A method for preparing protective liquid for paper cultural relics

Abstract

The present invention discloses a method for preparing a nano-ZnO modified waterborne polyurethane / carboxymethyl chitosan blended protective liquid that can be used for the protection of paper cultural relics. The method satisfies the anti-aging requirements of long-term preservation of cultural relics while maintaining the appearance. The protective liquid is made from the following raw materials calculated by weight: 27 parts of polypropylene glycol; 18 parts of isophorone diisocyanate; 0.1-0.5 parts of nano-ZnO; 1 part of 1,4-butanediol; 2 parts of 2,2-dihydroxymethylpropionic acid; 1.5 parts of triethylamine; and 0.3-2 parts of carboxymethyl chitosan. The present invention utilizes the carbamate groups in the waterborne polyurethane to form hydrogen bonds with fibers to improve the strength of paper cultural relics. In view of the fact that isocyanate groups in the synthetic waterborne polyurethane raw materials are easy to modify, the waterborne polyurethane is chemically modified using nano-zinc oxide with high photocatalytic activity, and the natural biopolymer material carboxymethyl chitosan is used to further enhance the reinforcement function of the protective liquid. After coating the rice paper with the protective liquid, it has multiple effects such as enhancement, water resistance, resistance to ultraviolet aging and resistance to dry heat aging, etc., which can extend the life of paper cultural relics without affecting the appearance.

Description

Technical Field

[0001] The invention relates to the protection of paper cultural relics, and in particular to a synthesis method and application of a nano ZnO modified waterborne polyurethane / carboxymethyl chitosan multifunctional protective liquid coated on paper cultural relics. Background Art

[0002] Paper has been a crucial medium for information transmission since the Han Dynasty, making significant contributions to the dissemination and inheritance of culture and technology. In modern times, paper artifacts provide a wealth of evidence for studying social and cultural change and the true development of history. Therefore, their historical, social, and cultural value is immeasurable. However, during the preservation process, paper can age and even deteriorate due to factors such as light, microorganisms, temperature, and humidity, severely impacting its aesthetic and research value.

[0003] Ultraviolet aging and heat aging are important causes of paper aging, which cause cellulose degradation and increase the degree of natural aging of paper artifacts. Therefore, in the protection of paper artifacts, shielding against ultraviolet light and enhancing the binding force of cellulose fibers are very important. Currently, the most researched method is the reinforcement method of natural polymer materials, such as: Study on the influence of natural polymers and their derivatives on the durability of paper artifacts, China Papermaking, 2023(12):77-85. The protective effect of three reinforcing agents made of chitosan, sodium alginate and hydroxyethyl cellulose on paper artifacts was discussed. Natural polymer materials are green and environmentally friendly, with good biocompatibility. At the same time, they are similar to cellulose structures and have better permeability to paper than resin protective liquids. They can effectively reinforce paper and reduce the damage caused by dry heat aging to paper. In the application of paper artifact protection, natural polymer materials have similar defects to cellulose and are relatively weak in anti-ultraviolet aging. Natural polymer materials and resin materials have complementary functions. The combined application of the two can obtain a multifunctional protective liquid with good research value and application prospects. Summary of the Invention

[0004] In view of the above situation, in order to overcome the defects of the prior art, the purpose of the present invention is to provide a nano-ZnO modified water-based polyurethane / carboxymethyl chitosan multifunctional protective liquid for the protection of paper cultural relics. The present invention can simultaneously strengthen and waterproof the paper, while delaying ultraviolet light aging and thermal aging, and can effectively solve the problem that natural polymer protection methods are relatively weak in dealing with aging.

[0005] The technical solution of the present invention is a multifunctional protective liquid used for protecting paper cultural relics. The raw materials are composed of the following parts by weight: 27 parts of polypropylene glycol; 18 parts of isophorone diisocyanate; 0.1-0.5 parts of KH-550 modified nano ZnO; 1 part of 1,4-butanediol; 2 parts of 2,2-dihydroxymethylpropionic acid; 1.5 parts of triethylamine; 0.1-2 parts of carboxymethyl chitosan;

[0006] The KH-550 modified nano ZnO is composed of the following weight parts: 1 part of nano ZnO; 15 parts of deionized water; 50 parts of anhydrous ethanol; 4.7 parts of 3-aminopropyltriethoxysilane (KH-550);

[0007] The synthesis steps of the KH-550 modified nano ZnO are as follows:

[0008] Use a measuring cylinder to measure 15 parts of deionized water and 30 parts of anhydrous ethanol in a beaker, slowly add nano-ZnO, and adjust the pH value to 8-9. After ultrasonic dispersion at room temperature for 0.5 hours, transfer it to a three-necked flask, fully mix 4.7 parts of KH-550 with 20 parts of anhydrous ethanol and slowly drop it into the flask. React at 80°C for 8 hours. After the reaction is completed, cool it and repeatedly centrifuge and wash it to obtain KH-550 modified nano-ZnO.

