A PET / PVA-based thermally responsive double-layer composite film, a preparation method and application thereof

Abstract

This invention provides a PET / PVA-based thermoresponsive bilayer composite film and its preparation method. The composite film has a helical coil structure, comprising a PET layer and a PVA layer; the PET layer is surface-treated before being laminated with the PVA layer; the thickness of the PET layer is 50 μm to 100 μm; the thickness of the PVA layer is 13-25 μm; the degree of coiling of the composite film changes with temperature. The preparation steps include preparing a PVA coating solution, performing surface pretreatment on the PET base film, solution coating, and drying to form the film. The composite film can achieve rapid and reversible bending deformation under temperature changes, with a response time in air reaching the second level, excellent deformation recovery, and the response temperature, deformation amplitude, and response speed can be precisely controlled by adjusting the thickness ratio and process parameters. Furthermore, the preparation process is simple and easy to control, requiring no complex equipment or harsh conditions, and has low raw material costs, making it suitable for large-scale production.

Description

Technical Field

[0001] This invention relates to the field of functional polymer materials, specifically to a PET / PVA-based thermally responsive bilayer composite film, its preparation method, and its applications. Background Technology

[0002] Smart responsive materials are a class of novel functional materials capable of reversible deformation or functional responses to external environmental stimuli such as temperature, humidity, electricity, and light, showing broad application prospects in fields such as flexible actuators, soft robots, and artificial muscles. Among them, thermally responsive materials have attracted widespread attention due to their simple actuation methods and ease of integration and control. Currently, common thermally responsive materials mainly include shape memory polymers, liquid crystal elastomers, and thermally responsive hydrogels.

[0003] However, existing technologies still have shortcomings in practical applications:

[0004] (1) The preparation process is complex and costly: Shape memory polymers and liquid crystal elastomers usually involve complex molecular design and synthesis processes, with high raw material costs and long preparation cycles; Although thermally responsive hydrogels are relatively simple to prepare, they have low mechanical strength, slow response speed and usually need to work in a liquid environment, which limits their application in dry environments.

[0005] (2) Insufficient response speed and deformation reversibility: Currently, most double-layer composite membranes are made of two synthetic polymer materials. Although they can achieve certain thermal deformation, due to the poor thermal conductivity of the materials themselves or the weak interfacial bonding, there are often problems such as response lag, incomplete deformation recovery, and poor cycle stability, which make it difficult to meet the high-frequency and long-life driving requirements.

[0006] (3) Poor adaptability to driving environment: Some thermal response materials rely on solvent absorption and volatilization or phase transformation to achieve deformation. They fail in the air environment due to solvent volatilization or low heat conduction efficiency, which limits their application scenarios and makes it difficult to achieve rapid and stable reversible deformation in open environments.

[0007] The aforementioned defects have limited the widespread application of thermally responsive materials in fields such as flexible smart devices and wearable devices. Summary of the Invention

[0008] To address the aforementioned issues, this invention presents a PET / PVA-based thermally responsive bilayer composite film and its preparation method. Utilizing the difference in thermal expansion coefficients between the PVA and PET layers when heated, the bilayer film exhibits reversible bending motion due to the mismatch in deformation between the two layers when the ambient temperature changes. This has broad application prospects in fields such as flexible actuators, temperature sensors, and smart switches.

[0009] To achieve the above technical objectives, the present invention provides a PET / PVA-based thermally responsive bilayer composite film, wherein the composite film has a helical coil structure, comprising a PET layer and a PVA layer; the PET layer is surface-treated and then laminated with the PVA layer; the thickness of the PET layer is 50 μm to 100 μm; the thickness of the PVA layer is 13-25 μm; and the degree of coiling of the composite film changes with temperature.

[0010] Preferably, the coefficient of thermal expansion of the PET layer is between 16 and 22 K. -1 The coefficient of thermal expansion of the PVA layer is between -22.9 and -433.6 K. -1 Furthermore, the coefficients of thermal expansion of both the PET and PVA layers are temperature-dependent. This difference in thermal expansion coefficients provides the basis for the thermal response performance of the composite film.

