Effect of epoxydized carbon nanotube master batch on polypropylene film properties

Cite this paper: Vietnam J. Chem., 2021, 59(2), 263-269 Article 
DOI: 10.1002/vjch.202000160 
263 Wiley Online Library © 2021 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH 
Effect of epoxydized carbon nanotube master batch on polypropylene 
film properties 
Nguyen Van Khoi, Trang Vu Thang, Hoang Thi Phuong
*
Institute of Chemistry, Vietnam Academy of Science and Technology, 
18 Hoang Quoc Viet, Cau Giay, Hanoi 10000, Viet Nam 
Submitted September 14, 2020; Accepted February 24, 2021 
Abstract 
First, the surface of carbon nanotubes (CNTs) was modified by epoxidation reaction to create epoxidized CNTs 
(O<CNTs). Following step, master batches of O<CNTs (MB-O<CNTs) with different O<CNTs contents (5-12 wt%) 
were prepared by melt mixing in the presence of anhydride grafted polypropylene (PPgMAH). The CNTs content 
dispersed uniformly in master batch is 7 wt%. Finally, the effect of MB-O<CNTs contents on some properties of 
polypropylene film (PP film) was studied. The PP film samples with different MB-O<CNTs content (such that the 
O<CNTs content in the film varies from 0-1.0 wt%) were prepared on film blowing extruder. The effects of O<CNTs 
contents on the mechanical, thermal and electrical properties of PP film samples were investigated. The study found that 
tensile strength of PP films increased significantly with increasing O<CNTs content while elongation at break 
decreased. In addition, the presence of O<CNTs slightly increased the degree of crystallization and crystallization 
temperature of PP films while the melting behavior did not change much. From FE-SEM analysis, the good dispersion 
of O<CNTs in the PP films was obtained from PP films with O<CNTs content in the range of 0.2-0.8 wt%. The 
presence of O<CNTs also changed the electrical properties of PP. The PP films were achieved the antistatic effect at 
O<CNTs content in the range of 0.2-0.4 wt%. In addition, the results showed that the master batch processing helps 
O<CNTs to disperse more evenly in the PP film. 
Keywords. Polypropylene, carbon nanotubes, master batch. 
1. INTRODUCTION 
Polypropylene (PP) is one of the most widely used 
plastic in packaging material, textile, electric 
appliances, and automobile parts because of good 
physical and chemical properties and low-cost. 
Though, to be suitable for applications requiring 
higher mechanical and antistatic properties, PP is 
generally modified by various additives to improve 
its properties.
[1]
Recently, nano-additives are widely used in the 
reinforcement of PP, especially carbon nanotubes 
(CNTs). The CNTs has unique structure, nano-size 
diameter, low volume resistivity advantage and its 
current price has been greatly reduced. Therefore, 
the CNTs are an excellent material to reinforce for 
PP. However, the biggest drawback when melt 
mixing PP and CNTs can exhibit agglomerate 
phenomenon and poor interfacial adhesion. CNTs 
have a propensity to agglomerates in polymer 
matrix. CNTs are difficult to be dispersed because of 
high surface energy and strong Van der Waals 
force.
[2]
 Therefore, finding solution to improve the 
adhesion and compatibility between CNT and PP is 
an issue of research interest. To improve the 
interactions between CNTs and polymer matrix, 
different functional groups are attached directly to 
the CNTs’ sidewall [3-4]. At the nanotube surface, 
chemical functionalization helps functional groups 
(carboxylic acid, epoxy, hydroxyl,...) that may react 
with the functional groups of organic molecules, 
forming permanent bonds. In order to choose a 
suitable CNT functionalization method, the nature of 
the host polymer should be considered. In addition, 
the compatibility of PP and CNTs also could be 
improved by adding a compatibilizer. Some recent 
researches have reported that maleic anhydride - 
grafted polypropylene (PPgMAH) is able to use as a 
compatibilizer for improvement in the compatibility 
between PP and CNTs.
[2,5]
In addition, a kind of master batch technology 
was employed to support the process of dispersion 
of CNTs in PP. Usually, when using the melt 
blending method, CNT is directly mixed with the 
melted polymer. To uniformly disperse a large 
amount of CNT in the polymer matrix, the master 
Vietnam Journal of Chemistry Hoang Thi Phuong et al. 
