Toughening of Epoxy Systems by Brominated Epoxy.
Epoxy resins have been used on a wide range of applications among them as protective coatings, structural adhesives, and structural composites (based on glass, Aramid, and carbon fibers and fabrics) serving the electronics, automotive, aircraft, aerospace and marine industries. The most common epoxy is made of diglycidyl ether of bisphenol A (DGEBA) [1,2] prepolymer. Epoxy resins have wide range of advanced properties such as good mechanical properties, thermal stability, chemical resistance, dielectric and insulation properties, low shrinkage during cure, dimensional stability, and fatigue resistance [1, 3].
The epoxy network is formed during the curing reaction with wide variety of cross-linking agents such as aliphatic and aromatic amines and acids. Triethylenetetramine (TETA) is one of the most common amines for curing epoxy resins in adhesive systems for general purposes. It is widely used with DGEBA epoxy resins [1, 4], Polyether diamine (PEA) is one of the conventional hardeners used today for the preparation of tough epoxy resins. Due to the repeating ether unit in the network flexibility is introduced with an increased toughness [5, 6], PEA-cured epoxies are commonly employed for controlled cure, homogeneity, and fast [T.sub.g] and strength development , One of the major curing agents for high temperature structural adhesives and fiber composites is the 3,3'-diamino diphenyl sulfone (DDS) [8-10]. It has a higher heat resistance compared with other aromatic amines, making it widely employed in aerospace industry .
Generally high cross-linked epoxies possess superior characteristics accompanied with poor resistance to crack propagation. Toughening agents have been used to circumvent this shortcoming [12-16], Incorporation of toughening agents into the epoxy resin enables to increase resistance to peel, impact, and fatigue. A very effective way to toughen epoxy is by addition of reactive rubbers such as carboxyl-terminated butadiene nitrile rubber [17-19] in levels of about 5-10% (wt%) and forming 1 to 5 pm diameter rubber particles [13, 20]. However, the liquid rubbers depress the tensile and flexural strengths and the glass transition temperature ([T.sub.g]) of the modified epoxies [19, 21, 22], Thus, efforts have been made to investigate methods to increase toughness while preserving strength and [T.sub.g].
Brominated epoxy (BE) resins consist of tetrabromobisphenolA as the backbone of the glycidyl ether base resins. The high electronegativity of the bromine atom imposes dipole-dipole attraction in the epoxy bulk , This may result in reducing the free volume available for molecular motion and increase the rigidity of the molecule  resulting in enhanced thermal and mechanical properties of the 3D-cured network. Furthermore, it has been reported by Nae et al.  that BE resins could function as chain extenders to reduce brittleness of thermosetting systems.
BE resins are currently used as reactive additives for epoxy, polycarbonate and phenolic resins [26, 27]. The major use of these resins is for laminated printed circuit boards [26, 28, 29] containing up to 20% bromine [26, 27, 29]. Most of the studies related to BE resins deal with the fire-retardancy property [29-31] and waste decomposition [28, 29]. Only a few studies have been carried out using brominated epoxies as structural adhesives and matrices for fiber composites. Consequently, the aim of this investigation is to elucidate the thermo-mechanical advantages of thermoset systems based on blends of brominated epoxies and conventional epoxies compared with conventional epoxies. Two epoxy types were used: DGEBA and diglycidyl ether of tertabromobisphenol A (BE). Curing was carried out using: TETA, PEA4 (JEFFAMINE T-403), and DDS. The structure-property relationship of the epoxy systems were studied comprising: rheology, thermos-mechanical and, mechanical properties, adhesion properties and fracture morphology.
Blends of two epoxy resins were used for formulating adhesives: (1) Diglycidyl ether of bisphenol-A (DGEBA, DER 331, Dows Chemicals), with an epoxide equivalent range of 182-192 g/Eq. 2 A BE resin of diglycidyl ether of tetrabromobisphenol-A (BE, F-2200, ICL, IL) containg 48% of bromine, with an epoxide equivalent weight of 348 g /Eq. a solid resin . The epoxy blends were cured with three types of hardeners: (1) TETA (Sigma- Aldrich, St Louis, MO) aliphatic curing agent. (2) PEA4 (JEFFAMINE T-403, Huntsman, USA) an etheric curing agent. (3) DDS (Sigma- Aldrich St Louis, MO) an aromatic curing agent. Compositions and characteristics of the materials used are shown in Table 1. For aluminum bonded joints a glycidoxypropyltrimethoxysilane--epoxy silane (Silqeust A-187 Silane, Momentive Company, USA), was used as a primer to chemically modify the aluminum adherends.
