As a filler for rubber products, kaolin has been accepted by the majority of rubber manufacturers. Compared with carbon black and silica, kaolin has a considerable price advantage. In terms of technical support, Qingdao University of Science and Technology Shandong Key Laboratory of Rubber and Plastic Materials and Engineering has also released a number of research reports.

So, what are the effects of adding kaolin as a filler to rubber on its properties?

Strength: Kaolin fillers can increase the tensile strength, tear strength, and wear resistance of rubber, thus enhancing the durability and service life of rubber.

Hardness: After kaolin is added, the hardness of the rubber will increase. This is conducive to improving the compression resistance of rubber products and reducing permanent deformation.

Viscosity: The addition of kaolin to the rubber may increase the viscosity during mixing and increase the difficulty in processing. Therefore, when choosing a filler, it is necessary to weigh the amount of filler and the processing performance.

Thermal conductivity: kaolin has good thermal conductivity, which can improve the thermal conductivity of rubber. This is conducive to the use of rubber products in high temperature environments.

Electrical properties: kaolin is a non-conductive material, so adding kaolin to rubber can improve the electrical insulation properties of rubber.

Flexibility: Adding an appropriate amount of kaolin can improve the flexibility of the rubber. However, if too much is added, the flexibility of the rubber may decrease, resulting in brittle rubber products.

Both calcined kaolin and washed kaolin can be used as fillers in rubber processing. Calcined kaolin is made of coal gangue after high temperature calcination. After high temperature calcination, its dehydroxylation is complete, resulting in more obvious sintering phenomenon, more structural collapse, and then more bulk structures, and loss of flake structures. Washed kaolin maintains a natural flake structure and has obvious advantages in terms of airtightness.

In practical applications, washed kaolin needs to possess the following characteristics (data from network collation), which can relatively meet the processing requirements of the rubber industry.

Particle size distribution: washed kaolin as a rubber filler, its particle size is usually between 0.1-10 microns, finer particle size helps to improve the dispersion of rubber and improve the performance of rubber.

Water content: The water content of washed kaolin is usually between 1-2%. Lower water content is conducive to improving the processing performance of rubber during mixing.

pH value: The pH value of washed kaolin is usually between 6.5-8, which is conducive to ensuring the chemical stability of rubber.

Weight loss by burning: The weight loss by burning of washed kaolin is usually in the range of 5-15%. Lower weight loss by burning indicates that the content of organic matter and crystal water in kaolin is low, which is conducive to improving the thermal stability of rubber.

Purity: The kaolinite content of washed kaolin should be higher than 95%.

Whiteness: The whiteness of washed kaolin is usually between 80-90%. Higher whiteness helps to improve the aesthetics of rubber products.

Oil adsorption capacity: The oil adsorption capacity of washed kaolin is usually between 40-80 g/100 g. Higher oil adsorption capacity indicates that kaolin has a better filling effect.

Sieve residue: The sieve residue of washed kaolin is usually less than 1% on a 325 mesh sieve, which helps to improve the surface finish of rubber products.

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