Recycled paper with flame retardant effect and preparation method thereof

Abstract

The invention belongs to the technical field of papermaking, and particularly discloses recycled paper with a flame retardant effect and a preparation method of the recycled paper. The recycled paper provided by the invention is prepared from the following components in parts by weight: 45 to 51 parts of pretreated recycled paper, 30 to 34 parts of raw paper wood pulp board, 1.8 to 2.1 parts of composite reinforcing agent and 15 to 25 parts of kaolin-based flame retardant, wherein the kaolin-based flame retardant is gemini quaternary ammonium salt modified calcined kaolin; the composite reinforcing agent is prepared from maleic anhydride acylated chitosan and cellulose nanofibrils. On the premise of meeting the paper performance, the flammability of the recycled paper provided by the invention is effectively inhibited. The invention also provides a preparation method of the recycled paper with the flame retardant effect, the recycled paper is prepared by adopting an in-pulp addition method, and the preparation method has the advantages of simple process, easily available raw materials, safety in operation, high production efficiency, easiness in popularization and application and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of papermaking, and in particular relates to recycled paper with flame retardant effect and a preparation method thereof. Background Art

[0002] Paper is a multifunctional material that is widely used in daily life, such as wallpaper, wrapping paper, decorative paper, office paper, etc. The flammability of traditional paper made from natural plant fibers not only increases the difficulty of preservation, but also may cause serious fires, seriously endangering human life and property safety. With the enhancement of people's awareness of fire prevention, fire disasters are increasingly valued by people. Therefore, people have higher and higher requirements for the flame retardant properties of paper.

[0003] There are generally two methods for producing flame-retardant paper: one is to use special fibers with flame-retardant properties, mainly including inorganic fibers with flame-retardant properties such as carbon fiber, glass fiber, ceramic fiber, aramid fiber and asbestos fiber. The other is to use traditional papermaking technology to directly add flame retardants into the production process of paper to make flame-retardant paper. In practical applications, the second production method requires flame retardants to meet some special requirements, such as good dispersibility and filler retention, which limits the use of some flame retardants.

[0004] Calcined kaolin is processed from coal gangue, an industrial waste resource. It has high whiteness, rich pore structure and excellent light scattering performance. On the basis of existing calcined kaolin, it can be further modified to increase the interlayer spacing of kaolin and improve its flame retardant performance. In addition, currently, paper flame retardant usually adopts impregnation and coating methods, but the resulting flame retardant paper does not have flame retardant durability or only makes the surface of the paper achieve flame retardant effect, and it is easy to absorb moisture and deform, affecting the performance.

[0005] As the world's environment continues to deteriorate, the problem of energy shortage has become increasingly prominent. Making full use of resources to turn waste into treasure has received widespread attention worldwide, and the demand for recycling resources is increasing day by day. The recycling of old corrugated boxes (such as express packaging boxes, food or electrical appliances, etc.) is a strategy to reduce carbon emissions from the pulp and paper industry. However, during the recycling process, waste paper fibers will be destroyed and their performance will be reduced. In order to improve their mechanical properties and increase their recycling rate, a certain amount of papermaking enhancers need to be used in the waste paper recycling process. However, existing papermaking enhancers generally need to be improved in terms of improving comprehensive properties such as strength and degradability. Summary of the invention

[0006] In view of the deficiencies in the prior art, the purpose of the present invention is to modify calcined kaolin with gemini quaternary ammonium salt to obtain a kaolin-based flame retardant, and then further prepare it with a portion of recycled paper fibers to form a recycled paper with flame retardant effect. The present invention further provides a method for preparing recycled paper with flame retardant effect.

