A fully green preparation method of a high-performance cellulose friction material and its application in real-time detection of fruit and vegetable freshness

Abstract

The present invention discloses a fully green preparation method of a high-performance cellulose friction material and its application in real-time detection of the freshness of fruits and vegetables, belonging to the field of self-powered fruit and vegetable freshness indicators. The technical solution adopted is as follows: After culturing softwood pulp with xylanase solution and using a sheet former to make sheets, white paper sheets can be obtained. Using the obtained enzymatically hydrolyzed paper as the positive triboelectric material and commercial electrode polyvinylidene fluoride as the negative triboelectric material, an enzymatically hydrolyzed paper-based triboelectric nanogenerator is prepared. The TENG output electrical signal has a good linear relationship with the change in the humidity of the microenvironment during the storage of fruits and vegetables. According to the change in the electrical signal, the freshness of the stored fruits and vegetables can be detected in real time. The present invention has low energy consumption, a simple process flow, is easy to mass-produce in large areas, has good repeatability between product batches, and its fully green production method endows it with high biocompatibility, environmental friendliness, good sensitivity, and is expected to be widely used in the field of fruit and vegetable freshness indicators.

Description

Technical Field

[0001] The present invention belongs to the field of self-powered fruit and vegetable freshness indication, and in particular relates to a paper-based triboelectric nanogenerator with a high-performance (high dielectric properties, high sensitivity, high stability, degradability, etc.) developed by a fully green production method, and its application in real-time detection of fruit and vegetable freshness. Background Art

[0002] In recent years, with the economic development and the improvement of people's living standards, food safety issues have gradually attracted everyone's attention. During transportation, fruits may be oxidized and eroded by harmful microorganisms, resulting in rot and spoilage, which can endanger human health. Fresh fruits are still living individuals during transportation and storage, with respiration and metabolism. During transportation and storage, they continuously release water molecules, and the humidity inside the packaging environment increases continuously, accelerating fruit spoilage, reducing fruit freshness and nutrient content, and causing serious food waste. Monitoring the weight change of fruits is crucial for reflecting the quality status of fruits. However, detecting the freshness of fruits and vegetables through humidity sensor devices can provide consumers with an intuitive judgment to decide whether to purchase. Traditional humidity sensor devices often require an external power supply. However, commercial secondary batteries for recharge have fatal drawbacks, such as short lifespan, possible leakage or pollution of electrolytes, poor flexibility, etc., which seriously hinder the development of sensor devices towards being convenient, safe, and environmentally friendly. Collecting energy from the surrounding environment and converting it into electrical energy is widely regarded as a promising green and sustainable power solution. Mechanical energy widely present in the environment can easily be converted into electrical energy through many advanced technologies, such as electromagnetic effect, piezoelectric effect, and triboelectric effect, etc. In recent years, triboelectric nanogenerator (TENG) is a representative of advanced technologies for converting environmental energy into electrical energy. It has characteristics such as a wide range of material selection, high output performance, sustainability, and portability, which have established its position in the field of energy conversion and have broad application prospects. Based on triboelectrification and electrostatic induction, TENG can effectively convert the irregular and low-frequency mechanical energy of organisms in the natural environment into electrical energy. TENG is usually composed of triboelectric pairs of dielectric materials with different electron gain and loss abilities. So far, most of the materials used in TENG are synthetic polymers or metal electrodes. These polymers are usually non-biodegradable and have complex structures, thus limiting the development prospects of economically efficient, eco-friendly, and flexible TENG. Therefore, constructing high-performance TENG-based humidity detection devices using natural polymers has important guiding significance for the field of food safety.

