Study on Preparation and Performance of Carbon Nanotube/Epoxy Resin Composite Powder Coating

XiaoGuang, Jiang Guohua, Wang Xiaohong, Li Xia, Tang Berlin, Wei Zhen
Semenic polymer synthesis and functional structure laboratory of Zhejiang University of Technology
Abstract:
By using BPA and epoxy chloropropane as raw materials, nano Carbon tube as an enhanced and thermal conductive filler, in-place polymerization legal system prepared carbon nanotube / epoxy resin composite materials, and research composite powder coating storage stability, impact resistance, adhesion, resistance to neutral salt spray corrosion, thermal properties.
results show that with the increase of carbon nanotube content, the properties of powder coatings gradually improve, when the carbon nanotube mass fraction of 3%, the storage stability of composite powder coatings than pure epoxy resin increased by 1 times;
has a impact resistance of 33kg.cm, which is 65% higher than pure epoxy resin, and adhesion and neutral salt spray corrosion grade of 2, which is 2 levels higher than pure epoxy resin, and thermal conductivity of 0.541W/mK, which is 2.8 times that of epoxy resin.
as carbon nanotube content continues to increase, performance is reduced, which may be related to the dispersion of carbon nanotubes in composites

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introduction:
With the rapid development of modern technology, the high frequency, high speed and dense and miniaturized integrated circuits of electronic devices have led to a significant increase in the total power density and heat generated per unit volume electronic device, thus making the cooling problem of electronic devices more and more prominent.
And conventional cooling system can achieve the cooling capacity is greatly challenged, especially in the energy, automotive, air conditioning, agriculture, chemical, heating, aerospace, microelectronics, information and other fields, to strengthen heat transmission, improve thermal efficiency and other technologies put forward higher requirements.
thermal coating is a special coating that improves the cooling efficiency of the surface of the object and reduces the temperature of the system.
epoxy resin is very important as one of the thermoosteroid polymer materials, with high bonding strength, good electrical insulation performance, low shrinkage, good processing performance and other advantages, is widely used in electronics, machinery, construction and other fields.
nanotube has a high thermal conductivity, so the nanotube as a filling material filled into epoxy resin as a cooling material has a good application prospects, but because of the nano-effect of nanotubes, nanotubes in epoxy resin is difficult to disperse.
to improve the dispersion of nanotubes in epoxy resins, scholars have made many efforts.
Youn and so on first carbon nanotube acidification, so that carbon nanotubes on the base, and then it and dichloroacetone reaction, and then with hexamine or streptanylamine amine amine reaction to get amine carbon nanotubes, amineized carbon nanotubes added to epoxy resin, amined carbon nanotubes in epoxy resin dispersion greatly improved
; Liu and other silicone coupled agent to change the carbon nanotubes, modified carbon nanotubes in epoxy resin dispersion is good.
although the above method improves the dispersion of carbon nanotubes, it destroys the structure of carbon nanotubes to produce defects, which are conducive to the scattering of onnuts and reduce the thermal conductivity of carbon nanotubes.
in-place polymerization is legal because of the small molecular weight and low viscosity of the monomer, which is conducive to the dispersion of nanoparticles in the substation during the polymerization process of the monomer, and in-place polymerization is legal and does not destroy the structure of carbon nanotubes.
In this paper, Bisphenol A and epoxy chloropropane as raw materials, carbon nanotubes as thermal conductive fillers, through in-place polymerization methods to synthesize carbon nanotubes / epoxy resin composite materials, and the coating storage stability, impact resistance, adhesion, corrosion resistance, thermal properties of research and analysis.
1, experimental part
1.1 experimental raw materials
bisphenol A (analysis pure, Tianjin BASF); epoxy chloropropane (analytical pure, East China Pharmaceutical Co., Ltd.); sodium hydroxide (analytical pure, Tianjin Northern Tian medical chemical reagent plant); nanotubes (>97%, 10 to 20nm, Shenzhen Nanoport Co., Ltd.); MB68 solidizer (Huangshan Deping Chemical Co., Ltd.).
1.2 Main instruments and equipment
thermal conductivity tester (DRL-II. type, Xiangtan Xiangyi Instrument Co., Ltd.);
electrostitive sprayer (DY series, Yuyao City Dan transport coating equipment factory);
transmission mirror (JSM-2100);
DSC tester (Pekin Elmer DSC-7);
); Salt mist corrosion test box (YWX/Q series, Hangzhou Lihui Environmental Testing Equipment Co., Ltd.);
paint film impactor (QCJ type, Tianjin Dongwen pressure material tester Co., Ltd.) lacquer film slicing instrument (Tianjin Haiya Material Tester Co., Ltd.);
buckle swing small shredder (Guangzhou Xuxulang Machinery Co., Ltd.);
double screw extruder (SHJ series, Nanjing Jinji Machinery Co., Ltd.).
