A method for treating mechanical pulp with bio-enzymes extracted from pure plants and paper products prepared from the treated mechanical pulp.

Abstract

This application provides a method for applying a plant-extracted bioenzyme to paper pulp treatment. Specifically, it involves applying plant-extracted peroxidase to the pre-bleaching delignification treatment of mechanical pulps from bamboo, reeds, and eucalyptus using H2O2. Key parameters in the treatment process, such as enzyme dosage, treatment time, and H2O2 addition, are optimized. The optimal treatment scheme is determined by measuring the total lignin and surface lignin content and fiber morphology of the treated samples. This optimal scheme is more effective in improving the fiber strength and brightness of the treated pulp compared to conventional enzyme treatment methods. Furthermore, molecular docking simulations are performed using a model of the plant-extracted peroxidase and lignin model compounds (LMCs) with different degrees of polymerization to obtain information on the interaction between the enzyme and LMCs, revealing the mechanism of action between peroxidase and lignin. This provides reliable evidence and technical reference for the feasibility of using plant-extracted peroxidase to remove surface lignin from mechanical pulp and promote subsequent H2O2 bleaching.

Description

Technical Field

[0001] This application relates to the field of lignin removal technology in papermaking mechanical pulp, specifically to a method for treating mechanical pulp with a bio-enzyme extracted from pure plants and paper products prepared from the treated mechanical pulp. Background Technology

[0002] Removing lignin from the surface of pulp is an important approach to modifying and improving mechanical pulp. In 2021, Professor Schuur's team in Sweden proposed that "removing lignin from low-energy mechanical pulp using deep eutectic solvent (DES) under mild conditions could serve as a green alternative to traditional delignified fibers (chemical pulp) used in papermaking." They experimented with DES composed of lactic acid and choline chloride, using it to gently cook Norway spruce mechanical pulp at 100–130°C. The final lignin content was reduced to 14%, the yield of delignified pulp was approximately 50%, and the fiber length was 0.6 mm. Schuur's research points to an important direction for the development of mechanical pulp technology, but the chemical reagents they used still present problems such as large consumption, difficulty in recycling, and potential environmental pollution. Furthermore, scholars believe that, unlike chemical pulping, for the purpose of mechanical pulp modification, simply removing surface lignin is sufficient to improve fiber surface hydrophilicity and bonding strength. Enzymatic treatment combined with hydrogen peroxide bleaching for removing surface lignin from mechanical pulp is a more practical solution than gentle cooking with DES.

[0003] In research on the gentle removal of lignin, the Nanjing Institute of Forestry Chemistry, Chinese Academy of Forestry, conducted such studies in 2000. They treated wheat straw chemimechanical pulp with xylanase (X) followed by H2O2 bleaching (P), increasing the brightness by 9% ISO. Using the XP1P2 bleaching sequence, they ultimately obtained pulp with a brightness of 60% ISO. Chandra et al. treated fir TMP pulp with laccase followed by H2O2 bleaching. Laccase treatment increased the final brightness by 1.5–2.5% ISO, while reducing H2O2 consumption by 15–20%. Qiu Wenxiu of Qilu University of Technology treated hardwood APMP pulp with a laccase / 1-hydroxybenzotriazole (HBT) system. With an enzyme dosage of 2 U / g, the brightness increased from 56.3% ISO to 57.6% ISO, the tensile strength increased from 23.0 N·m / g to 24.9 N·m / g, and the tear index increased from 2.8 mN·m. 2 / g increased to 3.4mN·m 2Peroxidase also has the function of directly removing lignin from mechanical pulp, but to date, there are few research reports in this field on the direct removal of lignin from the surface of mechanical pulp by peroxidase, as well as its role in promoting H2O2 bleaching and improving fiber strength. In particular, there is a lack of research on how to apply natural plant peroxidase extracted from plants to the removal of lignin in papermaking mechanical pulp, exploring and determining the lignin removal mechanism and optimizing the process conditions to improve the efficiency and quality of lignin removal from papermaking mechanical pulp, thereby improving the strength and brightness of pulp fibers, and ultimately improving the brightness and strength of the paper obtained after mechanical pulp sheet formation. At the same time, the use of natural enzymes can reduce the application of other chlorinated chemical reagents in the lignin removal process during papermaking, thus improving environmental safety and reducing environmental pollution. This is of great significance and has promising application prospects for those skilled in the art. Summary of the Invention

[0004] To address the aforementioned problems, this application provides a method for applying a purely plant-extracted bio-enzyme to paper pulp for delignification. Specifically, a purely plant-extracted peroxidase is applied to three different types of pulps used in paper products: bamboo, reed, and eucalyptus mechanical pulps, before H2O2 bleaching for delignification treatment. Key parameters during the treatment process, such as enzyme dosage, treatment time, and H2O2 addition, are optimized. The optimal treatment scheme is determined by measuring the total lignin and surface lignin content and fiber morphology of the treated samples. This optimal scheme significantly improves the fiber strength and brightness of the treated pulp compared to conventional enzyme treatment methods. Furthermore, the inventors used a model of the purely plant-extracted peroxidase to perform molecular docking simulations with lignin model materials (LMCs) of different degrees of polymerization to obtain information on the interaction between the enzyme and LMCs. This provides a deeper understanding of the mechanism of action between peroxidase and lignin, offering reliable evidence and technical reference for the feasibility of using purely plant-extracted peroxidase to remove surface lignin from mechanical pulp and promote subsequent H2O2 bleaching.

[0005] The specific technical solution adopted in this application is as follows:

[0006] A method for treating mechanical pulp using bio-enzymes extracted from pure plants, specifically comprising: the treatment method being carried out according to any one of the following processing procedures:

[0007] Processing procedure (A): The mechanical pulp is treated with naturally extracted peroxidase at pH 5.0 and a temperature of 60°C for 2-6 hours. The amount of peroxidase added is 0.5-1.5 g / kg oven-dry pulp, and the reaction concentration of the mechanical pulp is 10%. The mechanical pulp is washed with deionized water to balance the moisture content and complete the treatment.

[0008] Process (B): First, naturally extracted peroxidase is used to treat the mechanical pulp at pH 5.0 and 60℃ for 2-6 hours. The amount of peroxidase added is 0.5-1.5 g / kg oven-dry pulp. 5 g / L of ethylenediaminetetraacetic acid (EDTA) is added to the peroxidase-treated mechanical pulp. The pulp to be treated with EDTA is placed in a polyethylene sealed bag and kneaded to mix the pulp and the solution evenly. It is then placed in a 60℃ constant temperature water bath for 60 minutes. After the bath, it is cooled to room temperature and washed with deionized water to adjust the solid content to 10%. The EDTA-treated mechanical pulp is then bleached with H2O2 under the following conditions: 40 g / L H2O2 and NaOH. The mixture was prepared with 20 g / L MgSO4 and 5 g / L MgSO4, and a mechanical pulp concentration of 10%. The reaction was carried out at 80℃ for 120 min. During the reaction, the pulp was kneaded every 15 min to ensure uniform reaction. After bleaching, the pulp was washed with deionized water until neutral to balance the moisture content. The treatment was then complete. As a further improvement to the above method, the peroxidase was extracted from the leaves of *Pholiota rubescens*, and the peroxidase activity was 35.64 ± 4.77 U / mL.

