Effect of components of a sulfur-containing vulcanizing system on the structure and properties of isotactic polypropylene

With the use of methods of X-ray diffraction analysis and differential scanning calorimetry, the structure and melting and crystallization of isotactic polypropylene are studied in the presence of components of a sulfur-containing vulcanizing system composed of sulfur, zinc oxide, stearic acid, Altax, and thiuram, which is used for synthesis of thermoplastic vulcanizates. It is found that the addition of zinc oxide results in the formation of the β phase of polypropylene, and the content of this product depends on the concentration of a nucleating agent. The heat pretreatment of samples has a strong effect on the formation of β -polypropylene. The addition of residual compounds to polypropylene at the studied concentrations has practically no effect on its structure. With an increase in the content of the β phase, the elastic modulus and elongation at neck formation of polypropylene increase, whereas its tensile strength, elongation at yield, and elongation at break decrease.