Abstract
For the design of stretchable and flexible high-performing materials, the reinforcement of elastomeric grades plays a crucial role. State-of-the-art fillers such as carbon black benefit from a high reinforcement but often negatively affect the processing and mixing properties of rubber compounds. To overcome this drawback, the synergistic properties of hybrid in situ filler systems are studied for EPDM compounds comprising a phenol novolac resin and ionic coagents such as zinc (meth)acrylates (ZD(M)A. With the help of a combined novolac/ZD(M)A system, the compounds could be tailored in a unique way towards higher toughness and enhanced cross-link density. Further, the fracture surface of the EPDM–novolac compounds was analyzed by scanning electron microscopy, revealing a significant change of the morphology from rough and disordered to smooth and homogenous for samples with coagents. In addition, the results clearly showed that the introduction of ionic coagents is able to compensate shares of carbon black filler in the EPDM compound. The toughening of samples with zinc (meth)acrylates is attributed to the synergistic formation of an interpenetrating polymer-filler network by simultaneous covalent and ionic cross-linking.
Highlights
Ethylene-propylene-diene rubber (EPDM) is a terpolymer of ethylene, propylene, and a nonconjugated diene, and characterized by a fully saturated, hydrocarbon main chain with low levels of unsaturation in the side groups
EPDM compounds used for V-belt production typically contain a high amount of carbon black to meet the demands for high tensile strength
The mixing and processing performance of the EPDM compound is already negatively affected by the high viscosity of the filler system
Summary
Ethylene-propylene-diene rubber (EPDM) is a terpolymer of ethylene, propylene, and a nonconjugated diene, and characterized by a fully saturated, hydrocarbon main chain with low levels of unsaturation in the side groups. The presence of the diene enables sulfur vulcanization of EPDM and enhances peroxide cross-linking efficiency. This low unsaturated, nonpolar rubber polymer is known for its good resistance against ozone, oxygen, irradiation, and heat and against polar media, such as aqueous solutions and polar solvents [1]. To obtain superior vulcanizate properties, most rubbers, including EPDM, need to be reinforced with fillers. Carbon black (CB) and silica are the most common reinforcing fillers in the rubber industry [3,4]. The reinforcing effect is governed by the chemical nature of the filler and by several other factors, for example, the size, surface area, shape, and structure of the filler particles, and their dispersion and distribution [5–7]. The dispersion of the filler within the rubber matrix plays a distinctive role in the overall reinforcement.
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