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工 學 碩 士 學 位 論 文
Poly(butylene succinate)(PBS)/탄소나노튜브,
탄소나노섬유 나노복합체 발포체의 제조와 특성 분석
Preparation and Characterization of Poly(butylene
succinate)(PBS)/Carbon Nanotube, Carbon
Nanofiber Nanocomposite Foams
2009年 2月
仁荷大學校 大學院
高分子工學科
李 錫 仁

工 學 碩 士 學 位 論 文
Poly(butylene succinate)(PBS)/탄소나노튜브,
탄소나노섬유 나노복합체 발포체의 제조와 특성 분석
Preparation and Characterization of Poly(butylene
succinate)(PBS)/Carbon Nanotube, Carbon
Nanofiber Nanocomposite Foams
2009年 2月
指導敎授 陳 仁 柱
이 論文을 碩士學位 論文으로 提出함
仁荷大學校 大學院
高分子工學科
李 錫 仁

이 論文을 李 錫 仁의 碩士學位論文으로 認定함.
2009年 2月
主審
副審
委員

Abstract
Recently, due to the environmental problems caused by synthetic
non-degradable plastic waste, biodegradable polymers have received
extensive attention as the potential candidate to replace the non-
degradable counterparts. One of the promising synthetic aliphatic
polyesters is poly(butylene succinate) (PBS), which has a high melting
temperature (115 o C), good biodegradability by microorganism, and
outstanding processability. However, it is known that its tensile
properties, gas barrier properties and melt viscosity for further
processing are not quite desirable in some end-use applications.
In the polymer nanocomposite foam, the nanoscale filler distributed
in the polymer matrix may act as the nucleation site during the foaming
process, inducing smaller cell size and increased cell density. In
addition, the presence of well-dispersed fillers can improve mechanical
and physical properties, and the heat distortion temperature of polymer
foams. The cell morphology, which depends strongly on the interaction
with the filler, is expected to affect such characteristic properties as
weight, specific strength, heat conductivity and isolation to sound.
The purpose of this study is to develop the biodegradable polymer
nanocomposite foam having high blowing ratio and closed-cell
i

structure. Multi-walled carbon nanotube(MWNT) and carbon
nanofiber(CNF) were used as the nano-sized filler for PBS. After
establishing the optimum condition for producing the polymer
nanocomposite foam, we prepared the PBS nanocomposite foams
using a chemical blowing agent. Physico-chemical properties of the
PBS nanocomposite foams were characterized.
Keyword : Poly(butylene succinate)(PBS), Carbon Nanotube,
Carbon Nanofiber, Nanocomposite Foam, Chemical Blowing Agent
ii

국 문 요 약
최근 비분해성 플라스틱 폐기물로 인한 환경문제가 대두되면서
비분해성 고분자를 대체하기 위한 일환으로 생분해성 고분자가 각
광을 받아 왔다. 그 중 가장 유망한 합성 지방족 폴리에스터 계열
중의 하나인 Poly(butylene succinate)(PBS)는 115 o C 근처의 높은
융점을 가지며 미생물에 의한 생분해도가 높고, 가공성이 훌륭하다.
그러나 인장 성질, 가스 차단성, 용융점도가 낮아 최종 응용적인 측
면에서 제한을 받아 왔다.
고분자 나노복합체 발포체에서 고분자 매트릭스 내에 분산되어
있는 나노사이즈의 충전제는 발포과정에서 기핵제로서의 역할을 할
수 있으며 더 작은 셀의 크기와 셀 밀도의 증가를 유도시킬 수 있
다. 더욱이 잘 분산된 나노사이즈의 충전제로 인해 고분자 발포체의
기계적, 물리적 성질, 열 변형 온도 등의 물성을 향상시킬 수 있다.
충전제와의 상호작용에 강하게 의존하는 셀의 형태는 발포체의 무
게(밀도), 강도, 열 전도도, 차음성과 같은 특성에 영향을 준다.
본 실험의 목적은 고배율의 밀폐형 구조를 가지는 생분해성 고분
자 나노복합체 발포체를 개발하는 것이다. 이에 나노사이즈의 충전
제로서 탄소나노튜브와 탄소나노섬유를 이용하였다. 발포체 제조를
위한 고분자 나노복합체의 최적 조건을 확립한 후 화학발포제를 이
용하여 고분자 나노복합체 발포체를 제조하고, 그들의 특성을 분석
하였다.
iii

Keyword: Poly(butylene succinate)(PBS), 탄소나노튜브,
탄소나노섬유, 나노복합체 발포체, 화학발포제
iv

CONTENTS
Abstract ………………………………………………………………… i
국문요약 ……………………………………………………………… iii
CONTENTS …………………………………………………………… v
LIST OF TABLES …………………………………………………… vii
LIST OF FIGURES …………………………………………………… vii
SECTION I. Processing of Poly(butylenes succinate)(PBS)/Carbon
Nanotube Nanocomposite Foams
1. Introduction…………………………………………………………… 1
2. Experimental………………………………………………………… 6
2. 1. Materials………………………………………………………… 6
2. 2. Preparation of polymer nanocomposite……………………… 6
2. 3. Foaming of nanocomposite…………………………………… 8
2. 4. Characterization of nanocomposites and their foams……… 8
3. Results and discussion…………………………………………… 11
3. 1. PBS/MWNTs nanocomposites……………………………… 11
3. 2. Nanocomposite morphology and dispersion of MWNTs… 11
3. 3. Thermal behavior…………………………………………… 12
3. 4. Mechanical testing…………………………………………… 14
3. 5. Foam behavior and cell geometry………………………… 16
4. Conclusions………………………………………………………… 19
5. References………………………………………………………… 21
v

SECTION II. Preparation and Characterization of PBS/Carbon
Nanofiber Nanocomposite Foams
1. Introduction………………………………………………………… 26
2. Experimental………………………………………………………… 29
2. 1. Materials……………………………………………………… 29
2. 2. Nanocomposite preparation………………………………… 29
2. 3. Foaming……………………………………………………… 31
2. 4. Characterization of nanocomposites and their foams…… 31
3. Results and discussion…………………………………………… 33
4. Conclusions………………………………………………………… 39
5. References………………………………………………………… 40
vi

