- Email: [email protected]
phthalonitrile resin system
Thermochimica Acta 683 (2020) 178442
Contents lists available at ScienceDirect
Thermochimica Acta journal homepage: www.elsevier.com/locate/tca
Study of the curing kinetics of melamine/phthalonitrile resin system Jiangbo Lv, Jinlang Hong, Bo Liang, Erjin Zhao, Ke Zeng, Menghao Chen, Jianghuai Hu*, Gang Yang*
T
State Key Laboratory of Polymer Materials Engineering, College of Polymer Science and Engineering, Sichuan University, Chengdu, 610065, PR China
ARTICLE INFO
ABSTRACT
Keywords: Phthalonitrile Melamine Curing behavior Non-isothermal DSC Autocatalytic model
The exploration of curing process is important for the application of phthalonitrile resins in advanced materials. In this study, the curing behaviors of 1,3-bis (3,4-dicyanophenoxy) benzene (3BOCN) and melamine (MI) system was studied by differential scanning calorimetry (DSC) at different heating rates. An autocatalytic model could describe the curing reaction of 3BOCN-MI. The curing parameters including apparent activation energy, reaction orders and pre-exponential factor were calculated. The average activation energies for the three different proportions of 3BOCN-MI (8:1, 8:2, 8:3) system were 93, 98 and 96 kJ/mol, respectively. Besides, the predicted models for the reaction of 3BOCN-MI curing fitted well with the experimental data.
1. Introduction
curing agent to prepare the phthalonitrile resin. And the phthalonitrile resin cured by MI exhibited superior processability, thermal performance and dynamic mechanical property [17]. However, the curing process and curing mechanism of 3BOCN-MI system remain inexplicable. The curing process of phthalonitrile resin is very complicated and involving high temperature processing. Therefore, the fundamental investigation of 3BOCN-MI system curing reaction kinetics is an important and basic topic to gain a better understanding of the curing behavior as well as for the control and optimization of production processes and performance of final products. A variety of techniques have been employed to study the curing kinetics of polymers, such as differential scanning calorimetry (DSC) [18–22], Fourier Transform Infrared Spectroscopy (FTIR) [21] and rheology measurement [22,23]. Among them, one frequently used technique is DSC. It can investigate the curing behavior by measuring the change of heat flow with temperature and time during the curing process. In previous studies, DSC was widely used in the study of thermosetting polymer, such as phenolic resin [18], epoxy resin [20,21] and benzoxazine resin [19]. And the kinetic parameters were determined by fitting the data obtained from DSC to the appropriate kinetic model to further investigate the curing behaviors. According to the Kinetics Committee of the International Confederation for Thermal Analysis and Calorimetry (ICTAC) recommendation, various kinetic methods have been suggested to calculate kinetic parameters such as Kissinger method [24], Vyazovkin method [25], Starink method [26] and Kissinger-Akahira-Sunose method [27,28]. In this paper, the curing behavior of the 3BOCN-MI system was
Phthalonitrile resins are high-performance polymers which can be synthesized through thermal crosslink reaction of phthalonitrile monomer to produce void-free thermosets with high crosslinking density. Phthalonitrile resins and composites have been extensively studied for several decades, presenting valuable properties such as excellent thermal and oxidative stability, outstanding mechanical properties, low water absorption, and high flame retardancy [1–3]. These properties permitted the phthalonitrile resins to be applied in many fields, such as aerospace, microelectronics [4]. However, the polymerization of neat phthalonitrile monomer is extremely sluggish, requiring several days at elevated temperature before gelation [5]. To accelerate the curing reaction, considerable research has focused on the development of various curing agents, such as metallic salts [6], organic acids/amine salts [7], organic amines [8]. The addition of these curing agents can accelerate the curing reaction significantly. Nevertheless, these curing agents show many defects, such as volatilize, which may slow down the reaction and even result in defects in phthalonitrile resin [7,9–11], which limit the further application of phthalonitrile resin. To address this problem, researchers proposed the self-promoted phthalonitrile [12,13], which was synthesized by introducing active groups into phthalonitrile monomer. However, the synthesis of the self-promoted phthalonitrile monomer costs too much, which limits the application. The melamine (MI) shows diversified hydrogen bonding modes and supramolecular architectures [14–16], which can reduce the volatility of small molecules. In our previous paper, MI was used as a distinctive ⁎
Corresponding authors. E-mail addresses: [email protected] (J. Hu), [email protected] (G. Yang).
https://doi.org/10.1016/j.tca.2019.178442 Received 28 June 2019; Received in revised form 22 October 2019; Accepted 23 October 2019 Available online 03 November 2019 0040-6031/ © 2019 Elsevier B.V. All rights reserved.
Thermochimica Acta 683 (2020) 178442
J. Lv, et al.
Scheme 1. Synthesis of phthalonitrile monomers and preparation of 3BOCN-MI system.
studied by non-isothermal DSC, and the relevant curing kinetic parameters were calculated by iso-conversional method. Autocatalytic kinetic model was employed to further explore the curing behavior of the 3BOCN-MI resin, gaining the relevant parameters including pre-exponential factors and reaction orders and the corresponding equations. 2. Experimental 2.1. Materials Melamine (MI) (99.0 %) was purchased from Chengdu Kelong Chemical Co., Ltd. 4-Nitrophthalonitrile (99.0 %) was acquired from Ji’nan Weido Chemical Co., Ltd. Dimethyl sulfoxide (DMSO) (99.5 %), resorcinol (99.5 %) and potassium carbonate (99.5 %) were all obtained from Chengdu Kelong Chemical Co., Ltd. And all the materials were used as received without further treatment. 2.2. Synthesis of 1,3-bis (3,4-dicyanophenoxy) benzene (3BOCN) The phthalonitrile monomer 1,3-bis (3,4-dicyanophenoxy) benzene (3BOCN) was synthesized according to the previous literature[29,30]. FTIR (KBr), 2232 (C≡N), 1284 (Ar-O-Ar). 1H NMR (300 MHz, DMSO-d6): d 8.11–8.14 (d, 2H, Ar-H),7.91–7.92 (d, 2H, Ar-H), 7.60–7.63 (dd, 1H, Ar-H), 7.53–7.59 (dd, 2H, Ar-H), 7.13–7.14 (s, 2H, Ar-H), 7.12 (s, 1H, Ar-H). The melting peak at 183 °C (sharp) (DSC) with a heat rate of 10 °C/min. 2.3. Preparation of the 3BOCN-MI system The 3BOCN-MI systems were prepared by mixing 3BOCN and MI in different molar ratios (8:1, 8:2, 8:3), named 3BOCN-MI-81, 3BOCN-MI82 and 3BOCN-MI-83, in which the numbers represent the molar ratios of nitrile group and amino group, respectively. The synthetic route is shown in Scheme 1. The mixture was prepared by stirring the blends in acetone solvent in a ratio of 25% (w/v) for 24 h. Acetone was then removed by vacuum distillation.
Fig. 1. DSC curves of different molar ratio of (a) 3BOCN-MI-81, (b) 3BOCN-MI82 and (c) 3BOCN-MI-83 system at various heating rates.
crucible were tested under a high purity nitrogen with a flow rate of 60 mL/min, and the samples were scanned from 40 to 350 °C at various heating rates of 2.5, 5.0, 7.5 and 10.0 °C/min. For the isothermal DSC curing of 3BOCN-MI-81, the temperature was increased rapidly to the specified value at heating rate of 50 °C/min. The testing temperature was 240 °C under a high purity nitrogen with a flow rate of 60 ml/min.
2.4. DSC measurements Non-isothermal curing kinetics of 3BOCN-MI system was analyzed by using a TA instrument Q200 differential scanning calorimeter. Approximately 5 mg of samples placed into aluminum hermetic
2
Thermochimica Acta 683 (2020) 178442
J. Lv, et al.
Table 1 Curing characteristics of 3BOCN-MI system derived from DSC curves at various heating rates. Sample
( /min)
3BOCN-MI-81
2.5 5.0 7.5 10.0 2.5 5.0 7.5 10.0 2.5 5.0 7.5 10.0
3BOCN-MI-82
3BOCN-MI-83
Ti ( )
Tp ( )
Tf ( )
221.51 234.14 243.14 247.86 222.46 233.53 239.40 244.78 222.96 233.67 241.08 247.72
247.63 261.36 269.73 278.34 247.96 261.57 270.29 275.89 248.44 263.49 272.84 279.22
278.18 298.82 309.72 318.32 274.68 295.73 307.68 313.20 274.80 297.40 310.33 318.67
β: heating rate, oC/min; Ti: Initial temperature, oC; Tp: Peak temperature, oC; Tf: Final temperature, oC.
