Process for improving stiffness of chemi-mechanical pulp fibers and chemi-mechanical pulp prepared by same

Abstract

The invention belongs to the technical field of papermaking pulping, and particularly relates to a process for improving the stiffness of chemi-mechanical pulp fibers and chemi-mechanical pulp prepared by the same, and the process comprises the following steps: (1) washing, extruding and presoaking chemi-mechanical pulp wood chips, and then carrying out high-concentration pulping to obtain pulp; (2) sequentially performing first-stage medium-concentration bleaching and second-stage high-concentration bleaching on the pulp subjected to high-concentration pulping; (3) squeezing the pulp subjected to the second-stage high-concentration bleaching, and enabling the pulp to enter a latency tank for latency; (4) the pulp subjected to latency elimination is subjected to low-concentration pulp grinding and then subjected to a screening procedure, accepted pulp enters multiple discs for pulp washing, and finally the accepted pulp enters a pulp storage tower through pulp squeezing; in the latency process, a compound additive is added, and the compound additive comprises a dispersing agent and a swelling agent. The stiffness of the prepared chemi-mechanical pulp fiber is improved, and meanwhile, the bulk and the tensile index are improved.

Description

Technical Field

[0001] This invention belongs to the field of papermaking and pulping technology, specifically relating to a process for improving the stiffness of chemimechanical pulp fibers and the chemimechanical pulp prepared therefrom. Background Technology

[0002] Mechanical pulps (such as BCTMP) are widely used in paperboard and cultural paper due to their high yield, low cost, and good bulk. Fiber stiffness is a key factor affecting the bulk, stiffness, compressive strength, and printability of finished paper. Poplar is one of the mainstream raw materials for mechanical pulps; however, poplar fibers are short and thick, and their natural stiffness is lower than that of coniferous wood. In existing production processes, insufficient fiber stiffness is often caused by the following problems: 1. Excessive fibrillation: Excessive or uneven energy input during pulping leads to excessive fiber crushing, fibrillation, and decreased rigidity. 2. Fiber cutting: Improper grinding tooth profile or parameters lead to excessive fiber cutting and a reduction in long fiber components; 3. Resin obstruction: Poplar has a high resin content, which affects fiber swelling and hydrogen bonding, reducing fiber stiffness; 4. Process fluctuations: Unstable parameters in processes such as preimpregnation, pulping, and de-emergence affect the consistency of fiber morphology.

[0003] There is a lack of systematic process solutions for improving the stiffness of poplar chemimechanical pulp fibers in the existing technology. There is an urgent need for an optimization method that can take into account fiber length, thickness, swelling degree and bonding strength. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a process for improving the stiffness of chemimechanical pulp fibers. This process improves the stiffness of the chemimechanical pulp fibers, while also increasing the bulk and tensile index. This invention also provides chemimechanical pulp prepared using the above process.

[0005] The process for improving the stiffness of chemimechanical pulp fibers according to the present invention includes the following steps: (1) The chemimechanical pulp wood chips are washed, extruded, pre-impregnated and then subjected to high-consistency refining to obtain pulp; (2) The slurry after high-consistency grinding is subjected to a first-stage medium-consistency bleaching and a second-stage high-consistency bleaching. (3) The high-consistency bleached pulp from the second stage is pressed and then enters the desulfurization tank for desulfurization. (4) After the low-concentration grinding of the pulp after the anti-potential process, the good pulp enters the multi-plate washing process and finally enters the storage tower through the extrusion process. In the anti-potential process, composite additives are added to the pulp, including dispersants and swelling agents.