[0011] Preferably, the surface treatment includes at least one of vacuum plasma treatment and alkaline etching treatment.

[0012] Preferably, the surface treatment includes vacuum plasma treatment and alkali treatment.

[0013] This invention also provides a method for preparing a PET / PVA-based thermally responsive bilayer composite film, the method comprising at least the following preparation steps:

[0014] Step 1: Prepare PVA coating solution: Dissolve PVA in solvent and stir to dissolve, so as to obtain a uniform PVA solution;

[0015] Step 2, PET base film pretreatment: Cut the PET base film into strips and perform surface treatment;

[0016] Step 3, Coating and Film Formation: Coat the PVA solution obtained in step S1 onto the surface of the PET film that has undergone surface treatment in step 2;

[0017] Step 4, Drying: Dry the PET film coated in step 3 to obtain the spiral thermally responsive bilayer film.

[0018] Preferably, the solvent in step 1 is water. Further, the mass concentration of the PVA solution is 15-18%.

[0019] Preferably, the PVA in step 1 has a degree of polymerization of 1500-2000 and a degree of hydrolysis of >98%. The thermal response coefficient range of PVA resin within this range of degree of polymerization and hydrolysis is more suitable, and it can achieve better thermal response effect when laminated with PET film.

[0020] Preferably, the specific steps for dissolving PVA in step 1 include: stirring PVA in a solvent at 23-26°C for 25-35 minutes to allow it to swell, with a stirring speed of 180-220 r / min; raising the temperature to 90-100°C, reducing the stirring speed to 140-160 r / min, and continuing to stir until completely dissolved.

[0021] Preferably, the surface treatment in step 2 includes at least one of vacuum plasma treatment and alkaline etching treatment.

[0022] Preferably, the surface treatment in step 2 includes vacuum plasma treatment and alkaline etching treatment. The PET film is first subjected to alkaline etching treatment to increase the surface roughness of the film and increase the surface energy of the film. Then, plasma treatment is used to adjust the surface roughness of the PET film to be more uniform, further improving the bonding performance with PVA resin, thereby improving the thermal response of the composite film.

[0023] Furthermore, the vacuum plasma treatment power is 140-160W, and the treatment time is 280-320s.

[0024] Furthermore, the alkaline etching treatment uses an alkaline solution including an aqueous sodium hydroxide solution. Even further, the mass concentration of the aqueous sodium hydroxide solution is 14-16%.

[0025] Furthermore, the alkaline etching process needs to be carried out under heating conditions, with a heating temperature of 75-85℃ and a heating time of 18-25 minutes.

[0026] Preferably, the thickness of the PET base film in step 2 is 50-100 μm.

[0027] Preferably, the aspect ratio of the PET base film cut in step 2 is (18-25):1.

[0028] Preferably, the coating thickness of the PVA solution in step 3 is 50-300 μm.

[0029] Preferably, the drying conditions in step 4 are a temperature of 24-28°C, a humidity of 38-42%, and a time of 15-18 hours.

[0030] Building upon this, the present invention further provides an application of a PET / PVA-based thermoresponsive bilayer composite film, including a thermally driven device. The application utilizes the difference in curling and stretching of the bilayer composite film at different temperatures to achieve thermally responsive actuation of the device.

[0031] Preferably, by reducing the thickness of the PET film, its curing shrinkage rate and heat-driven deformation rate are increased, which can be applied to intelligent robotic arms that require a large stroke shrinkage rate; by increasing the thickness of the PET film, its curing shrinkage rate and heat-driven deformation rate are reduced, which can show broad application prospects in intelligent switches and other applications with small shrinkage rates.

