The problem of the mechanism of macromolecule orientation occurring in the formation of fibers from polymer melts has been qualitatively analyzed. As a result of birefringence, x‐ray, and spinning stress investigations carried out on polycapronamide fibers, the main parameters determining orientation have been established. They are the parallel velocity gradient along the spinning length, G = dV/dl, and the relaxation factors. The deformation ratio S (the ratio of final to original linear velocity), analogous to the draw ratio λ = 1/10 in the cold‐drawing process, has no influence on the degree of orientation. The orientation by spinning is not accompanied by any such structural transformations as occur through cold‐drawing. The fibers spun at high velocity gradients consist of well‐oriented β‐polycapronamide. It is thus assumed that the orientation proceeds in the region of the liquid melt‐stream as a result of simultaneous action of velocity gradient and thermal relaxation. This mechanism, analogous to that causing the familiar streaming orientation of polymer solutions in capillaries or in a Couette apparatus, is different in principle from that of the cold‐drawing process.
The principal regularities of molecular orientation occurring by fiber formation from polymer melts have been proved for several polyamides, copolyamides, polyurethane, and polyester. It has been found for these polymers, as for the formerly investigated polycapronamide, that fiber birefringence (used as a comparative measure of the mean degree of macromolecular orientation) practically does not depend on the deformation ratio S = VE/V0, and monotonically increases with velocity difference (VE − V0) and reciprocal fiber diameter ϕE−1 (measure of cooling rate). Hence the general character of the postulated mechanism of orientation, simultaneous action of velocity field and thermal relaxation, seems to be proved for the typical fiberforming polymers. The differences between the shapes of characteristics birefringence–velocity difference, birefringence–spinning stress, and between the x‐ray patterns of polyamides and polyester have been interpreted in terms of molecular structure and occurrence of H bonds.
The effect of spinning conditions on fiber birefringence and spinning stress has been studied on high‐pressure polyethylene and two atactic polystyrenes. The general character of the relations observed is similar to that found for polycondensation polymers, but some deviations concerning the effect of deformation ratio have been noted. The x‐ray patterns of the obtained fibers have been presented and discussed. A general interpretation of the observed structural phenomena in the molten linear polymers, based upon the relative crystallization and orientation rates has been given.
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