阅读说明：本技术 一种聚偏氟乙烯压电复合薄膜的制备方法 (Preparation method of polyvinylidene fluoride piezoelectric composite film ) 是由 唐超 李华 迟庆国 张天栋 冯宇 张昌海 于 2020-12-27 设计创作，主要内容包括：本发明属于压电材料技术领域,具体涉及一种聚偏氟乙烯压电复合薄膜的制备方法。其包括如下步骤：制备碳纳米管悬浮液、PVDF悬浮聚合、拉伸成膜和冷却卷收。本发明提供的技术方案在悬浮聚合制备PVDF过程中加入碳纳米管悬浮液,有效防止了纳米微粒的团聚问题,保证了其在PVDF中重复发挥结晶核的作用,从而制备出了β晶含量很高的PVDF压片,然后通过控制后续成膜过程,防止了在成膜过程中β晶向α晶的转化,最终获得了高β晶含量的PVDF压电薄膜。(The invention belongs to the technical field of piezoelectric materials, and particularly relates to a preparation method of a polyvinylidene fluoride piezoelectric composite film. Which comprises the following steps: preparing carbon nano tube suspension, PVDF suspension polymerization, stretching to form a film, and cooling and coiling. According to the technical scheme provided by the invention, the carbon nanotube suspension is added in the process of preparing PVDF by suspension polymerization, so that the agglomeration problem of nanoparticles is effectively prevented, and the repeated exertion of the function of crystal nuclei in PVDF is ensured, thereby preparing the PVDF tabletting with high beta crystal content, and then the conversion of beta crystal to alpha crystal in the film forming process is prevented by controlling the subsequent film forming process, and finally the PVDF piezoelectric film with high beta crystal content is obtained.)

1. The preparation method of the polyvinylidene fluoride piezoelectric composite film is characterized by comprising the following steps:

1) preparing a carbon nanotube suspension: adding carbon nano tubes, a modifier and a surfactant into water, and mixing to form a stable carbon nano tube suspension;

2) PVDF suspension polymerization: adding a VDF monomer, an initiator, a dispersant, a chain transfer agent and water into a polymerization reaction kettle for free radical suspension polymerization reaction, heating to 60-80 ℃, adding the carbon nanotube suspension prepared in the step 1) into the polymerization reaction kettle after the polymerization reaction is carried out for 8-14h, adding a terminator for discharging after the pressure is reduced to 0.1-0.3MPa, filtering, washing and drying to obtain PVDF composite resin;

3) stretching to form a film: performing biaxial stretching on the PVDF composite resin tablet prepared in the step 2) in film stretching equipment, wherein the longitudinal stretching ratio is 3-5, and the transverse stretching ratio is 1.1-1.5;

4) cooling and coiling: and the stretched film is cooled by a cooling roller and then wound, and the cooling roller is cooled by cooling water.

2. The method for preparing the polyvinylidene fluoride piezoelectric composite film according to claim 1, wherein the modifier in the step 1) is cetyl trimethyl ammonium salt or vinyl benzene trimethyl ammonium chloride; the surfactant is alkyl phenyl sulfonate, preferably sodium dodecyl benzene sulfonate.

3. The method for preparing the polyvinylidene fluoride piezoelectric composite film according to claim 1, wherein the carbon nanotubes in the step 1) are multi-walled carbon nanotubes.

4. The preparation method of the polyvinylidene fluoride piezoelectric composite film according to claim 1, wherein the components in the step 1) are as follows in parts by weight:

5. the method for preparing the polyvinylidene fluoride piezoelectric composite film according to claim 1, wherein the initiator in the step 2) is selected from diethyl peroxydicarbonate, cyclohexyl peroxydicarbonate or diisopropyl peroxydicarbonate; the dispersant is selected from methyl cellulose ether, hydroxyethyl cellulose ether or polyethylene glycol; chain transfer agents ethyl acetate or diethyl carbonate.

6. The preparation method of the polyvinylidene fluoride piezoelectric composite film according to claim 1, wherein the polymerization reaction system in the step 2) comprises the following components in parts by weight:

7. the preparation method of the polyvinylidene fluoride piezoelectric composite film according to claim 1, wherein the weight of the carbon nanotube suspension added in the step 2) is 12.5-25 wt% of the weight of the VDF monomer.

8. The method for preparing a polyvinylidene fluoride piezoelectric composite film according to claim 1, wherein the temperature of the biaxial stretching in the step 3) is set to a temperature of 70 to 90 ℃ for longitudinal stretching and then a temperature of 70 to 90 ℃ for transverse stretching.

