CN112229317A

CN112229317A - Flexible sensing film with large deformation performance and monitoring function and preparation method thereof

Info

Publication number: CN112229317A
Application number: CN202011071059.1A
Authority: CN
Inventors: 袁涌
Original assignee: Dunhuda Wuhan Technology Co ltd
Current assignee: Dunhuda Wuhan Technology Co ltd
Priority date: 2020-10-09
Filing date: 2020-10-09
Publication date: 2021-01-15

Abstract

The invention discloses a flexible sensing membrane with large deformation performance and a monitoring function and a preparation method thereof, wherein two ends of a carbon nano tube polyurethane composite material film are respectively connected with a conducting wire through conductive silver paste to form the flexible sensing membrane, and the preparation method comprises the following steps: s1, preparing a carboxylated carbon nanotube; s2, preparing a DMF dispersion liquid of the carbon nano tube; s3, preparing a DMF solution of medical thermoplastic polyurethane; s4 mixing and preparing the solution; s5 drop coating and drying to obtain the carbon nano tube polyurethane composite material; s6, electrode film preparation is configured. The flexible sensing membrane can effectively realize monitoring of large deformation of structures such as bridges and the like, has the functions of strain and tension monitoring, and still has higher sensitivity under the large deformation of 300-350%; the preparation process is simple, the operability is strong, the repeatability is good, and the like.

Description

Flexible sensing film with large deformation performance and monitoring function and preparation method thereof

Technical Field

The invention belongs to the technical field of sensing membrane materials, and particularly relates to a flexible sensing membrane with thermoplastic polyurethane as a matrix and carbon nano tubes added and a preparation method thereof.

Background

The carbon nano tube has good mechanical property and ultrahigh conductivity as the carbon-based conductive material with the most research potential at present, has good compatibility with most flexible base materials, and is very suitable for preparing flexible functional composite materials, wherein the flexible conductive composite materials are mainly prepared from the good mechanical and electrical properties of the carbon nano tube by combining the flexibility and the tensile property of the flexible base materials. The flexible conductive composite material has wide application prospect, such as flexible sensors, aircraft flexible skins, material structure health monitoring and the like. The flexible sensor is an important application field, and the flexible sensor made of the carbon nano tube conductive composite material is based on piezoresistive effect and can realize the monitoring of strain by converting the strain into resistance change.

Because the strain range of the traditional flexible sensor monitoring is very small, the method is difficult to be applied to the structural health monitoring of the large-scale cross-sea and cross-river bridge. Large bridges are affected by wind vibration or earthquake, and many parts of the bridges are greatly deformed, but the large deformation is difficult to measure by devices such as strain gauges and laser measuring instruments in many cases.

Thermoplastic polyurethane elastomers (TPU for short) are block-type linear high-molecular polymers which contain urethane groups (-NHCOO-) in molecular chains and have excellent elasticity and physical and mechanical properties. Generally, the polyurethane is prepared by the mutual reaction of diisocyanate and hydroxyl-terminated polyether/polyester/polycaprolactone polyol and micromolecular alcohol/amine as chain extender. Conventional TPUs have excellent mechanical properties, elasticity, processing flowability, abrasion resistance, transparency, low temperature resistance and other properties.

However, for special application fields such as military industry, automobiles, wires and cables, engineering accessories and the like, the differences still exist in the aspects of special functions such as flame retardance, wear resistance, static resistance and the like, so that the functional TPU with special performance or enhanced performance is produced. TPU's are becoming increasingly popular because of their superior performance and environmental protection concepts. The TPU HAs wide hardness range of 60 HA-95 HA, is wear-resistant, oil-resistant, transparent and good in elasticity, and is widely applied to the fields of daily necessities, sports goods, toys, decorative materials and the like. The compounding of the carbon nano tube and the thermoplastic polyurethane integrates the advantages of the carbon nano tube and the thermoplastic polyurethane into a whole, and becomes a material with a novel function.

