Filled polymers observations

It should be noted that this is quite an unusual law, since in other known cases durability of solids is expressed by stronger laws, namely, exponential or power laws. Thus, in the given example we cannot give a unified definition of yield stress. The work cited is the only published observation of the durability of a filler s structure in dispersion systems. Therefore at present it is difficult to say how much such phenomena are typical for filled polymers, but we cannot exclude them. 

The peculiarities of dynamic properties of filled polymers were described above in connection with the discussion of the method of determining a yield stress according to frequency dependence of elastic modulus (Fig. 5). Measurements of dynamic properties of highly filled polymer melts hardly have a great independent importance at present, first of all due to a strong amplitude dependence of the modulus, which was observed by everybody who carried out such measurements [3, 5]. 

The results of the above section show that the significant nonuniformity of the distribution of the filler particles in the thickness of sample is observed during injection moulding of the filled polymers. This nonuniformity must affect the electrical properties of CCM owing to the strong dependence of the CCM conductivity on the filler concentration. Although there are no direct comparisons of the concentration profiles and conductivity in the publications, there is data on the distribution of conductivity over the cross-section of the moulded samples. 

An overview of the origins of yield stress and parameters which can lead to variations in behaviour with highly filled polymer dispersions is given by Malkin [1]. Much of the following literature, describing experimental work undertaken, demonstrates that yield phenomena can be correlated with the extent of interaction between the filler particles and the formation of a network structure. However, the actual behaviour observed during experimentation may also depend on the deformation history of the material, or the time and temperature of imposed deformation, especially if the material exhibits thixotropic properties. 

The effect of aging and of process variables on the rheological properties of solid proplnts has been the subject of mechanical shear relaxation spectroscopy (Ref 4). The technique is of interest to such filled polymer systems generally in that anisotropy in the viscoelastic properties can be readily observed... 

A three-dimensional network formed in the presence of the dispersed filler and therefore the process proceeded in the thin surface layer on the surface of the previously hardened resin (filler). The use of such a system enables the physical structure of the polymer to be changed without changing its chemical nature. At the same time, all the effects usually observed for filled polymers may be expected to be present. 

The dependence of the debonding stress on adhesion and particle size can be used to explain the observed yield and fracture stress in mineral particle filled polymer [29]. In the case of not treated precipitated CaC03 or Si02, the debonding stress ctd is higher than the local fracture... 

Shapes of vesicular aggregates range from tubular to spherical, from more exotic large compound (LCV) and starfish vesicles to simpler extended lamellae. Both unilamellar [75] and multilamellar ( onions ) [47,76] vesicles have been observed. One of the possible morphologies formed in solution are tubular vesicles, also known as tubes (rods) [77,78], Soft, water-filled polymer tubes of nanometer-range diameters and several tens of millimeters in length have been prepared via self-assembly of amphiphilic ABA triblock copolymer in aqueous media (Fig. 4). The tubes were mechanically and chemically stable and could be loaded with water-soluble substances [23],... 

The response of unvulcanized black-filled polymers (in the rubbery zone) to oscillating shear strains (151) is characterized by a strong dependence of the dynamic storage modulus, G, on the strain amplitude or the strain work (product of stress and strain amplitudes). The same behavior is observed in cross-linked rubbers and will be discussed in more detail in connection with the dynamic response of filled networks. It is clearly established that the manyfold drop of G, which occurs between double strain amplitudes of ca. 0.001 and 0.5, is due to the breakdown of secondary (Van der Waals) filler aggregation. In fact, as Payne (102) has shown, in the limit of low strain amplitudes a storage modulus of the order of 10 dynes/cm2 is obtained with concentrated (30 parts by volume and higher) carbon black dispersions made up from low molecular liquids or polymers alike. Carbon black pastes from low molecular liquids also show a very similar functional relationship between G and the strain amplitude. At lower black concentrations the contribution due to secondary aggregation becomes much smaller and, in polymers, it is always sensitive to the state of filler dispersion. 

An interesting observation with some non-newtonian mixtures is that at high shear they appear to violate the zero-velocity boundary condition at the wall. For multiphase fluids such as suspensions and fiber-filled polymers, this effect is believed to be the result of a thin layer near the wall that is depleted of particulates... 

The scaling described in Equation 2 indicates that the modulus is a strong function of the hybrid loading and is consistent with the data obtained for other filled polymer systems as well as the scaling observed for block copolymers with spherical microdomains. ... 

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]. 

In highly filled polymers, solid-like 5delding can be observed even at temperatures above the quiescent melting temperature (T ) or glass transition temperature (T ) of the polymer [9-13]. 

Tsagaropoulos, G., and Eisenburg, A., Direct observation of two glass transitions in silica-filled polymers Implications to the morphology of random ionomers. Macromolecules, 28, 6067-6077 (1995). 

Samples of unfilled polyetherimide plaques or films were pretreated and metallized with copper. Peel strengths of -170 g/mm were achieved. Both sets of samples failed cohesively within the polymer layer. This failure mode has been discussed previously for filled-polymer resinsS S.H. Fracture patterns on the polymer side of the peel were found to be similar for both materials when viewed at high magnification (20,000 X), Figure 5. The ductile failure model 8 observed for the polyetherimide film was not apparent at low magnifications (300X). 

Study of the process of swelling of the polymeric coatings and filled polymers found that the crosslinked concentration when the network forms with surface present is significantly less than in bulk. In addition, instances were observed of nonmonotonic dependence of the molecular weight of the polymer between crosslinks in the network on the filler concentration, which indicates that the surface can order the arrangement and growth of chains [23]. The nature of the polymer and the type of simface determine the course of the process. 

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