3. Theoretical background The data from DSC exists relationship with time and the degree of cure, which is as follows:
(t) =
Ht Htotal
(1)
where is the degree of cure process, t is the reaction time, Ht is the released heat when reaction time reaches t, Htotal is the total heat of the curing reaction. In non-isothermal system
d d = = dt dT
dH(t) Htotal dt
(2)
Where =dT dt. The curing reaction rate d /dt is generally expressed as:
d =k(T)f( ) dt
(3)
Where, k(T) is the reaction rate constant depending on temperature, T is the absolute temperature. f( ) is the reaction model, which depends on the curing mechanism, k(T) can be expressed by the Arrhenius equation:
k(T) =Aexp
E RT
(4)
Where E is the activation energy, R is the gas constant, A is the preexponential factor. The kinetic equation for non-isothermal curing can be described as
d d E = =Aexp dt dT RT
f( )
(5)
In this study, Starink method was employed to calculate the values of activation energy (Eα) [27], which is as follows:
ln
i
T1.92 ,i
=const
1.0008
E RT
(6)
Fig. 2. Plots of conversion α vs temperature of (a) 3BOCN-MI-81, (b) 3BOCNMI-82 and (c) 3BOCN-MI-83 at different heating rates.
Where, is the temperature at the same conversion (α) at different heating rates. The activation energy can be obtained according to the plot of ln( i /T1.92 ,i ) vs 1/T . Different systems have various curing mechanisms. In previous reports, there were two common models for curing reaction mechanism of thermosetting resin: autocatalytic model and nth-order model [31,32]. The equations are as follows:
T1.92 ,i
Autocatalytic model:
d /dt=Aexp(-E/RT)
m (1-
nth-order model：
3
)n
(7)
Thermochimica Acta 683 (2020) 178442
J. Lv, et al.
Fig. 4. Plot of E system.
exothermic peak can be seen in each curve, which is caused by the exothermic heat of the nitrile group curing reaction under the action of the curing agent. Moreover, as the heating rate increases, the exothermic peak in the DSC curve corresponding to the three proportions tends to move toward the higher temperature, which is mainly because the thermal hysteresis when heated [27]. In order to quantitatively study the non-isothermal DSC curing curves of the samples, the relevant characteristic parameters are summarized in Table 1. From Table 1, it is obvious that the initial, the peak and the final temperatures of the curing reaction about all three samples have been shifted to the higher values with increasing the heating rate from 2.5 to 10.0 °C/min. However, with the increasing of melamine content, the initial, the peak and the final temperature for the curing phthalonitrile are almost same. Higher melamine content did not decrease the curing temperature of phthalonitrile. This may be due to the curing reaction is heterogenous and microphase separation occurs [22]. The micro-heterogenous structure may limit the mobility and diffusion of the reactive species. The degree of conversion (α) as a function of curing temperature obtained from DSC data is shown in Fig. 2. It can be seen that all these conversional curves show a sigmoid profile, and the corresponding curing process can be roughly divided into three stages. The first stage is the initial stage of curing. During this period, the system has not yet entered the gel state, and the curing reaction rate increases slowly, which is characterized by a gentle increase in the slope of the curve. Then, as the degree of curing increases, the resin gradually enters the gel state, and the curing reaction rates increase rapidly, and reach a maximum. During further heating, the degree of cross-linking of the resin increases, and the resin gradually forms a network structure and transforms from gel stage to glassy stage, which is called the middle stage of curing. The molecular motion gradually slows down and the curing reaction rate gradually decreases. During this period, as the curing reaction proceeds, the microgel formed by the intermediate product will rapidly cross-link and grow, and form a macromolecular gel network. The viscosity also increases correspondingly. In general, the curing stage of thermosetting resin can be regarded as that with the increase of curing degree, the resin transforms from molten state to gel stage and then to glassy stage, and finally tends to be fully cross-linked. In the post-stage, the viscosity increases to a certain degree, and the reaction between macromolecules is difficult. The curing reaction of the resin possibly changes from the initial chemical control to diffusion control.
Fig. 3. Plots of ln( i /T1.92 ,i ) vs 1/T of (a) 3BOCN-MI-81, (b) 3BOCN-MI-82 and (c) 3BOCN-MI-83 system at different conversion.
d /dt=Aexp(-E/RT)(1- ) n
vs α of 3BOCN-MI-81, 3BOCN-MI-82 and 3BOCN-MI-83
(8)
Where, m and n are reaction orders, m + n is the total reaction order. 4. Results and discussion The heat flows of the different proportions of blends (molar ratio 3BOCN-MI = 8:1, 8:2, 8:3) system with different heating rates of 2.5, 5.0, 7.5 and 10.0 °C/min are shown in Fig. 1. From these plots, a single
4
Thermochimica Acta 683 (2020) 178442
J. Lv, et al.
In this paper, the kinetic parameters of the curing reaction were calculated by using Straink method. From Eq. (6), Eα can be calculated from the plot of ln( i /T1.92 ,i ) vs 1/T value at the same fraction extent of conversion from a series of dynamic DSC experiment data at different heating rates. The Starink plots for different proportions of blends at various α are shown in Fig. 3. As can be seen in Fig. 3, the calculated data by Starink method exhibited a good linear relation. The activation energies secured from the slope at various heating rates value for α = 0.1-0.9 shown a little difference, and the average values of 3BOCNMI-81, 3BOCN-MI-82 and 3BOCN-MI-83 system are 93, 98 and 96 kJ/ mol, respectively. From the result, it can be observed that the average apparent activation energy values are almost the same as previous study of phthalonitrile resins (87–105 kJ/mol) [33,34]. For the sake of intuitively expressing the relationship between Eα and α, the plots of activation energy of different proportions of system as a function of conversion are shown in Fig. 4 and the apparent activation energy of different conversion are listed in Table S1. The apparent activation energy of different molar ratio of 3BOCN-MI blends are approximate each other, indicating that different 3BOCN-MI blends follow the same curing mechanism. From the Table S1, it is worth noting that, in the post-curing stage, the apparent activation conversion of different molar ratio 3BOCN-MI system slightly decreased. Finding in the previous study, the curing reaction conversion rate of phthalonitrile resin increased, its internal crosslinking degree increased, the free volume decreases, so the chain segment movement is restricted, even gradually "frozen". This leads to the single movement within a small range, which to some extent explains the activation energy decreases [35–37]. According to the experimental data and the average activation energy value obtained from Starink method, the plots of ln(da/dt)+Ea/RT vs ln(1-a) was produced in Fig.5. In Fig.5, the peak points of the lines correspond to the peak point of the point DSC curve. It can be observed that there is nonlinear increase before the peak points and a linear decrease after them. The plot would show a maximum of ln(da/dt) +Ea/RT at ln(1-a) approximately -0.43. The reaction rate (da/dt) reaches its maximum value at a certain intermediate conversion (Fig. S1). And n-order model can be excluded since the plots was not linearly related. This suggested that the curing reaction may follow the autocatalytic model [38]. As shown in Fig. S2, the autocatalytic model was also confirmed by isothermal DSC of 3BOCN-MI-81. From the plot, the reaction rate of 3BOCN-MI-81 system increased to a maximum after a certain time. This further indicated that the curing reaction of 3BOCNMI system may accord with autocatalytic kinetics [40]. In the study of autocatalytic reaction, Eq. (9) can be obtained by taking the logarithm of Eq. (7).
ln
d d E =ln =+nln(1- ) +mln +lnA dt dT RT
(9)
According to Eq. (9), the pre-exponential factor A , reaction order n and m can be obtained through multiple linear regression. Therefore, the values of A, m and n can be obtained using the Ea from the Starink
Fig. 5. The plots of ln(da/dt)+Ea/RT vs ln(1-a) at different heating rates for (a) 3BOCN-MI-81, (b) 3BOCN-MI-82 and (c) 3BOCN-MI-83 system. Table 2 The kinetic parameters evaluated for the 3BOCN-MI system. Sample
Β ( /min)
lnA(s-1)
mean
n
mean
m
mean
Correlation coefficient (R2)
3BOCN-MI-81
2.5 5.0 7.5 10.0 2.5 5.0 7.5 10.0 2.5 5.0 7.5 10.0
19.91 19.84 19.88 19.63 21.46 21.18 21.16 21.17 20.62 20.44 20.28 20.21
19.82
1.23 1.27 1.29 1.24 1.51 1.30 1.32 1.49 1.33 1.25 1.23 1.16
1.26
0.40 0.39 0.37 0.28 0.59 0.41 0.41 0.38 0.48 0.41 0.35 0.29
0.36
0.9972 0.9966 0.9938 0.9945 0.9995 0.9971 0.9948 0.9976 0.9997 0.9966 0.9928 0.9887
3BOCN-MI-82
3BOCN-MI-83
21.24
20.39
β: heating rate, oC/min; A: pre-exponential factor, s−1; m, n: reaction order.
