Abstract

To investigate the reinforcing effects of functional fillers in nitrile rubber (NBR) materials, high-structure carbon black (HS45), coated calcium carbonate (C-CaCO₃), silica (200MP), and multi-walled carbon nanotubes (MWCNTs) were used as functional filler, and carbon black (SRF) as a common filler were used for oil-resistant rubber. The curing and mechanical properties of HS45-, 200MP-, and MWCNT-filled NBR compounds were improved compared to those of the SRF-filled NBR compound. The reinforcing effect also increased with a decrease in the particle size of the fillers. The C-CaCO₃-filled NBR compound exhibited no reinforcing effect with increasing filler concentration because of their large primary particle size (2 μm). The reinforcing behavior based on 100% modulus of the functional filler based NBR compounds was compared by using several predictive equation models. The reinforcing behavior of the C-CaCO₃-filled NBR compound was in accordance with the Smallwood–Einstein equation whereas the 200MP- and MWCNT-filled NBR compounds fitted well with the modified Guth–Gold (m-Guth-Gold) equation. The SRF- and HS45-filled NBR compounds exhibited reinforcing behavior in accordance with the Guth–Gold and m-Guth–Gold equations, respectively, at a low filler content. However, the values of reinforcement parameter (100M_f/100M_u) of the SRF- and HS45-filled NBR compounds were higher than those determined by the predictive equation model at a high filler content. Because the chains of SRF composed of spherical filler particles are similarly changed to rod-like filler particles embedded in a rubber matrix and the reinforcement parameter rapidly increased with a high content of HS45, the higher-structured filler. The reinforcing effective-ness of the functional fillers was numerically evaluated on the basis of the effectiveness index (ϕ_SRF/ϕ_f) determined by the ratio of the volume fraction of the functional filler (ϕ_f) to that of the SRF filler (ϕ_SRF) at three unit of reinforcing parameter (100M_f /100M_u). On the basis of their effectiveness index, MWCNT-, 200MP-, and HS45-filled compounds showed higher reinforcing effectiveness of 420%, 70%, and 20% than that of SRF-filled compound, respectively whereas C-CaCO₃-filled compound exhibited lower reinforcing effectiveness of -50% than that of SRF-filled compound.

Keywords: NBR;functional fillers;smallwood-einstein equation;guth-gold equation;modified guth-gold equation