A toughening and cross-linking reinforcement material and reinforcement method for fragile paper cultural relics

Abstract

The present invention provides a toughening and cross-linking reinforcement material and reinforcement method for fragile paper artifacts with broken marks, wherein the reinforcement material is composed of a nanocellulose aqueous dispersion and an epoxy resin aqueous dispersion; wherein the nanocellulose is bacterial cellulose, nanocellulose fibrils, or nanocellulose whiskers. The toughening and cross-linking reinforcement material of the present invention can not only physically fill the fragile broken marks of paper artifacts, but also chemically cross-link the two. While increasing the strength of the fragile broken marks, it also produces a large number of hydrophilic groups, reduces the rigidity of the fragile paper at the broken marks, and improves the flexibility of the paper. At the same time, this operation does not form a significant height difference on the surface of the paper. In the restoration of scroll artifacts, the problem of secondary folds caused by the height difference caused by the folded paper can be well avoided, which is of great significance in the restoration of paper artifacts.

Description

Technical Field

[0001] The present invention belongs to the technical field of protection and restoration of paper cultural relics, and specifically relates to a reinforcement material and a reinforcement method for paper cultural relics with broken marks that are toughened and cross-linked by multiple epoxy groups, so as to minimize the damage to the paper cultural relics and restore the integrity and aesthetics of their images. Background Art

[0002] Paper artifacts are not only the primary vehicle for the dissemination of human civilization, but also recorders and witnesses of it, representing a precious, irreplaceable legacy. Paper artifacts preserved in museums, libraries, and archives worldwide are a vital component of the world's historical and cultural heritage, possessing both high social and artistic value. During long-term preservation, paper artifacts can break due to factors such as cellulose degradation and improper preservation, impacting their integrity and aesthetics. Traditional methods of reinforcing broken and damaged paper, such as spraying nanocellulose or applying folding strips to wrinkled and cracked areas of ancient calligraphy and paintings, are commonly used to reinforce the damaged core of the painting. However, these methods physically fill the broken areas of paper artifacts and offer limited improvement in the mechanical properties of fragile paper artifacts. As cellulose ages, its mechanical strength decreases, and it becomes hard and brittle over time.

[0003] Wang Wenhua et al. developed a method for reinforcing creases in damaged scroll-like artwork by spraying an aqueous dispersion containing hydroxypropyl methylcellulose as the primary component onto the damaged artwork. This crease, manifested as fiber breakage, is addressed by filling the creases with hydroxypropyl methylcellulose, which acts as a bridge to improve the mechanical properties of the damaged area, thereby reinforcing the damaged artwork. However, this method requires spraying the entire piece of artwork. While this not only reinforces the damaged area but also improves the strength of the intact portion, the strength difference between the intact and damaged areas persists. Furthermore, the method requires applying creases to the paper, which can create secondary creases at the edges during subsequent curling and storage due to differences in height and strength. Chen Xiaoli et al. from the Nanjing Museum prepared an aqueous solution using bacterial cellulose as the primary component and applied it to the creases of paper samples, improving mechanical properties such as tensile strength, folding resistance, and tear resistance without affecting the thickness of the paper. Gong Decai and others at the Shanxi Museum placed scattered paper fibers in a sandblaster, applied paste to the creases, and then spray-repaired the creases to improve the mechanical strength of the damaged areas. However, these methods physically fill the broken areas of paper artifacts, which has limited improvement in the mechanical properties of fragile paper artifacts. As the fibers age, their strength, toughness, and heat resistance decrease, which in turn has a certain impact on the paper artifacts. Summary of the Invention

[0004] The purpose of the present invention is to overcome the problems existing in the above-mentioned prior art and provide a toughening and cross-linking reinforcement material and reinforcement method for fragile paper artifacts with broken marks, so as to improve the strength and flexibility of the fragile broken marks and reduce the rigidity of the fragile paper at the broken marks. At the same time, no obvious height difference will be formed on the surface of the paper, thereby minimizing the damage to the paper artifacts and restoring the integrity and aesthetics of the picture.

[0005] In order to achieve the above-mentioned purpose, the present invention provides a toughening and cross-linking reinforcement material for fragile paper cultural relics, which is composed of a nanocellulose aqueous dispersion and an aqueous epoxy resin aqueous dispersion.