[0003] Cellulose is one of the most abundant natural polymers on Earth, with excellent biodegradability, biocompatibility, and flexibility, which has made it the most promising triboelectric material for realizing environmentally friendly TENGs and attracted much attention in recent years. Each glucose unit in the cellulose molecule of cellulose fibers contains three hydroxyl groups, which endows cellulose-based materials with good chemical reaction properties. Cellulose paper easily loses electrons and becomes positively charged, but the fiber friction polarity is low and the surface charge density is low, resulting in a low output signal of TENG. To overcome the weak electron-donating property of the paper, commonly used methods include physical doping, surface morphology design, chemical grafting modification, etc. First, physical doping is a composite material formed by combining a high dielectric constant material with a matrix material, thereby improving the charge acquisition ability. Existing research has shown that by mixing cellulose with BaTiO3 nanoparticles and then crosslinking through epichlorohydrin, cellulose / BaTiO3 paper with a maximum V OC of 50 V was prepared. Secondly, surface morphology design is to increase the surface roughness of the triboelectric material, thereby increasing the contact area of the friction layer and generating more charges. It has been reported that the triboelectric charge density of a material is determined by the potential difference between the surfaces of the triboelectric materials, and chemical grafting modification can adjust the surface potential of the triboelectric materials. Existing research has shown that by reacting CNFs with a mixture of dimethyl sulfate and nitrating acid respectively, methyl and nitro groups were introduced onto the cellulose, and nitrated and methylated CNFs films were successfully prepared, and the triboelectric surface potential was increased by 4-6 times, effectively improving the output performance of cellulose-based TENGs. However, these methods usually have the disadvantages of using a large amount of chemical reagents, high requirements for equipment, cumbersome operation, and time-consuming. Therefore, exploring simple and green processing methods to improve the polarity of cellulose-based tribo-nanomaterials plays a crucial role in constructing green TENGs.

[0004] Xylanase is a general term for a group of enzymes that can specifically degrade hemicellulose xylan into xylooligosaccharides and xylose. The complete degradation of xylan can only be achieved through the synergistic action of multiple enzymes, among which endo-xylanase and exo-xylosidase play a major role. Under mild conditions of 45-55 °C, pH 4.8-5.0, and 150 rpm, KDN06 xylanase can effectively enzymatically hydrolyze the hemicellulose component in natural cellulose fibers into monosaccharides and leave a microscopically rough structure in the original position. In addition, enzymes are mainly composed of amino acid molecules and contain rich electron-donating groups -NH2. According to the literature, introducing -NH2 on the cellulose surface is beneficial to improving the frictional polarity and surface charge density of cellulose. Theoretically, enzymatic hydrolysis treatment of natural cellulose fibers will effectively improve the output signal of cellulose-based TENG without affecting its biocompatibility and skin affinity. Moreover, the enzymes remaining on the cellulose surface have rich polar groups, can adsorb water molecules, and aggregate on the surface layer of the contact layer to form a water film. As the water evaporates, it accelerates the dissipation of surface charges, and then the water content in the environment and the freshness of fruits can be effectively monitored through changes in electrical signals. To our knowledge, there has been no report on using an enzymatic hydrolysis green treatment method under mild conditions to improve the output electrical signal of cellulose paper-based TENG and explore its application in the field of self-powered fruit and vegetable freshness detection. Summary of the Invention

[0005] Based on this, the purpose of the present invention is to provide a fully green preparation method of a high-performance cellulose friction material and its application in real-time detection of fruit and vegetable freshness.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0007] A fully green preparation method of a high-performance cellulose friction material, comprising the following steps:

[0008] The ground pulp is cultured in a mixed solution of xylanase solution and citric acid-sodium citrate buffer solution for a period of time for enzymatic hydrolysis, and then the enzymatically hydrolyzed pulp is sheeted using a paper former to obtain white paper.

[0009] Based on the above technical solution, preferably, the pulp is wood pulp, straw pulp or cotton pulp, preferably softwood pulp.

[0010] Based on the above technical solution, preferably, the concentration of citric acid in the citric acid-sodium citrate buffer solution is 0.02-0.04 mol / L, preferably 0.02-0.03 mol / L; the concentration of sodium citrate is 0.02-0.05 mol / L, preferably 0.03-0.04 mol / L.

[0011] Based on the above technical solutions, preferably, in the mixed solution of the xylanase solution and the citric acid-sodium citrate buffer solution, the volume ratio of the xylanase solution to the citric acid-sodium citrate buffer solution is 1:400 to 2000, preferably 1:600 to 1000.

[0012] Based on the above technical solutions, preferably, the method for grinding softwood pulp in the above step is as follows: Tear the pulp board into small pieces of 1-25 cm 2 and soak them in water, then use a PFI refiner for refining; the rotational speed of the refiner beater disc is 600-1440 revolutions per minute, and the refining time is 3-20 minutes.

[0013] Based on the above technical solutions, preferably, the pulp enzymatic hydrolysis culture method is: Put the wet pulp and the enzyme solution into the citric acid-sodium citrate buffer solution, store them in a conical flask, seal it, and place it in a water bath shaker for culturing for different times.

