A method for preparing high-strength fibers from calcium crosslinked carboxylated straw pulp and its products

Abstract

This invention provides a method for preparing high-strength fibers from calcium-crosslinked carboxylated straw pulp and its products. The steps are as follows: (1) Disperse straw pulp in water to prepare a straw pulp fiber dispersion; (2) Add TEMPO reagent, NaBr and NaClO solution to the straw pulp dispersion to carry out a TEMPO oxidation reaction to prepare carboxylated straw pulp; (3) Disperse carboxylated straw pulp in water to prepare a carboxylated straw pulp fiber dispersion; (4) Adjust the pH of the carboxylated straw pulp fiber dispersion with an alkaline solution; (5) Add calcium salt to the carboxylated straw pulp fiber dispersion to prepare high-strength Ca2+. 2+ Crosslinked carboxylated straw-based mechanical pulp. This invention uses a TEMPO oxidation system to prepare carboxylated straw-based mechanical pulp fibers and introduces Ca... 2+ It is highly cross-linked with carboxylated straw pulp, resulting in a significant improvement in the mechanical properties of straw pulp.

Description

[Technical Field]

[0001] This invention relates to the field of pulp research and production, specifically to a method for preparing high-strength fibers from calcium crosslinked carboxylated straw mechanical pulp and its products. [Background Technology]

[0002] Since the beginning of the 21st century, my country's paper industry has developed rapidly and has become one of the most important industries in the national economy. However, my country is a country with relatively scarce forest resources, and the shortage of fiber raw materials has gradually become an obstacle to the further development of my country's paper industry.

[0003] my country is a major agricultural country with abundant non-timber resources. Non-timber fibers are characterized by their variety and high content, including straw, reeds, bamboo, and bagasse. Among these, the annual output of straw reaches 828 million tons, but only 40% of it is utilized, resulting in a significant waste of straw resources. Furthermore, straw fiber used in pulp production accounts for only 3.40% of the total utilization rate. Therefore, developing straw resources as a fiber raw material for pulping and papermaking is of great significance for increasing straw utilization, enhancing its added value, and optimizing the supply of pulp fiber in my country.

[0004] Based on the differences in the pulping process, straw pulp can be divided into mechanical pulp, chemical pulp, and chemimechanical pulp (CMP). Mechanical pulp has a high yield but poor pulp properties; chemical pulp has better properties but low pulp yield and high pollution load; CMP is prepared through mechanical treatment and chemical action, thus combining the advantages of both mechanical and chemical pulps, such as higher yield and better properties. However, because straw fibers are short and contain more impurities, the strength of its fiber products is relatively low, and current methods for preparing straw CMP make it difficult to match the mechanical properties of wood pulp.

[0005] Existing publicly available technologies include: Chinese patent CN106012636A, which discloses a method for enzyme-modified straw pulp. This method is suitable for herbaceous plants and crop straws such as corn, wheat, rice, Artemisia annua, and Artemisia annua, as well as agricultural straws. The raw materials are inexpensive. Enzymatic hydrolysis is used to modify the surface of the pulp fibers, removing gums, xylan, and hemicellulose components, increasing the content of crystalline cellulose, and thus improving the mechanical strength of the composite material. However, this process is time-consuming, costly, and its effects are not significant. Chinese patent CN104611984A discloses an ATRP method for modifying pulp. 1g of hardwood sulfate pulp with a freeness of 30-50°SR is used as the fiber substrate. 4mL of isoprene is added as the reactant, 0.45g of copper bromide as the catalyst, and 50mL of N,N-dimethylformamide as the solvent. After synthesis at 40°C for 24 hours, modified pulp fibers are obtained. However, this method is not suitable for chemimechanical pulps with high lignin content. Chinese patent CN104098704B discloses a method for preparing pulp containing multifunctional functional groups, comprising the following steps: providing plant fiber raw materials; cooking the plant fiber raw materials to obtain pulp; and after the cooking step, adding an oxidation system to the pulp to oxidize and modify the fiber raw materials. This oxidation system uses one of the following: TEMPO catalytic oxidation system, periodate, nitrite, sodium chlorite, and sodium hypochlorite. Adding an oxidation system after the cooking step to oxidize the fibers yields pulp rich in aldehyde and carboxyl functional groups. The aldehyde groups are beneficial for improving the wet strength of paper, while the carboxyl groups are beneficial for reducing beating energy consumption and increasing paper strength. However, this method is not suitable for chemimechanical pulp with high lignin content, and its effect is not significant. Overall, there is a need to develop a method to efficiently improve the mechanical properties of straw chemimechanical pulp, thereby meeting the requirements of various types of paper and improving paper quality, which will further expand the application fields of straw chemimechanical pulp. [Summary of the Invention]

