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chicken eggshell biowaste composites: Isothermal calorimetric and chemorheological analyses
Progress in Organic Coatings 114 (2018) 208–215
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Cure kinetics of epoxy/chicken eggshell biowaste composites: Isothermal calorimetric and chemorheological analyses
MARK
⁎
Mohammad Reza Saeba, , Hadi Rastinb, Milad Nonahalb, Seyed Mohammad Reza Paranc, Hossein Ali Khonakdard, Debora Pugliae a
Department of Resin and Additives, Institute for Color Science and Technology, P.O. Box 16765-654, Tehran, Iran School of Chemical Engineering, College of Engineering, University of Tehran, P.O. Box 11155-4563, Tehran, Iran c Department of Polymer Processing, Iran Polymer and Petrochemical Institute, P.O. Box 14965-115, Tehran, Iran d Leibniz Institute of Polymer Research Dresden, Hohe Straße 6, D-01069, Dresden, Germany e University of Perugia, Department of Civil and Environmental Engineering, Strada di Pentima 4, 05100, Terni, Italy b
A R T I C L E I N F O
A B S T R A C T
Keywords: Chicken eggshell Epoxy Calcium carbonate Rheokinetic study Isothermal DSC
Chicken eggshell (ES) is a biowaste powder comprising peptide functional groups and proteins, which give it potential to play the role of curing aid when added to the epoxy resin. In this work, pristine and terpolymermodified ES (mES) were used in epoxy-based composites and their performance in network formation was compared with pristine calcium carbonate (CaCO3) and terpolymer-modified CaCO3 (mCaCO3) additives, via comprehensive isothermal calorimetric and chemorheological analyses. The mechanism and progression of the crosslinking of identical composites containing very low amount of additives were also discussed. Rheokinetic evaluations revealed that, despite the almost identical chemical structure of the ES and CaCO3, the former can more appropriately contribute to crosslinking reaction in the pristine form, since terpolymer modification causes a physical hindrance to its cure potential towards epoxy rings after surface modification. In the case of calorimetric studies, in contrast to nonisothermal cure kinetics, a more comprehensive image of the catalytic role of mES was identified in view of overall reaction order and apparent activation energy calculated for both types of systems.
1. Introduction Epoxy is a well-known thermosetting resin possessing considerable beneficial properties such as sufficient adhesiveness, curing ability with various hardeners, superior mechanical and corrosion characteristics, that makes it one of the most widely used resins in surface coating industry [1–5]. However, its brittleness and poor impact strength have limited its use in coating and engineering composites applications [6,7]. In this regard, a great deal of efforts has been made to find an effective approach for toughening of epoxy. It has been revealed that introduction of second inorganic component into the epoxy matrix could substantially improve its impact strength [8,9]. Beyond the exceptional characteristics of nanomaterials as reinforcing agents in epoxy resin (namely high surface area, excellent mechanical and thermal properties), one should take into account that their use in practical and industrial scale is still far from perfect, because of their high expense and difficulties in their processing, due to high surface energy that causes agglomeration of nanoparticles [10,11]. By contrast, environmental concerns induce industrial centers to move forward ⁎
using new material with renewable resources. From this standpoint, an increasing attention has been directed toward the use of biowaste materials (such as husk ash, fly ash, bagasse) in polymeric industries, as potential alternatives for existing additives, because of their low cost, recyclability, biodegradability, and use of renewable resources [12–14]. Within different kinds of biowaste additives, widely available inexpensive chicken eggshell (ES) is a promising candidate as reinforcing agent in polymeric industries, due to its good mechanical characteristics such as acceptable toughness and impact strength [15]. However, over the last decades, landfill disposing of ES as by-product of egg processing industry has brought about serious environmental concerns [16]. From environmental problems and economic perspectives, biowaste ES has been recently applied in various applications areas, for instance for absorption of heavy metals [17,18], synthesis of hydroxyapatite [19] and sorption of CO2 [20,21]. It is recognized that ES is composed of calcium carbonate (94%) with just 3–4% of organic materials including proteins, collagen, and sulfated polysaccharides, that makes it an excellent substituting material for mineral-based calcium
Corresponding author. E-mail addresses: [email protected], [email protected] (M.R. Saeb).
http://dx.doi.org/10.1016/j.porgcoat.2017.10.018 Received 28 September 2017; Received in revised form 16 October 2017; Accepted 19 October 2017 Available online 02 November 2017 0300-9440/ © 2017 Elsevier B.V. All rights reserved.
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parameters that allow for higher accuracies. In this work, we aim to investigate the curing reaction of epoxy resin in the presence and absence of ES and CaCO3 through isothermal calorimetric and rheological tests. In this way, autocatalytic and noncatalytic reaction models were considered on the basis of provided isothermal DSC data, showing how ES and CaCO3 (in the pristine and modified form) have a completely different role in epoxy cure.
carbonate (CaCO3), such as chalk or calcite in polymer industries [22]. From structure features perspective, existing nanoporosities in ES structure are capable of forming strong interaction between polymeric matrix and ES, leading to improved mechanical properties. Toro et al. [23] compared performance of ES with commercial talc and calcium carbonate additives in improving mechanical characteristics, showing how ES is able to increase Young’s modulus of PP matrix more than carbonate additives, as a result of better interfacial adhesion between PP and ES interfaces. Elsewhere, PP composites containing ES modified with stearic acid were prepared via melting extrusion and their mechanical and thermal properties were studied in detail [24]. It was found that mechanical properties of PP/ES composite were modified at low-strain by two times, while a deteriorating effect caused by ES was observed at higher strains. Kumar et al. [25], however, reported that the use of ES powders modified with isophthalic acid in PP composites improved mechanical properties compared to identical composites containing pristine ES or CaCO3. In another study on PP/ES composites [26], it was reported that ES modified by pimelic acid significantly improved the dispersion state of ES, as well as interfacial bonding between continuous and dispersed phases, causing a slight variation in tensile modulus but a noticeable increase in the value of impact strength by almost more than 200%. ES has been also used as reinforcing agent in thermosetting rubber [27,28]. Vulcanization features of acrylonitrile butadiene rubber, natural rubber and styrene butadiene rubber compounds in the presence of ES were comprehensively studied, showing decrease in the optimum curing time by incorporation of ES powder, irrespective of rubber type [28], while curing time was dependent on rubber type. In the case of epoxy thermosetting resin, Ji et al. [12] have shown that incorporation of 5 wt.% ES into the epoxy resin increased its impact strength by approximately two times compared to the neat epoxy, probably due to the presence of protein on the ES surface. Moreover, it was found that existing functional groups on ES surface could move forward curing reaction, acting as secondary curing agent in the improvement of interfacial bonding with epoxy resin [15]. It is well-established that ultimate properties of thermosetting materials are highly dictated by their curing characteristic, allowing one to control processing parameters. Moreover, study on cure kinetics of filled epoxy provides quantitative information regarding the effect of additive on microstructural features of 3D cured resin [29–31]. In a consecutive works, we investigated the cure kinetics of epoxy based nanocomposites filled with different kinds of nanomaterials such as graphene oxide [32], multi-walled carbon nanotubes (MWCNTs) [33,34] and magnetic nanoparticles [35] using calorimetric and rheokinetic analyses. Overall, it was found that curing mechanism cannot be individually detected by nonisothermal analysis, since the simultaneous change of temperature and rate constant makes it difficult to recognize the suitable model reaction. For example, in some previous works, we prepared epoxy-based nanocomposites containing various contents of MWCNTs [33,34]. Nonisothermal differential scanning calorimetry (DSC) analysis of cure kinetics provided useful information about the crosslinking of the epoxy in the presence of functionalized MWCNTs, but the use of chemorheological along with isothermal DSC analysis fulfilled in a complementary manner the role of MWCNTs as a secondary curing agent. In our previous study, we comprehensively studied the cure kinetics of epoxy resin containing the ES modified by terpolymer of poly(Nvinyl-2-pyrrolidone-co-maleic acid-co-acrylic acid) through nonisothermal DSC analysis [15]. In this way, isoconversional methods including differential (Friedman) and integral (Ozawa and Kissinger–Akahira–Sunose) methods were employed to detect the effect of ES and CaCO3 additives. Actually, nonisothermal analyses are based on dynamic heating programs over a specified temperature range; hence, the kinetic constants may experience a wide transition leading to poor accuracy of the resulting kinetic parameters obtained from kinetic models. It is believed that isothermal methods can provide some more insights into the network formation through complementary kinetic
