THE ROLE OF THE

88 The Role of the Chemist in Automotive Design
Unlike inert fillers that have little effect on physical properties, reinforcing fillers
such as carbon black and Teflon add to the mechanical properties of the polymer [6].
Both of the polymers for rotating dynamic seals examined here contain carbon black
as a reinforcing filler. Teflon is added to polyetheretherketone to increase the lubricity
properties of the polymer. Ninety percent of carbon black is obtained through
furnace black, which involves the combustion of thermal cracking of hydrocarbons
[7]. This reaction takes place at 1,200–1,400°C:
–CH 2– → C + H 2
–CH 2– + 1½ O 2 → CO 2 + H 2O (6.1)
Another benefit of carbon black may be the potential for protection against oxidation.
Due to the higher temperatures over an extended period of time, thermal
oxidation can occur in a polymer. The mechanism for thermal oxidation is given in
Figure 6.2.
There are three states in thermal oxidation: initiation, propagation, and oxidative
chain branching [8]. Chain-breaking antioxidants are effective in the propagation
Thermal Oxidation Process Initiation:
or
R O
R O
Propagation:
R
and
OH
OH
∆
∆
O O + R H
R + O O
Oxidative Chain Branching:
R O
O
H
R O + HO
R O + R O
R
O O
R O
O
R O + HO
R O + R H
R OH + R
FIgure 6.2 Thermal oxidation process.
H
O
+
+
R