Method for detecting content of active hydroxyl in plant fiber

Abstract

The invention belongs to the field of detection, and particularly relates to a method for detecting the content of active hydroxyl groups in plant fibers. The invention relates to a method for detecting the content of active hydroxyl in plant fiber, which comprises the following steps: (1) dynamic solvation pretreatment: sequentially immersing plant fiber powder into n-hexane, acetone and a dimethyl sulfoxide solvent system containing 0.5% LiCl, carrying out ultrasonic treatment (40kHz, 10min) on each stage of solvent, stirring at 60 DEG C for 2 hours, and carrying out vacuum drying; (2) labeling with a characteristic probe: mixing the pretreated sample with a 0.1 mol / L 9-anthracenecarbonyl chloride-tetrahydrofuran solution according to a mass ratio of 1: 50, reacting for 4 hours at 60 DEG C under the protection of nitrogen, and removing the unreacted probe through Soxhlet extraction; and the like. The detection method is low in detection limit and high in sensitivity.

Description

Technical Field

[0001] The present invention belongs to the field of detection, and particularly relates to a method for detecting the content of active hydroxyl groups in plant fibers. Background Art

[0002] Plant fibers are an important natural polymer material and are widely used in fields such as textiles, papermaking, and composite materials. Their chemical structure is mainly composed of cellulose, hemicellulose, lignin, etc. Among them, cellulose is the main component, accounting for 40% to 50% of the dry weight of plant fibers. Cellulose is a high molecular polymer composed of glucose units connected by β-1,4-glycosidic bonds, and its molecular chain contains a large number of hydroxyl groups. These hydroxyl groups are not only the basis for the formation of hydrogen bonds between cellulose molecules but also the main source of its chemical reactivity.

[0003] The hydroxyl groups in plant fibers are divided into two categories: hydroxyl groups in the crystalline region and hydroxyl groups in the non-crystalline region (or amorphous region). The hydroxyl groups in the crystalline region have low reactivity because the molecular chains are arranged closely and participate in strong hydrogen bond interactions; while the hydroxyl groups in the non-crystalline region have higher chemical reactivity because the molecular chains are arranged more loosely and the hydrogen bond interactions are weaker. These active hydroxyl groups play a key role in the chemical modification, functionalization, and preparation of composite materials of plant fibers. For example, by esterification, etherification, or grafting reactions of hydroxyl groups, special functions such as hydrophobicity, antibacterial property, and flame retardancy can be imparted to plant fibers.

[0004] Detecting the content of active hydroxyl groups in plant fibers is of great significance for evaluating their chemical reactivity, optimizing the modification process, and developing new functional materials. The content of active hydroxyl groups directly affects the chemical modification efficiency of plant fibers and the performance of the final products. In fields such as papermaking, textiles, and bio-based composite materials, the content of active hydroxyl groups in plant fibers is an important indicator for measuring the quality of raw materials. By preparing bio-based composite materials through hydroxyl group modification, reducing the dependence on petroleum-based plastics, and utilizing the strong polarity of hydroxyl groups to design functional adsorption materials for wastewater treatment, the hydroxyl group content is closely related to the enzymatic hydrolysis efficiency of cellulose and affects the production efficiency of biomass fuels. Detecting the content of active hydroxyl groups in plant fibers not only provides key data support for material performance optimization, industrial production, and scientific research but also promotes the development and application of environmentally friendly materials. This technology has far-reaching significance in promoting sustainable development and efficient utilization of resources. Therefore, developing accurate and efficient methods for detecting active hydroxyl groups has become one of the key technologies in the research and application of plant fibers.

[0005] Currently, the methods for detecting the content of active hydroxyl groups in plant fibers mainly include chemical titration, spectroscopic analysis (such as infrared spectroscopy, nuclear magnetic resonance spectroscopy), and chemical derivatization combined with chromatographic analysis. Chemical titration is a classical method that determines the hydroxyl content through the quantitative reaction of hydroxyl groups with specific reagents (such as acetic anhydride), but its operation is complex and the accuracy is limited. Spectroscopic analysis can provide qualitative and quantitative information of hydroxyl groups, but it has high requirements for sample pretreatment. The method of chemical derivatization combined with chromatographic analysis has high sensitivity and selectivity, but the cost is high and the operation is complex. In addition, existing methods may not be able to effectively distinguish the hydroxyl groups in the crystalline and non-crystalline regions, or are not accurate enough in quantitative analysis. Although certain progress has been made in the existing technologies, there are still many challenges in practical applications. First, the composition of plant fibers is complex, and the proportions of cellulose, hemicellulose, and lignin in fibers from different sources vary significantly, which makes it difficult for a single detection method to meet the diverse analysis needs. Second, the active hydroxyl groups may change during the chemical modification process, and how to accurately evaluate the change in hydroxyl content before and after modification remains a research difficulty. Finally, some traditional methods are time-consuming and difficult to meet the rapid detection requirements in industrial production.

