There should be further studies on the reinforcement possibility of
CNT- Vast to the rubber nanocomposite material, especially the
chemical denatured reaction CNT- Vast to improve its dispersion
possibility in the polymer substrate. Also, there should be researches
on the use of dispersion auxiliraries, compatible vegetable oil in
manufacturing rubber nanocomposite materials reinforced CNT
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VIETNAM ACADEMY OF SCIENCE AND TECHNOLOGY
GRADUATE UNIVERSITY SCIENCE AND TECHNOLOGY
...***
CHU ANH VAN
STUDY ON PREPARATION AND PROPERTIES
OF RUBBER NANOCOMPOSITE MATERIALS
BASED ON SOME KINDS OF RUBBER AND ITS
BLENDS WITH CARBON NANOTUBES
Major: Organic chemistry
Code: 62.44.01.14
SUMMARY OF CHEMICAL DOCTORAL THESIS
Ha Noi – 2016
1
A: Overview of the thesis
1. Problem statement
Since having been discovered, carbon nanotube (CNT) is always
a hot topic attracting many researches and practical applications by its
outstanding mechanical-physical-chemical properties. CNT is known
for its high flexibility, low density and high specific surface.
Therefore, many real experiments have shown that this material has
high modular and durability, and the results of thermal
conductivity, electrical conductivity of polymer nanocomposite
manufactured on the basis of CNT are also very noticable. However,
CNT requires an appropriate dispersion method to avoid being rolled
and sticked together. To increase the ability to link between the CNT
and the polymer substrate, researchers have offered some measures
such as changing the fabrication method or using a combination of
auxiliary materials, but the additional functional groups attached to
the surface of CNT is more popular. This means that generating the
functional groups which react or physically interact with the polymer
substrate; thus, it can improve interfacial interaction between the CNT
and the substrate, as well as enhance thermodynamic capacity of the
nanotube with the polymer substrate.
Currently, that nanotechnology has become a develpoment
strategy on which researches of different science fields focus like
materials, electronics and biomedical attracts large investments. In our
country, the studies on the applications of CNT to nanocomposite
technology as well as to rubber and plastics industries have already
implemented at the level of exploration. So far, no research on this
field is applied to real production, but only one research result has
been published in journals and conferences. Vietnam has an abundant
human resourses and rational treatment policies so that many large
electronic firms like Samsung and Canon have built pretty many
manufacturing and assembly companies in many industrial areas. The
development of electronic industry leads to the demand for anti-static
mats spread on the assembly-tables in order to avoid conflicts of
unwanted currents with IC, boards in particular and electronic
products in general. Besides, textile industry and atomic explosive
industry also have a high demand for anti-static. Therefore, the study
of fabrication and application of rubber material CNT/nanocomposite
that has not only mechanical durability, abrasion resistance but also
2
anti-static ability is necessary because it brings about high scientific
and practical values. Derived from these reasons, the thesis aims to the
issue: “Study on preparation and properties of rubber
nanocomposites material based on some kinds of rubber and its
blend with carbon nanotubes” as the subject of research.
2. Objectives of research and its content
The objective of the research is to assess the reinforcement
possibility of CNT in the rubber substrate and blend rubber in order to
create rubber nanocomposite materials with a high mechanical
properties, sustainability in the solvent, and suitable electrical
conductivity.
The content of the research:
- Study on the denatured surfaced CNT by various methods.
- Study on the reinforcement possibility of CNT and dispersion
auxiliaries, compatible origin of vegetable oils with natural rubber
(NR).
- Study on manufacturing rubber nanocomposite and its properties
based on the blend of NR/NBR with CNT.
- Study on manufacturing rubber nanocomposite and its properties
based on the blend of NR/CR with CNT.
- Study on the possibility of manufacturing anti-static mats made from
rubber/CNT nanocomposite.
3. Contributions of research
- The carbon nanotubes were denatured by using some organic factors
such as: 24,85 phr bis-(3-triethoxysilylpropyl) tetrasulfide; 3,29phr
polyethylene glycol, 23 phr polyvinyl chloride, which was a basis of
creating rubber nanocomposite.
- Sucessfully manufactured NR/ NBR materials reinforced 4% CNT
or 3% modified CNT, in which CNT-PVC was well compatible with
the NBR substrate.
- Sucessfully manufactured NR/ NBR materials reinforced 4% CNT
or 3,5% modified CNT, in which CNT-TESPT dispersed best in the
NR/CR substrate.
- By the semi-dry method, CNT (CNT-Nanocyl và CNT-Vast) was
dispersed in the substrate of rubber blend based on NR/CR regularly
and isotropously. Besides, applying experimental planning and
building a regression equation to identify the optimal levels of
reinforcement of CNT in the NR/CR substrate quite fitted the results
obtained.
3
- The rubber nanocomposite materials on the basis of NR/CR
reinforced CNT had electrical conductivity that was suitable to
creating anti-static mats.
4. The thesis structure
The research includes 140 pages with 23 tables, 53 figures, 120
references.
The thesis structure:
Introduction (2 pages)
Chapter 1: Overview (38 pages)
Chapter 2: Materials and research methodology (11 pages)
Chapter 3: Results and discussion (72 pages)
Chapter 4: Conclusion (2 pages)
The publications relating to the thesis (1 page)
References (14 pages)
B: Content of the thesis
Introduction
The introduction mentions the scientific and practical meaning,
then set targets and research content of the thesis.
Chapter 1: Overview
The overview sythesizes materials inside and outside the country
relating to the topic of the thesis such as:
Nanocomposite materials, nanocomposite rubber with its
classification, its specific advantages and disadvantages.
