KR101730437B1

KR101730437B1 - Epoxy composites having enhanced thermal stability and mechnical behaviors and manufacturing method of the same

Info

Publication number: KR101730437B1
Application number: KR1020150135231A
Authority: KR
Inventors: 박수진; 강우석
Original assignee: 인하대학교 산학협력단
Priority date: 2015-09-24
Filing date: 2015-09-24
Publication date: 2017-04-26
Also published as: KR20170036273A

Abstract

The present invention relates to an epoxy composite material having improved thermal stability and mechanical properties compared to conventional epoxy resins by using expanded graphite and graphite as a filler to fill the epoxy resin, and a method for producing the same. More particularly, the present invention relates to an epoxy composite material, Graphite.
As described above, according to the present invention, expanded graphite and graphite oxide are added to an epoxy resin as a filler to simultaneously use expanded graphite and graphite, which are carbon-based fillers having excellent heat resistance, Which has a stable effect. Further, the excellent dispersibility of the graphite as a carbon-based filler and the fact that many functional groups of the graphite oxide lead to strong interface bonding with the epoxy resin double the effect of enhancing the epoxy to bring about the synergy effect, thereby increasing the mechanical strength.

Description

[0001] EPOXY COMPOSITES HAVING ENHANCED THERMAL STABILITY AND MECHANICAL BEHAVIORS AND MANUFACTURING METHOD OF THE SAME [0002]

The present invention relates to an epoxy composite material improved in thermal stability and mechanical properties by using expanded graphite and graphite as fillers and added to an epoxy resin, and a method for producing the same.

Epoxy resin is a typical thermosetting resin and it is easy to process and has excellent adhesiveness and heat resistance. It is not only used for coating adhesion but also widely applied to various fields such as aerospace, ship, automobile, coating, have. However, the high crosslinking reaction of the cured epoxy resin increases the brittleness of the epoxy composite material, which is very vulnerable to impact and has a disadvantage in that thermal and mechanical properties are deteriorated. As a method for improving this, researches have been continued to improve heat resistance, abrasion resistance and physical strength by uniformly dispersing nano-sized fillers such as layered silica, clay and graphite in the matrix.

In recent years, polymer composite materials having excellent physical properties have been developed by using various carbon-based fillers such as carbon black, carbon nanotubes, carbon fibers, and graphene in polymer resins, and currently, Studies have been actively carried out to improve the thermal stability and mechanical properties by inducing a reduction in the content of the entire filler by simultaneously using two types of carbon-based fillers having the function .

Korean Patent Publication No. 10-2014-0067577

An object of the present invention is to provide an epoxy composite material which is improved in thermal stability and mechanical strength than conventional epoxy resin by adding expanded graphite and graphite oxide as fillers to an epoxy resin.

To achieve the above object, an epoxy composite material according to an aspect of the present invention includes expanded graphite and graphite oxide as a filler in an epoxy resin.

The expanded graphite may be used in an amount of 0.1 to 1 part by weight based on 100 parts by weight of the epoxy resin, and the graphite oxide may be used in an amount of 0.1 to 1 part by weight based on the weight of the epoxy resin.

According to another aspect of the present invention, there is provided a method for producing an epoxy composite material, comprising the steps of: (1) preparing expanded graphite by heat treatment of a first graphite; (2) preparing graphite oxide by oxidizing the second graphite; (3) adding the expanded graphite produced in the step (1) and the oxidized graphite prepared in the step (2) to the epoxy resin; And (4) defoaming the epoxy resin to which expanded graphite and graphite have been added in the step (3), followed by curing.

In the step (1), the acid treatment is to immerse the first graphite in a mixed solution obtained by mixing an oxidizing agent and an acidic solution, and the ratio of the oxidizing agent to the acidic solution may be 1: 1 to 10 by volume.

The expanded graphite to be added to the epoxy resin in the step (3) is 0.1 to 1 part by weight based on 100 parts by weight of the epoxy resin. The graphite to be added to the epoxy resin is 0.1 to 1 part by weight Can be.

In the step (4), the defoaming may be to remove bubbles for 5 to 120 minutes.

As described above, according to the present invention, expanded graphite and graphite oxide are added to an epoxy resin as a filler to simultaneously use expanded graphite and graphite, which are carbon-based fillers having excellent heat resistance, Which has a stable effect.

