CN113265088B - Preparation method of ethylene-vinyl acetate copolymer porous shape memory material - Google Patents

Abstract

The invention relates to the technical field of polymer materials, in particular to a preparation method of an ethylene-vinyl acetate copolymer porous shape memory material. The method firstly uses ethylene-vinyl acetate copolymer as raw material, dissolves it in a mixed solvent of toluene and n-propanol, induces thermally induced phase separation through cooling to obtain porous EVA with uniform pore size, and then immerses the porous EVA in benzene peroxide The acetone solution of formyl is heated, cross-linked, washed and dried to obtain a porous shape memory polymer material. The preparation process of the method is environmentally friendly, the involved solvents can be recycled, the cost of raw materials is low, the pore size of the prepared material is uniform, simple and easy to adjust, and the porous shape memory polymer material with uniform pore size can be effectively prepared.

Description

A kind of preparation method of ethylene-vinyl acetate copolymer porous shape memory material

technical field

The invention relates to the technical field of polymer materials, in particular to a preparation method of an ethylene-vinyl acetate copolymer porous shape memory material.

Background technique

Porous shape memory polymers are a class of smart polymer materials. This kind of polymer material has the advantages of large specific surface area, high porosity and low density, and can realize the shape fixation and spontaneous recovery of the material by responding to external stimuli (such as light, heat, electricity, magnetism, pH changes, etc.). This process is also accompanied by flexible adjustment of application characteristics such as internal pore structure and compression performance. This makes such materials show good application potential in the fields of adsorption/separation, intelligent control of surface catalysis, and intelligent design of ergonomic structures.

At present, in the preparation of porous shape memory polymer materials, the commonly used methods are: physical/chemical foaming method, sacrificial template method, freeze-drying method, etc. Although these methods can prepare porous shape memory polymers that meet the basic properties However, these methods have some problems in the preparation and final preparation of finished materials. These problems are not only reflected in the problem of uneven pore size affecting the comprehensive quality and performance of materials, but also in the difficulty of structural control, which limits the diversity of materials. In addition, the preparation process of these methods is usually cumbersome, resulting in high production costs. The current problems of these methods not only limit the product quality of the final material, but also limit the large-scale production and commercial application of the material due to the increase in cost.

The development trend of porous shape memory polymer materials is light weight, high porosity, uniform pore size, and good shape memory performance. Ethylene-vinyl acetate copolymer (EVA) porous shape memory material has become a research hotspot in the field of porous shape memory materials due to its advantages of light weight, complete pore structure and high chemical stability. However, the existing preparation process of EVA porous shape memory material is mostly based on physical/chemical foaming method, which requires complex mixing and molding equipment, high processing temperature and molding pressure, and the pore size of the obtained material is uneven. The sacrificial template method can be used to obtain EVA porous materials with uniform pore size, but the use of template raw materials significantly increases the production cost and limits its large-scale production, and the high temperature of the existing cross-linking process will melt the EVA and destroy the original open-cell structure. Therefore, the existing preparation process not only has unfavorable factors of production cost such as high equipment/raw material requirements and complex process flow, but also cannot affect the final product quality of the material, which limits the large-scale production and commercial application of the material.

Therefore, it is of great practical significance to develop a new method to solve the problems existing in the existing preparation methods of EVA porous shape memory polymer materials.

SUMMARY OF THE INVENTION

The invention provides a preparation method of an ethylene-vinyl acetate copolymer (EVA) porous shape memory material. First, this method proposes to realize EVA pore fabrication by mixed solvent thermally induced phase separation method. By optimizing the types and proportions of mixed solvents, the principle of thermally induced phase separation is used to achieve uniform pore formation and rapid prototyping of EVA. Second, the cross-linking reaction temperature is effectively reduced by the solid-liquid reaction, avoiding the structural collapse of the EVA porous material, and endowing the EVA with high shape memory properties. Through the optimization of the above method, the present invention can effectively control the microporous structure of the EVA porous shape material by adjusting the phase separation conditions. At the same time, the energy consumption and equipment requirements of the preparation process are significantly reduced, and the solvent can be recovered without loss, realizing low-cost green production, thus solving many problems existing in the current preparation process of porous EVA shape memory polymer materials and their products.