2. Experimental 2.1. Materials In this work, epoxy resin under trade name of EPIKOTE (RIMR145) was provided by Momentive (USA) (epoxide equivalent weight of 170–210 g/eq.). Curing agent and catalyst used in this work were methyltetrahydrophthalic anhydride (EPIKURE-RIMH145) and EPIKURE catalyst (RIMC145), respectively. Chicken ES was obtained from local farms. The ALBAFIL®PCC CaCO3 was supplied by CARY Co., USA. It should be noticed that in all prepared samples, additives were firstly washed and dried at 80 °C overnight and then grounded by milling (Retsch PM-400MA planetary ball mill with stabilized zirconia) for 6 h. Details of bare and modified ES (mES) and CaCO3 have been reported in our previous work [15]. 2.2. Preparation of epoxy-based nanocomposites Pristine CaCO3 and ES were modified with poly(N-vinyl-2-pyrrolidone-co-maleic acid-co-acrylic acid) terpolymer, to prevent aggregation of particles in the epoxy matrix, as discussed elsewhere [15]. Epoxy resin containing 0.1 and 0.3 wt.% of the pristine and modified CaCO3 (or ES) were then mixed with curing agent in a weight ratio of 100:85. 2.3. Measurements and analyses A Q2000 differential scanning calorimeter (DSC) (TA Instruments, New Castle, DE, USA) was employed to study the curing behavior of epoxy-based nanocomposites. In this regard, about 5 mg of each sample were placed in the aluminum cell and experienced heating from ambient temperature up to the isothermal temperature (120, 150, and 180 °C) by heating rate of 50 °C/min under nitrogen purge at 50 ml/ min. According to the literature, curing reaction is completed once the heat flow curve level off. Rheological behavior of epoxy resin during curing reaction was traced by using Ares-G2 rheometer (TA). All tests were tested in their linear viscoelastic behavior, at 25 °C and fixed strain of 1%. 3. Results and discussion 3.1. Rheokinetic analysis of cure reaction It is well-established that processing of thermosetting resin strongly depends on its rheological behavior, especially viscosity [36,37]. Understanding the interrelationship between curing characteristics and rheological behavior allow engineers to optimize cure parameters and consequently achieve desirable ultimate properties. Generally, contributing factors in curing reaction, such as temperature, flow characteristic, and conversion rate, dominantly control the viscosity behavior of thermoset resin [38,39]. Fig. 1 shows the variation of complex viscosity of blank epoxy resin as a function of curing time at two heating isothermal temperatures of 120 and 150 °C. It can be clearly observed that viscosity profile shifts, as expected, towards lower gel times upon increasing heating temperature from 120 to 150 °C. As a matter of fact, higher temperature means higher mobility for curing reaction moieties, raising the possibility of effective collusion between particles [34]. Moreover, upon increasing heating temperature form 120–150 °C, ultimate viscosity 209
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schematic illustration of possible chemical reactions occurring in Epoxy/0.1-mES system. Existing protein and peptide groups on ES surface could react by oxirane group of Epoxy resin. Modification of ES put more functional groups on its surface facilitating the reaction between epoxy and ES powder. On the other hand, completely contradictive behaviors were observed for CaCO3 system (Fig. 2B). It can be observed that viscosity profile corresponding to epoxy/0.1-CaCO3 composite follows a more abrupt ascending trend when compared to neat resin, while in the case of epoxy/0.3-CaCO3, if takes a very slower trend. Although at lower loading content of CaCO3 participation of functional group on its surface in curing reaction overcomes hindrance effect, further addition of CaCO3causes hindrance effect that dominates the reaction. Interestingly, functionalization of CaCO3 by terpolymer leads to decrease final viscosity value of the assigned system. Results from nonisothermal analysis of epoxy resin containing CaCO3 evidenced indicate the same behavior, in detail peak (Tp) and onset temperatures (Tons) of curing reaction were decreased with addition of 0.1 wt.% of CaCO3, while an increase was observed for 0.3 wt.% CaCO3. However, in opposition to the results obtained by nonisothermal approaches in our previous paper [15], modification of CaCO3 caused crosslinking density plummet, showing a negative effect of CaCO3 surface treatment. In fact, modification of CaCO3 deteriorates its performance by disturbing the effective contribution of carbonate group on its surface.
Fig. 1. Complex viscosity of epoxy resin studied over time at two different temperatures.
increased, which can be considered as a finger print of crosslinking density enhancement. Viscosity profiles of the epoxy systems containing ES, mES, CaCO3, and mCaCO3 at temperature of 150 °C are compared in Fig. 2. When ES was used as a modifier (Fig. 2A), irrespective of loading content or modification, a shift of viscosity profile toward higher time was observed, signifying a delay in the curing reaction compared to blank epoxy, as a result of physical hindrance caused by introduction of additive into the epoxy matrix. As a matter of fact, addition of additive leads to the formation of physical barrier between curing agent and functional groups of epoxy resin, preventing them to reach and react together. Furthermore, reduction in curing reaction time together with increase in ultimate viscosity of the system was observed upon increasing ES loading level from 0.1 to 0.3 wt.%, owing to the presence of existing functional groups on the surface of ES, that it supposed to be more evident at higher contents. Modification of 0.1-ES surface by terpolymer significantly leads to faster curing reaction when compared to pristine 0.1-ES, thanks to participation of the attached functional groups on additive surface in curing reaction. Furthermore, higher viscosity values in Epoxy/0.1-mES system in comparison to pristine 0.1ES were observed, suggesting that presence of further chemical reactions generated by the modification can induce higher crosslinking density. This result contrasts with our finding in our previous paper applied by nonisothermal method [15]. As a matter of fact, nonisothermal analysis suffers from inadequate accuracy because several chemical reactions may occur over the heating scan, that make difficult distinguishing the curing reaction from homopolymerization or other side chemical reactions occurring over the cure. Fig. 3 provides a
3.2. Isothermal DSC analysis Curing conversion, α at a given time, t is determined by dividing the area under the peak of heat flow curve (ΔHt) by total heat released in dynamic DSC (ΔHT), as follows [40]:
α=
ΔHt ΔHT
dα 1 dΔHt =( ). ( ) dt ΔHT dt
(1)
(2)
As an example, DSC profile for isothermal tests, conversion and curing rate curves of epoxy/0.1-ES system at the three different isothermal temperatures are provided in Fig. 4. The presence of single exothermic peak over the heating scan shows the reliability of single curing mechanism, as discussed elsewhere [34]. Furthermore, an enhancement in the curing rate was observed upon increasing heating temperature from 120 to 180 °C, as a result of more available energy and increasing molecular movement. In the initial stage of curing reaction, rate of curing reaction increased, due to the high concentration of reactive groups. After a while, concentration of curing agent and epoxy groups reach to the balance, bringing constant curing rate. Fig. 2. Complex viscosity of epoxy containing pristine and modified ES (A) and CaCO3 (B) at 150 °C.
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Fig. 3. Schematic illustration of possible chemical reactions between mES and epoxide.
samples was studied in detail. In this way, rate of curing conversion as a function of temperature and conversion can be calculated using the following equation [35]:
Finally, curing rate shows downward trend, because of the increasing viscosity and low concentration of functional groups as well. In order to better understand the curing reaction of epoxy resin in the presence and absence of ES and CaCO3, cure kinetic of prepared
Fig. 4. DSC thermographs (A), conversion, α (B) and conversion rate (C) of 0.1-ES system at three different isothermal temperatures.
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Fig. 5. (A) Plots of ln tα,i vs. 1/Ti for the epoxy resin containing 0.1 mES and (B) resulting activation energy for modified samples.
Fig. 6. (A) Plots of ln(dα/dt) versus ln(1−α) and (B) lnk versus 1/T for epoxy resin containing 0.1-mES.
Table 1 Kinetic parameters obtained using Eq. (6). Sample
0.1-mES 0.1-mCaCO3
T (°C)
120 150 120 150
dα = k (T ) f (α ) dt
nth order n
k*103 (s−1)
LnA (s−1)
Ea(kJ/mol)
0.66 0.97 0.84 1.07
0.94 4.05 1.17 5.02
13.62
70
13.74
65
(3)
where k(T) and f(α) denote the reaction rate constant and reaction model. It should be noticed that reaction rate constant is usually described by Arrhenius equation, as follows [40]:
k (T ) = A exp(−
Ea ) RT
(4) Fig. 7. ln(1-α) as a function of time for modified additives at 120 °C.