[0006] The nanocellulose is any one of bacterial cellulose, nanocellulose fibrils and nanocellulose whiskers.

[0007] Preferably, when the nanocellulose is bacterial cellulose, the mass concentration of the bacterial cellulose in the bacterial cellulose aqueous dispersion is 0.5% to 1.0%.

[0008] Preferably, when the nanocellulose is nanocellulose fibrils, the mass concentration of the nanocellulose fibrils in the nanocellulose fibril aqueous dispersion is 0.3% to 0.8%.

[0009] Preferably, when the nanocellulose is nanocellulose whiskers, the mass concentration of the nanocellulose whiskers in the nanocellulose whisker aqueous dispersion is 5% to 10%.

[0010] Preferably, the mass concentration of the water-based epoxy resin in the water-based epoxy resin aqueous dispersion is 0.2% to 0.6%.

[0011] More preferably, the water-based epoxy resin is B-63 water-based epoxy resin.

[0012] The method for reinforcing fragile paper cultural relics with broken marks provided by the present invention comprises the following steps: using a soft-bristle brush or writing brush to dip a nanocellulose aqueous dispersion in a reinforcing material, uniformly applying a layer of the nanocellulose aqueous dispersion to the broken portion of the paper cultural relic to be repaired, and naturally drying the layer after applying; then using a spray gun, a soft-bristle brush or writing brush to apply a layer of the water-based epoxy resin aqueous dispersion in the reinforcing material to the position where the nanocellulose aqueous dispersion was applied, and naturally drying the layer after applying.

[0013] The beneficial effects of the present invention are as follows:

[0014] The present invention uses multiple epoxy groups to toughen and cross-link hydroxyl groups to reinforce broken paper artifacts. Taking water-based epoxy resin B-63 and nanocellulose fibrils as examples, the nanocellulose fibrils are sprayed as a filler on the broken areas during reinforcement. After the nanocellulose fibrils are naturally dried, the water-based epoxy resin B-63 is applied to the nanocellulose fibrils as a crosslinking agent. Due to the crosslinking effect of epoxy groups and hydroxyl groups, not only can the fragile broken areas of the paper artifacts be physically filled, but the two will also produce chemical crosslinking, while increasing the strength of the fragile broken areas, a large number of hydrophilic groups will be generated, reducing the rigidity of the fragile paper at the broken areas and improving the flexibility of the paper. At the same time, this operation will not form a significant height difference on the paper surface, which can effectively avoid the problem of secondary folding caused by the height difference caused by folded paper in the restoration of scroll artifacts. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a comparison of infrared spectra of CNF reinforced paper and CNF / B-63 reinforced paper.

[0016] Figure 2 This is a test of the softness of rice paper reinforced with different concentrations of B-63 water-based epoxy resin.

[0017] Figure 3 This is a test of the hydrophilicity of rice paper reinforced with different concentrations of B-63 water-based epoxy resin.

[0018] Figure 4 These are scanning electron microscope images of paper samples after treatment with traditional folded paper reinforcement (a) and toughening and cross-linking reinforcement (b) according to Example 1.

[0019] Figure 5 The surface morphology of damaged ancient calligraphy and painting paper before (a) and after (b) toughening and cross-linking reinforcement treatment, and the surface morphology of traditional folded paper before (d) and after (e) reinforcement treatment, as well as their respective roughness parameters (c) and (f) after reinforcement treatment.

[0020] Figure 6 The following are comparison diagrams of the effects of samples reinforced by different reinforcement methods before and after aging, where a and b are photos of traditional folded paper reinforcement before and after aging, respectively; c is a magnified photo of the traditional folded paper reinforcement after aging; d and e are photos of toughened and cross-linked reinforcement before and after aging, respectively; and f is a magnified photo of the toughened and cross-linked reinforcement after aging. DETAILED DESCRIPTION

[0021] The present invention will be further described in detail below with reference to the accompanying drawings and examples, but the protection scope of the present invention is not limited to these examples.

