CN113999442A

CN113999442A - Highly sensitive humidity sensing conductive rubber film and preparation method thereof

Info

Publication number: CN113999442A
Application number: CN202111188206.8A
Authority: CN
Inventors: 徐传辉; 郑仲杰; 林梦转
Original assignee: Guangxi University
Current assignee: Guangxi University
Priority date: 2021-10-12
Filing date: 2021-10-12
Publication date: 2022-02-01
Anticipated expiration: 2041-10-12
Also published as: CN113999442B

Abstract

The invention discloses a highly sensitive humidity sensing conductive rubber film and a preparation method thereof, wherein the highly sensitive humidity sensing conductive rubber film is prepared from the following components in parts by weight: 100 parts of rubber latex, 10-40 parts of aldehyde modified natural polysaccharide, 10-30 parts of nano silver, 1-5 parts of polyvinylpyrrolidone and 2500 parts of distilled water. The product of the invention is produced by a safe formula, has mild reaction conditions, only needs the temperature of 30-50 ℃, has high humidity sensing performance, and can be applied to monitoring the breathing condition of a human body and monitoring the relative humidity change of the environment. The preparation method of the product is simple, is favorable for saving the production cost, is easy to master, is convenient to popularize and is expected to realize large-scale production.

Description

Highly sensitive humidity sensing conductive rubber film and preparation method thereof

Technical Field

The invention belongs to the technical field of sensing materials, and particularly relates to a highly sensitive humidity sensing conductive rubber film and a preparation method thereof.

Background

Humidity is closely related to our daily life. Research shows that the rheumatism is easy to suffer from the dampness when people work and live in places with high humidity for a long time. When the humidity is too low, the evaporation of the skin on the surface of the human body is accelerated, and the dry air can take away the moisture of the human body more easily, so that the skin is dry, the nasal mucosa is stimulated, and the respiratory system diseases are easily induced. In addition, excessive or insufficient air humidity can cause the propagation and spread of some bacteria and viruses. Scientifically determined, when the air humidity is more than 65% or less than 40%, the germs breed fastest, and when the relative humidity is 45% -55%, the germs die faster. Thus, humans typically feel the most comfortable at 45-55% relative humidity. In addition, the humidity level in the warehouse determines the ripening and preservation of the fruit. Many other goods such as chemicals, cigarettes, wine, sausages, wood, art, integrated circuits, etc. must also be stored at a certain humidity or at zero humidity. Therefore, air conditioning devices are used in many warehouses, museums, libraries, computer centers, and certain factories (e.g., microelectronics industry) to control the humidity within the room.

In the prior art, there are various main forms of sensors for measuring humidity, wherein an electrical humidity meter is a form of humidity sensor commonly used in industry, and the principle is as follows: the hygroscopic substance can change the electrical property of the hygroscopic substance in response to the change of the relative humidity of the environment, and has little dependence on the temperature, the resistance and the capacitance between electrodes of the hygroscopic film or the coating are changed by the water vapor in the air, and the moisture value is converted through the point position change value and is used for manufacturing an electrical humidity meter. Has the characteristics of high corresponding speed and wide humidity measuring range.

In recent years, materials that achieve a humidity response with natural polysaccharides as a matrix have been widely reported. However, due to the weak conductivity, pure natural polysaccharide-based humidity responsive materials cannot respond quickly to changes in external humidity, resulting in a longer response (often greater than 10 s). Such response speed has not been well suited to the high-speed developments in the field of electronics in recent years. Therefore, there is a need to increase the speed of the response of natural polysaccharides to humidity. It has been shown that during latex film formation, natural polysaccharides can be regenerated between latex particles to form a continuous isolated network. When the matrix contains ions, the material can conduct electricity well under the condition of water or high humidity, so that the conducting capacity of the natural high polymer is improved. In addition, the use of the rubber latex endows the natural polysaccharide with good flexibility, and further expands the application of the natural polysaccharide. However, the improvement of the conductivity of the natural polysaccharide by the above method has a fatal disadvantage that the material conductivity is greatly reduced or even non-conductive in the absence of water or low humidity.

And (3) searching keywords: humidity sensitivity, humidity sensing, electronic humidity, resistance, capacitance, rubber, polysaccharide, silver nano-meter and polyvinyl pyrrolidone

1. A composite flexible humidity-sensitive sensor and a preparation method thereof; application No.: CN 202110620813.0; the applicant: the university of west ampere traffic; and (3) abstract: a composite flexible humidity sensor and a preparation method thereof, comprising a two-dimensional material/LiCl coating and a paper-based substrate; the two-dimensional material/LiCl coating covers the paper-based substrate, and an electrode is arranged between the paper-based substrate and the two-dimensional material/LiCl coating. Meanwhile, the composite material of the two-dimensional material and the lithium chloride can conduct electrons and ions, and the composite humidity sensing mechanism is beneficial to improving the performance of the humidity sensitive detector.

