The Regularities of polyurethane foam chemical degradation with thiodiglycol

Article abstract of DOI:10.1134/S1070363212090162

Abstract-A pattern was studied of the process of chemical degradation of elastic polyurethane foam under the action of thiodiglycol and its mixture with oxypropylated oligopolyol. It was established that in the systems simulating the process of polyurethane degradation the introduction of sulfur atoms in the hydrocarbon chain of glycol reduced its activity in the reaction with the urethane and reduced the thermodynamic stability of the urethanes formed. On the basis of recycled sulfur-containing oligoether-urethane a polyurethane sealant resistant against oil and petrol was obtained.

Full text of DOI:10.1134/S1070363212090162

ISSN 1070-3632, Russian Journal of General Chemistry, 2012, Vol. 82, No. 9, pp. 1546–1551. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © I.N. Bakirova, E.I. Galeeva, A.Ya. Samuilov, 2012, published in Zhurnal Obshchei Khimii, 2012, Vol. 82, No. 9, pp. 1511–1516.
The Regularities of Polyurethane Foam Chemical Degradation
with Thiodiglycol
I. N. Bakirova, E. I. Galeeva, and A. Ya. Samuilov
Kazan State Technological University, ul. K. Marksa 68, Kazan, Tatarstan, 420015 Russia
e-mail: galeeva-el@mail.ru
Received July 7, 2011
Abstract—A pattern was studied of the process of chemical degradation of elastic polyurethane foam under the
action of thiodiglycol and its mixture with oxypropylated oligopolyol. It was established that in the systems
simulating the process of polyurethane degradation the introduction of sulfur atoms in the hydrocarbon chain of
glycol reduced its activity in the reaction with the urethane and reduced the thermodynamic stability of the
urethanes formed. On the basis of recycled sulfur-containing oligoether-urethane a polyurethane sealant
resistant against oil and petrol was obtained.
DOI: 10.1134/S1070363212090162
Recycling of plastic waste can solve the problem of
environmental protection and shortage of raw material.
A lot of research concerns the chemical processing of
polyurethane waste [1–3]. One of the reasonable and
efficient ways of processing the waste is the method of
alcoholysis based on the thermochemical interaction of
polyurethane with hydroxy compounds [4]. To date a
number of such compounds is known, but they do not
include polyols. The use of the latter would lead to the
formation in the process of alcoholysis of the reactive
oligomers containing in the chain, for example, atoms
of sulfur, phosphorus, and silicon. Such oligomers in
the future might be of interest for polymer composites
with a complex of special properties.
to reduce the concentration of hydroxy groups in the
degradation product. Use of the Laprol 3603 for these
purposes was due to the identity of its structure with
that of the oligoether block of the foam to be
destructed, which simplifies the structure of the
products. This fact contributes to a better repro-
ducibility of the technology of recycled raw materials
and the quality of the products based on it.
Quantum-Chemical Study of the Thermodynamic
Regularities in the Reactions of Alcoholysis
of the Model Compounds
To determine the effect of glycols on the
equilibrium in the reaction of the foam alcoholysis we
carried out quantum-chemical calculations of the
thermodynamic parameters in the model trans-
formations, the reactions of thiodiglycol, dithiodig-
lycol, diethylene glycol, and butanediol with phenyl-N-
phenylurethane [Eqs. (1)–(4)]. The data obtained are
compiled in Table 1.
This idea formed the basis of the present study of
the pattern of chemical degradation of the elastic
polyurethane foam waste under the action of
thiodiglycol and its mixture with oxypropylated
oligopolyol, and of the application of the alcoholysis
products in the synthesis of polyurethanes. The
presence of a sulfur atom and hydroxy groups in the
structure of thiodiglycol, as well as relatively high
thermal stability (bp 283°C) make this compound
promising for use in the chemical degradation of
elastic polyurethane foam waste.
