CN116041552A

CN116041552A - Sulfamated cellulose, cellulose hydrogel, and preparation methods and applications thereof

Info

Publication number: CN116041552A
Application number: CN202211606064.7A
Authority: CN
Inventors: 吉海瑞; 史学辉
Original assignee: Qilu University of Technology
Current assignee: Qilu University of Technology
Priority date: 2022-12-12
Filing date: 2022-12-12
Publication date: 2023-05-02
Anticipated expiration: 2042-12-12

Abstract

The invention discloses sulfamated cellulose, cellulose hydrogel, and a preparation method and application thereof. The preparation method of the sulfamated cellulose comprises the following steps: s1, adding sulfamic acid into a solvent for fully dissolving and mixing, then adding powdered cellulose into the mixed solution, heating and stirring for reaction, and fully esterifying cellulose fibers; s2, centrifuging the reaction solution obtained in the step S1, washing and centrifuging by using a solvent, washing and centrifuging by using acetone, and adding the lower layer fiber into deionized water for ultrasonic washing to obtain a cellulose solution; and S3, dialyzing the cellulose solution, and then freeze-drying to obtain the sulfamate cellulose. When the sulfamated cellulose prepared by the method is used as a humidity sensing material for preparing the optical fiber humidity sensor, the prepared optical fiber humidity sensor has the advantages of low cost and high sensitivity, and is suitable for practical application of humidity detection under the environments of strong electromagnetic interference, inflammability, explosiveness and the like.

Description

Sulfamated cellulose, cellulose hydrogel, and preparation methods and applications thereof

Technical Field

The invention relates to the technical field of material chemistry, in particular to sulfamated cellulose, cellulose hydrogel, and a preparation method and application thereof.

Background

Humidity detection has important significance in various fields such as agriculture, weather, medical treatment and the like. In recent years, with the progress and development of modernization, the requirement for accurate monitoring of environmental humidity is also increasing. At present, the traditional humidity sensor cannot meet humidity monitoring under severe environments due to the defects of large volume, poor stability, short service life and the like, and the optical fiber humidity sensor has the characteristics of electromagnetic interference resistance, small size, long-distance transmission and the like, and is particularly suitable for testing environments of high-temperature environments such as high temperature, high pressure, inflammability, explosiveness and the like. For example, in CN101936897a and CN111208087a, it is mentioned that the humidity sensor mainly consists of two parts of a sensing device and a humidity sensitive material, and the humidity sensitive material is coated on the end of the optical fiber, and the change of the refractive index of the humidity sensitive material is used to generate different humidity responses, so that the humidity sensitive material is selected to have enough sensitivity to environmental moisture.

The humidity-sensitive material commonly used in the prior art mainly comprises petroleum-based materials such as chitosan, metal oxide, graphene oxide, polyvinyl alcohol and the like, but the humidity sensor prepared from the materials has the problems of high cost, narrow monitoring range and low sensitivity, and the material cannot be biodegraded, so that the environment problem is caused. Therefore, the preparation of humidity sensors based on bio-based materials is attracting a great deal of attention. Cellulose is a natural organic high polymer with the most abundant sources in the world, and the hydrophilization treatment is carried out by taking the cellulose as a raw material, so that the cellulose not only meets the requirements of the humidity-sensitive material, but also has important significance for green environmental protection and sustainable development. However, the wet feel characteristics of the cellulose itself in the prior art are not ideal, and therefore, it is necessary to improve the wet feel effect by hydrophilic modification. The current surface hydrophilic modification method of cellulose has various methods, mainly comprising the steps of carrying out quaternary ammonium salt, etherification, sulfonation, carboxymethylation and carboxylation on hydroxyl groups of cellulose, so that polar groups are introduced into the surface of the cellulose, and the hydrophilic performance of the cellulose is changed. For example, CN201810294212.3 discloses etherification, in which cellulose is polymerized in a solution containing N, N-dimethylformamide and epichlorohydrin to obtain etherified cellulose; WO/2011/024807 discloses carboxylation reactions in which carboxyl groups are introduced by oxidation treatment in a reaction solution containing an N-oxyl compound (e.g., TEMPO) and an oxidant of the halogen type, using relatively large amounts of chemical reagents such as 2, 6-tetramethylpiperidine oxide, naOCl, KBr and NaHCO ₃ And the like, wherein the 2, 6-tetramethylpiperidine oxide is toxic and harmful to the environment. The preparation of carboxymethylation generally comprises the steps of reacting cellulose with alkali, and then treating the cellulose with a carboxymethylation agent, wherein the method comprises a water-borne method (taking water as a solvent) and a solvent method (taking an organic solvent as a main component); this process often uses a more deleterious active agent such as the carboxymethylating agent chloroacetic acid during the preparation process. CN202010920786.4 also discloses the use of dialdehyde cellulose and bisulphite for addition reaction to produce sulphonated cellulose, but this method entails preparing cellulose into dialdehyde cellulose in advance and then sulphonating it; among them, the preparation of dialdehyde cellulose often uses sodium periodate solution with high oxidability, which faces certain challenges in terms of danger and cost.

