CN111781132A - A method for analyzing the natural aging degree of paper - Google Patents

Abstract

The invention is applicable to the technical field of paper analysis, and provides a method for analyzing the natural aging degree of paper, the analysis method comprising the following steps: analysis method based on Fourier transform infrared spectroscopy, X-ray crystal diffraction analysis method, and scanning electron microscope analysis method , Atomic force microscopy and ion chromatography to analyze the structure and composition of the paper to be analyzed to obtain the characteristic peaks of each functional group in the paper to be analyzed, the crystallinity of the paper to be analyzed, the microstructure of the paper to be analyzed, and the paper to be analyzed. According to the analysis results of the fiber surface characteristics and the content of each ion in the paper to be analyzed; the natural aging degree of the paper to be analyzed can be judged according to the above analysis results. The present invention can accurately and quickly judge the aging degree and storage time of paper through the above analysis method, thereby providing a basis for identification of physical evidence, restoration of cultural relics, identification of age of calligraphy and painting, and the like.

Description

A method for analyzing the natural aging degree of paper

technical field

The invention belongs to the technical field of paper analysis, and in particular relates to a method for analyzing the natural aging degree of paper.

Background technique

Paper is the material of newspapers, documents, archives and books, etc. Its main components are cellulose and a small amount of hemicellulose and lignin. During long-term storage, paper will age. The causes of ageing are oxidation, acid-base hydrolysis and microbial degradation, all of which partially degrade the paper. The oxidation will lead to the formation of the anhydroglucose ring and the C=C double bond on the carbonyl group, which are further oxidized to the carboxyl group. Oxidation also results in the cleavage of cellulose or the opening of rings, making it more susceptible to acid-base hydrolysis. The aging process of paper causes changes in the microstructure of the paper.

In order to study the aging process of paper, some researchers use physical and chemical methods to accelerate the aging of paper to study the changes in the microstructure and composition of paper after accelerated aging. For example, in order to restore the books of the Moroccan library, Latifa Hajji et al. accelerated the aging of the paper, and used Fourier transform attenuated total reflection infrared spectroscopy (ATR-FTIR), X-ray crystal diffraction and energy dispersive X-ray fluorescence spectroscopy. paper was studied. M.Ali et al. put paper in high temperature oil to accelerate aging, and used near-infrared spectroscopy (NIR) to measure the chemical bond changes closely related to aging, and found that carbonyl/carboxyl bonds are closely related to the degree of paper aging. Giovanna Piantanida et al. carried out accelerated aging of pure cellulose paper, analyzed its chemical properties, and used atomic force microscopy to observe the accelerated aging process of paper. M.Manso et al. studied the structural changes of cellulose in modern paper and papyrus by artificially accelerated aging methods such as ultraviolet rays, sunlight, high temperature, and oxidation. They used energy dispersive X-ray fluorescence spectroscopy to measure ion changes before and after treatment, and X-ray diffraction to compare crystallinity changes in accelerated-aged papers.

However, the above studies are all accelerated aging of paper by artificial means to obtain aged paper samples for research. However, the aging of paper during preservation is a natural aging process. During the long storage time, the paper will show the characteristics of aging. Therefore, it is of great significance to study the aging characteristics and laws of natural aging paper. For example, in the field of physical evidence appraisal, when it is necessary to determine whether there are forged pages in the old contracts, wills and other physical evidence materials, it is necessary to analyze and identify the suspicious pages and other aged papers to determine whether the suspicious pages are forged. Establishing a method for judging the characteristics and laws of natural aging paper can effectively identify naturally aging paper and provide a basis for forensic identification.

SUMMARY OF THE INVENTION

The purpose of the embodiments of the present invention is to provide a method for analyzing the natural aging degree of paper, which is aimed at solving the problems raised in the background art.

The embodiment of the present invention is implemented in this way, a method for analyzing the natural aging degree of paper, which comprises the following steps:

Based on Fourier transform infrared spectroscopy, X-ray crystal diffraction, scanning electron microscopy, atomic force microscopy and ion chromatography, the structure and composition of the paper to be analyzed were analyzed to obtain the functional groups in the paper to be analyzed. The characteristic peaks of the paper to be analyzed, the crystallinity of the paper to be analyzed, the microstructure of the paper to be analyzed, the fiber surface characteristics of the paper to be analyzed, and the analysis results in the content of each ion in the paper to be analyzed;

According to the characteristic peaks of each functional group in the paper to be analyzed, the crystallinity of the paper to be analyzed, the microstructure of the paper to be analyzed, the fiber surface characteristics of the paper to be analyzed, and the content of each ion in the paper to be analyzed. The degree of natural aging of the paper.

