CHARACTERIZATION OF THE TWIN SCREW EXTRUSION PROCESS

摘要

In contrast to the well developed field of polymer characterization, the advances of extrusion process characterization lagged far behind. Engineers have to deal with problems such as process scale-up and product quality control primarily by empirical means. Practically no quantitative expressions exist between the operating conditions and the important process parameters such as degree of mixing, intensity of mixing and melting, the nature of polymer melting or plasticization, or energy consumption. We propose along with new supporting data that the parameters introduced previously, δP/δQ and δP/δN, that is, energy per unit of additional mass and energy per unit of screw revolution could be used to characterize the melting behavior of a polymer in an in-termeshing, co-rotating twin screw extrusion process. The parameters appeared to be independent upon the extrusion rate (Q) and screw speed (N) in the ranges examined (4.5 to 36kg/hr and 100 to 500RPM). We further propose that additional parameters, such as those defining the kinetics of melting, average residence time (for melting and the over all) and residence time distribution obtainable by the pulse perturbation technique may be required in order to sufficiently define a given extrusion process. One can also predict with excellent agreement the observed specific mechanical energy input of extrusion, defined by extrusion power/throughput (P/Q), with simple linear expressions (Eqs. 1 and 2). The parameters c_1 (δP/δQ), c_2 (δP/δN), and a constant c_3, can be determined directly by steady state extrusion experiments without employing pulse or step perturbation methods.