[0009] As a further improvement to the above scheme, when the mechanical pulp is bamboo mechanical pulp, the peroxidase dosage during the peroxidase treatment is 1.5 g / kg. 绝干浆 The treatment time was 4 hours, and the H2O2 addition during the H2O2 bleaching process was 0.3 g / L; when the mechanical pulp was reed mechanical pulp, the peroxidase dosage during the peroxidase treatment was 1.5 g / kg. 绝干浆 The treatment time was 6 hours, and the H2O2 addition during the H2O2 bleaching process was 0.3 g / L; when the mechanical pulp was eucalyptus mechanical pulp, the peroxidase dosage during the peroxidase treatment was 1.5 g / kg. 绝干浆 The processing time was 4 hours, and the amount of H2O2 added during the H2O2 bleaching process was 0.3 g / L.

[0010] As a further improvement to the above scheme, when the mechanical pulp is bamboo mechanical pulp, reed mechanical pulp, and eucalyptus mechanical pulp, the acid-soluble lignin of the bamboo mechanical pulp, reed mechanical pulp, and eucalyptus mechanical pulp treated according to process (B) decreased by 34.8%, 19.0%, and 26.8% respectively, and / or, Klason lignin decreased by 13.4%, 15.9%, and 21.4% respectively, and / or, the total lignin decreased by 14.8%, 12.5%, and 17.9% respectively.

[0011] As a further improvement to the above scheme, when the mechanical pulp is bamboo mechanical pulp, reed mechanical pulp, or eucalyptus mechanical pulp, the acid-soluble lignin of the bamboo mechanical pulp, reed mechanical pulp, and eucalyptus mechanical pulp treated according to process (A) is reduced by 8.7%, 4.8%, and 7.3%, respectively, and / or, Klason lignin is reduced by 1.6%, 2.3%, and 5.5%, respectively, and / or, total lignin is reduced by 3.7%, 4.2%, and 3.6%, respectively.

[0012] As a further improvement to the above scheme, when the mechanical pulp is bamboo mechanical pulp, reed mechanical pulp, or eucalyptus mechanical pulp, the content of C atoms bonded only to saturated C atoms or hydrogen atoms in the bamboo mechanical pulp, reed mechanical pulp, and eucalyptus mechanical pulp after treatment process (A) decreases by 3.1%, 1.9%, and 11.4% respectively, while the content of C atoms bonded to one carbonyl O atom or two non-carbonyl O atoms increases by 8.8%, 11.41%, and 3.8% respectively.

[0013] As a further improvement to the above scheme, when the mechanical pulp is bamboo mechanical pulp, reed mechanical pulp, or eucalyptus mechanical pulp, the content of C atoms bonded only to saturated C atoms or hydrogen atoms in the bamboo mechanical pulp, reed mechanical pulp, and eucalyptus mechanical pulp after treatment process (B) decreases by 16.8%, 20.4%, and 39.4%, respectively, while the content of C atoms bonded to one non-carbonyl O atom increases by 15.8%, 17.7%, and 37.3%, respectively.

[0014] As a further improvement to the above scheme, the specific improvements include: when the mechanical pulp is reed mechanical pulp, after treatment process (A), the O / C ratio is increased by 1.61% compared to the original pulp; after treatment in stage X, the O / C ratio of the reed mechanical pulp is increased by 1.61% compared to the original pulp, and the surface lignin concentration is reduced by 3.22%; when the mechanical pulp is bamboo mechanical pulp, after treatment process (A), the O / C ratio of the bamboo mechanical pulp is increased by 1.36% compared to the original pulp, and the surface lignin concentration is reduced by 2.72%; when the mechanical pulp is eucalyptus mechanical pulp, after treatment process (A), the O / C ratio of the eucalyptus mechanical pulp is increased by 1.24%, and the surface lignin concentration is reduced by 2.48%.

[0015] As a further improvement to the above scheme, when the mechanical pulp is bamboo mechanical pulp, reed mechanical pulp, or eucalyptus mechanical pulp, the fiber length of bamboo mechanical pulp, reed mechanical pulp, and eucalyptus mechanical pulp after processing (B) is reduced by 9.2%, 7.6%, and 6.7%, respectively.

[0016] This application also provides a paper product prepared from mechanical pulp obtained by the aforementioned method of treating mechanical pulp with bio-enzymes extracted from pure plants, wherein the paper product satisfies at least one of the following conditions (1)-(5):

[0017] (1) The whiteness of the paper products made from bamboo mechanical pulp, reed mechanical pulp and eucalyptus mechanical pulp obtained by process (A) is 40.70% ISO, 40.1% ISO and 40.61% ISO respectively.

[0018] (2) The paper products made from the mechanical pulp of bamboo, reed and eucalyptus obtained by the treatment process (A) have a whiteness that is 3.68% ISO, 3.35% ISO and 5.51% ISO higher than that made from the original pulp.

[0019] (3) The paper products prepared from the mechanical pulp of bamboo, reed and eucalyptus obtained by the process (B) have tensile indices of 8.57 N·m / g, 5.60 N·m / g and 25.69 N·m / g, respectively.

[0020] (4) The paper products made from the mechanical pulp of bamboo, reed and eucalyptus obtained by the treatment process (B) have tensile indices that are 50.7%, 61.1% and 22.3% higher than those of their original pulps, respectively.

[0021] (5) Paper products made from the mechanical pulp of bamboo, reed and eucalyptus obtained by the treatment process (B) have a tear index that is 53.2%, 36.2% and 11.0% higher than that made from the original pulp, and a burst index that is 2.4%, 10.2% and 7.3% higher, respectively.

[0022] Beneficial technical effects

[0023] This invention focuses on mechanical pulps made from bamboo, reeds, and eucalyptus. It investigates the delignin removal process using peroxidase PRLP (peroxidase extracted from the leaves of the natural plant *Pycnodon dactylon*, denoted as PRLP; for brevity, the naturally extracted peroxidase used in this application will be abbreviated as PRLP) extracted from the leaves of *Pycnodon dactylon* (X stage), EDTA chelation treatment (Q stage), and H2O2 bleaching treatment (P stage). The changes in lignin concentration and the effects of XQP treatment on the physical properties and fiber morphology of the pulp are analyzed, including:

[0024] Peroxidase, a natural plant-derived enzyme used in the pretreatment of three types of mechanical pulp, can improve brightness and enhance mechanical strength. Through investigation and optimization of enzyme dosage, treatment time, and the amount of H2O2 cofactor added, the optimal enzyme treatment scheme for X-segment bamboo mechanical pulp, reed mechanical pulp, and eucalyptus mechanical pulp was obtained, with an enzyme dosage of 1.5 g / kg. 绝干浆The treatment times were 4h, 6h, and 4h, respectively, with H2O2 added at 0.3g / L. After XQP treatment, the brightness of bamboo pulp, reed pulp, and eucalyptus pulp increased by 11.67%, 15.06%, and 18.03% ISO, respectively, ultimately reaching 48.69%, 51.81%, and 53.13% ISO. XQP treatment increased the tensile index of bamboo pulp, reed pulp, and wood pulp by 59.3%, 66.2%, and 22.3%, respectively, and the tear index by 53.2%, 36.2%, and 11.0%, respectively, with better results than peroxidase extracted from other plants.

