Particle Fillers and Reinforcements

The elongations to break in uniaxial stretching among polymers vary considerably. They not only vary among different polymers, but change considerably with factors such as temperature, crystallinity, and polymer chain orientation. 

Solid polymers are often characterized with small sinusoidal oscillations. This is done both in uniaxial extension and shear. In imiaxial extension in the linear region 

Similar sinusoidal oscillation experiments are carried out on polymer melts. This is always done in shear flow with shear moduli G (tt ) and G w) in place of ( ) and ( ). 

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Fillers are available in many forms including particles, fibers, and mats or fabrics. Table 9.4 lists common forms of fillers and reinforcements that are used with epoxy adhesives. Note that epoxy adhesive film carriers such as fabrics or mats can be considered as a type of filler. 

Transparency. Some applications of plastics require transparency. Amorphous plastics should be able to transmit light. Some factors which prevent transparency include unsatura-tion/light absorption, crystallinity, fillers and reinforcing fibers, and use of rubber particles to increase impact strength. The plastics most often used for their transparency are poly(4-methylpentene-l) (TPX), poly(methyl methacrylate) (almost equal to glass), cellulose acetate, propionate, and butyrate, polycarbonate, and polysulfones (slightly yellow). As a research challenge, it is quite possible that fillers and rubber particles could... 

Is the tradename for wollastonite. It is available in three grades varying in particle size. An acicular calcium silicate, it is used as a filler and reinforcing agent in plastics, cement, wallboard, soil conditioner and in casting plasters. 

Table 4.2 Common fillers and reinforcements for plastics Table 4.3 Some properties of silica particles and the...

Incorporation of fillers and reinforcements in PO is a complex procedure occurring in various ways, as a function of the characteristics of the materials used (shape, particle dimensions, wetting by polymer, etc.) and of the quantity to be incorporated in the polymer as powder or melting. 

Fibers and anisotropic particles reinforce polymers, and the effect increases with the anisotropy of the particle. In fact, fillers and reinforcements are very often differentiated by their degree of anisotropy (aspect ratio). Plate-like fillers, like talc and mica, reinforce polymers more than spherical fillers and the influence of glass fibers is even stronger [17]. Anisotropic particles orientate during proeessing, and the reinforcing effect depends very much also on orientation distribution. 

The relative amounts and nature of these ingredients depend upon the desired application. The fillers and reinforcing particles increase modulus and tensile strength as well as reducing cost. The oils and plasticizers reduce these same mechanical properties but introduce flexibility. The processing aids improve the extrusion and moldability of the compounds. Curatives and curative accelerators allow for the efficient crosslinking of polymer systems, which prevent creep and cold flow. 

In this chapter we consider types of ternary compounds other than those discussed in Chapter 6. The compoimds we discuss here contain polymers, particle fillers, and additives including processing aids and curatives. Additives mixed into polymer-filler compounds have a strong influence on the interaction of particles with each other and with the polymer matrix. The treatment of reinforcing fillers with additives is very important in the processing industry. Sections 7.2 and 7.3 may be considered a continuation to Chapter 2. Curatives, notably sulfur and its compounds, are usually used with organic accelerators to control the rate of curing step. Section 7.5 continues section 4.10. 

The mbber compound usually requires an inert inorganic filler and small particle sise carbon particle for reinforcement. The mbber polymers vary in inherent tensile strength from very high in the case of natural mbber to almost nonexistent for some synthetic polymers, eg, SBR. The fillers most commonly used for mbber compounds include carbon black, clay, calcium carbonate, siUca, talc (qv), and several other inorganic fillers. 

The furnace process involves injecting low end fraction of cmde oil, eg. Bunker Euel C, into a heated chamber. The temperature, shape of the injectors of the oil, rate of injection, and other factors are controlled to produce black fillers of different particle si2e and stmcture. The particle si2e and stmcture control the reinforcing character of the carbon black. There are 30 common grades of carbon black used in the mbber industry. There are numerous specialty grades produced, and several hundred are used in plastic, conductive appHcations, and other uses. 

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