Method for papermaking reinforced paper with lignin under assistance of hot pressing

Abstract

The invention discloses a method for manufacturing reinforced paper with lignin under the assistance of hot pressing. The method comprises the following steps: (1) preparing lignin / copper ion nanoparticles from an alkali lignin solution and a Cu (NO3) 2 solution through an autocatalytic oxidation-reduction reaction; (2) adding the lignin / copper ion nanoparticles prepared in the step (1) into paper pulp to make paper, and drying; and (3) performing hot pressing on the formed paper sheet to prepare the reinforced paper. The invention provides a simple, feasible, green and sustainable method for paper enhancement, and is beneficial to promoting high-value utilization of alkali lignin generated by a paper mill and increasing economic benefits.

Description

Technical Field

[0001] The invention belongs to the field of papermaking, and in particular relates to a method for making reinforced paper using lignin assisted by hot pressing. Background Art

[0002] Lignin, as one of the main components of plant cell walls, has a unique three-dimensional polyphenol structure that tightly binds to cellulose and hemicellulose to provide strength to the cell walls. In the papermaking industry, lignin is usually partially or completely removed to improve paper quality. The lignin produced by the papermaking industry is mostly a condensed structure, which is difficult to utilize at a high value. It is usually burned to provide heat energy for paper mills, resulting in great waste. In the papermaking process, in order to improve the strength and performance of paper, it is usually necessary to add paper strengthening agents. Modifying lignin and using it for paper strengthening can achieve high-value utilization of lignin and increase the economic benefits of paper mills.

[0003] After chemical modification, lignin can be used as a papermaking additive. It can be added to paper through surface sizing, impregnation, etc. to improve paper strength, surface hydrophobicity and other properties. Studies have found that adding 4-6% modified lignin to pulp can increase paper strength by 10-16%, and can also improve the retention rate of fine fibers during papermaking. Dai Xin et al. found that layer-by-layer loading of lignin phenol onto the surface of paper significantly improved the surface hydrophobicity of the paper, with the surface water contact angle reaching 110°. In addition, the strength performance of paper was significantly improved by impregnation with lignin phenol. In addition, Wen Yangbing et al. added lignin as a filler to paper-based materials to assist in hot pressing to prepare a paper-based material with a high lignin content. Its barrier effect was significantly improved, but its strength performance was not significantly improved (patent CN 118880651A). Therefore, modifying lignin by a suitable method and then adding it to the inside or surface of paper is a very promising method for paper sheet enhancement.

[0004] Lignin is the world's most abundant natural polyphenol and has enormous application potential. However, lignin's heterogeneous structure and tendency to agglomerate make it difficult to be compatible with the matrix. Preparing lignin into nanoparticles can effectively solve this problem. However, due to the lack of polar groups on the surface of the nanoparticles, the improvement in compatibility with the matrix is limited. Studies have found that the methoxy and phenolic hydroxyl groups in lignin can be oxidized by metal ions through an autocatalytic system to form quinone / hydroquinone or catechol structures, forming lignin / metal ion nanoparticles. This method can simultaneously complete the preparation of nanoparticles and surface modification. The quinone / hydroxyl or catechol groups on the surface of the nanoparticles can interact with polar groups through hydrogen bonds (H bonds), forming strong interfacial interactions with the matrix. Among the reported lignin-metal nanoparticles, lignin-copper nanoparticles (LNP@Cu) exhibit excellent antibacterial properties and low cytotoxicity, and have very broad application prospects. Summary of the Invention

[0005] Purpose of the Invention: The technical problem to be solved by the present invention is to address the shortcomings of the existing technology and provide a material and preparation method for hot-pressing-assisted lignin-enhanced paper. By preparing lignin into LNP@Cu rich in o-quinone and o-phenol groups to promote its uniform dispersion on the surface of paper fibers, hot pressing is further used to enhance the bonding strength between lignin and paper fibers, thereby achieving paper reinforcement. This application provides a simple, environmentally friendly and sustainable method for paper reinforcement, and is conducive to promoting the high-value utilization of alkali lignin produced by paper mills, thereby increasing economic benefits.

[0006] In order to solve the above technical problems, the present invention discloses a method for hot pressing assisted lignin papermaking to strengthen paper, comprising the following steps:

[0007] (1) preparing lignin / copper ion nanoparticles by reacting an alkaline lignin solution with a Cu(NO3)2 solution through an autocatalytic redox reaction;

[0008] (2) adding the lignin / copper ion nanoparticles prepared in step (1) into paper pulp to make paper and drying;

[0009] (3) The formed paper sheets are hot pressed to prepare reinforced paper.

