- Email: [email protected]
Thermal degradation of semi-interpenetrating polymer networks based on polyurethane and epoxy maleate of bisphenol A
Polymer Testing 22 (2003) 45–49 www.elsevier.com/locate/polytest
Material Behaviour
Thermal degradation of semi-interpenetrating polymer networks based on polyurethane and epoxy maleate of bisphenol A C.N. Cascaval ∗, D. Rosu, L. Rosu, C. Ciobanu Petru Poni Institute of Macromolecular Chemistry, Romanian Academy, Aleea Gr. Ghica Voda, No 41A, Iasi 6600, Romania Received 9 February 2002; accepted 22 April 2002
Abstract Two polyurethane–epoxy maleate of bisphenol A semi-interpenetrating polymer networks were synthesized and their thermal behavior studied. The data obtained by thermogravimetry showed that the decomposition of the tested samples is complex, occurs in three steps, and depends on the degree of crosslinking. The main decomposition takes place between 290 and 480 °C, with weight losses between 62 and 66%. The apparent thermal stability of the sample synthesized with a low content of epoxy maleate of bisphenol-A (11.11 wt%) is lower compared with polyurethane, while the sample with high content of epoxy maleate of bisphenol-A (27.3 wt%) shows a higher stability. 2002 Elsevier Science Ltd. All rights reserved.
1. Introduction Thermoplastic polyurethane (TPU), because of its high tensile strength, chemical resistance, good processability and mechanical properties, is being used in many technical applications [1]. It is generally inappropiate for structural applications due to its low stability to the thermoxidative processes. The thermal stability of TPU can be much improved by modification with caesium cations [2], incorporation of mica in its structure [3,4], or by chemical combination with other polymers, in order to obtain properties with specific needs. In recent years, there is considerable interest in mixtures with a second reactive polymer, so as to generate interpenetrating polymer networks (IPNs) [4,5]. In many cases, IPNs show excellent engineering properties due to a synergestic effect induced by the forced compatibility of the individual components, as was shown for PU-epoxy resin IPNs [6–10].
∗ Corresponding author. Tel.: +40-32-217-454; fax: +40322-112-99. E-mail address: [email protected] (C.N. Cascaval).
In our previous work, TPU–epoxy maleate of bisphenol-A (EMBA) blends [11], as well as TPU– EMBA semi-interpenetrating polymer networks (S-IPNs) [12] were synthesized and characterized according to their miscibility and the physico-mechanical properties. Differential scanning calorimetry (DSC) measurements evidenced a good miscibility of the studied systems. The physico-mechanical properties of the blends are lower as compared to TPU–EMBA S-IPNs. Presently, no data are available concerning the study of TPU–EMBA S-IPNs thermoxidative degradation. The aim of this paper is to report some data regarding the thermal behavior of PU–EMBA S-IPNs.
2. Experimental 2.1. Materials TPU used in this study was synthesized starting from poly (ethylene adipate) diol (PEA) and poly (ethylene diethylene adipate) diol (PEDA) in reaction with 4,4⬘diphenyl-methane diisocyanate (MDI), as was reported elsewhere [13].
