FILLER DISTRIBUTION

As established in [214], in roller-mixed PVC-based composites one observes a much better uniformity of filler distribution over the matrix volume the relative viscosity is thereby considerably reduced. That is, for a fixed filler content, the viscosity of a system with agglomerates is always higher than that of the well-dispersed sample. 

The important thing is that in all works where the uniformity of filler distribution in the matrix has been studied (cf., e.g. [316, 317]) a better dispersion of the filler has been reported for PFCM than could be achieved in the case of mechanical mixing of ingredients even if carried out in a solvent. 

A thorough study of the distribution of filler in the molded specimen was carried out by Helger and Mennig [352], The authors found that the filler distribution in... 

The maximum values of the percolation threshold are characteristic of matrix systems in which the filler does not form the chain-like structures till large concentrations are obtained. In practice, statistical or structurized systems are apparently preferable because they become conductive at considerably smaller concentrations of the filler. The deviation of the percolation threshold from the values of Cp to either side for a statistical system ( 0.15) can be used to judge the nature of filler distribution. 

The study of filler distribution by the methods of optical and electronic microscopy has shown that in all compositions obtained by method 4 the filler is distributed rather uniformly as in an individual polymer. In the mixtures of incompatible polymers, obtained by methods 1 and 2, the filler is distributed nonuniformly and there are zones of high concentration of the filler and almost empty ones. The size of such zones is close to the size of polymer regions known for mixtures of thermodynamically incompatible polymers — 1 to 10 p. 

The above-described laws of filler distribution in heterogeneous mixtures of polymers are true when the particle size is significantly less than the size of the polymer zones in such mixtures (1 to 10 p). So, powders of graphite and molibdenum (Ss = = 2 m2/g) are distributed equally uniformly in all the studied mixtures of polymers irrespective of the mixing conditions for in this case the particle size is comparable with the size of the polymer zones. 

Thus, the use of heterogeneous blends of polymers is a successful example of creating the ordered structure of the filler distribution conductance occurs when the filler concentration exceeds the threshold cpf in the polymer phase the concentration... 

Effects of processing on the properties of the snap joints (orientation of the molecules and of the filler, distribution of the filler, binding seams, shrinkage, surface, roughness and structure)... 

The filler and latex are in suspension and/or emulsion form leading to better filler distribution compared to dry blending techniques and this in turn leads to better performance properties. 

It is known, that physical and mechanical properties of carbonic composites on the base of this polymer (UPA 6-15,. .., UPA 6-40), where carbon fibrous materials Ural and Viskum are applied as a filler, depend on its weight fraction and uniformity of the filler distribution in the composite. 

We have shown that grafted surface silicon hydride groups can influence the structure of filled polymers and polymerization of unsaturated monomers owing to formation of polymer-filler covalent Si-C bonds.3,4 The presence of both methylsilyl and chemically active silicon hydride groups on silica may provide improved compatibility, to obtain a more uniform filler distribution of the filled composite. 

Figure 3.14. CNT/polymer nanocomposites observed in SEM (a) and (b) P(S-ABu)/MW CNT films surface respectively prepared by evaporation and film formation or freeze-drying and hot-pressing but showing similar fillers distribution (c) and (d) PS matrix containing ungrafted or PS-grafted N-doped CNT a fracture performed at ambient temperature highlights the difference in fillers/matrix interface strength. Scale bars 1 pm.

Because the resistivity is very sensitive to any change in filler distribution, electrical properties of composite filled with conductive particles should be affected by a mechanical deformation. Significant changes in electrical conductivity against degree of elon-gational strain have already been reported in the literature (53-55). 

It is well known that the reinforcing potential of fillers can only be realized if a good dispersion of the filler is achieved. Traditionally, various carbon blacks have been used as fillers, more recently (modified) silica particles are being increasingly utilized. As shown below, the filler distribution can be directly assessed by AFM. 

Intermittent Contact Phase Imaging of Filler Distributions... 

