KR100836503B1 - Re-entrant porous structure with negative poisson's ratio and method for manufacturing of the same - Google Patents

Abstract

A method for preparing a concave porous structure with a negative poisson's ratio is provided to produce the structure easily, and to control physical properties of the structure properly by changing the size, porosity, and shape of pores in the structure. A method for preparing a concave porous structure with a negative poisson's ratio includes the steps of: (S1) mixing salt particles with polyethylene particles, heating the mixture to attach the polyethylene particles to the salt particles, immersing the polyethylene-adhered salt particles in a brine to dissolve polyethylene-free parts, and drying the partially dissolved salt particles to prepare concave salt particles; (S2) mixing polymethyl methacrylate powder with the concave salt particles in a volume ratio of 2:8 to 4:6; (S3) mixing the mixture with a methyl methacrylate solution, and polymerizing the mixture; (S4) removing the concave salt particles from the polymers using distilled water; and (S5) drying the concave porous structure free of the concave salt particles.

Description

A concave porous structure having a negative Poisson's ratio and a method of manufacturing the same {RE-ENTRANT POROUS STRUCTURE WITH NEGATIVE POISSON'S RATIO AND METHOD FOR MANUFACTURING OF THE SAME}

1 is a flow chart showing a method of manufacturing a concave porous structure having a negative Poisson's ratio according to the present invention;

2 is a flow chart showing a method for producing concave salt particles of the present invention;

Figure 3a is a micrograph photographing the state before partial dissolution as salt particles attached to polyethylene particles,

Figure 3b is a photomicrograph of the salt particles partially dissolved in a salt solution of 20% concentration,

Figure 4 is a PTFE (Polytetrafluoroethylene) frame used in the production method of the present invention, the block specimen prepared from the PTFE frame,

5 is a structural diagram showing a schematic shape of a concave porous structure in which concave salt particles are leached out;

Figure 6a is a photomicrograph of the concave porous structure produced by the manufacturing method according to the present invention,

Figure 6b is a micrograph of the porous structure prepared using convex salt particles as a control,

7 is a graph comparing the measured values and theoretical values of Poisson's ratio when the volume mixing ratio of the salt particles 70% and 80% in the concave porous structure prepared according to the present invention,

8 is a graph comparing elastic modulus measurements and theoretical values at a volume mixing ratio of 70% and 80% of salt particles in convex and concave microporous structures prepared according to the manufacturing method of the present invention;

9 is a photograph of each specimen of the convex and concave porous structure prepared according to the manufacturing method of the present invention,

10 is a photograph taken of the impact tester and test scene for measuring the impact resistance of each specimen shown in FIG.

11 is a table showing the impact test results of convex and concave porous structures at volume mixing ratios of concave salt particles 70%, 75% and 80%.

The present invention relates to a concave porous structure having a negative Poisson's ratio and a method for manufacturing the same, the manufacturing method is relatively easy, by adjusting the volume mixing ratio of the salt particles and resin powder, the size, porosity and shape of the pores of the structure It relates to a concave porous structure having a negative Poisson's ratio that can control the physical properties of the structure appropriately by changing the and the manufacturing method.

Poisson's Ratio refers to the absolute value of the transverse strain ratio in the longitudinal direction at the time of tension or compression of the material.

For example, when σ _X acts on the material in the X-axis direction under simple stress, strain ε _X occurs in the X-axis direction, and strain ε _Y , in the Y- and Z-axis directions perpendicular to the X-axis. ε _Z occurs. At this time, in the same material, the ratio of the size to ε _Y and ε _Z with respect to ε _X is always constant, and the ratio of the absolute value or the constant of the proportion is called Poisson's ratio (υ). (ε _Y = ε _Z = -υε _X )

Therefore, when the tensile force is applied in the longitudinal direction to the material having a positive Poisson's ratio, it is contracted in the transverse direction, and conversely, when the compressive force is applied in the longitudinal direction, it is extended in the transverse direction.

On the other hand, in contrast to the behavior of most materials having a positive Poisson's ratio, the material having a negative Poisson's ratio increases in the transverse direction during tension in the longitudinal direction, It has the characteristic of decreasing the transverse direction during compression.

Due to the above properties, structures having a negative Poisson's ratio have various advantageous properties such as improved shear modulus, fracture toughness, Piezoelectric property, indentation resistance, thermal shock resistance, impact absorption, abrasion resistance and energy absorption. In particular, there is an advantage in that the contact stress is reduced when two objects are in contact with each other, and the stress concentration at the defective portion of the object is reduced.

