Int.J.Curr.Microbiol.App.Sci (2014) 3(6): 10-24
ISSN: 2319-7706 Volume 3 Number 6 (2014) pp. 10-24
http://www.ijcmas.com
Original Research Article
Chemical modification of Cellulose Acetate by Diallylamine
Abir S. Abdel-Naby 1* and Azza A. Al-Ghamdi2
1
Chemistry Department, Faculty of science, Fayium University, Fayium, Egypt
2
Chemistry Department, Faculty of science, Dammam University, Dammam,
Saudi Arabia
*Corresponding author
ABSTRACT
Keywords
Cellulose
acetate,
Diallylamine,
Thermal
properties,
Morphology.
Cellulose acetate (CA) was modified using Diallylamine (DAA). The structure of
the modified polymer was characterized by 13C-NMR. The chemical modification
is based on the reaction between the active hydrogen of the amino group of
Diallylamine molecule and acetyl group of the glucopyranose ring in cellulose
acetate. The thermo gravimetry (TG) was used to investigate the thermal stability
of the modified polymeric sample. The modified cellulose acetate exhibits higher
thermal stability as compared to the unmodified CA, Which is attributed to the
presence of thermally stable pyrrolidine rings throughout the polymeric chains.
The crystallinity and morphology of the modified polymeric sample were
investigated using X-Ray diffraction (XRD) and emission scanning electron
microscope (ESEM) respectively. The presence of Diallylamine moieties (as
pyrrolidine ring) in the cellulose acetate matrix improved its mechanical property.
Also, the organic nature of Diallylamine moieties inside CA matrix reduced its
wettability.
Introduction
The interest in polymers from renewable
resources increased considerably in the
last few decades. These materials are
available in large quantities and they have
numerous advantages (Mohanty et al
2000; Bledzki and Gassan 1999; Zhang et
al 2005).
thermoplastic polymers (Schroeter and
Felix 2005; Heinze and Liebert 2001;
Pereira and Campana, 1997). As a
consequence, they are often modified both
to improve process ability and to adjust
their properties to the intended application.
Natural polymers can be modified
physically by plasticization, or chemically
through the reaction of their active (-OH)
groups (Joly et al 2005; Frisoni et al 2001;
Nishio 2006). The benzylation of wood
Natural polymers, mainly polysaccharides,
consist of large, rigid molecules, thus they
cannot be processed very easily with the
usual processing technologies of
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Int.J.Curr.Microbiol.App.Sci (2014) 3(6): 10-24
(Hon and Ou 1989), the plasticization of
starch (Ma et al 2005; Gomes et al 2001),
and the grafting of cellulose (Mayumi et al
2006) or cellulose acetate are typical
examples of such modifications (Lee and
Shiraishi 2001; Yoshioka and Hagiwara
1999; Hatakeyama et al 2000; Guruprasad
and Shashidhara 2004; Warth et al 1997;
Teramoto et al 2004; Teramoto et al 2002;
Teramoto and Nishio 2002; Abdel-Naby
and Aboubshait 2013).
properties. The choice of diallylamine is
due to the presence of active hydrogen
atom of the amino (-NH) group, which
possesses the ability to attraact the acetyl
group of glucopyranose ring, thus
enhancing the chemical modification
process.
Materials and Methods
Materials
Cellulose acetate (CA) was purchased
from Aldrich with a degree of
polymerization and degree of substitution
160 and 2,4 respectively. Diallylamine
was
purchased
from
Aldrich.
Cyclohexanone purchased from Prolabo.
Other reagents and solvents were of
analytical grades.
Cellulose acetate (CA) is often used in
these attempts, since this polymer is a
commercial product and can be handled
relatively easily compared to cellulose or
to most of the other natural polymers
(Simon et al 1998).
Modification is carried out under a wide
variety of conditions. Because of these
wide range of methods and conditions, the
effect of various parameters on grafting
efficiency and on the structure product
obtained are not completely clear yet
(Sz mel et al 2008).
Despite the
advantages of low cost and high
productivity, the serious problems facing
cellulose acetate are its poor heat stability
at high temperatures as well as its
hydrophilic nature.
Preparation
acetate
of
modified
cellulose
The modified polymers were prepared by
gradually adding (0.2mol) of diallylamine
to a solution of cellulose acetate (8 mol)
dissolved in 100 ml of cyclohexanone.
Both solutions had been prepared under
nitrogen atmosphere. The reaction was
allowed to occur for 10 h at 70 C, in
ultrasonic bath of power 1050 watt. The
reaction product was precipitated in cold
methanol, filtered, and washed with hot
methanol using soxhlet
system. The
recovered polymer was then dried under
vacuum at 40 C.
