Synthesis and physicochemical properties of low-substituted cationic ethers of starch

Article abstract of DOI:10.1134/S107042720811030X

The kinetics of the formation of cationic starch ethers under the action of 3-chloro-2-hydroxypropyltrimethylammonium chloride is studied in relation to the reactant molar ratio, temperature, and concentration of the starch suspension. Comparative data on

Full text of DOI:10.1134/S107042720811030X

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2008, Vol. 81, No. 11, pp. 2026–2032. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © S.M. Butrim, N.S. Butrim, T.D. Bil’dyukevich, T.L. Yurkshtovich, F.N. Kaputskii, 2008, published in Zhurnal Prikladnoi Khimii,
2
008, Vol. 81, No. 11, pp. 1911–1917.
MACROMOLECULAR COMPOUNDS
AND POLYMERIC MATERIALS
Synthesis and Physicochemical Properties of Low-Substituted
Cationic Ethers of Starch
S. M. Butrim, N. S. Butrim, T. D. Bil’dyukevich, T. L. Yurkshtovich, and F. N. Kaputskii
Research Institute of Physicochemical Problems, Belarussian State University, Minsk, Belarus
Received March 27, 2008
Abstract—The kinetics of the formation of cationic starch ethers under the action of 3-chloro-2-
hydroxypropyltrimethylammonium chloride is studied in relation to the reactant molar ratio, temperature, and
concentration of the starch suspension. Comparative data on how the content of the introduced catoinic groups
depends on the origin of native starch are presented. The efficiency of starch cationization and the physico-
chemical properties of the synthesized samples are examined by chemical analysis, scanning electron micros-
copy, X-ray diffraction analysis, and thermal gravimetric analysis.
DOI: 10.1134/S107042720811030X
Starch derivatives containing cationic groups
amino, ammonium, sulfonium, phosphonium, etc.) in
Such cationic starches can be prepared by different
procedures (dry, wet, extrusion), by introducing into
the starch macromolecule functional groups bearing a
positive charge [3–5]. The range of reagents used for
this purpose is fairly wide, and the most widely used
are 3-chloro-2-hydroxypropyltrimethylammonium
chloride (CHPTMAC) and 2,3-epoxypropyltrimeth-
ylammonium chloride (EPTMAC).
(
ether substituents are important commercial products
widely used ad effective additives in pulp-and-paper,
textile, cosmetic, and other industries. The most widely
used are cationic starches with tertiary amino and qua-
ternary ammonium groups in ether substituents [1],
which have been efficiently used in the past decades in
production of paper and cardboard to increase the re-
tention of the fiber and filler, decrease dust formation,
and enhance the surface and tearing strength of paper
and its resistance to fracture [2].
Cationic starch ethers are prepared by the reaction
of native starch (potato, corn, waxy corn, etc.) with a
cationic reagent (CHPTMAC or EPTMAC) under vari-
ous conditions, following the general scheme
or
Wet cationization procedures involve heterogene-
ous reactions of starch grains in a suspension and ho-
mogeneous reactions of gelatinized starch in the paste
[6]. Products of these reactions should be washed and
dried before use. The main requirement to the starch
intended for use in paper industry is its good retention
2
026

SYNTHESIS AND PHYSICOCHEMICAL PROPERTIES
2027
by fiber. Depending on the degree of substitution of
starch with cationic groups and its natural base, it is
retained differently. As the initial substrate for cationi-
zation it is preferable to use potato starch, as it was
determined experimentally that, at a degree of substitu-
tion from 0.030 to 0.040, potato starch is retained on
the fiber to more than 95%, against 60% for corn
starch and 50% for native starch. Cationic starch is
retained and fixes adhesive particles on the fiber only
at a degree of substitution higher than 0.020.
and enthalpy of paste formation from starch granules [9,
12, 13] but increases their dispersibility and swelling [11].
In this study we examined the effect of various fac-
tors (reactant molar ratio, temperature, starch concentra-
tion in suspension, reaction time, origin of native starch)
on synthesis and properties of cationic starch ethers,
with 60 wt % aqueous solution of 3-chloro-2-hydroxy-
propyltrimethylammonium chloride synthesized by the
specialy developed procedure used as cationic reagent.
