Re-pulping of wet strength paper (2)

1.2 Handsheet process The pH of the recovered pulp and puree (concentration 0.5%) was adjusted to 7 using a 8inMark IV type dynamic sheeter to make a handsheet of 4g in weight and rolled on the felt by hand. The wet paper sheet was pressed, dried on a 105°C Williams dryer for 10 minutes, aged in an oven for 10 minutes, and the dry tensile strength of the handsheets was measured using an Instron tester.
2 Discussion Paper samples from this study were taken from several paper mills in the United States and listed in Table 1. The paper sample contains PAE or polyamine-epichlorohydrin wet strength resin, and the amount of wet strength resin contained is provided by the factory. Paper samples C-F were also sized using 0.1% to 0.2% AKD. The (% wet/dry) wet strength of paper is greater than 20%.
Table 1 Industrial paper used in the repulp study. All paper samples contained PAE wet strength resin. B used wet strength agent in polyamine-epichlorohydrin paper. %
Unbleached cardboard A 0.6
Unbleached cardboard B 0.4
Unbleached surface board C 1.0
Bleached advertising cardboard D 1.0
Unbleached Advanced Packaging Paper E 1.0
Unbleached raisin color tray paper F 1.0
The sample was treated with the reagent at a specific temperature and pH, placed in a sealed stainless steel container, and gently stirred with a three-blade propeller. Except that potassium persulfate (KHSO5 or MPS) is added as a trimeric salt, the oxidizing agent is active when added. During the repulping test, the stirring is carefully controlled to increase the performance of the reagents used in the process. After treatment, the pulp mixture (A-D) was cut in a rod fiber disintegrator at 3000 r/min for 3 min, and the paper samples (E, F) required 6 min. Paper samples E and F require greater shear force to completely disintegrate the fibers, probably due to the high content of AKD in the paper.
2.1 Alkaline repulping Bleached and unbleached paper containing permanent wet strength resins (PAE or polyamine-epichlorohydrin) is repulped at a pH of 11, despite the addition of various forms and amounts of oxidizing agents. The effect is still not good (see Table 2). The repulping of the unbleached paper B, using sodium hypochlorite as the oxidizing agent, requires at least 0.4% of the wet strength resin in the paper. Because the effect is very poor, it cannot be tested with sodium hypochlorite. The propoxylate-added linear alcohol (rewetting agent) reduces the surface tension of the repulping solution (from 60 to 28 dynes/cm), improving the wetting of the paper sample A, but this also does not improve the repulping effect. For bleached advertising cardboard containing 1% PAE resin and AKD sizing agent, the effect of the reagents used was also poor.
Table 2 Alkaline pulping of bleached and unbleached paper containing PAE and polyamine-epichlorohydrin wet strength resin at a temperature of 70° C. After treatment with a reagent, shearing at 3000 r/min for 30 min, adding NaOH to adjust the pH To 11
Reagent dosage, % pH re-pulping time, min Re-pulping ratio, %
Unbleached paperboard A NaOH 7.0 11 60 50 Na2S4O8 1.0 11 60 66 KHSO5 1.0 11 60 66 KHSO 5+0.1% 5.0 11 60 67 Then add moistened unbleached board B NaOH 7.0 11 60 64 Na2S4O8 10.0 11 60 74 KHSO5 10.0 11 60 77 NaOCl 10.0 6 60 15
Unbleached board C NaOH 7.0 11 60 32 Na2S4O8 10.0 11 60 58 KHSO5 10.0 11 60 61
Bleached advertising cardboard D NaOH 7.0 12 60 48 Na2S4O8 2.5 11 60 56 KHSO5 2.5 12 60 58

(to be continued)