[0009] The synthesis steps of the ZnO modified waterborne polyurethane / carboxymethyl chitosan protective solution are as follows:

[0010] 1) Weigh a certain amount of KH-550 modified nano-ZnO and a certain amount of isophorone isocyanate into a four-necked flask, place the four-necked flask in an oil bath, and carry out in-situ polymerization reaction under the conditions of a stirring device, a condenser and nitrogen protection, at a speed of 280 rpm, a reaction temperature of 85°C, and a reaction time of 2 h;

[0011] 2) Weigh a certain amount of polypropylene glycol and slowly add it to the four-necked flask in step 1), keep the reaction conditions unchanged, and react until the -NCO groups in the system reach the theoretical value;

[0012] 3) Weigh a certain amount of 2,2-dimethylolpropionic acid and 1,4-butanediol and slowly add them to the four-necked flask in step 2) to carry out a chain extension reaction. Change the reaction temperature to 75° C., the stirring speed to 360 rpm, and the reaction time to 6 h;

[0013] 4) After the chain extension reaction is completed, triethylamine is added to the four-necked flask in step 3) for neutralization reaction, and the reaction temperature is changed to 40° C. and the neutralization time is 1 hour. After the neutralization is completed, distilled water is added to adjust the solid content, and high-speed cutting emulsification is simultaneously performed for 0.5 hour and the stirring speed is 1200 rpm to obtain a nano-ZnO modified waterborne polyurethane emulsion;

[0014] 5) Physically blending the nano-ZnO modified aqueous polyurethane emulsion obtained in step 4) with the weighed carboxymethyl chitosan by stirring and ultrasonic dispersion to obtain a paper cultural relic protection liquid.

[0015] The beneficial effects of the present invention are:

[0016] (1) The present invention chemically modifies waterborne polyurethane by adding nano-ZnO modified by KH-550. During use, the waterborne polyurethane is alternately composed of soft segments composed of polyols and hard segments containing isocyanate groups. Hydroxyl groups react with isocyanate groups to form carbamate groups, which can form hydrogen bonds with cellulose and hemicellulose inside the paper, thereby enhancing the mechanical properties of the paper. At the same time, the polyurethane wraps the fibers, enhancing the bonding force between the fibers, thereby enhancing the aging resistance of the paper. Nano-ZnO is an excellent ultraviolet light shielding agent. Nano-ZnO modified with silane coupling agent KH-550 can be added to the waterborne polyurethane by chemical bond connection through in-situ polymerization. This is because the silane coupling agent contains -NH2 groups that can react with -NCO groups, so that the nano-ZnO is evenly distributed in the waterborne polyurethane without agglomeration, thereby giving the system ultraviolet light shielding and antibacterial capabilities. At the same time, the protective liquid forms a hydrophobic network structure between the fibers to limit the fiber water absorption and swelling, thereby increasing the water resistance of the coated rice paper.

[0017] (2) The present invention adds carboxymethyl chitosan to the blend. Chitosan compounds have a similar chemical structure to cellulose. Compared with chitosan, carboxymethyl chitosan is easily soluble in water and increases the viscosity of the system after dissolving in water, thereby further increasing the application performance of the protective liquid on paper. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The SEM images of the microscopic morphology changes of rice paper before and after coating with protective liquid. Figure 1 (a) is untreated rice paper with clear lines on the fiber surface; Figure 1 (b) shows the Xuan paper treated with the protective liquid in Example 4. The fiber lines are shallow and the surface is smooth. The protective liquid successfully encapsulates the fibers, forming a protective film. After treatment, the inter-fiber spaces are somewhat filled. This protective liquid film enhances fiber strength and bonding, preventing breakage and reducing damage to the fibers from external factors. This is the primary reason for the increased mechanical strength and aging resistance of the paper.