[0022] Example 1

[0023] 1. Preparation of reinforcement materials

[0024] 50 g of deionized water and 0.25 g of nanocellulose fibrils were added to a 100 mL beaker, and the mixture was heated and stirred in a magnetic stirrer for 30 minutes until the nanocellulose fibrils were evenly dispersed, thereby preparing a nanocellulose fibril aqueous dispersion with a mass concentration of 0.5%.

[0025] 50 g of deionized water and 0.1 g of B-63 waterborne epoxy resin were added to a 100 mL beaker and stirred in a magnetic stirrer for 10 minutes to prepare a B-63 waterborne epoxy resin dispersion with a mass concentration of 0.2%.

[0026] 2. The process of strengthening the creases of fragile paper artifacts with toughened cross-linked reinforcement materials

[0027] Use a soft brush to dip the above-prepared 0.5% mass concentration of nanocellulose fibril aqueous dispersion, and evenly apply a layer on the back of the crease of the old calligraphy and painting to be repaired, and let it dry naturally after coating; after the sample is dried, use a soft brush to apply a layer of 0.2% mass concentration of B-63 water-based epoxy resin dispersion on the position where the nanocellulose fibril aqueous dispersion was originally applied, and let it dry naturally after coating.

[0028] Example 2

[0029] 1. Preparation of reinforcement materials

[0030] 50 g of deionized water and 0.40 g of bacterial cellulose were added to a 100 mL beaker, and the mixture was heated and stirred in a magnetic stirrer for 30 minutes until the bacterial cellulose was evenly dispersed, thereby preparing a bacterial cellulose aqueous dispersion with a mass concentration of 0.8%.

[0031] 50 g of deionized water and 0.1 g of B-63 waterborne epoxy resin were added to a 100 mL beaker and stirred in a magnetic stirrer for 10 minutes to prepare a B-63 waterborne epoxy resin dispersion with a mass concentration of 0.2%.

[0032] 2. The process of strengthening the creases of fragile paper artifacts with toughened cross-linked reinforcement materials

[0033] Use a brush to dip into the above-prepared bacterial cellulose aqueous dispersion with a mass concentration of 0.8%, and evenly apply a layer on the back of the crease of the old calligraphy and painting to be repaired. Let it dry naturally after application; after the sample is dried, use a brush to apply a layer of B-63 water-based epoxy resin dispersion with a mass concentration of 0.2% on the position where the bacterial cellulose aqueous dispersion was originally applied, and let it dry naturally after application.

[0034] Example 3

[0035] 1. Preparation of reinforcement materials

[0036] 50 g of deionized water and 8 g of nanocellulose whiskers were added to a 100 mL beaker, and the mixture was heated and stirred in a magnetic stirrer for 30 minutes until the nanocellulose whiskers were evenly dispersed, thereby preparing a nanocellulose whisker aqueous dispersion with a mass concentration of 8%.

[0037] 50 g of deionized water and 0.1 g of B-63 waterborne epoxy resin were added to a 100 mL beaker and stirred in a magnetic stirrer for 10 minutes to prepare a B-63 waterborne epoxy resin dispersion with a mass concentration of 0.2%.

[0038] 2. The process of strengthening the creases of fragile paper artifacts with toughened cross-linked reinforcement materials

[0039] Use a soft brush to dip the above-prepared 8% mass concentration nanocellulose whisker aqueous dispersion, and evenly apply a layer on the back of the crease of the old calligraphy and painting to be repaired, and let it dry naturally after coating; after the sample is dried, use a soft brush to apply a layer of 0.2% mass concentration B-63 water-based epoxy resin dispersion on the position where the nanocellulose whisker aqueous dispersion was originally applied, and let it dry naturally after coating.

[0040] In order to demonstrate the beneficial effects of the present invention, the inventors conducted relevant experimental studies using the reinforcement materials and reinforcement methods in Example 1 above. The specific experiments and test results are as follows:

[0041] (1) Infrared comparison before and after chemical crosslinking

[0042] Use a brush to dip into a 0.5% mass concentration of nanocellulose fibril aqueous dispersion, evenly apply a layer on the paper, dry it after film formation, and record it as CNF reinforced paper.

[0043] Use a brush to dip into a 0.5% mass concentration of nanocellulose fibril aqueous dispersion, evenly apply a layer on the paper, and dry it after coating. Then use a brush to apply a layer of 0.2% mass concentration of B-63 water-based epoxy resin dispersion on the paper, and dry it after coating. This is recorded as CNF / B-63 reinforced paper.

