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This paper reports a systematic study of the effects on composite properties of different chemical treatments on natural fibers. Both short flax fibers and flax cellulose pulp in a polypropylene matrix have been investigated. The influence of treatments on fiber properties was investigated by means of spectroscopic, thermal and mechanical tests. Moreover, the effects of fiber treatment on the crystallinity of the matrix were analyzed using differential scanning calorimetry and optical microscopy. The mechanical properties of the composites obtained were studied using tensile and bending tests. It is shown that most of the main properties of the composites can be improved by adequately treating the fibers. The results of this study provide a database mainly devoted to material selection for the automotive industry. This research has been performed as a part of the ECOFINA project in the framework of the 5th European Research Program of the European Community. Polym. Compos. 25:470–479, 2004. © 2004 Society of Plastics Engineers.

A high temperature thermosetting bisphenol-A dicyanate (BADCy) was modified with polyetherimide (PEI) at various compositions. The effects of the morphology of the blends on the fracture toughness and mechanical properties were investigated. For this purpose, fracture, flexural, and compression tests were carried out. The fracture surfaces of the broken specimens were examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The morphology was controlled by changing the curing conditions and PEI content. A good correlation between fracture properties and microstructural features of the mixtures has been observed. The phaseinverted morphologies showed the highest fracture toughness, which was further increased by increasing the cure temperature. The mechanical properties of the matrix (modulus, yield strength) were not affected by the addition of the thermoplastic. Fracture energy values show similar trends for the different mechanical tests performed.

The phase-separation behavior and morphology of polycarbonate-based polyurethanes were investigated as a function of the soft-segment molecular weight and chemical structure and the 4,4 0 -diphenylmethane diisocyanate/1,4-butanediol based hard-segment contents. Polarized optical microscopy and atomic force microscopy images showed that the surface morphologies changed as the soft-segment molecular weight and hard-segment content varied and also when the sample preparation conditions were modified. An increase in the soft-and hardsegment lengths led to increased phase separation with respect to the lower molecular weight soft segment, and this showed an interlocked and connected morphology of intermixed soft and hard domains. The surface morphology of phase-separated polyurethanes with hard segments composed of more than four to five 4,4 0 -diphenylmethane diisocyanate units contained globular hard-segment domains formed by spherulites, in which the size and connectivity between the branched lamellae changed with the hard-segment size. Interlamellar areas related to the soft segment were seen in the spherulites. Variations in the hard-segment spherulites were observed for polyurethanes based on soft segments of different molecular weights.

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