FORMATION OF FREE RADICALS IN PHOTOIRRADIATED CELLULOSE - 6. EFFECT OF LIGNIN.

Abstract

The effect of lignin on free-radical formation in photoirradiated pulp was studied by means of electron spin resonance spectroscopy. Samples were irradiated with light of wavelength longer than 3400 A as well as longer than 2537 A. Radical formation in aspen lignin was observed before and after irradiation with light of wavelength longer than 3400 A. Upon irradiation, free radicals were formed in a pulp sample with 0% lignin content only when oxygen was present. On irradiation with light longer than 2537 A, in the presence of nitrogen, oxygen, and under vacuum, free-radical formation was found in all cases. The largest concentration of radicals was obtained under vacuum, the smallest in oxygen. It is evident that cellulose was protected from radiation by the presence of lignin. Irradiation with light in the presence of oxygen caused significant yellowing of the pulp sample, and these photooxidation and discoloration reactions occurred primarily on the surface of the sample irradiated.