Semnan University Press Mechanics of Advanced Composite Structures 2423-4826 14 1 2027 04 01 Comparative Investigation of Epoxy-terminated and Carboxyl-terminated Butadiene Nitrile Rubber for Toughened Epoxy Resins 99 122 10480 10.22075/macs.2026.37580.1846 EN Purva Uniyal Department of Mechanical & Aerospace Engineering, School of Advanced Engineering, Bidholi Campus, UPES, Dehradun, 248007, India Piyush Gaur Department of Mechanical & Aerospace Engineering, School of Advanced Engineering, Bidholi Campus, UPES, Dehradun, 248007, India Jitendra Yadav Department of Mechanical & Aerospace Engineering, School of Advanced Engineering, Bidholi Campus, UPES, Dehradun, 248007, India Punya Bansal Department of Mechanical & Aerospace Engineering, School of Advanced Engineering, Bidholi Campus, UPES, Dehradun, 248007, India Neelanchali Asija Bhalla Mechanical Engineering Department, School of Engineering and Applied Sciences, Bennett University, Greater Noida, UP, 201310, India Journal Article 2025 05 02 The research presents how Carboxyl Terminated Butadiene Nitrile (CTBN) and Epoxy Terminated Butadiene Nitrile (ETBN) types of Reactive Liquid Rubber (RLR) influence epoxy resins through rheological, thermal, and mechanical property assessments. The use of recycled waste rubber creates sustainable high-performance additives through waste material transformation. Various mechanical, thermal, and rheological tests assessed the effects of CTBN and ETBN concentrations on their viscosity behaviour, mechanical properties, and curing process of the epoxy system used. The thermal stability of the ETBN and CTBN systems was analyzed by using Thermogravimetric Analysis (TGA) to determine decomposition temperatures and stability measurements. A complete set of mechanical tests measured tensile strength, flexural strength, and impact strength. Toughness improvements reached their peak with 2.5 wt.% ETBN addition resulting in a 42.2% increase in ultimate tensile strength, a 103.8% increase in tensile modulus, a 26.9% improvement in toughness, and a 67.65% increase in impact strength while maintaining all other properties. Also, 5 wt.% CTBN incorporation into the epoxy polymer leads to 30% increment in ultimate tensile strength, 49.5% increase in ultimate flexural strength, 68% increase in tensile modulus, and 300% increase in impact strength. So, both CTBN and ETBN are said to be effective tougheners that can be used to enhance the toughness of the overall matrix system while balancing other mechanical properties. The investigation highlights how the termination chemistry affects phase separation and interfacial adhesion, ultimately leading to improved performance for its applications in automotive and aerospace industries. The innovative use of recycled ETBN and CTBN thus creates a way for the development of sustainable solutions that deliver economic benefits and environmental advantages. https://macs.semnan.ac.ir/article_10480_cbbf844cee82936573febba90ac7b4e3.pdf