Therefore, it can be usefully used for artificial organ materials, structural materials, clothing, textiles, pads, etc. requiring impact protection.

Conventionally, various structures having such a negative Poisson's ratio have been proposed, for example, polygonal sponge structures (US Pat. No. 4,668,557, etc.), honeycomb structures (Korean Patent Application No. 1997-0010, Korean Patent Application No. 2005-7018305, etc.), microstructures using nodes and fibrils (International Patent Publication No. 91/01210) or concave porous structures.

Among these, in particular, the concave porous structure has an advantage of being a three-dimensional isotropic structure exhibiting a uniform negative Poisson's ratio with respect to various stress directions compared to the other structures described above.

However, in the related art, only the physical properties of such concave porous structures have been mainly discussed, and there is a problem that a specific and suitable manufacturing method for manufacturing the concave porous structure has not been proposed.

Accordingly, an object of the present invention is to provide a negative program which is easy to manufacture and which can control the physical properties of the structure by changing the size, porosity and shape of the pores of the structure by adjusting the volume mixing ratio of the salt particles and the resin powder. To provide a concave porous structure having a vortex ratio and a method of manufacturing the same.

The object is, according to the present invention, a first step of producing concave salt (NaCl) particles; A second step of mixing the resin powder and the concave salt particles in a volume ratio of 2: 8 to 4: 6; A third step of mixing and polymerizing the mixture and the monomer solution; A fourth step of leaching the concave salt particles from the polymer using distilled water; And a fifth step of drying the concave porous structure in which the concave salt particles are leached out.

The second step may be mixed in a volume ratio of 3: 7 of the resin powder and concave salt particles.

In the fifth step, after removing the concave porous structure from the mold, it may be dried for 8 to 12 minutes at 75 ~ 85 ℃ and completely dried at room temperature.

The resin may be made of polymethyl methacrylate (PMMA).

On the other hand, the first step, a step of mixing the salt particles and polyethylene particles; Heating the mixture to attach polyethylene particles to salt particles; C) dissolving the polyethylene particles attached salt in the brine solution to melt the polyethylene particles attached portion; It may include d; drying the partially dissolved salt particles.

In the step a, the salt particles and polyethylene particles may be mixed in a volume ratio of 4: 3.

The step b, the first step of attaching the mixture of the salt particles and polyethylene at 168 ~ 172 ℃ for 4 to 6 minutes, the step of cooling the mixture at room temperature, and the polyethylene particles not attached to the salt particles Straining using a sieve, and the second step of heating the polyethylene-attached salt particles at 168 ~ 172 ℃ for 8 to 12 minutes may include the step of completely attaching the polyethylene to the salt particles.

In step b, the polyethylene-attached salt particles may be dissolved in a 20% concentration of brine solution for 1 minute.

Hereinafter, with reference to the accompanying drawings, it will be described in detail with respect to the present invention.

Referring to the drawings, a method of manufacturing a concave porous structure having a negative Poisson's ratio according to the present invention, the first step (S1) for producing concave salt (NaCl) particles, PMMA (polymethyl methacrylate) powder and the concave A second step (S2) of mixing salt particles in a volume ratio of 2: 8 to 4: 6, a third step (S3) of polymerizing the mixture using a monomer solution as a solvent, and the concave salt particles in the polymer And a fourth step (S4) of leaching and removing using distilled water, and a fifth step (S5) of drying the concave porous structure in which the concave salt particles are leached and removed.

Hereinafter, a method of manufacturing a concave porous structure having a negative Poisson's ratio according to the present invention will be broadly divided into a step of preparing concave salt particles and a step of preparing a microporous structure from the concave salt particles. .

Preparation of concave salt particles (S1)

With reference to Figure 2, the step of preparing the concave salt particles will be described in detail.

① mixing the convex salt particles with polyethylene particles in a predetermined volume ratio (S11);

First, the salt (Nacl) particles are pulverized and sieved through a sieve so that each particle has a diameter ranging from 100 μmm to 200 μmm.

Next, polyethylene particles are prepared.

For example, polyethylene particles may use Hoecst's GHR 4120 grade, in which case the molecular weight is about 3 million, the diameter is 50 to 90 μmm, and the melting point is differential scanning calorimeter (DSC). The measurement result is about 140 ° C.