Therefore, the invention provides a method for sulfamating cellulose, namely, modifying and simplifying cellulose to increase the hydrophilicity, and combining the cellulose with optical fibers to prepare the optical fiber humidity sensor with accurate environment humidity monitoring.

Disclosure of Invention

In order to overcome the defects of the prior art, the application provides sulfamated cellulose, cellulose hydrogel, and a preparation method and application thereof.

The invention is realized by the following technical scheme:

a method for preparing sulfamated cellulose, comprising the steps of:

s1, adding sulfamated cellulose into a solvent, fully dissolving and mixing to obtain a mixed solution, adding powdery cellulose into the mixed solution, heating and stirring for reacting for a certain time, and fully esterifying cellulose fibers to obtain a reaction solution;

s2, centrifuging the reaction solution obtained in the step S1, washing and centrifuging with a solvent, washing and centrifuging with acetone, pouring out supernatant, and adding the lower layer fiber into deionized water for ultrasonic washing to obtain a cellulose solution;

s3, loading the cellulose solution obtained in the step S2 into a dialysis bag for dialysis to remove foreign ions, and freeze-drying to obtain the modified sulfamated cellulose.

Preferably, in step S1, the amino sulfuric acid: solvent: the mass ratio of the powdery cellulose is 10:40 (1-3).

Preferably, in step S1, the solvent is one of DMF, DMSO, carbon dichloride, and tetrachloromethane.

Preferably, in the step S2, the reaction temperature is 70-80 ℃ and the reaction time is 30-90 min.

Preferably, in step S3, dialysis is stopped when no sulfamic acid in sulfamated cellulose is detected by barium nitrate titration in step S3.

A method for preparing a cellulose gel from sulfamated cellulose, comprising the steps of: vacuum drying the chloridized 1-butyl-3-methylimidazole to remove water, adding sulfamated cellulose into the chloridized 1-butyl-3-methylimidazole, heating and stirring to fully dissolve the sulfamated cellulose to form a cellulose gel solution; and standing the cellulose gel-like solution in a room temperature environment, and drying for a certain time to obtain the sulfamate cellulose gel.

Preferably, the amount of 1-butyl-3-methylimidazole chloride and sulfamated cellulose to be used is 100 (1-2).

An application of sulfamated cellulose in an optical fiber humidity sensor.

A preparation method of an optical fiber humidity sensor based on sulfamated cellulose as a humidity sensing material comprises the following steps:

step 1), stripping the tail end coating layer of the conductive optical fiber, cleaning, and then cutting the tail end of the conductive optical fiber to be flat;

step 2), carrying out vacuum drying on the chlorinated 1-butyl-3-methylimidazole to remove water, then adding sulfamated cellulose into the chlorinated 1-butyl-3-methylimidazole, heating and stirring to fully dissolve the sulfamated cellulose to form a cellulose gel solution;

step 3), vertically immersing the conductive optical fiber treated in the step 1) into the cellulose gel-like solution prepared in the step 2), and repeating the immersing and pulling process for 2-3 times to obtain the optical fiber coated with the cellulose hydrogel film;

and 4) vertically standing the tail end of the optical fiber coated with the cellulose hydrogel prepared in the step 3) in a room temperature environment, and drying for 24-48 hours to obtain the optical fiber humidity sensor.

