Specific heat of plastics

For most plastics the specific heat value (calories per gram per °C) lies between 0.3 and 0.4. On a weight basis this value is much higher than that of most metals. Both iron and copper, for example, have specific heats of about 0.1 at ordinary temperatures. However, along a volume basis, the specific heats of plastics are lower than those of common metals, because of the substantially lower density of plastics. 

Thermal conductivity coefficients, densities, and specific heats of plastics... 

The specific heat of amorphous plastics increases with temperature in an approximately linear fashion below and above Tg, but a steplike change occurs near the Tg. No such stepping occurs with crystalline types. 

Fillers usually increase the thermal conductivity of polytetrafluoroethylene as with other plastics (Table 3.38). Specific heat of PTFE at various temperatures is given in Table 3.39. Enthalpy of molded PTFE is given in Fig. 3.33. 

The equations are, however, suitable for drawing some direct practical conclusions. At a given heat flux, the rise in surface temperature is inversely proportional to the square root of thermal conductivity, density, and specific heat of the material. Plastics foams have very low thermal conductivity and a low density, consequently, their surface warms up very quickly on a given heat flux, reaching the ignition temperature more rapidly than a similar dense object. 

Plasticating capacity n. Of an extruder or injection molder, the maximum rate at which the machine can melt room-temperature feedstock and raise it to the temperature suitable for extrusion or molding. This rate is determined mainly by the quotient of the available screw power, divided by the means specific heat of the... 

Specific heats of expanded plastics may be determined using the Kopp-Neumann additivity rule. The total Cp is given by the sum of specific heats of each constituent times the respective weight fraction. This method was used to calculate Cp for the two densities of PS shown in Fig. 21. A second method of computing Cp for expanded plastics makes use of the relationship... 

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. 

TaWeM Specific Heat of Fiberglass Reinforced Plastics... 

The specific heat of amorphous plastics increases with temperature in an approximately linear fashion below and above Tg, but a steplike change occurs near the Tg. No such stepping occurs widi crystalline types. The high degree of die molecular order for crystalline TPs makes their values tend to be twice those of the amorphous types. The TSs has the highest values. To increase TC the usual approach is to add metallic fillers, glass fibers, foamed structure, or electrically insulating fillers such as alumina. 

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