Heating of polymers

The specific heats of polymers are large - typically 5 times more than those of metals when measured per kg. When measured per m, however, they are about the same because of the large differences in density. The coefficients of thermal expansion of polymers are enormous, 10 to 100 times larger than those of metals. This can lead to problems of thermal stress when polymers and metals are joined. And the thermal conductivities are small, 100 to 1000 times smaller than those of metals. This makes polymers attractive for thermal insulation, particularly when foamed. 

Why are the specific heats of polymers higher than those of metals ... 

The second example used visible light absorption that increased the temperature locally within the thermosensitive gel [39]. The gel consisted of a covalently cross-linked copolymer network of N-isopropylacrylamide and chloro-phyllin, a combination of a thermo-sensitive gel and a chromophore. In the absence of light, the gel volume changed sharply but continuously as the temperature was varied. Upon illumination the transition temperature was lowered, and beyond a certain irradiation threshold the volume transition became discontinuous. The phase transition was presumably induced by local heating of polymer chains due to the absorption and subsequent thermal dissipation of light energy by the chromophore. The details will be discussed in a later section. 

Both expressions (29 a, b) reduce to the zero solvation term P = 0 at the theta point, where 8Q/K - 0, kg - kg and e, -> 0 for any P. After eliminating it, the relationship between the chain contributions to the heat of polymer transfer gel - sol in a flow-equilibrium and in a reversible-thermodynamic equilibrium can be obtained ... 

As an example of the application of the general relationships and definitions let us analyze a specific polymerization. We shall discuss anionic activated polymerization of co-dodecalactam, which has been thoroughly investigated.209 It is important that polymerization of this monomer can be treated as approximately isothermal, because the heat of polymer formation from co-dodecalactam is very low and, so the increase in temperature caused by this source can be neglected.210... 

Figure 4. DSC curves for PMCS-4 (Table 2.3) of various stereo regular structure 1 - atactic, 2, 2 - transtactic polymer 2 (2- heating, 2 - cooling) 3 - heating of polymer 3 4—heating of polymer 4...

Investigation of the kinetic of mass loss at thermooxidative destruction of modified CDA showed that modification increases its stability to the heating at elevated temperatures (Figure 2.33). Loss of mass of modified CDA in much less in comparison with initial values during prolonged heating of polymer samples in the air (150°-200°C). These conclusions are proved by the results of complex thermogravimetric analysis (TGA). 

Specific heat of polymer blends is usually measured by differential thermal analysis (DTA) [Slade and Jenkins, 1966] or differential scanning calorimetry (DSC) [Strella and Erhardt, 1969 Richardson and Burlington, 1974]. DTA measures... 

Cp = specific heat of polymer material (assumed constant)... 

THE SPECIFIC HEATS OF POLYMERS IN THE TEMPERATURE RANGE OF -150 TO 180 DEGREES. 

ADIABATIC CALORIMETER FOR INVESTIGATION OF SPECIFIC HEATS OF POLYMERS. 

TABLE 53.4. Ignition temperature, thermal conductivity, and specific heats of polymers. ... 

Specific heat of polymer blends is usually measured by differential thermal analysis (DTA) (Slade and Jenkins 1966) or differential scanning calorimetry (DSC) (Strella and Erhardt 1969 Richardson and Burrington 1974). DTA measures the difference in temperature between the sample and a standard for the same rate of heat input, while DSC compares the rate of heat inputs for the same rate of temperature rise. The results of DSC are easier to analyze as they give a direct measure of the rate of heat input. 

SMPs have most notably been promoted because of their potential in minimally invasive surgery, where a compacted device could be passed through a smaller incision and deployed to its full shape once inside the body [40]. For biomedical devices, the heating of polymer to activate SMEs has been proposed by body, temperature, optical/laser heating, and remote inductive heating [41]. As each of these thermal activation methods is possible within the body, control over SMP geometry is possible with implantable devices. 

Various techniques discussed in the next sections have been used to measure the specific heat of polymers. 

In summary, melting of thermoplastic matrixes by the incorporation of ferromagnetic particles is possible by inductive means. Particles, which only fulfill electric properties, are unsuitable for particulate induction heating. The relationship between particle and machine parameters, seem to be mainly (with some exceptions) of a complex kind, which impedes the choice of adequate particles. Nevertheless, concerning the heating of polymer-polymer composites, the induction heating is regarded to be a suitable approach. 

Bayerl T, Schledjewski R and Mitschang P (2010) Inductive heating of polymer matrixes by particulate heating promoters, Proc. Ifth European Conference on Composite Materials (ECCM-I4), June 7-10, Budapest, Hungary. 

KOCH mixer heat exchangers are available either in monotube or multitube versions. These static mixers increase the heat transfer coefficient by a factor of 6 to 8 compared with empty pipe configurations. They are used not only for rapid heating up applications, for example, the heating of polymer solutions during manufacture of low density polyethylene and similar types of plastics, but also for the efficient cooling of viscous media. 

Table 1.4 presents the melting heats of polymers and polymer-composite materials at temperatures of solid-phase transitions of nitric salts, coinciding with sevilene fluidity temperature of 80°C. According to [4], ammonium nitrates have sohd-phase transitions at temperatures of SO C and 130°C with AH equal to 0.32 eeal/mol and 1.01 ceal/mol, respectively the salt KNO has the solid-phase transition at 130°C with AH equal to 1.3 ccal/mol. 

TABLE 1.4 Melting heats of polymers and their composites at temperatures of solid-phase transitions of nitric salts (J/g)... 

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