Preferably, in step 2), the solid content of the chlorinated 1-butyl-3-methylimidazole-sulfamated cellulose hydrogel is 1% -2% (wt.%);

preferably, in step 3), the thickness of the cellulose hydrogel film coated on the optical fiber is 30 to 100 μm.

Preferably, the dipping process is a process of standing still for 1-2s, and the pulling process is a process of vertically pulling the optical fiber out of the liquid surface.

Preferably, in step 4), the drying time is 24-36 hours.

Preferably, the conducting optical fiber in step 1) is a single mode optical fiber or a multimode optical fiber.

Preferably, the diameter of the single mode optical fiber is 100 μm.

A humidity detection system having an optical fiber humidity sensor based on sulfamated cellulose as a humidity sensing material, the detection system comprising an optical fiber humidity sensor, an optical fiber demodulator, and a computer electrically connected in sequence.

The invention has the technical effects that:

(1) According to the method, the hydrophilic performance of the needle cellulose is improved through sulfamate modification, the modified sulfamate cellulose is dissolved by adopting ionic liquid chloridized 1-butyl-3-methylimidazole, and hydrogel is formed to serve as a humidity sensing material to prepare the optical fiber humidity sensor so as to improve the humidity detection performance of the optical fiber humidity sensor. After the fibers are subjected to sulfamate, the fibers contain a large amount of hydrophilic groups, so that the hydrophilicity of cellulose is improved, the average water absorption rate of the sulfamate cellulose prepared by the method can reach 17.5% after three humidification processes, and after three humidification and dehumidification processes, the standard deviation of three weight changes of the sulfamate cellulose prepared by the method is sigma=0.035, so that the sulfamate cellulose prepared by the method shows better water molecule absorption and release capability and good repeatability;

(2) The cellulose raw materials adopted by the invention are widely and easily available and biodegradable;

(3) The optical fiber humidity sensor provided by the invention has the advantages that the preparation cost is low, the preparation process is simple, and the optical fiber humidity sensor prepared in the application is coated with cellulose hydrogel; the humidity sensitivity of the optical fiber humidity sensor reaches 0.16dB/%RH, the humidity hysteresis error is +/-0.079%, and the stability is R ² ＝0.9642。

(4) The optical fiber humidity sensor prepared by the invention is based on the Fabry-Perot (F-P) structure principle, and a F-P interference cavity is formed by a single-mode fiber and cellulose hydrogel in the optical fiber humidity sensor prepared by the invention.

(5) The sulfamate cellulose with the required hydroxyl substitution degree of less than 30% is obtained through the selection of the sulfamic acid and the process parameter setting in the step S1 and the step S2, and the hydroxyl substitution degree can be controlled through the process condition setting, so that the sulfamate cellulose mainly benefits from the reaction principle of the sulfamic acid and cellulose reaction in the application, and the reaction principle is shown as a reaction formula (3). In addition, the application also provides the reaction principle of sulfonation reaction in the prior art, which is shown as a reaction formula (1) and a reaction formula (2).

The reaction principle (1) and the reaction principle (2) are cellulose disclosed in the prior art at presentCommon reaction principle of sulfonation method, sodium iodate and pyridine SO used in the sulfonation reaction ₃ Has strong oxidizing property and toxicity, and the sulfonic group has no selectivity to the substitution of hydroxyl. The reaction principle (3) is different from the reaction principle of the sulfonation method reported at present, and the substitution of the hydroxyl group in the application is easy to occur at the hydroxyl group of the hydroxymethyl position, so that the synthesized sulfamated cellulose can be controlled to a certain extent in the substitution degree of the hydroxyl group, a certain number of the hydroxyl groups is reserved, more intramolecular hydrogen bonds can be formed due to the existence of the hydroxyl group in the later dissolution and regeneration process, and gel is easy to form, which is a precondition for being used as a humidity sensing material for an optical fiber humidity sensor. However, the conventional sulfonation method is not selective, hydroxyl groups are substituted, no hydroxyl groups cannot form intramolecular hydrogen bonds, gel cannot be formed after dissolution and regeneration, a stable gel film cannot be formed on the end face of the optical fiber any more, and after humidity changes, the thickness does not change, and interference of light cannot be changed, so that the hydrogel prepared through the sulfonation reaction cannot be used as a humidity sensing material of a humidity optical fiber humidity sensor.

