CN116041552A - Aminosulfated cellulose, cellulose hydrogel, preparation method and application thereof - Google Patents

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

Aminosulfated cellulose, cellulose hydrogel, preparation method and application thereof

technical field

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

Background technique

Humidity detection is of great significance to many fields such as agriculture, meteorology, and medical treatment. In recent years, with the progress and development of modernization, the requirements for accurate monitoring of environmental humidity have become higher and higher. At present, traditional humidity sensors cannot meet the humidity monitoring in harsh environments due to their shortcomings such as large size, poor stability, and short life. Optical fiber humidity sensors have the characteristics of anti-electromagnetic interference, small size, and long-distance transmission, and are especially suitable for high temperature High-pressure, flammable and explosive high-temperature environment test environment. For example, in patents CN101936897A and CN111208087A, it is mentioned that the humidity sensor is mainly composed of a sensor device and a moisture-sensitive material. The moisture-sensitive material is coated at the end of the optical fiber, and the change of its refractive index is used to produce different humidity responses. Therefore, the selected humidity-sensitive material Sufficient sensitivity to ambient moisture.

Humidity-sensitive materials commonly used in the prior art mainly include petroleum-based materials such as chitosan, metal oxides, graphene oxide, and polyvinyl alcohol. However, humidity sensors made of these materials have high cost and narrow monitoring range. , the problem of low sensitivity, and the non-biodegradable material will cause environmental problems. Therefore, the preparation of humidity sensors based on bio-based materials has attracted extensive attention. Cellulose is the most abundant source of natural organic polymers in the world. Hydrophilic treatment of cellulose not only meets the requirements of moisture-sensitive materials, but also has great significance for environmental protection and sustainable development. However, the moisture-feeling property of cellulose itself in the prior art is not very ideal, therefore, it is necessary to improve its moisture-feeling effect through hydrophilic modification. At present, there are many methods for the surface hydrophilic modification of cellulose, mainly the quaternization, etherification, sulfonation, carboxymethylation and carboxylation of the hydroxyl groups of cellulose, so that the surface can be introduced into Polar groups that change their hydrophilic properties. For example, CN201810294212.3 discloses an etherification reaction. In this patent, cellulose is polymerized in a solution containing N, N-dimethylformamide and epichlorohydrin to obtain etherified cellulose; WO/ 2011/024807 discloses a carboxylation reaction. In the carboxylation reaction, carboxyl groups are introduced by oxidation treatment in a reaction solution containing an N-oxygen compound (such as TEMPO) and an oxidizing agent such as a halogen. This method uses more chemical reagents. Such as 2,2,6,6-tetramethyl piperidine oxide, NaOCl, KBr and NaHCO ₃ etc., among which 2,2,6,6-tetramethyl piperidine oxide is toxic and harmful to the environment. The preparation of carboxymethylation is generally a method of reacting cellulose with alkali first, and then treating it with a carboxymethylating agent. It is divided into "water method" (using water as a solvent) and "solvent method" (using organic solvent Mainly); This method often uses harmful active reagents such as carboxymethylating agent chloroacetic acid in the process of preparation. CN202010920786.4 also discloses the use of dialdehyde cellulose and bisulfite to undergo an addition reaction to prepare sulfonated cellulose, but this method must prepare cellulose into dialdehyde cellulose in advance and then perform sulfonation; wherein, In the preparation process of dialdehyde cellulose, highly oxidative sodium periodate solution is often used, which faces certain challenges in terms of risk and cost.

Therefore, the present invention provides a method for aminosulfatizing cellulose, that is, cellulose is modified and simplified to increase its hydrophilicity, and combined with an optical fiber to prepare an optical fiber humidity sensor that can accurately monitor environmental humidity.

Contents of the invention

In order to make up for the defects of the prior art, the present invention proposes aminosulfated cellulose, cellulose hydrogel and its preparation method and application.