9. The method for preparing the polyvinylidene fluoride piezoelectric composite film according to claim 1, wherein the carbon nanotube suspension is slowly added through a feeding pump, and the flow rate is controlled to be 10-15 ml/min.

10. The preparation method of the polyvinylidene fluoride piezoelectric composite film according to claim 1, wherein in the step 4), the water temperature of cooling water is 5-10 ℃, and the coiling is 4-8 m/min.

Technical Field

The invention belongs to the technical field of piezoelectric materials, and particularly relates to a preparation method of a polyvinylidene fluoride piezoelectric composite film.

Background

Piezoelectric materials are divided into piezoelectric single crystals, piezoelectric ceramics, piezoelectric polymers and piezoelectric composites according to properties and compositions. Piezoelectric composites include polymer/nanoparticle composites and PZT/polymer composites. The polymer/nano particle composite material is prepared by adding nano particles into a piezoelectric polymer, and the piezoelectric performance of the piezoelectric polymer is enhanced under the condition of keeping the advantages of flexibility, light weight and the like.

PVDF (polyvinylidene fluoride), a semi-crystalline polymer compound. During polymerization, when VDF (vinylidene fluoride) monomer expands into a molecular chain, C atoms are linked to form a main carbon chain, and H and F atoms rotate around chemical bonds to form different spatial configurations, i.e., configurations. Approximately 180 ° relationship between adjacent substituents, termed trans configuration (TTT); and adjacent substitutes are approximately 60 ° in relation to each other, called twisted configuration (TGTG). PVDF is known to have at least five crystal structures of alpha, beta, gamma, delta and epsilon, wherein the alpha crystal phase is most easily obtained and stable, but the molecular chain configuration is TGTG (triglygtg) which does not show piezoelectricity; the beta crystal phase with molecular chain configuration of TTT has far better piezoelectric properties than other crystal phases. The TTT configuration has dipole moments parallel in the unit cell, favoring superposition of polarities, and exhibits piezoelectric properties in the direction in which the dipole moment in the polar direction in the crystal is not equal to zero under compression and stretching by an external force.

The current methods for obtaining high beta crystal PVDF mainly include mechanical stretching and nanofiller methods. The mechanical stretching method is characterized in that when mechanical stretching is carried out under the conditions of specific stretching temperature and stretching ratio, transformation from alpha crystal form to beta crystal form is induced, the transformation rate of the method is limited, if the content of the alpha crystal form is higher, high-content beta crystal form PVDF is difficult to obtain, in addition, the control is not good, the phenomenon that reverse beta crystal form is transformed into the alpha crystal form can also occur in the stretching process, and structural defects can be caused by stretching, so that the crystallinity of the material is reduced, and the piezoelectric performance of the material is weakened. The nano-filler method is to add proper nano-filler into a PVDF system so as to improve the content of beta crystal in the PVDF film, and is a commonly used technical means for improving the piezoelectric film at present because the nano-filler method is simple and easy to operate and can obtain a product with extremely high content of beta crystal by proper control. At present, the PVDF and the nano filler are mixed and formed by a solution or melting method, the adding method is not ideal in dispersibility and processability, and the defects are more obvious particularly when more nano filler is required to be added for improving the content of beta crystals.

Disclosure of Invention

The invention provides a preparation method of a polyvinylidene fluoride piezoelectric composite film, which is used for solving the problems of poor dispersibility and low beta crystal content when the PVDF piezoelectric property is improved by adding a nano filler at present.

In order to solve the technical problems, the technical scheme of the invention is as follows: the preparation method of the polyvinylidene fluoride piezoelectric composite film comprises the following steps:

1) preparing a carbon nanotube suspension: adding carbon nano tubes, a modifier and a surfactant into water, and mixing to form a stable carbon nano tube suspension;

2) PVDF suspension polymerization: adding a VDF monomer, an initiator, a dispersant, a chain transfer agent and water into a polymerization reaction kettle for free radical suspension polymerization reaction, heating to 60-80 ℃, adding the carbon nanotube suspension prepared in the step 1) into the polymerization reaction kettle after the polymerization reaction is carried out for 8-14h, adding a terminator for discharging after the pressure is reduced to 0.1-0.3MPa, filtering, washing and drying to obtain PVDF composite resin;

3) stretching to form a film: performing biaxial stretching on the PVDF composite resin tablet prepared in the step 2) in film stretching equipment, wherein the longitudinal stretching ratio is 3-5, and the transverse stretching ratio is 1.1-1.5;

4) cooling and coiling: and the stretched film is cooled by a cooling roller and then wound, and the cooling roller is cooled by cooling water.

