CN110328796B

CN110328796B - Preparation method of polymer-based micro-foaming interlayer gradient material

Info

Publication number: CN110328796B
Application number: CN201910575650.1A
Authority: CN
Inventors: 罗国强; 黄志宏; 黄莹; 张睿智; 沈强; 张联盟; 李家劲
Original assignee: Wuhan University of Technology WUT
Current assignee: Wuhan University of Technology WUT
Priority date: 2019-06-28
Filing date: 2019-06-28
Publication date: 2020-12-01
Anticipated expiration: 2039-06-28
Also published as: CN110328796A

Abstract

The invention discloses a preparation method of a polymer-based micro-foaming interlayer gradient material, which comprises the following steps of firstly, placing a thermoplastic polymer in a reaction kettle to obtain a polymer-based micro-foaming material by a high-pressure physical foaming method; and then the polymer-based micro-foaming interlayer gradient material is obtained by a thermal desorption process at a certain temperature and pressure, wherein the two sides of the polymer-based micro-foaming interlayer gradient material are provided with dense polymers, and the middle layer is in a cellular structure. The gradient material prepared by the invention has no bonding layer, the diameter of the foam hole of the middle layer can be controlled in micron order, the thickness of the outer compact polymer layer can be controlled by the temperature, pressure and time of thermal desorption, and the yield strength can be improved by 1-3 times through the thickness change, so that the gradient material has a certain buffer performance and more excellent mechanical properties, and has wide application prospects in the fields of biomedicine, product packaging, aerospace, traffic buildings and the like.

Description

Preparation method of polymer-based micro-foaming interlayer gradient material

Technical Field

The invention relates to the technical field of materials, in particular to a preparation method of a polymer-based micro-foaming interlayer gradient material.

Background

Gradient materials refer to a class of heterogeneous composite materials whose properties change gradually in response to changes in structure and composition through continuous or quasi-continuous changes in structure and composition elements. Due to the existence of such special composition and structure, gradient materials generally have superior properties to general materials, thereby drawing more and more attention and attention from researchers. Compared with the common micro-foaming material, the gradient micro-foaming material is a micro-foaming material with a cell structure changing in a gradient manner along a certain direction, has the characteristics of insulation, heat insulation, light weight, wear resistance, scraping resistance and the like of a homogeneous micro-foaming material, has designability and controllability of the gradient material, and has excellent application prospect in the fields of impact protection, heat insulation, heat preservation and the like.

Various preparation methods have been developed for gradient composite materials of different systems, such as a lamination sintering method, a bonding method, a self-propagating high-temperature synthesis method, a laser heating synthesis method, a temperature gradient sintering method, a particle co-precipitation method, a vapor deposition method and the like. The conventional bonding method is limited by the difference of the performances of the adhesive and the micro-foaming material, and the prepared gradient material has a bonding layer, low interlayer strength and easy falling of the bonding layer, and the continuity of the material is damaged. The laminated hot-pressing foaming method needs to consider the thermal expansion coefficient of each layer of material and the fluidity of the melt, so that the thickness of each layer cannot be estimated, and the application of the laminated hot-pressing foaming method is limited to a certain extent. The unsaturated foaming method obtains a gradient micro-foaming material with two sides of a cellular structure and a middle layer of a dense polymer by controlling the saturation time. The micro-foaming layer of the gradient material prepared by the method is positioned on the outer layer of the gradient material, the energy absorption performance cannot be improved, and the micro-foaming layer is easy to wear and low in mechanical strength.

In recent years, supercritical fluid foaming techniques using carbon dioxide as a foaming agent have been studied. Chinese patent document CN102424706A reports a preparation method of polymethyl methacrylate cell gradient material, and the obtained gradient material has the following structure: the surface layer has smaller diameter of cells and thinner hole walls, the middle part has larger diameter of cells and thicker hole walls, and the innermost layer is a compact polymethyl methacrylate matrix. The method is to obtain the gradient material with gradually changed cell diameters by regulating and controlling the concentration of carbon dioxide in the polymer, and the application of the gradient material is limited because the pore diameter change range along the thickness direction of the material is small, the thickness of a compact layer is small, and the energy absorption performance of the material is poor. Chinese patent document CN107283709A reports a preparation method of a polymer-based density gradient micro-foaming material, in the method, composite materials with different densities are melted and hot-pressed together, then the composite materials are placed in supercritical carbon dioxide, and the gradient micro-foaming material is prepared by controlling the foaming temperature and the saturation pressure. The structure is as follows: along the thickness direction of the material, the cellular structure and the density of the material are in gradient change. The gradient material prepared by the method has the advantages that the thermal expansion coefficients of the materials of all layers are different, so that the thickness of each layer is difficult to predict in the melting and hot-pressing process, the layers are easy to separate in the foaming process, and the bonding force between the layers is weak.

