Morphology, static and dynamic mechanical properties of in situ microfibrillar composites based on polypropylene/poly (ethylene terephthalate) blends

In situ composites based on blends of polypropylene (PP) and poly (ethylene terephthalate) (PET), were prepared by melt extrusion, followed by continuous drawing and isotropization. The blending of the mixture was carried out in a single screw extruder and the isotropization of the stretched blend was achieved by injection moulding. Scanning electron microscopy (SEM) studies showed that the extruded blends were isotropic, but both phases became highly oriented after drawing (stretching). The stretched blends were converted into in situ composites after injection moulding at temperatures below the melting point of PET. The size of the PET fibrils generated decreased with increasing stretch ratio. The tensile and impact properties were found to be higher for the samples drawn at stretch ratios 5 and 8. Dynamic mechanical properties such as the storage modulus (E), loss modulus (E '') damping behavior (tan delta) and static mechanical properties were investigated as a function of stretch ratio. The E' values were found to be increasing up to a stretch ratio 8. The tan delta and E '' modulus spectra showed a strong influence of the microfibrils on the alpha and beta relaxation of PP. Finally, the tensile properties obtained experimentally were compared with those determined using theoretical equations. (c) 2007 Elsevier Ltd. All rights reserved.