Interface Internal mixer

The devolatilization of a component in an internal mixer can be described by a model based on the penetration theory [27,28]. The main characteristic of this model is the separation of the bulk of material into two parts A layer periodically wiped onto the wall of the mixing chamber, and a pool of material rotating in front of the rotor flights, as shown in Figure 29.15. This flow pattern results in a constant exposure time of the interface between the material and the vapor phase in the void space of the internal mixer. Devolatilization occurs according to two different mechanisms Molecular diffusion between the fluid elements in the surface layer of the wall film and the pool, and mass transport between the rubber phase and the vapor phase due to evaporation of the volatile component. As the diffusion rate of a liquid or a gas in a polymeric matrix is rather low, the main contribution to devolatilization is based on the mass transport between the surface layer of the polymeric material and the vapor phase. 

Flow also induces the formation of micro-emulsions, as it can detach the pinch-offs from the interface. As shown by Kim et al. [76] for a bilayer of reactive PS-end-carboxylic and PMMA-ran-epoxy, micro-emulsions could be observed in a shear fiow under a shear rate of 100 s after less than 50 min, while for static conditions they would form after 15 h [57[. In the case of melt blends prepared in internal mixers, micro-emulsions could be detected after less than 5 min of mixing, thus demonstrating again the importance of fiow [68[. 

Keywords particulate filled composites, filler, aggregate, homogenization, mixing, internal mixer, single-screw extruder, twin-screw extruder, mechanical properties, tensile yield stress, tensile strength, stiffness, impact resistance, structure-property relationships, interface, interphase, reactive treatment, nonreactive treatment, surfactant, encapsulation, functionalized PP, coupling, specific surface area, application. 

The mass mi corresponds to the rubber compound before extracting, and it is the sum of the mass of the bonded rubber part Rf the mass of the soluble rubber part and filler, m2 is the mass of the rubber-filler gel, which is the sum of the bonded rubber part and filler, is the mass concentration of filler in the single rubber mixture or binary blends. 1 is the mixing time in an internal mixer. The difference between the terms rubber layer L and bound rubber, which has been commonly used in rubber technology, was discussed in our previous work. To understand the physical background of the rubber layer L, we correlated the wetting behaviour determined from our extraction experiment with the infiltration behaviour reported in the literature." In a capillary flow of a Newtonian fluid in a small gap between two parallel plates, the position x of the liquid-air interface at time t is given by Equation (6.27) ... 

The blending of two polymers has been described by several authors and is discussed in Part 2 of Volume 7. Here we will just describe how it interacts with the previous discussion of the interface. When two polymers are mixed in commercial equipment such as extruders and internal mixers they are subject to complex, nonuniform shear and elongational fields. Furthermore, polymers are viscoelastic. Qualitatively, however, the drop break up process can be understood in terms of a simple model. 

One of the widely used methods to qualitatively assess the matrix effect consists of post-column addition of analytes to the LC-eluent flowing from the column to the ESI interface of the mass spectrometer (Figure 13-11) [35]. Briefly, an analyte and the internal standard (IS) dissolved in the same EC eluent are infused (e.g., flow rate lOpL/min) using a syringe pump, through a tee-mixer, located between the column eluent (e.g., flow rate 200pL/min) and the ESI interface of the mass spectrometer. An extract (using LEE or SPE) or supernatant (if PPT is used) from an analyte-free matrix, such as blank or control plasma, is injected via the autosampler, while the test article and the internal standard are introduced, post-column, to the MS ionization... 

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