SynopsisChanges in the dynamic mechanical properties of nylon 6 (a-form) under ultraviolet light irradiation were investigated. On irradiation with spectrally dispersed ultraviolet light in the wavelength range of 219-415 nm, the dynamic modulus E'and the density of nylon 6 were increased below about 300 nm. It was found that the increment in E' and the density were the result of crosslinking. When E' was measured with time elapsed during irradiation by light of 253.7 nm, E' initially decreased with time, increased at a longer time, and then reached a limiting value asymptotically. From the result of the change in E' with time, it was assumed that the scission and crosslinking reactions occur simultaneously during ultraviolet light irradiation. Thus, the change in E' with elapsed time was expressed by the equation E; = Eb exp (-kit) + Eb.[1-exp ( -k z t ) ] , where E ; is the dynamic modulus at time t , Eb is the E' at t = 0, Eb. is the limiting value of E', and k l and kz are the rate constants. The apparent activation energies for k l and k z were 3.23 and 2.50 kcal/mole, respectively, and the former value agreed with the activation energy for the scission of the amide groups. The effects of the photodegradation on the temperature dispersion of nylon 6 were also investigated. On irradiation with light at 253.7 nm, the a-relaxation which appeared at about 90°C was broadened and the intensity of the y-relaxation at -95OC in the tan 6-versus-temperature curve was lowered. The B-relaxation which appeared at -45OC for the wet nylon 6 decreased its intensity.

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