Compound color fixing agent as well as preparation method and application thereof

Abstract

The invention discloses a compound color fixing agent and a preparation method and application thereof, and belongs to the technical field of papermaking chemicals, the preparation method of the compound color fixing agent comprises the following steps: adding a bio-based polycation component into an acetic acid solution, heating and stirring to obtain a bio-based polycation stock solution; and adding amphiphilic polycyclodextrin and a surfactant into the bio-based polycation stock solution, and carrying out homogenization treatment to obtain the compound color fixing agent. The compound color fixing agent provided by the invention comprises bio-based polycations, amphiphilic polycyclodextrin and a surfactant, the amphiphilic polycyclodextrin with a hydrophobic cavity is connected with C3-C5 alkyl and quaternary ammonium salt groups, through a multi-component compounding design, by utilizing a synergistic effect of host-guest inclusion, electrostatic interaction and hydrophobic interaction, the color fixing agent has a good color fixing effect, and the color fixing agent has a good color fixing effect. And a coating with an interpenetrating network structure is constructed on the surface of the paper, so that fixation of the dye is realized.

Description

Technical Field

[0001] This invention belongs to the field of papermaking chemicals technology, and in particular relates to a compound fixing agent, its preparation method and application. Background Technology

[0002] Paper dyeing is a crucial process in the papermaking industry, but traditional dyeing techniques suffer from low dye utilization and poor color fastness. Color fastness is a key indicator of specialty paper quality. Currently, improving color fastness mainly relies on charge neutralization or film formation, but this often leads to uneven dye distribution or a stiff feel. In related fields, research has been conducted on using cyclodextrin (CD) to encapsulate dyes and reduce the hydrolysis of reactive groups. For example, patent CN121379196A discloses a scheme using β-cyclodextrin-pyridinecarboxylic acid to encapsulate reactive dyes and assisting with zirconium salt chelation for color fixation; patent CN121319645A discloses a method for improving the water solubility of bio-indigo by compounding β-cyclodextrin with povidone. However, existing solutions mostly rely on metal ion chelation (such as zirconium salts) for color fixation, which not only increases industrial production costs but also puts environmental pressure on the recycling of papermaking white water due to the presence of metal ions, and may lead to fiber keratinization, hindering the recycling of waste paper fiber resources. In addition, although simple solubilizing compounding schemes (such as patent CN121319645A) can improve the water solubility of dyes, they do not fundamentally solve the problem of long-term adhesion stability of dyes on fibers. Summary of the Invention

[0003] In current paper dyeing processes, traditional fixing agents suffer from poor environmental friendliness, high cost, and weak chemical bonding between dyes and cellulose fibers, resulting in low color fastness and susceptibility to fading due to environmental humidity. This invention provides a compound fixing agent, its preparation method, and its application.

[0004] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for preparing a compound fixing agent, comprising the following steps: adding a bio-based polycation to an acetic acid solution and heating and stirring to obtain a bio-based polycation stock solution; adding an amphiphilic polycyclodextrin and a surfactant to the bio-based polycation stock solution and homogenizing to obtain the compound fixing agent.

[0005] Further, the bio-based polycation is selected from chitosan, and the molecular weight of the chitosan is 50,000-60,000 Da; the concentration of the acetic acid solution is 1 wt.%; the amphiphilic polycyclodextrin has a hydrophobic cavity structure of cyclodextrin molecules, and the amphiphilic polycyclodextrin molecular chain is connected with hydrophobic modifying groups and hydrophilic modifying groups; the hydrophobic modifying groups are C3-C5 straight-chain or branched alkyl groups; the hydrophilic modifying groups are cationic groups containing quaternary ammonium salts; the hydrophobic modifying groups and hydrophilic modifying groups are connected to the C6 position or C2 / C3 position of the cyclodextrin unit through ether bonds or ester bonds; the surfactant includes sodium dodecylbenzenesulfonate and fatty alcohol polyoxyethylene ether.

[0006] Furthermore, the mass ratio of the bio-based polycation, amphiphilic polycyclodextrin, surfactant, and acetic acid solution is (5-10):(20-30):(1.0-1.5):(63.5-69).

[0007] Furthermore, the heating and stirring temperature is 40~60℃; the specific operation of the homogenization process is: stirring at 400-600 r / min for 30 min.

[0008] Secondly, the present invention provides a compound fixing agent, which is prepared by the above preparation method.

[0009] Thirdly, the present invention provides an application of the compound fixing agent in paper dyeing.