© 2021 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 264 
batch process is an appropriate technique and 
necessary.
[6]
In this study, master batch MB-O<CNTs with 
different O<CNTs contents were prepared by melt 
mixing in the presence of PPgMAH. In this study, 
the effect of MB-O<CNTs contents on some 
properties of PP films was investigated. 
2. EXPERIMENTAL 
2.1. Materials 
PP resin 1126NK was supplied by IRPC (Thailand). 
The MFI and density of PP is 11 g/10 min and 0,93 
g/cm
3
, respectively. PPgMAH with a percentage of 
MAH 1.0 % was supplied by Addivant, USA. The 
CNTs was provided by Kumho petrochemical Co., 
Ltd, Korea (diameter 5-15 nm, length 10-20 µm). 
Methyltrioxorhenium (MTO) grade M1296 of 
Tokyo Chemical Industry Co., LTD and 
Triphenylphosphine grade T84409 of Sigma were 
used. 
2.2. Methods 
Epoxidation of CNTs
[7]
: 2 g CNTs were placed in a 
500 mL Schlenk flask attached with addition funnel. 
After evacuation for 30 min to remove any adsorbed 
O2, a toluene (150 mL) solution of MTO (0.4 g) was 
added. Triphenylphosphine (0.456 g dissolved in 
150 ml of toluene) was added dropwise to the 
suspension over 15 min. The reaction was stirred at 
55 °C for 24 hours. The sample was centrifuged at 
4000 rpm for 15 min, washed with fresh toluene 
(3×280 mL). After drying overnight under vacuum 
at 60 
o
C, a solid was obtained O<CNTs. 
- Preparation of master batch content O<CNTs: 
Master batch of PP, O<CNTs, PPgMAH were 
prepared  ... 
Samples 
O<CNTs 
contents 
(%) 
Tensile 
strength
-MD 
(MPa) 
Elongation 
at break-
MD (%) 
PP-0 0 30.24 268.2 
PP/O<CNT
s0.2 
0.2 32.31 134.4 
PP/O<CNT
s0.4 
0.4 34.51 98.2 
PP/O<CNT
s0.6 
0.6 35.27 74.6 
PP/O<CNT
s0.8 
0.8 36.54 52.1 
PP/O<CNT
s1.0 
1.0 34.11 21.6 
Tensile strength is significantly affected when 
adding O<CNTs to the PP. Tensile strength of PP 
increased from 30.24 MPa in PP film to 36.51 MPa 
for PP/O<CNTs0.8. The rate of increase in tensile 
strength is 20.8 % compared to sample without 
O<CNTs. This showed good dispersion and 
adhesion between CNTs and PP phase. This may be 
due to the O<CNTs was distributed in the PP matrix 
which master batch was used.
[6]
However, the tensile strength of PP has a slight 
decrease when the content of O<CNTs is increased 
1.0 wt%. With increasing of O<CNTs content, the 
tensile strength of PP/O<CNTs nanocomposites 
decreases due to the formed aggregates act as 
mechanical failure concentrators.
[11]
 In contrast to 
the tensile strength, the elongation at break is 
significantly decreased when increasing the 
O<CNTs content in PP. The elongation at break is 
related to the flexibility of the polymer chains. The 
presence of O<CNTs in PP phase restricted the 
mobility of polymer chains. Therefore, the 
percentage elongation of PP decreased with 
increasing O<CNTs content from 0-1.0 wt%.
[12]
Prashantra et al. reported that when adding 
PPgMAH, CNT dispersed better in the PP matrix but 
elongation at break decreased when the O<CNTs 
content increased.
[13] 
3.2.2. Thermal properties 
The thermal properties (melting temperature (Tm), 
melting enthalpy (∆Hm) and degree of crystallinity 
(Xc), crystallization temperature (Tc) crystallization 
enthalpy (∆Hc)) of samples were investigated using 
DSC and result are reported in table 3. 
