Abstract. The plane-stress ductile fracture of poly(#-caprolactone) (PCL) has been investigated as a function of molecular weight and related crystalline structure. Because of the interacting effects in semi-crystalline polymers a separate study of a given structural parameter is rather challenging. Nevertheless, this polymer seems to be a good model material to study the effect of molecular weight on the essential work of fracture, as the interactions between the separate parameters, at room temperature, are negligible. The molecular characteristics of PCL were determined by size exclusion chromatography. To confirm the entangled molecular structure of studied polymers rheological measurements were performed. The crystalline morphology has been characterized by differential scanning calorimetry and wide angle X-ray diffraction. Quasi-static tensile tests and essential work of fracture tests were performed to study the mechanical behavior. Based on the experimental observations an empirical model has been proposed to outline the molecular weight and crystallinity dependence of the essential work of fracture in this semi-crystalline polymer.
In this work the influence of synthetic boehmite alumina (BA) nanoparticles with various surface treatments on the morphology, crystallization behavior and mechanical properties of polypropylene copolymer (PP) nanocomposites was studied. In particular, a series of PP/BA nanocomposites, containing up to 10 wt% of untreated and of octylsilane-functionalized BA nanoparticles, were prepared by melt compounding and film blowing. A third type of composites was produced by incorporation of BA nanoparticles treated with benzene-sulfonic-acid.Scanning electron microscopy indicated that BA nanoparticles were finely and uniformly dispersed, though agglomerated, in the PP nanocomposites. Surface treated BA nanoparticles were better dispersed in the matrix than the untreated BA nanocomposites. The melt viscosity of nanocomposites remained unaltered or decreased by nanofiller incorporation at low contents (2.5 and 5 wt%), while it slightly increased at higher contents (10 wt%).Uniaxial tensile tests indicated that the nanoparticles can induce a remarkable stiffening effect even at a rather low filler content, especially in the case of surface treated particles. The plane stress fracture toughness of the material, evaluated by the essential work of fracture approach, showed a noticeable improvement due to BA incorporation, with an optimal effect for a filler concentration of about 2.5 wt%.4
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