Buna N and Buna S Rubber

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Buna-N and Buna-S Rubber — Note

Buna-N and Buna-S Rubber

1. Introduction

Buna rubbers are synthetic rubbers produced by copolymerisation of dienes with vinyl monomers. Developed in Germany during the 1930s, they are widely used in tires, seals, hoses, gaskets, and industrial applications.

Main types: Buna-N (Nitrile Rubber, NBR) and Buna-S (Styrene-Butadiene Rubber, SBR).

2. Buna-N Rubber (Nitrile Rubber, NBR)

Monomers: Butadiene (CH2=CH–CH=CH2) + Acrylonitrile (CH2=CH–CN)

2.1 Polymerisation

Free radical copolymerisation in emulsion or solution. Acrylonitrile content usually 18–50%.

n CH2=CH–CH=CH2 + m CH2=CH–CN → –[CH2–CH=CH–CH2]n–[CH2–CH–CN]m–

2.2 Properties

  • Excellent oil and fuel resistance
  • Good abrasion resistance
  • Moderate mechanical strength
  • Poor resistance to ozone and sunlight

2.3 Applications

  • Fuel hoses, gaskets, O-rings
  • Oil-resistant seals and diaphragms
  • Automotive and aerospace components

3. Buna-S Rubber (Styrene-Butadiene Rubber, SBR)

Monomers: Butadiene (CH2=CH–CH=CH2) + Styrene (C6H5–CH=CH2)

3.1 Polymerisation

Emulsion polymerisation using free radical initiators. Styrene content typically 20–25%.

n CH2=CH–CH=CH2 + m C6H5–CH=CH2 → –[CH2–CH=CH–CH2]n–[CH2–CH(C6H5)]m–

3.2 Properties

  • Good abrasion and heat resistance
  • Moderate tensile strength and elasticity
  • Better resistance to aging and ozone than natural rubber

3.3 Applications

  • Automobile tires (SBR blends with natural rubber)
  • Conveyor belts, gaskets, footwear soles
  • Mechanical goods requiring moderate heat and wear resistance

4. Comparison of Buna-N and Buna-S

Property Buna-N (NBR) Buna-S (SBR)
Monomers Butadiene + Acrylonitrile Butadiene + Styrene
Oil/Fuel Resistance Excellent Poor
Heat Resistance Moderate Good
Abrasion Resistance Moderate Good
Elasticity Moderate Good
Applications Fuel hoses, oil seals Tires, footwear, belts

5. Summary

Buna rubbers are important synthetic rubbers tailored for specific applications: Buna-N (NBR) is best for oil, fuel, and chemical resistance, while Buna-S (SBR) is best for abrasion resistance, heat, and general-purpose applications like tires and belts.

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