During the coagulation step in the wet spinning process, a concentrated, highly viscous polymer solution is transformed into protofibers which require further processing before they acquire textile fiber properties. The structure of these protofibers is strongly influenced by coagulation conditions, and this structure, in turn, influences the extent to which desirable properties can be developed in the finished product. In this study, the effect of several coagulation variables on the structure of protofibers preserved by freeze drying has been determined and related to the further processability and final properties of the fibers. Coagulation temperature, coagulation bath composition, extrusion rate, and take-up rate are shown to influence the cross-sectional shape, initial density, and void structure of the protofibers. Higher initial fiber density and more homogeneous internal structure permit the development of higher strength at lower stretches, higher elongation at a given strength level, high maximum strength and modulus at high stretch ratios, and improved fatigue and abrasion behavior.

The fine structure of acrylic fiber has been characterized using techniques based on gas adsorption, density, electron microscopy, and light microscoly. The techniques are complementary and have heen applied to acrylic fiber prepared under current commercial conditions. The existence of a fibril-void type of structure, with voids and fibrils of the order of 200 Å diameter, has been established for wet-spun fibers. This structure was shown to originate during coagulation and has been followed through stretching and collapsing. Dry-spun samples developed a similar structure, which becomes evident after the orientation step.

Studies of the flow properties of merged spinning solutions have led to new methods for spinning bicomponent acrylic fibers. The underlying principle is that two or more spinning solutions can be merged into a common-flow stream without any significant mixing between component streams. With proper control, the technique produces a flow stream with a predetermined arrangement of the component streams. The arrangement of component streams can be very regular or seemingly random.When a mixed-component stream is spun from a spinnerette, a bicomponent fiber is produced. The distribution of components between and along filaments is determined by the arrangement of components in the common stream and the arrangement of holes on the spinnerette. Readily controllable variations in the mixed-stream patterning and spinnerette-hole arrangement are sufficient to permit production of a whole family of bicomponent fibers, ranging from "true" conjugate (similar to those produced with conventional conjugate spinnerettes) to fibers with a truly random distribution of components.