The present invention is achieved through the following technical solutions:

A preparation method of aminosulfated cellulose, comprising the steps of:

S1. Add aminosulfated cellulose to the solvent to fully dissolve and mix to obtain a mixed solution, then add powdered cellulose to the mixed solution, heat and stir for a certain period of time to fully esterify the cellulose fibers to obtain a reaction solution ;

S2, centrifuging the reaction solution obtained in step S1, then washing and centrifuging with a solvent, then washing and centrifuging with acetone, then pouring off the supernatant, taking the lower fiber and adding it to deionized water for ultrasonic washing to obtain a cellulose solution;

S3. Put the cellulose solution obtained in step S2 into a dialysis bag for dialysis to remove heteroions, and freeze-dry to obtain modified aminosulfated cellulose.

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

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

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

Preferably, in step S3, in step S3, when it is detected by barium nitrate titration that there is no aminosulfuric acid in the aminosulfated cellulose, the dialysis is stopped.

A method for preparing cellulose gel by using aminosulfuric acid to sulfate cellulose, comprising the steps of vacuum-drying 1-butyl-3-methylimidazole chloride to remove moisture, and then chlorinating 1-butyl - Add aminosulfated cellulose to 3-methylimidazole, heat and stir to fully dissolve the aminosulfated cellulose to form a cellulose gel solution; the cellulose gel solution is left to dry at room temperature After a certain period of time, aminosulfated cellulose gel can be obtained.

Preferably, the dosage relationship between 1-butyl-3-methylimidazole chloride and aminosulfated cellulose is 100:(1-2).

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

A preparation method of an optical fiber humidity sensor based on aminosulfated cellulose as a moisture-sensitive material, comprising the steps of:

Step 1), stripping off the coating layer at the end of the conductive optical fiber and cleaning it, and then cutting the end of the conductive optical fiber flat;

Step 2), vacuum-dry 1-butyl-3-methylimidazole chloride to remove moisture, then add aminosulfated cellulose to 1-butyl-3-methylimidazole chloride, heat and stir, Fully dissolve the aminosulfated cellulose to form a cellulose gel-like solution;

Step 3), vertically immerse the conductive optical fiber treated in step 1) into the cellulose gel-like solution prepared in step 2), repeat the dipping and pulling process 2-3 times, and obtain a cellulose hydrogel film coated the optical fiber;

In step 4), the end of the optical fiber coated with cellulose hydrogel prepared in step 3) is vertically placed in room temperature and dried for 24-48 hours to obtain an optical fiber humidity sensor.

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

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

Preferably, the dipping process refers to the static keeping for 1-2s, and the pulling process refers to the process of vertically pulling the optical fiber out of the liquid surface.

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

Preferably, the guiding fiber in step 1) is a single-mode fiber or a multi-mode fiber.

Preferably, the single-mode optical fiber has a diameter of 100 μm.

A humidity detection system with an optical fiber humidity sensor based on aminosulfated cellulose as a moisture sensitive material, the detection system includes an optical fiber humidity sensor, an optical fiber demodulator and a computer that are electrically connected in sequence.

Technical effect of the present invention:

(1) This application improves the hydrophilic property of needle cellulose through aminosulfate modification, and uses ionic liquid 1-butyl-3-methylimidazole chloride to carry out the modified aminosulfate cellulose Dissolving and forming a hydrogel as a humidity-sensing material to prepare an optical fiber humidity sensor to improve the humidity detection performance of the optical fiber humidity sensor. After aminosulfate, the fiber of the present invention contains a large number of hydrophilic groups, which improves the hydrophilicity of the cellulose. The average water absorption rate of the aminosulfate cellulose prepared by this application can reach 17.5% after three humidification processes , and, after three humidification and dehumidification processes, the standard deviation of the three weight changes of the aminosulfated cellulose prepared in Example 2 of the present application is σ=0.035, which shows that the aminosulfated cellulose prepared in Example 2 shows Better water molecule absorption and release ability with good repeatability;

(2) The cellulose raw material that the present invention adopts is widely easy to get, biodegradable;

(3) The optical fiber humidity sensor of the present invention has low preparation cost and simple preparation process, and the optical fiber humidity sensor prepared in the application is an optical fiber humidity sensor coated with cellulose hydrogel; the humidity sensitivity of the optical fiber humidity sensor reaches 0.16dB/%RH, hysteresis error is ±0.079%, and stability is R ² =0.9642.

