Radical formation and fracture of highly drawn crystalline polymers

In tensile strength experiments of highly drawn crystalline polymers by using electron spin resonance the appearance of radicals is observed all over the strained sample long before its fracture. It is generally considered that the radical formation is the consequence of rupture of the most strained tie molecules. The maximum number of radicals at sample failure is much larger than twice the number of ruptured tie molecules in the fracture plane and much smaller than the total number of tie molecules in the sample. In order to explain this situation, one has to take into account the defect distribution of the microfibrillar superlattice of the fiber structure. The highest strain and stress concentration in such a lattice occurs at the point vacancies or point dislocations at the ends of microfibrils where the material connection by tie molecules with the rest of the sample is interrupted so that nearly the whole load has to be borne by adjacent microfibrils. About 1015 such defects exists per cubic centimeter of fiber yielding, under stress, disk-shaped microcracks perpendicular to the fiber axix. The cracks grow laterally by fracture overstrained adjacent microfibrils, requiring the rupture of all intrafibrillar tie molecules in one amorphous cross section, or longitudinally along the boundary between microfibrils which, as a rule, contains very few interfibrillar tie molecules. In the former case representing the situation with nylon 6, a great many, and in the latter case representing the situation with polyethylene, very few tie molecules are ruptured.