Along with these commonly used processes, there
are two more methods which can be used for preparing
cationic starches. For example, in the dry procedure
EXPERIMENTAL
As investigation objects we used potato starch
GOST (State Standard) 7699–78; content, %: amylose
3.8, P 0.08, N 0.044, ash residue 0.31, moisture 12.0]
and also, for comparison, corn, waxy corn, and wheat
starches. All the chemicals used in this study were of
chemically pure or analytically pure grade. The cati-
onic reagent was prepared by the scheme
[
2
[
5], an aqueous solution of an alkali and a cationic re-
agent is sprayed onto starch, and then this mixture is
heat-treated. The products thus obtained can be used
directly, without any additional treatment.
In the extrusion method, the reagent is added to a
dry mixture of starch and NaOH in the course of extru-
sion [7, 8]. The reaction occurs under the conditions of
high shear stresses and high temperatures (up to 170°C).
Therefore, cationic starches prepared by this method,
in contrast to other starches, are soluble in cold water,
which largely facilitates manipulations with them in
the course of paper and cardboard production. As in
the dry procedure, extrusion cationic starches can be
used directly, but in both processes the final product
can contain salts, residual reagents, and by-products.
Alkylation of starch with the cationic reagent.
A 500-ml round-bottomed flask equipped with a
power-driven stirrer, a dropping funnel, and a ther-
mometer and placed on a water bath was charged with
81.0 g (0.50 mol) of starch, 200 ml of distilled water,
and 25 g of NaCl (to prevent starch gelatinization in
the course of the reaction). The resulting suspension
was stirred at room temperature, and the required
amount of a 10% aqueous NaOH solution was slowly
added from a dropping funnel. In so doing, the water
bath temperature was raised to the required level with
continuous stirring. After that, a calculated amount of
the cationic reagent was slowly added. In the course of
the reaction, at definite intervals, ~10-ml samples of
the suspension were withdrawn and transferred into a
beaker with 200 ml of distilled water preliminarily
acidified with 0.2 ml of 25% HCl. Then the precipitate
of cationic starch was separated by decantation and
washed on the filter with a water–isopropanol mixture
The physicochemical properties of cationic starches
strongly depend on the production procedure, type of
cationic groups, and degree of substitution. Variations
in the properties of starches in relation to the botanical
origin, cationic substituents introduced [9–12], or de-
gree of substitution [13] are described in numerous
papers. For example, Manelius et al. [9] and Viher-
vaara et al. [14] suggest that dry cationization of potato
starch involves predominantly surface modification of
the granules, whereas in wet cationization starch gran-
ules are also modified in the bulk. However, Hamunen
[
10] showed that the difference in the distribution of
nitrogen from cationic groups in modified starches pre-
pared by the dry and wet procedures was insignificant.
Generally, in the dry procedure the native structure of
starch granules strongly affects the process, in contrast
to the wet procedure. In turn, the degree of crystallinity
of starch was lower after dry cationization [9], but did
not change noticeably after wet cationization [12, 13]
compared to the crystallinity of native starch grains.
Introduction of cationic groups into the structure of the
polysaccharide leads to a decrease in the temperature
–
(1 : 1) until the qualitative reaction for Cl in wash wa-
ters became negative. After that, the precipitate was
washed with an additional 50-ml portion of isopropa-
nol and dried in an oven at 50°C. The cationic starch
prepared is sized in hot water. We determined by the
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028
BUTRIM et al.
RE, %
DScat
(
a)
DScat
(b)
RE, %
τ, h
τ, h
(
c)
(d)
DScat
RE, %
DScat
τ, h
τ, h
Fig. 1. Kinetic curves of cationization of potato starch. (DScat) Degree of substitution with cationic groups, (RE) reaction efficiency,
and (τ) time. (a) Concentration of aqueous starch suspension 33%; molar ratios NaOH/CHPTMAC = 2.8, CHPTMAC/AGU = 0.06;
temperature of reaction medium, °C: (1) 25, (2) 35, (3) 45, and (4) 55. (b) Concentration of aqueous starch suspension 33%; 35°C;
molar ratio CHPTMAC/AGU = 0.06; molar ratio NaOH/CHPTMAC: (1) 1.6, (2) 2.2, (3) 2.8, and (4) 3.3. (c) 35°C: molar ratios
NaOH/CHPTMAC = 2.8, CHPTMAC/AGU = 0.06; concentration of aqueous starch suspensoin, %: (1) 24, (2) 33, and (3) 42.
