Apparent energy of bond scission

The largest energy available to one RCONHCH2-CH2R bond within a time period of 1/kt, is (Eq. 5.57 for nc = 1)  

Using as before a value of coq equal to 10 s, a value of 0 of 5.53 10 m /mol, and a rate k = 1/rb = 1/48 s the thermal term in Eq. (7.3) has, at a temperature of 20 °C, a value of 77.2 kJ/mol. The stress term must reach, therefore, a value of 110.8 kJ/mol before U(T) is larger than the Uq of PA 6 and bond rupture at room temperature can occur. At 200 K the thermal term has decreased to 52.7 kJ/mol. In order to provide a total energy of 188 kJ/mol, the mechanical term must now reach 135.3 before bond breakage will occur within 48 s. For a chain segment containing ng weak bonds the rate of scission, l/r., employed in the above calculations will be 1/tc = 

If one assumes that neither 0 nor Uq depend on temperature, one has to conclude that at 200 K it is possible to raise the molecular stress to a level which is 17% higher than the largest molecular stress attainable at room temperature. In other words, a polyamide fiber highly strained at 200 K will quite stable contain many bonds with values between 110 and 135 kJ/mol. Those bonds will break, of course, if the temperature is raised to room temperature provided that no other means of stress relaxation (slip, uncoiling) become available to the strained chain segment. 

The search for chain scission events during an upward temperature scan can be called a critical experiment for the validity of both the kinetic equation (Equation 5.57) and the morphological model (Fig. 7.5). These investigations have been carried out in the Deutsches Kunststoff-Institut in Darmstadt. Following earlier experiments 

The equivalence of thermal and mechanical action on a given network of chains is further illustrated by calculating the relative length L/Lo of those intrafibrillar chains which are just about to break. One considers that condition to be fulfilled if the jj (L), calculated from Eq. (7.1) for = Lq and introduced into Eq. (7.3), yields Uq  

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