Plastics properties, filler effects

When plastics act as a physical cross-link and strength properties are indirectly related to the modulus of hard phase and morphology of the blend, the filler effect is analyzed by the following equation ... 

Thermal expansion-contraction of inorganic fillers is much lower compared with that of plastics. Therefore, the higher the filler content, the lower the coefficient of expansion-contraction of the composite material (see Chapter 10). Many inorganic nonmetallic fillers decrease thermal conductivity of the composite material. For example, compared with thermal conductivity of aluminum (204 W/deg Km) to that of talc is of 0.02, titanium dioxide of 0.065, glass fiber of 1, and calcium carbonate of 2-3. Therefore, nonmetallic mineral fillers are rather thermal insulators than thermal conductors. This property of the fillers effects flowability of filled plastics and plastic-based composite materials in the extruder. 

Fillers exert a specific effect on plastics properties, including mechanical strength, hardness, chemical stability, thermal, electrophysical characteristics and frictional parameters (see Table 1.4). The fillers are often impregnated to cut the cost of CM. The fillers are classified according to their... 

Table 1.4. Effect of sofid fillers on plastics properties...

Basically, birefringence is the contribution to the total birefringence of two-phase materials, due to deformation of the electric field associated with a propagating ray of light at anisotropically shaped phase boundaries. The effect may also occur with isotropic particles in an isotropic medium if they dispersed with a preferred orientation. The magnitude of the effect depends on the refractive index difference between the two phases and the shape of the dispersed particles. In thermoplastic systems the two phases may be crystalline and amorphous regions, plastic matrix and microvoids, or plastic and filler. See amorphous plastic coefficient of optical stress compact disc crystalline plastic directional property, anisotropic ... 

TSs has little use as pure resin, but requires addition of other chemicals to render them processable. For RPs, the compounds usually comprise a resin system [with curing agents (catalysts), hardeners, inhibitors, plasticizers] and fillers and/or reinforcement. The resin system provides the binder, to a large extent dictating the cost, properties, dimensional stability, heat, chemical resistance, and basic flammability. The reinfisrce-ment influences primarily the effect of tensile strength and toughness. 

The concentration of API in a solid solution formulation is typically evaluated to understand the effect of dmg loading on solid solution properties such as propensity for phase instability. The addition of some APIs directly influences properties critical to melt extrusion process design and development. For example, APIs influence melt rheology as plasticizers, anti-plasticizers, or fillers. 

In addition to the molecular structure of the polymer the Tg may be affected by the presence of monomers, solvents and plasticizers. These may be considered as providing the system with a high concentration of chain ends and such groups of chemicals commonly depress the Tg and improve the low temperature properties. Fillers usually have only a small effect, increasing the Tg slightly. 

Fillers with respect to plastics are inert substances. They are used to increase the characteristic strength in plastics. Normally fillers are used to lower the cost of the product. Use of filler beyond certain limits leads to decrease in mechanical properties. The selection of filler is based on the final properties of the end product and the plastics used. In order to know the effect of concentration of filler, it must be selected according to size by screening and chemical compatibility with the plastics [85-86]. 

ASTM D883 defines a filler as "...a relatively inert material added to a plastic to modify its strength, permanence, working properties, or other quaHties or to lower costs." EiHers (qv) that modify the properties and characteristics of epoxies are employed in epoxy resins for a variety of reasons. Then principal functions are to control viscosity, reduce shrinkage and the coefficient of thermal expansion, effect a cost reduction, and color the epoxy resins. 

Plasticizers. These are used to improve compound processibiHty, modify vulcani2ate properties, and reduce cost. Por many appHcations, where cost and processibiHty are the objective, naphthenic and aromatic oils are preferred. They are inexpensive yet effective in improving processibiHty at high filler levels. The compatibiHty of the naphthenic oils is limited to about 20 parts per hundred mbber. Aromatic oils are more compatible and can be used at higher levels (132). 

As Carfagna et al. [61] suggested, the addition of a mesophasic polymer to an amorphous matrix can lead to different results depending on the properties of the liquid crystalline polymer and its amount. If a small amount of the filler compatible with the matrix is added, only plasticization effect can be expected and the dimensional stability of the blend would be reduced. Addition of PET-PHB60 to polycarbonate reduced the dimensionality of the composite, i.e., it increased the shrinkage [42]. This behavior was ascribed to the very low... 

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