[0044] from Figure 1 It can be seen that CNF / B-63 reinforced paper is 3420cm -1 The left and right are the characteristic peaks corresponding to -OH, 2900cm -1 The left and right sides are the characteristic peaks corresponding to CH stretching vibration, 1425cm -1 and 1368cm -1 It is the characteristic peak corresponding to CH bending vibration, 1610cm -1 The corresponding C=C bond stretching vibration peak is 1063cm -1The corresponding COC stretching vibration; all the characteristic peaks of nanocellulose fibrils can be seen in the infrared spectrum of CNF / B-63 reinforced paper, indicating that the composite of nanocellulose fibrils and B-63 waterborne epoxy resin does not affect the basic structure of nanocellulose fibrils. In addition, after cross-linking, the peak at 3420 cm -1 The corresponding -OH absorption peak increases, indicating that the sample has stronger hydrophilicity after cross-linking and reinforcement.

[0045] (2) Softness test before and after chemical crosslinking

[0046] Dip a brush into a 0.5% mass concentration of nanocellulose fibril aqueous dispersion and evenly apply a layer on the rice paper. After forming a film, dry it and record it as CNF reinforced rice paper.

[0047] Use a brush to dip into a 0.5% mass concentration of nanocellulose fibril aqueous dispersion, and evenly apply a layer on the rice paper. Dry it after coating. Then use a brush to apply a layer of B-63 water-based epoxy resin dispersion with a mass concentration of 0.2%, 0.4%, and 0.6% on the rice paper, respectively. Dry it after coating. This is recorded as CNF / B-63 reinforced rice paper.

[0048] from Figure 2 As can be seen from the graph, for both bamboo-grain and line-grain rice paper, the softness of the rice paper samples gradually increases with increasing B-63 waterborne epoxy resin concentration. The CNF-reinforced rice paper without B-63 waterborne epoxy resin exhibits the lowest softness and the highest stress resistance. This suggests that rice paper treated with B-63 waterborne epoxy resin after crosslinking nanocellulose fibrils exhibits increased softness.

[0049] (3) Comparison of hydrophilicity before and after chemical crosslinking

[0050] like Figure 3 The contact angle test results at zero seconds for blank rice paper, the aforementioned CNF-reinforced rice paper, and CNF / B-63-reinforced rice paper are shown in the figure. As can be seen, the contact angles for blank and CNF-reinforced rice paper at zero seconds are 76.7° and 53.8°, respectively. This is because the surface roughness of blank rice paper is relatively high, creating a high resistance for water diffusion between paper fibers. Upon contact, water droplets first wet the surface and then slowly diffuse. With the addition of B-63 waterborne epoxy resin, the hydrophilicity of the sample surface increases. The contact angles for CNF / B-63-reinforced rice paper with varying concentrations of B-63 waterborne epoxy resin are 27.9°, 27.6°, and 25.3°, respectively. This is due to the large number of exposed hydroxyl groups present in the crosslinked nanocellulose fibrils with B-63 waterborne epoxy resin, resulting in good hydrophilicity.

[0051] (4) Comparison of micromorphology between traditional reinforcement and toughened cross-linked reinforcement

[0052] Taking the reinforcement of the folding strips in the ancient calligraphy and painting as an example, according to the composition structure of the ancient calligraphy and painting, the folding strips of the ancient calligraphy and painting are pasted on the back of the paper layer during the restoration process. In order to determine its surface morphology, SEM was used to observe its surface morphology. The experimental results are as follows Figure 4 shown.

[0053] Figure 4 Scanning electron microscope images of paper samples reinforced with traditional folded paper strips (a) and reinforced with toughening and cross-linking (b) using Example 1. As can be seen from the images, the folded paper strips attached to the broken part of the calligraphy and painting with traditional folded paper strips cause new creases at the edges of the strips during the winding process due to the height difference between the folded paper strips and the painting. This is known as secondary creases, whereas the toughened and cross-linked reinforced areas do not experience this phenomenon.

