The effect of processing conditions on the mechanical properties and thermal stability of highly oriented PP tapes

It has previously been shown possible to use highly oriented polypropylene (PP) tapes to create self-reinforced (all-PP) composites. It is desirable to understand the relationship between tape processing parameters and the mechanical properties and thermal stability of the tapes, as these tape properties will govern the ultimate properties of the all-PP composite. In this paper, the effects of the tape drawing parameters such as draw ratio (λ), drawing temperature and thermal annealing on the final mechanical properties, density and dimensional thermal stability of the tapes are presented. PP tapes drawn to λ = 17 possess tensile moduli of ∼15 GPa and tensile strengths of ∼450 MPa. PP tapes with high draw ratios, λ > 9.3, show a decrease in density, a change from transparent to opaque appearance and increased dimensional thermal stability with increasing draw ratio. The results of an investigation into the effects of a thermal annealing step, targeted at improving the dimensional thermal stability of these highly oriented PP tapes, are also presented.