High-temperature-resistant and solvent-resistant foam with high foaming ratio as well as preparation method and application thereof

Abstract

The invention discloses a preparation method of high-foaming-ratio high-temperature-resistant and solvent-resistant foam. The preparation method comprises the following steps: carrying out melt blending on a matrix and a plasticizer, and molding to obtain a blend profile; the plasticizer is prepared from at least one of diphenylmethane diisocyanate and polymethylene polyphenyl polyisocyanate; the blend profile is placed in supercritical fluid, and polymer foam is obtained through pressure maintaining, pressure relief and cooling shaping; the pressure relief time is 5-10 seconds; and placing the polymer foam in water for cross-linking and curing to obtain the high-temperature-resistant and solvent-resistant foam with high foaming ratio. The high-temperature-resistant solvent-resistant foam with the high foaming ratio can reach the ultra-low density of 0.052 g / cm < 3 >, the processing temperature is far lower than the glass-transition temperature of a matrix, and the high-temperature-resistant solvent-resistant foam has good solvent resistance and excellent high-temperature mechanical properties.

Description

Technical Field

[0001] The invention relates to the field of foaming materials, and in particular to a high-foaming-ratio, high-temperature-resistant and solvent-resistant foam and a preparation method and application thereof. Background Art

[0002] With the development of aerospace, rail transit and drone technology, high temperature resistant and multifunctional engineering plastics and special engineering plastics have received extensive attention. This is mainly because these polymers not only have a higher glass transition temperature than general plastics, but also have a lower density than metals and other materials, and have broader application prospects in various fields. However, the further lightweighting and functionalization of materials remains a severe challenge. Due to the characteristics of low density, high specific strength, low thermal conductivity, and anti-seismic buffering, polymer foam materials are widely used in aerospace and other fields. However, engineering plastics have high melt strength, face problems such as difficult processing and low foaming ratio, which limits the application and development of their foaming materials. Therefore, it is of great research significance to prepare foam materials that are easy to process, have high foaming ratio and are resistant to high temperatures.

[0003] At present, the foaming methods for preparing engineering plastics include chemical method, freeze-drying method, water vapor induced phase separation method, etc. However, these processing methods are often complicated, involving the use of a large amount of organic solvents, causing damage to the environment and human body, and have low foaming ratios.

[0004] Carbon dioxide (CO2) foaming uses CO2 as a foaming agent. At a certain temperature and pressure, carbon dioxide enters the polymer matrix, reaches a saturated state, and forms a polymer / gas homogeneous system. Through a sudden increase in temperature or a sudden drop in pressure, the gas in the homogeneous system reaches an oversaturated state, thereby inducing bubble nucleation, and the bubble nucleus gradually grows, and finally a polymer foaming material is obtained.

[0005] It is also difficult to prepare foam with high expansion ratio by simply using carbon dioxide for foaming, and the saturation temperature is high, so chemical co-solvents are needed to assist foaming in order to obtain foam materials with high expansion ratio. At the same time, the use of chemical reagents is also contrary to the concept of environmental protection.

[0006] For example, the patent specification with the publication number CN108659251A discloses a method for preparing polyetherimide foamed particles. The preparation method includes the following steps: obtaining polyetherimide raw materials; extruding the polyetherimide raw materials into thermoplastic polyetherimide particles by means of melt extrusion; injecting the thermoplastic polyetherimide particles into a high-pressure mixed fluid composed of supercritical fluid carbon dioxide and an organic solvent to obtain polyetherimide foamed particles. Although the patent technology claims that its technical effect is that polyetherimide can achieve high magnification expansion at a relatively low foaming temperature, it actually does not disclose the specific expansion ratio. The inventor's research found that the maximum foaming ratio of pure polyetherimide using supercritical fluid carbon dioxide can only reach about 2.5 times. Moreover, the above patent technology still requires the use of a large amount of organic solvents, which not only increases costs but also harms the environment and the human body.

[0007] Therefore, it is a challenging task to prepare foam materials with high foaming ratio and high temperature resistance through a simple and environmentally friendly method. Summary of the Invention

[0008] In view of the above technical problems and the deficiencies existing in the art, the present invention provides a high foaming ratio, high temperature resistant and solvent resistant foam, and its preparation method and application. The high foaming ratio, high temperature resistant and solvent resistant foam of the present invention is a microcellular foam, and its cell structure is a closed cell with good uniformity. Compared with non-microcellular foams, the compressive strength of the microcellular foam of the present invention is higher.