Disclosure of Invention

Aiming at least one of the defects or the improvement requirements in the prior art, the invention provides a preparation method of a flexible sensing film with large deformation performance and a monitoring function thereof, wherein the flexible sensing film can effectively realize the monitoring of large deformation of structures such as bridges and the like, has the functions of strain and tension monitoring and still has higher sensitivity under the large deformation; the preparation process is simple, the operability is strong, the repeatability is good, and the like.

To achieve the above object, according to one aspect of the present invention, there is provided a flexible sensor film having large deformation performance and a monitoring function thereof, characterized in that: the conductive carbon nanotube polyurethane composite material comprises a carbon nanotube polyurethane composite material film, conductive silver paste and a lead, wherein two ends of the carbon nanotube polyurethane composite material film are respectively connected with one lead through the conductive silver paste;

the percolation threshold value of the flexible sensing membrane is 3-5 wt%, and the conductivity is 3 multiplied by 10^-5～2×10^-3S/m; coefficient of strain sensitivity (k ═ Δ R/R)₀) /epsilon) is more than or equal to 25; the effective stretching range is 0-350%.

In order to achieve the above object, according to another aspect of the present invention, there is provided a method for manufacturing a flexible sensor film having a large deformation property and a monitoring function thereof, comprising the steps of:

the method comprises the following steps:

(1) acidifying the carbon nano tube to prepare a carboxylated carbon nano tube: adding a carbon nano tube into protonic acid for mixing, wherein the reaction temperature is 50-70 ℃, condensing and refluxing for 3-5 h in an ultrasonic cleaner with the ultrasonic power of 200W and the ultrasonic frequency of 40KHz, diluting with 250-350 ml of deionized water after ultrasonic treatment, performing suction filtration by using a microfiltration membrane with the diameter of 0.2 mu m, repeatedly washing with the deionized water until the deionized water is neutral, finally drying for 12h at 80 ℃, and grinding to powder, thus obtaining the carboxylated carbon nano tube; wherein, the amount of the carbon nano tube added per 100ml of protonic acid is 0.1 g-0.5 g.

The carbon nanotube material is a carbon nanotube with high purity and high length-diameter ratio prepared by a Chemical Vapor Deposition (CVD) method, and has good conductivity. Additives commonly used in polymers, catalysts, electromagnetic wave absorption and shielding, energy conversion, lithium battery anodes, hydrogen storage, nanotube composites (by filling or coating), sensors, reinforcement in composites, supercapacitors, and the like. The carbon nano tube is a multi-walled carbon nano tube (MWNT) with the model of XFM31, the purity of 95 (wt)%, the outer diameter of 50nm, the length of less than 10 mu m and the conductivity (S/cm) >100, and is produced by Nanjing XFNANO Materials Tech.

The protonic acid is one of nitric acid and sulfuric acid, or a mixed acid of sulfuric acid and nitric acid;

(2) and (2) preparing DMF (dimethyl formamide) dispersion liquid of the carbon nano tube, namely adding the carboxylated carbon nano tube prepared in the step (1) into 20ml of DMF solvent, and performing ultrasonic dispersion for 2-4 h under the conditions of 200W of power and 40KHz of frequency to obtain a mixed solution I.

(3) And preparing a DMF (dimethyl formamide) solution of polyurethane to obtain a mixed solution II.

The polyurethane is Thermoplastic Polyurethane (TPU), Tecoflex, model LM-95A, density 1100kg/m3, hardness 94Shore A, available from Lubrizol, USA. 30g of TPU were dissolved in 100ml of DMF to give a mixed solution II.

(4) And stirring the mixed solution I and the mixed solution II at 100-120 ℃ for 1-2 h until the mixed solution I and the mixed solution II are uniformly stirred to obtain a mixed solution III.

(5) And pouring the mixed solution III into a mold, standing at room temperature until the mixed solution III is uniformly distributed in the mold, and putting the mold into a vacuum drying oven at 100-120 ℃ to remove DMF (dimethyl formamide) to obtain the carbon nano tube polyurethane composite material.

