Method for preparing high-performance waste paper composite material and application

Abstract

The invention belongs to the technical field of composite material preparation, and discloses a method for preparing a high-performance waste paper composite material and application of the high-performance waste paper composite material, and the method comprises the following steps: crushing a waste corrugated carton, pulping, making paper into quantitative waste paper of 100-200g / m < 2 >, dipping the waste paper in an ethanol solution of esterified modified lignin, and then carrying out low-temperature hot pressing treatment to prepare the composite material. According to the invention, the reinforcing process of the waste paperboard is optimized, and the lignin forms a compact cross-linked network among fibers by adopting a modified lignin impregnation and hot pressing combined technology, so that the problem of poor performances of the waste paperboard during secondary recycling is solved. The esterified modified lignin has good dispersity and permeability in an ethanol solution, and can be uniformly distributed in a waste paper fiber network; and after the composite material is hot-pressed for 20-30 minutes under the pressure of 10MPa, the tensile strength and burst index of the composite material are improved.

Description

Technical Field

[0001] This invention belongs to the field of composite material preparation technology, and in particular to a method and application for preparing high-performance waste paper composite materials. Background Technology

[0002] With increasing global environmental awareness and the continuous advancement of the world's sustainable development strategy, how to more efficiently utilize renewable resources and waste has become a common research hotspot in the scientific research and industrial sectors. Among these, waste paper, as a recyclable resource, has become one of the effective ways to alleviate forest resource depletion and reduce solid waste. However, in existing waste paper recycling technologies, physical pulping causes irreversible fiber damage after multiple cycles. Each reuse reduces the average fiber length by about 30%, and after three cycles, the tensile strength decreases by more than 50%. Strengthening waste paper fibers with synthetic resins relies excessively on chemical additives, requiring 0.5-1.2% synthetic resin to maintain basic strength, leading to increased costs and hindering subsequent recycling. Therefore, problems such as shorter fibers, decreased strength, and increased costs lead to the gradual deterioration of recycled paperboard performance, limiting its high-value applications.

[0003] Lignin, the second most abundant natural polymer, is a major byproduct of the papermaking industry. In traditional pulping and papermaking, large amounts of lignin are discarded as "black liquor," causing resource waste and environmental pollution. Therefore, utilizing lignin to improve waste paper properties, enhance its mechanical strength, and reduce production costs offers a new approach for the sustainable development of recycled resources and waste. However, directly combining unmodified lignin with waste paper fibers results in poor interfacial bonding and unsatisfactory mechanical properties due to lignin's poor dispersibility and strong polarity. Therefore, developing an efficient and environmentally friendly method for preparing modified lignin / waste paper composites is of great significance. Research has found that chemically modified lignin exhibits significantly improved interfacial compatibility with waste paper fibers. Combining the two and optimizing the composite process holds promise for achieving high-value utilization of waste while obtaining high-performance, biodegradable, and environmentally friendly materials, providing new ideas for the sustainable development of packaging, building materials, and other fields.

[0004] The search revealed the following two patent publications related to this invention's patent application:

[0005] 1. A method for preparing waste paper fiber / polylactic acid (PLA) composite material (CN 113717509 A). Waste corrugated cardboard boxes are pulped, crushed, dehydrated, dried by forced air, and ground to obtain uniformly dispersed flocculent waste paper fibers. A silane coupling agent KH-550 is added to a solution of water and ethanol, stirred until homogeneous, and then mixed evenly with the flocculent waste paper fibers. After sealing and standing, and forced air drying, modified waste paper fibers are obtained. The flocculent waste paper fibers are uniformly mixed with polylactic acid powder, poured into a twin-screw extruder for melt co-extrusion, and then sheared to obtain waste paper fiber / PLA composite material particles. However, this preparation method requires multiple drying and melt extrusion processes (high temperature 170–190℃), resulting in high energy consumption and expensive PLA. Although PLA is biodegradable, it requires industrial composting conditions, and melt processing may generate trace amounts of volatile organic compounds, potentially impacting human health and the environment.

[0006] 2. An eco-friendly composite material and its preparation method (CN 102260386 B). Waste paper is broken down into fragments using a shredder and then directly impregnated in an alcohol-water mixture of one or two of vinyl silane and vinyl silane oligomers. After filtration and draining, the waste paper fragments are heat-treated to obtain modified waste paper fragments, which are then subjected to high-speed mixing and shearing shredding, filtered, and dried to obtain modified waste paper fiber powder. The modified waste paper fiber powder, wood flour, polyethylene, and additives are mixed evenly and then extruded in a twin-screw extruder. After drying and molding, the eco-friendly composite material is obtained. However, this preparation method has high energy consumption, complex processes, and is difficult to scale up. Polyethylene is a petroleum-based plastic, which is difficult to degrade in the natural environment. Even with biomass fillers, the overall material is still "partially eco-friendly" and cannot be completely degraded, resulting in low environmental friendliness.