[0006] Preferably, the process for improving the stiffness of chemimechanical pulp fibers includes the following steps: (1) After two stages of wood chip washing in the wood chip washing group, the wood chips enter the wood chip silo, and then enter the preimpregnator for one stage of preimpregnation after being extruded by the extrusion screw. The preimpregnated wood chips enter the reaction chamber and are then conveyed to the high-consistency mill by the leveler. The high-consistency mill produces pulp. (2) After the high-consistency pulping is completed, the pulp is dewatered by a cyclone separator to remove excess steam and chemicals. Then, the chemicals required for the first stage of bleaching are added to the chemical mixing screw. The pulp is then subjected to a first stage of medium-consistency bleaching in a medium-consistency bleaching tower. After the first stage of medium-consistency bleaching, the pulp is dewatered by a screw. Then, the chemicals required for the second stage of bleaching are added to the chemical mixing screw. The pulp is then subjected to a second stage of high-consistency bleaching in a high-consistency bleaching tower. (3) The high-consistency bleached pulp after the second stage is pressed by two rollers and then enters the de-deposition tank for de-deposition. In the de-deposition process, composite additives are added to the pulp in the de-deposition tank. The composite additives include dispersants and swelling agents. (4) After the slurry is de-concentrated, it enters the pressure screen after passing through two low-concentration grinding stages. The slurry from the pressure screen enters the slurry screen, and the good slurry from the pressure screen and the slurry screen enters the multi-disc washing screen. Then, it enters the slurry storage tower after passing through the slurry extrusion screw of the extruder.

[0007] Dispersants can remove the resin coating on the fiber surface, exposing the hydroxyl groups (-OH) of cellulose, which is beneficial for subsequent hydrogen bonding between fibers; swelling agents can penetrate into the fine structure of fiber cell walls, enhance the water absorption capacity of fibers, increase fiber diameter, thicken cell walls, make the structure of the fibers more complete, enhance internal hydrogen bonding, and improve fiber stiffness.

[0008] Preferably, the extrusion screw is an ADI screw.

[0009] Preferred anti-latency process conditions: temperature ≥ 85℃, time ≥ 45 min, slurry mass concentration 3.5%-4.5%.

[0010] Preferably, the dispersant is a polyoxyethylene ether dispersant, and the dosage is 0.5-0.8 kg / ton of slurry.

[0011] Preferably, the swelling agent is sodium carboxymethyl cellulose, and the dosage is 0.1-0.3 kg / ton of slurry.

[0012] Preferably, by mass fraction, the wood chips in step (1) comprise 40%-90% poplar and 10%-20% acacia. If there is a surplus, the surplus can be mixed with other woods. Introducing acacia into the wood chips can further improve tensile strength while maintaining stiffness and bulk.

[0013] Preferably, high-concentration milling uses stepped toothed grinding discs. Toothed grinding discs can reduce fiber cutting and excessive buffing.

[0014] The chemimechanical pulp prepared by the process described in this invention for improving the stiffness of chemimechanical pulp fibers.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. Fiber morphology optimization: Fiber stiffness increased by more than 2%; 2. Improved paper properties: Bulk increased by more than 2%, tensile strength increased by 3%-5%; 3. Enhanced process stability: The compound use of additives makes process parameters highly controllable; 4. Wide applicability: Suitable for the production of chemimechanical pulp whose main component is poplar wood. Attached Figure Description

[0016] Figure 1 This is a process flow diagram of an embodiment of the present invention for improving the stiffness of mechanical pulp fibers. Detailed Implementation

[0017] The technical solution of the present invention will now be clearly and completely described in conjunction with the accompanying drawings and embodiments.

[0018] Unless otherwise specified, all raw materials used in the examples were commercially available.

[0019] The process for improving the stiffness of chemimechanical pulp fibers in the embodiments is as follows: Figure 1 As shown, it includes the following steps: (1) After two stages of wood chip washing in the wood chip washing group, the wood chips enter the wood chip silo, and then enter the preimpregnator for one stage of preimpregnation after being extruded by the extrusion screw. The preimpregnated wood chips enter the reaction chamber and are then conveyed to the high-consistency mill by the leveler. The high-consistency mill produces pulp. (2) After the high-consistency pulping is completed, the pulp is dewatered by a cyclone separator to remove excess steam and chemicals. Then, the chemicals required for the first stage of bleaching are added to the chemical mixing screw. The pulp is then subjected to a first stage of medium-consistency bleaching in a medium-consistency bleaching tower. After the first stage of medium-consistency bleaching, the pulp is dewatered by a screw. Then, the chemicals required for the second stage of bleaching are added to the chemical mixing screw. The pulp is then subjected to a second stage of high-consistency bleaching in a high-consistency bleaching tower. (3) The high-consistency bleached pulp after the second stage is pressed by two rollers and then enters the de-deposition tank for de-deposition. In the de-deposition process, composite additives are added to the pulp in the de-deposition tank. The composite additives include dispersants and swelling agents. (4) After the slurry is de-concentrated, it enters the pressure screen after passing through two low-concentration grinding stages. The slurry from the pressure screen enters the slurry screen, and the good slurry from the pressure screen and the slurry screen enters the multi-disc washing screen. Then, it enters the slurry storage tower after passing through the slurry extrusion screw of the extruder.

