Synthesis and characterization of Epoxy/ Reduced graphene oxide composites for anti static electricity: Faculty of high quality training Graduation''s thesis of the Materials technology

GENERAL INTRODUCTION

Introduction

Nowadays, the demand for polymeric materials has attracted a lot of attention due to the convenience of use, variety of designs and low cost Thermosetting resin, specifically epoxy resin will be mentioned in this study Epoxy resin is quite popular in the field of coating and molding One of the advantages of epoxy resin is that it cures easily under ambient conditions As well as high hardness, high temperature performance, resistance to many chemicals and solvents, epoxy resin shows considerable potential in many fields However, epoxy resin is quite brittle and has very low flexibility The crosslinking density will increase the hardness of the resin but this is the cause of it being brittle at a very low strain To overcome this shortcoming, scientists have actively researched to improve it Such as modifying plastic with liquid thiokol for application as a specialized glue for the aviation industry [1] And reinforced to increase toughness and impact resistance, a study used microfibrillated cellulose to strengthen epoxy resin, glass fibers, and carbon fibers were also included as reinforcing fibers for epoxy [2]

A new material that is also of interest to scientists because of its outstanding properties is graphene Being one of the materials with the highest mechanical properties, pure graphene expresses Young's modulus of 1 TPa, a strength of 130 GPa, along with high electron mobility, as well as good thermal conductivity [3] Graphene has been applied in lithium batteries, supercapacitors, gas sensors, water filters, etc High purity graphene could be fabricated via various methods including bottom-up methods (CVD, epitaxial growth) or top-down methods (mechanical exfoliation, liquid phase and exfoliation) [4] In the production of graphene, the aforementioned method offers optimal synthesizing conditions and high purity, but they are very expensive and the amount of product obtained is very small Therefore, a new method going from graphite by oxidation and reduction reactions to form graphene nanolayers with functional groups was investigated Specifically, graphite is oxidized by physical and chemical agents to graphene oxide Because

GO has many functional groups, although it is very compatible with some polar polymers, it has poor electrical conductivity To improve conductivity GO will be reduced functional groups, to reduce graphene oxide Although graphene oxide is not completely pure and its mechanical properties are somewhat inferior, functional groups have opened up another application for this material that is as a

2 reinforcement phase for polymer materials There have been studies on the reinforcement of rGO into polymers such as poly vinyl alcohol [5], poly methyl methacrylate [6], epoxies, in general, adding a small amount of rGO filler has improved properties for materials such as improved mechanical properties, increased electrical conductivity, hardness,

There are two major challenges when synthesizing rGO-reinforced composites Firstly, to choose a suitable synthesis method that reduces graphene oxide without breaking its structure, the reduction process must remove functional groups to obtain products with high electrical mobility Secondly, rGO materials must be really well dispersed in the polymer matrix, the aggregation will lead to structural defects thereby reducing the properties of the composites The methods for dispersing reinforcement have been mentioned such as melt mixing, solution mixing, in-situ polymerization [4] which will be clarified in the following section.

The in-situ polymerization method is highly efficient because the reduction of

GO is performed after it has dispersed into the matrix resin Samples obtained after this process often have improved properties [6] However, this method is suitable for more polar polymers because GO has functional groups such as epoxy, carboxyl and hydroxyl groups that make graphene oxide highly polar Non-polar polymers such as polypropylene, polystyrene, and natural rubber [6] often use solvent dispersion or melt mixing.

Epoxy resin with high tensile strength, good chemical resistance, high adhesion, However, it is quite brittle, has poor abrasion resistance and poor crack propagation, so it is easy to break when subjected to bending force rGO material can be a good reinforcement for this resin.

Research motivation

In this dissertation, we will learn the basic theories of epoxy resin, reduced graphene oxide, and methods of rGO synthesis and composite formation The knowledge learned about the chemical bonds of epoxy and rGO will be mentioned The challenge for the synthesis is to ensure the purity of rGO, and its lattice defects, and minimize the agglomeration dispersion of rGO into the epoxy resin matrix.

Research objectives

The aim of this study is to synthesize composites with epoxy as continuous matrix and rGO as reinforced phase The main objectives of the thesis are as follows:

(i) Using a modified Hummers method to synthesize graphene oxide from graphite through 2 stages: production of expanded graphite and forming graphene oxide through oxidation.

(ii) Using reducing agents such as hydrazine, vitamin C, and heat to synthesize rGO

(iii) Using the solution mixing method to disperse rGO into an epoxy resin matrix with various mixing times

(vi) Analysis of mechanical properties, FTIR spectrum; Raman spectrum; diagram TGA; surface morphology such as OM; electrical conductivity.

Outline of dissertation

This dissertation is divided into five chapters to present our work and learnings along the way:

Chapter I is an overview of the project, the goals achieved after learning and experimenting.

Chapter II is an overview of basic knowledge of starting materials, synthesis procedures and characterized methods.

Chapter III includes chemicals, tools and equipment during your experiment The process will also be discussed in this chapter

In chapter IV, we will evaluate the mechanical property improvement between neat epoxy with EP/rGO instrument due to tensile strength Methods of observing surface morphology will also be included Two types of spectra, FTIR and Raman, will also be included to evaluate the characteristic functional groups of rGO and the association between the ground phase and the reinforcement phase An electrical conductivity survey will be conducted

Finally, the chapter V Conclusions and recommendations will be made to develop the topic.

BASIC THEORY

Introduction of epoxy resin

In the late 1890s, scientists synthesized epoxy compounds, which was a great turning point for the epoxy resin industry in particular as well as the polymer industry in general Until 1934s, IG Farben, a Germany dyeing company, was patented a synthetic product from amines with epoxies, including epoxy resins based on bisphenol A and epichlorohydrin The first commercial applications of epoxy resins were in surface coatings during World War II, i.e., Sylvan Greenlee had patented a line of high-molecular-weight (high MW) epoxy resins for coatings Products with flame retardant properties based on tetrabromobisphenol A was synthesized, developed and commercialized in the field of heat-resistance, composite materials in the 1960s Nowadays, coatings are also the main application of epoxy [7]

In the 1970s, the breakthrough development of waterborne epoxy coating technology helped establish a dominant position in the markets: powder coating for the automotive industry and furniture coating While epoxy resins are known for their excellent chemical resistance properties, the development and commercialization of epoxy vinyl ester resins in the 1970s by Shell and Dow provided very good chemical resistance properties such as acids, bases, and organic solvents [8] In 1980, along with the development of the computer and electronics industry, higher performance from epoxy resins was required The Dow Chemical Company introduced a high-performance product such as epoxy hydrocarbon novolacs based on dicyclopentadiene [7].

