CN113773564B

CN113773564B - Composite foam material and preparation method and application thereof

Info

Publication number: CN113773564B
Application number: CN202110929204.3A
Authority: CN
Inventors: 刘子瑾; 于晖; 刘熙; 吴清华; 林江华; 唐玉
Original assignee: Wuyi University
Current assignee: Wuyi University
Priority date: 2021-08-13
Filing date: 2021-08-13
Publication date: 2023-07-21
Anticipated expiration: 2041-08-13
Also published as: CN113773564A

Abstract

The invention discloses a composite foam material and a preparation method and application thereof. The composite foam material comprises an open-cell foam matrix material and a first carbon-based filler, wherein the open-cell foam matrix material is provided with cells with an open-cell structure, and the inner walls of the cells are attached with a second carbon-based filler. The invention realizes the effective construction of the carbon material filler net structure, regulates and controls the spatial distribution of the carbon filler, avoids the stacking of the carbon filler and prepares the compressible conductive composite foam material.

Description

Composite foam material and preparation method and application thereof

Technical Field

The invention belongs to the technical field of foam materials, and particularly relates to a composite foam material, and a preparation method and application thereof.

Background

Some two-dimensional carbon materials have the characteristics of high conductivity, high aspect ratio, high specific surface area, low density, good flexibility and the like, and are ideal fillers for improving the conductivity of the composite material under the condition of low filler consumption.

However, these carbon materials have a disadvantage in that they are easily stacked, which is disadvantageous in their dispersion in the polymer, and their agglomeration in the polymer may cause the formation of defect sites, which seriously affect the conductive properties of the carbon material/polymer composite.

How to inhibit or even avoid stacking of carbon materials in carbon material/polymer composites, and where to distribute carbon materials in carbon material/polymer composites, is a matter of concern.

Disclosure of Invention

The first technical problem to be solved by the invention is as follows:

a method of preparing a composite foam material is provided.

The second technical problem to be solved by the invention is as follows:

there is provided a composite foam material prepared by the above method.

The third technical problem to be solved by the invention is:

the use of the above composite foam.

The invention also provides a pressure sensor, which comprises the composite foam material.

In order to solve the first technical problem, the invention adopts the following technical scheme:

a method of making a composite foam comprising the steps of:

(1) Dispersing a first carbon-based filler in a solvent to obtain a first carbon-based filler dispersion, and diluting a foam base material with the first carbon-based filler dispersion to obtain a mixed dispersion system in which the solid content of the foam base material is 6.25% or less;

(2) Freeze-drying the mixed solution to obtain an open-cell foam matrix material;

(3) And adsorbing a second carbon-based filler into the open-cell foam matrix material to obtain the composite foam material.

When the solid content of the foam matrix material is 6.25% -1%, the foam material with an open-cell structure is obtained.

The composite foam material is prepared by a vacuum freeze drying method. In the water dispersion system, water is crystallized at a low temperature to form ice crystals, other components in the system are extruded by the generated ice crystals, the other components are rearranged and assembled, the components are mutually piled to form a three-dimensional structure, and the three-dimensional porous foam material is obtained after the ice sublimates. The structure and morphology of the foam material are regulated by changing the process of the vacuum freeze drying method and the composition of the material.

According to one embodiment of the present invention, the step (1) further includes adding an auxiliary agent to the foam base material, and stirring to obtain the foam base material with the auxiliary agent added system. In this step, the stirring time was 2 hours, and the ultrasonic treatment was performed for 10 minutes after the completion of the stirring. The above-mentioned additional vulcanization system functions to carry out curing crosslinking.

According to an embodiment of the present invention, in the step (2), the mixed solution is placed in a container, the container is covered with an insulating layer, the container is placed in an ice chest at a temperature of 0 ℃ or lower, preferably at-18 ℃, and the ice chest is frozen overnight; after complete freezing, the container was taken out, and rapidly placed in a pre-refrigerated freeze dryer, and freeze-dried for 48 hours to obtain the open-cell foam matrix material.

According to one embodiment of the present invention, in the step (3), the method further comprises immersing the open-cell foam base material in the second aqueous dispersion of carbon-based filler, then placing the immersed material in a vacuum oven, vacuum deaerating at room temperature overnight, taking out the immersed material, and vacuum drying the immersed material at 50 ℃.

