NBR-HNBR-XNBR

NBR

 

Common name:

NBR or nitrile rubber

 

Common chemical composition:

Butadiene-acrylonitrile copolymer (with an ACM content ranging from 18% to 50%)

General properties:strong>

NBR is a family of unsaturated copolymers of 2-propenenitrile and various monomers of butadiene (1,2-butadiene and 1,3-butadiene). Choice among the various NBR polymers depends on the acrylonitrile (ACN) content which determines the main properties of these types of polymer: the higher the ACN content, the better the resistance to fuels and oils; the lower the content, the better the resistance to low temperatures. The main problem with this rubber is finding the optimal compromise between resistance to oil and fuel on one hand and elasticity and resistance to the cold on the other.

In addition to these properties, nitrile rubber demonstrates:

  • High tensile strength;
  • Low permanent deformation;
  • Low gas permeability;
  • Good abrasion resistance;
  • Good heat and aging resistance;
  • Good compatibility with other types of polymers and materials.

The most commonly used NBR polymers are those with a 33% to 38% ACN content.

Fields of Application:

NBR is mainly used for products in the automotive industry. For example, for the production of fuel supply pipes, throttle support plates, oil and heat resistant head gaskets etc.

The main limitation in the extrusion and calendering of NBR is nerve control. However, NBR with internal cross-links exists, resulting in low “die swell”; for the most commonly used ACN content, various values of Mooney viscosity can also be planned.

Other fields of application for nitrile rubber are:

  • Production of disposable gloves;
  • Synthetic leather;
  • Printing rollers;
  • Cable sheaths;

NBR can also be used as a binder in the preparation of adhesives.

HNBR

 

Common name:

HNBR or NSN (Highly saturated nitrile)

 

Common chemical composition:

Hydrogenated butadiene-acrylonitrile copolymer (with ACM content ranging from 18% to 50%)

General properties:

HNBR is widely known for its physical strength and retention of properties after long-term exposure to heat, oils and chemicals. This type of rubber has a high tensile strength ranging from 21 to 31 Mpa.

HNBR can be used with a wide range of temperatures (-40°C to 165°C) with minimal degradation of the compound. To obtain HNBR able to resist low temperatures, it is necessary to select polymers with low ACN content; conversely, to obtain HNBR able to resist high temperatures, polymers with high ACN content must be chosen.

As elastomers, HNBR polymers have excellent resistance to fluids used in the automotive industry (motor oils, fuel, coolants etc.) and chemicals used in the industry.

Fields of Application:

In terms of volume, the largest consumer of this type of rubber is the automotive sector. It is primarily used for making dynamic and static gaskets, pipes and belts. It is also used for the production of O-rings.

This type of rubber is also used in the oil drilling sector as sealants.

Other fields of application include:

  • Manufacture of rollers for steel mills;
  • Manufacture of rollers for paper production;
  • Gaskets for air-conditioning systems.

XNBR

 

Common name:

XNBR (carboxylated nitrile rubber)

 

Common chemical composition:

Carboxylated butadiene-acrylonitrile copolymer (with ACM content ranging from 18% to 50%)

General properties:

An improved version of NBR and XNBR. In these polymers, carboxylic groups (R-COO-) are found on the double bond of the butadiene part, in addition to the sulfur bridges. These groups establish chemical bonds (ionic) with zinc (Zn2+), thereby improving the physical properties of the rubber. Normal types of this rubber contain about 7% of carboxyls; however types with 2% also exist.

XNBR is nitrile rubber that cross-links with all the vulcanization systems of normal NBR: in addition, the presence of -COOH groups makes it cross-link with metal oxides such as ZnO or Pb3O4.3O4.

These free groups are introduced in order to increase the degree of cross-linking of the vulcanization systems and improve abrasion resistance and elastic resilience..

Fields of Application:

These types of rubber are used for particular industrial accessories in the textile industry which require oil resistance with good abrasion resistance and elastic resilience.

UAt one time, XNBR was also used in the footwear sector: its use ensures abrasion resistance as with certain polyurethanes but its high cost later prevented this type of use.

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