WET SPINNING OF NYLON 6: EFFECT OF SOLVENT ON FIBER PROPERTIES

Wet spinning of nylon 6 with molecular weight of 3×104 was studied by using five solvent systems of phenol (Ph), o-chlorophenol (OCP), sulfuric acid (SA), formic acid (FA) and dichloroacetic acid (DCA). Each of the solvent systems except OCP contained 10% water.It is supposed from the data of solubility parameter, intrinsic viscosity, and Huggins' constant that FA, SA and Ph are very good, OCP is fairly good, and DCA is rather poor solvent for nylon 6. Coagulating behaviors of phenolic solvent systems (Ph and OCP) differ from those of other solvent systems, and it is expected that phenolic solvent systems results in the homogeneous and dense fiber structure, and other solvent systems results in the inhomogeneous and sponge-like coarse fiber structure.The results of wet spinning are as follows; Fibers from Ph and OCP solvent systems have the homogeneous structure and good mechanical properties at lower alkali concentration in coagulating bath. Fibers from FA solvent system have the skin-core structure similar to viscose rayon, and have extraordinary low densities probably due to the presence of many voids. But when they are drawn, their fiber structure turns to homogeneous and their densities increase remarkably. The mechanical properties of drawn fibers from FA solvent system are best among five solvent systems. Fibers from DCA and SA solvent systems have the coarse fiber structure with macro-voids, and poor mechanical properties.Moisture regains of wet spun fibers are generally greater than those of melt spun fibers, but vary considerably depending on solvent systems. Moisture regains of fibers from DCA and FA solvent system depend remarkably upon relative humidity, and that from FA solvent system decrease with drawing, while that from Ph solvent system depend slightly upon relative humidity, and increase with drawing. These intresting hygroscopic behaviors are probably due to the finestructural characteristics such as micro-voids which may be influenced by the type of solvent and the drawing ratio.