Carbon nanotubes and four methods of surface denaturation,
which also indicate that the denaturation method for packaging
the molecular is not applied in nanocomposite rubber
manufacturing technology.
The situation of CNT applications in nanocomposite rubber
technology.
Some points left open are also the thesis objectives.
Chapter 2: Materials and research methods
2.1. Raw materials and chemicals
Carbon nanotubes multi wall: NC7000 Nanocyl S.A. ( Kingdom
of Belgium), 95% purity, size 10- 15 nm.
Bis- (3- trietoxysilylpropyl) tetrasunfide (Si 69. TESPT), China:
the transparent yellow liquid, fat-soluble and aromatic as
alcohol, ether, keton. Boiling point: 250°C, density: 1.08.
4
Polyetylenglicol: PEG 6000 (BDH Chemicals Ltd company
Poole-UK), the melting temperature of 61°C.
Polyvinylclorua: 710 SG Vietnam, a white powder, size: 20-150
micrometers, specific mass: 0,46- 0,48g / cm
3
.
D01: refined tung-tree oil, yellow liquid, the proportion (at
20°C): 1.500 to 1.520, acid index: 1.4; iodine index: 149.5 to
170.58; soap index: 193.38 to 196.73.
Cetyl trimetylamoni bromua (CTAB): Merck (Germany), M =
364.46g / mol, purity & gt; 97%.
Pure AlCl3: Merck (Germany).
Natural Rubber (NR): SVR- 3L, Viet Trung rubber company,
Quang Binh.
Natural Rubber Latex: type pH & gt; 7; Dry content 60%, Phuoc
Hoa Rubber Company, Vietnam.
Nitrile rubber (NBR): Kosyn- KNB35, Korea, containing
acrylonitril 34%.
Clopren Rubber (CR): Baypren® 110 MV 49 ± 5, Lanxess.
Vulcanizing additives include:
+ Sulfur, Sae Kwang Chemical Ind firm. Co. Ltd. (South Korea)
+ Indian Zinc Oxide Zincollied
+ Stearic acid, PT. Orindo Fine Chemical (Indonesia)
+ Accelerators DM (Dibenzothiazolil disunfit), China
+ Accelerators D (N, N-diphenyl guanidine), China
+ Aging antioxidants D (Phenyl β-naphtylamin), China
Other chemicals
Hydrochloric acid, toluene, KOH, iso-octane, ethanol 96%, acid
acetic, DMF, petroleum ether, SOCl2, H2O2, NH3, tetrahydrofuran
(THF), chloroform (CHCl3), CaCl2, acetone, petroleum ether of China.
2.2. Process of denaturing CNT surface and manufacturing
rubber nanocomposite material reinforced-CNT
2.2.1. Denaturing CNT surface by Fischer esterification reaction
The residual metal is removed from CNT by being soaked with
special HCl and stirred for 2 hours at 50° C under a normal condition,
washed several times with distilled water until pH = 7, dried for 12
hours, signed p-CNT. Disperse 0,3g p-CNT in 25ml mixture of
NH4OH and H2O2 (1: 1). Stir the mixture for 5 hours at 80°C under
normal pressure. Mixed product is filtered by a PTFE membrane
(capillary size: 0.2 micron), washed with distilled water in neutral
5
environment and cleaned by acetone several times. The denatured
product (CNT-COOH) is dried for 48 hours at 80°C.
- Chlorinated CNT
Put 0,5gam CNT-COOH into a flask 100ml with 20ml SOCl2
and 10ml DMF available inside, and stir under a normal pressure for
24 hours at 70°C. By the end of the reaction will be a dark brown
mixture CNT-COCl, filter and wash with THF and dry at normal
temperature.
- Synthesis of CNT-PEG
Melt 1g PEG at 90°C, then put into a flask containing 0,1g CNT-
COCl, stir for 10 minutes, then add the 40ml mixture of benzene/THF
(3:1). Conduct the reaction at 80°C in 40 hours. When the reaction
ends, put the mixed product in ultrasonic vibration for 30 minutes at
60°C, speed 3000 rpm, then filter it through the PTFE membrane, the
mixed black solid is washed with acetone and petroleum ether 3 times,
dry at 90°C for 12 hours.
- Synthesis of CNT-TESPT
5ml TESPT hydrolyzed in 20ml C2H5OH 96°, 10ml distilled water
and 5ml NaOH 10% at 50°C for 2 hours, conduct to remove the
solvent, then the yellow solid TESPT-OH is dried at 50°C for 4 hours
[106]. Put 0.1g CNT-COCl and 1g TESPT-OH into a flask 100ml
with 30ml anhydrous C2H5OH available inside, start to stir for 5 hours
at 60°C, the mixed product is put in ultrasonic vibration for 60
minutes at 60°C, speed 6000 rpm, then filtered by the PTFE
membrane, washed many times with hot water to remove residual
silane components, dried and washed with acetone. The last product is
vacuum-dried at 60°C in 5 hours.
2.2.2. Alkylize CNT surface
Put 0.2g CNT and 0.5g PVC into a 3-neck flask with 30ml
anhydrous CHCl3 available inside, the flask is connected to a canister
of anhydrous CaCl2 and another pipe embedded in NaOH liquid 10%
to remove HCl released during the reaction. Add 0.5 g AlCl3, and mix
in nitrogen environment at 60°C for 30 hours. After cooling the
mixture down to the normal temperature, the CNT-PVC product is
stirred in ultrasonic vibration in the tetrahydrofuran solvent (THF) for
10 minutes, filtered and washed several times with petroleum ether
and acetone, dried at 60°C in 10 hours.
