Method for recycling residue from MXene preparation and use of residue in biosensor

Abstract

The present disclosure discloses a method for recycling a residue from MXene preparation, including the following steps: recovering a bottom residual sediment produced in preparation of MXene through etching in a minimally intensive layer delamination (MILD) method, mixing the bottom residual sediment with a molten polyvinyl alcohol (PVA) solution, and drying to prepare a Ti.sub.3C.sub.2T.sub.x-Ti.sub.3AlC.sub.2/PVA composite film. The present disclosure can effectively utilize a residue from an MXene process to prepare a composite film with both excellent mechanical properties and electrical conductivity. The composite film has extremely-high sensitivity for stress-strain and prominent stability, and is suitable for flexible connection and sensing of biosensors, robots, or the like. The present disclosure has significant economic and environmental benefits, and is suitable for promotion and application.

Claims

1. A method for recycling a residue from MXene preparation, comprising the following steps: recovering a bottom residual sediment produced in preparation of MXene through etching in a minimally intensive layer delamination (MILD) method, mixing the bottom residual sediment with a molten polyvinyl alcohol (PVA) solution to obtain a mixture, and drying the mixture to prepare a Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2/PVA composite film, wherein the bottom residual sediment is a Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2-based mixture.

2. The method according to claim 1, wherein the etching comprises the following steps: 1) Adding MAX phase powder to an aqueous solution of an etchant, and stirring and heating to allow a reaction; adding water, conducting centrifugation, and adjusting a pH to 6 to 7; and conducting an ultrasonic treatment, suction filtration, and drying to obtain a preliminarily-etched MXene product; 2) Adding an intercalator to a solution of the preliminarily-etched MXene product, and conducting stirring, an ultrasonic treatment, and centrifugation to obtain a bottom sediment; and 3) Recovering the bottom sediment, and vacuum-drying the bottom sediment to a constant weight to obtain the residue from MXene preparation.

3. The method according to claim 2, wherein the etchant is selected from a group consisting of HF, HCl/LiF, NaHF.sub.2, KHF.sub.2, and NH.sub.4HF.sub.2; and a mass ratio of the etchant to the MAX phase powder is 1:(0.5-3).

4. The method according to claim 2, wherein in the step 1), the reaction under the heating and stirring is conducted at 40 C. to 80 C. for 12 h to 96 h.

5. The method according to claim 2, wherein the intercalator is one or more selected from a group consisting of ethanol, dimethylsulfoxide (DMSO), tetramethylammonium hydroxide (TMAOH), and tetrabutylammonium hydroxide (TBAOH), and a mass ratio of the intercalator to the MAX phase powder is 1:(5-20).

6. The method according to claim 2, wherein a solid-to-liquid ratio of PVA to water in the molten PVA solution is 1 g:(0.02-1) mL; and a temperature of heat-melting for the PVA is 60 C. to 150 C.

7. The method according to claim 2, wherein an amount of the Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2-based mixture is 10% to 25% of a mass of PVA particles.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram showing a method for recycling a residue from MXene preparation and a preparation process of a Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2/PVA composite film in Example 1;

(2) FIG. 2 shows an X-ray diffraction (XRD) pattern (a) and a Fourier transform infrared spectroscopy (FTIR) spectrum (b) of Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2 adopted in Example 1;

(3) FIG. 3 shows scanning electron microscopy (SEM) images of composite films with different Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2 contents in Example 1, where (a) is for a composite film with a Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2 content of 10%, (b) is for a composite film with a Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2 content of 20%, (c) is for a composite film with a Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2 content of 25%, and (d) is for a composite film with a Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2 content of 30%;

(4) FIG. 4 shows tensile stress-strain curves of a 25% Ti.sub.3C.sub.2T.sub.x-Ti.sub.3AlC.sub.2/PVA composite film obtained in Example 2 and a pure PVA film;

(5) FIG. 5 shows resistance changes of the 25% Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2/PVA composite film obtained in Example 2, where (a) shows resistance changes under different bending radii, (b) shows output current changes of the composite film at a given voltage of 1 V under different bending radii, and (c) shows a change of resistance of the composite film with a tensile strain;

(6) FIG. 6 shows use effects of the composite film obtained in Example 2 in preparation of a biosensor, where (a) is for an index finger, (b) is for a middle finger, (c) is for a ring finger, (d) is for a little finger, (e) is for wrist joint bending, and (f) is for wrist joint twisting;

(7) FIG. 7 shows tensile stress-strain curves of Ti.sub.3C.sub.2T.sub.x-Ti.sub.3AlC.sub.2/PVA composite films with different contents in Examples 3 to 5 and a pure PVA film; and

(8) FIG. 8 shows tensile stress-strain curves of 5% and 30% Ti.sub.3C.sub.2T.sub.x-Ti.sub.3AlC.sub.2/PVA composite films obtained in Comparative Examples 1 and 2 and a pure PVA film.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(9) In order to well understand the present disclosure, the content of the present disclosure is further illustrated below with reference to specific examples. However, the content of the present disclosure is not limited to the following examples.