[0006] The technical problem to be solved by this invention is to provide a method and product for preparing high-strength fibers from calcium-crosslinked carboxylated straw pulp. This method uses a TEMPO oxidation system to prepare carboxylated straw pulp fibers, and further introduces Ca... 2+ It is highly cross-linked with carboxylated straw pulp, resulting in a significant improvement in the mechanical properties of straw pulp.

[0007] This invention is implemented as follows:

[0008] A method for preparing high-strength fibers from calcium crosslinked carboxylated straw pulp, characterized by the following steps:

[0009] (1) Disperse straw chemimechanical pulp in water to prepare straw chemimechanical pulp fiber dispersion;

[0010] (2) Add TEMPO reagent, NaBr and NaClO solution to the straw chemimechanical pulp dispersion to carry out TEMPO oxidation reaction to prepare carboxylated straw chemimechanical pulp;

[0011] (3) Disperse carboxylated straw-based mechanical pulp in water to prepare a carboxylated straw-based mechanical pulp fiber dispersion;

[0012] (4) Adjust the pH of the carboxylated straw pulp fiber dispersion with an alkaline solution;

[0013] (5) Add calcium salt to the carboxylated straw-based mechanical pulp fiber dispersion to prepare high-strength Ca2+. 2+ Cross-linked carboxylated straw pulp.

[0014] Furthermore, the raw material for the straw slurry in step (1) is one of corn straw, wheat straw, and sorghum straw.

[0015] Furthermore, in step (1), the concentration of the straw chemimechanical pulp fiber dispersion is 0.1-1%.

[0016] Furthermore, the reaction time in step (2) is 0.5-4 h.

[0017] Furthermore, in step (3), the concentration of the carboxylated straw pulp fiber dispersion is 0.1-1%.

[0018] Furthermore, the alkaline solution in step (4) is one of NaOH, KOH and saturated Ca(OH)2 solutions with a concentration of 0.1 mol / L.

[0019] Furthermore, the pH range in step (4) is 9-14.

[0020] Furthermore, the calcium salt in step (5) is one of CaCl2, CaSO4 and Ca3(PO4)2; the mass ratio of calcium salt to pulp fiber is 1:10 to 1:40.

[0021] Furthermore, the reaction time in step (5) is 0.5-5h.

[0022] Furthermore, a product prepared according to the method for preparing high-strength fibers from calcium crosslinked carboxylated straw pulp.

[0023] The present invention has the following advantages:

[0024] This invention uses a TEMPO oxidation system to prepare carboxylated straw-based mechanical pulp, which can enhance the electronegativity of the pulp fiber surface and increase anionic groups (carboxyl functional groups); at the same time, Ca is introduced into the system. 2+ The cations, constructing C a2+The chelation with the carboxyl functional groups of fibers strengthens the cross-linking between chemical components in the system, thereby preparing high-strength Ca 2+ Cross-linked carboxylated straw pulp.

[0025] This invention introduces carboxyl groups into pulp fibers and maintains the morphology of the pulp fibers by controlling the reaction time of the TEMPO oxidation system, thereby improving the electronegativity of the pulp fibers. Through crosslinking with different types of calcium salts in different alkaline environments, the strength of the pulp fibers is significantly improved.

Detailed Implementation Methods

[0026] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0027] Example 1: Ca 2+ Cross-linked carboxylated straw pulp

[0028] Step (1) Disperse straw slurry in water to prepare a 1% straw slurry fiber dispersion;

[0029] Step (2) Add TEMPO reagent, NaBr and NaClO solution to the straw chemimechanical pulp dispersion and react for 0.5 h to prepare carboxylated straw chemimechanical pulp;

[0030] Step (3) Disperse the carboxylated straw mechanical pulp in water to prepare a 1% carboxylated straw mechanical pulp fiber dispersion;

[0031] Step (4) Adjust the pH of the carboxylated straw pulp fiber dispersion to 9 using 0.1 mol / L NaOH solution;