2.2.3. Denatured by surfactants
6
Fuse 0.1g CTAB, then absorb 1g CNT, place in a warm cabinet
at 60°C for 72 hours. Put 0.1g CTAB into 50ml distilled water and stir
for 1 hour at normal temperature, add more 1g CNT and continue to
stir for 1 hour. Add 50ml distilled water, and put the mixture in
ultrasonic vibration at 60°C for 2 hours. Dry the last mixture at 60°C
in 12 hours.
2.2.4. Method of creating a rubber nanocomposite sample
2.2.4.1. Sample NR/CNT
CNT and NR components are presented in the following table:
Table 2.1. CNT and NR components of researched samples
Ingredients
Content (%)
NR 100
Zinc oxide 4,5
Aging antioxidants A 0,6
Aging antioxidants D 0,6
Stearic acid 1
Accelerators D 0,2
Accelerators DM 0,4
Sulfur 2,0
D01 1-4%
CNT 1-5%
2.2.4.2. Rubber blend sample based on NR
Based on the mixing from NR, the thesis surveyed the effects of
CNT content (denatured or not denatured) on the properties of blend
system NR/NBR 80/20 and NR/CR 70/30 with the following process:
(the sign CNT in this process for both CNT that is denatured and not
denatured)
7
natural rubber NR or CR
mixer
mixed CNT or CNT/ethanol
produc 1 8 minutes, 75
0C, 50 rpm
ZnO, acid, Antioxidant
produc 2
S, accelerator
semi-produc
sheet
nanocomposite
20-25 minutes, 1450Cvulcanization
10 minutes
mixer
3 minutes, 500C, 50 rpm
Figure 2.2. The chart of creating nanocomposite / CNT rubber
To study the possibility of dispersing CNT in a polymer
substrate, the thesis uses 3 different methods such as mixing the
solution, using surfactants or compatible auxiliaries (the additive
content, closed mixing conditions as well as vulcanization are
constant) follow the process:
NR, CR CNT/toluen
mixer 3 hours, 500C
mixer
Toluen, 96 hours ultrasonic, 2 hours
masterbatch
(a)
D01 CNT
mixer 3 hours, 500C
mixer
600C, 72 hours
CNT/D01 NR CR
(b)
8
CTAB/H2O CNT
mixer
mixer, 3hours, 500C
mixer, 1 hour
ultrasonic, 2 hours
masterbatch
CNT/CTAB
CR
latex natual rubber
(c)
Figure 2.3. Optimizing the CNT dispersion conditions in NR / CR
substrate: the solution method(a), using dispersion auxiliaries (b),
using cationic surfactant (c)
2.2.5. Research methods of structure and properties of denatured CNT
The structure and properties of denatured CNT are determined
by means of Infrared Radiation (IR) on the FTS-6000 P (Biorad,
USA), Raman radiation method with a HR LabRAM 800 (France),
UV -vis on SP3000 nano (Japan) and Thermal Gravimetric Analysis
method on Setaram (France), heating rate is 10°C/ minute in the
atmosphere, the temperature range from 25°C to 800°C.
The image of a denatured CNT is researched on its
morphological structure by means of Transmitting Electron
Microscope (TEM) on JEOL 1010 (Japan).
2.2.6. The method of determining the structure and properties of
materials
Determination of tensile strength, elongation of the blend rubber
material sample follows the standard TCVN 4509 – 2006.
Determination of hardness (Shore A hardness) of the blend rubber
materials follows TCVN 1595-1 : 2007. Determination of abrasion
(Acron) of materials follows TCVN 1594 – 87. Determination of
aging factor follows TCVN 2229-2007. Determination of the swell of
the blend rubber materials in toluene solvent: iso-octane follows
TCVN 2752 - 2008. Studying morphological structure of materials by
means of Field Emisson Scanning Electron Microscope (FESEM) and
thermal stability of materials by Thermal Gravimetric Analysis
(TGA).
9
Chapter 3 - RESULTS AND DISCUSSION
3.1. Denature carbon nanotubes surface
3.1.1. The study on the process of the carbon nanotubes oxidation
Raman radiation results:
Figure 3.3. CNT and CNT Raman oxidation
The increase in intensity ratio ID / IG proved that there was a
change in the CNT structure corresponding with the process of
transforming Csp
2
into Csp
3
by oxidation to successfully attach
COOH group to the CNT edge. Attaching this functional group
increases CNT’s size significantly.
a
Figure 3.5. TEM of CNT (a) and CNT- oxidation (b)
TGA result showed that about 27.85% COOH and NH2 are
attached successfully during oxidation process.
3.1.2. Fischer esterification reaction with TESPT and PEG
On the Raman spectrum, it can be seen that the ratio ID/IG
increased from 1.7 to 2.05 (CNT-PEG) and to 2.0 (CNT-TESPT),
which means that increased the degree of chaos of the graphite during
denaturation.
The TEM image showed that the sizes of CNT-TESPT and
CNT- PEG increased to about 25 and 30nm, respectively. The content
of the Ester functional group is determined by means of TGA, the
results are shown in Table 3.1 below:
10
(CH2 CH)
Cl
AlCl3
CHCl3 AlCl4
n
(CH2 CH)n
AlCl4
(CH2 CH)n CHCl3
CH
CH2
Cl
+
+
Table 3.1. TGA analysis results of the CNT-PEG and CNT- TESPT
Material
samples
The starting
temperature of
decomposition
The
maximum
temperature of
decomposition
1
The
maximum
temperature of
decomposition
2
Weight
loss to
750
o
C
CNT 500
0
C 577
0
C - 53,67%
CNT-PEG 400
0
C 443
0
C 607
0
C 78,52%
CNT-
TESPT
400
0
C 441
0
C 687
0
C 56,96%
3.1.3. CNT denatured by polyvinylclorua
CNT’s structure composed of many atoms C 2sp linked together to
form an equilateral hexagon which are nearly like the benzene circle.