(4) The optical fiber humidity sensor prepared by the present invention is based on the principle of Fabry-Perot (F-P) structure. In the optical fiber humidity sensor prepared by the application, the single-mode optical fiber and cellulose hydrogel constitute the F-P interference cavity. The optical fiber humidity sensor prepared by the invention also has the characteristics of anti-electromagnetic interference and small size, and is suitable for humidity detection in high-risk environments such as strong electromagnetic interference and inflammable and explosive environments.

(5) This application obtains aminosulfated cellulose with a required degree of substitution of hydroxyl groups less than 30% through the selection of amino sulfuric acid and the setting of process parameters in steps S1 and S2, and the degree of substitution of hydroxyl groups in this application can be obtained through process conditions The setting control is mainly benefited from the reaction principle of amino acid and cellulose reaction in this application, and the reaction principle is shown in the reaction formula (3). In addition, the present application also provides the reaction principle of the sulfonation reaction in the prior art, as shown in reaction formula (1) and reaction formula (2).

Reaction principle (1) and reaction principle (2) are the common reaction principles of the cellulose sulfonation method disclosed in the prior art. The sodium iodate and pyridine SO used in the above sulfonation reaction have _strong oxidizing properties And toxicity, and the substitution of sulfonic acid group to hydroxyl group is not selective. Reaction principle (3) is the reaction principle of the present application. It is different from the reaction principle of the sulfonation method reported at present. In this application, the substitution of the hydroxyl group is easy to occur at the hydroxyl group at the methylol position. Therefore, the synthesized aminosulfated cellulose The degree of hydroxyl substitution can be controlled to a certain extent, and a certain number of hydroxyl groups is retained. In the later dissolution and regeneration process, due to the existence of hydroxyl groups, more intramolecular hydrogen bonds will be formed, and gels are easy to form. A moisture-sensitive material is used as a prerequisite for an optical fiber humidity sensor. However, the conventional sulfonation method is not selective, and the hydroxyl groups are replaced. Without hydroxyl groups, intramolecular hydrogen bonds cannot be formed. After dissolution and regeneration, gel cannot be formed, and a stable gel film cannot be formed on the end face of the optical fiber. After the change, the thickness does not change, and the interference of light cannot be changed. Therefore, the hydrogel prepared by the sulfonation reaction cannot be used as a moisture-sensing material for a humidity optical fiber humidity sensor.

Description of drawings

The present invention will be further described below in conjunction with accompanying drawing and specific implementation method, in the accompanying drawing:

Fig. 1 is the infrared (FT-IR) picture of the aminosulfated cellulose prepared in Example 1, the aminosulfated cellulose prepared in Example 2, and the cellulose raw material;

Fig. 2 is the XPS figure of the aminosulfated cellulose prepared in Example 1, the aminosulfated cellulose prepared in Example 2, and the cellulose raw material;

Fig. 3 is the mass change spectrogram of the aminosulfated cellulose prepared in Example 1 and Example 2 for three cycles of humidification (RH80%) and dehumidification (RH45%);

Fig. 4 (a) is coated with the structural representation of cellulose hydrogel film on the optical fiber of the present invention; Fig. 4 (b) testing system schematic diagram;

Fig. 5 is the interference spectrum when the relative humidity of the fiber optic humidity sensor prepared in Example 2 is 45%, 50%, 60%, 70%, and 80%, respectively;

Fig. 6 is the response curve diagram that the interference fringe contrast of the optical fiber humidity sensor prepared in embodiment two changes with humidity;

Fig. 7 is a response curve of the interference fringe contrast of the optical fiber humidity sensor prepared in Example 2 as a function of temperature.

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

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments. The following implementations are only used to illustrate the present invention, and are not intended to limit the present invention.

