1070-4272/02/7508-1223 $27.00 C 2002 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 75, No. 8, 2002, pp. 1223!1226. Translated from Zhurnal Prikladnoi Khimii, Vol. 75, No. 8, 2002,
Original Russian Text Copyright C 2002 by Nikolaev, Lebedeva.
AND INDUSTRIAL INORGANIC CHEMISTRY
Inorganic Phosphate Curing Agents for Epoxy
P. V. Nikolaev and L. N. Lebedeva
Ivanovo State Academy of Chemical Technology, Ivanovo, Russia
Received March 20, 2002
Abstract-Fundamental aspects of how epoxy polymeric materials are formed on the basis of phosphate
curing systems undergoing homopolycondensation were studied. The advisability of using phosphate curing
agents in a microheterogeneous colloid-dispersed state was demonstrated.
The wide use of epoxy composite materials (ECM)
containing no organic solvents has shown that they
have, together with numerous advantages and, oc-
casionally, unique properties, also disadvantages as-
sociated with the toxicity of the volatile components
(epichlorohydrin, toluene) contained in epoxy oligo-
mers (EO). The assortment of curing agents used in
ECM containing no organic solvents is rather narrow.
The most widely used at present are aliphatic amines,
which allow deposition of polymeric epoxy coatings
without heating. As a rule, the amines used are toxic.
Important disadvantages of epoxy polymeric systems
obtained with the use of most of amine curing agents
is their poor thermal stability and high combustibility.
In this connection, development of new ecologically
safe curing agents improving the thermal stability and
lowering the combustibility of epoxy polymeric ma-
terials is an urgent task.
Particularly noteworthy is the use of orthophos-
phoric acid as a curing agent for ECM, since one of
the best fire retardants, phosphorus, and an environ-
mentally pure fire retardant, water, are introduced into
the material in this case. However, investigations of
the systems epoxy oligomer ED-203H
demonstrated that the lifetime of the composites is
short, and the degree of their curing strongly depends
on the content of water in the acid .
In order to make lower the activity of H
to improve the technological properties of the systems
being cured, and to enhance their thermal stability and
diminish combustibility, a technique for obtaining
new phosphate curing agents (PCA) of inorganic ori-
gin was developed.
As a raw material for their preparation served large-
tonnage commercial products: H
, red iron oxide
pigment, and talc. The components of phosphate
pastes (PP) were mixed without heating. The relative
contents of the solid and liquid phases, as a rule, cor-
responded to acid capacity of the first degree. In the
initial state, PCAs are pastes that can spontaneously
undergo homopolycondensation without heating of
the system. Owing to this circumstance, it is possible
not to perform precise dosage of the components in
formulating an epoxy composite.
The reactions in which condensed phosphates
(PCA prepolymers) are formed in curing agents
(homopolycondensation) occur in stages. It is known
forms with iron(III) oxide three types
of salts: 2Fe(H
O (hydrophosphate), and 2FePO
O (orthophosphate). Curing of PPs and their po-
lycondensation yields polymeric phosphate stone.
The intermediate products of homopolycondensa-
tion, iron dihydro- and hydrophosphates, are reactive
toward EOs and can cure them. The functionality of
incomplete phosphates with respect to EO, follow-
ing from their structure, is 6 and 3 for, respectively,
dihydro- and hydrophosphates. This ensures prepara-
tion of an epoxy-phosphate organo-inorganic poly-
meric material with three-dimensional network struc-
ture, which may contain
fragments. The final products of homopolyconden-
sation, iron orthophosphate and polymeric inorganic
phosphate , are inert toward the EO.
In their aggregation state, the curing agents are
phosphate pastes of color determined by the presence