[0032] Preferably, changing the degree of polymerization of PVA, reducing its degree of polymerization, can be applied to biomimetic devices and flexible actuators; increasing its degree of polymerization, can be applied to applications such as intelligent robotic arms.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] 1. The bilayer composite film provided by this invention utilizes the significant difference in thermal expansion coefficients between the PVA layer and the PET layer to achieve rapid and reversible bending deformation under temperature changes, achieving a response within seconds even in an air environment, and exhibiting excellent deformation recovery. The PET base layer and the PVA response layer are coupled and synergistic in their deformation mechanism, forming a bilayer composite system through a strong interfacial bond. By optimizing the thickness ratio of the two layers and the preparation process parameters, key performance indicators such as response temperature, deformation amplitude, and response speed can be controlled.

[0035] 2. The preparation process of the bilayer composite film provided by this invention involves surface treatment of the PET base film using vacuum plasma or alkaline etching, which significantly improves the interfacial bonding force between the PET and PVA layers and avoids interlayer delamination. Simultaneously, using the PET base film as the base layer provides the composite film with good mechanical strength and dimensional stability, giving it both excellent flexibility and tensile strength, thus extending its service life. The solution coating method eliminates the need for complex equipment, high temperature and pressure, and organic solvents. The PVA solution preparation, coating, and curing process parameters are precise and easily controllable, with a wide process window, good repeatability, and low raw material costs, making it suitable for large-scale industrial production. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 A schematic diagram of the preparation process of the PET / PVA-based thermally responsive bilayer composite film provided by this invention;

[0038] Figure 2 : Schematic diagram of the thermally driven deformation testing device of Embodiment 1 of the present invention. Detailed Implementation

[0039] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. These described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0040] Example 1

[0041] Step 1: Place 5.1g of PVA particles (model 1799) in 24.9g of deionized water and allow them to swell for 30min at 25℃ and 200r / min. Then heat and stir at 95℃ and 150r / min for 30min to obtain a PVA solution.

[0042] Step 2: Slowly add 30g of sodium hydroxide granules to 170g of deionized water in batches to prepare a sodium hydroxide aqueous solution with a mass fraction of 15%.

[0043] Step 3: Cut the 50μm thick PET base film into thin strips with a size of 1cm x 20cm, and perform surface treatment on it. Alkali etching is performed under heating conditions at a temperature of 80℃ for 20min. Then, vacuum plasma treatment is performed at a power of 150W for 300s.

[0044] Step 4: Use a coating applicator to uniformly coat the PVA solution obtained in step S1 onto one side of the PET base film to form a wet film layer with a PVA wet film thickness of 300 μm.

[0045] Step 5: Place the film coated in Step 4 in a constant temperature and humidity chamber, set the temperature to 25℃ and the humidity to 40%, and dry and cure for 15 hours to form a spiral double-layer film.

[0046] The thickness of the PVA layer in the PET / PVA-based thermally responsive bilayer composite film was 24.3 μm.

[0047] Example 2

[0048] The only difference from Example 1 is that the thickness of the PET base film is 70 μm. The thickness of the PVA layer in the PET / PVA-based thermally responsive bilayer composite film is 24.1 μm.

[0049] Example 3

[0050] The only difference from Example 1 is that the thickness of the PET base film is 100 μm. The thickness of the PVA layer in the PET / PVA-based thermally responsive bilayer composite film is 24.2 μm.

[0051] Example 4

[0052] The only difference from Example 1 is that the coating thickness of the PVA solution is 150 μm. The PVA layer thickness of the PET / PVA-based thermally responsive bilayer composite film is 15.3 μm.

[0053] Example 5

[0054] The only difference from Example 1 is that the coating thickness of the PVA solution is 50 μm. The PVA layer thickness of the resulting composite film is 13.0 μm.

[0055] Example 6

[0056] The only difference from Example 1 is that the PVA resin grade is 2488 (degree of polymerization approximately 2400, degree of hydrolysis 88%). The thickness of the PVA layer in the resulting composite film is 15.5 μm.

[0057] Example 7

[0058] The only difference from Example 1 is that the PET film was not subjected to vacuum plasma treatment. The thickness of the PVA layer in the resulting composite film was 14.9 μm.