SECTION I.
LIST OF TABLES
Table 1 Morphological parameters of PBS/2 wt% MWNTs
nanocomposite foam obtained by the SOAM method (blowing time = 5
min) …………………………………………………………………… 42
SECTION II.
Table 1 Thermal stability for PBS/CNFs nanocomposites……… 43
Table 2 Temperature and CBA content dependence of morphological
parameters …………………………………………………………… 44
SECTION I.
LIST OF FIGURES
Figure 1 FT-Raman spectra of the PBS nanocomposites with 2 wt%
content prepared by three different methods: (a) MWNT (b) solution
blending (c) melt mixing and (d) SOAM method …………………… 45
Figure 2 SEM images of the PBS nanocomposites with 2 wt% content
prepared by three different methods: (a) solution blending (b) melt
mixing (c) SOAM method, and (d) TEM micrograph of the 2 wt%
PBS/MWNTs nanocomposites prepared by SOAM method … 46
vii

Figure 3 TGA thermograms of the PBS nanocomposites containing
various MWNTs content prepared by the SOAM method ………… 47
Figure 4 DSC traces of the PBS nanocomposites containing various
MWNTs content prepared by the SOAM method: (a) melting and (b)
crystalline behaviors ………………………………………………… 48
Figure 5 Tensile strength and elongation at break curves of the PBS
nanocomposites with various MWNTs content prepared by three
different methods …………………………………………………… 49
Figure 6 Optical micrographs of PBS nanocomposite foams with 2
wt% MWNTs content prepared by the SOAM method as a function of
blowing temperature and CBA content. The blowing time was fixed at 5
min ……………………………………………………………………… 50
Figure 7 Cell size distribution of PBS nanocomposite foams with 2
wt% MWNTs content prepared by the SOAM method at 150 o C: (a) 4
(b) 6 and (c) 8 phr. The blowing time was fixed at 5 min ………… 51
Figure 8 Blowing ratio of PBS nanocomposite foams with 2 wt%
MWNTs content prepared by the SOAM method as a function of
blowing time and temperature and CBA content: (a) 4 (b) 6 and (c) 8
phr ……………………………………………………………………. 52
viii

SECTION II.
Figure 1 TGA thermograms of PBS/CNFs nanocomposites by means
of different preparation methods ……………………………………… 53
Figure 2 The Effect of CNFs content and different preparation
methods on the (a) tensile strength and (b) elongation at break …… 54
Figure 3 SEM images of PBS/2 wt% CNFs nanocomposite prepared
by (a) solution blending (b) melt mixing and (c) SOAM method …… 55
Figure 4 The Effect of blowing time and temperature on the cross-
sectional cell morphology of PBS/2 wt% CNFs nanocomposite foams
measured by the optical microscope. CBA content was fixed at 4 phr
………………………………………………………………………… 56
Figure 5 Blowing temperature and time dependence on the blowing
ratio of PBS/2 wt% CNFs nanocomposite foams with different CBA
loading: (a) 4 (b) 6 and (c) 8 phr ……………………………………… 57
Figure 6 Cell size distribution of the PBS/2 wt% CNFs nanocomposite
foams as a function of the blowing temperature: (a) 150 (b) 160 and (c)
170 o C. The blowing time and CBA content were fixed for 5 min and at
4 phr, respectively …………………………………………………… 58
ix

SECTION I. Processing of Poly(butylenes succinate)(PBS)/Carbon
Nanotube Nanocomposite Foams
1. Introduction
Over the past decade, numerous nano-scaled reinforcing fillers have
been investigated. Among them, study on polymeric composites with
carbon nanotubes (CNTs) has actively carried out due to the unique
properties of the composites. [1-4] The extraordinary properties of CNTs
such as large aspect ratio, low density, high flexibility, modulus and
strength have spurred much research. Especially, it was revealed that
polymer-CNTs nanocomposites exhibit dramatically enhanced thermal,
mechanical and electrical properties as compared with those of pristine
polymer. [5-7] This has led to the utilization of polymer-CNTs
nanocomposites in numerous application fields. [1,8] However, the
following two prior conditions should be established in order to realize
desired performance: (i) a homogeneous dispersion of the CNTs
throughout the polymer matrix and (ii) strong polymer-CNTs interfacial
adhesion. As in most fiber or particle reinforced composite materials, in
order to achieve the most efficient enhancement of properties, the
reinforcement phase should be uniformly dispersed in the polymer
1

matrix. However, CNTs are strongly affected by van der Waals force
due to their small size and large surface area. These forces give rise to
the formation of aggregates, which in turn, make dispersion of CNTs in
the polymers difficult. In order to attain an efficient dispersion of CNTs
by the physical approach, ultrasound can be applied to a dispersion of
CNTs. [9] In addition, chemical methods such as covalent attachment
involving the introduction of a chemical group to the nanotube wall,
and non-covalent adsorption methods have been employed in order to
provide chemical compatibility with the polymers, and dissolution of
CNTs in organic solvents. [10-12]
Generally, the following three methods for the preparation of
polymer-CNTs nanocomposite are employed to promote the dispersion
of controlled CNTs throughout the polymer matrix: (i) solution blending,
a method for precipitating or casting a polymer-CNTs solution
dissolved in a solvent, [13,14] (ii) melt mixing, which requires high
temperature and shear force according to the polymer species in the
mixer without a solvent and (iii) in-situ polymerization, a method to
polymerize the monomer in the presence of the dispersed-CNTs. This
last approach has outstanding potential which can include covalent
bonding between the polymer matrix and modified-CNTs. [16,17]
2

A nanoscale filler dispersed in a polymer matrix can act as a
nucleation agent during the foaming process, resulting decreased cell
size and increased cell density. [18,19] Also, the cell morphology, which
depends strongly on the interaction with the reinforced-filler, is related
with the properties such as lightweight, high specific strength, poor
heat conductivity, and good isolation to sound. And, several groups
have developed physical and chemical foaming methods and
investigated the properties of the final foams. Nam et al. prepared
PP/clay nanocomposite foams by using a supercritical CO2 in the
autoclave. Their products exhibited the homogeneity in cell size of 30
~ 120 μm, the high cell density of about 10 7 ~ 10 8 cell/mL, and the high
cell wall thickness of 5 ~ 15 μm. The clay particles also induced the
improvement of the strength of foam in mechanical properties. Di et al.
reported PLA/organoclay nanocomposite foams formed by using the
mixture of CO2 and N2. The improvements of viscous and elastic
properties for PLA/clay nanocomposites allowed them to produce PLA
foams with much smaller cell size and higher cell density than those of
pure PLA even at low clay content. With supercritical CO2 via the batch
foaming process, CNFs and CNTs have been used to prepare PS
nanocomposite foams by Shen et al. They compared the nucleation
3