[0020] Example 1 The process for improving the stiffness of chemimechanical pulp fibers includes the following steps: (1) The mechanical pulp wood chips (wood chip ratio: poplar, acacia and ash in a mass ratio of 40:20:40) are washed in two stages in the wood chip washing group and then enter the wood chip silo. After being extruded by ADI screw extrusion, they enter the preimpregnator. The preimpregnated wood chips enter the reaction chamber and are conveyed to the high-consistency mill by the leveler. The high-consistency mill produces pulp. Process parameters: Washing tank temperature 86℃; Pre-immersion tank level 30%; Reaction chamber level 63%; Reaction chamber temperature 96℃; ADI screw torque 3.9kN·m; ADI screw back pressure 3.5BAR; High concentration mill power 14MW; High concentration mill output 25t / h; High concentration mill energy consumption 0.57MWh / BDT; High concentration mill chamber pressure 350kPa.

[0021] (2) After the high-consistency pulping is completed, the pulp is dewatered by a cyclone separator to remove excess steam and chemicals. Then, the chemicals required for the first stage of bleaching are added to the chemical mixing screw. The pulp is then subjected to a first stage of medium-consistency bleaching in a medium-consistency bleaching tower. After the first stage of medium-consistency bleaching, the pulp is dewatered by a screw. Then, the chemicals required for the second stage of bleaching are added to the chemical mixing screw. The pulp is then subjected to a second stage of high-consistency bleaching in a high-consistency bleaching tower. Process parameters: Cyclone separator load 49%; medium-concentration bleaching tower liquid level 60%, temperature 99℃; high-concentration bleaching tower liquid level 51%, temperature 86℃; (3) The high-consistency bleached pulp from the second stage is pressed by two rollers and then enters the desulfurization tank for desulfurization. In the anti-potential process, a dispersant and a swelling agent are added to the slurry in the anti-potential tank. The dispersant is polyoxyethylene ether dispersant PEO, with a dosage of 0.8 kg / ton of slurry, and the swelling agent is sodium carboxymethyl cellulose, with a dosage of 0.1 kg / ton of slurry. Process parameters: Submersion removal tank level 55%; submersion removal tank temperature 90℃, time 45min, slurry mass concentration 4%; (4) After the slurry is de-concentrated, it enters the pressure screen after passing through two stages of low-concentration grinding. The slurry from the pressure screen enters the slurry screen, and the good slurry from the pressure screen and the slurry screen enters the multi-disc washing screen. Then, it enters the slurry storage tower after passing through the slurry extrusion screw of the extruder. Process parameters: Slurry mill power 1822kW.

[0022] Example 2 The process for improving the stiffness of chemimechanical pulp fibers includes the following steps: (1) The mechanical pulp wood chips (wood chip ratio: poplar, acacia and ash in a mass ratio of 40:20:40) are washed in two stages in the wood chip washing group and then enter the wood chip silo. After being extruded by ADI screw extrusion, they enter the preimpregnator. The preimpregnated wood chips enter the reaction chamber and are conveyed to the high-consistency mill by the leveler. The high-consistency mill produces pulp. Process parameters: Washing tank temperature 84℃; Pre-immersion tank level 26%; Reaction chamber level 58%; Reaction chamber temperature 93℃; ADI screw torque 3.7kN·m; ADI screw back pressure 3.5BAR; High concentration mill power 13.2MW; High concentration mill output 25t / h; High concentration mill energy consumption 0.53MWh / BDT; High concentration mill chamber pressure 340kPa.