[0006] In summary, the detection of the content of active hydroxyl groups in plant fibers is an important link in the research on the chemical modification and functionalization of plant fibers. Developing a rapid, accurate, and economical detection method is of great significance for promoting the application of plant fibers in high-value-added fields. Summary of the Invention

[0007] This method innovatively combines dynamic solvation pretreatment technology with near-infrared-Raman dual-modal spectroscopic analysis. By regulating the solvent polarity gradient, the selective exposure of active hydroxyl groups is achieved. A quantitative model is established by using the synergistic response of the hydroxyl vibration modes in the dual spectra, breaking through the limitation of traditional methods in distinguishing the hydroxyl groups in the crystalline / non-crystalline regions.

[0008] The purpose of the present invention is to provide a method for detecting the content of active hydroxyl groups in plant fibers, including the following steps: (1) Dynamic solvation pretreatment: Immerse the plant fiber powder successively in n-hexane, acetone, and a dimethyl sulfoxide solvent system containing 0.5% LiCl. Ultrasonic treatment (40 kHz, 10 min) is performed for each stage of the solvent, and after stirring at 60 °C for 2 h, it is dried under vacuum; (2) Characteristic probe labeling: Mix the pretreated sample with a 0.1 mol / L 9-anthroyl chloride-tetrahydrofuran solution at a mass ratio of 1:50, react at 60 °C for 4 h under nitrogen protection, and remove the unreacted probes by Soxhlet extraction; (3) Dual-modal spectrum acquisition: Collect the near-infrared diffuse reflection spectrum in the range of 1200 - 2400 nm and the Raman spectrum excited by a 785 nm laser in the range of 800 - Raman spectrum; (4)Multi-level derivatization quantification: Gradient reagents such as acetic anhydride, propionic anhydride, and benzoyl chloride are successively reacted with the sample. The characteristic absorption peak of benzoyl chloride at 254 nm is detected by ultraviolet spectrophotometry, and the content of active hydroxyl groups is calculated in combination with the Lambert-Beer law.

[0009] Through the targeted labeling strategy of 9-anthroyl chloride probe, the vibration signal of hydroxyl groups is enhanced by 20 - 50 times. After the anthracene ring conjugated structure of the probe forms an ester bond with hydroxyl groups, the intensity of its Raman characteristic peak ( C=C stretching vibration at ) is linearly correlated with the hydroxyl concentration (R² = 0.998). Meanwhile, the second derivative spectrum of near-infrared spectroscopy at 1450 nm can detect the change of hydroxyl concentration of 0.05 μmol / g, and the detection limit is as low as 0.12 μmol / g (6.7 times higher than the traditional infrared method).

[0010] Furthermore, the solvent polarity gradient in step (1) is as follows: n-hexane is used to remove surface hydrophobic impurities; acetone swells the amorphous region and expands the accessibility of hydroxyl groups; dimethyl sulfoxide / LiCl selectively dissociates the hydroxyl groups at the edge of the crystalline region through coordination.

[0011] This method gradually destroys the hydrogen bond network of fibers through the physical-chemical synergistic effect of a three-level gradient solvent system (n-hexane → acetone → dimethyl sulfoxide / LiCl): n-hexane preferentially removes surface hydrophobic impurities, acetone swells the amorphous region to expand the accessibility of hydroxyl groups, and the dimethyl sulfoxide / LiCl system selectively dissociates the weakly bound hydroxyl groups at the edge of the crystalline region through the coordination of strong polar solvents and metal ions.

[0012] Furthermore, the nitrogen protection pressure for the probe labeling reaction in step (2) is 0.1 - 0.3 MPa, and the Soxhlet extraction is carried out with tetrahydrofuran solvent for 6 - 8 cycles of cleaning.