(10) The MAX, or M.sub.n+1AX.sub.n, phases are layered, hexagonal, early transition-metal carbides and nitrides, where n=1, 2, or 3, M is an early transition metal, A is an A-group (mostly group 13 or 14) element, and X is C and/or N.

(11) In the following examples, the Ti.sub.3C.sub.2T.sub.x-Ti.sub.3AlC.sub.2-based mixture is a bottom residual sediment collected during preparation of MXene Ti.sub.3C.sub.2T.sub.x filter membrane through etching in an MILD method. A specific preparation method of the Ti.sub.3C.sub.2T.sub.x filter membrane includes: 1) 2 g of LiF and 40 mL of 9 M hydrochloric acid are mixed and stirred in a polytetrafluoroethylene (PTFE) beaker for 30 min. Then the beaker is placed in ice water, 2 g of Ti.sub.3AlC.sub.2 is slowly added to the beaker, then a reaction temperature is adjusted to 40 C., and continuous stirring is conducted for 45 h to allow a reaction. A mixed solution produced after the reaction is completed is centrifuged, adjusted to a pH of 6 to 7, and subjected to an ultrasonic treatment, vacuum suction filtration, and drying to obtain a black preliminary MXene (Ti.sub.3C.sub.2T.sub.x) product. 2) DMSO is added to a beaker with the preliminary MXene product, stirring is conducted for 4 h, and then an ultrasonic treatment is conducted (150 W, 2 h). Then, deionized water is added to the beaker and centrifugation is conducted (rotational speed: 8,000 rpm, time: 5 min) to remove the residual intercalator, and a main product is collected. Deionized water is further added to the main product, and centrifugation is conducted (rotational speed: 3,500 rpm, time: 30 min) to obtain a bottom residual sediment. The bottom residual sediment is dried under vacuum to obtain Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2. A main component of Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2 is a mixture of incompletely-etched Ti.sub.3C.sub.2Tx and Ti.sub.3AlC.sub.2.

Example 1

(12) A method for recycling a residue from MXene preparation was provided. A flow chart of the method was shown in FIG. 1. The method specifically included the following steps: 1) A Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2-based mixture was ground into fine particles (100 m to 400 m) for later use. 1 g of PVA was taken and added to 50 mL of deionized water, and heated at 100 C. until the PVA was completely molten to obtain a molten PVA solution. 2) 20 mL of deionized water was added to the fine particles of the Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2-based mixture, and ultrasonic dispersion was fully conducted to obtain a particle dispersion. The particle dispersion was slowly poured into the molten PVA solution under stirring, and further stirring was fully conducted (temperature: 100 C., stirring rate: 120 rpm, and time: 15 min) to obtain a mixed solution. Different contents of PVA were set (corresponding amounts of Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2 were 10%, 20%, 25%, and 30% of a mass of PVA, respectively). Before PVA began to be cured, resulting mixed solutions each were filtered through a gauze, then poured into a standard PTFE mold of 7.5101 cm.sup.3, and dried naturally for 48 h to obtain PVA/Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2 composite films with excellent toughness.

(13) FIG. 1 shows the method for recycling a residue from MXene preparation and the preparation process of a Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2/PVA composite film in Example 1. After etching and intercalation with DMSO, layered MXene is obtained through repeated centrifugation processes (supernatants are collected). The layered MXene can be used for other experiments. A clay-like mixture settled at a bottom of a centrifuge tube is extracted by operations such as suction filtration and drying to obtain the residue from MXene preparation (Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2) in the present disclosure. Then Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2 was ground into a powder, and the powder and PVA were mixed in different ratios and then naturally dried to obtain the composite films. The above process can ensure that the composite films have excellent flexibility and mechanical strength.

(14) FIG. 2a shows an XRD pattern of 25% Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2 obtained in this example. It can be seen that, in the bottom sediment, in addition to the same characteristic peak (002) at 9.5 as the MAX phase and a characteristic peak (104) at 39.5 for Al, there is a strong characteristic peak at 6.2 lower than 9.5, which is the same angle as the characteristic peak (002) of DMSO-MXene. It can also be seen that the bottom sediment is mainly a mixture of MAX and MXene.