The second carbon-based filler is impregnated into the cells of the open-cell foam matrix material through three-dimensionally connected cell channels of the open-cell foam matrix material and is adsorbed on the inner walls of the cells; wherein the carboxylated open-cell foam matrix material is capable of interacting with groups on the surface of the second carbon-based filler.

According to one embodiment of the invention, the auxiliary comprises the following components in parts by weight:

0.5-3 parts of sulfur, 0.1-3 parts of zinc oxide, 0.3-5 parts of accelerator N-ethyl-N-phenyl dithiocarbamic acid zinc, 0.1-1 part of accelerator diethyl dithiocarbamic acid zinc, 0.5-3 parts of anti-aging agent 2, 6-di-tert-butyl-4-methylphenol, 0.01 part of methylene dinaphthyl sodium sulfonate dispersing agent and 0.01-1 part of potassium hydroxide.

In order to solve the second technical problem, the invention adopts the following technical scheme:

a composite foam material:

the composite foam material comprises the open-cell foam matrix material and the first carbon-based filler, wherein cells with open-cell structures are formed in the open-cell foam matrix material, and the second carbon-based filler is attached to the inner walls of the cells.

According to one embodiment of the present invention, the foam base material includes at least one or a combination of several of carboxylated styrene-butadiene latex, nitrile-butadiene latex, styrene-butadiene latex and neoprene latex and polyacrylate emulsion.

According to an embodiment of the present invention, the first carbon-based filler includes at least one of graphene, fullerene, activated carbon, acetylene black, carbon nanotubes, carbon fibers, and derivatives thereof.

According to an embodiment of the present invention, the second carbon-based filler includes at least one of graphene, fullerene, activated carbon, acetylene black, carbon nanotubes, carbon fibers, and derivatives thereof.

According to one embodiment of the present invention, the concentration of the first carbon-based filler dispersion is 2 mg/ml.

According to one embodiment of the present invention, the preparation process of the first carbon-based filler dispersion liquid includes dispersing the first carbon-based filler in water, stirring for 2 hours, and then ultrasonic treating in an ice water bath for 10 minutes.

A method for reducing the composite foam material comprises the step of in-situ reducing the composite foam material to obtain a reduced composite foam material.

According to one embodiment of the invention, the method for reducing the composite foam material comprises the steps of placing a bracket in a polytetrafluoroethylene liner of a hydrothermal kettle, placing the prepared composite foam material on the bracket, placing the prepared composite foam material under the bracket into a hydrazine hydrate solution, reacting for 3 hours at 95 ℃ to obtain the reduced composite foam material, filtering, washing with water, and vacuum drying at 60 ℃ for later use. After the reduction treatment, the brown-yellow composite foam material is converted into the black reduced composite foam material.

The reduced composite foam is then vulcanized and crosslinked in a forced air oven. The vulcanization temperature is 110 ℃ and the vulcanization time is t ₉₀ The above-mentioned reduced composite foam material with orderly distributed filler is obtained.

In another aspect, the invention also relates to the use of the above composite foam in flexible materials.

In yet another aspect of the present invention, there is also provided a pressure sensor comprising a syntactic foam as described above.

One of the above technical solutions has at least one of the following advantages or beneficial effects:

(1) Converting the closed-cell composite foam material into an open-cell composite foam material by a vacuum freeze-drying method, and attaching a carbon-based filler on the inner wall of the cell to enhance the conductivity and mechanical properties of the composite foam material;

(2) The solid content of the composite foam material is regulated to regulate the cell structure, so that the cell size is precisely controlled.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention.

FIG. 1 is a schematic representation of the preparation of GSBR and GSBR/GO foams.

FIG. 2 (a) a physical representation of a GSBR/GO foam and (b) a physical representation of a GSBR/rGO foam.

FIG. 3 is a graph of apparatus for testing the resistance of GSBR/rGO foam as a function of compression set.

FIG. 4 (a) GSBR-50, (b) GSBR-25, (c) GSBR-12.5 and (d) low magnification SEM images of GSBR-6.25 foams.

FIG. 5 (a, b) cross-sectional SEM images of GSBR-50, (c, d) GSBR-25, (e, f) GSBR-12.5 and (g, h) GSBR-6.25 foams.

FIG. 6 (a) GSBR-50, (b) GSBR-25, (c) GSBR-12.5 and (d) GSBR-6.25 foam cell size distribution.

Fig. 7 is a graph of the average cell size of GSBR foam materials of different solids content.

Figure 8 SEM images of GSBR/rGO foam (a, b) before compression and (c, d) after compression.