[0023] (2) After the high-consistency pulping is completed, the pulp is dewatered by a cyclone separator to remove excess steam and chemicals. Then, the chemicals required for the first stage of bleaching are added to the chemical mixing screw. The pulp is then subjected to a first stage of medium-consistency bleaching in a medium-consistency bleaching tower. After the first stage of medium-consistency bleaching, the pulp is dewatered by a screw. Then, the chemicals required for the second stage of bleaching are added to the chemical mixing screw. The pulp is then subjected to a second stage of high-consistency bleaching in a high-consistency bleaching tower. Process parameters: Cyclone separator load 49%; medium-concentration bleaching tower liquid level 60%, temperature 98℃; high-concentration bleaching tower liquid level 46%, temperature 86℃; (3) The high-consistency bleached pulp from the second stage is pressed by two rollers and then enters the desulfurization tank for desulfurization. In the anti-potential process, a dispersant and a swelling agent are added to the slurry in the anti-potential tank. The dispersant is polyoxyethylene ether dispersant PEO, with a dosage of 0.5 kg / ton of slurry, and the swelling agent is sodium carboxymethyl cellulose, with a dosage of 0.3 kg / ton of slurry. Process parameters: Submersion elimination tank level 76%; submersion elimination tank temperature 92℃, time 45min, slurry mass concentration 4%; (4) After the slurry is de-concentrated, it enters the pressure screen after passing through two stages of low-concentration grinding. The slurry from the pressure screen enters the slurry screen, and the good slurry from the pressure screen and the slurry screen enters the multi-disc washing screen. Then, it enters the slurry storage tower after passing through the slurry extrusion screw of the extruder. Process parameters: Slurry mill power 1807kW.

[0024] Example 3 The process for improving the stiffness of chemimechanical pulp fibers includes the following steps: (1) The mechanical pulp wood chips (wood chip ratio: poplar, acacia and ash in a mass ratio of 40:20:40) are washed in two stages in the wood chip washing group and then enter the wood chip silo. After being extruded by ADI screw extrusion, they enter the preimpregnator. The preimpregnated wood chips enter the reaction chamber and are conveyed to the high-consistency mill by the leveler. The high-consistency mill produces pulp. Process parameters: Washing tank temperature 80℃; Pre-soak level 30%; Reaction chamber level 63%; Reaction chamber temperature 91℃; ADI screw torque 3.9kN·m; ADI screw back pressure 3.5BAR; High concentration mill power 14MW; High concentration mill output 25t / h; High concentration mill energy consumption 0.57MWh / BDT; High concentration mill chamber pressure 336kPa.

[0025] (2) After the high-consistency pulping is completed, the pulp is dewatered by a cyclone separator to remove excess steam and chemicals. Then, the chemicals required for the first stage of bleaching are added to the chemical mixing screw. The pulp is then subjected to a first stage of medium-consistency bleaching in a medium-consistency bleaching tower. After the first stage of medium-consistency bleaching, the pulp is dewatered by a screw. Then, the chemicals required for the second stage of bleaching are added to the chemical mixing screw. The pulp is then subjected to a second stage of high-consistency bleaching in a high-consistency bleaching tower. Process parameters: Cyclone separator load 49%; medium-concentration bleaching tower liquid level 58%, temperature 97℃; high-concentration bleaching tower liquid level 44%, temperature 87℃; (3) The high-consistency bleached pulp from the second stage is pressed by two rollers and then enters the desulfurization tank for desulfurization. In the anti-potential process, a dispersant and a swelling agent are added to the slurry in the anti-potential tank. The dispersant is polyoxyethylene ether dispersant PEO, with a dosage of 0.6 kg / ton of slurry, and the swelling agent is sodium carboxymethyl cellulose, with a dosage of 0.1 kg / ton of slurry. Process parameters: Submersion removal tank level 64%; submersion removal tank temperature 90℃, time 45min, slurry mass concentration 4%; (4) After the slurry is de-concentrated, it enters the pressure screen after passing through two stages of low-concentration grinding. The slurry from the pressure screen enters the slurry screen, and the good slurry from the pressure screen and the slurry screen enters the multi-disc washing screen. Then, it enters the slurry storage tower after passing through the slurry extrusion screw of the extruder. Process parameters: Slurry mill power 1780kW.