[0032] Step (5) Add CaCl2 to the carboxylated straw-based mechanical pulp fiber dispersion at a mass ratio of 1:10 with the pulp fiber, and react for 0.5 h to prepare CaCl2. 2+ Crosslinked carboxylated straw pulp (Mechanical properties: tear index: 3.53 mN·m) 2 ·g -1 Tensile index: 30.72 N·m·g -1 Bursting strength index: 2.03 kPa·m 2 ·g -1 );

[0033] Example 2: Ca 2+Cross-linked carboxylated straw pulp

[0034] Step (1) Disperse straw slurry in water to prepare a straw slurry fiber dispersion with a concentration of 0.1%;

[0035] Step (2) Add TEMPO reagent, NaBr and NaClO solution to the straw chemimechanical pulp dispersion and react for 1 h to prepare carboxylated straw chemimechanical pulp;

[0036] Step (3) Disperse the carboxylated straw mechanical pulp in water to prepare a 1% carboxylated straw mechanical pulp fiber dispersion;

[0037] Step (4) Adjust the pH of the carboxylated straw pulp fiber dispersion to 11 using 0.1 mol / L KOH solution;

[0038] Step (5) Add CaSO4 to the carboxylated straw-based mechanical pulp fiber dispersion at a mass ratio of 1:30 with the pulp fiber, react for 1 hour, and prepare CaSO4. 2+ Crosslinked carboxylated straw pulp (Mechanical properties: tear index: 3.58 mN·m) 2 ·g -1 Tensile index: 31.47 N·m·g -1 Bursting strength index: 1.89 kPa·m 2 ·g -1 ).

[0039] Example 3: Ca 2+ Cross-linked carboxylated straw pulp

[0040] Step (1) Disperse straw slurry in water to prepare a straw slurry fiber dispersion with a concentration of 0.2%;

[0041] Step (2) Add TEMPO reagent, NaBr and NaClO solution to the straw chemimechanical pulp dispersion and react for 2 hours to prepare carboxylated straw chemimechanical pulp;

[0042] Step (3) Disperse the carboxylated straw mechanical pulp in water to prepare a 0.2% carboxylated straw mechanical pulp fiber dispersion;

[0043] Step (4) Adjust the pH of the carboxylated straw pulp fiber dispersion to 12 using 0.1 mol / L KOH solution;

[0044] Step (5) Add Ca3(PO4)2 to the carboxylated straw-based mechanical pulp fiber dispersion at a mass ratio of 1:20 with the pulp fiber, react for 2 hours, and prepare Ca 2+ Crosslinked carboxylated straw pulp (Mechanical properties: tear index: 3.64 mN·m) 2·g -1 Tensile index: 34.12 N·m·g -1 Bursting strength index: 2.39 kPa·m 2 ·g -1 ).

[0045] Example 4: Ca 2+ Cross-linked straw pulp

[0046] Step (1) Disperse straw slurry in water to prepare a straw slurry fiber dispersion with a concentration of 0.8%;

[0047] Step (2) Add TEMPO reagent, NaBr and NaClO solution to the straw chemimechanical pulp dispersion and react for 3 hours to prepare carboxylated straw chemimechanical pulp;

[0048] Step (3) Disperse the carboxylated straw mechanical pulp in water to prepare a 0.4% carboxylated straw mechanical pulp fiber dispersion;

[0049] Step (4) Adjust the pH of the carboxylated straw pulp fiber dispersion to 12 using a saturated Ca(OH)2 solution;

[0050] Step (5) Add CaCl2 to the carboxylated straw-based mechanical pulp fiber dispersion, and react with the pulp fiber at a mass ratio of 1:25 for 3 hours to prepare CaCl2. 2+ Crosslinked carboxylated straw pulp (Mechanical properties: tear index: 3.87 mN·m) 2 ·g -1 Tensile index: 33.31 N·m·g -1 Bursting strength index: 2.25 kPa·m 2 ·g -1 ).

[0051] Example 5: Ca 2+ Cross-linked carboxylated straw pulp

[0052] Step (1) Disperse straw slurry in water to prepare a 1% straw slurry fiber dispersion;

[0053] Step (2) Add TEMPO reagent, NaBr and NaClO solution to the straw chemimechanical pulp dispersion and react for 4 hours to prepare carboxylated straw chemimechanical pulp;

[0054] Step (3) Disperse the carboxylated straw mechanical pulp in water to prepare a 0.1% carboxylated straw mechanical pulp fiber dispersion;

[0055] Step (4) Adjust the pH of the carboxylated straw pulp fiber dispersion to 14 using 0.1 mol / L NaOH solution;

[0056] Step (5) Add CaSO4 to the carboxylated straw-based mechanical pulp fiber dispersion, and react with the pulp fiber at a mass ratio of 1:40 for 5 hours to prepare CaSO4. 2+ Crosslinked carboxylated straw pulp (Mechanical properties: tear index: 3.88 mN·m) 2 ·g -1 Tensile index: 35.26 N·m·g -1 Bursting strength index: 2.44 kPa·m 2 ·g -1 ).