[0007] In order to achieve the above-mentioned object of the invention, the embodiment of the present invention adopts the following technical solution: In a first aspect, the present invention provides a flame retardant recycled paper, which comprises the following components in parts by weight: 45 to 51 parts of pretreated recycled paper, 30 to 34 parts of virgin wood pulp, 1.8 to 2.1 parts of a composite reinforcing agent, and 15 to 25 parts of a kaolin-based flame retardant; Wherein, the kaolin-based flame retardant is calcined kaolin modified by gemini quaternary ammonium salt; The structural formula of the gemini quaternary ammonium salt is: ; The composite reinforcing agent comprises maleic anhydride acylated chitosan and cellulose nanofibrils.

[0008] The present invention prepares a gemini quaternary ammonium salt by quaternization reaction of benzyl dibromide and triethylamine, and then modifies the calcined kaolin with the gemini quaternary ammonium salt prepared by combining the gemini quaternary ammonium salt with calcined kaolin. The bridging group in the gemini quaternary ammonium salt is a benzene ring, which is adsorbed on the calcined kaolin to improve the hydrophobicity of the calcined kaolin; in addition, since the benzene ring structure has a large steric hindrance, it will form a hydrophobic protective film after being adsorbed on the surface of the calcined kaolin, thereby improving the flame retardant effect of the flame retardant. In addition, the composite reinforcing agent of the present invention includes maleic anhydride acylated chitosan and cellulose nanofibrils, which form a binary reinforcing system and can significantly improve the strength of recycled paper. The flammability of the paper prepared by the kaolin-based flame retardant and the composite reinforcing agent is effectively suppressed while meeting the paper performance.

[0009] Compared with conventional calcined kaolin modified by adding hexadecyltrimethylammonium bromide, the flame retardant recycled paper prepared by the present invention and modified by adding gemini quaternary ammonium salt has better flame retardant properties.

[0010] Preferably, the preparation method of the gemini quaternary ammonium salt comprises the following steps: subjecting p-dibrombenzyl and triethylamine to a quaternization reaction at 76° C. to 80° C. to obtain the gemini quaternary ammonium salt.

[0011] Further preferably, the reaction time of the quaternization reaction is 6h~7h;.

[0012] In the quaternization reaction, the mass ratio of p-dibrombenzyl and triethylamine is 1.1:1 to 1.3:1.

[0013] Preferably, the preparation method of the gemini quaternary ammonium salt modified calcined kaolin comprises the following steps: mixing a calcined kaolin suspension with a gemini quaternary ammonium salt solution, and reacting at 76° C. to 80° C. for 3 h to 4 h to obtain the gemini quaternary ammonium salt modified calcined kaolin.

[0014] Further preferably, the mass ratio of the gemini quaternary ammonium salt in the gemini quaternary ammonium salt solution to the calcined kaolin in the calcined kaolin suspension is 0.8:3 to 1.2:3; The mass concentration of the calcined kaolin suspension is 0.04 g / mL to 0.06 g / mL; The mass concentration of the gemini quaternary ammonium salt solution is 0.04 g / mL to 0.06 g / mL.

[0015] Preferably, the method for preparing the pretreated recycled paper comprises: removing free impurities from old corrugated paper boxes, chopping them, and moistening them with water to obtain the pretreated recycled paper.

[0016] Preferably, in the composite reinforcing agent, the mass ratio of the maleic anhydride acylated chitosan to the cellulose nanofibrils is 2:1-3:1.

[0017] Further preferably, the maleic anhydride acylated chitosan is prepared from chitosan and maleic anhydride in a mass ratio of 1:1.6 to 1:1.8; The fiber diameter of the cellulose nanofibrils is 3nm-5nm; the fiber length is 500nm-1000nm.

[0018] In a second aspect, the present invention further provides a method for preparing the above-mentioned recycled paper with flame retardant effect, wherein the recycled paper is prepared by an in-slurry addition method, and specifically comprises the following steps: S1. crushing and soaking the original paper pulp board to obtain original paper pulp; humidifying the pretreated recycled paper with water, pulping, deinking, screening and purifying to obtain recycled paper pulp; mixing the original paper pulp with the recycled paper pulp to obtain a mixed pulp; S2. adding the gemini quaternary ammonium salt-modified calcined kaolin and the composite reinforcing agent to the mixed slurry, dissociating to obtain a flame retardant paper suspension; S3. The flame retardant paper suspension is formed, pressed and dried to obtain recycled paper with flame retardant effect.

