Aminosilane-Modified Multiwalled Carbon Nanotubes and Their Influence on the Mechanical Performance and Swelling Characteristics of Ethylene Propylene Diene Monomer/Styrene Butadiene Rubber Blend Systems

Abstract

Multi-walled carbon nanotubes (MWCNTs) were initially acid-treated and subsequently functionalized with 3-aminopropyltriethoxysilane (APTES), a widely used silane coupling agent, to enhance interfacial compatibility with the rubber matrix. This study investigates the influence of both pristine CNTs and APTES-functionalized CNTs (sCNTs) on the performance of vulcanized EPDM/SBR blend composites. The properties evaluated include curing characteristics, mechanical performance, abrasion resistance, compression set, crosslink density, and solvent swelling resistance. Rheological analysis revealed that increasing CNT and sCNT loading reduced scorch time and optimum cure time, while minimum torque, maximum torque, torque difference, and cure rate index increased. These changes are attributed to improved filler–rubber interactions, particularly in sCNT-filled systems, which promote more efficient crosslink network formation. Mechanical testing showed significant improvements in tensile strength and stress at 100% elongation up to 5 phr sCNT loading. Beyond this level, the reinforcing effect plateaued or slightly decreased due to intensified filler–filler interactions, which restrict effective stress transfer. In contrast, other properties such as tear strength, hardness, abrasion resistance, compression set, crosslink density, and swelling resistance continued to improve with increasing sCNT content. Overall, APTES-functionalized CNTs exhibited superior reinforcing efficiency compared to pristine CNTs. Compared to the unfilled blend, CNT-filled composites showed improvements of 99% in tensile strength, 29% in stress at 100% elongation, and 73% in tear strength, whereas sCNT-filled systems exhibited even higher enhancements of 144, 40, and 109%, respectively, confirming the effectiveness of surface functionalization in optimizing composite performance.