Preparation method of refined cotton

Abstract

A preparation method of refined cotton comprises the following steps: 1) taking cotton linters, and treating the cotton linters with biological enzyme; 2) boiling and bleaching to obtain a slurry containing refined cotton, in the step of biological enzyme treatment, cotton linters are added into an enzyme solution for treatment, the bath ratio of a system is 1: (8-15), the treatment temperature is 50-60 DEG C, the pH is 6-7, and the treatment time is 3-6 hours, in the step of boiling and bleaching, the cotton linters treated by the biological enzyme are added into a boiling and bleaching solution for treatment, the bath ratio of the system is 1: (8-15), the pH is 6-7, and the boiling and bleaching time is 3-6 hours. The treatment temperature is 80-100 DEG C, the alkali concentration of the system is 3-8 g / L, and the treatment time is 30-60 min. The method is short in treatment time, mild in treatment condition, small in influence on the polymerization degree of the cotton linters and low in treatment difficulty of generated wastewater.

Description

Technical Field

[0001] The present invention relates to the field of materials, and particularly to a method for preparing refined cotton. Background Art

[0002] Cotton linter is the short fiber remaining on the surface of cotton seeds after ginning. Cotton linter has short and fine fibers, is in a fluffy state, has a certain degree of curl, and its color is mostly white or slightly yellowish. It has a relatively high cellulose content, generally reaching about 90%, which endows it with good chemical stability and physical and mechanical properties, such as relatively high strength, flexibility, etc.

[0003] First-class cotton linter: It is peeled by the first peeling machine and is mostly the longer fibers remaining on the cotton seeds after breaking during ginning. The main body length is usually above 13 mm. Second-class cotton linter: It is peeled by the second peeling machine and is the main component of cotton linter, accounting for about 50 - 60% of the cotton linter output. Its length is 3 - 6 mm, and it has the highest maturity among the three types of cotton linter. Third-class cotton linter: It is obtained by the third peeling machine, has the shortest length (generally less than 3 mm), and a high impurity content. Although the fiber maturity is not as good as that of the second-class linter, it is better than that of the first-class linter.

[0004] Cotton fibers are mainly divided into four parts: epidermis, primary cell wall, secondary cell wall, and cell cavity. The natural impurities contained in cotton fibers mainly exist in the outer structure, among which the contents of wax and pectin are the highest. Pectin has properties similar to glue and can adhere wax and other impurities to the fibers. In addition to various impurities derived from the cotton fibers themselves, cottonseed hull impurities will also be mixed in during the processing. It is necessary to remove the impurities in the cotton linter so that the cellulose content reaches more than 98% to obtain a high-purity cellulose product - refined cotton, which has the characteristics of high cellulose content, high degree of polymerization, high whiteness, good reaction performance, etc., and is widely used in multiple fields such as manufacturing cellulose ethers, cellulose esters, pharmaceuticals, food, cosmetics, electronics, etc. For example, in the pharmaceutical industry, refined cotton is used to manufacture pharmaceutical excipients, disposable medical supplies, and wound dressings; in the chemical industry, it is the basic raw material for producing various cellulose derivatives, such as viscose fiber, nitrocellulose, carboxymethyl cellulose, cellulose acetate, etc.; in addition, refined cotton is also used in the paper industry to produce high-quality papers, especially those special papers that require high whiteness, high strength, and good printing performance.

[0005] Patent CN 103603219 B discloses a method for producing ultra-high viscosity food-grade purified cotton. Class II cotton linters with a maturity of ≥80%, a fiber length of 10-13 mm, and no visible impurities on the surface are used as raw materials. The ultra-high viscosity food-grade purified cotton is obtained through the processes of cooking, bleaching with chlorine dioxide and sodium hypochlorite, washing, rolling to remove water, and drying. The content of sodium hydroxide in the cooking liquid is 25-35 g / L, and the cooking temperature is 125-135 °C. Patent CN 116905263 B discloses a method for producing special purified cotton with a high uniform degree of polymerization. Through material selection, cotton opening, impurity removal, alkali preparation, impregnation, cooking, pre-impurity removal, washing, beating and refining, pre-bleaching, alkali treatment, bleaching, dechlorination, and post-impurity removal, and finally drying, a flocculent finished product is obtained. The content of sodium hydroxide in the cooking liquid is 30-35 g / L, and the cooking temperature is 118-140 °C.