Therefore, the implementation of a reaction between polyvinylclorua
and CNT with anhydrous AlCl3 as a catalyst is determined by the
mechanism of the alkylized Fridel- Craft reaction as follows:
From the result of Thermal Gravimetric Analysis, we could
identify the content of PVC attached to CNT surface is about 23% by
weight (at 400°C). That PVC was attached to CNT edge successfully
increased its size to about 25nm.
3.1.4. CNT denatured by surfactants
As we know, CNT was completely insoluble in water despite
under the ultra-sound condition for a long time, so it can not obtain the
signals in the visible light area . Conversely CNT/CTAB can be fully
dispersed in water, so the signal UV-vis can be obtained in the 200-
800nm waveband.
Two characteristic absorption peaks in the area of 240- 265 cm
-1
are corresponding to the shift of the electron π π
*
of conjugate
atom Csp2.
11
TGA results of CNT- CTAB sample is shown in Figure 3.18.
Figure 3.18. TGA schema of CNT-CTAB
Thus, it is possible to estimate that about 17% CTAB are
absorbed at 300°C
3.2. Research on manufacturing and material properties of
NR/CNT by means of melting mixing.
The thesis surveyed CNT content and dispersion auxiliraries,
D01. The results are presented in Table 3.2 and 3.3 below:
Table 3.2. Effects of CNT content on the mechanical properties of the
material on the basis of NR and additives
CNT
content
(%)
Tensile
strength
(MPa)
Elongation
(%)
Abrasion
(cm
3
/1,61km)
Hardness
(Shore A)
0 14,14 920 0,93 42
1 15,25 900 0,85 44
3 16,03 860 0,81 45
5 17,92 860 0,75 46
7 16,94 820 0,79 47
10 15,96 600 0,86 50
Table 3.3. Effects of D01 content on the mechanical properties of NR /
5% CNT
Content D01
(%)
Tensile
strength
(MPa)
Elongation
(%)
Abrasion
(cm
3
/1,61km)
Hardness
(Shore A)
0 17,92 860 0,75 46
1 18,89 870 0,70 45,9
12
2 20,13 890 0,63 45,5
3 19,24 915 0,60 44,6
4 17,03 940 0,58 43
- Optimal content of CNT that are reinforced for NR is 5% by weight
(compared to NR). In this denaturation ratio, materials have superior
mechanical properties rather than control samples such as tensile
strength increased by 27%, the starting temperature of decompositon
increased by 7°C, the maximum temperature of decomposition
increased 5,4°C, the aging factor of the material in the environment
also increased significantly.
- With 2% more dispersion auxiliaries, compatibility (D01) made
materials structure tighter and steadier, increased mechanical
properties, thermal durability as well as environmental durability of
the material.
3.3. Research on manufacturing and material properties of NR /
NBR / CNT samples by means of wet mixing
3.3.1. Influences of CNT content on mechanical - thermal properties
of NR / NBR.
Based on the research results of Ngo Ke The and his colleagues
on creating the NR / NBR blend system, the ratio of 80/20 was chosen
to study the reinforement possibility of CNT.
Mechanical properties of NR / NBR reached the maximum value
with 4% CNT content or 3% denatured CNT content. At these levels,
the CNT (not denatured and denatured) has significantly improved
thermal durability of the materials. CNT- PVC interacted well with
the NR / NBR substrate rather than CNT-PEG. Therefore, NR / NBR /
CTN-PVC sample had mechanical properties and thermal stability that
were higher than NR / NBR / CNT- PEG sample.
Figure 3:24. Effects of reinforcing substances content on the
elongation of the materials NR/NBR/CNT
13
That denatured CNT was easily compatible with the polymer
substrate improved mechanical properties of the materials more
clearly than non-denatured CNT. CNT-PEG had hydrogen-bonded
with the rubber substrate as the following model [93]:
Despite not having too much differences, CNT- PVC had higher
mechanical properties than CNT- PEG. This could be explained by the
well compatibility between PVC and NB so that the presence of PVC
on the surface (as well as partially absorbed in the process of
denaturation) made CNT-PVC be compatible with the rubber substrate
better. Therefore, the mechanical properties of the material were
improved better.
Denatured CNT made the structure of the material tighter and
steadier, which increased the environmental durability: the aging
factor in the air and salt water was high, the solvent durability was
improved.
Figure 3:29. Morphological structure of reinforced materials
NR/NBR: CNT (a), CNT-PVC (b), CNT- PEG (c)
14
Table 3.9. Aging factor of NR/NBR/CNT materials at 70°C during 72
hours
Samples
Aging factor in the
air
Aging factor in salt
water
NR/NBR 0,82 0,8
NR/NBR/4%CNT 0,89 0,87
NR/NBR/3%CNT-PVC 0,91 0,89
NR/NBR/3%CNT-PEG 0,9 0,88
0
20
40
60
80
100
120
140
160
180
200
220
240
0 8 16 24 32 40 48 56 64 72
Thời gian (giờ)
Đ
ộ
t
rư
ơ
n
g
CSTN/NBR/CNT CSTN/NBR/CNT-PVC CSTN/NBR/CNT-PEG CSTN/NBR
Figure 3:30. The swell levels of NR/NBR reinforced CNT solvent
3.3.2. Influences of carbon nanotubes on vulcanization of the NR/NBR
materials
Mechanical properties of the materials are also presented in the
perspective of vulcanization. Selecting right vulcanization conditions
would increase the durability of technical rubber. The survey result of
the CNT’s influence on the process of vulcanization NR/NBR blend is
shown in Table 3.8.
