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Changes in void content and free volume in fibers during heat setting and their influence on dye diffusion and mechanical properties
Author(s) -
Murthy N. S.,
Reimschuessel A. C.,
Kramer V.
Publication year - 1990
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.1990.070400120
Subject(s) - materials science , porosity , fiber , void (composites) , composite material , scattering , diffusion , volume (thermodynamics) , thermodynamics , optics , physics
Abstract The contributions of the changes in porosity and free volume to the differences in the properties of dry and wet heat set fibers are analyzed. Nylon 6 fibers heat set in wet atmosphere (autoclave and Superba process) show a significantly higher small‐angle X‐ray scattering intensity between 0.5° and 1.5° (Cu Kα) relative to corresponding non‐heat‐set fibers, whereas the fibers heat set in dry atmosphere (Suessen process) do not. This scattering arises from the electron density contrast due to pores and free volume which lower the elctron density between the fibrils. The average diameter of the crystalline fibrils, as calculated from the Guinier analysis of diffuse scattering, increases from ca. 50 to 65 Å in all fibers upon heat setting. Additional scattering at much lower angles is attributed to aggregates of fibrils. Transmission electron microscopic studies of fibers stained by AgI, through I 2 /methanol/AgNO 3 treatment, suggest that as AgI crystallizes in a dendritic network along the paths opened up by the diffusion of iodine, it brings about large structural changes in the polymer; this process reveals defects and latent diffusion paths in the fiber. The dendritic structures of AgI are more extensive in wet heat set fibers than in dry heat set and non‐heat‐set fibers. The ordering within the crystalline domains, the interlamellar spacing, and the density of the fiber increase during both wet and dry processes. The role of these changes in the structure and the morphology of the fibers on the dyeing and ozone fading behavior, and on the strength and the modulus of the fibers, are discussed.