[0026] Example 4 The process for improving the stiffness of chemimechanical pulp fibers includes the following steps: (1) The mechanical pulp wood chips (wood chip ratio: poplar, acacia and ash in a mass ratio of 40:20:40) are washed in two stages in the wood chip washing group and then enter the wood chip silo. After being extruded by ADI screw extrusion, they enter the preimpregnator. The preimpregnated wood chips enter the reaction chamber and are conveyed to the high-consistency mill by the leveler. The high-consistency mill produces pulp. Process parameters: Washing tank temperature 84℃; Pre-immersion tank level 33%; Reaction chamber level 60%; Reaction chamber temperature 91℃; ADI screw torque 3.9kN·m; ADI screw back pressure 3.5BAR; High concentration mill power 13.9MW; High concentration mill output 25t / h; High concentration mill energy consumption 0.56MWh / BDT; High concentration mill chamber pressure 343kPa.

[0027] (2) After the high-consistency pulping is completed, the pulp is dewatered by a cyclone separator to remove excess steam and chemicals. Then, the chemicals required for the first stage of bleaching are added to the chemical mixing screw. The pulp is then subjected to a first stage of medium-consistency bleaching in a medium-consistency bleaching tower. After the first stage of medium-consistency bleaching, the pulp is dewatered by a screw. Then, the chemicals required for the second stage of bleaching are added to the chemical mixing screw. The pulp is then subjected to a second stage of high-consistency bleaching in a high-consistency bleaching tower. Process parameters: Cyclone separator load 52%; medium-concentration bleaching tower liquid level 58%, temperature 96℃; high-concentration bleaching tower liquid level 43%, temperature 87℃; (3) The high-consistency bleached pulp from the second stage is pressed by two rollers and then enters the desulfurization tank for desulfurization. In the anti-potential process, a dispersant and a swelling agent are added to the slurry in the anti-potential tank. The dispersant is polyoxyethylene ether dispersant PEO, with a dosage of 0.5 kg / ton of slurry, and the swelling agent is sodium carboxymethyl cellulose, with a dosage of 0.3 kg / ton of slurry. Process parameters: Submersion removal tank level 64%; submersion removal tank temperature 90℃, time 45min, slurry mass concentration 4%; (4) After the slurry is de-concentrated, it enters the pressure screen after passing through two stages of low-concentration grinding. The slurry from the pressure screen enters the slurry screen, and the good slurry from the pressure screen and the slurry screen enters the multi-disc washing screen. Then, it enters the slurry storage tower after passing through the slurry extrusion screw of the extruder. Process parameters: Slurry mill power 1738kW.

[0028] Example 5 The process for improving the stiffness of chemimechanical pulp fibers includes the following steps: (1) The mechanical pulp wood chips (wood chip ratio: poplar, acacia and ash in a mass ratio of 40:20:40) are washed in two stages in the wood chip washing group and then enter the wood chip silo. After being extruded by ADI screw extrusion, they enter the preimpregnator. The preimpregnated wood chips enter the reaction chamber and are conveyed to the high-consistency mill by the leveler. The high-consistency mill produces pulp. Process parameters: Washing tank temperature 84℃; Pre-immersion tank level 31%; Reaction chamber level 60%; Reaction chamber temperature 90℃; ADI screw torque 3.7kN·m; ADI screw back pressure 3.5BAR; High concentration mill power 14.8MW; High concentration mill output 32t / h; High concentration mill energy consumption 0.47MWh / BDT; High concentration mill chamber pressure 363kPa.