So far, epoxy resin is still widely used in surface coatings, protective coatings for electronic components, substrates for composite materials, etc.

Epoxy resin is characterized by the presence of 1,2-epoxy group The monomer may contain two or more ring-like epoxy groups Epoxy resin is a polymeric material with many common applications in the fields of paint and coatings, electrical, composites, … [9]

Figure 2.1 Ring-like epoxy groups

+ Diglycidyl ether of bisphenol A (DGEBA)

The bisphenol A group has provided typical properties such as hardness, heat resistance, and toughness The epoxy group and the hydroxyl group help the resin adhere better, increase the reactivity of the resin with a variety of chemicals to enhance properties without affecting the structure The ether bonds, which link the carbon chains, increase chemical resistance [7].

This is the most commonly used resin Bisphenol A-based epoxy can be easily seen in factory floor coatings, molded products, coatings in electronic equipment,

Figure 2.3 Equation for the formation of DGEBA from Bisphenol A and

In this process, the added NaOH acts as a catalyst for the nucleophilic ring opening of the epoxy group at epichlorohydrin and as a dehydrochlorinating agent for the change of the chlorohydrin to the epoxide group (epoxy ring-closing reaction) [7] The initial step will be the coupling reaction, which is normally

6 exothermic After completing the coupling reaction, the dechlorination phase will proceed.

The structure is similar to the bisphenol A-based resin, but bisphenol F has a bridge between the two benzene rings by a methylene group instead of the isopropylidene group found in bisphenol A Therefore, it will reduce the viscosity of the resin (Bisphenol A with viscosities of 11,000–16,000 cps, Bisphenol F with viscosity of 4000–6000 cps) [7] The methylene bridge also makes bisphenol F more stable at high temperature and higher resistant with various chemical environments Increases its curing ability.

Bisphenol F epoxy resin is often used in high-class construction systems such as tanks, pipelines, industrial floors,

The molecular weight of novolac is higher than that of epoxy resins based on bisphenol A and bisphenol F This increases its functionality Novolac after curing

7 has a fairly high improvement in properties The heat resistance is especially high in the range from 150 to 260 o C [7], leading to the resistance to most solvents, inorganic acids and alkaline solutions as well as high temperature, high pressure, high abrasion,

This type of plastic is often applied in the field of powder coating, aerospace composites, chemical processing equipment, anti-corrosion coating,

2.1.2 Curing agents for epoxy resins

Table 2.1 Common curing agents for epoxy resins [7] [4]

Curing agents Representative sample Advantages Disadvantage s

• Resistant to inorganic acids, water and some solv ents

• Requires a slightly higher curing temperature than room temperature

• Poorly resistant to many organic solvents

• High temperatu re resistance up to

• Difficult to compatible with resin because it is solid

Table 2.1 shows some typical examples of curing agents The process is simplified by the ring-opening reaction of the epoxy group or of the hydroxyl group

[10] to form cross-links There are two main curing agents: catalysts and chemicals with functional groups that cross-link the epoxy ring Usually, one of two agents or both can be used to create a cross-bridge for the resin [9]

Figure 2.6 Curing reaction between diglycidyl ether of epoxy bisphenol A resin

(DGEBA) and poly-ether-amine based hardener [11]

Cross-links are formed from the addition of nucleophiles [12] With primary amines, an additional reaction will take place to form a secondary amine and a hydroxyl group The secondary amine then continues to react with another oxirane ring, forming a hydroxyl group and a tertiary amine. chemical resistance higher than aliphatic amine process takes a long time and the high temperature about

Epoxy has outstanding physical and mechanical properties such as high tensile strength, low shrinkage, very high adhesion, high modulus, so it is applied in many fields such as coatings for factories and especially as a base phase for composites

[4] One disadvantage of epoxy is high brittleness, low elongation at break, and poor resistance to crack propagation.

The outstanding properties of epoxy are chemical resistance, water resistance and corrosive resistance, thanks to the epoxy structure with aromatic rings and phenolic ether bonds [7] Epoxy resin is also used as the main adhesive ingredient for concrete, wood, metal, ceramics and many other plastics

Figure 2.7 Fracture surface morphology of EP/rGO imaged by FEG-SEM

In the FEG-SEM image, we can see the characteristic river lines of epoxy resin after curing This also suggests that when bending force is applied to it, it will easily break [12]

Table 2.2 Some physical properties of cured epoxy [4]

Overview of graphene, graphene oxide and reduced graphene oxide

Graphene is a monolayer form of graphite, discovered in 2004 by two Russian scientists Geim and Novoselov using the scotch tape method that comes from graphite [13][14] Graphene is a single-layered plane in which carbon atoms are arranged in a tight hexagonal structure in a 2D honeycomb lattice Graphene, on the other hand, can arrange the coil to form a fullerene (0D) shape or be wrapped up to form carbon nanotube (1D), or stacked to form a graphite (3D) shape

Regardless of its shape, the typical structural feature of graphene is that the atoms are arranged atop even hexagons, each carbon atom bound up to the next three carbons by the covalent bonds formed by orbital hybridization sp 2 The distance between the links is 1.42 Å [14]

Graphene is known to be a film-like material that is almost transparent with light, it absorbs only 2.3% of the intensity of light and the air is completely unable to pass through even the smallest molecules [4] Besides, flexible graphene film can be easily bent, folded or rolled up Some reports suggest that electrons can penetrate graphene more easily than copper Moreover, electrons passing through graphene almost do not encounter resistance, so they rarely generate heat, and graphene itself is also a good conductor of heat (5000 W.m -1 K -1 ), which is better than other carbon structures [4]

On the other hand, graphene has a defect-free structure, carbon atoms are linked together by covalent bonds and have high mobility, thus creating some outstanding properties such as mechanical properties, electrical properties The mechanical properties of graphene have been shown by some studies "Graphene is found to be one of the strongest natural materials with a mechanical strength higher than diamond and over 300 times greater than a steel film of the same thickness"

[4] Including Young's modulus (1100 GPa), fracture strength (125 GPa), the quantum Hall effect at room temperature, pure graphene conducts electricity faster than any other material [16]