2. A humidity sensitive capacitor and a preparation method thereof; application No.: CN 201510405840.0; the applicant: shanghai Chang hope Meteorological science and technology, Inc.; and (3) abstract: a humidity sensitive capacitor and its preparation method, the said humidity sensitive capacitor is made up of substrate, bottom electrode, humidity sensitive polyimide coating and top electrode; wherein the humidity-sensitive polyimide is prepared by reacting organic silicon diamine, aromatic diamine and aromatic dianhydride. The preparation method comprises the following steps: cleaning a substrate with a cleaning solution, then placing the substrate into a drying oven for drying, then manufacturing a lower electrode by vacuum evaporation, leading a lower electrode lead wire with JP-6 conductive adhesive, spin-coating a humidity-sensitive polyimide precursor solution, imidizing, manufacturing an upper electrode by vacuum evaporation, slicing, washing with deionized water, drying, screening, performing surface modification, and leading an upper electrode lead wire with JP-6 conductive adhesive to obtain the humidity-sensitive capacitor. The invention has the advantages of high sensitivity, small wet retardation, simple manufacturing process, low cost and the like, and has good marketization prospect.

3. A biphenyl polyimide humidity sensitive capacitor and a preparation method thereof; application No.: CN 201510405830.7; the applicant: university of east China; shanghai Rui rabbit electronic materials, Inc.; and (3) abstract: a biphenyl type polyimide humidity sensitive capacitor and a preparation method thereof, wherein the humidity sensitive capacitor consists of a substrate, a lower electrode, a biphenyl type humidity sensitive polyimide coating and an upper electrode; wherein, the biphenyl type humidity sensitive polyimide is obtained by the reaction of 3,3 '-diamino-4, 4' -dihydroxybiphenyl, aromatic diamine and aromatic dianhydride. The preparation method comprises the following steps: cleaning a substrate with cleaning solution, placing the substrate into a drying oven for drying, then manufacturing a lower electrode by vacuum evaporation, leading a lower electrode lead with JP-6 conductive adhesive, spin-coating a biphenyl type humidity-sensitive polyimide precursor solution, imidizing, manufacturing an upper electrode by vacuum evaporation, slicing, washing with deionized water, drying, screening, performing surface modification, leading an upper electrode lead with JP-6 conductive adhesive, and manufacturing the biphenyl type polyimide humidity-sensitive capacitor. The invention has the advantages of high sensitivity, small wet retardation, simple manufacturing process, low cost and the like, and has good marketization prospect.

Although the prior art relates to some flexible humidity-sensitive materials and preparation methods thereof, no document is provided for preparing a high-sensitivity humidity-sensitive material rubber membrane by using a rubber latex as a substrate and using natural polysaccharide and a nano silver material as a compound.

Disclosure of Invention

The invention prepares a highly sensitive humidity sensing conductive rubber film by using rubber latex/natural polysaccharide. On the premise of keeping a certain mechanical property strength, in the latex film forming period, as the silver nano sheets are spontaneously stacked to form an integrated continuous silver network, the product has better conductivity. Therefore, the product has high humidity response function due to the hydrophilic natural polysaccharide and the silver nanoparticles with high specific surface. Compared with the conductive material which is generally only formed by uniformly dispersing silver nano particles in a matrix, the product can more easily form a conductive path and improve the conductive performance because the matrix contains the integrated silver nano sheets.

The highly sensitive humidity sensing conductive rubber film is prepared by a simple method. The aldehyde modified natural polysaccharide is rich in a large amount of polar groups, such as hydroxyl, carboxyl and the like. These groups can interact with moisture in the air through hydrogen bonding, and adsorb moisture in the air. Then, the adsorbed moisture is rapidly diffused into the matrix due to the presence of the integrated silver network formed by stacking the silver nano-sheets. Meanwhile, the electrolyte (aldehyde-based natural polysaccharide reacts to form carboxylate, and the reaction equation is as follows) in the matrix is dissociated by moisture to form ammonium positive ions and carboxyl negative ions. Under the action of the electric field, the ions move directionally. Under different humidity, the amount of dissociated ions is also different, so that resistance change is generated, and a humidity response function is brought.

The reaction equation of the sodium hydroformylation modification of the carboxymethyl starch is as follows:

the formula for the reaction of the silver ammonia solution and the aldehyde carboxymethyl starch sodium to generate the silver nano-particles is as follows:

the formula of the silver ammonia solution reacting with the aldehyde carboxymethyl starch sodium to generate the silver nanosheet is as follows:

the invention can be realized by the following technical scheme:

a highly sensitive humidity sensing conductive rubber film comprises the following raw material components in parts by weight: 100 parts of rubber latex, 10-40 parts of aldehyde modified natural polysaccharide, 10-30 parts of nano silver, 1-5 parts of polyvinylpyrrolidone and 2500 parts of distilled water.

