Energy release in chain scission

The total elastic energy stored in a segment of elastic modulus E, length L, and cross-section q amounts to 

Chain scission events, therefore, have been justly termed micro-explosion by Zhurkov and his colleagues. 

On the other hand at a (large) concentration of (0.6 10 ) bond ruptures per (i.e. of 0.83 mol/m ) the total energy having been stored in the retracting chain ends amounts to an average of 722 kJ per m which will be dissipated as heat Ch,. 

The important problem of how the external work W done on a polymer sample during a loading-unloading cycle serves to increase the internal energy U, to change the entropy S, or to be irreversibly dissipated as heat Qjr = TdjS was attacked by Muller in 1956 in his classical experiments [59—62]. According to Eqs. 5.2 and 5.3 one can write 

The latter hypothesis was further tested by Godovskii et al. [31]. PA-6 fibers drawn to X = 5.5 at 210 were repeatedly stretched at room-temperature. The authors found for PA 6 the same characteristic difference between the first and the following loading cycles as did Muller for PIB 6 U was essentially different from zero only in the first loading cycle. The ratio of 6 Wi/5Ui was found, independent of the macroscopic stress, to amount to 7.0. This constancy of 5 Wj /5 Uj is in fact remarkable. It indicates that processes are responsible for the increase of internal energy which occur, independent of a, if locally a critical excitation is surpassed. Godovskii et al. assume that these processes are chain ruptures. They derive from 

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