[0019] Preferably, the fiber concentration in the mixed slurry is 2% to 3%.

[0020] The virgin paper fibers used in the present invention may be derived from hardwood pulp or softwood pulp, etc.; the present invention only uses unbleached hardwood pulp board as a raw material to prepare recycled paper as an example for explanation.

[0021] After the dissociation in step S2, a certain amount of conventional papermaking aids in the art is added, such as sizing agents, preservatives, degassing agents, etc. The present invention is described by taking the addition of a cationic dispersed rosin size with a solid content of 35% as an example, and the addition amount is 1.5% of the absolute dry pulp mass.

[0022] Compared with the traditional impregnation or coating method for producing flame-retardant recycled paper, the preparation method of recycled paper with flame retardant effect provided by the present invention has the advantages of simple process, easy availability of raw materials, safe operation, high production efficiency, and easy promotion and application. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0024] The parameters of the calcined kaolin in the present invention are as follows: Al2O3 44%~46%, SiO2 50%~53%, Fe2O3≤0.2%, 325 mesh sieve residue <0.02%, whiteness 90~94%; The cellulose nanofibrils used in the present invention were purchased from Nanjing Tianlu Nanotechnology Co., Ltd., and the molecular formula is (C6H 10 O5) n , the fiber diameter is 3nm~5nm, and the fiber length is 500nm~1000nm.

[0025] Example 1 This embodiment provides a flame retardant recycled paper, which includes the following components in parts by weight: 48 parts of pretreated recycled paper, 32 parts of virgin wood pulp board, 1.95 parts of composite reinforcing agent and 20 parts of kaolin-based flame retardant; wherein: The kaolin-based flame retardant is calcined kaolin modified by gemini quaternary ammonium salt; The composite reinforcing agent comprises maleic anhydride acylated chitosan and cellulose nanofibrils.

[0026] The preparation method of the kaolin-based flame retardant comprises the following steps: Step 1: Preparation of Gemini Quaternary Ammonium Salt Add 10mL of anhydrous ethanol to a three-necked flask equipped with a reflux condenser, take 116.4g (1.13mol) of triethylamine and 131.98g (0.5mol) of p-dibromobenzyl and carry out quaternization reaction at 80℃ for 6h; magnetic stirring is performed during the quaternization reaction at a stirring speed of 100rpm. After the quaternization reaction, cool to room temperature to obtain a colorless transparent liquid, and remove the solvent by reduced pressure distillation at 60℃; then rinse with ethyl acetate and acetone in a volume ratio of 1:1 for 3 times, filter to obtain a white solid, and vacuum dry at 40℃ to obtain 176.1g of substance A; The above substance A contains quaternary ammonium salt N + The characteristic peaks indicate that the tertiary amine has undergone a quaternization reaction; substance A is a gemini quaternary ammonium salt, and its structural formula is: .

[0027] Step 2: Preparation of Gemini Quaternary Ammonium Salt Modified Calcined Kaolin 100g of calcined kaolin and 2L of deionized water were mixed, heated in a water bath at 80°C and mechanically stirred until uniformly dispersed to obtain a calcined kaolin suspension. 33.3g of the above-prepared gemini quaternary ammonium salt and 832mL of deionized water were weighed, and fully stirred until completely dissolved to obtain a gemini quaternary ammonium salt solution. The above gemini quaternary ammonium salt solution was mixed with the calcined kaolin suspension, mechanically stirred at 78°C for 3h, and then the mixed suspension was centrifuged and washed 3 times with deionized water, placed in a drying oven and dried at 80°C for 10h, and ground to 300 mesh to obtain gemini quaternary ammonium salt modified calcined kaolin.

