A Simplified Model for the Melting of Polymer Pellets under Compression in a Twin-Screw Extruder
Plastic energy dissipation (PED) is an important mechanism involving the melting of polymer in a twin-screw extruder. In the present study, the melting behavior of polymer pellets under compression is studied by a simplified model with the finite element method, based on the fact that mechanical energy from the deformation of a single pellet is converted into heat energy. The model shows that the heating of the pellet is not uniform. Under compression, the contact area of the pellet yields first, and the deformation in the pellet depends on the compression ratio and properties of the pellet. The simulated results show that the temperature in the volume around the line passing through the contacting point and the center of the pellet is higher than the temperature further from the contact area.
Modeling of Pressure-Induced Melt Removal Melting in Vane Extruder for Polymer Processing
The assembled vane extruder with seven groups of vane plasticizing and conveying units (VPCUs) was designed to study the melting phenomenon and mechanisms in vane extruder. There were two melting stages during the melting process, including the solid-rich melting stage and the melt-rich melting stage, and there were no obvious boundaries between the solids and melts. The pressure-induced melt removal melting was the dominant melting mechanism in the solid-rich stage. The theoretical model of the pressure-induced melt removal mechanism was established. The melting percentage was defined to evaluate the boundaries between the solid-rich melting stage and melt-rich melting stage. The melting percentage is proportional to a three-quarters power of the temperature at stator's inner surface, a quarter power of solids’ pressure, as well as inversely proportional to the rotating speed of rotor. By comparing theoretical calculations with experimental measurements of the melting percentage of material low-density polyethylene extruded by the first VPCU, it was indicated that the theoretical model and experimental measurements were consistent with the same tendency.
Characterization of Aqueous Dispersions and Gels Made of Sodium Caseinate and Basil Seed Gum: Phase Behavior, Rheology, and Microstructure
The interactions between sodium caseinate (NaCas) and basil seed gum (BSG) in the presence of calcium chloride (CaCl 2 ) were investigated. The phase behavior of the mixed aqueous dispersions and their gels revealed a homogeneous mixture, obtained at the higher concentrations of both CaCl 2 and BSG. The Herschel-Bulkley model sufficiently fitted the flow behavior of the mixture solution data. Apparent viscosity increased significantly ( p  < 0.05) by increasing the concentration of BSG, where the addition of CaCl 2 had no significant effect on the viscosity of the samples ( p  > 0.05). Furthermore, there was an increase in thixotropy due to the higher concentrations of BSG and CaCl 2 . Based on the frequency sweep test, at the low frequencies, a more gel-like behavior was observed in the case of the higher concentrations of either BSG or CaCl 2 . The rheological and SEM data suggested that the stronger structure of NaCas-BSG gel in the presence of the higher concentrations of CaCl 2 was related to the induction of complex formation between the two biopolymers.