As a preferred solution of the embodiment of the present invention, Fourier transform infrared spectroscopy specifically comprises the following steps:

Cut the paper to be analyzed to a transparent but unbroken state, and remove the scraps;

The scraps of paper and potassium bromide are mixed and ground to obtain powder;

The powder is compressed into a tablet, and the tablet is placed in a Fourier transform infrared spectrometer for analysis to obtain the analysis results of the characteristic peaks of each functional group in the paper to be analyzed.

As another preferred solution of the embodiment of the present invention, the mass ratio of the paper scraps to potassium bromide is 1:(80-120).

As another preferred solution of the embodiment of the present invention, the analysis results of the characteristic peaks of each functional group in the paper to be analyzed include the analysis results of the hydroxyl characteristic peaks of the paper to be analyzed, the -C-H characteristic peaks and the characteristic peaks of the fingerprint region of cellulose .

As another preferred solution of the embodiment of the present invention, the X-ray crystal diffraction analysis method specifically includes the following steps:

The paper to be analyzed is placed in an X-ray diffractometer and scanned at a speed of 0.01-0.03°/min to obtain the diffraction intensity peak of the crystalline region and the diffraction intensity peak of the amorphous region of the paper to be analyzed;

According to the diffraction intensity peak of the crystalline region of the paper to be analyzed and the diffraction intensity peak of the amorphous region, the analysis result of the crystallinity of the paper to be analyzed is calculated and obtained.

As another preferred solution of the embodiment of the present invention, the scanning electron microscope analysis method specifically includes the following steps:

After the paper to be analyzed is cut into pieces, then soaked in deionized water to obtain a suspension;

After the suspension is dried, it is sprayed with gold to obtain a gold-sprayed sample;

The gold-sprayed sample is placed in a scanning electron microscope for scanning, and an analysis result of the microstructure of the paper to be analyzed is obtained.

As another preferred solution of the embodiment of the present invention, the atomic force microscope analysis method specifically includes the following steps:

The paper to be analyzed is placed in an atomic force microscope, and the paper to be analyzed is scanned with a quartz fiber probe in a knocking mode with a resonance frequency of 250-300 kHz to obtain the analysis results of the fiber surface characteristics of the paper to be analyzed.

As another preferred version of the embodiment of the present invention, the ion chromatography method specifically includes the following steps:

After the paper to be analyzed is cut into pieces, it is mixed with deionized water to obtain a suspension;

The suspension is filtered, the filtrate is taken and placed in an ion chromatograph, and sodium bicarbonate solution or methanesulfonic acid is used as the eluent to detect the content of each ion in the paper to be analyzed, and the content of each ion in the paper to be analyzed is obtained. analysis results.

As another preferred solution of the embodiment of the present invention, the analysis results of the content of each ion in the paper to be analyzed include the analysis results of potassium ion content, sodium ion content, phosphate ion content and chloride ion content in the paper to be analyzed .

As another preferred solution of the embodiment of the present invention, the method for judging the natural aging degree of the paper to be analyzed according to the analysis result of the content of each ion in the paper to be analyzed specifically includes the following steps:

The higher the content of potassium ions, phosphate ions and chloride ions in the paper to be analyzed, the more severe the natural aging of the paper to be analyzed; and/or

The lower the sodium ion content in the paper to be analyzed, the more serious the degree of natural aging of the paper to be analyzed.

A method for analyzing the natural aging degree of paper provided by the embodiment of the present invention, by using Fourier transform infrared spectroscopy analysis method, X-ray crystal diffraction analysis method, scanning electron microscope analysis method, atomic force microscope analysis method or ion chromatography analysis method, etc. Methods By analyzing the structure and composition of the paper, the aging degree and storage time of the paper can be judged accurately and quickly, which can provide the basis for the identification of physical evidence, the restoration of cultural relics, and the identification of the age of calligraphy and painting.

Description of drawings

Figure 1 shows the Fourier transform infrared spectra of People's Daily papers of different ages.

Figure 2 shows the scanning electron microscope images of People's Daily papers of different ages.

Figure 3 shows the atomic force microscope images of People's Daily papers of different ages.

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

Example 1

This embodiment provides a method for analyzing the natural aging degree of paper, which includes the following steps:

S1, using Fourier transform infrared spectroscopy to analyze the structure of the paper, which specifically includes the following steps:

(1) Use a scalpel to gently cut the blank of the paper to be analyzed to a transparent but unbroken state, and take out the scraps of paper and weigh them for later use.

