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The fundamental radiation‐chemical reactions under irradiation, destruction and crosslinking of macromolecules, primarily depend on the molecular structure. However, the action of radiation on polymeric fibers (anomalous deterioration of strength properties) obtained out of the same polymer occurs depending on the dose. This results from the character of the conformation of the macromolecules in the stretched polymer. To solve this question, the change of solubility, characteristic viscosity, and gelation under irradiation were studied. The orientation parameter was studied by the optical microscope, and isometrical heating, the radiothermoluminescence and roentgen‐structure were analyzed, also. The obtained dependences were compared with the change in tensile strength of polyolefin fibers (polyethylene, polypropylene) under irradiation. It was determined that the degree of orientation of the polymer has an essential influence upon the radiation yield of the reaction of destruction and crosslinking of macromolecules. Structure changes in polyethylene fibers exposured to a radiation dose of from 0 to 2000 Mrads were studied. The influence of the postirradiation treatment on the structure was studied, too. The behavior of fibrous material after irradiation is predominantly influenced by its chemical shructure; the behavior of a fiber is not very different from that of the base polymer in some other form. The rather remarkable effects that have been observed with some materials (e.g., polyethylene) during irradiation have stimulated research toward finding improved fibers for use in textiles. This trend is reflected in much of the literature that deals with radiation effects on fibrous materials. The modification of textile fiber properties by radiation per se to produce improved products does not appear promising. As a gross effect, the properties of all textile materials are harmed by exposure to radiation under ordinary conditions. Hence the action of radiation on polymeric fibers obtained from the same polymer causes the anomalous deterioration of strength depending on the dose. This investigation was concerned with the effect of orientation on the radiation behavior of polymers, and was carried out on manufactured polyolefin fibers (polyethylene (PE), and polypropylene (PP)). The change of solubility, characteristic viscosity, and gelation mechanical properties by radiation were studied. The orientation parameter by the optical microscope, the isometrical heating, the radiothermoluminescence, and roentgen structure were analyzed, too.

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