The Dependence of Processability on Molecular Weight Distribution of Elastomers

After examining the mechanism of mixing of elastomer with filler by both internal mixers and open mills, the failure characteristics of an elastomer (extension to break and ratio of elasticity to plasticity) were found to be important properties affecting the filler wetting and dispersion rates. The failure characteristics have also been shown to depend on the polymer MWD, branching, and microstructure. A quantitative characterization of deformational behavior and failure of uncured material has been presented. Also, an attempt has been made to establish a link between the more basic properties of elastomers and processability, particularly the rate of filler dispersion in mixing. The variation of compound Mooney torque and die swell with mixing time can be explained theoretically by taking account of the occluded rubber trapped by the carbon black agglomerates. As filler dispersion increases, the amount of such occluded rubber decreases, Mooney torque decreases, and die swell increases as expected from the theory of rheology of composites.