0142-9418/02/$ - see front matter 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 1 4 2 - 9 4 1 8 ( 0 2 ) 0 0 0 4 7 - 8
46
C.N. Cascaval et al. / Polymer Testing 22 (2003) 45–49
EMBA resin was obtained by reaction between maleic anhydride and Dinox epoxy resin, in the presence of water [11]. Dinox resin was a commercial product obtained from bisphenol-A in reaction with epichlorohydrin. TPU–EMBA S-IPNs were prepared after a sequential procedure by mixing of both TPU and EMBA solutions in dimethylformamide (DMF) [12]. The mixtures were cast on glass slides and subsequently soft baked at 120 °C for 3 h on a hot plate. The solvent was completely removed and EMBA resin was thermally cured in the presence of 1 wt% benzoyl peroxide. The crosslinked EMBA resin included in its network structure the linear PU. Two S-IPNs were synthesized, the first one (S-IPN1) with low EMBA content (11.11 wt%) and the second one (S-IPN-2) with 27.3 wt% EMBA. 2.2. Apparatus and analysis Themogravimetry (TG) and derivative thermogravimetry (DTG) measurements were carried out using a MOM Budapest derivatograph, under the following operational conditions: sample weight 50 mg, heating rate 12 °C min⫺1, in atmospheric air and reference material α-Al2O3. All kinetic studies start with a basic equation which assumes that the rate of conversion at constant temperature, da/dt, is a linear function of conversion, a, through a rate constant k: da ⫽ kf(a) dt
冕
T
p
A ⫺E /RT da ⫽ e a dT f(a) b
a0
(2)
(5)
T0
If T0 is low, a0 ⫽ 0, and Eq. (5) can be expressed as
冕
a
p
g(a) ⫽
0
冕
T
p
da A ⫺E /RT e a dT ⫽ f(a) b
(6)
0
where g(a) is the integral function of conversion. Analysis of the thermogravimetric data obtained by thermal degradation of the tested S-IPNs was investigated using some integral methods which involve an approximate integration of Eq. (6), namely Coats– Redfern [14], Flynn–Wall–Ozawa [15,16] and Reich– Levi [17]. The Coats–Redfern method uses an asymptotic approximation for the resolution of Eq. (6), obtaining ln
AR Ea g(a) ⫽ ln ⫺ T2 bE RT
(7)
The Flynn–Wall–Ozawa method integrates Eq. (6) using the Doyle approximation [18] and the result is Eq. (8): 0.457Ea AE ⫺2.315⫺ logb ⫽ log g(a)R RT
(8)
The Reich–Levi method gives Ea on utilization of two different heating rates, b1 and b2 Ea ⫽
where A is the pre-exponential factor, Ea is the activation energy, T the absolute temperature and R the rate constant. In a nonisothermal condition the sample temperature is changed by a constant heating rate, b(b ⫽ dT / dt). In this case, the temperature being dependent on the time of heating, the reaction rate can be expressed as da da da dT ⫽ ⫽b . dt dT dt dT
p
(1)
In isothermal conditions, using the Arrhenius relationship, Eq. (1) can be written as follows: da ⫽ Af(a)e⫺Ea / RT dt
冕
a
2.3.R.log[b1 / b2(T2 / T1)2] (T1)⫺1⫺(T2)⫺1
(9)
3. Results and discussion The general structure of the synthesized TPU is as follows:
where,
(3)
A combination of Eqs. (2) and (3) leads to da A ⫺E ⫽ e a / RT dt b
(4)
Intergration of Eq. (4) from an initial temperature, T0 , when a ⫽ a0, to a peak temperature, Tp, when a ⫽ ap, gives
Fig. 1 shows TG and DTG curves recorded for both TPU and EMBA crude samples, as well as for the synthesized S-IPNs, respective of S-IPN-1 and S-IPN-2.
C.N. Cascaval et al. / Polymer Testing 22 (2003) 45–49
Fig. 1. Typical TG and DTG curves of TPU (쎲), EMBA (䊊), S-IPN-1 (䊏) and S-IPN-2 (䊐).
The TG plots in Fig. 1 show a typical sigmoidal form. Generally, the thermal degradation of the synthesized SIPNs in dynamic conditions and in the presence of oxygen shows three decomposition stages. The degradation onset temperature (T0) of the TPU networks was around 240 °C (start for the first stage), an increasing decomposition rate being observed between 290 and 480 °C (the second stage), when the weight loss W reaches about 60– 70 wt%. The third stage of decomposition for temperatures higher than 500 °C corresponds to the advanced fragmentation of the chain formed in the first and the second stages of decomposition, as well as to the secondary reactions of dehydrogenation and gasification processes. Almost complete decomposition was observed at 600 °C. The initial slow weight loss around 240–290 °C
47
