1070-4272/02/7509-1506$27.00C2002 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 75, No. 9, 2002, pp. 1506 !1509. Translated from Zhurnal Prikladnoi Khimii, Vol. 75, No. 9,
2002, pp. 1538!1541.
Original Russian Text Copyright + 2002 by Baranov, Zheleznov.
AND POLYMERIC MATERIALS
Influence of n-Alkanes on Hardening and Selected Properties
of Gelatin Shells of Microcapsules
A. V. Baranov and K. N. Zheleznov
Institute of Chemistry of Solutions, Russian Academy of Sciences, Ivanovo, Russia
Received May 13, 2002
Abstract-The influence of aliphatic hydrocarbons encapsulated in gelatin shells on hardening and heat
resistance of these shells was studied by linear dilatometry, gravimetry, and pH-metry.
Microencapsulation attracts now particular atten-
tion owing to the fact that microcapsules of functional
substances, obtained by such technologiles, endow
conventional and new articles, products, and materials
with a set of valuable properties and new benefits.
Of greatest importance in storage, processing, and
utilization of microcapsules are heat resistance, mech-
anical strength, and permeability of the shells, i.e.,
characteristics governed by the shell structure .
The performance characteristics, in particular,
thermophysical properties, of gelatin shells of micro-
capsules are largely determined by the course of their
hardening. Therefore, the conditions of this process
are of decisive importance. It should be noted that,
despite a great number of papers devoted to micro-
encapsulation technologies and the properties of the
resulting microcapsules, the influence exerted by the
core substance on hardening of the shells and their
properties still remains to be understood.
In this work, we studied the influence of aliphatic
on hardening and selected prop-
erties of gelatin shells of microcapsules.
As core substances we used homologs of saturated
hydrocarbons (n-alkanes) C
(n =6310). The
shell material for microcapsules was active, brand A,
low-viscosity photographic gelatin [OST (Branch
Standard) 6-17-421384] with the isoelectric point
pI 4.7. Microencapsulation was performed by simple
coacervation of gelatin dissolved in water at 50355oC
using sodium sulfate (see ). The dispersion of the
microcapsules with primary coacervation shells was
cooled and subjected to chrome3syntane3tannide har-
dening . This involved two-stage successive treat-
ment with solutions of chromium3potash alums
O and synthetic hardening agent
no. 2 (syntane no. 2). The latter is the product of con-
densation of phenol and formaldehyde, sulfonated
with sulfuric acid. The aqueous dispersions of the
microcapsules were washed to remove the chemicals
until the washing and initial waters had identical pH.
The microcapsules were hardened, washed, and dried
at room temperature. The encapsulation product was
a friable powder containing microcapsules with the
average diameter of 70 mm. The hydrocarbon content
in the capsules was 82387 wt %.
To study the properties of the shells, we withdrew
microcapsules in various stages of the process, and
dried and opened them mechanically, whereupon the
contents (core) was left to evaporate.
Model samples were fluoroplastic-supported films
prepared from the initial gelatin solutions. Selected
samples were kept in n-alkanes and hardened by
chrome3syntane3tannide procedure .
The behavior of the initial gelatin, its coacervate,
and microcapsule shells on heating was studied by
linear dilatometry, which is particularly sensitive to
changes in the mobility of the molecules and struc-
tural elements in polymeric systems. We used a spe-
cially designed setup shown schematically in Fig. 1.
The setup was equipped with a balance producing a
minimal mechanical effect on the sample, which is
very important for studying polymers transforming to
devitrified state during heating. The samples studied
were shaped as cylinders 5 mm in diameter and
20 mm in length made from the shell material. The
sample heating rate was 5 deg min
Figure 2 presents the temperature dependences of
the linear dimensions for the initial gelatin, gelatin