[0009] The specific technical solution is as follows:

[0010] [1] A method for preparing a high foaming ratio, high temperature resistant and solvent resistant foam, including:

[0011] Melting and blending a matrix and a plasticizer and then molding to obtain a blend profile; the plasticizer includes at least one of diphenylmethane diisocyanate and polymethylene polyphenyl polyisocyanate (PMDI);

[0012] Placing the blend profile in a supercritical fluid, and performing pressure holding, pressure releasing and cooling and shaping to obtain a polymer foam; the pressure releasing time is 5 - 10 s;

[0013] Placing the polymer foam in water for crosslinking and curing to obtain the high foaming ratio, high temperature resistant and solvent resistant foam.

[0014] Generally speaking, the matrix has a very high melt strength, so rapid pressure relief is usually required to prepare foams with a high foaming ratio. However, the inventors have found through research that in the preparation method of the present invention, if the pressure relief time is too fast, such as rapid (e.g., within 1 s) or instantaneous pressure relief as in the conventional means of the prior art, foams with a high foaming ratio cannot be obtained, and the foam morphology is also poor, with problems such as incomplete foams. Accordingly, the preparation method of the present invention proposes that the pressure relief time is in the range of 5 to 10 s. This slow pressure relief foaming method allows the cell holes to have enough time to grow, and the cell walls are not easily broken, which is beneficial to obtaining foams with a high foaming ratio and good morphology.

[0015] In some embodiments, for the preparation method of the high-foaming-ratio, high-temperature-resistant and solvent-resistant foam, the matrix can be pre-treated for water removal.

[0016] In some embodiments, for the preparation method of the high-foaming-ratio, high-temperature-resistant and solvent-resistant foam, the matrix can include at least one of polyetherimide (PEI), polysulfone, polyethersulfone, polyamide, polycarbonate, polyformaldehyde, polytetrafluoroethylene, polyphenylene sulfide, and polybutylene terephthalate.

[0017] In some embodiments, for the preparation method of the high-foaming-ratio, high-temperature-resistant and solvent-resistant foam, the plasticizer can further include at least one of trimellitic anhydride and methylhexahydrophthalic anhydride.

[0018] In some embodiments, for the preparation method of the high-foaming-ratio, high-temperature-resistant and solvent-resistant foam, based on the total mass of the matrix and the plasticizer being 100%, the mass proportion of the plasticizer can be 1% to 50%, such as 2%, 3%, 5%, 8%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, etc. Further, it can be any value listed above or the range value between any two of the above, such as 30% to 50%, etc.

[0019] In some embodiments, for the preparation method of the high-foaming-ratio, high-temperature-resistant and solvent-resistant foam, before the melt blending, the matrix and the plasticizer can be mechanically blended first.

[0020] In some embodiments, for the preparation method of the high-foaming-ratio, high-temperature-resistant and solvent-resistant foam, the temperature of the melt blending can be 20 to 200 °C, and further can be 150 to 200 °C.

[0021] In some embodiments, for the preparation method of the high-foaming-ratio, high-temperature-resistant and solvent-resistant foam, a kneader can be used for the melt blending.

[0022] In some embodiments, for the method of preparing the high-foaming-ratio heat-resistant and solvent-resistant foam, the molding can be compression molding, specifically carried out under the conditions of 20 - 200 °C (such as 150 - 200 °C, etc.) and 1 - 20 MPa (such as 10 MPa, 15 MPa, etc.).

[0023] In some embodiments, for the method of preparing the high-foaming-ratio heat-resistant and solvent-resistant foam, a flat vulcanizer can be used for compression molding to obtain a blend profile.

[0024] In some embodiments, for the method of preparing the high-foaming-ratio heat-resistant and solvent-resistant foam, the blend profile can be a sheet. Further, the thickness of the sheet can be 0.1 - 50 mm, such as any value among 1 mm, 3 mm, 5 mm, 10 mm, 20 mm, 30 mm, 50 mm or the range value between any two of the above.

[0025] In some embodiments, for the method of preparing the high-foaming-ratio heat-resistant and solvent-resistant foam, the supercritical fluid can include supercritical carbon dioxide and / or supercritical nitrogen. When the supercritical fluid includes supercritical carbon dioxide and supercritical nitrogen, the volume ratio of the supercritical carbon dioxide to the supercritical nitrogen can be (1:19) - (19:1).