is attributed to the presence of EMBA in TPU–EMBA S-IPNs. Some characteristics related to the temperature corresponding to 10% (T10) and 50% (T50) weight loss from the initial weight, as well as the temperature taken for the maximum rate of decomposition (Tm) along with initial decomposition temperature (Ti) are listed in Table 1. The curves in Fig. 1 and the data in Table 2 show that the synthesized S-IPNs exhibit little differences in thermal behavior as against the crude TPU. Taking Ti into consideration, it can be noted that the thermal stability of S-IPN-1 is lower than that of TPU, while S-IPN2 shows a higher thermal stability. To have a more complete picture of the thermal behavior of the studied S-IPNs, the modification of activation enegy, Ea, of the degradation process was investigated using Coats–Redfern, Flynn–Wall–Ozawa and Reich–Levi computational methods. The first two methods were used to calculate the Ea values, the order of reaction (n) and the pre-exponential factor (ln A), while by the third one, the change of Ea with conversion during degradation was evaluated. To use the Flynn– Wall–Ozawa method, the samples were decomposed at various heating rates, 10, 12 and 16 °C min⫺1. Some kinetic data obtained for the tested S-IPNs and for the crude polymers, in the second stage of degradation, are listed in Table 2. As can be noted, EMBA content has an important influence on the thermal degradation of the synthesized S-IPMs. Thus, S-IPN-1, with a low content of EMBA (11.11 wt%) shows a decrease of both W and Ea against TPU. The decrease of W can be assigned to an incipient beginning of crosslinking in the TPU–EMBA mixture. The decrease of Ea suggests that S-IPN-1 has a lower thermal stability as against the crude TPU. In our opinion this is due to the fact that, in the conditions employed, EMBA plays a small part as the crosslinked agent. Simultaneously, EMBA can act as a plasticizer in the PU– EMBA matrix, as was previously observed and reported for TPU–EMBA blends [11]. In contrast, S-IPN-2, with high content of EMBA [27.3 wt%], shows a pronounced increase of both Ea and n values versus the crude PU, along with a decrease of W and ln A. This means that EMBA is in the most part crosslinked and included in Table 1 Thermal behavior of TPU, EMBA, S-IPN-1 and S-IPN-2 macromolecular compounds Sample
T10 (°C)
TPU S-IPN-1 S-IPN-2 EMBA
311 315 313 319
T50 (°C) 419 416 413 411
Tm (°C)
Ti (°C)
404 418 392 390
247 238 251 157
48
C.N. Cascaval et al. / Polymer Testing 22 (2003) 45–49
Table 2 Kinetic and TG characteristics of the studied samples in the second stage of degradation Sample
Temperature range (⌬T)
W (%) Methods Coats–Redfern Ea (kJ mol⫺1)
PU S-IPN-1 S-IPN-2 EMBA
319–454 298–462 340–431 280–443
70 66 62 67
52 47 70 59
its matrix the linear PU. As a consequence, a network is generated with an apparent thermal stability much higher than that of TPU. Important modifications of Ea against composition of the studied samples are shown in Fig. 2. The plots in Fig. 2 do not show a very important difference in the thermal behavior of the tested samples. All the analyzed samples have a very sharp decrease of Ea with conversion. EMBA and S-IPN-1 show a pronounced decrease of Ea for conversion up to 0.2 and than Ea remains constant up to 0.6 conversion. In comparison with EMBA and S-IPN-1, the samples S-IPN-2 and PU start to decompose with measurable values at higher conversions (0.32 for S-IPN-2 and 0.45 for TPU). This behavior shows that the thermal decomposition of the tested S-IPNs is complicated and depends very much on the EMBA content in the synthesized S-IPNs.
Fig. 2. Dependence of Ea on conversion for TPU (쎲), EMBA (䊊), S-IPN-1 (䊏) and S-IPN-2 (䊐).
Flynn–Wall–Ozawa Ea(kJ mol⫺1)
n 0.7 0.6 1.2 0.9
50 47 68 62
n
ln A 0.6 0.7 1.1 0.8
9.1 6.0 5.1 9.3
4. Conclusions Two TPU–EMBA S-IPNs with 11.11 wt% EMBA (SIPN-1) and 27.3% EMBA (S-IPN-2) were synthesized and studied by the TG technique. The thermal decomposition of the synthesized S-IPNs is complicated and depends on the EMBA content in the TPU–EMBA mixture. S-IPN-1 shows an apparent thermal stability lower than that of TPU, while S-IPN-2 has an apparent thermal stability higher. This is due to the higher entanglement density of S-IPN-2.