Further, the excellent dispersibility of the graphite as a carbon-based filler and the fact that many functional groups of the graphite oxide lead to strong interface bonding with the epoxy resin doubly enhance the mechanical strength of the epoxy by enhancing the synergy effect.

1 is a SEM analysis result of expanded graphite produced according to the production method of the present invention.
FIG. 2 is a TGA analysis result of the epoxy composite material produced according to the manufacturing method of the present invention.
3 shows the results of UTM analysis of the epoxy composite material produced according to the production method of the present invention.

Hereinafter, the present invention will be described in detail.

The epoxy composite material according to one embodiment of the present invention includes expanded graphite and graphite oxide as fillers in an epoxy resin.

The epoxy resin is selected from the group consisting of Bisphenol-A type epoxy, Bisphenol-F type epoxy, Novolac epoxy and Flame-retardant epoxy. Lt; / RTI >

The expanded graphite may be 0.1 to 1 part by weight based on 100 parts by weight of the epoxy resin, and the graphite oxide may be 0.1 to 1 part by weight based on the weight of the epoxy resin. The filler preferably has a sum of the expanded graphite and the graphite oxide of 1 part by weight based on 100 parts by weight of the epoxy resin. When the sum of the expanded graphite and the graphite oxide is more than 1 part by weight based on 100 parts by weight of the epoxy resin, the dispersibility is lowered and mutual aggregation occurs between the fillers to form a non-uniform phase, thereby reducing physical properties.

The step (1) is a step for producing expanded graphite which is used as a filler, and the expanded graphite can be produced by heat treatment after acid treatment. The acid treatment may be to immerse the first graphite in a mixed solution obtained by mixing an oxidizing agent and an acidic solution, and react at room temperature for 12 to 24 hours to prepare a layered compound. When the reaction time is less than 12 hours, the surface treatment effect is insignificant, and when the reaction time is more than 24 hours, the structure of the layered compound can be modified. The oxidizing agent may be one or more selected from the group comprising hydrogen peroxide, nitric acid, potassium permanganate, and potassium perchlorate, the acidic solution is sulfuric acid (H ₂ SO _4), nitric acid (HNO ₃₎ and phosphoric acid (H ₃ PO ₄₎ And may be at least one selected from the group including. At this time, the mixing ratio of the oxidizing agent and the acidic solution may be 1: 1 to 10 by volume. Preferably, the volume ratio of the oxidizing agent to the acidic solution may be 1: 1, 1: 2, 1: 4, 1: 6, 1: 8 and 1:10. More preferably, the volume ratio of the oxidizing agent and the acidic solution may be 1: 8. The heat treatment may be performed by washing the layered compound with distilled water, drying it, and then heat-treating the layered compound at 700 to 1000 ° C. for 30 to 90 seconds to obtain expanded graphite. When the temperature is lower than 700 ° C, there is no expansion effect, and when it exceeds 1000 ° C, the structure of the expanded graphite is destroyed. Also, if it is less than 30 seconds, there is no expansion effect, and if it exceeds 90 seconds, the expanded graphite structure is destroyed.

The step (2) is a step of producing oxidized graphite to be used as a filler, and the oxidized graphite can be produced by an oxidation process. In the oxidation step, the second graphite is supported on the acidic solution, the metal salt selected from the group consisting of potassium permanganate, potassium perchlorate and sodium nitrate is gradually added thereto, and then magnetically stirred. Thereafter, distilled water and hydrogen peroxide are sequentially added to react The compound may be washed several times with hydrochloric acid and distilled water and neutralized to produce graphite oxide.

In the step (3), the expanded graphite produced in the step (1) and the graphite oxide produced in the step (2) are used as fillers, and the step (3) 0.1 to 1 part by weight of expanded graphite may be added to the heated epoxy resin with respect to 100 parts by weight of the epoxy resin and 0.1 to 1 part by weight of graphite may be added to 100 parts by weight of the epoxy resin. The filler preferably has a sum of the expanded graphite and the graphite oxide of 1 part by weight based on 100 parts by weight of the epoxy resin. When the sum of the expanded graphite and the graphite oxide is more than 1 part by weight based on 100 parts by weight of the epoxy resin, the dispersibility is lowered and mutual aggregation occurs between the fillers to form a non-uniform phase, thereby reducing physical properties.

In the step (3), the dispersion may be performed with an ultrasonic disperser for 5 to 120 minutes so that the filler can be evenly dispersed. If it is less than 5 minutes, the effect of dispersion is insignificant. If it exceeds 120 minutes, the filler may be damaged.

