SUPERSTRUCTURAL DESCRIPTION OF DEFORMATION PROCESS IN UNIAXIAL EXTENSION OF PREORIENTED ISOTACTIC POLYPROPYLENE

The strains on uniaxial extension of preoriented isotactic polypropylene are separated over the whole range of deformation into three processes: crystallite boundary slip (A1 process), uniform shear deformation of crystallites (A2 process), and restoration of molecular orientation from the sheardeformed state (Ā2 process). They are separately evaluated by the use of the parameters of superstructure varying in deformation. Both the A1 and A2 processes predominate before the A2 → Ā2 transition takes place. Wide‐ and small‐angle x‐ray goniometries detect this transition. After the A2 → Ā2 transition takes place, the specimen cannot be deformed by the A1 or A2 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 A1 and A2 processes it is deduced that the initial shear compliance for the A1 process is smaller than that for the A2 process. Copyright © 1979 John Wiley & Sons, Inc.