The concrete technical scheme adopted by the present invention to solve its technical problems is:

A preparation method of an ethylene-vinyl acetate copolymer porous shape memory material, comprising the following steps:

Step 1, dissolving ethylene-vinyl acetate copolymer (EVA) in a mixed solvent of toluene and n-propanol to obtain an EVA solution;

Step 2, the above-mentioned EVA solution is transferred to the mold, and the low temperature water bath treatment is carried out to induce phase separation to obtain porous EVA material;

Step 3, transferring the above-mentioned porous EVA material into a cross-linking agent solution, carrying out a cross-linking pre-soak treatment, heating the cross-linking reaction, completing the cross-linking, and obtaining a cross-linking product;

In step 4, the above-mentioned cross-linked product is washed and dried under reduced pressure to obtain an ethylene-vinyl acetate copolymer porous shape memory material.

Preferably, the content of vinyl acetate in the EVA is 18%-32%.

Preferably, the dissolution temperature when the EVA is dissolved is 70°C.

Preferably, the volume ratio of toluene and n-propanol in the mixed solvent is 3:1.

Preferably, the concentration of EVA in the EVA solution is 100-180 mg/mL.

Preferably, the temperature of the low-temperature water bath is 0-50° C., and the treatment time is 0.5-1 hour.

Preferably, the crosslinking agent solution is an acetone solution of benzoyl peroxide, wherein the concentration of benzoyl peroxide is 0.01-0.1 g/mL.

Preferably, the time for the cross-linking pre-soak treatment is 3 hours.

Preferably, the crosslinking reaction temperature is 70°C, and the reaction time is 2-6 hours.

In the present invention, EVA is dissolved in a mixed solvent of toluene (good solvent) and n-propanol (non-solvent) to configure a polymer solution that can constitute a thermal phase separation system; then the polymer solution is moved into a mold to perform phase separation, During this process, the liquid-liquid phase separation of the solution is induced by cooling, so that the homogeneous polymer solution is transformed into a polymer-enriched phase and a solvent-enriched phase, and the polymer-enriched phase is dispersed in the solvent-enriched phase to form a three-dimensional A coherent pore structure is obtained to obtain an EVA porous material; finally, the EVA porous material is transferred into an acetone solution dissolved with benzoyl peroxide, soaked, and cross-linked to impart shape memory properties to the EVA porous shape memory material.

The beneficial effects of the present invention are:

(1) The provided preparation method does not involve complex molding equipment, the process is simple and feasible, and the process conditions are mild;

(2) The preparation process does not involve high temperature and high pressure, does not use any foaming agent, and the solvent used can be recycled and used, which is green and environmentally friendly, and the cost is low;

(3) The cross-linking process is a low-temperature solid-liquid reaction process, which does not involve the melting of thermoplastic resin, which effectively avoids the collapse and damage of the microporous structure;

(4) The obtained porous shape memory polymer material has uniform pore size, and the pore structure is easy to control;

(5) The prepared porous shape memory polymer material has a considerable shape memory effect, and its shape memory fixation rate and recovery rate are both above 98.0%.

Description of drawings

FIG. 1 is a test chart of the shape memory performance of the sample prepared in Example 1 of the present invention.

Fig. 2 is the scanning electron microscope image of the sample prepared in Example 2 of the present invention; wherein: the concentration of EVA in the solution in a is 120 mg/mL, and the concentration of EVA in the solution in b is 100 mg/mL.

3 is a scanning electron microscope image of the sample prepared in Example 3 of the present invention; wherein: the phase separation temperature in a is 25°C, and the phase separation temperature in b is 50°C.

Detailed ways

Representative embodiments based on the figures shown in the figures will now be further refined. It should be understood that the following description is not intended to limit the embodiments to one preferred embodiment. On the contrary, it is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the described embodiments as defined by the appended claims.