The epoxy composite material according to the present invention is prepared by defoaming and curing the epoxy resin to which the filler is added in the step (3), wherein the step (4) And then removing the bubbles by using a vacuum pump for 5 to 120 minutes in order to remove the bubbles generated in the mixing process. If it is less than 5 minutes, air bubbles are not removed, and if it exceeds 120 minutes, the performance of the epoxy composite material is deteriorated. The bubbles generated in the mixing process form pores in the finally produced epoxy composite to weaken the strength of the composite. The curing agent may be one or more selected from the group including diaminodiphenylmethane (DDM), diaminodiphenylsulfone (DDS), triethylenetetramine (TETA), and diethylenetriamine (DETA).

In the step (4), the epoxy resin to which the filler is added in the step (3) may be cured in a temperature hardening oven at 130 to 210 ° C for 1 to 4 hours. At 130 ° C for less than 1 hour, complete curing will not occur. At 210 ° C for more than 4 hours, the physical properties will deteriorate.

Hereinafter, the present invention will be described in more detail with reference to Examples. It is to be understood by those skilled in the art that these examples are for illustrative purposes only and that the scope of the present invention is not construed as being limited by these examples.

Example 1.

Expanded graphite is dipped in a mixed solution of sulfuric acid and nitric acid (10: 1) and reacted at room temperature for 24 hours to produce a layered compound, which is washed several times with distilled water. Dried in an oven for 12 hours, and then heat-treated at 1000 ° C for 30 seconds to produce expanded graphite. The graphite oxide is immersed in sulfuric acid, and the graphite is added to the ice, and potassium permanganate is slowly added thereto, followed by magnetic stirring. Thereafter, distilled water and hydrogen peroxide are sequentially added and reacted. The obtained compound is washed several times with hydrochloric acid and distilled water. And finally dried for 48 hours to prepare graphite oxide. The composite material was prepared by adding 40 parts by weight of epoxy to 0.9 parts by weight of expanded graphite and 0.1 part by weight of graphite oxide as a filler, stirring at 50 rpm, melt mixing, dispersing the filler, Provides effective dispersion with dispersing machine. The curing agent is added to the epoxy resin which has been dispersed and mixed, followed by defoaming for 5 minutes in order to remove the bubbles generated in the mixing process. After the bubbles are removed, the resulting mixture is cured at 130 ° C to produce an epoxy composite.

Example 2.

Expanded graphite was prepared in the same manner as in Example 1 except that the ratio of sulfuric acid and nitric acid was changed to 9: 1, and the amount of filler was changed from 0.8 weight part of expanded graphite to 100 weight part of epoxy and 0.2 weight And the mixture was agitated at 100 rpm and dispersed by ultrasonic wave for 15 minutes, followed by defoaming for 15 minutes to prepare an epoxy composite material.

Example 3.

Expanded graphite was prepared in the same manner as in Example 1 except that the ratio of sulfuric acid to nitric acid was changed to 8: 1, and the amount of filler was changed from 0.7 weight part of expanded graphite to 100 weight part of epoxy and 0.3 weight And the mixture was agitated at 100 rpm and dispersed by ultrasonic wave for 15 minutes, followed by degassing for 15 minutes, followed by curing at 150 ° C. to prepare an epoxy composite material.

Example 4.

Expanded graphite was prepared in the same manner as in Example 1 except that the ratio of sulfuric acid to nitric acid was changed to 8: 1 and the amount of filler was changed from 0.6 weight part of expanded graphite to 100 weight part of epoxy and 0.4 weight And the mixture was agitated at 100 rpm and dispersed by ultrasonic wave for 15 minutes, followed by degassing for 15 minutes, followed by curing at 150 ° C. to prepare an epoxy composite material.

Example 5.

Expanded graphite was prepared in the same manner as in Example 1 except that the ratio of sulfuric acid to nitric acid was changed to 8: 1, and the amount of filler was changed from 0.5 weight part of expanded graphite to 100 weight part of epoxy and 0.5 weight And the mixture was agitated at 300 rpm and dispersed by ultrasonic wave for 30 minutes, followed by degassing for 30 minutes, followed by curing at 170 ° C. to prepare an epoxy composite material.

Example 6.

