Structure and properties of isotactic polypropylene oriented by rolling with side constraints

The rolling of isotactic polypropylene (iPP) with a new method of rolling with side constraints (inside a channel) was studied. It was found that deformation processes by compression in a channel die and by rolling with side constraints proceed in very similar fashions (plane-strain conditions) and result in materials of similar orientations and mechanical properties. The difference between the two processes is that rolling causes the destruction of the lamellar structure at a higher strain than compression. Dynamic mechanical measurements showed that rolling to a high strain produces not only a well-developed orientation of the crystalline component but also high orientation and transverse ordering of the amorphous phase, leading to its transverse anisotropy. iPP deformed by rolling with side constraints has tensile properties similar to those of iPP deformed by other methods, such as conventional rolling or plane-strain compression. The elastic modulus and ultimate strength measured along the rolling direction increase with an increasing deformation ratio. For samples deformed to a deformation ratio of 10.4, the ultimate strength reaches 340 MPa and can be further increased by postdeformation annealing. The oriented iPP also demonstrates extremely high impact toughness, especially in the direction of side constraints. Izod impact tests demonstrated that the material fracture on impact is veri limited and that the impact strength exceeds 170 kJ/m(2). In contrast to the tensile properties, there is an optimum deformation ratio around 5, for which the impact strength is the highest. (C) 2002 Wiley Periodicals, Inc.