[0026] In some embodiments, for the method of preparing the high-foaming-ratio heat-resistant and solvent-resistant foam, the dosage of the supercritical fluid can be 0.5% - 10% of the mass of the blend profile.

[0027] In some embodiments, for the method of preparing the high-foaming-ratio heat-resistant and solvent-resistant foam, the pressure of the supercritical fluid can be 8 - 20 MPa, and the saturation temperature can be -10 - 200 °C, further can be 70 - 200 °C, such as 75 °C, 80 °C, 85 °C, 90 °C, 95 °C, 100 °C, 110 °C, 120 °C, 130 °C, 140 °C, 150 °C, 160 °C, 165 °C, 170 °C, 175 °C, 180 °C, 185 °C, 190 °C, 195 °C, etc. The foaming ratio can be regulated by adjusting the saturation temperature.

[0028] In some embodiments, for the method of preparing the high-foaming-ratio heat-resistant and solvent-resistant foam, the pressure relief is carried out at the saturation temperature.

[0029] In some embodiments, for the method of preparing the high-foaming-ratio heat-resistant and solvent-resistant foam, the pressure holding time can be 1 - 9000 minutes, such as 2 hours, etc.

[0030] In some embodiments, for the method of preparing the high-foaming-ratio heat-resistant and solvent-resistant foam, ice water can be used for cooling and shaping to stabilize the pore structure.

[0031] In some embodiments, for the preparation method of the high-foaming ratio, high-temperature resistant and solvent-resistant foam, the temperature of crosslinking and curing can be 10 to 100 °C, such as 20 °C, 30 °C, 40 °C, 50 °C, 60 °C, 70 °C, 80 °C, 90 °C, etc.

[0032] The present invention hereby provides a preferred preparation method for an exemplary high-foaming ratio, high-temperature resistant and solvent-resistant foam, comprising:

[0033] Melting and blending a matrix and a plasticizer and then molding to obtain a blend profile; the matrix comprises polyetherimide, and the plasticizer comprises polymethylene polyphenyl polyisocyanate;

[0034] Placing the blend profile in a supercritical fluid, and obtaining a polymer foam through pressure holding, pressure releasing, and cooling and shaping; the time for pressure releasing is 5 to 10 s;

[0035] Placing the polymer foam in water for crosslinking and curing to obtain the high-foaming ratio, high-temperature resistant and solvent-resistant foam.

[0036] The above preferred preparation method combines polyetherimide with the plasticizer polymethylene polyphenyl polyisocyanate, and develops a simple and environmentally friendly strategy to prepare a foam material with a high-foaming ratio and high-temperature and solvent resistance. Inspired by the mechanical crosslinking and polyurea (PUA) reaction, a PEI / PUA foam material with a crosslinked structure is prepared through foaming and curing treatments. Supercritical fluid foaming such as supercritical carbon dioxide is used to prepare a high-temperature resistant PEI / PUA composite foam material, which undergoes a crosslinking and curing reaction in water, and finally a PEI / PUA high-foaming ratio and high-temperature and solvent-resistant foam material is prepared. Due to the plasticizing effect of the plasticizer PMDI, the PEI / PUA composite foam material has a high foaming ratio (up to 5 to 30 times). After crosslinking and curing, the formed PUA and the PEI molecular chains form mechanical crosslinks, significantly improving the heat resistance of the composite foam material, and the glass transition temperature is increased by about 30 °C. At the same time, the PEI / PUA composite foam material is given excellent chemical reagent resistance.

[0037] [2] The high-foaming ratio, high-temperature resistant and solvent-resistant foam prepared by the preparation method according to [1].

[0038] In some embodiments, the foaming ratio of the high-foaming ratio, high-temperature resistant and solvent-resistant foam can be 5 to 30 times, such as 10 times, 20 times, 25 times, etc.

[0039] In some embodiments, the average cell size of the high-foaming ratio, high-temperature resistant and solvent-resistant foam is 1 to 100 μm.

[0040] [3] Application of the high expansion ratio, high temperature resistant and solvent resistant foam described in [2] in the fields of military, aerospace, rail transit, unmanned aerial vehicles or new energy.

[0041] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0042] The high expansion ratio, high temperature resistant and solvent resistant foam of the present invention can achieve an ultra-low density of 0.052 g / cm 3 , the processing temperature is far lower than the glass transition temperature of the matrix, has good solvent resistance (the mass residue rate can reach more than 99.8%), and excellent high temperature mechanical properties. Description of the Drawings

[0043] Figure 1 It is a cross-sectional morphology photo of the composite material sheet PEI / PMDI50 in Example 1.