[0014] Based on the above technical solutions, preferably, the enzyme activity of the xylanase in the above step is 60000 U / g.

[0015] Based on the above technical solutions, preferably, the xylanase solution is prepared from solid xylanase and citric acid-sodium citrate buffer solution. Activate the solid xylanase with the citric acid-sodium citrate buffer solution, and the concentration of the prepared xylanase solution is 200-1000 U / ml.

[0016] Based on the above technical solutions, preferably, the xylanase is KDN06 xylanase.

[0017] Based on the above technical solutions, preferably, the enzymatic hydrolysis conditions in the above step are: temperature 40-60 °C, preferably 45-55 °C, environmental pH 4.0-6.0, preferably 4.8-5.0, shaker rotational speed 100-200 rpm, preferably 120-150 rpm, time 2-200 h, preferably 12-120 h, more preferably 48-72 h.

[0018] Based on the above technical solutions, preferably, the ratio of the pulp by absolute dry mass to the xylanase solution is 2-10 g: 0.1-0.8 ml, preferably 4 g: 0.25 ml.

[0019] Based on the above technical solutions, preferably, the preparation process of the pulp and the enzyme solution is as follows: For 2-10 g (preferably 4 g) of absolute dry softwood pulp, corresponding to 0.1-0.8 ml (preferably 0.25 ml) of KDN06 xylanase solution, culture it for 12-120 h under the conditions of 45-55 °C, pH 4.8-5.0, and 120-150 rpm. Based on the above technical solutions, preferably, use a sheet former to make sheets from the enzymatically hydrolyzed pulp, and the basis weight of the paper is 60-120 g / m 2, the obtained white paper has a thickness of 0.10 - 0.30 mm.

[0020] The present invention also relates to protecting the high-performance cellulose friction material (paper-based triboelectric nanogenerator) manufactured by the above-mentioned all-green production method.

[0021] The present invention also relates to the application of the high-performance cellulose friction material prepared by the above method in the field of fruit and vegetable freshness indication (real-time detection), especially in the field of self-powered fruit and vegetable freshness indication.

[0022] Based on the above technical solutions, preferably, the enzymatically hydrolyzed paper (high-performance cellulose friction material) prepared above is used as the positive friction material, and the commercial electrode polyvinylidene fluoride (PVDF) is used as the negative friction material to construct a TENG, and the freshness of fruits and vegetables is detected according to the change in humidity in the detection packaging microenvironment.

[0023] In the present invention, softwood pulp is cultured with xylanase solution and then sheeted with a paper former to obtain a white paper sheet. The enzymatic hydrolysis treatment will change the microscopic morphology of the fiber surface, and the residual xylanase will adhere to the fiber surface. The polar group amino group in its main component protein will improve the electron-donating ability of the paper. Using the obtained enzymatically hydrolyzed paper as the positive triboelectric material and the commercial electrode polyvinylidene fluoride (PVDF) as the negative triboelectric material, an enzymatically hydrolyzed paper-based triboelectric nanogenerator (TENG) is prepared. The output electrical signal of the TENG has a good linear relationship with the change in humidity in the microenvironment of fruit and vegetable storage, and the freshness of stored fruits and vegetables is detected in real time according to the change in the electrical signal. The product prepared by the present invention has the advantages of simple process flow, low energy consumption, easy batch and large-area production, and good repeatability between product batches. The all-green production method endows it with high biocompatibility, environmental friendliness, good sensitivity, and is conducive to monitoring the freshness state of fruits and vegetables at any time.

[0024] Compared with the prior art, the preparation method provided by the present invention has the following advantages:

[0025] 1. The paper-based TENG prepared by the present invention adopts an all-green production method and has the characteristics of high performance (high dielectric properties, high mechanical strength, high sensitivity, high stability and degradability, etc.), and is expected to be widely used in the field of fruit and vegetable freshness indication.

[0026] 2. The production process of the paper-based TENG prepared by the all-green production method involved in the present invention is simple, has low energy consumption, is easy for batch and large-area production, and has good repeatability between product batches. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1To implement the triboelectric signal output of the enzymatically hydrolyzed paper TENG in Examples 1-4. In the figure: Due to the enzymatic hydrolysis treatment of the pulp fibers, changes in the surface morphology of the fibers and the structure of the enzyme itself occur, generating V OC , I SC , and Q SC , all of which are enhanced. When the enzymatic hydrolysis time is 72 h, the maximum V OC is 91.48 V, the maximum I SC is 4.84 μA, and the maximum Q SC is 73.48 nC.

