Rate and Stepwise Loading of Fibers

Historically, the first ESR experiments with mechanically produced free radicals have been made in the Ioffe-Institute in Leningrad in 1959 [1] with ground or milled polymers, the samples being investigated after completion of the fracture process. 

In view of the fact that the slippage of chains, microfibrils, or fibrils reduces or prevents the mechanical scission of chains highly oriented thermoplastic fibers with little potential for plastic deformation are the most suitable objects for a study of chain scission kinetics. ESR investigations using fibers of polyamide 6, 66, and 12, 

If a semicrystalline microfibril is subjected to stresses, the resulting deformation will be non-homogeneous at the molecular level. The bulk of the deformation will be born by the amorphous regions. As discussed in Chapter 5 the largest stresses are transferred upon extended chain segments which share the strain imparted onto an amorphous region. The stress induced scission of chains must, therefore, be expected to occur within the amorphous regions. 

At first the phenomenology of free radical production in preoriented yarns will be discussed taking 6 and 66 polyamide as examples. In constant load rate tests a 

In the first paper on this subject [7] Kausch and Becht gave a detailed discussion of the notable fact that within each strain step the radical concentration increases concurrently with a decrease of the macroscopic tensile stress. The conclusion was drawn that the local molecular stresses are unevenly distributed. They are not simply a constant multiple of the macroscopic stresses. The chain segments breaking towards the end of a strain interval quite obviously do not participate in the macro- 

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