HOCH2CH2SCH2CH2OH + С6Н5NHC(O)ОС6Н5
→ С6Н5NHC(O)ОCH2CH2SCH2CH2OH + С6Н5ОН, (1)
НOCH2CH2S–SCH2CH2OH + С6Н5NHC(O)ОС6Н5
→ С6Н5NHC(O)ОCH2CH2S–SCH2CH2OH
+ С6Н5ОН,
(2)
HOCH2CH2OCH2CH2OH + С6Н5NHC(O)ОС6Н5
→ С6Н5NHC(O)ОCH2CH2OCH2CH2OH + С6Н5ОН, (3)
The process of destruction was carried out by the
action both of individual thiodiglycol, and mixtures
thereof with Laprol 3603. The replacement of a part of
thiodiglycol by Laprol 3603 was dictated by the need
НOCH2CH2CH2CH2OH + С6Н5NHC(O)ОС6Н5
→ С6Н5NHC(O)ОСН2СН2СН2СН2ОН + С6Н5ОН. (4)
1546

THE REGULARITIES OF POLYURETHANE FOAM CHEMICAL DEGRADATION
1547
Table 1. Enthalpy (ΔHr0), entropy (ΔSr0), and the equilibrium
constant (Keq) of the reactions of phenyl-N-phenylurethane
with thiodiglycol, dithiodiglycol, diethylene glycol, and
butanediol in the gas phase at 298, 333 and 473K
All the considered reactions are characterized by
small transformation entropy. This is primarily due to
the fact that during the interaction the number of
translational and rotational degrees of freedom of
movement does not change but only the numerical
values alter. Enthalpies of the same reactions were
significantly more sensitive to the changes in the
structure of glycols. The reaction with butanediol is
exothermic and is characterized by the highest values
of the equilibrium constants (Table 1). In all other
cases the transformation is endothermic. While in the
reactions with butanediol an increase in the tem-
perature leads to a decrease in the equilibrium con-
stant, in the reactions with other glycols the opposite
trend is observed: an increase of the equilibrium
constants with increasing temperature. The lowest
values of equilibrium constants occur in the transf-
ormation with dithiodiglycol. These data suggest that
the use of dithiodiglycol for the process of poly-
urethane foam alcoholysis is problematic.
ΔHr0,
ΔSr0,
Reaction
1
Kp298
Kр373
Kp473
kJ mol–1 J K–1 mol–1
7.11
24.66
1.11
1.99
З.21
2
3
4
10.58
5.77
21.11
24.20
23.00
0.17
1.84
0.41
2.94
0.86
4.27
–30.01
3.1×106 3.47×105 3.43×104
phenol and phenyl isocyanate at 147°C. After 125°C
begins immediately the mass loss by phenyl-N-
phenylurethane due to the transition into the gas phase
of the produced phenyl isocyanate and phenol. These
data give grounds to assume that at temperatures below
125°C the reaction of glycols with phenyl-N-
phenylurethane will mainly occur along the second
pathway.
Kinetic Study of the Model Alcoholysis Reactions
with Phenyl-N-phenylurethane
The kinetic studies were performed at 80°C. We
found that the non-catalyzed conversion proceeds very
slowly. Therefore, the reaction of the glycols with
phenyl-N-phenylurethane was carried out in the
presence of tin(II) octanoate as a catalyst. Table 2 lists
the second order reaction rate constants of the studied
reactions of glycols with phenyl-N-phenylurethane.
The thermodynamic parameters of reactions do not
allow us to estimate the activity of the considered
glycols in the process of alcoholysis of phenyl-N-
phenylurethane. Therefore, we carried out a study of
the kinetics of the alcoholysis process in model
reactions of phenyl-N-phenylurethane with thiodi-
glycol, dithiodiglycol and butanediol. These trans-
formations may proceed in two directions [10]. The
first path involves the thermal dissociation of phenyl-
N-phenylurethane to form phenyl isocyanate and
phenol, followed by reaction of phenyl isocyanate with
glycol to form urethane. The second path is the direct
replacement of the phenol group at the carbonyl carbon
atom in the phenyl-N-phenylurethane [Eqs. (5)–(7)].