[0028] In this embodiment, the calcined kaolin is a commercially available product, and the parameters of each index are as follows: Al2O3 44.56%, SiO2 53.25%, Fe2O3 ≤ 0.2%, pH 6.4, whiteness 93.1%, particle size 79.36 μm, 325 mesh sieve residue ≤ 0.005%.

[0029] This embodiment also provides a method for preparing the above-mentioned recycled paper with flame retardant effect, and the preparation method comprises the following steps: S1. Mixing recycled paper pulp with virgin paper pulp, beating in a Valley beater to obtain a slurry, and diluting with water to 3% fiber slurry to obtain a mixed slurry; S2. The prepared gemini quaternary ammonium salt modified calcined kaolin and composite reinforcing agent are added to the mixed slurry, dissociated with a fiber dissociator, and 1.5% of the absolute dry pulp mass of cationic dispersed rosin glue (solid content 35%) is added to obtain a flame retardant paper suspension; S3. The prepared flame-retardant paper suspension is formed into wet paper sheets on a paper sheet former, and the excess water is pressed out by a sheet press while the fibers are made tight, and then dried on a high-speed dryer to obtain recycled paper with flame-retardant effect, which is recorded as flame-retardant recycled paper I.

[0030] The composite reinforcing agent in this embodiment includes maleic anhydride acylated chitosan and cellulose nanofibrils, wherein the mass ratio of maleic anhydride acylated chitosan to cellulose nanofibrils is 2:1, and the preparation method of maleic anhydride acylated chitosan includes the following steps: Step A. Dissolve 10 g of chitosan (absolutely dry) in 1000 mL of 0.5% by volume acetic acid aqueous solution, filter to obtain a chitosan solution, and place it in a three-necked flask; Step B. dissolving maleic anhydride in acetone to prepare a maleic anhydride acetone solution having a maleic anhydride mass concentration of 30%; Step C. adding the maleic anhydride acetone solution dropwise to the three-necked flask containing the chitosan solution, and completing the addition when the mass ratio of chitosan to maleic anhydride is 1:1.6, and reacting at room temperature for another 16 hours to obtain a reaction mixture; Step D. The reaction mixture is slowly added to 5L of 95% by volume ethanol sodium hydroxide saturated solution under magnetic stirring at 100rpm to precipitate a filamentous precipitate. The filamentous precipitate is separated by filtration and washed with 5 to 8 times of 95% ethanol until neutral, and then the separated filaments are washed with ether and vacuum dried at 50°C for 14h to obtain the maleic anhydride acylated chitosan.

[0031] The preparation method of recycled paper pulp comprises: placing old corrugated paper boxes in a fluidized bed to remove free impurities, and then chopping them to obtain pre-treated recycled paper; humidifying the pre-treated recycled paper with water in an amount of 4 times the weight of the old corrugated paper boxes, inputting the pre-treated recycled paper into a pulper, and then pulping, de-inking, screening and purifying, and discharging impurities to obtain recycled paper pulp; The unbleached hardwood pulp board was added with 10 times purified water, soaked for 24 hours, and then beaten in a Valley beater to obtain virgin pulp.

[0032] Example 2 This embodiment provides a flame retardant recycled paper, which includes the following components in parts by weight: 45 parts of pretreated recycled paper, 30 parts of virgin wood pulp board, 1.8 parts of composite reinforcing agent and 25 parts of kaolin-based flame retardant; wherein: The kaolin-based flame retardant is calcined kaolin modified by gemini quaternary ammonium salt; The composite reinforcing agent comprises chitosan acylated with maleic anhydride and cellulose nanofibrils in a mass ratio.