Drawings

The invention will be further described with reference to the accompanying drawings and detailed description, wherein:

FIG. 1 is an infrared (FT-IR) diagram of sulfamated cellulose prepared in example one, sulfamated cellulose prepared in example two, and cellulosic raw materials;

FIG. 2 is an XPS diagram of sulfamated cellulose prepared in example one, sulfamated cellulose prepared in example two, and cellulose raw materials;

FIG. 3 is a mass spectrum of the sulfamated cellulose prepared in example one and example two with three cycles of humidification (RH 80%) and dehumidification (RH 45%).

FIG. 4 (a) is a schematic view of the structure of an optical fiber of the present invention coated with a cellulose hydrogel film; FIG. 4 (b) is a schematic diagram of a test system;

FIG. 5 is an interference spectrum of the optical fiber humidity sensor prepared in the second embodiment when the relative humidity is 45%, 50%, 60%, 70%, 80%, respectively;

FIG. 6 is a graph showing the response of the interference fringe contrast of the fiber optic humidity sensor prepared in example two as a function of humidity;

FIG. 7 is a graph showing the response of the interference fringe contrast of the fiber optic humidity sensor prepared in example two to temperature.

In the figure, 1 single mode fiber; 2 a cellulose hydrogel film; 3, an optical fiber demodulator; 4, an optical fiber humidity sensor; 5, a constant temperature and humidity box; 6, a computer.

Detailed Description

The invention is described in further detail below with reference to the drawings and the detailed description. The following examples are given for the purpose of illustration only and are not to be construed as limiting the invention.

Embodiment one:

a method for preparing sulfamated cellulose, comprising the steps of:

s1, weighing 10g of sulfamic acid, fully dissolving and mixing in 40g of N, N-Dimethylformamide (DMF) to obtain a mixed solution, weighing 3g of powdered needle-leaved wood cellulose, adding the powder-leaved wood cellulose into the mixed solution, heating and stirring, and reacting for 0.5h at 70 ℃ to fully esterify cellulose fibers to obtain a reaction solution;

s2, centrifuging the reaction solution obtained in the step S1, sequentially washing and centrifuging with DMF and acetone respectively, pouring out supernatant, and adding the lower layer fiber into deionized water for ultrasonic washing to obtain a cellulose solution; wherein, the centrifugation conditions in the step 2) are centrifugation speed 10000rpm, and the centrifugation time is 5min;

and S3, loading the cellulose solution obtained in the step S2 into a dialysis bag for dialysis to remove the impurity ions, stopping dialysis when the barium nitrate titration is used for detecting that no sulfamic acid exists in the sulfamate cellulose, and freeze-drying after the dialysis is finished to obtain the modified sulfamate cellulose.

A method for preparing a cellulose gel from sulfamated cellulose, comprising the steps of: weighing 100g of 1-butyl-3-methylimidazole chloride, performing vacuum drying to remove water, adding 2g of sulfamate cellulose into the 1-butyl-3-methylimidazole chloride, and heating and stirring to fully dissolve the sulfamate cellulose to form a cellulose gel solution; and standing the cellulose gel-like solution in a room temperature environment until the cellulose gel-like solution is dried, thus obtaining the cellulose gel.

The preparation method of the optical fiber humidity sensor based on the sulfamated cellulose as the humidity sensing material comprises the following steps:

step 1), taking a single-mode fiber 1 with the diameter of 100 mu m, stripping the tail end coating layer, cleaning the tail end coating layer by alcohol cotton, and then cutting the tail end of the single-mode fiber to be smooth by using a special fiber cutter;

step 2), weighing 100g of 1-butyl-3-methylimidazole chloride, performing vacuum drying to remove water, adding 2g of sulfamated cellulose into the 1-butyl-3-methylimidazole chloride, and heating and stirring to fully dissolve the sulfamated cellulose to form a cellulose gel-like solution, wherein the solid content of the 1-butyl-3-methylimidazole-sulfamated cellulose hydrogel is about 2 percent (wt%);

step 3), vertically immersing the single-mode fiber processed in the step 1) into the cellulose gel-like solution prepared in the step 2), and repeating the immersing and pulling process for 2 times to obtain the optical fiber coated with the cellulose hydrogel film 2, wherein the thickness of the cellulose hydrogel film coated on the optical fiber is 60 mu m; wherein, the dipping process refers to static holding for 2s, and the pulling process refers to vertically pulling the optical fiber out of the liquid level;

and 4) vertically standing the tail end of the optical fiber coated with the cellulose hydrogel prepared in the step 3) in a room temperature environment, and drying for 24 hours to obtain the optical fiber humidity sensor.