[0007] By comparison, the patent application of this invention differs fundamentally from the aforementioned patent publications. Compared to patent publication 1, this invention reduces raw material costs by replacing the PLA matrix with esterified modified lignin, while achieving lower processing temperatures and more thorough biodegradability. Compared to patent publication 2, this invention, through a biomass-based full-component design, avoids the fatal flaws of non-degradable petroleum-based plastics, the high energy consumption problems caused by complex multi-step processes, and the environmental risks that chemical additives may pose. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method and application for preparing high-performance waste paper composite materials.

[0009] The technical solution adopted by the present invention to solve its technical problem is:

[0010] A method for preparing high-performance waste paper composite materials, wherein waste corrugated cardboard boxes are crushed, pulped, and formed into sheets with a basis weight of 100-200 g / m³. 2Waste paper was impregnated with an ethanol solution of esterified lignin and then subjected to low-temperature hot pressing to prepare composite materials.

[0011] The waste paper is immersed in an esterified lignin ethanol solution with a mass concentration of 5-10 wt% for 15 min, then removed and air-dried at room temperature for 12 h. The above operation is repeated 1-2 times, and then hot-pressed at 140℃ to obtain the composite material.

[0012] Furthermore, the tensile strength of the composite material is in the range of 6.02 to 7.82 kN / m, and its burst strength is in the range of 612.11 to 713.56 kPa.

[0013] Furthermore, the esterified modified lignin is obtained by mixing industrial lignin with two different silane reagents, 1H,1H,2H,2H-perfluorooctyltriethyloxysilane (FS, 98%) and 3-(2-aminoethylamino)-propyltrimethoxysilane (AS, 98%), followed by stirring, acid precipitation, centrifugation, washing, and freeze drying.

[0014] Furthermore, the specific preparation steps of the esterified modified lignin are as follows:

[0015] 1) Industrial lignin was mixed with ethanol at a solid-liquid ratio of 1:49 g:mL and ultrasonically dissolved for 30 min. FS and AS were added to the obtained lignin solution at a ratio of 0.6% and 0.9% of the total solution volume, respectively. The mixture was stirred at 500 r / min for 8 h at 25 °C to obtain an esterified lignin solution.

[0016] 2) The modified lignin solution obtained in step 1) is added dropwise to a hydrochloric acid aqueous solution with pH 2-3. After standing for precipitation for 2 hours, it is placed in a centrifuge and centrifuged at 4000-5000 r / min for 10 min. It is then washed 3-4 times with a hydrochloric acid aqueous solution with pH 2-3. Finally, the washed lignin component is freeze-dried at -60 to -70℃ for 48 hours to obtain esterified modified lignin.

[0017] Further, in step 1), the industrial lignin is at least one of alkali lignin, sulfate lignin, enzymatic hydrolysis residue lignin, and pre-hydrolyzed lignin.

[0018] Furthermore, the specific steps are as follows:

[0019] (1) Waste corrugated cardboard boxes are shredded and soaked in water for 12 hours. The mixture is then pulped using a Wali pulping machine, squeezed and dewatered to obtain waste paper pulp. The obtained pulp is then formed using a paper forming machine to obtain a basis weight of 100-200 g / m³. 2 Waste paperboard;

[0020] (2) The lignin from the paper industry was chemically modified with two different silane reagents, 1H,1H,2H,2H-perfluorooctyltriethyloxysilane and 3-(2-aminoethylamino)-propyltrimethoxysilane, to obtain an esterified lignin solution.

[0021] (3) The esterified modified lignin solution obtained in step (2) is added dropwise to a hydrochloric acid aqueous solution with pH 2-3, and allowed to stand for 2 hours to allow the lignin components to fully precipitate. The precipitated lignin is centrifuged, washed and freeze-dried to obtain an esterified modified lignin sample, which is the modified lignin.

[0022] (4) The waste paperboard obtained in step (1) is immersed in an ethanol solution of modified lignin with a mass concentration of 5-10 wt% obtained in step (3) so that the lignin is evenly penetrated between the paper fibers to obtain the impregnated paperboard.

[0023] (5) After drying the impregnated cardboard obtained in step (4), put it into a hot press and press it at a pressure of 8-12 MPa and a hot pressing temperature of 130-150℃ for 20-30 minutes to melt the lignin and form a dense cross-linked network with the fiber to obtain the composite material.