(2) The above-mentioned paper scraps and potassium bromide (analytical grade, purchased from Shanghai Marcklin Biochemical Company) were mixed in a ratio of 1:100, and were placed in an agate mortar for grinding to obtain powder.

(3) passing the above-mentioned powder through a 5000-mesh sieve, sieving out the powder with a particle size of less than 2.5 microns, and pressing it into a transparent thin tablet with a tablet press; then, the tablet is placed in the sample holder of the Fourier transform infrared spectrometer Analysis was carried out in the paper to obtain the analysis results of hydroxyl characteristic peaks, -CH characteristic peaks and cellulose fingerprint region characteristic peaks in the paper to be analyzed. Among them, the Fourier transform infrared spectrometer can be a commercially available Shimadzu IRPrestige-21 Fourier transform infrared spectrometer (Shimadzu Corporation, Japan). During the analysis, the wavenumber scanning range of the Fourier transform infrared spectrometer is 400 ~ 4000cm ^-1 , the resolution is 4cm ^-1 , and a single sample is accumulated 32 times.

S2, using the X-ray crystal diffraction analysis method to analyze the structure of the paper, which specifically includes the following steps:

(1) Cut the blank of the paper to be analyzed into a square sample of 1.3cm×1.3cm; then, place the square sample flat in the sample groove of the X-ray diffractometer; then, adjust the current of the X-ray diffractometer To 30mA, the voltage was adjusted to 40kV, the scanning range was set between 10° and 50°, and the above-mentioned square sample was scanned at a speed of 0.02°/min to obtain the diffraction intensity peak (002 lattice) of the crystalline region of the paper to be analyzed. Diffraction angle peaks) and diffraction intensity peaks of amorphous regions. Wherein, the X-ray diffractometer can be a commercially available Bruker D8 crystal diffractometer (Bruker, Germany).

(2) According to the diffraction intensity peak of the crystalline region of the paper to be analyzed and the diffraction intensity peak of the amorphous region, the analysis result of the crystallinity of the paper to be analyzed can be obtained by calculation. Specifically, the formula for calculating the crystallinity (CrI) of the paper to be analyzed is as follows:

CrI (%)=[(I ₀₀₂ -I _am )/I ₀₀₂ ]×100;

In the formula, I ₀₀₂ is the peak of the 002 lattice diffraction angle, that is, the diffraction intensity peak of the crystalline region; I _am is the diffraction intensity peak of the amorphous region.

S3, using scanning electron microscope analysis method to analyze the structure of the paper, which specifically includes the following steps:

(1) After cutting 0.1 g of blanks of the paper to be analyzed, immersed in 1 mL of deionized water to obtain a suspension.

(2) after the above-mentioned suspension is placed on the sample stage to be dried, then fixed on the sample stage with conductive double-sided tape, and placed in the sample chamber of the ion sputtering apparatus to carry out gold spraying treatment, and after the gold spraying treatment is obtained Among them, the ion sputtering instrument can be a commercially available K570 ion sputtering instrument. During the gold spraying treatment, the vacuum degree is 0.2 mbar, the current is set to 8 mA, and the gold spraying time is 1 min.

(3) Put the gold-sprayed sample in the sample chamber of the scanning electron microscope, and vacuumize it. After the vacuum degree reaches below 1.3×10 ^-4 , select the normal mode and select the SE1 probe to scan the sample. Among them, the probe The needle current is set to 50pA, the filament current is set to 2.7A, the acceleration voltage is set to 20kV, the working distance is controlled to 10mm, and the magnification is set to 1000 times to observe the sample and obtain the analysis results of the microstructure of the paper to be analyzed. The scanning electron microscope can be a commercially available FEI Quanta200 scanning electron microscope (FEI, Netherlands).

S4, using atomic force microscope analysis method to analyze the structure of the paper, which specifically includes the following steps:

Cut the blank space of the paper to be analyzed into a sample with a size of 1cm × 1cm; then, fix the sample on the sample holder of the atomic force microscope with double-sided tape; then, use a quartz fiber probe with a tapered tip (diameter 50nm) Scan different positions on the sample fiber in the tapping mode with the resonance frequency of 280 kHz, and perform phase imaging in the tapping mode, and then the analysis results of the fiber surface characteristics of the paper to be analyzed can be obtained. Among them, the atomic force microscope can be a commercially available Dimension Fastscan Bio atomic force microscope (Bruker, Germany).

