Fibers and Polymers 2014, Vol.15, No.2, 322-325

322

Enhanced Mechanical Performance of CNT/Polymer Composite Yarns

by γ-Irradiation

Jackie Y. Cai1*, Jie Min

1,4, Menghe Miao

1, Jeffrey S. Church

1, Jill McDonnell

1, Robert Knott

2,

Stephen Hawkins3, and Chi Huynh

3

1CSIRO Materials Science and Engineering, Waurn Ponds, VIC 3216, Australia 2Australian Nuclear Science and Technology Organisation, PMB 1 Menai, NSW 2234, Australia

3CSIRO Materials Science and Engineering, Clayton, VIC 3168, Australia4College of Chemistry, Chemical Engineering and Biotechnology, Donghua University, Shanghai 201620, China

(Received May 2, 2013; Revised July 8, 2013; Accepted July 14, 2013)

Abstract: Multiwall carbon nanotube (CNT) spun yarns were subjected to γ-irradiation in an oxygen rich environment,followed by the application of epoxy to form CNT/epoxy composite yarns with a high CNT fraction. The method forfabrication of the CNT/polymer composite yarns was presented, and the effect of γ-irradiation on the mechanicalperformance of the pure CNT spun yarns and their epoxy composite yarns were studied. The γ-irradiated CNT yarns werealso characterized by X-ray Photoelectron Spectroscopy and Raman spectroscopy. The results of this study havedemonstrated that the γ-irradiation is an effective micro-engineering tool to improve mechanical properties of the CNT spunyarn and its epoxy composite yarn.

Keywords: Carbon nanotube, Yarn, Mechanical property, Epoxy, Gamma irradiation

Introduction

It is known that γ-irradiation in air introduces defects and

intertube crosslinks on single-wall CNTs, resulting in improved

mechanical property of CNT bucky papers [1]. It has also

been reported that γ-irradiation increases the reactivity of

CNTs, leading to an increased efficiency of chemical

functionalisation of single and multi-walled CNTs [2,3]. It

would be expected that under suitable conditions γ-irradiation

might be an effective micro-engineering technique for

improving the performance of CNT spun yarns and CNT/

polymer composite yarns through the γ-induced improvement

in the strength of the CNT spun yarns themselves and their

interfacial properties.

At present, the strength of CNT spun yarn, formed by

drawing and spinning directly from a super-aligned CNT

array, is substantially lower than that of the individual CNTs

in the yarn [4,5], which highlights a need to increase the

strength utilization of CNTs in the yarn.

This type of CNT spun yarn can also be processed into a

CNT/polymer composite yarn with a high CNT fraction. In

this case, improving the adhesion between the CNTs and

polymers is another critical issue for achieving high strength

of the CNT composite yarn.

In this study, highly aligned multiwalled CNT forests,

produced by chemical vapor deposition (CVD), were spun

into yarns. The CNT spun yarns were subjected to γ-

irradiation in oxygen rich conditions, and the irradiated CNT

spun yarns were then processed into CNT/polymer composite

yarns. The effect of γ-irradiation on the mechanical perfor-

mance of the resultant CNT composite yarns was investigated.

Experimental

The CNT forests, produced by chemical vapor deposition,

were spun into yarns at a twist level of 6000 turns per meter

and a relatively high spinning tension using a spinning

process developed at CSIRO [6]. Gamma irradiation of the

CNT spun yarns was carried out in oxygen rich environment

using a cobalt-60 (60Co) irradiator at ANSTO (Australian

Nuclear Science and Technology Organisation) Radiation

Technology. The irradiation dose was about 200 kGy. For

comparison, a CNT yarn from one bobbin (spun from a

single wafer) was divided into two parts, half of which was

subjected to γ irradiation and the other half was kept as

untreated control.

The irradiated and untreated CNT spun yarns were then

processed into CNT/polymer composite yarns using the

method described below.

A commercial epoxy resin Kinetex R118 and hardener

H103 were mixed in a 100:25 weight ratio, the mixture was

further diluted with acetone to 55 % (w/w) of its original

concentration in order to minimise the chemical pick up and

improve the penetration of the epoxy on CNT yarns.

