John H. Southern

Investigations of Polyester Fiber Process/Structure/Property Relationships Part I

Polyester structure and properties are examined as a function of spinning and texturing processes. Spun fiber tensile and shrinkage properties are related to amorphous orientation and crystallinity. Particularly notable are the observations of textured yarn dyeability dependency on yarn crystallite size and spun yarn crystalline content. Dye path tortuosity is hypothesized to control the disperse dyeing of textured polyester.

Nylon 6,6 Fiber Tensile Properties as a Function of Morphology

Nylon 6,6 amorphous and crystalline orientation and content data are reported herein for a fiber series produced by varying the degree of stretch in conventional spinning and drawing operations. Tensile elongation and tenacity are correlated exponentially with the amorphous orientation function. Crystalline orientation values were observed to be consistently high, varying only slightly with significant tensile property changes. In addition, crystalline and amorphous contents varied by no more than 12% and did not consistently correlate with tensile properties. Extrapolation of the tensile property/amorphous orientation correlations to perfect amorphous chain orientation in the fiber direction implies that, in principle, a nylon 6,6 fiber having 20 gpd (1765 kN.m/kg) tenacity and 5.4% elongation is attainable.

Solution Fracture Barrier in Wet Spinning

The dry jet wet spinning of various molecular weight aromatic polyhydrazide solutions is used to exemplify tenacity and spinnability reduction due to solution fracture, an elastic flow instability initiating in the capillary entrance region. Signif icantly, fiber spun at shear rates an order of magnitude above that required for fracture initiation evidences no tenacity loss. A flow visualization apparatus, used to photo graph the solution orientation changes resulting from fracture, verified reduced in stability amplitude at high shear rates.

Improved Sheath/Core Adhesion in Biconstituent Fibers via Interface Mixing

Biconstituent melt-flow through a porous unit, known as the Interface Mixer Insert, is used to achieve adhesion within sheath/core fibers spun from two incompatible polymers, as exemplified herein by nylon and polyester. Sheath splitting and void formation at the interface are documented for nylon sheath/polyester core filaments having essentially no adhesion between the sheath and the core. Improved adhesion as a function of Interface Mixer Insert filtration media is examined via optical and electron microscopy and correlated with a qualitative fabric-endurance evaluation as well as a quantitative adhesion-peel-strength test.

Polymer Modifications for Improved Textured Nylon 66 Yarns and Processes

Increased molecular weight and branching agents are used in melt spinning partially oriented nylon 66. The fiber solidifies more rapidly during spinning and has larger crystallites and increased elongation-to-break versus conventional PON, consistent with a stress-induced crystallization mechanism. When textured, the fiber produces higher crimp. Gains in both spinning and texturing productivity are documented.