Abstract
Nanosized calcium oxide (CaO) featuring a surface grafted with allylmalonic acid (ALA) was used to increase the efficiency of the peroxide crosslinking of an ethylene–propylene copolymer (EPM) filled with silica nanoparticles. In this study, 1-butyl-3-methylimidazolium ionic liquids (ILs) with different anions were applied to improve the dispersion of CaO/ALA and silica nanoparticles in the EPM copolymer, as well as to catalyze the interfacial crosslinking reactions. In this article, we discuss the effects of CaO/ALA and ILs on the curing characteristics, vulcanization temperature, crosslink density, mechanical properties, and thermal stability of EPM, as well as the resistance of EPM to weather aging. The CaO/ALA with ILs reduced the vulcanization time of the rubber compounds without a significant effect on the vulcanization temperature. Their application resulted in an increased vulcanizate crosslink density, as well as improved tensile strength compared to the pure peroxide system. The influence of 1-butyl-3-methylimidazolium ILs on EPM vulcanization and performance depends on the anion present in the molecules of the ionic liquid. The most active IL seems to be that with the tetrafluoroborate anion.
Highlights
The vulcanization of rubber is one of the most important processes in elastomer technology.During this process, crosslinking reactions occur, resulting in useful materials that possess the required physical properties, such as high tensile or tear strengths, a low compression set, recoverable elongation, and improved dynamic performance
These are labile ionic links that allow for considerable chain slippage and reformation of bonds, resulting in the increased ability of the material to relax stress. Its mechanical properties, such as tensile strength and tear resistance, are greatly improved [11,12]. Another approach to improve the efficiency of rubber peroxide crosslinking and the mechanical properties of the vulcanizates are hybrid coagents consisting of an inorganic core and an organic shell, which were reported in our previous works [13,14,15]
These coagents are based on nanosized metal oxides (ZnO, calcium oxide (CaO), MgO) and layered minerals modified with unsaturated carboxylic acids, which possess cleavable protons and double bonds, that are readily accessible for reactions with free radicals or polymer chains
Summary
The vulcanization of rubber is one of the most important processes in elastomer technology. Another approach to improve the efficiency of rubber peroxide crosslinking and the mechanical properties of the vulcanizates are hybrid coagents consisting of an inorganic core and an organic shell, which were reported in our previous works [13,14,15] These coagents are based on nanosized metal oxides (ZnO, CaO, MgO) and layered minerals (hydrotalcite, boehmite) modified with unsaturated carboxylic acids, which possess cleavable protons and double bonds, that are readily accessible for reactions with free radicals or polymer chains. It is necessary to develop substances that improve the dispersion degree of coagent nanoparticles in the elastomer matrix These potential dispersing agents can be ionic liquids (ILs) that, owing to their catalytic activity in interfacial reactions (including crosslinking reactions), can increase the efficiency of crosslinking [16]. ILs with Bmim cation were observed to be more introduced into the rubber during the preparation of rubber compounds compared to ILs with shorter alkyl chains, which is important for technological reasons
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