Degradation Mechanism and Stabilization of Polypropylene Induced by Chemical Solutions

Abstract

The mechanism of degradation of homo polypropylene (PP) and block PP due to treatment with heated chemical solutions was examined by three-point bending tests with U-notched bars in a plane strain state. In nitric acid solution, tie molecules that connect lamellar crystals were ruptured near the surface of the specimen. This resulted in a decrease in the molecular weight and in the formation of surface crazes. Since surface crazes easily transformed into cracks with small radius, the strong strain constraint caused stress concentration, resulting in brittle fracture of homo PP. In block PP, since the nucleation of numerous voids from the dispersion phase caused the relaxation of stress concentration with release of strain constraint, brittle fracture did not occur and durability due to chemical solutions was improved.