(6) And cooling the carbon nanotube polyurethane composite material, and connecting two leads to two ends of the carbon nanotube polyurethane composite material respectively by using conductive silver paste to obtain the flexible sensing film.

Preferably, in step S5, the mixed solution iii is uniformly distributed in the mold by pouring the mixed solution iii into a micropipette, and dropping the mixed solution iii on the flat glass sheet by using the micropipette at normal temperature to form a thin liquid layer.

The above-described preferred features may be combined with each other as long as they do not conflict with each other.

Generally, compared with the prior art, the above technical solution conceived by the present invention has the following beneficial effects:

1. according to the flexible sensing film with large deformation performance and monitoring function and the preparation method thereof, the flexible sensing film can effectively realize monitoring of large deformation of structures such as bridges and the like, has the functions of strain and tension monitoring, and still has high sensitivity under large deformation; the preparation process is simple, the operability is strong, the repeatability is good, and the like.

2. The flexible sensing membrane with the large deformation performance and the monitoring function has the large deformation performance of 300-350% and can be used for monitoring the large deformation of civil engineering structures such as bridges and the like.

3. According to the flexible sensing film with the large deformation performance and the monitoring function of the flexible sensing film, medical-grade thermoplastic polyurethane is adopted as polyurethane, the carbon nano tubes are well dispersed, and the composite material still has a good strain sensing function under the large deformation of 300-350%.

4. The invention successfully provides a new way for preparing the novel functional TPU nano composite material, and also provides a new thought and exploration for developing the novel high-performance polymer nano composite material in the future, so that the invention has innovative research value in academia and has wide social and economic benefits and strategic values in practical application.

Drawings

Fig. 1 is a schematic view showing an SEM photograph of the composite thin film.

FIG. 2 is a schematic diagram showing a tensile test performed on a flexible sensing membrane.

FIG. 3 is a graph of stress, strain, rate of change of resistance over time for a flexible sensing film under a stretch-shrink cycle.

FIG. 4 is a graph of rate of change of resistance versus strain reflecting the strain sensitivity coefficient of a flexible sensing film.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other. The present invention will be described in further detail with reference to specific embodiments.

Example 1

1) Preparing a solution: adding 150.8mg of carboxylated multi-walled carbon nanotubes into 20ml of DMF solution, performing ultrasonic treatment to form stable graphite oxide DMF dispersion liquid, and performing ultrasonic dispersion for 2-4 hours under the conditions of 200W of power and 40KHz of frequency to obtain a mixed solution I; 30g of TPU (Tecoflex, model LM-95A, manufactured by Lubrizol, USA) was dissolved in 100ml of DMF to obtain a mixed solution II; and stirring the mixed solution I and the mixed solution II at 100-120 ℃ for 1-2 h until the mixed solution I and the mixed solution II are uniformly stirred to obtain a mixed solution III.

2) And (3) dripping: and pouring the mixed solution III into a micropipette, and carrying out drip coating on a flat glass sheet with the size of 15cm x 15cm by using the micropipette at normal temperature to form a thin liquid layer.

3) Drying: and drying the obtained thin liquid layer in an oven at 120-150 ℃, removing DMF (dimethyl formamide), controlling the thickness of the film to be 0.07-0.1 mm, and drying to obtain the composite film (marked as 1# MCNT/TPU). The composite film was subjected to electron microscope analysis to obtain an SEM image shown in FIG. 1.

4) Configuring an electrode: and respectively connecting two leads to two ends of the carbon nano tube thermoplastic polyurethane composite film by using conductive silver paste to obtain the flexible sensing film (the content of the carbon nano tube is 3 wt%).

5) And (3) breaking test: as shown in FIG. 2, the film material was subjected to a stretch-break test on a universal tensile machine, and the elongation at break was 300% to 350%.