In this relation, A is the frequency factor, Ea the activation energy, R the universal gas constant, and T is the absolute temperature. Substitution of Eq. (4) into Eq. (3) and rewriting of the resulting 212
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Fig. 8. (A) Plots of Eq. (8), (B) Eq. (9), and (C) Eq. (10) at 150 °C for epoxy resin containing 0.1-mES.
mES and estimated activation energy based on Eq. (5) for modified samples. Accordingly, activation energy of epoxy resin containing 0.1mES stands over the activation energy of 0.1-mCaCO3. This result completely agrees with activation energy calculations made by using Friedman model in nonisothermal approaches. Assuming the reaction model of curing reaction being nth order, the rate of curing reaction can simply be obtained as follows [30]:
ln(
(6)
Slope and intercept of ln(dα/dt) vs. ln(1−α) plot give n and ln(k), respectively (Fig. 6A). Moreover, according to Eq. (4), plot of ln(k) vs. 1/T leads to a line with slope of Ea as shown in Fig. 6B. Table 1 tabulated the kinetic parameters of cure reaction for epoxy systems containing modified additives. It can be seen that Epoxy/0.1-mES nanocomposites take the higher value of activation energy when compared to Epoxy/0.1-CaCO3 system, confirming the results of model-free approach (Fig. 5). According to the literature, mechanism of epoxy resin is complex, causing the deviation of its reaction model from nth order model. In order to evaluate the appropriate model, plots of −ln(1-α) vs. time at 120 °C have been reported in Fig. 7 for modified ES and CaCO3 samples. It is visible how, at the late stage of the reaction time, it deviates sharply from linear plot, confirming complexity of the reaction model. Kamal model could coverage the deviation of nth order model by incorporation of autocatalytic parameters, as follows[41]:
Fig. 9. Plots of dα/dt versus α for 0.1-mES at 150 °C, experimental and theoretical models profiles.
relation leads to following correlation, in which slope of ln tα,i vs. 1/Ti l indicates Ea/R [34]:
g (α ) ⎤ E ln tα, i = ln ⎡ + a ⎢ ⎥ A RT a i ⎣ ⎦
dα ) = ln(k ) + n ln(1 − α ) dt
(5)
where g(α) is the result of reaction model integration and tα,i denote the time in which conversion reaches to a certain value at Ti temperature. Fig. 5 provide the plots of ln tα,i vs. 1/Ti for epoxy resin containing 0.1 213
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5. Conclusions
Table 2 Kinetic parameters of Kamal model for modified additives. Sample
0.1-mES 0.1-mCaCO3
T(°C)
120 150 120 150
Cure kinetics of epoxy/anhydride system containing 0.1 and 0.3 wt. % of pristine calcium carbonate (CaCO3), copolymer-modified CaCO3 (mCaCO3), pristine eggshell (ES), and copolymer-modified ES (mES) was studied by rheological and DSC analyses. Results from rheological tests of filled epoxy with ES have shown that the incorporation of 0.1 wt.% ES into epoxy resin caused a decrease in curing reaction rate and crosslinking density; on the other hand, increase of ES content from 0.1 to 0.3 wt.% compensated for the retardation effect. Interestingly, the modification of ES by poly(N-vinyl-2-pyrrolidone-co-maleic acid-coacrylic acid) terpolymer increased the crosslinking density and rate of reaction, thanks to the presence of functional groups attached on ES surface, that effectively participated to the curing reaction. It was also demonstrated that Calcium carbonate behaves in a different direction: although the addition of 0.1%wt. of CaCO3 was able to increase the reaction rate and crosslinking density of neat epoxy, terpolymer modification of CaCO3 deteriorates its performance, negatively affecting the carbonate performance in the curing reaction. Model-free and modelfitting approaches for evaluation of cure kinetics by using permitted us to deeply investigate the curing mechanism of epoxy system containing ES and CaCO3. It was revealed that mES took higher activation energy values if compared to mCaCO3, as a confirmation of viscosity upturn, already evidenced by rheological analysis.
Kamal model k1*103 (s−1)
k2*103 (s−1)
n
m
Ea2(kJ/mol)
7.30E3 1.75 0.18 3.32
1.38 4.35 1.39 2.34
0.95 1.28 1.06 1.16
0.26 0.4 0.21 0.23
52.8
dα = (k1 + k2 α m)(1 − α )n dt
23.5
(7)
In order to determine the meaningful kinetic parameters from Eq. (7), Kenny analytical–graphical method was utilized by employing the following steps [42]: i. k1 is equal to the value of dα/dt at t = 0 ii. first guess value of kinetic parameters including n and m are measured from the slope of following relations, respectively:
ln(
dα ) = ln(k1 + k2 α m) + n ln(1 − α ) dt
(8)
dα
⎤ ⎡ dt − k1⎥ = ln(k2) + m ln(α ) ln ⎢ n − α (1 ) ⎥ ⎢ ⎦ ⎣
(9)
References
It should be noticed that k2 can be estimated from the intercept of Eq. (9). iii. Rewritten Eq. (6) leads to following equation:
[1] M. Mecklenburg, D. Mizushima, N. Ohtake, W. Bauhofer, B. Fiedler, K. Schulte, On the manufacturing and electrical and mechanical properties of ultra-high wt.% fraction aligned MWCNT and randomly oriented CNT epoxy composites, Carbon 91 (2015) 275–290. [2] P.K. Ghosh, K. Kumar, N. Chaudhary, Influence of ultrasonic dual mixing on thermal and tensile properties of MWCNTs-epoxy composite, Compos. Part B-Eng. 77 (2015) 139–144. [3] O. Starkova, E. Mannov, K. Schulte, A. Aniskevich, Strain-dependent electrical resistance of epoxy/MWCNT composite after hydrothermal aging, Compos. Sci. Technol. 117 (2015) 107–113. [4] D. Ratna, Handbook of Thermoset Resins, ISmithers, Shawbury, Shrewsbury Shropshire, 2009. [5] H. Gu, C. Ma, J. Gu, J. Guo, X. Yan, J. Huang, Q. Zhang, Z. Guo, An overview of multifunctional epoxy nanocomposites, J. Mater. Chem. C 4 (2016) 5890–5906. [6] Q.-S. Yang, X.-Q. He, X. Liu, F.-F. Leng, Y.-W. Mai, The effective properties and local aggregation effect of CNT/SMP composites, Compos. Part B-Eng. 43 (2012) 33–38. [7] B. Koh, W. Cheng, Mechanisms of carbon nanotube aggregation and the reversion of carbon nanotube aggregates in aqueous medium, Langmuir 30 (2014) 10899–10909. [8] J.R. Choi, K.Y. Rhee, S.J. Park, Post-annealing effects of electroless Ni–B-plated MWCNTs on thermal conductivity of epoxy-based composites, J. Ind. Eng. Chem. (2015). [9] M.R. Zakaria, H. Md Akil, M.H. Abdul Kudus, A.H. Kadarman, Improving flexural and dielectric properties of MWCNT/epoxy nanocomposites by introducing advanced hybrid filler system, Compos. Struct. 132 (2015) 50–64. [10] B. Wetzel, P. Rosso, F. Haupert, K. Friedrich, Epoxy nanocomposites – fracture and toughening mechanisms, Eng. Fract. Mech. 73 (2006) 2375–2398. [11] C. Zilg, R. Mülhaupt, J. Finter, Morphology and toughness/stiffness balance of nanocomposites based upon anhydride-cured epoxy resins and layered silicates, Macromol. Chem. Phys. 200 (1999) 661–670. [12] G. Ji, H. Zhu, C. Qi, M. Zeng, Mechanism of interactions of eggshell microparticles with epoxy resins, Polym. Eng. Sci. 49 (2009) 1383–1388. [13] M.M. Rahman, A.N. Netravali, B.J. Tiimob, V.K. Rangari, Bioderived green composite from soy protein and eggshell nanopowder, ACS Sustain. Chem. Eng. 2 (2014) 2329–2337. [14] D. Cree, A. Rutter, Sustainable bio-Inspired limestone eggshell powder for potential industrialized applications, ACS Sustain. Chem. Eng. 3 (2015) 941–949. [15] M.R. Saeb, M. Ghaffari, H. Rastin, H.A. Khonakdar, F. Simon, F. Najafi, V. Goodarzi, P. Vijayan, P.D. Puglia, F.H. Asl, K. Formela, Biowaste chicken eggshell powder as a potential cure modifier for epoxy/anhydride systems: competitiveness with terpolymer-modified calcium carbonate at low loading levels, RSC Adv. 7 (2017) 2218–2230. [16] A. Mittal, M. Teotia, R. Soni, J. Mittal, Applications of egg shell and egg shell membrane as adsorbents: a review, J. Mol. Liq. 223 (2016) 376–387. [17] M. Pettinato, S. Chakraborty, H.A. Arafat, V. Calabro, Eggshell A green adsorbent for heavy metal removal in an MBR system, Ecotoxicol. Environ. Saf. 121 (2015) 57–62. [18] H.J. Park, S.W. Jeong, J.K. Yang, B.G. Kim, S.M. Lee, Removal of heavy metals using waste eggshell, J. Environ. Sci. 19 (2007) 1436–1441. [19] S.-C. Wu, H.-C. Hsu, S.-K. Hsu, Y.-C. Chang, W.-F. Ho, Effects of heat treatment on