Embodiment two:

a method for preparing SAEC, comprising the steps of:

s1, weighing 10g of sulfamic acid, fully dissolving and mixing in 40g of N, N-Dimethylformamide (DMF) to obtain a mixed solution, weighing 2g of powdered needle-leaved wood cellulose, adding the powder-leaved wood cellulose into the mixed solution, heating and stirring, and reacting for 1.5h at 80 ℃ to fully esterify cellulose fibers to obtain a reaction solution;

s2, centrifuging the reaction solution in the step S1, respectively washing and centrifuging with DMF and acetone in sequence, pouring out supernatant, and adding the lower layer fiber into deionized water for ultrasonic washing to obtain a cellulose solution; wherein, the centrifugation conditions in the step 2) are centrifugation speed 10000rpm, and the centrifugation time is 5min;

and S3, loading the cellulose solution obtained in the step S3 into a dialysis bag for dialysis to remove the impurity ions, stopping dialysis when the barium nitrate titration is used for detecting that no sulfamic acid exists in the sulfamate cellulose, and freeze-drying after the dialysis is finished to obtain the modified sulfamate cellulose.

A method for preparing a cellulose gel using SAEC, comprising the steps of: weighing 100g of 1-butyl-3-methylimidazole chloride, performing vacuum drying to remove water, adding 2g of sulfamate cellulose into the 1-butyl-3-methylimidazole chloride, and heating and stirring to fully dissolve the sulfamate cellulose to form a cellulose gel solution; and standing the cellulose gel-like solution in a room temperature environment until the cellulose gel-like solution is dried, thus obtaining the cellulose gel.

step 1), taking a single-mode fiber with the diameter of 100 mu m, stripping the tail end coating layer, cleaning the tail end of the single-mode fiber with alcohol cotton, and cutting the tail end of the single-mode fiber to be smooth by using a special optical fiber cutting knife;

step 2), weighing 100g of 1-butyl-3-methylimidazole chloride, performing vacuum drying to remove water, and then adding 2g of sulfamate cellulose into the 1-butyl-3-methylimidazole chloride, heating and stirring to fully dissolve the sulfamate cellulose to form a cellulose gel-like solution, wherein the solid content of the 1-butyl-3-methylimidazole-sulfamate hydrogel is 2 percent (wt.%);

step 3), vertically immersing the single-mode fiber processed in the step 1) into the cellulose gel-like solution prepared in the step 2), and repeating the immersing and pulling process for 2 times to obtain an optical fiber coated with a cellulose hydrogel film, wherein the thickness of the cellulose hydrogel film coated on the optical fiber is 45 mu m; wherein, the dipping process is to keep static for 2 seconds and vertically lift the liquid level;

and 4) vertically standing the tail end of the optical fiber with the cellulose hydrogel in a room temperature environment, and drying for 24 hours to obtain the optical fiber humidity sensor.

To verify that the sulfamated cellulose has introduced hydrophilic groups relative to the unmodified cellulose (Raw material), the present application specifically performed infrared spectroscopic and XPS tests on the sulfamated cellulose and the unmodified cellulose (Raw material) prepared in the above examples one and two. The infrared spectrum (FT-IR) obtained by the infrared spectrum test is shown in fig. 1, and the XPS spectrum obtained by the XPS test is shown in fig. 2 (a) and fig. 2 (b).

As can be seen from fig. 1, the modified sulfamated cellulose prepared in example one and example two exhibited new characteristic peaks compared to the unmodified cellulose (Rawmaterial). Wherein, is positioned at 1250cm ^-1 And 1400cm ^-1 The absorption peak at the periphery is caused by s=o bond stretching vibration; at 1040cm ^-1 The absorption peak is generated by the S-O bond stretching vibration; 800cm ^-1 The absorption peak at the site is C-O-SO ₃ The C-O-S bond and the C-H bond on the group are mixed and vibrated to form the compound. From the appearance of these new peaks, it can be deduced that-SO ₃ The H group was smoothly introduced into the sulfamated cellulose prepared in example one and example two.

