RESEARCH ARTICLE Influence of partial substitution of carbon black with silica on mechanical, thermal, and aging properties of super specialty elastomer based composites Sipra Khanra | Abhay Kumar | Sanjoy Kumar Ghorai | Debabrata Ganguly | Santanu Chattopadhyay Rubber Technology Centre, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal, India Correspondence Santanu Chattopadhyay, Rubber Technology Centre, IIT Kharagpur, PIN- 721302, West Bengal, India. Email: santanuchat71@yahoo.com Funding information Indian Institute of Technology Kharagpur Abstract The reduction of the carbon black quantity in elastomeric composites is a mas- sive requirement from environmental perspective and a huge challenge for industrial implementation. The present work consists of the replacement of half amount of carbon black with silica without compromising the basic prop- erties along with ushering of superior characteristics of fluoroelastomer and silicone rubber blends. The comparative study of carbon black-silica hybrid filler (1:1 ratio) with carbon black and silica at different loadings shows much superior aging behavior and thermal stability compared with the other com- posites with unforeseen increment of tensile strength (56%). The fundamentals of rubber-filler interaction and reinforcement phenomenon of the hybrid filler composites have been determined by the correlation of the experimental find- ings with different models like Nicolais-Narkis, Nielsen, Guth, and Kerner model. Furthermore, enhanced compatibility between the two rubber phases has been observed in terms of T g shifting (3.8  C) and reduced FKM domain size (from 450 to 300 nm) in the silicone rubber matrix for hybrid filler com- posites. Morphological studies reflect the selected homogeneous dispersion of the carbon black in fluoroelastomer domain and silica in silicone rubber phase. These super specialty elastomeric composites can be used as oil and fuel resistant gaskets and O-rings for wide temperature range. KEYWORDS compatibility, hybrid filler, reinforcement, rubber blend, super speciality elastomers, thermal stability 1 | INTRODUCTION In the majority of applications, rubbers need to be strengthened with reinforcing fillers to improve the fail- ure properties in particular along with upliftment of other technical properties. [1] However, the degree of rein- forcement grossly depends on the size of the fillers, sur- face functionalities and their state of dispersion and distribution in the rubber matrix. [2] The main two con- ventional reinforcing fillers used in the rubber industry are carbon black and silica. [3] Carbon black is the most utilized filler as it provides good mechanical properties alongside the improvements in thermal and electrical properties. [4] Generally, furnace grade carbon black is used for reinforcement of the rubber which possesses an average particle size of 15-96 nm .[5] It also has very high Received: 29 April 2020 Revised: 4 June 2020 Accepted: 18 June 2020 DOI: 10.1002/pc.25720 Polymer Composites. 2020;1–18. wileyonlinelibrary.com/journal/pc © 2020 Society of Plastics Engineers 1