dα
⎡ ⎤ dt ln ⎢ = n ln(1 − α ) m⎥ + k k α 1 2 ⎢ ⎥ ⎣ ⎦
(10)
Slope of the above relation is equal to new value of n that used again in previous step help to find the new values of m and k2 parameters. Second and third steps have been repeated up to reach an acceptable error. Plots of Eq. (8) up to Eq. (10) for the epoxy/0.1-mES system have been reported in Fig. 8. As an example, the experimental data of isothermal DSC along with predicted value according to nth order and Kamal models for 0.1-mES are reported in Fig. 9. Kamal model could appropriately follow the experimental data even at low conversion value; however, nth order model was not able to fit with experimental data when conversion is below 0.3. Activation energy of the system at higher conversion can be measured from the slope of the plot of lnk2 vs. 1/T. The kinetic parameters calculated according to Kamal model utilizing Kenny analytical–graphical method are given in Table 2. In all cases, the overall order of the reaction (m + n) exceeds the value one, demonstrating the complexity of the reaction mechanism [43,44]. Moreover, the m + n increased upon increase of heating temperature from 120 °C to 150 °C, as a result of increasing the kinetic energy of the system. Such a rise is more significant in the case of eggshell additive. It is also interesting to mention that higher values of m are attained at 150 °C due to enhanced autocatalytic reactions. Thus, it can be concluded that temperature appeared as a key controlling parameter in curing reaction. In agreement with other models, activation energy of epoxy resin containing 0.1-mES took higher value than those of 0.1-mCaCO3. The functional groups attached to the ES surface can contribute to crosslinking reaction of epoxy leading to a viscosity upturn (Fig. 2) that might restrict the mobility of chains, as featured by a rise in activation energy value (Fig. 5B). By contrast, incorporation of mCaCO3 into the epoxy resin could to a lesser extent enhance crosslinking and the rate of reaction with lesser viscosity compared to eggshell-incorporated systems (Fig. 2). 214
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[20] [21]
[22] [23] [24] [25] [26] [27]
[28]
[29]
[30] [31]
[32]
1002/pc.24415. [33] M.R. Saeb, H. Rastin, M. Nonahal, M. Ghaffari, A. Jannesari, K. Formela, Cure kinetics of epoxy/MWCNTs nanocomposites: Nonisothermal calorimetric and rheokinetic techniques, Journal of Applied Polymer Science, 2017, DOI: 10.1002/app. 4522. [34] P. Vijayan, P.D. Puglia, H. Rastin, M.R. Saeb, B. Shojaei, K. Formela, Cure kinetics of epoxy/MWCNTs nanocomposites: isothermal calorimetric and rheological analyses, Prog. Org. Coat. 108 (2017) 75–83. [35] M.R. Saeb, H. Rastin, M. Shabanian, M. Ghaffari, G. Bahlakeh, Cure kinetics of epoxy/β-cyclodextrin-functionalized Fe 3 O 4 nanocomposites: experimental analysis, mathematical modeling, and molecular dynamics simulation, Prog. Org. Coat. 110 (2017) 172–181. [36] P.J. Halley, M.E. Mackay, Chemorheology of thermosets—an overview, Polym. Eng. Sci. 36 (1996) 593–609. [37] C.D. Han, K.-W. Lem, Chemorheology of thermosetting resins. I. The chemorheology and curing kinetics of unsaturated polyester resin, J. Appl. Polym. Sci. 28 (1983) 3155–3183. [38] A. Yousefi, P.G. Lafleur, R. Gauvin, Kinetic studies of thermoset cure reactions: a review, Polym. Compos. 18 (1997) 157–168. [39] G. Lelli, A. Terenzi, J.M. Kenny, L. Torre, Modelling of the chemo–rheological behavior of thermosetting polymer nanocomposites, Polym. Compos. 30 (2009) 1–12. [40] 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. [41] R. Ren, X. Xiong, X. Ma, S. Liu, J. Wang, P. Chen, Y. Zeng, Isothermal curing kinetics and mechanism of DGEBA epoxy resin with phthalide-containing aromatic diamine, Thermochim. Acta 623 (2016) 15–21. [42] C.S. Wang, C.H. Lin, Novel phosphorus-containing epoxy resins. Part II: curing kinetics, Polymer 41 (2000) 8579–8586. [43] M. Abdalla, D. Dean, P. Robinson, E. Nyairo, Cure behavior of epoxy/MWCNT nanocomposites: the effect of nanotube surface modification, Polymer 49 (2008) 3310–3317. [44] F. Ferdosian, M. Ebrahimi, A. Jannesari, Curing kinetics of solid epoxy/DDM/nanoclay: isoconversional models versus fitting model, Thermochim. Acta 568 (2013) 67–73.
the synthesis of hydroxyapatite from eggshell powders, Ceram. Int. 41 (2015) 10718–10724. T. Witoon, Characterization of calcium oxide derived from waste eggshell and its application as CO2 sorbent, Ceram. Int. 37 (2011) 3291–3298. M. Mohammadi, P. Lahijani, A.R. Mohamed, Refractory dopant-incorporated CaO from waste eggshell as sustainable sorbent for CO2 capture: experimental and kinetic studies, Chem. Eng. J. 243 (2014) 455–464. S.H. Katz, W.W. Weaver, Encyclopedia of Food and Culture, Scribner, New York, 2003. P. Toro, R. Quijada, M. Yazdani-Pedram, J.L. Arias, Eggshell, a new bio-filler for polypropylene composites, Mater. Lett. 61 (2007) 4347–4350. T. Ghabeer, R. Dweiri, S. Al-Khateeb, Thermal and mechanical characterization of polypropylene/eggshell biocomposites, J. Reinf. Plast. Compos. 32 (2013) 402–409. R. Kumar, J. Dhaliwal, G. Kapur, Mechanical properties of modified biofillerpolypropylene composites, Polym. Compos. 35 (2014) 708–714. Z. Lin, Z. Zhang, K. Mai, Preparation and properties of eggshell/β-polypropylene bio-composites, J. Appl. Polym. Sci. 125 (2012) 61–66. P. Intharapat, A. Kongnoo, K. Kateungngan, The potential of chicken eggshell waste as a bio-filler filled epoxidized natural rubber (ENR) composite and its properties, J. Polym. Environ. 21 (2013) 245–258. M.R. Saeb, H. Ramezani-Dakhel, H.A. Khonakdar, G. Heinrich, U. Wagenknecht, A comparative study on curing characteristics and thermomechanical properties of elastomeric nanocomposites: the effects of eggshell and calcium carbonate nanofillers, J. Appl. Polym. Sci. 127 (2013) 4241–4250. D. Galpaya, M. Wang, G. George, N. Motta, E. Waclawik, C. Yan, Preparation of graphene oxide/epoxy nanocomposites with significantly improved mechanical properties, J. Appl. Phys. 116 (2014) 053518. M. Ghaemy, M. Barghamadi, H. Behmadi, Cure kinetics of epoxy resin and aromatic diamines, J. Appl. Polym. Sci. 94 (2004) 1049–1056. M.R. Saeb, E. Bakhshandeh, H.A. Khonakdar, E. Mäder, C. Scheffler, G. Heinrich, Cure kinetics of epoxy nanocomposites affected by MWCNTs functionalization: a review, Sci. World J. 2013 (2013) 14. M. Nonahal, M.R. Saeb, S. Hassan Jafari, H. Rastin, H.A. Khonakdar, F. Najafi, F. Simon, Design, preparation, and characterization of fast cure epoxy/amine-functionalized graphene oxide nanocomposites, Polymer Composites, 2017, DOI: 10.