6) And (3) performing a sensitivity test: and (3) performing stretching circulation on the composite material by using a universal material stretching machine, connecting a resistance instrument at an electrode of the flexible sensing membrane, and performing real-time resistance recording in the stretching circulation process. Tensile strain is 300% -350%; the stretching rate is 1 mm/s; the experiment was carried out for 5 cycles in total to obtain a graph of the change rate of the stress, strain and resistance of the flexible sensor film with time shown in fig. 3. And a graph of the rate of change of the resistance of the flexible sensing film with strain was plotted, as shown in fig. 4, and the strain sensitivity coefficient (k ═ Δ R/R) was measured₀) Has a value of/epsilon) of 25, wherein R₀The initial resistance value of the flexible sensing film, Δ R, and the strain value of the flexible sensing film (═ Δ l/l), respectively₀)，l₀The initial length of the flexible sensing film is delta l, and the length change value of the flexible sensing film is delta l.

Example 2

1) Preparing a solution: adding 303mg of carboxylated multi-walled carbon nanotubes into 40ml of DMF solution, performing ultrasonic treatment to form stable graphite oxide DMF dispersion liquid, and performing ultrasonic dispersion for 2-4 hours under the conditions of 200W of power and 40KHz of frequency to obtain a mixed solution I; 30g of TPU (Tecoflex, model LM-95A, manufactured by Lubrizol, USA) was dissolved in 100ml of DMF to obtain a mixed solution II; pouring a TPU solution which is swelled in DMF in advance after the TPU solution is stabilized, stirring for 2-5 h at normal temperature, ultrasonically dispersing for 1-2 h at 100W, removing air in the pasty liquid, and standing for 1-2 h; and stirring the mixed solution I and the mixed solution II at 100-120 ℃ for 1-2 h until the mixed solution I and the mixed solution II are uniformly stirred to obtain a mixed solution III.

3) Drying: and drying the obtained thin liquid layer in an oven at 120-150 ℃, removing DMF (dimethyl formamide), controlling the thickness of the film to be 0.07-0.1 mm, and drying to obtain the composite film (marked as 2# MCNT/TPU). The composite film was subjected to electron microscope analysis to obtain an SEM image shown in FIG. 1.

4) Configuring an electrode: and respectively connecting two leads to two ends of the carbon nano tube thermoplastic polyurethane composite film by using conductive silver paste to obtain the flexible sensing film (the content of the carbon nano tube is 5 wt%).

6) And (3) performing a sensitivity test: and (3) performing stretching circulation on the composite material by using a universal material stretching machine, connecting a resistance instrument at an electrode of the flexible sensing membrane, and performing real-time resistance recording in the stretching circulation process. Tensile strain is 300% -350%; the stretching rate is 1 mm/s; the experiment was performed for a total of 5 cycles. And a graph of the change rate of the resistance of the flexible sensing membrane with the strain is drawn, as shown in fig. 4, and the measured strain sensitivity coefficient is 30.

In summary, compared with the prior art, the scheme of the invention has the following significant advantages:

It will be appreciated that the embodiments of the system described above are merely illustrative, in that elements illustrated as separate components may or may not be physically separate, may be located in one place, or may be distributed over different network elements. Some or all of the modules can be selected according to actual needs to achieve the purpose of the scheme of the embodiment. One of ordinary skill in the art can understand and implement it without inventive effort.

In addition, it should be understood by those skilled in the art that in the specification of the embodiments of the present invention, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.

In the description of the embodiments of the invention, numerous specific details are set forth. It is understood, however, that embodiments of the invention may be practiced without these specific details. In some instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description. Similarly, it should be appreciated that in the foregoing description of exemplary embodiments of the invention, various features of the embodiments of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects.

