Introduction to NBR Rubber
NBR, or Nitrile Butadiene Rubber (also known as Buna-N), is a synthetic copolymer produced by the emulsion polymerization of acrylonitrile (ACN) and butadiene. The acrylonitrile content typically ranges from 18% to 50%, which significantly influences its properties—higher ACN content enhances oil resistance but reduces low-temperature flexibility. Developed in the 1930s, NBR was created to address the limitations of natural rubber in oil-exposed environments. It is often compounded with fillers like carbon black, plasticizers, and antioxidants to tailor its performance. Variations include hydrogenated NBR (HNBR) for improved heat and ozone resistance, and carboxylated NBR (XNBR) for better abrasion resistance.
Characteristics of NBR Rubber
NBR offers a versatile profile of properties, particularly excelling in chemical resistance. Here are its key characteristics:
- Mechanical Properties: NBR has good tensile strength (10-20 MPa), elongation at break (200-600%), and abrasion resistance. It provides moderate tear strength and resilience, making it suitable for dynamic applications. However, it can be brittle at low temperatures unless formulated with plasticizers.
- Chemical Resistance: This is NBR's standout feature. It exhibits excellent resistance to oils, fuels, greases, and many hydrocarbons due to the polar acrylonitrile groups. It also resists water, dilute acids, and alkalis. However, it has poor resistance to ozone, weathering, ketones, esters, and aromatic solvents, requiring protective additives.
- Thermal Properties: NBR operates effectively from -40°C to +120°C (or up to +150°C for short periods). Low-ACN grades offer better low-temperature performance, while high-ACN grades handle higher temperatures but may stiffen in cold conditions.
- Durability and Aging: It has fair resistance to heat aging and compression set, improved with antioxidants. Ozone and UV resistance is low without antiozonants or blending with other rubbers like EPDM.
- Processing and Cost: NBR is easy to process via extrusion, injection molding, and compression molding. It's more expensive than general-purpose rubbers like SBR but cost-effective for oil-resistant applications.
- Other Properties: Low gas permeability, good adhesion to metals (useful for bonded parts), and compatibility with polar fluids. It can be vulcanized with sulfur or peroxides. Electrical insulation is moderate, and it's not ideal for food-contact without FDA-approved grades.
In formulations, NBR is often blended with PVC for improved ozone resistance or with other elastomers to balance properties.
Applications of NBR Rubber
NBR's oil resistance makes it ideal for demanding environments across various sectors:
- Automotive and Aerospace: Used in O-rings, seals, gaskets, fuel hoses, and oil seals for engines, transmissions, and hydraulic systems due to its resistance to petroleum-based fluids.
- Oil and Gas Industry: Essential for drilling equipment, pump seals, and blowout preventers where exposure to crude oil and chemicals is constant.
- Industrial Hoses and Belts: In hydraulic hoses, conveyor belts, and diaphragms for handling oils and chemicals.
- Gloves and Protective Gear: Nitrile gloves are popular in medical, laboratory, and industrial settings for their puncture resistance, chemical protection, and latex-free nature.
- Seals and Gaskets: In plumbing, appliances, and machinery for water and oil sealing.
- Other Uses: Rollers in printing and textiles, footwear soles, adhesives, and foam insulation. HNBR variants are used in high-performance automotive timing belts.
NBR is produced in large volumes globally, with ongoing developments in bio-based and recyclable versions to reduce environmental impact. It's a critical material where durability in harsh chemical environments is required.