Fig. 9 GO, GSBR/GO and GSBR/rGO foam raman spectra.

FIG. 10 shows the relative change in resistance of SBR/rGO foam at maximum strain of (a) 37%, (b) 55%, (c) 78% in this orderσ _ν Change with strain curve sum (d)σ _ν Peak contrast analysis of (c).

FIG. 11 is a graph showing the relative resistivity of GSBR/rGO foams over time (the inset shows a compression-recovery process).

Detailed Description

Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to like or similar elements or elements having like or similar functions throughout.

The embodiments described below by referring to the drawings are illustrative only and are not to be construed as limiting the invention.

In the description of the present invention, the description of the first, second, third, etc. is only for the purpose of distinguishing technical features, and should not be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated or implicitly indicating the precedence of the technical features indicated.

In the description of the present invention, it should be understood that references to orientation descriptions, such as directions of up, down, left, right, etc., are based on the orientation or positional relationship shown in the drawings, are merely for convenience of description and simplification of the description, and do not indicate or imply that the apparatus or element in question must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as limiting the invention.

In the description of the present invention, unless explicitly defined otherwise, terms such as arrangement, installation, connection, etc. should be construed broadly and the specific meaning of the terms in the present invention can be determined reasonably by a person skilled in the art in combination with the specific content of the technical solution.

In order to describe the technical contents, the achieved objects and effects of the present invention in detail, the following description will be made with reference to the embodiments.

Example 1

In the above method for preparing a composite foam material, a graphene/styrene-butadiene latex composite material (GSBR) is prepared.

(1) Experimental raw materials and reagents:

carboxylated SBR latex (carboxylated styrene-butadiene latex), having a solids content of 50%, manufactured by the company of the morning rubber industry, inc.

Graphene Oxide (GO) purchased from nanjing first-come nanomaterial technologies.

Deionized (DI) water was produced by a Barnstead Smart 2 pure water purification system (Thermo Scientific).

Sulfur, zinc oxide, NF diffusant (sodium methylene dinaphthyl sulfonate), KOH (potassium hydroxide), accelerator PX (zinc N-ethyl-N-phenyl dithiocarbamate), accelerator ZDC (zinc diethyl dithiocarbamate) and anti-aging agent 264 (2, 6-di-tert-butyl-4-methylphenol) are technical grade adjuvants.

NF diffusant (sodium methylene dinaphthyl sulfonate) and KOH (potassium hydroxide) are directly added into carboxylated SBR latex under the stirring condition, and other assistants are ground into emulsion by adopting a ball mill for later use.

(2) Preparation of GSBR:

under stirring, a vulcanization aid was added to the SBR latex in the following vulcanization formulation (100 parts SBR, 1 part sulfur, 0.7 part zinc oxide, 0.35 parts accelerator PX, 0.1 part accelerator ZDC, 1.0 part antioxidant 264, 0.05 part NF dispersant, and 0.05 part KOH) by mass; stirring is continued for 2 hours, ultrasonic treatment is carried out for 10 minutes, and the SBR latex added with the vulcanization system is obtained and stirred for standby.

GO was dispersed in water and stirred for 2 hours and sonicated in an ice-water bath for 10 minutes to give GO dispersion (2 mg/ml). The SBR latex is diluted by adopting GO dispersion liquid with different volumes, and the latex of SBR and GO blend (GSBR for short) with solid content of 50%, 25%, 12.5% and 6.25% is prepared and marked as GSBR-50, GSBR-25, GSBR-12.5 and GSBR-6.25 respectively.

Placing GSBR in a container, coating an insulating layer on the outside, standing in a freezer at-18 ℃, and freezing overnight; and taking out the material after complete freezing, rapidly placing the material in a pre-refrigerated freeze dryer, and freeze-drying the material for 48 hours to obtain the GSBR foam material, wherein the preparation process is shown in figure 1.

(3) Preparing GSBR/GO foam material:

the vacuum auxiliary impregnation method is adopted to adsorb GO into the GSBR foam material with the open cell structure, and the specific steps are as follows:

and (3) dipping the GSBR-6.25 foam material into the GO aqueous dispersion, placing the foam material into a vacuum oven, vacuum defoaming overnight at room temperature, taking out the foam material, and vacuum drying at 50 ℃ to obtain the GSBR/GO foam material. GO is soaked into the GSBR cells through three-dimensionally connected cell channels of the GSBR and adsorbed on the inner walls of the cells; wherein carboxylated SBR interacts with the content groups on the GO surface, the preparation process is shown in fig. 1.

