Solid-state forming of polypropylene

The replacement of some high-performance structural materials, such as fiber reinforced composites, by more conventional materials forces scientists and engineers to look at new processes to enhance the properties of the latter. In fact, the utilization of composites has some shortcomings among which weight, recyclability and fiber to matrix adhesion should be mentioned. Hence, the development of ultrahigh modulus polymer products is of paramount importance, in view of their significantly lower density. The carbon-carbon bond being the strongest one, a full alignment of these bonds in the same direction would lead to a material with a very high modulus and strength. Polypropylene (PP) has a theoretical ultimate modulus of 50 GPa and an ultimate tensile strength of 16 GPa. These values are considered unlikely to be achieved because the polymer assumes a random entangled and twisted configuration which has a low bearing capacity. In recent years, it was realized that the greatest modulus and strength would result from an anisotropic structure of highly oriented, extended and densely packed chains [1-3].