Autoclaving is a sterilization method that uses high-pressure steam to eliminate microorganisms. When considering plastics for this process, the answer is not a simple yes or no; some plastics can withstand the conditions, while others cannot. Knowing the difference is important for safety and material integrity, preventing damage and ensuring effective sterilization.
Understanding the Autoclave Process
An autoclave sterilizes items by exposing them to saturated steam under high pressure and temperature. Typical operating conditions involve temperatures around 121°C (250°F) or 132°C (270°F), with a pressure of approximately 15 psi. This combination of heat and moisture efficiently transfers thermal energy to the items, effectively denaturing proteins and destroying bacteria, viruses, fungi, and spores. Steam penetration ensures even heating and thorough sterility.
Before sterilization, air is removed from the chamber, often by vacuum or steam displacement, to ensure complete steam penetration. The chamber then fills with saturated steam, raising temperature and pressure to set parameters. After a predetermined holding time, the steam is exhausted, and the chamber depressurizes. This “wet heat” method is effective for microbial inactivation.
Identifying Autoclavable Plastics
Many types of plastics are designed to withstand the high temperatures and pressures of autoclaving, provided they are specifically labeled as “autoclave-safe”. Polypropylene (PP) is a common choice due to its durability and ability to endure repeated autoclaving cycles without significant degradation. Polytetrafluoroethylene (PTFE), along with other fluoropolymers like FEP and PFA, also demonstrate excellent resistance to autoclaving conditions.
Polycarbonate (PC) is another plastic that can be autoclaved, though it may experience some loss of mechanical strength after repeated cycles, typically with a lifespan of 30-50 cycles. Identification of autoclavable plastics often involves looking for specific symbols, such as an autoclave symbol, or checking recycling codes. Manufacturers usually provide documentation or labels indicating a plastic item’s maximum allowable temperature and suitability for steam sterilization. It is always advisable to consult manufacturer instructions to confirm compatibility before autoclaving.
What Happens to Non-Compatible Plastics
Submitting non-autoclavable plastics to the high heat and pressure inside an autoclave leads to undesirable outcomes. Common plastics such as polyethylene (PE), including low-density (LDPE) and high-density (HDPE) variants, polystyrene (PS), and polyvinyl chloride (PVC) are not suitable for autoclaving. These materials have lower melting points or reduced thermal stability. For instance, flexible PVC film begins to soften at approximately 60°C (140°F), far below typical autoclave temperatures.
When exposed to autoclave conditions, non-compatible plastics can melt, warp, or deform significantly. This physical degradation can render the items unusable and potentially damage the autoclave itself. Beyond physical changes, some non-autoclavable plastics may leach harmful chemicals into the sterilized contents or release toxic fumes into the environment. This chemical instability poses risks to both the integrity of the materials being sterilized and the safety of personnel.
Safe Practices for Autoclaving Plastics
Proper preparation and loading are important for safely autoclaving compatible plastics. All plastic items should be thoroughly cleaned and rinsed with distilled water before being placed in the autoclave to prevent contaminants from baking onto the surface. When loading, ensure sufficient space is left between items to allow for proper steam circulation and heat distribution. Overcrowding the chamber can hinder effective sterilization.
Caps and closures on plastic containers, such as bottles, must be loosened or completely removed before autoclaving to prevent pressure buildup, which can cause containers to collapse or explode. Using appropriate autoclave bags or secondary containers, preferably made of autoclavable plastic or stainless steel, helps contain contents and catch spills. After the cycle is complete, allow the items to cool inside the autoclave or in a designated cooling area before handling, as hot plastic is more susceptible to deformation.