(
(
d) 35°C; concentration of aqueous starch suspension 33%; molar ratio NaOH/CHPTMAC = 2.8; molar ratio CHPTMAC/AGU:
1) 0.03, (2) 0.06, and (3) 0.12.
Kjeldahl method the nitrogen content N (%), and from
the gain in the nitrogen content after cationization we
cording. The samples were prepared by cold pressing
of the polymer in the form of monolithic round pellets
2 mm thick and 18 mm in diameter. The morphology
of structural elements constituting particles of native
potato starch and of the prepared samples of cationic
starch was examined with an LEO 1420 scanning elec-
tron microscope (Germany). Thermal decomposition
of the samples was studied on an STA 449C synchro-
nous thermal analyzer (Netzsch, Germany) in a dy-
namic nitrogen atmosphere at a nitrogen feed rate of
calculated the degree of substitution DS and the reac-
cat
tion efficiency RE by the formulas
cat
DScat = 162.1Ncat/(1401 – 151.6Ncat),
RE = (DScat/DStheor) × 100%,
where Ncat = N – N ; DS
= nCHPTMAC/nAGU; Ncat is
init
theor
the content of nitrogen introduced into starch with cati-
onic groups (%); N, nitrogen content in cationic starch
3
–1
–1
22 cm min ; heating rate 5 deg min , sample weight
50 mg; freshly calcined aluminum oxide was used as
reference.
(
%); N , nitrogen content in native starch (%); DStheor,
init
theoretical degree of substitution with cationic groups
2-hydroxypropyltrimethylammonium chloride
(
RESULTS AND DISCUSSION
groups); nCHPTMAC, amount of CHPTMAC in the modi-
fying agent added in the course of the reaction (mol);
AGU, anhydroglucopyranose unit; and nAGU, amount
of starch taken for cationization (mol AGU).
The performance of the cationic reagent was esti-
mated by studying the kinetics of the preparation of
cationic ethers of potato starch using the synthesized
reagent in the temperature range 25–55°C at various
molar ratios of the components and various solid-to-
liquid ratios. It can be seen (Fig. 1a) that the rate of
The diffraction patterns were recorded with an
HZG-4A X-ray diffractometer (Carl Zeiss, Jena, Ger-
many), CuK radiation, Ni filter, point-by-point re-
α
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SYNTHESIS AND PHYSICOCHEMICAL PROPERTIES
2029
alkylation of potato starch with 3-chloro-2-hydroxy-
propyltrimethylammonium chloride (main active sub-
stance in the cationic reagent) regularly increases with
temperature. However, at T > 45°C, despite the pres-
ence of NaCl, cationization of starch leads to its gelati-
nization in alkaline solution, which severely compli-
cates isolation of the final product and its washing to
remove salts.
It should be noted (Fig. 1b) that, at the NaOH :
CHPTMAC molar ratio in the range 2.2–3.3, the reac-
tion rate in the initial period is essentially the same. It
can also be seen that the highest rate and the highest
degree of starch cationization are attained already at
the NaOH/CHPTMAC molar ratio of 2.8. Hence, fur-
ther increase in the amount of alkali is not appropriate.
In turn, the deficiency of NaOH in the reaction mixture
does not allow the desired results to be attained, even
in a prolonged reaction.
2θ, deg
Fig. 2. Diffraction patterns of (1) native potato starch and
(2–7) cationic potato starch samples differing in the cati-
onic group content and preparation temperature. (I) Rela-
tive intensity and (2θ) Bragg angle. T, °C: (2–5) 35, (6) 45,
and (7) 55.