(15) FIG. 2b shows an FTIR spectrum of a Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2/PVA (20%) composite film obtained in this example. It can be seen from this figure that MXene-MAX has a stretching vibration peak of OH at 3,430 cm.sup.1, while the Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2/PVA film sample has a significant red shift (3,250 cm.sup.1). The above results indicate that, after being added, Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2 can produce hydrogen bonding with a PVA molecular chain. The same red shift is also observed at a vibration peak of OH at 1,550 cm.sup.1.

(16) FIG. 3 shows SEM images of the composite films with different Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2 contents in Example 1. As shown in this figure, in a sample including 10% of a Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2 mixture, lumpy particles are scattered in PVA (FIG. 3a), and the clear stacking of layered structures can be observed at a high magnification, but a continuous conductive network is not formed. When a content of the mixture increases to 20% (FIG. 3b), sheets overlap and are stacked, with a specified gap. When the content of the mixture further increases to 25% (FIG. 3c), it can be seen that a surface is relatively smooth and Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2 is uniformly distributed. Under a 5,000 magnification, it can be observed that MXene sheets with two-dimensional layered structures are stacked in a composite film, which also proves that the improvement in electrical conductivity is mainly attributed to a role of Ti.sub.3C.sub.2Tx (Ti.sub.3AlC.sub.2 is non-conductive).

Example 2

(17) A method for recycling a residue from MXene preparation and a use of the residue in a biosensor were provided, including the following steps: 1) 1 g of PVA was taken and added to 50 mL of deionized water, and heated at 100 C. until the PVA was completely molten to obtain a molten PVA solution. 2) 20 mL of deionized water was added to a Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2-based mixture, and ultrasonic dispersion was fully conducted to obtain a mixture dispersion. The mixture dispersion was slowly poured into the molten PVA solution under stirring, and further stirring was fully conducted (temperature: 120 C., stirring rate: 80 rpm, and time: 20 min) to obtain a mixed solution. A mass of Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2 was 25% of a mass of PVA. Before PVA began to be cured, the mixed solution was filtered through a gauze, then poured into a standard PTFE mold of 7.5101 cm.sup.3, and dried naturally for 48 h to obtain a PVA/Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2 composite film.

(18) FIG. 4 shows tensile stress-strain curves of the 25% Ti.sub.3C.sub.2T.sub.x-Ti.sub.3AlC.sub.2/PVA composite film in Example 2 and a pure PVA film. The addition of a small amount of Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2 allows hydrogen bonding with PVA, which is conducive to improving a tensile strength of a material. However, the further increase of an amount of Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2 leads to a limited improvement effect for a tensile strength of a material. A large amount of Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2 will destroy the hydrogen bonding between PVA, such that a strength of a material is weakened. As shown in FIG. 4, the addition of 25% of Ti.sub.3C.sub.2T.sub.x-Ti.sub.3AlC.sub.2 significantly reduces a tensile strength of PVA. When a content of Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2 is 25%, an elongation at break is 78.9%, a tensile strength is 17.6 MPa, a Young's modulus is 1.1 GPa, and a resistance is 1.2510.sup.6.

(19) FIG. 5 shows resistance changes of the 25% Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2/PVA composite film in Example 2. FIG. 5a shows resistance changes under different bending radii. The resistance of the composite film changes significantly with the gradual decrease of a bending radius. When the bending radius is merely 1 cm, the resistance increases by 17%. When the bending radius reaches 0.8 cm, the resistance increases by about 60%. When the bending radius reaches 0.5 cm, the resistance changes by 80%. Moreover, the resistance of the composite film can return to an initial value after a bending process, indicating that the composite film has excellent flexibility and stability. FIG. 5b shows output current changes of the composite film at a given voltage of 1 V under different bending radii. When a bending radius is greater than 1, an output current does not change significantly. As a bending degree increases, a resistance increases and an output current decreases correspondingly. When a bend radius is smaller than 0.4 cm, a current change is relatively stable, which is attributed to the efficient connection established inside the material. Even when folded in half, the composite film is still conductive. FIG. 5c shows a change of resistance of the composite film with a tensile strain. When the tensile strain is less than 10%, GF is 533, indicating very high sensitivity. When the tensile strain exceeds 10%, GF still reaches 290. When the tensile strain exceeds 52%, the composite film is basically not conductive due to the fracture of connection inside the composite film. According to GF measurement results of the material, the Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2/PVA exhibits high sensitivity in detection of motion changes in a small range, and thus can be used in various types of sensors.