S5, using ion chromatography to analyze the composition of the paper, which specifically includes the following steps:

(1) Use sodium chloride (analytical grade, purchased from Sigma-Aldrich Company in the United States), potassium chloride (analytical grade, purchased from Sigma-Aldrich Company in the United States), disodium hydrogen phosphate (analytical grade, purchased from Sigma-Aldrich Company in the United States) Sigma-Aldrich Company) respectively prepared 1000μg/mL sodium ion, potassium ion, chloride ion, phosphate ion stock solution, and then took different volumes of stock solution and placed them in 10mL volumetric flasks, and made up to the mark with ultrapure water. Shake well to prepare mixed standard solutions of different concentrations for use. The concentration ranges of the mixed standard solutions of the four ions are: sodium ion 0-100 μg/mL, potassium ion 0-100 μg/mL, chloride ion 0-100 μg/mL, and phosphate ion 0-100 μg/mL.

(2) Start the ion chromatograph and run it for 30 min. After the baseline is stable, take 25 μL of the above mixed standard solutions of different concentrations and place them in the ion chromatograph for detection to obtain the standard curve of each ion. Specifically, the ion chromatograph can be a commercially available ICS-5000 ion chromatograph (DIONEX, USA). During detection, Dionex IonPacAS23 anion chromatographic column and Dionex IonPac CS12A cation chromatographic column can be used as chromatographic columns; The column can use 100mmol/L sodium bicarbonate solution as the eluent, and the eluent speed is set to 1.0mL/min; the cation chromatography column can use 20mmol/L methanesulfonic acid (MSA) as the eluent, the eluent The speed was set to 1.2 mL/min.

(3) After cutting 0.1g of blank space (accurate to 0.001g) of the paper to be analyzed, mix it with 10mL of deionized water, and shake it at room temperature for 40min to obtain a suspension; After the water-based filter membrane is filtered, the filtrate is taken and transferred into a chromatographic bottle, and placed in the above-mentioned ion chromatograph, and detected by the same method and parameters, and then according to the standard curve of each ion, the potassium ion content in the paper to be analyzed can be obtained. , the analysis results of sodium ion content, phosphate ion content and chloride ion content.

S6, according to the analysis results such as the characteristic peaks of each functional group in the paper to be analyzed, the crystallinity of the paper to be analyzed, the microstructure of the paper to be analyzed, the fiber surface characteristics of the paper to be analyzed, the content of each ion in the paper to be analyzed, etc. Determine the natural aging degree of the paper to be analyzed.

Specifically, if the characteristic peaks such as hydroxyl characteristic peaks at 3000-3600 cm ^-1 and -CH characteristic peaks at 2700-3000 cm ^-1 of the paper to be analyzed are weaker, it indicates that the intramolecular and intermolecular forces of cellulose are weaker. The more severe the natural aging of the paper to be analyzed.

If the crystallinity of the paper to be analyzed is smaller, the degree of natural aging of the paper to be analyzed is more serious.

If the degree of fracture and depression of the microstructure of the paper to be analyzed is more serious, the degree of natural aging of the paper to be analyzed is more serious.

If the degree of fragmentation of the bulk structure on the fiber surface of the paper to be analyzed is more serious, the degree of natural aging of the paper to be analyzed is more serious.

If the content of potassium ions, phosphate ions and chloride ions in the paper to be analyzed is higher, the natural aging degree of the paper to be analyzed is more serious; if the content of sodium ions in the paper to be analyzed is lower, the natural aging of the paper to be analyzed is more serious.

Example 2

This embodiment provides a method for analyzing the natural aging degree of paper, which is different from Embodiment 1 only in that the steps of Fourier transform infrared spectroscopy, X-ray crystal diffraction and atomic force microscopy are different, as follows. :

The structure of the paper is analyzed by Fourier transform infrared spectroscopy, which specifically includes the following steps:

(1) Use a scalpel to gently cut the blank of the paper to be analyzed to a transparent but unbroken state, and take out the scraps of paper and weigh them for later use.

(2) The above-mentioned paper scraps and potassium bromide (analytical grade, purchased from Shanghai Marcklin Biochemical Company) are mixed in a ratio of 1:80, and placed in an agate mortar for grinding to obtain powder.