Cyclizaion or cyclopolymerization of
diallylamine, as symmetrical nonconjugated diolefin, was found to be
possible only in the presence of ultrasound
and peroxodisulfate (Vivekanandam et al
2000). While, the cyclization and
cyclopolymerization of N-substituted
diallylamine salts was found to possible
with the help of either ultrasound or
chemical initiator (Zaikov et al 2001;
Abdel-Naby and Al-Harthi 2013 ). In the
present work, diallylamine is suggested to
modify cellulose acetate aiming to
improve its thermal and mechanical
Preparation of cellulose acetate samples
films
The films were prepared by casting
polymeric sample solution in THF on
glass petri-dish, then allowing the solvent
to evaporate at room temperature then
dried at 40 C in vacuum oven. The
thickness of the film was 0.5 ± 0.01mm
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Int.J.Curr.Microbiol.App.Sci (2014) 3(6): 10-24
Perkin-Elmer
differential
scanning
calorimeter (Model DSC 2010, USA) by
heating from 20 to 500 C, under nitrogen
atmosphere. The DSC curves were
recorded.
Characterizations
Spectroscopic characterization
13
C-NMR analysis
The 13C-NMR spectra of monomers and
polymeric samples were collected on a
Bruker Advance- 600 MHz spectrometer.
All the chemical shifts were reported in
part per million (ppm) using tetra methyl
silane (TMS) as the internal standard.
DMSO or CDCl3 or a mixture of both
solvents was used.
Mechanical properties characterization
Young s modulus of the polymeric films
was measured using a Shimadzu autograph
in air at room temperature.The correlation
between stress ( in MPa) and elongation
( in %) was determined (El Hadi et al
2008).
Morphological surface analysis
= E
where, E
= Young s modulus in MPa
= ( Lo-L) / L
Lo =
original length L = length after
elongation
Cellulose acetate surfaces were examined
by
Emission
Scanning
Electron
Microscopy (ESEM) using a (FEGSEM/EDS)or LEO 440 ZEISS/LEICA
model.
Thermomechanical properties
X-Ray Diffraction
The films were analyzed by dynamic
mechanical thermal analysis (DMTA)
using a Rheometric Solid Analyzer II
(Rheometric Scientific, Piscataway, NJ)
under nitrogen. A film sample of 19.28
mm × 6.35 mm was prepared and its
thickness was measured. The sample was
subjected to a small axial force of 5 g and
a modulating frequency of 16 Hz and
heated at a rate of 5 C/min until the
length of the sample was stretched by 0.5
mm. The temperature at which the film
was stretched by 0.5mm was recorded as
the rejuvenated temperature (Tr).
X-ray diffraction patterns were recorded
using a Rigaku D/max 2500 v/pc X-ray
diffractometer. The diffractograms were
measured at 2 in the range of 5- 80°
using Cu K as the monochromatic
radiation source ( = 1.54 ) by applying
a parabolic filter, at a tube voltage of 40
kV and a tube current of 200 mA.
Thermal characterization
Thermal analysis TGA / DTA
The thermal stability was examined, under
nitrogen,
using
a
Perkin-Elmer
(TGA/DTA) thermogravimetric analyzer
from room temperature to 500 °C at a
heating rate of 10°C
Wettability
The wettability of the polymeric film was
examined by measuring the contact angles
of water droplets on the film with video
contact
angle
system
(VCA
2000Advanced
surface technology,
Billerica, MA) at three different locations
on the film.
Differential scanning calorimetry (DSC)
The glass transition temperature Tg of the
CA/ PVC blend films was measured on a
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Int.J.Curr.Microbiol.App.Sci (2014) 3(6): 10-24
4. The presence of a peak in the methyl
region ( 18.4 ppm) with considerable
intensity
confirms
the
structure
indicated in ( Figure 3 )( Eq.2). Figure 3
represents
the suggested reaction
mechanism of the modification of CA
by DAA.
Results and Discussion
Characterization of modified cellulose
acetate
The modification of cellulose acetate by
diallylamine (DAA) occurred according to
the method previously described.
The elemental analysis indicated the
presence of nitrogen atom in the CA/DAA
sample, which confirmed the modification
process between CA and DAA, as CA lack
the presence of nitrogen atom in its matrix.
13
Thermal properties of the modified
cellulose acetate
Thermogravimetry (TG)
This work aims to improve the thermal
stability of cellulose acetate at high
temperatures
through
chemical
modification by DAA. The thermal
stability
was
examined
using
thermogravimetry (TG). The initial
decomposition temperature (To) and the
total weight loss percentage (Wt loss %)
values of the modified sample as well as
those of unmodified cellulose acetate are
complied in Table 2.