[0028] Figure 2 shows the change in the dielectric constant of the enzymatically hydrolyzed paper prepared in Example 1. In the figure: The dielectric constant of the enzymatically hydrolyzed paper is better than that of the blank paper. The dielectric constant is related to the polarity of the electrolyte molecules. The increase in the dielectric constant of the enzymatically hydrolyzed paper is mainly due to the fact that the main component of the enzyme is protein, and protein is composed of amino acids with polar groups. The amino group is an electron-donating group, which will enhance the electron-donating ability of the enzymatically hydrolyzed paper as the triboelectric positive electrode.

[0029] Figure 3 shows the stability test of the enzymatically hydrolyzed paper TENG prepared in Example 1. In the figure: During 7500 repeated measurements in an air environment at room temperature and a relative humidity of 27-30% RH, the voltage does not decrease.

[0030] Figure 4 shows the change in the electrical signal of the enzymatically hydrolyzed paper TENG prepared in Example 1 at room temperature under different relative humidity conditions (25-95% RH).

[0031] Figure 5 shows the change in the fruit freshness to be monitored by the enzymatically hydrolyzed paper TENG prepared in Example 1.

[0032] Figure 6 shows the electrical signal evaluation of the fruit freshness indication by the enzymatically hydrolyzed paper TENG prepared in Example 1.

[0033] Figure 7 shows the mechanical property test of the enzymatically hydrolyzed paper and the blank paper prepared in Examples 1-4. In the figure: The enzymatic hydrolysis treatment can improve the elongation at break and tensile strength of the paper. When the enzymatic hydrolysis time is 48 h, the maximum elongation at break is 2%, and the maximum tensile strength is 8.9 MPa. Specific embodiments

[0034] The following embodiments are provided to better further understand the present invention. They are not limited to the described optimal embodiment, and do not limit the content and protection scope of the present invention. Any product obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other existing technologies that is the same as or similar to the present invention falls within the protection scope of the present invention.

[0035] In the examples, if the specific experimental procedures or conditions are not specified, they are all carried out according to the operations or conditions of the conventional experimental procedures described in the literature in this field. For the reagents or instruments whose manufacturers are not specified, they are all conventional reagents that can be obtained through commercial purchase.

[0036] Example 1

[0037] (1) Preparation of citric acid-sodium citrate buffer solution: Accurately weigh 4.8 g of citric acid, dissolve it in 750 ml of deionized water, add 7.9 g of sodium citrate while stirring with a glass rod. After dissolution, transfer it to a 1000 ml volumetric flask, make up the volume to 1000 ml with water, mix well and then pour it into a 1000 ml beaker. Measure the pH value with a pH meter, and the pH value should be in the range of 4.8 - 5.0.

[0038] (2) Preparation of KDN06 xylanase solution: The xylanase solution is prepared from solid xylanase and citric acid-sodium citrate buffer solution. Activate the solid xylanase with citric acid-sodium citrate buffer solution, and the concentration of the prepared xylanase solution is 800 U / ml.

[0039] (3) Tear the softwood pulp board into 2×2 cm squares, soak it in water for 4 h. After soaking, weigh 300 g of wet pulp and put it into the PFI refiner. The rotational speed of the refiner beating cutter head is 1440 revolutions per minute, and refine for 350 s. According to 4 g of absolute dry pulp corresponding to 0.25 ml of KDN06 xylanase solution and 200 ml of citric acid-sodium citrate buffer solution, culture it at 55 °C, pH 4.8 - 5.0, and 150 rpm for 48 h. The enzymatically hydrolyzed pulp is sheeted according to the paper basis weight of 80 g / m 2 Sheet making: First, put the wet pulp into the cylinder, stir evenly, then filter and form. Then put the wet paper sheet into a hot press dryer and hot press and dry it at 93 °C to form a white paper with a diameter of 20 cm and a thickness of 0.15 mm.

[0040] (4) Attach the enzymatically hydrolyzed paper to a copper tape as the friction positive electrode layer, and attach polyvinylidene fluoride (PVDF) to another copper tape on the other side as the friction negative electrode layer, then the enzymatically hydrolyzed paper TENG can be obtained. The working mode of the TENG adopts the vertical contact-separation type.