[0029] (2) After the high-consistency pulping is completed, the pulp is dewatered by a cyclone separator to remove excess steam and chemicals. Then, the chemicals required for the first stage of bleaching are added to the chemical mixing screw. The pulp is then subjected to a first stage of medium-consistency bleaching in a medium-consistency bleaching tower. After the first stage of medium-consistency bleaching, the pulp is dewatered by a screw. Then, the chemicals required for the second stage of bleaching are added to the chemical mixing screw. The pulp is then subjected to a second stage of high-consistency bleaching in a high-consistency bleaching tower. Process parameters: Cyclone separator load 45%; medium-concentration bleaching tower liquid level 54%, temperature 99℃; high-concentration bleaching tower liquid level 45%, temperature 91℃; (3) The high-consistency bleached pulp from the second stage is pressed by two rollers and then enters the desulfurization tank for desulfurization. In the anti-potential process, a dispersant and a swelling agent are added to the slurry in the anti-potential tank. The dispersant is polyoxyethylene ether dispersant PEO, with a dosage of 0.5 kg / ton of slurry, and the swelling agent is sodium carboxymethyl cellulose, with a dosage of 0.3 kg / ton of slurry. Process parameters: Submersion elimination tank level 73%; submersion elimination tank temperature 89℃, time 48min, slurry mass concentration 4.2%; (4) After the slurry is de-concentrated, it enters the pressure screen after passing through two stages of low-concentration grinding. The slurry from the pressure screen enters the slurry screen, and the good slurry from the pressure screen and the slurry screen enters the multi-disc washing screen. Then, it enters the slurry storage tower after passing through the slurry extrusion screw of the extruder. Process parameters: Slurry mill power 2188kW.

[0030] Example 6 The process for improving the stiffness of chemimechanical pulp fibers includes the following steps: (1) The mechanical pulp wood chips (wood chip ratio: poplar, acacia and ash in a mass ratio of 40:20:40) are washed in two stages in the wood chip washing group and then enter the wood chip silo. After being extruded by ADI screw extrusion, they enter the preimpregnator. The preimpregnated wood chips enter the reaction chamber and are conveyed to the high-consistency mill by the leveler. The high-consistency mill produces pulp. Process parameters: Washing tank temperature 84℃; Pre-soak level 30%; Reaction chamber level 65%; Reaction chamber temperature 88℃; ADI screw torque 3.7kN·m; ADI screw back pressure 3.5BAR; High concentration mill power 14.5MW; High concentration mill output 31t / h; High concentration mill energy consumption 0.47MWh / BDT; High concentration mill chamber pressure 339kPa.

[0031] (2) After the high-consistency pulping is completed, the pulp is dewatered by a cyclone separator to remove excess steam and chemicals. Then, the chemicals required for the first stage of bleaching are added to the chemical mixing screw. The pulp is then subjected to a first stage of medium-consistency bleaching in a medium-consistency bleaching tower. After the first stage of medium-consistency bleaching, the pulp is dewatered by a screw. Then, the chemicals required for the second stage of bleaching are added to the chemical mixing screw. The pulp is then subjected to a second stage of high-consistency bleaching in a high-consistency bleaching tower. Process parameters: Cyclone separator load 45%; medium-concentration bleaching tower liquid level 64%, temperature 99℃; high-concentration bleaching tower liquid level 52%, temperature 93℃; (3) The high-consistency bleached pulp from the second stage is pressed by two rollers and then enters the desulfurization tank for desulfurization. In the anti-potential process, a dispersant and a swelling agent are added to the slurry in the anti-potential tank. The dispersant is polyoxyethylene ether dispersant PEO, with a dosage of 0.5 kg / ton of slurry, and the swelling agent is sodium carboxymethyl cellulose, with a dosage of 0.3 kg / ton of slurry. Process parameters: Submersion elimination tank level 73%; submersion elimination tank temperature 87℃, time 50min, slurry mass concentration 3.5%; (4) After the slurry is de-concentrated, it enters the pressure screen after passing through two stages of low-concentration grinding. The slurry from the pressure screen enters the slurry screen, and the good slurry from the pressure screen and the slurry screen enters the multi-disc washing screen. Then, it enters the slurry storage tower after passing through the slurry extrusion screw of the extruder. Process parameters: Slurry mill power 2005kW.

[0032] Comparative Example 1 The process for improving the stiffness of chemimechanical pulp fibers includes the following steps: (1) The mechanical pulp wood chips (wood chip ratio: poplar, acacia and ash in a mass ratio of 40:20:40) are washed in two stages in the wood chip washing group and then enter the wood chip silo. After being extruded by ADI screw extrusion, they enter the preimpregnator. The preimpregnated wood chips enter the reaction chamber and are conveyed to the high-consistency mill by the leveler. The high-consistency mill produces pulp. Process parameters: Washing tank temperature 85℃; Pre-soak level 33%; Reaction chamber level 57%; Reaction chamber temperature 94℃; ADI screw torque 3.5kN·m; ADI screw back pressure 3.5BAR; High concentration mill power 13.5MW; High concentration mill output 25t / h; High concentration mill energy consumption 0.54MWh / BDT; High concentration mill chamber pressure 347kPa.