A simple and easy method for preparing EVA porous shape memory material, which comprises the following steps:

Step 1: Dissolve ethylene-vinyl acetate copolymer (EVA) with a vinyl acetate content of 18%-32% in a mixed solvent of toluene and n-propanol (3:1) at 70°C to obtain a concentration of 100-180mg/ mL of EVA solution;

Step 2, transfer the above EVA solution to a mold, and conduct a low temperature (0-50°C) water bath for 0.5-1 hour to induce phase separation to obtain a porous EVA material;

Step 3: Transfer the above porous EVA material to an acetone solution (concentration 0.01-0.1 g/mL) dissolved with benzoyl peroxide, soak for 3 hours, heat to 70°C and react for 2-6 hours to complete cross-linking , to obtain a cross-linked product;

In step 4, the above-mentioned cross-linked product is washed and dried under reduced pressure to obtain an EVA porous shape memory material.

The mass fraction of vinyl acetate in the ethylene-vinyl acetate copolymer used in the present invention is 18%, the density is 0.94g/cm3, and the melt index is 8g/10min (190°C/2.16kg).

The present invention will be further described below through specific implementation examples.

Example 1:

Step 1: Dissolve EVA (Elvax460, DuPont) pellets with a vinyl acetate content of 18% in a mixed solvent of toluene and n-propanol (3:1) at 70 °C to obtain an EVA solution with a concentration of 180 mg/mL .

In step 2, the above solution was transferred to a cylindrical mold, and a low temperature water bath was performed at 45° C. for 0.5 hours to induce phase separation to obtain a porous EVA material.

Step 3: Transfer the above EVA material to an acetone solution (concentration 0.05 g/mL) dissolved with benzoyl peroxide, soak for 3 hours, heat to 70° C. and react for 5 hours to complete cross-linking.

Step 4, taking out the cross-linked porous EVA, washing with ethanol, drying under reduced pressure at room temperature, and obtaining the EVA porous shape memory material.

Example 2:

Step 1: Dissolve EVA (Elvax460, DuPont) pellets with a vinyl acetate content of 18% in a mixed solvent of toluene and n-propanol (3:1) at 70 °C to obtain a concentration of 120 mg/mL and 100 mg/mL. mL of EVA solution.

In step 2, the above solution was transferred to a cylindrical mold, and was placed in a low temperature water bath at 45° C. for 0.5 hours to induce phase separation to obtain a porous EVA material.

Step 3: Transfer the above porous EVA material to an acetone solution (concentration 0.05 g/mL) dissolved with benzoyl peroxide, soak for 3 hours, heat to 70° C. and react for 5 hours to complete cross-linking.

Step 4, taking out the cross-linked porous EVA, washing with ethanol, drying under reduced pressure at normal temperature, and obtaining the EVA porous shape memory material.

Example 3:

Step 1: Dissolve EVA (Elvax460, DuPont) pellets with a vinyl acetate content of 18% in a mixed solvent of toluene and n-propanol (3:1) at 70°C to obtain an EVA solution with a concentration of 140 mg/mL .

In step 2, the above solution was transferred to a cylindrical mold, and a low temperature water bath was performed at 0° C. and 50° C. for 0.5 hours to induce phase separation to obtain porous EVA material.

Step 3: Transfer the above EVA material to an acetone solution (concentration 0.05 g/mL) dissolved with benzoyl peroxide, soak for 3 hours, heat to 70° C. and react for 5 hours to complete cross-linking.

Step 4, taking out the cross-linked porous EVA, washing with ethanol, drying under reduced pressure at normal temperature, and obtaining the EVA porous shape memory material.

The shape memory performance test process of the above product is as follows: firstly, the obtained material is heated to 80°C, and a uniform compressive stress is applied, until the compressive strain reaches 50-60%, cooled to room temperature, and the shape of the material is fixed; heated to 80°C again, The material spontaneously recovered to its original shape, and the test results are shown in Table 1 below.

Table 1 Preparation conditions and shape memory performance test results of Examples 1-3

Concentration (mg/mL) Phase separation temperature (℃) Compression set (%) Shape fixation rate (%) Shape recovery rate (%) Example 1 180 45 56.9 98.5 99.0 Example 2 120 45 58.3 99.2 99.0 100 45 56.1 98.7 98.6 Example 3 140 0 52.4 98.2 98.8 140 50 55.7 98.8 98.5

The shape fixation rate ( R _f ) and the shape recovery rate ( R _r ) in Table 1 were calculated by the following formulas, respectively.

。

.