Table 3.8. Effects of CNT on the process of NR/NBR blend
vulcanization
Samples
Mmin
(kgf.cm
)
Mmax
(kgf.cm
)
Ts1
(min:sec)
Tc90
(min:sec)
NR/NBR/CNT 0,2 4,75 02:19 7:57
NR/NBR/CNT-PVC 0,17 5,26 02:42 8:55
NR/NBR/CNT-PEG 0,16 4,83 02:26 7:51
15
The minimum value of torque presented softness or flexibility of
rubber in soft initial state. The results showed that in which sample
containing CNT, Mmin was highest. This was appropriate because
CNT had no strong polarized groups, so the possibility to mix with the
blend system containing polar rubber NBR decreased. Meanwhile,
samples containing PVC and PEG, the occurrence of polar functional
groups like Cl, NH2, OH will increased the ability to blend.
The maximum value of torque was often related to chemical
bonding or crosslinking density. This value of the samples containing
CNT-PVC was higher, corresponding to the hardness of the samples
containing CNT-PVC was also higher. By that time, S-S bonding of
sulfur reached the highest point.
Vulcanization time Tc90 of the samples containing PEG was
lowest because CNT-PEG contains a NH2 group which was an agent
to boost the process of vulcanization. The pretty high Tc90 value of
the samples containing CNT-PVC was also an obstacle to the process
of manufacturing products.
3.4. Research on manufacturing and material properties of NR /
CR / CNT by means of wet mixing
3.4.1. Effects of CNT on the NR / CR vulcanization
Based on the research results of Do Quang Khang and his
colleagues on creating the NR / CR blend system, the ratio of 70/30
was selected to study the reinforcement possibility of CNT by means
of wet mixing with CNT/ ethanol. They have studied of the possibility
of vulcanization of the material samples containing CNT and
denatured CNT. The maximum and munimum values of torque,
vulcanization time 90% (Tc90) are presented as below:
Table 3.11. Effects of CNT on the possibility of vulcanization of blend
NR / CR
Samples
Mmin
(kgf.cm)
Mmax
(kgf.cm)
Ts1
(min:sec)
Tc90
(min:sec)
CSTN/CR/CNT 2,35 20,58 01: 32 14:54
CSTN/CR/CNT-PVC 1,6 18,63 01: 27 14:44
CSTN/CR/CNT-PEG 1,96 20,03 01:28 14:24
CSTN/CR/CNT-TESPT 1,31 21,71 01:21 12:48
16
Vulcanization time Tc90 of the samples containing TESPT was
lowest (12 minutes 48 seconds). This could be explained that CNT-
TESPT contained a NH2 as an accelerator and the appearance of S-S
formed by slightly decomposition under high temperature (Figure
3.37), which directly participated in the crosslinking and coupling
system in rubber. This caused a premature vulcanized phenomenon
(ts1 value is lowest) and reduced the vulcanization time. Tc90 short
vulcanization time has an economic value in the process of
manufacturing products so that CNT- TESPT is very noteworthy.
3.4.2. Effects of CNT content on the mechanical properties of
materials NR / CR
From the results above, it can be seen that only 1% CNT (not
denatured and denatured) has significantly increased the mechanical
properties of the blend NR / CR. When the CNT and CNT- TESPT
content increased, the mechanical properties (tensile strength,
elongation) of the materials also increased and reached the maximum
value with 4% CNT by content or 3.5% CNT-TESPT. Mechanical
properties of materials NR/CR/CNT- TESPT were higher than
CSTN/CR/CNT. This was explained that CNT- TESPT had better
interaction than CNT. Also, they created a link with rubber vessel,
because the thermal decomposition process of silane did appear S-S
bond which not only directly involved in vulcanizing a tight network,
but also created a chemical bond with the rubber substrate. Releasing
HCl molecule increased the thermodynamic durability and created a
direct link Si-O-C to consolidate the durability of nanocomposite.
Assuming the links in the nanocomposite network as the following
model 3:37.
Figure 3:33. Effects of reinforced substances content on the
elongation of the materials NR / CR / CNT
17
Figure 3:37. Description of surfaced link between the CNT-TESPT
and CSTN / CR
The structure of materials NR / CR / CNT- TESPT was tight and
had a steady distribution, so it influenced the thermal durability, the
aging factor as well as the swell in the solvent.
Figure 3:38. Morphological structure of materials NR / CR
reinforced- CNT (a) and CNT- TESPT (b)
NH2
OOC
Si
HO
(CH2)3 S4 (CH2)3Si(OH)3HO
NH2
OOC
Si
HO
CH2CH2CH2 S SHHO
t0
H3C
C
H 2
C
=
C
H
C
H 2
Cl
C
H 2
C
=
C
H
C
H 2
OOC
Si OH(CH2)3
HO
COO
Si
HO
(CH2)3 S SHO
S S
NH2CH2
CH2
C
CH2
CH3
COO
Si
HO
(CH2)3 S4HO
(CH2)3Si(OH)3
COO
Si
HO
(CH2)3 S SHHO
CH2
CH2
C
CH2
Cl
t0
-HCl
OOC
Si OH(CH2)3
HO
COO
Si (CH2)3 S SHO
S S
NH2CH2
CH2
C
CH2
CH3
CH2
CH2
C
CH2
ClO- H
OOC
Si OH(CH2)3
HO
COO
Si (CH2)3 S SHO
S S
NH2CH2
CH2
C
CH2
CH3
CH2
CH2
C
CH2
O
18
Table 3.13. TGA analysis results of of some material samples on the
basis of NR / CR
3.5. Research on optimizing the possibility of CNT dispersion in
the rubber blend substrate NR / CR
From the research results presented above, it can be seen that
NR / CR system has higher properties than NR / NBR when using
CNT and denatured CNT. To further enhance the properties of this
blend system, the thesis also mentions the optimal conditions to
disperse CNT by using 3 methods of dispersion as follow:
- Method of solution: NR / CR / CNT / toluene.