2.2.2 Graphene oxide and reduced graphene oxide

There is a clear difference between graphene and graphene oxide (GO) that

GO has additional oxygen-containing functional groups such as ether (-O-), epoxy (-COC-), carbonyl (-C=O), carboxyl (-COOH), hydroxyl (-OH), [14] on the surface and edges, GO is polarized, hydrophilic so it can be easy dispersed in a

12 well-polarized environment On the other hand, due to the formation of oxygen- containing functional groups, part of the sp 2 bond in the lattice has degraded and become sp 3 bond The negative charges of these functional groups have given the appearance of electrostatic thrust that adds to GO's ability to interact on their surface Furthermore, the creation of hydrogen bonds between the GO layers through hydroxyl, epoxy, and carboxylic groups with the -OH group of water This causes the distance between GO layers to be significantly widened compared to graphite The thickness of the GO monolayer has been reported to be approximately 1-2 nm, four times the thickness of a graphene layer (approximately 0.34 nm) GO is a gray-brown solid with a C:O ratio between 2:1 and 2:9 [17] Besides, the electrical and thermal conductivity of GO is much lower than graphene because it has a large number of defects in the crystal network

Figure 2.10 The structure of GO according to Lerf – Klinowski [18]

According to Gao et al., GO's electronic conductivity is at 0.408 S.cm -1 This can be explained because the structure of GO contains many oxygen-containing functional groups, making the electron exchange on the surface limited as well as reducing the number of π bonds leading to poor electrical conductivity Because of that, it is necessary to remove some functional groups containing oxygen on the surface, such a process is called GO reduction The product of this process is called reduced graphene oxide (rGO) [18]. rGO is not quite the same as GO or graphene, it is located between these two materials rGO conducts electricity well because the structure is partially restored to the aromatic ring, but still not as good as graphene, the mechanical properties are more similar to GO In the structure of rGO, there are still some functional groups containing oxygen, so it can still be dispersed in water or some types of organic solvents, but to some extent rGO is not as easy to use as GO but it is easy to synthesize by reducing GO by dechemical, biological methods, [4]

Figure 2.11 The diagram illustrates GO reduction according to Huang et al

Two common methods: the top-down and bottom-up approach Oxidation is top-down

Graphene oxide can be synthesized by oxidation with powerful oxidants with conditions, appropriate reaction times and varying degrees When oxidizing GO, the C=C double bonds are gradually replaced by polarized functional groups such as epoxy (-COC-), carbonyl (-C=O), carboxyl (-COOH), hydroxyl (-OH), The color of GO varies depending on the method and type of graphite used (with a large C/O ratio, the solution is black-brown and the small C/O ratio of the solution is yellow)

[17] In summary, GO is synthesized using three main methods: Brodie method

(1859), Staudenmaier method (1899) and Hummer’s method (1958) with commonly used oxidizing agents H2SO4 solid, HNO3, KMnO4, KNO3, [17] Of the three methods, the Hummers method is the most commonly used

Figure 2.12 Graphene Oxide synthesis method [13]

+ Brodie method: This is the earliest method born in 1859 with a combination of NaClO3 and a dense HNO3 solution By using the elemental analysis method, the end product has the molecular formula C11H4O5 This product is lightly acidic and has the ability to disperse in alkaline environments, but is small in size, thickness is limited and has an imperfect structure [13]

+ Staudenmaier method: Staudenmaier 1899 studied and improved the Brodie method by adding H2SO4 acid to increase the acidity of the reactive mixture as well as increase the oxidation level of the agent mixture However, both of these methods are very dangerous because there is KClO3 which is easy to break down into ClO2 gas that is prone to explosions in the air

+ Hummer’s method: This method, introduced in 1958, has overcome the fire hazard disadvantages of the two methods by combining H2SO4 with KMnO4 and NaNO3 solid This mixture helps the GO product to form a higher level of oxidation

[19] Although KMnO4 is used as an oxidizer, MnO7 is actually the main agent involved in the oxidation of graphene to GO in the following reaction:

MnO7 is an active oxidizer, however, it is easily detonated when heated to a temperature of 55°C or when exposed to organic compounds [13] Therefore, to avoid this dangerous situation, it is necessary to control the temperature closely in the reaction, especially on an industrial scale.

According to this group of authors, in the same system of oxidants is KMnO4/

H2SO4 but conducted under different conditions, GO products with functional groups containing oxygen with different levels of oxygen are obtained For example, under the condition that the reaction is at normal temperature, the resulting product contains groups -OH, -COOH, -COC- at the same rate When the presence of water is further conducted, the group -OH and epoxy (-COC-) prevail, while at a temperature of 95 o C, the GO product has a large number of carboxylic functional groups (-COOH)

Figure 2.13 The effect of oxidative conditions according to the Hummers method [16]

In addition, this method does not produce explosive gas products, but still generates a mixture of NO2 and N2O4 due to the presence of NaNO3 during the reaction In addition, the Hummers method also has a disadvantage of being an incompletely disassembled single-layer graphene oxide product This exfoliation process requires the use of high-energy methods such as ultrasound, microwave, mechanical, thermal, [16] Therefore, in recent years, the Hummers method has been further studied to eliminate the use of NaNO3 to avoid the generation of harmful gasses, this method is also known as the modified Hummers method.

+ Modified Hummers method: Published in 2010 by a university research team in the USA with a change from the old method of not using NaNO3, increasing the amount of KMnO4 [16] In addition, in the process of stopping the reaction, hydrogen peroxide (H2O2) is used for the purpose of increasing the level of oxidation and removing excess Mn2O7 The GO extraction process is performed by stirring vigorously together with deionized water or using ultrasound The strength

Introduction of methods for the preparation of polymer/rGO composites

There are three main methods for the synthesis of polymer-based and rGO- reinforced nanocomposites Depending on factors such as the hydrophobicity of the polymer, the polarity of the polymer and the functional groups of the two phases interact with each other Then choose a suitable method for that polymer The specific methods are as follows:

Figure 2.14 Schematic illustration for solution mixing method

This is a simple composite technique With three basic steps that are to disperse the filler into the solvent, then the polymer is added to combine with the filler, reducing the solvent and gasses generated during the reaction between the filler and the substrate [24] Some equipment is required to apply this method such as a stirrer and ultrasonic machine to disperse the filler into the solvent and polymer Normally, sonication will be preferred as it avoids the disruption of rGO films from stirring Degassing requires equipment such as heating devices, drying ovens, and vacuum furnaces [4].

The compatibility between the polymer, the filler and the solvent are believed to be an important factor in achieving a sample with good dispersion [24] Degassing and solvent are also a factor that helps the sample avoid defects due to air bubbles.