[0010] Wherein, in step (1), the alkali lignin solution is prepared by the following steps: dispersing alkali lignin at a concentration of 10 to 30 mg / mL in a sodium hydroxide solution with a pH of 10 to 11.5, ultrasonicating in a water bath for 6 to 10 hours, then standing overnight, and taking the upper layer to obtain the alkali lignin solution;

[0011] Preferably, the Cu(NO3)2 solution is prepared by the following steps: dissolving the Cu(NO3)2 at a concentration of 1.88 to 3.75 mg / mL in a sodium hydroxide solution with a pH of 10 to 11.5, and then reacting with alkali lignin.

[0012] In step (1), during the reaction, the alkali lignin solution is heated to 80-95°C, and then the Cu(NO3)2 solution is added dropwise to the alkali lignin solution. Preferably, the volume ratio of the alkali lignin solution to the alkali lignin solution is 1:1. After complete dropwise addition, the reaction is continued at 80-95°C with stirring for 2-3 hours to obtain a lignin / copper ion nanoparticle suspension. The suspension is then placed in deionized water for 2-3 days for dialyzation, with the water changed several times a day, to obtain neutral lignin / copper ion nanoparticles for paper modification.

[0013] In the papermaking in step (2), the amount of lignin / copper ion nanoparticles added is 1 to 4% of the dry weight of the pulp.

[0014] 6. The method according to claim 1, characterized in that the pulp used is a semi-chemical pulp or a chemimechanical pulp prepared from any one of hardwood, softwood, bamboo and herb.

[0015] Specifically, in step (2), the papermaking step is as follows: the pulp should be placed in a standard deaggregator in advance and deagulated with 80-100°C hot water, preferably for about 10 minutes, and the deagged wet pulp is prepared into a 0.1-0.2% pulp dispersion for papermaking, and the papermaking paper has a basis weight of 60-120g / m 2 The wet paper sheets are placed on a drying table for drying. Preferably, the wet paper sheets are placed on a drying table at 105° C. for drying for 5 minutes, and then placed in a hot press for hot pressing to prepare reinforced paper.

[0016] Preferably, the hot pressing temperature is 120-150° C., the pressure is 0.1-0.2 MPa, and the hot pressing time is 5-20 min.

[0017] The reinforced paper prepared by the method is also within the protection scope of the present application.

[0018] The present invention also proposes the application of the reinforced paper in preparing packaging paper or medical materials.

[0019] This patent uses alkali lignin produced by the papermaking industry as raw material, and prepares LNP@Cu rich in o-quinone and o-phenol groups through an autocatalytic redox reaction with Cu(NO3)2. It is added to paper to improve the mechanical properties of the paper. In order to further increase the bonding strength between lignin and paper fibers, the prepared paper is hot-pressed to investigate the effects of additives and hot-pressing processes on paper performance, laying a theoretical and practical foundation for the development of high-strength paper products.

[0020] Beneficial effects: Compared with the prior art, this application has the following advantages:

[0021] (1) Alkali lignin is made into LNP@Cu, which can significantly increase the surface active functional groups of lignin and make it more evenly dispersed on the surface of paper fibers;

[0022] (2) Hot pressing further enhances the interaction between lignin and paper fibers, achieving paper reinforcement. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 XPS (ac) and FTIR (d) spectra of alkali lignin and LNP@Cu;

[0024] Figure 2 Shown are the high-resolution transmission electron microscopy (HRTEM) images and Cu element distribution maps of LNP@Cu;

[0025] Figure 3 The tensile strength of the paper is shown;

[0026] Figure 4 The displayed value is the paper bursting index;

[0027] Figure 5 Displayed is the paper tear index;

[0028] Figure 6 It shows the air permeability of the paper;

[0029] Figure 7 Shows the whiteness of the paper. DETAILED DESCRIPTION

[0030] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments, and the above and / or other advantages of the present invention will become more apparent.

[0031] The alkali lignin used in this application was provided by Shandong Huatai Paper Co., Ltd. The papermaking process was based on TAPPI T402sp-98 (2008) standards. The pulp used was laboratory-made eucalyptus semi-chemical pulp with a freeness of 440 mL.

