Thermal conductivity of polymers

The associated temperature profiles are shown in Figures 10 through 12. Metal in contact with Dowtherm is at 240°C, whereas in the middle of the plate, the metal temperature ranges from 226 to 234°C. Because of this effect, as well as the relatively low thermal conductivity of polymer melt, large temperature gradients exist along the y and z directions. At the walls the polymer temperature reaches 240°C, whereas at the center of the channel the polymer temperature is only 213°C, at the outlet. 

CNTs can enhance the thermal properties of CNT-polymer nanocomposites. The reinforcing function is closely associated with the amount and alignment of CNTs in the composites. Well-dispersed and long-term stable carbon nanotubes/ polymer composites own higher modulus and better thermal property as well as better electronic conductivity (Valter et al., 2002 Biercuk et al., 2002). Both SWNT and MWNT can improve the thermal stability and thermal conductivity of polymer, the polymer-CNT composites can be used for fabricating resistant-heat materials. 

For most processing equipment, the low thermal conductivity of polymers strongly influences the overall heat transfer coefficient between the bulk of the polymer and the contacting metal surfaces, creating limitations in heat transfer rates. Heat transfer rates between processing equipment and the polymer depend on many factors, including thermal conductivity, machine clearances, and screw... 

Lobo, H. and Cohen, C., Measurement of Thermal Conductivity of Polymer Melts by the Line-Source Method, Polym. Eng. Set, 30, 65 (1990)... 

As with other disordered materials, the thermal condnctivities of polymers are low due to phonon scattering. As a resnlt, even thongh polymers tend to have heat capacities of the same order of magnitude as metals (1.5 to 3.5 J/g K), their thermal conductivities (0.1 to 1.0 W/m K) are 1000 times lower than metals. Polymers, therefore, are generally good insulators, as long as their use temperature is below their thermal stability temperature. Few correlations for heat capacity and thermal conductivity of polymers... 

Compared to other materials such as metals, the thermal conductivity of polymers is 100 to 1000 times smaller (see Figure 8.5). Fillers increase the conduction by a factor of 3 to 4. 

The thermal conductivity of polymers is temperature-dependent. Fig. 17.2 shows a generalized curve as a function of T/Tg based on the available experimental data. According to Bicerano (2002) the results may be approximated by (the drawn lines in Fig. 17.2) ... 

It is interesting to compare the thermal conductivities of polymers with those of other materials. Fig. 17.5 gives a survey. 

Kline, D.E. and Hansen, D., Thermal Conductivity of Polymers. John Wiley and Sons, New York, 1984. 

From the variation of Gt with temperature in Figure 27.7, it can be seen that Ta tends to increase as G decreases. Since the yield stress varies with temperature, there seems to be a correlation between these fracture resistance parameters and the plastic zone in front of the crack tip. Furthermore, at an impact speed of 2 m/s, because the thermal conductivity of polymers is relatively low, it could be expected that the heat generated in the plastic zone could not dissipate away. The rise in temperature at the crack tip could therefore result in a localized reduction in the yield stress and a blunting effect of the crack tip [24,25]. 

Improvements in the ability to predict the thermal conductivities of polymers... 

It is useful to be able to estimate the thermal conductivities of polymers, both for optimizing certain processes and for evaluating end-use performance ... 

If a polymer is intended for use in applications requiring high thermal insulation, its thermal conductivity is very important. The low thermal conductivities of polymers, and of foams [12] made by expanding polymers and incorporating pockets of air or other gas molecules in the "cells" resulting from the expansion, when coupled with other desirable properties, have made polymers and polymeric foams the insulating materials of choice in many applications. 

A.4. Improvements in the Ability to Predict the Thermal Conductivities of Polymers... 

An improvement we made in the ability to predict the thermal conductivities of polymers was to develop new correlations for UR, V(298K), Cp(298K), and for the quantities entering the... 

As another (and perhaps more important for making reasonable practical predictions in a very simple manner) improvement in the ability to predict the thermal conductivities of polymers, a direct correlation was developed between the i(298K) of amorphous polymers and some of their most important structural features. This correlation will be presented in Section 14.B. While the indirect relationship (Equation 14.6) describes the physics of thermal... 

The thermal conductivity of polymers is found to depend on the degree of crystallinity. The crystalline portions of the structure have a higher thermal conductivity than do the disordered regions of the solid. Materials with high porosity, such as plastic foams, have particularly low thermal conductivities. Foamed plastics such as polystyrene are widely used as insulating materials. 

Generally speaking, the thermal conductivity of polymers is much less than FS (see Table 18.2) so that the temperature difference across the capillary walls and the rise in temperature of the electrolyte are both significantly greater for polymeric capillaries under the same conditions (see Figure 18.5) [14]. 

THERMAL CONDUCTIVITY OF POLYMERS. SMITH TG HOGEAR SPE/SOC PLASTENG/J 23 4 67-9... 

EFFECTS OF CROSSLINKING AND CHAIN DEGRADATION ON THE THERMAL CONDUCTIVITY OF POLYMERS. 

Henderson, J.B., Verma, Y.P., Tant, M.R., and Moore, G.R. (1983) Measurement of the thermal conductivity of polymer composites to high temperature using the line source techniques. Polym. Compos., 4 (4), 219-224. 

Enhanced Thermal Conductivity of Polymer Composites Filled with 3D Brush I 83... 

Quantitative DTAs have been modified by experienced researchers in order to measure the thermal conductivity of polymer systems [6-8], The procedure outlined below is reservedfor experienced DSC users. The sample is placed in direct contact with the sample holder, so that the instrument can record the temperature and the heat flow on one side of the sample. A heat sink of known temperature is placed in contact with the other side of the sample. Knowing the sample dimensions, the temperature difference between the sample holder and the heat sink and the recorded heat flow, the thermal conductivity of the sample can be calculated as follows ... 

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