(3) passing the above-mentioned powder through a 5000-mesh sieve, sieving out the powder with a particle size of less than 2.5 microns, and pressing it into a transparent thin tablet with a tablet press; then, the tablet is placed in the sample holder of the Fourier transform infrared spectrometer Analysis was carried out in the paper to obtain the analysis results of hydroxyl characteristic peaks, -CH characteristic peaks and cellulose fingerprint region characteristic peaks in the paper to be analyzed. Among them, the Fourier transform infrared spectrometer can be a commercially available Shimadzu IRPrestige-21 Fourier transform infrared spectrometer (Shimadzu Corporation, Japan). During the analysis, the wavenumber scanning range of the Fourier transform infrared spectrometer is 400 ~ 4000cm ^-1 , the resolution is 4cm ^-1 , and a single sample is accumulated 32 times.

The structure of the paper is analyzed by X-ray crystal diffraction analysis, which specifically includes the following steps:

(1) Cut the blank of the paper to be analyzed into a square sample of 1.3cm×1.3cm; then, place the square sample flat in the sample groove of the X-ray diffractometer; then, adjust the current of the X-ray diffractometer To 30mA, the voltage was adjusted to 40kV, the scanning range was set between 10° and 50°, and the above-mentioned square sample was scanned at a speed of 0.01°/min to obtain the diffraction intensity peak (002 lattice) of the crystalline region of the paper to be analyzed. Diffraction angle peaks) and diffraction intensity peaks of amorphous regions. Wherein, the X-ray diffractometer can be a commercially available Bruker D8 crystal diffractometer (Bruker, Germany).

(2) According to the diffraction intensity peak of the crystalline region of the paper to be analyzed and the diffraction intensity peak of the amorphous region, the analysis result of the crystallinity of the paper to be analyzed can be obtained by calculation.

The structure of the paper is analyzed by atomic force microscopy, which specifically includes the following steps:

Cut the blank space of the paper to be analyzed into a sample with a size of 1cm × 1cm; then, fix the sample on the sample holder of the atomic force microscope with double-sided tape; then, use a quartz fiber probe with a tapered tip (diameter 50nm) Scan different positions on the sample fiber in the tapping mode with the resonance frequency of 250 kHz, and perform phase imaging in the tapping mode, and then the analysis results of the fiber surface characteristics of the paper to be analyzed can be obtained. Among them, the atomic force microscope can be a commercially available Dimension Fastscan Bio atomic force microscope (Bruker, Germany).

Example 3

This embodiment provides a method for analyzing the natural aging degree of paper, which is different from Embodiment 1 only in that the steps of the Fourier transform infrared spectroscopy analysis method are different, and the details are as follows:

The structure of the paper is analyzed by Fourier transform infrared spectroscopy, which specifically includes the following steps:

(1) Use a scalpel to gently cut the blank of the paper to be analyzed to a transparent but unbroken state, and take out the scraps of paper and weigh them for later use.

(2) The above-mentioned paper scraps and potassium bromide (analytical grade, purchased from Shanghai Marcklin Biochemical Company) were mixed in a ratio of 1:120, and were placed in an agate mortar for grinding to obtain powder.

(3) passing the above-mentioned powder through a 5000-mesh sieve, sieving out the powder with a particle size of less than 2.5 microns, and pressing it into a transparent thin tablet with a tablet press; then, the tablet is placed in the sample holder of the Fourier transform infrared spectrometer Analysis was carried out in the paper to obtain the analysis results of hydroxyl characteristic peaks, -CH characteristic peaks and cellulose fingerprint region characteristic peaks in the paper to be analyzed. Among them, the Fourier transform infrared spectrometer can be a commercially available Shimadzu IRPrestige-21 Fourier transform infrared spectrometer (Shimadzu Corporation, Japan). During the analysis, the wavenumber scanning range of the Fourier transform infrared spectrometer is 400 ~ 4000cm ^-1 , the resolution is 4cm ^-1 , and a single sample is accumulated 32 times.

Example 4

This embodiment provides a method for analyzing the natural aging degree of paper, which is different from Embodiment 1 only in that the steps of the X-ray crystal diffraction analysis method and the atomic force microscope analysis method are different, as follows:

The structure of the paper is analyzed by X-ray crystal diffraction analysis, which specifically includes the following steps:

(1) Cut the blank of the paper to be analyzed into a square sample of 1.3cm×1.3cm; then, place the square sample flat in the sample groove of the X-ray diffractometer; then, adjust the current of the X-ray diffractometer to 30mA, the voltage is adjusted to 40kV, the scanning range is set to be between 10° and 50°, and the above-mentioned square sample is scanned at a speed of 0.03°/min to obtain the diffraction intensity peak (002 lattice) of the crystalline region of the paper to be analyzed. Diffraction angle peaks) and diffraction intensity peaks of amorphous regions. Wherein, the X-ray diffractometer can be a commercially available Bruker D8 crystal diffractometer (Bruker, Germany).