(20) FIG. 6 shows bending resistance changes of the composite film in Example 2 applied to different motion parts, where (a) is for an index finger, (b) is for a middle finger, (c) is for a ring finger, (d) is for a little finger, (e) is for wrist joint bending, and (f) is for wrist joint twisting. As shown in FIG. 6a to FIG. 6d, after a finger is bent, the resistance increases significantly with an extremely-short response time (less than 100 ms), indicating very high sensitivity (there are slight differences among resistance changes tested due to different flexibilities of knuckles of a tester). After the composite film is bent, it takes a specified time for resistance of the composite film to return to an initial value, which is attributed to a specified fracture of connection inside the composite film after being bent. Therefore, it takes a specified time to rebuild an internal connection during a recovery process. As shown in FIG. 6e to FIG. 6f, the composite film also has an excellent response rate and sensitivity for a wrist joint, and the resistance of the composite film increases significantly after the wrist joint is bent. However, it takes a longer time to recover for the wrist joint than the knuckles. The motion in a wide range has a great impact on the inside of the material, and thus it takes a long time to recover. Resistance changes for wrist twisting and bending are significantly different. After twisting, the resistance does not increase, but decreases significantly. This may be because the twisting will cause unconnected Ti.sub.3C.sub.2Tx MXene sheets inside the composite film to be cross-stacked, such that the resistance of the composite film can be significantly reduced. A response time for wrist twisting is also short. The resistance is significantly reduced by 50% after twisting. After the twisting is recovered, the resistance will slightly increase and then decrease. This is because the internal MXene undergoes a misalignment and reconnection process during a film recovery process. However, a twisting resistance recovery process takes a shorter time than a bending resistance recovery process. The above results show that the Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2/PVA composite film can be fully used in biosensors.

Example 3

(21) A method for recycling a residue from MXene preparation was provided, including the following steps: 1) 1 g of PVA was taken and added to 50 mL of deionized water, and heated at 100 C. until the PVA was completely molten to obtain a molten PVA solution. 2) 20 mL of deionized water was added to a Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2-based mixture, and ultrasonic dispersion was fully conducted to obtain a mixture dispersion. The mixture dispersion was slowly poured into the molten PVA solution under stirring, and further stirring was fully conducted (temperature: 120 C., stirring rate: 80 rpm, and time: 20 min) to obtain a mixed solution. A mass of Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2 was 10% of a mass of PVA. Before PVA began to be cured, the mixed solution was filtered through a gauze, then poured into a standard PTFE mold of 7.5101 cm.sup.3, and dried naturally for 48 h to obtain a PVA/Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2 composite film.

(22) FIG. 7 shows tensile stress-strain curves of the 10% Ti.sub.3C.sub.2T.sub.x-Ti.sub.3AlC.sub.2/PVA composite film in Example 3 and a pure PVA film. The composite film has an elongation at break of 147.0%, a tensile strength of 29.0 MPa, a Young's modulus of 2.1 GPa, and resistance of 8.510.sup.6.

(23) According to test results, the composite film has high sensitivity (response time: less than 100 ms) in detection of motion changes in a small range and excellent mechanical properties, and thus can be used in various types of sensors.

Example 4

(24) A method for recycling a residue from MXene preparation was provided, including the following steps: 1) 1 g of PVA was taken and added to 50 mL of deionized water, and heated at 100 C. until the PVA was completely molten to obtain a molten PVA solution. 2) 20 mL of deionized water was added to a Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2-based mixture, and ultrasonic dispersion was fully conducted to obtain a mixture dispersion. The mixture dispersion was slowly poured into the molten PVA solution under stirring, and further stirring was fully conducted (temperature: 120 C., stirring rate: 80 rpm, and time: 20 min) to obtain a mixed solution. A mass of Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2 was 15% of a mass of PVA. Before PVA began to be cured, the mixed solution was filtered through a gauze, then poured into a standard PTFE mold of 7.5101 cm.sup.3, and dried naturally for 48 h to obtain a PVA/Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2 composite film.

(25) FIG. 7 shows tensile stress-strain curves of the 15% Ti.sub.3C.sub.2T.sub.x-Ti.sub.3AlC.sub.2/PVA composite film in Example 4 and a pure PVA film. The composite film has an elongation at break of 145.2%, a tensile strength of 29.2 MPa, a Young's modulus of 3.5 GPa, and resistance of 6.510.sup.6.