[0013] Furthermore, the integration time of near-infrared spectroscopy in step (3) is 200 ms, the laser power of Raman spectroscopy is 20 mW, and the correlation matrix includes the synergistic response signals of NIR 1450 nm and Raman 3400 cm⁻¹.

[0014] Furthermore, the molar concentrations of the gradient reagents in step (4) are as follows: acetic anhydride: 1.0 - 1.5 mol / L; propionic anhydride: 0.5 - 0.8 mol / L; benzoyl chloride: 0.2 - 0.4 mol / L.

[0015] Furthermore, the establishment of the standard curve in ultraviolet spectrophotometric quantification includes: preparing a standard solution containing 0.1 - 5.0 mmol / L methyl benzoate; measuring the absorbance at 254 nm and fitting a linear equation (R² ≥ 0.995).

[0016] Furthermore, the crystallinity of the fiber sample after dynamic solvation pretreatment is reduced to 25%-35%, which is verified by the XRD full width at half maximum method.

[0017] The traditional chemical titration method requires more than 12 hours of sample hydrolysis, neutralization and titration operations. However, in this method, through dynamic solvation pretreatment (2.5 hours) combined with dual-mode spectroscopy (8 minutes / sample), the single-sample detection cycle is compressed to within 3 hours, and the efficiency is increased by 15 times. More importantly, the sample after probe labeling can be recycled through tetrahydrofuran solvent (recovery rate > 95%), avoiding the problem of sample destruction in the traditional derivatization method.

[0018] Furthermore, the probe labeling efficiency in step (2) is verified by fluorescence microscopy, and the labeling rate ≥ 90%.

[0019] Furthermore, it is applicable to the detection of active hydroxyl groups in bamboo, cotton and hemp fibers, with a detection limit ≤ 0.15 μmol / g and a relative standard deviation ≤ 2.5%.

[0020] Compared with the prior art, the advantages and beneficial effects of the present invention are: 1. Traditional detection methods (such as chemical titration) cannot distinguish the hydroxyl groups in the crystalline region from those in the amorphous region, resulting in generally higher detection values by 15% - 20%. Through the physical-chemical synergistic effect of the three-level gradient solvent system (n-hexane → acetone → dimethyl sulfoxide / LiCl), the hydrogen bond network of the fiber is gradually destroyed: n-hexane preferentially removes surface hydrophobic impurities, acetone swells the amorphous region to expand the accessibility of hydroxyl groups, and the dimethyl sulfoxide / LiCl system selectively dissociates the weakly bound hydroxyl groups at the edge of the crystalline region through the coordination of strong polar solvents with metal ions. Combining with the high-specificity recognition of the Raman spectrum for molecular vibration modes ( The separation degree between the hydroxyl vibration peak and the cellulose backbone peak at [specific position] reaches 4.2 times), the interference of the hydroxyl groups in the crystalline region can be controlled within 3%. For example, in the detection of bamboo fibers, the content of active hydroxyl groups measured by this method is 2.81 mmol / g, compared with 3.35 mmol / g measured by the traditional titration method, which more truly reflects the effective hydroxyl groups available for chemical modification and provides reliable data support for the interface design of composite materials.

[0021] 2. Through the targeted labeling strategy of the 9-anthroyl chloride probe, the vibration signal of hydroxyl groups is enhanced by 20 - 50 times. After the anthracene ring conjugate structure of the probe forms an ester bond with hydroxyl groups, its Raman characteristic peak ( The intensity of the C=C stretching vibration (at this point) is linearly correlated with the hydroxyl concentration (R² = 0.998). Meanwhile, the second derivative spectrum of the near-infrared spectrum at 1450 nm can detect a change in hydroxyl concentration of 0.05 μmol / g, with a detection limit as low as 0.12 μmol / g (6.7 times higher than the traditional infrared method). Experimental data shows that the relative standard deviation (RSD) for repeated detection of cotton fibers 5 times is only 1.8%, while the RSD of the traditional method is as high as 5.2%. This high-precision feature is particularly suitable for monitoring the nanocellulose modification process. For example, in the TEMPO oxidation reaction, it can track the dynamic changes in the hydroxyl content during the carboxylation process in real time (detection time resolution is 30 seconds / sample).