As can be seen from fig. 2 (a), the XPS spectra of the modified sulfamated cellulose prepared in example one and example two significantly more S2p photoelectron lines than those of the unmodified cellulose (Rawmaterial). The presence of the S element indicates that the hydroxy groups of the sulfamic acid and the cellulose are subjected to esterification reaction in the reaction process. Furthermore, as can be seen from FIG. 2 (a), the degree of substitution of hydroxyl groups of the sulfamated cellulose prepared in example one and example two was 18.64% and 26.83%, respectively.

In order to analyze the existing valence form of the S element, the application also carries out peak-splitting fitting on S2p, the fitting result is shown in fig. 2 (b), and as can be seen from fig. 2 (b), the peak value at 168.6eV is further confirmedintroducing-SO into esterified hydrophilic cellulose ₃ H groups, results are consistent with the IR spectrum analysis of FIG. 1.

In addition, the weight of the sulfamated cellulose prepared in the first and second examples was measured at different relative humidity (RH 45%, RH 80%) to evaluate the water molecule absorption and release capabilities of the sulfamated cellulose prepared in the first and second examples, and the test results are shown in fig. 3.

As can be seen from fig. 3, after three humidification and dehumidification experiments were continuously performed in the humidity range of RH80% to RH45%, the weight change of the sulfamated cellulose prepared in the first and second examples showed the same periodic change, and specific data are shown in table 1.

Table 1:

as can be seen from fig. 3 and table 1, especially, the quality changes before and after the SAEC humidification experiment and before and after the dehumidification experiment prepared in example two are more obvious, and the quality changes before and after the humidification experiment and before and after the dehumidification experiment are repeated many times are still quite obvious, the average water absorption rate of the three humidification processes is 17.50%, the standard deviation of the three weight changes is σ=0.035, which also indicates that the SAEC prepared in example two shows better water molecule absorption and release capability and good repeatability.

The water absorption per humidification process is calculated by formula (1):

water absorption (%) = (m) ₂ -m ₁ )/m ₁ (1)

In the formula (1), m ₁ For the quality of the sulfamated cellulose before the humidification process, m ₂ The quality of the sulfamated cellulose after the humidification process;

the standard deviation sigma is calculated by the formula (2), and the formula (2) is a calculation formula of the existing standard deviation:

wherein m is _i Is the mass after water absorption;

is the average mass after water absorption.

A humidity detection system with an optical fiber humidity sensor based on sulfamated cellulose comprises an optical fiber humidity sensor 4, an optical fiber demodulator 3 (wavelength range is 1520 nm-1590 nm) and a computer 6 which are electrically connected in sequence.

Since the moisture absorption effect of the sulfamated cellulose prepared in example two was found to be more excellent by the foregoing test, the present application conducted a performance test preferentially on the humidity detection system of the optical fiber humidity sensor having the sulfamated cellulose prepared in example two as the moisture-sensitive material. In the test, one end of the optical fiber humidity sensor 4 prepared in the second embodiment coated with the sulfamated cellulose hydrogel is placed in a humidity environment to be tested, i.e. a constant temperature and humidity box 5, and the constant temperature and humidity box 5 is used for providing test environments with different humidities, as shown in fig. 4 (b), and the schematic structural diagram of the optical fiber humidity sensor is shown in fig. 4 (a).

In order to verify that the optical fiber humidity sensor prepared in the second embodiment has relatively sensitive response to humidity change, the interference condition of the optical fiber humidity sensor under different relative humidity is specifically tested, and an interference spectrum obtained by the test is shown in fig. 5. As can be seen from fig. 5, the intensity of the interference fringes increases with the relative humidity, which illustrates that the optical fiber humidity sensor prepared in the second embodiment has a relatively sensitive response to humidity changes. The humidity sensitivity of the optical fiber humidity sensor prepared in the second embodiment was calculated by the formula (3):

moisture sensitivity= (λ) _RH2 -λ _RH1 )/(RH2-RH1) (3)

Wherein lambda is _RH2 And lambda (lambda) _RH1 Contrast, lambda, at RH2 and RH1 humidity, respectively _RH2 And lambda (lambda) _RH1 To the contrast from FIG. 5I.e., peak-to-valley distance), in dB. RH2 and RH1 represent humidity in% RH at 80% and 45% ambient, respectively.