[0033] (2) After the high-consistency pulping is completed, the pulp is dewatered by a cyclone separator to remove excess steam and chemicals. Then, the chemicals required for the first stage of bleaching are added to the chemical mixing screw. The pulp is then subjected to a first stage of medium-consistency bleaching in a medium-consistency bleaching tower. After the first stage of medium-consistency bleaching, the pulp is dewatered by a screw. Then, the chemicals required for the second stage of bleaching are added to the chemical mixing screw. The pulp is then subjected to a second stage of high-consistency bleaching in a high-consistency bleaching tower. Process parameters: Cyclone separator load 45%; medium-concentration bleaching tower liquid level 61%, temperature 100℃; high-concentration bleaching tower liquid level 60%, temperature 87℃; (3) The high-consistency bleached pulp from the second stage is pressed by two rollers and then enters the desulfurization tank for desulfurization. Process parameters: Submersion elimination tank level 56%; submersion elimination tank temperature 92℃, time 45min, slurry mass concentration 4%; (4) After the slurry is de-concentrated, it enters the pressure screen after passing through two stages of low-concentration grinding. The slurry from the pressure screen enters the slurry screen, and the good slurry from the pressure screen and the slurry screen enters the multi-disc washing screen. Then, it enters the slurry storage tower after passing through the slurry extrusion screw of the extruder. Process parameters: Slurry mill power 1947kW.

[0034] Comparative Example 2 The process for improving the stiffness of chemimechanical pulp fibers includes the following steps: (1) The mechanical pulp wood chips (wood chip ratio: poplar, acacia and ash in a mass ratio of 40:20:40) are washed in two stages in the wood chip washing group and then enter the wood chip silo. After being extruded by ADI screw extrusion, they enter the preimpregnator. The preimpregnated wood chips enter the reaction chamber and are conveyed to the high-consistency mill by the leveler. The high-consistency mill produces pulp. Process parameters: Washing tank temperature 84℃; Pre-soak level 28%; Reaction chamber level 65%; Reaction chamber temperature 95℃; ADI screw torque 3.5kN·m; ADI screw back pressure 3.5BAR; High concentration mill power 12.4MW; High concentration mill output 27t / h; High concentration mill energy consumption 0.47MWh / BDT; High concentration mill chamber pressure 388kPa.

[0035] (2) After the high-consistency pulping is completed, the pulp is dewatered by a cyclone separator to remove excess steam and chemicals. Then, the chemicals required for the first stage of bleaching are added to the chemical mixing screw. The pulp is then subjected to a first stage of medium-consistency bleaching in a medium-consistency bleaching tower. After the first stage of medium-consistency bleaching, the pulp is dewatered by a screw. Then, the chemicals required for the second stage of bleaching are added to the chemical mixing screw. The pulp is then subjected to a second stage of high-consistency bleaching in a high-consistency bleaching tower. Process parameters: Cyclone separator load 42%; medium-concentration bleaching tower liquid level 65%, temperature 101℃; high-concentration bleaching tower liquid level 57%, temperature 88℃; (3) The high-consistency bleached pulp from the second stage is pressed by two rollers and then enters the desulfurization tank for desulfurization. Process parameters: Submersion elimination tank level 54%; submersion elimination tank temperature 88℃, time 48min, slurry mass concentration 4.2%; (4) After the slurry is de-concentrated, it enters the pressure screen after passing through two stages of low-concentration grinding. The slurry from the pressure screen enters the slurry screen, and the good slurry from the pressure screen and the slurry screen enters the multi-disc washing screen. Then, it enters the slurry storage tower after passing through the slurry extrusion screw of the extruder. Process parameters: Slurry mill power 1957kW.

[0036] Performance testing The mechanical pulp sheets obtained from the examples and comparative examples were tested for fiber stiffness, bulk, and tensile index. The results are shown in Table 1.