Figure 2.15 Schematic illustration for the in-situ polymerization method

This process is carried out at the polymerization stage The filler will be added to a monomer or multiple monomers [4] The system will be mixed and then polymerization will be performed:

+ The GO plates are distended within the monomer Solvents were added to reduce the viscosity and increase the dispersibility of GO.

+ Next, an initiator will be added to this process which can be catalyzed such as temperature, UV, radiation, [24]

+ Finally, the process of converting GO to rGO will be reacted in the presence of the polymer

GO or rGO layers will easily disperse into monomers (in particular, GO has many functional groups, so it is easy to bond with monomers) These functional groups will create a covalent bond between GO and the polymer through chemical reactions [8] With this good dispersion, nanocomposites have improved

20 mechanical properties compared to the other two methods The disadvantage of this process is that the viscosity must not be too high, the inclusion of GO films also hinders the efficiency of the polymerization [4].

Figure 2.16 Schematic illustration for melt blending method [25]

This is also a fairly simple, practical method The preferred polymers are thermoplastics The technique uses the principle of physical mixing between the polymer and the filler The combination of shear force and high temperature will blend the two phases together [25] A great advantage of this method is that it does not use solvents, which avoids the risk of toxicity, fire, and cost Mass production will favor this technique However, a strong shear force will rupture the thin film structure of rGO to form smaller films and reduce the mechanical properties [24] Equipment such as extruders and injection molding have often used this technique to produce composites.

Applications of epoxy/rGO composites

Static electricity is an imbalance of charge, too much accumulation of charges of the same sign on the surface of a material will cause an electrical discharge or be transmitted through a conductive object when in contact with an electrostatic surface This causes a lot of damage to equipment, machinery, electronic components and especially can affect human health Therefore, the combination of rGO and epoxy can be applied to antistatic.

Figure 2.17 Static electricity from the friction between the shoe and the floor

The fields of application of this material are also very typical, which can be mentioned in industry, electronic equipment, aerospace, There have been studies on antistatic polymer composites for applications in aerospace Specifically, airplanes often fly at high speeds, so they will have friction with air, dust, rain, Then the surface at these locations will accumulate a large charge, when it exceeds the threshold, it will cause electrical discharges that cause fire, damage to equipment and even interfere with radio signals When there is too large a charge difference, it is also easy to be struck by lightning [27].

Figure 2.18 The friction between the plane's surface and the airflow creates negative charges [28]

Figure 2.19 Classified resistivity ranges of materials [26]

As shown in the Figure 2.19, there are 3 groups of materials classified by resistance, conductor, and electrostatic discharge Specifically, ESD materials are also divided into 2 types:

+ Anti-static material: This material will prevent the accumulation of static electricity on the surface from the friction between the 2 surfaces The required surface resistance is from 10 9 - 10 12 Ω/sq, the required volumetric resistance is from

+ Static dissipative materials: The charges of this type of material will move to the ground slowly The required surface resistance is from 10 5 - 10 9 Ω/sq, the required volumetric resistance is from 10 4 to less than 10 8 Ω.cm.

MATERIALS AND METHODS

Chemicals, tools and equipment

Table 3.1 The chemicals used in the thesis

Panjin G-High Carbon Materials Co., Ltd

CTCP Chemical Corporation Duc Giang

Ratio of epoxy resin:curing polyamine = 10:3

Guangzhou Guanghua Technology Co., Ltd

Guangdong Guanghua Sci- Tech Co., Ltd

Table 3.2 The tools and equipment used in the thesis

No Tools and equipment Parameters Figures

Experimental method

3.2.1 Synthesis of Graphene oxide (GO)

Scheme 1 Graphene oxide synthesis procedure.

In this article, we selected the modified Hummers method to synthesize graphene oxide, the process consists of the following steps:

Step 1: Mixed 5 g graphite powder into 150ml concentrated sulfuric acid (H2SO4 95-98%) and stirred at 200 rpm

Step 2: 50 ml nitric acid (HNO3) was added to the above mixture and stirred for 24 hours at room temperature

Step 3: Slowly add 200 ml of DI water to the mixture The resulting mixture was then washed 3 times with DI water, centrifuged and dried at 60 o C for 24 hours to obtain graphite intercalated compound (GIC)

Step 4: Dried GIC powder is placed in the microwave at 800 W for 15 seconds The resulting product was expanded graphite (EG)

Step 5: Put 50 ml of concentrated H2SO4 into the 0 o C ice bath, then slowly add 0.5 g EG and 3 g KMnO4, control the temperature below 20 o C, and stir the mixture above 35 o C for 2 hours

Step 6: The mixture was put in an ice bath and added 100 ml DI water, controlled the temperature below 70 o C, stirred the solution for 1 hour

Step 7: Continue to keep the solution in the ice bath and put in 5 ml H2O2

30% Used 45 ml of HCl 10% to remove excess H2O2 in the solution Finally, the sample was filtered and washed several times with DI water until pH = 6-7 The final GO product was formed

3.2.2 Synthesis of reduced Graphene oxide (rGO)

The rGO synthesis process was performed by chemical reduction (by hydrazine hydrate or vitamin C) and microwave reduction (heat shock)

Scheme 2 Reduced Graphene oxide synthesis procedure by hydrazine hydrate reduction agent

Step 1: The GO solution was ultrasonicated for 30 minutes to create a homogeneous solution

Step 2: Added hydrazine hydrate with a weight to GO ratio of 7:10 and stirred at 80°C for 60 minutes.

Step 3: The rGO sample was formed and washed with DI water to remove the excess reducing agent

Scheme 3 Reduced graphene oxide synthesis process by vitamin C reduction agent

Step 1: The GO solution mixture was ultrasonicated for 30 minutes to create a homogeneous solution

Step 2: Vitamin C 0.1M was added to 50 ml GO (0.1 mg/ml) with a volume ratio of 1:1 and magnetically stirred at 70 o C for 30 min At this time the solution changed from brown (GO) to black (rGO).