Under these conditions, dithiodiglycol reacts so
slow that the rate constant of its reaction could not be
described quantitatively. The highest rate constant was
found in the reaction involving butanediol. It follows
С6Н5NHC(O)ОС6Н5 ⇄ С6Н5NCO + С6Н5ОН,
С6Н5NCO + ROH → С6Н5NHC(O)ОR,
(5)
(6)
С6Н5NHC(O)ОС6Н5 + ROH
→ С6Н5NHC(O)ОR + С6Н5ОН.
(7)
To estimate the temperature range of the mono-
molecular decay of phenyl-N-phenylurethane to
phenylsocyanate and phenol, we performed the DSC-
TGA study of the process (Fig. 1).
The DSC curve of phenyl-N-phenylurethane
includes two endothermic peaks. The first one cor-
responds to the melting of phenyl-N-phenylurethane at
125°C, the second to its intense decomposition into
Т, °С
Fig. 1. DSC (1) and TGA (2) curves of phenyl-N-phenyl-
urethane.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 9 2012

1548
BAKIROVA et al.
Table 2. The second order reaction rate constants of phenyl-
N-phenylurethane with glycols in chlorobenzene in the
presence of tin(II) octanoate at 80°Ca
R1NHC(O)NHR1 + R2OH
→ R1NHC(O)OR2 + R1NH2.
(9)
Due to the complexity of the separation of amino
and hydroxy groups, the monitoring of the alcoholysis
process extent was carried out by the determination of
their total concentration c(OH+NH2) in the system.
The determination of c(OH+NH2) in the initial period
of decomposition showed a wide variation of this
value. Given that the concentration of OH and NH2
groups in the system should remain unchanged
because the decomposition proceeds by the reactions
of the exchange type, the changes in the content of
these groups in the early hours of alcoholysis are of
tentative character. Obviously, this is due to the lack of
homogeneity of the system when analyzed samples
contain along with the products of alcoholysis the
particles of undestructed polyurethane foam. Therefore
in the figures we used dotted lines for this time
interval.
Glycol
kII×104 l mol–1 s–1
b
Dithiodiglycol
Thiodiglycol
Butane-1,4-diol
9.64
3.7
a
Initial concentration: [c(phenyl-N-phenylurethane)]0 = 0.1 M,
[c(glycol)]0 = 0.1 M, [c(tin(II) octanoate)]0 = 0.01 M. b Reaction
proceeds very slowly.
from the data in Tables 1 and 2 that the introduction of
sulfur atoms into the glycol structure and the increase
in their number lead to a decrease in the kinetic and
thermodynamic feasibility of the reactions as
compared with the butanediol.
Patterns of Chemical Degradation of Elastic
Polyurethane Foam
At higher conversions, the c(OH+NH2) value
stabilized in time, and for the system (polyurethane
foam + thiodiglycol) it was 20.2 wt. %, and for the
system (polyurethane foam + thiodiglycol + Laprol
3603), 12.2% wt. (Fig. 2). The reduction of the plateau
level in the second case is due to the replacement of
thiodiglycol by Laprol 3603, having a low con-
centration of hydroxy groups. This increases the
duration of the establishment of the equilibrium in the
system. A further increase in the destruction time leads
to a decrease in the content of OH and NH2 groups,
connected obviously with the beginning of the process
of secondary structization. Raising the temperature has
almost no effect on the c(OH+NH2) equilibrium value,
but can significantly reduce the time needed to achieve
it (Fig. 3).
Further we studied the alcoholysis of polyurethane
foam at the action of thiodiglycol and its mixture with
Laprol 3603. An important technological parameter
that allows the control of the process of the chemical
degradation and the recycling the alcoholysis products
is the concentration of terminal functional groups. In
the tested substance their role play the hydroxy and
amino groups. Their formation is due to the
alcoholysis of urethane and urea bonds in the poly-
urethane foam [Eqs. (8), (9)].
