Viscosity ratio influence

Viscosity ratio. influences the relative flow rates directly and indirectly through the... 

In manufacturing and processing polymer blends, it is thus important that the viscosity ratio be within the optimal range in the actual processing conditions. Not only the polymers to be blended but also the temperature and processing conditions (shear, elongation) should be carefully selected. Other factors, such as interfacial tension [46,47] and elasticity of the blended polymers, may also influence the blend morphology. 

The influence of the vi.scosity ratio 8 on the flow behavior in a capillary was discussed by Rumscheidt and Mason [lOj. They pointed out that when the viscosity ratio is small, the dispersed droplets are drawn out to great lengths but do not burst, and when the viscosity ratio is of the order of unity, the extended droplets break up into smaller droplets. At very high viscosity ratios, the droplets undergo only very limited deformations. This mechanism can explain our observations and supports our theoretical analysis assumptions, summarized previously as points 2, 3, and 4. 

As demonstrated, Eq. (7) gives complete information on how the weight fraction influences the blend viscosity by taking into account the critical stress ratio A, the viscosity ratio 8, and a parameter K, which involves the influences of the phenomenological interface slip factor a or ao, the interlayer number m, and the d/Ro ratio. It was also assumed in introducing this function that (1) the TLCP phase is well dispersed, fibrillated, aligned, and just forms one interlayer (2) there is no elastic effect (3) there is no phase inversion of any kind (4) A < 1.0 and (5) a steady-state capillary flow under a constant pressure or a constant wall shear stress. 

Various correlations for mean droplet size generated by plain-jet, prefilming, and miscellaneous air-blast atomizers using air as atomization gas are listed in Tables 4.7, 4.8, 4.9, and 4.10, respectively. In these correlations, ALR is the mass flow rate ratio of air to liquid, ALR = mAlmL, Dp is the prefilmer diameter, Dh is the hydraulic mean diameter of air exit duct, vr is the kinematic viscosity ratio relative to water, a is the radial distance from cup lip, DL is the diameter of cup at lip, Up is the cup peripheral velocity, Ur is the air to liquid velocity ratio defined as U=UAIUp, Lw is the diameter of wetted periphery between air and liquid streams, Aa is the flow area of atomizing air stream, m is a power index, PA is the pressure of air, and B is a composite numerical factor. The important parameters influencing the mean droplet size include relative velocity between atomization air/gas and liquid, mass flow rate ratio of air to liquid, physical properties of liquid (viscosity, density, surface tension) and air (density), and atomizer geometry as described by nozzle diameter, prefilmer diameter, etc. 

In this section, the parameters influencing the mean diameter dR resulting from the Rayleigh instability are examined. Hereafter, the second fragmentation regime is not considered because a narrow size distribution is already obtained after the first one. The parameters that influence dR are the applied stress a, the viscosity ratio p, the rheological behavior, and the way the shear is applied. 

To explore the influence of p, the viscosity of the internal phase was varied over four decades, everything else being constant [149]. As can be seen in the log-log plot of Fig.. 9, dp (identically Cflcr) scales with the viscosity ratio as p - the low value of the exponent indicates that dp is only weakly dependent on p. In Fig. 1.20, the evolution of the polydispersity P as a function of p is plotted. As... 

The introduction of HF reduces the pH value of the final suspension and increases its viscosity this influences further the polymerization mode of silicate species, leading to the formation of regular hexagonal silica framework. The experimental results reveal that, for F7Si molar ratio of 0.20-0.39, the pH value of the suspension changes from 12.5 to 9.5 and the XRD patterns of the synthesized materials display distinct four-peak profiles. 

For bulk materials, a co-continuous blend structure is often desirable as it offers synergetic effects [71, 85], For this purpose, numerous investigations on the blend morphology formation were performed, but the precise prediction of the final structure is still rather complex [86-90], Nevertheless, based on numerous investigations concerning the influence of the processing conditions and the blend composition on the morphology development, two key factors can be deduced [43, 87, 91, 92] - the blend composition and the viscosity ratio. 

