Filled melt rheology

Various investigations have considered the effects of titanate treatments on melt rheology of filled thermoplastics [17,41]. Figure 10, for example, shows that with polypropylene filled with 50% by weight of calcium carbonate, the inclusion of isopropyl triisostearoyl titanate dispersion aid decreases melt viscosity but increases first normal stress difference. This suggests that the shear flow of the polymer is promoted by the presence of titanate treatment, and is consistent with the view that these additives provide ineffective coupling between filler particles and polymer matrix [42]. 

Rubber-based nanocomposites were also prepared from different nanofillers (other than nanoclays) like nanosilica etc. Bandyopadhyay et al. investigated the melt rheological behavior of ACM/silica and ENR/silica hybrid nanocomposites in a capillary rheometer [104]. TEOS was used as the precursor for silica. Both the rubbers were filled with 10, 30 and 50 wt% of tetraethoxysilane (TEOS). The shear viscosity showed marginal increment, even at higher nanosilica loading, for the rubber/silica nanocomposites. All the compositions displayed pseudoplastic behavior and obeyed the power law model within the experimental conditions. The... 

Finally, at higher particulate loadings, above 50% vol, the rheological behavior of filled melts is dominated by particle-to-particle interactions, due to both interparticle forces and physical flow-caused movement hindrances of the suspended particulates, particularly during pressure flows. One consequence of this is the creation of a particulate-free wall film that creates a lubricity slip layer and pluglike flows. Such slip velocities have to be considered in flow rate versus pressure drop design expressions, as well as the viscometric rheological characterization (91). 

The rheological properties of filled melts are governed by the diverse properties of polymeric melts, discussed in Chapter 3, compounded by the equally diverse and complex properties of suspensions, discussed in this chapter. In addition, the adhesive characteristics of the junction between polymer and particle can affect the rheology of the filled melt. Thus, the range of possible rheological phenomena in filled melts is immense. Because of limited space, only a few aspects can be touched on here the interested reader is directed to a review article by Khan and Prud homme (1987), and references therein. 

There is much more to tell about the rheology of filled melts, but space limitations preclude further discussion here. The interested reader is directed to the articles by Khan and Prud homme (1987), Metzner (1985), amd White (1982), the book by Han (1981), and references therein. Viscoelastic theories for filled melts, especially for rubbers containing carbon black, can be found in Montes and White (1993), Witten et al. (1993), and references therein. 

Filled polymer melts show diverse behavior that can include rheology typical of unfilled melts, rheology typical of dense suspensions, and novel thixotropic behavior and sensitivity to particle surface treatment. 

Seymour et al. (1982) highlighted the rheology of linear and gelled random styrene acrylate resins filled with carbon black for toner usage. The melt rheology was strongly affected by the initial structure in the resin and by the dispersion of the carbon black. 

Doraiswamy et al. (1991) developed a non-linear rheological model combining elastic, viscous and yielding phenomena for filled polymers. The model predicts a modified Cox Merz relationship for filled melts ... 

J. L. White, Rheological behavior of molten polymer blends and particle-filled melts, in Polymer Compatibility and Incompatibility, Principles and Practices, K. Sole (ed.), Harwood Academic Publishers, Chur, 1980. 

Muksing, N., Nithitanakul, M., Grady, B. P., Magaraphan, R. (2008). Melt rheology and extrudate swell of organobentonite-filled polypropylene nanocomposites. Polym. Test, 17, 470-479... 

Injection pressure is a fimction of flow length, wall thickness, and melt rheology, and it is calculated to achieve uniform mold filling. The Arnitel injection pressure range is <5000 to >20,000 Ib/in (<34 to >137 MPa). Thermoplastic elastomers may not require back pressure, and when back pressure is applied, it is much lower than for thermoplastics that are not elastomeric. Back pressure for Amitel is about 44 to 87 Ib/in (0.3 to 0.6 MPa). Back pressure is used to ensure a homogeneous melt with no bubbles. 

We prescribe the change in the miscibility of components in the filled melt to both the favorable change in composition in the surface and unperturbed zone and to the change in conditions of interactions between various segments due to the conformation rearrangements. It is evident that the rheological... 

The model representation of the filled polymer mixture shows a very important feature of filled polymer mixtures The properties of a binary matrix between two filler particles are not the same as for the initial unfilled mixture. In analyzing rheological properties of the filled binary melt, one should keep in mind that relative changes of the viscosity in the filler presence should be considered in relation to the matrix properties changed under the influence of the filler. Such an approach was developed for filled melts by Droste and Dibenedetto [15]. 

Saini, D.R., Shenoy, A.V. and Nadkami, V.M. (1986) Melt rheology of highly loaded ferrite-filled polymer composites, Polym. Composites, 7, 193-200. 

It was also shown that rheological properties of filled melts may be changed when some modification of the filler surface takes place. This effect is... 

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