Disclosure of Invention

Aiming at the defects of the prior traditional technology and the supercritical fluid foaming technology, the preparation method of the polymer-based micro-foaming interlayer gradient material is provided, the gradient material prepared by the method has no bonding layer and a novel structure, can solve the problems of small bonding strength, difficult control of the thickness of a bonding interface and the like of a bonding method, enhances the yield strength of the material, and can design and control the size and the density of cells.

In order to solve the technical problems, the invention provides a preparation method of a polymer-based micro-foaming interlayer gradient material, which comprises the following steps:

(1) placing a thermoplastic polymer in a reaction kettle, and foaming by a high-pressure physical foaming method to obtain a polymer-based micro-foaming material;

(2) the polymer-based micro-foaming material is subjected to a thermal desorption process to obtain a gradient composite material with a compact polymer layer on the outer side and a cellular structure in the middle.

As a preferred aspect of the above technical solution, the method for preparing a polymer-based micro-foamed interlayer gradient material provided by the present invention further comprises a part or all of the following technical features:

as an improvement of the technical scheme, in the step (1), the thermoplastic polymer is a sheet formed by placing polymer particles under a tablet press for high-temperature melting and hot pressing, the temperature control range of the high-temperature melting and hot pressing is 150-250 ℃, and the hot pressing time is 60-90 min.

As an improvement of the above technical solution, in the step (1), the high-pressure physical foaming method comprises: and (3) putting the polymer into a high-pressure reaction kettle, injecting high-pressure gas, controlling the pressure to be 8-18 MPa and the temperature to be 50-140 ℃, keeping the temperature and the pressure for 10-24 hours, opening a pressure release valve to reduce the pressure to normal pressure, and finally cooling and shaping.

As an improvement of the technical scheme, the high-pressure gas is high-pressure carbon dioxide gas or high-pressure nitrogen gas.

As an improvement of the above technical solution, in the step (1), the thermoplastic polymer is polymethyl methacrylate (PMMA), Polystyrene (PS) or Polycarbonate (PC).

As an improvement of the technical scheme, in the step (2), the fixed temperature of the thermal desorption device is 120-160 ℃.

As an improvement of the technical proposal, in the step (2), the time for the thermal desorption is 1 to 24 hours.

As an improvement of the technical scheme, in the step (2), the thermal desorption set pressure is 0-80 KPa.

As an improvement of the technical scheme, in the thermal desorption process in the step (2), the foam material is placed in a blast drying oven, the temperature is set to be 120-160 ℃, the time is set to be 1-24 hours, the pressure is 0-80 KPa, and gradient composite materials with different structures can be obtained by controlling the temperature, the pressure and the time.

The polymer-based micro-foaming interlayer gradient material is prepared by any one of the methods.

Compared with the prior art, the technical scheme of the invention has the following beneficial effects:

1. the polymer-based micro-foaming interlayer gradient material prepared by the invention has a novel structure, the whole body is of an interlayer gradient structure, the outer layer of the material is a dense polymer, and the middle layer of the material is of a cellular structure. The interlayer has no bonding layer, thus solving the problems of small bonding strength, difficult control of the thickness of a bonding interface and the like in a bonding method.

2. The outer layer of the polymer-based micro-foaming interlayer gradient material prepared by the invention is a dense polymer with a certain thickness, and the thickness change of the dense polymer can be realized by controlling the constant-temperature heating time, temperature and pressure in a heating device. Along with the rise of the thermal desorption temperature and pressure and the extension of time, the thickness of the compact layer is increased, and the pore diameter of the pore close to the compact layer is slightly reduced. The greater the thickness, the better the mechanical strength and dimensional stability of the gradient material. In the known experimental process, the yield strength of the polymer-based micro-foaming interlayer gradient material can be increased from 12MPa to 50MPa by 1-3 times, and the buffering and energy absorption properties of the material are greatly improved.