C-NMR spectroscopic analysis
13
C-NMR spectroscopy was used to
identify the reaction sites in both CA and
DAA monomer involved in the
modification process. The 13C-NMR
spectral characteristic data of (CA/DAA)
(Table 1) and (Figure 1) showed the
following additional peaks as compared to
that of CA (Figure 2).
The data indicated that the thermal
stability of the modified CA sample is
improved as shown by the decrease in
weight loss % at (500 C) (85%) and the
increase in the value of initial
decomposition temperature (To)( 320 C)
as compared to those of unmodified CA,
where (To = 250 C) and the total weight
loss % at (500 C) reached (89.3 %). The
increase in the thermal stability of the
modified sample is mainly attributed to the
stability of the highly thermal stable
pyrrolidine rings built throughout the
cellulose acetate matrix.
1. A new peak at (58.5 ppm) indicating the
formation of new bond between
nitrogen atom of (-NH) group of DAA
and carbon atom (1) of glucopyranose
ring of cellulose acetate after the release
of acetic acid molecule. Absence of
vinyl C=C of the monomer confirms the
cyclization
process
since
this
cyclization was known to occur only if
the nitrogen atom of DAA was
substituted (Zaikov et al 2001) ( Figure
3)( Eq. 1)
2. Appearance of a new peak at (41 ppm)
(with double intensity), representing
carbon atoms (2 and 2 ). The double
intensity confirmed the symmetry of
carbon atoms in the pyrrolidine ring.
The thermogravimetry curves of both
modified sample and that of unmodified
CA are illustrated in Figure 4. The figure
emphasizes the extra thermal stability of
the modified cellulose acetate as compared
to the unmodified CA.
3. Appearance of new peak at (30.9 ppm)
corresponding to carbon atoms (3 and
3 ).
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Int.J.Curr.Microbiol.App.Sci (2014) 3(6): 10-24
The XRD pattern of CA /DAA polymer
exhibits higher crystallinity as shown from
the sharpness and intensity of the peaks
(Figure 7). The aforementioned results
revealed that the modification of CA by
DAA increased the percentage of
crystallinity due to the presence of the
pyrollidine rings inside the modified
polymer matrix.
Differential scanning calorimetry (DSC)
The differential scanning calorimetry
(DSC) of CA/DAA is shown in Figue 5.
The data show that the modified polymer
exhibits only one glass transition
temperature Tg ( 191.83), different from
that of the unmodified CA ( 189.49). The
single Tg confirmed the formation of a
new modified polymer. Also, the increase
in the Tg value of CA/DAA indicates the
increase in its degree of of crystallinity as
compared to CA.
Morphological characterization
A half gram of the modified CA/DAA
sample was dissolved in THF and then
poured into suitable petri-dish. for some
interval of time, then the later was put in a
vacuum oven at 40 °C to obtain the film.
The film was of 0.5 mm thick. The
morphology of the surface of CA modified
by DAA film shows the modified regions
as compared to that of unmodified CA
(Figure 8).
Differential thermal analysis (DTA)
The DTA curve of CA/DAA sample
exhibits a large sharp exotherm peak at
temperature of flow ( Tf ) near (400 °C), as
shown in Figure 6 , which is related to the
crystal structure. While the DTA curve of
CA exhibits a broad peak at lower
temperature of flow Tf ( (388°C). This
result implies that the degree of
crystallinity of the modified sample is
higher than that of the unmodified CA.
Characterization of crystallinity
modified CA/DAA sample
Mechanical properties characterization
To adjust the semi crystalline CA polymer
for various fibre applications, its
mechanical property should be improved.
The aim of this work is to produce
modified CA with high mechanical
property. The measurement of the value
of Young s modulus reflects the ability of
the sample to retain its original form after
release of the stress (Okui and Sakai
1987). CA is known to exhibit Young's
modulus
around
(600-3000
MPa)
depending on the degree of substitution
and the average molecular weight (Wu et
al 2008).
of
To confirm the efficiency of pyrrolidine
rings inside the CA/DAA matrix in
increasing the degree of crystallinity, it
was of interest to check the X-Ray pattern
of the modified CA/DAA sample and
compare it to that of unmodified CA.
The XRD pattern of CA showed three
sharp peaks at (2 = 9°, 10.6°, 13.4°)
related to the crystalline part of the
polymer and a broad peak at (2 = 18.2°)
related to the amorphous part of the
polymer. For this reason cellulose acetate
is known to be a semicrystalline polymer
(Abdel-Naby and Aboubshait 2013).
The results revealed that the modified CA
sample by DAA possessed higher Young's
modulus value than CA at room
temperature (Table 3). Thus, the
modification of CA by DAA increased
Young's
modulus
value.