[0044] Figure 2 It is a pore morphology photo of the composite foam material PEI / PUA50-25 in Example 1.

[0045] Figure 3 It is a high temperature mechanical property test chart of the composite foam material PEI / PUA50-5 in Example 2.

[0046] Figure 4 It is a loss tangent (Tanδ) curve graph of the dynamic thermomechanical analysis (DMA) test of the PEI / PMDI composite material sheet in Example 2 and the PEI sheet in Comparative Example 1.

[0047] Figure 5 It is a solvent resistance test result chart of the composite foam material PEI / PUA50-5 in Example 2 and the polyetherimide foam material PEI-2.45 in Comparative Example 1. Detailed Embodiments

[0048] The present invention will be further described below in conjunction with the drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. The operation methods without specific conditions noted in the following embodiments are usually carried out under conventional conditions or according to the conditions recommended by the manufacturer.

[0049] Example 1:

[0050] To prepare the PEI / PUA composite foam materials, the following steps were carried out. Initially, the PEI powder was dried in a vacuum oven at 100 °C. After that, the liquid PMDI and the PEI powder were mixed in a self-sealing bag for 10 minutes to form a PMDI@PEI mixture. Subsequently, 150 g of the mixture was weighed and placed in a mixer at 150 °C and melt-blended at a speed of 65 r / min for 5 minutes. The resulting blend was compression-molded in a flat vulcanizer at 150 °C and 15 MPa to obtain a uniformly mixed PEI / PMDI composite material sheet. These PEI / PMDI composite material sheets were labeled as PEI / PMDIX, where X represents the mass fraction of PMDI in PEI and PMDI, in %. In this example, X is 50, indicating that PEI and PMDI are of equal mass, and the mass fraction of PMDI in PEI and PMDI is 50%. The cross-sectional morphology of the composite material sheet PEI / PMDI50 is as shown in Figure 1 shown.

[0051] The PEI / PUA composite foam materials with a high foaming ratio were prepared using the supercritical carbon dioxide (scCO2) foaming technology. First, the PEI / PMDI composite material sheet was placed in an autoclave and saturated in a carbon dioxide atmosphere at a pressure of 20 MPa for 2 hours. Subsequently, the high-pressure CO2 was slowly released at a saturation temperature of 95 °C, and the pressure relief time was 10 s. To stabilize the pore structure, the pressure-relieved sheet was immersed in ice water. Then it was placed in water at 30 °C for crosslinking and curing treatment to obtain the PEI / PUA composite foam materials with a high foaming ratio and high temperature and solvent resistance. The obtained foam was named PEI / PUAX-Y, where the definition of X is the same as above, and Y represents the foaming ratio of the foam material, in times. In this example, Y is 25, that is, the foaming ratio is 25 times. The pore morphology of the composite foam material PEI / PUA50-25 is as shown in Figure 2 shown, and the density of the composite foam material PEI / PUA50-25 is 0.052 g / cm 3 .

[0052] Example 2:

[0053] The difference from Example 1 is only that the saturation temperature is 70 °C, and the rest are the same, and the composite foam material PEI / PUA50-5 with a foaming ratio of 5 times is obtained.

[0054] Figure 3The high-temperature mechanical property test process and results of the composite foam material PEI / PUA50-5 are shown. It can be seen from this that the foam prepared by the method of the present invention has good high-temperature mechanical properties. The high-temperature mechanical property test was carried out in a forced-air drying oven (DHG-9245A). The composite foam material PEI / PUA50-5 was cut into rectangles, about 40 mm in length, about 10 mm in width, and about 2.3 mm in thickness. The weight of the weight was 100 g. After the oven temperature was raised to 270 °C, it was kept warm for 20 minutes.

[0055] Comparative Example 1:

[0056] Prepare a PEI sheet and a polyetherimide foam material PEI-2.45 with a foaming ratio of 2.45 times. The steps are as follows: Weigh 150 g of PEI powder and put it into the oven, dry it at 100 °C for 24 hours, then put it into a mixer and knead it at 300 °C for 10 minutes, with a rotation speed of 65 r / min. Place the obtained material in a flat vulcanizer and press it into a sheet. The pressure of the pressing plate is 15 MPa and the time is 10 minutes to obtain a PEI sheet. Use the supercritical carbon dioxide (scCO2) foaming technology: Place the obtained PEI sheet in a foaming kettle, saturate it at 185 °C for 2 hours under a carbon dioxide atmosphere of 20 MPa, and then quickly depressurize (within 1 second) to foam to obtain a PEI foam material PEI-2.45 with a foaming ratio of 2.45.