[0025] After treatment with PRLP peroxidase, the lignin in bamboo pulp, reed pulp, and eucalyptus pulp was significantly removed. Compared with untreated pulp, the total lignin content decreased by 3.7%, 4.2%, and 3.6%, respectively; the surface lignin content decreased by 2.72%, 3.22%, and 2.48%, respectively. PRLP peroxidase not only removed lignin from the surface of pulp fibers but also had a significant auxiliary effect on subsequent H2O2 bleaching for lignin removal. Specifically, the total lignin content of bamboo pulp, reed pulp, and wood pulp decreased by 14.8%, 12.5%, and 17.9%, respectively, and the surface lignin content decreased by 25.72%, 28.92%, and 36.80%, respectively, after XQP treatment. After PRLP and subsequent H2O2 treatment, the morphology of the three types of mechanical pulp fibers did not change significantly, but the microstructure showed a reduction in hydrophobic particles on the fiber surface and the exposure of more hydrophilic microfibrils. Further molecular docking revealed that lignin monomers, dimers, trimers, tetramers, and pentamers can all enter or approach the peroxidase active region, forming stable bindings with PRLP enzymes. The size and structure of these structural groups determine their binding energy at the effective sites. The molecular volume of the lignin model compound exhibits a roughly linear relationship with the binding energy; the larger the molecular volume, the smaller the absolute value of the binding energy. Computer simulations have demonstrated that PRLP can interact with lignin. This provides broad theoretical and data support for the application of naturally extracted bioenzymes, especially peroxidases, in the mechanical removal of lignin from pulp, and further expands the simplified, efficient, and widespread application of naturally extracted bioenzymes in lignin removal. Attached Figure Description

[0026] Figure 1 XPS full spectrum and C1s peak decomposition spectrum of mechanical pulp;

[0027] Figure 2 Microscopic image of XQP-treated mechanical pulp fibers;

[0028] Figure 3 AFM images of mechanical pulp before and after XQP treatment;

[0029] Figure 4: Relationship between PRLP docking binding energy and lignin model material and molecular volume. Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below in conjunction with various specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise specified, the experimental methods described in the following embodiments are conventional methods; the reagents and materials, unless otherwise specified, can be obtained through ordinary commercial channels.

[0031] Instructions for experimental reagents

[0032] Ethylenediaminetetraacetic acid (analytical grade) was purchased from Aladdin Reagent Company; magnesium sulfate (analytical grade) was purchased from Sinopharm Chemical Reagent Company; all other reagents were analytical grade.

[0033] The methods for obtaining raw materials and related testing methods in this application include:

[0034] The naturally extracted biological enzyme used in this application is a peroxidase, obtained from the leaves of the soft-leaved prickly prickly palm, denoted as PRLP. The extraction method includes:

[0035] A. Obtaining crude peroxidase solution

[0036] The natural plant was collected for peroxidase extraction, a process that included:

[0037] After rinsing with deionized water and draining, weigh 100g of leaves (cut to less than 2cm), mix with 150mL of phosphate buffer solution (0.01mol / L, pH 5), and blend in a plant cell wall blender for 1 minute to obtain a homogenate. Then filter through 8 layers of degreased cotton gauze and centrifuge for 10 minutes to remove the filter residue, obtaining a clear liquid, which is used as the initial liquid for subsequent separation and extraction, and is referred to as the aqueous extract. Slowly add the aqueous extract dropwise to a certain volume of acetone while stirring, let it stand at 4℃ for 15 minutes, centrifuge for 8-11 minutes to remove the supernatant, and obtain a precipitate. Dissolve the precipitate with phosphate buffer solution, make up to 100mL, and centrifuge again to remove insoluble matter, obtaining crude enzyme solution.

[0038] B. Purification of crude peroxidase solution

[0039] The crude enzyme solution obtained from acetone extraction is pumped into an ion exchange chromatography column to remove pigments and impurities, specifically including:

[0040] (1) Ion exchanger pretreatment: DEAE cellulose-DE52 was soaked in deionized water for 3 hours to swell, then soaked in 0.5 mol / L NaOH solution for 30 minutes, then washed with deionized water until neutral, and then soaked in 0.5 mol / L HCl solution for 30 minutes and washed again until neutral.

[0041] (2) Column packing: The pretreated DEAE cellulose-DE52 was packed into the chromatography column and the chromatography column was fully equilibrated with 0.01 mol / L phosphate buffer solution at pH 5.

[0042] (3) Sample loading: Add 7 mL of crude enzyme solution and equilibrate with 15 mL of phosphate buffer solution;

[0043] (4) Elution and collection: During elution, a gradient mixing of 2 mol / L NaCl solution and phosphate buffer solution was used for elution. One tube of sample was collected every 5 min, and the elution time was 2 h. A total of 24 tubes of samples were collected. The peroxidase activity of each tube of sample was detected.

[0044] (5) Regeneration of the exchanger: Regeneration is carried out by conversion with 1 mol / L HCl and 1 mol / L NaOH. If the regenerated ion exchanger is not used for a long time, it should be stored at 4°C to prevent microbial growth.

[0045] C. Desalting and freeze-drying of peroxidase

[0046] The enzyme solution after ion exchange chromatography was desalted using ultrafiltration centrifuge tubes. The enzyme solution was loaded into ultrafiltration centrifuge tubes and centrifuged at 5000 rpm for 8-11 min. The enzyme retained in the centrifuge tubes was dissolved in deionized water and centrifuged again. The above operation was repeated several times until Cl- could not be detected in the centrifuged liquid that had passed through the filter membrane. Finally, the retained enzyme was dissolved in phosphate buffer and freeze-dried into powder using a vacuum freeze dryer to obtain peroxidase.

[0047] In step A, the centrifugation conditions are 4℃ and the rotation speed is 9000-12000rpm; in step B, the diameter of the chromatography column is 1.3-1.7cm and the length is 30cm.

[0048] After extraction, the activity of the obtained natural catalase was measured to be 35.64±4.77 U / mL, the optimal reaction pH was 5.0, and the temperature was 60℃.

[0049] The mechanical pulp raw materials used in this application are laboratory-made reed, bamboo, and eucalyptus mechanical pulps (to avoid redundancy, they will be referred to as bamboo pulp, reed pulp, and wood pulp respectively in the following description), and the preparation process is as follows:

[0050] Cut reed stalks into 3-5cm long sections, and cut bamboo shoots and eucalyptus wood chips into 0.5cm x 2cm pieces. Soak them in deionized water for 12 hours. Then, directly grind the soaked reed stalks and bamboo shoots into a high-consistency disc mill (2500-Ⅱ, KRK Corporation, Japan). The eucalyptus wood chips were heat-treated at 121℃ for 1 hour, cooled, and then ground. The first grinding stage used a 0.5mm disc gap and a solids content of 20%; the second grinding stage used a 0.15mm disc gap and a solids content of 10%.