。

.

where ε _unload is the compressive strain after stress removal, ε _rec is the compressive strain after reheating and recovery, ε _initial is the initial compressive strain after eliminating the thermal history, and ε _load is the maximum compressive strain under load.

As can be seen from Table 1, the EVA porous shape memory materials prepared by the present invention all show good shape memory performance, and their shape fixation rate and recovery rate can reach more than 98%.

Table 2 Preparation conditions of Examples 1-3 and their density and average pore size

Concentration (mg/mL) Phase separation temperature (℃) Density (g·cm-3) Average pore size (μm) Example 1 180 45 0.42 10.13 Example 2 120 45 0.29 7.12 100 45 0.23 14.36 Example 3 140 0 0.36 5.52 140 50 0.39 17.59

As can be seen from Table 2, the EVA porous shape memory material prepared by the present invention has low density and light weight. At the same time, by adjusting the polymer concentration and phase separation temperature, porous materials with different pore sizes can be prepared, and the microporous structure and density of the material can be controlled.

Figure 1 is a test chart of the shape memory performance of the sample prepared in Example 1 of the present invention. It can be seen from Figure 1 that after the material is compressed and fixed in shape, the pore diameter is significantly reduced due to compression, but the pore structure does not collapse significantly. After reheating to restore the shape of the material, the pore structure and size were almost completely restored, and the pore structure did not change significantly from that before compression. During the whole testing process, the shape fixation rate of the material was 98.5%, and the shape recovery rate was 99.0%, showing excellent shape memory performance.

Fig. 2 is the scanning electron microscope image of the sample prepared in Example 2 of the present invention. As can be seen from Fig. 2 and Table 2, adjusting the concentration of the polymer solution can effectively control the microporous structure of the EVA porous shape memory material, while maintaining a uniform pore size .

Fig. 3 is the scanning electron microscope image of the prepared sample of Example 3 of the present invention. As can be seen from Fig. 3 and Table 2, adjusting the phase separation temperature effectively regulates the microporous structure of the EVA porous shape memory material while maintaining uniform pore size.

The above-mentioned embodiments are used to illustrate the present invention, but not to limit the present invention. Within the spirit of the present invention and the protection scope of the claims, any modifications and changes to the present invention all fall into the protection scope of the present invention.

Claims (9)

1. a preparation method of ethylene-vinyl acetate copolymer porous shape memory material, is characterized in that: may further comprise the steps: Step 1, dissolving ethylene-vinyl acetate copolymer (EVA) in a mixed solvent of toluene and n-propanol to obtain an EVA solution; Step 2, the above-mentioned EVA solution is transferred to the mold, and the low temperature water bath treatment is carried out to induce phase separation to obtain porous EVA material; Step 3, transferring the above-mentioned porous EVA material into a cross-linking agent solution, carrying out a cross-linking pre-soak treatment, heating the cross-linking reaction, completing the cross-linking, and obtaining a cross-linking product; In step 4, the above-mentioned cross-linked product is washed and dried under reduced pressure to obtain an ethylene-vinyl acetate copolymer porous shape memory material. 2. preparation method according to claim 1 is characterized in that: the content of vinyl acetate in described EVA is 18%-32%. 3. preparation method according to claim 1 is characterized in that: the dissolving temperature when described EVA dissolves is 70 ℃. 4. preparation method according to claim 1, is characterized in that: in described mixed solvent, the volume ratio of toluene and n-propanol is 3:1. 5. preparation method according to claim 1 is characterized in that: the concentration of EVA in described EVA solution is 100-180mg/mL. 6 . The preparation method according to claim 1 , wherein the temperature of the low-temperature water bath is 0-50° C., and the treatment time is 0.5-1 hour. 7 . 7 . The preparation method according to claim 1 , wherein the crosslinking agent solution is an acetone solution of benzoyl peroxide, wherein the concentration of benzoyl peroxide is 0.01-0.1 g/mL. 8 . 8 . The preparation method according to claim 1 , wherein the time for the cross-linking pre-soak treatment is 3 hours. 9 . 9 . The preparation method according to claim 1 , wherein the cross-linking reaction temperature is 70° C. and the reaction time is 2-6 hours. 10 .

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