efficiency of different particles, suggesting that CNFs exhibited an
excellent nucleation effect due to its food dispersion in the polymer
matrix, as well as the favorable wettability and surface curvature in that
foaming process. On the contrary, using a chemical blowing agent,
Guan et al. manufactured the poly(propylene carbonate) (PPC) foams
with a blowing ratio of 16. The decomposition behavior of the blowing
agent was investigated, and the effect of blowing agent content and
[20-24, 36]
the foaming condition on the foaming of PPC studied.
Recently, synthetic petroleum-based polymers have caused serious
environmental problems due to their limited degradation. For this
reason, biodegradable polymers have drawn substantial attention
owing to environmental concerns. Among these polymers,
biodegradable aliphatic polyester types, i.e., poly(ε-caprolactone)
(PCL), poly(lactic acid) (PLA), poly(3-hydroxybutyrae) (PHB) and
poly(butylene succinate) (PBS), have currently been the focus of much
attention. [25-30] However, they lack price competitiveness and a
practically acceptable level of processability, and their usage is due to
relatively poor physical properties in particular. Therefore, the
incorporation of nanoscale fillers into biodegradable aliphatic
polyesters has been studied by many research groups with the aim of
4

enhancing the physical properties of the polyesters. [31-35] Poly(butylene
succinate) (PBS) is a biodegradable aliphatic polyester resin
synthesized by a condensation reaction between 1, 4-butandiol and
succinic acid, which has a high fusion temperature (115 o C),
remarkable biodegradation, and outstanding processability by means
of the extruder used for polyolefins. [26,29] However, it is known that its
tensile property, gas barrier properties, melt viscosity for further
processing and so on are deficient in various end-use applications. [27]
In this study, three different nanocomposite fabrication approaches
such as solution blending, melt mixing and the SOAM method were
applied to compare the degree of dispersion of MWNTs in the PBS
domain. Herein, we have mainly focused on the SOAM method
because it can achieve a much better MWNTs dispersion by melt-
mixing the nanocomposite prepared by solution blending, under strong
shear force. In order to verify the reinforcing effect of MWNTs as
compared to neat PBS, as well as to establish the optimal conditions
for expanding nanocomposites, the thermal and mechanical properties
were investigated. We obtained PBS nanocomposite foams with a
closed-cell structure using a chemical blowing agent and characterized
the foam behavior.
5

2. 1. Materials
2. Experimental
The Poly(butylene succinate)(PBS) used in this study was Enpol
G4560 (MI = 1.5 g/10 min) from Ire Chemical LTD., Korea. MWNTs
(HollowCNT 75L, purity of higher than 95%, inner/outer diameter
distribution 30~50 / 60~80 nm) were purchased from Nanokarbon Co.,
LTD., Korea. A high purity treatment using HCl and a density treatment
were applied according to the manufacturer’s instructions. Chloroform
was used as a solvent in the solution blending step and was supplied
by Dongyang chemical, Korea. Cellecom ACP-4 acted as a chemical
blowing agent (CBA) and was obtained by Kumyang Co., Korea. All
materials were used without further purification.
2. 2. Preparation of polymer nanocomposites
In this work, three approaches were employed to evaluate the
dispersion of MWNTs in the PBS matrix: solution blending, melt mixing,
and the SOAM method (solution blending and subsequent melt mixing),
respectively. PBS pellets and MWNTs were dried in a vacuum oven at
60 o C for 24 h prior to being used. First, in the case of solution
6

lending, PBS pellets were dissolved in chloroform at 40 o C and stirred
for 5 h to obtain a complete polymer solution. At the same time,
MWNTs were dispersed in chloroform at ambient temperature for 3 h
and then sonicated for 2 h at 90 W by a ultrasonic generator (Kodo
Technical Research Co., Japan). Then, the MWNTs-dispersed solution
was added to PBS solution and then mixed under strong stirring at 40
o C for 24 h to induce a nanocomposite with a uniform dispersion of
MWNTs. After the removal of chloroform under the rotary hood, the
nanocomposite film was dried under a vacuum at 60 o C for 24 h.
Second, melt mixing was performed by a torque rheometer (Haake
Rheometer 90, Germany) at 120 o C for 15 min with a rotor speed of 60
rpm. After the PBS pellets were melted for 3 min, MWNTs having
different contents were gradually added. Third, some nanocomposite
films prepared by solution blending were melt-mixed for 10 min inside
a twin screw mixer under the aforementioned conditions, The SOAM
method exhibited higher torque than that of simple melt mixing at an
early state. The mass fraction of MWNTs loaded to the polymer matrix
was varied from 0.1 to 3 wt%. The sample codes were named, for
example, PBS2S, PBS2M, and PBS2SM, where the numbers
7

epresent the mass fraction of MWNTs, and the ‘S’ stands for solution
blending, ‘M’ for melt mixing, and ‘SM’ for the SOAM method.
2. 3. Foaming of nanocomposites
Nanocomposite films fabricated by solution blending and having a
uniform size (25 mm width × 50 mm long) were put into a Haake
rheometer and mixed into a molten state at 120 o C for 10 min with a
screw speed of 60 rpm. Afterwards, ACP-4 with different contents was
slowly added to the mixer and blended for a further 10 min. The
resulting products were prepared by compression molding at 135 o C
for 8 min into strips of 12 mm × 60 mm × 3 mm. Each strip was
again cut into samples of 12 mm × 20 mm, followed by foaming at
150, 160, and 170 o C for 5, 10, 20, and 30 min in a forced convection
oven, respectively.
2. 4. Characterization of nanocomposites and their foams
FT-Raman spectra were acquired to evaluate the formation of MWNT-
reinforced PBS nanocomposites using a RFS 100/S (Bruker,
Germany) with a spectral resolution of 4 cm -1 . The excitation length
was the 1064 nm line of a 60 mW Nd-YAG laser. The cryo-fractured
8

surface morphology of the nanocomposites was observed by field
emission scanning electron microscopy using a S-4300 (Hitachi,
Japan). The samples were freeze-fractured in liquid nitrogen and
sputter-coated with Pt. TEM observations were performed on a JEM
2100F (JEOL, Japan) operated at an accelerated voltage of 200 kV to
examine the dispersion of MWNTs embedded in the PBS matrix.
Ultrathin sections with a thickness of 50nm were microtomed using a
MTX (RMC, Japan) with a diamond knife. A thermal analysis was
conducted with a modulated DSC 2920 (TA Instruments, USA) in a
nitrogen atmosphere at a heating rate of 10 o C/min. To erase the
thermal history of the nanocomposite, a second heating scan was
applied at temperatures ranging from 30 o C to 170 o C. Thermal stability
was investigated out on a TGA Q50 (TA Instruments, USA). All
samples were heated to 700 o C under air at a heating rate of 20 o C/min.
Mechanical properties of the nanocomposites films under uniaxial
elongation at room temperature were measured using a UTM
(Hounsfield Test Equipment, UK). Each sample was provided as a
dog-bone type and the resulting value was an average of at least
seven measurements.
9

