Effect of various efficient vulcanization (EV) sulfur cure systems on the compression set of a nitrile rubber filled with carbon black and silica/silane fillers was examined. The cure systems had different amounts of thiuram and sulfenamide accelerators and elemental sulfur, whilst the loading of zinc oxide and stearic acid activators was kept constant. The fillers had surface areas from 35 to 175 m2/g. In this study, the lowest compression set was measured for the rubber filled with carbon black with 78 m2/g surface area, which was cured with an EV cure system made of a small amount of elemental sulfur and large amounts of the two accelerators. Interestingly, a small change in the amount of elemental sulfur had a bigger effect on the compression set than did large changes in the loading of the accelerators in the cure system. Among the fillers, carbon black caused less compression set of the rubber vulcanizate than the silica/silane system did. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41512.

The effect of the same amount of precipitated silica nanofiller on the curing and mechanical properties of natural rubber and synthetic polyisoprene was investigated. The silica surfaces were pretreated with bis(3-triethoxysilylpropyl) tetrasulfide (TESPT) to chemically bond silica to rubber. The rubbers were primarily cured by using sulfur in TESPT, and the cure was optimized by the addition of accelerator and activator, which helped to form sulfur chemical bonds between the rubber and filler. Different amounts of accelerator and activator were needed to fully crosslink the filled rubbers. The hardness, tensile strength, elongation at break, stored energy density at break, tearing energy, and modulus of the vulcanizates improved substantially by the incorporation of the filler in the rubber. This was due to high level of rubber-filler adhesion and formation of chemical bonds between the rubber and TESPT. Interestingly, natural rubber benefited more from the filler than did synthetic polyisoprene.

Extensive use of rubber in industrial articles and their eventual disposal at the end of their useful service life has created a major concern for the environment. In automotive applications, ethylene–propylene–diene rubber (EPDM) is used to manufacture various parts which will be difficult to dispose of or scrap. A microwave oven was used as a heating source, and with the aid of some chemical agents and aromatic and aliphatic oils, cured EPDM waste powder was devulcanized at temperatures ranging from 200°C to 260°C. The devulcanized waste powder was then revulcanized with a sulfur cure system and its cure and mechanical properties were measured. It emerged that with the aid of the chemical agents, the waste powder devulcanized more efficiently in the aromatic oil than it did in the aliphatic one. The chemical agents had different effects on the devulcanization of the waste powder and mechanical properties of the revulcanized compound. In addition, devulcanization was more efficient at higher temperatures. The hardness, tensile strength, and elongation at break of the revulcanized compounds were in the range of 49–79 Shore A, 2.0–3.7 MPa, and 34–211%, respectively. These properties were influenced mainly by the composition and devulcanization conditions of the waste powder. There is scope to recycle and reuse some of these compounds in automotive applications.

Rubbers do not decompose easily and therefore disposal of rubber waste is a serious environmental concern. Raw material costs, diminishing natural resources, and the growing awareness of environmental issues and sustainability have made rubber recycling a major area of concern. Reclaiming and recycling rubber waste is a major scientific and technological challenge facing rubber scientists today. This paper reviews a number of important areas related to the reclaiming, characterizing, testing and recycling of rubber waste. These include: chemical and microbial devulcanization with particular emphasis on main chain scission and kinetics of chemical devulcanization reactions; the cutting-edge techniques for reclaiming devulcanized rubber waste by the action of large shearing forces, heat and chemical agents: and analytical techniques and methods for characterizing composition and testing of devulcanized rubber waste, respectively. In addition, some aspects of the recycling of devulcanized ethylene-propylenediene rubber (EPDM) waste will be reported. EPDM is used extensively in automotive components world-wide and recycling the rubber at the end of its useful service life is of major importance to manufacturers of automotive components.

Rubber recycling is growing worldwide because of increasing raw material costs. In addition, extensive use of rubber articles and their eventual disposal is a major concern for the environment. Butyl rubber (IIR) was devulcanized by microwave radiation with the aid of devulcanizing reagents and oil. The effect of several devulcanizing reagents, hexadecylamine (HAD), diphenyl disulfide (DPDS), N‐cyclohexyl‐2‐benzothiozyl sulfenamide (CBS), and tetramethylthiuram disulfide (TMTD) on devulcanization process, was studied. The investigation was carried out in various microwave radiation temperatures and different amounts of aromatic and paraffinic oils. The results showed that waste rubber powder with a median particle size of 279 normalμnormalm was devulcanized efficiently. It was confirmed when devulcanization % of the devulcanizates were measured by swelling tests. Among of the devulcanizing reagents and based on Horix analysis, HDA with the sol fraction, crosslink density (CLD), and devulcanization percent of 14%, 25 normalmol/normalm3 and 64%, respectively, was the most suitable devulcanizing reagent. In addition, compound with 30 and 6 phr paraffinic oil and HDA in formulation, respectively, had maximum devulcanization % (83%). The devulcanizing temperature of this compound was 180 °normalC . For the most of all compounds, during microwave radiation, a part of disulfides crosslinks were broken and released sulfurs giving new mono and polysulfides bridges. This resulted in the higher CLDs for some compounds when they compared with CLD of the initial waste rubber. In the morphological study of the devulcanized compounds, vulcanized rubbers clearly showed in the SEM micrographs surrounded by a matrix of devulcanized rubber. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43363.