As shown in table 3, when O<CNTs is added to 
the samples, it can be seen that melting temperature 
(Tm) and the melting behavior have not change 
much. The melting temperature of PP/O<CNTs and 
PP is in range of 175-177 °C. This shows that the 
presence of O<CNTs with concentrations up to 1 % 
did not affect the melting behavior and melting 
temperature of PP. The results of this research are 
consistent with those reported by other authors.
[14]
On the contrary, the crystallization temperature 
(Tc) of PP films contents O<CNTs increased from 
roughly 3 to 7 
o
C compared neat PP film. In 
addition, the degree of crystallization slightly 
increased with increasing O<CNTs content. It 
indicated that CNTs acted as nucleating agents, 
which induce easier and faster crystallization under 
isothermal and non-isothermal condition. When the 
O<CNTs continued to increase to 1.0 wt%, the Xc 
value reduced to 41.1 %. This can be explained by 
the existence of CNTs aggregations in PP that acted 
as barriers to the crystal growth. Salid Hakan 
Yetgin
[15]
 has obtained similar results in his study of 
the thermal properties of PP/CNTs composites. 
3.2.3. Surface resistivity 
Table 4 shows the effect of O<CNTs content on the 
surface resisvity of PP films. 
Vietnam Journal of Chemistry Effect of epoxydized carbon nanotube 
 © 2021 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 267 
Table 3: Melting and crystallization parameters of PP and PP/O<CNTs films with 
different contents of O<CNTs 
Sample 
Melting crystallization 
Tm (
o
C) ∆Hm (J/g) Tc (
o
C) ∆Hc (J/g) X (%) 
PP-0 175 80.1 113 83.01 40.1 
PP/O<CNTs0.2 176 82.6 116 84.25 40.7 
PP/O<CNTs0.4 176 83.08 117 85.35 41.2 
PP/O<CNTs0.6 177 84.2 118 86.73 42.01 
PP/O<CNTs0.8 176 84.6 120 89.91 43.02 
PP/O<CNTs1.0 177 84.1 118 85.9 41.1 
Table 4: The surface resistivity of PP films with 
various O<CNTs contents 
Sample 
Content of 
O<CNTs 
(wt%) 
Surface 
resistivity 
(Ω/sq) 
PP-0 0.0 >10
12 
PP/O<CNTs0.2 0.2 10
9 
PP/O<CNTs0.4 0.4 10
6 
PP/O<CNTs0.6 0.6 10
4 
PP/O<CNTs0.8 0.8 10
3 
PP/O<CNTs1.0 1.0 <10
3 
The industry standards ANSI/EIA-541-1988 
(USA) and ANSI/ESD S541-200 (USA) defined 
and classified based on the surface resistivity. 
Accordingly, conductive, static dissipative, antistatic 
and insulator materials have surface resistivity of 
10
1
-10
5
, 10
6
-10
8
, 10
9
-10
11
 and 10
12
-10
16 Ω/sq, 
respectively. Therefore, it can be seen that surface 
resistivity of neat PP film is higher than 10
12
 Ω/sq, it 
was insulator material. However, the surface 
resistivity of PP/O<CNTs0.2 and PP/O<CNTs0.4 
films was 10
9
 and 10
6
 Ω/sq, respectively. This 
indicates that both of the PP/O<CNTs0.2 and 
PP/O<CNTs0.4 films could be as antistatic 
materials. The antistatic mechanism of CNTs is 
explained by the CNTs as conductive particles, in PP 
matrix lies in that static is dissipated by a conductive 
network of CNTs. Thus the dissipation of static 
charges can be promoted. However, Chensha Li et 
al.
[16]
 stated that if CNTs were blended directly in 
PP, to have antistatic effect, the content of CNT 
must be greater than 15 wt%. This may be due to 
that unmodified CNTs has very poor interaction with 
PP resin, the process of mixing is not uniform, to 
achieve antistatic effect, a large amount of CNTs is 
required. But PP films can not be produced in such 
high CNTs content. While, in this study, the PP 
films were achieved the antistatic effect at O<CNTs 
content in range of 0.2-0.4 wt%. This shows that the 
epoxy functionalized CNTs and through the master 
batch process containing O<CNTs has significantly 
improved the dispersion of the O<CNTs phase in the 
PP matrix, helped the O<CNTs phase to be evenly 
distributed in the PP matrix. The uniform 
distribution of O<CNTs formed conductive channels 
of O<CNTs in PP phase that static is dissipated. 
