In filled polymers

The fact that the appearance of a wall slip at sufficiently high shear rates is a property inwardly inherent in filled polymers or an external manifestation of these properties may be discussed, but obviously, the role of this effect during the flow of compositions with a disperse filler is great. The wall slip, beginning in the region of high shear rates, was marked many times as the effect that must be taken into account in the analysis of rheological properties of filled polymer melts [24, 25], and the appearance of a slip is initiated in the entry (transitional) zone of the channel [26]. It is quite possible that in reality not a true wall slip takes place, but the formation of a low-viscosity wall layer depleted of a filler. This is most characteristic for the systems with low-viscosity binders. From the point of view of hydrodynamics, an exact mechanism of motion of a material near the wall is immaterial, since in any case it appears as a wall slip. 

Yield stress values can depend strongly on filler concentration, the size and shape of the particles and the nature of the polymer medium. However, in filled polymer melts yield stress is generally considered to be independent of temperature and polymer molecular mass [1]. The method of determining yield stress from flow curves, for example from dynamic characterization undertaken at low frequency, or extrapolation of shear viscosity measurements to zero shear rate, may lead to differences in the magnitude of yield stress determined [35]. 

Knollman, R.H. Martinson J.L. Beilin, Ultrasonic Assessment of Cumulative Internal Damage in Filled Polymers , JApplPhys 50 (1) (1979),... 

In addition, in polymeric compositions, i.e. in filled polymers, as a rule a broadening of the relaxation spectra takes place81. All these characteristics are closely associated with molecular parameters and free-volume, therefore it is interesting to consider how structural changes, induced in the same polymer by the action of the solid surface, may influence the applicability of the free-volume concept and the approach to such systems via the iso-free-volume state. In 82 the applicability of the... 

Damage Assessment in Filled Polymers by Ultrasonics , Paper Presented at the 15th Joint Meeting of the JANNAF Service Life Subcommittee, Monterey, CA (April 1978) 71) W J. 

This mechanism, very often mentioned in metallic alloys and in filled polymers, can also be considered in the case of low-modulus particles (Fig. 13.4). 

Wu G, Asai S, Sumita M, Hattori T, Higuchi R, Washiyama J (2000) Estimation of flocculation structure in filled polymer composites by dynamic rheological measurements. Colloid Polym Sci 278 220-228... 

Typically, titanate-treated inorganic fillers or reinforcements are hydrophobic, organophilic, and organofunctional and, therefore, exhibit enhanced dispersibility and bonding with the polymer matrix. When used in filled polymer systems, titanates claim to improve impact strength, exhibit lower viscosity, and enhance the maintenance of mechanical properties during aging. 

The 4th and 5th sessions of the Conference were held on October 5 at the Emanuel Institute of Biochemical Physics. The 4th session included seven reports. Dr. G.E. Zaikov presented the information about the latest achievements on reduction of inflammability of polymer materials and the use of nanocomposites as antipyrenes (substances that reduce the inflammability of polymer materials) Dr. A.A. Popov reported on the kinetics of destruction of strained polymers (strained molecules reactivity). The structural and dynamic parameters of interfacial layers in filled polymers were the subject of the report by A.L. Kovarskii and... 

Figure 7.10. Schematic model of morphological transformations in filled polymers. A - silica content less than 10 wt% (d>d ), B - silica content 10 wt% (d=d ), C - silica content 20 wt% (d

Malkin (1990) reviews the rheology of filled polymers and highlights the importance of yield stresses, non-Newtonian flow, wall slip and normal stresses in filled polymer flow. Details of the effects of particle shape, concentration and adsorption on these phenomena are discussed. 

J. Schofield. New coupling agents enhance mechanical properties in filled polymers. In Plastics Additives Compounding, March/April 2005. 

Even two-step non-linearities have been found in filled polymer blends. Not only are percolation theoretical approaches unable to predict this phenomenon, they are also unable to explain it once it has been seen. This is because percolation theory does not allow a structural change at the critical volume concentration—but the non-linear density increase leads to the assumption that a structural change, or phase transition, occurs at the critical concentration, in contradiction to all topological theories. 

In filled polymer systems, it has been observed that the effect of filler content on viscosity decreases as shear rate increases [14, 49]. In the case of nanocomposite flllers, this effect has been explained in terms of a detachment/reattachment mechanism [49]. With respect to the dimensions of the flllers, it has been observed that as the surface area of the filler increases so does the viscosity of the filled polymer melt [18, 48]. For particles with similar shapes, an increase in the surface area means a reduction in particle size. In this sense, nanoflllers are expected to significantly increase the viscosity of polymer melts in relation to flllers with sizes in the range of micrometers. An analysis of filler shape and other relevant aspects of polymer flllers can be found in the work by Shenoy [50]. 

From the results described, one can conclude that a significant change of the mechanical properties of a polymeric material on a substrate or with a solid filler surface present can be expected in rather thin layers or in the thin interlayer of the polymeric matrix in filled polymers when the thickness becomes comparable with the thickness of the boundary layer. 

As Table 2.1 shows, the concept of the wetting coefficient has been successfully applied in filled polymer blends containing various fillers, such as carbon black [36], silica [26,27,37], or nano-CaCOs particles [38,39]. Limitations of this criterion include strong discrepancies in interfacial tensions, due to the lack of data in the literature regarding polymer/filler interfaces and issues of extrapolation to the appropriate temperature. Also, this criterion assumes that thermodynamic equilibrium has been reached, which is not always the case experimentally due to the limited processing time. 

S. Westermann, W. Pyckhout-Hintzen, M. Kreitschmann, D. Richter, E. Straube, Microscopic Deformations in Filled Polymer Networks , Proceedings Kautschuk-Heibst-KoUoquium 2002, Hannover (FRG), 99-107, 30 October-1 November 2002. 

Turcsanyi B, Pukanszky B etal (1988) Composition dependence of temsile yield stress in filled polymers. J Mater Sci Lett 7 160-162... 

The application of conpling agents to an inorganic surface provides a powerful way of affecting the bonding properties of the surface. This plays an important part both in filled polymers and (see Fibre composites - introduction). 

Titanate coupling agents impart increased functionality to fillers in plastics. The different ways that these additives work in filled polymers can be explained by breaking down the various mechanisms of the titanate (or zirconate) molecule into six distinct functions. Filler pretreatment and in situ reactive compounding with titanates and zirconates to effect coupling, catalysis, and heteroatom functionality in the polymer melt are also discussed. 

A variety of commercial products specifically aimed at being used in filled polymers are available, notably from Arkema (Lotader and Orevac ), DuPont (Fusabond ), Westlake Chemicals (Epolene ), ExxonMobil (Exxelor ), and Crompton (Polybond ). The terminology used in this discussion is as follows acrylic acid grafted PE or PP=AA-g-PE or AA-g-PP maleic anhydride grafted = MA-g-PE or MA-g-PP. 

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