A method for deacidifying paper using hydroxyapatite

Abstract

The application discloses a method for paper deacidification by using hydroxyapatite. The method selects the mass percentage concentration of HA water suspension to be 0.05%-0.5%, adopts the atomization spraying method, uniformly sprays the liquid to the surface of filter paper, and horizontally places the filter paper in the air for 1h-12h, preferably 5h after spraying; then, the water is naturally evaporated, and then the filter paper is placed in a constant-temperature and constant-humidity chamber to balance the moisture for 12h-48h, preferably 24h, and then the filter paper is detected; the source of the HA is chemical precipitation synthesis or commercial reagent. The atomization spraying method is adopted to spray the HA dispersion liquid on the surface of the paper, and the deacidification effect comparable to that of calcium carbonate and calcium hydroxide is obtained. After further treatment by the dry heat aging method, the physical properties of the paper deacidified by the chemical precipitation method even reversely appear to be improved.

Description

Technical Field

[0001] This invention belongs to the field of paper deacidification, specifically relating to a method for paper deacidification using hydroxyapatite. Background Technology

[0002] Ancient books and archives, among other paper documents, are an important part of traditional Chinese culture. They serve as the primary carriers of traditional culture and historical information, and bear witness to Chinese culture and history, possessing extremely high historical, cultural, and academic value. Therefore, the preservation of paper documents is of paramount importance.

[0003] Over time, paper undergoes irreversible aging, primarily manifested as increased acidity (decreased pH), decreased mechanical strength, color changes, breakage, and even crumbling. Essentially, paper aging is caused by the breakage of β-1,4-glycosidic bonds between cellulose sugar rings, leading to a decrease in the degree of polymerization (DP) of cellulose. The fundamental cause is acid catalysis; the attack of insects and fungi is also significant. The sources of acid are multifaceted: on one hand, changes in temperature and humidity, heat, and ultraviolet radiation cause the slow degradation of cellulose and hemicellulose in paper, producing endogenous acidic substances; on the other hand, and more importantly, fillers added to paper, surface coating sizing agents, writing inks, and air pollutants all generate large amounts of acidic substances, greatly accelerating paper aging. Especially in modern times, my country has introduced Western papermaking technology, using machine manufacturing and aluminum sulfate-rosin as sizing agents, resulting in the fastest aging rate for modern documents (late 19th to mid-20th century), making their protection urgent.

[0004] The best way to protect acidified documents is through deacidification treatment. Deacidification involves introducing alkaline substances into the paper document, which neutralize existing acidic substances and create an alkaline reserve to further neutralize any future acidic substances. Deacidification is a primary method for delaying paper degradation and extending its lifespan. Current deacidification methods include gas-phase and liquid-phase methods. Gas-phase deacidification mainly uses alkaline gases, but the alkaline reserve is relatively small and sometimes poses a flammability hazard. Liquid-phase deacidification is more commonly used, including aqueous solutions and organic solutions. The solution contains alkaline substances that can neutralize the acid; the most commonly used substances include calcium hydroxide, calcium carbonate, magnesium hydroxide, and magnesium oxide. However, the method of adding hydroxyapatite (HA) to acidified paper using liquid-phase spraying has not yet been reported. HA is the most stable calcium-phosphate mineral and also contains hydroxyl (OH) ions. - HA can neutralize acidic substances and remains stable for a long time. HA also contains phosphate (PO4) ions. 3- ) and OH -This facilitates the formation of more hydrogen bonds, resulting in better bonding with paper. Summary of the Invention

[0005] This invention overcomes the above-mentioned shortcomings and provides a method for deacidifying paper using hydroxyapatite. This invention employs an atomized spraying method to apply a HA dispersion to the paper surface, achieving a deacidification effect comparable to that of calcium carbonate and calcium hydroxide. After further treatment with dry heat aging, the physical properties of the paper deacidified by the chemical precipitation method even show a reverse improvement.

[0006] The technical solution of this invention is as follows.

[0007] A method for deacidifying paper using hydroxyapatite involves selecting an HA aqueous suspension with a mass percentage concentration of 0.05% to 0.5%, preferably 0.1%. The liquid is uniformly sprayed onto the surface of the filter paper using an atomizing spray method. After spraying, the paper is left to stand horizontally in the air for 1 to 12 hours, preferably 5 hours, to allow the moisture to evaporate naturally. Then, the paper is placed in a constant temperature and humidity chamber to equilibrate the moisture for 12 to 48 hours, preferably 24 hours, before testing.

[0008] The temperature of the constant temperature and humidity chamber is 23℃~27℃, preferably 26℃, and the humidity is 40-60%.

[0009] The HA is derived from chemical precipitation synthesis or commercially available reagents.

