In hydrogen peroxide bleaching of thermomechanical pulp (TMP), reaction temperature and time are the main factors that can improve the bleachability of pulp fibers. However, high temperatures can induce some problems such as cellulose degradation, yield loss, low fiber strength, and high environmental load. These negative effects of high temperature are mainly caused by radicals formed from the decomposition of hydrogen peroxide. To avoid the adverse effects of high temperature, we used two-step thermal treatments during hydrogen peroxide bleaching of TMP. The temperatures used in the two-step thermal treatments were 80 and 45 ˚C for a total bleaching time of 1 hour. In H2O2 bleaching of TMP, two-step thermal treatments were found to have had positive effects on the optical and physical properties of the pulp. The ISO brightness of the pulp bleached by two-step thermal treatments with hydrogen peroxide was identical to that of pulp bleached by conventional hydrogen peroxide bleaching. The post color number (PC number) of TMP was sharply increased after bleaching at 80 ˚C for 40 minutes. The post color number of TMP bleached by two-step thermal treatments is lower than that of TMP bleached by a one-step thermal treatment. The zero-span tensile index was also improved by two-step thermal treatments.
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