3. The method has simple process and better designability, and can regulate and control the size of the cells of the middle micro-foaming layer through the foaming process and regulate and control the thickness of the outer compact polymer layer through the thermal desorption process, thereby realizing the control of the density of the gradient material.

4. The foaming process adopts a supercritical fluid technology, and the process is mature and controllable; the thermal desorption process is to carry out secondary molding on the micro-foaming material according to the rheological behavior of the polymer matrix: at room temperature, when a large amount of gas is dissolved in the polymer, the system is in a glassy state. If the temperature is raised, the gas expands and rapidly escapes from the polymer, the system undergoes reversion, the glass state enters a high elastic state, two sides close to the air are changed from a cellular structure to a compact polymer, and thus a gradient micro-foaming material with two sides being compact polymers and a middle layer being a cellular structure is formed.

5. Has wide application prospect in the fields of biomedicine, product packaging, aerospace, traffic construction and the like.

The foregoing description is only an overview of the technical solutions of the present invention, and in order to make the technical means of the present invention more clearly understood, the present invention may be implemented in accordance with the contents of the description, and in order to make the above and other objects, features, and advantages of the present invention more clearly understood, the following detailed description is given in conjunction with the preferred embodiments.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings of the embodiments will be briefly described below.

FIG. 1 is a microscopic morphology diagram of a sample prepared by foaming a PMMA sheet at 50 ℃ and 18MPa for 24 hours, and then insulating at 120 ℃ for 24 hours;

FIG. 2 is a microscopic morphology diagram of a sample prepared by foaming a PMMA sheet at 65 ℃ and 18MPa for 12h under heat preservation and pressure preservation, and then preserving heat for 2h at 140 ℃;

FIG. 3 is a microscopic morphology diagram of a sample prepared by foaming a PMMA sheet at 65 ℃ and 18MPa for 12h under heat preservation and pressure maintenance, applying a pressure of 8KPa in an environment of 150 ℃ and preserving heat for 1 h;

FIG. 4 is a microscopic morphology of a sample prepared by foaming a PMMA sheet at 95 ℃ and 18MPa for 10h under heat preservation and pressure maintenance, applying a pressure of 20KPa at 140 ℃ and preserving heat for 90 min;

FIG. 5 is a microscopic morphology diagram of a sample prepared by foaming a PS sheet at 140 ℃ under 8MPa for 24h, applying 80KPa in an environment of 160 ℃ and keeping the temperature for 2 h;

FIG. 6 is a graph of compressive stress strain for a gradient microfoamed sample and a homogeneous microfoamed sample, the yield strength of the homogeneous microfoamed sample is 12MPa, and the yield strength of the gradient microfoamed sample 2 is increased to 50 MPa;

FIG. 7 is a graph of the variation of the densified layer thickness of a gradient microfoamed sample with thermal desorption temperature.

Detailed Description

Other aspects, features and advantages of the present invention will become apparent from the following detailed description, which, when taken in conjunction with the drawings, illustrate by way of example the principles of the invention.

The method provided by the invention selects the thermoplastic polymer as the matrix material. Firstly, polymer particles with certain mass are placed under a tablet press for high-temperature melting and hot pressing, the temperature control range is 150-250 ℃, and the hot pressing time is 60-90 min. Then placing the hot-pressed slice into a reaction kettle for foaming by using supercritical carbon dioxide, wherein the foaming process comprises the following steps: and controlling the pressure to be 8-18 MPa and the temperature to be 50-140 ℃, keeping the temperature and the pressure for 10-24 h, opening a pressure relief valve to reduce the pressure to normal pressure, and then cooling and shaping to obtain the polymer-based foam material. And finally, placing the prepared foam material in a blast drying oven, setting the temperature to be 120-160 ℃, the time to be 1-24 hours and the pressure to be 0-80 KPa, and controlling the temperature, the pressure and the time to obtain the gradient composite material with different structures.

The present invention is further illustrated by, but is not limited to, the following examples.

Specific example 1:

1. a PMMA sheet with a thickness of 0.42mm was placed in a constraining mold.

2. Placing the binding mould in a high-pressure reaction kettle, introducing a small amount of carbon dioxide for washing for 3min, raising the temperature of the reaction kettle to 50 ℃ through an oil bath kettle, then injecting the carbon dioxide by using an injection plug pump to enable the pressure of the carbon dioxide to reach 18MPa, and saturating for 24h at constant temperature and constant pressure.