[0041] Example 2

[0042] (1) Preparation of citric acid-sodium citrate buffer solution: Accurately weigh 5.0 g of citric acid, dissolve it in 750 ml of deionized water, add 8.5 g of sodium citrate while stirring with a glass rod. After dissolution, transfer it to a 1000 ml volumetric flask, make up the volume to 1000 ml with water, mix well and then pour it into a 1000 ml beaker. Measure the pH value with a pH meter, and the pH value should be in the range of 4.8 - 5.0.

[0043] (2) Preparation of KDN06 xylanase solution: The xylanase solution is prepared from solid xylanase and citric acid - trisodium citrate buffer solution. The solid xylanase is activated with citric acid - trisodium citrate buffer solution, and the concentration of the prepared xylanase solution is 800 U / ml.

[0044] (3) Tear the softwood pulp board into 2×2 cm squares, soak them in water for 5 h. After soaking, weigh 300 g of wet pulp and put it into the PFI refiner. The rotational speed of the beating cutter head of the refiner is 1440 revolutions per minute, and beat for 280 s. Mix the refined pulp according to 2 g of absolute dry pulp corresponding to 0.25 ml of KDN06 xylanase solution and 200 ml of citric acid - trisodium citrate buffer solution, and culture at 55 °C, pH 4.8 - 5.0, and 150 rpm for 12 h. The enzymatically hydrolyzed pulp is sheeted according to the paper basis weight of 80 g / m 2 Sheet making. First, put the wet pulp into the cylinder, stir evenly, then filter and form. Then put the wet paper sheet into a hot - press dryer and hot - press dry and form at 93 °C to obtain a white paper with a diameter of 20 cm and a thickness of 0.15 mm.

[0045] (4) Attach the enzymatically hydrolyzed paper to a copper strip as the friction positive layer, and attach polyvinylidene fluoride (PVDF) to another copper strip on the other side as the friction negative layer, then the enzymatically hydrolyzed paper TENG can be obtained. The working mode of the TENG adopts the vertical contact - separation type.

[0046] Example 3

[0047] (1) Preparation of citric acid - trisodium citrate buffer solution: Accurately weigh 4.7 g of citric acid, dissolve it in 750 ml of deionized water, stir with a glass rod and add 8.2 g of trisodium citrate. After dissolution, transfer it to a 1000 ml volumetric flask, make up the volume to 1000 ml with water, mix well and then pour it into a 1000 ml beaker. Measure the pH value with a pH meter, and the pH value should be in the range of 4.8 - 5.0.

[0048] (2) Preparation of KDN06 xylanase solution: The xylanase solution is prepared from solid xylanase and citric acid - trisodium citrate buffer solution. The solid xylanase is activated with citric acid - trisodium citrate buffer solution, and the concentration of the prepared xylanase solution is 800 U / ml.

[0049] (3) Tear the softwood pulp board into 2×2 cm squares, soak them in water for 7 h. After soaking, weigh 300 g of the wet pulp and put it into the PFI refiner. The rotational speed of the beating cutter head of the refiner is 1440 revolutions per minute, and refine for 560 s. According to 3 g of absolute dry pulp corresponding to 0.3 ml of KDN06 xylanase solution and 200 ml of citric acid - trisodium citrate buffer solution, culture the refined pulp for 72 h at 55 °C, pH 4.8 - 5.0, and 150 rpm. The enzymatically hydrolyzed pulp is made into sheets according to a paper basis weight of 80 g / m 2 Sheet forming: First, put the wet pulp into the cylinder, stir evenly, then filter and form. Then put the wet paper sheet into a hot press dryer and hot press and dry it at 93 °C to obtain a white paper with a diameter of 20 cm and a thickness of 0.15 mm.

[0050] (4) Attach the enzymatically hydrolyzed paper to a copper strip as the friction positive electrode layer, and attach polyvinylidene fluoride (PVDF) to another copper strip on the other side as the friction negative electrode layer, then the enzymatically hydrolyzed paper TENG can be obtained. The working mode of the TENG adopts the vertical contact - separation type.