Step 3: The product was washed with ethanol and water three times and dried at a temperature of 80 o C for 24 hours

Scheme 4 Reduced graphene oxide synthesis process by heat shock

Step 1: GO paste was dried in an oven at 80 o C for 24 h

Step 2: GO after drying was weighed 100 mg in a heat shock The sample is concentrated in a ceramic beaker and covered with a ceramic lid

Step 3: Use a commercial microwave oven to dry samples at the power option of 800 W for 2 minutes

3.2.3 Synthesis of EP/rGO composites [33]

Scheme 5 EP/rGO composites synthesis process

Step 1: rGO with 0.5 wt%, 0.75 wt%, and 1 wt% was dispersed in acetone and sonicated for 1 h to form a homogeneous mixture

Step 2: Added epoxy resin to the mixture and continued sonication for 2-3 hours

Step 3: Evaporated the acetone solvent with a drying oven, then added the curing agent, stirred the mixture for about 2 minutes and poured into the mold The final product was cured in 24 hours at room temperature

Composite films with 0.5 wt%, 0.75 wt%, 1 wt% at 2h sonication time were denoted as EP/rGO-2h-0.5%, EP/rGO-2h-0.75%, EP/rGO-2h-1%, respectively

Analytical methods

This evaluation is done to observe the composite sample surface and the dispersion of rGO in epoxy Images of EP/rGO composites samples obtained with Olympus MX51 microscopes at the Materials Technology Laboratory, Technology and Education University, Ho Chi Minh City

The Raman scatter spectroscopy method is used in chemistry to study the characteristic vibrational mechanism of the molecule and the group of atoms in the composite material The Raman spectrum is based on the inelastic scattering of the stimulating photon on the oscillations of the sample to be analyzed [15] The GO and rGO samples were measured using the Raman Microscopy Labram 300 at the Institute of Nanotechnology

3.3.3 Fourier transform infrared spectroscopy (FTIR)

The infrared spectrum is a curve that shows the dependence of the intensity of a substance's absorption of infrared radiation on the number of waves or wavelengths On the infrared spectrum, the horizontal axis represents the wavelength (μm) or the number of waves (cm -1 ), and the vertical axis represents the absorption intensity The vibrations of atoms in the molecule create a fluctuating spectrum There are two types of vibrations in molecules: valence vibrations (or stretching vibrations) and bending vibrations [13] This method is sensitive to functional groups, from which it is possible to analyze the bonds present in the structure of the sample and the interaction between the components in the composites The thesis used infrared spectroscopy to measure EP and EP/rGO samples by Nicolet 6700 of Thermo brand at the Institute of Applied Materials Science

TGA is a technique in which the weight of the material increases or decreases when it is heated In this method, the weight of the sample was measured while the material is heated or cooled in the drying oven In this method, the Thesis measured Neat Epoxy and EP/rGO composites using the Labsys Evo 1600 [4]

Characterization of mechanical properties in polymers usually refers to the measurement of the strength of polymer films Tensile strength and elastic modules are of particular interest to describe the stress properties of the polymer film Other techniques include viscosity, rheology, and hardness measurements [35] Tensile strength, strain at break and elastic modulus for each material were measured at room temperature with a Shimadzu tensile tester at the Laboratory of Materials Technology, Ho Chi Minh City University of Technology and Education, according to ASTM D638-00 Type I standard [36]

Tensile strength is defined as a stress, as measured by force per unit area For some heterogeneous materials (or for assembled components), it can be reported to be just a force or a force per unit width In the International Unit System (SI), the unit is the Pascal (Pa) (or its multiple, usually Megapascal (MPa), using the prefix SI; or, equivalent to pascal, newtons per square meter (N/m²)

Young's modulus is a mechanical property of linear elastic solid material It determines the relationship between stress (force per unit area) and strain (proportional strain) in the material [35]

The tensile measuring sample was machined with dimensions according to ASTM D638-00 standards shown in the figure and table below:

Figure 3.1 Illustrative image of a mechanical measurement sample based on

Table 3.3 Dimensions of EP/RGO composites samples according to ASTM

Measured the width (Wc) and thickness (T) at multiple points on the waist area of the sample, and took the average value Then, started up and set the device parameters according to the measurement standard and sample size measurement (length x width x thickness), the tensile speed is 12.5 mm/min Placed the sample in two clamps and proceed to measure the sample Recording data: Tensile force at break yield, module/slope, yield tensile stress, breaking stress and data processing

- Tensile strength: Tensile strength is the maximum tensile stress of the specimen before breaking When the maximum stress occurs at the yield point (the first point on the stress-strain curve at which there is an increase in strain without an increase in stress), the tensile strength is recorded at yield point When the maximum stress occurs at break, the tensile strength will be recorded as the breaking strength

Tensile strength is calculated according to the formula: σ = F

S: The section is at the waist of the sample S = W x T (mm 2 )

Strain: strain is the change in the length of the sample when stretched compared to the original length ɛ = L−L 0

L: Sample length after deformation (mm)

Young’s modulus: ratio of strain between tensile stress at break and strain at break.

It is possible to estimate the toughness from the stress-strain curve Specifically, the area of the curve is the toughness value [37]

Toughness = σ x δ= Area of stress-strain curve

The insulation resistivity of EP/rGO materials was measured according to the ASTM- D257 standard by using a ''High voltage insulation tester, model 3121'' at Eastern Quality Measurement Standard Co., Ltd (QUATEST Miền Đông)

Figure 3.2 Resistivity samples (left), volume resistivity (right)

Figure 3.3 OM photograph of sample width due to resistivity coated on paper surface

The resistivity is calculated as:

Graphene oxide rGO-vtmC rGO-heat shock rGO-hydrazine

A: the cross-sectional area of the specimen (m 2 ). l: the length (m) σ: electrical conductivity (S/m).

The volume resistivity is calculated as: ρv = R x A

T: thickness (cm) σv: volume electrical conductivity (S/cm).

Surveys on the synthesis of EP/rGO composite

Table 3.4 Survey of parameters from the process

STT Sample Mixing time (hours)* rGO content (wt%) x y

* Mixing time is the sonication time to disperse the rGO solution into epoxy resin

Table 3.5 Survey of various reduction agents

Reducing chemicals Hydrazine Vitamin C Heat shock z z z

Table 3.6 Survey of the mixing of dispersed phases

STT Samples Dispersed phases rGO EG Graphite

Table 3.7 Survey of the effect of dispersed phase concentration on resistivity

RESULTS AND DISCUSSION

Appearance of GO and rGO materials

Figure 4.1 Expanded graphite (left), GO solution (right)

After the oxidation process, it can be seen that the size of the original graphite has become smaller and dispersed very well into the aqueous solvent GO solution is very well dispersible in water, according to our observation, there is no effect on it for 2 months, there is still no sedimentation of GO

Figure 4.2 Sample volume increased after thermal shock; GO (left), rGO

Microwave reduction increased the rGO volume significantly The GO sample was also brown in color after drying, but after heat shock turned black The reduction process resulted in a drastic increase in temperature, which can be seen inside the microwave oven, the burning and shaking of the ceramic cup

Figure 4.3 rGO after drying with hydrazine reducing agent (a), vitamin C reducing agent (b) and heat shock(c)

GO suspensions are light brown in color due to their very good dispersion in aqueous solvents After reduction and oven drying, rGO tended to agglomerate as shown in Figure 4.3; the size of hydrazine-reduced rGO blocks can be seen to be smaller With the reducing agent is vitamin C, the block is quite large and the size is not uniform The thermal shock agent gives the best sample size, the rGO plates are even and smooth.

