Re-pulping of wet strength paper (1)

For paper mills, waste paper fiber is an important source of raw materials, with economic advantages, paper mills can use fibril and secondary fiber copying and reuse paper and paper cut edges to reduce raw material costs.
As the demand for secondary fibers increases, paper made using permanent wet strength resins such as polyamide polyamine-epichlorohydrin becomes an important fiber raw material. However, these papers, especially unbleached paper and waste corrugated cartons (OCC), are difficult to repulp.
Sodium Hypochlorite is generally used for repulping of bleached wet strength papers because it cannot completely repulping unbleached wet strength papers and environmental regulations require paper mills to reduce the production of absorbable organic halogen (AOX) waste water produced, thus limiting the The use of sodium hypochlorite.
It has been reported that peroxydisulfate (M2S2O8) and potassium persulphate (active ingredient in trimeric salt 2KHSO5.KHSO4.K2SO4 is KHSO5) are effective agents for repulping of bleached wet strength paper. However, under the normal neutral or alkaline repulping conditions, this reagent is less effective for OCC wet strength paper and unbleached paper.
We do not expect side reactions between oxidants and lignin to make unbleached paper difficult to re-slurry. An oxidant that breaks down into free radicals can extract hydrogen from lignin to form inactive radicals, leaving behind the largest amount of unoxidized The wet-strength resin with excess oxidizer can overcome the side reactions. However, this is expensive, inefficient, and has damage to the fiber.
After further study of the chemical properties of organic and inorganic peroxides, it was found to be important in the oxidation-reduction and polymerization processes. Under appropriate reaction conditions, the oxidant is activated by the metal or forms a radical by thermal decomposition.
A large number of reactivated radicals can extract hydrogen or other atoms from saturated and unsaturated reactants, add to unsaturated reactants to combine with other radicals or polymerize into dimers, or undergo redox reactions. , including electron and ligand transfer processes. The reactants such as polyhexamethylene diamide (NyLon-6.6), a linear polyamide similar to the PAE backbone, are oxidized by H2O2 ions.
It has been reported that an oxidant catalyzed by a metal ligand undergoes a nucleophilic reaction with amines on the oxidized reactants by an oxidation reaction, cleaving the polypeptide. The reaction between hydroxyl groups in hydrogen peroxide and model compounds representing phenol and non-phenol nuclei in lignin was found to be dependent on the pH of the reaction.
The above studies have shown that free radicals can effectively repulase unbleached wet-strength paper under conditions conducive to radical wet-strength resin reactions rather than free radical lignin reactions. In this study, inorganic oxidizers were used to test the repulping of wet strength paper. pH, time, temperature, rewetting agent, shear force and reagent concentration all had effects on repulping.
The repulped pulp was screened with a vibrating screen having a gap of 0.15 mm, and the degree of repulping was quantitatively determined. In this study, dry tensile strength comparisons were made with repulped handsheets and base paper. In addition, the new repulping process performance was compared with alkaline unpigmented board repulping process in different paper mills.
1 Experiment 1.1 Re-pulping process 1.1.1 Alkaline process Industrial paper was cut into pieces of 1×1 in, diluted with tap water containing iron and copper of less than 0.15 ppm and 0.30 ppm to a concentration of 2%, and heated to Before the desired reaction temperature (70-90°C), the pH was adjusted to 11 with NaOH solution while gently stirring the pulp. If an oxidizing agent is needed, add NaOH and adjust the pH to 11. Then, the pulp was mixed at the reaction temperature for 60 min, sent to a fiber separator, and sheared at 3000 r/min for several minutes. The screen was screened for 20 min using a vibrating screen with a gap of 0.15 mm. The screen residue (non-distilled components) was dried at a temperature of 105°C.
1.1.2 Two-stage pH process The industrial paper was cut into 1×1 in pieces and diluted with tap water with iron and copper ion contents of less than 0.15 ppm and 0.30 ppm to a concentration of 2%. Optionally, a humectant may be added and the pH adjusted with a mineral acid, in the range of 3-7, while gently agitating, prior to heating at the desired reaction temperature (ie, 70-90°C).
Add oxidizer and mix for at least 30 minutes at reaction temperature. The pH was then adjusted to 11 with NaOH solution and mixed for at least 30 min at the reaction temperature. The pulp mixture was sent to a bar mill and sheared at 3000 r/min for several minutes. A vibrating mesh sieve with a gap of 0.15 mm was used to screen for 20 min to obtain a paper sample, which was dried at 105°C. (to be continued)