A spectroscopic study of photoirradiated cellulose

Abstract

The influence of photoirradiation on cellulose was studied by means of fluorescence, Fourier transform IR and UV—visible reflectance spectroscopy. Samples of cellulose were irradiated with the entire spectrum of a medium pressure Hg lamp, with the light from the Hg lamp filtered through a glass filter, or selectively with monochromatic light of different wavelengths. The emission spectra of untreated cellulose samples and of differently irradiated samples were recorded after various exposure times. Irradiation with the unfiltered radiation from the Hg lamp caused a strong increase in the emission intensity and a gradual shift in the emission maximum to longer wavelengths. After irradiation for 96 h a pronounced band at 1733 cm −1 was seen in the diffuse reflectance IR Fourier transform spectrum of the sample, indicating the formation of carbonyl groups as a result of the treatment. Irradiation with filtered light from the Hg lamp caused a small decrease in the emission intensity and shifted the emission maximum from 445 to 462 nm. Exposure of cellulose to monochromatic light of 350 nm wavelength caused a gradual fading of the fluorescence with increased exposure time and a small shift in the emission maximum to longer wavelengths. After the sample had been allowed to stand in the dark, the emission intensity was almost completely restored to its original value, but the red shift of the emission maximum caused by the irradiation remained unchanged.