However, the disclosed method should not be interpreted as reflecting an intention that: that is, the claimed embodiments of the invention require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of an embodiment of this invention.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the embodiments of the present invention, and not to limit the same; although embodiments of the present invention have been described in detail with reference to the foregoing embodiments, it should be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. Flexible sensing membrane with big deformation performance and monitor function, its characterized in that: the conductive carbon nanotube polyurethane composite material comprises a carbon nanotube polyurethane composite material film, conductive silver paste and a lead, wherein two ends of the carbon nanotube polyurethane composite material film are respectively connected with one lead through the conductive silver paste; the polyurethane is medical thermoplastic polyurethane;

the percolation threshold value of the flexible sensing membrane is 3-5 wt%, and the conductivity is 3 multiplied by 10^-5～2×10^-3S/m; the strain sensitivity coefficient is more than or equal to 25; the effective stretching range is 0-350%.

2. The preparation method of the flexible sensing membrane with large deformation performance and monitoring function is characterized by comprising the following steps:

s1, acidifying the carbon nano tube to prepare a carboxylated carbon nano tube;

s2, preparing a DMF dispersion liquid of the carbon nano tube, and performing ultrasonic dispersion to obtain a mixed solution I;

s3, preparing a DMF (dimethyl formamide) solution of medical thermoplastic polyurethane to obtain a mixed solution II;

s4, stirring the mixed solution I and the mixed solution II at a preset temperature range for a preset time till the mixed solution I and the mixed solution II are uniformly stirred to obtain a mixed solution III;

s5, pouring the mixed solution III into a mold, standing at room temperature until the mixed solution III is uniformly distributed in the mold, and putting the mold into a vacuum drying oven to remove DMF to obtain the carbon nano tube polyurethane composite material;

and S6, cooling the carbon nanotube polyurethane composite material, and respectively connecting two leads to two ends of the carbon nanotube polyurethane composite material by conductive silver paste to obtain the flexible sensing film.

3. The method for preparing a flexible sensor film having high deformability and a function of monitoring the same as claimed in claim 2, wherein:

step S1 specifically includes:

adding the carbon nano tube into protonic acid for mixing, wherein the reaction temperature is 50-70 ℃, condensing and refluxing for 3-5 h in an ultrasonic cleaner, diluting with 250-350 ml of deionized water after ultrasonic treatment, then performing suction filtration by using a microporous filter membrane, repeatedly washing with the deionized water until the deionized water is neutral, finally drying at a preset temperature for a preset time, and grinding the mixture to be powder, thereby obtaining the carboxylated carbon nano tube.

4. The method for preparing a flexible sensor film having high deformability and a function of monitoring the same as claimed in claim 3, wherein:

in step S1, the amount of carbon nanotubes added per 100ml of protonic acid is 0.1g to 0.5 g.

5. The method for preparing a flexible sensor film having high deformability and a function of monitoring the same as claimed in claim 3, wherein:

the carbon nano tube is prepared by adopting a chemical vapor deposition method.

6. The method for preparing a flexible sensor film having high deformability and a function of monitoring the same as claimed in claim 3, wherein:

the carbon nano-tube is a multi-wall carbon nano-tube.

7. The method for preparing a flexible sensor film having high deformability and a function of monitoring the same as claimed in claim 3, wherein:

the protonic acid is one of nitric acid and sulfuric acid, or a mixed acid of sulfuric acid and nitric acid.

8. The method for preparing a flexible sensor film having high deformability and a function of monitoring the same as claimed in claim 2, wherein:

step S2 specifically includes:

and (4) adding the carboxylated carbon nanotube prepared in the step (S1) into a DMF solvent, and performing ultrasonic dispersion for 2-4 h to obtain a mixed solution I.

9. The method for preparing a flexible sensor film having high deformability and a function of monitoring the same as claimed in claim 2, wherein:

step S3 specifically includes:

and dissolving the thermoplastic polyurethane in a DMF solvent to obtain a mixed solution II.

10. The method for preparing a flexible sensor film having high deformability and a function of monitoring the same as claimed in claim 2, wherein:

in step S5, the method for uniformly distributing the mixed solution iii in the mold is to pour the mixed solution iii into a micropipette, and drip-coat the flat glass sheet with the micropipette at normal temperature to form a thin liquid layer.