[0054] (5) Surface morphology and roughness analysis

[0055] The surface morphology of the samples reinforced with traditional folded paper and toughened and cross-linked using Example 1 was observed using a Keyence VK-X260K shape analysis laser confocal microscope, and their three-dimensional surface roughness parameters were obtained. The experimental data were corrected and analyzed using Keyence multi-file analysis software VK-H1XMC. The analysis and test results are shown in Figure 5 .

[0056] Take the reinforcement of broken strips in old scrolls and calligraphy and painting as an example. Figure 5 The surface roughness comparison diagrams of the crease area of ​​toughened cross-linked reinforced paper (a, b) and the crease area of ​​traditional folded paper reinforced paper (d, e) measured using a laser confocal microscope are respectively. Figure 5 (c) and (f) record the detailed roughness parameters of the two reinforcement methods. Figure 5 As can be seen in (c), the Str value of the paper reinforced by toughening and cross-linking is 0.738, which is close to 1. The reason is presumably that due to the large pores in the paper fibers, the nanocellulose fibrils adhere to the paper fibers after cross-linking with the B-63 water-based epoxy resin and do not form a clear film, which cannot completely cover some of the paper fibers with larger protrusions. Figure 5 As can be seen from (f), the Str value of the paper reinforced by the traditional folding paper reinforcement method is 0.093, which is close to 0. The reason is that the traditional folding paper reinforcement method requires brushing paste on the folding paper, which makes the surface texture of the folding paper similar. Figure 5 From the values ​​in (c) and (f), it can be seen that the Sz value of the traditional folded paper reinforcement method is 1.7 times that of the toughened cross-linked reinforcement method, indicating that the surface height difference of the sample reinforced by the traditional folded paper method is large.

[0057] (6) Comparison of the effects of traditional reinforcement and toughened cross-linked reinforcement samples before and after aging

[0058] Take the reinforcement of broken strips in old scrolls and calligraphy and painting as an example. Figure 6 a and d are two samples of paper reinforced with traditional folded paper before aging and toughened and cross-linked paper reinforced in Example 1, taken under uniform lighting. It can be seen that the overall surface is flat and there are no creases around the folded paper. Figure 6 Figures b and e are samples of the traditional folded paper reinforcement and the paper reinforced by toughening and cross-linking in Example 1 after curling and aging for 3 days, which were obtained by taking pictures under uniform light. Figures c and f are local enlarged pictures. It can be seen that after aging for 3 days, creases appeared around the folds of the paper sample reinforced with folded paper, affecting the appearance of the paper sample. The paper sample reinforced with toughening and cross-linking was flat as a whole after aging, and no obvious creases appeared on the reinforced edges, which had no obvious impact on the original appearance of the sample.

Claims

1. A method for reinforcing fragile paper cultural relics, characterized by: Dip a soft brush or writing brush into the nanocellulose aqueous dispersion and apply a layer evenly to the broken part of the paper artifact to be repaired. Let it dry naturally after application. Then, use a spray gun or soft brush or writing brush to apply a layer of water-based epoxy resin aqueous dispersion to the place where the nanocellulose aqueous dispersion was applied. Let it dry naturally after application. The nanocellulose is any one of bacterial cellulose, nanocellulose fibrils and nanocellulose whiskers; The water-based epoxy resin is B-63 water-based epoxy resin.

2. The method for reinforcing fragile paper cultural relics according to claim 1, characterized in that: When the nanocellulose is bacterial cellulose, the mass concentration of the bacterial cellulose in the bacterial cellulose aqueous dispersion is 0.5% to 1.0%.

3. The method for reinforcing fragile paper cultural relics according to claim 1, characterized in that: When the nanocellulose is nanocellulose fibrils, the mass concentration of the nanocellulose fibrils in the nanocellulose fibril aqueous dispersion is 0.3% to 0.8%.

4. The method for reinforcing fragile paper cultural relics according to claim 1, characterized in that: When the nanocellulose is nanocellulose whiskers, the mass concentration of the nanocellulose whiskers in the nanocellulose whisker aqueous dispersion is 5% to 10%.

5. The method for reinforcing fragile paper cultural relics according to claim 1, characterized in that: The mass concentration of the water-based epoxy resin in the water-based epoxy resin aqueous dispersion is 0.2% to 0.6%.

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