The Role of Molecular Weight in Controlling the Structure and Properties of High-Speed Melt Spun Nylon-6 Filaments

A comprehensive study of the structure development during high speed melt spinning of nylon-6 was performed. The major emphasis of the research was on the effect of molecular weight in the structure development of high speed melt spun nylon-6 filaments. The various measurements done on the filaments to determine their morphology included diameter, tensions in spin-line, density as well as x-ray diffraction and birefringence measurements. The effects of mass throughputs were also studied. Tensile properties of conditioned fibers were measured and related to the spinning variables and molecular weight.

The spin-line stresses measured increased rapidly with take-up velocity and molecular weight. The increase with molecular weight was more rapid at higher take-up velocities than at lower take-up velocities. The wide angle x-ray diffraction pattern indicated a significant level of crystallinity, and a high y-phase content at high take-up velocities in low molecular weight samples.

The chain axis crystalline orientation function increased rapidly at the beginning with take-up velocity and then started to level off after reaching an attainable maximum at higher take-up velocities. Increase in spin-line stresses increased crystalline orientation but not independent of molecular weight. Increased molecular weights resulted in increased crystalline orientation functions at low take-up speeds and they decreased at higher take-up speeds.

Birefringence measurements showed increases with take-up speeds and molecular weights and decreases with increased mass throughputs.

The tensile strength and modulus of the conditioned filaments increased, but the elongation at break decreased with increasing take-up velocity and spin-line stress. Modulus and tensile strength increased with molecular weight. The increase in modulus with molecular weight was rapid at high take-up speeds, producing very high modulus fibers at high speeds and high molecular weight. The tensile properties correlated with spin-line stress and birefringence, but not independent of mass throughput and molecular weight.