[0059] Comparative Example 1

[0060] The only difference from Example 1 is that the PET base film was not surface-treated. The thickness of the PVA layer in the resulting composite film was 15.1 μm.

[0061] Comparative Example 2

[0062] The only difference from Example 1 is that the PET base film surface is not coated with PVA resin. The thickness of the PVA layer in the resulting composite film is 0 μm.

[0063] Comparative Example 3

[0064] The only difference from Example 1 is that the base film is replaced with a polyimide (PI) film. The thickness of the PVA layer in the resulting composite film is 15.3 μm.

[0065] Test methods

[0066] 1. Curing shrinkage rate: Place the PET film coated with PVA solution in a constant temperature and humidity chamber for complete drying and curing for 15-18 hours. Weigh the film every 20 minutes until two consecutive weighings are the same. Measure the length of the completely dried double-layer film.

[0067]

[0068] Where l0 is the length of the double-layer film before it is dried and cured, and l1 is the length after it is completely dried and cured.

[0069] 2. Thermally driven deformation rate: The spirally rolled double-layer film is suspended in an oven for thermal driving at a temperature range of 40-80℃. The length change of the double-layer film is measured with a ruler, and the entire change process is captured by a high-speed camera to calculate its thermally driven deformation rate.

[0070] Under thermally driven conditions, the spiral bilayer film elongates in the 40℃-60℃ range and contracts in the 60℃-80℃ range.

[0071]

[0072]

[0073] Wherein, l1 is the length of the bilayer film at 40℃ after it has been completely dried and cured, l2 is the length of the bilayer film at 60℃, and l3 is the length of the bilayer film at 80℃.

[0074] 3. Load-driven thermal deformation rate: A 0.5g weight is suspended at the lower end of the double-layer membrane, and the position change of the weight is measured with a ruler. The entire change process is captured by a high-speed camera to test its thermal deformation rate.

[0075] 4. Response time: The time taken for the double-layer film to undergo thermal deformation when the double-layer film is placed in an oven and the film is filmed using a high-speed camera.

[0076] Table 1 shows the performance indicators of the PET / PVA-based thermally responsive bilayer composite films prepared in Examples 1-3.

[0077]

[0078] Based on the performance indicators of the PET / PVA-based thermally responsive bilayer composite film in the above embodiments, it can be seen that the present invention achieves effective control of the thermal response performance of the bilayer film by adjusting the thickness of the PET base film and the thickness of the PVA wet film coating. While ensuring good interfacial bonding and molding stability, it obtains adjustable and controllable thermal deformation capability.

[0079] As can be seen from Examples 1-3, gradually increasing the thickness of the PET base film from 50μm to 100μm resulted in a decrease in the curl shrinkage rate after curing from 28.5% to 15%, and a decrease in the heat-driven deformation shrinkage rate from 8.2% to 4.3%. This indicates that increasing the thickness of the PET base layer significantly reduced the overall flexibility and thermal response sensitivity of the double-layer film.

[0080] Compared with Example 1, Examples 4 and 5 gradually reduced the PVA wet film thickness from 300 μm to 50 μm. The curl shrinkage rate after curing was 27%, which was basically the same as that of Example 1. However, the thermally driven deformation rate decreased from 8.2% to 7.8%, indicating that reducing the thickness of the PVA response layer reduced the driving ability of thermally induced deformation, but had little effect on the self-curling behavior during the curing process.

