Flash-spinning process

In a continuous process for flash-spinning a web of fibrillated plexifilamentary material including the steps of:

• continuously supplying under pressure into a dissolution zone molten polyolefin polymer and a solvent for the polymer, the concentration of polymer being 8 to 20% by weight of the solution,
• dissolving the polyolefin polymer in the solvent and forming a polymer solution having a temperature of at least about 175.degree. and a pressure above the two-liquid-phase pressure boundary for the solution,
• forwarding the solution through a transfer zone while maintaining the pressure of the solution above the two-liquid-phase pressure boundary for the solution,
• passing the solution into a pressure letdown chamber for lowering the pressure of the solution to below the two-liquid-phase pressure boundary for the solution to cause nucleation of polymer from the-solution,
• discharging the solution from the letdown chamber through a spinneret orifice of restricted size to an area of substantially atmospheric pressure and temperature, and
• forming a web of fibrillated plexifilamentary material;
• the improvement comprising the step of mixing the solution and the nucleating polymer within the letdown chamber by passing the solution and polymer through a static mixing device disposed within the letdown chamber.