Experimental and Numerical Simulation Study of Devolatilization in a Self-Wiping Corotating Parallel Twin-Screw Extruder

Devolatilization is an important process for separating and removing unnecessary residual volatile substances or solvents during the production of polymers using twin-screw extruders. Latinen proposed a surface renewal model to determine the concentration of volatile components in the extrudate of a single-screw extruder. When a twin-screw extruder is used to calculate the concentration, it is necessary to use the exposed surface area of the resin in the starved region of Latinen’s model, which, however, is difficult to estimate. In our previous work, we numerically determined resin profiles of the screws using the 2.5D Hele–Shaw flow model and the finite element method, which helps in estimating the surface area of devolatilization. In this study, we numerically analyzed the volatile concentration of the extrudate in a self-wiping corotating twin-screw extruder using Latinen’s surface renewal model along with our resin profile calculation method. The experimental results of the concentrations of the volatile component (toluene) in the extrudate of polypropylene agreed well with its numerical calculation with a relative error of 6.5% (except for the data of the lowest rotational speed). Our results also showed that decreasing the flow rate and increasing the pump capacity were effective for removing the volatile component. The screw pitch of a full-flight screw was not affected by the devolatilization efficiency with a fixed flow rate and screw speed.

Engineering Analysis of Devolatilization of Various Additives in Intermeshing Co-rotating Twin Screw Extruders

An experimental study of devolatilization of nonane, xylene and 1-hexanol from molten polyethylene in a modular co-rotating twin screw extruder is described. Various modular screw designs, as well as different feed rates, screw speeds, and barrel temperatures were used. It was found possible to correlate the extent of devolatilization in different modular screw designs with a mass transfer coefficient which depends on screw speed and LDPE feed rate. The mass transfer coefficient depended on the liquid being devolatilized, being highest with 1-hexanol and lowest with nonane. In addition, the values of the mass transfer coefficient were obtained through experiments on the twin-screw extrusion of PE with nonane, xylene and hexanol. Interpretations of these results are described.

Modeling and Practice of Ethanol-devolatilization of Silica-silane Rubber Compoundsin an Internal Mixer

During mixing of a rubber compound containing silica and silane, the mixer is not only used for the dispersion of the filler and other ingredients, but also for a chemical reaction. These two functionalities of the mixer result in opposite processing requirements: A good dispersion is reached by high shearing forces, increasing the compound temperature. The silanization is not dependent on high shearing forces; it is positively influenced by high temperatures, but with an increasing risk of scorch. Another drawback is the equilibrium between the ethanol concentration in the vapor phase in the void space of the mixing chamber and in the rubber phase, which is limiting the reaction rate of the silanization. Devolatilization of the compound is a crucial factor for the efficiency of the silanization reaction.

In this article a model for devolatilization of a rubber compound in an internal mixer is developed, including a chemical reaction replenishing the volatile component during the devolatilization process. The model is based on the penetration theory, with the main contribution to the devolatilization being convective mass transfer. The main influencing factors, theoretically deducted and practically verified, are temperature, mixer volume, fill factor, rotor speed, reaction time and partial pressure of the volatile component in the void volume of the mixer.