Polymer Degradation and Stability 129 (2016) 56e62 Contents lists available at ScienceDirect Polymer Degradation and Stability journal homepage: www.elsevier.com/locate/polydegstab A new approach for reclaiming of waste automotive EPDM rubber using waste oil * Malihe Sabzekar a, Gholamhossein Zohuri b, c, , Mahdi Pourafshari Chenar a, Seyed Mohammadmahdi Mortazavi d, Majid Kariminejad e, Said Asadi e a Chemical Engineering Department, Faculty of Engineering, Ferdowsi University of Mashhad, P.O. Box 91775-1111, Mashhad, Iran b Department of Chemistry, Faculty of Science, Ferdowsi University of Mashhad, P.O. Box 91775-1111, Mashhad, Iran c Environmental Chemistry Research Center, Department of Chemistry, Faculty of Science, Ferdowsi University of Mashhad, Mashhad, Iran d Polymerization Engineering Department, Iran Polymer and Petrochemical Institute (IPPI), P.O. Box 14965/115, Tehran, Iran e Baspar Sazeh Toos Co. of Part Lastic Group, P.O. Box 91895-196, Mashhad, Iran article info abstract Article history: The disposal of polymeric and especially rubber materials is an important global issue. In this work we Received 28 July 2015 have used disulfide oil (DSO), the oily waste produced in gas refineries, as a chemical agent for mech- Received in revised form anochemical reclaiming of waste EPDM rubber at a specific operation condition. The devulcanization 6 January 2016 reaction was performed using different concentrations of DSO (5 and 7 phr) and different temperatures Accepted 4 April 2016 (220, 250 and 290 C). The results confirmed the effectiveness of DSO in decreasing the crosslink density Available online 5 April 2016 up to 73% at specific reaction conditions. Subsequently, two different portions of the devulcanized rubber (RR) (20 and 40 wt %) were blended with the virgin EPDM rubber to assess the reusability of the recycled Keywords: Waste EPDM product. Accordingly, replacing 40 wt% of RR had no effect on the scorch and the optimum curing time Mechanochemical reclaiming and similar curing rates were obtained. Moreover, the mechanical properties of the revulcanized blends DSO were not worsened and surprisingly were improved in some cases including tensile strength and Mechanical properties elongation at break up to 14% and 26% respectively. These results can be used to propose a new method for solving both rubber and disulfide oil disposal issues. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction process developed for plastisizing ground rubber powder and to improve the final properties of the recycled material. The selective Ethyleneepropyleneediene rubber (EPDM) has applications in crosslink scission in the latter method transforms the vulcanized wide variety of areas specifically in automotive industry. The world rubber back to its original form, while reclaiming process includes consumption of both natural and synthetic rubbers has been combination of both crosslink and main chain scission resulting in 24.845 kt in 2010 [1]. Nowadays, the disposal and recycling of the formation of shorter chains and consequently leading to poor me- discarded EPDM automotive parts is a growing issue, and the chanical properties. An ideal reclaiming process would only break associated economy is significant. Different recycling methods for the crosslinks and leave the main chains intact [13]. However, there the scrap rubber have been proposed including rubber incineration is always a balance between crosslink scission and backbone and pyrolysis [2e5], application of ground rubber powder (GRP) in breakdown. The challenge is to shift this balance towards devul- civil engineering [6e9], pulverizing [10,11] and direct addition of canization as far as possible and avoid main chain degradation [14]. recycled material to the virgin rubber. However, the remaining There are several technologies that use different processes for crosslinked structure of the rubber and the weak interfacial adhe- reclaiming including mechano chemical [15e18], thermo me- sion between the rubber particles and matrix has been reported to chanical [19,20], microwave [21,22], ultrasonic [23,24], biotechno- cause poor mechanical properties [12]. Devulcanization is superior logical [25e27], devulcanization in supercritical carbon dioxide [28e30] and chemical reclaiming process [31e34]. Continuous devulcanization in a twin-screw extruder is one of the modern fi fi * Corresponding author. Department of Chemistry, Faculty of Science, Ferdowsi methods in this eld that bene ts from continuous operation, University of Mashhad, P.O. Box 91775-1111, Mashhad, Iran. environmental protection, high speed, high efficiency and energy E-mail address: [email protected] (G. Zohuri). http://dx.doi.org/10.1016/j.polymdegradstab.2016.04.002 0141-3910/© 2016 Elsevier Ltd. All rights