[0024] Further, in step (1), the disintegration time of the Wali pulper is 10-15 min, the pulping speed is 1500-3000 rad / min, the pulping time is 20-30 min, and the pulping degree is 30-50°SR;

[0025] Furthermore, in step (2), the mass concentration of lignin from the paper industry in the solution is 1 wt%, the reaction temperature is 25℃, and the reaction time is 2 h.

[0026] Furthermore, in step (5), the hot pressing temperature is 120℃ for 30 minutes;

[0027] In step (1), the waste corrugated cardboard boxes are crushed, pulped, and formed into sheets with a basis weight of 150g / m³. 2 Waste paper.

[0028] Application of the composite material prepared by the method described above in the preparation of linerboard and / or kraft paper and / or paper tube paper and / or paperboard core.

[0029] The advantages and positive effects of this invention are as follows:

[0030] 1. This invention optimizes the reinforcement process of waste paperboard by employing modified lignin impregnation combined with hot pressing technology. This allows lignin to form a dense cross-linked network between fibers, thereby improving the poor performance of waste paperboard during secondary recycling. The esterified modified lignin used has good dispersibility and permeability in ethanol solution and can be uniformly distributed in the waste paper fiber network. After hot pressing at 10 MPa for 20–30 min, the tensile strength and bursting index of the composite material are improved (see Table 1).

[0031] 2. The technical problem to be solved by this invention is how to improve the performance of waste paperboard while simplifying the process. Through the impregnation-hot pressing process, the performance of paperboard composite materials is significantly improved, while maintaining their biodegradability, reducing environmental pollution and promoting sustainable development.

[0032] 3. The preparation method of this invention includes the papermaking of recycled paperboard, the esterification modification of lignin, and the impregnation reinforcement and hot pressing of waste paperboard. Compared with traditional methods, this process directly utilizes the natural adhesive properties of lignin, directly impregnating waste paper in esterified lignin without adding any reinforcing agents or additives. The resulting composite material can achieve strong bonding between fibers at a relatively low temperature (<160℃), resulting in a composite material with significantly improved mechanical properties, reduced energy consumption, and broad prospects for production applications. This method can reduce the preparation cost of high-performance waste paperboard and realize the high-value utilization of waste paper and lignin, which is of great significance for promoting the development of green packaging materials.

[0033] 4. This invention uses industrial lignin and two different silane reagents for chemical modification, and through esterification modification of lignin impregnation and low-temperature hot pressing process, the performance of waste paper-based composite materials is significantly improved. No reinforcing agents or additives are needed. The resulting high-performance waste paper composite material has higher mechanical properties than the original industrial lignin composite material. Detailed Implementation

[0034] The present invention will be further described below with reference to the embodiments. The following embodiments are descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0035] The various experimental operations involved in the specific embodiments are all conventional techniques in the field. For parts not specifically annotated in this document, those skilled in the art can refer to various commonly used reference books, scientific and technological documents or related instructions and manuals prior to the filing date of this invention to carry out the operations.

[0036] A method for preparing high-performance waste paper composite materials, wherein waste corrugated cardboard boxes are crushed, pulped, and formed into sheets with a basis weight of 100-200 g / m³. 2Waste paper was impregnated with an ethanol solution of esterified lignin and then subjected to low-temperature hot pressing to prepare composite materials.

[0037] The waste paper is immersed in an esterified lignin ethanol solution with a mass concentration of 5-10 wt% for 15 min, then removed and air-dried at room temperature for 12 h. The above operation is repeated 1-2 times, and then hot-pressed at 140℃ to obtain the composite material.

[0038] Preferably, the tensile strength of the composite material is in the range of 6.02 to 7.82 kN / m, and its burst strength is in the range of 612.11 to 713.56 kPa.

[0039] Preferably, the esterified lignin is obtained by mixing industrial lignin with two different silane reagents, 1H,1H,2H,2H-perfluorooctyltriethyloxysilane (FS, 98%) and 3-(2-aminoethylamino)-propyltrimethoxysilane (AS, 98%), followed by stirring, acid precipitation, centrifugation, washing, and freeze-drying.

[0040] Preferably, the specific preparation steps of the esterified modified lignin are as follows:

[0041] 1) Industrial lignin was mixed with ethanol at a solid-liquid ratio of 1:49 g:mL and ultrasonically dissolved for 30 min. FS and AS were added to the obtained lignin solution at a ratio of 0.6% and 0.9% of the total solution volume, respectively. The mixture was stirred at 500 r / min for 8 h at 25 °C to obtain an esterified lignin solution.