Embodiment one:

A preparation method of aminosulfated cellulose, comprising the steps of:

S1. Weigh 10g of amino sulfuric acid in 40g of N,N-dimethylformamide (DMF), fully dissolve and mix to obtain a mixed solution, weigh 3g of powdered coniferous wood cellulose and add it to the mixed solution, heat and stir, and react at 70°C 0.5h, to fully esterify the cellulose fibers to obtain a reaction solution;

S2, centrifuging the reaction solution obtained in step S1, then washing and centrifuging in sequence with DMF and acetone respectively, then pouring off the supernatant, taking the fibers of the lower layer and adding them to deionized water for ultrasonic washing to obtain a cellulose solution; Wherein, the centrifugation conditions in step 2) are all centrifugation speed 10000rpm, centrifugation time 5min;

S3. Put the cellulose solution obtained in step S2 into a dialysis bag and perform dialysis to remove miscellaneous ions. When it is detected by barium nitrate titration that there is no amino sulfuric acid in the aminosulfated cellulose, stop the dialysis. After the dialysis, freeze-dry , that is, the modified amino sulfated cellulose is obtained.

A method utilizing aminosulfated cellulose to prepare cellulose gel, comprising the steps of: taking 100g of chlorinated 1-butyl-3-methylimidazole and carrying out vacuum drying to remove moisture, and then to chlorinated 1- Add 2g of aminosulfated cellulose to butyl-3-methylimidazole, heat and stir to fully dissolve the aminosulfated cellulose to form a cellulose gel-like solution; the cellulose gel-like solution is allowed to stand at room temperature In the environment until dry, the cellulose gel can be obtained.

A method for preparing an optical fiber humidity sensor based on aminosulfated cellulose as a moisture-sensitive material, comprising the steps of:

Step 1), take a single-mode optical fiber 1 with a diameter of 100 μm, strip off the coating layer at the end, clean it with alcohol cotton, and then use a special optical fiber cutter to cut the end of the single-mode optical fiber flat;

Step 2), take 100g of chlorinated 1-butyl-3-methylimidazole and carry out vacuum drying to remove moisture, then add 2g aminosulfated cellulose in chlorinated 1-butyl-3-methylimidazole , heated and stirred to fully dissolve the aminosulfated cellulose to form a cellulose gel-like solution, wherein the solid content of 1-butyl-3-methylimidazole chloride-aminosulfated cellulose hydrogel is about 2% (wt.%);

Step 3), vertically immerse the single-mode optical fiber treated in step 1) into the cellulose gel-like solution prepared in step 2), repeat the dipping and pulling process twice, and get coated with cellulose hydrogel film 2 The thickness of the cellulose hydrogel film coated on the optical fiber is 60 μm; the dipping process refers to keeping it stationary for 2 seconds, and the pulling process refers to pulling the optical fiber vertically out of the liquid surface;

Step 4), the end of the optical fiber coated with cellulose hydrogel prepared in step 3) was vertically placed in a room temperature environment and dried for 24 hours to obtain an optical fiber humidity sensor.

Embodiment two:

A preparation method for SAEC, comprising the steps of:

S1. Weigh 10g of amino sulfuric acid in 40g of N,N-dimethylformamide (DMF), fully dissolve and mix to obtain a mixed solution, weigh 2g of powdered coniferous wood cellulose and add it to the mixed solution, heat and stir, and react at 80°C 1.5h, the cellulose fiber is fully esterified to obtain a reaction solution;

S2, centrifuge the reaction solution in step S1, then wash and centrifuge successively with DMF and acetone respectively, then pour off the supernatant, take the lower fiber and add it to deionized water for ultrasonic washing to obtain a cellulose solution; , the centrifugal conditions in step 2) are centrifugal speed 10000rpm, centrifugal time 5min;

S3. Put the cellulose solution obtained in step S3 into a dialysis bag and perform dialysis to remove miscellaneous ions. When it is detected by barium nitrate titration that there is no amino sulfuric acid in the aminosulfated cellulose, stop the dialysis. After the dialysis ends, freeze-dry , that is, the modified amino sulfated cellulose is obtained.

A method utilizing SAEC to prepare cellulose gel, comprising the steps of: taking by weighing 100g of chlorinated 1-butyl-3-methylimidazole and carrying out vacuum drying to remove moisture, and then to chlorinated 1-butyl-3- Add 2g of aminosulfated cellulose to methylimidazole, heat and stir to fully dissolve the aminosulfated cellulose to form a cellulose gel-like solution; the cellulose gel-like solution is left standing at room temperature until dry, The cellulose gel can be obtained.