Expanded graphite was prepared in the same manner as in Example 1 except that the ratio of sulfuric acid and nitric acid was changed to 6: 1, and the amount of filler was changed from 0.4 weight part of expanded graphite to 100 weight part of epoxy and 0.6 weight And the mixture was agitated at 300 rpm and dispersed by ultrasonic wave for 60 minutes, followed by degassing for 60 minutes, followed by curing at 170 ° C. to prepare an epoxy composite material.

Example 7.

Expanded graphite was prepared in the same manner as in Example 1 except that the ratio of sulfuric acid to nitric acid was 4: 1. The amount of filler was changed from 0.3 weight part of expanded graphite to 100 weight part of epoxy and 0.7 weight The mixture was agitated at 500 rpm for 60 minutes, dispersed by ultrasonic for 60 minutes, degassed for 60 minutes, and then cured at 190 ° C to prepare an epoxy composite material.

Example 8.

Expanded graphite was prepared in the same manner as in Example 1 except that the ratio of sulfuric acid and nitric acid was 2: 1, and the amount of filler was changed from 0.2 weight part of expanded graphite to 100 weight part of epoxy and 0.8 weight And the mixture was agitated at 500 rpm, dispersed by ultrasonic wave for 90 minutes, degassed for 90 minutes, and then cured at 190 DEG C to prepare an epoxy composite material.

Example 9.

Expanded graphite was prepared in the same manner as in Example 1 except that the ratio of sulfuric acid to nitric acid was 1: 1, and the amount of filler was changed from 0.1 weight part of expanded graphite to 100 weight part of epoxy and 0.9 weight The mixture was agitated at 700 rpm and dispersed by ultrasonic wave for 120 minutes. After degassing for 120 minutes, the epoxy composite was cured at 210 ° C.

Comparative Example 1

40 g of epoxy are mixed by stirring at 400 rpm, and a hardener is added to the epoxy resin and mixed, followed by defoaming for 30 minutes in order to remove the bubbles generated in the mixing process. After bubbles are removed, an epoxy resin is prepared by curing at 170 ° C using a curing oven.

Comparative Example 2

Expanded graphite is dipped in a mixture of sulfuric acid and nitric acid (8: 1) and reacted at room temperature for 24 hours to produce a layered compound, which is washed several times with distilled water. Dried in an oven for 12 hours, and then heat-treated at 1000 ° C for 30 seconds to produce expanded graphite. To 40 g of epoxy, 1 part by weight of expanded graphite was added to 100 parts by weight of epoxy, and the mixture was melt-mixed at 400 rpm and dispersed with an ultrasonic disperser for 30 minutes to disperse the filler. After the curing agent is added to the dispersed epoxy resin, the mixture is degassed for 30 minutes in order to remove the bubbles generated in the mixing process. After removing the air bubbles, the composite material is cured at 170 ° C to produce a composite material.

Comparative Example 3

The graphite is immersed in sulfuric acid, and the mixture is ice-cooled. Potassium permanganate is slowly added thereto, and then magnetic stirring is performed. Thereafter, distilled water and hydrogen peroxide are sequentially added and reacted. The obtained compound is washed several times with hydrochloric acid and distilled water. And finally dried for 48 hours to prepare graphite oxide. The composite material is prepared by adding 1 part by weight of graphite as a filler to 40 g of epoxy and 100 parts by weight of epoxy, stirring it at 400 rpm, melt mixing and dispersing the filler with an ultrasonic disperser for 30 minutes. After the curing agent is added to the dispersed epoxy resin, the mixture is degassed for 30 minutes in order to remove the bubbles generated in the mixing process. After removing the bubbles, the composite material is cured at 170 ° C to produce an epoxy composite material.

Measurement example 1. Scanning electron microscope (SEM)

Expansion graphite and graphite oxide were prepared and measured using a scanning microscope. The results are shown in FIG.

Measurement example 2. Thermogravimetric analyzer (TGA)

Thermal stability measurements such as the thermal decomposition initiation temperature (IDT), the integral thermal decomposition progress temperature (IPDT), the residual amount of the sample after thermal analysis, etc. of the epoxy composite prepared according to the above examples were measured using a thermogravimetric analyzer (TGA) The results are shown in Fig.

Measurement example 3. Critical stress intensity factor (K _IC )

Mechanical properties of the epoxy composite material produced by the above-described embodiment was measured as the critical stress intensity factor (K _IC) were used to prepare a single-edge notched bending (SENB) specimen is added to the notch, the prepared specimen is a universal testing machine (UTM ), And the results are shown in Fig.

Analysis.

The epoxy composites prepared by the above examples were analyzed using SEM, TGA, and K _IC .