[0033] The preparation method of the kaolin-based flame retardant comprises the following steps: Step 1: Preparation of Gemini Quaternary Ammonium Salt Add an appropriate amount of anhydrous ethanol to a three-necked flask equipped with a reflux condenser, take 101.2g (1mol) of triethylamine and 131.98g (0.5mol) of benzyl bromide, and carry out quaternization reaction at 78°C for 6.5h; magnetic stirring is performed during the quaternization reaction, and the stirring speed is 100rpm. After the quaternization reaction, cool to room temperature to obtain a colorless transparent liquid, and remove the solvent by reduced pressure distillation at 60°C; then rinse with ethyl acetate and acetone in a volume ratio of 1:1 for 3 times, filter to obtain a white solid, and vacuum dry at 40°C to obtain 163.2g of substance B; The above substance B contains quaternary ammonium salt N + The characteristic peaks of , indicating that the tertiary amine has undergone quaternization reaction; substance B is a gemini quaternary ammonium salt, and its structural formula is: .

[0034] Step 2: Preparation of Gemini Quaternary Ammonium Salt Modified Calcined Kaolin 100g of calcined kaolin and 1.67L of deionized water were mixed, heated in a 76°C water bath and mechanically stirred until uniformly dispersed to obtain a calcined kaolin suspension. 26.7g of the above-prepared gemini quaternary ammonium salt and 445mL of deionized water were weighed, and fully stirred until completely dissolved to obtain a gemini quaternary ammonium salt solution. The above gemini quaternary ammonium salt solution was mixed with the calcined kaolin suspension, mechanically stirred at 76°C for 4h, and then the mixed suspension was centrifuged and washed 3 times with deionized water, placed in a drying oven and dried at 80°C for 12h, and ground to 300 mesh to obtain gemini quaternary ammonium salt modified calcined kaolin.

[0035] In this embodiment, the calcined kaolin is a commercially available product, and the parameters of various indicators are as follows: Al2O3 45.2%, SiO2 52.3%, Fe2O3 ≤ 0.2%, pH 6.8, whiteness 94%, and 325 mesh sieve residue ≤ 0.005%.

[0036] This embodiment also provides a method for preparing the above-mentioned recycled paper with flame retardant effect, and the preparation method comprises the following steps: S1. Mixing recycled paper pulp with virgin paper pulp, beating in a Valley beater to obtain a slurry, and diluting with water to 2% fiber slurry to obtain a mixed slurry; S2. The prepared gemini quaternary ammonium salt modified calcined kaolin and composite reinforcing agent are added to the mixed slurry, dissociated with a fiber dissociator, and 1.5% of the absolute dry pulp mass of cationic dispersed rosin glue (solid content 35%) is added to obtain a flame retardant paper suspension; S3. The prepared flame-retardant paper suspension is formed into wet paper sheets on a paper sheet former, and is passed through a sheet press to remove excess water and make the fibers tight, and then dried on a high-speed dryer to obtain recycled paper with flame-retardant properties, which is recorded as flame-retardant recycled paper II.

[0037] The composite reinforcing agent in this embodiment comprises maleic anhydride acylated chitosan and cellulose nanofibrils, wherein the mass ratio of maleic anhydride acylated chitosan to cellulose nanofibrils is 3:1; wherein the preparation method of maleic anhydride acylated chitosan comprises the following steps: Step A. Dissolve 10 g of chitosan (absolutely dry) in 1000 mL of 0.5% by volume acetic acid aqueous solution, filter to obtain a chitosan solution, and place it in a three-necked flask; Step B. dissolving maleic anhydride in acetone to prepare a maleic anhydride acetone solution having a maleic anhydride mass concentration of 30%; Step C. dropping the maleic anhydride acetone solution into the three-necked flask containing the chitosan solution, and completing the dropping when the mass ratio of chitosan to maleic anhydride is 1:1.8, and reacting at room temperature for another 16 hours to obtain a reaction mixture; Step D. The reaction mixture is slowly added to 5L of 95% by volume ethanol sodium hydroxide saturated solution under magnetic stirring at 100rpm to precipitate a filamentous precipitate. The filamentous precipitate is separated by filtration and washed with 5 to 8 times of 95% ethanol until neutral, and then the separated filaments are washed with ether and vacuum dried at 50°C for 14h to obtain the maleic anhydride acylated chitosan.

