Preparation and properties of starch-based film using N,N-bis(2-hydroxyethyl)formamide as a new plasticizer

Article abstract of DOI:10.1016/j.carbpol.2009.08.012

N,N-Bis(2-hydroxyethyl)formamide (BHF) was synthesized efficiently and used as a new plasticizer for corn starch to prepare flexible starch film. The hydrogen bond interaction between BHF and starch was proven by Fourier-transform infrared (FT-IR) spectroscopy. By scanning electron microscope (SEM), starch granules were completely disrupted and a continuous phase was obtained. The crystallinity of corn starch and BHF-plasticized starch film (BSF) was characterized by X-ray diffraction (XRD). The water resistance of BSF was better than that of glycerol-plasticized starch film (GSF). Water vapor permeability of BSF was lower than that of GSF. Tensile strengths of BSF were inferior to those of GSF, while the elongations at break of BSF were higher than those of GSF.

Full text of DOI:10.1016/j.carbpol.2009.08.012

Carbohydrate Polymers 79 (2010) 306–311
Contents lists available at ScienceDirect
Carbohydrate Polymers
journal homepage: www.elsevier.com/locate/carbpol
Preparation and properties of starch-based film using
N,N-bis(2-hydroxyethyl)formamide as a new plasticizer
Hongguang Dai , Peter R. Chang , Fengying Geng , Jiugao Yu a,*, Xiaofei Ma a
a
b,c
a
a
School of Science, Tianjin University, Tianjin 300072, PR China
Agriculture and Agri-Food Canada, Biobased Platforms, 107 Science Place, Saskatoon, SK, S7N 0X2, Canada
Department of Agricultural and Bioresource Engineering, University of Saskatchewan, Saskatoon, SK, S7N 5A 9, Canada
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
N,N-Bis(2-hydroxyethyl)formamide (BHF) was synthesized efficiently and used as a new plasticizer for
corn starch to prepare flexible starch film. The hydrogen bond interaction between BHF and starch
was proven by Fourier-transform infrared (FT-IR) spectroscopy. By scanning electron microscope
Received 16 September 2008
Received in revised form 23 July 2009
Accepted 6 August 2009
(SEM), starch granules were completely disrupted and a continuous phase was obtained. The crystallinity
Available online 12 August 2009
of corn starch and BHF-plasticized starch film (BSF) was characterized by X-ray diffraction (XRD). The
water resistance of BSF was better than that of glycerol-plasticized starch film (GSF). Water vapor perme-
ability of BSF was lower than that of GSF. Tensile strengths of BSF were inferior to those of GSF, while the
elongations at break of BSF were higher than those of GSF.
Keywords:
N,N-Bis(2-hydroxyethyl)formamide
New plasticizer
Ó 2009 Elsevier Ltd. All rights reserved.
Starch film
1
. Introduction
properties of films. In views of the application and development of
starch film, it is very important to prepare a low cost and nontoxic
Over the past few years, there has been a renewed interest in
film made from renewable and natural polymers such as starch
Mali, Grossmann, Garcia, Martino, & Zaritzky, 2002; Mathew &
Abraham, 2008). Several studies have analyzed the properties of
starch-based films. Edible or biodegradable films are not meant
to totally replace synthetic packaging films; however, they do have
the potential to replace the conventional packaging in some appli-
cations. Starch is quite cheap, abundant, biodegradable, and edible
plasticizer, which is used to produce film with desirable properties.
In basic research, the preparation of new plasticizers is also necessary
to study the relationship of plasticizers structure and film properties
(Tarvainen, Sutinen, Somppi, Paronen, & Poso, 2001).
N,N-Bis(2-hydroxyethyl)formamide (BHF) is one of hydrox-
yalkylformamides that serve as physiologically harmless humidifi-
ers for cosmetics (Coupland & Smith, 1986) or for the impregnation
of tire-cord made from nylon (Kibler & Richard, 1973). Many syn-
thetic methods for preparation of BHF have been reported. How-
ever, some of these methods have drawbacks such as high
pressure (Ricci, Sbrana, & Braca, 1991), and use of much methanol
as solvent (Frings & Grahe, 1992).
