Modification of Polymer Properties with Functional Fillers

Modification of Polymer Properties with Functional Fillers 

Parameters affecting the performance of polymer composites containing functional fillers are related to 

1) the characteristics of the filler itself including its geometry (particle shape, particle size and size distribution, and aspect ratio), its surface area and porosity, and its physical, mechanical, chemical, thermal, optical, electrical, and other properties. Relevant concepts introduced in Chapter 1 are further discussed in this chapter and also in other chapters dealing vith specific fillers and surface modifiers  

2) the type and extent of interactions at the phase boundaries, vhich affect adhesion and stress transfer from the matrix to the filler. Interfacial interactions are also related to surface characteristics of the filler, such as surface tension and surface reactivity. These are parameters that control its vetting and dispersion characteristics. The importance of the interface is also emphasized in Chapters 4-6  

3) the method of filler incorporation into the polymer melt (discussed in Chapter 3) and its distribution in the final product part processing/structure/property relationships are briefiy discussed in this chapter and are elaborated in other chapters covering specific fillers. 

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In developing reinforcing fillers, the aims of process or material modifications are to increase the aspect ratio of the particles and to improve their compatibility and interfacial adhesion with the chemically dissimilar polymer matrix. Such modifications may not only enhance and optimize the primary function of the filler (in this case, its use as a mechanical property modifier) but also introduce or enhance additional functions. New functions attained by substitution or modification of existing fillers, thus broadening their range of applications, are illustrated in the examples below. 

An innovative strategy to enhanee the mechanieal properties of biodegradable polymers is the ineorporation of nanomaterials as fillers within polymer matrices. With the appropriate modifications to facilitate dispersion into polymers and to enhance interactions with the snrronnding matrix, nanocomposites have demonstrated improved mechanical properties compared with unfilled polymers or polymers loaded with larger, micrometersized particles. A few studies have also shown enhanced cell function when bone cells are cultured on nanophase ceramic materials. 

A variety of discontinuous (short) functional fillers may be combined with thermoplastic or thermoset matrices to produce composites. The fillers may differ in shape (fibers, platelets, flakes, spheres, or irregulars), aspect ratio, and size. When the fully dispersed (exfoliated or deagglomerated) fillers are of nanoscale dimensions, the materials are known as nanocomposites. They differ from conventional microcomposites in that they contain a significant number of interfaces available for interactions between the intermixed phases. As a result of their unique properties, nanocomposites have great potential for applications involving polymer property modification utilizing low filler concentrations for minimum weight increase examples include mechanical, electrical, optical, and barrier properties improvement and enhanced flame retardancy. 

The surface properties of particles are very important with respect to their end use. Many particles are used for fillers and to impart properties that enhance a materials function. In order to do so, the particles need to be compatible with the environment into which they are placed. Often this is in a polymer matrix such as a film. To enhance particle compatibility of the surface of 2-5 pm silica particles and silica glass beads, surface modification of these particles was carried out. Surface modifications were accomplished by surface polymerization, surface polymer grafting, by surface dendrimerization and by developing organo-silicone particles. The surfaces obtained can have a wide variety of properties, fi om highly hydrophilic to highly hydrophobic, from anionic and cationic to nonionic, as well as being environmentally responsive. 

Thermosets have been used successfully as functional fillers for thermoplastic materials [3]. Fillers are cheaper than polymer and can help reduce the cost of the final compound. In this particular process, the thermoset is physically and chemically modified. When it is combined with polymer it produces enhanced material properties. The modifications are necessary to optimise the bond between the recyclate and the virgin polymer. This work was carried out as part of the Recycling and Recovery from Composite Materials (RRECOM), a UK based alliance of 16 companies and two universities, Brunei and Nottingham. 

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