Herein, the particles for attaching to the salt particles are not limited to the polyethylene particles, and various kinds may be used as long as they satisfy the results required in this step.

Next, salt particles and polyethylene particles are mixed.

Here, the salt particles and the polyethylene particles may be mixed in various volume ratios. However, since the average size of polyethylene particles is about 1/2 of that of salt particles, and repeated experiments show the most desirable effect when six polyethylene particles are attached to one salt particle, salt particles and polyethylene particles are 4: 3. It is preferable to mix by volume ratio of.

② heating the mixture of salt particles and polyethylene particles to melt the polyethylene particles and attach them to the salt particles (S12);

Here, there is no particular limitation on the heating temperature and heating time when heating the mixture, for example, it can be heated to a temperature between the melting point of the salt particles (about 800 ℃) and the melting point of the polyethylene particles, preferably The polyethylene particles may be attached to the salts by preheating at 168 to 172 ° C. for 4 to 6 minutes.

This was confirmed that the particles were heated at 160 ° C., 170 ° C. and 180 ° C. for 4 to 6 minutes to attach the particles to the salt particles, and the particles were identified by SEM (Scanning electron microscope). It did not melt much so much was not attached to the salt, and at 180 ℃ not only attached to the salt but also polyethylene particles were dissolved and attached to each other. Therefore, in the preheating step of first attaching polyethylene particles to salt, it was found that 5 minutes at 170 ° C. showed the most optimal result.

③ cooling the mixture of salt particles and polyethylene at room temperature (S13);

④ sieving the mixture through a sieve of 100 μmm size (S14);

As described above, after the mixture of the salt particles and the polyethylene particles is first preheated, the mixture is cooled at room temperature and cooled at room temperature so that the polyethylene particles attached to the salt particles are solidified.

At this time, the polyethylene particles that are not attached to the salt particles remain in the mixture, and the polyethylene particles are filtered using a sieve.

⑤ reheating the mixture (S15);

After filtering out the polyethylene particles, the mixture of salt particles and polyethylene particles is again heated to allow the polyethylene particles to adhere completely to the salt particles.

At this time, the reheating temperature is not particularly limited, but may preferably be reheated for 8 to 12 minutes at 168 to 172 ° C, more preferably at 170 ° C for 10 minutes.

⑥ partial dissolution step of salt particles (S16);

This step is to dissolve the portion of the salt particles to which the polyethylene particles are not attached and to partially dissolve and concave the portion to which the polyethylene is not attached.

Partial dissolution of the salt particles may be performed by various methods, for example, a mixture of salt particles and polyethylene particles may be immersed in a brine solution to dissolve a portion in contact with the brine solution.

Here, it is possible to set the optimum conditions by checking each particle with an electron microscope as a result of partial dissolution while controlling the dissolution conditions, that is, the concentration and dissolution time of the brine solution in various ways.

That is, the lower the% concentration of the brine solution and the longer the dissolution time, the higher the solubility of the salt particles. Therefore, in order to obtain the optimal dissolution condition for obtaining concave salt particles, the concentration of 10%, 20%, 30% Dissolved in brine solution at 1 minute intervals from 1 minute to 5 minutes each.

Electron microscopy confirmed that the salt particles obtained from each experiment resulted in the majority of salt particles dissolved in the salt solution at 10% concentration even after 1 minute dissolution, and similar results were obtained even after soaking in the salt solution at 20% concentration for 2 minutes or more. . In the salt solution of 30% concentration, concave salt particles were observed after dissolution for 5 minutes.

In particular, when the salt particles are dissolved for 1 minute in a 20% concentration of brine solution, A relatively probable concave salt particle could be obtained.

Here, Figure 3a is a micrograph taken before the partial dissolution as a salt particle attached to polyethylene particles, Figure 3b is a micrograph photographing the salt particles partially dissolved in a salt solution of 20% concentration.

⑦ drying the partially dissolved salt particles (S17);

At this time, the drying temperature of the salt particles is in the range of about 40 to 60 ℃, preferably about 50 ℃ is suitable, and once again filter the mixture of dried salt particles and polyethylene particles to sieve so that only concave salt particles remain.

Concave porous structure fabrication

Hereinafter, the step of producing a concave porous structure having a negative Poisson's ratio using the concave salt particles prepared by the above-described method will be described in detail.

