Thermoplastics particulate fillers

Finally, metal- and resin-bonded composites are also classified as particulate composites. Metal-bonded composites included structural parts, electrical contact materials, metal-cutting tools, and magnet materials and are formed by incorporating metallic or ceramic particulates such as WC, TiC, W, or Mo in metal matrixes through traditional powder metallurgical or casting techniques. Resin-bonded composites are composed of particulate fillers such as silica flour, wood flour, mica, or glass spheres in phenol-formaldehyde (Bakelite), epoxy, polyester, or thermoplastic matrixes. 

In particulate-filled thermoplastics, the matrix is the load-bearing component and all deformation processes take place in the matrix. Particulate fillers are, in most cases, not capable of carrying any substantial portion of the load due to the absence of interfacial friction as the means of stress transfer. This is evidenced by the lack of broken particles on the surfaces of fractured filled thermoplastics. Hence, it seems appropriate to start this volume with a brief overview of the basic structural levels and manifestation of these levels in governing the mechanical properties of semicrystaUine thermoplastics used in compounding. 

The surface tension of two thermoplastics and three fillers are listed in Table 2. Large differences can be observed both in the dispersion, but especially in the polar component. The surface tension of the majority of polymers is in the same range, in fact between that of PP and PMMA. Those listed in Table 2 represent the most important particulate fillers, and also reinforcements used in practice, since clean glass fibers possess similar surface tensions to Si02. Surface treatment lowers the surface tension of fillers significantly (see Sect. 6.1). 

Combining particulate fillers, such as carbon black, into thermoplastics involves the following sequential,but to some extent, overlapping stages [83] ... 

Preparation of thermoplastics compounds containing particulate fillers is dominated by the use of continuous screw extruders which are available com-... 

Chopped strands of glass 1/32-1/2 in. in length can be incorporated in thermoset or thermoplastic materials about as easily as the particulate fillers. Each strand maybe made up of 204 individual filament whose diameter is 2-7.5X10 in. 

Non-compatibilized blends of PS with either PEST or PEST and PMMA have been used for decorative applications or as the so-called plastic paper (Kamata et al. 1980). Similarly, PAr blends with either SAN (Brandstetter et al. 1983a, b, c) or high-performance blends of LCP with thermoplastic polymers (e.g., PP, PS, PC, PI) (Haghighat et al. 1992) showed adequate performance for the envisaged applications. However, most PS blends with engineering resins require compatibi-lization. Thus, for example, PS with PA-6 was compatibilized by addition of either methylmethacrylate-styrene copolymer (SMM) (Fayt et al. 1986b) or SMA (e.g., used in PARA/PS blends) (Lee and Char 1994). POM was blended with a small amount of either PS poly(a-methyl styrene) (MPS) or SAN and with particulate fillers (Tajima et al. 1991). PAr/PS blends were compatibilized with PAr-PS segmented copolymer (Unitika Ltd. 1983). 

In its simplest terms, the titanate function (1) mechanism may be classed as proton-reactive through solvolysis (monoalkoxy) or coordination (neoalkoxy) without the need of water of condensation, while the silane function (1) mechanism may be classed as hydroxyl-reactive through a silanol-sUoxane mechanism requiring water of condensation. The silane s silanol-siloxane water of condensation mechanism limits its reactions to temperatures below 100 °C, thereby reducing the possibility of in situ reaction in the thermoplastic or elastomer melt above 100 °C as is possible with titanates. In addition, a variety of particulate fillers such as carbonates, sulfates, nitrides, nitrates, carbon, boron and metal powders used in thermoplastics, thermosets, and cross-linked elastomers do not have surface silane-reactive hydroxyl groups, while almost all three-dimensional particulates and species have surface protons, thereby apparently making titanates universally more reactive. 

The properties of particulate fillers in a number of other thermoplastics are being investigated by plastics producers and academic institutions but usually with a low priority rating. This activity has been growing less and less in recent years as companies, in particular, have been reducing the staffing levels in the research and development departments. 

Andersen, P. J., and Hodson, S. K. 2001. Thermoplastic Starch Compositions Incorporating a Particulate Filler Component. U.S. Patent 6.231.970. 

In the work of Rong et al. [108], various polymers were grafted on the surface of nanoscale silica filler particles through the simultaneous irradiation polymerization technique. In this way, the modified nanoparticles can be more effectively utilized in thermoplastics (such as PP) than conventional particulate fillers, when using the same direct compounding technology. 

The action of particulate fillers on a thermoplastic is dependent on factors that can be classified as extensity, intensity and geometrical factors. The extensity factor is the amount of filler surface area per m of the composite in contact with the plastic. The intensity factor is the specific activity of this solid surface per m of interface, determined by the chemical and physical nature of the filler surface in relation to the plastic. Geometrical factors are the structure including shape of filler (anisotropic such as such as lamellar, plate, needle and isotropic such as spherical), their particle size and size distribution as well as porosity. Among those the chemical nature of the filler surface plays most vital role in determining the degree of plastic-filler interaction. 

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