Polymer characterization thermal conductivity

For common thermally thick combustible materials (greater than a few millimeters) the time to ignition is proportional to the product k p c (where k is the thermal conductivity, p is the density, and c is the heat capacity), which represents the thermal inertia of the sample. Thermal inertia characterizes the rate of surface temperature rise of the material when exposed to heat. Low values of thermal inertia lead to a rapid temperature rise for a given applied heat flux and hence, to a rapid ignition.4 Polymeric foams have much lower thermal conductivity and density than the corresponding solid materials, thus the surface temperature of the first heats up more rapidly than that of the latter. Foam surface may reach the ignition temperature 10 times faster than the solid polymer.5... 

Both theoretical and experimental studies show that not only are aromatic ladder polymers more thermally stable but they are also more highly conducting than analogously structured nonladder systems.In this communication, we report the synthesis and electronic properties of a ladder aromatic polymer, poly(8-methyl, 2.3-6,7-quinolino) (PMQ). The experimental procedures for preparation and characterization of PMQ are described in refs. 5 and 6. 

The ionic conductivities of sulfonated polyetherketone/imidazole (pyrazole) systems were first studied by Kreuer et al. [161]. The intercalation of imidazole (pyrazole) into the polymer with Bronsted add functions was shown to produce a high protonic conductivity (ca. 10 S cm ). However, the volatility of these heterocycles hampers their application for high-temperature PEMFCs. In order to improve the thermal stability, the immobilization of these heterocyde systems was evaluated [162-164]. When Schuster et al. characterized the conductivity of imidazole-terminated ethylene... 

Most of the processes of polymer synthesis are characterized by a high exother-micity combined with a low thermal conductivity coefficient of the monomer-polymer mixture. This relationship between the thermophysical characteristics of the polymerization medium, in combination with the reaction rates observed in actual practice, results in the overheating of the reaction mass and the appearance of a non-uniform distribution of temperature and degree of conversion in space and time. 

The modest pressures of 5 kbar (0.5 GPa) necessary to cause transitions to columnar phases in polymers make the design of apparatus using large specimens relatively straightforward and it is easy to accommodate associated characterization techniques such as thermal conductivity or nuclear magnetic resonance (NMR) probes. Much of the author s early work was with a piston-cylinder apparatus with a working length of 5 cm and a diameter of... 

For many applications of filled polymers, knowledge of properties such as permeability, thermal and electrical conductivities, coefficients of thermal expansion, and density is important. In comparison with the effects of fillers on mechanical behavior, much less attention has been given to such properties of polymeric composites. Fortunately, the laws of transport phenomena for electrical and thermal conductivity, magnetic permeability, and dielectric constants often are similar in form, so that with appropriate changes in nomenclature and allowance for intrinsic differences in detail, a general solution can often be used as a basis for characterizing several types of transport behavior. Useful treatments also exist for density and thermal expansion. 

As the measurements have shown, thermal properties of filled polymers depend considerably on filler orientation. Thermal conductivity and specific heat of glass plastics with formaldehyde and epoxy binder increase with increasing temperature, whereas thermal diffusivity falls in inverse proportion with temperature. The direction of the heat flux and orientation of the filler are responsible for the conductance and thermal diffusion in a given direction. Specific heat does not practically depend on the heat flux direction, since it characterizes the scalar value, i.e., energy accumulation. 

Mechanical Load. Static mechanical load by strain leads to stretching of random-coil polymer chains in the direction of sample elongation and chain compression in the orthogonal directions. The value of the residual dipolar and quadrupolar couplings is increased by the mechanical load, and moreover, the distribution of the correlation times is also modifled. Therefore, many NMR parameters sensitive to the residual dipolar couplings and slow motions can be used for characterization of the local strain-stress effects in heterogeneous elastomers (158,160,161,179). Dynamics mechanical load leads to sample heating where the temperature distribution in dynamic equilibrium is determined by the temperature-dependent loss-modulus and the thermal conductivity of the sample. Because transverse relaxation rate (approximated by the T2 relaxation) scales with the temperature for carbon fllled SBR, a T2 map provides a temperature map of the sample. Such temperature maps have been measured for carbon-black filled SBR cylinders for different filler contents and mechanical load (180). 

Carbon nanotnbes are regarded as ideal filler materials for polymeric fiber reinforcement dne to their exceptional mechanical properties and cylindrical geometry (nanometer-size diameter). Polymer chains in the vicinity of carbon nanotubes (interphase) have been observed to have a more compact packing, higher orientation, and better mechanical properties than bulk polymers due to the carbon nanotube polymer interaction. The existence of interphase polymers in composite fibers, their strnctnral characterization, and fiber properties are summarized and discussed in the literature (Liu and Satish 2014). Besides improvements in tensile properties, the presence of carbon nanotubes in polymeric fibers also influences other factors (thermal stability, thermal transition temperature, fiber thermal shrinkage, chemical resistance, electrical conductivity, and thermal conductivity). 

Thermal Conductivity (Ready RG (1996) Thermodynamics. Pleum Publishing Company, New York Pethrick RA, Pethrick RA (eds ) (1999) Modern techniques for polymer characterization. Wiley, New York). 

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