[0038] The preparation method of recycled paper pulp comprises: placing old corrugated paper boxes in a fluidized bed to remove free impurities, and then chopping them to obtain pre-treated recycled paper; humidifying the pre-treated recycled paper with water in an amount of 5 times the weight of the old corrugated paper boxes, inputting the pre-treated recycled paper into a pulper, and then pulping, de-inking, screening and purifying, and discharging impurities to obtain recycled paper pulp; The preparation method of the original paper pulp is the same as that in Example 1.

[0039] Example 3 This embodiment provides a flame retardant recycled paper, which includes the following components in parts by weight: 51 parts of pretreated recycled paper, 34 parts of virgin wood pulp board, 2.1 parts of composite reinforcing agent and 15 parts of kaolin-based flame retardant; wherein: The kaolin-based flame retardant is calcined kaolin modified by gemini quaternary ammonium salt; The composite reinforcing agent comprises chitosan acylated with maleic anhydride and cellulose nanofibrils in a mass ratio.

[0040] The preparation method of the kaolin-based flame retardant comprises the following steps: Step 1: Preparation of Gemini Quaternary Ammonium Salt Add an appropriate amount of anhydrous ethanol to a three-necked flask equipped with a reflux condenser, take 110.3g (1.09mol) of triethylamine and 131.98g (0.5mol) of p-dibromobenzyl to carry out quaternization reaction at 76°C for 7h; magnetic stirring is performed during the quaternization reaction at a stirring speed of 100rpm. After the quaternization reaction, cool to room temperature to obtain a colorless transparent liquid, and remove the solvent by reduced pressure distillation at 60°C; then rinse with ethyl acetate and acetone in a volume ratio of 1:1 for 3 times, filter to obtain a white solid, and vacuum dry at 45°C to obtain 168.4g of substance C; The above substance C contains quaternary ammonium salt N + The characteristic peaks indicate that the tertiary amine has undergone a quaternization reaction; substance C is a gemini quaternary ammonium salt, and its structural formula is: .

[0041] Step 2: Preparation of Gemini Quaternary Ammonium Salt Modified Calcined Kaolin 100g of calcined kaolin and 2.5L of deionized water were mixed, heated in a 76°C water bath and mechanically stirred until uniformly dispersed to obtain a calcined kaolin suspension. 40g of the above-prepared gemini quaternary ammonium salt and 800mL of deionized water were weighed, and fully stirred until completely dissolved to obtain a gemini quaternary ammonium salt solution. The above gemini quaternary ammonium salt solution was mixed with the calcined kaolin suspension, mechanically stirred at 80°C for 3h, and then the mixed suspension was centrifuged and washed 3 times with deionized water, placed in a drying oven and dried at 80°C for 12h, and ground to 300 mesh to obtain gemini quaternary ammonium salt modified calcined kaolin.

[0042] Al2O3 46.0%, SiO2 51.4%, Fe2O3 ≤ 0.2%, pH 6.6, whiteness 92.5%, 325 mesh sieve residue ≤ 0.005%.

[0043] This embodiment also provides a method for preparing the above-mentioned recycled paper with flame retardant effect, and the preparation method comprises the following steps: S1. Mixing recycled paper pulp with virgin paper pulp, beating in a Valley beater to obtain a slurry, and diluting with water to 2% fiber slurry to obtain a mixed slurry; S2. The prepared gemini quaternary ammonium salt modified calcined kaolin and composite reinforcing agent are added to the mixed slurry, dissociated with a fiber dissociator, and 1.5% of the absolute dry pulp mass of cationic dispersed rosin glue (solid content 35%) is added to obtain a flame retardant paper suspension; S3. The prepared flame-retardant paper suspension is formed into wet paper sheets on a paper sheet former, and is passed through a sheet press to remove excess water and make the fibers tight, and then dried on a high-speed dryer to obtain recycled paper with flame-retardant properties, which is recorded as flame-retardant recycled paper III.