The foam density was measured by a gas pycnometer (Accupyc 1330,
Micrometrics Co., USA). The blowing ratio was calculated using the
following equation:
3
the density of neat PBS (1.268 g/cm )
ratio =
the density of PBS/MWNTs nanocomposite
foam (g/cm
Blowing 3
The cross-sectional morphology of the expanded PBS nanocomposite
foams was observed with an optical microscope (i-Camscope,
Sometech, Korea). The average cell size d was estimated by
measuring the maximum diameter of each cell perpendicular to the
skin from an OM micrograph. To determine the cell size distribution,
the size of at least 75 cells in the OM micrograph was measured. The
cell density Nc and the mean wall thickness δ are given by [36]
N
c
=
1-
( ρ / ρ )
10
f
−4
d
3
p
and ⎟ ⎟
⎛
⎞
⎜ 1
δ = d
− 1
⎜
⎝
1−
( ρf
/ ρ p )
⎠
where ρp, ρf, and d are the pre-foamed density, the post-foamed
density in g/cm 3 , and the average cell size in mm, respectively.
10
)

3. Results and discussion
3. 1. PBS/MWNTs nanocomposites
Figure 1 shows Raman signals of MWNT and nanocomposites
produced by different preparation schemes. Disorder (D) and
tangential (G) bands of MWNT at about 1298 cm -1 and 1582 cm -1 were
distinctly observed at 1064 nm excitation. We confirmed two
characteristic absorption peaks caused by MWNT in the case of the
nanocomposites, indicating that nanocomposites based on MWNTs
were successfully formed regardless of preparation methods.
3. 2. Nanocomposite morphology and dispersion of MWNTs
Figure 2 illustrates the morphology and dispersion of nanocomposites
containing 2 wt% MWNTs, obtained from solution blending, melt
mixing, and the SOAM method, respectively. Overall, MWNTs
randomly dispersed throughout the PBS matrix are shown in Figures
2a, 2b, and 2c. However, in Figures 2a and 2b, bundles of MWNTs are
partially seen, because of their van der Waals interaction, and the pull-
out phenomenon of MWNTs from the PBS matrix also existed due to
the weak interfacial adhesion between the matrix and MWNTs as
11

compared with Figure 2c. Therefore, it can be noted that the
nanocomposites fabricated by the SOAM method showed better
MWNTs dispersion and stronger polymer-MWNTs interfacial force than
those obtained by means of solution blending and melt mixing,
respectively. Figure 2d shows a TEM micrograph of a nanocomposite
with 2 wt% MWNTs produced using the SOAM method. Individual
MWNTs were randomly dispersed within the PBS matrix, and are
oriented toward the ultratoming direction as well. Because they are
affected by a strong shear force during additional melt mixing, shorter
nanotubes can be seen in some locations.
3. 3. Thermal behavior
Figure 3 shows representative TGA thermograms of the PBS/MWNTs
nanocomposites prepared by the SOAM method. It is evident that the
thermal stability was remarkably enhanced with the addition of MWNTs.
This is attributed to not only the uniform dispersion of MWNTs within
the PBS matrix but also the excellent thermal property of the MWNTs
themselves. In case of 5 % weight loss, the degradation temperature of
all nanocomposites produced via the SOAM method exhibited an
12

improvement of approximately 25 o C relative to that of neat PBS (Td =
331.89 o C).
DSC scans were conducted to determine the effect of MWNTs on the
melting and crystallization behavior of PBS nanocomposites. Figure 4
presents the DSC trace of PBS/MWNTs nanocomposites containing
different MWNTs contents, prepared by the SOAM method. In Figure
4a, the neat PBS and its nanocomposites show the double melting
endotherms in a temperature range of 103 ~ 112 o C, respectively.
Some evidence of double and multiple melting behavior has been
previously reported. [37] Especially in the case of PBS and its
composites, these double melt peaks originate from recrystallization.
The first melting point depends on the presence of metastable lamellae,
which have a large surface/volume ratio and fold surfaces with high
surface-free enthalpies during recrystallization. [38] In other words, two
morphologically different crystalline structures existed during the
heating scans. It can be seen that the first melting temperature of the
nanocomposites shifts toward the lower temperature region relative to
that of the neat PBS, indicating that MWNTs play a crucial role in the
reorganization behavior of metastable lamellae. The second melting
temperature, attributed to crystallites with high thermal stability,
13

decreased slightly but increased gradually with increasing MWNT
content. Figure 4b shows the crystallization behavior of the neat PBS
and its composites. The neat PBS was crystallized at 89.55 o C, and
the addition of MWNTs into the PBS matrix led to a shift of the Tc of the
nanocomposites to around 87 o C. This behavior indicates that the
MWNTs do not act as the efficient nucleating agent but impede the
crystallization process of the nanocomposites in all samples.
Consequently, lower temperature was needed to crystallize, as
indicated by the cooling scans. It is shown that the PBS
nanocomposite with 2 wt% MWNTs loading had a higher crystallization
temperature than the other samples.
3. 4. Mechanical testing
The tensile strength and elongation at break curves for the neat PBS
and its composites with different MWNT loadings are shown in Figure
5. The three preparation methods were also compared. It was found
that the nanocomposites prepared by the SOAM method exhibited a
better tensile property than those prepared by solution blending and
melt mixing, respectively. In this study, the ranking of high tensile
mechanical property of the MWNT-reinforced nanocomposites is the
14

SOAM method, the melt mixing method, and the solution blending. In
Figure 5a, it can be observed that the tensile strength of the
nanocomposite increased sharply when a small amount of MWNTs
was added, and gradually achieved a peak value when 2 wt% MWNTs
were loaded, and thereafter decreased with greater MWNT content. It
is believed that the increase in the tensile strength can be ascribed to
the interfacial adhesion between the host polymer matrix and well-
dispersed MWNTs with a high modulus and aspect ratio. In general,
upon the incorporation of the filler into the polymer matrix, the
elongation at break of the nanocomposite was decreased along with
increased tensile strength. However, novel behavior of the elongation
at break of the nanocomposites is shown in Figure 5b. It can seen that
the elongation at break of the nanocomposite was enhanced to a level
higher than that of the neat PBS, and increased up to 2 wt% MWNT
loading, and thereafter decreased with a further increase in MWNT
content. These results could be explained by the MWNTs, having an
outstanding elastic response to deformation, being strongly embedded
within the matrix, thereby inducing efficient load transfer and, in turn, a
homogeneous dispersion.
15