References [1] J.H. Saunders, K.C. Frisch, Polyurethane Chemistry and Technology, Part I. Chemistry, Wiley, New York, 1962. [2] G. Moroi, C. Ciobanu, N. Baˆ lba, M. Palamaru, Polym. Degrad. Stab. 65 (1999) 253. [3] D. Baral, P.P. De, G.B. Nando, Polym. Degrad. Stab. 65 (1999) 47. [4] L.H. Sperling, Interpenetrating Polymer Networks and Related Materials, Plenum Press, New York, 1981. [5] D. Klempner, L.H. Sperling, L.A. Utraki, Interpenetrating Polymer Networks, American Chemical Society, Washington, DC, 1994. [6] Z.S. Petrovic´ , J. Badinski-Simendic, V. Divjakovic´ , J. Appl. Polym. Sci. 42 (1991) 779. [7] E.F. Cassidy, H.X. Xiao, K.C. Frisch, H.L. Frisch, J. Polym. Sci., Polym. Chem. Ed. 22 (1984) 1851. [8] H.L. Frisch, K.C. Frisch, D. Klempner, Polym. Eng. Sci. 22 (1982) 1143. [9] K.H. Hsich, S.T. Lee, D.C. Liao, D.W. Wu, C.C.M. Ma, in: Interpenetrating Polymer Networks, American Chemical Society, Washington, DC, 1994, p. 427. [10] D. Rosu, C. Ciobanu, C.N. Cascaval, Eur. Polym. J. 37 (2001) 587. [11] C. Ciobanu, C.N. Cascaval, D. Rosu, L. Rosu, J. Macromol., Sci. Pure Appl. Chem. A38 (2001) 991. [12] C.N. Cascaval, C. Ciobanu, D. Rosu, L. Rosu, J. Appl. Polym. Sci. 83 (2002) 138.
C.N. Cascaval et al. / Polymer Testing 22 (2003) 45–49
[13] C. Ciobanu, P. Afloarei, C. Baˆ rla˘ deanu, C. Culic, Patent Romania 93590 (1987). [14] A.W. Coats, J.P. Redfern, Nature 207 (1965) 290. [15] J.H. Flynn, L.A. Wall, J. Res. Natl. Bur. Stand. A. Phys. Chem. 70A (1966) 487.
49
[16] T. Ozawa, Bull. Chem. Soc. Jpn. 38 (1965) 1881. [17] L. Reich, D.W. Levi, Makromol. Chem. 66 (1963) 102. [18] C.D. Doyle, Nature 38 (1965) 1881.
Material Behaviour
Thermal degradation of semi-interpenetrating polymer networks based on polyurethane and epoxy maleate of bisphenol A C.N. Cascaval ∗, D. Rosu, L. Rosu, C. Ciobanu Petru Poni Institute of Macromolecular Chemistry, Romanian Academy, Aleea Gr. Ghica Voda, No 41A, Iasi 6600, Romania Received 9 February 2002; accepted 22 April 2002
Abstract Two polyurethane–epoxy maleate of bisphenol A semi-interpenetrating polymer networks were synthesized and their thermal behavior studied. The data obtained by thermogravimetry showed that the decomposition of the tested samples is complex, occurs in three steps, and depends on the degree of crosslinking. The main decomposition takes place between 290 and 480 °C, with weight losses between 62 and 66%. The apparent thermal stability of the sample synthesized with a low content of epoxy maleate of bisphenol-A (11.11 wt%) is lower compared with polyurethane, while the sample with high content of epoxy maleate of bisphenol-A (27.3 wt%) shows a higher stability. 2002 Elsevier Science Ltd. All rights reserved.
1. Introduction Thermoplastic polyurethane (TPU), because of its high tensile strength, chemical resistance, good processability and mechanical properties, is being used in many technical applications [1]. It is generally inappropiate for structural applications due to its low stability to the thermoxidative processes. The thermal stability of TPU can be much improved by modification with caesium cations [2], incorporation of mica in its structure [3,4], or by chemical combination with other polymers, in order to obtain properties with specific needs. In recent years, there is considerable interest in mixtures with a second reactive polymer, so as to generate interpenetrating polymer networks (IPNs) [4,5]. In many cases, IPNs show excellent engineering properties due to a synergestic effect induced by the forced compatibility of the individual components, as was shown for PU-epoxy resin IPNs [6–10].
∗ Corresponding author. Tel.: +40-32-217-454; fax: +40322-112-99. E-mail address: [email protected] (C.N. Cascaval).