In this paper, an efficient and practical method is used to syn-
thesize BHF without any solvent. As a new plasticizer, BHF is used
to prepare BHF-plasticized starch film (BSF). Glycerol is commonly
used as a plasticizer of starch film. Here glycerol-plasticized starch
film (GSF) is regarded as the contrast. This work is focused on pro-
cessing and characterization of BSF in terms of FT-IR, morphology,
XRD, water vapor absorption, water vapor permeability and
mechanical properties.
(
(Alves, Mali, Beleia, & Grossmann, 2007). Starch is polysaccharide
composed of amylose, a linear or sparsely branched polymer, and
amylopectin, a highly branched polymer.
The properties of starch film can be modified by the addition of
various chemicals in minor amounts. For example, plasticizers,
such as glycerol and sorbitol are often used to modify the mechan-
ical properties of the film. These compounds decrease intermolec-
ular attractions between adjacent polymeric chains, thus
increasing film flexibility. Incorporation of these additives may,
however, cause significant changes in the barrier properties of
the film (Rodriguez, Oses, Ziani, & Mate, 2006).
In mostliteraturefor starchfilm, polyols asplasticizers usually are
used such as glycerol, sorbitol, ethylene glycol (Lourdin, Coignard,
Bizot, & Colonna, 1997). Urea can be used as plasticizer for starch film
2
. Experimental
(Lourdin et al., 1997). However, the properties of starch film do not
reach what people expect. The type of plasticizer influences the
2.1. Materials
Corn starch (7.62% moisture) was obtained from the
*
Corresponding author. Tel.: +86 22 27406144; fax: +86 22 27403475.
E-mail address: tjusmd@yahoo.com.cn (J. Yu).
Langfang Starch Company (Langfang, Hebei, China). Glycerol,
0
144-8617/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carbpol.2009.08.012

H. Dai et al. / Carbohydrate Polymers 79 (2010) 306–311
307
diethanolamine and ethyl formate (analytical grade) were pur-
chased from Tianjin Chemical Reagent Ltd. (Tianjin, China).
2.5. Scanning electron microscopy (SEM)
Corn starch and the fracture surfaces of the BSF samples were
investigated with the scanning electron microscope Phillips XL-3
(FEI Company, Hillsboro, OR, USA), operating at an acceleration
voltage of 20 kV.
Starch powders were suspended in acetone. The suspension
drops were drawn on the glass slide, dried for removing the ace-
tone, and then vacuum-coated with gold for SEM. The conditioned
BSF samples were cryo-fractured in liquid nitrogen. The fracture
faces were vacuum-coated with gold for SEM.
2
.2. Synthesis of N,N-bis(2-hydroxyethyl)formamide
One mole diethanolamine was introduced into a 500 mL flask
equipped with a stirrer, a reflux condenser, a dropping funnel
and a thermometer, it was cooled to 27 °C in an ice bath and then
1
mol ethyl formate was added during 30 min. The temperature in
the flask rose to 30 °C. The reaction mixture was stirred for 1 h at
0 °C by monitoring with thin layer chromatography (TLC). Then
the byproduct ethanol evaporated under reduced pressure at
0 °C until ethanol was not distilled from the mixture again. Sub-
6
2.6. X-ray diffraction (XRD)
6
sequently the mixture was cooled to 27 °C in an ice bath, followed
by addition of 0.05 mol ethyl formate. The reaction mixture was
stirred for 0.5 h at 60 °C, and then the byproduct ethanol evapo-
rated under reduced pressure at 60 °C until ethanol was not dis-
tilled from the mixture again. The residue was cooled to 27 °C in
an ice bath, followed by addition of 0.05 mol ethyl formate. The
reaction mixture was stirred for another 0.5 h at 60 °C, heated un-
der reduced pressure at 110 °C until the mass of the liquid was
constant. A viscous liquid was gotten. The purity was 97% accord-
ing to the column chromatography on neutral aluminum oxide
The starch films were placed in a sample holder for X-ray dif-
fractometry. The corn starch powders were packed tightly in the
sample holder. X-ray diffraction patterns were recorded in the
reflection mode at an angular range of 10–30° (2h) at the ambient
temperature by a Rigaku D diffractometer (Japan) operated at the
Cu/K
a radiation.