[0051] The pulp was finely ground using a PFI refiner (Mark V1, Hamjern, Norway) at a pressure of 3.33 N / mm and a rotation speed of 10,000 rpm. The finely ground mechanical pulp was then sieved using a plate screen (PAPTACC.11P, Messmer Somerville, Germany) with a sieve opening size of 2.5 mm. The screen residue for all three types of mechanical pulp did not exceed 3%. The screened pulp was then filtered through a 200-mesh nylon screen, dispersed, and dried in a 50°C constant-temperature ventilated drying oven for later use. The freeness of the reed pulp, bamboo pulp, and wood pulp were measured to be 11.7°SR, 10.5°SR, and 12.8°SR, respectively, with brightness values ​​of 36.75% ISO, 37.02% ISO, and 35.10% ISO, respectively.

[0052] Enzyme treatment stage (Segment X)

[0053] pH 5.0 and temperature 60℃ were selected as the experimental conditions for enzyme treatment, and the pulp concentration of untreated mechanical pulp was set to 10%. It should be noted that H2O2 cofactor is crucial for peroxidase delignination. Although it has the ability to oxidize lignin, the amount added and the reaction temperature are insufficient to meet the conditions required for hydrogen peroxide bleaching.

[0054] Chelation treatment (Q segment)

[0055] After X treatment, the pulp concentration was set to 10% in the chelation treatment stage. 0.5% ethylenediaminetetraacetic acid (EDTA) was added. The mechanical pulp to be treated with EDTA was placed in a sealed polyethylene bag, kneaded to ensure uniform mixing of the pulp and the chemical solution, and then placed in a 60°C constant temperature water bath for 60 minutes to remove metal ions in the pulp that might catalyze the decomposition of H₂O₂. After chelation, the pulp was cooled to room temperature, washed with deionized water, and finally adjusted to a solids content of 10% for later use.

[0056] Hydrogen peroxide treatment (P-stage)

[0057] The pulp after X and Q stage treatment was bleached with H2O2 under the following conditions: 4% H2O2, 2% NaOH, 0.5% MgSO4, 10% pulp consistency, 80℃ temperature, and 120 min time. During the reaction, the pulp was kneaded every 15 min to ensure uniform reaction. After bleaching, the pulp was washed with deionized water until neutral to balance the moisture content, and then set aside for later use.

[0058] Copying

[0059] The XQP-treated pulp was decomposed in a deflator at 2000 revolutions, and then paper was formed using a Kaiser process automatic papermaking system (RK3AKWT, Austrian RK3A). The paper basis weight was 60 ± 1.5 g / m³. 2 Then, it was placed in a constant temperature and humidity chamber (temperature 23℃, relative humidity 50%) for 24 hours, and then cut as required for strength performance testing.

[0060] Pulp performance testing methods

[0061] Whiteness measurement

[0062] The whiteness of the transparencies was measured using a whiteness meter (CTP-ISO, Technidyne ColorTouch, USA). The samples were placed on the test bench for testing, and the data was recorded. For each set of conditions, five measurements were taken on both the front and back sides, and the average value was recorded.

[0063] Tensile strength determination

[0064] The tensile index of the sheet was measured using a tensile strength tester (L&WCE062, Lorentzen & Wettre, Sweden). The sample width was 15 mm and the length was 150 mm. The maximum tensile strength, i.e., the maximum tension the paper can withstand, was measured. Measurements were taken three times for each condition, and the average value was used. The tensile index was calculated by dividing the tensile strength by the paper's basis weight.

[0065] Bursting strength test

[0066] The maximum bursting strength (bursting index, the ratio of bursting strength to basis weight) of the paper sheet was determined using a bursting strength tester (L&W CE180, Lorentzen & Wettre, Sweden), which measures the maximum pressure the paper can withstand per unit area. The test sample was placed above the instrument's diaphragm, the "Start" button was pressed, and the data was recorded. Each condition was measured three times, and the average value was taken.

[0067] Tear strength test

[0068] The tear strength of the paper sheet was tested in a tear strength tester (L&W009, Lorentzen & Wettre, Sweden) (the tear index is the ratio of tear strength to the basis weight of the paper sheet). The paper sample size was 63mm × 50mm, fixed on the fixture, the paper was cut by pressing the "CLAMP" key, and the test was performed by pressing the "PEND" key. The data was recorded. Each set of conditions was measured 3 times and the average value was taken.

[0069] Determination of acid-soluble lignin and Klason lignin

[0070] Acid-soluble lignin and Klason lignin were determined according to the methods of GB / T10337—2008 and GB / T747—2003, respectively.

[0071] Accurately weigh 2g of pulp, extract with acetone for 6 hours. After extraction, air-dry the pulp and react with 40mL of 72% sulfuric acid solution at 25℃ for 2 hours. Then dilute with water to an acid concentration of 3% and boil for 4 hours, continuously adding hot water to maintain a constant solution volume of 1540mL. After the reaction, wash the residue with distilled water and dry in an oven at 105℃ to constant weight. The Klason lignin content (%) in eucalyptus pulp is calculated by dividing the mass of the dried residue by the mass of the oven-dried pulp sample. For bamboo and reed pulp, the dried residue needs to be transferred to a high-temperature furnace and calcined (900℃) to obtain the ash mass. Klason lignin content (g / g) of bamboo and reed pulp. 干浆 The content of acid-soluble lignin is calculated by subtracting the mass of ash after high-temperature calcination from the mass of the dried residue, and then dividing by the mass of the oven-dried pulp sample. Acid-soluble lignin is determined by measuring the supernatant obtained after filtering out acid-insoluble lignin, using a 3% sulfuric acid solution as a control. The absorbance of the filtrate at 205 nm is measured, and the acid-soluble lignin content (g / g) is calculated using the following formula. 干浆 Two parallel measurements were taken for each group of samples, and the average value was recorded.

[0072]

[0073] Where A is the absorbance at 205 nm; 110 is the absorption coefficient, in L·g. -1 ·cm -1 m0 — Mass of oven-dried pulp, in grams.

[0074] X-ray photoelectron spectroscopy (XPS)

[0075] Accurately weigh 2.0 g of oven-dry pulp, wrap it in pre-extracted filter paper, and extract it with acetone in a Soxhlet extractor for 6 hours to remove the extract. Then wash with deionized water until neutral, flatten it on a glass plate to form a pulp sheet, and air-dry it at room temperature. Analyze the pulp using X-ray photoelectron spectroscopy. Use the formula below to estimate the lignin content on the fiber surface.

[0076]

[0077] Among them, O / C 碳水化合物 =0.83, O / C 木质素 =0.33.

[0078] Fiber morphology detection

[0079] Optical microscopy observation: After the fibers with different treatment levels are fully dispersed, the fiber morphology is observed under an optical microscope at a magnification of 100x.

[0080] The fiber analyzer process for fiber determination is as follows: Prepare a fiber suspension with a concentration of 20-35 mg / L, preferably 30 mg / L: Weigh 30 mg of sample, disperse the sample by stirring up and down in a dedicated dispersant until the sample is evenly dispersed, then pour it into a graduated cylinder and add water to 1000 mL, stirring thoroughly. Select the "rotary mode" in the testing software for testing. The fiber analyzer will calculate the length, diameter, crimp content, and fine fiber content of approximately 10,000 fibers.