The rubber latex is carboxyl styrene-butadiene rubber latex, carboxyl nitrile-butadiene rubber latex, styrene-butadiene rubber latex or natural rubber latex.

The aldehyde group modified natural polysaccharide comprises starch, sodium carboxymethyl starch, chitosan, carboxymethyl chitosan or sodium carboxymethyl cellulose.

The nano silver comprises silver nanoparticles and silver nanosheets. The nano silver comprises silver nanoparticles and silver nanosheets, the silver nanoparticles are 50-250 nm in diameter, and the silver nanosheets are 40 nm in thickness and 0.4-10 microns in length.

The preparation method comprises the following steps:

(1) at room temperature, firstly, using sodium periodate to aldehyde-modify the natural polysaccharide in aqueous solution;

(2) after reacting for 1-6 hours, removing small molecules in the natural polysaccharide water solution by using a dialysis bag;

(3) dissolving aldehyde modified natural polysaccharide in water, and dividing into two parts, wherein one part is added with polyvinylpyrrolidone to obtain solution A, and the other part is not added with polyvinylpyrrolidone to obtain solution B;

(4) respectively adding silver ammonia solution with the same amount into the solution A and the solution B, reacting for 0.5-2 hours to generate silver nano particles in the solution A and silver nano sheets in the solution B;

(5) and mixing the solution A, the solution B and the rubber latex, stirring for 0.5-2 hours, carrying out tape casting to form a membrane, and drying to obtain the highly sensitive humidity sensing conductive rubber membrane.

The silver ammonia Ag (NH)₃)₂The concentration of the OH solution is 0.42-1.25 wt%.

After the dialyzed natural polysaccharide aqueous solution is obtained in the step (2), the natural polysaccharide aqueous solution can be freeze-dried for later use, and a proper amount of natural polysaccharide dry powder is taken to carry out the operation in the step (3).

Compared with the prior art, the invention has the following advantages and effects:

1) according to the invention, the humidity sensing rubber film with high sensitivity is formed by utilizing the hydrophilic effect of the aldehyde-modified natural polysaccharide and the improved material conductivity of the silver nano-sheet and silver nano-particle conductive filler generated by reaction. In the material, silver nano sheets are mutually stacked to form an integrated conductive path; the silver nanoparticles with high specific surface energy and natural polymers play a hydrophilic role together, so that the humidity response performance of the material is improved, the material can quickly respond to humidity and is converted into an electric signal for output. Compared with commercially available electronic hygrometers, the humidity sensing adhesive film provided by the invention has faster and more sensitive humidity response.

2) Based on the excellent performance of the invention, compared with the traditional natural polysaccharide-based material, the invention has better flexibility, can be suitable for wider application scenes, and can be used for devices such as a humidity alarm device, a human breath monitoring device and the like; compared with the commercially available electronic hygrometers, the humidity sensor has a faster humidity response function.

3) The preparation method is simple, complex synthesis is not needed, the reaction time is short, and the required reaction device is simple; the reaction temperature is normal temperature, so the method has the advantages of low time consumption, low cost, low energy consumption, low industrial implementation difficulty and convenient industrial popularization.

Drawings

FIG. 1 is a SEM micrograph of comparative example 3, only silver nanoplates formed without the addition of polyvinylpyrrolidone;

FIG. 2 is a SEM micrograph of comparative example 4 showing only silver nanoparticles formed with the addition of polyvinylpyrrolidone;

FIGS. 3 and 4 are SEM micrographs of example 4 with silver nanoplates spontaneously stacked to form an integrated continuous silver network;

FIG. 5 is a diagram of a humidity sensor adhesive film in example 4;

FIG. 6 is the relative resistance change at 33%, 57%, 75% and 93% relative humidity in the order named for example 4;

FIG. 7 shows the relative resistance changes recorded during respiration monitoring in example 4.

Detailed Description

Examples 1 to 4 differ in that the nano silver content accounts for 5 wt%, 10 wt%, 20 wt%, 30 wt% of the rubber matrix, respectively;

example 1

10 g of sodium carboxymethyl starch is firstly dissolved in 300 ml of water at room temperature, 5.8 g of sodium periodate is added to carry out aldehyde modification, and after 2 hours of reaction, a dialysis bag (diameter 44 mm, molecular cut-off 8000- "14000 Da) is used to remove small molecules in the solution. It is then freeze dried and left to stand. 4 g of aldehyde-modified sodium carboxymethyl starch are dissolved in 120 ml of water and divided into two portions on average, one of which is added with 0.2 g of polyvinylpyrrolidone and the other is not. And adding a silver-ammonia solution into the two parts of aldehyde carboxymethyl starch sodium solution, wherein the silver content accounts for 5 wt% of the rubber matrix, and reacting for 1 hour to respectively generate silver nano particles and silver nano sheets. Finally, the two mixed solutions were mixed with the rubber latex and stirred for 0.5 hour. The high-sensitivity humidity sensing conductive rubber film prepared from the rubber latex/natural polysaccharide is obtained after the film is dried by a tape casting film forming method.

