# Polybenzimidazole (PBI)

PBI is a thermoset plastic. It has the highest mechanical heat stability among thermoset plastics. In addition, it has a moderately low density and a fairly high dielectric strength. The graph bars on the material properties cards below compare PBI to other thermoset plastics (top) and the entire database (bottom). A full bar means this is the highest value in the relevant set. A half-full bar means it's 50% of the highest, and so on.

## Mechanical Properties

Compressive (Crushing) Strength

350 *MPa* 50 *x 10 ^{3} psi*

Elastic (Young's, Tensile) Modulus

5.9 *GPa* 0.85 *x 10 ^{6} psi*

Elongation at Break

3.0 *%*

Fatigue Strength

56 *MPa* 8.1 *x 10 ^{3} psi*

Flexural Modulus

6.5 *GPa* 0.95 *x 10 ^{6} psi*

Flexural Strength

220 *MPa* 32 *x 10 ^{3} psi*

Impact Strength: Notched Izod

27 *J/m* 0.5 *ft-lb/in*

Tensile Strength: Ultimate (UTS)

160 *MPa* 23 *x 10 ^{3} psi*

## Thermal Properties

Glass Transition Temperature

410 *°C* 770 *°F*

Heat Deflection Temperature At 1.82 MPa (264 psi)

430 *°C* 810 *°F*

Maximum Temperature: Decomposition

590 *°C* 1090 *°F*

Maximum Temperature: Mechanical

340 *°C* 640 *°F*

Specific Heat Capacity

930 *J/kg-K* 0.22 *BTU/lb-°F*

Thermal Conductivity

0.41 *W/m-K* 0.24 *BTU/h-ft-°F*

Thermal Expansion

23 *µm/m-K*

## Electrical Properties

Dielectric Constant (Relative Permittivity) At 1 Hz

3.4

Dielectric Constant (Relative Permittivity) At 1 MHz

3.8

Dielectric Strength (Breakdown Potential)

23 *kV/mm* 0.88 *V/mil*

Electrical Resistivity Order of Magnitude

13 *10 ^{x} Ω-m*

## Otherwise Unclassified Properties

Density

1.3 *g/cm ^{3}* 81

*lb/ft*

^{3}Limiting Oxygen Index (LOI)

58 *%*

Water Absorption After 24 Hours

0.4 *%*

## Common Calculations

Stiffness to Weight: Axial

2.5 *points*

Stiffness to Weight: Bending

46 *points*

Strength to Weight: Axial

34 *points*

Strength to Weight: Bending

50 *points*

Thermal Diffusivity

0.34 *mm ^{2}/s*

Thermal Shock Resistance

84 *points*

## Followup Questions

## Further Reading

Thermosets: Structure, Properties and Applications, Qipeng Guo (editor), 2012

Modern Plastics Handbook, Charles A. Harper (editor), 1999

Plastics Materials, 7th ed., J. A. Brydson, 1999