Patent ID: 7527841

Claim:
A method for dissolving PPTA or copolymers thereof in sulfuric acid using a twin screw extruder having transporting, mixing, and kneading elements with 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 that prevents sulfuric acid from entering the entering zone; introducing liquid sulfuric acid in the immediate zone; substantially fully to fully filling the mixing zone to allow sufficient time to mix and dissolve the PPTA or copolymer thereof in the sulfuric acid to obtain a PPTA sulfuric acid solution or a copolymer sulfuric acid solution; creating, after the mixing zone, the negative transport zone to obtain a product lock between the mixing zone and the degassing zone; creating a thin film of the PPTA sulfuric acid solution or the copolymer sulfuric acid solution in the degassing zone to degas the solution; and entering the solution into the output pressure build-up zone to partially fill the output pressure build-up zone and to leave the twin screw extruder.