[0032] In the following examples, LNP@Cu was prepared as follows: 3.2 g of alkali lignin was dispersed in 160 mL of sodium hydroxide solution (pH 10.8). After water bath sonication for 3 hours, the dispersion was allowed to stand overnight to remove any undissolved matter. 675 mg of Cu(NO3)2 was dissolved in 160 mL of sodium hydroxide solution (pH 10.8). After heating the lignin solution to 90°C, the Cu(NO3)2 solution was slowly added dropwise to the lignin solution while maintaining heating and stirring. The mixture was stirred at 90°C for 2 hours. After the reaction, the reaction solution was dialyzed in pure water for 2 days to obtain a neutral LNP@Cu suspension.

[0033] Comparative Example

[0034] The pulp was placed in a standard deflaker and deflaked with 100°C hot water for 10 minutes. The wet pulp concentration after deflaking was 0.9%. 2.22 kg of the wet pulp was dispersed in 10 L of water and paper was made using a standard paper former (produced by Messmer, UK). The paper weight was 100 g / m 2 The wet paper sheets were placed in a drying cage and dried at 23°C and 50% relative humidity for 24 h. The prepared paper sheets were marked as 0-RT.

[0035] Example 1

[0036] The pulp was placed in a standard deflaker and deflaked with 100°C hot water for 10 minutes. The wet pulp concentration after deflaking was 0.9%. 2.22 kg of the wet pulp was dispersed in 10 L of water and paper was made using a standard paper former (produced by Messmer, UK). The paper weight was 100 g / m 2 The wet paper was placed on a drying table at 105°C for 5 minutes and then placed in a hot press for 10 minutes at a temperature of 120°C and a pressure of 0.14 MPa. The prepared paper was labeled 0-HP.

[0037] Example 2

[0038] The pulp was placed in a standard deflaker and deflaked with 100°C hot water for 10 minutes. The wet pulp concentration after deflaking was 0.9%. 2.22 kg of the wet pulp was dispersed in 10 L of water, 0.2 g of alkali lignin powder was added, and the mixture was stirred vigorously for 10 minutes. A standard sheet former (manufactured by Messmer, UK) was used to make paper. The paper weight was 100 g / m 2 The wet paper sheets were placed in a drying cage and dried at 23°C and 50% relative humidity for 24 h. The prepared paper sheets were labeled 1-RT.

[0039] Example 3

[0040] The pulp was placed in a standard deflaker and deflaked with 100°C hot water for 10 minutes. The wet pulp concentration after deflaking was 0.9%. 2.22 kg of the wet pulp was dispersed in 10 L of water, 0.2 g of alkali lignin powder was added, and the mixture was stirred vigorously for 10 minutes. A standard sheet former (manufactured by Messmer, UK) was used to make paper. The paper weight was 100 g / m 2 The wet paper was placed on a drying table at 105°C for 5 minutes and then placed in a hot press for 10 minutes at a temperature of 120°C and a pressure of 0.14 MPa. The prepared paper was labeled 1-HP.

[0041] Example 4

[0042] The slurry was placed in a standard deflaker and deflaked with 100°C hot water for 10 minutes. The wet pulp concentration after deflaking was 0.9%. 2.22 kg of the wet pulp was dispersed in 10 L of water. 0.2 g of the LNP@Cu dispersion was added and stirred vigorously for 10 minutes. Paper was then produced using a standard sheet former (manufactured by Messmer, UK). The paper weight was 100 g / m². 2 The wet paper sheets were placed in a drying cage and dried at 23°C and 50% relative humidity for 24 hours. The prepared paper sheets were labeled 2-RT.

[0043] Example 5

[0044] The slurry was placed in a standard deflaker and deflaked with 100°C hot water for 10 minutes. The wet pulp concentration after deflaking was 0.9%. 2.22 kg of the wet pulp was dispersed in 10 L of water. 0.2 g of the LNP@Cu dispersion was added and stirred vigorously for 10 minutes. Paper was then produced using a standard sheet former (manufactured by Messmer, UK). The paper weight was 100 g / m². 2 The wet paper was placed on a drying table at 105°C for 5 minutes and then placed in a hot press for 10 minutes at a temperature of 120°C and a pressure of 0.14 MPa. The prepared paper was labeled 2-HP.

[0045] The mechanical properties, air permeability, and whiteness of the papers prepared in the comparative examples and examples were tested, and the test results are listed in Table 1. Tensile strength was measured according to TAPPIT 494 om-01 (2001) using a BR-165 horizontal tensile tester (Messmer Instruments Ltd., UK); burst strength was measured according to TAPPIT 403 om-01 (2001) using an ME-05 burst tester (Techlab Systems SL, Spain); tear strength was measured according to TAPPI T414 om-04 (2004) using an ME1653D tear tester (Messmer Instruments Ltd., UK); and whiteness was measured according to GB8940.2-2002 using a WS-SD colorimeter (Wenzhou Instruments Co., Ltd.). Ten sheets of paper were prepared under each condition and their properties were measured. The mean and standard deviation of the test results were calculated.