1.41
1.24
5
0.45
0.38
Thermochimica Acta 683 (2020) 178442
J. Lv, et al.
curves based on the determined kinetic parameters of the curing reaction were shown in Fig. 6. It can be seen that the calculated results from the model are in good agreement with the experimental data. Consequently, the reaction rate equations for autocatalytic kinetics of 3BOCN-MI-81, 3BOCN-MI-82, 3BOCN-MI-83 are shown as Eqs. (10)(12), respectively.
3 BOCN
MI
81:
d = e19.81e( dt
3 BOCN
MI
82:
3 BOCN
MI
83:
11184.7 T
)
0.36 (1-
)1.26.
(10)
d = e 21.24 e(-11842.7/T) dt
0.45 (1-
)1.41.
(11)
d = e 20.39e( dt
0.38 (1-
)1.24 .
(12)
11491.5 T
)
To further verify the applicability and accuracy of the autocatalytic kinetic model and describe the kinetics of melamine cured phthalonitrile resin, the reaction rates d /dt of the three blends were calculated based on Eqs. (10)-(12). The experimental results are compared with the calculated equation curves as shown in Fig. 6. It can be seen from Fig. 6 that the experimental data of the three blends had a good consistency with the fitting results obtained by the autocatalytic kinetic model, which indicates that the autocatalytic model can describe the curing process of 3BOCN-MI curing reliably. Aromatic amine is a class of important curing additive for phthalonitrile, which can effectively promote the curing reaction of phthalonitrile. The melamine (MI) is trifunctional monomer with a stable heterocyclic structure (triazine ring). And it also shows diversified hydrogen bonding models and supramolecular architectures [14–16]. To further explore the curing reaction between phthalonitrile and MI, the curing kinetic of this system was studied. The results suggested that the apparent activation energies of different ratio 3BOCN-MI system are almost same and they may follow the same curing mechanism. According the research, generally organic cyano compounds react with amines when the cyano group is activated and the activated cyano group is towards nucleophilic attack by amine to yield triazine and isoindolenine [39]. The apparent activation energy of the reaction may contain multiple reaction producing heterocyclic crosslinked structures of high aromatic character. The cyano group is activated and the activated cyano group nucleophilic attacks by an amine forming imine. Aromatic amine and Imine accelerate the curing reaction of cyano group forming triazine, isoindoline and phthalocyanine. The possible curing reaction mechanism of the 3BOCN-MI system showed as Scheme 2. 5. Conclusion The curing kinetic of three different proportions of melamine as additive of phthalonitrile monomer (3BOCN) were studied based on the DSC results. The results indicated that DSC curves of different ratio 3BOCN-MI (8:1, 8:2, 8:3) system exhibited only single exothermic peak. Starink methods was chosen to investigate the curing kinetics and calculate the activation energy. The average activation energies for the three different proportions of 3BOCN-MI system were 92.99, 98.46 and 95.54 kJ/mol, respectively. The curing kinetic model of this system was evaluated by multi-heating-rate DSC methods assisted with the isoconversion method. An autocatalytic model for the phthalonitrilemelamine resin was confirmed and the calculated data of the curing reaction are in good agreement with the experimental data that obtained from the DSC results.
Fig. 6. Comparison between experimental (symbols) and calculated (solid lines) DSC curves of (a) 3BOCN-MI-81, (b) 3BOCN-MI-82 and (c) 3BOCN-MI-83 system.
method and the kinetic parameters evaluated for all heating rates were listed in Table 2. It can be seen from Table 2 that different heating rates have little effect on the values of pre-exponential factor and reaction order. Therefore, the average values can be used to represent the kinetic parameters of different system. The experimental curves and predicted
6
Thermochimica Acta 683 (2020) 178442
J. Lv, et al.
Scheme 2. Possible curing reaction mechanism of the 3BOCN-MI system.
Declaration of Competing Interest
10.1002/app.33949. [13] W. Peng, F. Yao, J. Hu, Y. Liu, Z. Lu, Y. Liu, Z. Liu, K. Zeng, G. Yang, Renewable protein-based monomer for thermosets: a case study on phthalonitrile resin, Green Chem. 20 (2018) 5158–5168, https://doi.org/10.1039/C8GC01824C. [14] A. Ranganathan, V. Pedireddi, C. Rao, Hydrothermal synthesis of organic channel structures: 1: 1 hydrogen-bonded adducts of melamine with cyanuric and trithiocyanuric acids, J. Am. Chem. Soc. 121 (1999) 1752–1753, https://doi.org/10. 1021/ja983928o. [15] Y. Zhang, L. Jianmin, M. Nishiura, T. Imamoto, Melamine-bifunctional metal complex: self-assembly of high ordered organic-inorganic sandwich layers via hydrogen bonds and π-π interactions, Chem. Lett. 28 (1999) 543–544, https://doi. org/10.1246/cl.1999.543. [16] J.A. Zerkowski, J.C. MacDonald, C.T. Seto, D.A. Wierda, G.M. Whitesides, Design of organic structures in the solid state: molecular tapes based on the network of hydrogen bonds present in the cyanuric acid. cntdot. melamine complex, J. Am. Chem. Soc. 116 (1994) 2382–2391, https://doi.org/10.1021/ja00085a018. [17] E. Zhao, J. Hu, J. Wang, M. Shi, Z. Wang, K. Zeng, G. Yang, Preparation and properties of phthalonitrile resins promoted by melamine, High Perform. Polym. 30 (2018) 561–570, https://doi.org/10.1177/0954008317709892. [18] L. Granado, R. Tavernier, G. Foyer, G. David, S. Caillol, Comparative curing kinetics study of high char yield formaldehyde-and terephthalaldehyde-phenolic thermosets, Thermochim. Acta 667 (2018) 42–49, https://doi.org/10.1016/j.tca.2018.06. 013. [19] J. Xu, H. Li, K. Zeng, G. Li, X. Zhao, C. Zhao, Curing kinetics and thermal stability of novel siloxane-containing benzoxazines, Thermochim. Acta 671 (2019) 119–126, https://doi.org/10.1016/j.tca.2018.11.016. [20] M. Zolghadr, M.J. Zohuriaan-Mehr, A. Shakeri, A. Salimi, Epoxy resin modification by reactive bio-based furan derivatives: curing kinetics and mechanical properties, Thermochim. Acta 673 (2019) 147–157, https://doi.org/10.1016/j.tca.2019.01. 025. [21] G. Yamini, A. Shakeri, M. Vafayan, M.J. Zohuriaan-Mehr, K. Kabiri, M. Zolghadr, Cure kinetics of modified Lignosulfonate/Epoxy blends, Thermochim. Acta (2019), https://doi.org/10.1016/j.tca.2019.03.003. [22] (a) J. Hu, P. Yuan, K. Zeng, G. Yang, Study of the curing kinetics of a benzimidazole/phthalonitrile resin system, Thermochim. Acta 590 (2014) 30–39, https:// doi.org/10.1016/j.tca.2014.06.006; (b) B. Lucio, J.L. de la Fuente, Rheological cure characterization of an advanced functional polyurethane, Thermochim. Acta 596 (2014) 6–13, https://doi.org/10. 