[0006] In the existing alkaline cooking process for the production of purified cotton, maintaining high temperature and high pressure consumes a large amount of energy, driving up costs. The wastewater contains complex pollutants such as alkaline liquid and lignin, making it difficult to treat and increasing the cost of wastewater treatment. In addition, strong alkali and high temperature also seriously damage cotton fibers, reducing product quality. These factors have become bottlenecks in the industry's development, and there is an urgent need to develop more environmentally friendly and efficient alternative technologies to reduce pollution and energy consumption and improve fiber quality. Summary of the Invention

[0007] The object of the present invention is to provide a method for preparing purified cotton in view of the deficiencies of the existing technology. The method has a short treatment time, mild treatment conditions, little impact on the degree of polymerization of cotton linters, and low difficulty in treating the generated wastewater.

[0008] The technical solution of the present invention is as follows: A method for preparing purified cotton, comprising the following steps:

[0009] 1) Take cotton linters and perform biological enzyme treatment;

[0010] 2) Obtain a slurry containing purified cotton through boiling and bleaching treatment.

[0011] Preferably, the cotton linters in step 1) are secondary cotton linters and / or tertiary cotton linters, with a degree of polymerization of 2900-3100 and an α-cellulose content of 96-99 wt%.

[0012] Further, the biological enzyme treatment in step 1) is to add the cotton linters to the enzyme solution for treatment. The bath ratio of the system is 1:8-15, the treatment temperature is 50-60 °C, the pH is 6-7, and the treatment time is 3-6 h.

[0013] Preferably, the enzyme solution comprises 1 wt% pectinase, 0.5 wt% xylanase, 0.125 wt% ligninase, 1 wt% penetrant JFC, and the balance is water.

[0014] Preferably, the pectinase is one or more of pectin lyase, pectin esterase, and protopectinase, with a comprehensive enzyme activity of 2000 u / g; the xylanase is one or more of exo-β-1,4-xylanase, endo-β-1,4-xylanase, and β-1,4-xylosidase, with a comprehensive enzyme activity of 10000 u / g; the ligninase is one or more of lignin peroxidase, manganese peroxidase, and laccase, with a comprehensive enzyme activity of 10000 u / g.

[0015] Further, in step 2), the scouring and bleaching is to add the cotton linters after biological enzyme treatment into the scouring and bleaching liquor for treatment. The bath ratio of the system is 1:8 - 15, the treatment temperature is 80 - 100 °C, the alkali concentration of the system is 3 - 8 g / L, and the treatment time is 30 - 60 min.

[0016] Preferably, the scouring and bleaching liquor comprises component H 2 O 2 1 - 5 wt%, KRD-3 0.5 - 1 wt%, caustic soda 3 - 8 wt%, TAED 1 - 2 wt%, and the balance is water.

[0017] Further, it also includes the steps of:

[0018] 3) Washing with water;

[0019] 4) Drying.

[0020] Further, in step 3), the washing with water is to wash the slurry containing refined cotton with water at 30 - 50 °C. The single washing time is 10 - 30 min, and it is washed 2 - 3 times. Meanwhile, the pH is adjusted until the reaction is completed.

[0021] Preferably, in step 3), an inorganic acid is used to adjust the pH. The inorganic acid is hydrochloric acid, citric acid, or sulfuric acid, and the pH is adjusted to 6.5 - 7.5.