In our previous work, TPU–epoxy maleate of bisphenol-A (EMBA) blends [11], as well as TPU– EMBA semi-interpenetrating polymer networks (S-IPNs) [12] were synthesized and characterized according to their miscibility and the physico-mechanical properties. Differential scanning calorimetry (DSC) measurements evidenced a good miscibility of the studied systems. The physico-mechanical properties of the blends are lower as compared to TPU–EMBA S-IPNs. Presently, no data are available concerning the study of TPU–EMBA S-IPNs thermoxidative degradation. The aim of this paper is to report some data regarding the thermal behavior of PU–EMBA S-IPNs.
2. Experimental 2.1. Materials TPU used in this study was synthesized starting from poly (ethylene adipate) diol (PEA) and poly (ethylene diethylene adipate) diol (PEDA) in reaction with 4,4⬘diphenyl-methane diisocyanate (MDI), as was reported elsewhere [13].
0142-9418/02/$ - see front matter 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 1 4 2 - 9 4 1 8 ( 0 2 ) 0 0 0 4 7 - 8
46
C.N. Cascaval et al. / Polymer Testing 22 (2003) 45–49
EMBA resin was obtained by reaction between maleic anhydride and Dinox epoxy resin, in the presence of water [11]. Dinox resin was a commercial product obtained from bisphenol-A in reaction with epichlorohydrin. TPU–EMBA S-IPNs were prepared after a sequential procedure by mixing of both TPU and EMBA solutions in dimethylformamide (DMF) [12]. The mixtures were cast on glass slides and subsequently soft baked at 120 °C for 3 h on a hot plate. The solvent was completely removed and EMBA resin was thermally cured in the presence of 1 wt% benzoyl peroxide. The crosslinked EMBA resin included in its network structure the linear PU. Two S-IPNs were synthesized, the first one (S-IPN1) with low EMBA content (11.11 wt%) and the second one (S-IPN-2) with 27.3 wt% EMBA. 2.2. Apparatus and analysis Themogravimetry (TG) and derivative thermogravimetry (DTG) measurements were carried out using a MOM Budapest derivatograph, under the following operational conditions: sample weight 50 mg, heating rate 12 °C min⫺1, in atmospheric air and reference material α-Al2O3. All kinetic studies start with a basic equation which assumes that the rate of conversion at constant temperature, da/dt, is a linear function of conversion, a, through a rate constant k: da ⫽ kf(a) dt
冕
T
p
A ⫺E /RT da ⫽ e a dT f(a) b
a0
(2)
(5)
T0
If T0 is low, a0 ⫽ 0, and Eq. (5) can be expressed as
冕
a
p
g(a) ⫽
0
冕
T
p
da A ⫺E /RT e a dT ⫽ f(a) b
(6)
0
where g(a) is the integral function of conversion. Analysis of the thermogravimetric data obtained by thermal degradation of the tested S-IPNs was investigated using some integral methods which involve an approximate integration of Eq. (6), namely Coats– Redfern [14], Flynn–Wall–Ozawa [15,16] and Reich– Levi [17]. The Coats–Redfern method uses an asymptotic approximation for the resolution of Eq. (6), obtaining ln
AR Ea g(a) ⫽ ln ⫺ T2 bE RT
(7)
The Flynn–Wall–Ozawa method integrates Eq. (6) using the Doyle approximation [18] and the result is Eq. (8): 0.457Ea AE ⫺2.315⫺ logb ⫽ log g(a)R RT
(8)
The Reich–Levi method gives Ea on utilization of two different heating rates, b1 and b2 Ea ⫽
where A is the pre-exponential factor, Ea is the activation energy, T the absolute temperature and R the rate constant. In a nonisothermal condition the sample temperature is changed by a constant heating rate, b(b ⫽ dT / dt). In this case, the temperature being dependent on the time of heating, the reaction rate can be expressed as da da da dT ⫽ ⫽b . dt dT dt dT
p
(1)
In isothermal conditions, using the Arrhenius relationship, Eq. (1) can be written as follows: da ⫽ Af(a)e⫺Ea / RT dt
冕
a
2.3.R.log[b1 / b2(T2 / T1)2] (T1)⫺1⫺(T2)⫺1
(9)
3. Results and discussion The general structure of the synthesized TPU is as follows:
where,
(3)
A combination of Eqs. (2) and (3) leads to da A ⫺E ⫽ e a / RT dt b
(4)
Intergration of Eq. (4) from an initial temperature, T0 , when a ⫽ a0, to a peak temperature, Tp, when a ⫽ ap, gives
Fig. 1 shows TG and DTG curves recorded for both TPU and EMBA crude samples, as well as for the synthesized S-IPNs, respective of S-IPN-1 and S-IPN-2.