2
.7. Water vapor absorption
Measurement of water contents of new GSF, BSF and
plasticizers.
The pieces of films were cut into small pieces and the pieces
weighed immediately. They were then dried in an oven at 105 °C
overnight and weighted. The original water content (k) of starch
film was calculated as follows:
(
200–300 mesh) eluted with mixture of dichloromethane and
methanol. The yield of BHF was 97%. The product was confirmed
1
by H NMR, IR, MS. The chemical reaction equation was shown in
Fig. 1.
1H NMR spectra were measured on a VARIAN INOVA 500 MHz
3 3
spectrometer using TMS as internal standard and CD SOCD as sol-
w
2
ꢀ w
1
vent. The IR spectra were recorded with a BIO-RAD FTS3000 IR
spectrometer (KBr). Mass spectra were determined on an LCQ
Advantage MAX spectrometer (ESI).Data for N,N-bis(2-hydroxy-
k ¼
ꢁ 100%
ð1Þ
w
1
Here w (g) was the mass of the dried sample and w (g) the mass of
1
2
ethyl)formamide:
m
max (KBr): 3461–3332 (OH), 2943 (–CH
2
–),
, d ppm):
.950 (s, 1H, HCON), 4.738 (t, 1H, J = 5.5 Hz, –OH), 4.701 (t, 1H,
O–), 3.305–3.264 (m,
the sample before drying.
ꢀ1
1
2
7
886 (–CH
2
–), 1659 (C@O) cm
;
H NMR (CD
3
SOCD
3
Glycerol and BHF were stored in a closed container in the pres-
ence of distilled water (providing relative humidity (RH) 100%) at
20 °C and weighed. According to the Eq. (1) above-mentioned,
the water content of plasticizer was calculated. w2 and w1 were
the mass of plasticizer containing water and pure plasticizer,
respectively. The data were averages of 3 specimens.
J = 5.5 Hz, –OH), 3.475–3.439 (m, 4H, –CH
2
+
+
4
2
H, –CH N); m/z (%): 134 (MH , 100), 156 (MNa , 8.1).
2.3. Starch film preparation
Measurement of water contents of bars of GSF and BSF stored at
different relative humidities (RHs) for a period.
Films were obtained by the casting method. Starch and plasti-
The pieces of GSF and BSF were stored in closed containers in
cizer were first mixed and dispersed in water. The mixture con-
tained 5 g of starch/100 g of water and 25, 30, 35 g of
plasticizer/100 g of starch. The film-forming suspension was
heated with continuous stirring and kept at 85 °C for 30 min.
The film-forming solution was casted on a polystyrene plate.
Starch-based films were obtained by evaporating water in an
oven at 50 °C.
the presence of different compounds, namely, a saturated MgCl
solution, a saturated K CO solution, a 35.64% CaCl solution, a sat-
urated CuCl solution, a saturated NaCl solution and a saturated
NH SO solution (providing RHs of 33%, 44%, 50%, 68%, 75
and 80%, respectively) at 20 °C (Godbillot, Dole, Joly, Rogé, &
Mathlouthi, 2006; Ma & Yu, 2004). The samples were weighed
every day. Equilibrium was reached when three consecutive daily
weighing were constant (±1 mg/day) (Quirijins, van Boxtel, van
Loon, & van Straten, 2005; Raj, Raj, Madan, & Siddaramaiah,
2
2
3
2
2
(
4
)
2
4
2.4. Fourier-transform infrared (FT-IR) spectroscopy
2
003). The water contents of GSF and BSF at different RHs were cal-
culated on the base of mass of dried GSF and BSF. The data were
averages of 3 specimens. Equilibrium formulae of water vapor
absorption of GSF and BSF were obtained by fitting the data in Ori-
gin 6.1 software.