A method for preparing an optical fiber humidity sensor based on aminosulfated cellulose as a moisture-sensitive material, comprising the steps of:

Step 1), take a single-mode optical fiber with a diameter of 100 μm, strip off the coating layer at the end and clean it with alcohol cotton, and use a special optical fiber cutter to cut the end of the single-mode optical fiber flat;

Step 2), weighing 100g of chlorinated 1-butyl-3-methylimidazole and carrying out vacuum drying to remove moisture, then adding 2g of aminosulfated cellulose in chlorinated 1-butyl-3-methylimidazole , heated and stirred to fully dissolve the aminosulfate to form a cellulose gel-like solution, wherein the solid content of 1-butyl-3-methylimidazole chloride-aminosulfate hydrogel is 2% (wt. %);

Step 3), vertically immerse the single-mode optical fiber processed in step 1) into the cellulose gel-like solution prepared in step 2), repeat the dipping and pulling process twice, and obtain a cellulose hydrogel film coated Optical fiber, the thickness of the cellulose hydrogel film coated on the optical fiber is 45 μm; wherein, the dipping process refers to keeping it still for 2 seconds, and pulling it out of the liquid surface vertically;

Step 4), the end of the optical fiber with cellulose hydrogel was placed vertically at room temperature and dried for 24 hours to obtain an optical fiber humidity sensor.

In order to verify that the aminosulfated cellulose has introduced a hydrophilic group relative to the unmodified cellulose (Raw material), the applicant specially compared the aminosulfated cellulose prepared in the above-mentioned Examples 1 and 2 and the unmodified Cellulose (Rawmaterial) (ie, powdered cellulose) was tested by infrared spectroscopy and XPS. Among them, the infrared spectrum (FT-IR) obtained by the infrared spectrum test is shown in Figure 1, and the XPS spectrum obtained by the XPS test is shown in Figure 2(a) and Figure 2(b).

It can be seen from FIG. 1 that compared with the unmodified cellulose (Rawmaterial), the modified aminosulfated cellulose prepared in Example 1 and Example 2 has new characteristic peaks. Among them, the absorption peaks around 1250cm ^-1 and 1400cm ^-1 are caused by the stretching vibration of S=O bond; the absorption peak at 1040cm ^-1 is caused by the stretching vibration of SO bond; the absorption peak at 800cm ^-1 is the CO The COS bond and the CH bond on the _-SO3 group are formed by mixing and vibrating. From the appearance of these new peaks, it can be deduced that -SO ₃ H groups were successfully introduced into the aminosulfated cellulose prepared in Example 1 and Example 2.

It can be seen from Figure 2(a) that the XPS spectrum of the modified aminosulfated cellulose prepared in Example 1 and Example 2 has significantly more S2p than the XPS spectrum of unmodified cellulose (Rawmaterial) the photoelectron spectrum. The appearance of the S element shows that the esterification reaction between amino sulfuric acid and the hydroxyl group of cellulose has taken place during the reaction. Moreover, it can also be seen from Fig. 2(a) that the hydroxyl substitution degrees of the aminosulfated cellulose prepared in Example 1 and Example 2 are 18.64% and 26.83%, respectively.

In order to analyze the existing valence form of the S element, the present application also performs peak fitting of S2p, and the fitting result is shown in Figure 2(b). As can be seen from Figure 2(b), the peak at 168.6eV is further It was confirmed that -SO ₃ H groups were introduced into the esterified hydrophilic cellulose, and the results were consistent with the infrared spectrum analysis in Figure 1 .

In addition, the present application also measures the weight of the aminosulfated cellulose prepared in embodiment one and embodiment two at different relative humidity (RH45%, RH80%) to evaluate the aminosulfate prepared in embodiment one and embodiment two The water molecule absorption and release ability of chemical cellulose, the test results are shown in Figure 3.

It can be seen from Figure 3 that after three consecutive humidification and dehumidification experiments in the humidity range of RH80% to RH45%, the weight changes of the aminosulfated cellulose prepared in Example 1 and Example 2 showed the same periodic change , see Table 1 for details.

