THE COLD-DRAWING OF NYLON 6.6

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Abstract
An investigation has been made into the variation in shape of the loadelongation curve of undrawn polyhexamethylene adipamide (nylon 6.6) filaments with change in ambient conditions, isotropic refractive index of the undrawn filament and speed of extension at low speeds of extension (0.008cm/sec–0.43cm/sec). The interaction of these variables and their resultant effect on the load-elongation curve are traced to a change in molecular mobility within the amorphous regions of the filament. The internal fracture which occurs when a nylon filament is drawn at a “neck” under particular conditions is discussed, and the experimental results are shown to be consistent with the formation of a negative hydrostatic pressure at the cusp of the neck. Drawn filaments which have fractured internally have, compared with normal nylon filaments, approximately the same strength, 20% lower density and a much higher opacity. A general molecular mechanism for the drawing process is put forward which combines ideas set out previously by Bunn and Alcock, Jackl, and Marshall and Thompson. A suggestion is made that drawing at a neck is equivalent to melting at reduced pressure at the centre of the neck, and an attempt has been made to express this idea quantitatively. The theory produced inter-relates the latent heat of fusion of the undrawn filament, the maximum natural draw ratio and the work of drawing.

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