The IR spectra were measured with a BIO-RAD FTS3000 IR Spec-
trum Scanner (Hercules, CA, USA). The starch films were measured
in reflection mode.
2.8. Water vapor permeability (WVP)
OH
OH
OH
OH
O
Granular anhydrous CaCl was used as a desiccant in a cylindri-
2
cal bowl that was covered with the studied films attached with
tape to the bowel. The distance between the surface of the desic-
cant and the film was about 3 mm, as suggested by National stan-
dard of China GB1037-88. The thickness of each film was measured
with a micrometer (accuracy of 0.01 mm) at six randomly selected
2
HCOOC H5
+
HN
HC
N
+
C H OH
2
5
Fig. 1. Chemical reaction equation of synthesizing N,N-bis(2-hydroxyethyl)formamide.

3
08
H. Dai et al. / Carbohydrate Polymers 79 (2010) 306–311
points before the film was attached to the bowel. The bowel was
placed in a disiccator at a RH of 75%, resulting in relative vapor
pressures gradient of 0/75% across the film at 20 °C. The progress
of water vapor permeation was determined gravimetrically as a
function of time for 7 days. The bowl was shaken horizontally
of the C–O–H group in starch. The characteristic peaks at 1082
ꢀ1
and 1029 cm
were attributed to C–O bond stretching of the
C–O–C group in the anhydroglucose ring of starch (Fang, Fowler,
ꢀ1
Tomkinson, & Hill, 2002). The peak wavenumber 3396 cm was
attributed to starch O–H bond stretching. In BSF, all the peaks
shifted to lower wavenumbers, for example, the peaks 1157 and
ꢀ1
ꢀ1
ꢀ1
after every weighing. WVP (g m
Eq. (2), where m was the weight of the water permeated
through the film, d was the thickness of the film, A was the per-
meation area of the film, t was the time of permeation and
s
Pa ) was calculated with
ꢀ1
ꢀ1
ꢀ1
D
1082 cm in starch shifted to 1150 cm and around 1076 cm
in BSF, respectively.
D
p
The analysis of FT-IR spectra of the blends enabled the hydro-
gen bond interactions to be identified (Aoi, Takasu, Tsuchiya, &
Okada, 1998). Hydrogen bonds between plasticizer and starch
are directly related to the wavenumber shift of the stretching
bands of functional groups in starch. The lower the peak wave-
number is, the stronger the interaction is (Pawlak & Mucha,
was the water vapor pressure difference between both sides of
the film. WVP was given in SI units. The tests were carried out
in triplicate.
D
A ꢂ t ꢂ
m ꢂ d
WVP ¼
ð2Þ
D
p
2
003). All these results indicated that stronger hydrogen bonds
were formed between BHF and starch compared with intra- and
intermolecular hydrogen bonds in starch. FT-IR spectra had been
analyzed, because of the groups –O–H and –CO–N in BHF, stable
hydrogen bonds were formed between BHF and starch, which
could weaken the intra- and intermolecular hydrogen bonds in
starch.
2
.9. Mechanical testing
Mechanical testing (National standard of China GB1040-79) of
samples was determined in the AX M350-10KN Materials Testing
Machine (Testometric, Rochdate, UK) at a crosshead speed of
1
0 mm/min. The data were averages of 5 specimens.
3.2. Scanning electron microscopy (SEM)
3
. Results and discussion
The morphology of starch and the BSF was shown in Fig. 3.
Compared with starch granules, BSF formed a continuous phase.
