Flash spinning process

A process for the preparation of plexifilamentary film-fibril strands of synthetic fiber-forming polyolefin which comprises:

• generating a spin fluid consisting essentially of (a) 5 to 30 wt. % synthetic fiber-forming polyolefin, (b) a primary solvent selected from the group consisting of methylene chloride and 1,2-dichloroethylene, and (c) a co-solvent selected from the group consisting of hydrofluoroethers and cyclic perfluorinated hydrocarbons said co-solvent having (i) 3 to 7 carbon atoms and (ii) an atmospheric boiling point between 15.degree. and 100.degree. C., said co-solvent being present in the spin fluid in an amount sufficient to raise the cloud point pressure of the spin fluid by at least 50 pounds per square inch;
• and
• flash-spinning the spin fluid at a pressure that is greater than the autogenous pressure of the spin fluid into a region of lower pressure to form plexifilamentary film-fibril strands of said synthetic fiber forming polyolefin.