(4) Preparation of GSBR/rGO foam material by in-situ reduction

And adopting hydrazine hydrate to perform in-situ reduction treatment on the GSBR/GO foam material to obtain the GSBR/rGO foam material. The method comprises the following specific steps:

placing a bracket in a polytetrafluoroethylene liner of a hydrothermal kettle, placing the prepared GSBR/GO foam material on the bracket, placing a hydrazine hydrate solution under the bracket, reacting for 3 hours at 95 ℃ to obtain the GSBR/rGO foam material, filtering, washing with water, and vacuum drying at 60 ℃ for later use.

As shown in fig. 2, after the reduction treatment, the brown-yellow GSBR/GO foam was converted to black GSBR/rGO foam.

The GSBR/rGO foam was vulcanization crosslinked in a forced air oven. The vulcanization temperature is 110 ℃ and the vulcanization time is t ₉₀ And (3) obtaining the GSBR/rGO foam material with orderly distributed filler.

The ordered distribution refers to the ordered distribution of rGO on the inner wall of the cell.

The resistance of the above GSBR/rGO foam was tested as a function of compression set, and the device tested is shown in FIG. 3.

Performance test:

in the process of preparing GSBR, ice crystals are formed in the GSBR, the size of the ice crystals is related to the solid content of the latex, and the size of the ice crystals can be regulated and controlled by changing the solid content, so that foam materials with different cell sizes are obtained. The structure and morphology of cells in GSBR foam was observed using SEM of fig. 4.

As can be seen in FIG. 4a, cells in GSBR-50 foam are oval in shape, which is formed by the extrusion rearrangement of spherical ice crystals. The cells are closely adjacent and are randomly distributed.

As shown in FIG. 4b, the cell size of the GSBR-25 foam is significantly greater than the cell size of the GSBR-50 foam, and the number of cells per unit area of the GSBR-25 foam is significantly less than the GSBR-50 foam.

The size of the cells in the GSBR-12.5 foam in fig. 4c is further increased compared to the GSBR-25 foam and the number of cells per unit area is reduced.

Further reduction of the solids content of the GSBR latex to 6.25% did not increase the cell size of the GSBR-6.25 foam compared to the GSBR-12.5 foam, as shown in FIG. 4 d.

As can be seen by comparing the GSBR-50, GSBR-25, GSBR-12.5 and GSBR-6.25 foams, the cells of the GSBR-50 and GSBR-25 foams are mostly closed cell structures, while the GSBR-6.25 has a distinct open cell structure.

As shown in FIG. 5, SEM was used to investigate the structural morphology of GSBR-50, GSBR-25, GSBR-12.5 and GSBR-6.25 foams. The process of transitioning GSBR foam from a closed cell structure to an open cell structure was analyzed.

Wherein fig. 5b, 5d, 5f, 5h are enlarged partial views of fig. 5a, 5c, 5e, and 5g in order.

FIG. 5a is a cross-sectional morphology of a GSBR-50 foam showing cells in an oval shape, distributed more uniformly, and cells in a closed cell structure.

As can be seen in fig. 5b, some areas of the GSBR-50 foam material exhibit cell wall perforation, adjacent cells are connected, but no significant three-dimensionally connected cell channels are present. Extrusion between adjacent cells, as indicated by the white arrows, results in thinner cell walls, which can be as low as 20 μm thick.

As shown in FIG. 5c, the cross-section of the GSBR-25 foam material shows an irregular circular shape of cells, which are randomly distributed.

As shown in FIG. 5d, the cell walls of the GSBR-25 foam material have a generally decreasing thickness (indicated by white arrows) compared with the cell walls of GSBR-50, and the areas of white circles show the interconnection between adjacent cells, forming locally interconnected channels.

As shown in FIG. 5e, the cell size of the GSBR-12.5 foam is further increased.

The small white circles in fig. 5f are the communication channels between cells and adjacent cells, and the large white circles are cells of a large size up to 200 μm in size, but still of a closed cell structure.

FIG. 5g is a cross-sectional profile of a GSBR-6.25 foam, the large cell size in the GSBR-6.25 foam being about 120 μm, while a large number of small cells are present. The inner walls of the cells are carriers loaded by GO, and the more small cells are, the larger the total surface area of the cells is, the more GO can be adsorbed.