[0051] Example 4

[0052] (1) Preparation of citric acid - trisodium citrate buffer solution: Accurately weigh 4.9 g of citric acid, dissolve it in 750 ml of deionized water, stir with a glass rod and add 9.0 g of trisodium citrate. After dissolution, transfer it to a 1000 ml volumetric flask, make up the volume to 1000 ml with water, mix well and then pour it into a 1000 ml beaker. Measure the pH value with a pH meter, and the pH value should be in the range of 4.8 - 5.0.

[0053] (2) Preparation of KDN06 xylanase solution: The xylanase solution is prepared from solid xylanase and citric acid - trisodium citrate buffer solution. Activate the solid xylanase with the citric acid - trisodium citrate buffer solution, and the concentration of the prepared xylanase solution is 800 U / ml.

[0054] (3) Tear the softwood pulp board into 2×2 cm squares, soak them in water for 4 h. After soaking, weigh 300 g of the wet pulp and put it into the PFI refiner. The rotational speed of the beating cutter head of the refiner is 1440 revolutions per minute, and refine for 770 s. According to 5 g of absolute dry pulp corresponding to 0.35 ml of KDN06 xylanase solution and 250 ml of citric acid - trisodium citrate buffer solution, culture the refined pulp for 108 h at 55 °C, pH 4.8 - 5.0, and 150 rpm. The enzymatically hydrolyzed pulp is made into sheets according to a paper basis weight of 80 g / m 2 Sheet forming: First, put the wet pulp into the cylinder, stir evenly, then filter and form. Then put the wet paper sheet into a hot press dryer and hot press and dry it at 93 °C to obtain a white paper with a diameter of 20 cm and a thickness of 0.15 mm.

[0055] (4) Attach the enzymatically hydrolyzed paper to a copper tape as the frictional positive electrode layer, and attach polyvinylidene fluoride (PVDF) to another copper tape on the other side as the frictional negative electrode layer, then the enzymatically hydrolyzed paper TENG can be obtained. The working mode of the TENG adopts the vertical contact-separation mode.

[0056] Comparative example

[0057] Prepared according to the method of Example 1, except that the pulp fibers were not enzymatically hydrolyzed, and finally a blank paper material was obtained. It was used as the frictional positive electrode layer of the paper-based TENG, that is, the blank paper-based triboelectric nanogenerator.

[0058] Example 5

[0059] Performance test of manufacturing high-performance paper-based triboelectric nanogenerators by a fully green production method and evaluation of fruit and vegetable freshness indication:

[0060] 1. Triboelectric output performance

[0061] Test method:

[0062] Use the enzymatically hydrolyzed paper material as the frictional positive electrode layer and polyvinylidene fluoride (PVDF) as the frictional negative electrode layer. Cut the enzymatically hydrolyzed paper material and a PVDF film into rectangles of 50×50 mm, and attach them to two copper tapes respectively to make enzymatically hydrolyzed paper / Cu electrodes and PVDF / Cu electrodes. Test in the vertical contact-separation mode at room temperature.

[0063] Compare the effects of the paper-based TENGs prepared in the above Example 1 and the comparative example. The results are as Figure 1 .

[0064] As Figure 1 can be seen, the triboelectric performance of the enzymatically hydrolyzed paper TENG obtained in Example 1 is significantly better than that of the comparative example.

[0065] Similarly, the enzymatically hydrolyzed papers prepared in Examples 2-4 have good triboelectric output performance.

[0066] 2. Dielectric properties

[0067] Examine the dielectric properties of the paper-based TENGs prepared in Example 1 and the comparative example. The results are as Figure 2 shown.

[0068] As Figure 2 can be seen, the product prepared in Example 1 has excellent dielectric properties, and the dielectric constant has increased from 5.8 to 6.5. The increase in the dielectric constant means that the enzymatically hydrolyzed paper TENG has a higher capacitance capacity than the blank paper TENG.

[0069] Similarly, the enzymatically hydrolyzed paper TENGs prepared in Examples 2-4 also have good dielectric properties.

[0070] 3. Stability

[0071] Test method:

[0072] Measure 7500 times repeatedly in an air environment at room temperature and a relative humidity of 27 - 30% RH.

[0073] The enzymatic paper TENG prepared in Example 1 was used to investigate the stability performance of the product, and the results are as Figure 3 shown.

[0074] As Figure 3 can be seen, the product has good stability performance, and the voltage does not decrease during 7500 cycles, meeting the stability performance requirements in the practical application of TENG.

