Viscosity polypropylene blends

Figure 13.30 Blends of low viscosity polymers (— propylene (-----), 70/30 nylon-polypropylene blend.

Han and Kim (14) have observed a similar phenomenon in a completely different system consisting of polypropylene blended with polystyrene. The conclusion of that work was that the polystyrene and polypropylene have no interaction at the interface and do not form an interphase. Han and coworkers (14) have studied other systems which display minima in the viscosity versus composition graphs and have concluded that there is little chemical interaction between the two phases. 

Figure 7.13. The experimental (points) and computed from Equation 7.80 relation between viscosity and composition for polypropylene blends with styrene-ethylene-butene-styrene block copolymer [Steller and Z uchowska, 1990].

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.

Li, S. Jarvela, P.K. Jarvela, P.A. (1997). A Comparison Between Apparent Viscosity and Dynamic Complex Viscosity for Polypropylene/Maleated Polypropylene Blends. Polymer Engineering and Science, Vol.37, No.l, pp. 18-23 ISSN 0032-3888... 

Danes and Porter [90], studying (polypropylene/ethylene propylene rubber) blends, found that finer dispersions were obtained when the minor phase had an equal or lower viscosity than the major phase. If the minor phase had a higher viscosity, coarser blends were obtained. 

Melt flow index and melt viscosity of NR and polypropylene blend in the ratio of 90 10 that was extruded in the presence of a peroxide [If-bisf-butylperoxy)benzene] and coagent (trimethylolpropanetriacrylate, TMPTA) were investigated by Yoon et al. The variation of melt viscosity that was characterized based on the crosslinking and chain scission of PP was studied. It was remarkable that at a constant content of the coagent, melt viscosity increased at a low and decreased at a high content of the peroxide, while, melt viscosity increased monotonically with the coagent concentration at constant peroxide content. 

The experimental part of this chapter consists of two separate but closely related parts. Our overall aim was to carefully study the effects of viscosity ratio (Part I) and blending conditions (Part II) on the morphology of LCP/PP (polypropylene) blends. The viscosity ratio was varied between 0.1 and 3.6 by using five different grades of polypropylene and two LCPs (see Ref. 44). 

In preliminary tests, melt mixed blends of PP and LCP were processed at six different temperatures (Tcyi 230, 240, 250, 260, 270, and 280°C) with a Brabender Plasti-Corder PLE 651 laboratory single-screw extruder. The measured melt temperatures were about 10°C higher than the cylinder temperatures (Tcyi). The objective was to study the influence of temperature on the size and shape of the dispersed LCP phase. Two different polypropylenes were used to ascertain the effect of the viscosity of the matrix on the final morphology. Different draw ratios were obtained by varying the speed of the take-up machine. 

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... 

By modifying the functional groups they can be used,for example, as crosslinkers in high solid or powder coatings and in thermosets. Because of their good miscibility and low melt viscosity, they find applications as melt modifiers and as blend components. Modified hyperbranched polymers, like alkyl chain substituted poiy(ether)s and po-ly(ester)s sometimes exhibit amphiphilic behavior.They can, therefore, be used as carriers for smaller molecules,for example, dyestuff into polypropylene. 

If the melt viscosities of polypropylene and poly(ethylene terephthalate) polymers are reasonably matched under extrusion conditions, a finely dispersed blend may be produced in fiber form. Orientation of such fibers yields strong filaments in which microfibrils of the two partially crystallized polymers are intertwined and unable to separate. Similar fibers with a sheath of one polymer surrounding a core of the other have no mechanical integrity [27]. 

Figure 9.12 Droplet radius versus wt% dispersed polystyrene (PS) in a blend with polypropylene (PP) at an average shear rate of 10 sec in a single twin screw extruder at T = 200°C. The viscosities of pure PS and PP at these conditions are about 5 x 10 and 2 X 10 Pa-s, respectively both melts are modestly shear thinning (power-law slopes —1/3). The interfacial tension T was measured to be 4.9 dyn/cm. The predicted Taylor limit, a = 0.5 T/rfsy, is shown. (From Elmendorp and van der Vegt 1986, reprinted with permission from the Society of Plastics Engineers.)...

A carbon black addition above a percolation threshold of 5 vol% increases the conductivity until a plateau is reached at 20 vol%. " As the level increases above 10 vol%, the viscosity of the filled polypropylene increases rapidly (see Figure 9.9). As with polyethylene, carbon black is preferentially contained in one phase of a two phase blend."" This phenomenon is used in practice to lower the concentration of carbon black required for a certain level of conductivity. Here, again, carbon black is concentrated in the preferred location. Carbon black and copper powder were used to improve connectivity of YBaCuO in ceramic superconductors. "" Dispersion of copper particles and the related changes in conductivity were enhanced by the presence of acrylic acid modifier. ... 

Eor the typical commercial polypropylene copolymer systems the viscosity of the matrix phase is quite high, and the molecular diffusion and solubility of the minor phase component in the matrix phase are relatively high. These factors tend to favor the evaporation/condensation, that is, Ostwald ripening, mechanism and suppress the coalescence mechanism in these systems. Mirabella and coworkers studied a series of multiphase systems, including a hiPP (30), a high density polyethylene (HOPE)/ hydrogenated polybutadiene (HPB) blend, (31) and an unbranched PE molecular... 

Results given in Table VII show that the viscosity versus shear rate variation of these three Santoprene grades fits the power law over the entire range from 10 to 5200 s . Both the viscosity and the extrudate swell at constant shear rate increase with decreasing rubber particle content (or increasing hardness). Thus, these olefinic thermoplastic vulcanizates essentially behave like highly filled fluids in flow. When compared with unvulcanised rubber (see previous sections) or polypropylene - EPDM blends (32), the extrudate swell appears low and there is no Newtonian viscosity plateau. 

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.)... 

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