METHOD FOR DISSOLVING PPTA IN SULFURIC ACID USING A TWIN SCREW EXTRUDER

The invention pertains to a method for dissolving PPTA or copolymers thereof in sulfuric acid using a twin screw extruder having transporting, mixing, and kneading elements comprising an entering zone, an intermediate zone, a mixing zone, a negative transport zone, a degassing zone, and a pressure build-up zone, the method comprising the steps: . transporting PPTA or copolymer thereof into the entering zone at a transport capacity low enough as to prevent sulfuric acid entering the entering zone; . introducing sulfuric acid in the entering or intermediate zone; . essentially fully filling the mixing zone to allow sufficient time to mix and dissolve PPTA or copolymer thereof in the sulfuric acid to obtain a PPTA or copolymer thereof-sulfuric acid solution; . creating after the mixing zone a negative transport zone to obtain a product lock between the mixing zone and the degassing zone; . creating a thin film of the PPTA or copolymer thereof-sulfuric acid solution in the degassing zone to degas the solution; entering the solution into the output pressure build-up zone to partially fill this zone and to leave the twin screw extruder.