Table 1:

It can be seen from Figure 3 and Table 1 that, especially, the quality changes of the SAEC prepared in Example 2 before and after the humidification test and before and after the dehumidification test are more obvious, and after repeating the humidification test and dehumidification test many times, the quality of the SAEC before and after the humidification test and before and after the dehumidification test The mass change is still very obvious, the average water absorption rate of the three humidification processes is 17.50%, and the standard deviation of the three weight changes is σ=0.035, which also shows that the SAEC prepared in Example 2 shows better water molecule absorption and release capabilities And good repeatability.

The water absorption rate of each humidification process is calculated by formula (1):

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

In formula (1), m ₁ is the quality of aminosulfated cellulose before the humidification process, m ₂ is the quality of aminosulfated cellulose after the humidification process;

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

为吸水之后的平均质量。Among them, m _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 aminosulfated cellulose, the detection system includes an optical fiber humidity sensor 4, an optical fiber demodulator 3 (with a wavelength range of 1520nm-1590nm) and a computer 6 electrically connected in sequence.

Since the moisture absorption effect of the aminosulfated cellulose prepared in Example 2 is found to be more excellent through previous tests, the application gives priority to the humidity of the optical fiber humidity sensor having the aminosulfated cellulose prepared in Example 2 as a moisture-sensitive material. The detection system was tested for performance. During the test, one end of the optical fiber humidity sensor 4 prepared in Example 2 coated with aminosulfated cellulose hydrogel was placed in the humidity environment to be measured, that is, the constant temperature and humidity chamber 5, and the constant temperature and humidity chamber 5 was used to provide different The humidity test environment is shown in Figure 4(b), and the structure diagram of the optical fiber humidity sensor is shown in Figure 4(a).

In order to verify that the optical fiber humidity sensor prepared in Example 2 has a relatively sensitive response to humidity changes, this application specially tested the interference of the optical fiber humidity sensor under different relative humidity, and the interference spectrum obtained from the test is shown in Figure 5. It can be seen from Figure 5 that the intensity of interference fringes increases with the increase of relative humidity, which shows that the optical fiber humidity sensor prepared in Example 2 has a relatively sensitive response to humidity changes. The humidity sensitivity of the optical fiber humidity sensor prepared in the present embodiment 2 is calculated by formula (3):

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

Wherein, λ _RH2 and λ _RH1 are the contrast ratios under the humidity of RH2 and RH1 respectively, and λ _RH2 and λ _RH1 are the contrast ratios (that is, the distance from the peak to the trough) derived from Fig. 5, and the unit is dB. RH2 and RH1 respectively represent the humidity of 80% and 45% environment, the unit is %RH.

It can be seen from the calculation of the formula (3) that 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 the interference fringe contrast with the change of relative humidity, and the test results are shown in FIG. 6 . In Fig. 6, the relationship between relative humidity and interference fringe contrast is obtained by taking humidity (x) as an independent variable and fringe contrast (y) as a dependent variable. It can be seen from the figure that when the relative humidity is cycled, the response curves basically coincide. The formula of the fitting curve is: y=0.00188x ² -0.13539x+5.10326, and the confidence factor (R ² ) is 0.9642. It shows that the results of repeated experiments are basically consistent, and the hysteresis error of the prepared optical fiber humidity sensor is small, which is ±0.079%, which shows that it has good repeatability.

In addition, the present application also tested the interference of the optical fiber humidity sensor at different temperatures under the condition of constant relative humidity (RH40%), and the interference spectrum obtained from the test is shown in FIG. 7 . It can be seen from Fig. 7 that the contrast and intensity of the interference fringes do not change significantly with the change of the external temperature, indicating that the temperature change has almost no influence on the measurement accuracy of the optical fiber humidity sensor of the present invention.

The above content is a further detailed description of the present invention in combination with specific embodiments, and is not intended to limit the protection scope of the present invention. On the basis of the technical solution of the present invention, various modifications or deformations that can be made by those skilled in the art without creative efforts are still within the protection scope of the present invention.

Claims (10)

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:

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.

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.

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