As previously shown for PPE/SAN blends, the foaming behavior of immiscible blend systems is affected by both the properties of the blend phases and the overall blend structure [1], In the present blend system, the viscosity of one specific blend phase is varied as a result, not only the foaming behavior of the blend phase is altered but also the microstructure of the blend is affected [94]. By investigating blend systems with constant PPE to PS ratios of 75/25 and 50/50, and varying the SAN content in the range of 20-40 wt%, the influence of both the microstructure and the viscosity ratio can be analyzed (Table 3). 

For further understanding the influence of the viscosity ratio on the foaming behavior, an additional blend system with a PPE/PS ratio of 25/75 and a SAN content of 40 w% was investigated. Due to the high PS content, the PPE/PS matrix phase shows a lower viscosity and a similar glass transition temperature when compared to the dispersed SAN phase. As can be seen in Fig. 29a, the decrease in viscosity of the PPE/PS clearly promotes the formation of elevated SAN phase in comparison to the previously shown blends. 

Everaert V, Aerts L, Groeninckx G (1999) Phase morphology development in immisdble PP/(PS/PPE) blends influence of the melt-viscosity ratio and blend composition. Polymer 40 6627-6644... 

The aim of this first section is to describe the rupturing mechanisms and the mechanical conditions that have to be fulfilled to obtain monodisperse emulsions. A simple strategy consists of submitting monodisperse and dilute emulsions to a controlled shear step and of following the kinetic evolution of the droplet diameter. It will be demonstrated that the observed behavior can be generalized to more concentrated systems. The most relevant parameters that govern the final size will be listed. The final drop size is mainly determined by the amplitude of the applied stress and is only slightly affected by the viscosity ratio p. This last parameter influences the distribution width and appears to be relevant to control the final monodispersity. 

In this example, the two fluids to be mixed have a specific gravity difference of 0.4 and a viscosity ratio of 1200. On the basis of the process capabilities associated with bulk velocities of 0.2 and 0.6 ft/s in Table 12.1, a bulk velocity of 0.4 ft/s (0.12 m/s) should be adequate for this example. Special circumstances, such as a reaction taking place or experience with a similar process, may influence the selection of a bulk velocity. 

Figure 14.2 Influence of viscosity ratio and continuous phase viscosity (/i) on drop breakup [15]. Reprinted with permission from H. J. Karam and J. C. Bellinger, Ind. Eng. Chem. Fundam., 7, 575 (1968). Copyright 1968 American Chemical Society...

Properties of Component Phases The composition and physicochemical properties of both the oil and aqueous phases influence the size of the droplets produced during homogenization (52). Variations in the type of oil or aqueous phase will alter the viscosity ratio, ri ,/ri(-, which determines the minimum size that can be produced under steady-state conditions. The interfacial tension of the oil-water interface depends on the chemical characteristics of the lipid phase, e.g., molecular structure or presence of surface-active impurities, such as free fatty acids, monoacylglycerols, or diacylglycerols. These surface-active hpid components tend to accumulate at the oil-water interface and lower the interfacial tension, thus lowering the amount of energy required to disrupt a droplet. 

Furtheron, the dispersed droplets are the smaller the closer to unity the viscosity ratio of the components is (62-64). Their sizes decrease also if the first normal stress difference of the dispersed phase becomes smaller than that of the matrix (61). The droplet size, moreover, is influenced by the tendency to further break down of elongated particles due to capillary instabilities (61) as well as by coalescence via an interfacial energy driven viscous flow mechanism. All these procedures and dependences affect the structure formation within their typical time scales (61,62). 