- Method of using a combination of NR latex with surfactants: LNR /
CR / CNT-CTAB.
- Method of using compatible dispersion auxiliraries: NR / CR / CNT /
D01.
The most noticeable result is the ability of the CNT dispersion
under the influence of CTAB within NR latex as the following
mechanism:
Samples
The starting
temperature of
decomposition
(
o
C)
The maximum
temperature of
decomposition
1
(
o
C)
The
maximum
temperature of
decomposition
2
(
o
C)
Weight loss to
600
o
C
(%)
NR/CR 268,7 349,7 434,5 91,02
NR /CR/4CNT 272,4 350,2 433,2 86,67
NR/CR/3,5CNT-
TESPT
274,5 353,6 428,4 90,66
NR /CR/3,5CNT-PVC 273 344 438,8 91,14
NR /CR/3,5CNT-PEG 274 347,7 432,9 92
19
Figure 3.46: The CNT detached-connected mechanism of CTAB and
the dispersed mechanism of CNT-CTAB in NR latex
The natural rubber latex particles had high flexibility. In spite
of a very small amount, only 1% CNT also significantly increased the
tensile strength from 13,32 to 16,12 MPa for LNR / CR and from
14.32 to 17.02 MPa for NR/ CR. The levels of 3% CNT and 3% CNT-
CTAB were optimal contents for rubber molecules and CNT to form a
polymeric network – a closed filler. The polymeric network- filler as
described in Figure 3:43 is stabilized by Van der Walls link, hydrogen
link and ion link (generated by negative electrons in the latex
molecule and positive electrons in nitrogen atoms of CTAB). This
increased the tensile strength of the material samples.
Figure 3:43. Interaction between the CNT / CTAB and the polymer
substrate
3.5.1. Manufacturing of rubber nanocomposite material by using
CNT-Vast
Based on the processing of the materials LNR / CR / CNT-
CTAB, the thesis also did a research on using CNT manufactured at
the Institute of Material Science - Vietnam Academy of Science and
20
Technology Institute (CNT- Vast) to reinforce the properties of the
blend NR / CR. CNT-Vast was ultrasonicly vibrated in ethanol or
dispersed in water with CTAB before being mixed with natural
rubber, rubber clopren as the preparation process in section 2.2. Here
are the results of mechanical properties obtained:
Table 3.17. Effect of CNT- Vast content on the mechanical properties
of materials NR / CR
Samples
Tensile
strength
(MPa)
Elongation
(%)
Hardness
(Shore A)
NR/CR 13,32 610 51,2
NR /CR/1%CNT- Vast/etanol 15,12 603 51,9
NR /CR/2%CNT- Vast/etanol 17,28 592 52,6
NR /CR/3%CNT- Vast/etanol 16,53 584 53,0
LNR/CR/4%CNT- Vast/etanol 15,76 578 53,8
NR /CR/1% CNT- Vast/CTAB 15,52 600 51,8
NR /CR/2% CNT- Vast/CTAB 18,14 593 52,3
NR /CR/3% CNT- Vast/CTAB 17,09 567 54,0
NR /CR/4% CNT- Vast/CTAB 16,76 579 54,4
Mechanical properties of the material samples NR / CR / CNT-
Vast / CTAB were pretty better than that of NR / CR / CNT- Vast /
eatnol. To explain this, the thesis used the research results of the
authors [97]. When comparing the size of the CNT- Vast and CNT-
Nanocyl (the kind used primarily in the thesis), it could be seen that
CNT- Nanocyl had small diameter and the equal diametral distribution
rather than CNT- Vast. On the other hand, purity of CNT- Nanocyl
(95%) is also larger than that of CNT- Vast (about 90%). Thus, it was
obviously suitable that the reinforcement ability of CNT- Vast also
declined slightly, and the CNT- Vast content optimally reinforced
(2%) was lower than CNT- Nanocyl (3%).
3.5.2. The regression equation describing the dependence of the
mechanical properties of the material LNR / CR on CNT-CTAB
When calculating by FORTRAN algorithmic language program and
proceeding the data, a regression equation was obtained as follows:
-Tensile strength:
2
1
^
693,0202,4024,13 xxy , with θ = 0,958
21
Easily realize that
1y
reached the maximum value at:
dx
d y1
= -2. 0,693
x+ 4,202 =0, solving this equation and refer x = 3,03%,
1y
max =
19,394 Mpa.
This result indicated that around the value x = 3,03%, the value of
tensile strength was the highest
- Elongation: xy 14,1186,6142
^
with r = -0,973
That r had negative value was completely suitable with the sign of x
- Abrasion: 23
^
032,0202,0836,0 xxy with θ = 0,988
-Hardness: xy 82,067,514
^
with r = 0,979
Thus: Proceeding data to find out the regression equations
describing experimental correspondence with high precision, enable to
evaluate the rules of the CNT-CTAB influences on the mechanical
properties of the materials. From that, we can solve optimization
problems, find out the domain of CNT-CTAB for the mechanical
properties of the materials.