[0042] 2) The modified lignin solution obtained in step 1) is added dropwise to a hydrochloric acid aqueous solution with pH 2-3. After standing for precipitation for 2 hours, it is placed in a centrifuge and centrifuged at 4000-5000 r / min for 10 min. It is then washed 3-4 times with a hydrochloric acid aqueous solution with pH 2-3. Finally, the washed lignin component is freeze-dried at -60 to -70℃ for 48 hours to obtain esterified modified lignin.

[0043] Preferably, in step 1), the industrial lignin is at least one of alkali lignin, sulfate lignin, enzymatic residue lignin, and pre-hydrolyzed lignin.

[0044] Preferably, the specific steps are as follows:

[0045] (1) Waste corrugated cardboard boxes are shredded and soaked in water for 12 hours. The mixture is then pulped using a Wali pulping machine, squeezed and dewatered to obtain waste paper pulp. The obtained pulp is then formed using a paper forming machine to obtain a basis weight of 100-200 g / m³. 2 Waste paperboard;

[0046] (2) The lignin from the paper industry was chemically modified with two different silane reagents, 1H,1H,2H,2H-perfluorooctyltriethyloxysilane and 3-(2-aminoethylamino)-propyltrimethoxysilane, to obtain an esterified lignin solution.

[0047] (3) The esterified modified lignin solution obtained in step (2) is added dropwise to a hydrochloric acid aqueous solution with pH 2-3, and allowed to stand for 2 hours to allow the lignin components to fully precipitate. The precipitated lignin is centrifuged, washed and freeze-dried to obtain an esterified modified lignin sample, which is the modified lignin.

[0048] (4) The waste paperboard obtained in step (1) is immersed in an ethanol solution of modified lignin with a mass concentration of 5-10 wt% obtained in step (3) so that the lignin is evenly penetrated between the paper fibers to obtain the impregnated paperboard.

[0049] (5) After drying the impregnated cardboard obtained in step (4), put it into a hot press and press it at a pressure of 8-12 MPa and a hot pressing temperature of 130-150℃ for 20-30 minutes to melt the lignin and form a dense cross-linked network with the fiber to obtain the composite material.

[0050] Preferably, in step (1), the disintegration time of the Wali pulper is 10-15 min, the pulping speed is 1500-3000 rad / min, the pulping time is 20-30 min, and the pulping degree is 30-50°SR;

[0051] Preferably, in step (2), the mass concentration of lignin from the paper industry in the solution is 1 wt%, the reaction temperature is 25℃, and the reaction time is 2 h.

[0052] Preferably, in step (5), the hot pressing temperature is 120℃ and the hot pressing is carried out for 30 minutes;

[0053] In step (1), the waste corrugated cardboard boxes are crushed, pulped, and formed into sheets with a basis weight of 150g / m³. 2 Waste paper.

[0054] Application of the composite material prepared by the method described above in the preparation of linerboard and / or kraft paper and / or paper tube paper and / or paperboard core.

[0055] Specifically, the relevant preparation and testing methods are as follows:

[0056] Example 1:

[0057] A method for preparing high-performance waste paper composite materials includes the following steps:

[0058] 1) Cut waste corrugated cardboard boxes into 4×4cm pieces and wash them. Soak the pieces in a bucket at room temperature for 12 hours with a solid-liquid ratio (g:mL) of shredded paper to deionized water of 1:100-200. Pour the resulting mixture into a Wali pulper, add three times the volume of deionized water, and then break down the paper pieces at room temperature (25℃) for 10-15 minutes. Then beat the pulp at a speed of 1500-3000 rad / min for 20-30 minutes, achieving a freeness of approximately 30-50°SR. Filter and squeeze the resulting pulp through a pulp bag to remove most of the water. Seal the pulp in a bag for 24 hours to equilibrate the moisture content and measure the moisture level. Take 10.60g of dry pulp, add deionized water at a solid-liquid ratio (g:mL) of 1:10, and stir evenly with a small desizing machine. Then pour it into a paper forming machine to form wet paper sheets with a radius of 0.15m. Place the wet paper sheets in a circular vacuum dryer and dry at 90℃ for 15min to obtain waste paperboard with a basis weight of 150g.

[0059] 2) Lignin was dissolved by sonication in ethanol at a solid-liquid ratio (g:mL) of 1:49 for 30 min. 1H,1H,2H,2H-perfluorooctyltriethyloxysilane (FS, 98%) and 3-(2-aminoethylamino)-propyltrimethoxysilane (AS, 98%) were added to the resulting lignin solution at ratios of 0.6 v / v% and 0.9 v / v% of the total solution volume, respectively. The mixture was stirred vigorously at 25°C for 8 h to obtain an esterified lignin solution. This lignin solution was added dropwise to a hydrochloric acid aqueous solution with pH 2–3. After standing for 2 h to precipitate, the solution was centrifuged at 4000–5000 r / min for 10 min and washed 3–4 times with a hydrochloric acid aqueous solution with pH 2–3. Finally, the washed lignin component was freeze-dried at -60–-70°C for 48 h to obtain esterified lignin.