As a result of TGA analysis, epoxy composite materials using expanded graphite and graphite as fillers simultaneously show that the thermal stability is increased as shown in FIG. This demonstrates that the use of both expanded graphite and graphite oxide, which are carbon-based fillers excellent in thermal resistance, leads to a decrease in the content of the entire filler and is thermally stable.

As a result of K _IC analysis using epoxy graphite and graphite as fillers at the same time, it was found that the excellent dispersibility of the graphite as a carbon-based filler and the strong functional groups of the graphite oxide were strong interfacial coupling with the epoxy resin , Demonstrates that mechanical strength is increased by reinforcing the epoxy to double the synergy effect.

When the above results are summarized, it can be seen that the addition of expanded graphite and graphite to the epoxy enhances thermal stability and mechanical strength by good dispersion of expanded graphite and interfacial bonding with epoxy base of graphite oxide.

The production conditions of the epoxy composite material according to the present invention The ratio of sulfuric acid / nitric acid (v: v) Expanded graphite (wt.%) Graphite oxide (wt.%) Stirring rpm ultrasonic wave
(min) Vacuum oven (min) Curing temperature (℃) Example 1 10: 1 0.9 0.1 50 5 5 130 Example 2 9: 1 0.8 0.2 100 15 15 130 Example 3 8: 1 0.7 0.3 100 15 15 150 Example 4 8: 1 0.6 0.4 300 30 30 150 Example 5 8: 1 0.5 0.5 300 30 30 170 Example 6 6: 1 0.4 0.6 300 60 60 170 Example 7 4: 1 0.3 0.7 500 60 60 190 Example 8 2: 1 0.2 0.8 500 90 90 190 Example 9 1: 1 0.1 0.9 700 120 120 210 Comparative Example 1 - - - 300 170 Comparative Example 2 1: 8 1.0 - 300 170 Comparative Example 3 - - 1.0 300 170

The thermal stability of the epoxy composites according to the present invention IPDT (占 폚) Example 1 391.5 Example 2 395.7 Example 3 398.4 Example 4 400.7 Example 5 406.0 Example 6 399.2 Example 7 396.9 Example 8 394.5 Example 9 393.0 Comparative Example 1 391.0 Comparative Example 2 396.6 Comparative Example 3 391.9

The mechanical strength of the epoxy composite according to the present invention K _IC (MPa m2 m2) Example 1 1.19 Example 2 1.24 Example 3 1.29 Example 4 1.31 Example 5 1.56 Example 6 1.22 Example 7 1.21 Example 8 1.18 Example 9 1.14 Comparative Example 1 0.95 Comparative Example 2 1.03 Comparative Example 3 1.06

Having described specific portions of the present invention in detail, those skilled in the art will appreciate that these specific embodiments are merely preferred embodiments and that the scope of the present invention is not limited thereby. something to do. Accordingly, the actual scope of the present invention will be defined by the appended claims and their equivalents.

Claims

0.1 to 1 part by weight of expanded graphite and 0.1 to 1 part by weight of graphite oxide as 100 parts by weight of an epoxy resin as a filler in the epoxy resin,
The epoxy resin is selected from the group consisting of Bisphenol-A type epoxy, Bisphenol-F type epoxy, Novolac epoxy and Flame-retardant epoxy. By weight based on the total weight of the epoxy composite material.

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(1) acid-treating the first graphite and then producing expanded graphite by heat treatment;
(2) preparing graphite oxide by oxidizing the second graphite;
(3) adding 0.1 to 1 part by weight of the expanded graphite prepared in the step (1) and 0.1 to 1 part by weight of the graphite oxide prepared in the step (2) to the epoxy resin with respect to 100 parts by weight of the epoxy resin; And
(4) defoaming and curing the epoxy resin to which the expanded graphite and the graphite are added in the step (3)
The epoxy resin is selected from the group consisting of Bisphenol-A type epoxy, Bisphenol-F type epoxy, Novolac epoxy and Flame-retardant epoxy. Of the total weight of the epoxy composite material.

The method of claim 3,
In the step (1)
The acid treatment is to immerse the first graphite in a mixed solution obtained by mixing an oxidizing agent and an acidic solution,
Wherein the ratio of the oxidizing agent to the acidic solution is in the range of 1: 1 to 10 by volume.

delete

The method of claim 3,
Wherein the bubbles are removed for 5 to 120 minutes in the step (4).