[0081] Micromorphological analysis

[0082] Pulp fibers were dispersed in deionized water (pulp concentration ≤ 0.2%). The pulp suspension was dropped onto a mica sheet pre-attached to a metal plate using a dropper and allowed to air dry in a clean environment, avoiding surface contamination by dust. The fiber surface was measured using an atomic force microscope (AFM) (Multimode 8, Bruker, Germany) in tapping mode.

[0083] PRLP molecular docking with lignin model compounds

[0084] Referring to the lignin model database of the USDA Forest Products Laboratory (FPL), 3D models of lignin monomers, dimers, trimers, and tetramers were drawn using Chem3D (Table 3-2). Molecular docking was performed between the lignin monomers and PRLP models using AutodockVina. The molecular docking and result processing steps are as follows:

[0085] The 3D molecular structure of guaiacol was obtained from the PubChem database (https: / / pubchem.ncbi.nlm.nih.gov / ), saved as an SDF file, opened in Chimera software, and saved as a PDB file. The protein structure PDF file was opened in Autodock software, and dehydrated, hydrogenated, and balanced its charge, then output as a PDBQT file. The ligand molecule was also output as a PDBQT file in the Ligand option of Autodock software. The protein and ligand molecules were opened in the Grid option, and the box size was set to [value missing]. Grid length is The box region completely covers the protein. Docking parameters are set in the Docking options, and AutodockVina is run for molecular docking, with 20 docking attempts per condition. After docking, the optimal docking conformation is selected to generate a PDB file. Chimera software is used to redraw the image and measure dimensions, and LigPlus software is used to analyze the amino acid residues that interact with the ligand.

[0086] Examples 1-10

[0087] Examples 1-9 (see Table 1) are different examples of using bamboo mechanical pulp.

[0088] Table 1 Summary of each scheme and measurement results in Examples 1-9

[0089]

[0090]

[0091] Note: Raw pulp is untreated bamboo mechanical pulp, the same applies below.

[0092] As shown in Table 1, the enzyme dosage has a more significant impact on whiteness and burst strength index than the treatment time and H2O2 addition amount. Treatment time, however, has a greater impact on tensile index and tear index. For bamboo pulp whiteness, the optimal solution is the one described in Example 8, with an enzyme dosage of 1.5 g / kg. 绝干浆 The treatment time was 4 hours, and the H2O2 addition was 0.1 g / L. After treatment with this scheme, the brightness of bamboo mechanical pulp increased from 37.02% ISO to 40.65% ISO. Under these conditions, compared to the original pulp, the tensile index increased by 15.2%, the bursting index increased by 0.9%, and the tear index did not increase. Regarding strength indicators, the bursting index and tear index did not change significantly. Both of these indicators are closely related to the fiber length itself, and peroxidase treatment has little effect on fiber length. Therefore, enzyme treatment has a limited effect on improving the bursting index and tear index of the pulp. The tensile index increased significantly after enzyme treatment at an enzyme dosage of 0.5 g / kg. 绝干浆 When the treatment time is 4 hours and the H2O2 addition is 0.5 g / L, the tensile strength can be increased from 5.38 N·m / g to 6.37 N·m / g, an increase of 18.4%. Under these conditions, the whiteness increases by 2.58% ISO, the bursting index increases by 3.4%, and the tear index increases by 1.6%. Besides fiber length, the bonding strength between fibers is the most important influencing factor on the tensile index. After enzyme treatment, the lignin on the fiber surface is removed, exposing the fibers and allowing for more hydrogen bonding between them, thus improving the tensile index.

[0093] The inventors calculated the range of experimental results for each factor level. The magnitude of the range reflects the degree of influence of that factor on the result; a larger range indicates a greater influence of that factor on the experimental result. Based on the range, it can be seen that enzyme treatment has the greatest impact on the whiteness index. Theoretically, the optimal solution differs from the solution in Example 8 above, specifically: enzyme dosage 1.5g / kg. 绝干浆 The treatment time was 4 hours, and the H2O2 addition amount was 0.3 g / L. Experiments and verifications were conducted on this scheme, and the paper made from the treated pulp showed a whiteness of 40.70% ISO, a tensile index of 6.39 N·m / g, a burst index of 3.27 kPa·m² / g, and a tear index of 0.63 mN·m² / g. Compared to the scheme in Example 8, except for a decrease in the burst index...

[0094] Except for 0.6%, all other indices were higher than the optimal experimental scheme. Therefore, this scheme, namely, enzyme dosage of 1.5g / kg, is preferred for subsequent use of bamboo pulp. 绝干浆 The scheme with a processing time of 4 hours and an H2O2 addition amount of 0.3 g / L is also used as the technical solution of Example 10 of this application.

[0095] Examples 11-20

[0096] Examples 11-19 are examples of reed mechanical pulp treatment and corresponding results. See Table 2. Analysis of the effects of each factor shows that enzyme treatment time has the largest range of effects on whiteness, tensile index, and tear index, while enzyme dosage has the largest range of effects on burst index. The scheme of Example 8 was adopted, i.e., enzyme dosage of 1.5 g / kg. 绝干浆 The treatment time was 4 hours, and the H2O2 addition was 0.1 g / L. After treatment, the brightness of reed pulp could be increased by up to 3.64% ISO. In this scheme, the tensile index of the paper increased by 25.5%, the burst index increased by 2.9%, and the tear index increased by 3.4%. Enzyme treatment had a significant impact on the tensile index of reed mechanical pulp, with an enzyme dosage of 0.5 g / kg. 绝干浆 When the treatment time was 6 hours and the H2O2 addition was 0.3 g / L, the tensile index increased by a maximum of 44.81%. Simultaneously, the tear index also increased significantly, by 37.9%. The tear index is closely related to the contact area between fibers; the larger the contact area, the greater the frictional resistance. Therefore, an increase in the tear index indicates that enzyme treatment of pulp fibers removes lignin, increasing the contact area between fibers and thus improving their strength properties.

[0097] Table 2 Summary of each scheme and measurement results in Examples 11-19

[0098]

[0099] Range analysis revealed that the theoretically optimal solution for controlling the tensile index is an enzyme dosage of 1.5 g / kg.绝干浆 The treatment method with a processing time of 4 hours and an H2O2 addition of 0.3 g / L was validated, yielding a whiteness of 40.10% ISO, a tensile index of 4.90 N·m / g, and a burst index of 3.16 kPa·m. 2 / g, tearing index is 0.68mN·m 2 / g, compared to the preferred embodiment of Example 8 in Table 2 above, except for a 15% reduction in the tear index, all other indices are higher than the optimal embodiment of Example 8. Therefore, this treatment scheme is selected for subsequent processing of reed mechanical pulp: enzyme dosage 1.5g / kg. 绝干浆 The processing time was 6 hours, the amount of H2O2 added was 0.3 g / L, and this verification scheme was used as the scheme of Example 20 of this application.