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Int.J.Curr.Microbiol.App.Sci (2014) 3(6): 10-24
Fig.1 13 C NMR spectrum of CA modified by DAA
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Int.J.Curr.Microbiol.App.Sci (2014) 3(6): 10-24
Fig.2 13C NMR spectrum of cellulose acetate
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Int.J.Curr.Microbiol.App.Sci (2014) 3(6): 10-24
Fig.3 Suggested mechanism of the modification of Cellulose acetate by diallylamine
CH2OCOCH3
Eq 1
O
H
N
O
OH
OCOCH3
CH3COOH
CH2OCOCH3
O
O
OH
N
Ultrasonic waves
CH 2 OAc
O
OH
O
N
Eq2
CH 3
17
CH 3
Int.J.Curr.Microbiol.App.Sci (2014) 3(6): 10-24
Fig.4 Thermogravimetry (TG) , under nitrogen atmosphere, of (b) CA modified by DAA as
compared to that of (a). CA .
CA-DAA
Fig.5 Differential scanning calorimetry (DSC) , under nitrogen atmosphere, of (a) CA and (b)
CA/DAA.
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Int.J.Curr.Microbiol.App.Sci (2014) 3(6): 10-24
Fig.6 Differential thermal analysis (DTA), under nitrogen atmosphere, of CA/DAA as
compared to that of CA
Fig.7 XRD patterns of (a) CA, (b) CA / DAA
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Int.J.Curr.Microbiol.App.Sci (2014) 3(6): 10-24
Fig.8 ESEM morphology of polymeric films (a) CA and (b) CA / DAA
a
b
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Int.J.Curr.Microbiol.App.Sci (2014) 3(6): 10-24
Table.1 13C NMR spectral characteristics of CA/ DAA modified polymer
Structure
Carbon atom
in CA/DAA
1
C H 2O A c
13
C NMR
( ppm)
58.5
O
OH
O
2,2'
41
3,3'
30.9
4,4'
18.4
1
N
2
2'
3'
CH3
4'
3
CH3
4
Table.2 Thermal analysis of CA/DAA as compared to CA
Sample
CA
CA/DAA
To
250 C
320 C
Total weight loss at 500 C
89.3 %
85%
Table.3 Mechanical properties and wettability of CA/DAA as compared to CA
Sample code
CA
CA/DAA
Rejuvenated
temperature (Tr)
210 ºC
333 ºC
Young's Modulus
(MPa)
1500
1850
Dynamic mechanical thermal analysis was
used to determine the rejuvenated
temperature (Tr) of a film sample. The
films with higher degree of elasticity
exhibited lower rejuvenated temperatures.
The results revealed that the modified
CA/DAA sample exhibited higher
rejuvenated temperature (333 C) than
that of the unmodified CA (210 C).
The
aforementioned
results
were
consistent with the XRD results,
confirming the increase in the percentage
of crystallinity of the modified CA as
compared to CA, which could adjust it
for various fibre applications.
Contact angle of
water droplets
64
76
Wettability characterization
The wetting behavior of modified
cellulose acetate film was examined by
measuring the contact angles of water
droplets on the film (Table 3). The results
revealed that the modified CA/DAA film
exhibited higher contact angle (76o) than
unmodified CA film (64o). This is
attributed to the presence of organic
pyrrolidine rings throughout the backbone
of CA. Apparently, the organic pyrrolidine
rings reduced the wettability of CA.
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Int.J.Curr.Microbiol.App.Sci (2014) 3(6): 10-24
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ber
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2005, 65(15/16) , 2514-2525.
Schroeter, J. ; Felix, F. Melting cellulose.
Cellulose 2005, 12(2) ,159-165.
Heinze, T. Liebert, T. Unconventional
methods
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cellulose
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2001, 26(9) , 1689-1762.
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Benzylated pulps from sugarcane
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Conclusions
1. This piece of work is an attempt to
modify cellulose acetate structure in
order to improve its thermal and
mechanical
properties.
Increasing
crystallinity and reducing wettability of
the polymer are also considered as
essential targets to enable the
adjustment of the polymer for fibre
applications.
2. Diallylamine, as an organic compound
possessing
active
hydrogen,
is
suggested to modify CA.
3. The structures of the modified
polymeric sample is confirmed by 13C
NMR.
4. The incorporation of DAA into the
cellulose acetate matrix led to the
cyclization of the DAA moieties and
formation
of
pyrrolidine
rings
throughout the modified polymer
chains. These rings gave the modified
polymer its extra thermal stability as
compared to the CA.
5. The results of mechanical properties
revealed that the modified CA sample
by DAA possessed higher Young's
modulus than CA at room temperature .
Also, the presence of the organic
pyrrolidine ring throughout the CA
matrix reduced its wettability.
6. The modified CA/DAA sample was
found to exhibit higher percentage of
crystallinity as compared to the
unmodified CA which could adjust it
for various fibre applications.
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