C.N. Cascaval et al. / Polymer Testing 22 (2003) 45–49
Fig. 1. Typical TG and DTG curves of TPU (쎲), EMBA (䊊), S-IPN-1 (䊏) and S-IPN-2 (䊐).
The TG plots in Fig. 1 show a typical sigmoidal form. Generally, the thermal degradation of the synthesized SIPNs in dynamic conditions and in the presence of oxygen shows three decomposition stages. The degradation onset temperature (T0) of the TPU networks was around 240 °C (start for the first stage), an increasing decomposition rate being observed between 290 and 480 °C (the second stage), when the weight loss W reaches about 60– 70 wt%. The third stage of decomposition for temperatures higher than 500 °C corresponds to the advanced fragmentation of the chain formed in the first and the second stages of decomposition, as well as to the secondary reactions of dehydrogenation and gasification processes. Almost complete decomposition was observed at 600 °C. The initial slow weight loss around 240–290 °C
47
is attributed to the presence of EMBA in TPU–EMBA S-IPNs. Some characteristics related to the temperature corresponding to 10% (T10) and 50% (T50) weight loss from the initial weight, as well as the temperature taken for the maximum rate of decomposition (Tm) along with initial decomposition temperature (Ti) are listed in Table 1. The curves in Fig. 1 and the data in Table 2 show that the synthesized S-IPNs exhibit little differences in thermal behavior as against the crude TPU. Taking Ti into consideration, it can be noted that the thermal stability of S-IPN-1 is lower than that of TPU, while S-IPN2 shows a higher thermal stability. To have a more complete picture of the thermal behavior of the studied S-IPNs, the modification of activation enegy, Ea, of the degradation process was investigated using Coats–Redfern, Flynn–Wall–Ozawa and Reich–Levi computational methods. The first two methods were used to calculate the Ea values, the order of reaction (n) and the pre-exponential factor (ln A), while by the third one, the change of Ea with conversion during degradation was evaluated. To use the Flynn– Wall–Ozawa method, the samples were decomposed at various heating rates, 10, 12 and 16 °C min⫺1. Some kinetic data obtained for the tested S-IPNs and for the crude polymers, in the second stage of degradation, are listed in Table 2. As can be noted, EMBA content has an important influence on the thermal degradation of the synthesized S-IPMs. Thus, S-IPN-1, with a low content of EMBA (11.11 wt%) shows a decrease of both W and Ea against TPU. The decrease of W can be assigned to an incipient beginning of crosslinking in the TPU–EMBA mixture. The decrease of Ea suggests that S-IPN-1 has a lower thermal stability as against the crude TPU. In our opinion this is due to the fact that, in the conditions employed, EMBA plays a small part as the crosslinked agent. Simultaneously, EMBA can act as a plasticizer in the PU– EMBA matrix, as was previously observed and reported for TPU–EMBA blends [11]. In contrast, S-IPN-2, with high content of EMBA [27.3 wt%], shows a pronounced increase of both Ea and n values versus the crude PU, along with a decrease of W and ln A. This means that EMBA is in the most part crosslinked and included in Table 1 Thermal behavior of TPU, EMBA, S-IPN-1 and S-IPN-2 macromolecular compounds Sample
T10 (°C)
TPU S-IPN-1 S-IPN-2 EMBA
311 315 313 319
T50 (°C) 419 416 413 411
Tm (°C)
Ti (°C)
404 418 392 390
247 238 251 157
48
C.N. Cascaval et al. / Polymer Testing 22 (2003) 45–49
Table 2 Kinetic and TG characteristics of the studied samples in the second stage of degradation Sample
Temperature range (⌬T)
W (%) Methods Coats–Redfern Ea (kJ mol⫺1)
PU S-IPN-1 S-IPN-2 EMBA
319–454 298–462 340–431 280–443
70 66 62 67
52 47 70 59
its matrix the linear PU. As a consequence, a network is generated with an apparent thermal stability much higher than that of TPU. Important modifications of Ea against composition of the studied samples are shown in Fig. 2. The plots in Fig. 2 do not show a very important difference in the thermal behavior of the tested samples. All the analyzed samples have a very sharp decrease of Ea with conversion. EMBA and S-IPN-1 show a pronounced decrease of Ea for conversion up to 0.2 and than Ea remains constant up to 0.6 conversion. In comparison with EMBA and S-IPN-1, the samples S-IPN-2 and PU start to decompose with measurable values at higher conversions (0.32 for S-IPN-2 and 0.45 for TPU). This behavior shows that the thermal decomposition of the tested S-IPNs is complicated and depends very much on the EMBA content in the synthesized S-IPNs.