[0081] Compared to Example 1, Example 6 shows a reduction in both curing shrinkage and heat-driven shrinkage of the bilayer film as the degree of polymerization and hydrolysis decrease. Example 7, compared to Example 1, only underwent alkali treatment for surface modification, and subsequent vacuum plasma treatment improved surface roughness uniformity. In Comparative Example 1, compared to Example 1, the PET film, without surface modification, delaminated during drying and curing, leading to failure in the subsequent heat-driven process. In Comparative Example 2, compared to Example 1, only the PET film layer failed to deform under heat-driven conditions; heat-driven deformation was achieved by utilizing the difference in thermal expansion coefficients between the PVA and PET layers. The PET base layer and the PVA responsive layer are coupled and synergistic in their deformation mechanism: the PET layer provides elastic recovery force, and the PVA layer provides thermally induced driving force; the two are firmly bonded at the interface to form a complete bilayer composite system. In Comparative Example 3, compared to Example 1, using a PI film as the base film, even after surface treatment and composite with PVA to form a curled structure, it failed to exhibit temperature response changes. Comparing the thermally driven deformation rate of the double-layer film before and after loading, under a load of 0.5g, although the elongation and shrinkage rate decreased to some extent, it showed a good deformation rate, which makes it show good prospects in fields such as intelligent robotic arms.

[0082] Finally, it should be noted that although the present invention has been described in detail above with general descriptions and specific embodiments, the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A PET / PVA-based thermally responsive bilayer composite film, characterized in that, The composite film has a spiral curled structure, including a PET layer and a PVA layer; the PET layer is surface treated and then laminated with the PVA layer; the thickness of the PET layer is 50μm to 100μm; the thickness of the PVA layer is 13-25μm; the degree of curling of the composite film changes with temperature.

2. The PET / PVA-based thermally responsive bilayer composite film according to claim 1, characterized in that, The coefficient of thermal expansion of the PET layer is 16~22 K. -1 The coefficient of thermal expansion of the PVA layer is between -22.9 and -433.6 K. -1 Furthermore, the coefficients of thermal expansion of both the PET layer and the PVA layer are temperature-dependent.

3. A method for preparing a PET / PVA-based thermally responsive bilayer composite film, characterized in that, The preparation method includes at least the following preparation steps: Step 1: Prepare PVA coating solution: Dissolve PVA in solvent and stir to dissolve, so as to obtain a uniform PVA solution; Step 2, PET base film pretreatment: Cut the PET base film into strips and perform surface treatment; Step 3, Coating and Film Formation: Coat the PVA solution obtained in step S1 onto the surface of the PET film that has undergone surface treatment in step 2; Step 4, Drying: Dry the PET film coated in step 3 to obtain the spiral thermally responsive bilayer film.

4. The method for preparing the PET / PVA-based thermally responsive bilayer composite film according to claim 3, characterized in that, The solvent used in step 1 is water; the mass concentration of the PVA solution is 15-18%.

5. The method for preparing the PET / PVA-based thermally responsive bilayer composite film according to claim 3, characterized in that, The PVA mentioned in step 1 has a degree of polymerization of 1500-2000 and a degree of hydrolysis of >98%.

6. The method for preparing the PET / PVA-based thermally responsive bilayer composite film according to claim 3, characterized in that, The specific steps for dissolving PVA in step 1 include: stirring PVA in a solvent at 23-26℃ for 25-35 minutes to allow it to swell, with a stirring speed of 180-220 r / min; raising the temperature to 90-100℃, reducing the stirring speed to 140-160 r / min, and continuing to stir until completely dissolved.

7. The method for preparing the PET / PVA-based thermally responsive bilayer composite film according to claim 3, characterized in that, The surface treatment described in step 2 includes at least one of vacuum plasma treatment and alkaline etching treatment.

8. The method for preparing the PET / PVA-based thermally responsive bilayer composite film according to claim 3, characterized in that, The aspect ratio of the PET base film cut in step 2 is (18-25):

1.

9. The method for preparing the PET / PVA-based thermally responsive bilayer composite film according to claim 3, characterized in that, The coating thickness of the PVA solution in step 3 is 50-300 μm.

10. The application of a PET / PVA-based thermally responsive bilayer composite film prepared according to any one of claims 3-9, characterized in that, The application includes a thermally driven device that achieves thermal response driving based on the difference in the curling and stretching of the bilayer composite film at different temperatures.

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