  Citation: Bartosik, D.; Szadkowski, B.; Ku´ smierek, M.; Rybi ´ nski, P.; Mirkhodzhaev, U.; Marzec, A. Advanced Ethylene-Propylene-Diene (EPDM) Rubber Composites Filled with Raw Silicon Carbide or Hybrid Systems with Different Conventional Fillers. Polymers 2022, 14, 1383. https://doi.org/10.3390/ polym14071383 Academic Editor: Emin Bayraktar Received: 4 March 2022 Accepted: 26 March 2022 Published: 29 March 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). polymers Article Advanced Ethylene-Propylene-Diene (EPDM) Rubber Composites Filled with Raw Silicon Carbide or Hybrid Systems with Different Conventional Fillers Dominik Bartosik 1 , Boleslaw Szadkowski 1, * , Malgorzata Ku´ smierek 1 , Przemyslaw Rybi ´ nski 2 , Ulugbek Mirkhodzhaev 3 and Anna Marzec 1, * 1 Instituteof Polymerand Dye Technology, Faculty of Chemistry, Lodz University of Technology, Stefanowskiego 16, 90-537 Lodz, Poland; 224011@edu.p.lodz.pl (D.B.); malgorzata.kusmierek@dokt.p.lodz.pl (M.K.) 2 Institute of Chemistry, The Jan Kochanowski University, Uniwersytecka 7, 25-369 Kielce, Poland; przemyslaw.rybinski@ujk.edu.pl 3 Department of Biophysics, National University of Uzbekistan, Tashkent 100174, Uzbekistan; u.z.mirkhodjaev@gmail.com * Correspondence: boleslaw.szadkowski@p.lodz.pl (B.S.); anna.marzec@p.lodz.pl (A.M.) Abstract: We studied the effects of silicon carbide (SiC) and SiC hybrid systems with different conven- tional fillers (silica, carbon black, graphene, hydrotalcite, halloysite) on the rheometric measurements, crosslink density, mechanical performance, aging stability, morphology, thermal behaviour, and flammability of ethylene-propylene-diene (EPDM) rubber composites. The hybrid filler systems showed technically promising synergetic effects on the performance of the EPDM composites. A pronounced reinforcing effect in EPDM composites filled with hybrid SiC filler systems was noted. Tensile strength increased in the systems with carbon black, silica, and graphene nanoplatelets, by 21%, 37%, and 68%, respectively, compared to the neat EPDM. Dynamic-mechanical analysis (DMA) revealed a shift of the glass transition temperature (Tg) of EPDM composites towards higher values following the incorporation of hybrid SiC fillers, indicating that the mobility of the macromolecule chains was restricted by the presence of filler particles. Importantly, the application of SiC as a filler in EPDM rubber composites contributed to a considerable reduction in flammability, as demonstrated by microscale combustion calorimetry (MCC). The most promising results were obtained for HAL/SiC and LDH/SiC hybrid systems, which produced final composites with high flame retardancy and good mechanical performance. The study highlights the significant potential of SiC and SiC hybrid systems as effective fillers improving the properties of elastomer composites. Keywords: elastomer composites; ethylene-propylene-diene rubber; silicon carbide; mineral fillers; polymer composite properties; hybrid fillers 1. Introduction Flame retardants are widely used in plastics, coatings, and rubbers to reduce the risks of fire in applications in areas where safety is essential, such as aircraft, build- ing/construction, public transport, and housings for electronic elements. Flame retardants must be incombustible, or at least difficult to ignite and burn [1–3]. The main problem with many flame retardant additives used in coatings as well as in plastic and rubber composites is that they release toxic gases during thermal decomposition. This concerns compounds with halogens, phosphorous, and metals. Legislation in industrialized countries has tended towards prohibiting the use of some flame retardants. At the same time, there is a require- ment for finished products with limited flammability [4,5]. As a consequence, there is much interest from industry in finding efficient, cost-effective, and environmentally friendly flame retardant systems [6]. Previous reports have focused on the use of hydrated fillers, such as ATH and Mg(OH) 2 , which can act as flame retardants and smoke suppressor in Polymers 2022, 14, 1383. https://doi.org/10.3390/polym14071383 https://www.mdpi.com/journal/polymers