As shown in FIG. 5h, the GSBR-6.25 cell walls are thinner, the surface is rough, the cell bottoms are connected, and an open cell structure (shown by white circles) is shown compared with the GSBR-12.5 foam material; the cells are mutually communicated to form a three-dimensional communicated cell channel.

FIG. 6 is a cell size distribution plot of a foam material:

as shown in FIG. 6a, the GSBR-50 foam has a narrow pore size distribution, with 75% or more of the cells having a size of 30 to 40. Mu.m.

The distribution of cell sizes for GSBR-25 foams is broader than for GSBR-50 foams, with cells being predominantly distributed between 30 and 90 μm, with a cell size of about 50 μm having the greatest cell ratio and a maximum cell size of up to 150 μm (FIG. 6 b).

For GSBR-12.5 foam (FIG. 6 c), the cell size distribution is further broadened compared to GSBR-50 foam, and the maximum cell size can reach 280 μm.

For GSBR-6.25 foam (FIG. 6 d), the cell size does not continue to increase with increasing water content. The larger size cells exceeding 150 μm in the GSBR-6.25 foam were reduced compared to the GSBR-12.5 foam, and the GSBR-6.25 cell size distribution was narrowed, shifting toward the smaller size direction.

FIG. 7 is a graph of average cell size for a foam:

as shown in fig. 7a, as the solids content decreases, the average cell size of the GSBR foam increases, and when the solids content is 12.5%, the average cell size of the GSBR foam is maximized; at a solids content of 6.25%, a decrease in the average cell size occurred.

Calculating cell density of GSBR foam according to FIG. 1The degree, the cell density of the GSBR foam is decreased and then increased. As can be seen from FIG. 7b, the GSBR foam has a cell density of 1X 10 ¹¹ ~ 6×10 ¹¹ cells/cm ³ Within the range.

The GSBR-6.25 foam material with an open-cell structure is immersed in the GO aqueous dispersion liquid by a vacuum auxiliary immersion method, and then GO adsorbed in cells is reduced in situ by hydrazine hydrate to obtain the GSBR/rGO foam material. FIG. 8 is a cross-sectional SEM morphology of GSBR/rGO foam before and after compression.

FIG. 8a is an SEM image of a cross section of a GSBR foam prior to compression, the cells being oval in shape and having a size of 50-200 μm; the walls of the foam holes are mutually extruded, and the foam holes are obviously deformed; adjacent cells are mutually communicated (the direction indicated by white arrows) to form communicated cell channels.

FIG. 8b is an enlarged view of a portion of FIG. 8a, with black arrows indicating the walls of the cells of the GSBR foam, with smooth cross-section and no rGO coating; the white arrow points to the inner wall of the cells of the GSBR foam material, and the surface of the inner wall is coated with rGO sheets.

The rGO has an obvious fold structure, and rGO sheets are closely adsorbed on the inner walls of cells of the GSBR foam material, which indicates that the ordered distribution of the rGO sheets on the inner walls of the cells of the GSBR foam material, which are mutually communicated, is successfully realized by adopting a vacuum auxiliary impregnation method.

Fig. 8c and 8d are SEM images of cross-sections of the GSBR foam material after compression.

As shown in fig. 8c, after compression, the structure of the GSBR foam did not change significantly from before compression (fig. 8 a), indicating that the GSBR foam had compressible-recovery characteristics;

as can be seen from fig. 8d, the rGO sheets are tightly adsorbed on the cell inner walls (indicated by white arrows) of the GSBR foam, no significant change compared to before compression treatment. This suggests that rGO is able to adsorb tightly in GSBR foam, which may be related to rGO having good flexibility, capillary action during impregnation and drying, and good interaction of rGO with SBR, etc.

FIG. 9 is a Raman spectrum of GO, GSBR/GO and GSBR/rGO foams:

as shown in FIG. 9, the distinct D peak and G peak appear in the Raman spectra of GO, GSBR/GO and GSBR/rGO foam, respectively at 1342 cm ^-1 And 1583 cm ^-1 Where they respectively correspond to sp ³ Disordered structural regions and sp of hybridized carbon ² A graphite structural region of the hybridized carbon.

In raman spectroscopy, the intensity ratio of the D and G peaks (ID/IG) is often used to characterize the structural defects and degree of disorder of the carbon material.

The intensity ratio (ID/IG) of the D and G peaks of GO was 0.97, which is consistent with previous experimental results.

