Shamban, where he has held various positions, including European Technical Manager Isolast. He conducts market projects for the company’s Pharmaceuticals and Food and Chemicals and Process Technology divisions. Busak+Shamban is one of the world’s largest seal developers and manufacturers. As the sales and marketing arm of Trelleborg Sealing Solutions, they have 30 production facilities globally and more than 40 marketing companies. For more information about Busak+Shamban and your local contact, visit www.busakshamban.com.
eF