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Progress in Organic Coatings journal homepage: www.elsevier.com/locate/porgcoat
Cure kinetics of epoxy/chicken eggshell biowaste composites: Isothermal calorimetric and chemorheological analyses
MARK
⁎
Mohammad Reza Saeba, , Hadi Rastinb, Milad Nonahalb, Seyed Mohammad Reza Paranc, Hossein Ali Khonakdard, Debora Pugliae a
Department of Resin and Additives, Institute for Color Science and Technology, P.O. Box 16765-654, Tehran, Iran School of Chemical Engineering, College of Engineering, University of Tehran, P.O. Box 11155-4563, Tehran, Iran c Department of Polymer Processing, Iran Polymer and Petrochemical Institute, P.O. Box 14965-115, Tehran, Iran d Leibniz Institute of Polymer Research Dresden, Hohe Straße 6, D-01069, Dresden, Germany e University of Perugia, Department of Civil and Environmental Engineering, Strada di Pentima 4, 05100, Terni, Italy b
A R T I C L E I N F O
A B S T R A C T
Keywords: Chicken eggshell Epoxy Calcium carbonate Rheokinetic study Isothermal DSC
Chicken eggshell (ES) is a biowaste powder comprising peptide functional groups and proteins, which give it potential to play the role of curing aid when added to the epoxy resin. In this work, pristine and terpolymermodified ES (mES) were used in epoxy-based composites and their performance in network formation was compared with pristine calcium carbonate (CaCO3) and terpolymer-modified CaCO3 (mCaCO3) additives, via comprehensive isothermal calorimetric and chemorheological analyses. The mechanism and progression of the crosslinking of identical composites containing very low amount of additives were also discussed. Rheokinetic evaluations revealed that, despite the almost identical chemical structure of the ES and CaCO3, the former can more appropriately contribute to crosslinking reaction in the pristine form, since terpolymer modification causes a physical hindrance to its cure potential towards epoxy rings after surface modification. In the case of calorimetric studies, in contrast to nonisothermal cure kinetics, a more comprehensive image of the catalytic role of mES was identified in view of overall reaction order and apparent activation energy calculated for both types of systems.
1. Introduction Epoxy is a well-known thermosetting resin possessing considerable beneficial properties such as sufficient adhesiveness, curing ability with various hardeners, superior mechanical and corrosion characteristics, that makes it one of the most widely used resins in surface coating industry [1–5]. However, its brittleness and poor impact strength have limited its use in coating and engineering composites applications [6,7]. In this regard, a great deal of efforts has been made to find an effective approach for toughening of epoxy. It has been revealed that introduction of second inorganic component into the epoxy matrix could substantially improve its impact strength [8,9]. Beyond the exceptional characteristics of nanomaterials as reinforcing agents in epoxy resin (namely high surface area, excellent mechanical and thermal properties), one should take into account that their use in practical and industrial scale is still far from perfect, because of their high expense and difficulties in their processing, due to high surface energy that causes agglomeration of nanoparticles [10,11]. By contrast, environmental concerns induce industrial centers to move forward ⁎
using new material with renewable resources. From this standpoint, an increasing attention has been directed toward the use of biowaste materials (such as husk ash, fly ash, bagasse) in polymeric industries, as potential alternatives for existing additives, because of their low cost, recyclability, biodegradability, and use of renewable resources [12–14]. Within different kinds of biowaste additives, widely available inexpensive chicken eggshell (ES) is a promising candidate as reinforcing agent in polymeric industries, due to its good mechanical characteristics such as acceptable toughness and impact strength [15]. However, over the last decades, landfill disposing of ES as by-product of egg processing industry has brought about serious environmental concerns [16]. From environmental problems and economic perspectives, biowaste ES has been recently applied in various applications areas, for instance for absorption of heavy metals [17,18], synthesis of hydroxyapatite [19] and sorption of CO2 [20,21]. It is recognized that ES is composed of calcium carbonate (94%) with just 3–4% of organic materials including proteins, collagen, and sulfated polysaccharides, that makes it an excellent substituting material for mineral-based calcium
Corresponding author. E-mail addresses: [email protected], [email protected] (M.R. Saeb).
http://dx.doi.org/10.1016/j.porgcoat.2017.10.018 Received 28 September 2017; Received in revised form 16 October 2017; Accepted 19 October 2017 Available online 02 November 2017 0300-9440/ © 2017 Elsevier B.V. All rights reserved.
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parameters that allow for higher accuracies. In this work, we aim to investigate the curing reaction of epoxy resin in the presence and absence of ES and CaCO3 through isothermal calorimetric and rheological tests. In this way, autocatalytic and noncatalytic reaction models were considered on the basis of provided isothermal DSC data, showing how ES and CaCO3 (in the pristine and modified form) have a completely different role in epoxy cure.
carbonate (CaCO3), such as chalk or calcite in polymer industries [22]. From structure features perspective, existing nanoporosities in ES structure are capable of forming strong interaction between polymeric matrix and ES, leading to improved mechanical properties. Toro et al. [23] compared performance of ES with commercial talc and calcium carbonate additives in improving mechanical characteristics, showing how ES is able to increase Young’s modulus of PP matrix more than carbonate additives, as a result of better interfacial adhesion between PP and ES interfaces. Elsewhere, PP composites containing ES modified with stearic acid were prepared via melting extrusion and their mechanical and thermal properties were studied in detail [24]. It was found that mechanical properties of PP/ES composite were modified at low-strain by two times, while a deteriorating effect caused by ES was observed at higher strains. Kumar et al. [25], however, reported that the use of ES powders modified with isophthalic acid in PP composites improved mechanical properties compared to identical composites containing pristine ES or CaCO3. In another study on PP/ES composites [26], it was reported that ES modified by pimelic acid significantly improved the dispersion state of ES, as well as interfacial bonding between continuous and dispersed phases, causing a slight variation in tensile modulus but a noticeable increase in the value of impact strength by almost more than 200%. ES has been also used as reinforcing agent in thermosetting rubber [27,28]. Vulcanization features of acrylonitrile butadiene rubber, natural rubber and styrene butadiene rubber compounds in the presence of ES were comprehensively studied, showing decrease in the optimum curing time by incorporation of ES powder, irrespective of rubber type [28], while curing time was dependent on rubber type. In the case of epoxy thermosetting resin, Ji et al. [12] have shown that incorporation of 5 wt.% ES into the epoxy resin increased its impact strength by approximately two times compared to the neat epoxy, probably due to the presence of protein on the ES surface. Moreover, it was found that existing functional groups on ES surface could move forward curing reaction, acting as secondary curing agent in the improvement of interfacial bonding with epoxy resin [15]. It is well-established that ultimate properties of thermosetting materials are highly dictated by their curing characteristic, allowing one to control processing parameters. Moreover, study on cure kinetics of filled epoxy provides quantitative information regarding the effect of additive on microstructural features of 3D cured resin [29–31]. In a consecutive works, we investigated the cure kinetics of epoxy based nanocomposites filled with different kinds of nanomaterials such as graphene oxide [32], multi-walled carbon nanotubes (MWCNTs) [33,34] and magnetic nanoparticles [35] using calorimetric and rheokinetic analyses. Overall, it was found that curing mechanism cannot be individually detected by nonisothermal analysis, since the simultaneous change of temperature and rate constant makes it difficult to recognize the suitable model reaction. For example, in some previous works, we prepared epoxy-based nanocomposites containing various contents of MWCNTs [33,34]. Nonisothermal differential scanning calorimetry (DSC) analysis of cure kinetics provided useful information about the crosslinking of the epoxy in the presence of functionalized MWCNTs, but the use of chemorheological along with isothermal DSC analysis fulfilled in a complementary manner the role of MWCNTs as a secondary curing agent. In our previous study, we comprehensively studied the cure kinetics of epoxy resin containing the ES modified by terpolymer of poly(Nvinyl-2-pyrrolidone-co-maleic acid-co-acrylic acid) through nonisothermal DSC analysis [15]. In this way, isoconversional methods including differential (Friedman) and integral (Ozawa and Kissinger–Akahira–Sunose) methods were employed to detect the effect of ES and CaCO3 additives. Actually, nonisothermal analyses are based on dynamic heating programs over a specified temperature range; hence, the kinetic constants may experience a wide transition leading to poor accuracy of the resulting kinetic parameters obtained from kinetic models. It is believed that isothermal methods can provide some more insights into the network formation through complementary kinetic