R1NHC(O)OR2 + R3OH → R1NHC(O)OR3 + R2OH, (8)
Another sensitive indicator of the impact of
degradation conditions on the state of the system is the
dynamic viscosity. This characteristic made it possible
for us to cover the entire time range of the studied
process, including the initial period when the products
of the alcoholysis are still heterogeneous and contain
gel-like inclusions of polyurethane foam.
Investigation of dynamic viscosity at the
alcoholysis (Fig. 4) showed its monotonic decrease in
the initial steps of the process due to the deepening of
the processes of destruction. Over time, the viscosity
stabilized. Further heating, coinciding with the fall in
c(OH+NH2), led to an increase in viscosity, connected
obviously with the negative impact of the process of
τD, min
Fig. 2. Dependence of the total concentration of OH and
NH2 groups [c(OH+NH2)] in the alcoholysis products on
the degradation time (tD) at 180°C: (1) polyurethane foam
+ thiodiglycol, (2) polyurethane foam + thiodiglycol +
Laprol 3603.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 9 2012

THE REGULARITIES OF POLYURETHANE FOAM CHEMICAL DEGRADATION
1549
τD, min
τD, min
Fig. 3. Dependence of the total concentration of OH and
NH2 groups [c(OH+NH2)] in the products of alcoholysis of
(polyurethane foam + thiodiglycol + Laprol 3603) vs. the
time of degradation (tD) at different temperatures: (1) 180°C,
(2) 200°C.
Fig. 4. Dependence of dynamic viscosity (η50°C) of the
products of alcoholysis of (polyurethane foam + thio-
diglycol + Laprol 3603) vs. the time of degradation (tD) at
different temperatures: (1) 180°C, (2) 200°C.
polycondensation of the formed products of alco-
holysis.
EXPERIMENTAL
The quantum-chemical calculations of the
thermodynamic parameters of the model reactions
were carried out by nonempirical hybrid method
B3LYP in the extended basis STO-6-31G(d) with full
geometry optimization of compounds using the
software package Gaussian-03 [5].
IR spectroscopic study of the products obtained
showed the presence of the absorption bands
characteristic of an ether bond (1074 cm–1), C–S bond
(800–600 cm–1), vibrations of the C–C bond of
aromatic fragment (1636–1600 cm–1), and urethane
bonds (1540, 1718 cm–1), as well as hydroxy and
amino groups (region of 3360–3340 cm–1). The
presence of these groups in the spectrum allow us the
characterization of the recycled raw material as a
mixture of compounds with terminal hydroxy and
amino groups containing in the backbone sulfide,
urethane, and ether bonds.
Synthesis of phenyl-N-phenylurethane was per-
formed in accordance with the method of [6].
DSC-TGA studies of phenyl-N-phenylurethane
were carried out with a Simultaneous DSC-TGA
thermoanalyzer Q Series TM. The heating rate was
2 deg min–1 in the temperature range 25–300°C.
Properties of the Polyurethane Sealants on the Basis
of a Sulfur-Containing Recycled Oligoether-Urethane
Kinetic studies of reactions of thiodiglycol, 1,4-
butanediol, and dithiodiglycol with the phenyl-N-
phenylurethane were carried out using infrared
spectroscopy on a Perklin-Elmer instrument in a cell
with windows of KBr (dcell = 0.22). The reaction was
monitored by the change in intensity of the absorption
band of the stretching vibrations of the carbonyl group
at 1757 cm–1 (the original phenyl-N-phenylurethane)
and 1730 cm–1 (stretching vibrations of the carbonyl
group of the formed urethane). The process was
carried out at 80°C in chlorobenzene medium at
equimolar ratio of the reagents in the presence and
absence of tin(II) octanoate catalyst. The initial
concentration of phenyl-N-phenylurethane and glycol
were 0.1 M, catalyst concentration, 0.01 M.