The microrheology makes it possible to expect that (i) The drop size is influenced by the following variables viscosity and elasticity ratios, dynamic interfacial tension coefficient, critical capillarity number, composition, flow field type, and flow field intensity (ii) In Newtonian liquid systems subjected to a simple shear field, the drop breaks the easiest when the viscosity ratio falls within the range 0.3 < A- < 1.5, while drops having A- > 3.8 can not be broken in shear (iii) The droplet breakup is easier in elongational flow fields than in shear flow fields the relative efficiency of the elongational field dramatically increases for large values of A, > 1 (iv) Drop deformation and breakup in viscoelastic systems seems to be more difficult than that observed for Newtonian systems (v) When the concentration of the minor phase exceeds a critical value, ( ) >( ) = 0.005, the effect of coalescence must be taken into account (vi) Even when the theoretical predictions of droplet deformation and breakup... 

The theoretical predictions of drop deformation and breakup are limited to infinitely diluted, monodispersed Newtonian systems. However, it is possible to obtain valid relationships between processing parameters and morphology. Thus it was found that in the system PS/HDPE the viscosity ratio, blend composition, screw configuration, temperature, and screw speed significantly influence the blend morphology [Bordereau et al., 1992]. For more detail on the topic see Chapter 9, Compounding Polymer Blends, in this Handbook. 

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. 

Permeate flux increases on decreasing viscosity and therefore a higher permeability is achieved at higher temperatures. A common method to account for this change with temperature is to multiply the obtained flux with the viscosity ratio with respect to a reference temperamre. If temperature effects on flux are only influenced by changes in viscosity, then the product of flux and viscosity should be constant. 

When reaction is instantaneous relative to mixing, the intermediate R does not survive but is fully converted to S. Thus A, = 1. Between these two limits of slow and instantaneous reaction, the reaction is said to be fast and A, takes an intermediate value. In the fast regime physical factors such as viscosity of the solution, feed location, stirrer speed, concentration level at constant stoichiometric ratio influence A,. 

It is very important to be able to control the individual layer distribution across the width of the die. It is normal, as the viscosity ratio, or the thickness ratio, of the polymers being combined increases, for the individual layer distribution(s) of the composite film to become displaced. Viscosity differences influence reduction and saving of materials. 

A second factor that is important for the final morphology - and therefore the product quality - of the blend is the viscosity ratio. The main theories about this influence can be summarized as The major component should have the highest viscosity and the viscosity difference should be as small as possible . To reduce the viscosity ratio, a particular amount of CO2 can be dissolved in a high-viscosity material such that its viscosity is reduced to the viscosity of a low-viscosity material. 

The type of emulsion that will be formed is also influenced by the critical Weber number [36-38,40]. Figure 4.6 shows that for a given viscosity ratio, 172/171, between the dispersed (172) and continuous (171) phases, reducing the interfacial tension increases the Weber number, and lowers the energy needed to cause droplet breakup (see [37,40]). For a given flowing system involving a viscous oil, the viscosity ratio will be smaller, and an emulsion is easier to form, if it is a W/0 emulsion rather than an 0/W emulsion. 

The fibrillation of LCPs in thermoplastic melts is influenced by several parameters, including the thermal characteristics of the component polymers and their compatibility, and processing parameters such as viscosity ratio, melt temperature, flow mode, and shear rate. Among these parameters, thermal characteristics of LCPs are basic factors for the formation of LCP fibrils. They should have the matched processing window with the matrix resin, when the former is in the liquid crystal state. It has been found that the spinnability of LCPs can be taken as a prerequisite for the accomplishment of submicrometer reinforcing with LCP fibrils [18]. 

Willemse et al. (1999) studied the influence of interfacial tension on the composition range within which fully co-continuous polymer blend structures can exist for different blends with selected matrix viscosities and viscosity ratios. The critical composition for full co-continuity was found to increase with increasing interfacial tension, narrowing the composition range. The effect of the interfacial tension on the critical composition was found to be composed of two counteracting effects the stability of the co-continuous morphology and the phase dimensions. The latter effect was smaller than the former. 

Based on microrheology, it is possible to expect that (i) the drop size is influenced by the following variables viscosity and elasticity ratios, dynamic interfacial tension coefficient, critical capillary number, composition, flow field type, and flow field intensity (ii) in Newtonian liquid systems subjected to a simple shear field, the drop breaks most easily when the viscosity ratio falls within the... 

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