2. Experimental 2.1. Materials In this work, epoxy resin under trade name of EPIKOTE (RIMR145) was provided by Momentive (USA) (epoxide equivalent weight of 170–210 g/eq.). Curing agent and catalyst used in this work were methyltetrahydrophthalic anhydride (EPIKURE-RIMH145) and EPIKURE catalyst (RIMC145), respectively. Chicken ES was obtained from local farms. The ALBAFIL®PCC CaCO3 was supplied by CARY Co., USA. It should be noticed that in all prepared samples, additives were firstly washed and dried at 80 °C overnight and then grounded by milling (Retsch PM-400MA planetary ball mill with stabilized zirconia) for 6 h. Details of bare and modified ES (mES) and CaCO3 have been reported in our previous work [15]. 2.2. Preparation of epoxy-based nanocomposites Pristine CaCO3 and ES were modified with poly(N-vinyl-2-pyrrolidone-co-maleic acid-co-acrylic acid) terpolymer, to prevent aggregation of particles in the epoxy matrix, as discussed elsewhere [15]. Epoxy resin containing 0.1 and 0.3 wt.% of the pristine and modified CaCO3 (or ES) were then mixed with curing agent in a weight ratio of 100:85. 2.3. Measurements and analyses A Q2000 differential scanning calorimeter (DSC) (TA Instruments, New Castle, DE, USA) was employed to study the curing behavior of epoxy-based nanocomposites. In this regard, about 5 mg of each sample were placed in the aluminum cell and experienced heating from ambient temperature up to the isothermal temperature (120, 150, and 180 °C) by heating rate of 50 °C/min under nitrogen purge at 50 ml/ min. According to the literature, curing reaction is completed once the heat flow curve level off. Rheological behavior of epoxy resin during curing reaction was traced by using Ares-G2 rheometer (TA). All tests were tested in their linear viscoelastic behavior, at 25 °C and fixed strain of 1%. 3. Results and discussion 3.1. Rheokinetic analysis of cure reaction It is well-established that processing of thermosetting resin strongly depends on its rheological behavior, especially viscosity [36,37]. Understanding the interrelationship between curing characteristics and rheological behavior allow engineers to optimize cure parameters and consequently achieve desirable ultimate properties. Generally, contributing factors in curing reaction, such as temperature, flow characteristic, and conversion rate, dominantly control the viscosity behavior of thermoset resin [38,39]. Fig. 1 shows the variation of complex viscosity of blank epoxy resin as a function of curing time at two heating isothermal temperatures of 120 and 150 °C. It can be clearly observed that viscosity profile shifts, as expected, towards lower gel times upon increasing heating temperature from 120 to 150 °C. As a matter of fact, higher temperature means higher mobility for curing reaction moieties, raising the possibility of effective collusion between particles [34]. Moreover, upon increasing heating temperature form 120–150 °C, ultimate viscosity 209
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schematic illustration of possible chemical reactions occurring in Epoxy/0.1-mES system. Existing protein and peptide groups on ES surface could react by oxirane group of Epoxy resin. Modification of ES put more functional groups on its surface facilitating the reaction between epoxy and ES powder. On the other hand, completely contradictive behaviors were observed for CaCO3 system (Fig. 2B). It can be observed that viscosity profile corresponding to epoxy/0.1-CaCO3 composite follows a more abrupt ascending trend when compared to neat resin, while in the case of epoxy/0.3-CaCO3, if takes a very slower trend. Although at lower loading content of CaCO3 participation of functional group on its surface in curing reaction overcomes hindrance effect, further addition of CaCO3causes hindrance effect that dominates the reaction. Interestingly, functionalization of CaCO3 by terpolymer leads to decrease final viscosity value of the assigned system. Results from nonisothermal analysis of epoxy resin containing CaCO3 evidenced indicate the same behavior, in detail peak (Tp) and onset temperatures (Tons) of curing reaction were decreased with addition of 0.1 wt.% of CaCO3, while an increase was observed for 0.3 wt.% CaCO3. However, in opposition to the results obtained by nonisothermal approaches in our previous paper [15], modification of CaCO3 caused crosslinking density plummet, showing a negative effect of CaCO3 surface treatment. In fact, modification of CaCO3 deteriorates its performance by disturbing the effective contribution of carbonate group on its surface.
Fig. 1. Complex viscosity of epoxy resin studied over time at two different temperatures.
increased, which can be considered as a finger print of crosslinking density enhancement. Viscosity profiles of the epoxy systems containing ES, mES, CaCO3, and mCaCO3 at temperature of 150 °C are compared in Fig. 2. When ES was used as a modifier (Fig. 2A), irrespective of loading content or modification, a shift of viscosity profile toward higher time was observed, signifying a delay in the curing reaction compared to blank epoxy, as a result of physical hindrance caused by introduction of additive into the epoxy matrix. As a matter of fact, addition of additive leads to the formation of physical barrier between curing agent and functional groups of epoxy resin, preventing them to reach and react together. Furthermore, reduction in curing reaction time together with increase in ultimate viscosity of the system was observed upon increasing ES loading level from 0.1 to 0.3 wt.%, owing to the presence of existing functional groups on the surface of ES, that it supposed to be more evident at higher contents. Modification of 0.1-ES surface by terpolymer significantly leads to faster curing reaction when compared to pristine 0.1-ES, thanks to participation of the attached functional groups on additive surface in curing reaction. Furthermore, higher viscosity values in Epoxy/0.1-mES system in comparison to pristine 0.1ES were observed, suggesting that presence of further chemical reactions generated by the modification can induce higher crosslinking density. This result contrasts with our finding in our previous paper applied by nonisothermal method [15]. As a matter of fact, nonisothermal analysis suffers from inadequate accuracy because several chemical reactions may occur over the heating scan, that make difficult distinguishing the curing reaction from homopolymerization or other side chemical reactions occurring over the cure. Fig. 3 provides a
3.2. Isothermal DSC analysis Curing conversion, α at a given time, t is determined by dividing the area under the peak of heat flow curve (ΔHt) by total heat released in dynamic DSC (ΔHT), as follows [40]:
α=
ΔHt ΔHT
dα 1 dΔHt =( ). ( ) dt ΔHT dt
(1)
(2)
As an example, DSC profile for isothermal tests, conversion and curing rate curves of epoxy/0.1-ES system at the three different isothermal temperatures are provided in Fig. 4. The presence of single exothermic peak over the heating scan shows the reliability of single curing mechanism, as discussed elsewhere [34]. Furthermore, an enhancement in the curing rate was observed upon increasing heating temperature from 120 to 180 °C, as a result of more available energy and increasing molecular movement. In the initial stage of curing reaction, rate of curing reaction increased, due to the high concentration of reactive groups. After a while, concentration of curing agent and epoxy groups reach to the balance, bringing constant curing rate. Fig. 2. Complex viscosity of epoxy containing pristine and modified ES (A) and CaCO3 (B) at 150 °C.
210
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Fig. 3. Schematic illustration of possible chemical reactions between mES and epoxide.
samples was studied in detail. In this way, rate of curing conversion as a function of temperature and conversion can be calculated using the following equation [35]:
Finally, curing rate shows downward trend, because of the increasing viscosity and low concentration of functional groups as well. In order to better understand the curing reaction of epoxy resin in the presence and absence of ES and CaCO3, cure kinetic of prepared
Fig. 4. DSC thermographs (A), conversion, α (B) and conversion rate (C) of 0.1-ES system at three different isothermal temperatures.
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Fig. 5. (A) Plots of ln tα,i vs. 1/Ti for the epoxy resin containing 0.1 mES and (B) resulting activation energy for modified samples.
Fig. 6. (A) Plots of ln(dα/dt) versus ln(1−α) and (B) lnk versus 1/T for epoxy resin containing 0.1-mES.
Table 1 Kinetic parameters obtained using Eq. (6). Sample
0.1-mES 0.1-mCaCO3
T (°C)
120 150 120 150
dα = k (T ) f (α ) dt
nth order n
k*103 (s−1)
LnA (s−1)
Ea(kJ/mol)
0.66 0.97 0.84 1.07
0.94 4.05 1.17 5.02
13.62
70
13.74
65
(3)
where k(T) and f(α) denote the reaction rate constant and reaction model. It should be noticed that reaction rate constant is usually described by Arrhenius equation, as follows [40]:
k (T ) = A exp(−
Ea ) RT
(4) Fig. 7. ln(1-α) as a function of time for modified additives at 120 °C.