3. And (3) quickly unscrewing the pressure release valve to release the pressure to normal pressure, then removing the heating device, and putting the high-pressure kettle into an ice-water mixture to cool and shape to obtain the homogeneous micro-foaming material.

4. And (3) placing the prepared foam material in a forced air drying oven, setting the temperature to be 120 ℃, setting the time to be 24 hours, and not applying pressure to obtain the gradient composite material.

The microstructure of the upper half of the gradient composite is shown in FIG. 1, the whole material is almost filled with cells, the average cell diameter is 3.56 μm, the thickness of the dense layer on the upper surface is extremely thin, and the average thickness value is 2.32 μm.

Specific example 2:

1. and (3) putting the PMMA particles under a tablet press for hot pressing at the temperature of 170 ℃ for 70min to obtain PMMA sheets with the thickness of 0.3 mm.

2. The PMMA sheets were cut into disks of a certain size and placed in a restraining mold.

3. Placing the binding mould in a high-pressure reaction kettle, introducing a small amount of carbon dioxide for washing for 3min, raising the temperature of the reaction kettle to 65 ℃ through an oil bath kettle, then injecting the carbon dioxide by using an injection plug pump to enable the pressure of the carbon dioxide to reach 18MPa, and saturating for 12h at constant temperature and constant pressure.

4. And (3) quickly unscrewing the pressure release valve to release the pressure to normal pressure, then removing the heating device, and putting the high-pressure kettle into an ice-water mixture to cool and shape to obtain the homogeneous micro-foaming material.

5. And (3) placing the prepared foam material in a forced air drying oven, setting the temperature to be 140 ℃, setting the time to be 2 hours, and not applying pressure to obtain the gradient composite material.

The microstructure of the gradient composite material is shown in FIG. 2, the upper surface and the lower surface of the gradient composite material are dense layers without bubble holes, and the average thicknesses of the gradient composite material are 65.76 μm and 69.05 μm respectively. Along the thickness direction, the diameter of the foam pores gradually increases from outside to inside and can be divided into 3 areas, and the diameters of the foam pores are respectively 0, 2.47 and 6.72 mu m and are in gradient change.

Specific example 3:

1. a PMMA sheet with a thickness of 0.35mm was placed in a constraining mold.

2. Placing the binding mould in a high-pressure reaction kettle, introducing a small amount of carbon dioxide for washing for 3min, raising the temperature of the reaction kettle to 65 ℃ through an oil bath kettle, then injecting the carbon dioxide by using an injection plug pump to enable the pressure of the carbon dioxide to reach 18MPa, and saturating for 12h at constant temperature and constant pressure.

4. And (3) placing the prepared foam material in a forced air drying oven, setting the temperature at 150 ℃, the time at 1h and the pressure at 8KPa, and obtaining the gradient composite material.

The microstructure of the gradient composite material is shown in figure 3, the whole material can be divided into three layers, the upper surface and the lower surface are compact layers, no foam holes exist, the thicknesses of the compact layers and the foam holes are 113 micrometers and 122 micrometers respectively, the middle part is a foam hole layer, the average diameter of the foam holes is 4.16 micrometers, and the thickness of the foam hole layer is 160.24 micrometers. The whole material is changed into a three-layer gradient material from a foam material, and the appearance of the material is as follows: colorless and transparent-white-colorless and transparent.

Specific example 4:

1. a PMMA sheet with a thickness of 1mm was placed in a restraining mold.

2. Placing the binding mould in a high-pressure reaction kettle, introducing a small amount of carbon dioxide for washing for 3min, raising the temperature of the reaction kettle to 95 ℃ through an oil bath kettle, then injecting the carbon dioxide by using an injection plug pump to ensure that the pressure of the carbon dioxide reaches 18MPa, and saturating for 10h at constant temperature and constant pressure.

4. And (3) placing the prepared homogeneous micro-foaming material in a forced air drying oven, setting the temperature at 140 ℃, the time at 90min and the pressure at 20KPa, and obtaining the gradient composite material.

The microstructure of the upper half part of the gradient composite material is shown in figure 4, the outermost layer is a compact layer from top to bottom, cells gradually appear from the outside to the inside, and the average cell diameters of the cells are respectively 0, 4.79 and 8.75 mu m and are in gradient change. The compressive stress strain curve is shown in the gradient foam sample 1 of fig. 6, and it can be seen that the yield strength of the gradient material is obviously improved, and the energy absorption capacity is improved accordingly.

