Investigation of Dispersion of Nano-Graphite Particles in

Investigation of Dispersion of Nano-Graphite Particles in

Polyamide using SEM & XRD

Dr. Aravind K. U1

1. Professor & Head, Department of Mechanical Engineering, East West College of Engineering

ABSTRACT

The purpose of investigation is to understand dispersion of graphite reinforced polyamide

composites. The test was conducted as per design of experiment using pin-on-disc wear tester.

Researchers have studied wear mechanism of nano-graphite in polyamide. The dispersion of the

graphite particles were studied using SEM and XRD. Dispersion of graphite particles in

polyamide composites and crystalline phase are found by using XRD. The relative intensities and

their peak positions indicate the crystalline phase of the polyamide and graphite particles. SEM

microscopy of polyamide and graphite composites with different wt% of graphite, load, sliding

speed and distance conditions.

1. INTRODUCTION

Researchers [1-5] have studied the microscopy of polymer blends with various fillers like

graphite, carbon fibers etc. By observing the microscopy we can understand the formation of

transfer film formed on specimen and against which the specimen had slid, wear particles

dispersion etc. Researchers studied the worn surface of neat nylon6 and nylon6/graphite (4%)[1-

5]. We can see that there are deep grooves in neat nylon and no formation of transfer film. But for

nylon/graphite composite the surface is smooth [8]. Other researchers studied microscopy of

nylon6/graphite and pure RG (reduced graphite). They observed a core like material in

nylon6/graphite and by observing the surface of reduced graphite they found that the core like

material was RG. [7-8] Someresearchers studied the worn surface of PA6/graphite nano

composites. They blended variety of graphite – expandable graphite, virgin graphite and expanded

graphite.

2. EXPERIMENTAL STUDY

Wear test was carried out to study the tribological behavior of PA66/Gr composite journal

bearing. First the shaft is mounted on to a lathe machine, the shaft is constrained at both ends.

Then the shaft is rotated at a certain speed (the can be varied according to the requirement). The

bearing is then mounted on the shaft. This bearing is constrained using a clamp, so that only the

shaft rotates and not bearing. Then a load is applied on the bearing as shown in the figure. The

load was varied for different set of tests. Finally the shaft is rotated at the required speed. Before

Journal of Shanghai Jiaotong University ISSN: 1007-1172

Volume 17, Issue 2, February - 2021 Page No: 68

starting the test the bearing is weighed so this is the initial weight. The bearing is weighed again

after the test. The wear rate was calculated using following equation:

Wear rate = x 103 mm3/N-m

M = Mass loss in grams

= Density of the composite

L = Load applied in newton

D = Distance in meters

3. SELECTION OF PARAMETERS AND THEIR VARIABILITY LEVELS

Four values for weight % of graphite 0, 10, 20 and 30 were taken into consideration to setup the

test specimens. Load, speed and sliding distance of specimen were chosen on the basis of the wear

testing conditions. The normal loads of 25N, 50N, 75N and 100N were put on using standard

weights to invigorate different contact pressures. The sliding speed for disc 0.4, 0.8, 1.2 and 1.6

m/s were utilized. The sliding distance for pin specimen 1000, 2000, 3000 and 4000m were used.

The factors and their subsequent levels are listed in Table 1)

Table 1) Factors and their corresponding variability levels

Table 2) Experimental layout acquired through MINITAB statistical software

Expt. No Wt. % of Graphite

(A)

Load (B)

in N

Speed (C)

in m/s

Sliding Dist. (D)

in m

1 0 25 0.4 1000

2 0 50 0.8 2000

3 0 75 1.2 3000

4 0 100 1.6 4000

5 10 25 0.8 3000

6 10 50 0.4 4000

7 10 75 1.6 1000

8 10 100 1.2 2000

9 20 25 1.2 4000

10 20 50 1.6 3000

11 20 75 0.4 2000

12 20 100 0.8 1000

13 30 25 1.6 2000

14 30 50 1.2 1000

15 30 75 0.8 4000

16 30 100 0.4 3000



4. MICRO STRUCTURAL STUDY (X-RAY DIFFRACTION-XRD)

Dispersion of graphite particles in PA66 composites and crystalline phase are found by using

XRD. The relative intensities and their peak positions indicate the crystalline phase of the PA66

and graphite particles and thus, it can be easily known. The intensities of the peak positions allow

enumerating the phases, to find the orientations of the crystals and to establish the atomic

arrangement of the crystals. The Fig. 1) shows the XRD pattern of pure PA66 with two broad

peaks at 20.58º and 23.52º. The broad peaks indicate the existence of amorphous materials and

also the crystals present in the polymers are very small in size.

The Fig 2) shows the XRD patterns of PA66/Gr composites in comparison with pure PA66.

5 10 15 20 25 30

0

5000

10000

15000

20000

25000

Inte

nsity

(cps

)

2 Theta (degrees)

ab

cd

a) PA66

b) PA66+10%Gr

c) PA66+20%Gr

d) PA66+30%Gr

While pure PA66 shows a broad peak, the PA66/Gr composites show sharp peaks at 2Ө of near

26.82º which corresponds to a d-spacing of 3.32Å. This is also the characteristic peak of pure

graphite with the standard JCPDS card no 41-1487. Therefore, the occurrence of peaks confirms

the presence of graphite. However, less intense peaks indicate uniform dispersion of graphite

particles. We know that graphite is a layered material which is characterized by strong covalent

bond within the carbon layers and weak van der waals interaction between successive carbon

5 10 15 20 25 30

0

1000

2000

3000

4000

Inte

nsity

(cps

)

2 Theta (degrees) Fig. 1) XRD pattern of the pure PA-66

Fig. 2) XRD patterns of the PA66/Gr composites



layers. Thus variety of atoms and molecules can be intercalated between carbon sheets, resulting

in the formation of intercalated graphite and yielding an increased d-spacing.