Example 2

10 g of sodium carboxymethyl starch is firstly dissolved in 300 ml of water at room temperature, 5.8 g of sodium periodate is added to carry out aldehyde modification, and after 2 hours of reaction, a dialysis bag (diameter 44 mm, molecular cut-off 8000- "14000 Da) is used to remove small molecules in the solution. It is then freeze dried and left to stand. 4 g of aldehyde-modified sodium carboxymethyl starch are dissolved in 120 ml of water and divided into two portions on average, one of which is added with 0.2 g of polyvinylpyrrolidone and the other is not. Adding silver-ammonia solution into the two parts of aldehyde carboxymethyl starch sodium solution, wherein the silver content accounts for 10 wt% of the rubber matrix, and reacting for 1 hour to respectively generate silver nano particles and silver nano sheets. Finally, the two mixed solutions were mixed with the rubber latex and stirred for 0.5 hour. The high-sensitivity humidity sensing conductive rubber film prepared from the rubber latex/natural polysaccharide is obtained after the film is dried by a tape casting film forming method.

Example 3

10 g of sodium carboxymethyl starch is firstly dissolved in 300 ml of water at room temperature, 5.8 g of sodium periodate is added to carry out aldehyde modification, and after 2 hours of reaction, a dialysis bag (diameter 44 mm, molecular cut-off 8000- "14000 Da) is used to remove small molecules in the solution. It is then freeze dried and left to stand. 4 g of aldehyde-modified sodium carboxymethyl starch are dissolved in 120 ml of water and divided into two portions on average, one of which is added with 0.2 g of polyvinylpyrrolidone and the other is not. Adding silver-ammonia solution into the two parts of aldehyde carboxymethyl starch sodium solution, wherein the silver content accounts for 20 wt% of the rubber matrix, and reacting for 1 hour to respectively generate silver nano particles and silver nano sheets. Finally, the two mixed solutions were mixed with the rubber latex and stirred for 0.5 hour. The high-sensitivity humidity sensing conductive rubber film prepared from the rubber latex/natural polysaccharide is obtained after the film is dried by a tape casting film forming method.

Example 4

10 g of sodium carboxymethyl starch is firstly dissolved in 300 ml of water at room temperature, 5.8 g of sodium periodate is added to carry out aldehyde modification, and after 2 hours of reaction, a dialysis bag (diameter 44 mm, molecular cut-off 8000- "14000 Da) is used to remove small molecules in the solution. It is then freeze dried and left to stand. 4 g of aldehyde-modified sodium carboxymethyl starch are dissolved in 120 ml of water and divided into two portions on average, one of which is added with 0.2 g of polyvinylpyrrolidone and the other is not. Adding silver-ammonia solution into the two parts of aldehyde carboxymethyl starch sodium solution, wherein the silver content accounts for 30 wt% of the rubber matrix, and reacting for 1 hour to respectively generate silver nano particles and silver nano sheets. Finally, the two mixed solutions were mixed with the rubber latex and stirred for 0.5 hour. The high-sensitivity humidity sensing conductive rubber film prepared from the rubber latex/natural polysaccharide is obtained after the film is dried by a tape casting film forming method.

Comparative example 1

Comparative example 1 contains no silver nanoplatelets and only 30 wt% silver nanoparticles;

10 g of sodium carboxymethyl starch is firstly dissolved in 300 ml of water at room temperature, 5.8 g of sodium periodate is added to carry out aldehyde modification, and after 2 hours of reaction, a dialysis bag (diameter 44 mm, molecular cut-off 8000- "14000 Da) is used to remove small molecules in the solution. It is then freeze dried and left to stand. 4 g of aldehyde-modified sodium carboxymethyl starch was dissolved in 120 ml of water, and 0.4 g of polyvinylpyrrolidone was added. Adding silver-ammonia solution into the aldehyde natural polysaccharide solution, wherein the silver content accounts for 30 wt% of the rubber matrix, and reacting for 1 hour to generate silver nanoparticles. Finally, it was mixed with the rubber latex and stirred for 0.5 hour. And (3) carrying out tape casting film forming, and drying to obtain the conductive rubber film.