We found that preparation of cationic ethers de-
pends on the starch suspension concentration insignifi-
cantly. When this parameter was varied in the range
can involve significant changes in the supramolecular
structure of the polysaccharide, depending primarily
on the process temperature. For example, the diffrac-
tion patterns shown in Fig. 2 (curves 6, 7) indicate that
the degree of crystallinity of starch after its cationiza-
tion at temperatures leading to gelatinization of starch
in the reaction mixture considerably decreases, and the
extent of these changes is the greater, the higher the
reaction temperature. It can be seen that the main re-
flections characteristic of native potato starch (2θ
2
4–42%, at a constant stirring rate, we found no sig-
nificant differences in the reaction rate and maximal
degree of substitution with cationic groups (Fig. 1c).
As can be seen (Figs. 1a–1c), it is quite appropriate
to use the synthesized modifying agent for preparing
cationic starches, because its use allows attainment of
high reaction efficiency (RE = 70–80%) which, in
turn, shows that the major fraction of CHPTMAC is
spent for binding with starch rather than for formation
of by-products.
1
7.0°, 19.5°, and 22.1°) are virtually lacking in the
patterns of cationic starch (Fig. 3, curves 6, 7) prepared
at T ≥ 45°C. As under such conditions of starch modi-
fication not only amorphous but also crystalline re-
gions of the structure are involved in the process, the
introduced 2-hydroxypropyltrimethylammonium chloride
groups are, apparently, distributed fairly uniformly.
A strong influence on both the reaction rate and the
limiting degree of substitution is exerted by the
CHPTMAC/AGU molar ratio (Fig. 1d). As this ratio is
increased, with the solution volume remaining con-
stant, the CHPTMAC concentration in the solution
increases. As a result, the starch alkylation rate in-
creases. An increase in the CHPTMAC/AGU molar
ratio also leads to a proportional increase in the limit-
ing content of cationic groups in the polysaccharide.
The diffraction patterns of cationic starch samples
with different degrees of substitution (Fig. 2, curves 2–
5
), prepared at 35°C, are characterized by the lack of
the reflection at 2θ = 19.5° and the presence of well-
defined peaks at about 17.0° and 22.1°. However, cal-
culation of the relative degree of crystallinity (DC) of
these cationic starches shows that DC for sample nos.
Preliminary studies showed that introduction of a
quaternary ammonium group into the anhydroglu-
copyranose unit of starch decreases the temperature of
paste formation. Solutions prepared from modified
starch are stable even at low pH values and are not
prone to retrogradation, which is important for their
further practical use.
2
and 3 is higher, and for sample nos. 4 and 5, lower
than that of the native starch (Table 1). Such character
of changes in the degree of crystallinity of modified
starch samples may be due to the fact that, in washing
with a water–isopropanol mixture, the more soluble
(
amorphous) fraction of the modified polysaccharide
Alkylation of starch with 3-chloro-2-hydroxyprop-
yltrimethylammonium chloride in an alkaline solution
remains in the filtrate. Therefore, the fraction of crys-
talline regions in the isolated and studied cationic
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2
030
BUTRIM et al.
Table 1. Degrees of crystallinity (DC) of the examined
samples
of predominantly round shape and very large granules
d > 60 μm) of oval shape. The breaking effect of
(
NaOH whose ions under definite conditions can induce
the gelatinization of starch in solution is well consis-
tent with the observed changes in the morphological
structure of starch granules (Fig. 3): With an increase
in the synthesis temperature, starch granules undergo
more and more pronounced changes. Cavities, frac-
tures, and folds appear in starch granules, and all these
changes are enhanced with increasing temperature. For
example, at 35°C, when starch cationization through-
out the reaction occurs in a suspension (without gelati-
nization), granules of cationic starch insignificantly
differ from the initial granules in the shape and size:
only small cavities and surface defects are observed
(Figs. 3a, 3b). At T ≥ 45°C, in the alkaline solution, the
reaction occurs under the conditions of starch gelatini-
zation when the granules strongly swell and are de-
stroyed. As a result, in the electron micrographs of
cationic starch more significant granule defects are
observed (Fig. 3c, 3d): large cavities and even through
holes, as well as fine fragments of granules.