[0075] Similarly, the enzymatic paper TENGs prepared in Examples 2 - 4 and the comparative examples all have good stability.

[0076] 4. Humidity - sensitive characteristics:

[0077] The enzymatic paper TENG prepared in Example 1 was used to investigate the humidity - sensitive characteristics of the product, and the results are as Figure 4 shown.

[0078] As Figure 4 can be seen, the product prepared in Example 1 has good humidity - sensitive characteristics, meeting the humidity - sensitive requirements in its practical application for indicating the freshness of fruits and vegetables.

[0079] Similarly, the paper - based TENGs prepared in Examples 2 - 4 all have good humidity - sensitive characteristics.

[0080] 5. Fruit freshness indication effect:

[0081] Test method:

[0082] After carefully washing and drying the freshly purchased strawberries, place the enzymatic paper, the hygrometer and the strawberries together in a sealed container and place it at room temperature. Take pictures regularly to observe the changes in the appearance of the strawberries.

[0083] The enzymatic paper TENG prepared in Example 1 was used to investigate the freshness indication effect of the product, and the results are as Figure 5 and Figure 6 shown.

[0084] As Figure 5 and Figure 6 can be seen, the product prepared in Example 1 has good fruit freshness indication effect, can timely monitor the process of fruit spoilage, and meets the timely monitoring requirements in the practical application of fruit freshness.

[0085] Similarly, the enzymatically hydrolyzed paper TENGs prepared in Examples 2-4 all have good effects on indicating the freshness of fruits and vegetables.

[0086] A fully green preparation method of a high-performance cellulose friction material provided by the present invention and its application in real-time detection of fruit and vegetable freshness belong to the field of self-powered fruit and vegetable freshness indication. Experimental results show that the prepared enzymatically hydrolyzed paper TENG has good biocompatibility, is green and environmentally friendly, has lower costs, and is easy to mass-produce in batches.

Claims

1. A fully green preparation method for a high-performance cellulose friction material, characterized in that: It includes the following steps: Cultivate the ground pulp in a mixed solution of xylanase solution and citric acid - trisodium citrate buffer for a period of time for enzymatic hydrolysis, and then use a sheet former to make sheets of the enzymatically hydrolyzed pulp to obtain white paper. The ratio of the absolutely dry mass of the pulp to the xylanase solution is 2 - 10 g: 0.1 - 0.8 ml; the xylanase solution is prepared from xylanase and citric acid - trisodium citrate buffer, and the concentration of the xylanase solution is 200 - 1000 U / ml. The enzyme activity of the xylanase is 60000 U / g. The enzymatic hydrolysis conditions are: temperature 40 - 60 °C, pH 4.0 - 6.0, shaker speed 100 - 200 rpm, cultivation time 2 - 200 h.

2. The method according to claim 1, characterized in that: The pulp is wood pulp, straw pulp or cotton pulp.

3. The method according to claim 1, characterized in that: The pulp is softwood pulp.

4. The method according to claim 1, characterized in that: In the citric acid - trisodium citrate buffer, the concentration of citric acid is 0.02 - 0.04 mol / L, and the concentration of trisodium citrate is 0.02 - 0.05 mol / L.

5. The method according to claim 1, characterized in that: In the mixed solution of the xylanase solution and citric acid - trisodium citrate buffer, the volume ratio of the xylanase solution to citric acid - trisodium citrate buffer is 1: 400 - 2000.

6. The method according to claim 1, characterized in that: The method for grinding the pulp is: tear the pulp board into small pieces, soak it in water, and then grind it with a pulper.

7. The method according to claim 1, characterized in that: The basis weight of the white paper is 60 to 120 g / m 2 , and the thickness of the prepared paper is 0.10 to 0.30 mm.

8. A high - performance cellulose friction material prepared by any of the methods of claims 1 - 7.

9. The application of the high - performance cellulose friction material according to claim 8 in the real - time detection of the freshness of fruits and vegetables.

10. The application according to claim 9, wherein, Using the high - performance cellulose friction material as the positive friction material and polyvinylidene fluoride as the negative friction material, detect the freshness of fruits and vegetables according to the change in humidity in the detection packaging micro - environment.

11. The application according to claim 9, characterized in that, The application of the high - performance cellulose friction material in the field of self - powered freshness indicators for fruits and vegetables.

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