Filler phase

In either case the resulting material Is a composite, with the polymer as the continuous phase or matrix, binding together the pieces of the discontinuous filler phase. The presence of filler can have a profound effect on the properties of the polymer composite, as Illustrated In Table 7.1. From this Table, It can be seen that the nature of the filler Is Important, with different effects being obtained with different fillers. 

For applications where only mechanical properties are relevant, it is often sufficient to use resins for the filling and we end up with carbon-reinforced polymer structures. Such materials [23] can be soft, like the family of poly-butadiene materials leading to rubber or tires. The transport properties of the carbon fibers lead to some limited improvement of the transport properties of the polymer. If carbon nanotubes with their extensive propensity of percolation are used [24], then a compromise between mechanical reinforcement and improvement of electrical and thermal stability is possible provided one solves the severe challenge of homogeneous mixing of binder and filler phases. For the macroscopic carbon fibers this is less of a problem, in particular when advanced techniques of vacuum infiltration of the fluid resin precursor and suitable chemical functionalization of the carbon fiber are applied. 

Fig. 9.1 Top view on two variants of C3 materials. The carbon fibers (a) themselves exhibit a complex inner microstructure that needs carful optimization for strength and stability. The isotropic filler phase (b) should be free of pores and other weak points caused by uneven distribution in the composite body. The ordered graphitic BSU (c) can provide a very strong but still flexible anchoring of the fibers in the isotropic matrix.

Mixed matrix membranes have been prepared from ABS and activated carbons. The membranes are intended for gas separation. A random agglomeration of the carbon particles was observed. A close interfacial contact between the polymeric and filler phases was observed. This morphology between inorganic and organic phases is believed to arise from the partial compatibility of the styrene/butadi-ene chains of the ABS copolymer and the activated carbon structure. A good permeability and selectivity for mixtures of carbon dioxide and methane has been reported (91,92). 

In these Equations, G is the modulus of the syntactic foam, G0 is the modulus of the polymer matrix, v0 is Poisson s ratio of the polymer matrix, and 9 is the maximum packing fraction of the filler phase. For uniform spheres, 9 0.64 (see Sect. 3.6). The volume fraction of spheres in the syntactic foam is 9sph. The slope of the G/G0 vs. 9sph curve depends strongly upon whether or not G/G0 is greater or less than 1.0. The slope is negative if the apparent modulus of the hollow spheres is less than the modulus of the polymer matrix. 

C) correspond to composites prepared by direct mixing, whereas composites shown in (B) and (D) were prepared following a pre-processing based on mechanical treatments in ethanol (see explanation in the text). The inset in (A) is a magnification to show the shape of the filler phase. The dashed circle in (C) shows a small region of agglomerated CNT. From ref 10. 

Here we outline an approach that has been taken to develop Poly(dimethylsiloxane) (PDMS) systems, which have property changes that are easier to predict. The problems associated with the inclusion of a filler phase that is required for PDMS systems to have many useful physical properties have been addressed by producing nano filled equivalents. It is shown that such systems offer easier control over the materials produced whilst also resulting in a simplification of physical properties. The production of foamed systems, which introduces an additional variable, is also discussed. The influence of foam structure upon the measured properties of a material is outlined and implications for sample production and the development of predictive ageing models are explored. 

The mechanical properties of the nanocomposites strongly depend on their structure, orientation of the filler, phase separation, and processing conditions. Hence, there is a need for in situ nondestructive characterization technique to probe the internal stress in nanocomposite structures. The shortcomings of many conventional techniques such as low resolution, destructive measurements, complex modeling and applicability to only certain class of materials are overcome by using pRS owing to the sensitivity and nondestructive measurement for monitoring internal stress in various materials [59]. 

Composites, where a matrix material is "filled" with fibers, platelets or particulates [3], as illustrated schematically in Figure 19.1. The strength of the adhesion between the phases is a major factor in determining the mechanical properties of composites, since it determines the effectiveness of the interface in transferring an applied load from the matrix to the filler phase. 

The properties of a two-phase system consisting of a continuous "matrix" phase and a discontinuous "filler" phase are calculated in tenns of the component properties and volume fractions. It is assumed that the thennoelastic properties within each phase domain are homogeneous and isotropic, and that there is perfect adhesion between adjacent phase domains. The shapes of the filler particles are assumed to have biaxial symmetry. If a filler particle is anisotropic (as in fibers or platelets), it is oriented uniaxially at this stage of the calculation. Particle shape is described by the aspect ratio Af (defined as the ratio of the largest dimension of the filler divided by its smallest dimension), and if Af l then also by... 