[0022] 3. The traditional chemical titration method requires more than 12 hours of sample hydrolysis, neutralization, and titration operations. In contrast, this method combines dynamic solvation pretreatment (2.5 hours) with dual-modal spectroscopy (8 minutes / sample) to compress the single-sample detection cycle to within 3 hours, with a 15-fold increase in efficiency. More importantly, the sample after probe labeling can be recycled through a tetrahydrofuran solvent cycle (recovery rate > 95%), avoiding the problem of sample destruction in the traditional derivatization method. With the design of an optical fiber probe and a flow cell, it can be integrated into the papermaking production line for in-situ detection: during the pulp molding stage, by monitoring the fiber hydroxyl activity in real time (detection frequency of 10 times / minute), the spraying amount of the hydrophobic modifier can be dynamically adjusted, reducing the tensile strength fluctuation range of the paper from ±15% to ±5%, while reducing the chemical aid dosage by 20%.

[0023] 4. The traditional method requires the use of a large amount of toxic reagents (such as pyridine for acetylation titration), while this method uses a recyclable solvent system of tetrahydrofuran / dimethyl sulfoxide (recovery rate > 90%), reducing waste emissions by 80%. In the probe labeling step, the dosage of 9-anthroyl chloride is only 1 / 10 of that of the traditional derivatization reagent (0.1 mol / L vs 1.0 mol / L), reducing the single-sample reagent cost and being suitable for industrial promotion. Specific Embodiments

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

[0025] Example 1 This example provides a method for detecting the content of active hydroxyl groups in plant fibers, including the following steps: Step 1: Dynamic Solvation Pretreatment: Immerse 100-mesh plant fiber powder successively in a polar gradient solvent system: n-hexane, acetone, dimethyl sulfoxide. Ultrasonically treat each solvent for 15 min at 50 kHz. Add a 0.4% LiCl catalytic system to the dimethyl sulfoxide phase and stir at 62 °C for 2 - 3 h to complete the activation of hydroxyl groups in the amorphous region. After vacuum drying, a hierarchically activated fiber sample is obtained; Step 2: Characteristic Probe Labeling: Prepare a 0.1 mol / L 9-anthroyl chloride-tetrahydrofuran solution. Mix the pretreated sample (5 g) with the probe solution at a mass ratio of 1:55. React at 62 °C for 5 h under nitrogen protection. Remove the unreacted probe through a Soxhlet extractor to obtain a labeled sample; Step 3: Dual-Mode Spectral Acquisition: Near-infrared spectroscopy: Use an optical fiber probe to collect diffuse reflectance spectra in the 1200 - 2400 nm region with an integration time of 200 ms. Raman spectroscopy: Excite with a 785 nm laser and collect the signal in the fingerprint region from 800 - Establish a correlation matrix of characteristic hydroxyl peaks. O-H stretching vibration: NIR 1450 nm + ; Step 4: Multi-Stage Derivatization Reaction: Prepare an acylating reagent gradient with different reaction activities: acetic anhydride, propionic anhydride, benzoyl chloride in sequence. React with the pretreated fiber sample in sequence, controlling the temperature: 25 °C, 60 °C, 100 °C in sequence and the time: 1 h, 3 h, 6 h. Achieve selective labeling through the stepwise esterification of non-active hydroxyl groups. UV spectrophotometric quantification: Use the characteristic absorption peak of benzoyl chloride at 254 nm to establish a standard curve to calculate the content of active hydroxyl groups.

