Morphological investigations of polypropylene single-fibre reinforced polypropylene model composites

The tensile properties of polypropylene fibers, produced in a short-spin line, are correlated with the parameters of the three processing stages (spinning, drawing, and annealing), and with the molecular weight distribution. In general, tensile stiffness and strength increase with increasing molecular orientation, while the elongation at break decreases. The degree of orientation is determined by the deformation ratios and temperatures of the first two stages. Tensil modulus and strength also increase with increasing annealing stage shrinkage ratio. All the tensile properties, including the elongation at break, increase with increasing average molecular weight. The mechanisms of crystallization and deformation are related to the molecular weight distribution in different ways. Hence, the tensile modulus is highest for broad distributions when the draw ratio is low, and for narrow distributions when the draw ratio is high. The tensile strength increases and the elongation at break decreases as the width of the molecular weight distribution decreases, for all combinations of processing parameters. The distribution of tensile strength, for fibers with high draw ratios, broadens as the molecular weight distribution narrows. The total draw ratio of fibers, as experienced during processing and testing, and the true stress at break, are discussed in terms of deformation rates and relaxation times. © 1994 John Wiley & Sons, Inc.

Effects of processing parameters and molecular weight distribution on the tensile properties of polypropylene fibers

Mechanical properties of melt-spun and postdrawn isotactic polypropylene (iPP) are studied to examine the dependence on the temperature in the postdrawing stage. In accordance with the literature, the Young's modulus is uniquely determined by the applied draw ratio. However, in contrast to the literature, we found that the overall mechanical behavior strongly depends on the applied postdrawing temperature. For a fixed draw ratio, a significant drop in yield stress can be observed with decreasing drawing temperature. At a certain drawing temperature, this drop leads to a transition from brittle to ductile failure behavior. From this study it can be concluded that a proper choice of drawing conditions offers control on several mechanical properties (e.g., stiffness, strength) at the same time.

Influence of postdrawing temperature on mechanical properties of melt-spun isotactic polypropylene

A two-dimensional position-sensitive 6 Li glass scintillation detector for neutrons has been constructed and put into operation in a 40 m long small angle neutron scattering instrument. The detector has a detection area of 60 × 60 cm, a neutron capture probability of 96% for subthermal neutrons of 8 A wavelength, a spatial resolution of 8 mm adapted to the scattering experiments, and a counting ability of 100 kHz. The Anger type camera consists of 8 × 8 photomultipliers of 3 in. diameter arranged in a square lattice with 8.4 cm lattice constant. In a coarse fine procedure a neutron capture event is addressed by determining the photomultiplier with maximum anode signal and by a division procedure involving the nine relevant signals of the 3 × 3 photomultiplier matrix centered at the maximum photomultiplier signal. The gain of each photomultiplier is kept constant in time by a gain stabilizing system. Construction, data processing and properties of the detector are described. A few small angle scattering patterns from polymer samples are presented.

A two-dimensional scintillation detector for small angle neutron scattering

The morphology and mechanical properties of melt-spun and post-drawn isotactic polypropylene (iPP) tapes have been studied in order to examine their dependence on the post-draw ratio applied. Special attention is focused on the characterization of the so-called overdrawing behavior of the tapes; at a certain draw ratio, a change of the optical appearance of the tape from transparent to opaque is observed. Overdrawing is accompanied with changes in the mechanical properties, surface, and morphology of the tapes. For post-draw ratios without overdrawing, and for highly overdrawn tapes, the variation in the mechanical properties measured is very small, but for slightly overdrawn tapes, a large scattering of mechanical properties has been measured. In the latter case, this behavior is related to the start of internal delamination of the tapes during post drawing. It is shown that strongly overdrawn tapes have excellent mechanical properties, in particular, high specific stiffness and strength. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2920–2931, 2007

On the overdrawing of melt-spun isotactic polypropylene tapes

Determination of the chain conformation in fast-spun polypropylene fibers by small-angle neutron scattering

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Determination of the chain conformation in fast-spun polypropylene fibers by small-angle neutron scattering