Nitrile Rubber Introduction 1

by Dongrubber on November 17, 2006 · 0 comments

1. Brief introduction of nitrile rubber

World nitrile rubber production output is more than 5 hundred thousand tons, about 4% of synthetic rubber. Although nitrile rubber total output is not very big, then its product brand is very complex, over 300 varieties in total. Different nitrile rubber has different production methods, and different contents of acrylonitrile, also different mooney viscosity and apperance and properties, etc. According to the combined acrylonitrile contents, the nitrile rubber can be divided into 5 catogories: super high acrylonitrile content (with 42%~51% acrylonitrile), high acrylonitrile content (with 31%~35% acrylonitrile of nitrile rubber), middle high acrylonitrile content (with 25%~35% acrylonitrile of nitrile rubber) and low acrylonitrile acrylonitrile nitrile rubber (with 18%~24% acrylonitrile of nitrile rubber). The mooney viscosity of nitrile rubber has big changing range, as high as 100 and as low as 25. Normally nitrile rubber can be divided into high, medium, low three grades according to nitrile rubber. Mooney viscosity over 80 is called high mooney viscosity nitrile rubber, lower than 45 is called low mooney viscosity nitrile rubber, around 60 is called medium mooney viscosity nitrile rubber. Besides there’re special appearance nitrile rubber such as liquid nitrile rubber, powder nitrile rubber; different chemical structure nitrile rubber such as carbox-nitrile rubber, pre-crosslinked nitrile rubber and polymerization stable nitrile rubber (with combined antiager in copolymer) etc species. Production method of nitrile rubber can be categorized according to temperature during polymerization, which divides into high temperature polymerization and low temperature polymerization. High temperature polymerization is adopting 40℃ temperature, low temperature polymerization is adopting 5~10℃; High temperature polymerization products are called hot polymerization nitrile rubber and low temperature polymerization products are called cold polymerization nitrile rubber.

2. Basic properties of nitrile rubber

1) Universal nitrile rubber

Universal nitrile rubber includes hot polymerization nitrile rubber, cold polymerization nitrile rubber and soft nitrile rubber

High temperature polymerization is the earliest adopting production method of nitrile rubber, and the produced hot polymerization nitrile rubber has higher mechanical property, however with poor processability. Def plasticity of raw rubber is around 1500~3000. Hot polymerization has difficulty plasticity and its consumption of powder is slow.

Cold polymerization nitrile rubber has better processability than hot polymerization than hot one: the consumption power for processing is smaller, quicker to powder, smooth extrusion, rolling rubber piece, and stable size. It also has good solubility in solution. Actually cold polymerization nitrile rubber has not low mooney viscosity. Cold polymerization nitrile rubber has equal or even better physical properties than hot polymerization nitrile rubber.

Soft nitrile rubber has about 1000 plasticity, that it can not be plastified with machine, having better processability than former, but its disadvantage is poorer mechanical property.

(1) Mechanical property

Nitrile rubber is ruleless nitrile copolymer, it does not crystallize in tension state, so the pure nitrile vulcanized rubber has same mechanical property with SBR rubber, far lower than natural rubber, the nitrile vulcanized rubber after reinforcing can reach the same level tension force with natural rubber, generally at 24.50MPa plus.

Nitrile rubber has poorer elasticity than natural rubber and SBR rubber. Its elasticity has close relationship with temperature. The higher the temperature, the bigger the elasticity, meanwhile the trend of increase is bigger than natural rubber. Therefore, nitrile rubber is very applicable to produce anti-vibration articles with high oil resistivity.

The abrasion resistant of NBR rubber is also not good as natural rubber, but with the increase of temperature(0~100℃), the decrease rate of nitrile rubber abrasion resistant is smaller than natural rubber, meanwhile it has fairly good high temperature abrasion resistance.

The stress at definite elongation and hardness of nitrile rubber can change in a very wide scope. They have less dependency to combined acrylonitrile. While the definite elongation is big affected by degree of polymerization. High polymerization nitrile rubber has high crosslinking density, and higher definite elongation.

The low temperature property of nitrile rubber sheet is largely related to the content of acrylonitrile. With the decrease of acrylonitrile the low temperature flexing resistance of nitrile rubber can get big improvement.

Nitrile rubber vulcanizates containing reinforcing filler has better abrasion performance than the natural rubber, and improved abrasion resistance increased with the increase of active filler sheets. NBR rubber sheeting abrasion resistance is about 20% and 30% lower than the natural rubber, but it is better than that of styrene butadiene rubber.

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