Mixing the resin powder and the concave salt particles in a volume ratio of 2: 8 to 3: 7 (S2);

The resin may be provided in various kinds, for example, polymethyl methacrylate (PMMA), polymethyl acrylate (PMA), or polyurethane may be used.

Here, when using PMMA, there is an advantage that it is relatively easy to handle compared to other polymer materials.

Hereinafter, the production method of the present invention will be described in detail taking the case where PMMA powder is used as an example.

In this manufacturing process, Perfex ^® of International Dental Product, which is used as a dental molding material, was used. In this case, the particle diameter of PMMA powder was about 50 μmm on average, about 1/2 to 1/4 of the salt particle diameter. to be.

Next, the PMMA powder and the concave salt particles should be mixed at an appropriate volume mixing ratio. If the PMMA powder is mixed less, the pores become too large, and if the PMMA powder is mixed a lot, the pores cannot be connected to each other.

Therefore, about 70% of the porosity is suitable for the pores to be connected to each other without being too large, so that the PMMA powder and the concave salt particles are in a volume ratio of 2: 8 to 3: 7, more preferably 4: 6. Mix.

This is because in concave porous structures, the pore size, porosity, and shape are the factors that have the greatest influence on the physical properties of the structure, in particular the Poisson's ratio.

Therefore, according to the production method according to the invention it is possible to appropriately control the physical properties of the concave porous structure by adjusting the mixing ratio of the concave salt particles and the resin powder.

For comparative analysis, convex salt particles with polyethylene are mixed in the same volume ratio.

Mixing the monomer solution as a solvent and then pouring the polymer into a mold (S3);

 After mixing PMMA powder and concave salt particles, the monomer solution is mixed, poured into a mold and polymerized at room temperature. At this time, the monomer solution to be used can be freely selected depending on the type of mixed resin. For example, in the case of PMMA powder, MMA (Methyl Metacrylate) solution may be used.

Figure 4 is a PTFE (Polytetrafluoroethylene) frame used in the manufacturing method of the present invention, and a block specimen prepared from the PTFE frame. This is a mold prepared for the physical property test of the concave porous structure produced by the manufacturing method according to the present invention, the size of the mold is 60 x 60 x 5 mm.

After the polymerization is completed, the polymer may be taken out of the mold and dried at 40 to 60 ° C.

Removing the concave salt particles on the PMMA powder and the salt particle complex by distilling in distilled water (S4);

The dried polymer is immersed in distilled water or passed through distilled water to leach out the salt particles.

5 is a structural diagram showing a schematic shape of the concave porous structure in which the concave salt particles are leached out, and FIG. 6A is a mixed volume ratio of the concave salt particles as a micrograph of the concave porous structure manufactured by the manufacturing method according to the present invention. Is 70%, and FIG. 6B is a micrograph of the porous structure prepared using convex salt particles as a control.

Referring to FIG. 5, the inside of the structure (see) is a space where contaminated salt particles were leached out, and the outside (see (b)) shows that the PMMA polymer forms a concave structure according to the external shape of the salt particles. have. Referring to FIG. 6A, it can be seen that concave voids are formed around the PMMA particles.

Drying the concave porous structure (S5);

At this time, preferably, after removing the concave porous structure from the mold and dried for 8 to 12 minutes at 75 ~ 85 ℃, it is appropriate to completely dry at room temperature for a sufficient time.

Analysis of Physical Properties of Concave Porous Structures Prepared by the Manufacturing Method According to the Present Invention

(One) Poisson's (υ) and modulus of elasticity (E)

First, summarizing the theoretical results of the Poisson's ratio for the concave polyhedron, the Poisson's ratio of the concave microstructure in each behavior region is as follows.

(식 1)

(Equation 1)

(식 2)

(Equation 2)

(식 3)

(Equation 3)

Where υ _el is the Poisson's ratio in the elastic region, υ _pl Is the Poisson's ratio in the plastic zone, and υ _{el - pl} represents the Poisson's ratio in the elastoplastic transition zone.

In addition, each Ψ representing the concave degree of the microstructure may have a value of 0 ° to 90 °. When the angle Ψ is larger than 45 °, the microstructure has a negative Poisson's ratio by the above equation.

7 shows the Poisson's ratio of the concave porous structure when Ψ = 82 ° in the above equations.

Specimens use standard size specimens in accordance with the American Society for Testing and Materials (ASTM) d638 test method.