[0022] Adopting the above technical solution has the following beneficial effects:

[0023] 1. The preparation method of the present invention first undergoes biological enzyme treatment to specifically treat impurities in cotton linter, such as pectin, hemicellulose, lignin, etc., reducing the dosage of chemical reagents in the subsequent cooking and bleaching stages. At the same time, the biological enzyme treatment has mild conditions, can effectively reduce energy consumption, and thus reduce production costs. Among them, pectinase can hydrolyze or cleave glycosidic bonds, ester bonds, etc. in pectin molecules, destroy the molecular structure of pectin, and degrade it into small molecule substances. It can specifically decompose pectin substances in cotton linter. After removing pectin, the pores between fibers become more unobstructed, which is beneficial to the absorption and transmission of moisture, thereby improving the moisture absorption. High moisture absorption enables refined cotton to come into full contact with reaction reagents when preparing carboxymethyl cellulose, effectively ensuring the reaction activity. At the same time, uniform liquid absorption promotes synchronous and balanced reactions, ensuring good and uniform reaction quality of carboxymethyl cellulose products. Moreover, reducing pectin residues is also beneficial to the subsequent bleaching process, making the bleached whiteness better. Among them, xylanase can hydrolyze xylan and further decompose impurities such as hemicellulose in cotton linter, making the fibers purer, increasing the hydrophilicity of the fibers, and improving the moisture absorption. Among them, ligninase can provide a non-specific, radical-based chain reaction process. Lignin peroxidase and manganese peroxidase, in the presence of H 2 O 2 , through the heme or Mn 2+ etc. in their active centers, generate highly reactive free radicals. Laccase is a copper-containing polyphenol oxidase, and its active center contains copper ions. Free radicals are generated under the action of copper ions. The generated free radicals attack various chemical bonds in the lignin molecule, such as aryl-alkyl ether bonds, carbon-carbon bonds, etc., causing these bonds to break, thereby destroying the complex structure of lignin. After the enzyme treatment with the above combined enzymes, the contents of impurities such as pectin, hemicellulose, wax, and lignin in the linter decrease, reducing the difficulty of subsequent treatment.

[0024] The intermediate product after enzyme treatment is then subjected to cooking and bleaching treatment. By limiting the ratio of each component in the cooking and bleaching liquor used, the alkali consumption is significantly reduced, and the alkali concentration in the treated system is < 2 g / L, reducing the difficulty and cost of sewage treatment and reducing environmental pollution. Among them, H 2 O 2 is used for bleaching, and can also oxidize and decompose organic impurities such as residual grease, wax, and protein in cotton linter, and at the same time decompose part of the lignin, improving the purity and cleanliness of the fibers. In addition, the decomposition products of hydrogen peroxide are water and oxygen, without harmful residues, and are more in line with environmental protection requirements compared with traditional chlorine-containing bleaching agents (such as sodium hypochlorite), especially suitable for fields with high safety requirements such as food packaging paper and medical gauze. And by controlling H 2 O 2The addition amount is 1-5% of the mass of cotton linter, which can not only ensure sufficient reaction in the cooking process, but also effectively avoid excessive reduction of the degree of polymerization of the pulp, thus ensuring stable and excellent quality of the subsequent pulp; KRD-3 therein, as an alkali-resistant hydrogen peroxide stabilizer, can keep the hydroperoxyl ion (HO 2 - ) stable, enabling it to participate more effectively in the bleaching reaction, giving full play to the bleaching effect of hydrogen peroxide, achieving a better bleaching effect on cotton linter, improving the utilization rate of hydrogen peroxide, and at the same time reducing the damage to cotton linter fibers. TAED is tetraacetylethylenediamine, which can be used as a hydrogen peroxide reaction activator. Under alkaline cooking conditions, TAED can promote the decomposition of hydrogen peroxide in the direction beneficial to the bleaching reaction, generating more reactive oxygen species with bleaching effects, such as hydroxyl radicals (·OH), hydroperoxyl radicals (HO 2 ·), etc., and finally obtaining a pulp containing purified cotton.

[0025] 2. The pulp of purified cotton obtained in the present invention is first washed with water at 30-50 °C, aiming to prevent the sudden drop in temperature from causing the closure of fiber pores and hindering the washing out of internal soluble impurities. Then, inorganic acid is added to adjust the pH, which can reduce the ash content of the pulp, improve the whiteness of the pulp, and make the treated pulp meet the usage requirements of the third-grade purified cotton for production.