[0019] Figure 2 The appearance of rice paper before and after treatment with protective liquid. Figure 2 (a) Untreated rice paper and Figure 2 (b) After the protective liquid was applied to the rice paper, it was found that there was no obvious ink bleeding phenomenon and no obvious change in the handwriting. The protective liquid had little effect on the appearance of the rice paper. Figure 2 (c) The appearance of the rice paper in the water resistance test shows that water droplets can remain on the treated raw rice paper for a considerable period of time without wetting the paper, thus improving the water resistance of the rice paper work. Figure 2(d) shows the appearance of rice paper after the reversibility test. After washing away the protective liquid with acetone, there is still no obvious impact on the appearance, indicating that the protective liquid has good reversibility. DETAILED DESCRIPTION

[0020] Below in conjunction with specific examples, the specific embodiment of the present invention is further described. These examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, after reading the content taught by the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms also fall within the scope limited by the appended claims of the application.

[0021] Example 1:

[0022] 1) Weigh 0.1 parts of KH-550 modified nano-ZnO and 18 parts of isophorone isocyanate into a four-necked flask, place the flask in an oil bath, and carry out in-situ polymerization reaction under the conditions of a stirring device, a condenser and nitrogen protection at a speed of 280 rpm, a reaction temperature of 85°C, and a reaction time of 2 hours;

[0023] 2) Weigh 27 parts of polypropylene glycol and slowly add it to the four-necked flask in step 1), keep the reaction conditions unchanged, and react until the -NCO groups in the system reach the theoretical value;

[0024] 3) Weigh 1 part of 2,2-dimethylolpropionic acid and 2 parts of 1,4-butanediol, and slowly add them to the four-necked flask in step 2) to carry out a chain extension reaction. Change the reaction temperature to 75° C., the stirring speed to 360 rpm, and the reaction time to 6 h;

[0025] 4) After the chain extension reaction is completed, 1.5 parts of triethylamine is added to the four-necked flask in step 3) for neutralization reaction, and the reaction temperature is changed to 40° C. and the neutralization time is 1 hour. After the neutralization is completed, distilled water is added to adjust the solid content to 30%, and high-speed cutting emulsification is simultaneously performed for 0.5 hour and the stirring speed is 1200 rpm to obtain a nano-ZnO modified waterborne polyurethane emulsion;

[0026] 5) Physically blending the nano-ZnO modified aqueous polyurethane emulsion obtained in step 4) with 1.8 parts of carboxymethyl chitosan by stirring and ultrasonic dispersion, while adjusting the solid content of the protective liquid to 15% to obtain a paper cultural relic protective liquid.

[0027] Example 2:

[0028] 1) Weigh 0.2 parts of KH-550 modified nano-ZnO and 18 parts of isophorone isocyanate into a four-necked flask, place the flask in an oil bath, and carry out in-situ polymerization reaction under the conditions of a stirring device, a condenser and nitrogen protection at a speed of 280 rpm, a reaction temperature of 85°C, and a reaction time of 2 hours;

[0029] 2) Weigh 27 parts of polypropylene glycol and slowly add it to the four-necked flask in step 1), keep the reaction conditions unchanged, and react until the -NCO groups in the system reach the theoretical value;

[0030] 3) Weigh 1 part of 2,2-dimethylolpropionic acid and 2 parts of 1,4-butanediol, and slowly add them to the four-necked flask in step 2) to carry out a chain extension reaction. Change the reaction temperature to 75° C., the stirring speed to 360 rpm, and the reaction time to 6 h;

[0031] 4) After the chain extension reaction is completed, 1.5 parts of triethylamine is added to the four-necked flask in step 3) for neutralization reaction, and the reaction temperature is changed to 40° C. and the neutralization time is 1 hour. After the neutralization is completed, distilled water is added to adjust the solid content to 30%, and high-speed cutting emulsification is simultaneously performed for 0.5 hour and the stirring speed is 1200 rpm to obtain a nano-ZnO modified waterborne polyurethane emulsion;

[0032] 5) Physically blending the nano-ZnO modified aqueous polyurethane emulsion obtained in step 4) with 1.8 parts of carboxymethyl chitosan by stirring and ultrasonic dispersion, while adjusting the solid content of the protective liquid to 15% to obtain a paper cultural relic protective liquid.

