Filled polymer examples

Particulate Composites. These composites encompass a wide range of materials. As the word particulate suggests, the reinforcing phase is often spherical or at least has dimensions of similar order ia all directions. Examples are concrete, filled polymers (18), soHd rocket propellants, and metal and ceramic particles ia metal matrices (1). 

This article addresses the synthesis, properties, and appHcations of redox dopable electronically conducting polymers and presents an overview of the field, drawing on specific examples to illustrate general concepts. There have been a number of excellent review articles (1—13). Metal particle-filled polymers, where electrical conductivity is the result of percolation of conducting filler particles in an insulating matrix (14) and ionically conducting polymers, where charge-transport is the result of the motion of ions and is thus a problem of mass transport (15), are not discussed. 

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. 

In practice, the phenomenon of creeping flow at x < Y can usually be neglected. Thus, certainly, it is insignificant in the treatment of filled polymers, though it may be important, for example, in the discussion of the cold flow of filled elastomers. However, we cannot forget the existence of this effect, to say nothing of the particular interest of the physist in this phenomenon, which is probably similar to the mechanism of flow of plastic crystals. 

A comparison of values of yield stress for filled polymers of the same nature but of different molecular weights is of fundamental interest. An example of experimental results very clearly answering the question about the role of molecular weight is given in Fig. 9, where the concentration dependences of yield stress are presented for two filled poly(isobutilene)s with the viscosity differing by more than 103 times. As is seen, a difference between molecular weights and, as a result, a vast difference in the viscosity of a polymer, do not affect the values of yield stress. 

There are known very few investigations of the behavior of filled polymer melts at different stress states, distinct from shear, for example at uniaxial extension. One... 

Note 2 An example of the use of a coupling agent is in a mineral-filled polymer material where one part of the coupling agent molecule can chemically bond to the inorganic mineral while the other part can chemically bond to the polymer. 

The characteristics of particulate filled polymers are determined by the properties of their components, composition, structure and interactions [2]. These four factors are equally important and their effects are interconnected. The specific surface area of the filler, for example, determines the size of the contact surface between the filler and the polymer, thus the amount of the interphase formed. Surface energetics influence structure, and also the effect of composition on properties, as well as the mode of deformation. A relevant discussion of adhesion and interaction in particulate filled polymers cannot be carried out without defining the role of all factors which influence the properties of the composite and the interrelation among them. 

The durability of the particle network structure imder the action of a stress may also be time-dependent. In addition, even at stresses below the apparent yield stress, flow may also take place, although the viscosity is several orders of magnitude higher than the viscosity of the disperse medium. This so-called creeping flow is depicted in Fig. 11 where r (. is the creep viscosity. In practice this phenomenon is insignificant in the treatment of filled polymer melts, but may be relevant, for example, in consideration of cold flow of filled elastomers. 

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]. 

Rotation of the core (or its reciprocating rotary vibration) can be even more efficient in processing of high-viscous melts, for example, filled polymers, high- and superhigh-molecular polyethylene (with MM > 10s). We may assume that this is dependent upon two major causes. The introduction of a filler results in a changed spectrum of relaxation time H(9) 41-42-45). Thus, for example, introduction of 10% of chalk (by volume) into polyolefins shifts the spectrum along the axis of coordinates towards... 

Among conventional electrode materials are Pb and Hg as cathodes (they have a high H overpotential and hence are likely to prefer to give electrons to compounds that will accept them at less cathodic potentials than that needed for H2 solutions). Pb02, Fe203, and SiC are examples of useful anode materials. Since about 1980, several newer electrode materials have found a place. For cathodes, Ni has become important. Cr203, TiC, and carbon-black-filled polymers have been used as anodes. 

Both the Carreau and the Cross models can be modified to include a term due to yield stress. For example, the Carreau model with a yield term given in Equation (2.16) was employed in the study of the rheological behavior of glass-filled polymers (Poslinski et al., 1988) ... 

The plastic structures can again be filled with metal in a second electroforming (electrodeposition) process. Thus, metallic microstructures can be fabricated in an economic, low cost and effective way. The plastic inicrostructures can also serve as so called lost molds for the production of ceramic microstructures. In this case, the mold is filled, for example by means of a slip casting process. During firing of the ceramic, the polymer is completely degraded and evaporates. 

The relationship between steady-shear viscosity and dynamic-shear viscosity is also a common fundamental rheological relationship to be examined. The Cox-Merz empirical rule (Cox, 1958) showed for most materials that the steady-shear-viscosity-shear-rate relationship was numerically identical to the dynamic-viscosity-frequency profile, or r] y ) = r] m). Subsequently, modified Cox-Merz rules have been developed for more complex systems (Gleissle and Hochstein, 2003, Doraiswamy et al., 1991). For example Doriswamy et al. (1991) have shown that a modified Cox-Merz relationship holds for filled polymer systems for which r](y ) = t] (yco), where y is the strain amplitude in dynamic shear. 

The critical indices estimated from these relations fall into the admissible ranges of variation P = 0.39-0.40, V = 0.8-0.9, and t = 1.6-1.8, determined in terms of the percolation model for three-dimensional systems. The researchers [7] noted that not only numerical values but also the meanings of these values coincide. Thus the index P characterises the chain structure of a percolation cluster. The 1/p value, which serves as the index of the first subset of the fractal percolation cluster in the model considered [7], also determines the chain structure of the cluster. The index v is related to the cellular texture of the percolation cluster. The 2/df index of the second subset of the fractal percolation cluster is also associated with the cellular structure. By analogy, the index t defines the large-cellular skeleton of the fractal percolation cluster. The relationship between the critical percolation indices and the fractal dimension of the percolation cluster for three-dimensional systems and examples of determination of these values for filled polymers are considered in more detail in the book cited [7]. Thus, these critical indices are universal and significant for analysis of complex systems, the behaviour of which can be interpreted in terms of the percolation theory. 

Larger disparities in peel strengdi were detected when the line width changed as well. Table IX. Superior adhesion (202-257 g/mm) was measured for all filler contents when the metal trace was 0.5 mm wide. While there was minimal effect of line width for the 20 and 30 % filled polymers, the peel strength for the 50 % filled substrate decreased as the line width increased. This phenomenon is more easily seen in Table X which presents the peel stiei th variation as a function of line width relative to the 3.9 nun trace. Approximately 36 % less adhesion resulted in the most heavily-filled example. 

In any case, experience tends to confirm the qualitative prediction of lower strengths for filled polymers under many circumstances [see Piggott and Leidner (1974) and also the discussion of fracture in Section 12.1.2.4]. For example, Wambach et al. (1968) found that the tensile yield strength of... 

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