[0026] Verified by the applicant's experiments, for the purified cotton product prepared by the preparation method of the present invention, the degree of polymerization of the raw material cotton linter is reduced within 150, meeting the quality requirements of the purified cotton for special use (GB / T 9017-2003). The alkali concentration in the cooking system of the present invention is 3-8 g / L, which is significantly reduced by 22-27 g / L compared with the alkali concentration of 30 g / L in the traditional system.

[0027] The following is further described in conjunction with specific embodiments. Specific Embodiments

[0028] In the present invention, the cotton linter is secondary cotton linter and / or tertiary cotton linter, with a degree of polymerization of 2900-3100, an α-cellulose content of 96-99 wt%, a pectinase enzyme activity of 2000 u / g, a xylanase enzyme activity of 10000 u / g, and a ligninase enzyme activity of 10000 u / g. The cooking alkali liquor is prepared with 50% sodium hydroxide solution, the H 2 O 2 content is 27.5%, and both KRD-3 and TAED are industrial grades.

[0029] Example 1

[0030] Preparation method of purified cotton:

[0031] The first step: Biological enzyme pretreatment:

[0032] Add 1.6 kg (dry weight) of prepared cotton linters (after opening and impurity removal) to the wire cage, add 17 kg of soft water at 30 °C to the system, add potassium hydrogen phosphate - potassium dihydrogen phosphate buffer solution, adjust the pH of the system to 6, add 25 g of pectinase SPA-6, 12 g of xylanase, 3 g of ligninase, and 16 g of penetrant JFC. Under the condition of 55 °C, treat for 6 h, and inactivate at high temperature of 80 °C after the treatment is completed.

[0033] The second step of scouring and bleaching:

[0034] Add 17 kg of scouring and bleaching liquor to the pulp system after enzyme treatment and inactivation, heat up to 60 - 70 °C, then seal the reactor, continue to heat up to 100 °C, and keep warm for 30 min.

[0035] The components of the cooking and bleaching liquor include H 2 O 2 3 wt%, KRD-3 0.5 wt%, caustic soda wt 8%, TAED 1%, and the balance is water.

[0036] The third step of washing and drying:

[0037] After scouring and bleaching, wash three times with soft water at 30 °C, 17 kg of water each time. Add hydrochloric acid during the second washing to adjust the pH, ensuring that the pH value of the final product is 7. Drying is carried out by air flow drying method.

[0038] Finally, the yield of highly polymerized micro-bleached refined cotton can reach 90.3%, the moisture absorption is 138, the degree of polymerization is above 2800, the α-cellulose content is 99.4%, and the whiteness is 75.

[0039] Example 2

[0040] The preparation method of refined cotton:

[0041] The first step of biological enzyme pretreatment:

[0042] Add 1.6 kg (dry weight) of prepared cotton linters (after opening and impurity removal) to the wire cage, add soft water at 30 °C - 50 °C to the system, add potassium hydrogen phosphate - potassium dihydrogen phosphate buffer solution, adjust the pH of the system to 6, add 20 g of pectinase SPA-6, 8 g of xylanase, 3 g of ligninase, and 16 g of penetrant JFC. Under the condition of 55 °C, treat for 6 h, and inactivate at high temperature of 80 °C after the treatment is completed.

[0043] The second step

[0044] Scouring and bleaching: Add scouring and bleaching liquor to the pulp system after enzyme treatment and inactivation, heat up

[0045] From 60°C to 70°C, add hydrogen peroxide, hydrogen peroxide stabilizer and activator, then seal the reactor and continue heating to 100°C, and keep the temperature for 30 minutes.

[0046] The components of the cooking and bleaching liquor involved in the cooking and bleaching process include H 2 O 2 2%, KRD - 30.5%, caustic soda 5%, TAED 1%, and the balance is water.