The CNT/epoxy composite yarns were fabricated by using

the facility developed at CSIRO as shown in Figure 1. The

irradiated and untreated CNT spun yarns were run through

the diluted epoxy formulation, series of drawing pins, and a

curing zone. The composite yarns were then further cured in

an oven at 120oC for 3-4 h. The percentage of the total

polymer pick-up was controlled at around 20 %.

The tensile properties of the CNT yarns were evaluated on*Corresponding author: Jackie.cai@csiro.au

DOI: 10.1007/s12221-014-0322-9

γ-irradiated CNT Yarn/Epoxy Composite Fibers and Polymers 2014, Vol.15, No.2 323

a Chatilon TCD 200 tensile testing machine. The average of

8-10 measurements was reported. The morphologies of the

yarns were examined by using a SEM (Hitachi S4300 SE/N,

Tokyo, Japan). X-ray Photoelectron Spectroscopy (XPS)

and Raman spectroscopy were also used to characterise the

CNT yarns produced. XPS analysis was performed using an

AXIS Ultra-DLD spectrometer (Kratos Analytical, Manchester,

UK). Raman analysis was performed using an inVia confocal

microscope system (Renishaw, Gloucestershire, UK).

Results and Discussion

Mechanical Properties of the CNT Yarns

The tensile properties of the CNT yarns, including the

untreated CNT spun yarn, γ-irradiated CNT yarn and their

epoxy composite yarns, were assessed and compared. The

results in Figure 2(a) show that the breaking strength of the

γ-irradiated dry spun CNT yarn is about 30 % higher than

that of the untreated control yarn. The CNT/polymer composite

yarns exhibit overall higher tensile strength than their pure

CNT yarn counterparts, and the composite yarn derived

from the γ-irradiated CNT spun yarn shows higher strength

compared to the composite yarn derived from the untreated

CNT spun yarn.

Figure 2(b) presents the stress-strain curves of selected

yarn samples, and their Young’s moduli are summarised in

Table 1. The results the demonstrate different tensile

properties and Young’s moduli of four types of CNT yarns.

The outstanding characteristics of the irradiated CNT/epoxy

composite yarn lie in its higher Young’s modulus and

breaking stress over the other CNT yarns examined. It can

be seen that both the γ-irradiation and polymer application

significantly increased the Young’s modulus of the CNT spun

yarn, and the combination of the γ-irradiation and polymer

application yielded a yarn with the highest tensile strength and

Young’s modulus.

The Morphologies and Breaking Behaviors of the CNT

Yarns

The morphologies of the untreated and γ-irradiated pure

CNT spun yarns were studied, and there was no significant

difference in their morphologies as identified from the SEM

examination.

The breaking behaviours of the dry spun CNT yarns and

their composite yarns were also examined. Figure 3(a)

shows a slipped or tapered broken end of an untreated CNT

spun yarn, indicating significant slippage between CNTs in

the yarn under tension, due to insufficient fibre cohesion,

while the irradiated CNT spun yarn exhibits slightly different

breaking behaviour with less fibre slippage (Figure 3(b)). In

contrast, the breaking behaviours of the CNT/epoxy composite

yarn have changed considerably from that of the pure CNT

spun yarn. The application of epoxy to the CNT spun yarn

has changed the yarn tensile failure mode from a fibre

slippage type of failure to a sharper and more brittle failure

mode. In addition, the textures/twisted structures are clearly

noticeable on the CNT composite yarns, suggesting that the

epoxy layer is thin. Furthermore, the CNT composite yarn

produced using the irradiated CNT yarn (Figure 3(d)) shows

less fibre slippage and pilling off effect as compared to the

Figure 1. The polymer application equipment.

Figure 2. Effect of the γ-irradiation on tensile properties of the dry spun CNT yarns and their epoxy composite yarns; (a) breaking stress of

the yarns and (b) stress-strain curves of the yarns.

Table 1. Young’s moduli of the CNT yarns

Yarn type Young’s modulus (GPa)

Untreated CNT spun yarn 17.5

γ-irradiated CNT spun yarn 29.8

CNT/epoxy composite yarn 46.8

γ-irradiated CNT/epoxy composite yarn 77.1

324 Fibers and Polymers 2014, Vol.15, No.2 Jackie Y. Cai et al.

CNT composite yarn formed using the untreated CNT

control yarn (Figure 3(c)).

