SYNOPSISThe contribution of elastomer polarity and reactivity to bound rubber formation has been investigated. In this study, a number of elastomers of different chemical nature have been tested. The surface of the carbon black (N110) has also been modified by nitric acid oxidation in order to increase the concentration of surface functional groups. The experimental results have shown that the bound rubber formation is barely related to the polarity of the polymers. It is the reactive sites in both the elastomer and carbon black which are mainly responsible for bound rubber formation. It therefore appears that the elastomer/carbon black interaction leading to the formation of bound rubber is essentially a chemical process involving primary bond formation between elastomer and carbon black. The oxidized carbon black exhibits a higher surface activity which may be due to an increased concentration of oxygen-containing reactive surface sites, namely, phenolic hydroxyl, carboxyl, lactone, and quinone groups. 0 1995 John Wiley & Sons, Inc.
The surface of precipitated silica was modified by heat treatment (800°C, 4 h) and hexadecanol treatment. Diffuse reflectance infrared Fourier transform spectroscopic (DRIFTS) measurements reveal that the modification of the silica surface reduces the silanol content. Heat treatment causes condensation of the silanol groups forming siloxane linkages, while hexadecanol treatment causes esterification, thereby, shielding the free silanol groups. As a result, the modified silicas exhibit much less interaction with polar molecules (e.g. water, chloroform), compared to the unreacted silica. Bound rubber formation in the chlorosulfonated polyethylene (CSM)/silica system is also adversely affected by the modification of the filler surface. CSM upon heat treatment (180°C, 1 h) loses -SO2Cl groups and the modified polymer lacks in its ability to form bound rubber. Accordingly, it is believed that the rubber-filler interaction occurs between the silanol groups of the silica and sulfonyl chloride groups of CSM.
SYNOPSISEpoxidized natural rubber (ENR) reacts with surface oxygen groups of carbon black. The higher the concentration of these groups, the higher the intensity and the extent of reaction and the better the reinforcing ability of the black. Oxidized furnace blacks and channel blacks, which are known to have high quantities of oxygen functional groups, are thus more reinforcing than are the conventional furnace blacks, particularly in the case of blackfilled epoxidized natural rubber. 0 1993 John Wiley & Sons, Inc.
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