Micromixing of a polymer melt in twin-screw extruders with kneading discs.

摘要

The current research applies the Frey-Denson (1987) reactive tracer system to analyze commercially significant polymer mixing equipment used to develop new and improved polymeric materials. Micromixing has been experimentally and theoretically investigated in right-handed, left-handed and neutral kneading disc sections of a co-rotating, self-wiping, twin-screw extruder. The reactive tracer measures extent of micromixing via the competitive-consecutive reactions (A + B {dollar}to{dollar} R, R + B {dollar}to{dollar} S) of p-phenylene diamine (A) and phthalic anhydride (B), which are dissolved separately at dilute concentrations in viscous polymer melts.; Micromixing was measured over the full range from complete segregation to complete mixing on each type of kneading disc. Mixing inside the kneading discs was analyzed by cooling and removing samples from the extruder, and the results help to explain the macromixing and micromixing mechanisms in twin-screw extruders. The experimental results concluded that neutral kneading discs were the best mixing elements to perform micromixing. The left-handed and right-handed kneading discs did not provide much difference in mixing results though their pumping characteristics were quite different.; A model superimposing an extensional flow model with residence time distributions of twin-screw extruders was developed. This approach combined macromixing and micromixing in one mixing model. The mixing model predictions qualitatively agree with the experimental data that the extent of micromixing increases with higher screw speeds. The results presented here provide the first step towards improving the design and prediction of micromixing in extruders.; The flow was also simulated using the Boundary Element Method (BEM) though the results were limited to two-tipped neutral kneading discs and to C-shell chambers of twin-screw extruders. This numerical method was proven to involve a high computational cost in simulating the flow in twin-screw extruders.