Comparative example 2

Comparative example 2 contains no silver nanoparticles, only 30 wt% silver-containing nanoplates;

10 g of sodium carboxymethyl starch is firstly dissolved in 300 ml of water at room temperature, 5.8 g of sodium periodate is added to carry out aldehyde modification, and after 2 hours of reaction, a dialysis bag (diameter 44 mm, molecular cut-off 8000- "14000 Da) is used to remove small molecules in the solution. It is then freeze dried and left to stand. 4 g of aldehyde-modified sodium carboxymethyl starch are dissolved in 120 ml of water. Adding a silver-ammonia solution into the aldehyde natural polysaccharide solution, wherein the silver content accounts for 30 wt% of the rubber matrix, and reacting for 1 hour to generate the silver nanosheet. Finally, it was mixed with the rubber latex and stirred for 0.5 hour. And (3) carrying out tape casting film forming, and drying to obtain the conductive rubber film.

The conductivity experiment method of silver nano-particles with different contents comprises the following steps:

the samples prepared in examples 1 to 4 and comparative examples 1 to 4 were cut into rectangles of 10X 30 mm, respectively, and the electrical conductivity of the products was measured. The specific implementation method is that a rectangular sample is fixed on a non-conductive polypropylene plastic plate, probes are clamped at two ends and connected with a digital multimeter (DMM 7510, Keithley, USA), and the resistance is obtained through testing. The conductivity of the product was calculated by equation 1.

Where σ is the conductivity of the product, L is the length of the product, here 0.03 m, R is the resistance obtained by means of a digital multimeter, b is the sample width, here 0.01 m, d is the sample thickness, on average 0.0003 m.

TABLE 1 conductivity (S/m) of examples 1-4, comparative example 1

Comparing the results in table 1, it can be seen that the conductivity of the material is proportional to the content of the added nano silver, and in the same case of containing 30 wt% of nano silver, the conductivity of the combination of the silver nanoparticles and the silver nanosheets is significantly higher than that of the rubber membrane material containing the pure silver nanoparticles and the pure silver nanosheets. From this, it can be demonstrated that the combination of silver nanoparticles + silver nanoplates has a high sensitivity of humidity.

Note: when the content of the nano silver ions is more than 30 wt%, the silver ions can not be completely reduced to generate simple substance silver.

Example 5

In examples 5-8, the total silver content was unchanged at 30 wt% of the rubber matrix, with the difference that the ratio of silver nanoparticles to silver nanoplates was 3: 1, 2: 1, 1: 2, 1: 3, respectively;

10 g of sodium carboxymethyl starch is firstly dissolved in 300 ml of water at room temperature, 5.8 g of sodium periodate is added to carry out aldehyde modification, and after 2 hours of reaction, a dialysis bag (diameter 44 mm, molecular cut-off 8000- "14000 Da) is used to remove small molecules in the solution. It is then freeze dried and left to stand. 4 g of aldehyde-modified sodium carboxymethyl starch is dissolved in 120 ml of water and then divided into two parts according to the ratio of 3: 1, namely a solution A and a solution B, wherein 0.3 g of polyvinylpyrrolidone is added into the solution A, and the solution B is not added. And similarly, adding a silver-ammonia solution into the solutions A and B according to the proportion of 3: 1, wherein the total silver content accounts for 30 wt% of the rubber matrix, and reacting for 1 hour to respectively generate silver nano particles and silver nano sheets. Finally, the two mixed solutions were mixed with the rubber latex and stirred for 0.5 hour. The high-sensitivity humidity sensing conductive rubber film prepared from the rubber latex/natural polysaccharide is obtained after the film is dried by a tape casting film forming method.

Example 6

10 g of sodium carboxymethyl starch is firstly dissolved in 300 ml of water at room temperature, 5.8 g of sodium periodate is added to carry out aldehyde modification, and after 2 hours of reaction, a dialysis bag (diameter 44 mm, molecular cut-off 8000- "14000 Da) is used to remove small molecules in the solution. It is then freeze dried and left to stand. 4 g of aldehyde-modified sodium carboxymethyl starch is dissolved in 120 ml of water and divided into two parts according to the ratio of 2: 1, namely a solution A and a solution B, wherein 0.27 g of polyvinylpyrrolidone is added into the solution A, and the solution B is not added. And similarly, adding a silver-ammonia solution into the solutions A and B according to the ratio of 2: 1, wherein the total silver content accounts for 30 wt% of the rubber matrix, and reacting for 1 hour to respectively generate silver nano particles and silver nano sheets. Finally, the two mixed solutions were mixed with the rubber latex and stirred for 0.5 hour. The high-sensitivity humidity sensing conductive rubber film prepared from the rubber latex/natural polysaccharide is obtained after the film is dried by a tape casting film forming method.

