Characterization of the Physical and Chemical Networks in Filled Rubber Compounds

This study has been completed in order to further understand the key interactions between rubber, filler, and coupler in compounds and how they lead to final properties of a tire such as rolling resistance, treadwear, etc. The two primary analytical techniques utilized were low-field (LF) NMR and pyrolysis (PY) GC-MS. 36 different compounds comprised from two different couplers (NXT and Si-75), two different fillers (silica and carbon black), and two different polymers (cis-polyisoprene, NATSYN, and styrene butadiene, SBR 1502) were studied.

For the LF NMR technique, a Bruker Minispec was used to determine the proton T2 relaxation rates of both uncured and cured samples. Typically, three types of populations occurred designated as the rigid (Tr), 1st mobile (Tm1), and 2nd mobile (Tm2) population. The reciprocal of the rigid population, has been used to obtain the crosslink density (XLD) of the sample. The PY GC-MS technique was used to examine the major volatile products. Intensity ratios for the samples were calculated by dividing by the isoprene area for the PI samples, and the styrene area for the SBR samples.

Both techniques suggest that there is a different mechanism of interaction between coupler and filler for the carbon black-filled and silica-filled samples. The suggested mechanisms are a physical adsorption interaction between coupler, filler, and polymer for carbon black-filled samples and a chemisorption interaction for silica-filled samples. Further investigations are being undertaken to understand the differences that occur when NXT or Si-75 are used as the coupler. In addition, future work will focus on correlation between LF NMR, PY-GC/MS, and physical properties data.