[0060] 3) Take 13.5g of esterified modified lignin and add it to 325mL of ethanol solution. Dissolve it by sonication for 15min to obtain an esterified modified lignin ethanol solution with a mass concentration of 5wt%. Pour it into a large petri dish and put in the waste cardboard obtained in step 1). Start timing when the waste cardboard is completely submerged in it. After soaking for 15min, take it out and air dry for 12h.

[0061] 4) The dried cardboard is hot-pressed in a hot press to obtain lignin waste paper composite material. The hot press processing parameters are as follows: heating temperature is set to 130-150℃, pressure is set to 8-12T, preheating time is set to 5-15min, and running time is set to 2-3min.

[0062] Example 2:

[0063] A method for preparing high-performance waste paper composite materials includes the following steps:

[0064] Step 1) is the same as in Example 1.

[0065] Step 2) is the same as in Example 1.

[0066] 3) Take 13.5g of esterified modified lignin and add it to 325mL of ethanol solution. Dissolve it by sonication for 15min to obtain a 5wt% esterified modified lignin ethanol solution. Pour it into a large petri dish and put the waste cardboard obtained in step 1) into it. Start timing when the waste cardboard is completely submerged. After soaking for 15min, take it out and air dry for 12h. Repeat the above soaking and drying steps twice.

[0067] Step 4) is the same as in Example 1.

[0068] Example 3:

[0069] A method for preparing high-performance waste paper composite materials includes the following steps:

[0070] Step 1) is the same as in Example 1.

[0071] Step 2) is the same as in Example 1.

[0072] 3) Take 27g of esterified modified lignin and add it to 308mL of ethanol solution. Dissolve it by sonication for 15min to obtain an esterified modified lignin ethanol solution with a mass concentration of 10wt%. Pour it into a large petri dish and put in the waste cardboard obtained in step 1). Start timing when the waste cardboard is completely submerged. After soaking for 15min, take it out and air dry for 12h.

[0073] Step 4) is the same as in Example 1.

[0074] Example 4:

[0075] A method for preparing high-performance waste paper composite materials includes the following steps:

[0076] Step 1) is the same as in Example 1.

[0077] Step 2) is the same as in Example 1.

[0078] 3) Add 27g of esterified lignin to 308mL of ethanol solution and sonicate for 15min to obtain a 10wt% esterified lignin ethanol solution. Pour the solution into a large petri dish and place the waste cardboard obtained in step 1) inside. Start timing when the waste cardboard is completely submerged. After soaking for 15min, remove and air dry for 12h. Repeat the above soaking and drying steps twice.

[0079] Step 4) is the same as in Example 1.

[0080] Comparative Example 1:

[0081] A method for preparing waste paper composite materials includes the following steps:

[0082] 1) Cut waste corrugated cardboard boxes into 4×4cm pieces and wash them. Place the shredded paper and deionized water in a bucket at a solid-liquid ratio (g:mL) of 1:100-200. Soak at room temperature for 12 hours. Pour the resulting mixture into a Wali pulper. Add three times the volume of deionized water and dissolve at room temperature (25°C) for 10-15 minutes. After the paper pieces are completely broken down, switch to pulping and pulp at a speed of 1500-3000 rad / min for 20-30 minutes, achieving a freeness of approximately 30-50°SR. Filter the resulting pulp through a pulp bag and squeeze out some of the water. Seal the pulp in a bag for 24 hours to equilibrate the moisture content and measure the moisture level. Take 10.60g of dry pulp, add deionized water at a solid-liquid ratio (g:ml) of 1:10, and stir evenly with a small desizing machine. Then pour it into a paper forming machine to form wet paper sheets with a radius of 0.15m. Place the wet paper sheets in a circular vacuum dryer and dry at 90℃ for 15min to obtain waste paperboard with a basis weight of 150g.

[0083] 2) Take 13.5g of sulfate lignin (KL) and add it to 325mL of ethanol solution. Dissolve it by sonication for 15min to obtain a 5wt% sulfate lignin ethanol solution. Pour it into a large petri dish and put the waste cardboard obtained in step 1) into it. Start timing when the waste cardboard is completely submerged. After soaking for 15min, take it out and air dry for 12h.

[0084] 3) The dried cardboard is hot-pressed in a hot press to obtain sulfate lignin waste paper composite material. The hot press processing parameters are as follows: heating temperature is set to 130~150℃, pressure is set to 8~12T, preheating time is set to 5~15min, and running time is set to 2~3min.