reserved. M. Sabzekar et al. / Polymer Degradation and Stability 129 (2016) 56e62 57 saving of the reclaiming process, compared to the traditional composition according to Table 1 and Fig. 1. Virgin EPDM (KEP 270, methods [35e38]. Kumho Polychem, Korea), carbon black (N330, Pars Co., Saveh, Sutanto et al. used a kinetic model to describe EPDM devulca- Iran), process oil (oil 840, Behran Co., Tehran, Iran), ZnO (Pars nization in an extrusion process [39]. They used two types of EPDM, Rangineh Co., Tehran, Iran), stearic acid (Uni Chemical, Malaysia), i.e. efficient vulcanized (EV) and a semi-efficient vulcanized (SEV), antioxidant (NA 4010), MBTS, TMTD, zinc dibutyl dithio carbamate to produce devulcanized rubber in a co-rotating twin-screw (Perkacit ZDBC) and elemental sulfur (Bayer Co., Germany) were extruder. The revulcanized blends of devulcanized with virgin used in this study. DSO as a devulcanizing agent was supplied by material have shown that at least 25% of the devulcanized rubber South Pars Oil and Gas Company, Iran. The solvents (toluene and can be added to the virgin material without making significant acetone) used in characterization of the devulcanized samples were change in the final mechanical properties [40]. Shi and co-workers supplied by Shazand Petrochemical Co. (Arak, Iran). devoted an effort on the reclamation of ground tire rubber (GTR) by using different methods including twin-screw extruder. Finally, 2.2. Devulcanization method and sample preparation they recommended an optimum reclaiming method with an oxygen-free medium, without high shear force, and at relatively Reclamation of the waste EPDM rubber was carried out using a low temperature [28]. Mangili et al. studied and optimized the laboratory intermeshing co-rotating twin screw extruder (Model ultrasonic devulcanization of a ground tire rubber in a co-rotating TSE 20, Brabender Co., Germany). The extruder contained five twin-screw extruder using the response surface methodology heating/cooling zones and a screw diameter of 20 mm with L/D based on an experimental design. They intend to evaluate the in- ratio of 40. The last three zones of extruder have been adjusted at fluence of process variables including ultrasonic amplitude, tem- constant temperature and reported as barrel temperature. The perature, screw speed and flow rate on devulcanization. Their applied necessary reclaiming pressure is built up by combination of results showed the ultrasonic amplitude is the most effective reversed flighted section and kneader along the screw (shown in parameter [41]. Maridass and Gupta have used counter rotating Fig. 2). Constant feed rate was achieved by using a fixed screw twin-screw extruder to devulcanize the ground NR powder [42]. speed of 120 rpm for all samples. The reclamation additives were Jalilvand et al. produced devulcanized EPDM using diphenyl di- process oil (5phr) and DSO (different concentrations). Experiments sulfide as a devulcanizing agent in a laboratory intermeshing co- were carried out at different conditions presented in Table 2 using rotating twin-screw extruder. According to their results, shear variable DSO concentration and temperature. Finally, the reclaimed stress is an important factor for increasing percent of devulcani- samples were rolled by using a laboratory two roll mill. zation and the temperature is the most important factor deter- mining the sol fraction [43]. Many industries prefer to use chemical 2.3. Characterization reclaiming agents, generally organic disulfides or mercaptans, for the reclaiming processes. These chemicals are used for natural and 2.3.1. Sol-gel measurement fi fi synthetic rubbers including diphenyl disul de, dibenzyl disul de, Soxhlet extraction method was used to separate the sol fraction fi fi diamyl disul de, bis(alkoxy aryl) disul des, butyl mercaptan, of the reclaimed rubber. Small amount of the sample (5 gr) was fi fi phenol sul des and other disul des [44]. There are many reports in extracted for at least 12 h, using acetone as the solvent to remove fi the literature on the effect of disul des as a chemical agent on the low molecular weight substances such as processing oil. The reclaiming of natural and synthetic rubbers [45e50]. extracted sample was dried and weighed (m1) allowed swelling by The main objective of this study is to introduce a novel chemical immersing in toluene (approximately 400 ml) for 72 h at room agent for reclaiming of waste automotive EPDM rubber using the temperature. Then, specimen was taken out from toluene, weighed extrusion technology. This chemical, which is produced in gas re- (m ) and dried to a constant weight (m ). Swelling test, which was fi fi s 2 neries, is called disul de oil (DSO). Since this byproduct is used to analyze the network structure of the reclaimed