On the basis of a sulfur-containing recycled
oligoether-urethane a protecting-sealant composition
was developed with the properties listed in Table 3.
The developed sealant, due to the presence in its
structure of the sulfur atoms and the additional amount
of urethane fragments through the application in the
synthesis of recycled oligoether-urethane is superior to
the commercially available polyurethane analogs (UG-2,
and Forsage) in oil and fuel resistance. In comparison
with thiocol compositions (U30M), the developed
composition surpasses them in strength properties and
water resistance, but exhibits less resistance to
hydrocarbon solvents.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 9 2012

1550
BAKIROVA et al.
Table 3. Properties of the developed and commercial sealing compositions of the thiocol and polyester-urethane nature
Sealants
industrial
UG-2
Property
proposed
6.2–7.3
U30M
forsage
1.5–2.0
Conditional tensile strength, MPa
Elongation, %
1.2–2.0
8–12
250–350
150–300
350–450
300–400
Relative residual deformation, %
0–2
0–8
0.3–0.5
–
2–4
2.1
10–12
0.3–0.5
–
Adhesion to metal at peeling, kN m–1
1.5–2.5
24–28
Elasticity, %
15–18
Hardness, conventional units
60–65
50–60
55–60
–
Equilibrium swelling degree, %
Water
2
5
4
12
<1
<1
2
13
9
3
Gasoline
15
10
Transformer oil
The rate constants were calculated from the initial
rates determined from the kinetic curves of phenyl-N-
phenylurethane consumption and the accumulation of
the urethane produced in the reaction, according to a
second order equation.
the products of alcoholysis was determined on a
Heppler viscometer at 50°C.
The chemical structure of products of alcoholysis
was determined by IR spectroscopy on a Perklin-Elmer
spectrometer. To obtain spectra a sample drop was
sandwiched between KBr glasses.
Alcoholysis was carried out in a flask equipped
with a stirrer and a reflux condenser at 180 and 200°C.
In this temperature range the urethane fragments do
not decompose to isocyanates and alcohols, and
alcoholysis reactions proceed along the mechanism of
substitution at the carbonyl carbon atom [7]. The flask
was charged with degrading agent: thiodiglycol or its
mixture with oxypropylated oligopolyol Laprol 3603
(M ~3600, the functionality with respect to the OH
group was three). Then the temperature was adjusted
to a predetermined level and a crumb of elastic poly-
urethane foam with nominal diameter of 3–5 mm was
continuously injected. The feed rate of the foam crumb
was adjusted in accordance with the rate of its
dissolution. The weight ratio of polyurethane
foam:degrading agent was 40:60, which was chosen
experimentally on the basis of calculating the
maximum amount of waste foam and a minimum of
degrading agent. To prevent the development of the
processes of thermal oxidative degradation, the
alcoholysis was carried out in a flow of nitrogen. The
start of the process of destruction was the moment of
the introduction of the polyurethane foam crumb to the
degrading agent. In the course of alcoholysis of the
polyurethane foam samples for analysis were taken.
The total content of hydroxy and amino groups
[c(OH+NH2)] in the samples was determined by
chemical method [8]. The dynamic viscosity (η50°C) of
The sealant was synthesized by the reaction of the
isocyanate component with
a
sulfur-containing
recycled oligoether-urethane [9]. The molar ratio
NCO:(OH+NH2) was 1:1. Carbon black was used as a
filler. To accelerate the curing, the tin octanoate
catalyst was injected. Physical and mechanical tests of
the sealants were carried out according to the
following standards: conventional tensile strength,
elongation at break, residual elongation at break
according to GOST 2151-76, the strength of adhesion
to the metal (steel 3) at peeling by the GOST 21981-
76, the hardness by the GOST 263-75, elasticity
rebound according to GOST 6950-73, the equilibrium
degree of swelling by GOST 421-59.