1016/j.tca.2014.09.012. [23] M. Zhongliang, Q. Le, H. Wei, H. Liming, A novel approach on the study of cure kinetics for rheological isothermal and non-isothermal methods, Compos. Part B Eng. 162 (2019) 242–249, https://doi.org/10.1016/j.compositesb.2018.10.066. [24] H.E. Kissinger, Variation of peak temperature with heating rate in differential thermal analysis, J. Res. Bur. Stand. 57 (1956) 217–221. [25] S. Vyazovkin, N. Sbirrazzuoli, Isoconversional kinetic analysis of thermally stimulated processes in polymers, Macromol. Rapid Commun. 27 (2006) 1515–1532, https://doi.org/10.1002/marc.200600404. [26] M. Starink, The determination of activation energy from linear heating rate experiments: a comparison of the accuracy of isoconversion methods, Thermochim. Acta 404 (2003) 163–176, https://doi.org/10.1016/S0040-6031(03)00144-8. [27] S. Vyazovkin, A.K. Burnham, J.M. Criado, L.A. Pérez-Maqueda, C. Popescu, N. Sbirrazzuoli, ICTAC Kinetics Committee recommendations for performing kinetic computations on thermal analysis data, Thermochim. Acta 520 (2011) 1–19,
The authors declared that they have no conflicts of interest to this work. We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted. Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.tca.2019.178442. References [1] D.D. Dominguez, T.M. Keller, Properties of phthalonitrile monomer blends and thermosetting phthalonitrile copolymers, Polymer 48 (2007) 91–97, https://doi. org/10.1016/j.polymer.2006.11.003. [2] K. Zeng, G. Yang, Phthalonitrile Matrix Resins and Composites, Wiley Encyclopedia of Composites, 2011, https://doi.org/10.1002/9781118097298.weoc169 1-14. [3] B. Liang, J. Hu, P. Yuan, C. Li, R. Li, Y. Liu, K. Zeng, G. Yang, Kinetics of the pyrolysis process of phthalonitrile resin, Thermochim. Acta 672 (2019) 133–141, https://doi.org/10.1016/j.tca.2018.12.025. [4] T. Keller, High-performance, electrically conductive polymers, Chemtech 18 (1988) 635–639. [5] D. Wu, Y. Zhao, K. Zeng, G. Yang, A novel benzimidazole‐containing phthalonitrile monomer with unique polymerization behavior, J. Polym. Sci. Part A: Polym. Chem. 50 (2012) 4977–4982, https://doi.org/10.1002/pola.26331. [6] T.M. Keller, J.R. Griffith, The Synthesis of a New Class of Polyphthalocyanine Resins, (1980), https://doi.org/10.1021/bk-1980-0132.ch003 25. [7] P. Burchill, On the formation and properties of a high‐temperature resin from a bisphthalonitrile, J. Polym. Sci. Part A: Polym. Chem. 32 (1994) 1–8, https://doi. org/10.1002/pola.1994.080320101. [8] T.M. Keller, T.R. Price, Amine-cured bisphenol-linked phthalonitrile resins, J. Macromol. Sci. Part A - Chem. 18 (1982) 931–937, https://doi.org/10.1080/ 00222338208077208. [9] D.D. Dominguez, H.N. Jones, T.M. Keller, The effect of curing additive on the mechanical properties of phthalonitrile‐carbon fiber composites, Polym. Compos. 25 (2004) 554–561, https://doi.org/10.1002/pc.20049. [10] Z. Wang, X. Yang, M. Xu, J. Wei, X. Liu, Effect of elevated annealing temperature on the morphology, microstructure, conductivity and microwave absorption properties of phthalocyanine polymer, J. Mater. Sci.-Mater. Electron. 24 (2013) 2610–2618, https://doi.org/10.1007/s10854-013-1140-3. [11] S.B. Sastri, T.M. Keller, Phthalonitrile cure reaction with aromatic diamines, J. Polym. Sci. Part A: Polym. Chem. 36 (1998) 1885–1890, https://doi.org/10.1002/ (SICI)1099-0518(199808)36:11<1885::AID-POLA23>3.0.CO;2-9. [12] X. Yang, J. Zhang, Y. Lei, J. Zhong, X. Liu, Effect of different aromatic amines on the crosslinking behavior and thermal properties of phthalonitrile oligomer containing biphenyl ethernitrile, J. Appl. Polym. Sci. 121 (2011) 2331–2337, https://doi.org/
7
Thermochimica Acta 683 (2020) 178442
J. Lv, et al. https://doi.org/10.1016/j.tca.2011.03.034. [28] T. Akahira, T. Sunose, Joint convention of four electrical institutes, Res. Report Chiba Inst. Technol. (Sci. Technol.) 16 (1971) 22–31. [29] T.M. Keller, D.D. Dominguez, High temperature resorcinol-based phthalonitrile polymer, Polymer 46 (2005) 4614–4618, https://doi.org/10.1016/j.polymer.2005. 03.068. [30] S. Ji, P. Yuan, J. Hu, R. Sun, K. Zeng, G. Yang, A novel curing agent for phthalonitrile monomers: curing behaviors and properties of the polymer network, Polymer 84 (2016) 365–370, https://doi.org/10.1016/j.polymer.2016.01.006. [31] W. Peng, Y. Liu, Z. Lu, J. Hu, K. Zeng, G. Yang, Curing kinetics study on highly efficient thermal synergistic polymerization effect between alicyclic imide moiety and phthalonitrile, Thermochim. Acta 659 (2018) 27–33, https://doi.org/10.1016/ j.tca.2017.09.020. [32] L. Zhao, X. Hu, Autocatalytic curing kinetics of thermosetting polymers: a new model based on temperature dependent reaction orders, Polymer 51 (2010) 3814–3820, https://doi.org/10.1016/j.polymer.2010.05.056. [33] T. Zhang, J. Wang, M. Derradji, N. Ramdani, H. Wang, Z.-w. Lin, W.-b. Liu, Synthesis, curing kinetics and thermal properties of a novel self-promoted fluorenebased bisphthalonitrile monomer, Thermochim. Acta 602 (2015) 22–29, https:// doi.org/10.1016/j.tca.2015.01.005. [34] M. Xu, Y. Luo, Y. Lei, X. Liu, Phthalonitrile-based resin for advanced composite
[35] [36] [37] [38]
[39] [40]
8
materials: curing behavior studies, Polym. Test. 55 (2016) 38–43, https://doi.org/ 10.1016/j.polymertesting.2016.08.008. T. Zhou, M. Gu, Y. Jin, J. Wang, Studying on the curing kinetics of a DGEBA/EMI2,4/nano-sized carborundum system with two curing kinetic methods, Polymer 46 (2005) 6174–6181, https://doi.org/10.1016/j.polymer.2005.03.114. G. Sun, H. Sun, Y. Liu, B. Zhao, N. Zhu, K. Hu, Comparative study on the curing kinetics and mechanism of a lignin-based-epoxy/anhydride resin system, Polymer 48 (2007) 330–337, https://doi.org/10.1016/j.polymer.2006.10.047. N. Sbirrazzuoli, S. Vyazovkin, Learning about epoxy cure mechanisms from isoconversional analysis of DSC data, Thermochim. Acta 388 (2002) 289–298, https:// doi.org/10.1016/S0040-6031(02)00053-9. T. Feng, J. Wang, L. Pan, M. Derradji, N. Ramdani, W. Liu, H. Zhou, Tunable properties of novel tetra-functional fluorene-based benzoxazines from mixed amines: synthesis, characterization and curing kinetics, Thermochim. Acta 633 (2016) 1–11, https://doi.org/10.1016/j.tca.2016.03.027. P.J. Burchill, On the formation and properties of a high-temperature resin from a bisphthalonitrile, J. Polym. Sci. Part A: Polym. Chem. 32 (1994) 1–8, https://doi. org/10.1002/pola.1994.080320101. J. Šesták, G. Berggren, Study of the kinetics of the mechanism of solid-state reactions at increasing temperatures, Thermochim. Acta 3 (1971) 1–12, https://doi.org/ 10.1016/0040-6031(71)85051-7.
