Viscosity PE blends

In an earlier study (44), dedicated to functionalization of PP/PE blends, there was considered the effects of MAH and DCP concentration on the viscosity of the product (PEZPP)-g-MAH and on the MAH-grafted level. It was found that on increasing DCP concentration from 0.05 to 0.3 wt%, the viscosity of (PEZPP)-g-MAH melt—polymer components ratio being 90 10—varies but negligibly (Fig. 10.2a). 

For PP/PE blends with polymer component ratios of 50 50 and 25 75, both components most likely formed the continuous phase in the blend and, as a result, the apparent viscosity was observed to rise sharply (MFI decreased). These blends have MFIs close to the values for the neat PP and PE. 

P = 5kg (Table 10.5). The only difference is that a greater number of systems differing in composition show higher MFIs (several times exceeding MFI of the PP-g-IA and PE-g-IA), while the viscosity begins to increase sharply only with <25 wt% of PP. It is quite probable that at T = 230°C, a low viscous PP-g-IA melt forms a continuous phase up to its concentration of 25 wt%. It is only after the phase inversion at PP <25 wt% that the viscosity of blended systems depends on the viscosity of PE-g-IA, which forms a continuous phase. The related viscosity of the materials varies in the inverse manner to MFI variations (Table 10.5). 

The analysis of MFI values (Fig. 10.6b) shows that with a PP concentration up to 25 wt%, the blends have a low MFI value (the melt viscosity is high). Low additions of EPR, same as PE additions (Table 10.5), cause an increase in MFI values. Since propylene units belong to the molecular structure of EPR, it appears that at equal concentrations of PE and EPR in blends with PP, the concentration of hydrogen atoms, bonded to tertiary carbon atoms, is higher in the second case. That is why, specificities of I A-grafting reaction, related to the concentration and the reactivity of macroradicals, are more pronounced in PP/EPR than in PP/PE blends. 

It was found for PP/PE blends functionalized by lA grafting, as initiated by L-101 peroxide, that low (up to 25 wt%) quantities of PE (which undergoes cross-linking during functionalization) caused a decrease in the melt viscosity of... 

Reactive compounding of PA6 with HOPE compatibilized with a mixture of HDPE/copolymer of octene and ethylene with grafted MAH (Fig. 18.4) gives an increased viscosity of the melts especially at low shear rates (66). An increased concentration of the compatibilizer in a blend between 15 and 30 wt% causes the viscosity to rise. Unlike pure PA6, PA6/g-PE blends show 10-fold or higher increase in viscosity at low shear rates. 

Figure 18.4 Effect of shear rate on melt viscosity at 275° C of PA6, PE, and PA6/PE blend compatibi-lized by PE-g-MAH containing 0.27 wt% of grafted MAH. Ciphers on curves stand for compatibilizer concentration in wt%, PE stands for LDPE/LHDPE (88 12) blend LHDPE is copolymer of ethylene and octene. Reproduced from Reference (66) with permission from John Wiley Sons. Inc.

Morphology of three polypropylene (PP)/polyethylene (PE) blends with different viscosity ratios. The viscosity ratio is 3.9 for PP/PE-1 (a), 1 for PP/PE-2 (b), and 0.5 for PP/PE-3 (c). The surface of the blend was etched with xylene to improve morphology observation. (Reproduced from Hong, J. S., K. H. Ahn, and S. J. Lee. 2005a. Strain hardening behavior of polymer blends with fibril morphology. Rheologica Acta 45 202-208, with permission.)... 

Blends of a PO (PE, PP, PB, P4MP, their blends, and copolymers, e.g., with 1-aIkenes, vinyl esters, vinyl chloride, methacrylic esters, and methacrylic acid) with 0.2-50 wt% of a graft copolymer showed high tensile modulus and high sag resistance without increased melt viscosity. The blends could be shaped into foamed profiles at T = 200-230 °C. 

The double reptation model was used to evaluate viscoelastic behavior of metallocene-catalyzed polyethylene and low-density polyethylene blends by Peon et al. (2003). They compared their results with those obtained for HDPE/BPE blends prepared under similar conditions. Since this model assumes miscibility between the mixed species, the experimental viscosity of HDPE/BPE blends showed only small deviation compared to that expected according to the reputation miscible model. However, the model underestimated the compositional dependence of the zero-shear viscosity for mPE/LDPE blends, especially at intermediate levels. The enhanced zero-shear viscosity in immiscible blends such as PETG/EVA, PP/EVA, or EVA/PE blends was found to be more abrupt than it is for mPE/LDPE blends (Lacroix et al. 1996, 1997 Peon et al. 2003). 

Figure 12.18. The apparent viscosity (at shear rate of 12.5 s ) vs. PC and PET concentration. The test temperature is 170°C for both PC/PE and PET/PE blends...

The ratio of polymer viscosity values, imder which a substantial drop in local interfacial CB concentration is observed, differs for various polymer pairs. The greater is the difference in wetting forces of polymers, the more times the viscosity of the second (having higher wetting force) polymer, can exceed the viscosity of the preliminarily filled polymer. So, this ratio is about four for the PE + PMMA blend, and about two for the PS+PE blend. The best conditions for particles to localize at the interface are provided when viscosity of the second polymer is slightly lower than that of a preliminarily filled polymer component. 

A number of other models and theories have been proposed for evaluating viscosity data. Two models that are referred to as emulsion models predict the complex modulus or viscosity of an immiscible blend with spherical inclusions of one phase in a continuous phase (Oldroyd [263] and Paherne [264] models). The emulsion models can predict a positive deviation as noted in Fig. 6.21. Application of the Palierne model showed good agreement for viscosity data for EVAc/PE blends [265,266]. Another emulsion model proposed by Choi and Schowalter [267] is based on a cell model composed of a viscous matrix with viscous dispersed spheres (droplets). The viscosity of these models in the limit of zero shear viscosity can be expressed by the following equations. 

Poly(phthalazinoneethersulfoneketone) (PPESK) is a recent high performance, high temperature resistance polymer, but with high viscosity. However, blends with PEI or PES were found to improve processability and allowed reinforcement with carbon fiber. The blends showed excellent mechanical properties. PPESK was also found to be an excellent basic material for the production of a diversity of membranes with applications ranging from water purification to fuel cell. " ... 

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