1070-4272/01/7408-1358 $25.00 C 2001 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 74, No. 8, 2001, pp. 1358!1363. Translated from Zhurnal Prikladnoi Khimii, Vol. 74, No. 8, 2001,
Original Russian Text Copyright C 2001 by Bochek, Zabivalova, Lavrent’ev, Lebedeva, Sukhanova, Petropavlovskii.
AND POLYMERIC MATERIALS
Formation of Physical Thermally Reversible Gels
in Solutions of Methyl Cellulose in Water
and Dimethylacetamide and Properties of Films Thereof
A. M. Bochek, N. M. Zabivalova, V. K. Lavrent’ev, M. F. Lebedeva,
T. E. Sukhanova, and G. A. Petropavlovskii
Institute of Macromolecular Compounds, Russian Academy of Sciences, St. Petersburg, Russia
Received April 25, 2001
Abstract-Gelation conditions in solutions of methyl cellulose in water and dimethylacetamide were studied.
The gelation mechanisms were studied by X-ray diffraction and photocolorimetry, and their differences in
the two systems were revealed. The physicomechanical properties of methyl cellulose films prepared from
solutions with preliminary gelation were determined.
Recently there has been increased interest in self-
associated polymer systems based on natural poly-
mers, which are environmentally safe and biodegrad-
able. It is known that a number of cellulose deriv-
atives, in particular, methyl cellulose (MC), hydroxy-
propyl cellulose (HPC), hydroxypropyl methyl cellu-
lose (HPMC), and methyl ethyl cellulose (MEC),
form physical thermally reversible gels in aqueous
solutions. These cellulose derivatives are widely used
as gelating agents, thickeners, stabilizers, and emulsi-
fiers in food industry, cosmetics, and perfumery .
The most widely used compound is MC.
The gelation mechanism in aqueous solutions of
MC was studied in detail by various methods. It was
found that gelation conditions depend on many factors,
such as molecular weight and degree of substitution
(DS) of MC, concentration of the polymer in solution,
and uniformity of the substituent distribution in anhy-
droglucose units and along the macrochain .
There are several viewpoints on the gelation mechan-
ism in aqueous solutions of MC. Some authors be-
lieve that gelation in aqueous solutions of MC is due
to local crystallization of macrochain fragments con-
taining predominantly trisubstituted MC units .
In other papers, it is assumed that incompletely dis-
solved residual crystallites of the polymer (weakly
substituted or unsubstituted sections of cellulose mac-
rochains) may exist in aqueous solutions of MC at
low temperatures and initiate gelation on heating .
At present, it is generally believed, on the basis of
numerous experimental data, that gelation in aqueous
solutions of MC occurs in two stages. At low temper-
atures, water molecules solvate methoxy and hydroxy
groups of MC, forming specific structures in solution.
On heating, the H bonds between water molecules and
methoxy groups are broken; as a result, hydrophobic
interactions (association) are enhanced, and the size
and shape of associates (clusters) in solution change
(stage I). Further heating induces gelation accompa-
nied by phase separation (stage II) [1, 639]. The two-
stage gelation mechanism was described theoretically
by Tanaka and Ishida .
It should be noted that gelation on heating is ob-
served in aqueous solutions of MC only with polymer
samples in which the distribution of substituents in
the anhydroglucose units and along the macrochain is
nonuiform, i.e., with MC prepared by a heterogeneous
procedure. Methyl cellulose with uniform distribution
of substituents in macromolecules does not undergo
gelation in aqueous solutions (the polymer precipi-
tates) . Therefore, commercial MC prepared under
heterogeneous conditions can be considered a multi-
block copolymer consisting of randomly alternating
blocks of unsubstituted, mono-, di-, and trisubstituted
units. The diffraction patterns of the MC samples with
various molecular weights and degrees of substitution
in gel form are similar to those of trisubstituted MC.
This fact suggests that the centers of local crystalliza-
tion (formation of a new phase) are trisubstituted MC
units [1, 4].