To measure Poisson's ratio, a biaxial CAS strain gauge was attached to the specimen, and a tensile test was performed at a strain rate of 0.05 mm / sec with an Intron 8511 attached with a 2.5 kN load cell.

For the acquisition and analysis of experimental data, Signal Conditioning Amplifier 2310 from Measurement Group Inc., Data shuttle from Srawberry, And workbench PC software was used.

The specimen was processed by cutting from the concave microstructure block when the volume mixing ratio of the salt particles was 70% and 80%. Twenty experiments were conducted for the same mixing ratio, and each experimental value was obtained from the average value.

Figure 7 is a concave porous structure produced by the manufacturing method according to the present invention, when the strain (ε, X-axis) and Poisson's ratio (υ, Y-axis) when the volume% of the salt particles are 70%, 80% A graph showing the relationship.

Referring to the drawings, the Poisson's ratio is -0.53 (70% volume mixing ratio) and -0.75 (80% volume mixing ratio) at the strain (ε) of about 0.001, respectively, and the Poisson's ratio increases gradually as the strain increases, but is still You can see that it keeps negative values.

For reference, the Poisson's ratio of the convex porous structure is 0.28 (70% volume mixing ratio) and 0.32 (80% volume mixing ratio) at a strain of about 0.001, respectively, and the Poisson's ratio increases as the volume percentage of salt particles increases. Seemed.

On the other hand, when the salt particles were 80% by volume, the results were most similar to the theoretical Poisson's ratio obtained when P was 82 ° from the above equation.

Figure 8 (a) is a graph comparing the elastic modulus measurements and theoretical values at the volume mixing ratio of 70% and 80% salt particles in the convex and concave microporous structure prepared according to the manufacturing method of the present invention, the Y axis is concave The elastic modulus (E _r ) of the porous structure is divided by the elastic modulus (E _s , about 8.42 GPa) of PMMA, and the X axis is the angle Ψ representing the degree of concaveness of the concave porous structure.

Here, each Ψ is determined to give the most suitable Poisson's ratio by comparing the Poisson's ratio obtained from the experiment with the theoretical value, and the theoretical value compensates for the decrease in density of the convex structure according to the degree of concaveness.

FIG. 8 (b) is an enlarged view of the main portion (hatched area) of FIG. 8 (a). Referring to the drawings, it is understood that the concave porous structure manufactured by the present manufacturing method has an elastic modulus value similar to the theoretical value. In addition, it can be seen that the elastic modulus decreases as the negative Poisson effect increases (ie, as the angle Ψ increases).

On the other hand, when the volume mixing ratio of the concave salt particles is 70% and 80%, respectively, the average modulus of elasticity of the convex porous structure is 2.52 and 1.42 GPa, respectively, and the average modulus of elasticity of the corresponding concave porous structure is 2.14 and 1.12 GPa, respectively. appear.

That is, at the same mixing ratio, the average value of the elastic modulus of the concave porous structure was 15 to 20% smaller than the average value of the elastic modulus of the convex porous structure.

Therefore, the elastic modulus of the concave porous structure at the same volume mixing ratio decreases compared to the elastic modulus of the convex porous structure, indicating that there is a possibility that the concave porous structure having a negative Poisson's ratio can have excellent elastic energy. .

That is, the modulus of resilience, which represents the ability of a material to absorb energy in an elastic region, can be expressed as follows.

, (Y는 재료의 항복강도) 식 4)

(Y is the yield strength of the material)

 Larger modulus of elasticity means that more energy can be absorbed until the material breaks.

However, as shown in the above equation, assuming that the yield strength (Y) is the same, the elastic energy modulus is inversely proportional to the elastic modulus (E), the smaller the elastic modulus (E) can be said to be larger the elastic energy modulus.

Therefore, since the elastic modulus of the concave porous structure is less than that of the convex porous structure at the same mixing ratio, it can be seen that the concave porous structure has an improved modulus of elastic energy.

(2) impact resistance

9 is a convex and concave porous structure specimen when the volume mixing ratio of concave salt particles made of standard specimens is 70%, 75% and 80%. Here, the left side of each group is a convex porous structure, and the right side is a concave porous structure.

Each specimen was prepared by cutting from the block specimen shown in Figure 4, the size of the specimen was 12.7 x 60.3 x 3.17 mm, the length of the non-bite portion of the impact tester was 31.75mm.