Contents lists available at ScienceDirect
Thermochimica Acta journal homepage: www.elsevier.com/locate/tca
Study of the curing kinetics of melamine/phthalonitrile resin system Jiangbo Lv, Jinlang Hong, Bo Liang, Erjin Zhao, Ke Zeng, Menghao Chen, Jianghuai Hu*, Gang Yang*
T
State Key Laboratory of Polymer Materials Engineering, College of Polymer Science and Engineering, Sichuan University, Chengdu, 610065, PR China
ARTICLE INFO
ABSTRACT
Keywords: Phthalonitrile Melamine Curing behavior Non-isothermal DSC Autocatalytic model
The exploration of curing process is important for the application of phthalonitrile resins in advanced materials. In this study, the curing behaviors of 1,3-bis (3,4-dicyanophenoxy) benzene (3BOCN) and melamine (MI) system was studied by differential scanning calorimetry (DSC) at different heating rates. An autocatalytic model could describe the curing reaction of 3BOCN-MI. The curing parameters including apparent activation energy, reaction orders and pre-exponential factor were calculated. The average activation energies for the three different proportions of 3BOCN-MI (8:1, 8:2, 8:3) system were 93, 98 and 96 kJ/mol, respectively. Besides, the predicted models for the reaction of 3BOCN-MI curing fitted well with the experimental data.
1. Introduction
curing agent to prepare the phthalonitrile resin. And the phthalonitrile resin cured by MI exhibited superior processability, thermal performance and dynamic mechanical property [17]. However, the curing process and curing mechanism of 3BOCN-MI system remain inexplicable. The curing process of phthalonitrile resin is very complicated and involving high temperature processing. Therefore, the fundamental investigation of 3BOCN-MI system curing reaction kinetics is an important and basic topic to gain a better understanding of the curing behavior as well as for the control and optimization of production processes and performance of final products. A variety of techniques have been employed to study the curing kinetics of polymers, such as differential scanning calorimetry (DSC) [18–22], Fourier Transform Infrared Spectroscopy (FTIR) [21] and rheology measurement [22,23]. Among them, one frequently used technique is DSC. It can investigate the curing behavior by measuring the change of heat flow with temperature and time during the curing process. In previous studies, DSC was widely used in the study of thermosetting polymer, such as phenolic resin [18], epoxy resin [20,21] and benzoxazine resin [19]. And the kinetic parameters were determined by fitting the data obtained from DSC to the appropriate kinetic model to further investigate the curing behaviors. According to the Kinetics Committee of the International Confederation for Thermal Analysis and Calorimetry (ICTAC) recommendation, various kinetic methods have been suggested to calculate kinetic parameters such as Kissinger method [24], Vyazovkin method [25], Starink method [26] and Kissinger-Akahira-Sunose method [27,28]. In this paper, the curing behavior of the 3BOCN-MI system was
Phthalonitrile resins are high-performance polymers which can be synthesized through thermal crosslink reaction of phthalonitrile monomer to produce void-free thermosets with high crosslinking density. Phthalonitrile resins and composites have been extensively studied for several decades, presenting valuable properties such as excellent thermal and oxidative stability, outstanding mechanical properties, low water absorption, and high flame retardancy [1–3]. These properties permitted the phthalonitrile resins to be applied in many fields, such as aerospace, microelectronics [4]. However, the polymerization of neat phthalonitrile monomer is extremely sluggish, requiring several days at elevated temperature before gelation [5]. To accelerate the curing reaction, considerable research has focused on the development of various curing agents, such as metallic salts [6], organic acids/amine salts [7], organic amines [8]. The addition of these curing agents can accelerate the curing reaction significantly. Nevertheless, these curing agents show many defects, such as volatilize, which may slow down the reaction and even result in defects in phthalonitrile resin [7,9–11], which limit the further application of phthalonitrile resin. To address this problem, researchers proposed the self-promoted phthalonitrile [12,13], which was synthesized by introducing active groups into phthalonitrile monomer. However, the synthesis of the self-promoted phthalonitrile monomer costs too much, which limits the application. The melamine (MI) shows diversified hydrogen bonding modes and supramolecular architectures [14–16], which can reduce the volatility of small molecules. In our previous paper, MI was used as a distinctive ⁎
Corresponding authors. E-mail addresses: [email protected] (J. Hu), [email protected] (G. Yang).
https://doi.org/10.1016/j.tca.2019.178442 Received 28 June 2019; Received in revised form 22 October 2019; Accepted 23 October 2019 Available online 03 November 2019 0040-6031/ © 2019 Elsevier B.V. All rights reserved.
Thermochimica Acta 683 (2020) 178442
J. Lv, et al.
Scheme 1. Synthesis of phthalonitrile monomers and preparation of 3BOCN-MI system.
studied by non-isothermal DSC, and the relevant curing kinetic parameters were calculated by iso-conversional method. Autocatalytic kinetic model was employed to further explore the curing behavior of the 3BOCN-MI resin, gaining the relevant parameters including pre-exponential factors and reaction orders and the corresponding equations. 2. Experimental 2.1. Materials Melamine (MI) (99.0 %) was purchased from Chengdu Kelong Chemical Co., Ltd. 4-Nitrophthalonitrile (99.0 %) was acquired from Ji’nan Weido Chemical Co., Ltd. Dimethyl sulfoxide (DMSO) (99.5 %), resorcinol (99.5 %) and potassium carbonate (99.5 %) were all obtained from Chengdu Kelong Chemical Co., Ltd. And all the materials were used as received without further treatment. 2.2. Synthesis of 1,3-bis (3,4-dicyanophenoxy) benzene (3BOCN) The phthalonitrile monomer 1,3-bis (3,4-dicyanophenoxy) benzene (3BOCN) was synthesized according to the previous literature[29,30]. FTIR (KBr), 2232 (C≡N), 1284 (Ar-O-Ar). 1H NMR (300 MHz, DMSO-d6): d 8.11–8.14 (d, 2H, Ar-H),7.91–7.92 (d, 2H, Ar-H), 7.60–7.63 (dd, 1H, Ar-H), 7.53–7.59 (dd, 2H, Ar-H), 7.13–7.14 (s, 2H, Ar-H), 7.12 (s, 1H, Ar-H). The melting peak at 183 °C (sharp) (DSC) with a heat rate of 10 °C/min. 2.3. Preparation of the 3BOCN-MI system The 3BOCN-MI systems were prepared by mixing 3BOCN and MI in different molar ratios (8:1, 8:2, 8:3), named 3BOCN-MI-81, 3BOCN-MI82 and 3BOCN-MI-83, in which the numbers represent the molar ratios of nitrile group and amino group, respectively. The synthetic route is shown in Scheme 1. The mixture was prepared by stirring the blends in acetone solvent in a ratio of 25% (w/v) for 24 h. Acetone was then removed by vacuum distillation.
Fig. 1. DSC curves of different molar ratio of (a) 3BOCN-MI-81, (b) 3BOCN-MI82 and (c) 3BOCN-MI-83 system at various heating rates.
crucible were tested under a high purity nitrogen with a flow rate of 60 mL/min, and the samples were scanned from 40 to 350 °C at various heating rates of 2.5, 5.0, 7.5 and 10.0 °C/min. For the isothermal DSC curing of 3BOCN-MI-81, the temperature was increased rapidly to the specified value at heating rate of 50 °C/min. The testing temperature was 240 °C under a high purity nitrogen with a flow rate of 60 ml/min.
2.4. DSC measurements Non-isothermal curing kinetics of 3BOCN-MI system was analyzed by using a TA instrument Q200 differential scanning calorimeter. Approximately 5 mg of samples placed into aluminum hermetic
2
Thermochimica Acta 683 (2020) 178442
J. Lv, et al.
Table 1 Curing characteristics of 3BOCN-MI system derived from DSC curves at various heating rates. Sample
( /min)
3BOCN-MI-81
2.5 5.0 7.5 10.0 2.5 5.0 7.5 10.0 2.5 5.0 7.5 10.0
3BOCN-MI-82
3BOCN-MI-83
Ti ( )
Tp ( )
Tf ( )
221.51 234.14 243.14 247.86 222.46 233.53 239.40 244.78 222.96 233.67 241.08 247.72
247.63 261.36 269.73 278.34 247.96 261.57 270.29 275.89 248.44 263.49 272.84 279.22
278.18 298.82 309.72 318.32 274.68 295.73 307.68 313.20 274.80 297.40 310.33 318.67
β: heating rate, oC/min; Ti: Initial temperature, oC; Tp: Peak temperature, oC; Tf: Final temperature, oC.