[0010] Fourthly, the present invention provides an amphiphilic synergistic in-situ paper fixation method, comprising the following steps: adding an organic dye to the compound fixation agent, stirring in a water bath in the dark to allow the dye molecules to fully enter the hydrophobic cavity of the polycyclodextrin to form a host-guest inclusion structure, obtaining a host-guest inclusion complex solution, compounding the host-guest inclusion complex solution with an oxidized starch solution to obtain a coating liquid, and coating the coating liquid onto the surface of the base paper for in-situ fixation.

[0011] This invention provides a method for in-situ paper fixation based on the synergistic effect of multiple components and without the need for metal ions. The method utilizes the inclusion capacity of amphiphilic polycyclodextrin to protect dye molecules, and leverages the cationic and alkyl groups on the molecular chain to construct a protective layer on the fiber surface in combination with chitosan and starch. This improves the fixation rate and water resistance of the dye, overcoming the technical bottleneck of insufficient adsorption and weak hydrophobicity of single fixatives leading to easy dye loss.

[0012] Furthermore, the organic dye is selected from reactive red dispersion or indigo dispersion; the concentration of the reactive red dispersion is 10-20 wt.%, the concentration of the indigo dispersion is 20-40 wt.%, and the concentration of the oxidized starch solution is 5-8 wt.%.

[0013] Furthermore, the mass ratio of the organic dye to the compound fixing agent is 1:(4-10); the volume ratio of the host-guest inclusion complex solution to the oxidized starch solution is 1:5.

[0014] Furthermore, the temperature of the water bath is 40~60 ℃; after the coating liquid is applied to the surface of the base paper, the wet weight gain of the base paper is 60%~80%; the specific operation of the in-situ color fixing is: drying the coated paper at 105 ℃ for 5 min.

[0015] During the drying process, chitosan and oxidized starch in the coating solution form a coating with an interpenetrating network structure on the paper surface. This coating tightly fixes the amphiphilic polycyclodextrin to the paper surface, and the hydrophobic cavities of the amphiphilic polycyclodextrin encapsulate the dye molecules. In addition, the hydrophilic groups of the amphiphilic polycyclodextrin bind to the fibers, while the hydrophobic groups provide water resistance on the coating surface. This solves the problem of weak chemical bonding between the dye and cellulose fibers, which leads to low color fastness and susceptibility to fading due to environmental humidity.

[0016] This invention utilizes the synergistic effect of host-guest inclusion, electrostatic interaction, and hydrophobic groups to develop a process for in-situ dye fixation based on amphiphilic structure, electrostatic interaction, and hydrophobic interaction. This process not only avoids the drawbacks of traditional metal fixatives but also significantly improves the color stability of paper in complex environments, which is of great significance for promoting the development of green papermaking and high-performance specialty paper.

[0017] The technical principle of this invention is as follows: To improve the color fastness of dyes on paper, this invention constructs a ternary stable coating structure composed of dye, a compound fixing agent, and oxidized starch. The amphiphilic polycyclodextrin in the compound fixing agent contains hydrophobic cavities that encapsulate dye molecules. The quaternary ammonium salt group at one end binds to the hydroxyl groups on the fiber surface through electrostatic interactions, while the hydrophobic alkyl groups at the other end are oriented on the coating surface at drying temperatures, imparting water resistance to the paper surface. The bio-based polycations in the compound fixing agent provide a high density of positively charged sites, acting as a molecular binder and forming an interpenetrating network coating structure on the fiber surface together with oxidized starch. The surfactant in the compound fixing agent regulates the surface tension of the system, promoting the penetration and spreading of the inclusion complex in the fiber pores.

[0018] Compared with the prior art, the present invention has the following advantages and technical effects: The compound fixing agent provided by this invention includes a bio-based polycationic component, an amphiphilic polycyclodextrin, and a surfactant. The amphiphilic polycyclodextrin, with hydrophobic cavities, is linked to C3-C5 alkyl groups and quaternary ammonium salt groups. Through a multi-component compound design, this invention utilizes the synergistic effects of host-guest inclusion, electrostatic interactions, and hydrophobic interactions to construct a coating with an interpenetrating network structure on the fiber surface of paper, achieving in-situ dye locking. This invention requires no metal ions, exhibits high color fastness, does not affect the air permeability of paper, and provides a certain degree of physical reinforcement. Detailed Implementation

[0019] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0020] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0021] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0022] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0023] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0024] In the embodiments of this invention, unless otherwise specified, "parts" refers to "parts by mass".