According to the gelatinization mechanism, starch granules swol-
len and broken into pieces with releasing amylose and amylopectin
molecules into solution during heat treatment of starch dispersion.
Fig. 3 showed that there was no starch granules and remnant pre-
senting in the film at the present of BHF. This meant the starch
polymer was solubilized completely.
3
.1. FT-IR analysis
The wavenumber shift of stretching vibrations of corn starch
could be observed in Fig. 2 (corn starch and BSF). The peak
wavenumber 1157 cm was ascribed to the C–O bond stretching
ꢀ1
b
c
d
During the gelatinization of the starch granules, amylose and
amylopectin molecules released into the solution. According to
Liu and Han (2005), without plasticizers, amylose and amylopec-
tin would form a film with a biphasic structure, which had an
amylose-rich phase and an amylopectin-rich phase. The network
of amylose-rich clusters was embedded in the amylopectin-rich
amorphous background. The interactions between the amylose
and amylopectin molecules contributed to the film formation,
but were so strong that the starch films were readily brittle and
rigid. According to the analysis of FT-IR above-mentioned, the
plasticizers in the starch films could form hydrogen bonds with
starch molecules, which weakened the strong action of starch
intermolecular and intramolecular hydrogen bonds, and then re-
duce the interaction between amylose and amylopectin molecules
making the starch film flexible. No pores or cracks were detected
by SEM observations. SEM observations of films with different
plasticizer contents did not show structural differences.
1
150
150
1
078
076
1
1018
018
1
a
1
1
150
1
076
a corn starch
b 25% BHF
c 30% BHF
d 35% BHF
1
018
1
157
1
082
1
029
1000
1
200
1150
1100
1050
950
900
-
1
Wavenumber (cm )
b
c
3.3. X-ray diffraction analysis (XRD)
3
307
The X-ray diffraction patterns of corn starch and BSF exposed
d
to the air (The RH was around 50%) for 7 days were shown in
Fig. 4. Compared with starch, the crystal structure of BSF changed.
During the gelatinization of the starch granules, A-type crystallin-
ity of corn starch (Fig. 4, line a) disappeared. According to Bergo
et al. (2008), starch films could have an amorphous character be-
cause the thermal treatment of film-forming suspension provoked
starch gelatinization, causing disruption of the double helix con-
formations of corn starch, however, the plasticizer BHF in the
films may have increased the macromolecular mobility, allowing
the formation of microcrystalline junctions, i.e. some re-crystalli-
a
3
284
278
3
a corn starch
b 25% BHF
c 30% BHF
d 35% BHF
3
3400
396
3
800
3600
3200
3000
2800
-
1
Wavenumber (cm )
zation occurred. V
H
-type crystallinity was formed (Fig. 4, line c)
Fig. 2. FT-IR spectra of corn starch and BSF.
(van Soest, Hulleman, de Wit, & Vliegenthart, 1996).

H. Dai et al. / Carbohydrate Polymers 79 (2010) 306–311
309
Fig. 3. SEM micrograph of (A) corn starch, (B) BSF containing 25% BHF, (C) BSF containing 30% BHF, (D) BSF containing 35% BHF.
stored at RH 68% for 7 days were 19.1%, 20.4%, 21.3% and 14.3%,
a corn starch
b 25% BHF
c 30% BHF
d 35% BHF
1
3
4.7%, 15.8% (corresponding to the plasticizer contents 25%, 30%,
5%), respectively. The water resistance of BSF was better than that
AA
of GSF. With increasing BHF content, the water resistance of BSF
became worse at high RH.
A
In the opinion, the hydrophilicity of plasticizer was related to
water resistance of starch film. As shown in Fig. 5B, under the same
conditions, water vapor absorption of glycerol was higher than that
of BHF, so glycerol was more hydrophilic than BHF. The water
resistance of BSF was better than that of GSF.