1.3 carbon nanotube/epoxy composite powder coating preparation
typical preparation steps are as follows:
(1) called NaOH 10g, with 10% NaOH solution, added 33g BPA, heated to 60 oC;
(2) add a certain amount (mass fraction 1% to 5%) nanotube, 55 degrees C ultrasonic mechanical stirring 30min;
(3) add 14.75mL epoxychloropropane, heating to 80 degrees C, mechanical stirring 4h;
(4) First washed with cold water and then washed with 80 degrees C, repeatedly washed to neutral, dry in the oven 50 degrees C;
(5) will be dried carbon nanotube / epoxy resin crushed and mixed with curing agent evenly, added to the twin screw extruder melt extruded, to be cooled after crushing the sieve, to obtain carbon nanotube / epoxy composite powder coating.preparation of carbon nanotube/epoxy composite powder coating test model: using the steel plate specified in GB/T 1727, after rust removal treatment, electrostectrecturized spraying, put into the blowing drying tank at 150 degrees C curing 20min.
1.4 Performance Test
1.4.1 Carbon nanotubes are dispersed in epoxy resins
their dispersion is observed under the JSM-2100 transmission electron microscope by slicing epoxy resins containing nanotubes on an ultra-thin slicer.
1.4.2DSC test
10 mg sample, tested with the Pekin Elmer DSC-7 instrument. In the nitrogen atmosphere, the glassing transition temperature is determined from the DSC curve by rising from 20 degrees C to 120 degrees C at a speed of 10 degrees C/min.
1.4.3 Storage Stability Test
Storage Stability means that powder coatings do not form after storage under certain conditions and maintain their original physical and chemical properties.
this experiment was carried out in accordance with ISO-8130-8-1994 "Test of the storage stability of powder coatings". The test results are recorded against the evaluation criteria of Table 1.
test of 1.4.4 impact resistance
impact performance test is carried out in accordance with GB/T 1732-1993 Paint Film Impact Resistance Measurement Method.
1.4.5 adhesion test
paint film adhesion refers to the firmness of the paint film and the surface of the object being applied, is one of the important indicators to test the physical and mechanical properties of the coating. The adhesion test was carried out in accordance with GB 9286-1988's "Scratch Law". And compare the grades with the instructions (Table 2).
1.4.6 Test for neutral salt spray
The detection of neutral salt mist resistance for epoxy powder coatings was carried out according to GB/T 1771-1991 "Measurement of neutral salt spray resistance for lacquer film". the appearance of the model is rated according to GB/T 1740-2007 "Paint film moisture-resistant heat determination method".
1.4.7 thermal conductivity test
the powder coating with a tablet press press pressed into thin sheets, the diameter of the sheet is 3cm, with a sample calibration instrument, calibration of the sheet into the DRL-II. type thermal conductivity meter for testing. Test 3 times, average as the final result.
2, results and discussion of
2.1 nanometer carbon tube dispersion
Figure 1 is a transmission mirror photo of different carbon nanotube mass fraction composite carbon nanotube/epoxy resin. As can be seen from Figure 1, when the carbon nanotube content is 3%, the nanotube dispersion in the composite epoxy resin is relatively uniform. When the carbon nanotube content is 4%, some carbon nanotubes appear reunited (the part shown by the arrow).
2.2 Storage Stability
As can be seen from Figure 2, the glass transition temperature of epoxy resin is 59 degrees C, while the glass transition temperature of nanotube mass fraction of 3% carbon nanotube/epoxy powder coating is 66 degrees C, and the glass transition temperature is improved after adding nanocarbon tube.
This may be because nanotubes have a high diameter ratio to surface area, and when nanotubes are added to polymers, they may interact very well with the polymer's molecular chain, which can hinder the movement of the polymer molecular band.
when the movement of the polymer molecular chain is blocked, the glass transition temperature of the polymer increases. As can be seen from Figures 3 (a) and (b), pure epoxy powder coatings hold levels 1 and 2 for 2d and 3d.
