Fluoro Rubber Compounding Agents

Here we introduce typical compounding agents in fluoroelastomers.

Introduction of Typical Compounding Agents

Carbon

Among various types of carbon, MT (Medium Thermal) carbon is widely used, with particle size ranging from 201 to 500 nm.
This carbon has less reinforcing and conductive effects than other types of carbon and is rarely used in general-purpose rubbers, but in fluoro-rubbers, it has many advantages such as its high purity and the fact that the rate of hardness increase is moderate in relation to the amount blended. It is used as a standard additive that does not impair the characteristics of fluoroelastomer.

Magnesium oxide

Magnesium oxide has long been used as a gastrointestinal drug because its alkalinity neutralizes stomach acid and inhibits excessive gastrointestinal activity.
Fluoroelastomers also generate hydrofluoric acid during the vulcanization reaction, but the magnesium oxide neutralizes the acid to promote efficient vulcanization.
In the standard formulation of polyol vulcanization type, the primary vulcanization time is completed in about 10 minutes if the appropriate amount of magnesium oxide is blended, but if magnesium oxide is not blended, the vulcanization time becomes extremely slow and it becomes difficult to vulcanize properly.

Calcium hydroxide

Calcium hydroxide is hydroxide of calcium and is also called slaked lime. It is produced by adding water to calcium oxide (quicklime). It is widely used as a neutralizer in acidified rivers and soil, and as a pH adjuster in reagents, agriculture, food, and cosmetics. When added to fluoroelastomers, it has the effect of accelerating the vulcanization reaction by causing the water contained in the rubber to react with the fluorine rubber.
You may wonder, "Then why not just add water?" However, in the case of rubber kneading, it is unexpectedly difficult to add water directly to rubber, and there are various risks and disadvantages such as inducing agglomeration of other compounding agents and void formation during molding due to water remaining in the rubber.
As one would expect, materials that have been used for a long time have the reliability and track record to continue to be used.

Wollastonite

Wollastonite is the English name for a silicate mineral, also called silica limestone, with a chemical composition of CaSiO3.
It is used as an inorganic filler in fluoroelastomers that does not interfere with the properties of fluorine.
However, care must be taken when using it in peroxide vulcanization type. Addition to peroxide vulcanization type will cause inhibition of vulcanization.

Calcined clay

Like wollastonite, calcined clay is a type of silicate mineral with a chemical composition of Al4Si4O10(OH)8.
It is also commonly referred to as kaolin, kaolinite, or China clay, which is derived from Kaoling, the famous clay producing area in China.
In fluoroelastomers, it is used for applications that take advantage of its white color hiding power (the degree to which it visually masks surface conditions such as scratches and discoloration) and excellent weather resistance.

Titanium dioxide

Titanium dioxide is an oxide of titanium with chemical composition TiO2. It is white in color and has high hiding power, and is used as a pigment in white paints, paints, glazes, and synthetic fibers.
It is also often used in fluoroelastomers as a white compound, but it is also used as a filler or bulking agent because its physical properties do not change much even when added in large quantities.
There are two types of titanium dioxide, anatase and rutile. The rutile type has the most stable crystal structure, so this type is often used in fluoroelastomers.

Barium Sulfate

Barium sulfate has a chemical composition of BaSO4, is almost insoluble in water, acids, and alkalis, and is chemically very stable.
It is generally known for its use as a contrast agent in X-rays.
It is also utilized as an inorganic filler in fluoroelastomers.

Carnival wax

This wax is obtained from the leaves of the Brazilian wax palm and is a natural ester wax with excellent compatibility with resins and rubber.
It does not interfere with the properties of fluoroelastomer and has excellent mold-releasing and dispersing properties.

TAIC/Organic peroxide

TAIC is an essential cross-linking agent for peroxide vulcanization.
Due to the high molecular weight of fluoroelastomers, organic peroxides alone are insufficient to cross-link the molecular weight, and this is compensated for by TAIC.
In this sense, both materials are indispensable for peroxide vulcanization.