3. 5. Foam behaviors and cell geometry
Figure 7 presents optical micrographs of the cross-sectional surfaces
of the PBS nanocomposite foams with 2 wt% MWNTs content
produced via the SOAM method and foamed for 5 min as a function of
temperature and CBA content. All nanocomposites foamed by CBA
showed a homogeneously closed-cell structure, suggesting that the
presence of well-dispersed MWNTs plays an important role in
increasing melt viscosity of the nanocomposite so as not to destroy the
cell walls, as well as providing the nucleating sites for cell formation.
We note that the cell size increased with more adding the amount of
CBA, also increasing the temperature. If a proper melt viscosity that
restricts the expansion of cells is established, the cell geometry will be
strongly affected by the aforementioned two factors. From the optical
microscopy data, various morphological parameters of PBS/2 wt%
nanocomposite foams obtained by the SOAM method can be
quantitatively determined, as seen in Table 1. The post-foamed mass
density tended to decrease with an increase in both the CBA content
and temperature as a result of expansion of the PBS nanocomposite
foam, while the neat PBS density is 1.268 g/cm 3 . All nanocomposite
foams exhibit a structure ranging from 154.72 μm to 406.30 μm. The
16

cell density, calculated by equation (2), also decreased from 10.67 ×
10 5 cell/cm 3 to 1.09 × 10 5 cell/cm 3 with an increase in both the
blowing temperature and the content of CBA, respectively. These
results are attributed to the well-dispersed MWNTs, which act as a
nucleation agent, facilitating the cell formation process, namely,
heterogeneous nucleation could be achieved at the interfaces between
MWNTs and PBS. Also, the average cell size and cell density were
strongly influenced by the gas evolution as a result of the thermal
decomposition of CBA. The mean cell-wall thickness, based on
equation (3), also decreased in proportion to increased CBA content,
which was attributed to cell growth in accordance with foam expansion
to adjacent cells. We measured the cell size of nanocomposite foams
from optical micrographs and evaluated the distribution of the cell size,
as shown in Figure 8. All foams showed an approximate Gaussian
distribution. Moreover, it can be seen that the lower the blowing
temperature was, the narrower the width of the distribution peaks was.
The narrow peak indicates the high uniformity of cell size, which is
significantly related to the dispersion state of the MWNTs as well as
the applied blowing temperature.
17

Figure 9 illustrates the variation of the blowing ratio in accordance with
blowing temperature, time, and CBA amount. It is seen that the
blowing ratio, which is calculated by equation (1), tends to increase
steadily as the blowing time, temperature and CBA loading are
increased. The maximum values of the blowing ratio at different CBA
loading are ranged from 7.3 to 11.1, indicating that more addition of
CBA in the nanocomposite melt results in the release of more gases to
nanocomposite, and facilitates increased cell size.
18

4. Conclusions
Poly(butylene succinate) (PBS)/MWNTs nanocomposites were
successfully fabricated by three different methods. Via Raman
scattering, we observed two characteristic absorption peaks attributed
to MWNT-OH in the nanocomposites, and verified successful
formation of nanocomposites based on MWNT-OH. The morphology
and dispersion state of the MWNTs in the polymer domain were
examined by SEM and TEM, respectively. The results suggested that
the nanocomposite prepared by the SOAM method exhibited more
dispersed MWNTs and stronger interfacial force with PBS than the
nanocomposites fabricated by means of solution blending and melt
mixing, respectively. The thermal stability was measured by TGA, and
it was found that the thermal stability was enhanced by about 25 o C
relative to neat PBS (Td = 331.89 o C). Double melting endotherms,
which were attributable to a recrystallization process, were observed in
neat PBS and nanocomposites based on MWNTs. In addition, MWNTs
also impeded the crystallization behavior of nanocomposites, as
revealed by DSC measurements. The ranking of high tensile
mechanical property of nanocomposites is the SOAM method, melt
19

mixing, and solution blending. Furthermore, the nanocomposite with 2
wt% MWNTs content showed the highest tensile strength and
elongation at break.
Based on the properties of the nanocomposite described above, we
assumed that the nanocomposite containing 2 wt% MWNTs produced
via the SOAM method would be optimal for the high performance foam.
Well-dispersed MWNTs, which act as a nucleation site for cell
formation, induced an increase in the melt viscosity of the
nanocomposite to restrain cell rupture. As a result, we achieved
nanocomposite foams (>153 μm) with a closed-cell structure by means
of the decomposition of CBA. The morphological parameters such as
the post-foam density, average cell size, cell density, mean cell-wall
thickness, and blowing ratio were significantly affected by the blowing
time, temperature, and CBA content, respectively.
20

5. References
[1] Mohammad Moniruzzaman and Karen I. Winey,
Macromolecules 39, 5194 (2006)
[2] R. Baughman, Science 297, 787 (2002)
[3] X. L. Xie, Y. W. Mai, X. P. Zhou, Mater. Sci. Eng. R 49, 89
(2005)
[4] Jonathan N. Coleman, Umar Khan, and Yurii K. Gun’ko, Adv.
Mater. 18, 689 (2006)
[5] Jason J. Ge, Haoqing Hou, Qing Li, Matthew J. Graham,
Andreas Greiner, Darrell H. Reneker, Frank W. Harris, and
Stephen Z. D. Cheng, J. Am. Chem. Soc. 126, 15754 (2004)
[6] Tianxi Liu, In Yee Phang, Lu Shen, Shue Yin Chow, and Wei-
De Zhang, Macromolecules 37, 7214 (2004)
[7] J. B. Bai, A. Allaoui, Composites: Part A 34, 689 (2003)
[8] Liliane Bokobza, Polymer 48, 4907 (2007)
[9] S. Badaire, P. Poulin, M. Mauggey, C. Zakri, Langmuir 20,
10367 (2004)
[10] Dimitrios Tasis, Nikos Tagmatarchis, Alberto Bianco, Maurizio
Prato, Chemical Reviews 106, 1105 (2006)
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[11] Kannan Balasubramanian, Marko Burghard, Small 1, 180
(2005)
[12] V. Georgakilas, K. Kordatos, M. Prato, D. M. Guldi, M. Holzinger,
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Eng. Mater. 4, 109 (2002)
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Compos. Interfaces 10, 389 (2003)
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[18] L. James Lee, Changchun Zeng, Xia Cao, Xiangming Han,
Jiong Shen, Guojun Xu, Composites Science and Technology
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[19] Suprakas Sinha Ray, Masami Okamoto, Prog. Polym. Sci. 28,
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[20] D. J. Kim, S. W. Kim, H. J. Kang, K.H. Seo, Journal of Applied
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Polymer Physics 37, 1357 (1999)
25

