MWCNT´s Gum arabic treatment nanocomposites

Carbon Nanotube Modification Using Gum Arabic and Its Effect on the Dispersion and

Tensile Properties of Carbon Nanotubes/Epoxy Nanocomposites

November

9th, 2010

Jorge Ivan

MECHANICAL ENGINEERING

KyungHee Univ.

 Introduction  Previous Study Bandyopadhyaya et al. reported the formation of homogeneous dispersions of individual MWCNT in Gum Arabic (GA) solution and demostrated that adsorption of GA led to disruption of the intertube interactions in the crystalline ropes. [ Nano Letters, Vol. 2, No. 1, 25]  Bagheri et al. reported that more improved dispersion of MWCNTs was obtained when MWCNTs were dispersed in GA/modified water soluable polyacrylonitrile solution rather than in GA solution. [ Mat. Wiss. U. Werkstofftech, Vol. 41, No. 4.]

 Objective  Find a friendly environmental modification of MWCNTs using natural materials for MWCNT/epoxy nanocomposites instead of chemical surface modification as acid or silane treatment and its effect on tensile properties of MWCNTs/epoxy nanocomposites Nano Composite Lab.

 Experiment  Materials & Methods

 MWCNTs CM-95 (Iljin Nanotech, Korea), as reagents nitric acid (60-62 %, Junsei, Japan) sulfuric acid (95 %, Junsei, Japan), ethanol (99 % Aldrich, USA) distilled water,  Baker pure water(J.T. Baker USA), Gum Arabic (Junsei, Japan) Epoxy resin (DGEBA, Kukdo Chemical, Korea) Hardener (PAA, Kukdo Chemical)

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

The surface-modification of the MWCNTs was performed as follows :



- Three grams of untreated MWCNTs were dispersed in 300 ml of

concentrated H2 SO4/HNO3 (3:2 v/v) solution at 50 C and stirred for 20 h. The solution was filtered with distilled water until a neutral PH was obtained to eliminate mixing and acid solution.

The resulting oxidized

MWCNTs were then dried under vacuum at 80 C. for 12 H.

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 Experiment  Materials & Methods

The Gum Arabic modification of MWCNTs (G-MWCNTs) was performed as follows. Ten grams of Gum Arabic (GA) was dissolved in 200 ml of distilled water and stirred for 30 min. Then, two grams of untreated CNTs was dispersed in the GA solution and stirred for 1 h. The Gum treated MWCNTs (G-MWCNTs) were separated by filtration using ethanol and dried under vacuum ..

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 Experiment  Materials & Methods

Fabrication of MWCNT/epoxy nanocomposites and characterization:  U-MWCNTs, O-MWCNTs, and G-MWCNTs were dispersed in the ethanol solution and ultrasonication was performed for 5 min.

 After sonication, 0.3 wt. % each of U-MWCNTs, O-MWCNTs, and G-MWCNTs were mixed with the epoxy resin and then stirred for approximately 2 h at 80 C to completely evaporate the ethanol.

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Experiment

 . After removing the ethanol, a hardener was added (epoxy and hardener

at a 2:1 ratio) and the mixture poured into a Teflon mold.

 The mixture was de-gassed in a vacuum oven at 760 mm Hg for 30 min and hardened in an oven at 60 C for 6 h.



Tensile specimens were machined and tensile tests were performed in a universal test machine according to the ASTM D 638. Fracture surfaces of

the nanocomposites were observed by high-resolution scanning electron microscope (HR-SEM).

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Results & Discussion Dispersed MWCNTs.

Fig. 1. Sedimentation of dispersed MWCNTs (A: unmodified MWCNTs, B: acidtreated MWCNTs, C: Gum Arabic treated MWCNTs) in distilled water (a) 10 min after ultrasonication, (b) 240 h after ultrasonication.

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 Results & Discussion http://web.khu.ac.kr/~nanocomp/

Unmodified, acid-treated, and Gum-treated MWCNTs (U-MWCNTs, O-MWCNTs, and GMWCNTs) were dispersed in distilled water via ultrasonication to determine the effect of Gum treatment on dispersion in the aqueous solution. As shown in Figure 1a, U-MWCNTs,

O-MWCNTs, and G-MWCNTs showed good dispersion in distilled water after 10 min of ultrasonication.  However, the U-MWCNTs gradually settled due to their agglomeration and hydrophobic nature,

whereas the O-MWCNTs and G-MWCNTs exhibited good suspension stability

even after 240 h of sonication.