3. Theoretical background The data from DSC exists relationship with time and the degree of cure, which is as follows:
(t) =
Ht Htotal
(1)
where is the degree of cure process, t is the reaction time, Ht is the released heat when reaction time reaches t, Htotal is the total heat of the curing reaction. In non-isothermal system
d d = = dt dT
dH(t) Htotal dt
(2)
Where =dT dt. The curing reaction rate d /dt is generally expressed as:
d =k(T)f( ) dt
(3)
Where, k(T) is the reaction rate constant depending on temperature, T is the absolute temperature. f( ) is the reaction model, which depends on the curing mechanism, k(T) can be expressed by the Arrhenius equation:
k(T) =Aexp
E RT
(4)
Where E is the activation energy, R is the gas constant, A is the preexponential factor. The kinetic equation for non-isothermal curing can be described as
d d E = =Aexp dt dT RT
f( )
(5)
In this study, Starink method was employed to calculate the values of activation energy (Eα) [27], which is as follows:
ln
i
T1.92 ,i
=const
1.0008
E RT
(6)
Fig. 2. Plots of conversion α vs temperature of (a) 3BOCN-MI-81, (b) 3BOCNMI-82 and (c) 3BOCN-MI-83 at different heating rates.
Where, is the temperature at the same conversion (α) at different heating rates. The activation energy can be obtained according to the plot of ln( i /T1.92 ,i ) vs 1/T . Different systems have various curing mechanisms. In previous reports, there were two common models for curing reaction mechanism of thermosetting resin: autocatalytic model and nth-order model [31,32]. The equations are as follows:
T1.92 ,i
Autocatalytic model:
d /dt=Aexp(-E/RT)
m (1-
nth-order model：
3
)n
(7)
Thermochimica Acta 683 (2020) 178442
J. Lv, et al.
Fig. 4. Plot of E system.
exothermic peak can be seen in each curve, which is caused by the exothermic heat of the nitrile group curing reaction under the action of the curing agent. Moreover, as the heating rate increases, the exothermic peak in the DSC curve corresponding to the three proportions tends to move toward the higher temperature, which is mainly because the thermal hysteresis when heated [27]. In order to quantitatively study the non-isothermal DSC curing curves of the samples, the relevant characteristic parameters are summarized in Table 1. From Table 1, it is obvious that the initial, the peak and the final temperatures of the curing reaction about all three samples have been shifted to the higher values with increasing the heating rate from 2.5 to 10.0 °C/min. However, with the increasing of melamine content, the initial, the peak and the final temperature for the curing phthalonitrile are almost same. Higher melamine content did not decrease the curing temperature of phthalonitrile. This may be due to the curing reaction is heterogenous and microphase separation occurs [22]. The micro-heterogenous structure may limit the mobility and diffusion of the reactive species. The degree of conversion (α) as a function of curing temperature obtained from DSC data is shown in Fig. 2. It can be seen that all these conversional curves show a sigmoid profile, and the corresponding curing process can be roughly divided into three stages. The first stage is the initial stage of curing. During this period, the system has not yet entered the gel state, and the curing reaction rate increases slowly, which is characterized by a gentle increase in the slope of the curve. Then, as the degree of curing increases, the resin gradually enters the gel state, and the curing reaction rates increase rapidly, and reach a maximum. During further heating, the degree of cross-linking of the resin increases, and the resin gradually forms a network structure and transforms from gel stage to glassy stage, which is called the middle stage of curing. The molecular motion gradually slows down and the curing reaction rate gradually decreases. During this period, as the curing reaction proceeds, the microgel formed by the intermediate product will rapidly cross-link and grow, and form a macromolecular gel network. The viscosity also increases correspondingly. In general, the curing stage of thermosetting resin can be regarded as that with the increase of curing degree, the resin transforms from molten state to gel stage and then to glassy stage, and finally tends to be fully cross-linked. In the post-stage, the viscosity increases to a certain degree, and the reaction between macromolecules is difficult. The curing reaction of the resin possibly changes from the initial chemical control to diffusion control.
Fig. 3. Plots of ln( i /T1.92 ,i ) vs 1/T of (a) 3BOCN-MI-81, (b) 3BOCN-MI-82 and (c) 3BOCN-MI-83 system at different conversion.
d /dt=Aexp(-E/RT)(1- ) n
vs α of 3BOCN-MI-81, 3BOCN-MI-82 and 3BOCN-MI-83
(8)
Where, m and n are reaction orders, m + n is the total reaction order. 4. Results and discussion The heat flows of the different proportions of blends (molar ratio 3BOCN-MI = 8:1, 8:2, 8:3) system with different heating rates of 2.5, 5.0, 7.5 and 10.0 °C/min are shown in Fig. 1. From these plots, a single
4
Thermochimica Acta 683 (2020) 178442
J. Lv, et al.
In this paper, the kinetic parameters of the curing reaction were calculated by using Straink method. From Eq. (6), Eα can be calculated from the plot of ln( i /T1.92 ,i ) vs 1/T value at the same fraction extent of conversion from a series of dynamic DSC experiment data at different heating rates. The Starink plots for different proportions of blends at various α are shown in Fig. 3. As can be seen in Fig. 3, the calculated data by Starink method exhibited a good linear relation. The activation energies secured from the slope at various heating rates value for α = 0.1-0.9 shown a little difference, and the average values of 3BOCNMI-81, 3BOCN-MI-82 and 3BOCN-MI-83 system are 93, 98 and 96 kJ/ mol, respectively. From the result, it can be observed that the average apparent activation energy values are almost the same as previous study of phthalonitrile resins (87–105 kJ/mol) [33,34]. For the sake of intuitively expressing the relationship between Eα and α, the plots of activation energy of different proportions of system as a function of conversion are shown in Fig. 4 and the apparent activation energy of different conversion are listed in Table S1. The apparent activation energy of different molar ratio of 3BOCN-MI blends are approximate each other, indicating that different 3BOCN-MI blends follow the same curing mechanism. From the Table S1, it is worth noting that, in the post-curing stage, the apparent activation conversion of different molar ratio 3BOCN-MI system slightly decreased. Finding in the previous study, the curing reaction conversion rate of phthalonitrile resin increased, its internal crosslinking degree increased, the free volume decreases, so the chain segment movement is restricted, even gradually "frozen". This leads to the single movement within a small range, which to some extent explains the activation energy decreases [35–37]. According to the experimental data and the average activation energy value obtained from Starink method, the plots of ln(da/dt)+Ea/RT vs ln(1-a) was produced in Fig.5. In Fig.5, the peak points of the lines correspond to the peak point of the point DSC curve. It can be observed that there is nonlinear increase before the peak points and a linear decrease after them. The plot would show a maximum of ln(da/dt) +Ea/RT at ln(1-a) approximately -0.43. The reaction rate (da/dt) reaches its maximum value at a certain intermediate conversion (Fig. S1). And n-order model can be excluded since the plots was not linearly related. This suggested that the curing reaction may follow the autocatalytic model [38]. As shown in Fig. S2, the autocatalytic model was also confirmed by isothermal DSC of 3BOCN-MI-81. From the plot, the reaction rate of 3BOCN-MI-81 system increased to a maximum after a certain time. This further indicated that the curing reaction of 3BOCNMI system may accord with autocatalytic kinetics [40]. In the study of autocatalytic reaction, Eq. (9) can be obtained by taking the logarithm of Eq. (7).
ln
d d E =ln =+nln(1- ) +mln +lnA dt dT RT
(9)
According to Eq. (9), the pre-exponential factor A , reaction order n and m can be obtained through multiple linear regression. Therefore, the values of A, m and n can be obtained using the Ea from the Starink
Fig. 5. The plots of ln(da/dt)+Ea/RT vs ln(1-a) at different heating rates for (a) 3BOCN-MI-81, (b) 3BOCN-MI-82 and (c) 3BOCN-MI-83 system. Table 2 The kinetic parameters evaluated for the 3BOCN-MI system. Sample
Β ( /min)
lnA(s-1)
mean
n
mean
m
mean
Correlation coefficient (R2)
3BOCN-MI-81
2.5 5.0 7.5 10.0 2.5 5.0 7.5 10.0 2.5 5.0 7.5 10.0
19.91 19.84 19.88 19.63 21.46 21.18 21.16 21.17 20.62 20.44 20.28 20.21
19.82
1.23 1.27 1.29 1.24 1.51 1.30 1.32 1.49 1.33 1.25 1.23 1.16
1.26
0.40 0.39 0.37 0.28 0.59 0.41 0.41 0.38 0.48 0.41 0.35 0.29
0.36
0.9972 0.9966 0.9938 0.9945 0.9995 0.9971 0.9948 0.9976 0.9997 0.9966 0.9928 0.9887
3BOCN-MI-82
3BOCN-MI-83
21.24
20.39
β: heating rate, oC/min; A: pre-exponential factor, s−1; m, n: reaction order.