SECTION II. Preparation and Characterization of PBS/Carbon
Nanofiber Nanocomposite Foams
1. Introduction
Polymeric foams are the lightweight materials containing gaseous
voids by means of physical and chemical blowing agents, which have
been mainly used in the insulation, absorbents, cushion, packaging
and weight-bearing structures. [1] For the polymer nanocomposite
foams, the integration of the small amounts of nano-sized fillers into
the virgin polymer may provide enhanced thermal stability and
mechanical properties compared to those of the neat polymer foam,
and can effectively induce the nucleation of a large amount of bubbles
according to the geometry of the added-nanoparticles. [2]
In order to reduce the environmental problems caused by the non-
degradable plastics, the development of the biodegradable polymers
with the properties enough to compare with those of the commodity
plastics greatly have been required and steadily studied by extensive
research groups. Poly(butylene succinate) (PBS), one of the most
applied biodegradable plastics to the scientific and industrial fields, is a
26

thermoplastic, aliphatic polyester produced through polycondensation
reaction of 1, 4-butanediol and succinic acid. It also has melting points
ranging 90 ~ 120 o C, glass transition temperatures ranging -45 ~ -10
o C, and outstanding processability. [3]
Carbon nanofibers (CNFs) are generally known as a carbon allotrope
having diameters of 3 ~ 100 nm with lengths ranging from 0.1 to 1000
µm. Owing to their internal structural characteristics which could be
controlled by the specific synthetic conditions, CNFs display the
chemical stability, high surface area, remarkable electrical and
mechanical properties. So, they have been shown the diverse
applications, for example, the polymer additives for high performance
composites, gas storage materials, electronic components, catalyst
support materials and so on. [4] Especially, in order to act as the
polymer reinforcement, it is necessary to achieve not only the
homogeneous dispersion in the polymer matrix, but the strong
interfacial adhesion between the CNFs and the target polymer. Based
on these issues, the extensive studies related to the CNFs-reinforced
nanocomposites have been carried out. [5-8]
The aim of this study is to prepare the nanocomposite foams with the
closed-cell structures and the high blowing ratio by means of the
27

chemical blowing agent, and to characterize the effect of CNFs acted
as the nucleation sites in the closed-cell system, and the foam
behaviors. Prior to producing the nanocomposite foams, the thermal
and mechanical properties of PBS/CNFs nanocomposites employed by
different fabrication methods were investigated in detail.
28

2. 1. Materials
2. Experimental
PBS (Enpol G4560, MI=1.5 g/10 min), was provided by ire chemical
LTD., Korea. The vapor grown carbon nanofibers called CNF-100 were
obtained from Carbon nano-material technology Co., LTD., Korea.
CNFs have the herringbone structure, and the diameter ranged from
40 to 140 nm and the typical length of 2~10 μm. Chloroform, used as a
solvent in solution blending which was one of the preparation methods
for PBS/CNFs nanocomposite, was supplied by Dongyang chemical,
Korea. The chemical blowing agent (CBA) used was Cellecom ACP-4
grade which was obtained by Kumyang Co., Korea. It consists of a
compound with a specific proportion of azodicarbonamide, N,N'-
dinitrosopenta tetramine, and urea activator.
2. 2. Nanocomposite preparation
To compare the dispersion degree of CNFs in the PBS matrix, we
used three preparation methods such solution blending, melt mixing
and the SOAM method (solution blending and subsequent melt
mixing) [9] , respectively. PBS resin and CNFs were initially dried in
29

vacuo at 60 ºC for 6 h to remove any residual H2O. For solution
blending, PBS pellets were dissolved and stirred in chloroform at 40 ºC
for 5 h using mechanical stirrer. Also, CNFs were dispersed in same
solvent at room temperature for 3 h with spin-bar and then sonicated
for 2 h at 90 W by a ultrasonic bath (Kodo Technical Research Co.,
Japan). After CNFs solution was mixed with PBS solution at 40 ºC for
24 h under vigorous shear condition, nanocomposite casting films were
obtained on rotary hood, and additionally dried at 60 ºC for 24 h to
remove a solvent. For the melt blending, the torque rheometer
(Brabender Plastograph EC, Germany) was used to prepare the PBS
nanocomposite based on a various content of CNFs. The PBS pellets
was melted at 120 ºC for 5 min at a rotary speed of 60 rpm, and then
CNFs were introduced into the mixer, followed by compounding for 10
min. For the SOAM method, the casting films prepared by the solution
blending were firstly cut into the specific size, and then fed into the
torque rheometer and mixed at 120 ºC for 10 min at a rotary speed of
60 rpm. The mass fraction of CNFs ranged from 0.1 to 3 wt%. The
sample codes were named, for example, CNF2S, CNF2M and
CNF2SM, where the numbers represent the mass fraction of CNFs,
30

and the ‘S’ stand for solution blending, ‘M’ for melt mixing, and ‘SM’ for
the SOAM method.
2. 3. Foaming
After the dried solution casting films with different content of CNFs
were fed into the torque rheometer and mixed at 120 ºC for 10 min at a
speed of 60 rpm, ACP-4 varied from 4 to 8 phr was added to the
brabender and subsequently melt-compounded for 10 min. The
samples of the strip type (dimensions 12 mm × 20 mm × 3 mm)
were obtained by using the heating press at 135 ºC for 8 min. Then,
the nanocomposite foams were prepared in forced convection oven at
150, 160 and 170 ºC for 5, 10, 20 and 30 min on the Teflon film.
2. 4. Characterization of nanocomposites and their foams
The thermal gravimetric analysis (TGA) was performed on a TA
Instruments Q50 under air atmosphere using a heating rate of 20
ºC/min from room temperature to 700 ºC. The tensile strength and
elongation at break of nanocomposites were measured by using
Hounsfield Test Equipment at room temperature with the dog-bone
samples. The strain rate was 26 mm/min, and seven measurements
31

were at least performed for each nanocomposite. The dispersion of
CNFs in the PBS matrix was compared by field emission scanning
electron microscopy (FE-SEM) using Hitachi S4300 at 15 kV. The
surface morphology of nanocomposite foams was examined by an
optical microscopy using Sometech i-Camscope. The density of
nanocomposite foams was measured by using Micrometrics Co.
Accupyc 1330 gas pycnometer.
32

