Modified Mechanical Properties

The modification of mechanical properties by incorporation of fillers has been extensively discussed in Section 9.3 and, even where this is not the primary aim, the filler being incorporated for some other purpose, the effect on mechanical performance is always of importance. 

Probably the two physical property changes for which fillers are commonly added are to increase modulus and reduce coefficient of thermal expansion. The increased modulus allows a thinner part, for example, for equivalent centre span deflection of a rectangular beam  

Coefficients of linear thermal expansion a , for typical crosslinked thermoset polymers over the temperature range 10-70 °C, (i.e., below the T ), are in the range 60-100 ppm K. (Coefficients of volume expansion approximate to 3a .) This range of values is high 

The incorporation of filler does reduce the expansion anisotropy in glass-fibre laminates. The latter use either continuous or very high-aspect-ratio fibre, 1/d 1000 and the simple rule of mixtures for thermal expansion does not apply, as the expansion is governed principally by the fibre in the plane of the laminate (x-y direction). The consequence is that with an increase in temperature, the matrix, because it is coupled to the fibre, is constrained from expanding in the plane of the laminate and is thus put under compression. In this state, some stress relaxation by creep can occur. In the direction perpendicular to the plane (the z direction), the aspect ratio of the fibre is clearly one and the rule of mixtures can be applied. Thus, for a random chopped-strand laminate of fibre volume fraction 0.2, coefficient of thermal expansion in the plane of the laminate might be 25-35 ppm K, whereas in the perpendicular direction it would be 50-80 ppm K k Incorporation of 50 wt% filler in the matrix polymer could reduce this to 35-55 ppm K.  

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Unlike other pigments, carbon black used in plastics processing not only yields coloristic effects but also modifies the electrical properties, provides heat and UV resistance, and may act as a filler to modify mechanical properties. 

TABLE 11.2 Examples of Additives that Modify Mechanical Properties, Electrical Conductivity, and Flame Retardancy... 

Modification of Melt and Solution Properties. In addition to modifying mechanical properties resulting from polymer blending in the presence of a suitable compatibilizing agent, the melt and solution viscosities of the com-patibilized blend differ from those of the blend in the absence of the agent because the compatibilized blend is not truly compatible it is only partially or marginally so. 

For this reason many attempts have been made to modify polyamides and particularly polyesters in order to improve their elastic behavior. It is necessary, however, to recall here that this problem is far from being resolved, so that the following information is given otdy in order to complete the list of PET fibers having modified mechanical properties. 

For these teasons plasticizers are not used to modify mechanical properties of the final product but are still quite useful, especially in the modification of processing characteristics (viscosity) of epoxy resins. 

Temperatures do not depend on the amount or size of filler. The values of the bulk moduli and the thermal expansion coefficients are independent of filler size, but depend considerably on the volume fraction of filler. All filled and unfilled materials show a glass-rubber transition, at which temperature the thermal expansion coefficient increases considerably and the bulk modulus decreases sharply [84]. The mineral fillers seem to modify mechanical properties on three levels [85, 86] in terms of their nature, their size, shape and distribution, and in terms of the changes they bring about in the microstructure of the matrix. 

Frequently, fillers such as hard minerals or soft rubbers are combined with polymers to modify mechanical properties, such as elastic modulus or resistance to crack propagation... 

Fillers 20-400 Modify mechanical properties, processing characteristics and cost... 

Similarly, virtually all polymers in commercial use contain additives. Their purpose is two-fold to alter the polymer properties and to enhance ease of processing. Plasticizers are used to modify mechanical properties. Modifiers can be lubricants, cross-linking agents, emulsifiers, and thickening agents, just to name a few. Pigments and odorants are common additives used for aesthetic reasons. 

Keywords modification, copolymerization, stereocomplex, blending, composites, additives, modifiers, mechanical properties, crystallization... 

Deposition velocities define how fast the filaments are drawn onto the platform. Very few studies have addressed how this parameter impacts the overall quality of the parts, but Anitha et al. (2001) determined that this variable can contribute 15 % to the surface roughness of the part. However, within the microstructure of the printed parts, it is possible to observe the effect of varying such parameter and how it modifies mechanical properties. 

The mechanical behavior of these linear block copolymers is directly related to the composition and morphology (correlated stress-strain curves are presented in Fig. 3.8 in Part II). By changing the macromolecular architecture and processing conditions in block copolymers, very different morphologies with modified mechanical properties and partly new micromechanical mechanisms can be obtained (see Chapter II.3). 

Filler. A relatively inert material added to a plastic mixture to reduce cost, to modify mechanical properties, to serve as a base for color effects, or to improve the surface texture. 

Using Dye/amine/alkyl bromide, iridium-containing photoluminescent polyacrylate films have also been manufactured. Polyoxometallate (POM)/polymer hybrid materials exhibiting modified mechanical properties (polymerized EPOX/TMPTA matrix with inserted POM clusters [XIA 15]) were synthesized in a one-step process using a silicon or phosphor polyoxomolybdate/iodonium salt/silane system. 

After taking account of compounding costs, mica filled compounds are generally more expensive on a volume basis than the unfilled resin. Consequently, mica is not viewed as a cost saving filler, but rather as a means to modify mechanical properties. The key properties which mica affects are ... 

HDT, heat and chemical resistance Heat and chemical resistance, HDT, mechanical properties Mechanical properties Compatibilized-cum-impact modified Mechanical properties, HDT, dimensional and chemical stability... 

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