3.5.3. Assessment of thermal-mechanical properties of the material
CO- NR / CR sample CNT reinforced by three different dispersal
methods
The curves showed 3 distinct regions: the high module (glass
area), transition area (in which the value E' drops rapidly with
temperature) and the "rubber". Rubber had large accrued modules at
low temperatures, then plummetted at around -60°C (sample
containing CNT/toluene: -66°C, sample containing CNT- CTAB: -
64°C, sample containing CNT/D01: -63°C). The strong decrease of E'
at this temperature indicated the transition from glassy state to
"rubber" state. All three material samples were a little bit different
from each other under the effect of load. The value E' of the samples
containing CNT/ toluene was slightly higher due to the even
dispersion of CN. The surface- appearance of CNT became an
absorbing agent.
22
-120 -100 -80 -60 -40 -20 0 20 40
0,00E+000
5,00E+008
1,00E+009
1,50E+009
2,00E+009
2,50E+009
M
o
d
u
l E
'
Nhiet do
Figure 3:49. The chart of accrued modules change with temperature
Figure 3:50. The chart of mechanical loss factor change with
temperature
The Figure 3:50 shows that Tg value of NR and CR is in range
of -50°C and -27°C. Vitrification temperature of NR was lower than
that of CR due to the presence of Cl polarized groups. These groups
mutually interacted, which restricted the movement of molecular
circuits. Samples containing CNT / D01 had Tg1 = -51,2°C with high
pic intensity, Tg2 = -27,8°C. Meanwhile, samples containing CNT /
CTAB had Tg1 = -49°C with lower intensity, Tg2 = -27,5°C but with
slightly lower intensity. Tg1 and Tg2 of samples containing CNT /
toluene slightly decreased to -48,8°C and -27°C respectively, but the
decrease of pic intensity of Tg1 was the most significant one. The rise
of the Tg1 algebraic values to samples containing CNTs/D01 was due
to the appearance of a few bundles of CNT as a barrier to the
movement of the polymer chains around the temperature Tg. These
results showed that the blend of NR / CR reinforced CNT / D01 was
less compatible with each other. However, when using surfactants or
dispersing in toluene, the compatibility was increased. This result was
CNT/D01
CNT/toluen
CNT/CTAB
23
consistent with the assessment of the results of TGA analysis,
mechanical properties and morphological structure above.
Besides, the intensity and location of pic tgδ indicated
interaction between rubber substrate and CNT. If pic tgδ is wider, the
aggregation of nano particles into clouds would be greater, the
connection between the CNT and the substrate would became worse.
Conversely, if pic tgδ was narrower, the connection between the CNT
and the substrate would be better, CNT was dispersed evenly and hard
to conglomerate. By comparing 3 pic tgδ, it could be seen that
CNT/toluene and CNT/CTAB samples had narrow pic, the peak of pic
with Tg1 is sharp, which proved the better reinforcement effect.
3.5.4. Influence of the dispersion method on electrical properties of
NR/CR/ CNT materials
Many studies have shown that doing a research on the electrical
properties is also an effective mediate method to study the structure of
the polymer nanocomposite material, which allows to assess
interaction and the dispersion ability of the phases. Below are the
descriptions of the electrical conductivity of the material.
Figure 3:51. Electrical conductivity and the electric absorbent
threshold of the material sample by CNT weight
It could be seen that the CNT dispersion method had a strong
impact the electrical conductivity of the material. Only 2% used CNT
has increased the electrical conductivity of NR / CR / CNT by 10
6
times and that of LNR / CR / CNT by 10
4
times. Generally, the
electrical conductivity of polymer synthetic materials was explained
by the mechanism of the conduction theory (form a continuous
24
conductive network) and the mechanism of jump (electromagnetic
radiation) of the electrons overcoming very small distances. Simply
understanding, the arrangement of the CNT particles into the pipelines
created a continuous line. The dielectric loss was very small so that it
could be ignored. Moreover, the specific structure with the presence of
conjugated bonds in CNT supported electronic lines to move
continuously. That the appearance of the positive electron on nitrogen
atom of CTAB atoms became electron transit center of CNT
continuous network made the electronic transportation process more
advantageous; thus, resistivity decreased, which also means electrical
conductivity increased. When the content of CNT reached at 3%, the
electrical conductivity reached 10
-5
. It means that the network
structure was stable, CNT particles had the shortest average distance,
which led to the formation of a 3-D network of the conductive phase.
By that time, it has reached an electrical absorbent threshold (as
described in Figure 3:51). Therefore, increasing the level of CNT
content also made an increase of connected density among CNTs
without changing the electrical conductivity.
Table 3:21. The influence of the dispersion methods on the
vulcanization ability of the blend NR / CR
Samples
Mmin
(kgf.cm)
Mmax
(kgf.cm)
T90
(min:sec)
LNR/CR/CNT-CTAB 2,17 19,5 10:55
NR/CR/CNT/Toluen 2,32 20,82 10:06
NR/CR/CNT/D01 2,18 19,63 10:18
Vulcanization time Tc90 of the sample containing D01 was
lower due to D01 structure had the link C = C which directly involved
in crosslinking process, accelerated the process of vulcanization.
Although the starting time of the vulcanization and Tc90 of the
mixing solution sample were lowest, the most interesting thing was
that the Tc90 time of the sample using latex was relatively short, even
lower than that of the sample NR / CR / CNT-TESPT (Table 3:11).
This was quite an important orientation to apply CNT in industry.
3.6. Orient to manufacturing experimental anti-static rubber mats
Based on the above findings, they have created a prototype of
anti-static mats. Below is the quality standard of the anti-static mats
manufactured in factories of Technical Rubber Ltd Globe Company
compared to imported samples delivered by The Bao Nguyen Co., Ltd,
25
Dong Nai (
dien/Tham-cao-su-chong-tinh-dien-Kt-1-2m-x-10m-x-2mm-
474.html).
