Rubber raw materials

The most important raw materials for rubber are rubber, Fillers, Plasticiser, Crosslinking chemicals and Anti-ageing agent. Together they form a rubber mixture that often contains more than ten components and only becomes rubber through vulcanization. The quantities are indicated in phr (parts per hundred rubber), that is, in weight fractions based on 100 parts of rubber. Consequently, there are 100 phr in each rubber formulation. All other raw materials are indicated relative to this: 80 phr of carbon black correspond to 80 kg of carbon black per 100 kg of rubber. The weight percentage of a component is obtained by dividing its phr by the sum of all phr.

What is the typical composition of a rubber compound?

The individual composition varies depending on the intended use. The example shown shows a sulfur-crosslinked EPDM compound for profiles with a Shore A of 70, consisting of 100 phr EPDM, 80 phr carbon black, 35 phr mineral filler and 40 phr paraffinic mineral oil. Additionally, zinc oxide and stearic acid are used as activators, a combination of accelerators and sulfur donors, and 0.5 phr sulfur. In this EPDM formulation, the EPDM rubber makes up only about 36 percent of the rubber compound, while highly filled EPDM compounds sometimes have less than 25 percent EPDM by weight.