Dispersed phase size

In many compounding operations it is necessary to split the feed streams. This may be required in order to 1) achieve disperse phase size of an impact modifier 2) retain aspect ratio of reinforcing fiber filler or 3) obtain high level of loading for either low bulk density filler or incompatible low viscosity additives. 

Although immiscible polymer blends and ionomers share a common feature in that both exhibit more than a single phase, a major difference between the two systems involves the dispersed phase size. For blends, this is generally of the order of micrometers and may be detected optically. Ionomers, however, are microphase-separated with domain sizes of the order of nanometers. Thus, blends and ionomers represent two extremes of the subject of multiphase polymers. In this book, the reader will observe similarities as well as differences in the problems... 

Hagesaether L, Jakobsen HA, Svendsen HF (2002) Modeling of the Dispersed-Phase Size Distribution in Bubble Columns. Ind Eng Chem Res 41(10) 2560-2570. 

Hagesaether L, Jakobsen HA, Svendsen HF (2002) A Model for Turbulent Binary Breakup of Dispersed Fluid Particles. Chem Eng Sci 57(16) 3251-3267 Hagesaether L, Jakobsen HA, Svendsen HF (2002) Modeling of the Dispersed-Phase Size Distribution in Bubble Columns. Ind Eng Chem Res 41(10) 2560-2570... 

Bove [16] proposed a different approach to solve the multi-fluid model equations in the in-house code FLOTRACS. To solve the unsteady multifluid model together with a population balance equation for the dispersed phases size distribution, a time splitting strategy was adopted for the population balance equation. The transport operator (convection) of the equation was solved separately from the source terms in the inner iteration loop. In this way the convection operator which coincides with the continuity equation can be employed constructing the pressure-correction equation. The population balance source terms were solved In a separate step as part of the outer iteration loop. The complete population balance equation solution provides the... 

Dispersed-Phase Size Distribution in Liquid-Liquid and Gas-Liquid Systems..688... 

An interesting application of the direct relationship between nucleating interfaces and the total amount of the interfacial contact surface can be found in compatibilized immiscible blends. In these systems, the dispersed phase size becomes much smaller, strongly increasing the total amount of interface at which nucleation can occur. Some authors reported that this could cause an upward shift in the by up to 10°C [Wei-Berk, 1993]. However, other studies in which the crystallization behavior of a compatibilized blend was investigated did not always mention such a clear nucleating activity (Table 3.17). 

Lee and JGm examined the effect of lamellar structure of the dispersed EVA phase on the gas permeability of LDPE/EVA blends produced by film blowing (Lee and Kim, 1995, 1996). The viscosity ratio and dispersed domains size had a predominant influence on the formation of lamellae. An addition of LDPE-g-MA as a compatibilizer increased the number of particles and reduced the thickness of the layers. Between 5 and 6 wt% of compatibilizer produced a dispersed phase size of around 5 pm and the best oxygen permeability reduction (by a factor of 1600). Above this optimum concentration, the particle size becomes too small, resulting in shorter and thinner, and less effective, lamellae. Dispersed phase stretchability increased when a compatibilizer is present and when the viscosity ratio decreases, but it was not affected by the initial particle size. 

Because of the high interfacial tension, the morphology of the blends is not stable. Coalescence readily occurs in the molten state. As suggested by Macosko et al. (121), in melt mixing of immiscible polymer blends, the disperse phase is first stretched into threads and then breaks into droplets, which can coalesce together into larger droplets. The balance of these processes determines the final dispersed particle sizes. With increase of disperse phase fraction (usually more than 5 wt%), the coalescence speed increases and the dispersed phase sizes increase (121-123). 

The most commonly used compatibilizers for PP/PS blends are also di- or triblock copolymers of styrene and butadiene (SB and SBS) and their hydrogenated products (SEB and SEBS) (160-164). They form dispersed phases in both pure PP and PS. In PP/PS blends, they locate at the interface to connect both PP and PS phase together. Thus, the interfacial tension is decreased and the dispersed phase sizes are greatly decreased. 

Su et al. (8) studied the mechanical properties and morphological structure relationship of blends based on sulfated EPDM ionomer and PP. They synthesized Zn neutralized low degree sulfated EPDM (Zn-SEPDM) ionomer and PP blends and studied their mechanical properties. They found that Zn + neutralized low degree sulfated EPDM ionomer and PP blends have better mechanical properties than those of PP/EPDM blend, as shown in Fig. 14.4. They explained the reason why mechanical properties are higher for Zn-SEPDM and PP than for PP and EPDM using scanning electron microscopy (SEM) (Fig. 14.5). Finer dispersed phase size and the shorter interparticle distances are the main reasons for the improved mechanical properties of the PP/EPDM blend. 

Figure 27.7 Variation of dispersed phase size in an A/B polymer blend as a function of component B concentration.

As described earlier, compatibilizers can enhance compatibility in a polymer blend by promoting physical or chemical interactions with blend components. If the compatibilizer locates at the interface, it will bind the two components together interlacing their phases. The main effect of interfacial modification on the morphology of an immiscible blend is a reduction on the particle size and a narrowing of the particle size distribution. This reduction in particle size is related with a decrease in the interfacial tension and a reduction in the coalescence process. Interfacial modification seems to be the dominant factor for controlling the dispersed phase size, and the dependence of this phase size... 

In principle, the dispersed phase size distribution can be determined from small-angle scattering experiments, using either X-rays or neutrons. Since a comparatively large volume is sampled by the incident beam, scattering... 

The main difference between emulsions and microemulsions lies in the size and shape of the droplets of dispersed phase, which causes the differences in the thermodynamic stability of the two systems. Emulsions allow the drug to be administered as a dispersed oil solution and thus are kinetically stable but thermodynamically unstable. After storage or aging, droplets will coalesce and the two phases separate. Unlike emulsions, microemulsions are thermodynamically stable and phases do not separate on storage. Another important difference between the two systems is their appearance emulsions have a cloudy appearance, while microemulsions are transparent because of the lower dispersed phase size than macroemulsions. 

The thermal degradation stability and moisture absorption characteristics of thermoplastics are not only related to their chemical composition, but also to the effect of the dispersed phase size in polymer blends. The various forms and sizes of... 

In general. Equation 3.32 truly represents the effect of stirring intensity on the dispersed phase size in the liquid-gas system. By order of value, the calculated values djisp are comparable with values calculated using an empirical equation [39] ... 

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