Table 3:23. The quality standards of anti-static mats
The major quality
standards of the
product
Units of
measure
The results
Imported mats
Tensile strength MPa 19 3,6
Elongation % 650 188
Hardness Shore A 60 -
Abrasion cm
3
/1,61km 0,5 1,0
Electrical resistivity of
upper surface
10
6
10
4
– 106
Electrical resistivity of
lower surface
10
6
10
4
– 106
Bulk resistivity .cm 10
5 10
6
– 109
Other advantages of anti-static mat samples:
- High mechanical durability
- High environmental durability
- Long time for use
- Against grease and other common solvents
- Not containing Pb, Hg and other heavy metals
- The major material is natural rubber latex limiting the spread of
nanodust while being mixed (limiting the biggest drawback of the
material nanocomposite)
- Suitable for the factories to manufacture semiconductors, computers,
electronic components and for chemical laboratories
Conclusion
1. Has gained a success of denaturing CNT by 3 different methods,
when being oxidized by H2O2/NH3 approximately 27.85% of COOH
and NH2 groups were attached to the CNT surface. Then, through
Fischer esterification reaction, about 24.85% of PEG ester group and
3.29% of TESPT ester group were joined with the CNT surface.
Fridel Craft alkylation reaction helped to attach approximately 23% of
polyvinylclorua by weight to the CNT. That CTAB was absorbed up
to the CNT edge by Van der Walls link also helped to attach about 5%
of CTAB surrounding the CNT.
26
2. Has used 5% of CNT by weight to reinforce NR by means of melt-
mixing. The characteristic of the NR/CNT material system was
promoted by using 2% more of dispersion auxiliaries, compatible
D01.
3. Has used the wet-mixing method to disperse about 4% CNT or 3%
denatured CNT in the NR/NBR system. CNT- PVC was well
compatible with NBR so that it was well compatible with the NR /
NBR substrate rather than CNT-PEG (only formed a physical link).
4. The wet-mixing method also dispersed was 4% CNT and 3.5%
denatured CNT into the NR/CR system. Materials had a steadier and
tighter structure, which increased mechanical properties strongly
(tensile strength increased by 46.5%, elongation increased by 12%);
the starting temperature of decomposition rised by 6°C, aging factor
of the material in the environment also increased.
5. Dispersion of CNT in toluene solution was good but had some
disadvantages of solvent cost and environmental pollution when being
applied to industrial scale. The dispersion of CNT/ CTAB in latex got
high effects even when using powerful mechanical agitation without
using ultrasonic waves. Vulcanization time of LNR/CR/ CNT samples
were short, which had to be concerned about when manufacturing.
CTAB remarkable production deployment. Planning c Experimental
planning determined that the amount of 3.03% CNT reinforcement
was optimal. This confirmed the accuracy of experiments.
6. Initially identified the CNT-Vast content reinforced the blend
system NR/ CR (about 2%). This was consistent with CNT- Vast’s
diameter of about 40 nm, larger than CNT-Nanocyl’s diameter.
7. Rubber materials on the basis of the latex NR/ CR 4% reinforced
CNT-TESPT/ CTAB had high mechanical properties, positive grease
durability and electrical conductivity 4.1 ESD standard. This meet the
requirements of creating anti-static mats serving in the electronic and
textile fields.
Recommendations:
There should be further studies on the reinforcement possibility of
CNT- Vast to the rubber nanocomposite material, especially the
chemical denatured reaction CNT- Vast to improve its dispersion
possibility in the polymer substrate. Also, there should be researches
on the use of dispersion auxiliraries, compatible vegetable oil in
manufacturing rubber nanocomposite materials reinforced CNT.
27
LIST OF WORKS HAS BEEN PUBLISHED
1. Chu Anh Van, Hoang Thi Hoa, Luong Nhu Hai, Luu Duc Hung, Ho
Thi Oanh, Do Quang Khang, Some research results, manufacturing
and properties of natural rubber materials nanocomposite carbon
tubes, Journal of Chemistry, 2014, T52 (6A), 64-68.
2. Chu Anh Van, Le Hong Hai, Ho Thi Oanh, Do Quang Khang,
Research on denaturing carbon nanotubes’ surface by Fischer
esterification reaction, Journal of Chemistry, 2015, T53 (4), 520-525.
3. Chu Anh Van, Ho Thi Oanh, Luong Nhu Hai, Do Quang Khang,
Research preparation and properties of rubber nanocomposite material
based on blend NR/NBR and carbon nanotubes, Journal of Chemistry,
2015, T53 ( 5E3), 122-126.
4. Chu Anh Van, Vuong Quang Viet, Luong Nhu Hai, Do Quang
Khang, Research preparation and properties of rubber nanocomposite
material based on the blend of natural rubber and chloroprene rubber
with carbon nanotubes, Journal of Chemistry, 2015, T53 (5E1), 194-
198.
5. Chu Anh Van, Ngo Quang Hiep, Ho Thi Oanh, Luong Nhu Hai,
Ngo Trinh Tung, Do Quang Khang, Study on preparation of rubber
nanocoposites based on natural rubber/chloropene rubber blends
reinforced with carbon nanotube by semi-dried method, Journal of
Chemistry, 2016 (accepted for publication).
6. Do Quang Khang, Chu Anh Van, Ngo Trinh Tung, Do Trung Sy,
The process of manufacturing rubber nanocomposites material, patent
registration, application number 1-2016-00883, accept for the
application by the decision 19619 / QD-IP date 04.11.2016.
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