(2) According to the diffraction intensity peak of the crystalline region of the paper to be analyzed and the diffraction intensity peak of the amorphous region, the analysis result of the crystallinity of the paper to be analyzed can be obtained by calculation.

The structure of the paper is analyzed by atomic force microscopy, which specifically includes the following steps:

Cut the blank space of the paper to be analyzed into a sample with a size of 1cm × 1cm; then, fix the sample on the sample holder of the atomic force microscope with double-sided tape; then, use a quartz fiber probe with a tapered tip (diameter 50nm) Scan different positions on the sample fiber in the tapping mode with the resonance frequency of 300 kHz, and perform phase imaging in the tapping mode, and then the analysis results of the fiber surface characteristics of the paper to be analyzed can be obtained. Among them, the atomic force microscope can be a commercially available Dimension Fastscan Bio atomic force microscope (Bruker, Germany).

Experimental example:

Take the People's Daily newspapers from 1966, 1975, 1985, 1995, 2005, and 2015 (the People's Daily newspapers should be kept in a storage cabinet at room temperature, dry and protected from light), and use scissors to cut out about approx. 0.2 g of newspaper was used as the paper to be analyzed, packed in a sealed bag, stored at room temperature and protected from light, and used for later use.

Under the same experimental conditions, according to the Fourier transform infrared spectroscopy, X-ray crystal diffraction analysis, scanning electron microscope analysis, atomic force microscope analysis and ion chromatography analysis method provided in Example 1, respectively, for the above-mentioned years Newspaper samples were analyzed and the results were as follows:

1. Fourier transform infrared spectroscopy analysis results:

Using Fourier transform infrared spectroscopy to analyze the paper of People's Daily of different ages, the results are shown in Figure 1. As can be seen from Figure 1, at the characteristic peak of hydroxyl at 3000-3600 cm ^-1 , the absorption intensity becomes smaller and smaller with the passage of time, indicating that the hydroxyl group gradually decreases. In lignocellulose, cellulose molecules, cellulose, hemicellulose, and lignin are connected by hydrogen bonds to form a stable crystal structure. The hydroxyl groups gradually decreased, indicating that the hydrogen bonds between cellulose molecules, between cellulose and hemicellulose, and lignin were broken, and the interaction between cellulose and other components in the paper was weakened. In addition, the peak at 2700-3000 cm ^-1 is the -CH stretching vibration absorption peak. It can be seen from the results that the longer the age, the smaller the absorption intensity, which means that the -CH ₃ and -CH ₂ in the paper are less and the wood Cellulose carbon chains are destroyed. 900～1200cm ^-1 is the characteristic peak of the fingerprint region of cellulose, including: 1200cm ^-1 is the -COH in-plane bending vibration region, 1159cm ^-1 is the β-1-4 glycosidic bond stretching region of -COC, 1105cm ^-1 is the asymmetric glycosidic ring stretching region of -COC, 1055 cm ^-1 is the vibrational region of the -CO stretching secondary alcohol, 1026 cm ^-1 is the vibrational region of the -CO stretching primary alcohol and 872 cm ^-1 is the -COC plane symmetry region. From the above results, during the long-term preservation of paper, the characteristic peaks of paper in different ages change, indicating that the molecular structure of cellulose in paper changes regularly during the natural aging process of paper.

2. X-ray crystal diffraction analysis results:

The percentage of the crystalline region in the cellulose to the whole cellulose is called the crystallinity of the cellulose. The crystallinity of cellulose is an important indicator to measure cellulose, which reflects the degree of crystallization formed when cellulose is aggregated. The crystallinity of newspapers of different ages was analyzed by X-ray crystallography, and the results are shown in Table 1.

Table 1

As can be seen from Table 1, with the passage of time, the crystallinity of the paper gradually decreased. In 2015, the People's Daily paper had the highest crystallinity at 80.6%. The crystallinity of newspapers in 2005 was 78.1%, which was less than that of newspapers in 2015. The crystallinity of newspapers in 1995 was 77.5%, which was less than that of newspapers in 2005. The degree of crystallinity decreases with age, and in 1966 the degree of crystallinity of the newspaper dropped to 71.2%, lower than all other years. The above results show that with the aging of the paper, the crystal structure of the paper changes, and the crystallinity decreases accordingly. However, the accelerated aging of the paper was carried out by the heating method, and then the accelerated aging of the paper was analyzed by X-ray crystal diffraction, and it was found that the crystallinity of the paper first increased and then decreased after the accelerated aging. The reason for the first increase in crystallinity during artificial aging is the destruction of the cellulose amorphous region caused by heating. It can be seen that in the process of natural aging and artificial heating aging, the crystallinity of paper follows different changing laws.