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TEM http://web.khu.ac.kr/~nanocomp/ (b)

(a)

100 nm 100 nm

20 nm

20 nm

(c)

100 nm

20 nm

Fig. 2. TEM images of dispersion states : (a) untreated MWCNTs, (b) oxidized MWCNTs, (c) Gum treated MWCNTs

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 Results & Discussion http://web.khu.ac.kr/~nanocomp/

The microscopic structures of MWCNTs with different surface modifications were

investigated using TEM. Figure 2 presents TEM images of U-MWCNTs, O-MWCNTs, and G-MWCNTs. As shown in Fig. 2a, the U-MWCNTs were severely agglomerated and their end tips were closed, which are the features of unmodified MWCNTs.  for O-MWCNTs, as shown in Fig. 2b, the agglomeration of the carbon nanotubes was

reduced and the end tips of many carbon nanotubes were open, which enables the generation of functional groups at the open ends. Similar dispersion results were obtained for Gum treated MWCNTs. As show in Fig. 2c, the dispersion of the nanotubes was significantly improved compared to that of the U-MWCNTs. Figure 2 also shows that the MWCNTs retained their external average diameter of 10-15 nm after oxidation and Gum treatment, which is in good agreement with the suspension stabilities described in Fig. 1. Nano Composite Lab. Company Logo

Stress-Strain http://web.khu.ac.kr/~nanocomp/

Fig. 3 Tensile stress-strain curves of unmodified, oxidized, and Gum treated MWMWCNT/epoxy nanocomposites

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 Results & Discussion http://web.khu.ac.kr/~nanocomp/

Figure

3

shows

typical

tensile

stress-strain

curves

of

the

MWCNTs/epoxy

nanocomposites with unmodified, oxidized, and Gum-treated MWCNTs. As shown in the figure, the stress increased almost linearly with strain at an early stage, and then nonlinear

behavior occurred before reaching the maximum stress for the three nanocomposites.  In particular, the tensile strength and the modulus of the MWCNT/epoxy nanocomposites were improved by the oxidation and Gum treatment of the nanotubes.

However, the

functionalized MWCNTs resulted in more brittle tensile behavior.

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Tensile strength

Fig. 4. Comparison of tensile strength of unmodified, oxidized, and Gum treated MWMWCNT/epoxy nanocomposites. Nano Composite Lab.

 Results & Discussion http://web.khu.ac.kr/~nanocomp/

Figure 4 shows the comparison of the tensile strengths of untreated, acid-treated, and Gum-treated MWCNT/epoxy nanocomposites, in which the tensile strength was determined as the maximun stress in the stress-strain curve.  As shown in the figure, the tensile strength was on the order of the G-MWCNT, OMWCNT, and U-MWCNT/epoxy nanocomposites. Specifically, the tensile strength of the G-MWCNT/epoxy nanocomposites was 22 % higher, and Oxidized-MWCNT/epoxy was 15 % higher than that of the U-MWCNT/epoxy nanocomposite.

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Elastic Modulus http://web.khu.ac.kr/~nanocomp/

Fig. 5. Comparison of elastic modulus of unmodified, oxidized, and Gum treated MWMWCNT/epoxy nanocomposites. Nano Composite Lab. Company Logo

RESULTS & DISCUSSION http://web.khu.ac.kr/~nanocomp/

The elastic modulus was determined by measuring the slope in a linear region of the stress-strain curve. Figure 5 shows the comparison of the three nanocomposites. Similar the tensile strength results, the elastic modulus was improved by the Gum treatment, with

the elastic modulus of the G-MWCNT/epoxy nanocomposite being higher than that of the O-MWCNT/epoxy nanocomposites.  The elastic modulus of the G- MWCNT/epoxy nanocomposites was 29 % higher, and the O-MWCNT/epoxy nanocomposites was 13 % higher than that of the U-MWCNT/epoxy

nanocomposites.

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TEM http://web.khu.ac.kr/~nanocomp/

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TEM http://web.khu.ac.kr/~nanocomp/

Fig. 6 SEM photographs of fracture surfaces of (a) unmodified, (c) oxidized, and (e) Gum treated MWMWCNT/epoxy nanocomposites ; (b), (d), (f) are magnified images of boxed region in (a), (c), (e), Nano Composite Lab. Company Logo

 Conclusions

 The improved dispersion stability of Gum treated MWCNTs was due their

enhanced negative ion abilities due to the functionalization effect on their surfaces.  TEM analysis showed that little damage occurred on Gum-treated MWCNTs compared to acid-treated MWCNTs. The Tensile strength and modulus of G-MWCNTs/epoxy nanocomposites

were improved by 22 % and 29 % respectively, compared to the UMWCNTs/epoxy nanocomposites, whereas the improvements were 15 % and 13 % respectively, over O-MWCNTs/epoxy nanocomposites. Nano Composite Lab.

 Conclusions http://web.khu.ac.kr/~nanocomp/

This enhacement is attributed to the good dispersibility and strong interfacial bonding energy between the functionalized MWCNTs and the epoxy matrix. It was concluded that the functionalization of MWCNTs with

Gum Arabic is effective in improving dispersion and adhesion in an epoxy matrix.

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THANK YOU FOR YOUR ATTENTION

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