A
a
b
c
d
VH
VH
3.5. Water vapor permeability
10
15
20
25
30
Diffraction angle (2θ)
WVP were examined. As shown in Fig. 6, WVP increased as the
concentration of plasticizer increased in the range of plasticizer
content studied. These results could be related to structural mod-
ifications of the starch network produced by the plasticizer and to
the hydrophilic character of plasticizer, which favored the absorp-
tion and desorption of water molecules. Plasticizers reduced intra-
and intermolecular forces in starch. Plasticizers extended, diluted
and softened the structure effectively, the starch chain mobility
was increased. Plasticizer caused a greater flexibility in polymeric
structure, which increased water sorbed mobility within the
structure. As a result WVP increased with film plasticizer content
(Bertuzzi, Castro Vidaurre, Armada, & Gottifredi, 2007). For
example, the WVP of GSF containing 25%, 30%, 35% of plasticizer
Fig. 4. Diffractograms of corn starch and BSF exposed to the air for 7 days.
3
.4. Water vapor absorption
Starch film was sensitive to humidity, the influence of which on
the properties of starch film was important. BET and GAB model
were usually used to describe the water vapor absorption iso-
therms. Peleg defined a new sorption isotherm model based on four
ꢀ
ꢁ
ꢀ ꢁ
n
1
n
2
p
p
parameters: M ¼ k
1
þ k
2
1 1 2 2
, k , n , k , n were constants.
p
0
p
0
Although the parameters used in the Peleg model did not have fun-
damental meaning, it was a precise model to predict sorption iso-
therms, due to its four fitting parameters. Therefore, the Peleg
model had been successfully applied to many food systems for rel-
ative humidity of up to 95%. The Peleg model represented an alter-
native to the classic BET and GAB models. It could be used to
accurately represent sorption isotherms due to the presence of an
extra parameter in the equation. The drawback of using this model
was the lack of theoretical background in its development, and thus
it did little to improve the fundamental understanding of the differ-
ences in sorption behavior (Enrion, Hill, & Mitchell, 2007).
ꢀ12
ꢀ11
ꢀ11
ꢀ1 ꢀ1
ꢀ1
were 9.18 ꢁ 10 , 1.62 ꢁ 10 , 1.93 ꢁ 10
g m
s
Pa , res-
pectively.
The WVP of BSF were lower than those of GSF. For example, the
ꢀ
12
ꢀ1 ꢀ1
ꢀ1
WVP of BSF containing 25% BHF was 8.19 ꢁ 10
g m
s
Pa ,
while the WVP of GSF containing 25% glycerol was 9.18 ꢁ
ꢀ12
ꢀ1 ꢀ1
ꢀ1
10
g m
s
Pa . In the opinion, the hydrophilicity of plasti-
cizer was related to WVP of TPS. As shown in Fig. 5B, under the
same conditions, water vapor absorption of glycerol was higher
than that of BHF, so glycerol was more hydrophilic than BHF. GSF
was more hydrophilic than BSF. At the same experimental condi-
tions, GSF absorbed more water molecules than BSF. CaCl2 was
far more hydrophilic than both GSF and BSF. At the present of
CaCl , GSF containing more water lost more water to CaCl com-
In the paper, Peleg model was used to describe the relationship
of starch film water content and RH. The parameters for the sorp-
tion models for GSF and BSF were shown in Table 1. As shown in
Fig. 5, at the same RH, the balance water content of GSF was larger
than that of BSF. The highest balance water contents of GSF and BSF
2
2
pared with BSF. So the WVP of GSF was higher than that of BSF.

3
10
H. Dai et al. / Carbohydrate Polymers 79 (2010) 306–311
Table 1
Estimated values of coefficients obtained for Peleg sorption model applied to experimental absorption data for starch film.