[0010] A method for deacidifying paper using hydroxyapatite, specifically the chemical precipitation method for synthesizing HA, is as follows:

[0011] 1) Preparation of calcium and phosphorus sources;

[0012] 2) Add polyethylene glycol 6000 (PEG6000) to the calcium source and stir continuously; then add ammonia water to make the pH value of the calcium source greater than 11;

[0013] 3) Turn on the heating to keep the calcium source at 60℃; turn on the peristaltic pump to slowly add the phosphorus source to the calcium source, completing the addition in 2 to 5 hours, while continuously stirring;

[0014] 4) Aging at room temperature to ensure complete reaction;

[0015] 5) Centrifuge and discard the supernatant;

[0016] 6) Add deionized water to the precipitate and wash, centrifuge, discard the supernatant, and repeat the washing; wash with anhydrous ethanol.

[0017] 7) Dry in an oven, grind, and obtain the finished product.

[0018] In the above method, in step 1), the calcium source is a 0.5 mol / L Ca(NO3)2·4H2O solution.

[0019] In the above method, in step 1), the phosphorus source is 0.25 mol / L (NH4)3PO4·3H2O.

[0020] In the above method, in step 2), the mass percentage concentration of polyethylene glycol 6000 in the calcium source is 0.01% to 0.3%, preferably 0.1%; the stirring time is 15 min to 60 min.

[0021] In the above method, in step 4), the aging time is 12h to 72h.

[0022] In the above method, in step 6), the number of repeated washings is 1 to 3 times; the number of washings with anhydrous ethanol is 1 to 3 times.

[0023] In the above method, in step 7), the drying temperature is 50℃~80℃, preferably 60℃; the drying time is 3h~18h, preferably 12h.

[0024] Compared with the prior art, the advantages of the present invention are:

[0025] 1. Ca(OH)₂ and CaCO₃ are commonly used paper deacidifying agents. Overall, the differences in physical properties between commercial HA, chemically precipitated HA, and commercial Ca(OH)₂ and CaCO₃ deacidified filter paper are small, indicating that the deacidification effect of HA is comparable to that of Ca(OH)₂ and CaCO₃. However, the alkali reserve of HA is much lower than that of Ca(OH)₂ and CaCO₃ (only about 1 / 10), which is an unexpected result.

[0026] 2. Overall, after 5 days of dry heat aging, the deacidification effect of HA was still comparable to that of CaCO3, and even better than that of Ca(OH)2 (the filter paper deacidified by Ca(OH)2 and CaCO3 was not further subjected to dry heat aging). Therefore, the short-term dry heat method, which was originally intended to accelerate aging, can actually be used as a means to improve the deacidification effect of HA, producing unexpected results.

[0027] 3. After further treatment with dry heat aging, the physical properties of the paper deacidified by chemical precipitation HA even showed an improvement, producing unexpected results without any technological inspiration.

[0028] 4. The deacidification effect of chemical precipitation method of HA is better than that of commercial HA, which produces unexpected results. Attached Figure Description

[0029] Figure 1a Infrared spectra from commercial sources;

[0030] Figure 1bThe infrared spectrum of the chemical precipitation method;

[0031] Figure 2 Physical properties of acidified filter paper and blank filter paper after repair with commercial HA, chemical precipitation HA, commercial Ca(OH)2, and commercial CaCO3: a, whiteness; b, tensile index; c, tear index; d, folding endurance; e, air permeability (air permeability between 25 and 30 is more suitable);

[0032] Figure 3 The physical properties of acidified filter paper after 5 days of dry heat aging were compared between commercial HA, chemical precipitation HA-repaired filter paper, and blank acidified filter paper: a) whiteness; b) tensile index; c) tear index; d) folding endurance; e) air permeability (air permeability between 25 and 30 is more suitable). Green bars without shading lines represent the results before dry heat aging, and purple bars with shading lines represent the results after dry heat aging.

[0033] Figure 4 The image shows the morphology of HA under a scanning electron microscope, where a represents commercial sources and b represents chemical precipitation. Detailed Implementation

[0034] Example 1

[0035] (1) Acidification method: Whatman qualitative filter paper (18cm in diameter) was used, and a 0.03% aluminum sulfate aqueous solution was sprayed onto the filter paper surface using pressure atomization. The paper was left to air dry for 5 hours. Then it was placed in a constant temperature and humidity chamber (temperature 26℃, humidity 40-60%) for 24 hours to equilibrate the moisture before testing.

