Sterlization of Parylene

Regardless of the variant, Parylene, is highly acclaimed for the many advantages it offers as a protective conformal coating for medical, aerospace, defense, LEDs, and automotive applications. Chief among the coating’s benefits, however, is that it can withstand common sterilization techniques, such as electron beam (e-beam), gamma, ethylene oxide (EtO), and steam autoclave.

Like many chemicals, para-xylylene comes in several common variants:

• Parylene N – The most basic type of the compound is highly elastic and, as such, is very good at penetrating small areas on components. Parylene N maintains the highest electrical insulation capabilities of the Parylenes.
• Parylene C – The C variant of the chemical replaces one aromatic hydrogen component with a chlorine atom. It is less elastic and is extremely popular in medical applications, in part due to its high degree of moisture resistance and chemical barrier performance
• ParyFree^® – A proprietary, halogen-free molecule that combines the superior barrier properties of Parylene C with the electrical properties of Parylene N.
• Parylene HT^® – Formulated with fluorinated connecting bonds, providing ultra-high temperature capabilities and UV resistance.

While Parylene has a very high melting point — from 290°C to 420°C, depending on the variant — it suffers thermal stress at much lower temperatures, especially when it is heated in the presence of oxygen. Parylenes N and C can last up to 10 years at 220°C in a vacuum, but their temperature handling capabilities go down to 80°C and 100°C when in the presence of oxygen. Parylene HT, on the other hand, can withstand continuous service temperatures of 350°C  in the presence of oxygen due to its unique molecular structure. 

Parylene is somewhat of an anomaly when it comes to radiation sterilization. Although radiation sterilization methods such as e-beam and gamma are extremely common, they can compromise the integrity of certain materials, particularly polymeric thin films. “Thin part sections, thin films, and fibers present in a component or product can allow for excessive oxygen exposure during the irradiation process, thus causing degradation of the polymer material,” according to sterilization specialist Sterigenics.

Despite its status as a thin polymer film, however, Parylene is prized for its ability to withstand radiation sterilization methods, unlike many of its fellow films. Parylene C, commonly utilized in medical settings, preserves its chemical integrity when subjected to radiation sterilization using e-beam or gamma methods.