N.-M. Barkoula

Fatigue Properties of Highly Oriented Polypropylene Tapes and All-Polypropylene Composites

This paper describes the fatigue behaviour of newly developed all-polypropylene (all-PP) tapes and composites, with reference to the composite processing conditions, testing temperature and making a comparison with commercial alternatives. All-PP tapes are highly oriented and their failure behaviour follows that of other highly oriented polymers. All-PP woven composites fail ultimately due to PP tape failure. However, this failure mode is accompanied by delamination of fabrics in the woven structure. Consolidation pressure plays a decisive role in controlling the interlaminar properties and hence the delamination resistance and furthermore the fatigue limit of the composite. Comparison of all-PP woven composites with commercial alternatives based on glass and natural fibres reveals the excellent relative performance of all-PP composites under fatigue loads. Fatigue properties of all-PP composites are however sensitive to the testing temperature, and elevated temperatures can lead to a rapid reduction of the fatigue resistance of these all-polymer systems.

Effect of Compounding and Injection Molding on the Mechanical Properties of Flax Fiber Polypropylene Composites

The present study focuses on short flax fiber, as well as long flax fiber-reinforced polypropylene (flax/PP) composites, manufactured by the injection molding method. Compounding of flax with two different grades of PP (with and without maleic anhydride (MA-PP) grafting) is carried out by four methods: kneading process, Henschel kinetic mixer, extrusion compounding, and production of long fiber thermoplastic (LFT) granules through pultrusion. The effect of the compounding method and injection molding on the fiber length and mechanical properties of the composites is being investigated. Furthermore, the effect of fiber—matrix adhesion on the mechanical response is being discussed. It can be concluded that the reduction in fiber length, associated with injection molding, did not affect the tensile properties significantly for the studied systems due to improvements in fiber orientation along the polymer flow direction and increased fiber efficiency through dimensional changes due to fiber opening. The addition of MA-PP led to improvements in the tensile strength of injection-molded composites. Kneader compounded composites showed maximum tensile strength as well as stiffness when compared with other compounding methods.

Interface engineering through matrix modification in natural fibre composites

Abstract: The dependence of the mechanical performances and physical properties of natural fibre reinforced plastics on their interface properties is reviewed, with particular emphasis on low adhesion and the potential ways to overcome this problem via matrix modification. The focus is on polypropylene-based composites and maleic anhydride grafting. The way in which matrix modification improves the adhesion, as well as the parameters that influence the efficiency of bonding are considered. Finally, the effect of matrix modification on interfacial properties and on macroscopic properties of natural fibre composites is discussed. Two main composite categories are considered, long and short natural fibre reinforced polymer composites.