5. FRACTURE SURFACE STUDIES

Fig.3 a) , b) c) and d) show the tensile fractured surfaces of PA66/Gr composite filled with 0, 10,

20 and 30 wt.% of graphite powder respectively. The fracture surface of pure PA66 blend is not

smooth and some cavitations can be seen from Fig. 3) (A). From the figure it can be seen that

only few cracks (indicated by white arrows) were formed for matrix material but in composites

more crack are seen at the interface which causes fracture in the specimen. The SEM

morphologies of 10 wt%, 20 wt% and 30 wt% graphite powder filled PA66 composites are shown

in Fig. 3) B-D, respectively. Graphite with high strength and high modulus functions as the major

stress concentration point. Thus, some graphite particles were detached from the polymer matrix

as shown by the white circles in Fig. 3) B-D.

6. WORN-OUT SURFACE STUDIES

The Table 1) shows the worn surface SEM microscopy of PA66 and Gr composites with different

wt% of graphite, load, sliding speed and distance conditions. White arrows in the figures

indicate the sliding directions of the pin specimens.

A B

C D

Fig. 3) Tensile fractured surface of PA66/Gr composites: A) PA66, B) PA66+10%Gr,

C) PA66+20%Gr, D) PA66+30%Gr. Arrow indicating cracks.



6.1 EFFECT OF WT. % GRAPHITE ON WORN-OUT SURFACE

The Table 1)A shows the worn out surfaces of PA66/Gr composites with different wt% of

graphite. It is clear from the Table 1) A that pin surface of pure PA66 is highly rough surface with

higher depth of grooves. While PA66/Gr composites shows less number of grooves as shown in

Table 1) A. It can be seen that increase in the wt% of graphite decreases the wear rate.

6.2 EFFECT OF LOAD ON WORN-OUT SURFACE

The Table 1) B shows the worn out surfaces of PA66/Gr composites with different load

conditions. It can be seen that applied load influencing the wear rate and rough surfaces are

formed due to increase in the applied load and also detachment of graphite particles from polymer

matrix was found.

6.3 EFFECT OF SPEED ON WORN-OUT SURFACE

The Table 1) C shows the effect of different sliding speeds on worn out surfaces of PA66/Gr

composite. It can be seen that as Sliding speed increases the roughness of surface also increased

leads to more wear rate. The effect of sliding speed on the wear rate is much lower compared to

that of the rate of graphite reinforcement.

6.4 EFFECT OF SLIDING DISTANCE ON WORN-OUT SURFACE

The Table 1) D shows the effect of different sliding distances on worn out surfaces of PA66/Gr

composites. It is clear that sliding distance not much affected the surface of specimens and non-

uniform scratches are formed on the specimen surface. The effect of sliding distance on wear

surface is much lower than the rate of graphite reinforcement.

As to the polymer matrix composites which slide against steel surfaces, it is known that adhesion

occurs in the contact area and abrasion by the particles present on metal disk are the dominant

wear mechanisms. And the wear resistance of the materials is governed by its chemical and

mechanical properties at the interface. Seeing the worn surface morphologies of the PA66/Gr

composites shown in Table 1), graphite particles seem to extended out of the rubbing surface

indicating the fact that the major share of normal load was supported by the graphite particles,

which can be benefit the reduction of wear rate. However, many shearing micro-cracks were

observed at the surface either at the graphite-matrix boundary or at weak spots in the PA66

matrix. The micro-cracks, formed by the detachment of graphite particles and shearing of polymer

matrix under external mechanical forces, can lead to the generation of heavy wear rate.



Table 1) SEM micrographs of worn surface of PA66 and Gr composites with different

graphite contents and load conditions (arrow indicates sliding direction)

A) Wt% of Graphite (%) B) Load (N)

0

25

10

50

20

75

30

100



Table 1): SEM micrographs of worn surface of PA66 and Gr composites with different

sliding speeds and sliding distance conditions (arrow indicates sliding direction)

C) Sliding speed (m/s) D) Sliding distance (m)

0.4

1000

0.8

2000

1.2

3000

1.6

4000



7. CONCLUSION

Due to the poor interfacial adhesion between graphite particles and polymer matrix, particles can

be detached from the matrix under hard micro-ploughing and micro-cutting attacks by the steel

asperities. Besides, the lack of support and protection of graphite particles produces more weak

spots causing more polymer matrix to be transferred and removed from the composite. From the

reported, it was not easy to find abrasive characteristics thus adhesive wear is the primary

mechanism of the PA66/Gr composites.

During the experiment, graphite particles on the pin transferred to the disc surface were observed

and this film protects the rubbing of surfaces and has lubricant behavior. This process leads to

much lower friction temperature, which leads to reduction in material loss due to wear.

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Investigation of Dispersion of Nano-Graphite Particles in