Particulate reinforcing agents

As mentioned earlier, suspensions of particulate rods or fibers are almost always non-Brownian. Such fiber suspensions are important precursors to composite materials that use fiber inclusions as mechanical reinforcement agents or as modifiers of thermal, electrical, or dielectrical properties. A common example is that of glass-fiber-reinforced composites, in which the matrix is a thermoplastic or a thermosetting polymer (Darlington et al. 1977). Fiber suspensions are also important in the pulp and paper industry. These materials are often molded, cast, or coated in the liquid suspension state, and the flow properties of the suspension are therefore relevant to the final composite properties. Especially important is the distribution of fiber orientations, which controls transport properties in the composite. There have been many experimental and theoretical studies of the flow properties of fibrous suspensions, which have been reviewed by Ganani and Powell (1985) and by Zimsak et al. (1994). 

Incorporating fillers or reinforcing agents is another means of improving polymer properties. High particulate loadings improve the dimensional stability of electronic circuit boards so that the thermal expansion is greatly reduced. Particulate fillers (talc, mica, silica, clay, etc.) are used... 

It is not uncommon for there to be as many as 20 or more additives in one polymer, all present in relatively small amounts, but nevertheless essential to ensure that the performance of the base polymer is acceptable for a particular end use. Many products are blends of two or more polymers or comprise two or more materials combined in a strategic way. For example, packaging materials commonly have a sandwich structure of three or four different polymers polymer composites are an important class of engineering materials containing substantial amounts of particulate or fibrous reinforcing agents. 

The composites can be classified on the basis of the form of their structural components fibrous (composed of fibers in a matrix), laminar (composed of layers of materials), and particulate (composed of particles in a matrix). The particulate class can be further subdivided into flake (flat flakes in a matrix) or skeletal (composed of a continuous skeletal matrix filled by a second material). In general, the reinforcing agent can be either fibrous, powdered, spherical, crystalline, or whiskered and either an organic, inorganic, metallic, or ceramic material. 

TABLE 28.1. Physical properties of reinforcing agents—fiber, particulate. 

CONTROLLED INTERPHASES IN GLASS FIBER AND PARTICULATE REINFORCED POLYMERS STRUCTURE OF SILANE COUPLING AGENTS IN SOLUTIONS AND ON SUBSTRATES... 

Ishida, H. (1993) Controlled interphases in glass fiber and particulate reinforced polymers structure of silane coupling agents in solutions and on substrates. Appl. Sci., 230, 169-199. 

Reinforcing agents— particulate fillers, e.g. carbon black, fibrous fillers, e.g. glass or carbon fibres. 

Mechanical characterization under static loading of polymer-based nanocomposites has been widely studied in order to evaluate the influence of nanofiller content, dispersion, geometry, orientation, interfadal adhesion quality, and others on their mechanical performance. Layered silicates and CNTs are the most studied reinforcing agents in polymers due to their large aspect ratio and mechanical properties, but in the past decade particulate nanofillers such as sUica or functionalized graphene (FG) have received special interest. 

The word reinforcement will not be applied to particulate fillers, such as quartz or glass beads, because although these additives do increase the modulus, they cannot be relied on to improve the strength of the resin, nor will the word be applied to speciality rubber toughening agents that are used to improve the impact strength only. 

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