5 Types of Autoclavable Plastics
by dewi susanti
An autoclavable plastic is one that has the ability to effectively withstand harsh effects of an autoclave (an apparatus used in sterilizing processes through application of super-heated steam under high pressure). Other ordinary plastics may suffer degeneration under such extreme conditions. Due to their resilience, bottles or containers made of such strong plastics are highly suited for chemical and pharmaceutical packaging, environmental sampling and also handling laboratory samples.
How Autoclavable Plastics Are Made
A group of chemicals referred to as polymers form the molecular basis of all types of plastics. It is from the various polymers that varying resistance to autoclaving is derived. Such polymers come from the process of heating different types of hydrocarbons such as natural gas, oil, and coal. The term used for this process is cracking.
Basically, what occurs is the breaking up of large molecules down to much smaller units. The small units are called monomers, which include: ethylene (ethane), propylene (propene), C2H4, butane, C3H6, C4H8, styrene among many other types of hydrocarbons. Thereafter, monomers go through a process involving chemical bonding to form longer chains of polymers. Each type of polymer (plastic) has unique characteristics that differentiate one from the other. Among such polymers can be found types that are resistant to autoclaving and those that are not:
Polypropylene (pp) is a translucent plastic. It has the capacity of withstanding maximum temperatures of up to 135oC (275oF). It also has a brittleness temperature (temperature where the plastic may crack or break if dropped) of 0oC (32oF).
Polypropylene possesses a low impact strength. However, it has excellent compatibility with concentrated or weak bases, acids and alcohol (has a capacity of withstanding any damage from such chemicals for a period of 30 days, constant exposure). Due to its characteristics, this polymer is most often used in making vials, bottles, pumps, clothing and funnels.
Apart from being autoclavable, polymethylpentene has a transparent physical characteristic. It has the capacity of withstanding temperatures of up to 175oC (347oF). Its brittleness temperature is 20oC (68oF).
Just as with Polypropylene, this polymer bears superb compatibility with concentrated and weak acids, alcohol and bases. Polymethylpentene is generally used in the manufacture of graduated cylinders and beakers.
Polycarbonate is transparent and autoclavable. This polymer has a maximum temperature of 135oC (275oF) and a brittleness temperature of -135oC (-135oF).
Polycarbonate bears a high impact strength as well as high compatibility with weak acids. The most common use of this polymer is in making safety eyewear, non-breakable windows and face shields.
The PTFE resin is an opaque polymer that is autoclavable. Its brittleness temperature is -100oC (-100oF) and maximum temperature is 260oC (50oF).
This polymer has the unique aspect of bearing excellent compatibility with nearly all chemicals. Hence, it has many uses in producing stoppers, pumps, tubing, non-stick pans, containers and samplers.
Polymethyl Methacrylate (PMMA)
Polymethyl methacrylate is also called Acrylic. It is a clear and autoclavable polymer with a maximum temperature of 50oC (122oF) and brittleness temperature of 20oC (68oF). However, this polymer has no excellent compatibility with any chemical. It is used mostly for machine guards and bench top shields.
The varying characteristics of different types of autoclavable polymers (plastics) make them suitable for different functions. The variations provide useful characteristics for particular functions despite the major similarity that they have of bearing excellent resistance to autoclaving.
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