[0047] The third step is washing and drying:

[0048] After cooking and bleaching, wash three times with 30°C soft water. Add hydrochloric acid during the second washing to adjust the pH to ensure that the pH value of the final product is 7. Drying is carried out by air drying.

[0049] Finally, the yield of highly polymerized micro - bleached refined cotton can reach 90.4%, the moisture absorption is 130, the degree of polymerization is above 2800, the α - cellulose content is 99.3%, and the whiteness is 70.

[0050] Example 3

[0051] Preparation method of refined cotton:

[0052] The first step is biological enzyme pretreatment:

[0053] Add 1.6 kg (dry weight) of prepared cotton linters (after opening and impurity removal) to the cage, add 30°C - 50°C soft water to the system, add potassium hydrogen phosphate - potassium dihydrogen phosphate buffer solution, adjust the pH of the system to 6, add 16 g of pectinase SPA - 6, 8 g of xylanase, 2 g of ligninase, and 16 g of penetrant JFC. Under the condition of 55°C, treat for 6 h, and inactivate at 80°C after the treatment is completed.

[0054] The second step is cooking and bleaching:

[0055] Add the cooking and bleaching liquor to the slurry system after enzyme treatment and inactivation, heat up to 60°C - 70°C, add hydrogen peroxide, hydrogen peroxide stabilizer and activator, then seal the reactor and continue heating to 100°C, and keep the temperature for 30 minutes.

[0056] The components of the cooking and bleaching liquor involved in the cooking and bleaching process include H 2 O 2 1%, KRD - 30.5%, caustic soda 4%, TAED 1%, and the balance is water.

[0057] The third step is washing and drying:

[0058] After cooking and bleaching, wash three times with 30°C soft water. Add hydrochloric acid during the second washing to adjust the pH to ensure that the pH value of the final product is 7. Drying is carried out by air drying.

[0059] Finally, the yield of the highly polymerized micro-bleached refined cotton can reach 90.8%, the moisture absorption is 129, the degree of polymerization is above 2800, the α-cellulose content is 99.2%, and the whiteness is 69.

[0060] Comparative Example 1

[0061] The treatment method of refined cotton in this comparative example includes the following steps:

[0062] The wire cage stock preparation step is the same as that in Example 1.

[0063] The first step

[0064] High-temperature alkali cooking: Add sodium hydroxide to the system to keep the system concentration at 3%. Add cooking aid P-3 at 3% by mass of cotton. First, raise the cooking temperature to 100 °C and keep it for 1 h. After replacing the black liquor, raise the temperature to 130 °C and keep it for 6 h.

[0065] The second step

[0066] Washing and drying: After cooking, wash with soft water at 30 °C to 50 °C four times. Add hydrochloric acid during the third washing to adjust the pH to ensure that the pH value of the final product is between 6.5 and 7.5. The drying is carried out by air flow drying.

[0067] Finally, the yield of the highly polymerized refined cotton reaches 82%, the moisture absorption is 105, the degree of polymerization is above 2800, the α-cellulose content is 99.3%, and the whiteness is 52.

[0068] Comparative Example 2

[0069] The treatment method of refined cotton in this comparative example includes the following steps:

[0070] The wire cage stock preparation step is the same as that in Example 1.

[0071] The first step of high-temperature alkali cooking:

[0072] Add sodium hydroxide to the system to keep the system concentration at 3%. Add cooking aid P-3 at 3% by mass of cotton. First, raise the cooking temperature to 100 °C and keep it for 1 h. After replacing the black liquor, raise the temperature to 130 °C and keep it for 6 h.

[0073] The second step of adjusting pH:

[0074] After cooking, wash with soft water at 30 °C to 50 °C twice and adjust the pH to 10 - 11.

[0075] The third step of mild bleaching:

[0076] Add hydrogen peroxide to the system with a pH of 10 - 11 at 1% by the number of cotton, heat to 96 °C, and keep it for 1 h.