Consequently, to obtain a mixture that O<CNTs can 
evenly disperse in the polymer, the master batch 
process is a very efficient process. 
However, with an increase in the O<CNTs 
content from 0.6 wt% up to 1.0 wt%, there was a 
sharp decrease in surface resistivity, the PP films 
became electrically conductive. At high O<CNTs 
content, with the uniform dispersion of O<CNTs in 
the PP matrix, forming a percolated network of 
O<CNTs, which can be regarded as an electrical 
percolation threshold. 
3.2.4. Field emission scanning electron microscopy 
(FESEM) 
The distribution and dispersion of O<CNTs in PP 
were investigated using a Field Emission Scanning 
Electron Microscopy (FESEM). Micrographs took 
on cryogenically fractured surface of samples are 
reported in figure 3. 
The study results showed that the PP samples 
containing O<CNTs in range of 0-0.8 wt% had 
uniform dispersion, O<CNTs was evenly dispersed 
and mixed in the PP matrix. In this case, epoxy 
groups from O<CNTs surface are interacted with 
polar groups of PPgMAH, resulting in improved 
O<CNTs dispersion within the PP matrix. Indeed, 
Chen et al.
[17]
 reported a possible nucleophilic 
substitution reaction between the epoxy group and 
carboxyl group in melt blending of components. 
However, in the PP/O<CNTs1.0 sample, beside the 
uniform dispersion regions of the CNTs in the PP 
phases, there are appeared regions of CNTs 
Vietnam Journal of Chemistry Hoang Thi Phuong et al. 
© 2021 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 268 
agglomeration (figure 3f). The presence of 
agglomerates can also explain the progressive 
decrease of tensile strength and elongation at break 
for PP/O<CNTs1.0 compared to other samples. In 
addition, the appearance of the PP/O<CNTs1.0 
phase in the PP matrix can reduce the segmental 
mobility of matrix polymer. This is explained for the 
decrease in elongation at break of samples 
containing CNTs compared to neat PP.
[18]
Figure 3: FESEM micrographs of samples: (a) 0 wt%, (b) 0.2 wt%, (c) 0.4 wt%, (d) 0.6 wt%, (e) 0.8 wt% 
and (f) 1.0 wt% of O<CNTs in PP films
4. CONCLUSION 
A series of PP and PP films containing O<CNTs 
with different O<CNTs concentrations (i.e., 0, 0.2, 
0.4, 0.6, 0.8 and 1.0 wt%) were studied. The 
chemical modification of CNTs, using PPgMAH as 
a compatibilizer and mixing O<CNTs through a 
O<CNTs master batch process were performed to 
improve dispersion of O<CNTs in PP films. It was 
found that: the O<CNTs master batch with 7 wt% of 
O<CNTs could improve the dispersion of CNTs in 
PP films, tensile strength and crystallization 
properties of PP films. The mechanical test results 
showed that the presence of O<CNTs significantly 
increased the tensile strength while it decreased the 
elongation at break of PP films. Thermal analysis 
revealed that the O<CNTs addition slightly degree 
of crystallization and crystallization temperature of 
PP films. From FESEM analysis, the good 
dispersion of O<CNTs in the PP matrix can be 
revealed with CNTs contents in the range of 0.2-0.8 
wt%. For the electrical property, O<CNTs could 
change the electrical property of PP films. The PP 
films were achieved the antistatic effect at O<CNTs 
content in the range of 0.2-0.4 wt%. 
Acknowledgement. The authors would like to thank 
Institute of Chemistry, Vietnam Academy Science 
and Technology for financial support through the 
project code NCVCC06.02/20-20. 
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Corresponding author: Hoang Thi Phuong 
Institute of Chemistry, Vietnam Academy of Science and Technology 
18, Hoang Quoc Viet, Cau Giay, Hanoi 10000, Viet Nam 
E-mail: hoangphuong15@gmail.com; Tel.: +84- 979880160.