[0057] Figure 4 The results of the loss tangent (Tanδ) in the dynamic thermomechanical analysis (DMA) test of the PEI / PMDI composite material sheet in Example 2 and the PEI sheet in Comparative Example 1 are shown. The specimen sizes are all 25 mm in length, 10 mm in width, and 2 mm in thickness. From Figure 4 it can be seen that the PEI / PMDI composite material sheet prepared by the method of the present invention has a glass transition temperature much lower than that of the polyetherimide matrix, that is, the PEI sheet, before foaming and curing, enabling it to be melt-processed at a lower temperature. The process of the dynamic thermomechanical property test is introduced as follows: The specimen was tested in a single cantilever mode at a heating rate of 5 °C / min and a test frequency of 1 Hz.

[0058] Figure 5 The solvent resistance test results of the composite foam material PEI / PUA50-5 in Example 2 and the polyetherimide foam material PEI-2.45 in Comparative Example 1 are shown. It can be seen from this that the foam prepared by the method of the present invention has excellent solvent resistance. The process of the solvent resistance test is introduced as follows: Weigh PEI-2.45 and PEI / PUA50-5 and soak them in a glass bottle containing N-methylpyrrolidone (NMP) and N,N-dimethylformamide (DMF), place them at 25 °C for 24 hours, then take out the foam material and dry it, and weigh the final mass.

[0059]

[0060] M0 and M1 are the masses of the foam material before and after soaking respectively.

[0061] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

Claims

1. A preparation method of a high-foaming ratio heat-resistant and solvent-resistant foam, characterized in that Comprising: A blend profile is obtained by melt-blending a matrix and a plasticizer and then shaping; the plasticizer includes at least one of diphenylmethane diisocyanate and polymethylene polyphenyl polyisocyanate; The blend profile is placed in a supercritical fluid, and after pressure holding, pressure release, and cooling and shaping, a polymer foam is obtained; the time for pressure release is 5 to 10 s; The polymer foam is placed in water for crosslinking and curing to obtain the high expansion ratio, high temperature resistant, and solvent resistant foam.

2. The preparation method according to claim 1, characterized in that, The matrix includes at least one of polyetherimide, polysulfone, polyethersulfone, polyamide, polycarbonate, polyoxymethylene, polytetrafluoroethylene, polyphenylene sulfide, and polybutylene terephthalate.

3. The preparation method according to claim 1, wherein The plasticizer further includes at least one of trimellitic anhydride and methylhexahydrophthalic anhydride.

4. The preparation method according to claim 1, wherein, Based on the total mass of the matrix and the plasticizer being 100%, the mass proportion of the plasticizer is 1% to 50%, further 30% to 50%.

5. The preparation method according to claim 1, characterized in that, The temperature of the melt-blending is 20 to 200 °C, further 150 to 200 °C.

6. The preparation method according to claim 1, characterized in that, The shaping is compression molding, which is carried out under the conditions of 20 to 200 °C, preferably 150 to 200 °C, and 1 to 20 MPa.

7. According to the preparation method described in claim 1, characterized in that, The supercritical fluid includes supercritical carbon dioxide and / or supercritical nitrogen; The dosage of the supercritical fluid is 0.5% to 10% of the mass of the blend profile; The pressure of the supercritical fluid is 8 to 20 MPa, the saturation temperature is -10 to 200 °C, further 70 to 200 °C; The pressure release is carried out at the saturation temperature; The temperature of the crosslinking and curing is 10 to 100 °C.

8. A high expansion ratio, high temperature resistant, and solvent resistant foam prepared by the preparation method according to any one of claims 1 to 7.

9. The high-foaming-ratio high-temperature and solvent-resistant foam according to claim 8, wherein The expansion ratio of the high expansion ratio, high temperature resistant, and solvent resistant foam is 5 to 30 times.

10. Application of the high expansion ratio, high temperature resistant, and solvent resistant foam according to claim 8 or 9 in the fields of military, aerospace, rail transit, unmanned aerial vehicle, or new energy.

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