Appearance of EP/rGO composite

Figure 4.4 EP/Gr samples at concentrations of (a) 0.25 wt%, (b) 0.5 wt%, (c)

Color transition from transparent epoxy to dark black EP/Gr 1wt% After complete curing, the sample was cut with an electric saw and grind the surface flat.

Optical microscope (OM) results

Figure 4.5 Optical microscope image of EP/rGO-0.25% samples with vitamin

C reduction agent (a), heat shock sample (b), hydrazine reduction agent (c)

The OM result image of EP/rGO-0.25% samples with different reducing agents showed that for the reducing agent was vitamin C with sparse rGO layer density and uneven layer size in the epoxy substrate The gradual decrease in layer size along with this is a gradual increase in layer density expressed in Figure 4.5 (b) and Figure 4.5 (c), especially with hydrazine reduction agent This is explained by the strong impact of reducing chemicals to help remove oxygen-containing functional groups but at the same time reduce the formation of π-π bonds inherent in the structure of rGO, thus preventing agglomeration

Raman scattering spectrum result

Figure 4.6 Raman spectra of a) GO, b) rGO (hydrazine), c) rGO

(vitamin C) and d) rGO (heat shock)

Table 4.1 Statistics of Raman measurement results of samples

GO 1335.83 1610.78 1.09 rGO (hydrazine) 1332.93 1602.1 1.12 rGO (vitamin C) 1332.93 1602.1 1.22 rGO (heat shock) 1338.72 1590.52 1.49

To determine the significant structural change during the reduction of GO to rGO shown on the Figure 4.6 On the Raman spectrum of GO and rGO samples, there are characteristic spectral signals including D band and G band (Figure 4.6) in

45 which the G band is in the region of 1582 cm -1 and the D band in the region of 1350 cm -1 The G-peak corresponds to the oscillation of the phonons at the center of the Brillouin region (symmetry E2g) of graphite, indicating the oscillation of carbon atoms bound together by the hybridization of sp 2 (the bond between carbon atoms in the graphene network) Besides, there is also the appearance of the D band corresponding to the oscillations of the K-point phonons of the A1g symmetry, also known as the breathing vibrations of the graphite layers, that is the oscillation of sp 3 hybridized carbon atoms, which represents the loss of self or structural defects in the graphene lattice [6] From the results of GO's Raman analysis (Figure 4.6a) showed that the G band appeared weaker than the D band, which demonstrated that the oxidation attached to additional polarizing functional groups on the GO surface from the original π bonds in the graphene network increased the number of C-sp 3 bonds compared to C-sp 2 The rGO samples reduced with hydrazine (Figure 4.6b) and vitamin C (Figure 4.6c) reducing agent had an increased ratio of the relative intensity of D peak to G peak (ID/IG) compared with GO, this change shows a decrease in the average size of sp 2 domains because the newly formed graphitic domains are smaller in size than GO but more numerous [38] Besides, the results of Raman spectroscopy also show that rGO samples are strongly influenced by temperature or reducing chemicals, causing many edge defects due to the reduction of some C=C bonds in GO [39], specifically seen in the ID/IG ratio of rGO samples by heat shock method higher than chemical reduction and the ID/IG ratio to reducing agent is hydrazine is smaller than reducing agent is vitamin C

Fourier transform infrared spectroscopy (FTIR) results

Figure 4.7 FTIR spectra of Epoxy resin, rGO/EP dispersion reduced with hydrazine and vitamin C; blue is for rGO, red is for EP, and black is for both

The characteristic peaks of rGO materials such as O-H stretching oscillations typical for carboxylic acid groups are from 3300-2500 cm -1 , usually centered at

3000 cm -1 ; The C-O stretching vibration is typical for the aromatic ester at 1250 cm -

1, which is a group created by the reaction of the carboxylic group present in rGO with the -OH group, the epoxy ring of the epoxy resin (described more clearly in the figure below); C-H bending is specific to 1,2,3,4-tetrasubstituted at 830 cm -1 [40]

Figure 4.8 Reaction of -COOH group with -OH and epoxy ring

The characteristic peaks of epoxy resin such as C–H out of plane-bending vibrations of the aromatic ring at 570 cm -1 and at the peak of 791 cm -1 corresponds to the stretching of C–O–C of the ether bond [40], this is also the characteristic bond of epoxy resin

And finally, there are vertices in both like O-H stretching at about 3500 cm -1 ; stretching vibration C=C of the benzene ring at 1606 cm -1 ; C-C aromatic stretching vibration of the benzene ring at 1508 cm -1 ; the -O-C aromatic bond corresponding to the 1044 cm -1 [4] peak and finally to the high strength peaks such as 970 and 914 cm -1 is the bonding of the oxirane ring in the epoxy resin as well as the oxirane ring which is also a group for the position of rGO

Thermal gravimetric analysis (TGA) results

Figure 4.10 TGA analysis diagram of EP and EP/rGO composite samples

The TGA analysis diagram of neat EP and EP/rGO composite samples measured under the same conditions in N2 gas environment shows that there is only a single stage of thermal decomposition in the range of 300 - 500 o C, which is the stage of decomposition of polymer chains The results indicated that the decomposition temperature of neat EP is 353 o C while the EP/rGO composite sample is 350 ° C Thus, with the addition of rGO, the thermal conductivity of the epoxy substrate is increased The reason for this is that because rGO was reduced quite well, there were not many oxygen-containing functional groups, so the creation of hydrogen bonds with polarizing functional groups of EP decreases, this can be observed at a temperature range above 400 o C Besides, the ability of rGO to disperse evenly in the EP sample and conduct heat evenly should also reduce thermal strength [41] The enhancement of thermal properties is also related to the conductivity of the composite sample, which is suitable for some later conductive applications

Mechanical test results

Figure 4.11 Graphs of (a) tensile strength, (b) Young's modulus of EP/rGO reduced with hydrazine at sonication times

