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Among bleaching agents available in paper conservation, hydrogen peroxide (HP) is a versatile choice that has many advantages in the removal of discoloration from paper. However, its well-known radical formation in the presence of iron impurities in paper poses the risk of cellulose degradation and color reversion, i.e. return of staining. This study explores a method to diminish undesired HP reactions by adding an additional step using a calcium phytate solution as complexing agent to the recommended treatment sequence. Tests on model papers impregnated with different molar concentrations of iron ions to trace the effects of simulated HP treatments on weight average molar mass, carbonyl group content, and color indicate that the iron phytate complex is sufficiently stable to sustain limited HP bleaching and thereby keeps the iron ions to a certain extent from the reaction system. [ABSTRACT FROM AUTHOR]

An etching that was visibly damaged as a result of previous bleaching with a 5.6 % aqueous sodium borohydride solution underwent retreatment involving washing to stabilize the embrittled paper and to remove potentially present bleaching residues. During a final immersion in a dilute calcium hydrogen carbonate solution administered for deacidification, an unexpected and severe blistering occurred that is explained as a recurrence of previous bleaching-related blistering. The blisters were laid down. The treatment concluded with a consolidation of the bleach-damaged paper surface using a 0.5 % gelatine solution applied by misting. [ABSTRACT FROM AUTHOR]

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Abstract: The dihydroxyacetophenones 2,5-dihydroxyacetophenone (2,5-DHAP) and 2,6-dihydroxy-acetophenone (2,6-DHAP) belong to the key chromophores in cellulosic materials. The pulp and paper industry targets these key chromophores in their bleaching sequences to obtain brighter products. 2,5-DHAP and 2,6-DHAP were degraded with hydrogen peroxide in alkaline media, similar to conditions of peroxide bleaching (P stage) in industrial pulp bleaching. Degradation product analyses were performed by GC-MS and NMR. The degradation reaction starts by loss of acetic acid originating from the acetyl moiety of the dihydroxyacetophenones (Baeyer-Villiger rearrangement). Further reaction steps involve introduction of another hydroxyl group at C-1 (previously acetyl bearing), and further oxidation of the resulting trihydroxybenzene to quinone intermediates which are ultimately degraded to a mixture of low-molecular weight carboxylic acids. Graphical Abstract: [ABSTRACT FROM AUTHOR]

2,5-Dihydroxy-[1,4]-benzoquinone (DHBQ) is one of the key chromophores in cellulosics. Due to its special resonance stabilization, it is a prime survivor of bleaching treatments and its degradation is essential in pulp bleaching. The clarification of the degradation mechanism of this compound is indispensable for targeting improvements of pulp bleaching processes. Previous studies revealed that DHBQ degradation by hydrogen peroxide (H2O2) is influenced by salts. This study addresses the effects of alkaline metal salts, alkaline earth metal salts, and Al2(SO4)3 on the degradation of DHBQ under simulated conditions of pulp bleaching in a peroxide stage. The degradation by excess H2O2 followed first-order kinetics in the presence of alkaline metal salts and alkaline earth metal salts, which enhanced and retarded the reaction, respectively. Kinetic studies and theoretical computations provided detailed mechanistic insights: Li+, Na+, and K+ stabilize several reaction intermediates by complex formation, causing the enhancement of the degradation, whereas Mg2+ and Ca2+ coordinate and stabilize the reactant, resulting in the observed retardation. Al2(SO4)3 exhibited a strong enhancing effect, but the degradation followed second-order kinetics with regard to DHBQ, suggesting a fundamentally different degradation mechanism. [ABSTRACT FROM AUTHOR]