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Literature is strongly contradictory about the molecular reasons for yellowing and brightness reversion of pure (lignin-and hemicellulose-free) celluloses, such as in highly bleached pulps, bacterial cellulose, or cotton linters. While oxidized groupscarbonyls (CO) and carboxyls (COOH)-have been recognized as the initiators of yellowing, they are generally always found together; thus, their effects are permanently superimposed in real-world cellulose. For this reason, their individual contributions could not be reliably determined. To tackle this conundrum, we have used a two-stage study: the employment of glucopyranose-derived model compounds and the use of special cellulosic pulps. Both substrates had either only carbonyl functions, only carboxyl functions, or defined ratios of both functionalities present at the same time. The model compounds alone already provided strong indications of the CO-related and COOH-related effects, and further confirmation was obtained by the pulp study. Here, in regard to the polymer case, the carbonyl groups are the minimum functional unit in cellulose responsible for chromophore generation (termed as the ''CO effect''). The carbonyl groups are the precursors for the chromophores that are formed later upon yellowing/ aging. Chromophore formation increases strictly linearly with the carbonyl content at a constant given carboxyl content. Carboxyl groups alone (i.e., in the absence of carbonyl groups) are fully innocent regarding the color generation. However, they have a

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Mass deacidification has been an important topic in cellulose science and will continue to be a critical issue as long as acidic books and paper-based materials are-a often major-part of library and archive stocks. Different means are available to judge the result of a deacidification treatment and to address its sustainability and efficacy. The present study compares deacidification by dispersed particles with procedures that apply homogeneously dissolved alkaline compounds, both under humid and dry accelerated aging conditions. Analysis by size-exclusion chromatography coupled to light scattering detection is used in combination with accelerated aging. The number of chain scissions, i.e. cellulose degradation, is the parameter used for evaluation, expressed as stabilization factors relative to the non-treated specimen. Upon deacidification with homogeneous solutions stability factors of about four were reached, while deacidification with dispersed particles gave only two times longer life times (stability factor of two). Mechanistic aspects are discussed in terms of alkaline reserve, cellulose degradation and mobilities of deacidification agents.

As papers become acidic and brittle over time, libraries apply mass deacidification processes to their collections in order to neutralize acids and deposit an alkaline reserve in the paper. Books commonly treated by mass deacidification have undergone natural aging of up to 150 years. The risk of alkali-induced degradation of cellulosic material upon mass deacidification remains uncertain. In the present study, the extent of b-elimination-type degradation reactions was investigated by comparing deacidified and non-deacidified counterparts, using deacidified library materials and identical issues of non-deacidified books from second-hand book shops. The study dealt with only naturally-aged papers focusing on investigation of immediate effects of mass deacidification rather than a long-term impact. Gel permeation chromatography coupled with carbonyl group labeling gave insight into cellulose chain cleavage as well as into the behavior of oxidized functionalities. Processes occurring under natural aging conditions were compared to those upon artificial oxidation of model pulps. Library books did not show a significant reduction in molecular weight after mass deacidification compared to the non-deacidified controls, which stands in contrast to oxidized model pulps. The models showed a more pronounced loss of molecular weight upon deacidification treatments. A decrease in carbonyl groups other than reducing ends was found to occur. Thus, oxidized functionalities were found to be reactive in massdeacidification reactions; the different behavior was traced down to particular regions of oxidative damage along the cellulose chains. In general, b-elimination processes did not pose a large risk factor upon mass deacidification treatments of the naturally-aged library material tested.

Historical papers are often locally damaged by exogenous influences and/or have endogenously degraded paper areas. The stabilization of such papers is very important because further use of the object can cause additional damage. Different types of nanocellulose are interesting as a novel stabilizing materials for paper due to their close structural relation to the paper matrix. Therefore, the present study investigated whether the treatment of historical papers with nanocellulose suspensions is a novel method for paper stabilization. Two different types of nanocelluloses, bacterial cellulose and a mechanically nanofibrillated cellulose based on wood pulp, were tested with regard to their performance in stabilizing fragile papers. Concerning material handling and application in conservation steps, different ways to modify the suspensions were tested. The resulting suspensions were applied to historical papers from several centuries with different extents of damage. The paper-nanocellulose composites were characterized with regard to their optical and microscopic integrity and by physical and chemical analyses. The treatment of mechanical damage and the consolidation of weakened paper areas could be realized by the application of a nanocellulose suspension without an additional adhesive. The results of the treatment depend on the type of nanocellulose, on the paper material, on processing and application techniques. The paper discusses the applicability and stability of the differently prepared nanocellulose suspensions, also with regard to their mode of application and long-term performance. Advantages and limitations are addressed in detail.

According to published studies, certain nonaqueous solution-based treatments can be highly effective for prolonging the useful lives of bound volumes, within which the paper had been formed under acidic papermaking conditions. Such treatments, which typically use reactive alkoxide-based organometallic compounds dissolved in low-surfacetension liquids, have been shown to decrease the tendency of the paper to become brittle during long storage or during accelerated aging. This article reviews published evidence concerning the underlying mechanisms of such treatments. Evidence suggests that dissolved alkoxides and related carbonated alkoxide-based compounds are able to react directly with acidic species within acidic paper during treatment of books. Such reactions help explain the demonstrated effectiveness of nonaqueous solution-based deacidification treatments.

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