3. Results and discussion
Typical TGA thermograms of PBS/CNFs nanocomposites obtained
from different three approaches are given in Figure 1. The introduction
of CNFs with high thermal resistance into the PBS matrix caused the
enhancement of thermal stability in given CNFs content as compared
to the virgin PBS judging from Figure 1(a) and 1(b). The relative
thermal properties of PBS/CNFs nanocomposites were evaluated by
comparing both T95(temperature for 5% weight loss) and
T50(temperature for 50% weight loss) values (Table 1). In general,
PBS/CNFs nanocomposties produced by the SOAM method showed
much higher thermal stability than those produced by solution blending
and melt mixing. Also, PBS nanocomposite with 2 wt% loading of
CNFs prepared by the SOAM method particularly exhibited the highest
T50 value(409 ºC). Therefore, it could be thought that the SOAM
method was the effective way in order to provide a homogenous
dispersion of CNFs in the PBS matrix.
Figure 2 shows the variation of tensile strength and elongation at break
for neat PBS and PBS/CNFs nanocomposites as a function of CNF
loading. As shown in Figure 2(a), tensile strength of the
33

nanocomposites enhanced greatly with the addition of CNFs, and the
CNFs content at maximum tensile strength was only 2 wt% regardless
of the preparation methods. These results are due to the physical
interaction between the PBS matrix and reinforced-CNFs with high
mechanical property, and more uniform dispersion at the 2 wt%
loading of CNFs. However, the tensile strength of nanocomposites
slightly started to decrease after 2 wt%, which attributed to the
aggregation of CNFs in the PBS matrix. It was also found that
nanocomposites prepared by the SOAM method showed relatively
higher tensile strength than those of the other preparation methods.
As the CNFs content increased, the slight decrease in the elongation
at break was observed as indicated in Figure 2(b). This variation was
resulted in part from the modifications in crystalline fraction of the PBS
matrix as more CNFs added. It thus is believed that the CNFs led to a
decrease in ductility and an increase in brittleness.5 In addition, we
can found that the decrease in the elongation at break was less in
nanocomposite obtained from the SOAM method than in those of two
other preparation methods.
The relative state of dispersion of CNFs inside the PBS matrix was
compared by scanning electron microscopy (SEM) as presented in
34

Figure 3, respectively. Figure 3a shows that in nanocomposite
produced by solution blending, individual CNFs were locally
aggregated in the polymer matrix(in circle symbol), and several voids
attributed to a solvent were observed. In the case of nanocomposite
obtained from melt mixing, several CNFs, as shown by arrow in Figure
3b, were pulled out from the PBS matrix during the cryo-fracture,
indicating the poor polymer-CNFs wettability. In contrast, it was found
that not only the majority of CNFs were well-dispersed throughout the
polymer matrix, but also broken rather than being pulled out as
indicated by arrow in Figure 3c. The breakage of CNFs was as a result
of the strong interfacial adhesion between the polymer and CNFs
which acts as a key factor to produce a remarkable mechanical
property. It was also confirmed that the SOAM method plays an
important role to separate the CNFs into individual nanofibers well in
the PBS matrix. Consequently, we believed that the PBS
nanocomposite with 2 wt% CNFs loading fabricated by the SOAM
method was an ideal candidate to make a high performance-
nanocomposite foam by analyzing their thermal and mechanical
properties.
Cross-sectional morphology of nanocomposite foams expanded at 4
35

phr CBA loading was observed via optical microscopy as shown in
Figure 4. All samples showed the oval shape and homogeneous
closed-cell structure. In other words, each cell is surrounded by
connected faces with any ruptures. CBA started to decompose at
temperature higher than 135 ºC and released a gas in the
nanocomposite system, which can cause the bubble nucleation and
growth from the surface of CNFs used as a nucleant. [10,11] In addition,
to achieve the closed-cell system, the nanocomposite should have a
sufficient melt viscosity and strength not so as to break the cell wall. [12]
It thus can be thought that the presence of CNFs served as the
efficient nucleation sites, as well as contributed to produce a closed-
cell structure in foaming process. We also found that the average cell
size was prominently increased as the blowing time and temperature
increased. These two conditions facilitate the decomposition of blowing
agent.
In Table 2, we summarized the morphological parameters of PBS/2
wt% CNFs nanocomposite foaming for 5 min. Average cell size (d) was
calculated by measuring the maximum diameter of each cell
perpendicular to the skin from an OM micrograph, and cell density (Nc)
and mean cell-wall thickness (δ) are given by
36

N
c
=
1-
( ρ / ρ )
10
f
−4
d
p
3
and ⎟ ⎟
⎛
⎞
⎜ 1
δ = d
− 1
⎜
⎝
1−
( ρf
/ ρ p )
⎠
where ρp, ρf, and d are the pre-foamed density, the post-foamed
density in g/cm 3 , and the average cell size in mm, respectively. [13-15]
It was found that the neat PBS density was 1.26 g/cm3, but the post-
foamed density of nanocomposite foam decreased from 0.980 to 0.508
g/cm 3 with increasing the blowing temperature and CBA content. Also,
average cell size increased as the blowing temperature and CBA
loading increased, indicating that the high blowing temperature makes
it easier for the CBA to be decomposed in foaming duration, and the
addition of CBA determines the size and number of bubbles in a
nanocomposite melt. Moreover, we obtained the maximum value of cell
density especially at 6 phr of CBA content at each temperature,
suggesting the existence of a lot of bubbles in the same area. The
mean cell-wall thickness showed a tendency to decrease gradually
according to the further bubble growth.
Figure 5 represents the blowing ratio of PBS/2 wt% CNFs
nanocomposite foams as a function of the blowing temperature, time,
and CBA content. The blowing ratio was calculated as follows: [16]
37

