Silicone rubber might be one of the first materials that comes to mind for use in medical devices. However, there are certain applications that require low permeability, such as syringe stoppers, plungers for infusion therapy applications, closure seals for drug vials and blood collection containers. In this two-part blog based on material from our webinar, A Short Overview of Butyl Rubber and Its Applications, it is shown the butyl rubber polymer family offers what is needed for those situations―both high density and low permeability. Part one covers the butyl family, as well as chemical resistance. Part two focuses on life sciences offerings, types of leakage and butyl case studies.
The material used for medical devices plays a critical role in safeguarding the drug or blood throughout its lifecycle with good ageing characteristics. Failure of the material is not acceptable since the result could be serious side effects for the patient.
In situations using vials and pre-filled syringes, typically the stoppers are not removed, but instead, a needle is inserted through the stopper to access the drug. This is where the material used for the stopper is key. Risks to the patient can occur if small pieces of the rubber tear off when the needle pierces the rubber, contaminating the drug. The stopper must remain intact through multiple piercings, so the rubber must have the ability to reseal to prevent leakage, as well as to prevent oxidation and contamination of the drug. The use of the correct material for a stopper is essential to ensure the safe and easy collection and storage of drugs and blood. It’s important to remember that patient risk can be high if the stopper material cannot meet these requirements.
In particular, multidose drug packaging, which is found in scenarios such as vaccination campaigns, is a prime example of this type of use. In instances like this, the stopper of an injection vial is pierced several times, as each dose is administered. Using butyl rubber allows the stopper to reseal after being breached, ensuring long-lasting protection for drugs in multi-piercing applications.
Parker has found that these needs can be met with the use of butyl rubber polymers, which offer both the high density and low permeability needed for these applications.
To understand what butyl rubber (llR) is and why it is recommended for these applications, we must first go back in history. Butyl rubber is not new but was first introduced in early 1940s. Isobutylene-isoprene rubber is a synthetic rubber produced by copolymerizing isobutylene with small amounts of isoprene. It is heat resistant up to 120° C and has very good low temperature flexibility, up to -59°C.
Butyl rubber is compatible with hot water and steam, glycol-based brake fluids, many acids, salts solutions, polar solvents, silicone oils and greases. Most importantly, it is ozone resistance. On the other hand, it is not compatible with mineral oils and grease, fuels and chlorinated hydrocarbons. That description may sound very similar to EPDM at first glance.
Although EPDM is similar to butyl rubber in chemical compatibility, EPDM has a higher temperature resistance advantage. This explains why EPDM has replaced butyl in many sealing environments. Yet, butyl still plays an important role in medical applications material offerings.
The Bromine and Chlorine story
Still following the chemical’s history, a chemist found that bromine and chlorine could be added in small amounts to isoprene to make BIIR and CIIR – bromobutyl and chlorobutyl. Together, these two are known as halobutyls. The properties of halobutyl polymers are similar to those of butyl, but they can be cured more rapidly and with different and smaller amounts of curing agents.
To understand the difference between BllR and CllR, let’s begin with chlorobutyl, which was first introduced in 1961. It provides low permeation with both air and water vapor. Also, it’s known to be weather resistant, provides good abrasion and tear resistance, and is a non-toxic cure system. Chlorobutyl is used on tires and innertubes, hose, gaskets, and in pharmaceutical stoppers and syringes.
BIIR and CIIR can be co-cured more readily in contact with other elastomers making up a rubber product. BIIR is very similar to CIIR, but with greater choice in curatives. It generally cures faster, has shorter scorch times, and requires lower cure levels. The cost may be slightly higher than CIIR. BllR is used on tire inner liners and sidewalls, pharmaceutical closures, conveyor belts and tank linings. For both BIIR and CIIR, the physical properties can vary greatly depending on the recipe. Elongation, toxicity, abrasion resistance, and more, can be modified greatly through compounding.
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