Foldur Kraft

Materials. All paper samples were cut from a continuous length of machine-made rolls. Two different papers have been studied. One is a bleached Kraft wood pulp waterleaf (50-lb basis weight) made by Neenah Paper Mills from a stock that comprised northern softwoods (60Z) and Lake States hard woods (40J), and contained no additives. The second paper, Foldur Kraft, is a bleached Kraft paper (70-lb basis weight) made by Champion Paper Company from a stock of 90Z softwoods and 10Z hardwoods, with alum-rosin size and 8Z titanium dioxide filler. This paper was obtained 15 years ago. Since then it has been stored indoors in areas which have not enjoyed a carefully regulated environmental control. 

Of the two test papers employed in this study, the wood pulp waterleaf better represents natural cellulose, while Foldur Kraft paper, which is sized with alum-rosin, is fifteen years old and also fairly acidic, more closely resembles average library book paper. Both the papers were aged as sheets freely suspended on a rack, as... 

Figure 3 Effect of relative humidity on fold endurance of Foldur Kraft sheets aged at 90°C.

Effect of relative humidity on pH of Foldur Kraft paper... 

Foldur Kraft —Barrow Magnesium Bicarbonate Treatment° ... 

Hours in Oven Table V. Foldur Kraft—1% Na2C03 Fold Hr rn p meq/kg... 

Table VI. Foldur Kraft—50 ppm Copper, Magnesium Bicarbonate...

Foldur Kraft—50 ppm Copper, Barrow Two-Step Calcium Treatment... 

Allied Superior Offset Gov t. Printing Office JCPA-60 Champion Foldur Kraft... 

Figure 5. Plot for heating rate vs. reaction peak temperature for paper oxidation reactions. O, Foldur Kraft , JCPA-60 V, Allied Superior.

The above results agree with those of the folding endurance test carried out at 100°C—i.e., the Allied paper is most stable, the Foldur Kraft least stable, and the JCPA-60 is intermediate. 

Sample Preparation. Two papers were selected. One was Champion Foldur Kraft, a bleached southern kraft paper, containing rosin size and fillers, from a single roll of known composition. The other paper was newsprint that had already been cut into sheets when received by the laboratory. The newsprint was analyzed as follows 80% groundwood and 20% unbleached sulfite. 

For each paper, both Foldur Kraft and newsprint, there were ten sample sets and one unwashed set, which was used as a control. The air dried samples were subjected to accelerated aging in humid (90°C/50% relative humidity) and dry (100°C) circulating air ovens for one, two, three, and five weeks. At regular seven-day intervals one sheet from each sample set was removed and tested. 

Table II shows the calcium content in paper from the chemical feeder process. With the addition of 9.2 ppm Ca in DI water, the treated newsprint papers calcium content doubled in comparison with the control. The treated Foldur Kraft paper contained three times more calcium than did the unwashed paper. The more calcium that was added in the DI water, the higher the amounts of calcium absorbed in the papers during the washing and deacidification process. However, the absorption of calcium in the paper reached a saturation point. This is the reason why newsprint and Foldur Kraft papers that are treated with 36.4 ppm Ca in the Dl-Ca water imbibed the same amount of calcium as the papers washed with 112.8 ppm Ca in the Dl-Ca water.

Figure 2. Foldur Kraft paper washed for 1 h in chemical feeder process...

Table V. Aging Tests on Washed Paper, Effect on Brightness, Foldur Kraft Paper...

JCPA60 Foldur Kraft Newsprint Mead Bond Whatman 1 Superior Offset Book... 

The effect of impregnating Foldur Kraft with Kymene, with sorbitol, and with Kymene and sorbitol together is shown in Table II. The synergistic action of the two reagents on folding endurance is readily apparent. 

Further work was carried out with Foldur Kraft. However, the presence of the unusual effect was also demonstrated with GPO JCPA-60, which is the paper used in printing the Library of Congress Information Bulletin and Allied Superior book paper. Properties of the papers are given in Table III and the results when the papers were impregnated with Kymene and sorbitol in Table V. 

The cured sheets were conditioned at 23 °C and 50% relative humidity. MIT folding endurance was run on 1.5-cm wide strips at 0.5 kg load. Tensile was taken on the same width strip. Eight strips were run machine direction and eight cross direction. As mentioned by Raff et al. (4,5), standard deviation and coefficient of variation were increased greatly in the treated plasticized paper for example untreated Foldur Kraft gave ... 

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