Photoaging of Polyamides

Objects made from polyamides (fibers, films, etc.) change properties sharply under the action of ultraviolet rays they become brittle, infusible, turn yellow. 

The action of heat and oxygen is intensified during simultaneous ir- 

Chemical changes occur during irradiation if the incident light rays are absorbed by the substance. The spectra of polycaproamide, poly-hexamethyleneadipamide, and polyhexamethylenesebacamide, cited in Fig. 130, show that waves shorter than 350 mju are most sensitive for polyamides, since there is little absorption above 350 mju [67, 68]. 

When polyamides are irradiated, the viscosity of the solutions decreases [16, 69]. The amount of the substance that dissolves in water (determined after 4 hr extraction in a Soxhlet apparatus [69]) increases approximately in proportion to the time of irradiation of polycaproamide, which can be explained by cleavage of the molecular chains according to the laws of change. 

Under the action of short-wave (253.7 mM) and long-wave (300-400 mjLt) radiation on various polyamides (polycaproamide, polyhexa-methyleneadipamide, and polyhexamethylenesebacamide), in all cases of irradiation (in nitrogen, air, and oxygen), products incompletely soluble in m-cresol are obtained [67, 68]. 

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