(26) According to test results, the composite film has high sensitivity (response time: less than 100 ms) in detection of motion changes in a small range and excellent mechanical properties, and thus can be used in various types of sensors.

Example 5

(27) A method for recycling a residue from MXene preparation was provided, including the following steps: 1) 1 g of PVA was taken and added to 50 mL of deionized water, and heated at 100 C. until the PVA was completely molten to obtain a molten PVA solution. 2) 20 mL of deionized water was added to a Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2-based mixture, and ultrasonic dispersion was fully conducted to obtain a mixture dispersion. The mixture dispersion was slowly poured into the molten PVA solution under stirring, and further stirring was fully conducted (temperature: 120 C., stirring rate: 80 rpm, and time: 20 min) to obtain a mixed solution. A mass of Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2 was 20% of a mass of PVA. Before PVA began to be cured, the mixed solution was filtered through a gauze, then poured into a standard PTFE mold of 7.5101 cm.sup.3, and dried naturally for 48 h to obtain a PVA/Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2 composite film.

(28) FIG. 7 shows tensile stress-strain curves of the 20% Ti.sub.3C.sub.2T.sub.x-Ti.sub.3AlC.sub.2/PVA composite film in Example 5 and a pure PVA film. The composite film has an elongation at break of 109.7%, a tensile strength of 19.9 MPa, a Young's modulus of 1.1 GPa, and resistance of 3.410.sup.6.

(29) Control Group 1

(30) A method for recycling a residue from MXene preparation was provided, including the following steps: 1) 1 g of PVA was taken and added to 50 mL of deionized water, and heated at 100 C. until the PVA was completely molten to obtain a molten PVA solution. 2) 20 mL of deionized water was added to a Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2-based mixture, and ultrasonic dispersion was fully conducted to obtain a mixture dispersion. The mixture dispersion was slowly poured into the molten PVA solution under stirring, and further stirring was fully conducted (temperature: 120 C., stirring rate: 80 rpm, and time: 20 min) to obtain a mixed solution. A mass of Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2 was 5% of a mass of PVA. Before PVA began to be cured, the mixed solution was filtered through a gauze, then poured into a standard PTFE mold of 7.5101 cm.sup.3, and dried naturally for 48 h to obtain a PVA/Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2 composite film.

(31) FIG. 8 shows tensile stress-strain curves of the 5% Ti.sub.3C.sub.2T.sub.x-Ti.sub.3AlC.sub.2/PVA composite film in Comparative Example 1 and a pure PVA film. The composite film has an elongation at break of 134.8%, a tensile strength of 53.9 MPa, and a Young's modulus of 2.1 GPa. However, the composite film is basically non-conductive and is not suitable for stress-strain sensors.

(32) Control Group 2

(33) A method for recycling a residue from MXene preparation was provided, including the following steps: 1) 1 g of PVA was taken and added to 50 mL of deionized water, and heated at 100 C. until the PVA was completely molten to obtain a molten PVA solution. 2) 20 mL of deionized water was added to a Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2-based mixture, and ultrasonic dispersion was fully conducted to obtain a mixture dispersion. The mixture dispersion was slowly poured into the molten PVA solution under stirring, and further stirring was fully conducted (temperature: 120 C., stirring rate: 80 rpm, and time: 20 min) to obtain a mixed solution. A mass content of Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2 was 30%. The mixed solution was filtered through a gauze, then poured into a standard PTFE mold of 7.5101 cm.sup.3, and dried naturally for 48 h to obtain a PVA/Ti.sub.3C.sub.2Tx-Ti.sub.3AlC.sub.2 composite film.

(34) FIG. 8 shows tensile stress-strain curves of the 30% Ti.sub.3C.sub.2T.sub.x-Ti.sub.3AlC.sub.2/PVA composite film in Comparative Example 2 and a pure PVA film. The composite film exhibits excellent electrical conductivity, and has resistance of 110.sup.6. However, the addition of too much Ti.sub.3C.sub.2T.sub.x-Ti.sub.3AlC.sub.2 significantly reduces the elongation and tensile strength of PVA. The composite film has an elongation at break merely of 24%, a tensile strength of 10.9 MPa, and a Young's modulus of 2.0 GPa. The composite film is not suitable for stress-strain sensors.

(35) The above examples are merely intended to illustrate the technical conception and characteristics of the present disclosure, such that a person familiar with the technology can understand the content of the present disclosure and implement the content accordingly, and the above examples shall not limit the protection scope of the present disclosure. Any equivalent change or modification made in accordance with the spiritual essence of the present disclosure shall fall within the protection scope of the present disclosure.