[0077] The fourth step: washing and drying

[0078] After cooking, wash four times with soft water at 30°C to 50°C. Add hydrochloric acid during the third washing to adjust the pH and ensure that the pH value of the final product is between 6.5 and 7.5. The drying is carried out by air flow drying method.

[0079] Finally, the yield of high-polymer refined cotton reaches 81%, the moisture absorption reaches 125, the degree of polymerization is above 2700, the α-cellulose content is 99.5%, and the whiteness is 63.

[0080] Comparison of quality indicators between the example and the comparative example

[0081]

[0082] The quality requirements for industrial grade three cotton for cellulose ether in the national standard of refined cotton GB / T 9017-2003 are as follows:

[0083] Product Model Degree of Polymerization Moisture Absorption g Whiteness % α-Cellulose Content % M2000X-Ⅲ 2601～2800 ≥130 ≥70 ≥98 M3000X-Ⅲ ＞2800 ≥130 ≥70 ≥98

[0084] Compared with the traditional method, the product of this example meets the quality requirements of industrial grade three cotton in the refined cotton of GB / T 9017-2003. At the same time, the chemical oxygen demand (COD) of the black liquor obtained by boiling and refining is significantly reduced. This not only reduces the burden of black liquor treatment, simplifies the sewage treatment process, effectively reduces the treatment cost, but also reduces the potential pollution to the environment.

Claims

1. A method for preparing refined cotton, characterized in that: The following steps are involved: 1) Take cotton linters and treat them with biological enzymes; 2) After scouring and bleaching, a pulp containing refined cotton is obtained.

2. The method for preparing refined cotton according to claim 1, characterized in that: The cotton linters in step 1) are secondary cotton linters and / or tertiary cotton linters, with a degree of polymerization of 2900-3100 and an α-cellulose content of 96-99 wt%.

3. The method for preparing refined cotton according to claim 1, characterized in that: In step 1), the bio-enzyme treatment is to add cotton linters into enzyme solution for treatment, the bath ratio of the system is 1:8-15, the treatment temperature is 50-60°C, the pH is 6-7, and the treatment time is 3-6h.

4. The method for preparing refined cotton according to claim 3, characterized in that: The enzyme solution comprises components of pectinase 1.5wt%, xylanase 0.5wt%, ligninase 0.125wt%, penetrant JFC 1wt%, and the balance is water.

5. The method for preparing refined cotton according to claim 4, characterized in that: The pectinase is one or more of pectin lyase, pectinesterase, and protopectinase, with a comprehensive enzyme activity of 2000u / g; the xylanase is one or more of exo-β-1,4-xylanase, endo-β-1,4-xylanase, and β-1,4-xylosidase, with a comprehensive enzyme activity of 10000u / g; the ligninase is one or more of lignin peroxidase, manganese peroxidase, and laccase, with a comprehensive enzyme activity of 10000u / g.

6. The method for preparing refined cotton according to claim 1, characterized in that: Step 2) the scouring and bleaching is to add the cotton linters treated with biological enzymes into a scouring and bleaching solution for treatment, the system bath ratio is 1:8-15, the treatment temperature is 80-100°C, the system alkali concentration is 3-8g / L, and the treatment time is 30-60min.

7. The method for preparing refined cotton according to claim 6, characterized in that: The scouring and bleaching liquid comprises components of H2O2 1-5wt%, KRD-3 0.5-1wt%, flake caustic soda 3-8wt%, TAED 1-2wt%, and the balance is water.

8. The method for preparing refined cotton according to claim 1, characterized in that: Also includes the steps: 3) Washing; 4) Drying to obtain refined cotton products.

9. The method for preparing refined cotton according to claim 8, characterized in that: In step 3), the water washing is to wash the pulp containing refined cotton with water at 30-50° C., with a single washing time of 10-30 minutes, and wash 2-3 times, while adjusting the pH value until the reaction is completed.

10. The method for preparing refined cotton according to claim 9, characterized in that: Step 3) adjusting the pH with an inorganic acid, wherein the inorganic acid is hydrochloric acid, citric acid or sulfuric acid, and adjusting the pH to 6.5-7.5.

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