Experimental

All work was conducted using standard hydrogen peroxide bag bleaches. Bleaches were conducted at 15% peroxide for 2 h in which trace peroxide residuals were determined after the bleach. All bag bleaches were outfitted with several bags due to extensive gas production during the bleach. All runs were done at temperatures of 90 °C and conducted at 10% iron. A caustic solution of pH 12 was used for all make-up water, which was added to maintain all pulp-water solutions at a 10% solid level (mass of pulp/mass of pulp and water). A base-bleached sample was designated, as the H2O2 sample had the iron separated by several days of mixing on a magnetic stir plate in which the iron was extracted. Iron could not be easily extracted with normal washing. "25%" iron level sheets (m/m) were made by adding additional iron powder to the bleached pulp to achieve the mass balance ratio required. Tensile strength was tested using the TAPPI standard method on random handsheets. SEM was conducted using standard operational conditions. Surface carboxylic acid group levels were determined by standard potentiometric acid titration procedures. All percentages of iron were determined via ICP. Volume and surface resistivity

Figure 13.1. Setup for measure of magnetic susceptibility

were determined by ASTM D4949-94 and determination of DC resistivity of writing paper (Keithley Method). Magnetic susceptibility was determined using the setup depicted in Figure 13.1. The interpolar distance, l, for threshold of attractive adherence to the poles of the magnet was measured.

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