James P. Bell

Changes in the Structure of Wet-Spun Acrylic Fibers During Processing

The structural changes that occur during processing of a wet-spun 93% polyacrylonitrile -7% polyvinyl acetate co polymer are discussed. Stress-strain, x-ray diffraction, shrinkage, and electron microscopy data are explained in terms of a model in which the molecules are in an irregular helical conformation in the relaxed state and can extend during de formation. The molecules are arranged in fibrils which, in turn, form a three-dimensional network. The fibrillar ele ments remain intact through the coagulation, hot-stretching, and drying, although network junctures break and reform. The model proposed is an extension of that used by Rosenbaum to describe the behavior of acrylic fibers after processing and is in agreement with previous work on the structural characterization of polyacrylonitrile.

On the dynamic mechanical behaviour of drawn poly(ethylene terephthalate) fibers

The effect of drawing and annealing treatments on the α transition in poly(ethylene terephthalate), PET, yarns has been studied using a combination of X-ray and dynamic mechanical techniques. It was found that drawn, crystalline PET yarns exhibit a shift in the position of the α transition to lower temperatures for high annealing temperatures; this effect has been observed for unoriented, crystalline PET. The main difference between the results for the drawn and unoriented yarns lies in the position of the α transition on the temperature scale; the α transition occurs at higher temperatures the higher the draw ratio. The shift in the position of the α transition with anealing is interpreted in terms of the number of crystals whilst the change in position of the α transition brought about by drawing is explained by orientation in the amorphous regions.ZusammenfassungDer Einfluß von Verstreckung und Temperaturbehandlung auf den α-Übergang in Poly(äthylenterephthalat), PET, Garn wurde untersucht unter Anwendung von Röntgen- und dynamisch-mechanischen Methoden. Es wurde gefunden, daß für hohe Vergütungstemperaturen verstreckte, kristalline PET-Garne eine Verschiebung des α-Überganges zu niedrigeren Temperaturen aufweisen, ähnlich wie für nicht verstrecktes, kristallines PET. Der Hauptunterschied zwischen verstreckten und nicht verstreckten Garnen ist die Lage des α-Überganges auf der Temperaturskala; der α-Übergang liegt für höhere Verstreckung bei höheren Temperaturen. Die Verlagerung des α-Überganges durch Temperaturbehandlung wird auf die Anzahl der Kristallite zurückgeführt, während seine Verschiebung durch Verstreckung erklärt wird durch die Orientierung in den amorphen Bezirken.