3
the density of neat PBS (1.268 g/cm )
ratio =
the density of PBS/CNFsnanocomposite
foam (g/cm
Blowing 3
We can see that the increase of the blowing temperature, time, and
CBA content led to the blowing ratio increase. The maximum values of
the blowing ratio at 4, 6, and 8 phr CBA content were 5.028, 7.813,
and 12.025, respectively. It is also believed that the inter-relationship of
above foaming conditions plays a key role to determine the blowing
ratio.
The blowing temperature dependence on the cell size distribution of
PBS/2 wt% nanocomposite foams is represented in Figure 6. We
measured the size of more than 75 cells in fractured surface from the
OM micrograph. It is evident that the CNFs-reinforced nanocomposite
foams almost were in accordance with a Gaussian distribution. When
increasing the blowing temperature, the broad cell size distribution was
examined, indicating that the dispersity of the cell size is much larger.
Also, it was found that the presence of CNFs acted as an efficient
nucleation agent, and well-controlled the cell size accordingly.
38
)

4. Conclusions
Using a chemical blowing agent, PBS/CNFs nanocomposite foams
with a closed-cell structure and high blowing ratio was successfully
obtained. It was found that to produce the high performance-
nanocomposite foams, the optimal CNFs content was 2 wt%, and the
SOAM method was an effective way to disperse the CNFs in the PBS
matrix based on the enhancement of thermal and mechanical
properties for the nanocomposites. In foaming process, when the
decomposition of CBA occurred in a nanocomposite melt, well-
dispersed CNFs acted as the efficient nucleation sites in the PBS
matrix-CNFs interface. Nanocomposite foams exhibited the oval-shape
and the homogeneous closed-cell structures without any ruptures. A
high blowing ratio of about 12 was obtained at 170 ºC for 30 min, as
well as a uniform cell size distribution of nanocomposite foams
observed.
39

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[15] S. S. Ray and M. Okamoto, Macromol. Mater. Eng. 288, 936
(2003)
[16] L. T. Guan, M. Xiao, and Y. Z. Meng, Polym. Eng. Sci. 46, 153
(2006)
41

SECTION I. Processing of Poly(butylene succinate)(PBS)/Carbon
Nanotube Nanocomposite Foams
Table 1 Morphological parameters of PBS/2 wt% MWNTs
nanocomposite foam obtained by the SOAM method (blowing time = 5
min).
Blowing
temperature/ o C
CBA
content/phr
ρf/g·cm -3 d/μm
42
Nc × 10 -5
/cell·cm -3
δ/μm
4 0.767 154.72 10.67 91.422
150 6 0.690 207.87 5.82 79.955
8 0.616 230.73 4.50 79.582
4 0.607 200.82 5.63 96.622
160 6 0.525 231.61 4.72 70.954
8 0.397 249.75 3.95 69.896
4 0.567 234.50 3.99 95.523
170 6 0.487 320.88 2.08 66.282
8 0.344 406.30 1.09 69.660

SECTION II. Preparation and Characterization of PBS/Carbon
Nanofiber Nanocomposite Foams
Table 1 Thermal stability for PBS/CNFs nanocomposites.
Preparation
method
Solution
blending
Melt
mixing
SOAM
method
CNFs content (wt%) T95 ( o C) T50 ( o C)
0.1 346 408
0.5 325 405
1 325 404
2 327 405
3 349 405
0.1 344 400
0.5 352 404
1 340 400
2 355 406
3 343 403
0.1 350 407
0.5 352 406
1 355 402
2 353 409
3 352 404
43

Table 2 Temperature and CBA content dependence of morphological
parameters.
Blowing
temperature/ o C
CBA
content/phr
ρf/g·cm -3 d/μm
44
Nc × 10 -5
/cell·cm -3
δ/μm
4 0.980 109.30 17.40 120.041
150 6 0.792 119.18 22.18 75.337
8 0.702 148.62 13.60 73.826
4 0.912 126.36 13.91 112.119
160 6 0.748 135.51 16.48 76.099
8 0.716 161.66 10.30 83.356
4 0.860 163.54 7.36 124.764
170 6 0.671 171.97 9.26 78.655
8 0.508 207.23 6.74 60.445

SECTION I. Processing of Poly(butylene succinate)(PBS)/Carbon
Nanotube Nanocomposite Foams
Figure 1 FT-Raman spectra of the PBS nanocomposites with 2 wt%
content prepared by three different methods: (a) MWNT (b) solution
blending (c) melt mixing and (d) SOAM method.
45

Figure 2 SEM images of the PBS nanocomposites with 2 wt% content
prepared by three different methods: (a) solution blending (b) melt
mixing (c) SOAM method, and (d) TEM micrograph of the 2 wt%
PBS/MWNTs nanocomposites prepared by SOAM method.
46

Figure 3 TGA thermograms of the PBS nanocomposites containing
various MWNTs content prepared by the SOAM method.
47

Figure 4 DSC traces of the PBS nanocomposites containing various
MWNTs content prepared by the SOAM method: (a) melting and (b)
crystalline behaviors.
48

Figure 5 Tensile strength and elongation at break curves of the PBS
nanocomposites with various MWNTs content prepared by three
different methods.
49

Figure 6 Optical micrographs of PBS nanocomposite foams with 2
wt% MWNTs content prepared by the SOAM method as a function of
blowing temperature and CBA content. The blowing time was fixed at 5
min.
50

Figure 7 Cell size distribution of PBS nanocomposite foams with 2
wt% MWNTs content prepared by the SOAM method at 150 o C: (a) 4
(b) 6 and (c) 8 phr. The blowing time was fixed at 5 min.
51

Figure 8 Blowing ratio of PBS nanocomposite foams with 2 wt%
MWNTs content prepared by the SOAM method as a function of
blowing time and temperature and CBA content: (a) 4 (b) 6 and (c) 8
phr.
52

SECTION II. Preparation and Characterization of PBS/Carbon
Nanofiber Nanocomposite Foams
Figure 1 TGA thermograms of PBS/CNFs nanocomposites by means
of different preparation methods.
53

Figure 2 The effect of CNFs content and different preparation methods
on the (a) tensile strength and (b) elongation at break.
54

Figure 3 SEM images of PBS/2 wt% CNFs nanocomposite prepared
by (a) solution blending (b) melt mixing and (c) SOAM method.
55

Figure 4 The effect of blowing time and temperature on the cross-
sectional cell morphology of PBS/2 wt% CNFs nanocomposite foams
measured by the optical microscope. CBA content was fixed at 4 phr.
56

Figure 5 Blowing temperature and time dependence on the blowing
ratio of PBS/2 wt% CNFs nanocomposite foams with different CBA
loading: (a) 4 (b) 6 and (c) 8 phr.
57

Figure 6 Cell size distribution of the PBS/2 wt% CNFs nanocomposite
foams as a function of the blowing temperature: (a) 150 (b) 160 and (c)
170 o C. The blowing time and CBA content were fixed for 5 min and at
4 phr, respectively.
58