Brightness reversion

Since all of the model compounds examined were monomeric lignin-like structures, our current studies do not address the possibility of an intramolecular photochemical initiated reaction contributing to brightness reversion. Investigations directed at examining this latter issue are ongoing. 

Figure 12. Effects on brightness reversion of individual subfractions from...

Fomier de Violet, P., Nourmamode, A., Colombo, N., and Castellan, A., "Study of Brightness Reversion of Bleached Chemithermomechanical Pulp by Solid State Electronic Spectroscopy", Cellulose Chem. Technol., 1989, 23, 535. 

Francis, R.C., Dence, C.W. and Alexander, T.C., "Method For Reducing the Brightness Reversion in Lignin-Containing Pulps and Article of Manufacture Thereof, United States Patent 5,080,754, Jan. 14, 1992. 

The use of optical tests in the characterization of paper materials ranges from color analysis and matching to the standard techniques of chemical analysis by ultraviolet, visible light, and infrared spectroscopy. The test for yellowing, or brightness reversion of pulps and papers is often used as an indicator of their long term stability. 

Aging of bleached pulps in presence of high humidity results in higher values of peroxide formed than aging at low humidity. The total amount of peroxide increases linearly with the time of aging.. . . Moisture was found to promote not only peroxide formation but, to some extent, also, brightness reversion, particularly in absence of air. Aldehyde groups formed by hydrolysis were found to be involved in peroxide formation. 

Copper on the Brightness and Brightness Reversion of Oxidized Cellulose, Pulp Pap. Mag. Can. 1966, 67, T114-118. 

Spinner, I. H. "Brightness Reversion A Critical Review with Suggestions... 

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. 

Brightness reversion or yellowing has been attributed in the past to nearly every constituent of pulp and paper. A considerable amount of work has been published in recent years on the influence of various pulp constituents on brightness reversion. Yet, the mechanism of the color reversion is of a complex nature, and the various pulp constituents can either contribute directly or react with each other. 

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. 

In his excellent review paper, Spinner has summarized the factors causing brightness reversion (10). They are adapted as follows ... 

Other minor pulp constituents, the resins or extractives, also have pronounced bearing on brightness reversion (161-165). In removing the resin in a bleached sulfite pulp by extracting with alcohol, Tongren found that the reversion rate was reduced (162). Giertz (163) lowered the reversion of bleached sulfite pulps to about one-third of their original value by alcohol-benzene extraction. Aalto (164) found that an ether extraction of a sulfite pulp prevented reversion to some extent. It should be borne in mind that not all resin components cause reversion, but when resin does, the resultant reversion appears to be approximately linear with the resin content. 

In the preceding sections, discoloration and brightness reversion were discussed. Chemical constituents in modem papers exhibit a wide range of susceptibilities to oxidation that can be explained in part by differences in structures. Stabilization of color against thermal and photooxidation can be enhanced by modification of the polymer structure to eliminate the more reactive sites or chromophoric functional groups and to introduce groups that contribute to color stabilization. 

J.H. Spinner Brightness reversion. A critical review with suggestions for further research//"(1962), No 6, 495-514. 

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