[0044] Wherein: the composite reinforcing agent in this embodiment comprises maleic anhydride acylated chitosan and cellulose nanofibrils, wherein the mass ratio of maleic anhydride acylated chitosan to cellulose nanofibrils is 2.5:1; wherein the preparation method of maleic anhydride acylated chitosan is the same as that of Example 2.

[0045] The preparation method of the recycled paper wood pulp and the virgin paper pulp is the same as that of Example 2.

[0046] Comparative Example 1 Comparative Example 1 provides a recycled paper with flame retardant effect. The raw material and preparation method of the recycled paper with flame retardant effect in this comparative example are basically the same as those in Example 3, except that: in terms of raw materials, the selected flame retardant is calcined kaolin modified with hexadecyltrimethylammonium bromide. The preparation steps of calcined kaolin modified with hexadecyltrimethylammonium bromide are as follows: 100 g of calcined kaolin and 2 L of deionized water were mixed, heated in a 76° C. water bath and mechanically stirred until uniformly dispersed to obtain a calcined kaolin suspension; Weigh 40g of hexadecyltrimethylammonium bromide and 800g of deionized water, stir thoroughly until completely dissolved, and obtain a hexadecyltrimethylammonium bromide solution. Mix the above hexadecyltrimethylammonium bromide solution with the calcined kaolin suspension, stir mechanically at 80°C for 3h, then centrifuge and wash the mixed suspension with deionized water for 3 times, put it into a drying oven and dry it at 80°C for 12h, grind it to 300 mesh, and obtain hexadecyltrimethylammonium bromide modified calcined kaolin.

[0047] The method for preparing recycled paper with flame retardant effect in this comparative example is different from that in Example 3 only in that the "gemini quaternary ammonium salt modified calcined kaolin" is replaced by "hexadecyltrimethylammonium bromide modified calcined kaolin", and the other parameters are the same. The obtained product is recorded as flame retardant recycled paper pair I.

[0048] Effect Example 1 The oxygen index (LOI) of the flame retardant recycled paper prepared in Examples 1-3 and Comparative Example 1 was measured with reference to GB / T 2406.2-2009. The measurement results are shown in Table 1.

[0049] Table 1

[0050] It can be seen from the data in Table 1 that, compared with the calcined kaolin modified with hexadecyltrimethylammonium bromide, the oxygen index of the calcined kaolin modified with the gemini quaternary ammonium salt provided by the present invention is significantly greater.

[0051] Effect Example 2 The afterflaming time of the flame-retardant recycled paper prepared in Examples 1-3 and Comparative Example 1 was measured with reference to GB5455-2014. The measurement results are shown in Table 2.

[0052] Table 2 Flame retardant recycled paper Ⅰ Flame retardant regeneration Ⅱ Flame retardant recycled paper Ⅲ Flame retardant recycled paper Ⅰ Afterburning time (s) 6 5 8 12 It can be seen from the data in Table 2 that, compared with the flame-retardant recycled paper modified by adding hexadecyltrimethylammonium bromide to calcined kaolin, the flame-retardant recycled paper modified by adding gemini quaternary ammonium salt to calcined kaolin provided by the present invention has a significantly shorter afterflame time.

[0053] Effect Example 3 The tensile strength and folding endurance of the flame-retardant recycled paper prepared in Examples 1-3 and Comparative Example 1 were measured with reference to GB / T 12914-2018 and GB / T 457-2008. The results of the tensile strength and folding endurance measurements are shown in Table 3.

[0054] Table 3 Flame retardant recycled paper Ⅰ Flame retardant regeneration Ⅱ Flame retardant recycled paper Ⅲ Flame retardant recycled paper Ⅰ Tensile strength (N / mm) 3.1 2.9 3.4 3.2 Folding endurance (times) 76 73 79 80 It can be seen from the data in Table 3 that compared with the flame-retardant recycled paper modified with calcined kaolin by adding cetyltrimethylammonium bromide, the flame-retardant recycled paper modified with calcined kaolin by adding gemini quaternary ammonium salt provided by the present invention has significantly lower tensile strength and folding endurance.