[0057] Comparative Example 1: Straw Pulverization

[0058] Step (1) Take 1000g of absolutely dry straw, add a certain amount of water and NaOH, the solid-liquid ratio is 1:4, and the amount of NaOH used for absolutely dry straw is 4%;

[0059] Step (2) Place the straw in a cooking pot and cook it at 150°C for 3 hours;

[0060] Step (3) involves grinding the straw fibers twice using a disc mill with a grinding gap of 0.15 mm to prepare the original straw chemimechanical pulp (mechanical properties: tear index: 3.4 mN·m). 2 ·g -1 Tensile index: 14.72 N·m·g -1 Bursting strength index: 1.02 kPa·m 2 ·g -1 ).

[0061] In summary, the present invention uses a TEMPO oxidation system to prepare carboxylated straw-based mechanical pulp, which can enhance the electronegativity of the pulp fiber surface and increase anionic groups (carboxyl functional groups); at the same time, it introduces Ca into the system. 2+ The cations, constructing C a2+ The chelation with the carboxyl functional groups of fibers strengthens the cross-linking between chemical components in the system, thereby preparing high-strength Ca 2+ Cross-linked carboxylated straw pulp.

[0062] This invention introduces carboxyl groups into pulp fibers and maintains the morphology of the pulp fibers by controlling the reaction time of the TEMPO oxidation system, thereby improving the electronegativity of the pulp fibers. Through crosslinking with different types of calcium salts in different alkaline environments, the strength of the pulp fibers is significantly improved.

[0063] While specific embodiments of the present invention have been described above, those skilled in the art should understand that the specific embodiments described are merely illustrative and not intended to limit the scope of the present invention. Equivalent modifications and variations made by those skilled in the art in accordance with the spirit of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing high-strength fibers from calcium cross-linked carboxylated straw pulp, characterized in that: The method steps are as follows: (1) Take straw slurry and disperse it in water to prepare straw slurry fiber dispersion; (2) Add TEMPO reagent, NaBr and NaClO solution to the straw chemimechanical pulp fiber dispersion to carry out TEMPO oxidation reaction to prepare carboxylated straw chemimechanical pulp; the reaction time is 0.5-4 h; (3) Disperse carboxylated straw pulp in water to prepare a carboxylated straw pulp fiber dispersion; (4) Adjust the pH of the carboxylated straw pulp fiber dispersion with an alkaline solution; the pH range is 9-14; (5) Add calcium salt to the carboxylated straw pulp fiber dispersion to prepare high-strength Ca 2+ Cross-linked carboxylated straw pulp; reaction time is 0.5-5 h.

2. The method for preparing high-strength fibers from calcium cross-linked carboxylated straw pulp according to claim 1, characterized in that: In step (1), the raw material for straw slurry is one of corn straw, wheat straw or sorghum straw.

3. The method for preparing high-strength fibers from calcium cross-linked carboxylated straw pulp according to claim 1, characterized in that: In step (1), the concentration of the straw pulp fiber dispersion is 0.1-1%.

4. The method for preparing high-strength fibers from calcium cross-linked carboxylated straw pulp according to claim 1, characterized in that: In step (3), the concentration of the carboxylated straw pulp fiber dispersion is 0.1-1%.

5. The method for preparing high-strength fibers from calcium cross-linked carboxylated straw pulp according to claim 1, characterized in that: The alkaline solution in step (4) is one of NaOH, KOH or saturated Ca(OH)2 solution with a concentration of 0.1 mol / L.

6. The method for preparing high-strength fibers from calcium cross-linked carboxylated straw pulp according to claim 1, characterized in that: The calcium salt in step (5) is one of CaCl2, CaSO4 or Ca3(PO4)2; the mass ratio of calcium salt to fiber is 1:10~40.

7. A product prepared by a method for preparing high-strength fibers from calcium crosslinked carboxylated straw pulp according to any one of claims 1-6.