Brightness reversion, problem

Brightness reversion is one of the serious problems for paper industries, restorers, paper conservators, and librarians, because the brightness of neither unbleached nor bleached pulp is permanent, and the causes and prevention of reversion still are not known entirely. 

At the First International Bleaching Conference at Appleton, Wisconsin, in 1955, in the final panel discussion on bleaching problems, fourteen theories were put forward to account for brightness reversion. They are listed here for reference purposes (a) residual lignin (b) furfural (c) reductone formation from carbohydrates (d) residue resin (e) poor washing (f) pH (g) metallic catalysts (h) metallic resinates (i) diffusion (j) carbonyl groups (k) water impurities (1) microorganisms (m) low bleach residual and (n) UV radiation. 

The second category involves membrane processes, a contemporary topic of considerable importance with the promise of a bright future. Among the subcategories considered here are reverse osmosis, hemodialysis, and membrane gas separation, and the text provides some useful relations to address problems in these areas. 

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