Heterogeneous Structure in Blends of Rubber Polymers

Abstract The phase contrast microscope has been used to examine blends of rubber polymers. Mixing on a molecular scale was never observed, the more homogeneous blends consisting of a pair of interlocking “networks” with a mesh diameter of about a micron. Blending was less perfect when the polymers were of widely different viscosities, and in the worst cases consisted of lumps of the stiffer polymer embedded in the softer polymer. Blends prepared by drying mixed solutions were always exceedingly heterogeneous. Physical properties of gum stocks were not greatly affected by the size of this heterogeneity, although there was evidence from electron microscope surface replicas that rupture surfaces tend to follow the interface between the polymers. The distribution of filler, zinc oxide and protein in blends was studied using a variety of techniques. It was found that these materials (and probably many other compounding ingredients) are not always evenly distributed between the polymers, and this may be expected to affect adversely the physical properties.