Superstructural description of deformation process in uniaxial extension of preoriented isotactic polypropylene

Abstract

Abstract The strains on uniaxial extension of preoriented isotactic polypropylene are separated over the whole range of deformation into three processes: crystallite boundary slip (A 1 process), uniform shear deformation of crystallites (A 2 process), and restoration of molecular orientation from the sheardeformed state (Ā 2 process). They are separately evaluated by the use of the parameters of superstructure varying in deformation. Both the A 1 and A 2 processes predominate before the A 2 → Ā 2 transition takes place. Wide‐ and small‐angle x‐ray goniometries detect this transition. After the A 2 → Ā 2 transition takes place, the specimen cannot be deformed by the A 1 or A 2 process, but by a molecular process such as pulling out the isolated extending chains from the folded chain crystals followed by their refolding. From the quantitative evaluations of the strains associated with the A 1 and A 2 processes it is deduced that the initial shear compliance for the A 1 process is smaller than that for the A 2 process.