[0026] Example 2 This example provides a method for detecting the content of active hydroxyl groups in plant fibers, including the following steps: Step 1: Dynamic Solvation Pretreatment: Immerse 100-mesh plant fiber powder successively in a polar gradient solvent system: n-hexane, acetone, dimethyl sulfoxide. Ultrasonically treat each solvent for 10 min at 40 kHz. Add a 0.3% LiCl catalytic system to the dimethyl sulfoxide phase and stir at 60 °C for 2 h to complete the activation of hydroxyl groups in the amorphous region. After vacuum drying, a hierarchically activated fiber sample is obtained; Step 2: Characteristic Probe Labeling: Prepare a 0.1 mol / L 9-anthroyl chloride-tetrahydrofuran solution. Mix the pretreated sample (5 g) with the probe solution at a mass ratio of 1:50. React at 60 °C for 4 h under nitrogen protection. Remove the unreacted probe through a Soxhlet extractor to obtain a labeled sample; Step 3: Bimodal spectroscopy acquisition: Near-infrared spectroscopy: Use an optical fiber probe to collect diffuse reflection spectra in the 1200 - 2400 nm region, with an integration time of 200 ms. Raman spectroscopy: Excited by a 785 nm laser, collect signals in the 800 - fingerprint region, with a power of 20 mW. Establish a correlation matrix for hydroxyl characteristic peaks, O-H stretching vibration: NIR 1450 nm + ; Step 4: Multistage derivatization reaction: Prepare a gradient of acylation reagents with different reaction activities: acetic anhydride, propionic anhydride, benzoyl chloride in sequence, and react with the pretreated fiber samples in sequence. Control the temperature: 25°C, 60°C, 100°C in sequence and the time: 1 h, 3 h, 6 h; achieve selective labeling through the stepwise esterification of inactive hydroxyl groups; UV spectrophotometric quantification: Use the characteristic absorption peak of benzoyl chloride at 254 nm to establish a standard curve to calculate the content of active hydroxyl groups.

[0027] Example 3 This example provides a method for detecting the content of active hydroxyl groups in plant fibers, including the following steps: Step 1: Dynamic solvation pretreatment: Immerse 100-mesh plant fiber powder in a polar gradient solvent system in sequence: n-hexane, acetone, dimethyl sulfoxide. Ultrasonic treat each stage of the solvent for 20 min, 60 kHz; add a 0.5% LiCl catalytic system to the dimethyl sulfoxide phase, stir at 65°C for 3 h to complete the activation of hydroxyl groups in the amorphous region, and obtain a fractionally activated fiber sample after vacuum drying; Step 2: Characteristic probe labeling: Prepare a 0.1 mol / L 9-anthroyl chloride - tetrahydrofuran solution, mix the pretreated sample (5 g) with the probe solution at a mass ratio of 1:60, react at 65°C for 6 h under nitrogen protection, and remove the unreacted probe through a Soxhlet extractor to obtain a labeled sample; Step 3: Bimodal spectroscopy acquisition: Near-infrared spectroscopy: Use an optical fiber probe to collect diffuse reflection spectra in the 1200 - 2400 nm region, with an integration time of 200 ms. Raman spectroscopy: Excited by a 785 nm laser, collect signals in the 800 - fingerprint region, with a power of 20 mW. Establish a correlation matrix for hydroxyl characteristic peaks, O-H stretching vibration: NIR 1450 nm + ; Step 4: Multistage derivatization reaction: Prepare a gradient of acylation reagents with different reaction activities: acetic anhydride, propionic anhydride, benzoyl chloride in sequence, and react with the pretreated fiber samples in sequence. Control the temperature: 25°C, 60°C, 100°C in sequence and the time: 1 h, 3 h, 6 h; achieve selective labeling through the stepwise esterification of inactive hydroxyl groups; UV spectrophotometric quantification: Use the characteristic absorption peak of benzoyl chloride at 254 nm to establish a standard curve to calculate the content of active hydroxyl groups.

[0028] Traditional titration method (1) Take 100-mesh plant fiber powder, cut it into pieces with a length ≤ 5 mm, and dry it to a constant weight in an oven at 105 ± 2 °C (the difference between two weighings ≤ 0.2%); after drying, place the sample in a vacuum desiccator and cool it to room temperature for standby. Accurately weigh 5 g of the dried sample and record the mass m.

[0029] (2) Acetylation reaction: Place the weighed sample in a 250 mL conical flask, add 10 mL of acetic anhydride and 10 mL of pyridine, seal it, and react in a water bath at 50 ± 1 °C for 2 h; after the reaction is completed, add 50 mL of deionized water to terminate the reaction and let it stand for 10 min.

[0030] (3) Titrate the unreacted acetic anhydride: Add 3 drops of phenolphthalein indicator, and titrate with 0.1 mol / L NaOH standard solution until the solution turns pink (endpoint); record the volume of NaOH consumed V1, and simultaneously conduct a blank test without the sample, and record the volume of NaOH consumed V0.

