1070-4272/05/7804-0685 + 2005 Pleiades Publishing, Inc.
Russian Journal of Applied Chemistry, Vol. 78, No. 4, 2005, pp. 685!687. Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 4, 2005,
Original Russian Text Copyright + 2005 by V.Maslosh, Kotova, O.Maslosh.
Decreasing the Content of Free Formaldehyde
in Urea!Formaldehyde Resins
V. Z. Maslosh, V. V. Kotova, and O. V. Maslosh
Institute of Applied Chemistry, Ministry of Science and Education of the Ukraine, Rubezhnoe,
Lugansk oblast, Ukraine
Received June 14, 2004
Abstract-The possibility of decreasing the content of free formaldehyde in urea3formaldehyde resins by
varying the pH and urea3formaldehyde ratio in various synthesis steps was examined. Urea3formaldehyde
resins containing no free formaldehyde were prepared.
Urea3formaldehyde resins (UFRs) are widely used
binders. Their significant drawback is the toxicity
caused by the presence of free formaldehyde (FA); its
content depends on the preparation conditions .
The influence of process parameters on the prop-
erties and structure of UFRs was examined in nu-
merous studies , but the problem is far from
being solved because of the complexity of the reac-
tions involved in UFR formation. Polycondensation
in the urea3FA system is accompanied by many side
reactions (hydrolysis, cyclization, addition, etc.),
affecting the functional composition of the product.
The kinetic features and mechanisms of these reac-
tions are different . An additional factor complicat-
ing the mechanism of UFR formation is the polyfunc-
tional nature of urea and FA.
In this study, we examined how the process param-
eters affect the content of free FA in UFRs prepared
at varied pH values and urea : FA ratios in particular
UFRs were prepared at 82+3oC and varied pH in
three steps. The urea : FA molar ratio in these steps
was 1 : 4, 1 : 1.45, and 1 : 1.33. In the course of the
synthesis, we monitored the content of free FA and
methylol groups (MGs) . The experimental results
are shown in Fig. 1. In run nos. 1 and 2, step I was
performed in an acidic solution (pH 4.535.0), and
steps II and III, in an alkaline solution (pH 9.5310.0).
In run nos. 3 and 4, step I was performed in an alka-
line solution (pH 9.5310.0); step II, in an acidic solu-
tion (pH 4.535.0); and step III, again in an alkaline
solution (pH 9.5310.0). In run nos. 5 and 6, steps I
and III were performed similarly to run nos. 3 and 4,
and step II, at pH 2.032.5. In run nos. 7 and 8, all
the three steps were performed in an alkaline solution
(pH 9.5310.0). In run nos. 1, 3, 5, and 7, urea was
loaded in a single portion in each step; in run nos. 2,
4, 6, and 8, the same amounts of urea were loaded uni-
formly in equal portions during the course of the pro-
cess step. A detailed protocol of UFR preparation and
the UFR structure were reported in [7, 8].
Experimental data show that the properties and
toxicity of UFRs are appreciably influenced by such
process factors as the mode of loading urea, pH of
the medium, and reaction time, and also by the con-
centrations of urea and FA. In the UFR synthesis in
an alkaline solution, when urea is loaded in a single
portion, the content of free FA is 0.133
0.14, and that
of MGs, 18.6319.8 wt % (Fig. 1d, curves 1 and 1`);
when urea is loaded uniformly, the content of free
FA is 0.0530.09, and that of MGs, 18.5319.7 wt %
(Fig. 1, curves 2 and 2`). A longer reaction in alkaline
solution does not result in an appreciable decrease in
the free FA content.
In the synthesis of UFR in an alkaline solution,
a steady decrease in the free FA content is accompa-
nied by a smooth increase in the MG content, which
reaches 23.0323.5 wt % (Fig. 1, curves 1` and 2`).
It has been shown previously  that the UFR formed
under such conditions is of mostly linear structure,
with a high content of methylene ether bonds. The
ready hydrolysis of the methylene ether bonds and
the equilibrium character of MG formation account
for the reproducibly high content of free FA in UFR
samples prepared in alkaline solution.