Polymeric materials, requirements imposed

Requirements Imposed on Polymeric Materials by Structural Damping Applications... 

Modern technology thrusts challenging demands on the performance capabilities of materials, including polymers and their blends. A new approach to the science and technology of polymer blends has emerged recently, i.e., polymer blends by design, rather than by availability. These polymeric materials must perform under strenuous mechanical, chemical, thermal and electrical conditions imposed by the requirements of a specific application. Service in these applications usually involves several criteria to be fulhlled without a loss of economic advantage. Indeed, performance requirements of polymer blends are often at the limit of the properties that can be achieved. Moreover, these materials are expected to endure complex environmental conditions for extended time. All these factors stress the need for in-depth studies of the properties and performance of polymer blends. 

The optical elements of solar systems are Important applications for polymers. The use of polymers for optical elements will, however. Impose several unusual material requirements. Five examples of the current development of polymeric optical elements are considered below. Problems such as dirt accumulation and photodegradation, which are common to most optical elements, are considered In a later section. More conventional applications are then noted very briefly. 

Another test that shows the viscoelastic behavior of a polymeric material is the stress relaxation test, in which a sudden strain is imposed on the polymer sample at t = 0, and the stress, a, required to maintain the strain is recorded as a function of time. As time increases, the stress, a(t), necessary to maintain the constant strain, s, decreases due to relaxation of the entangled polymer chains that try to reach an equilibrium conformation. If the strain is released at short times, the sample will recover its original shape on the other hand, long relaxation times will produce permanent deformation on the sample. If the stress, which is a function of time, is divided by the strain, a modulus value as a function of time can be defined ... 

In the above it is implied that the symmetry of the oriented material is simply related to the geometry of the drawing deformation imposed upon the isotropic material. If this implication is accepted then it follows that the most general anisotropy to be expected in polymeric materials in which the orientation results only from a simple deformation process, which is a usual case, would have orthorhombic symmetry requiring only 9 independent compliance constants and not the more general anisotropy typical of a triclinic crystal which requires the lull 21 independent constants. 

The monitoring of dose can be performed with different techniques chemical systems (Fricke and ceric solutions [31]), radiochromic compounds (dyes [32, 33]), polymeric tapes (polyethylene [34], poly(vinyl chloride) [35, 36], poly(methyl methacrylate) [37-40], epoxy resin [41]), radiation thermoluminescence phosphors [42, 43]. Several requirements are imposed for a proper dosimeter similarity with processed material in respect with linear energy transfer, reproducibility, sensitivity, lack of the influence of humidity, stability after irradiation, easy to calibrate, appropriate dose range and dose rate, linearity and independency on the type of radiation, the response being constant in time, lack of post-irradiation modification. 

When very high requirements are imposed on the dielectric characteristics of polymer materials (e.g., when they are used as recording layers in thermoplastic and photothermoplastic data recording), TROP is the most suitable polymerization procedure [18, 22, 23] in the case of catalytic polymerization, there is a need to remove traces of metals from the polymers. The molecular weight of the polymers synthesized by TROP can be controlled with advantage due to the use of regulating polar additives, for example, -hexyl alcohol in the polymerization of carbazolyl-containing monomers [22],... 

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