3. Scanning electron microscope analysis results:

Scanning electron microscope was used to observe the changes in the microstructure of newspapers of different ages. The observation results are shown in Figure 2. In Figure 2, A to F are the years of 1966, 1975, 1985, 1995, 2005 and 2015, respectively. SEM image of a newspaper. With age, the fiber structure of paper gradually becomes loose. The fiber structure of the newspaper in 2015 is a neat, compact long tube with a very smooth surface without holes and collapses (as shown in F in Figure 2). The 2005 newspaper fiber tube wall is no longer smooth and begins to collapse. The paper fiber structure appeared messy, and part of the tubular structure was disrupted and cut (as shown in E in Figure 2). The 1995 paper fibers showed circular pores and significant chipping (D in Figure 2). With the passage of time, the fibrous structure of paper is damaged more and more seriously. On the 1966 sample, large pores appeared in the fibers, the fibers appeared loose, and the paper was severely shattered (as shown in Figure 2, A). It can be seen that with the passage of time, the fiber structure of the paper is destroyed, the surface becomes rough and uneven, concave holes appear, the fibers are peeled off from each other, and the structure is filamentous and sheet-like, indicating that the regular and ordered fiber structure is gradually destroyed. This is the main reason for the decrease in the crystallinity of paper fibers.

4. Atomic force microscope analysis results:

The surface structure of cellulose of newspapers of different ages was observed by atomic force microscope. The observation results are shown in Figure 3. In Figure 3, A to F are the years of 1966, 1975, 1985, 1995, 2005 and 2015, respectively. Atomic force microscope image of a newspaper. From the atomic force microscope results of the People's Daily paper (Figure 3), it can be seen that the surface of the paper in 2015 is regular, and the fibers are arranged in large squares (as shown in F in Figure 3); on the surface of the paper in 2005, although fibers can still be seen Large square shape, but the fibers started to fragment (as shown in E in Figure 3). With the passage of time, the surface fiber fragmentation became more and more serious, and the surface of the paper sample in 1966 was severely fragmented (as shown by A in Figure 3), which indicated that the surface structure of the paper cellulose was more fragmented , the more serious the aging.

5. Ion chromatography analysis results:

The content of potassium ion, sodium ion, phosphate ion and chloride ion in newspapers of different ages was determined by ion chromatography, and the determination results are shown in Table 2.

Table 2

It can be seen from Table 2 that from 2015 to 1966, with the passage of time, the sodium ion content gradually decreased, from 31.4 μg/mL to 21.1 μg/mL. The potassium ion content increased gradually, from 3.7 μg/mL to 15.3 μg/mL. The chloride ion content increased gradually, from 3.1 μg/mL to 5.3 μg/mL, and the phosphate ion content gradually increased from 52.0 μg/mL to 69.7 μg/mL. The results show that, during the preservation process of People's Daily paper, the content of ions will change regularly with the prolongation of preservation time.

To sum up, in the embodiment of the present invention, methods such as Fourier transform infrared spectroscopy, X-ray crystal diffraction, scanning electron microscopy, atomic force microscopy, and ion chromatography are used to analyze the paper of People's Daily from 1966 to 2015, and it is found that , With the passage of time, the microstructure and composition of newspapers and paper have changed regularly, the intramolecular and intermolecular bonds of cellulose are gradually destroyed, the crystallinity is gradually reduced, the microscopic morphology of the fibers has changed from dense to loose, and the fiber surface Showing a tendency of fragmentation, the concentration of sodium ions in the paper gradually decreased, and the concentrations of potassium ions, chloride ions and phosphate ions gradually increased. From the above results, it can be seen that the microstructure and composition of paper in each age are different from other ages. These characteristics can provide a standard for judging the natural aging degree of paper, thus providing a basis for identification of physical evidence, restoration of cultural relics, and identification of calligraphy and painting.

The above-mentioned embodiments only represent several embodiments of the present invention, and the descriptions thereof are specific and detailed, but should not be construed as a limitation on the scope of the patent of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can also be made, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the appended claims.