Table 4.2 Mechanical data of survey with hydrazine at sonication times

Samples UTS (MPa) Elongation at

There has been an improvement in tensile strength from the sample sonication time survey At sonication times 2 and 2.5 h, there was a reduction in specific UTS decreased by 57.4% and 32% compared to neat epoxy, respectively At sonication times 3 h, there was a 32.6% improvement in tensile stress compared to neat epoxy The improvement in elongation increased with extending sonication time (the highest increase was 17%) This is explained as rGO needs time to disperse and react with epoxy resin The ultrasonic agent also separates the agglomerated rGO layers after oven drying There was a reaction between rGO and epoxy resin, which improved elongation The bonds between rGO and EP increase the free range of motion for the polymer chain thereby making it more flexible [32] In addition to the rGO-hydrazine-0.25 wt% sample, which improved Young's modulus (16.5% increase compared to neat epoxy), the remaining samples tended to decrease Young's modulus

Figure 4.12 Graphs of (a), (b), (c) tensile strength; (d) Young's modulus of

EP/rGO was reduced with hydrazine, vitamin C and heat shock at concentrations ranging from 0.25 to 1 wt%; sonication time is 3 hours

Table 4.3 Mechanical data of survey with hydrazine and vitamin C at concentrations ranging from 0.25 to 1 wt%

Young’s modulus (GPa) EP/rGO-hydrazine-0.25 wt% 55.03 ± 2.63 3.89 ± 0.17 1.4543 ± 0.10 EP/rGO-hydrazine-0.5 wt% 31.70 ± 0.94 3.92 ± 0.64 1.0508 ± 0.04 EP/rGO-hydrazine-0.75 wt% 26.11 ± 1.03 4.32 ± 0.12 0.6871 ± 0.07 EP/rGO-hydrazine-1 wt% 28.29 ± 4.94 4.11± 1.49 0.8103 ± 0.05 EP/rGO-vitaminC-0.25 wt% 40.27 ± 5.71 4.28 ± 0.74 1.0052 ± 0.08 EP/rGO-vitaminC-0.5 wt% 22.70 ± 0.46 2.70 ± 0.06 1.1321 ± 0.08 EP/rGO-vitaminC-0.75 wt% 22.78 ± 1.12 2.21 ± 0.26 1.0881 ± 0.07

EP/rGO-vitaminC-1 wt% 20.80 ± 1.07 1.93 ± 0.18 1.1396 ± 0.01 EP/rGO-heat shock-0.25 wt% 36.33± 1.12 3.13± 0.08 1.1540 ± 0.21 EP/rGO-heat shock-0.5 wt% 35.16 ± 0.66 3.54 ± 0.23 1.1308 ± 0.09 EP/rGO-heat shock-0.75 wt% 30.2 ± 2.56 4.41 ± 0.35 0.8379 ± 0.07

As seen in Table 4.3, increasing the rGO content above 0.25 wt% did not increase the UTS of the sample However, in the hydrazine-reduced sample, a gradual increase in elongation could be observed with increasing rGO content, reaching the highest value at 0.75 wt% increasing by 30% For the vitamin C- reduced sample, the stress-strain curve is significantly reduced, the main reason is that the rGO samples reduced by vitamin C are severely agglomerated leading to structural defects thereby reducing the mechanical properties When increasing the concentration of rGO, Young' modulus has a decreasing direction The drop in tensile stress is thought to be a structural defect as well as an imbalance of the curing reaction and saturation of the filler content [12]

In the heat shock samples, the rGO content up to 0.5 wt% did not have much change in UST, whereas there was a decrease in tensile stress in the heat shock sample of 0.75 wt% However, when increasing the content from 0.25, 0.5 and 0.75 wt%, respectively, there was an improvement in elongation There is no increase in tensile stress as thermal reduction will cause lattice defects, forming the five- membered ring structure which in turn leads to a decrease in the mechanical properties of rGO, see Figure 4.12 [42]

Figure 4.13 Defects during the thermal reduction of GO [43]

Figure 4.14 Graphs of (a), (b) tensile strength; (c) Young's modulus of EP/Gr and EP/EG at concentrations ranging from 0.25 to 1 wt%; sonication time is 3 hours

Table 4.4 Mechanical data of survey with EP/Gr and EP/EG at concentrations ranging from 0.25 to 1 wt%

Young’s modulus (GPa) EP/Gr-0.25 wt% 28.55 ± 4.74 2.89 ± 0.56 0.9332 ± 0.08 EP/Gr-0.5 wt% 37.97 ± 4.83 4.11 ± 0.42 0.9338 ± 0.05 EP/Gr-0.75 wt% 23.96 ± 5.74 3.00 ± 0.43 0.7695 ± 0.04

EP/EG-0.5 wt% 27.40 ± 2.75 2.98 ± 0.82 0.9275 ± 0.09 EP/EG-0.75 wt% 40.06 ± 3.80 4.84 ± 1.03 1.0221 ± 0.14

In order to investigate the effects of reinforced phases in the composites, graphite (Gr) and expanded graphite (EG) was used instead of rGO, the results expressed in Table 4.4, there is no improvement in UTS or elongation at break It can be seen that after comparing with rGO sample, graphite filler and expanded graphite have no improvement in tensile stress.

Table 4.5 Determination of toughness of a sample from stress strain tensile curve

EP/rGO-heat shock-0.5 wt% 0.6223

There is an improvement in toughness when reinforcing graphene family materials The highest improved toughness belongs to rGO-hydrazine-0.25 wt% (up to 55.32 %) Studies have shown three factors: good dispersion of the filler into the matrix, compatibility of the two phases (through the covalent bonds between rGO and epoxy resin), and the layer size of the filler (The smaller the filler size, the higher the filling in the amorphous region of the epoxy resin) [44].

Conclusion: The model with the greatest ultimate tensile strength can be seen when adding rGO 0.25 wt% (32.6% increase) Gains above 0.25 wt% will reduce ultimate tensile strength However, the elongation at break of the sample increased gradually with increasing rGO content (the highest improvement was 30% in the hydrazine 0.75 wt%) The potential of EP/rGO is possible Concentrations of 0.25 wt% are suitable for bulk applications, while higher concentrations are suitable for film and coating applications due to improved elongation at break.