The ID/IG of GSBR/GO was 0.72, and after reduction with hydrazine hydrate, the ID/IG of GSBR/rGO increased to 1.31, indicating that GO was successfully reduced to rGO in situ.

FIG. 10 shows the relative change in resistance of SBR/rGO foam with maximum strain of (a) 37%, (b) 55%, (c) 78% in this orderσ _ν Change with strain curve sum (d)σ _ν Peak contrast analysis of (c):

as shown in fig. 10a, during compression (37% maximum compressive strain), as the strain increases,σ _ν continuously decreasing, negative values occur. This indicates that the resistance of the GSBR/rGO foam decreases continuously during compression, i.e. the electrical conductivity of the foam increases. In the recovery process, the recovery curve is linearly changed in the process of reducing the compressive strain from 37% to 20%, and the recovery curve is overlapped with the compression curve, so that the linear change interval exists in the compression-recovery process; when the compression strain is less than 20%,σ _ν continuing to increase, wherein the value of the restoring curve is higher than the value of the compression curve in the corresponding strain interval; when recovered, itσ _ν Above 0, indicating a decrease in the electrical conductivity of the GSBR/rGO foam after compression-recovery treatment.

As shown in fig. 10b, during compression (55% maximum compressive strain), as the strain increases,σ _ν the values were all below 0, similar to the 37% compression process. In the course of the reversion,σ _ν in the course of 55% to 10%, the recovery curve and the compression curve are substantiallyCoincidence, there is a linear variation interval; when the compression strain is less than 10%, the slope of the recovery curve is greater than that of the compression curve,σ _ν the value is greater than 0 but less than 37% of the corresponding value. As shown in fig. 10c, when the maximum compressive strain is 78%, during compression,σ _ν continuously descends, and in the recovery process,σ _ν continuously rising; while in the whole compression-recovery process,σ _ν values less than 0 indicate that the GSBR/rGO foam material has better electrical conductivity than its initial electrical conductivity during this process.

Notably, during compression-recovery at 37%, 55% and 78% strain, a region where the recovery curve and compression curve overlap appears and existsσ _ν The linear variation of the value with strain, this region may be referred to as the linear region. The characteristic of the linear region is beneficial to expanding the application of the GSBR/rGO foam material in the fields of pressure sensors and the like.

FIG. 10d shows the maximum strain (37%, 55% and 78%) of GSBR/rGO foam during compression recoveryσ _ν And (5) performing numerical comparison analysis. After compression, itσ _ν The values were all less than 0 and gradually decreased in the order of 37%, 55% and 78% strain. This suggests that the compression treatment resulted in an increase in the conductivity of the GSBR/rGO foam and that its conductivity increased with increasing compressive strain. This is probably because during compression, the rGO sheets adsorbed on the inner walls of the GSBR/rGO foam form a tighter and complete conductive network. After reversion treatment, the GSBR/rGO foam materialσ _ν The values decrease gradually in the order of 37%, 55% and 78%.

In order to further investigate the effect of compression set on GSBR/rGO foam structure, the following procedure was devised: the GSBR/rGO foam was compressed and then quickly returned to the original state as shown in the inset in fig. 11, recording the law of change in resistance of the GSBR/rGO foam over time.

Calculating the relative change rate of the resistance according to the formula 1σ _ν Time dependence. GSBR/rGO foam after compression-recoveryσ _ν The law of change with time is shown in FIG. 11Shown by the lines. The change in resistance of the GSBR/rGO foam material over time is in three phases; first quickly descending, then slowly descending, and finally gradually returning to 0. This indicates that the GSBR/rGO foam is able to revert to the original state.

After the compression-recovery treatment, the resistance of the GSBR/rGO foam material is continuously reduced, and the conductivity of the GSBR/rGO foam material is gradually recovered to the initial state. This is related to the redistribution of rGO sheets within the inner walls of GSBR/rGO foam. The compression-recovery process disrupts the conductive network formed by rGO and over time the conductive network resumes its original state.

In the first 5 min, GSBR/rGO foam materialσ _ν The value drops rapidly, this stage corresponds to the rapid restoration of the cell structure under large deformation; within 100 min, GSBR/rGO foam materialσ _ν The value slowly decreases, and the stage is related to the process of changing the adsorbed rGO sheet layers on the inner wall of the foam holes from loose contact to close contact; after a time of more than 100 min, GSBR/rGO foam materialσ _ν The value goes substantially towards 0, indicating that the GSBR/rGO foam has substantially reverted from the large deformation to the original state. Notably, changes in the shape and size of the foam material also have an effect on its electrical resistance.