Claims (10)

1. A method for analyzing the natural aging degree of paper is characterized by comprising the following steps:

analyzing the structure and components of the paper to be analyzed based on a Fourier transform infrared spectroscopy analysis method, an X-ray crystal diffraction analysis method, a scanning electron microscopy analysis method, an atomic force microscopy analysis method and an ion chromatography analysis method to obtain the characteristic peaks of the functional groups in the paper to be analyzed, the crystallinity of the paper to be analyzed, the microstructure of the paper to be analyzed, the fiber surface characteristics of the paper to be analyzed and the analysis results of the content of ions in the paper to be analyzed;

and judging the natural aging degree of the paper to be analyzed according to the characteristic peaks of the functional groups in the paper to be analyzed, the crystallinity of the paper to be analyzed, the microstructure of the paper to be analyzed and the analysis result of the content of the ions in the paper to be analyzed.

2. The method for analyzing the natural aging degree of paper as claimed in claim 1, wherein the Fourier transform infrared spectroscopy analysis method specifically comprises the following steps:

cutting the paper to be analyzed to be in a transparent but unbroken state, and taking the cut paper scraps;

mixing paper scraps and potassium bromide, and grinding to obtain powder;

and pressing the powder into a pressed sheet, and analyzing the pressed sheet in a Fourier transform infrared spectrometer to obtain an analysis result of the characteristic peak of each functional group in the paper to be analyzed.

3. The method for analyzing the natural aging degree of paper as claimed in claim 2, wherein the mass ratio of the paper scraps to the potassium bromide is 1 (80-120).

4. The method for analyzing the natural aging degree of paper according to claim 1 or 2, wherein the analysis result of the characteristic peak of each functional group in the paper to be analyzed includes the analysis results of the hydroxyl group characteristic peak, -C-H characteristic peak and fingerprint region characteristic peak of cellulose of the paper to be analyzed.

5. The method for analyzing the natural aging degree of paper according to claim 1, wherein the X-ray crystal diffraction analysis method specifically comprises the following steps:

scanning the paper to be analyzed in an X-ray diffractometer at the speed of 0.01-0.03 DEG/min to obtain the diffraction intensity peak value of a crystalline area and the diffraction intensity peak value of an amorphous area of the paper to be analyzed;

and calculating to obtain the analysis result of the crystallinity of the paper to be analyzed according to the diffraction intensity peak value of the crystalline region and the diffraction intensity peak value of the amorphous region of the paper to be analyzed.

6. The method for analyzing the natural aging degree of paper according to claim 1, wherein the scanning electron microscope analysis method specifically comprises the following steps:

cutting paper to be analyzed into pieces, and then soaking the paper in deionized water to obtain a suspension;

drying the suspension, and then carrying out gold spraying treatment to obtain a sample subjected to gold spraying treatment;

and (4) placing the sample subjected to the gold spraying treatment in a scanning electron microscope for scanning to obtain an analysis result of the microstructure of the paper to be analyzed.

7. The method for analyzing the natural aging degree of paper according to claim 1, wherein the atomic force microscopy specifically comprises the following steps:

and (3) placing the paper to be analyzed in an atomic force microscope, and scanning the paper to be analyzed by using a quartz fiber probe in a knocking mode with the resonance frequency of 250-300 kHz to obtain an analysis result of the fiber surface characteristics of the paper to be analyzed.

8. The method for analyzing the natural aging degree of paper as claimed in claim 1, wherein the ion chromatography specifically comprises the steps of:

cutting paper to be analyzed, and mixing the paper with deionized water to obtain a suspension;

and filtering the suspension, placing the filtrate in an ion chromatograph, and detecting the content of each ion in the paper to be analyzed by using sodium bicarbonate solution or methanesulfonic acid as leacheate to obtain the analysis result of the content of each ion in the paper to be analyzed.

9. The method for analyzing the natural aging degree of paper according to claim 1 or 8, wherein the analysis result of the content of each ion in the paper to be analyzed includes the analysis result of the content of potassium ion, the content of sodium ion, the content of phosphate ion, and the content of chloride ion in the paper to be analyzed.

10. The method for analyzing the natural aging degree of paper according to claim 9, wherein the method for judging the natural aging degree of paper to be analyzed according to the analysis result of the content of each ion in the paper to be analyzed specifically comprises the following steps:

the higher the content of ions in potassium ions, phosphate ions and chloride ions in the paper to be analyzed is, the more serious the natural aging degree of the paper to be analyzed is; and/or

The lower the sodium ion content in the paper to be analyzed, the more severe the natural aging degree of the paper to be analyzed.

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