[0033] Example 3:

[0034] 1) Weigh 0.3 parts of KH-550 modified nano-ZnO and 18 parts of isophorone isocyanate into a four-necked flask, place the flask in an oil bath, and carry out in-situ polymerization reaction under the conditions of a stirring device, a condenser and nitrogen protection at a speed of 280 rpm, a reaction temperature of 85°C, and a reaction time of 2 h;

[0035] 2) Weigh 27 parts of polypropylene glycol and slowly add it to the four-necked flask in step 1), keep the reaction conditions unchanged, and react until the -NCO groups in the system reach the theoretical value;

[0036] 3) Weigh 1 part of 2,2-dimethylolpropionic acid and 2 parts of 1,4-butanediol, and slowly add them to the four-necked flask in step 2) to carry out a chain extension reaction. Change the reaction temperature to 75° C., the stirring speed to 360 rpm, and the reaction time to 6 h;

[0037] 4) After the chain extension reaction is completed, 1.5 parts of triethylamine is added to the four-necked flask in step 3) for neutralization reaction, and the reaction temperature is changed to 40° C. and the neutralization time is 1 hour. After the neutralization is completed, distilled water is added to adjust the solid content to 30%, and high-speed cutting emulsification is simultaneously performed for 0.5 hour and the stirring speed is 1200 rpm to obtain a nano-ZnO modified waterborne polyurethane emulsion;

[0038] 5) Physically blending the nano-ZnO modified aqueous polyurethane emulsion obtained in step 4) with 1.8 parts of carboxymethyl chitosan by stirring and ultrasonic dispersion, while adjusting the solid content of the protective liquid to 15% to obtain a paper cultural relic protective liquid.

[0039] Example 4:

[0040] 1) Weigh 0.4 parts of KH-550 modified nano ZnO and 18 parts of isophorone isocyanate into a four-necked flask, place the flask in an oil bath, and carry out in-situ polymerization reaction under the conditions of a stirring device, a condenser and nitrogen protection at a speed of 280 rpm, a reaction temperature of 85°C, and a reaction time of 2 hours;

[0041] 2) Weigh 27 parts of polypropylene glycol and slowly add it to the four-necked flask in step 1), keep the reaction conditions unchanged, and react until the -NCO groups in the system reach the theoretical value;

[0042] 3) Weigh 1 part of 2,2-dimethylolpropionic acid and 2 parts of 1,4-butanediol, and slowly add them to the four-necked flask in step 2) to carry out a chain extension reaction. Change the reaction temperature to 75° C., the stirring speed to 360 rpm, and the reaction time to 6 h;

[0043] 4) After the chain extension reaction is completed, 1.5 parts of triethylamine is added to the four-necked flask in step 3) for neutralization reaction, and the reaction temperature is changed to 40° C. and the neutralization time is 1 hour. After the neutralization is completed, distilled water is added to adjust the solid content to 30%, and high-speed cutting emulsification is simultaneously performed for 0.5 hour and the stirring speed is 1200 rpm to obtain a nano-ZnO modified waterborne polyurethane emulsion;

[0044] 5) Physically blending the nano-ZnO modified aqueous polyurethane emulsion obtained in step 4) with 1.8 parts of carboxymethyl chitosan by stirring and ultrasonic dispersion, while adjusting the solid content of the protective liquid to 15% to obtain a paper cultural relic protective liquid.

[0045] Xuan paper was coated with the protective solutions prepared in Examples 1, 2, 3, and 4 above and compared to blank Xuan paper. The tensile strength of the paper was measured according to GB / T 12914-2018; the tear resistance of the paper was tested according to GB / T 455-2002; and the whiteness of the paper was measured according to GB / T 22879-2008. The test results are shown in Table 1.

[0046] Table 1 Effects of different protective liquids on paper properties before and after treatment

[0047] Pattern <![CDATA[Tensile strength (N·m·g -1 )]]> <![CDATA[Tear strength (mN·m 2 ·g -1 )]]> <![CDATA[R 457 Whiteness (%) Blank rice paper 15.18 0.89 72.2 Example 1 17.89 1.13 71.5 Example 2 18.42 1.34 71.1 Example 3 20.22 1.57 70.8 Example 4 20.05 1.35 70.3

[0048] Anti-aging test (results see Table 2):

[0049] (1) Ultraviolet aging experiment: Raw rice paper was used to replace the simulated paper cultural relics, and 254nm ultraviolet light was used to accelerate the simulated aging, and the ultraviolet aging time was 72h.

