Effect of Fibre-Orientation on Mechanical Properties of Polypropylene Composites

The mechanical and structural properties of a composite consisting of polypropylene fibres (PP) in a random poly(propylene-co-ethylene) (PPE) has been prepared and its properties evaluated. The mechanical properties of PPE laminates were largely determined by the presence of a complex fibre orientation distribution in the composite. The results showed that all-PP composites demonstrated enhanced stiffness and creep resistance with decrease in the orientation angle, θ, between the fibre axis and the load direction; the friction coefficient decreased linearly as θ increased from 0° to 90°. Composites with zero angle (unidirectional composites) between fibre axis and applied load (θ = 0°) possess the highest stiffness, because the fibre efficiency is inherently strong for this system as all the fibres are able to contribute to the composite stiffness and to carry the load. An increase in θ leads to a decrease in composite stiffness, which indicates that by increasing θ, a lower proportion of the applied load is transferred to the fibres and thus it is not completely distributed among the fibres. The composite with θ = 90° showed the highest relative creep, whereas the composite with θ = 0° displayed the lowest creep. In general, the relative creep increased steadily with increasing θ; also the increment in θ produced a decrease in the creep modulus, and it was observed up to 90°. Composites with woven fabric showed the best properties, after the unidirectional composites, due to the interlaced structure of the woven fabric. The bundles of plain fibre cloth restrict displacement in each other and result in high stiffness. In addition the mechanical properties of the composite with random fibres are somewhat between the composite with 0°< θ < 90°, due to alignment of fibers along any direction in the composite.