Analysis of distributive mixing during polymer blending in twin screw extruders using reactive polymer tracers

A novel quantitative method for analyzing distributive mixing during polymer blending in a co-rotating twin screw extruder was developed. This method employed a mixing limited interfacial reaction between two reactive polymer tracers to gain direct evidence of the generation of interfacial area during polymer blending. The tracers were based on a low molecular weight amorphous polyolefin wax containing a high concentration of terminal double bonds, which were targeted for functionalization with anhydride and primary amine functional groups. These functional groups were selected because their coupling reaction is extremely fast under the conditions employed during polymer processing in extruders. A melt-phase Alder Ene reaction between the terminal double bond of the polyolefin and the double bond of maleic anhydride was used to introduce a terminal succinic anhydride functional group. Hydroboration followed by amination was completed in solution with THF to introduce terminal primary amine functional groups. For the mixing experiments, the reactive polymers were blended into polypropylene (PP) resins at a concentration of 5wt%, which was adequate for quantitative analysis of the anhydride functional group conversion using a FT-IR spectrometer.; Distributive mixing, or the generation of interfacial area, was investigated during melt-melt blending of two segregated PP streams in a co-rotating twin screw extruder. Each PP stream contained one of the reactive polymers, which come into contact and react at the growing interface. A tandem single/twin screw extruder apparatus was used to perform the melt-melt blending experiments. One stream was metered to the beginning of the twin screw extruder, and the second was melt fed at a desired downstream position using the single screw extruder. As verified using model interfacial reactions, the coupling of anhydride and primary amine functional groups was mixing limited, and the anhydride conversion was linearly related to the interfacial area available for the reaction. A slit die at the end of the twin screw extruder was used to prepare a film for FT-IR analysis of the anhydride conversion, which was a direct measurement of the overall distributive mixing performance of the melt-melt blending section of the twin screw extruder. Experiments were completed to investigate the effects of operating conditions, screw configuration, and polymer viscosity on the overall distributive mixing. (Abstract shortened by UMI.)...