[0025] The room temperature / normal temperature in this invention refers to 25±2℃.

[0026] Unless otherwise specified, all materials used in this invention are commercially available products, and the molecular weight of chitosan is 50,000-60,000 Da.

[0027] The amphiphilic polycyclodextrin used in this embodiment of the invention has a hydrophobic cavity structure, with a hydrophobic modifying group and a hydrophilic modifying group connected at both ends by ether bonds or ester bonds, respectively. The hydrophobic modifying group is a C3-C5 straight-chain or branched alkyl group; the hydrophilic modifying group is a cationic group containing a quaternary ammonium salt; the hydrophobic modifying group and the hydrophilic modifying group are connected to the C6 position or C2 / C3 position of the cyclodextrin unit by ether bonds or ester bonds.

[0028] The amphiphilic polycyclodextrin used in this invention has a known structure in the prior art and can be prepared by etherification and esterification modification methods disclosed in existing literature. It is a known material that can be routinely obtained by those skilled in the art. The preparation method of the amphiphilic polycyclodextrin used in this invention is as follows: (1) Crosslinking of polycyclodextrin: Add 10.0 g of β-cyclodextrin and 80 mL of deionized water to a 500 mL four-necked flask, start the electric stirrer (speed: 250 r / min), and stir at room temperature until the β-cyclodextrin is completely dissolved to obtain a transparent solution. Place the four-necked flask in a constant temperature water bath, heat to 40℃, slowly add 4.0 g of sodium hydroxide, and continue stirring for 30 min to completely dissolve the sodium hydroxide, maintaining the pH of the system at 11-12. Install a constant pressure dropping funnel and a reflux condenser, and slowly add 12 mL of epichlorohydrin dropwise through the dropping funnel at a rate of 1 mL / min, keeping the stirring rate constant during the dropwise addition to avoid excessively vigorous local reactions. After the dropwise addition is complete, raise the water bath temperature to 60℃, turn on the reflux condenser, and maintain the reaction temperature for 6 h, continuously stirring (speed: 300 r / min) during the process. After the reaction was complete, the heating was turned off and the mixture was allowed to cool naturally to room temperature. The pH of the system was slowly adjusted to 6.8-7.2 with hydrochloric acid, and the mixture was allowed to stand for 1 hour to allow the product to precipitate completely. The precipitate was collected by vacuum filtration through a Buchner funnel. The product was washed three times with deionized water (50 mL each time) and then twice with anhydrous ethanol (30 mL each time) to remove unreacted β-cyclodextrin, epichlorohydrin, and salts, yielding a white polycyclodextrin solid. This solid was then placed in a vacuum drying oven and dried at 60°C for 4 hours for later use. (2) Hydrophobic modification of polycyclodextrin: 5.0 g of the dried polycyclodextrin was added to a 250 mL four-necked flask, and 60 mL of isopropanol-deionized water mixed solvent (volume ratio 1:1) was added. Stirring was started (speed: 200 r / min), and the temperature was raised to 50 °C to form a uniform suspension of polycyclodextrin. 1.5 g of sodium hydroxide was added and stirred for 30 min to activate the hydroxyl groups on the surface of the polycyclodextrin molecules (mainly C2 / C3 positions). 3.0 mL of 1-bromobutane was added to the system, and the temperature was raised to 55 °C. The reaction was maintained for 5 h to achieve the connection between the C4 alkyl chain and the hydroxyl group of the polycyclodextrin through the Williamson etherification reaction. After the reaction was completed, the mixture was cooled to room temperature, and the solid product was collected by vacuum filtration. The product was repeatedly washed with deionized water until no white precipitate was detected by silver nitrate solution (confirming no residual bromide ions). The product was then dried under vacuum at 60 °C for 3 h to obtain hydrophobically modified polycyclodextrin. (3) Hydrophilic modification of polycyclodextrin: 4.0 g of hydrophobically modified polycyclodextrin was added to a 250 mL four-necked flask, followed by 50 mL of deionized water. After dispersion by stirring (200 r / min), the temperature was raised to 40 °C, and 0.8 g of sodium hydroxide was added. The mixture was stirred for 20 min to activate the remaining hydroxyl groups. 4.5 mL of EPTAC (2,3-epoxypropyltrimethylammonium chloride) was slowly added dropwise through a constant pressure dropping funnel at a dropping rate of 0.8 mL / min. After the addition was complete, the temperature was raised to 45 °C and the reaction was maintained for 8 h. The hydrophilic groups of the quaternary ammonium salt were grafted onto the polycyclodextrin molecules through the epoxy ring-opening reaction. After the reaction was completed, the pH of the system was adjusted to 6.8-7.2 with hydrochloric acid to obtain a pale yellow suspension. The suspension was transferred to a dialysis bag and dialyzed with deionized water for 72 h, with the deionized water being replaced every 8 h to remove unreacted EPTAC and small molecule byproducts. The dialyzed solution was transferred to a vacuum drying oven and dried under reduced pressure at 60°C for 12 h to obtain a white, fluffy solid powder, which is the amphiphilic polycyclodextrin. The product was sealed in a desiccator for storage and later use.

