Contribution to the Study of the Porous Structure of Polyacrylonitrile (PAN) Fibers The Effects of Heat Treatments

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Abstract
The porous fraction of PAN fibers, as shown by the formation in situ of silver sulfide, consists of radial paths which may or may not be associated with different distributions of micropores. The radial paths generally originate from microlobes or surface faults. The size of these porous zones, their number, and their mode of distribution in the structure itself are generally affected by technological operations involving tension and heat treatment. During the dry heat treatments, the fibers have a tendency to collapse, with a simultaneously decrease of the void sizes and appearance of new gaps of the same sort that characterized the original sample. The wet-phase treatments are usually accompanied by swelling of the fibers, limited when fibers are maintained at constant length. The introduction of water molecules into the struc ture produces distortions in the ordered zones and the structural rearrangement that results eliminates the initial porosity but leaves many fine micropores which are localized in the periphery of the fibers. This latter effect can be compared to a fiber-skin rupture.