The results have demonstrated that γ-irradiation modified

the dry spun CNT yarn, and the interactions between CNTs

and the polymer, leading to improved mechanical performance

of the CNT/composite yarn.

Characterization of the γ-irradiated and Untreated Pure

CNT Spun Yarns with XPS and Raman Spectroscopy

To understand the effect of γ-irradiation on CNT structural

changes and surface properties under the irradiation conditions

used, the irradiated and untreated CNT spun yarns were

analysed using XPS and Raman spectroscopy.

For the XPS analysis, three points per sample were

analysed. The quantitative results in Table 2 were obtained

from a survey spectrum which was a sweep of the entire

binding energy range. The atomic concentrations of the

detected elements were calculated using integral peak

intensities and the sensitivity factors supplied by the

manufacturer.

It can be seen that the γ-irradiated yarn shows an increase

in the oxygen content compared to the untreated CNT

control yarn, suggesting the γ-irradiation has an oxidizing

effect on the CNT surface in the oxygen rich environment.

For Raman analysis, 10 spots on each yarn sample were

analyzed using the 514 nm laser line. The D/G band ratio,

which represents the structural defects of CNTs, was

calculated. The statistical results of the multi-point analyses

were obtained for each sample. The results in Table 3 show

that the multiwall CNTs in the yarn exhibited significant

inherent defects and variations, reflected by the high average

D/G ratio and high deviation of the untreated CNT yarn. In

comparison, the irradiated CNT yarn exhibits a statistically

higher D/G ratio and lower deviation, indicating that the

irradiation introduced further structural defects on the CNT

sample. These structural defects are considered to be most

likely associated with the interwall or intertube crosslinks

[1].

Conclusion

Dry spun CNT yarns have been successfully engineered

through gamma irradiation in an oxygen rich environment.

The irradiation-induced defects, interwall/intertube crosslinks

and oxidation effect on the CNTs improve the strength and

interfacial properties of the CNT spun yarns. As a result,

gamma irradiation is also shown to be an effective pre-

treatment for the production of CNT/polymer composite

yarns. The study has demonstrated that the mechanical

properties of the irradiated CNT spun yarn can be further

enhanced by polymer impregnation. The combined use of

the γ-irradiation and polymer impregnation significantly

increases the resultant yarn strength and Young’s modulus.

Acknowledgment

The authors would like to acknowledge Mrs Margaret Pate

and Mr Colin Veitch for the SEM examination of the CNT

yarns.

References

1. V. Skakalova, M. Hulman, P. Fedorko, P. Lukac, and S.

Roth, AIP Conference Proceedings, 685, 143 (2003).

Figure 3. Broken ends of the untreated and γ-irradiated CNT yarns (a and b), and their epoxy composite yarns (c and d) after tensile

breakage.

Table 2. Atomic ratios relative to the total concentration of Carbon

C (X/C)

Element

detected

Untreated γ-irradiated

Mean STDEV* Mean STDEV*

O 0.017 0.003 0.070 0.005

Si 0.003 0.0003 0.004 0.002

*Stands for standard deviation.

Table 3. Raman spectroscopic analysis of gamma irradiated and

untreated CNT yarns

Untreated γ-irradiated

Average D/G ratio STDEV Average D/G ratio STDEV

0.66 0.08 0.80 0.05

γ-irradiated CNT Yarn/Epoxy Composite Fibers and Polymers 2014, Vol.15, No.2 325

2. J. Guo, Y. Li, S. Wu, and W. Li, Nanotechnology, 16, 2385

(2005).

3. V. Skakalova, U. Dettlaff-Weglikowska, and S. Roth,

Diamond and Related Materials, 13, 296 (2004).

4. J. Min, J. Y. Cai, M. Sridhar, C. D. Easton, T. R.

Gengenbach, J. McDonnell, W. Humphries, and S. Lucas,

Carbon, 52, 520 (2013).

5. J. Y. Cai, J. Min, J. McDonnell, J. S. Church, C. D. Easton,

W. Humphries, S. Lucas, and A. L. Woodhead, Carbon,

50, 4655 (2012).

6. C. D. Tran, W. Humphries, S. M. Smith, C. Huynh, and S.

Lucas, Carbon, 47, 2662 (2009).