Optionally, the modifier in step 1) is cetyl trimethyl ammonium salt or vinyl benzene trimethyl ammonium chloride; the surfactant is alkyl phenyl sulfonate, preferably sodium dodecyl benzene sulfonate.

Optionally, the carbon nanotubes in step 1) are multi-walled carbon nanotubes.

Optionally, the components in the step 1) are as follows in parts by weight:

alternatively, the initiator in step 2) is selected from diethyl peroxydicarbonate, cyclohexyl peroxydicarbonate or diisopropyl peroxydicarbonate; the dispersant is selected from methyl cellulose ether, hydroxyethyl cellulose ether or polyethylene glycol; chain transfer agents ethyl acetate or diethyl carbonate.

Optionally, the polymerization reaction system in the step 2) comprises the following components in parts by weight:

optionally, the weight of the carbon nanotube suspension added in step 2) is 12.5-25 wt% of the weight of the VDF monomer.

Alternatively, the temperature of the biaxial stretching in the step 3) is set to perform longitudinal stretching at 70 to 90 ℃ and then transverse stretching at 70 to 90 ℃.

Optionally, the carbon nanotube suspension is slowly added through a feeding pump, and the flow rate is controlled to be 10-15 ml/min.

Optionally, in the step 4), the water temperature of the cooling water is 5-10 ℃, and the winding is 4-8 m/min.

According to the technical scheme provided by the invention, the carbon nanotube suspension is added in the process of preparing PVDF by suspension polymerization, so that the agglomeration problem of nanoparticles is effectively prevented, and the repeated exertion of the function of crystal nuclei in PVDF is ensured, thereby preparing the PVDF tabletting with high beta crystal content, and then the conversion of beta crystal to alpha crystal in the film forming process is prevented by controlling the subsequent film forming process, and finally the PVDF piezoelectric film with high beta crystal content is obtained.

Drawings

FIG. 1 is a FTIR spectrum of samples of example 1 and comparative example 1;

figure 2 is an XRD spectrum of the samples of example 1 and comparative example 1.

Shown in the figure:

sample # 1 to example 1 and sample # 2 to example 2.

Detailed Description

For the convenience of understanding, the preparation method of the polyvinylidene fluoride piezoelectric composite film is described below with reference to examples, which should be understood to be merely illustrative and not limiting.

The starting materials, reagents or reaction conditions employed in this example were, except as indicated, commercially available and conventional.

Example 1

The preparation method of the polyvinylidene fluoride piezoelectric composite film comprises the following steps:

1) preparing a carbon nanotube suspension: adding 80g of multi-walled carbon nanotube, 1.5g of vinylbenzene trimethyl ammonium chloride (modifier) and 2g of sodium dodecyl benzene sulfonate (surfactant) into 1L of water, and mixing to form a stable carbon nanotube suspension;

2) PVDF suspension polymerization: adding 600g of VDF monomer, 0.5g of diethyl peroxydicarbonate (initiator), 0.5g of polyethylene glycol (dispersant), 4g of ethyl acetate (chain transfer agent) and 2L of water into a 5L polymerization reaction kettle for free radical suspension polymerization, heating to 60-80 ℃, slowly adding 100g of the carbon nanotube suspension prepared in the step 1) into the polymerization reaction kettle through a feeding pump after the polymerization reaction is carried out for 12h, controlling the flow at 10ml/min, adding a terminator after the pressure is reduced to 0.1-0.3MPa, discharging, filtering, washing and drying to obtain the PVDF composite resin;

3) stretching to form a film: biaxially stretching the PVDF composite resin tablet prepared in the step 2) in film stretching equipment, wherein longitudinal stretching is carried out at 80 ℃, the longitudinal stretching ratio is 4, and transverse stretching is carried out at 90 ℃, and the transverse stretching ratio is 1.1;

4) cooling and coiling: and cooling the stretched film by a cooling roller, then coiling, introducing water into the cooling roller for cooling, wherein the water temperature of cooling water is about 5 ℃, and the coiling speed is 5 m/min.