[0029] Example 1: A method for preparing a compound fixing agent S1. Add 10 parts of chitosan to 69 parts of acetic acid solution (1 wt.%) and stir at 50 °C until completely dissolved to prepare a bio-based polycationic stock solution; S2. Add 20 parts of amphiphilic polycyclodextrin to the bio-based polycationic stock solution prepared in S1, followed by 0.5 parts of SDBS (sodium dodecylbenzenesulfonate) and 0.5 parts of AEO-9 (fatty alcohol polyoxyethylene ether). Stir mechanically at 400 r / min for 30 min to obtain the compound color-fixing agent.

[0030] Example 2: A method for preparing a compound color-fixing agent S1. Add 5 parts of chitosan to 63.5 parts of acetic acid solution (1 wt.%) and stir at 60°C until completely dissolved to prepare a bio-based polycationic stock solution; S2. Add 30 parts of amphiphilic polycyclodextrin to the bio-based polycationic stock solution prepared in S1, followed by 0.7 parts of SDBS (sodium dodecylbenzene sulfonate) and 0.8 parts of AEO-9 (fatty alcohol polyoxyethylene ether). Stir mechanically at 600 r / min for 30 min to obtain the compound color-fixing agent.

[0031] Comparative Example 1 Add 20 parts of amphiphilic polycyclodextrin to 80 parts of deionized water and mechanically stir at 400 r / min for 30 min to obtain a color-fixing agent.

[0032] Comparative Example 2 Ten parts of chitosan were added to 90 parts of acetic acid solution (1 wt.%) and stirred at 50°C until completely dissolved to obtain a bio-based polycationic stock solution.

[0033] Comparative Example 3 Add 5 parts of commercially available zirconium salt fixing agent to 95 parts of deionized water and mechanically stir at 400 r / min for 30 min to prepare a zirconium salt fixing agent solution.

[0034] Comparative Example 4 Same as Example 1, except that the amphiphilic polycyclodextrin is replaced by ordinary β-cyclodextrin.

[0035] Comparative Example 5 S1. Add 10 parts of chitosan to 89 parts of acetic acid solution (1 wt.%) and stir at 50 °C until completely dissolved to prepare a bio-based polycationic stock solution; S2. Add 0.5 parts of SDBS (sodium dodecylbenzenesulfonate) and 0.5 parts of AEO-9 (fatty alcohol polyoxyethylene ether) to the bio-based polycationic stock solution prepared in S1, and mechanically stir at 400 r / min for 30 min to obtain the color-fixing agent.

[0036] Comparative Example 6 Add 20 parts of amphiphilic polycyclodextrin to 79 parts of deionized water, followed by 0.5 parts of SDBS (sodium dodecylbenzenesulfonate) and 0.5 parts of AEO-9 (fatty alcohol polyoxyethylene ether). Stir mechanically at 400 r / min for 30 min to obtain a color-fixing agent.

[0037] Application Example 1 S1. Dye inclusion: The organic dye to be used (reactive red dispersion, concentration of 15 wt.%) was added to the compound fixing agent prepared in Example 1 at a mass ratio of 1:5. The mixture was stirred in a constant temperature water bath at 45°C for 1.5 hours in the dark to allow the dye molecules to fully enter the hydrophobic cavity of the amphiphilic polycyclodextrin to form a host-guest inclusion complex. S2. Paper dyeing process: The paper dyeing process is carried out by surface sizing. The host-guest inclusion complex solution prepared in S1 is mixed with 8 wt.% oxidized starch solution at a volume ratio of 1:5 to obtain a coating solution. The obtained coating solution is uniformly coated on the surface of undyed base paper using a laboratory coating machine, and the wet weight gain is controlled at 60%. S3. In-situ color fixation: Place the coated paper in a paper dryer and dry it continuously at 105℃ for 5 minutes to complete the in-situ color fixation of the paper with amphiphilic synergy.

