Elastomer Blends. Compatibility and Relative Response to Fillers

Abstract

Abstract The relative compatibility of eight different commercially available elastomers, blended in two-way combinations in three different proportions, was measured as a function of zone size on phase contrast optical micrographs using the Quantimet Image Analyzing Computer. Average cross sectional areas of the disperse phase in different blends were measured utilizing micrographs of the relatively noise-free QTM meter images which were characterized by greatly enhanced contrast. A study of the commercially important blends of polybutadiene with SBR was completed using both Differential Thermal Analysis and Electron Microscopy. Blends of several types of polybutadiene with SBR ordinarily exhibited only one glass transition temperature when examined in the vulcanized state. However, the same blends, uncured, showed the Tg's typical of each individual polymer. Moreover, electron micrographs of SBR blends with three different polybutadienes (Butyllithium, Ziegler, and Emulsion types) showed the existence of discrete polymer zones. Blends of BR/SBR, though more compatible than most polymer systems (e.g., NR/BR), were not homogeneous at the molecular level. A comprehensive study of carbon black distribution between 50/50 blends of several commercially important elastomers was completed. A high structure HAF carbon was added to elastomer preblends to give a 40 phr loading. Filler distribution was then assessed from the frequency of aggregates in the separate polymer zones. The studies indicated that BR and SBR have the highest affinity for a standard type carbon black. Polychlorobutadiene and Nitrile rubbers showed a somewhat lower affinity, though appreciably higher than that of natural rubber. EPDM and Butyl showed the lowest carbon black reactivity. Finally, carbon black transfer was investigated in a variety of polymer systems using Electron Microscopy and Pyrolytic Gas-Chromatography. The extent of carbon black transfer from Butyl to BR, NR and SBR was quite significant. In summary, transfer can occur when the adsorptive capacity of the filler has not been fully utilized. This situation can exist if the masterbatch has minimum heat or mechanical history, or involves low molecular weight or low unsaturation elastomers.