Fig. 3.65 Left TM-AFM images left height, right phase) showing the filler microdispersion in the unvulcanized compounds, (a) unvulcanized EPDM filled with modified silica (Compound 1) (z-scale height, 310 nm, phase, 30°) (b) unvulcanized EPDM filled with carbon black (Compound 2) (z-scale height, 365 nm, phase, 35°). Right (c), (d) filler distributions as determined from the analysis of the phase images (a) and (b) Reproduced with permission from reference [141]. Copyright 1999. American Chemical Society...

We use the standard pulsed force mode-AFM procedures (Sect. 3.2.4) for the investigation of the filler distribution. A contact mode AFM cantilever with a spring... 

In the context of polymers in industrial applications a number of key issues can be identified that are amenable to direct investigation and analysis by AFM approaches. From the preceding chapters the potential of probe microscopic techniques to conveniently visualize for instance surface (or bulk) morphologies and filler distributions has become obvious. Different classes of polymer materials, such as for instance thermoplastics, latexes, porous materials for membranes or thin films are subjected to different types of processing and treatments. The impact of all these modifications and the dependence on the process parameters can hence be closely monitored and in many cases quantitatively characterized by AFM. 

This chapter analyzes how a filler is distributed in materials and what interaction occurs between the filler and the matrix. These two factors make a major contribution to reinforcement of the filled materials. We will outline the principles governing filler distribution and interaction and explain the relevance of reported studies. Chapters 5, 6, and 10 contain discussion of other related phenomena such as particle size of fillers, chemical reactivity in filled systems, and morphology, respectively. Chapter 8 shows impact of organization and filler presence on mechanical properties of filled systems. The information included in the above chapters helps us to understand how to use fillers to improve the performance of a material. 

Idealized distribution of filler particles in a matrix can be predicted by various models as discussed in Chapter 5. Here, an attempt is made to examine empirical data on filler distribution and to determine factors in actual filler which cause that distribution differs from an ideal model used to predict packing density of the filler. 

At least two factors, filler surface availability and potential for interaction, contribute to improved filler distribution... 

We have outlined factors which affect particle distribution in a matrix. This distribution depends partly on filler properties but predominantly on the combination of properties of the pair filler-matrix. Filler distribution in a matrix depends on intended application. Some, such as applications which use fillers for reinforcement, require a homogeneous distribution of particles. In others, such as mentioned above electrical conductive materials, adhesives), a uniform distribution of filler particles may decrease their effectiveness. 

Warpage is a function of stress distribution within the material. Stress distribution depends, in turn, on the distribution of filler particles. If filler distribution is not uniform (see section 7.2) stress distribution will vary in different sections of the part. Typically, warpage close to the edges has a different direction of deflection than in the center of the part. Also, there is a higher negative deflection in the region of the part remote Irom the injection nozzle because these regions are filler deficient. 

Polymer blends and alloys have more complex behavior in the presence of fillers than the binary mixtures of polymer and filler. The same factors, such as filler distribution, filler-matrix interaction, filler-matrix adhesion, particle orientation, nucleation, chemical reactivity, etc. have influence on properties, but this influence is complicated by the fact that there are two or more polymers present which compete for the same filler particles. These complex interactions result in many interesting phenomena discussed below. 

Shaterzadeh et al. (1998) notes the importance of filler distribution as well as interphase in the generalized self-consistent three-phase model used to predict the dynamic moduli of an epoxy/A-glass-bead system. 

Preparation of Magnetic Polymer Gels with Uniform Filler Distribution. . 143... 

Fillers and pigments are added to polyethylene in the extrusion stage to change the color, stiffness, or magnetizability of the polymer. These same fillers— dyes, glass, ceramics, or metals —can function as supports for metallocene—MAO catalysts, improving the uniformity of filler distribution through the polymer. 

Additional reports [82] revealed that the volume concentrations of CB can be precisely determined using HAADF-STEM. In another study, the same authors reported that the filler distribution in polymer nanocomposite systems could be clearly determined [83]. They also observed the nanoscale organization in a photoactive layer of a polymer solar cell that could not be seen with CTEM [79]. 

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