In this relation, A is the frequency factor, Ea the activation energy, R the universal gas constant, and T is the absolute temperature. Substitution of Eq. (4) into Eq. (3) and rewriting of the resulting 212
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Fig. 8. (A) Plots of Eq. (8), (B) Eq. (9), and (C) Eq. (10) at 150 °C for epoxy resin containing 0.1-mES.
mES and estimated activation energy based on Eq. (5) for modified samples. Accordingly, activation energy of epoxy resin containing 0.1mES stands over the activation energy of 0.1-mCaCO3. This result completely agrees with activation energy calculations made by using Friedman model in nonisothermal approaches. Assuming the reaction model of curing reaction being nth order, the rate of curing reaction can simply be obtained as follows [30]:
ln(
(6)
Slope and intercept of ln(dα/dt) vs. ln(1−α) plot give n and ln(k), respectively (Fig. 6A). Moreover, according to Eq. (4), plot of ln(k) vs. 1/T leads to a line with slope of Ea as shown in Fig. 6B. Table 1 tabulated the kinetic parameters of cure reaction for epoxy systems containing modified additives. It can be seen that Epoxy/0.1-mES nanocomposites take the higher value of activation energy when compared to Epoxy/0.1-CaCO3 system, confirming the results of model-free approach (Fig. 5). According to the literature, mechanism of epoxy resin is complex, causing the deviation of its reaction model from nth order model. In order to evaluate the appropriate model, plots of −ln(1-α) vs. time at 120 °C have been reported in Fig. 7 for modified ES and CaCO3 samples. It is visible how, at the late stage of the reaction time, it deviates sharply from linear plot, confirming complexity of the reaction model. Kamal model could coverage the deviation of nth order model by incorporation of autocatalytic parameters, as follows[41]:
Fig. 9. Plots of dα/dt versus α for 0.1-mES at 150 °C, experimental and theoretical models profiles.
relation leads to following correlation, in which slope of ln tα,i vs. 1/Ti l indicates Ea/R [34]:
g (α ) ⎤ E ln tα, i = ln ⎡ + a ⎢ ⎥ A RT a i ⎣ ⎦
dα ) = ln(k ) + n ln(1 − α ) dt
(5)
where g(α) is the result of reaction model integration and tα,i denote the time in which conversion reaches to a certain value at Ti temperature. Fig. 5 provide the plots of ln tα,i vs. 1/Ti for epoxy resin containing 0.1 213
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5. Conclusions
Table 2 Kinetic parameters of Kamal model for modified additives. Sample
0.1-mES 0.1-mCaCO3
T(°C)
120 150 120 150
Cure kinetics of epoxy/anhydride system containing 0.1 and 0.3 wt. % of pristine calcium carbonate (CaCO3), copolymer-modified CaCO3 (mCaCO3), pristine eggshell (ES), and copolymer-modified ES (mES) was studied by rheological and DSC analyses. Results from rheological tests of filled epoxy with ES have shown that the incorporation of 0.1 wt.% ES into epoxy resin caused a decrease in curing reaction rate and crosslinking density; on the other hand, increase of ES content from 0.1 to 0.3 wt.% compensated for the retardation effect. Interestingly, the modification of ES by poly(N-vinyl-2-pyrrolidone-co-maleic acid-coacrylic acid) terpolymer increased the crosslinking density and rate of reaction, thanks to the presence of functional groups attached on ES surface, that effectively participated to the curing reaction. It was also demonstrated that Calcium carbonate behaves in a different direction: although the addition of 0.1%wt. of CaCO3 was able to increase the reaction rate and crosslinking density of neat epoxy, terpolymer modification of CaCO3 deteriorates its performance, negatively affecting the carbonate performance in the curing reaction. Model-free and modelfitting approaches for evaluation of cure kinetics by using permitted us to deeply investigate the curing mechanism of epoxy system containing ES and CaCO3. It was revealed that mES took higher activation energy values if compared to mCaCO3, as a confirmation of viscosity upturn, already evidenced by rheological analysis.
Kamal model k1*103 (s−1)
k2*103 (s−1)
n
m
Ea2(kJ/mol)
7.30E3 1.75 0.18 3.32
1.38 4.35 1.39 2.34
0.95 1.28 1.06 1.16
0.26 0.4 0.21 0.23
52.8
dα = (k1 + k2 α m)(1 − α )n dt
23.5
(7)
In order to determine the meaningful kinetic parameters from Eq. (7), Kenny analytical–graphical method was utilized by employing the following steps [42]: i. k1 is equal to the value of dα/dt at t = 0 ii. first guess value of kinetic parameters including n and m are measured from the slope of following relations, respectively:
ln(
dα ) = ln(k1 + k2 α m) + n ln(1 − α ) dt
(8)
dα
⎤ ⎡ dt − k1⎥ = ln(k2) + m ln(α ) ln ⎢ n − α (1 ) ⎥ ⎢ ⎦ ⎣
(9)
References
It should be noticed that k2 can be estimated from the intercept of Eq. (9). iii. Rewritten Eq. (6) leads to following equation:
[1] M. Mecklenburg, D. Mizushima, N. Ohtake, W. Bauhofer, B. Fiedler, K. Schulte, On the manufacturing and electrical and mechanical properties of ultra-high wt.% fraction aligned MWCNT and randomly oriented CNT epoxy composites, Carbon 91 (2015) 275–290. [2] P.K. Ghosh, K. Kumar, N. Chaudhary, Influence of ultrasonic dual mixing on thermal and tensile properties of MWCNTs-epoxy composite, Compos. Part B-Eng. 77 (2015) 139–144. [3] O. Starkova, E. Mannov, K. Schulte, A. Aniskevich, Strain-dependent electrical resistance of epoxy/MWCNT composite after hydrothermal aging, Compos. Sci. Technol. 117 (2015) 107–113. [4] D. Ratna, Handbook of Thermoset Resins, ISmithers, Shawbury, Shrewsbury Shropshire, 2009. [5] H. Gu, C. Ma, J. Gu, J. Guo, X. Yan, J. Huang, Q. Zhang, Z. Guo, An overview of multifunctional epoxy nanocomposites, J. Mater. Chem. C 4 (2016) 5890–5906. [6] Q.-S. Yang, X.-Q. He, X. Liu, F.-F. Leng, Y.-W. Mai, The effective properties and local aggregation effect of CNT/SMP composites, Compos. Part B-Eng. 43 (2012) 33–38. [7] B. Koh, W. Cheng, Mechanisms of carbon nanotube aggregation and the reversion of carbon nanotube aggregates in aqueous medium, Langmuir 30 (2014) 10899–10909. [8] J.R. Choi, K.Y. Rhee, S.J. Park, Post-annealing effects of electroless Ni–B-plated MWCNTs on thermal conductivity of epoxy-based composites, J. Ind. Eng. Chem. (2015). [9] M.R. Zakaria, H. Md Akil, M.H. Abdul Kudus, A.H. Kadarman, Improving flexural and dielectric properties of MWCNT/epoxy nanocomposites by introducing advanced hybrid filler system, Compos. Struct. 132 (2015) 50–64. [10] B. Wetzel, P. Rosso, F. Haupert, K. Friedrich, Epoxy nanocomposites – fracture and toughening mechanisms, Eng. Fract. Mech. 73 (2006) 2375–2398. [11] C. Zilg, R. Mülhaupt, J. Finter, Morphology and toughness/stiffness balance of nanocomposites based upon anhydride-cured epoxy resins and layered silicates, Macromol. Chem. Phys. 200 (1999) 661–670. [12] G. Ji, H. Zhu, C. Qi, M. Zeng, Mechanism of interactions of eggshell microparticles with epoxy resins, Polym. Eng. Sci. 49 (2009) 1383–1388. [13] M.M. Rahman, A.N. Netravali, B.J. Tiimob, V.K. Rangari, Bioderived green composite from soy protein and eggshell nanopowder, ACS Sustain. Chem. Eng. 2 (2014) 2329–2337. [14] D. Cree, A. Rutter, Sustainable bio-Inspired limestone eggshell powder for potential industrialized applications, ACS Sustain. Chem. Eng. 3 (2015) 941–949. [15] M.R. Saeb, M. Ghaffari, H. Rastin, H.A. Khonakdar, F. Simon, F. Najafi, V. Goodarzi, P. Vijayan, P.D. Puglia, F.H. Asl, K. Formela, Biowaste chicken eggshell powder as a potential cure modifier for epoxy/anhydride systems: competitiveness with terpolymer-modified calcium carbonate at low loading levels, RSC Adv. 7 (2017) 2218–2230. [16] A. Mittal, M. Teotia, R. Soni, J. Mittal, Applications of egg shell and egg shell membrane as adsorbents: a review, J. Mol. Liq. 223 (2016) 376–387. [17] M. Pettinato, S. Chakraborty, H.A. Arafat, V. Calabro, Eggshell A green adsorbent for heavy metal removal in an MBR system, Ecotoxicol. Environ. Saf. 121 (2015) 57–62. [18] H.J. Park, S.W. Jeong, J.K. Yang, B.G. Kim, S.M. Lee, Removal of heavy metals using waste eggshell, J. Environ. Sci. 19 (2007) 1436–1441. [19] S.-C. Wu, H.-C. Hsu, S.-K. Hsu, Y.-C. Chang, W.-F. Ho, Effects of heat treatment on
