Processing-structure-property relationships in elastic copolyester-ether filaments

Elastic filaments have been produced by melt-spinning poly(tetramethylene terethalate)/poly(tetramethylene oxide) (PTMT/PTMO) copolymers of various hard segment contents (HSC). The microstructure and mechanical properties were found to be strongly dependent on composition, spinning speed, and annealing treatment.

The crystallization rate and crystallization temperature both decrease as HSC decreases. Because of the sluggish crystallization kinetics in some compositions, a water quench bath was used in the spinning process.

All the samples exhibited two-point small angle x-ray scattering patterns which indicate a lamellar structure with some degree of preferred orientation. As the spin draw ratio increases, the lamellae become increasingly aligned with their long axis perpendicular to the fiber axis. Annealing promotes phase separation in these samples through hard segment crystallization. Larger crystallites grow primarily in their equatorial crystallographic directions, although some crystallite thickening was noted in compositions having a high HSC. There is some evidence that smaller crystallites may melt during the annealing treatment. The relationship of the long period to the hard segment content and the annealing temperature are discussed in terms of the interdomain spacing.

Mechanical tests were performed on the filaments and structure-property relationships were investigated. One interesting result is that the modulus of the copolymer filaments decreases upon annealing, while that of the PTMT homopolymer increases. These results and the effect of composition on the modulus were intepreted in terms of the relative portion of tie molecules and the modulus of the amorphous phase. Ultimate properties such as tenacity and elongation to break were found to depend more on the chain orientation than on the degree of phase separation.

Selected filaments were further processed by cold drawing, hot drawing, and by drawing and annealing. The effects of these operations on the stress-strain behavior and elastic properties are discussed and compared to the properties of the undrawn filaments. The relationship of the mechanical properties to the filament microstructure is discussed. Drawing reduces plastic deformation and increases elastic recovery. Different types of behavior are observed depending on whether the filaments are fixed or free annealed. There is a trade-off between high elastic recovery and high extensibility.