[0036] (2) Deacidification method: The concentration of the selected HA aqueous suspension was 0.1%, and the concentrations of the calcium carbonate aqueous suspension and calcium hydroxide aqueous solution were also 0.1%. HA came from two sources: chemical precipitation synthesis and commercially available reagents (manufacturer: Shanghai Maclean Biochemical Technology Co., Ltd.; item number: H875582; batch number: C14767668). Tests were conducted on the above solutions / suspensions, and the spraying method was still selected. Atomized spraying was used to evenly coat the liquid onto the filter paper surface. After spraying, the paper was left to air dry horizontally for 5 hours. Then, it was placed in a constant temperature and humidity chamber (temperature 26℃, humidity 40-60%) for 24 hours to equilibrate the moisture before testing.

[0037] In this embodiment, the chemical precipitation method for synthesizing HA is as follows: 1) Prepare 1 L each of 0.5 mol / L Ca(NO3)2·4H2O solution and 0.25 mol / L (NH4)3PO4·3H2O solution as calcium and phosphorus sources, respectively. 2) Add 0.1% polyethylene glycol 6000 (PEG6000) to the calcium source and stir continuously for 30 min; then add ammonia water to make the pH of the calcium source greater than 11. 3) Turn on the heater to maintain the calcium source at 60℃; turn on the peristaltic pump and slowly add the phosphorus source dropwise to the calcium source, completing the addition over 3 hours while continuously stirring. 4) Aging at room temperature for 24 h to ensure complete reaction. 5) Centrifuge and discard the supernatant. 6) Add deionized water to the precipitate for washing, centrifuge, discard the supernatant, and repeat the washing once; wash once with anhydrous ethanol. 7) Dry in an oven at 60℃ for 12 h, grind, and obtain the finished product.

[0038] Method for detecting alkali reserves: The detection shall be conducted according to GB / T 24998—2010. Cut filter paper into small pieces, add deionized water, and heat to a gentle boil. Add excess 0.1 mol / L HCl solution to neutralize the alkaline substance, add 1 drop of methyl red indicator, and then back-titrate the remaining hydrochloric acid with 0.1 mol / L NaOH solution. The titration endpoint is considered when the solution changes from pink to pale yellow, and the alkali reserves can be calculated accordingly.

[0039] The composition of HA was confirmed by infrared spectroscopy (IR), and the morphology of HA was observed by scanning electron microscopy (SEM).

[0040] Example 2

[0041] The composition of HA was confirmed by infrared spectroscopy (IR), and the morphology of HA was observed by scanning electron microscopy (SEM).

[0042] Component confirmation of HA

[0043] In Example 1, the infrared spectra of chemical precipitation and commercial HA (Figure 1) show the following values: 1033, 1096, 565, and 3570 cm⁻¹. -1 The characteristic peaks of HA were clearly identifiable, therefore both are pure hydroxyapatite. Scanning electron microscopy (SEM) images of commercial HA and chemically precipitated HA are shown below. Figure 4 As shown in the figure, commercial HA particles are primarily micron-sized, with a few nano-sized particles. However, chemically precipitated HA particles are primarily nano-sized needle-like, with even smaller particle sizes. Therefore, the smaller particle size of chemically precipitated HA may allow it to disperse better within paper fibers, resulting in a better deacidification effect.

[0044] Example 3

[0045] This example compares the deacidification effects of commercial HA, chemically precipitated HA, commercial Ca(OH)2, and commercial CaCO3:

[0046] The effects of four substances on the repair of acidified filter paper were investigated. (See...) Figure 2 Regarding whiteness, commercial HA and chemically precipitated HA are comparable to commercial CaCO3 and superior to commercial Ca(OH)2. Regarding tensile index, commercial HA and chemically precipitated HA are comparable to commercial CaCO3 and inferior to commercial Ca(OH)2. Regarding tear index, commercial HA and chemically precipitated HA are comparable to commercial Ca(OH)2 and commercial CaCO3, although the average values ​​of commercial HA and chemically precipitated HA are higher. Regarding folding endurance, commercial HA and chemically precipitated HA are inferior to commercial Ca(OH)2 and commercial CaCO3. Regarding air permeability, there are significant differences between commercial HA, chemically precipitated HA, and commercial Ca(OH)2 and commercial CaCO3; however, the suitable range for air permeability is between 25 and 30, which falls within the range for commercial HA and chemically precipitated HA, while it is greater than 30 for commercial Ca(OH)2 and commercial CaCO3.

[0047] Overall, the differences in physical properties between commercial HA, chemically precipitated HA, and commercial Ca(OH)2 and CaCO3 deacidification filter papers are small, indicating that the deacidification effect of HA is comparable to that of Ca(OH)2 and CaCO3. However, the alkali reserve of HA is much lower than that of calcium hydroxide and calcium carbonate (only about 1 / 10), making this result unexpected. Regarding air permeability, the value of HA deacidification filter paper is between 25 and 30, which is more suitable for paper repair than that of calcium hydroxide and calcium carbonate.