[0085] Comparative Example 2:

[0086] A method for preparing waste paper composite materials includes the following steps:

[0087] Step 1) Same as Comparative Example 1.

[0088] 2) Take 13.5g of sulfate lignin (KL) and add it to 325mL of ethanol solution. Dissolve it by sonication for 15min to obtain a 5wt% sulfate lignin ethanol solution. Pour it into a large petri dish and put the waste cardboard obtained in step 1) into it. Start timing when the waste cardboard is completely submerged. After soaking for 15min, take it out and air dry for 12h. Repeat the above soaking and drying steps twice.

[0089] Step 3) Same as Comparative Example 1,

[0090] Comparative Example 3:

[0091] A method for preparing waste paper composite materials includes the following steps:

[0092] Step 1) Same as Comparative Example 1.

[0093] 2) Take 27g of sulfate lignin (KL) and add it to 308mL of ethanol solution. Dissolve it by sonication for 15min to obtain a 5wt% sulfate lignin ethanol solution. Pour it into a large petri dish and put the waste cardboard obtained in step 1) into it. Start timing when the waste cardboard is completely submerged. After soaking for 15min, take it out and air dry for 12h.

[0094] Step 3) Same as Comparative Example 1,

[0095] Comparative Example 4:

[0096] A method for preparing waste paper composite materials includes the following steps:

[0097] Step 1) Same as Comparative Example 1.

[0098] 2) Take 27g of sulfate lignin (KL) and add it to 308mL of ethanol solution. Dissolve it by sonication for 15min to obtain a 5wt% sulfate lignin ethanol solution. Pour it into a large petri dish and put the waste cardboard obtained in step 1) into it. Start timing when the waste cardboard is completely submerged. After soaking for 15min, take it out and air dry for 12h. Repeat the above soaking and drying steps twice.

[0099] Step 3) Same as Comparative Example 1,

[0100] Comparative Example ①:

[0101] A method for preparing high-performance waste paper composite materials includes the following steps:

[0102] 1) Cut waste corrugated cardboard boxes into 4×4cm pieces and wash them. Soak the pieces in a bucket at room temperature for 12 hours with a solid-liquid ratio (g:mL) of shredded paper to deionized water of 1:100-200. Pour the resulting mixture into a Wali pulper, add three times the volume of deionized water, and then break down the paper pieces at room temperature (25℃) for 10-15 minutes. Then beat the pulp at a speed of 1500-3000 rad / min for 20-30 minutes, achieving a freeness of approximately 30-50°SR. Filter and squeeze the resulting pulp through a pulp bag to remove most of the water. Seal the pulp in a bag for 24 hours to equilibrate the moisture content and measure the moisture level. Take 10.60g of dry pulp, add deionized water at a solid-liquid ratio (g:mL) of 1:10, and stir evenly with a small desizing machine. Then pour it into a paper forming machine to form wet paper sheets with a radius of 0.15m. Place the wet paper sheets in a circular vacuum dryer and dry at 90℃ for 15min to obtain waste paperboard with a basis weight of 150g.

[0103] 2) Lignin was dissolved by sonication in ethanol at a solid-liquid ratio (g:mL) of 1:49 for 30 min. 1H,1H,2H,2H-perfluorooctyltriethyloxysilane (FS, 98%) and 3-(2-aminoethylamino)-propyltrimethoxysilane (AS, 98%) were added to the resulting lignin solution at ratios of 0.6 v / v% and 0.9 v / v% of the total solution volume, respectively. The mixture was stirred vigorously at 25°C for 8 h to obtain an esterified lignin solution. This lignin solution was added dropwise to a hydrochloric acid aqueous solution with pH 2–3. After standing for 2 h to precipitate, the solution was centrifuged at 4000–5000 r / min for 10 min and washed 3–4 times with a hydrochloric acid aqueous solution with pH 2–3. Finally, the washed lignin component was freeze-dried at -60–-70°C for 48 h to obtain esterified lignin.

[0104] 3) Take 13.5g of esterified modified lignin and add it to 325mL of ethanol solution. Dissolve it by sonication for 15min to obtain an esterified modified lignin ethanol solution with a mass concentration of 5wt%. Pour it into a large petri dish and put the waste paperboard obtained in step 1) into it. Start timing when the waste paperboard is completely submerged in it. After soaking for 15min, take it out and air dry for 12h to obtain lignin waste paper composite material.

[0105] Comparative Example 2:

[0106] A method for preparing high-performance waste paper composite materials includes the following steps:

[0107] Step 1) Same as comparative example ①.

