Shear viscosity, blends

Shear viscosities of the twin-screw blended materials were measured at 190°C and 290°C (Fig. 6), the same temperatures as the melt temperatures during processing 190°C for the composites and 290°C for the melt blends. 

The reactive extrusion of polypropylene-natural rubber blends in the presence of a peroxide (1,3-bis(/-butyl per-oxy benzene) and a coagent (trimethylol propane triacrylate) was reported by Yoon et al. [64]. The effect of the concentration of the peroxide and the coagent was evaiuated in terms of thermal, morphological, melt, and mechanical properties. The low shear viscosity of the blends increased with the increase in peroxide content initially, and beyond 0.02 phr the viscosity decreased with peroxide content (Fig. 9). The melt viscosity increased with coagent concentration at a fixed peroxide content. The morphology of the samples indicated a decrease in domain size of the dispersed NR phase with a lower content of the peroxide, while at a higher content the domain size increases. The reduction in domain size... 

As mentioned previously, and as expected, the mixtures containing a TLCP component exhibited shear viscosities lower than those of their original components, whether the TLCP weight fraction was 10% or 30%. The higher the TLCP weight fraction, the lower the blend viscosity. The viscosity curves of the two pure components crossed each other at a shear rate about 25 s , i.e., at this point the viscosity ratio was 1. 

The profile line runs a blend of virgin HIPS resin (2.1 dg/min at 200 °C and 5.0 kg) and between 0 and 20% of recycle material. The recycle material is from the same extruded parts and thus is composed of the same HIPS resin. The shear viscosity of the resin at 170, 190, and 210 °C is shown in Fig. 9.4. 

These essentially comprise a mixture of a skin-forming component, which comprises two distinct phases blended together, a high zero-shear viscosity material and a low zero-shear viscosity material, and a foam core-foaming component, which includes a blowing agent, physically dry blended together. The three materials are preferably selected from suitable homopolymers and copolymers of ethylene. CANADA... 

Similar observations were noted when FKM/o-MMT clay nanocomposites were prepared by melt blending and the as-prepared nanocomposites showed both intercalated as well as exfoliated structure [103]. The apparent shear viscosity of the FKM/o-MMT nanocomposites was lower than that of the pristine polymer at all shear rates and temperatures. The nanocomposites exhibited reduced equilibrium die swell with a smooth extrudate appearance. A comparison of the flow properties of the nanocomposites with the conventional composites revealed that the nanocomposites exhibited improved processability. 

Mendelson (169) studied the effect of LCB on the flow properties of polyethylene melts, using two LDPE samples of closely similar M and Mw plus two blends of these. Both zero-shear viscosity and melt elasticity (elastic storage modulus and recoverable shear strain) decreased with increasing LCB, in this series. Non-Newtonian behaviour was studied and the shear rate at which the viscosity falls to 95% of the zero shear-rate value is given this increases with LCB from 0.3 sec"1 for the least branched to 20 sec"1 for the most branched (the text says that shear sensitivity increases with branching, but the numerical data show that it is this shear rate that increases). This comparison, unlike that made by Guillet, is at constant Mw, not at constant low shear-rate viscosity. 

As previously demonstrated, the shear rheological properties are an important factor relevant for the processing and foaming. In addition, morphological features of the blend system can be detected at low shear rates [95], The shear viscosity and the storage modulus of the present blends are highlighted in Fig. 32. An in-... 

Since the homologous polymer blends are known to be miscible It Is not surprising that mixtures of HDR with HDR or IDK with U>BE are miscible as well (12, 13). However, due to the diversity of polymerization methods and the variety of resulting molecular characteristics LLDra/LLDra systems are not always miscible (10, 14-15). In our laboratory three series of blends were prepared by Identical procedure of mixing the same LLDPE with two other LLDPE resins and with LDPE. The zero-shear viscosity vs. composition dependence, n vs. W2, of these systems Is presented In Fig. 1. Only the LLDPE s prepared with the same Tl-catalyst were found to be miscible (curve 2). Neither blend of LLDPE with LDPE (curve 3) nor LLDPE prepared with a vanadium catalyst LLDPE (curve 1) were miscible. There are Indications In the literature (8) that... 

Figure 1. Compositional dependence of the zero-shear viscosity for blends of a linear low density polyethylene (LLDPE) with (1) and (2) different LLDPE resins, and (3) with low density polyethylene, LDPE.

Fig. 6 shows the curve-fit of n vs. m dependence for Series I and II blends by means of Equation 20. Ihe fitting procedure generated the numerical values of the four parameters of the equation ng, t, mj and m2. It was found that the zero shear viscosity of homopolymers and blends followed the relation ... 

Originally, the commercial PC resins were linear polymers with high shear viscosity and low melt strength, thus difficult to process in operation involving extensional flows, viz. blow molding stretching, foaming. Several years ago branched PC (bPC) became available. The resin is usually blended with linear PC at the ratio that on the... 

It seems that Chappelear [1964] was the first who applied this technique to measure the interfacial tension coefficient of polymer blends. Further refinements have been published [Elemans, 1989 Elemans et al., 1990 Elmendorp, 1986]. The method is simple, not requiring special equipment, but the zero-shear viscosity of the investigated polymers at the processing temperature must be known. Typical results obtained this method are shown in Table 4.3. 

Note that ( )jj = 1 - ( )2j and (l), is the volume fraction of liquid 1 and 2, respectively, at the phase inversion. Equation 7.6 is empirical, proposed by Paul and Barlow [1980] as a generalization of the experimental observations reported by Avgeropoulos et al. [1976]. Equation 7.7 was derived from the filament instability equation by Metelkin and Blekht [1984]. These relations are applicable to systems prepared at low stresses, thus in these equations the viscosity ratio, X, should correspond not to the ratio of the zero-shear viscosities, but to its value at the shear stress used to prepare the blends. The relations were found to describe the phase inversion for systems with nearly equal polymer viscosities, where > 1. 

Figure 7.22. Concentration dependence of shear viscosity of PP/LCP blends dotted line represents the fluidity equation,...

Figure 7.23. Five types of the relation between shear viscosity and concentration for immiscible polymer blends 1. PDB, 2. NDB, 3. additivity, 4. PNDB, and 5. NPDB [Utracki, 1991]...

As mentioned in Part 7.1, for polymer blends the relation between the steady-state shear viscosity and concentration can be quite complex. In the following discussion, the constant stress (not the constant rate) viscosity, corrected for the yield and time effects, will be considered. To illustrate flexibility of Equation 7.125 to describe (and thus to facilitate interpretation of the rheological results) r vs. < > dependence examples of computations are shown in Figures 7.24-7.31. 

Figure 7.26. Concentration dependence of shear viscosity of PS/PMMA blends. Points are experimental [Lyngaae-Jprgensen, 1983], while the lines were computed from Equation 7.125.

Figure 7.27. Concentration dependence of zero shear viscosity of polypropylene blends with two linear low density polyethylenes at 190°C. Points are experimental with error bars indicating the standard deviation [Dumoulin, 1988]. Lines are computed from Eq 7.125.

Figure 7.28. Concentration dependence of T and T, shear viscosities of LLDPE/PC blends at 245°C and at constant stresses G" = 1, 10 and 100 kPa and a,2 = 100 kPa, respectively. Points — experimental error bars of measurements 2% ]Utracki and Sammut, 1990].

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