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Extreme polymers are known for their performance at high temperatures that other polymers just can’t handle. In this blog post, we’ll take a look at PBI – the highest performing thermoplastic on the market today.

PBI Use in Firefighter Clothing.jpeg Source

What Is PBI?

PBI is short for Polybenzimidazole, but is probably best known by its trade name Celazole. This thermoplastic’s full name is poly-2,2′-(m-phenylene)-5,5′-bibenzimidazole.  It was first developed as a fire-resistant fiber for use by NASA 1961 by chemists H. Vogel and C.S. Marvel, and has found extensive application in recent years.

What Is PBI Known For?

PBI is primarily known for its performance under extreme temperatures.  It offers the highest heat resistance of any polymer known to man with excellent retention of mechanical properties even at temperatures exceeding 400°F.


Primarily, PBI is known for its outstanding resistance to combined heat and chemical attack.


 

What Are Some of PBI’s Other Characteristics?

Those who know about PBI often associate it with textiles, but as a molded resin it has a tensile strength of 23 ksi, a flexural strength of 32 ksi, and a compressive strength of 53 ksi (which is currently the highest compressive strength of any unfilled resin).  Compared to other polymers, it is considered strong, hard, and very stiff.


PBI remains stable at temperatures up to 700°F; this means that it retains its strength and stiffness up to this temperature. Some experts indicate its maximum continuous operating temperature lies around 1,000°F.  


In addition, PBI does not ignite or smolder.  It offers a low coefficient of thermal expansion, making it very dimensionally stable when subject to temperature fluctuations.  It is also resistant to high-pressure steam, making it well adapted for applications that require intense cleaning or sanitation.

This material is also abrasion resistant, mildew resistant, and resistant to radiation. PBI boasts the best wear resistance of any other polymer and its coefficient of friction is also quite low, at 0.19 to 0.27.

Drawbacks

The primary drawback of PBI is its cost relative to other polymers; however, the more inexpensive polymers don’t even come close it its level of performance at high temperatures.

Another drawback of PBI is moisture absorption.  It has a moisture absorption level of 0.4 as measured over 24 hours, which can cause it to be dimensionally unstable in very humid or wet environments.

Where Is PBI Used?

PBI found its original application in fiber form, and can be found in both welders’ and firemen’s protective gear, the membrane in fuel cells, and aircraft wall fabrics.  In later years, it became an effective replacement for asbestos, thanks to its temperature resistance.  Now, PBI is finding use in in industries as diverse as oil and gas, semiconductors, and aerospace.  

What Grades of PBI Are Available?

PBI is available in virgin form, carbon-reinforced, ultra-high purity, and electrostatic dissipative grades. There are also compounds of PBI combined with PEEK and PEKK that can be injection molded and extruded.  These are available in unfilled, carbon filled, glass filled, and self-lubricating grades.

Conclusion

PBI is the most heat-resistant polymer on the market today, and offers other benefits such as high strength, stiffness, chemical compatibility, excellent wear characteristics, and low friction.

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