Example 7

10 g of sodium carboxymethyl starch is firstly dissolved in 300 ml of water at room temperature, 5.8 g of sodium periodate is added to carry out aldehyde modification, and after 2 hours of reaction, a dialysis bag (diameter 44 mm, molecular cut-off 8000- "14000 Da) is used to remove small molecules in the solution. It is then freeze dried and left to stand. 4 g of aldehyde-modified sodium carboxymethyl starch is dissolved in 120 ml of water and then divided into two parts according to the ratio of 1: 2, namely a solution A and a solution B, wherein 0.13 g of polyvinylpyrrolidone is added into the solution A, and the solution B is not added. And similarly, adding a silver-ammonia solution into the solutions A and B according to the proportion of 1: 2, wherein the total silver content accounts for 30 wt% of the rubber matrix, and reacting for 1 hour to respectively generate silver nano particles and silver nano sheets. Finally, the two mixed solutions were mixed with the rubber latex and stirred for 0.5 hour. The high-sensitivity humidity sensing conductive rubber film prepared from the rubber latex/natural polysaccharide is obtained after the film is dried by a tape casting film forming method.

Example 8

10 g of sodium carboxymethyl starch is firstly dissolved in 300 ml of water at room temperature, 5.8 g of sodium periodate is added to carry out aldehyde modification, and after 2 hours of reaction, a dialysis bag (diameter 44 mm, molecular cut-off 8000- "14000 Da) is used to remove small molecules in the solution. It is then freeze dried and left to stand. 4 g of aldehyde-modified sodium carboxymethyl starch is dissolved in 120 ml of water and divided into two parts according to the ratio of 1: 3, namely a solution A and a solution B, wherein 0.13 g of polyvinylpyrrolidone is added into the solution A, and the solution B is not added. And similarly, adding a silver-ammonia solution into the solution A and the solution B according to the proportion of 1: 3, wherein the total silver content accounts for 30 wt% of the rubber matrix, and reacting for 1 hour to respectively generate silver nano particles and silver nano sheets. Finally, the two mixed solutions were mixed with the rubber latex and stirred for 0.5 hour. The high-sensitivity humidity sensing conductive rubber film prepared from the rubber latex/natural polysaccharide is obtained after the film is dried by a tape casting film forming method.

The experimental method for the proportion of the silver nanoparticles and the silver nanosheets in different proportions comprises the following steps:

the samples prepared in examples 4 to 8 were cut into a rectangular shape of 10X 30 mm, and the conductivity of the product was measured. The specific implementation method is that a rectangular sample is fixed on a non-conductive polypropylene plastic plate, probes are clamped at two ends and connected with a digital multimeter (DMM 7510, Keithley, USA), and the resistance is obtained through testing. The conductivity of the product was calculated by equation 1.

TABLE 2 examples 4-8 conductivity (S/m)

As can be seen from comparison table 2, the conductive performance is the best when the ratio of the silver nanoparticles to the silver nanoplates is 1: 1.

Example 9

Examples 9 to 12 differ in that: under the same condition, the used natural polysaccharide is starch, chitosan, carboxymethyl chitosan or sodium carboxymethyl cellulose;

10 g of starch was dissolved in 300 ml of water at room temperature, 5.8 g of sodium periodate was added to aldehyde-modify the starch, and after 2 hours of reaction, small molecules in the solution were removed by a dialysis bag (diameter 44 mm, molecular cut-off 8000-. It is then freeze dried and left to stand. 4 g of aldehyde-modified starch were dissolved in 120 ml of water and divided equally into two portions, one of which was added with 0.2 g of polyvinylpyrrolidone and the other was not. Adding silver-ammonia solution into the two aldehyde starch solutions, wherein the silver content accounts for 30 wt% of the rubber matrix, and reacting for 1 hour to respectively generate silver nano particles and silver nano sheets. Finally, the two mixed solutions were mixed with the rubber latex and stirred for 0.5 hour. The high-sensitivity humidity sensing conductive rubber film prepared from the rubber latex/natural polysaccharide is obtained after the film is dried by a tape casting film forming method.

Example 10

10 g of chitosan was dissolved in 300 ml of water at room temperature, 5.8 g of sodium periodate was added to perform aldehyde modification, and after 2 hours of reaction, small molecules in the solution were removed by a dialysis bag (diameter 44 mm, molecular cut-off 8000-. It is then freeze dried and left to stand. 4 g of aldehyde-modified chitosan was dissolved in 120 ml of water and divided into two portions on average, one of which was added with 0.2 g of polyvinylpyrrolidone and the other was not added. Adding silver-ammonia solution into the two aldehyde chitosan solutions, wherein the silver content accounts for 30 wt% of the rubber matrix, and reacting for 1 hour to respectively generate silver nano particles and silver nano sheets. Finally, the two mixed solutions were mixed with the rubber latex and stirred for 0.5 hour. The high-sensitivity humidity sensing conductive rubber film prepared from the rubber latex/natural polysaccharide is obtained after the film is dried by a tape casting film forming method.