[0038] Application Example 2 S1. Dye inclusion: The organic dye to be used (indigo dispersion, concentration of 25 wt.%) was added to the compound fixing agent prepared in Example 2 at a mass ratio of 1:5. The mixture was stirred in a constant temperature water bath at 55°C for 2 hours in the dark to allow the dye molecules to fully enter the hydrophobic cavity of the amphiphilic polycyclodextrin to form a host-guest inclusion complex. S2. Paper dyeing process: The paper dyeing process is carried out by surface sizing. The host-guest inclusion complex solution prepared in S1 is mixed with 5 wt.% oxidized starch solution at a volume ratio of 1:5 to obtain a coating solution. The obtained coating solution is uniformly coated on the surface of undyed base paper using a laboratory coating machine, and the wet weight gain is controlled at 60%. S3. In-situ color fixation: Place the coated paper in a paper dryer and dry it continuously at 105℃ for 5 minutes to complete the in-situ color fixation of the paper with amphiphilic synergy.

[0039] Comparative Application Examples 1-6 The compound fixing agent prepared in Example 1 of Application Example 1 was replaced by the fixing agents prepared in Comparative Examples 1, 4-6, the bio-based polycation stock solution prepared in Comparative Example 2, and the zirconium salt fixing agent solution prepared in Comparative Example 3, respectively, by equal mass.

[0040] Performance tests were conducted on the dyed papers prepared for corresponding use cases 1-2 and comparative application examples 1-6, including color fastness to color, dry rubbing fastness, wet rubbing fastness, tensile strength, and air permeability retention. The test results are shown in Table 1, and the specific test methods are as follows: Color fixation effect: The color fixation effect is measured by color difference ΔE To indicate, the initial colorimetry L of the paper surface was determined using a precision colorimeter, in accordance with GB / T 7974. a b The colorimetric value of the paper was measured again after soaking it in water for 30 minutes and then drying it. The color difference ΔE before and after water immersion was calculated using the CIE 1976 color difference formula. This is the fixation rate.

[0041] Color fastness to rubbing: Refer to national standard GB / T 3920-2008. Using a color fastness to rubbing tester, rub the paper surface 10 times with both dry and wet standard rubbing cloths under a pressure of 9N. Rate the staining of the rubbing cloths according to the standard staining gray scale (grades 1-5).

[0042] Tensile strength determination: Refer to national standard GB / T 12914-2018. Use a paper tensile strength tester to determine the tensile strength before coating (T0) and the tensile strength after coating (T1), and calculate the rate of change of tensile strength, rate of change (%) = (T1-T0) / T0×100%.

[0043] Air permeability retention rate determination: Refer to national standard GB / T 458-2008 (Schober method). Measure the air permeability P0 before coating and the air permeability P1 after coating, respectively. Retention rate (%) = P1 / P0 × 100%.

[0044] Table 1 Table 1 shows that the compound color-fixing agent provided by this invention exhibits a significant synergistic color-fixing effect between amphiphilic polycyclodextrin and chitosan. A comparison of Example 1, Comparative Example 1, and Comparative Example 2 reveals that while amphiphilic polycyclodextrin alone (Comparative Example 1) provides some color-fixing effect, its wet rubbing fastness is low. Conversely, while chitosan alone (Comparative Example 2) improves strength, its color difference value Δ... E A value as high as 4.88 indicates a significantly insufficient color-fixing effect. In Example 1, after blending the two ingredients, the color difference value Δ... E The viscosity was reduced to 0.65, and the wet rubbing fastness reached grade 4. This demonstrates that the chitosan-containing coating fixes the dye-loaded amphiphilic polycyclodextrin to the paper surface, achieving stable dye adhesion to the fibers.

[0045] Comparing Example 1 with Comparative Example 4, it was found that when using ordinary cyclodextrin, the color difference value Δ E The viscosity was as high as 4.12, and the rubbing fastness decreased significantly. This verifies that the amphiphilic structure of the amphiphilic polycyclodextrin in this invention plays a key role, that is, the coating of hydrophobic groups in the molecular structure endows the paper with excellent water resistance after drying and film formation.