[0100] Examples 21-30

[0101] Table 3 lists the various embodiments and results of the eucalyptus mechanical pulp treatment. Calculations show that the pulp's brightness and burst strength index are significantly affected by the enzyme dosage, the tensile index by the enzyme treatment time, and the tear index by the amount of H2O2 added. For pulp brightness, the order of influence is: enzyme dosage > treatment time > H2O2 addition. Therefore, compared to other embodiments, Example 3, with an enzyme dosage of 0.5 g / kg, is the optimal solution. 绝干浆 The treatment time was 6 hours, and the H2O2 addition was 0.3 g / L. Under these conditions, the whiteness increased by 7.6%, the ISO tensile index increased by 8.7%, the bursting index increased by 1.5%, and the tear index increased by 5.1%. Compared with Yu et al.'s use of Saccharomonosporaviridis to ferment a Dyp-type peroxidase SviDyP, which increased the whiteness of eucalyptus sulfate pulp by 3.0% ISO, the naturally extracted peroxidase (PRLP) used in this invention showed a better and superior effect in improving whiteness.

[0102] Table 3 Summary of Schemes and Results of Examples 21-29

[0103]

[0104] Enzyme treatment time also has a significant impact on the tensile index of eucalyptus machine pulp. Through range calculation and derivation, the theoretically optimal schemes for brightness and tensile index differ from the scheme in Example 3 above. Specifically, the schemes are: enzyme dosage 0.5 g / kg oven-dry pulp, treatment time 4 h, H2O2 addition 0.3 g / L, and enzyme dosage 1.5 g / kg oven-dry pulp, treatment time 4 h, H2O2 addition 0.3 g / L. Experiments and verifications were conducted on these two schemes, and the corresponding brightness values ​​were 40.73% ISO and 40, respectively. The tensile indices of 61% ISO were 23.54 N·m / g and 23.99 N·m / g, respectively; the burst indices were 3.45 kPa·m² / g and 3.51 kPa·m² / g, respectively; and the tear indices were 3.76 mN·m² / g and 3.80 mN·m² / g, respectively. Based on comprehensive analysis, the optimal enzyme treatment scheme for subsequent experiments was as follows: enzyme dosage of 1.5 g / kg oven-dry pulp, treatment time of 4 h, and H₂O₂ addition of 0.3 g / L. This scheme is also the scheme used in Example 30 of this application.

[0105] Effect of XQP treatment on lignin content

[0106] Based on the aforementioned research and work, the optimal X-stage process conditions were selected, and the acid-soluble lignin and Klason lignin content of pulps with different treatment levels were determined. The results are shown in Table 4. After treatment with peroxidase PRLP (X-stage), the contents of both acid-soluble lignin and Klason lignin in the three types of mechanical pulp decreased. The acid-soluble lignin content of bamboo pulp, reed pulp, and wood pulp decreased by 8.7%, 4.8%, and 7.3%, respectively; the Klason lignin content decreased by 1.6%, 2.3%, and 5.5%, respectively; and the total lignin content decreased by 3.7%, 4.2%, and 3.6%, respectively. As mentioned earlier, peroxidase mainly oxidizes lignin into free radicals. The free radicals further react to break the bonds between lignin monomers. These oxidized or partially degraded lignins require subsequent treatment to be separated from the pulp. After XQP treatment, lignin was significantly removed. Compared with the original pulp, the acid-soluble lignin in bamboo pulp, reed pulp, and wood pulp decreased by 34.8%, 19.0%, and 26.8%, respectively; Klason lignin decreased by 13.4%, 15.9%, and 21.4%, respectively; and total lignin decreased by 14.8%, 12.5%, and 17.9%, respectively. This experiment also included QP treatment as a control. Compared with QP treatment, XQP pretreatment had a slight effect on improving lignin removal from pulp, but it was not significant. The inventors believe that peroxidase, being a large molecule, is difficult to penetrate into the mechanical pulp fibers for reaction. It mainly degrades lignin on the fiber surface, and its effect requires more precise surface chemical analysis techniques to measure.

[0107] Changes in surface lignin content

[0108] After acetone extraction, the pulp in Table 4 was subjected to X-ray photoelectron spectroscopy (XPS) to quantitatively analyze the changes in lignin concentration on the surface of mechanical pulp fibers obtained by different treatment methods. The results are summarized in... Figure 1 And in Table 4. Full spectrum scan of pulp ( Figure 1 Only C and O showed obvious peaks; no other elements were observed. Based on the different ways C atoms bond with other atoms or groups of atoms, the C1s peaks in pulp can be divided into four categories: C1, C2, C3, and C4. C1 refers to C atoms bonded only to saturated C atoms or hydrogen atoms, or in other words, C atoms are bonded only to C or H atoms, i.e., C—C or C—H, with an electron binding energy of approximately 285 eV. In cellulose and hemicellulose molecules, all C atoms are bonded to at least one O atom, therefore, there are no C1-type C atoms. Thus, C1 mainly originates from lignin and extracts in pulp; for raw materials after extraction, C1 can be considered to come from lignin. C2 refers to C atoms bonded to one non-carbonyl O atom, i.e., C—O in alcohols and phenols. Cellulose and hemicellulose in pulp contain a large number of hydroxyl groups bonded to C atoms. The high electronegativity of hydroxyl groups increases the electron binding energy of C2 to approximately 286.5 eV. C3 is a carbon atom bonded to one carbonyl O atom or two non-carbonyl O atoms, i.e., a C=O or O-C-O structure. C3 mainly originates from the acetal structure in hemicellulose and the carbonyl group in lignin, with an electron binding energy of approximately 288 eV. C4 is a carbon atom bonded to one carbonyl O atom and one non-carbonyl O atom, i.e., an O-C=O structure. It mostly originates from the acetyl group in hemicellulose and fatty acids in extracts, with an electron binding energy of approximately 289 eV.

[0109] Table 4. Effects of several treatment methods on the lignin content of pulp.

[0110]

[0111]

[0112] Figure 1The C1s peak diagrams for several mechanical pulps are shown, calibrated with a standard C1s binding energy of 285 eV. Table 4 shows that after PRLP peroxidase treatment, the C1 content of bamboo pulp, reed pulp, and wood pulp decreased by 3.1%, 1.9%, and 11.4%, respectively, indicating a reduction in the lignin content on the pulp surface. The C3 content of bamboo pulp, reed pulp, and wood pulp increased by 8.8%, 11.41%, and 3.8%, respectively, possibly due to the oxidation of lignin abundant on the surface of the mechanical pulp as a substrate for peroxidase. The C2 and C4 contents of bamboo pulp remained almost unchanged, indicating that the products of PRLP oxidation of bamboo pulp lignin failed to dissolve and separate. The C2 contents of reed pulp and wood pulp increased by 3.1% and 12.7%, respectively, indicating that PRLP achieved partial oxidative removal of lignin from the surface of reed and wood pulp fibers, exposing more palm cellulose. The C4 content of reed pulp and wood pulp decreased by 61.3% and increased by 51.9%, respectively, corresponding to the simultaneous removal of acetyl groups from hemicellulose by PRLP. Compared with the original pulps, after XQP treatment, the C1 content of bamboo pulp, reed pulp, and wood pulp decreased by 16.8%, 20.4%, and 39.4%, respectively, while the C2 content increased by 15.8%, 17.7%, and 37.3%, respectively. This is because the H2O2 bleaching treatment removed a large amount of lignin from the pulp surface, exposing the cellulose. The C1 content of bamboo pulp, reed pulp, and wood pulp treated with QP was 2.8%, 1.5%, and 5.9% higher than that treated with XQP, respectively, while the C2 content was 0.5%, 0.5%, and 6.3% lower than that treated with XQP, respectively. This indicates that PRLP played a certain auxiliary role in delignin removal during the H2O2 bleaching process, especially with significant effects on eucalyptus mechanical pulp. In addition, the oxygen-to-carbon ratio (O / C) can reflect the lignin content on the surface of the pulp. The higher the O / C, the higher the carbohydrate content on the fiber surface, and the lower the O / C, the higher the lignin content on the fiber surface.