ACKNOWLEDGMENTS
This work was financially supported by the Federal
Target Program “Research and scientific-pedagogical
personnel of innovation in Russia” for 2009-2013,
state contract no. P478
REFERENCES
1. Pilz, E. and Lang, R.W., Kunststoffe, 1998, vol. 88,
no. 4, p. 547.
2. Sadykova, L.Sh., Radionova, A.I., Spiridonova, R.R.,
Bakirova, I.N., and Kochnev, A.M., Vestnik
Kazanskogo Tekhnol. Univ., 2010, no. 2, p. 279.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 9 2012

THE REGULARITIES OF POLYURETHANE FOAM CHEMICAL DEGRADATION
1551
3. Sendijarevic, V., J. Cell. Plast., 2007, vol. 43, p. 31.
Clifford, S., Cioslowski, J., Stefanov, B.B., Liu, G.,
Liashenko, A., Piskorz, P., Komaromi, I., Martin, R.L.,
Fox, D.J., Keith, T., Al-Laham, M.A., Peng, C.Y.,
Nanayakkara, A., Challacombe, M., Gill, P.M.W.,
Johnson, B., Chen, W., Wong, M.W., Gonzalez, C., and
Pople, J.A., Gaussian Inc., PA, 2003.
4. Bakirova, I.N., Valuev, V.I., Demchenko, I.G., and
Zenitova, L.A., Vysokomol. Soed., A, 2002, vol. 44,
no. 6, p. 987.
5. Frisch, M.J., Trucks, G.W., Schlegel, H.B., Scuseria, G.E.,
Robb, M.A., Cheeseman, J.R., Montgomery, J.A.,
Vreven, T., Kudin, K.N., Burant, J.C., Millam, J.M.,
Iyengar, S.S., Tomasi, J., Barone, V., Mennucci, B.,
Cossi, M., Scalmani, G., Rega, N., Petersson, G.A.,
Nakatsuji, H., Hada, M., Ehara, M., Toyota, K., Fukuda, R.,
Hasegawa, J., Ishida, M., Nakajima, T., Honda, Y.,
Kitao, O., Nakai, H., Klene, M., Li, X., Knox, J.E.,
Hratchian, H.P., Cross, J.B., Adamo, C., Jaramillo, J.,
Gomperts, R., Stratmann, R.E., Yazyev, O., Austin, A.J.,
Cammi, R., Pomelli, C., Ochterski, J.W., Ayala, P.Y.,
Morokuma, K., Voth, G.A., Salvador, P., Dannenberg, J.J.,
Zakrzewski, V.G., Dapprich, S., Daniels, A.D., Strain, M.C.,
Farkas, O., Malick, D.K., Rabuck, A.D., Raghavachari, K.,
Foresman, J.B., Ortiz, J.V., Cui, Q., Baboul, A.G.,
6. Shriner, R.L., and Fuson, R.C., The Systematic Iden-
tification
of
Organic
Compounds,
Moscow:
Inostrannaya Literatura, 1950.
7. Ulrich, H., Odinak, A., Tucker, B., and Sayigh, A.A.R.,
Polymer Eng. and Sci., 1978, vol. 18, no. 11, p. 844.
8. Siggia, S. and Hhana, J., Quantitative Organic Analysis
via Functional Groups, Moscow: Khimiya, 1983.
9. Galeeva, E.I., Bakirova, I.N., Samuilov, Ya.D.,
Samuilov, A.Ya., and Mitrofanova, S.E., RF Patent
no. 2332431, Byul. Izobr., 2008, no. 24, Ch. 4, p. 669.
10. Volodarskaya, Yu.I., Sal’nikova, G.A., and Shmidt, Ya.A.,
Dokl. Akad. Nauk SSSR, Ser. Khim., 1970, vol. 195,
no. 4, p. 841.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 82 No. 9 2012