Poisson's Ratio for Stretched Vulcanized Natural Rubber

Changes in the Poisson's ratio of natural vulcanized rubber due to elongation were investigated experimentally. The following results were obtained: If infinitesimal deformation at any instant during elongation is considered, it appears to be correct to take the Poisson's ratio at such instants as 0.5. If the apparent Poisson ratio when a certain standard mark is taken and a large deformation imparted is considered, and the elongation ratio is made α, the Poisson's ratio decreases from 0.5 in accordance with the equation log10 (1/m)=0.0204α2−0.261α−0.0628. This equation is valid for subsequent elongations, no matter what elongation situation is taken for the standard marks. These two results do not vary with the carbon black content or on repeated stretching.

Study of Polymer Blends. II. Blending SBR Varying in Styrene Content with Polybutadiene

For this study of effect of SBR styrene content on blends of SBR and BR, polymer solubility was investigated by phase contrast microscopy, dielectric loss, and dynamic characteristics. Physical properties of blended rubber were also measured.

Blends of cis-1,4-Polybutadiene with Natural or Styrene Butadiene Rubber

Temperature dependence of dielectric loss, mechancial loss, and dynamic modulus were measured to study polymer blending. Results were as follows: Dielectric loss and dynamic modulus of NR—BR blends showed two peaks corresponding to NR and BR, indicating that the blends were microheterogeneous. A single, broad maximum absorption band observed for SBR—BR blends indicated that the blends were microhomogeneous. Mill mixing and solution mixing of NR and BR made very little difference in blended state and physical properties. Nearly homogeneous SBR—BR blends can be obtained with a few minutes mill mixing. In vulcanization of NR—BR blends, BR was overcured rapidly due to migration of sulfur and accelerators from NR.