[0113] The calculation results listed in Table 5 show that after X-stage treatment, the O / C ratio of bamboo mechanical pulp increased by 1.36% compared to the original pulp, and the surface lignin concentration decreased by 2.72%. The surface lignin concentrations of bamboo mechanical pulp treated with XQP and QP were 53.80% and 59.08%, respectively, which were 25.72% and 20.44% lower than the original pulp, respectively. After X-stage treatment, the O / C ratio of reed mechanical pulp increased by 1.61% compared to the original pulp, and the surface lignin concentration decreased by 3.22%. The O / C ratio of reed mechanical pulp treated with XQP was 4.05% higher than that treated with QP, and the surface lignin concentration decreased by 7.96%. After X-stage treatment, the O / C ratio of eucalyptus mechanical pulp increased by 1.24%, and the surface lignin concentration decreased by 2.48%. After XQP treatment, the O / C ratio increased by 18.40% compared to the original pulp, and the surface lignin content decreased by 36.8%, which was 6.42% lower than that of the QP treatment. The above data indicate that PRLP peroxidase removes lignin from the surface of pulp fibers and also has a significant auxiliary effect on subsequent H2O2 bleaching to remove lignin.

[0114] Table 5 Summary of O / C and surface lignin concentration of different pulps

[0115]

[0116] Effects of XQP treatment on mechanical pulp properties and fiber morphology

[0117] The results of the pulp brightness and mechanical strength tests are shown in Table 6. Compared with the original pulps, after peroxidase X-stage treatment, the brightness of bamboo mechanical pulp, reed mechanical pulp, and eucalyptus mechanical pulp increased by 3.68%, 3.35%, and 5.51%, respectively; the brightness of XQP bamboo pulp, reed pulp, and wood pulp increased by 3.34%, 3.78%, and 2.12%, respectively, compared with their respective QP control samples. Therefore, it can be determined that the naturally extracted peroxidase pretreatment used in this application improves the bleachability of mechanical pulp and is beneficial to increasing the brightness of mechanical pulp. The tensile indices of XQP bamboo pulp, reed pulp, and wood pulp reached 8.57 N·m / g, 5.60 N·m / g, and 25.69 N·m / g, respectively, representing increases of 5.7%, 3.1%, and 6.3% compared to QP, and increases of 50.7%, 61.1%, and 22.3% compared to virgin pulp. Tensile index reflects the interfiber bonding strength and is related to the fiber interlacing and the fiber's inherent strength. XQP treatment removes some lignin from the surface of the mechanical pulp (Table 6), exposing more fibers and increasing the interfiber bonding strength. The tear indices of bamboo pulp, reed pulp, and wood pulp after XQP treatment increased by 53.2%, 36.2%, and 11.0% compared to virgin pulp, respectively, while the bursting indices increased by 2.4%, 10.2%, and 7.3%. The tear index of pulp is closely related to fiber length and surface roughness. XQP treatment did not increase fiber length, but microscopic images showed fiber surface fuzzing and increased roughness, thus improving the tear index of mechanical pulp. The bursting strength index is affected by the bonding force between fibers and their average length. As delignification proceeds, fiber cell walls are disrupted, exposing fine fibers and increasing the bonding force between fibers.

[0118] Table 6 Summary of XQP treatment on mechanical pulp properties

[0119]

[0120]

[0121] Fiber morphology analysis

[0122] The fiber length, width, crimp content, and fine fiber content of various pulps were determined, and the results are shown in Table 7.

[0123] After X-segment enzyme treatment, the fiber length difference was not significant. This may be because the fine fibers have a large specific surface area and are easily bonded by the oxidative cross-linking effect of the enzyme, thus their content decreased slightly, but the effect on the size and quantity of long fibers was not significant. After XQP treatment, the fiber length of bamboo, reed, and eucalyptus mechanical pulp decreased by 9.2%, 7.6%, and 6.7%, respectively. However, compared with the morphology of QP-treated fibers, the fiber length still showed a slight increase, increasing by 0.7%, 1.6%, and 0.5%, respectively. H2O2 bleaching, due to the addition of the strongly alkaline chemical NaOH, caused fiber swelling and damage, resulting in a decrease in fiber length and an increase in the content of fine fibers. The fiber morphology of XQP-treated mechanical pulp and the QP control group was not significantly different, indicating that palm peroxidase has no significant effect on fiber morphology.

[0124] Table 7 Summary of the effects of XQP treatment on the morphology of mechanical pulp fibers

[0125]

[0126]

[0127] Note: The fiber lengths in Table 7 are double weight average fiber lengths.

[0128] A compilation of optical microscope images of various pulp fibers Figure 2 In the XQP treatment, slight fuzzing and splitting of the fibers in all three types of pulp were observed, indicating that the peroxidase caused some damage while removing lignin. After XQP treatment, the fiber length of the three types did not change significantly, but fiber fuzzing and splitting were observed, and the fiber width increased. Fine fibers were clearly visible separating from the fiber ends, and the content of fine fibers in the pulp increased. This indicates that XQP treatment caused swelling and damage to the fibers, but the overall morphology of the fibers in the three types of pulp did not change significantly, and the fiber integrity remained good. The fiber morphology of XQP-treated fibers was similar to that of fibers treated with QP alone, which is consistent with the data measured by the fiber analyzer.

[0129] The surface morphology of bamboo pulp, reed pulp, and eucalyptus mechanical pulp fibers before and after XQP treatment was measured using tapping AFM. The results are as follows: Figure 3 As shown, Figure 3The bright, raised granules are typical characteristics of amorphous and hydrophobic lignin. The dark, striped, oriented portions are consistent with the characteristics of hydrophilic cellulose microfibrils and macrofibrils. The surface of the original pulp fibers is rough and covered with a large number of hydrophobic particles. After XQP treatment, the three-dimensional morphology of the fiber surface becomes smoother and more uniform. This is because peroxidase and H2O2 bleaching remove some of the lignin from the fiber surface, exposing the fibers. In particular, the surface of XQP eucalyptus mechanical pulp is smooth and the microfibrils are clearly defined. This is consistent with the results of XPS, which showed that XQP eucalyptus mechanical pulp removed 37% of the surface lignin.