And the nanotube mass fraction of 3% carbon nanotube / epoxy powder coating to maintain the first and second level of time of 4d and 7d, respectively, indicating that the carbon nanotube added, epoxy powder coating storage stability improved.
and it is generally believed that storage stability is related to the glass transition temperature, the greater the glass transition temperature, the better the storage stability of the coating.
2.3 Impact Resistance
Figure 4 shows that the impact resistance of carbon nanotubes/epoxy powder coatings varies with different mass fractions of carbon nanotubes.
can be seen from Figure 4, when carbon nanotubes are added, the impact resistance of carbon nanotubes/epoxy powder coatings is gradually improved and then decreased. When the carbon nanotube content reaches 3%, the impact resistance is 33kg.cm.
This is because carbon nanotubes have a relatively large surface activity, with the polymer chain of physical or chemical binding opportunities, and the base contact area increased, carbon nanotubes in the interface and epoxy group formed a much greater force than Van der Worrest, forming an ideal interface, conducive to the nanotube and epoxy resin stress transfer, improve the ability to bear loads.
when the composite material is subjected to external shock, epoxy resin passes the impact force to the carbon nanotube, allowing the carbon nanotube to absorb more energy, so that the composite material can withstand greater impact.
And when the carbon nanotube content continues to increase, the impact resistance of carbon nanotubes/epoxy resins decreases, which may be due to excessive carbon nanotube content, resulting in the reunification of carbon nanotubes, easy to cause stress concentration of the system, thereby reducing the strength of composite materials.
2.4 adhesion test
Figure 5 shows the relationship between the adhesion of carbon nanotubes/epoxy powder coatings with different mass fractions of carbon nanotubes.
can be seen from Figure 5, with the increase of carbon nanotube content, carbon nanotube / epoxy resin powder coating adhesion performance gradually improved.
When the carbon nanotube content is 3%, the adhesion performance of carbon nanotube/epoxy resin powder coating reaches level 2, and when the carbon nanotube content continues to increase, the adhesion performance of carbon nanotube/epoxy resin powder coating gradually decreases.
This is because the inner stress of the coating film is an important factor affecting the adhesion of the coating film, and the amount of carbon nanotube addition affects the shrinkage stress produced during the curing process of the coating film, thus improving the adhesion of the coating film.
However, when too much carbon nanotubes are added, it causes the nanotubes to reunite so that the carbon nanotubes and epoxy resins do not come into full contact, thereby reducing the mechanical and physical properties of the coating, thereby reducing the adhesion of the coating film.
2.5 Salt Mist Test
Figure 6 shows the relationship between the corrosion resistance of carbon nanotubes/epoxy powder coatings and changes in carbon nanotubes with different mass fractions.
As can be seen from Figure 6, with the increase of carbon nanotube content, the corrosion resistance of carbon nanotubes/epoxy resin gradually improves, when the carbon nanotube content reaches 3%, its corrosion resistance is the best, and when the carbon nanotube content continues to increase, its corrosion resistance gradually becomes worse.
This may be because when the carbon nanotube content of 3%, carbon nanotubes in-place polymerization of carbon nanotubes / epoxy resin in the dispersion of good, these well-dispersed carbon nanotubes can play an additional role in physical crosslinking points, so that the resulting nano-modified powder coating film tightness increased, salt spray resistance will also increase;
And as the carbon nanotube content continues to increase, carbon nanotubes in the carbon nanotubes / epoxy resin in a large number of reunion, so that the carbon nanotube / epoxy resin powder coating after coating the formation of coating defects, resulting in the coating of the salt spray performance gradually reduced.
2.6 thermal conductivity test
Figure 7 shows the relationship between the thermal conductivity of carbon nanotubes/epoxy powder coatings with different mass fractions of carbon nanotubes.
From Figure 7, it can be seen that with the increase of carbon nanotube content, the thermal conductivity of carbon nanotube/epoxy resin gradually increased, the thermal conductivity of pure epoxy resin was 0.19W/mK, and when the carbon nanotube content was 3%, the thermal conductivity of carbon nanotube/epoxy resin reached the highest, at 0.541W/mK, which is 2.8 times the thermal conductivity of pure epoxy resin.
And Li and so on by adding 10% boron nitride to polyimide thermal conductivity increased by only 50%, Hyungu and so on by adding 36% in polydymoxysilane Al2O3 to increase its thermal conductivity by 2 times.
The principle of increasing the thermal conductivity is shown in Figure 8, when the carbon nanotube content is less, there is no contact between the nanotubes, it is not easy to form a cooling channel, therefore, the thermal conductivity increased
modestly