[0108] Step 2) Same as comparative example ①,

[0109] 3) Take 13.5g of esterified modified lignin and add it to 325mL of ethanol solution. Dissolve it by sonication for 15min to obtain a 5wt% esterified modified lignin ethanol solution. Pour it into a large petri dish and put the waste paperboard obtained in step 1) into it. Start timing when the waste paperboard is completely submerged. After soaking for 15min, take it out and air dry for 12h. Repeat the above soaking and drying steps twice to obtain lignin waste paper composite material.

[0110] Comparative Example ③:

[0111] A method for preparing high-performance waste paper composite materials includes the following steps:

[0112] Step 1) Same as comparative example ①.

[0113] Step 2) Same as comparative example ①,

[0114] 3) Take 27g of esterified modified lignin and add it to 308mL of ethanol solution. Dissolve it by sonication for 15min to obtain an esterified modified lignin ethanol solution with a mass concentration of 10wt%. Pour it into a large petri dish and put the waste paperboard obtained in step 1) into it. Start timing when the waste paperboard is completely submerged in it. After soaking for 15min, take it out and air dry for 12h to obtain lignin waste paper composite material.

[0115] Comparative Example 4:

[0116] A method for preparing high-performance waste paper composite materials includes the following steps:

[0117] Step 1) Same as comparative example ①.

[0118] Step 2) Same as comparative example ①,

[0119] 3) Add 27g of esterified lignin to 308mL of ethanol solution and sonicate for 15min to obtain a 10wt% esterified lignin ethanol solution. Pour the solution into a large petri dish and place the waste paperboard obtained in step 1) inside. Start timing when the waste paperboard is completely submerged. After immersion for 15min, remove and air dry for 12h. Repeat the above immersion and drying steps twice to obtain the lignin waste paper composite material.

[0120] Performance testing methods:

[0121] The tensile strength of all the above-mentioned composite materials was measured according to the national standard GB / T 12914 "Determination of Tensile Strength of Paper and Paperboard". The specimens were cut according to the standard: width (15±0.1) mm, length ≥250 mm (clamping distance is usually 180 mm or 100 mm). At least 10 valid specimens were tested in each group, avoiding edge burrs or creases. The tensile strength properties of all the above-mentioned composite materials were measured, and the average value was taken.

[0122] The bursting strength of all the above composite materials was measured according to the national standard GB / T 454-2020 "Determination of Bursting Strength of Paper". The test specimens were cut according to the standard: ≥70mm×70mm (avoiding creases, water stains or obvious defects). At least 10 valid test specimens were tested in each group, and the average value was taken.

[0123] Table 1 Comparison of the properties of waste paper composite materials

[0124] <![CDATA[Quantitative (g / m 2 )]]> Tensile strength (kN / m) Bursting strength (kPa) Waste cardboard (unimpregnated) 150 2.66 285.67 Example 1 155 6.02 612.11 Example 2 160 6.95 687.60 Example 3 157 7.32 664.28 Example 4 162 7.82 713.56 Comparative Example 1 156 4.81 543.12 Comparative Example 2 163 5.17 598.32 Comparative Example 3 169 5.84 633.44 Comparative Example 4 174 6.24 678.39 Comparative Example ① 162 2.93 312.59 Comparative Example ② 169 3.62 346.61 Comparative Example ③ 165 3.34 324.25 Comparative Example 4 173 3.95 363.17

[0125] As can be seen from the experimental test data in Table 1 above, the tensile index and bursting strength of waste paperboard are significantly improved after impregnation with esterified lignin solution. Furthermore, the physical properties of the paper also improve with increasing lignin content and impregnation times. In particular, in Examples 2 and 4, when waste paperboard was impregnated twice with 5wt% and 10wt% esterified lignin ethanol solutions, respectively, the tensile strength of the waste paper composite material increased by approximately 244% and 293% respectively. From Examples and Comparative Examples 1-4, it can be seen that the samples prepared by the methods in the Examples are far superior to those prepared by the methods in the Comparative Examples, confirming that lignin esterification modification has a significant improving effect on the performance of the composite material. In addition, from Examples and Comparative Examples ①-④, it can be seen that whether or not the composite material is hot-pressed also has a significant impact on its performance; the various properties of the waste paper composite material after hot pressing are almost more than doubled. Meanwhile, the tensile strength of the lignin waste paper composite material prepared by this invention meets the requirements of the national standard for this type of material (GB / T 13023-2008: transverse ≥2.50kN / m, basis weight ≥125g / m). 2 It has great practical application value.

[0126] Meanwhile, by comparing Example 1, Comparative Example 1 and Comparative Example ①, it can also be seen that the esterified modified lignin obtained in step 2) and the hot pressing treatment step in step 4) have a synergistic effect, which can synergistically improve the relevant properties of the prepared composite material.