[0130] Molecular docking of PRLP with lignin model compounds

[0131] XPS analysis demonstrated that PRLP catalyzes the reaction of lignin in bamboo, reed, and eucalyptus. These lignins are natural polymers synthesized from p-coumarol (PA), coniferyl alcohol (CA), and sinapyl alcohol (SA). For these lignins to undergo oxidation, some structural groups enter or at least approach the active region of the peroxide. The size and structure of these structural groups determine their binding energy at the effective sites. Therefore, molecular docking energy corroborates the XPS data and helps understand the interaction between PRLP and lignin. The docking results of 12 lignin model compounds with PRLP are listed in Table 8. The three raw materials contain three lignin monomers—PA, CA, and SA—with increasing methoxy groups, and the binding energy (absolute value) with PRLP also increases sequentially. These monomers can all enter the active pocket of PRLP. All three monomers form hydrogen bonds with Arg70, Glu100, Ser105, and Arg207. The amino acid residues that bind to these monomers hydrophobically include Gln101, Ile1701, Pro171, Thr172, Pro173, Asn210, and heme groups. Model compounds 4-8 are dimers involving β-O-4, β-1, β-5, β-β, and 5-5 linkages. The high binding energies indicate that these different linkages can all enter the active region of PRLP and bind. Compounds 9-12 are trimers, tetramers, and pentamers. Due to their larger three-dimensional size than the monomers and dimers, they bind at the edge of the catalytic pocket. The absolute value of the binding energy generally decreases with increasing molecular volume. Figure 4 However, the binding energy of the pentamer is still -4.7 kcal / mol, indicating that the pentamer oligomer of lignin can stably bind to the catalytic region of PRLP, thereby initiating a reverse oxidation reaction. Liu Hao et al. studied the molecular docking of laccase with lignin model compounds. The docking binding energy between lignin tetramer and laccase was only -0.06 kcal / mol, indicating that the binding was extremely unstable and could not be effectively bound in the active region.

[0132] Table 8. Molecular docking results of PRLP with lignin model compounds

[0133]

[0134]

[0135] The above describes the specific experimental methods and preferred embodiments of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principle of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A method for treating mechanical pulp with a bio-enzyme extracted from pure plants, characterized in that, The processing method is completed according to the following procedure: Enzyme treatment: First, naturally extracted peroxidase is used, with the addition of H2O2 as a cofactor. The mechanical pulp is treated at pH 5.0 and a temperature of 60℃ for 2-6 hours. The amount of peroxidase added is 0.5-1.5 g / kg. 绝干浆 The mechanical pulp has a reaction concentration of 10%, and is washed with deionized water to adjust the solid content of the mechanical pulp to 10% for later use. Chelation treatment: Add 5 g / L ethylenediaminetetraacetic acid (EDTA) to the mechanical pulp treated with oxidase. Place the mechanical pulp to be treated with EDTA in a polyethylene sealed bag, knead it to mix the mechanical pulp and the solution evenly, and place it in a 60℃ constant temperature water bath for 60 min. After the treatment, cool it to room temperature, wash the mechanical pulp with deionized water, and adjust the solid content to 10%. Hydrogen peroxide treatment: The mechanical pulp treated with ethylenediaminetetraacetic acid was bleached with H2O2. The process conditions were: 40 g / L H2O2, 20 g / L NaOH, and 5 g / L MgSO4, with a mechanical pulp concentration of 10%. The reaction was carried out at 80℃ for 120 min. During the reaction, the pulp was kneaded every 15 min to ensure uniform reaction. After bleaching, the pulp was washed with deionized water until neutral to balance the moisture content. The treatment was then complete. The peroxidase was extracted from the leaves of the soft-leaved prickly pear, and the enzyme activity of the peroxidase was 35.64±4.77 U / mL. The mechanical pulp is any one of bamboo mechanical pulp, reed mechanical pulp, or eucalyptus mechanical pulp.

2. The method for treating mechanical pulp with bio-enzymes extracted from pure plants according to claim 1, characterized in that, When the mechanical pulp is bamboo mechanical pulp, the peroxidase dosage during the peroxidase treatment process is 1.5 g / kg. 绝干浆 The treatment time was 4 hours, and the H2O2 cofactor dosage was 0.3 g / L. When the mechanical pulp was reed mechanical pulp, the peroxidase dosage during the peroxidase treatment was 1.5 g / kg. 绝干浆 The treatment time was 6 hours, and the H2O2 cofactor dosage was 0.3 g / L. When the mechanical pulp was eucalyptus mechanical pulp, the peroxidase dosage during the peroxidase treatment was 1.5 g / kg. 绝干浆 The treatment time was 4 hours, and the amount of H2O2 cofactor added was 0.3 g / L.

3. The method for treating mechanical pulp with bio-enzymes extracted from pure plants according to claim 1 or 2, characterized in that, When the mechanical pulp is made of bamboo, reed, or eucalyptus, the acid-soluble lignin of the treated bamboo, reed, and eucalyptus mechanical pulp decreased by 34.8%, 19.0%, and 26.8%, respectively, and / or the Klason lignin of the treated bamboo, reed, and eucalyptus mechanical pulp decreased by 13.4%, 15.9%, and 21.4%, respectively, and / or the total lignin of the treated bamboo, reed, and eucalyptus mechanical pulp decreased by 14.8%, 12.5%, and 17.9%, respectively.

4. The method for treating mechanical pulp with bio-enzymes extracted from pure plants according to claim 1 or 2, characterized in that, When the mechanical pulp is bamboo mechanical pulp, reed mechanical pulp, or eucalyptus mechanical pulp, the content of C atoms bonded only to saturated C atoms or hydrogen atoms in the treated bamboo mechanical pulp, reed mechanical pulp, and eucalyptus mechanical pulp decreases by 16.8%, 20.4%, and 39.4%, respectively, while the content of C atoms bonded to one non-carbonyl O atom increases by 15.8%, 17.7%, and 37.3%, respectively.

5. The method for treating mechanical pulp with bio-enzymes extracted from pure plants according to claim 1 or 2, characterized in that, When the mechanical pulp is made of bamboo, reed, or eucalyptus, the fiber length of the processed bamboo, reed, and eucalyptus mechanical pulp is reduced by 9.2%, 7.6%, and 6.7%, respectively.

6. A paper product prepared from mechanical pulp obtained by the method of treating mechanical pulp with pure plant-extracted bio-enzymes as described in any one of claims 1-5, characterized in that, The paper product shall satisfy at least one of the following conditions (1)-(3): (1) The tensile indices of paper products prepared from the processed bamboo mechanical pulp, reed mechanical pulp and eucalyptus mechanical pulp were 8.57 N·m / g, 5.60 N·m / g and 25.69 N·m / g, respectively; (2) The tensile index of paper products made from the processed bamboo mechanical pulp, reed mechanical pulp and eucalyptus mechanical pulp increased by 50.7%, 61.1% and 22.3% respectively compared with the tensile index of paper products made from their original pulps; (3) The paper products made from the processed bamboo mechanical pulp, reed mechanical pulp and eucalyptus mechanical pulp had tear indices that were 53.2%, 36.2% and 11.0% higher than those made from their respective original pulps, and burst indices that were 2.4%, 10.2% and 7.3% higher, respectively.

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