Constant
25% glycerol
30% glycerol
35% glycerol
25% BHF
30% BHF
35% BHF
k
n
1
0.27304
1.07335
1.46647
14.08471
0.30505
1.16609
3.92872
18.30166
0.30716
1.04563
13.52489
23.40733
0.24339
1.44902
2.09851
18.36024
0.2399
1.33088
1.6765
0.26306
1.36757
10.59034
24.83634
1
k
2
n
2
16.84981
A
0.35 a 25% glycerol
c
A
16
14
12
10
8
25% glycerol
b 30% glycerol
c 35% glycerol
30% glycerol
35% glycerol
25% BHF
30% BHF
35% BHF
b
0
0
0
0
0
0
0
.30
a
.25 d 25% BHF
f
e 30% BHF
f 35% BHF
e
.20
d
.15
.10
.05
.00
6
4
2
-
0.05
0
0
.0
0.2
0.4
0.6
0.8
33%
44%
50%
68%
RH
RH
9
8
7
6
5
4
3
2
1
0
0
0
0
0
0
0
0
0
0
160
150
140
25% glycerol
B
B
a glycerol
b BHF
3
3
0% glycerol
5% glycerol
a
b
1
1
1
1
30
20
10
00
25% BHF
3
3
0% BHF
5% BHF
9
8
7
6
5
4
0
0
0
0
0
0
30
2
0
10
0
33%
44%
50%
68%
0
5
10
15
20
25
30
RH
Time (day)
Fig. 7. (A) Tensile strengths and (B) elongations at break of GSF and BSF stored at
different RHs for 7 days.
Fig. 5. (A) Water contents of GSF and BSF as function of relative humidities. (B)
Water contents of glycerol and BHF as function of storage time at 100% RH.
chosen as the contrast. Although the tensile strengths of BSF were
inferior to those of GSF, the elongations at break of BSF were higher
than those of GSF. As shown in Fig. 7, when starch film containing
2
1
1
1
1
1
8
6
4
2
.00E-011
.80E-011
.60E-011
.40E-011
.20E-011
.00E-011
.00E-012
.00E-012
.00E-012
.00E-012
glycerol
BHF
3
0% plasticizer was stored at RH 50% for 7 days, the tensile strength
and the elongation at break were 4.2 MPa and 34.9% for GSF, and
the ones were 1.3 MPa and 107.7% for BSF.
With increasing BHF content, the tensile strength of BSF de-
creased, whereas the elongation at break increased. For example,
after BSF was stored at RH 33% for 7 days, the tensile strengths
of BSF containing 25%, 30%, 35% of plasticizer were 9.9, 4.9,
2
2
.8 MPa, respectively. The elongations at break of BSF containing
5%, 30%, 35% plasticizer were 11.5%, 21.6%, 75.6%, respectively.
BHF acted as a dilutor and lowered the interaction of the mole-
cules, thus, the tensile strength decreased. At the same time, it also
acted as a plasticizer that improved the movement of the segments
and macromolecules, which led to the increase of the elongation at
break.
0
.00E+000
2
5%
30%
35%
Plasticizer content
Fig. 6. Water vapor permeability of GSF and BSF.
3.6. Mechanical properties
4. Conclusions
Tensile strength and elongation at break of TPS stored at 33%,
4%, 50%, 68% RHs, respectively, for 7 days were examined. In order
to introduce the mechanical properties of BSF clearly, GSF was
BHF was synthesized by an efficient and practical method and
proven to be effective as a new plasticizer for corn starch. BHF
formed strong and stable hydrogen bonds with starch, as shown
4

H. Dai et al. / Carbohydrate Polymers 79 (2010) 306–311
311
by the analysis of the FT-IR spectra. From the analysis of SEM,
starch granules were completely disrupted and a continuous phase
was obtained. X-ray diffraction analysis indicated A-type crystal-
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H
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formed. BSF was material with better water resistance than GSF.
WVP of BSF was lower than that of GSF. The tensile strengths of
BSF were inferior to those of GSF, while the elongations at break
of BSF were higher than those of GSF.
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5
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