[0046] Table 1 Comparison of mechanical properties, air permeability and whiteness properties of prepared paper

[0047]

[0048] Characterization of the chemical structure of alkali lignin raw materials and LNP@Cu shows that ( Figure 1 ), alkali lignin was prepared into LNP@Cu rich in o-quinone and o-phenol structures through self-assembly catalytic redox method. Figure 2As shown, the prepared lignin nanoparticles are spherical with a diameter of about 300nm. Analysis of the mechanical properties of the above four embodiments and comparative examples shows that LNP@Cu has a better reinforcing effect on paper than alkali lignin. This is because LNP@Cu is uniformly dispersed in the paper and increases the fiber binding sites. The tensile strength, bursting strength and tear strength of the paper (2-HP) prepared by adding LNP@Cu to the paper and hot pressing are the best, which are 27.5%, 50.0% and 9.6% higher than the unmodified paper respectively. In addition, hot pressing makes the fibers dense and significantly reduces the air permeability of the paper. This study provides new ideas and new methods for the design of high-strength paper. These excellent properties make paper have great application potential in packaging, medicine and other fields.

[0049] The present invention provides a concept and method for enhancing paper. There are numerous methods and approaches for implementing this technical solution. The above description is merely a preferred embodiment of the present invention. It should be noted that those skilled in the art may make various improvements and modifications without departing from the principles of the present invention, and such improvements and modifications are also within the scope of protection of the present invention. Any components not specified in this embodiment may be implemented using existing technologies.

Claims

1. A method for making reinforced paper using lignin assisted by hot pressing, characterized in that: The steps include: (1) Alkali lignin solution and Cu(NO3)2 solution were reacted by autocatalytic redox reaction to prepare lignin / copper ion nanoparticles; (2) adding the lignin / copper ion nanoparticles prepared in step (1) into paper pulp to make paper and drying; (3) The formed paper sheets are hot pressed to prepare reinforced paper.

2. The method according to claim 1, characterized in that In step (1), the alkali lignin solution is prepared by the following steps: dispersing alkali lignin at a concentration of 10-30 mg / mL in a sodium hydroxide solution with a pH of 10-11.5, ultrasonicating in a water bath for 6-10 h, then standing overnight, and taking the upper layer to obtain the alkali lignin solution.

3. The method according to claim 1, wherein the Cu(NO3)2 solution is prepared by the following steps: dissolving the Cu(NO3)2 at a concentration of 1.88-3.75 mg / mL in a sodium hydroxide solution with a pH of 10-11.5, and then reacting with alkali lignin.

4. The method according to claim 1, wherein In step (1), during the reaction, the alkaline lignin solution is heated to 80-95°C, and then the Cu(NO3)2 solution is added dropwise to the alkaline lignin solution. After the complete addition, the temperature is maintained at 80-95°C and the reaction is stirred for 2-3 hours to obtain a lignin / copper ion nanoparticle suspension. The suspension is then dialyzed in deionized water for 2-3 days, with the water changed several times a day, to obtain neutral lignin / copper ion nanoparticles for paper modification.

5. The method according to claim 1, wherein In the papermaking process in step (2), the amount of lignin / copper ion nanoparticles added is 1-4% of the dry weight of the pulp.

6. The method according to claim 1, characterized in that The pulp used is either semi-chemical pulp or chemimechanical pulp made from any one of hardwood, softwood, bamboo and herb.

7. The method according to claim 1, characterized in that In step (2), the papermaking process is as follows: the pulp should be placed in a standard deaggregator in advance and deagulated with 80-100°C hot water, and the deagulated wet pulp is prepared into a 0.1-0.2% pulp dispersion for papermaking, and the papermaking paper is 60-120 g / m 2 The wet paper sheets are placed on a drying table to dry, and then placed in a hot press to produce reinforced paper.

8. The method according to claim 1, characterized in that The hot pressing temperature is 120~150℃, the pressure is 0.1~0.2MPa, and the hot pressing time is 5~20 min.

9. The reinforced paper prepared by the method according to any one of claims 1 to 8.

10. Use of the reinforced paper according to claim 9 in preparing packaging paper or medical materials.

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