One of the major innovations of the last century was the invention and widespread use of plastic products, which replaced traditional materials, such as metal, glass, or cotton in daily life. Plastics have revolutionized many industries.
What is the strongest plastic? It’s a simple question, perhaps even naive. Take it to a chemical engineer or material scientist, and they won’t come up with a single, yes answer either, but (at least) two questions:
- What does “plastic” mean? Does the thermosetting material such as epoxy resin calculate? What about polymers reinforced with glass or carbon fiber fillers?
- What does “strong” mean? Did you say wear resistance, compressive strength or tensile strength, temperature tolerance, or, Chemical resistance?
However, suppose you limit the problem to thermoplastic materials that can be melted and molded, extruded, spun, and/or drawn into various shapes. And you exclude composites of any kind – just pure polymers without any reinforcement or padding.
The material is polybenzimidazole (PBI) and is marketed under the trade name Celazole as a bulk polymer. It has been reported to have the highest compressive strength of any unfilled plastic material, as well as the highest tensile strength, shear strength, and Rockwell hardness rating of any plastic.
It retains its mechanical properties at high temperatures better than any other unreinforced polymer and has been reported to be exposed for short periods at 1400°F, 200° higher than the melting point of aluminum.
Phrases such as “Today’s highest performing engineering thermoplastic” are commonly used to describe serazoles in the plastics industry literature.
Benzene, the five-membered heterocyclic chain polymer, contains two nitrogen atoms. It is generally formed by polycondensation and cyclization of aryltetramine and diphenyl phthalate.
The reaction can be carried out in a molten state or strong polar solvents. The thermal stability of aromatic PBI in nitrogen is greater than 500℃, and the introduction of flexible groups or side groups can improve the solubility, but the thermal stability is decreased.
Its trade name is Celazole PBI. The thermal deformation temperature of polyphenylene bibenzo imidazole plastic is 430℃, the ultimate oxygen index is 58, the compressive strength is 410MPa, the tensile strength is 165MPa, the bending strength is 227MPa, the friction coefficient with steel is 0.27, the dielectric constant is 3.3, along with good radiation resistance, boiling water resistance, solvent resistance, and the chemical resistance.
It can be used as a high temperature-resistant adhesive and high-performance composite material. It is widely used in aerospace, chemical machinery, oil exploitation, automobile, and other fields, and the fiber fabric is used as a protective suit against fire and atomic radiation.
Polyamines are fused and polycondensed with diacid or diester at high temperature to form soluble polyamine amide, and then imidazole ring polymer is formed by dehydration cyclization reaction.
After high temperature (400℃) treatment to complete curing, the polymer becomes insoluble and insoluble. Typical polymers are formed by condensation of 3,3 ‘-diamino diphenyl and diphenyl phthalate, whose fibers are called PBI fibers.
The main features of PBI:
- As today’s most high-grade thermoplastic, PBI has the advantage of having high-temperature resistance. Its continuous working time in the air can reach 20000 hours, long-term high-temperature resistance can reach 310 degrees, 500 degrees high temperature can still work for several hours, and instantaneous temperature tolerance can reach 760 degrees.
- PBI has excellent mechanical strength, rigidity, hardness and creep resistance, and excellent dimensional stability.
- Excellent wear and friction properties.
- Very low linear coefficient of thermal expansion.
- Excellent resistance to high-energy radiation (r-ray and x-ray). PBI has excellent corrosion resistance, and can still maintain stability in strong acid and alkali environments.
- Inherently low flammability.
- High purity under an ionic contamination environment.
- Low exhaust (dry material). In the presence of ionic impurities, PBI is clean and does not exhaust (except in water).
The material characteristics of PBI determine the machining characteristics. The plastic features high hardness and good wear resistance, so we should pay attention to the processing.
PBI notch stress is relatively large during processing but its feed speed isn’t fast, otherwise, it will cause cracking. In addition, the tool must choose sharp tools.
For parts with higher size requirements, diamond-coated tools are needed to prevent tool wear and size changes.
In addition, coolant must be used when processing. Its high price, complex preparation technology, and difficult processing affect its application and development. We hope our guide will help you make the right selection for your next project.