Example 11

10 g of carboxymethyl chitosan was dissolved in 300 ml of water at room temperature, 5.8 g of sodium periodate was added to perform aldehyde modification, and after 2 hours of reaction, small molecules in the solution were removed by a dialysis bag (diameter 44 mm, molecular cut-off 8000-. It is then freeze dried and left to stand. 4 g of aldehyde-modified carboxymethyl chitosan was dissolved in 120 ml of water and divided into two portions on average, one of which was added with 0.2 g of polyvinylpyrrolidone and the other was not added. Adding silver ammonia solution into the two aldehyde carboxymethyl chitosan solutions, wherein the silver content accounts for 30 wt% of the rubber matrix, and reacting for 1 hour to respectively generate silver nano particles and silver nano sheets. Finally, the two mixed solutions were mixed with the rubber latex and stirred for 0.5 hour. The high-sensitivity humidity sensing conductive rubber film prepared from the rubber latex/natural polysaccharide is obtained after the film is dried by a tape casting film forming method.

Example 12

10 g of sodium carboxymethylcellulose is firstly dissolved in 300 ml of water at room temperature, 5.8 g of sodium periodate is added to carry out aldehyde modification, and after 2 hours of reaction, a dialysis bag (diameter of 44 mm, molecular cut-off of 8000-. It is then freeze dried and left to stand. 4 g of aldehyde-modified sodium carboxymethylcellulose was dissolved in 120 ml of water and divided into two portions on average, one portion containing 0.2 g of polyvinylpyrrolidone and the other portion containing no polyvinylpyrrolidone. And adding a silver-ammonia solution into the two aldehyde sodium carboxymethylcellulose solutions, wherein the silver content accounts for 30 wt% of the rubber matrix, and reacting for 1 hour to respectively generate silver nanoparticles and silver nanosheets. Finally, the two mixed solutions were mixed with the rubber latex and stirred for 0.5 hour. The high-sensitivity humidity sensing conductive rubber film prepared from the rubber latex/natural polysaccharide is obtained after the film is dried by a tape casting film forming method.

TABLE 3 examples 9-12 conductivity (S/m)

As can be seen by comparing Table 3, the difference in conductivity between examples 10-12 is not large except for example 9.

Therefore, with tables 1, 2 and 3, we chose to use the more economical sodium carboxymethyl starch for the aldehydization modification, samples with a matrix containing 30 wt% nanosilver and a ratio of silver nanoparticles to silver nanoplates of 1: 1 for the subsequent study of humidity sensing.

Comparative example 3

In comparative example 3, polyvinylpyrrolidone was not added, and only 15 wt% silver nanoplates were formed;

10 g of sodium carboxymethyl starch is firstly dissolved in 300 ml of water at room temperature, 5.8 g of sodium periodate is added to carry out aldehyde modification, and after 2 hours of reaction, a dialysis bag (diameter 44 mm, molecular cut-off 8000- "14000 Da) is used to remove small molecules in the solution. It is then freeze-dried and left for subsequent use; 4 g of aldehyde-modified sodium carboxymethyl starch were dissolved in 120 ml of water. Adding silver-ammonia solution into the aldehyde natural polysaccharide solution, wherein the silver content accounts for 15 wt% of the rubber matrix, and reacting for 1 hour. Finally, it was mixed with the rubber latex and stirred for 0.5 hour. And (3) carrying out tape casting film forming, and drying to obtain the conductive rubber film. And (4) brittle fracture is carried out by using liquid nitrogen, and the appearance of the product is observed under a scanning electron microscope.

Comparative example 4

In comparative example 4, polyvinylpyrrolidone was added, and no silver nanosheets were formed, but only 15 wt% silver nanoparticles were formed;

at room temperature, 10 g of sodium carboxymethyl starch is firstly dissolved in 300 ml of water, 5.8 g of sodium periodate is added to carry out hydroformylation modification, and after 2 hours of reaction, a dialysis bag (diameter of 44 mm, molecular cut-off 8000-14000 Da) is used for removing small molecules in the solution; it is then freeze dried and left to stand. 4 g of aldehyde-modified sodium carboxymethyl starch was dissolved in 120 ml of water, and 0.4 g of polyvinylpyrrolidone was added. Adding silver-ammonia solution into the aldehyde natural polysaccharide solution, wherein the silver content accounts for 15 wt% of the rubber matrix, and reacting for 1 hour to generate silver nanoparticles. Finally, it was mixed with the rubber latex and stirred for 0.5 hour. Carrying out tape casting film forming, and drying to obtain a conductive rubber film; and (4) brittle fracture is carried out by using liquid nitrogen, and the appearance of the product is observed under a scanning electron microscope.