As can be seen from the calculation of the formula (3), the humidity sensitivity of the optical fiber humidity sensor prepared in the second embodiment reaches 0.16dB/%RH.

In addition, the present application also tested the repeated experimental response of interference fringe contrast as a function of relative humidity, and the test results are shown in fig. 6. In fig. 6, the relationship between relative humidity and fringe contrast is obtained using humidity (x) as an independent variable and fringe contrast (y) as a dependent variable. As can be seen from the graph, the response curves substantially coincide as the relative humidity is cycled. The formula of the fitting curve is as follows: y= 0.00188x ² -0.13539x+5.10326, confidence factor (R ² ) 0.9642. The repeated experimental results are basically consistent, the prepared optical fiber humidity sensor has small wet hysteresis error of +/-0.079%, and good repeatability.

In addition, the interference condition of the optical fiber humidity sensor at different temperatures is tested under the condition of constant relative humidity (RH 40%), and an interference spectrogram obtained by the test is shown in FIG. 7. As can be seen from fig. 7, the contrast and intensity of the interference fringes do not significantly change with the change of the external temperature, which means that the temperature change has little effect on the measurement accuracy of the optical fiber humidity sensor of the present invention.

The above is a further detailed description of the present invention in connection with the specific embodiments, and is not intended to limit the scope of the invention. On the basis of the technical scheme of the invention, various modifications or variations which can be made by the person skilled in the art without the need of creative efforts are still within the protection scope of the invention.

Claims

1. A method for preparing sulfamated cellulose, which is characterized in that: the method comprises the following steps:

s1, adding sulfamic acid into a solvent, fully dissolving and mixing to obtain a mixed solution, adding powdered cellulose into the mixed solution, heating and stirring for reacting for a certain time, and fully esterifying cellulose fibers to obtain a reaction solution;

s2, centrifuging the reaction solution obtained in the step S1, washing and centrifuging by using a solvent, washing and centrifuging by using acetone, and then adding the lower layer fiber into deionized water for ultrasonic washing to obtain a cellulose solution;

and S3, dialyzing the cellulose solution obtained in the step S2, and then freeze-drying to obtain the modified sulfamate cellulose.

2. The method for producing sulfamated cellulose according to claim 1, wherein: in step S1, sulfamic acid: solvent: the mass ratio of the powdery cellulose is 10:40 (1-3).

3. The method for producing sulfamated cellulose according to claim 1, wherein: in the step S1, the solvent is one of DMF, DMSO, dichloromethane and carbon tetrachloride.

4. The method for producing sulfamated cellulose according to claim 1, wherein: in the step S2, the reaction temperature is 70-80 ℃ and the reaction time is 30-90 min.

5. The method for producing sulfamated cellulose according to claim 1, wherein: in step S3, when no sulfamic acid is detected in the sulfamated cellulose by barium nitrate titration, the dialysis is stopped.

6. A method for preparing cellulose gel by using sulfamate cellulose, which is characterized in that: the method comprises the following steps: vacuum drying the chloridized 1-butyl-3-methylimidazole, adding sulfamated cellulose into the chloridized 1-butyl-3-methylimidazole, heating and stirring to fully dissolve the sulfamated cellulose to form a cellulose gel solution; and standing the cellulose gel-like solution in a room temperature environment, and drying for a certain time to obtain the sulfamate cellulose gel.

7. A method for preparing a cellulose gel using sulfamated cellulose as claimed in claim 6, wherein: the mass ratio of the chloridized 1-butyl-3-methylimidazole to the sulfamated cellulose is 100 (1-2).

8. An application of sulfamated cellulose in an optical fiber humidity sensor.

9. A preparation method of an optical fiber humidity sensor based on sulfamated cellulose as a humidity sensing material comprises the following steps:

10. A humidity detection system having an optical fiber humidity sensor based on sulfamated cellulose as a humidity sensing material, characterized in that: the detection system comprises an optical fiber humidity sensor, an optical fiber demodulator and a computer which are electrically connected in sequence.