[0048] Example 4

[0049] The result of continued dry heat aging

[0050] For filter paper already coated with HA deacidifying agent and for blank filter paper already acidified, continue dry heat aging for 5 days for testing. See Figure 3Due to the accelerated aging effect of dry heat, the physical properties of paper typically decrease. For example, when calcium carbonate is used for deacidification, whiteness, tensile strength, tear strength, and folding endurance all decrease after dry heat aging (Qi Shi. In-situ formation of calcium carbonate and its effect on deacidification of aged paper [D]. Guangzhou: South China University of Technology, 2022.). For whiteness and tear strength, both commercial HA and chemical precipitation HA deacidified filter paper showed a decrease, consistent with expectations. However, for tensile strength, after dry heat treatment, both commercial HA and chemical precipitation HA deacidified filter paper showed an increase, with a significant difference between the two. For folding endurance, commercial HA deacidified filter paper showed a slight decrease; however, chemical precipitation HA deacidified filter paper showed a significant increase, which was unexpected. For air permeability, both commercial HA and chemical precipitation HA deacidified filter paper showed no significant change after dry heat treatment, and both remained within the suitable range of 25-30.

[0051] Overall, after 5 days of dry heat aging, the deacidification effect of HA was still comparable to that of calcium carbonate, and even better than that of calcium hydroxide (the filter paper used for deacidification with both calcium carbonate and calcium hydroxide was not subjected to dry heat aging). Therefore, the short-term dry heat method, originally intended to accelerate aging, can actually be used as a means to improve the deacidification effect of HA, especially chemical precipitation-based HA. On the other hand, under natural conditions, HA has a better ability to resist long-term aging.

[0052] Example 4

[0053] This example compares the deacidification effects of commercial HA and HA obtained by chemical precipitation:

[0054] This invention also compares the deacidification effects of commercial HA and chemical precipitation HA. Before dry heat treatment, the deacidification effect of chemical precipitation HA was already superior to that of commercial HA. The whiteness, tensile index, and tear index of the filter paper treated with chemical precipitation HA were all higher than those of commercial HA, while the folding endurance and air permeability were comparable. After dry heat treatment, both showed a simultaneous decrease in whiteness and tear index; both showed a simultaneous increase in tensile index; the folding endurance of the filter paper treated with chemical precipitation HA showed a significant improvement, while that of the filter paper treated with commercial HA remained unchanged; and the air permeability remained unchanged for both. Therefore, the deacidification effect of chemical precipitation HA is superior to that of commercial HA.

Claims

1. A method for deacidifying paper using hydroxyapatite, characterized in that, The HA aqueous suspension was selected with a mass percentage concentration of 0.1%. It was sprayed evenly onto the paper surface using an atomization spray method. After spraying, it was left to dry naturally in the air for 5 hours. Then, it was placed in a constant temperature and humidity chamber at 26℃ and 40-60% humidity for 24 hours to equilibrate the moisture before testing. The coated paper will also undergo dry heat aging treatment. The HA is nano-sized hydroxyapatite synthesized by chemical precipitation.

2. The method according to claim 1, characterized in that, The method for synthesizing HA by chemical precipitation is as follows: 1) Preparation of calcium and phosphorus sources; 2) Add polyethylene glycol 6000 (PEG-6000) to the calcium source and stir continuously; then add ammonia water to make the pH value of the calcium source greater than 11; 3) Turn on the heating to keep the calcium source at 60℃; turn on the peristaltic pump to slowly add the phosphorus source to the calcium source, completing the addition in 2 to 5 hours, while continuously stirring; 4) Aging at room temperature to ensure complete reaction; 5) Centrifuge and discard the supernatant; 6) Add deionized water to the precipitate and wash, centrifuge, discard the supernatant, and repeat the washing; wash with anhydrous ethanol; 7) Dry in an oven, grind, and obtain the finished product.

3. The method according to claim 2, characterized in that, In step 1), the calcium source is a 0.5 mol / L Ca(NO3)2·4H2O solution.

4. The method according to claim 2, characterized in that, In step 1), the phosphorus source is 0.25 mol / L (NH4)3PO4·3H2O.

5. The method according to claim 2, characterized in that, In step 2), the mass percentage concentration of polyethylene glycol 6000 in the calcium source is 0.01%~0.3%; the stirring time is 15 min~60 min.

6. The method according to claim 2, characterized in that, In step 4), the aging time is 12 h to 72 h.

7. The method according to claim 2, characterized in that, In step 7), the drying temperature is 50℃~80℃; the drying time is 3 h~18 h.

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