Process for melt-spinning acrylonitrile polymer fiber using vertically disposed compression zone

A process for preparing acrylonitrile polymer fiber which comprises continuously feeding a particulate composition of about 70 to about 95 weight percent of a fiber-forming acrylonitrile polymer and, correspondingly, from about 30 to about 5 weight percent of water into the top of a vertically disposed compression zone operating at a compression ratio of greater than about 1:1 and less than about 1:3 and a temperature sufficient to provide a fusion melt at autogeneous pressure, said feeding being conducted at a rate which satisfies the operating capacity of said compression zone so as to provide a vapor seal, and extruding the resulting fusion melt from the bottom of said compression zone through a spinnerette assembly using the pressure generated within said compression zone, said extruding being directly into a steam-pressurized solidification zone maintained under conditions which control release of water from the nascent filaments to prevent deformation thereof.