Microscopic scanning microstructure morphology by electron microscope:

brittle fracture of the material by using liquid nitrogen, observing the appearance of a brittle fracture surface by using a scanning electron microscope,

as seen from fig. 1, comparative example 3 had only silver nanoplates formed without the addition of polyvinylpyrrolidone;

as seen from fig. 2, comparative example 4 had only silver nanoparticles formed when polyvinylpyrrolidone was added;

as seen in fig. 3 and 4, example 4 silver nanoplates spontaneously stack to form an integrated continuous silver network.

Material deformation test:

the rubber film obtained in example 4 was cut into a dumbbell shape with a cutter, and subjected to the following deformation:

1, bending and deforming the material, wherein the bending angle is from 0 to 540 degrees;

2, performing torsional deformation on the material, wherein the torsional angle is from 0 to 360 degrees;

3, performing tensile deformation on the material, wherein the tensile strain is 0-50%;

the results of the deformation experiment are shown in figure 5 below;

the high humidity-sensitive conductive rubber membrane obtained by the invention is proved to have better flexibility and strength.

Relative resistance change test:

the resistance changes of the material of example 4 at 33%, 57%, 75% and 93% relative humidity were recorded in this order. The specific test method was that the dried sample was cut into rectangular strips of 10X 30X 0.3 mm, fixed with polypropylene plastic plates, and then the probes were attached to digital multimeters (DMM 7510, Keithley, USA) by clipping the ends of the material. Successive changes in the resistance of the material were recorded after exposure to 33%, 57%, 75% and 93% relative humidity in that order. The results are shown in FIG. 6;

in the ordinate of FIG. 6, (R-R0)/R0, where R represents the resistance measured in real time, R0 represents the initial resistance, and the whole of (R-R0)/R0 represents the change in the relative resistance of the material with time;

as can be seen from fig. 6, the moisture-sensitive conductive rubber film shows significantly different relative resistance changes at different humidities of 33%, 57%, 75% and 93%, and can realize instant resistance response at different humidities.

Breath test experiments:

the rubber film material obtained in example 4 was cut into rectangular strips of 10X 30X 0.3 mm, fixed with polypropylene plastic plates, and then probes were attached to both ends of the material and connected to a digital multimeter (DMM 7510, Keithley, USA); the material was placed in front of the nose of a healthy volunteer at 27 ℃ in an indoor environment, approximately 3 cm from the nose, and the volunteer kept breathing uniformly. The curve graph of the resistance fluctuation change is obtained, the curve graph is highly consistent with the frequency of human breathing, and the application of the method to the breathing detection is proved to be completely feasible, and the curve graph is shown in fig. 7.

Claims

1. A highly sensitive humidity sensing conductive rubber film is characterized by comprising the following raw material components in parts by weight: 100 parts of rubber latex, 10-40 parts of aldehyde modified natural polysaccharide, 10-30 parts of nano silver, 1-5 parts of polyvinylpyrrolidone and 2500 parts of distilled water.

2. The highly sensitive humidity sensing conductive rubber film as claimed in claim 1, wherein the rubber latex is carboxylated styrene-butadiene rubber latex, carboxylated nitrile-butadiene rubber latex, styrene-butadiene rubber latex or natural rubber latex.

3. The highly sensitive humidity sensing conductive rubber film according to claim 1, wherein the aldehyde-modified natural polysaccharide comprises starch, sodium carboxymethyl starch, chitosan, carboxymethyl chitosan or sodium carboxymethyl cellulose.

4. The highly sensitive humidity sensing conductive rubber membrane according to claim 1, wherein the nano silver comprises silver nano particles and silver nano sheets, the diameter of the silver nano particles is 50-250 nm, the thickness of the silver nano sheets is 40 nm, and the length of the silver nano sheets is 0.4-10 μm.

5. The highly sensitive humidity sensing conductive rubber membrane according to claim 1, wherein the preparation method comprises the following steps:

6. The method for preparing a highly sensitive humidity sensing conductive rubber membrane according to claim 5Characterized in that: ag ammonia (NH)₃)₂The concentration of the OH solution is 0.42-1.25 wt%.

7. The method for preparing a highly sensitive humidity sensing conductive rubber membrane according to claim 5, wherein: after the dialyzed natural polysaccharide aqueous solution is obtained in the step (2), the natural polysaccharide aqueous solution can be freeze-dried for later use, and a proper amount of natural polysaccharide dry powder is taken to carry out the operation in the step (3).

8. The highly sensitive humidity sensing conductive rubber membrane of claim 1, wherein the membrane is used for monitoring human respiration and monitoring relative humidity changes in the environment.