Fig. 2. Dependence of Ea on conversion for TPU (쎲), EMBA (䊊), S-IPN-1 (䊏) and S-IPN-2 (䊐).
Flynn–Wall–Ozawa Ea(kJ mol⫺1)
n 0.7 0.6 1.2 0.9
50 47 68 62
n
ln A 0.6 0.7 1.1 0.8
9.1 6.0 5.1 9.3
4. Conclusions Two TPU–EMBA S-IPNs with 11.11 wt% EMBA (SIPN-1) and 27.3% EMBA (S-IPN-2) were synthesized and studied by the TG technique. The thermal decomposition of the synthesized S-IPNs is complicated and depends on the EMBA content in the TPU–EMBA mixture. S-IPN-1 shows an apparent thermal stability lower than that of TPU, while S-IPN-2 has an apparent thermal stability higher. This is due to the higher entanglement density of S-IPN-2.
References [1] J.H. Saunders, K.C. Frisch, Polyurethane Chemistry and Technology, Part I. Chemistry, Wiley, New York, 1962. [2] G. Moroi, C. Ciobanu, N. Baˆ lba, M. Palamaru, Polym. Degrad. Stab. 65 (1999) 253. [3] D. Baral, P.P. De, G.B. Nando, Polym. Degrad. Stab. 65 (1999) 47. [4] L.H. Sperling, Interpenetrating Polymer Networks and Related Materials, Plenum Press, New York, 1981. [5] D. Klempner, L.H. Sperling, L.A. Utraki, Interpenetrating Polymer Networks, American Chemical Society, Washington, DC, 1994. [6] Z.S. Petrovic´ , J. Badinski-Simendic, V. Divjakovic´ , J. Appl. Polym. Sci. 42 (1991) 779. [7] E.F. Cassidy, H.X. Xiao, K.C. Frisch, H.L. Frisch, J. Polym. Sci., Polym. Chem. Ed. 22 (1984) 1851. [8] H.L. Frisch, K.C. Frisch, D. Klempner, Polym. Eng. Sci. 22 (1982) 1143. [9] K.H. Hsich, S.T. Lee, D.C. Liao, D.W. Wu, C.C.M. Ma, in: Interpenetrating Polymer Networks, American Chemical Society, Washington, DC, 1994, p. 427. [10] D. Rosu, C. Ciobanu, C.N. Cascaval, Eur. Polym. J. 37 (2001) 587. [11] C. Ciobanu, C.N. Cascaval, D. Rosu, L. Rosu, J. Macromol., Sci. Pure Appl. Chem. A38 (2001) 991. [12] C.N. Cascaval, C. Ciobanu, D. Rosu, L. Rosu, J. Appl. Polym. Sci. 83 (2002) 138.
C.N. Cascaval et al. / Polymer Testing 22 (2003) 45–49
[13] C. Ciobanu, P. Afloarei, C. Baˆ rla˘ deanu, C. Culic, Patent Romania 93590 (1987). [14] A.W. Coats, J.P. Redfern, Nature 207 (1965) 290. [15] J.H. Flynn, L.A. Wall, J. Res. Natl. Bur. Stand. A. Phys. Chem. 70A (1966) 487.
49
[16] T. Ozawa, Bull. Chem. Soc. Jpn. 38 (1965) 1881. [17] L. Reich, D.W. Levi, Makromol. Chem. 66 (1963) 102. [18] C.D. Doyle, Nature 38 (1965) 1881.