[0031] Calculate the hydroxyl content according to the formula (unit: mmol / g):

[0032] Single-spectrum method Take 100-mesh plant fiber powder, cut it into pieces with a length ≤ 5 mm, and dry it to a constant weight in an oven at 105 ± 2 °C (the difference between two weighings ≤ 0.2%); after drying, place the sample in a vacuum desiccator and cool it to room temperature for standby. Accurately weigh 5 g of the dried sample, referring to CN102313734A "A Method for Determining the Content of Active Hydroxyl Groups in Natural Fibers by Titration".

[0033] Performance test Use the detection methods of Examples 1-3 of the present invention, the traditional titration method, and the single-spectrum method to determine the content of active hydroxyl groups in plant fibers. The results are shown in Table 1.

[0034] Table 1 Performance test results

[0035] From the results, it can be seen that the detection sensitivity is increased by about 20 times compared with the traditional titration method (2.5), and increased by 5-6 times compared with the single-spectrum method (0.8), and trace hydroxyl groups (such as low-concentration active sites in slightly damaged fibers) can be detected. The precision is much higher than that of the traditional titration method (5.2%) and the single-spectrum method (3.6%), indicating that the method has excellent repeatability and strong data reliability.

[0036] The above is the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for detecting the content of active hydroxyl groups in plant fibers, characterized in that, It includes the following steps: (1) Dynamic solvation pretreatment: Immerse the plant fiber powder successively in n-hexane, acetone, and a dimethyl sulfoxide solvent system containing 0.5% LiCl. Perform ultrasonic treatment (40 kHz, 10 min) on each stage of the solvent, stir at 60 °C for 2 h, and then dry under vacuum; (2) Characteristic probe labeling: Mix the pretreated sample with a 0.1 mol / L 9-anthroyl chloride-tetrahydrofuran solution at a mass ratio of 1:50, react at 60 °C for 4 h under nitrogen protection, and remove the unreacted probe by Soxhlet extraction; (3)Dual-modal spectral acquisition: Collect near-infrared diffuse reflectance spectra in the range of 1200 - 2400 nm and Raman spectra excited by 785 nm laser; (4) Multi-stage derivatization quantification: React the sample successively with gradient reagents of acetic anhydride, propionic anhydride, and benzoyl chloride, detect the characteristic absorption peak of benzoyl chloride at 254 nm by ultraviolet spectrophotometry, and calculate the content of active hydroxyl groups in combination with the Lambert-Beer law.

2. The method according to claim 1, wherein: The solvent polarity gradient described in step (1) is as follows: n-hexane is used to remove surface hydrophobic impurities; acetone swells the amorphous region and expands the accessibility of hydroxyl groups; dimethyl sulfoxide / LiCl selectively dissociates the hydroxyl groups at the edge of the crystalline region through coordination.

3. The method according to claim 1, wherein: The nitrogen protection pressure for the probe labeling reaction in step (2) is 0.1 - 0.3 MPa, and the Soxhlet extraction uses tetrahydrofuran solvent for cyclic cleaning 6 - 8 times.

4. The method according to claim 1, wherein: In step (3), the integration time of the near-infrared spectrum is 200 ms, the Raman spectrum laser power is 20 mW, and the correlation matrix contains the co-response signal of NIR 1450 nm and .

5. The method according to claim 1, wherein: The molar concentrations of the gradient reagents in step (4) are respectively: acetic anhydride: 1.0 - 1.5 mol / L; propionic anhydride: 0.5 - 0.8 mol / L; benzoyl chloride: 0.2 - 0.4 mol / L.

6. The method according to claim 1, wherein: The establishment of the standard curve in ultraviolet spectrophotometric quantification includes: preparing a standard solution containing 0.1 - 5.0 mmol / L methyl benzoate; Measuring the absorbance at 254 nm and fitting a linear equation.

7. The method according to claim 1, wherein: The crystallinity of the fiber sample after dynamic solvation pretreatment is reduced to 25% - 35%, which is verified by the XRD half-peak width method.

8. The method according to claim 1, wherein: The probe labeling efficiency in step (2) is verified by fluorescence microscopy, and the labeling rate ≥ 90%.

9. The method according to claim 1, characterized in that: It is applicable to the detection of active hydroxyl groups in bamboo, cotton, and hemp fibers, with a detection limit ≤ 0.15 μmol / g and a relative standard deviation ≤ 2.5%.

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