Resistivity results

Figure 4.15 Graph of resistivity of graphite after oxidation and reduction with different agents

Table 4.6 The data on samples Gr, EG, GO, rGO from there infer the resistivity

GO 1.66x10 -6 3 x10 -2 None None None rGO-hydrazine 1.66x10 -6 3 x10 -2 2650 0.15 6.67 rGO-vitamin C 1.66x10 -6 3 x10 -2 6.30x10 4 3.49 0.286

We used a multimeter to find the resistance of the samples Then deduce the resistivity and electrical conductivity The resistivity value of graphite is 0.09 Ω.m which is consistent with previous reports of resistivity of carbon powders & fibers in the range of 1-10 2 Ω.m [45] After oxidation to form expanded graphite, the resistivity has increased to 359.11 Ω.m, similarly after oxidation to graphene oxide, measuring the sample with a multimeter shows the result is due to the resistance of

GO is too large to exceed the device's maximum scale The resistivity values of rGO samples reduced by hydrazine, vitamin C and heat shock are 0.15, 3.49 and 5.69 Ω.m, respectively We can easily see the increase in electrical resistance when oxidizing graphite to form GO, which can be explained by the addition of functional groups that cause loss of electron mobility [32] The higher the degree of oxidation, the lower the conductivity of GO To improve electrical conductivity, GO will be reduced functional groups, to restore the original honeycomb structure of the carbon domain However, this reduction process will have structural effects, causing defects inside the crystal lattice, so the conductivity of rGO is not as high as that of graphite [46]

It can be seen that the resistivity of hydrazine is the lowest, showing that the reduction of this reducing agent is best at 0.15 Ω.m The reducing agent gives the lowest results by heat shock at 5.69 Ω.m It can be seen that chemical reduction gives better results Studies have shown that rapid heating reduction not only cuts the covalent bonds of functional groups, but also loses the continuity of the carbon regions, increasing the defect, thereby reducing its electrical conductivity [4]

Figure 4.16 The volume resistivity of the EP/rGO composite samples was reduced with different agents

Table 4.7 The data on the EP/rGO samples from there infer the resistivity.

Neat epoxy 1 0.05 None None None

EP/rGO-hydrazine-0.25 wt% 1 0.05 4.5x10 9 9x10 10 1.11x10 -11 EP/rGO-hydrazine-5 wt% 1 0.07 8x10 6 1.15x10 8 8.69x10 -9 EP/rGO-hydrazine-15 wt% 1 0.07 4x10 6 5.71x10 7 1.75x10 -8

EP/rGO-vitamin C-0.25 wt% 1 0.04 none none none

EP/rGO-vitamin C-5 wt% 1 0.05 1x10 10 1x10 11 1x10 -10 EP/rGO-vitamin C-15 wt% 1 0.09 5x10 7 5.55x10 8 1.80x10 -9 EP/rGO-heat shock-0.25 wt% 1 0.04 1x10 11 2.75x10 12 3.63x10 -13

EP/rGO-heat shock-5 wt% 1 0.04 8x10 6 2x10 8 5x10 -9

EP/rGO-heat shock-15 wt% 1 0.11 8x10 6 7.27x10 7 1.37x10 -8 EP/rGO-heat shock-50 wt% 1 0.28 2 x10 4 7.14 x10 4 1.40x10 -5

It can be seen that the reinforcement of rGO into epoxy improved the specific conductivity and decreased resistivity with increasing rGO content First, with EP/rGO-hydrazine, the resistivity gradually decreased with increasing concentration from 0.25, 5 and 15 wt% corresponding to 9x10 10 ,1.15x10 8 and 5.71x10 7 Ω.cm With the sample EP/rGO-heat shock, there is also a decrease in resistance with

57 increasing content Finally, with the EP/rGO-vitamin C sample at 0.25 wt%, the resistance is very high beyond the measurement threshold of the device (above 10 11 Ω.cm) The high electrical resistance in the EP/rGO-vitamin C-0.25 wt% sample can be explained by the high agglomeration of the rGO layers and their larger size than the other two reducing agents (based on the photograph after drying and OM images) The main factors affecting the conductivity of EP/rGO composite are good dispersion, poor dispersion of low rGO content into epoxy will lead to fragile rGO lattice, voids are created disrupting bonding rGO layers thereby drastically reducing electrical conductivity; free electron mobility, large scale π-bonds will help to increase the electrical conductivity of the composites [4]

EP/rGO has potential for application in the field of ESD At 0.25 wt% (9x10 10 Ω.cm) hydrazine reducing agent can be applied to antistatic, with vitamin C and heat shock reducing agent at 5 wt% (1x10 11 and 2x10 8 Ω.cm) Static dissipation applications are also possible with both hydrazine and heat shock reducing agents at

15 wt% (5.71x10 7 and 7.27x10 7 Ω.cm) [26] In addition, the sample EP/rGO-heat shock-50 wt% achieved a volume resistivity of 7.14x10 4 Ω.cm, which is suitable for application as a conductive polymer

CONCLUSIONS AND FUTURE PLAN

Conclusions

Through the implementation of the project " Synthesis And Characterization

Of Epoxy/Reduced Graphene Oxide Composites For Anti Static Electricity", the thesis has achieved:

1 Successfully synthesized GO from graphite via modified Hummers method

2 Investigating the effect of hydrazine, vitamin C and thermal treatment on the reduction of GO to form rGO

3 Successfully fabricating EP/rGO and investigating the effects of rGO content, with different reducing agents and the filler phases Sample EP/rGO- hydrazine-0.25 wt% shown the highest UST at 55.03 ± 2.63 MPa and rGO reduced with hydrazine has the lowest electrical resistivity at 0.09 Ω.m

4 There was covalent bonding between the two phases, and the rGO was optimized for dispersion into the polymer matrix

5 EP/rGO material has met the application in the ESD field When incorporating with 0.25 wt% rGO, the epoxy-based composite is able to apply on surface antistatic applications; with 5 wt% rGO, the properties of composite closes to the required level of the application in electrostatic dissipation; up to 50 wt% rGO, the EP/rGO is sufficient to be a conductive polymer.

Future plan

Our team has some recommendations on devices that should be further used in research to improve the quality of EP/rGO composites products Specifically, at the drying stage of rGO samples, it is necessary to use a freeze dryer to avoid the sample from agglomerating In addition, GO samples should be separated using a

In order to improve the topic, we have the above recommendations to choose a suitable device, survey more content below 0.25 wt% And expand the application directly into the field of EMI, as well as electrodes for supercapacitors To expand the direction for the topic

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GO sample rGO (hydrazine) sample rGO (vitamin C) sample

Reduced graphene oxide synthesis process by heat shock