Sample no.
Starch sample
DC, %
1
2
3
4
5
6
7
Native potato
33.2
39.5
36.5
32.4
28.0
Cationic (DScat = 0.0041)
Cationic (DScat = 0.021)
Cationic (DScat = 0.047)
Cationic (DScat = 0.035)
Cationic (DScat = 0.061) X-ray amorphous
Cationic (DScat = 0.045)
"
starch sometimes increases, which leads to a certain
increase in DC. Also, as seen from the data obtained,
by varying the cationization temperature it is possible
to prepare cationic starch samples with a close con-
tent of 2-hydroxypropyltrimethyammonium chloride
groups but with different degreese of crystallinity
(
Fig. 2, curves 4, 7), which can ultimately lead to dif-
ferences in the physicochemical properties. The nu-
merical values of the relative degree of crystallinity of
the samples studied are given in Table 1.
Nonisothermal thermogravimetric (TG) curves of
native potato starch and three samples of cationic po-
tato starch are shown in Fig. 4. As can be seen, intro-
duction into starch macromolecule of 2-hydroxyprop-
yltrimethylammonium chloride groups exerts a signifi-
As seen from Fig. 3a, granules of native potato
starch are very nonuniform in the size and shape.
Among them are both very small granules (d < 5 μm)
1
0 μm
20 μm
(
a)
(b)
(
c)
20 μm
10 μm
(d)
Fig. 3. Scanning electron micrographs of granules of (a) native potato starch and (b–d) cationic potato starch samples prepared at
b) 35, (c) 45, and (d) 55°C.
(
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SYNTHESIS AND PHYSICOCHEMICAL PROPERTIES
2031
m, %
220–287°C) involves degradation proper, with car-
bonization. Carbonization of all the samples of cationic
starch starts at lower temperatures (Table 2) compared
to native starch. As seen from Table 2, for all the cati-
onic starches the weighed of the carbonized residue at
5
00°C is higher compared to the native starch, and
with an increase in the content of cationic groups the
carbonization temperature decreases. At the same time,
the temperature at which the samples lose 50% of their
weight is independent of the degree of substitution of
cationic starch. Table 3 shows that the use for cationi-
zation of starches isolated from different sources al-
lows preparation of cationic starch ethers with close
degrees of substitution, i.e., the origin of native starch,
other conditions being the same, affects the content of
cationic groups insignificantly. The observed insignifi-
cant differences in DScat are apparently associated with
differences in the molecular weight and amylose con-
tent of the initial starches.
T, °C
Fig. 4. TG curves of (1) native potato starch and (2–
) cationic potato starch samples prepared at various tem-
peratures. (m) Sample weight and (T) temperature. Prepara-
tion temperature, °C: (2) 35 (DScat = 0.035), (3) 45 (DScat
.061), and (4) 55 (DScat = 0.045).
4
=
0
cant effect on the thermal characteristics of starch,
mainly on the onset temperature and mechanism of its
degradation. All the examined samples lose weight in
two steps: The first step (T = 70–100°C) involves re-
moval) of adsorbed moisture, and the second step (T =
CONCLUSIONS
(
1) The use of the synthesized modifying agent,
-chloro-2-hydroxypropyltrimethylammonium chlo-
ride, allows efficient cationization of various starches.
3
Table 2. Quantitative characteristics of thermal degradation
of starch samples
a
(
2) The examined conditions of starch alkylation
T
onset
T
50%
ensure preparation of cationic starches with the preset
degree of substitution (DScat = 0.01–0.06) and high
reaction efficiency (RE = 80%).
Starch
sample
Residue at 500°
C, %
DScat
°C
Potato
0
287
267
244
220
303
300
313
292
21.0
26.7
33.1
23.1
(
3) The structure and properties of cationic starch
0
0
0
.035
.045
.061
strongly depend on the temperature conditions of the
modification of native starch.
Cationic
potato
REFERENCES
a
(
T
onset, T50%) Temperatures of the onset of degradation (car-
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obtained with various native starches. Conditions of starch
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CHPTMAC/AGU = 0.06
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2
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1
6
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