PHOTOYELLOWING OF UNTREATED AND ACETYLATED ASPEN CHEMITHERMOMECHANICAL PULP UNDER ARGON, AMBIENT, AND OXYGEN ATMOSPHERES

Abstract

Untreated and acetylated hydrogen peroxide-bleached aspen chemithermomechanical pulp (CTMP) was subjected to accelerated light-induced aging in various atmospheres (argon, ambient, or oxygen). The photochemical changes that took place during irradiation were followed by solid-state UV/VIS diffuse reflectance spectroscopy. The degree of photoyellowing of the untreated CTMP decreased when the air in the surrounding atmosphere was replaced with oxygen-free argon. The decrease was only moderate, indicating that atmospheric oxygen is not of sole importance for the light-induced discoloration or that only a trace amount of oxygen (strongly adsorbed to the fiber material) is necessary to cause discoloration. Acetylation clearly diminished the kinetics of photoyellowing in all atmospheres resulting in substantially less absorption in the entire visible range (λ > 400 nm). However, the development of chromophores was attenuated in an oxygen-enriched atmosphere, suggesting that oxygen is important for the color-retarding or photobleaching reactions of acetylated lignocellulosic materials. Independently of the degree of acetylation and the surrounding atmosphere, irradiation with UV/VIS fluorescent lamps generated an apparent absorption maximum around 360 nm with a shoulder at approximately 420 nm.

ACKNOWLEDGMENTS

The authors gratefully acknowledge the United States Department of Agriculture for support (Agreement Nos. 96-35103-3800 and 98-35501-6911).