Example 2

The preparation method of the polyvinylidene fluoride piezoelectric composite film comprises the following steps:

1) preparing a carbon nanotube suspension: adding 120g of multi-walled carbon nanotube, 2g of vinylbenzene trimethyl ammonium chloride (modifier) and 2g of sodium dodecyl benzene sulfonate (surfactant) into 1L of water, and mixing to form a stable carbon nanotube suspension;

2) PVDF suspension polymerization: adding 400g of VDF monomer, 2g of cyclohexyl peroxydicarbonate (initiator), 0.2g of methyl cellulose ether (dispersant), 2g of diethyl carbonate (chain transfer agent) and 2L of water into a 5L polymerization reaction kettle for free radical suspension polymerization, heating to 60-80 ℃, slowly adding 50g of carbon nanotube suspension prepared in the step 1) into the polymerization reaction kettle through a feeding pump after the polymerization reaction is carried out for 8h, controlling the flow at 10ml/min, adding a terminating agent for discharging after the pressure is reduced to 0.1-0.3MPa, filtering, washing and drying to obtain the PVDF composite resin;

3) stretching to form a film: biaxially stretching the PVDF composite resin sheeting prepared in the step 2) in film stretching equipment, firstly, longitudinally stretching at 70 ℃, wherein the longitudinal stretching ratio is 5, and then, transversely stretching at 70 ℃, wherein the transverse stretching ratio is 1.3;

4) cooling and coiling: and the stretched film is cooled by a cooling roller and then wound, the cooling roller is cooled by cooling water, the water temperature of the cooling water is about 8 ℃, and the winding speed is 4 m/min.

Example 3

The preparation method of the polyvinylidene fluoride piezoelectric composite film comprises the following steps:

1) preparing a carbon nanotube suspension: adding 100g of multi-walled carbon nanotube, 1g of vinylbenzene trimethyl ammonium chloride (modifier) and 2g of sodium dodecyl benzene sulfonate (surfactant) into 1L of water, and mixing to form a stable carbon nanotube suspension;

2) PVDF suspension polymerization: adding 800g of VDF monomer, 3.5g of diisopropyl peroxydicarbonate (initiator), 0.8g of hydroxyethyl cellulose ether (dispersant), 6g of diethyl carbonate (chain transfer agent) and 2L of water into a 5L polymerization kettle for free radical suspension polymerization, heating to 60-80 ℃, slowly adding 200g of carbon nanotube suspension prepared in the step 1) into the polymerization kettle through a feeding pump after the polymerization reaction is carried out for 14h, controlling the flow at 15ml/min, adding a terminating agent for discharging after the pressure is reduced to 0.1-0.3MPa, filtering, washing and drying to obtain the PVDF composite resin;

3) stretching to form a film: biaxially stretching the PVDF composite resin tablet prepared in the step 2) in film stretching equipment, firstly longitudinally stretching at 90 ℃ with the longitudinal stretching ratio of 3, and then transversely stretching at 90 ℃ with the transverse stretching ratio of 1.5;

4) cooling and coiling: and the stretched film is cooled by a cooling roller and then wound, the cooling roller is cooled by cooling water, the water temperature of the cooling water is about 7 ℃, and the winding speed is 7 m/min.

Comparative example 1

1) Mixing a multi-walled carbon nanotube and a PVDF matrix under a heating and melting state, mixing, discharging, cooling, crystallizing and tabletting, wherein the weight ratio of the carbon nanotube to the PVDF is about 1: 20;

2) performing biaxial stretching in a film stretching device in the tabletting process, preheating at 160 ℃, performing longitudinal stretching at 200 ℃ with the longitudinal stretching ratio of 6, performing heat setting at 220 ℃, and finally performing transverse stretching at 200 ℃ with the transverse stretching ratio of 2;

3) the stretched film was cooled by a chill roll and then wound up at 5m/min with cooling water at a temperature of about 5 ℃.

Comparative example 2

The difference from example 1 is that the film stretched in step 4) was naturally cooled and then taken up at a speed of 15 m/min.

And (3) comparison test:

the crystal morphology of PVDFDE in the film material was tested using infrared spectroscopy and X-ray diffraction on the films prepared in example 1 and comparative example 1, as shown in figures 1 and 2: the sample of example 1 had an extremely high beta crystal content.

The ratio of the crystal forms in the pressed sheet and the film is determined by Fourier infrared spectrum test and observing the position and the relative intensity of an infrared absorption peak to obtain the information and the relative content (percentage of the total crystal quantity).

TABLE 1

	Example 1	Example 2	Example 3	Comparative example 1	Comparative example 2
						Tabletting	98％	95％	97％	70％	98％
Film(s)	99％	98％	98％	30％	75％

Finally, it should be noted that: the above examples are only for illustrating the technical solutions of the present invention, and are not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: it is to be understood that modifications may be made to the technical solutions described in the foregoing embodiments, or some or all of the technical features may be equivalently replaced, and such modifications or replacements may not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.