dα
⎡ ⎤ dt ln ⎢ = n ln(1 − α ) m⎥ + k k α 1 2 ⎢ ⎥ ⎣ ⎦
(10)
Slope of the above relation is equal to new value of n that used again in previous step help to find the new values of m and k2 parameters. Second and third steps have been repeated up to reach an acceptable error. Plots of Eq. (8) up to Eq. (10) for the epoxy/0.1-mES system have been reported in Fig. 8. As an example, the experimental data of isothermal DSC along with predicted value according to nth order and Kamal models for 0.1-mES are reported in Fig. 9. Kamal model could appropriately follow the experimental data even at low conversion value; however, nth order model was not able to fit with experimental data when conversion is below 0.3. Activation energy of the system at higher conversion can be measured from the slope of the plot of lnk2 vs. 1/T. The kinetic parameters calculated according to Kamal model utilizing Kenny analytical–graphical method are given in Table 2. In all cases, the overall order of the reaction (m + n) exceeds the value one, demonstrating the complexity of the reaction mechanism [43,44]. Moreover, the m + n increased upon increase of heating temperature from 120 °C to 150 °C, as a result of increasing the kinetic energy of the system. Such a rise is more significant in the case of eggshell additive. It is also interesting to mention that higher values of m are attained at 150 °C due to enhanced autocatalytic reactions. Thus, it can be concluded that temperature appeared as a key controlling parameter in curing reaction. In agreement with other models, activation energy of epoxy resin containing 0.1-mES took higher value than those of 0.1-mCaCO3. The functional groups attached to the ES surface can contribute to crosslinking reaction of epoxy leading to a viscosity upturn (Fig. 2) that might restrict the mobility of chains, as featured by a rise in activation energy value (Fig. 5B). By contrast, incorporation of mCaCO3 into the epoxy resin could to a lesser extent enhance crosslinking and the rate of reaction with lesser viscosity compared to eggshell-incorporated systems (Fig. 2). 214
Progress in Organic Coatings 114 (2018) 208–215
M.R. Saeb et al.
[20] [21]
[22] [23] [24] [25] [26] [27]
[28]
[29]
[30] [31]
[32]
1002/pc.24415. [33] M.R. Saeb, H. Rastin, M. Nonahal, M. Ghaffari, A. Jannesari, K. Formela, Cure kinetics of epoxy/MWCNTs nanocomposites: Nonisothermal calorimetric and rheokinetic techniques, Journal of Applied Polymer Science, 2017, DOI: 10.1002/app. 4522. [34] P. Vijayan, P.D. Puglia, H. Rastin, M.R. Saeb, B. Shojaei, K. Formela, Cure kinetics of epoxy/MWCNTs nanocomposites: isothermal calorimetric and rheological analyses, Prog. Org. Coat. 108 (2017) 75–83. [35] M.R. Saeb, H. Rastin, M. Shabanian, M. Ghaffari, G. Bahlakeh, Cure kinetics of epoxy/β-cyclodextrin-functionalized Fe 3 O 4 nanocomposites: experimental analysis, mathematical modeling, and molecular dynamics simulation, Prog. Org. Coat. 110 (2017) 172–181. [36] P.J. Halley, M.E. Mackay, Chemorheology of thermosets—an overview, Polym. Eng. Sci. 36 (1996) 593–609. [37] C.D. Han, K.-W. Lem, Chemorheology of thermosetting resins. I. The chemorheology and curing kinetics of unsaturated polyester resin, J. Appl. Polym. Sci. 28 (1983) 3155–3183. [38] A. Yousefi, P.G. Lafleur, R. Gauvin, Kinetic studies of thermoset cure reactions: a review, Polym. Compos. 18 (1997) 157–168. [39] G. Lelli, A. Terenzi, J.M. Kenny, L. Torre, Modelling of the chemo–rheological behavior of thermosetting polymer nanocomposites, Polym. Compos. 30 (2009) 1–12. [40] 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. [41] R. Ren, X. Xiong, X. Ma, S. Liu, J. Wang, P. Chen, Y. Zeng, Isothermal curing kinetics and mechanism of DGEBA epoxy resin with phthalide-containing aromatic diamine, Thermochim. Acta 623 (2016) 15–21. [42] C.S. Wang, C.H. Lin, Novel phosphorus-containing epoxy resins. Part II: curing kinetics, Polymer 41 (2000) 8579–8586. [43] M. Abdalla, D. Dean, P. Robinson, E. Nyairo, Cure behavior of epoxy/MWCNT nanocomposites: the effect of nanotube surface modification, Polymer 49 (2008) 3310–3317. [44] F. Ferdosian, M. Ebrahimi, A. Jannesari, Curing kinetics of solid epoxy/DDM/nanoclay: isoconversional models versus fitting model, Thermochim. Acta 568 (2013) 67–73.
the synthesis of hydroxyapatite from eggshell powders, Ceram. Int. 41 (2015) 10718–10724. T. Witoon, Characterization of calcium oxide derived from waste eggshell and its application as CO2 sorbent, Ceram. Int. 37 (2011) 3291–3298. M. Mohammadi, P. Lahijani, A.R. Mohamed, Refractory dopant-incorporated CaO from waste eggshell as sustainable sorbent for CO2 capture: experimental and kinetic studies, Chem. Eng. J. 243 (2014) 455–464. S.H. Katz, W.W. Weaver, Encyclopedia of Food and Culture, Scribner, New York, 2003. P. Toro, R. Quijada, M. Yazdani-Pedram, J.L. Arias, Eggshell, a new bio-filler for polypropylene composites, Mater. Lett. 61 (2007) 4347–4350. T. Ghabeer, R. Dweiri, S. Al-Khateeb, Thermal and mechanical characterization of polypropylene/eggshell biocomposites, J. Reinf. Plast. Compos. 32 (2013) 402–409. R. Kumar, J. Dhaliwal, G. Kapur, Mechanical properties of modified biofillerpolypropylene composites, Polym. Compos. 35 (2014) 708–714. Z. Lin, Z. Zhang, K. Mai, Preparation and properties of eggshell/β-polypropylene bio-composites, J. Appl. Polym. Sci. 125 (2012) 61–66. P. Intharapat, A. Kongnoo, K. Kateungngan, The potential of chicken eggshell waste as a bio-filler filled epoxidized natural rubber (ENR) composite and its properties, J. Polym. Environ. 21 (2013) 245–258. M.R. Saeb, H. Ramezani-Dakhel, H.A. Khonakdar, G. Heinrich, U. Wagenknecht, A comparative study on curing characteristics and thermomechanical properties of elastomeric nanocomposites: the effects of eggshell and calcium carbonate nanofillers, J. Appl. Polym. Sci. 127 (2013) 4241–4250. D. Galpaya, M. Wang, G. George, N. Motta, E. Waclawik, C. Yan, Preparation of graphene oxide/epoxy nanocomposites with significantly improved mechanical properties, J. Appl. Phys. 116 (2014) 053518. M. Ghaemy, M. Barghamadi, H. Behmadi, Cure kinetics of epoxy resin and aromatic diamines, J. Appl. Polym. Sci. 94 (2004) 1049–1056. M.R. Saeb, E. Bakhshandeh, H.A. Khonakdar, E. Mäder, C. Scheffler, G. Heinrich, Cure kinetics of epoxy nanocomposites affected by MWCNTs functionalization: a review, Sci. World J. 2013 (2013) 14. M. Nonahal, M.R. Saeb, S. Hassan Jafari, H. Rastin, H.A. Khonakdar, F. Najafi, F. Simon, Design, preparation, and characterization of fast cure epoxy/amine-functionalized graphene oxide nanocomposites, Polymer Composites, 2017, DOI: 10.
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