Reinforcing filler Phase

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. 

Abstract Plasma polymerization is a technique for modifying the surface characteristics of fillers and curatives for rubber from essentially polar to nonpolar. Acetylene, thiophene, and pyrrole are employed to modify silica and carbon black reinforcing fillers. Silica is easy to modify because its surface contains siloxane and silanol species. On carbon black, only a limited amount of plasma deposition takes place, due to its nonreactive nature. Oxidized gas blacks, with larger oxygen functionality, and particularly carbon black left over from fullerene production, show substantial plasma deposition. Also, carbon/silica dual-phase fillers react well because the silica content is reactive. Elemental sulfur, the well-known vulcanization agent for rubbers, can also be modified reasonably well. 

Additionally for rubber compounds, the differences in polarity and unsaturation of the various polymers cause different affinities for fillers and curing additives. In blends of different rubber polymers, the reinforcing filler carbon black for instance locates itself preferentially in the phase with the higher unsaturation and/or polarity, leaving the lower unsaturation or nonpolar phase unreinforced. The affinity for carbon black decreases in the following order of polymers [2] ... 

Research on the pyrolysis of thermoset plastics is less common than thermoplastic pyrolysis research. Thermosets are most often used in composite materials which contain many different components, mainly fibre reinforcement, fillers and the thermoset or polymer, which is the matrix or continuous phase. There has been interest in the application of the technology of pyrolysis to recycle composite plastics [25, 26]. Product yields of gas, oil/wax and char are complicated and misleading because of the wide variety of formulations used in the production of the composite. For example, a high amount of filler and fibre reinforcement results in a high solid residue and inevitably a reduced gas and oiFwax yield. Similarly, in many cases, the polymeric resin is a mixture of different thermosets and thermoplastics and for real-world samples, the formulation is proprietary information. Table 11.4 shows the product yield for the pyrolysis of polyurethane, polyester, polyamide and polycarbonate in a fluidized-bed pyrolysis reactor [9]. 

MAJOR PRODUCT APPLICATIONS experimental phase as reinforcing filler... 

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. 

Hi) Shear Dependence of Viscosity, Non-Newtonian Behavior The presence of reinforcing fillers also increases the non-Newtonian behavior of elastomers. This effect is mainly due to the fact that the incorporation of fillers in elastomers decreases the volume of the deformable phase. As discussed in the following text, this decrease is not limited to the actual volume of the filler, but must also include the existence of occluded mbber. So, when filled mixes are submitted to shear forces, because of the lower deformable volume, the... 

The example chosen here to illustrate this type of composite involves a polymeric phase that exhibits rubberlike elasticity. This application is of considerable practical importance since elastomers, particularly those which cannot undergo strain-induced crystallization, are generally compounded with a reinforcing filler. The two most important examples are the addition of carbon black to natural rubber and to some synthetic elastomers and silica to polysiloxane elastomers. The advantages obtained include improved abrasion resistance, tear strength, and tensile strength. Disadvantages include increases in hysteresis (and thus heat buUd-up) and compression set (permanent deformation). 

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. 

In recent years the incorporation of low concentrations of nanometer-sized fillers has become an important strategy to improve and diversify polymeric materials. A polymer nanocomposite can be defined as a two-phase system, where at least one dimension of the reinforcing filler is on the nanometer scale. Nanocomposites can vary from the inclusion of isodimensional... 

During the past decades, nanotechnology has attracted great attention due to its marvellous potential applications in numerous areas [90]. Polymer nanocomposite is a unique addition in the nanotechnology family. In polymer nanocomposite, one phase is dispersed in another phase in nanometer level [19]. Different types of reinforcing fillers such as sodium montmo-rillonite, sodium bentonite, layered double hydroxide, exfohated graphite, fullerene, carbon nanofiber, and carbon nanotube have been successfully used in the preparation of polymer nanocomposites [19]. Recently,... 

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