1.41
1.24
5
0.45
0.38
Thermochimica Acta 683 (2020) 178442
J. Lv, et al.
curves based on the determined kinetic parameters of the curing reaction were shown in Fig. 6. It can be seen that the calculated results from the model are in good agreement with the experimental data. Consequently, the reaction rate equations for autocatalytic kinetics of 3BOCN-MI-81, 3BOCN-MI-82, 3BOCN-MI-83 are shown as Eqs. (10)(12), respectively.
3 BOCN
MI
81:
d = e19.81e( dt
3 BOCN
MI
82:
3 BOCN
MI
83:
11184.7 T
)
0.36 (1-
)1.26.
(10)
d = e 21.24 e(-11842.7/T) dt
0.45 (1-
)1.41.
(11)
d = e 20.39e( dt
0.38 (1-
)1.24 .
(12)
11491.5 T
)
To further verify the applicability and accuracy of the autocatalytic kinetic model and describe the kinetics of melamine cured phthalonitrile resin, the reaction rates d /dt of the three blends were calculated based on Eqs. (10)-(12). The experimental results are compared with the calculated equation curves as shown in Fig. 6. It can be seen from Fig. 6 that the experimental data of the three blends had a good consistency with the fitting results obtained by the autocatalytic kinetic model, which indicates that the autocatalytic model can describe the curing process of 3BOCN-MI curing reliably. Aromatic amine is a class of important curing additive for phthalonitrile, which can effectively promote the curing reaction of phthalonitrile. The melamine (MI) is trifunctional monomer with a stable heterocyclic structure (triazine ring). And it also shows diversified hydrogen bonding models and supramolecular architectures [14–16]. To further explore the curing reaction between phthalonitrile and MI, the curing kinetic of this system was studied. The results suggested that the apparent activation energies of different ratio 3BOCN-MI system are almost same and they may follow the same curing mechanism. According the research, generally organic cyano compounds react with amines when the cyano group is activated and the activated cyano group is towards nucleophilic attack by amine to yield triazine and isoindolenine [39]. The apparent activation energy of the reaction may contain multiple reaction producing heterocyclic crosslinked structures of high aromatic character. The cyano group is activated and the activated cyano group nucleophilic attacks by an amine forming imine. Aromatic amine and Imine accelerate the curing reaction of cyano group forming triazine, isoindoline and phthalocyanine. The possible curing reaction mechanism of the 3BOCN-MI system showed as Scheme 2. 5. Conclusion The curing kinetic of three different proportions of melamine as additive of phthalonitrile monomer (3BOCN) were studied based on the DSC results. The results indicated that DSC curves of different ratio 3BOCN-MI (8:1, 8:2, 8:3) system exhibited only single exothermic peak. Starink methods was chosen to investigate the curing kinetics and calculate the activation energy. The average activation energies for the three different proportions of 3BOCN-MI system were 92.99, 98.46 and 95.54 kJ/mol, respectively. The curing kinetic model of this system was evaluated by multi-heating-rate DSC methods assisted with the isoconversion method. An autocatalytic model for the phthalonitrilemelamine resin was confirmed and the calculated data of the curing reaction are in good agreement with the experimental data that obtained from the DSC results.
Fig. 6. Comparison between experimental (symbols) and calculated (solid lines) DSC curves of (a) 3BOCN-MI-81, (b) 3BOCN-MI-82 and (c) 3BOCN-MI-83 system.
method and the kinetic parameters evaluated for all heating rates were listed in Table 2. It can be seen from Table 2 that different heating rates have little effect on the values of pre-exponential factor and reaction order. Therefore, the average values can be used to represent the kinetic parameters of different system. The experimental curves and predicted
6
Thermochimica Acta 683 (2020) 178442
J. Lv, et al.
Scheme 2. Possible curing reaction mechanism of the 3BOCN-MI system.
Declaration of Competing Interest
10.1002/app.33949. [13] W. Peng, F. Yao, J. Hu, Y. Liu, Z. Lu, Y. Liu, Z. Liu, K. Zeng, G. Yang, Renewable protein-based monomer for thermosets: a case study on phthalonitrile resin, Green Chem. 20 (2018) 5158–5168, https://doi.org/10.1039/C8GC01824C. [14] A. Ranganathan, V. Pedireddi, C. Rao, Hydrothermal synthesis of organic channel structures: 1: 1 hydrogen-bonded adducts of melamine with cyanuric and trithiocyanuric acids, J. Am. Chem. Soc. 121 (1999) 1752–1753, https://doi.org/10. 1021/ja983928o. [15] Y. Zhang, L. Jianmin, M. Nishiura, T. Imamoto, Melamine-bifunctional metal complex: self-assembly of high ordered organic-inorganic sandwich layers via hydrogen bonds and π-π interactions, Chem. Lett. 28 (1999) 543–544, https://doi. org/10.1246/cl.1999.543. [16] J.A. Zerkowski, J.C. MacDonald, C.T. Seto, D.A. Wierda, G.M. Whitesides, Design of organic structures in the solid state: molecular tapes based on the network of hydrogen bonds present in the cyanuric acid. cntdot. melamine complex, J. Am. Chem. Soc. 116 (1994) 2382–2391, https://doi.org/10.1021/ja00085a018. [17] E. Zhao, J. Hu, J. Wang, M. Shi, Z. Wang, K. Zeng, G. Yang, Preparation and properties of phthalonitrile resins promoted by melamine, High Perform. Polym. 30 (2018) 561–570, https://doi.org/10.1177/0954008317709892. [18] L. Granado, R. Tavernier, G. Foyer, G. David, S. Caillol, Comparative curing kinetics study of high char yield formaldehyde-and terephthalaldehyde-phenolic thermosets, Thermochim. Acta 667 (2018) 42–49, https://doi.org/10.1016/j.tca.2018.06. 013. [19] J. Xu, H. Li, K. Zeng, G. Li, X. Zhao, C. Zhao, Curing kinetics and thermal stability of novel siloxane-containing benzoxazines, Thermochim. Acta 671 (2019) 119–126, https://doi.org/10.1016/j.tca.2018.11.016. [20] M. Zolghadr, M.J. Zohuriaan-Mehr, A. Shakeri, A. Salimi, Epoxy resin modification by reactive bio-based furan derivatives: curing kinetics and mechanical properties, Thermochim. Acta 673 (2019) 147–157, https://doi.org/10.1016/j.tca.2019.01. 025. [21] G. Yamini, A. Shakeri, M. Vafayan, M.J. Zohuriaan-Mehr, K. Kabiri, M. Zolghadr, Cure kinetics of modified Lignosulfonate/Epoxy blends, Thermochim. Acta (2019), https://doi.org/10.1016/j.tca.2019.03.003. [22] (a) J. Hu, P. Yuan, K. Zeng, G. Yang, Study of the curing kinetics of a benzimidazole/phthalonitrile resin system, Thermochim. Acta 590 (2014) 30–39, https:// doi.org/10.1016/j.tca.2014.06.006; (b) B. Lucio, J.L. de la Fuente, Rheological cure characterization of an advanced functional polyurethane, Thermochim. Acta 596 (2014) 6–13, https://doi.org/10. 