Durability of polypropylene under stress: The effect of draw ratio and molecular orientation

Durability of oriented PP films at 20-110 degreesC was studied as a functio n of tensile stress, and comparison with the data obtained for the other am orphous-crystalline polymer films and fibers was performed. As was shown, t here is almost a single correlational dependence between the structural coe fficient gamma in the Zhurkov durability equation and the draw ratio lambda (gamma = gamma (0) + C/lambda). The activation energy of fracture U-0 was found to be constant and independent of the polymer draw ratio. The data ob tained for a modified PP suggest that the addition of CaCO3, TiO2, and a pl asticizing agent exerts no effect on U-0, that is, on the strength of chemi cal C-C bonds but has an effect on the coefficient gamma. As a result of th e latter trend, the durability of films increases by an order of magnitude.