Mechanisms in the Solvent Cleaning of Emulsion Polymerization Reactor Surfaces

Abstract

A new technique, fluid dynamic gauging (FDG), is introduced for studying the swelling and removal of polymer films from various surfaces. Films of two different polystyrene copolymers, labeled PX (30 kDA) and PA (125 kDa), were deposited in the laboratory on, inter alia, SS 316 plates. FDG was used to track, in situ and in real time, the films' evolving thickness during swelling and removal in three agents: NaOH, MEK, and a commercial aqueous cleaning solution, TPU. The effects of initial film thickness, solvent concentration, solvent temperature, nature of the substrate, and applied stress were investigated. Swelling profiles suggest that Type II diffusion is the governing transport process. Different modes of behavior were found. In NaOH, swelling occurred after a lengthy induction period, but no surface cleaning was detected. MEK and TPU swelled the films with a negligible induction period and then cleaned the surfaces, with the former working faster. For MEK applied to PX and PA, and for TPU with PX, the film was removed by dissolution, i.e., the cohesion of the film was attacked. By contrast, TPU applied to PA removed the film by destroying the adhesion. Application of TPU to films composed of mixed layers of PX and PA showed that the deposition sequence determines removal behavior. A simple model allows prediction of the removal kinetics of composite films from those of single-component films. The potential for substantially accelerated reactor cleaning by appropriate reactor scheduling is thereby identified.