Mechanical loss, epoxy resins

Grade G-10, glass fabric with epoxy resin binder, has extremely high mechanical strength (flexural, impact, and bonding) at room temperature and good dielectric loss and electric strength properties under both dry and humid conditions. 

Browning, C. E. The mechanism of elevated temperature property losses in high performance structural epoxy resin matrix materials after exposure to high humidity environments, 22nd National SAMPE Symposium and Exhibition, San Diego, CA 22, 365 (1977)... 

At very low temperatures, most degrees of freedom are frozen. The detailed chemical structure of the polymer chains does not remarkably influence most of the elastic and thermal properties at these temperatures. (Properties, such as mechanical strength or dielectric loss, may be influenced by the chemical structure because of factors such as steric hindrance and dielectric polarization.) Cross-linking is one structural feature of epoxy resins which might influence low-temperature properties. 

Fig. 10. Mechanical and dielectric loss vs. temperature for various epoxy resins and polyethylene.

Fig. 18. Mechanical loss for unfilled, fiber-filled and powder-filled epoxy resins vs. temperature.

Alkylation of biphenyl with cyclohexene gives dicyclohexylbiphenyl, which can be used as a secondary plasticizer for PVC. " " Synthesis of this plasticizer uses Friedel-Crafts reaction with aluminum chloride employed as a catalyst. The application data shows that weight loss and the retention of mechanical properties (tensile strength, elongation, and modulus) are greatly improved with this plasticizer. " A mixture of di- and tri-alkyl (usually propyl) biphenyls is used as a plastieizer for polystyrene, butadiene rubber, epoxy resin, and polyurethane. " ... 

At very low temperatures, many amorphous epoxy resins considered show roughly the same mechanical loss. 

Partially crystalline PE has a lower mechanical loss at low temperatures than amorphous epoxy resins. At elevated temperatures, the situation is reversed. 

Partially crystalline epoxy resins undergo less mechanical loss than amorphous ones. They are more like PE. The crystalline fraction has not yet been determined, but may well be similar to that of PE. 

Amorphous epoxy resins are polar polymers and have comparably higher losses. Some loss measurements on epoxy resins are plotted versus temperature in Fig. 11. It is interesting to note that the mechanical and dielectric losses are only different by a factor of roughly 2. Also, the dependence on temperature is rather similar. The dielectric and the mechanical parameters of Fig. 11 were determined at different frequencies. At low temperatures, this is a minor error. Mechanical measurements performed at a higher frequency, namely 50 Hz, would, at most yield lower values, more similar to the dielectric ones. Thus, for epoxy resins, the electrical and mechanical dipole forces are similar. 

The mechanical losses of partly crystalline epoxy resins were found to be lower than those for amorphous ones. First measurements also show a similar situation for dielectric low-frequency losses. The value plotted in Fig. 11 is an upper limit and the true value is probably lower. Further measurements are in preparation. However, despite the fact that plastic flow has not yet been found, because of their good dielectric properties, crystalline epoxy resins seem to be of advantage. 

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