[0055] In summary, compared with the flame-retardant recycled paper modified with calcined kaolin with cetyltrimethylammonium bromide, the flame-retardant recycled paper modified with calcined kaolin by gemini quaternary ammonium salt provided in Examples 1-3 of the present invention has no significant difference in tensile strength and folding endurance, but has better flame retardant properties.

[0056] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent substitution or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A flame retardant recycled paper, characterized in that: The invention comprises the following components in parts by weight: 45 to 51 parts of pretreated recycled paper, 30 to 34 parts of virgin wood pulp board, 1.8 to 2.1 parts of composite reinforcing agent and 15 to 25 parts of kaolin-based flame retardant; Wherein, the kaolin-based flame retardant is calcined kaolin modified by gemini quaternary ammonium salt; The structural formula of the gemini quaternary ammonium salt is: ； The composite reinforcing agent comprises maleic anhydride acylated chitosan and cellulose nanofibrils.

2. The flame retardant recycled paper according to claim 1, characterized in that: The preparation method of the gemini quaternary ammonium salt comprises the following steps: performing a quaternization reaction on p-dibrombenzyl and triethylamine at 76° C. to 80° C. to obtain the gemini quaternary ammonium salt.

3. The flame retardant recycled paper according to claim 2, characterized in that: The reaction time of the quaternization reaction is 6h~7h; and / or The mass ratio of p-dibrombenzyl and triethylamine is 1.1:1-1.3:

1.

4. The flame retardant recycled paper according to claim 1, characterized in that: The preparation method of the gemini quaternary ammonium salt modified calcined kaolin comprises the following steps: mixing a calcined kaolin suspension with a gemini quaternary ammonium salt solution, reacting at 76° C. to 80° C. for 3 h to 4 h to obtain the gemini quaternary ammonium salt modified calcined kaolin.

5. The flame retardant recycled paper according to claim 4, characterized in that: The mass ratio of the gemini quaternary ammonium salt in the gemini quaternary ammonium salt solution to the calcined kaolin in the calcined kaolin suspension is 0.8:3 to 1.2:3; and / or The mass concentration of the calcined kaolin suspension is 0.04 g / mL to 0.06 g / mL; The mass concentration of the gemini quaternary ammonium salt solution is 0.04 g / mL to 0.06 g / mL.

6. The flame retardant recycled paper according to claim 1, characterized in that: The method for preparing the pretreated recycled paper comprises: removing free impurities from old corrugated paper boxes, and chopping them to obtain the pretreated recycled paper.

7. The flame retardant recycled paper according to claim 1, characterized in that: In the composite reinforcing agent, the mass ratio of the maleic anhydride acylated chitosan to the cellulose nanofibrils is 2:1-3:

1.

8. The flame-retardant recycled paper according to claim 7, characterized in that: The maleic anhydride acylated chitosan is prepared from chitosan and maleic anhydride in a mass ratio of 1:1.6 to 1:1.

8.

9. The method for preparing recycled paper with flame retardant effect according to any one of claims 1 to 8, characterized in that: The recycled paper is prepared by the pulp addition method, which specifically includes the following steps: S1. crushing and soaking the original paper pulp board to obtain original paper pulp; humidifying the pretreated recycled paper with water, pulping, deinking, screening and purifying to obtain recycled paper pulp; mixing the original paper pulp with the recycled paper pulp to obtain a mixed pulp; S2. adding the gemini quaternary ammonium salt-modified calcined kaolin and the composite reinforcing agent to the mixed slurry, dissociating to obtain a flame retardant paper suspension; S3. Forming, tableting and drying the flame retardant paper suspension to obtain recycled paper with flame retardant effect.

10. The method for preparing recycled paper with flame retardant effect as claimed in claim 9, characterized in that: The fiber concentration in the mixed slurry is 2% to 3%.

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