In summary, the change in conductivity of the GSBR/rGO foam after compression-recovery treatment has a time delay effect.

The GSBR foam was tested for its thermal stability:

the thermal stability properties of GSBR foams were studied using thermogravimetric analysis (TGA). The content of graphene in the GSBR-50, GSBR-25, GSBR-12.5 and GSBR-6.25 foam materials is increased in sequence.

Table 1 shows the thermal weight loss parameters for GSBR-50, GSBR-25, GSBR-12.5 and GSBR-6.25 foams.

Initial decomposition temperature of GSBR-50 foamT ₅ The initial decomposition temperatures of the GSBR-25, GSBR-12.5 and GSBR-6.25 foams increased to 330.2, 331.9 and 345.7 ℃ in order, and the amplifications were 22.1, 23.8 and 37.6 ℃ in order.

This indicates that the graphene sheets act as physical barriers in SBR, delaying the degradation process of SBR. At the same time, GSBR-50, GSBR-25, GSBR-12.5 and GSBR-6.25 foam materials have the fastest decomposition temperatureT _max And a temperature at which the thermal weight loss is 50%T ₅₀ Sequentially increasing the fastest decomposition temperature of the GSBR-6.25 foamT _max Of foam material of ratio GSBR-50T _max Raised by 54.5 ℃ and GSBR-6.25 foam materialT ₅₀ Of foam material of ratio GSBR-50T ₅₀ The temperature is increased by 25.6 ℃.

This is also related to the physical barrier effect of graphene sheets, delaying the degradation process of GSBR.

TABLE 1 thermal weight loss parameters for GSBR-50, GSBR-25, GSBR-12.5 and GSBR-6.25 foams

Samples	GSBR-50	GSBR-25	GSBR-12.5	GSBR-6.25
					T5 (°C)	308.1	330.2	331.9	345.7
Tmax (°C)	395.4	437.9	437.8	449.9
					T50 (°C)	405.9	426.4	427.5	431.5
Carbon residue (%)	5.0	4.3	5.5	5.2

The foregoing is merely exemplary embodiments of the present invention and are not intended to limit the scope of the present invention, and all equivalent modifications made by the present invention or direct or indirect application in the relevant art are intended to be included in the scope of the present invention.

Claims

1. A method of making a composite foam, characterized by: the method comprises the following steps:

(1) Dispersing a first carbon-based filler in a solvent to obtain a first carbon-based filler dispersion, and diluting a foam matrix material with the first carbon-based filler dispersion to obtain a mixed solution, wherein the solid content of the mixed solution is 6.25%;

(3) Immersing the open-cell foam matrix material into the second carbon-based filler dispersion liquid, taking out and drying;

(4) Sequentially carrying out in-situ reduction and vulcanization crosslinking on the material obtained in the step (3) to obtain a composite foam material;

the foam matrix material is carboxyl styrene-butadiene latex;

the first carbon-based filler and the second carbon-based filler are both graphene oxide.

2. A method of preparing a composite foam according to claim 1, wherein:

the step (1) further comprises adding a vulcanization aid into the foam matrix material, and stirring to obtain the foam matrix material added with the vulcanization system.

3. A method of preparing a composite foam according to claim 2, characterized in that:

the vulcanization aid comprises the following components in parts by mass:

0.5-3 parts of sulfur, 0.1-3 parts of zinc oxide, 0.3-5 parts of accelerator N-ethyl-N-phenyl dithiocarbamic acid zinc, 0.1-1 part of accelerator diethyl dithiocarbamic acid zinc, 0.5-3 parts of anti-aging agent 2, 6-di-tert-butyl-4-methylphenol, 0.05-1 part of methylene dinaphthyl sodium sulfonate dispersing agent and 0.01-1 part of potassium hydroxide.

4. A composite foam material prepared by the method of any one of claims 1-3, characterized in that:

the composite foam material comprises a foam base material and reduced graphene oxide, wherein the open-cell foam base material is provided with open-cell structure cells, and the reduced graphene oxide is attached to the inner walls of the cells.

5. Use of a composite foam material according to claim 4 in flexible materials.

6. A pressure sensor, characterized by: a composite foam comprising the composition of claim 4.