Other testing

Below you will find a selection of other testing that is not covered under the mechanical, thermal and durability testing sections.

Dispersion - ISO 11345

Discoloration from rubber is due to the migration of substances from the rubber material to nearby materials. The substances that migrate are mainly antioxidants and softeners. Discoloration manifests itself as a slightly light brown to black surface on the material that is in contact with the rubber and often appears extra clearly if the surface that was in contact with the rubber is exposed to sunlight.

The discoloration is usually divided into the following types:
Contact discoloration: Discoloration in the contact surface between rubber and substrate.
Migratory discoloration: Discoloration that migrates even beyond the contact surface.
Penetration discoloration: Discoloration that penetrates a material in contact with the rubber.
Extraction discoloration: Discoloration that occurs when water flows over a rubber material and then flows over another surface to which discoloring substances are first transferred.

Permeability - ISO 6179, ISO 2782

Liquids and gases diffuse through rubber. The rate of diffusion depends on the rubber type, recipe composition and medium.

Diffusion is usually divided into three phases:
1, The medium dissolves in the rubber from one side.
2. Diffusion (migration) through the rubber.
3. Evaporation from the opposite surface.

Different rubber materials have different gas permeability and there are several methods available to determine the permeability.

To determine the liquid permeability, you can let rubber form a wall in a vessel with the liquid you wish to test. The container is weighed periodically to determine the weight loss due to diffusion.

To determine the gas permeability, a rubber plate can be placed between two chambers. One chamber is pressurized with the gas to be used, eg air, to a pressure of 0.3-1.5 MPa and the other chamber was kept at ambient pressure.

Fire test - ISO 16 22 22

All rubber materials are more or less flammable. To improve the fire resistance of a rubber material, you can add chlorine-containing substances, such as chlorinated paraffin.

The fire resistance of rubber can be tested by vertical or horizontal methods. The most common method of testing rubber is to light a strip at one end with a Bunsen burner and study how long the material burns after the flame is removed.

Electrical tests - ISO 1853, ISO 1278, ISO 2951

To determine the electrical conductivity or resistivity, one can proceed in several ways. However, the principle is to apply a voltage across a rubber sample and measure the current passing through the rubber. This may sound simple but is in practice very difficult as very small currents are often involved and the rubber's resistivity changes with temperature, time and load, among other things.

TGA: Thermogravimetric analysis - ISO 9924

Thermogravimetric analysis, TGA, is used to determine the contents of and plasticizers, rubber polymer, carbon black and ash.

A sample is weighed in and heated from 70°C to 300°C in a nitrogen atmosphere, which gives the content of volatile substances. Then the heating continues to 550°C. During this part, other organic substances, which mainly consist of the polymer, leave. Finally, the atmosphere is changed to air and the temperature is raised to 650°C, whereby the carbon black is burned off. The remainder is ash consisting of inorganic fillers.