Ultraviolet Stability of Crosslinked Polycaprolactam Systems

The relative ultraviolet stability of four chemically modified polycaprolactam (Nylon-6) systems is discussed: methylmethoxylated fibers and three other fibers having methylene, disulfide, and alkylene sulfide crosslinks, respectively. The ultraviolet degradation of these systems is studied by means of a sensitive analytical technique in which the methylene (—CH2—) groups remaining in the chemically modified fibers after irradiation are converted to formaldehyde; the liberated formaldehyde is then reacted with chromotropic acid to give a colored product, the absorbancy of which can be determined spectrophotometrically. The results indicate that the data can be expressed by first order rate equations from which the rate constants may be calculated. The scission of the crosslinks is accompanied by a decrease in the internal orientation of the networks as shown by X-ray diffraction photographs.