Symposium: Textiles and Fibres Oral Presentation
Structure development and mechanical properties of melt-spun amorphous filaments
Leal A. Andrés (1)*, Best James P. (2), Amacher Anneliese (2), Reifler Felix A (3), Hufenus Rudolf (1)
(1) Laboratory for Advanced Fibers, Empa - St. Gallen - Switzerland, (2) Laboratory for Mechanics of Materials and Nanostructures, Empa - Thun - Switzerland, (3) Laboratory for Advanced Fibers and Center for X-Ray Analytics, Empa - St. Gallen - Switzerland
Most synthetic fibers commercially available are spun from polymers that develop a semi-crystalline structure upon fiber drawing. Fibers with a substantial degree of crystallinity are typically preferred, since amorphous fibers usually show limited tensile properties. Nevertheless, amorphous polymers can show interesting characteristics for specific fields of application (e.g. optical) due to properties such as high transparency and low birefringence.
High-speed melt-spinning of different amorphous polymers has been successfully performed. Differential scanning calorimetry curves of the resulting monofilaments show that they remain in an amorphous state even after hot drawing. Wide angle x-ray diffraction (WAXD) patterns of undrawn and drawn filaments show that although the materials remain in an amorphous state, a degree of orientation is induced in the polymer after drawing. In order to further elucidate this behavior, an analysis of the influence of drawing ratio on the degree of molecular orientation is performed by means of Raman spectroscopy. Regarding mechanical performance, the amorphous filaments show an enhanced bending recovery with respect to different semi-crystalline monofilaments commercially available. However, single fiber axial compressive testing indicates that the amorphous filaments exhibit a compressive modulus value which is 50 % lower than what is observed for a reference semi-crystalline PET filament. Clearly, the moieties and substituents attached to the backbone of the amorphous polymers in order to prevent crystallization also hinder the formation of the lateral intermolecular interactions needed to achieve high compressive modulus values.