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EC number: 218-485-4
CAS number: 2162-73-4
In the tests with leachate from a refuse
tip, the macroscopic observation of the foams at the end of the
incubation time showed a partial breakdown of the structure depending on
the temperature and the PUR-foam involved. This degradation could best
be seen in the case of PUR-polyester foam incubated at 50 °C where a
considerable amount of the foam had been transformed into a pulverised
condition with a deep brown coloration; a much smaller change was
observed at 22 °C. Structural breakdown of the PUR-polyether foams (TDI-
and MDI-based) at 50 °C occurred only to a very small extent. At 22 °C
no change could be detected in these foams. These visual assessments of
the relative degrees of degradation were confirmed by the amounts of
activity found in the filtrates.
After the extraction of composted refuse
with acidified water, the radioactivities found in all extracts
indicated a degradation only to a very small extent. The highest values
(max. 0.3 % of the original activity) were found in the case of the
rigid polyether foam (MDI-based). The radioactivities found in the
extracts of the soil gave values within the range of normal background
activity so that further experimentation was pointless. The extraction
of the pure PUR-foams with acidified water (pH 1) gave no indication
that radioactivity was liberated by this procedure.
As a result of the low amounts of
radioactivity found in the chloroform extracts (see Table II), TLC
analysis could only be made with the extracts of the leachate
experiments carried out at 50 °C. These analyses showed that in the case
of PUR-polyester foam, an average of0.25~o(values from duplicate
experiments) of the original activity was identifical to the Rfvalue of
2,4-TDA and 0.38 %with that of 2,6-TDA. A further 0.26 % appeared as
unknown degradation products. Of the initial activity of the
PUR-polyether foam (T-DI-based), 0.015 %could be associated with 2,4-TDA
and 0.025 % with 2,6-TDA.
The weekly monitoring of 14CO2 indicated
that in the case of all leachate experiments, no liberation of
14C-labelled CO2 could be detected. In the test with composted refuse,
radioactivity could be found in the 14CO2 absorption systems but only as
a very small percentage of the originally applied activity. At the
incubation temperature of 22 °C, 0.015 % was released as 14CO2, at 50
°C, the values from all types of foams involved increased by a factor of
ten to 0.15 % In the experiment with the soil (22 °C), a release of 0.01
% (TDI- and MDI-based PUR-polyether foam) or 0.06 % (TDI-based PUR-ester
foam) was detected.
The experiments with TDI-based PUR-foams
(polyester and polyether types) incubated under environmental condition
in a refuse tip confirmed the results found in the laboratory test,
i.e., that the PUR-ether foams highly resist degradation and that the
PUR-ester-foams are quite susceptible (see Table III).
The test carried out to simulate a high
content of TDA- and MDA-polyureas after a spillage of the monomeric
isocyanates gave no indication of a degradation of these polymeric
products. Radioactivity was found neither in the extracts nor in the COE
absorption systems of all three soils under investigation.
In the experiments carried out in the
laboratory, two criteria of degradation were selected: (a) the
appearance of the aromatic amines in the extracts, and (b) the
liberation of 14CO2. The results obtained from the tests with PUR-foams
show that these two criteria did not correspond with one another. In the
case of all three PUR-foams in the leachate at 50°C, the presence of
TDAs and MDA was definitely detected, but no 14CO2. In the test with
soil and compost, the conversion of small amounts of the 14C-labelled
foams to 14CO2 was established, but no aromatic amines could be detected.
In interpreting these results, the
properties of the media, of the foam and of the aromatic amines must be
considered. It is well known that a combination of moisture and heat
favors the chemical hydrolysis, especially those of the polyester-based
PURfoams. It is reasonable to suppose that this mechanisms was
responsible for the formation of TDAs and MDA in the leachate
experiments carried out at 50 °C. In accordance with present knowledge
of the breakdown of aromatic compounds by microorganisms, the
possibility of microbial degradation of TDAs and MDA liberated can be
postulated. Therefore, it must be presumed that the microbial activity
in the leachate was so minimal that an accumulation of the aromatic
amines liberated by hydrolysis occurred.
In the tests with soil and refuse compost,
the foams were subjected to both chemical hydrolysis and microbial
attack. From the low amounts of radioactivity found in the extracts or
as 14CO2 it can be concluded that chemical as well as microbial
degradation was unimportant and negligible. The low amounts of aromatic
amines liberated in these media were obviously easily degraded to CO2.
The remarkable difference in degradation between the polyester-based
foam and the polyether-based foams as found in the leachate experiments
at 50 °C could not be confirmed in the tests with soil and compost.
Another factor influencing the appearance of
aromatic amines under all experimental conditions tested is the known
autoxidation of these compounds in the presence of water and air
(Beilstein, XIII, Nr. 1740-1871). This chemical reaction is
characterised by the formation of dark brown derivatives which are
obviously responsible for the staining of the partially degraded
PUR-foams, especially the PUR-ester foams.
The extent of such oxidation is a matter for
conjecture and the compounds thus produced could represent the major
part of the activity in the aqueous phase which could not be extracted
The results of the experiments carried out
in the refuse tip confirmed the high stability of polyether-type foam in
contrast to the susceptibility of the polyester-type foam. From the fact
that degradation of this foam was less in the stratified fill, where the
cubes had no direct contact with the strong basic caustic lime, it is
supposed that chemical breakdown was a main factor for the degradation
of the polyester-type foam.
To assess the possibilities of the
liberation of toxic aromatic amines under different conditions of
disposal, the degradation of different 14C-labelled polyurethane foams
was investigated in the leachate of a refuse tip, in composted municipal
waste and in an agricultural soil. With unlabelled foam cubes
experiments were run under the environmental conditions of a refuse tip.
In addition, the degradation of 14C-labelled polyureas was studied in
different agricultural soils. In the laboratory tests the criteria of
degradation were the liberation of aromatic amines and the production of
14CO2. The degradation in the refuse tip was estimated on the basis of
From the results it can be assumed that the
polyether based polyurethane foams are largely resistant to microbial as
well as chemical attack under all practical conditions of disposal.
Polyester based polyurethane foams are susceptible to chemical
hydrolysis favored by extreme environmental conditions such as high
temperature and/or low or high pH values. Under these circumstances an
accumulation of aromatic amines can occur if their further microbial
degradation is impeded by the lack of suitable conditions for the growth
of microorganisms. No indication of any degradation of the isocyanate
based polyureas was found.
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