[0050] (2) Dry heat aging test: Raw rice paper was used instead of simulated paper cultural relics. The dry heat aging test was carried out according to GB / T464-2008. Method C was selected. The paper sample was placed in a constant temperature drying oven with an aging temperature of 105°C and an aging time of 72 h.

[0051] Table 2 Performance changes of rice paper coated with protective liquid prepared in Example 3 before and after aging

[0052]

[0053] Experiments show that the mechanical properties of Xuan paper treated with protective liquid are enhanced, and it has resistance to ultraviolet light aging and dry heat aging; the protective liquid has little effect on the whiteness and transparency of Xuan paper.

[0054] In summary, the present invention is scientific and reasonable, with simple preparation conditions, and the protective liquid is non-toxic and harmless, and has an excellent reinforcing effect on paper; the chemical modification of nano ZnO makes the nano ZnO evenly dispersed in the protective liquid, providing the protective liquid with a certain ultraviolet light shielding performance; after the rice paper is treated with the protective liquid, a thin film (such as Figure 1 ), which increases the strength and water resistance of rice paper, while the protective liquid has little effect on the appearance of rice paper (such as Figure 2 ).

[0055] The above examples are merely specific embodiments of the present invention. The present invention is not limited to the above examples, and many variations are possible. All variations that can be directly derived or imagined by a person skilled in the art from the disclosure of the present invention should be considered to be within the scope of protection of the present invention.

Claims

1. A method for preparing a protective liquid for paper cultural relics, characterized in that Preparation of nano-ZnO modified waterborne polyurethane / carboxymethyl chitosan multifunctional protective solution to meet the anti-aging requirements of long-term preservation of cultural relics without affecting their appearance, including the following steps: 1) Preparation of KH-550-modified nano-ZnO: 15 parts deionized water and 30 parts anhydrous ethanol were measured sequentially into a beaker using a graduated cylinder. Nano-ZnO was slowly added and the pH was adjusted to 8-9. The mixture was ultrasonically dispersed at room temperature for 0.5 h and then transferred to a three-necked flask. 4.7 parts KH-550 and 20 parts anhydrous ethanol were thoroughly mixed and slowly added dropwise to the flask. The mixture was reacted at 80°C for 8 h. After completion of the reaction, the mixture was cooled and repeatedly centrifuged and washed to obtain KH-550-modified nano-ZnO. 2) The KH-550-modified nano-ZnO obtained in step 1) was mixed with a certain amount of isophorone isocyanate in a four-necked flask. The four-necked flask was placed in an oil bath and subjected to an in-situ polymerization reaction at a speed of 280 rpm, a reaction temperature of 85° C., and a reaction time of 2 h in an oil bath equipped with a stirring device, a condenser, and nitrogen protection. A certain amount of polypropylene glycol was slowly added to the four-necked flask and reacted until the -NCO group in the system reached the theoretical value. 3) Weigh a certain amount of 2,2-dimethylolpropionic acid and 1,4-butanediol and slowly add them to the four-necked flask in step 2) to carry out a chain extension reaction. Change the reaction temperature to 75°C, the stirring speed to 360 rpm, and the reaction time to 6 hours; 4) After the chain extension reaction is completed, triethylamine is added to the four-necked flask in step 3) for neutralization reaction, and the reaction temperature is changed to 40° C. and the neutralization time is 1 hour. After the neutralization is completed, a corresponding proportion of distilled water is added, and high-speed cutting emulsification is performed simultaneously for 0.5 hour and a stirring speed of 1200 rpm to obtain a nano-ZnO modified waterborne polyurethane emulsion; 5) Physically blending the nano-ZnO modified aqueous polyurethane emulsion obtained in step 4) with a certain amount of carboxymethyl chitosan by stirring and ultrasonic dispersion to obtain a paper cultural relic protection solution; wherein the mass ratio of the added amount of carboxymethyl chitosan to the added amount of nano-ZnO in the protection solution is 1:1, 2:1, 3:1, or 4:

1.

2. The method for preparing a protective liquid for paper cultural relics according to claim 1, characterized in that: The addition amount of silane coupling agent KH-550 modified nano ZnO accounts for 0.1%-2% of the total raw material mass except distilled water.

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