Specific example 5:

1. a PS sheet with a thickness of 0.56mm was placed in a confining mould.

2. Placing the binding mould in a high-pressure reaction kettle, introducing a small amount of carbon dioxide for washing for 3min, raising the temperature of the reaction kettle to 140 ℃ through an oil bath kettle, then injecting the carbon dioxide by using an injection plug pump to enable the pressure of the carbon dioxide to reach 8MPa, and saturating for 24h at constant temperature and constant pressure.

4. And (3) placing the prepared homogeneous micro-foaming material in a forced air drying oven, setting the temperature to be 160 ℃, the time to be 2 hours and the pressure to be 80KPa, and obtaining the gradient composite material.

The microstructure of the gradient composite material is shown in fig. 5, the whole material is changed from a micro-foaming material into a compact material, no foam holes exist, and the appearance of the material is changed from white to colorless and transparent.

Fig. 6 is a compressive stress strain curve diagram of the gradient microfoamed sample and the homogeneous microfoamed sample, the yield strength of the homogeneous microfoamed sample is 12MPa, and the yield strength of the gradient microfoamed sample 2 is increased to 50 MPa. The preparation process of the gradient micro-foaming sample 1 comprises the following steps: the PMMA sheet is subjected to heat preservation and pressure maintaining for 10 hours at the temperature of 95 ℃ and under the pressure of 18MPa, foamed, and then applied with pressure of 20KPa at the temperature of 140 ℃ and subjected to heat preservation for 90 min; the preparation process of the gradient micro-foaming sample 2 comprises the following steps: the PMMA sheet is subjected to heat preservation and pressure maintaining for 12 hours at the temperature of 65 ℃ and under the pressure of 18MPa, foaming is carried out, then the pressure of 49KPa is applied in the environment of 140 ℃, and heat preservation is carried out for 4 hours; the preparation conditions of the homogeneous microfoamed samples were: the PMMA sheet is prepared after foaming at the temperature of 95 ℃ and under the pressure of 18 MPa.

Fig. 7 is a graph showing the variation of the thickness of the densified layer of the gradient microfoamed sample along with the thermal desorption temperature, and the thickness of the densified layer increases along with the increase of the thermal desorption temperature. The preparation process of the gradient micro-foaming sample comprises the following steps: and (3) keeping the temperature and pressure of the PMMA sheet at 95 ℃ and 18MPa for 10h, foaming, applying pressure at 25KPa at different temperatures, and keeping the temperature for 4 h.

The raw materials listed in the invention, the upper and lower limits and interval values of the raw materials of the invention, and the upper and lower limits and interval values of the process parameters (such as temperature, time and the like) can all realize the invention, and the examples are not listed.

While the foregoing is directed to the preferred embodiment of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

1. A preparation method of a polymer-based micro-foaming interlayer gradient material is characterized by comprising the following steps:

the thermoplastic polymer is a sheet formed by putting polymer particles into a tablet press and performing high-temperature melting hot pressing, the temperature control range of the high-temperature melting hot pressing is 150-250 ℃, and the hot pressing time is 60-90 min;

the high-pressure physical foaming method comprises the following steps: putting a polymer into a high-pressure reaction kettle, injecting high-pressure gas, controlling the pressure to be 8-18 MPa and the temperature to be 50-140 ℃, keeping the temperature and the pressure for 10-24 hours, opening a pressure release valve to reduce the pressure to normal pressure, and finally cooling and shaping;

(2) carrying out thermal desorption on the polymer-based micro-foaming material to obtain a gradient composite material with a compact polymer layer on the outer side and a cellular structure in the middle; the thermal desorption process is to place the foam material in a blast drying oven, set the temperature to be 120-160 ℃, the time to be 1-24 hours and the pressure to be 0-80 KPa, and to control the temperature, the pressure and the time to obtain the gradient composite material with different structures.

2. The method of claim 1, wherein the polymer-based microfoamed sandwich gradient material is prepared by: in the step (1), the thermoplastic polymer is polymethyl methacrylate, polystyrene or polycarbonate.

3. A polymer-based microfoamed sandwich gradient material characterized by: the polymer-based microfoamed sandwich gradient material is prepared by any of the methods of claims 1-2.