Electrochemical degradation tests on a carbon-black-filled ethylene propylene diene monomer rubber under tensile strain

Abstract

Rubber hoses play an important role as a path for carrying the coolant liquid between the radiator and the automotive engine. However, the rubber hoses are apt to deteriorate because of the formation of a galvanic circuit between the rubber hose, the coolant water and the fitting metal part of the engine. Such electrochemical degradation can damage the inner skin of the hose in contact with the coolant liquid heated by the working engine, which often leads to leakage of the coolant water and thereby to hose failure. An ethylene propylene diene monomer rubber has mostly been utilized as the material for the coolant hoses of automotive engines because of the strong resistance to various environmental stresses. This study conducted experimental simulation tests and evaluation of the electrochemical degradation behaviours of the carbon-black-filled ethylene propylene diene monomer rubber used for the coolant hoses. The tests were performed by considering the actual circumstances together with the combined thermal, tensile strain and electrostatic voltage loadings on the rubber hoses. The behaviour of the change in the electrical resistance of a specimen and, thus, the apparent decrease in the current were analysed quantitatively. An Arrhenius life prediction by using the decrease in the current was reasonably expressed for the accelerated life tests. Many microhole networks were thus formed in the skin part of the specimen by the microbreaks in the carbon-black phase and the scission of the sulphur cross-links. The coolant liquid penetrated significantly into the skin, which resulted in a considerable swelling of the skin. The larger the strain application to the rubber, the lower are the strength and the elongation at the breaking point. An exponential index parameter can represent quantitatively the behaviours of the decreases in the mechanical properties used for accurate life prediction.

Enhancing electrochemical degradation resistance in EPDM/CB composites: A comprehensive approach to achieve optimal physico‐mechanical properties for automotive applications

“…In this study, composites E and F were prepared using a peroxide vulcanization system, forming stronger carboncarbon bonds instead of the weaker sulfur–sulfur linkages 1 . anions struggle to attack these robust carbon–carbon cross‐links, reducing the likelihood of crack formation.…”

“…In recent years, there has been a notable surge in the development of EPDM rubber composites for automotive applications, especially in the production of hoses for coolant transportation. However, these composites encounter challenges related to electrochemical degradation (ECD) stemming from the formation of galvanic cells and subsequent redox reactions within the material 1 . Despite extensive research on the physico‐mechanical properties of EPDM composites, studies specifically targeting ECD prevention are scarce.…”

“…Once a crack initiates on the surface, hydraulic pressure drives its propagation, eventually reaching the reinforcing fiber. This, in turn, leads to the attack of sulfur cross‐links, resulting in larger cracks, coolant leakage, and ultimately hose failure 1 …”

“…However, there is a scarcity of works specifically addressing the electrochemical degradation of EPDM composites. Han and Choi 1 conducted research on the electrochemical degradation tests of carbon‐black‐filled EPDM rubber under tensile strain. Similarly, Buhari et al 3 conducted a study on constructing a percolation zone for electrostatic discharge in EPDM/CB composites by optimizing the physico‐mechanical properties.…”

Characterization of Rubber Degradation in a Brake Wheel Cylinder under Cyclic Loading

“…The study of rubber degradation in automotive components has been reported in the literature such as car wiper rubber blade [5], rubber hoses for car radiators [6] and engine rubber mounting [7]. There are also many studies undertaken on fatigue damage on rubbers materials.…”