[0046] Color fixation effect of Example 1 (Δ) E =0.65) is superior to traditional zirconium salt fixation methods (Comparative Example 3, Δ E =1.35). More importantly, the air permeability retention rate of Example 1 (98.2%) was significantly higher than that of Comparative Example 3 (88.6%), and the tensile strength was also improved more. This shows that the compound system of the present invention can not only replace metal ion fixation, but also avoid fiber keratinization and pore blockage caused by metal ions, achieving the unity of fixation and paper physical properties, and is more conducive to the recycling of secondary fibers.

[0047] By comparing Example 1 with Comparative Examples 5 and 6, it can be observed that in the absence of amphiphilic polycyclodextrin (Comparative Example 5), the color difference is significantly increased, which is closely related to the inclusion of its hydrophobic cavity and the film-forming effect of its hydrophobic long chain; in the absence of chitosan (Comparative Example 6), the color difference is also significantly increased, because the system is difficult to form a coating with strong adhesion on the paper surface, resulting in a significant decrease in both color fixation performance and physical strength.

[0048] In summary, the amphiphilic structure of the amphiphilic polycyclodextrin and the charge network anchoring effect of chitosan in this invention produce a synergistic effect, reducing color difference Δ without affecting air permeability. E By reducing the level to below 1.0, efficient and stable color fixation of dyes on paper can be achieved.

[0049] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a compound fixing agent, characterized in that, Includes the following steps: Bio-based polycations were added to an acetic acid solution and heated and stirred to obtain a bio-based polycation stock solution. Amphiphilic polycyclodextrin and surfactants were added to the bio-based polycation stock solution and homogenized to obtain the compound fixing agent.

2. The method for preparing the compound fixing agent according to claim 1, characterized in that, The bio-based polycation is selected from chitosan, and the molecular weight of chitosan is 50,000-60,000 Da; The concentration of the acetic acid solution is 1 wt.%; The amphiphilic polycyclodextrin has a hydrophobic cavity structure of cyclodextrin molecules; The amphiphilic polycyclodextrin molecular chain is connected to a hydrophobic modifying group and a hydrophilic modifying group. The hydrophobic modifying group is a C3-C5 straight-chain or branched alkyl group; the hydrophilic modifying group is a cationic group containing a quaternary ammonium salt; the hydrophobic modifying group and the hydrophilic modifying group are connected to the C6 position or C2 / C3 position of the cyclodextrin unit through an ether bond or an ester bond. The surfactants include sodium dodecylbenzenesulfonate and fatty alcohol polyoxyethylene ether.

3. The method for preparing the compound fixing agent according to claim 2, characterized in that, The mass ratio of the bio-based polycation, amphiphilic polycyclodextrin, surfactant, and acetic acid solution is (5-10):(20-30):(1.0-1.5):(63.5-69).

4. The method for preparing the compound fixing agent according to claim 1, characterized in that, The heating and stirring temperature is 40~60℃; The specific operation of the homogenization process is as follows: stir at 400-600 r / min for 30 min.

5. A compound color-fixing agent, characterized in that, It is prepared by the preparation method described in any one of claims 1-4.

6. The application of the compound fixing agent according to claim 5 in paper dyeing.

7. A method for in-situ paper fixation with amphipathic synergy, characterized in that, The process includes the following steps: adding organic dye to the compound fixing agent described in claim 5, stirring in a water bath in the dark to obtain a host-guest inclusion complex solution, compounding the host-guest inclusion complex solution with an oxidized starch solution to obtain a coating liquid, and coating the coating liquid onto the surface of the base paper for in-situ fixing.

8. The amphiphilic synergistic in-situ paper fixation method according to claim 7, characterized in that, The organic dye is selected from reactive red dispersion or indigo dispersion; The concentration of the active red dispersion is 10-20 wt.%, and the concentration of the indigo dispersion is 20-40 wt.%. The concentration of the oxidized starch solution is 5-8 wt.%.

9. The amphiphilic synergistic in-situ paper fixation method according to claim 8, characterized in that, The mass ratio of the organic dye to the compound fixing agent is 1:(4-10); the volume ratio of the host-guest inclusion complex solution to the oxidized starch solution is 1:

5.

10. The amphiphilic synergistic in-situ paper fixation method according to claim 7, characterized in that, The temperature of the water bath is 45~55℃; After the coating solution is applied to the surface of the base paper, the wet weight gain of the base paper is 60%~80%; The specific operation of in-situ color fixing is as follows: the coated paper is dried at 105 ℃ for 5 min.

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