Buna N, Buna S

Definition

Buna N is a copolymer of 1,3-butadiene and acrylonitrile. It is also called nitrile rubber and is mainly used where resistance to oils, petrol, and solvents is required.

Buna S is a copolymer of 1,3-butadiene and styrene. It is also called styrene-butadiene rubber (SBR) and is one of the most widely used synthetic rubbers for tyres, footwear, conveyor belts, and many other products.

The word “Buna” comes from:

Bu

= butadiene

Na

= sodium, used as a catalyst in early manufacture

Main Content

1. Buna N (Nitrile Rubber)

Composition and structure

Buna N is formed by copolymerizing butadiene with acrylonitrile. The proportion of acrylonitrile can be adjusted to modify properties. A higher acrylonitrile content generally increases resistance to oils and fuels but reduces flexibility at low temperatures.

Properties and uses

Buna N has excellent resistance to petroleum oils, grease, gasoline, and many organic solvents, along with good abrasion resistance and mechanical strength. Because of these properties, it is used in fuel hoses, oil seals, gaskets, O-rings, printing rollers, and protective gloves.

2. Buna S (Styrene-Butadiene Rubber)

Composition and structure

Buna S is made by copolymerizing butadiene with styrene. It is usually produced by emulsion polymerization and can be modified by changing the ratio of the monomers and the polymerization conditions. This gives a material with good elasticity and wear resistance.

Properties and uses

Buna S is a general-purpose rubber with good abrasion resistance, resilience, and aging stability. It is cheaper than natural rubber and is extensively used in automobile tyres, shoe soles, floor tiles, conveyor belts, wire insulation, and adhesives.

3. Comparison and importance

Resistance and performance

Buna N is superior in oil and fuel resistance, whereas Buna S is better as a general-purpose rubber with balanced strength, elasticity, and abrasion resistance. Buna N is preferred in chemical and automotive sealing applications, while Buna S dominates tyre manufacturing.

Industrial importance

Both rubbers are important examples of how copolymerization can produce materials with tailored properties. Their development reduced dependence on natural rubber and helped industries create products suited to specific environmental and mechanical demands.

Working / Process

1. Preparation of monomers

The required monomers are first purified and prepared for polymerization.
For Buna N, butadiene and acrylonitrile are used.
For Buna S, butadiene and styrene are used.
The monomers are mixed in suitable proportions depending on the desired properties of the final rubber.

2. Polymerization by emulsion method

The monomers are polymerized mainly by free-radical emulsion polymerization in the presence of an emulsifier, water, initiator, and stabilizers.
In older processes, sodium was used as a catalyst; however, modern industrial production generally uses emulsions and radical initiators.
The reaction conditions such as temperature, pressure, and time are carefully controlled to obtain the desired chain structure and molecular weight.

3. Recovery, processing, and vulcanization

After polymerization, the rubber is recovered by coagulation, washed, and dried.
The raw rubber is then mixed with additives such as sulfur, carbon black, antioxidants, and accelerators.
Finally, it is vulcanized to improve elasticity, strength, durability, and heat resistance before being shaped into useful products.

Advantages / Applications

Buna N advantages and applications

It has excellent resistance to oils, fuels, greases, and many chemicals, making it ideal for seals, gaskets, fuel tanks, oil-resistant hoses, gloves, and industrial coatings.

Buna S advantages and applications

It is economical, tough, abrasion-resistant, and suitable for large-scale manufacture, so it is widely used in tyres, shoe soles, belts, mats, and general rubber goods.

Industrial significance

Both rubbers are easy to process and can be modified to meet specific needs, making them highly valuable in automotive, mechanical, electrical, and consumer industries.

Summary

Buna N is a copolymer of butadiene and acrylonitrile with excellent oil resistance.
Buna S is a copolymer of butadiene and styrene and is a widely used general-purpose rubber.
Both are important synthetic rubbers produced by copolymerization and used extensively in industry.
Important terms to remember: copolymer, butadiene, acrylonitrile, styrene, nitrile rubber, SBR, emulsion polymerization, vulcanization