1016/j.tca.2014.09.012. [23] M. Zhongliang, Q. Le, H. Wei, H. Liming, A novel approach on the study of cure kinetics for rheological isothermal and non-isothermal methods, Compos. Part B Eng. 162 (2019) 242–249, https://doi.org/10.1016/j.compositesb.2018.10.066. [24] H.E. Kissinger, Variation of peak temperature with heating rate in differential thermal analysis, J. Res. Bur. Stand. 57 (1956) 217–221. [25] S. Vyazovkin, N. Sbirrazzuoli, Isoconversional kinetic analysis of thermally stimulated processes in polymers, Macromol. Rapid Commun. 27 (2006) 1515–1532, https://doi.org/10.1002/marc.200600404. [26] M. Starink, The determination of activation energy from linear heating rate experiments: a comparison of the accuracy of isoconversion methods, Thermochim. Acta 404 (2003) 163–176, https://doi.org/10.1016/S0040-6031(03)00144-8. [27] S. Vyazovkin, A.K. Burnham, J.M. Criado, L.A. Pérez-Maqueda, C. Popescu, N. Sbirrazzuoli, ICTAC Kinetics Committee recommendations for performing kinetic computations on thermal analysis data, Thermochim. Acta 520 (2011) 1–19,
The authors declared that they have no conflicts of interest to this work. We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted. Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.tca.2019.178442. References [1] D.D. Dominguez, T.M. Keller, Properties of phthalonitrile monomer blends and thermosetting phthalonitrile copolymers, Polymer 48 (2007) 91–97, https://doi. org/10.1016/j.polymer.2006.11.003. [2] K. Zeng, G. Yang, Phthalonitrile Matrix Resins and Composites, Wiley Encyclopedia of Composites, 2011, https://doi.org/10.1002/9781118097298.weoc169 1-14. [3] B. Liang, J. Hu, P. Yuan, C. Li, R. Li, Y. Liu, K. Zeng, G. Yang, Kinetics of the pyrolysis process of phthalonitrile resin, Thermochim. Acta 672 (2019) 133–141, https://doi.org/10.1016/j.tca.2018.12.025. [4] T. Keller, High-performance, electrically conductive polymers, Chemtech 18 (1988) 635–639. [5] D. Wu, Y. Zhao, K. Zeng, G. Yang, A novel benzimidazole‐containing phthalonitrile monomer with unique polymerization behavior, J. Polym. Sci. Part A: Polym. Chem. 50 (2012) 4977–4982, https://doi.org/10.1002/pola.26331. [6] T.M. Keller, J.R. Griffith, The Synthesis of a New Class of Polyphthalocyanine Resins, (1980), https://doi.org/10.1021/bk-1980-0132.ch003 25. [7] P. Burchill, On the formation and properties of a high‐temperature resin from a bisphthalonitrile, J. Polym. Sci. Part A: Polym. Chem. 32 (1994) 1–8, https://doi. org/10.1002/pola.1994.080320101. [8] T.M. Keller, T.R. Price, Amine-cured bisphenol-linked phthalonitrile resins, J. Macromol. Sci. Part A - Chem. 18 (1982) 931–937, https://doi.org/10.1080/ 00222338208077208. [9] D.D. Dominguez, H.N. Jones, T.M. Keller, The effect of curing additive on the mechanical properties of phthalonitrile‐carbon fiber composites, Polym. Compos. 25 (2004) 554–561, https://doi.org/10.1002/pc.20049. [10] Z. Wang, X. Yang, M. Xu, J. Wei, X. Liu, Effect of elevated annealing temperature on the morphology, microstructure, conductivity and microwave absorption properties of phthalocyanine polymer, J. Mater. Sci.-Mater. Electron. 24 (2013) 2610–2618, https://doi.org/10.1007/s10854-013-1140-3. [11] S.B. Sastri, T.M. Keller, Phthalonitrile cure reaction with aromatic diamines, J. Polym. Sci. Part A: Polym. Chem. 36 (1998) 1885–1890, https://doi.org/10.1002/ (SICI)1099-0518(199808)36:11<1885::AID-POLA23>3.0.CO;2-9. [12] X. Yang, J. Zhang, Y. Lei, J. Zhong, X. Liu, Effect of different aromatic amines on the crosslinking behavior and thermal properties of phthalonitrile oligomer containing biphenyl ethernitrile, J. Appl. Polym. Sci. 121 (2011) 2331–2337, https://doi.org/
7
Thermochimica Acta 683 (2020) 178442
J. Lv, et al. https://doi.org/10.1016/j.tca.2011.03.034. [28] T. Akahira, T. Sunose, Joint convention of four electrical institutes, Res. Report Chiba Inst. Technol. (Sci. Technol.) 16 (1971) 22–31. [29] T.M. Keller, D.D. Dominguez, High temperature resorcinol-based phthalonitrile polymer, Polymer 46 (2005) 4614–4618, https://doi.org/10.1016/j.polymer.2005. 03.068. [30] S. Ji, P. Yuan, J. Hu, R. Sun, K. Zeng, G. Yang, A novel curing agent for phthalonitrile monomers: curing behaviors and properties of the polymer network, Polymer 84 (2016) 365–370, https://doi.org/10.1016/j.polymer.2016.01.006. [31] W. Peng, Y. Liu, Z. Lu, J. Hu, K. Zeng, G. Yang, Curing kinetics study on highly efficient thermal synergistic polymerization effect between alicyclic imide moiety and phthalonitrile, Thermochim. Acta 659 (2018) 27–33, https://doi.org/10.1016/ j.tca.2017.09.020. [32] L. Zhao, X. Hu, Autocatalytic curing kinetics of thermosetting polymers: a new model based on temperature dependent reaction orders, Polymer 51 (2010) 3814–3820, https://doi.org/10.1016/j.polymer.2010.05.056. [33] T. Zhang, J. Wang, M. Derradji, N. Ramdani, H. Wang, Z.-w. Lin, W.-b. Liu, Synthesis, curing kinetics and thermal properties of a novel self-promoted fluorenebased bisphthalonitrile monomer, Thermochim. Acta 602 (2015) 22–29, https:// doi.org/10.1016/j.tca.2015.01.005. [34] M. Xu, Y. Luo, Y. Lei, X. Liu, Phthalonitrile-based resin for advanced composite
[35] [36] [37] [38]
[39] [40]
8
materials: curing behavior studies, Polym. Test. 55 (2016) 38–43, https://doi.org/ 10.1016/j.polymertesting.2016.08.008. T. Zhou, M. Gu, Y. Jin, J. Wang, Studying on the curing kinetics of a DGEBA/EMI2,4/nano-sized carborundum system with two curing kinetic methods, Polymer 46 (2005) 6174–6181, https://doi.org/10.1016/j.polymer.2005.03.114. G. Sun, H. Sun, Y. Liu, B. Zhao, N. Zhu, K. Hu, Comparative study on the curing kinetics and mechanism of a lignin-based-epoxy/anhydride resin system, Polymer 48 (2007) 330–337, https://doi.org/10.1016/j.polymer.2006.10.047. N. Sbirrazzuoli, S. Vyazovkin, Learning about epoxy cure mechanisms from isoconversional analysis of DSC data, Thermochim. Acta 388 (2002) 289–298, https:// doi.org/10.1016/S0040-6031(02)00053-9. T. Feng, J. Wang, L. Pan, M. Derradji, N. Ramdani, W. Liu, H. Zhou, Tunable properties of novel tetra-functional fluorene-based benzoxazines from mixed amines: synthesis, characterization and curing kinetics, Thermochim. Acta 633 (2016) 1–11, https://doi.org/10.1016/j.tca.2016.03.027. P.J. Burchill, On the formation and properties of a high-temperature resin from a bisphthalonitrile, J. Polym. Sci. Part A: Polym. Chem. 32 (1994) 1–8, https://doi. org/10.1002/pola.1994.080320101. J. Šesták, G. Berggren, Study of the kinetics of the mechanism of solid-state reactions at increasing temperatures, Thermochim. Acta 3 (1971) 1–12, https://doi.org/ 10.1016/0040-6031(71)85051-7.