Effect of photodegradation on dynamic mechanical properties of nylon 6

Abstract

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.

UV Effects on Materials

“…Fig. 15.3 Activation spectrum for density of nylon 6 irradiated in air for 6 h. Based on data from Yano and Murayama (1980) High temperature alone can cause degradation of material properties for many materials, and the activation spectra can be increased at higher temperatures (Feller 1994). That is, higher temperatures can increase the photodegradation effects on materials.…”

“…The greatest bleaching effect on wool occurs around 450 nm but yellowing of wool is generated primarily by wavelengths below 360 nm (Lennox and King 1968). For nylon, the change in density and the elasticity as a function of UV wavelength has an apparent peak at 250 nm (Yano and Murayama 1980). Polymers may have absorption spectra with various peaks depending on the type and nature of the chromophores they contain (Gijsman et al 1999).…”

Accelerated Aging, Photochemical and Thermal Aspects

“…The work of Yano and Murayama (1980) serves as an additional example of the precise determination of the influence of wavelength. Films of nylon 30-micrometers thick were exposed to the radiation of a 2-kW xenon lamp dispersed in a grating spectrometer (Nihonbunko Co., model CRM-FA).…”

“…In this example, one type of resin (electron cured) was seriously affected by the source of radiation employed, whereas another (UV cured) was not. (Yano and Murayama 1980). Reproduced with permission of the publisher.…”

“…Hirt and Searle did this with sunlight in their original studies (Hirt et al 1959). The Japanese have used a similar approach in which the sample is placed in a spectrograph so that the dispersed wavelengths strike across the sample (Shimada and Kabuki 1968b;Johnson et al 1969;Yano and Murayama 1980;Kenjo 1985). In Australia, Holt and Waters (1985) similarly exposed wool to various narrow wavelength regions using a Jasco CRM-FA Spectroirradiator.…”