[0037] Table 1 Performance Test Tables for Examples and Comparative Examples

[0038] As shown in Table 1, Comparative Examples 1 and 2, which did not add composite auxiliaries in the anti-depression process, had an average fiber stiffness of 4.46 mN and an average bulk of 2.83 cm. 3 The average tensile index was 14.93 N·m / g, and after adding composite auxiliaries, the average fiber stiffness was 4.59 mN and the average bulk was 2.97 cm. 3The average tensile index was 15.45 N·m / g, with significant improvements in all three indicators: fiber stiffness increased by 2.91%, bulkiness increased by 4.95%, and tensile index increased by 3.48%, achieving the intended use target.

Claims

1. A process for improving the stiffness of chemimechanical pulp fibers, characterized in that, Includes the following steps: (1) The chemimechanical pulp wood chips are washed, extruded, pre-impregnated and then subjected to high-consistency refining to obtain pulp; (2) The slurry after high-consistency grinding is subjected to a first-stage medium-consistency bleaching and a second-stage high-consistency bleaching. (3) The high-consistency bleached pulp from the second stage is pressed and then enters the desulfurization tank for desulfurization. (4) After the low-concentration grinding of the pulp after the anti-potential process, the good pulp enters the multi-plate washing process, and finally enters the pulp storage tower through extrusion. In the anti-potential process, composite additives are added to the slurry, including dispersants and swelling agents.

2. The process for improving the stiffness of chemimechanical pulp fibers according to claim 1, characterized in that, The specific steps include: (1) After two stages of wood chip washing in the wood chip washing group, the wood chips enter the wood chip silo, and then enter the preimpregnator for one stage of preimpregnation after being extruded by the extrusion screw. The preimpregnated wood chips enter the reaction chamber and are then conveyed to the high-consistency mill by the leveler. The high-consistency mill produces pulp. (2) After the high-consistency pulping is completed, the pulp is dewatered by a cyclone separator to remove excess steam and chemicals. Then, the chemicals required for the first stage of bleaching are added to the chemical mixing screw. The pulp is then subjected to a first stage of medium-consistency bleaching in a medium-consistency bleaching tower. After the first stage of medium-consistency bleaching, the pulp is dewatered by a screw. Then, the chemicals required for the second stage of bleaching are added to the chemical mixing screw. The pulp is then subjected to a second stage of high-consistency bleaching in a high-consistency bleaching tower. (3) The high-consistency bleached pulp after the second stage is pressed by two rollers and then enters the de-deposition tank for de-deposition. In the de-deposition process, composite additives are added to the pulp in the de-deposition tank. The composite additives include dispersants and swelling agents. (4) After the slurry is de-concentrated, it enters the pressure screen after passing through two low-concentration grinding stages. The slurry from the pressure screen enters the slurry screen, and the good slurry from the pressure screen and the slurry screen enters the multi-disc washing screen. Then, it enters the slurry storage tower after passing through the slurry extrusion screw of the extruder.

3. The process for improving the stiffness of chemimechanical pulp fibers according to claim 1, characterized in that, The extrusion screw is an ADI screw.

4. The process for improving the stiffness of chemimechanical pulp fibers according to claim 1, characterized in that, Anti-latency process conditions: temperature ≥ 85℃, time ≥ 45 min, slurry mass concentration 3.5%-4.5%.

5. The process for improving the stiffness of chemimechanical pulp fibers according to claim 1, characterized in that, The dispersant is a polyoxyethylene ether dispersant, and the dosage is 0.5-0.8 kg / ton of slurry.

6. The process for improving the stiffness of chemimechanical pulp fibers according to claim 1, characterized in that, The swelling agent is sodium carboxymethyl cellulose, and the dosage is 0.1-0.3 kg / ton of slurry.

7. The process for improving the stiffness of chemimechanical pulp fibers according to claim 1, characterized in that, In terms of mass fraction, the wood chips in step (1) include: 40%-90% poplar and 10%-20% acacia.

8. The process for improving the stiffness of chemimechanical pulp fibers according to claim 1, characterized in that, The high-concentration mill uses stepped toothed grinding discs.

9. A chemimechanical pulp prepared by a process for improving the stiffness of chemimechanical pulp fibers as described in any one of claims 1-8.

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