10 is a photograph of the test scene in the impact tester. Referring to the drawing, the impacted surface is a plane perpendicular to the molded plane direction, and the impact weight is 1 kg.

The effective length for the pendulum needed to find the impact energy was obtained from the following equation.

식 5)

Equation 5)

Where g is gravity acceleration and p is the period of the pendulum.

The weight was rotated and dropped at an angle of 50 °, and measured in consideration of air resistance and energy loss due to friction.

Therefore, the impact resistance of the final specimen can be obtained by the following equation by subtracting the rotating energy after the collision from the initial energy of the corrected weight and dividing it by the width of the specimen.

식 6)

(6)

Where E _s is the calibrated initial energy, ETC is the energy after impact, and t is the width of the impacted specimen. The impact test results were calculated 20 times for each of the six test groups of convex and concave porous structures for each mixed volume ratio, and then the average value was calculated.

In this physical property test, ASTM D4812 specification for Izod test method suitable for PMMA material used as a medium was used. For convenience of experiment, Unnotched cantilever impact test method was used.

11 is a table showing the impact test results of the convex and concave porous structures at each mixing ratio.

Referring to the table, the impact resistance decreased in both the convex and concave porous structures as the volume mixing ratio of the salt particles increased (that is, as the porosity increased), and the concave porous structures in each mixing ratio had a higher impact resistance than the convex porous structures. It can be seen that the small amount increased from 35% (75% of the volume mixing ratio) to 50% (70% of the volume mixing ratio).

Therefore, it can be seen that the concave porous structure having a negative Poisson's ratio has a higher impact resistance due to the increase of the elastic energy due to the improved elastic deformation even though it has a lower elastic modulus than the convex porous structure.

The present invention is not limited to the above-described embodiment, and it is apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit and scope of the present invention. Accordingly, such modifications or variations will be considered to belong to the claims of the present invention.

Therefore, according to the method for producing a concave porous structure according to the present invention, it is possible to easily produce a concave porous structure having a negative Poisson's ratio using the salt leaching method.

In addition, by adjusting the volume mixing ratio of the salt particles and the resin powder, it is possible to appropriately control the physical properties of the concave porous structure by changing the size, porosity and shape of the pores of the structure.

Claims (9)

A step of mixing the salt particles (Nacl) and polyethylene particles; Heating the mixture to attach polyethylene particles to salt particles; C) dissolving the polyethylene particles attached salt in the brine solution to melt the polyethylene particles attached portion; A first step of preparing concave salt (NaCl) particles, including d; drying the partially dissolved salt particles; A second step of mixing PMMA (Polymethyl Metacrylate) powder and the concave salt particles in a volume ratio of 2: 8 to 4: 6; A third step of mixing and polymerizing the mixture and MMA (Methyl Metacrylate) solution; A fourth step of leaching the concave salt particles from the polymer using distilled water; And And a fifth step of drying the concave porous structure from which the concave salt particles have been leached out. 5. A method of manufacturing a concave porous structure having a negative Poisson's ratio comprising: a. The method of claim 1, The second step is a method of producing a concave porous structure having a negative Poisson's ratio, characterized in that the polymethyl methacrylate (PMMA) powder and concave salt particles are mixed in a volume ratio of 3: 7. The method of claim 1, The fifth step, After removing the concave porous structure from the mold, and dried for 8 to 12 minutes at 75 ~ 85 ℃ and completely dried at room temperature method of producing a concave porous structure having a negative Poisson's ratio. delete delete The method of claim 1, In the step a, the salt particles and polyethylene particles is a method of producing a concave porous structure having a negative Poisson's ratio, characterized in that the mixing ratio of 4: 3. The method of claim 1, Step b, Attaching the mixture of the salt particles and polyethylene by first heating at 168-172 ° C. for 4-6 minutes, Cooling the mixture at room temperature; Filtering the polyethylene particles not attached to the salt particles by using a sieve, Method for producing a concave porous structure having a negative Poisson's ratio comprising the step of secondly heating the polyethylene-attached salt particles at 168 ~ 172 ℃ for 8 to 12 minutes to completely adhere the polyethylene to the salt particles . The method of claim 1, The step b, the method of producing a concave porous structure having a negative Poisson's ratio, characterized in that the polyethylene-attached salt particles are dissolved in a brine solution of 20% concentration for 1 minute. A concave porous structure manufactured by the manufacturing method of claim 1.

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