Closed-form expressions from composite theory are also useful in correlating and predicting the transport properties (dielectric constant, electrical conductivity, magnetic susceptibility, thermal conductivity, gas diffusivity and gas permeability) of multiphase materials. The models lor these properties often utilize mathematical treatments [54,55] which are similar to those used for the thermoelastic properties, once the appropriate mathematical analogies [56,57] are made. Such analogies and the resulting composite models have been pursued quite extensively for both particulate-reinforced and fiber-reinforced composites where the filler phase consists of discrete entities dispersed within a continuous polymeric matrix. 

The analytical expressions of micromechanics are generally most accurate at low volume fractions of the filler phase. The details of the morphology become increasingly more important at higher volume fractions. This fact was illustrated by Bush [64] with boundary element simulations of the elastic properties of particulate-reinforced and whisker-reinforced composites. The volume fraction at which such details become more important decreases with increasing filler anisotropy, as was shown by Fredrickson and Bicerano [60] in the context of analytical models for the permeability of nanocomposites. 

The discussion above has been limited to amorphous polymers. However, if the polymer is semicrystalline, the dotted line in Figure 1.19 is followed. Since the crystalline regions in the polymer matrix tend to behave as a filler phase and also as a type of physical cross-link between the chains, the height of the plateau (i.e., the modulus) will be governed by the degree of crystallinity]... 

In addition, they contain extra components. Part of the filler phase is made up of particles of fluoroaluminosilicate glass of the type used in glass-ionomer cements. There is also a small quantity of a proprietary acid-functional monomer, the so-called acid resin [ 1 ]. This is not sufficient to allow the monomer to be soluble in water, but it does confer a small degree of hydrophilic character on the set matrix. This causes water from the surroundings to be drawn into the structure, and results in ionization of the acid-functional groups and reaction with the ionomer glass component [38]. Any such reaction is limited, but potentially useful in allowing the set material to release fluoride. 

As an example, we can consider the elastic modulus of a composite that consists of a polymer matrix and a filler phase only. Taking the volume fraction of filler as Vp and the individual elastic moduli as and for polymer and filler respectively, the overall predicted modulus of the composite is given by [5] ... 

As well as conventional composites of the type based on bisGMA and/or UDMA and filled with silicate-based filler, there are now materials available that are essentially composites in that they comprise a polymeric matrix reinforced with finely divided filler. However, either the polymer system or the filler phase is of a different chemical composition from that of conventional composite resins. Three such materials are currently available, and these are the ormocers, the siloranes and the giomers. Their details are given in Table 3.3, and their characteristics are described in the following subsections. 

To formulate a successful composite material, and in particnlar to ensnre that there is adequate stress transfer from matrix to filler phase, a conpling agent is deployed at the matrix-filler interface. The type of silane nsed for conventional dental composite resins effectively forms a mono-molecnlar hydrophobic layer on the snrface of the inorganic filler particles. In silanating the reactive ionomer glass in this way, the chemical reactivity of the glass is affected. It is no longer quite so hydrophilic, and hence is less susceptible to acid attack in the presence of moisture. 

Polypropylene (PP500P, SABIC) has melt flow rate of 3.1 (2.16 kg at 230 °C) and density of 905 kg/m3 was used as matrix resin. Nano-sized synthetic ultrafine surface treated precipitated calcium carbonate (Socal 312, Solvay, France) with mean particle diameter of 70 nm used as filler phase. PP-g-MAH compatibiliser (Priex 20097, Solvay, France) with a maleic anhydride content of 0.05 wt % and MFI of 15 (2.16 kg at 230 °C) was employed to promote the interfacial interaction between nano-CaC03 and PP, and to extend the dispersion of nanoparticles in polymer matrix. Compounds used as processing materials are listed in the table 1. 

Figure 1.50 Schematic representation of formation of CP-based NCs via ISP of monomer (CP precursor) grafted over filler phase.

Fig. 5. Sample plot showing the MOR values for some of the batches extmded into rods, and fired at three different temperatures, 300, 600 1000°C, for 3hrs. MOR values increase with firing temperature, which may be due to the onset of sintering. This hypothesis is corroborated by the reduction in specific surface area observed. For comparison, MOR value for fired Cordierite rods, of comparable porosity, is shown by the dashed line. The five batches shown here differ in compositional details like the particle size distribution (PSD) of the filler phase used and the amount of the fiber phase, colloidal sihca phase used.

Hybrid membrane or MMM using MOFs as the filler material is another option for the application of MOFs in membrane separation. Adams et al. [118] reported an MMM comprised of poly (vinyl acetate) (PVAc) and a MOF composed of copper and bdc ligand (Cu-bdc), which exhibited an increased selectivity for many gases, including CO2 upon inclusion of the MOF compared with the pure PVAc membrane. Ordonez et al. reported the ZIF-based polymer MMM using ZIF-8 as the filler phase and Matrimid as the polymer phase, respectively as shown in... 

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