Stability of paper

Treated papers should maintain at a pH in the range 7 and 8.5. The pH should not be higher than 8.5 to prevent alkaline hydrolysis of cellulose. The acidity or alkalinity may be determined as the amount of water-soluble acidity or as the hydrogen ion concentration (pH) of the paper extract. The pH is more indicative of the stability of paper than is the total acidity. The pH can be determined by either a hot or cold extraction method. In the cold extraction method,... 

Fold Loss Rate. A direct way of evaluating the effect of the morpholine process on the stabilization of paper is to measure the rate at which its folding endurance deteriorates before and after treatment. Figure 4 typifies the effect. The two lines are for the same paper aged in a dry oven at 100°C the line with the lesser slope reflects morpholine-treated... 

The data show that pH is not the only indicator of stability of paper, and that folding endurance is not a universal method of measuring degradation. For example, one would have expected the three alkaline papers to have retained a much higher percentage of their initial folding endurance (26). 

TAPPI Standard Method T-453ts-63, Relative Stability of Paper (by... 

The stabilities of bleached kraft paper samples containing copper and iron species were compared before and after neutralization. Paper samples with copper(II) and iron(II) species adsorbed from their sulfate solutions were treated with sodium bicarbonate solution to neutralize acidic species. Excess sodium bicarbonate was washed away. Thus, no extraneous cations were introduced in this treatment, and the formation of any complex with the transition metal species was thereby precluded. Therefore, any stabilization observed as a result of this treatment can be ascribed only to the neutralization of acidic species in the test paper. A decrease in acidic content would inevitably enhance the stability of paper toward acidic hydrolysis. The stability of the test samples may be further influenced if the neutralization treatment affects the nature of the catalytic species or if the acidic species in paper also participate in the oxidation process. 

To address a diverse but related concern, the effect of chelation of adsorbed copper and iron species on the catalytic degradation of paper was investigated. The stability of paper containing copper and iron species adsorbed from ionic solutions was compared with that of paper containing the acetylacetonate chelates of these metals. Nonpolar acetylacetonate complexes of metals have no affinity for adsorption on paper. These copper and iron chelates are neither adsorbed nor chemically bonded to the paper matrix. 

Tang and Jones (33) and Nelson et al. (34) have shown that the washing of paper by immersion in pure water can adversely affect its permanence. Some papers were shown to have an appreciably lower stability after washing with deionized or distilled water, whereas they remained relatively unaffected after washing in tap water. Similarly, Eirk (35) demonstrated that the immersion of paper in organic solvents can also affect its permanence. These observations suggest that the adsorption of catalytic species from a solvent bath, as practiced here, must lead to a compound effect on the permanence of test samples. To focus this study on the catalytic effect of copper and iron species, it was necessary to exclude as far as possible the influence of the solvent wash on the permanence of paper. Therefore, the stability of paper samples containing different metallic species was compared with that of control samples washed with the same solvent or solvent mixture as that used in the sorption of the metallic catalysts. 

Rates of degradation observed in the presence of ionic iron and copper systems have been compared with those obtained for the respective acetylacetonate chelate systems in Tables X and XI. Lower relative lifetime and relative stability values are observed for the copper(II) acetylacetonate catalyzed system than those obtained in the presence of higher concentrations of the ionic copper species. A similar increase in the catalytic efficiency of copper upon coordination has been reported by Ericsson et al. (10). However, iron(III) acetylacetonate shows no catalytic effect at all. This observation of contrary effects on the stability of paper with the same chelates of two highly active transition metal catalysts is most interesting. Unlike the relatively stable octahedral iron(III) acetylacetonate molecule, the tetrahedral, tetracoordinate copper(II) chelate could accept two more ligands if it were to assume an... 

Stabilization of Paper Through Sodium Borohydride Treatment... 

The treatment of bleached kraft pulp with sodium borohydride followed by incorporation of basic calcium salts increased the stability of paper made from this pulp by 1.5-2.6 times. When manufactured paper, rather than pulp, was subjected to sodium borohydride treatment followed by washing with an aqueous solution of calcium hydroxide, the stability of the paper increased by as much as 4 times for groundwood paper and 30 times for bleached kraft paper. 

The effect of a reducing sodium borohydride treatment followed by a mildly alkaline wash on the physical properties and stability of paper was studied. Test papers were characterized by measuring their initial pH value, brightness, and folding endurance. Then they were subjected to borohydride treatment and washed with dilute calcium hydroxide solution or deionized water. The concentrations of sodium borohydride... 

The stability of paper made from pulp reduced by sodium borohydride in the presence of calcium hydroxide or carbonate was studied. 

The fibre lignin content is a central issue since high lignin contents tend to impact negatively on strength development in paper and paper wettability, as well as on the long-term stability of paper. Figure 7.2 shows... 

Furthermore, the moisture content of paper impacts the dimensional stability of paper and board products. The physical dimensions of materials made of paper are sensitive to the moisture content as well as the history of its change. Most paper materials expand with moisture content due to the swelling of the fibers. This swelling is anisotropic and is predominant in the radial direction of the fibers. As a consequence of non-uniform fiber distributions inside them, paper sheets tend to curl and deform on a small scale locally. The local deformation is termed as cockle. Hence, knowledge of the interaction of moisture with paper will help in producing more dimensionally stable products [7]. 

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