Structure development in fiber formation of nylon-6

A comprehensive study of structure development in fiber formation from nylon-6 was performed. A major emphasis of the research involved on-line birefringenece measurements and studies of the development of orientation and crystallinity. The effects of annealing fibers in air, water and a 20 percent aqueous solution of formic acid were also studied. Tensile properties of as-spun and drawn fibers were measured and related to the spinning variables and structural characteristics.

The on-line structure development studies consisted of measuring changes in the birefringenece as the filament crystallized on the bobbin in ambient atmosphere. Previous work has shown that nylon-6 filaments remain amorphous in the running spinline even at very high spin draw ratios. Subsequently, nylon-6 crystallizes in a pseudohexagonal form on the bobbin in the presence of moisture. Higher spin draw ratios (SDR's) result in higher crystallinity. A sample with a high γ content can be produced directly by melt spinning at high speeds. The total crystallinity and the different crystalline fractions have been analyzed by means of a new γ index.

It is observed that the c-axis crystalline orientation function of the filaments increased with take-up velocity and spinline stress. Increasing the take-up speed resulted in higher tensile strength and modulus. The elongation to break however decreased with increasing take-up speed or spin-line stress.

The α-monoclinic structure had been found to result from drawing and iii

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annealing at elevated temperatures. The present study shows that drawing enhances the crystallinity of the filaments. Drawing to very high drawn ratios results in a higher α-content. On annealing the y-pseudohexagonal structure converts to an α-monoclinic form. This rate of change is greatest when annealed in formic acid, but lowest in vacuum, while intermediate in water.