[0127] Although embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, variations, and modifications are possible without departing from the spirit and scope of the invention and the appended claims. Therefore, the scope of the invention is not limited to the contents disclosed in the embodiments.

Claims

1. A method for preparing high-performance waste paper composite materials, characterized in that: The method involves crushing, pulping, and papermaking waste corrugated cardboard boxes into sheets with a basis weight of 100–200 g / m³. 2 Waste paper was impregnated with an ethanol solution of esterified lignin and then subjected to low-temperature hot pressing to prepare composite materials. The waste paper is immersed in an esterified lignin ethanol solution with a mass concentration of 5-10 wt% for 15 min, then removed and air-dried at room temperature for 12 h. The above operation is repeated 1-2 times, and then hot-pressed at 140℃ to obtain the composite material.

2. The method according to claim 1, characterized in that: The tensile strength of the composite material is in the range of 6.02 to 7.82 kN / m, and its burst strength is in the range of 612.11 to 713.56 kPa.

3. The method according to claim 1, characterized in that: The esterified lignin is obtained by mixing industrial lignin with two different silane reagents, 1H,1H,2H,2H-perfluorooctyltriethyloxysilane (FS, 98%) and 3-(2-aminoethylamino)-propyltrimethoxysilane (AS, 98%), followed by stirring, acid precipitation, centrifugation, washing, and freeze-drying.

4. The method according to claim 3, characterized in that: The specific preparation steps of the esterified modified lignin are as follows: 1) Industrial lignin was mixed with ethanol at a solid-liquid ratio of 1:49 g:mL and ultrasonically dissolved for 30 min. FS and AS were added to the obtained lignin solution at a ratio of 0.6% and 0.9% of the total solution volume, respectively. The mixture was stirred at 500 r / min for 8 h at 25 °C to obtain an esterified lignin solution. 2) The modified lignin solution obtained in step 1) is added dropwise to a hydrochloric acid aqueous solution with pH 2-3. After standing for precipitation for 2 hours, it is placed in a centrifuge and centrifuged at 4000-5000 r / min for 10 min. It is then washed 3-4 times with a hydrochloric acid aqueous solution with pH 2-3. Finally, the washed lignin component is freeze-dried at -60 to -70℃ for 48 hours to obtain esterified modified lignin.

5. The method according to claim 4, characterized in that: In step 1), the industrial lignin is at least one of alkali lignin, sulfate lignin, enzymatic hydrolysis residue lignin, and pre-hydrolyzed lignin.

6. The method according to any one of claims 1 to 5, characterized in that: The specific steps are as follows: (1) Waste corrugated cardboard boxes are shredded and soaked in water for 12 hours. The mixture is then pulped using a Wali pulping machine, squeezed and dewatered to obtain waste paper pulp. The obtained pulp is then formed using a paper forming machine to obtain a basis weight of 100-200 g / m³. 2 Waste paperboard; (2) The lignin from the paper industry was chemically modified with two different silane reagents, 1H,1H,2H,2H-perfluorooctyltriethyloxysilane and 3-(2-aminoethylamino)-propyltrimethoxysilane, to obtain an esterified lignin solution. (3) The esterified modified lignin solution obtained in step (2) is added dropwise to a hydrochloric acid aqueous solution with pH 2-3, and allowed to stand for 2 hours to allow the lignin components to fully precipitate. The precipitated lignin is centrifuged, washed and freeze-dried to obtain an esterified modified lignin sample, which is the modified lignin. (4) The waste paperboard obtained in step (1) is immersed in an ethanol solution of modified lignin with a mass concentration of 5-10 wt% obtained in step (3) so that the lignin is evenly penetrated between the paper fibers to obtain the impregnated paperboard. (5) After drying the impregnated cardboard obtained in step (4), put it into a hot press and press it at a pressure of 8-12 MPa and a hot pressing temperature of 140°C for 30 minutes to melt the lignin and form a dense cross-linked network with the fiber to obtain the composite material.

7. The method according to claim 6, characterized in that: In step (1), the desiccation time of the Wali pulping machine is 10-15 min, the pulping speed is 1500-3000 rad / min, the pulping time is 20-30 min, and the pulping degree is 30-50°SR.

8. The method according to claim 6 or 7, characterized in that: In step (2), the mass concentration of lignin from the paper industry in the solution is 1 wt%, the reaction temperature is 25℃, and the reaction time is 2 h.

9. The use of the composite material obtained by the method according to any one of claims 1 to 8 in the preparation of linerboard and / or kraft paper and / or paper tube paper and / or paperboard core.