Preparation of DGEBA/BE Blends
The liquid DGEBA resin was used as a solvent for the solid BE resin. When cured with TETA, DGEBA/BE mixtures were prepared in the weight ratios: 80/20, 70/30, 60/40, 50/50, and 40/ 60.When cured with PEA4 the epoxy weight ratios were: 80/20, 40/60, and 60/40, and when cured by DDS the mixing epoxy weight ratios were 50/50, 30/70, and 10/90. For homogenization, the blends were mechanically mixed at 60 rpm for 20 min in a pre-heated oil bath at 125[degrees]C, until absolute dissolution was achieved. Then, the blends were mixed with the three curing agents by the following procedures: (1) after thorough mixing, the mixtures were cooled to room temperature and TETA was added in a stoichiometric amount, followed by degassing. The curing reaction proceeded overnight at room temperature and additional 3 h of post-cure at 80[degrees]C. (2) After mixing and cooling the blends to room temperature PEA4 was added in a stoichiometric amount, followed by degassing. The blends were cured at 80[degrees]C for 2 h, followed by 3 h at 125[degrees]C. (3) Stoichiometric amounts of DDS were added to the mixture at about 125[degrees]C and mixed for 30 minutes. The curing reaction occurred at 170[degrees]C for 2 h and post cured at 200[degrees]C for 1 h. DGEBA epoxy specimens were prepared with each hardener as a reference.
Parallel Plate Viscometer. Parallel plate viscometer (Discovery- HR- 1 hybrid rheometer) was used to determine the viscosities of DGEBA/BE blends (without the hardeners) at different ratios in a liquid state, by using a 25-mm diameter parallel plate and a 2-mm gap mode. Dynamic thermal measurements were taken in 25-90[degrees]C temperature range with a heating rate of 2[degrees]C/ min, and a constant frequency of 1 Hz.
Dynamic Mechanical Analysis. To analyze the effect of BE on the thermomechanical properties of the DGEBA, the tangent delta (tan a) and [T.sub.g], measurements were carried out by dynamic mechanical analysis (DMA) analysis (DMA Q800, TA Instruments, USA). DMA specimens were cast in a silicone rubber molds with the dimension of 30 X 2 X 1 [mm.sup.3]. Before testing, all specimens' surfaces and edges were polished to remove surface defects and to guarantee specimens with flat and parallel sides. Each specimen was, loaded in a tension mode with strain control at a frequency of 1 Hz, and a temperature ramp of 3[degrees]C/min. The test temperature ranged from 25 to 150[degrees]C for blends cured by TETA and PEA4, and 25 to 250[degrees]C for blends cured by DDS.
Three-Point Flexural Test. The flexural tests were carried out by means of mechanical tester (Instron, model 4481). The samples were cast to shape using a silicone cavity mold of approximately 38 X 12.7 X 2 [mm.sup.3]. The test yielded values of flexural stress, flexural modulus, and flexural strain of DGABE/BE blends cured with TETA. All measurements were conducted in three-point bending using a crosshead speed of 1 mm/min, with a span equal to 32 mm. The average of at least three specimens was determined for each blend. The dimension of the specimen, span, and speed of test was according to AS[T.SUB.M] D 790-03. Measurements were performed at 23[degrees]C, and the results average value and standard deviation were determined.
Tensile Test. Tensile tests were carried out by means of a mechanical Tester (LLOYD instruments, model LR 10K). Test specimens were cast into silicone molds with a dog-bone geometry. All measurements were conducted using a crosshead speed of 1 mm/min, at 23[degrees]C. The average of at least three specimens was determined for each blend. The specimens dimension, span, and speed of the test were according to AS[T.SUB.M] D 638-02a (for rigid plastics). The tests were performed to characterize the tensile strength, elongation and Young's modulus of DGEBA/BE blends cured with PEA 4 and DDS hardeners.
Hardness. Hardness levels were determined using a Shore D Durometer (Mitutoyo Hardness Dial Durometer, Japan), according to AS[T.SUB.M] D2240 (for "harder" plastics). Test specimens were of 4-mm thickness and the test was carried out on hard flat surface. Average values of hardness were calculated from five measurements for each specimen. The average of at least three specimens was taken for each blend.
Lap Shear Adhesion Strength. Single lap shear test was carried out for the DGABE/BE blends, using a mechanical tester (Instron, model 4481). Chromic anodized aluminum plates of 25 X 100 X 1.6 [mm.sup.3], were used as adherends. The average of at least three specimens was taken for each blend. Both adherends were surface treated using l%v/v glycidoxypropyltrimethoxysilane dissolved in isopropanol and water solution with a ratio of (99:1% v/v). The solution was at pH of 4. Then, the different adhesive blends were applied on the respective two adherends with an area of 25 X 13 [mm.sup.2]. The coated substrates were pressed together forming an adhesive thickness of approximately 0.1 mm and then cured according to the curing conditions for each hardener as mentioned above. The specimens dimension, span, and speed of testing were according to AS[T.SUB.M] D 1002 for metal substrates.
Scanning Electron Microscopy Image. High-resolution scanning electron microscopy (SEM) (Zeiss Gemini Ultra plus, Oberkochen, Germany) analysis was conducted to investigate the morphology of the DGEBA/BE blends specimens. Samples were coated with gold in an Argon environment, to prevent electron charging of the specimens. The SEM was operated by accelerated voltage of 1 kV.
RESULTS AND DISCUSSION
Viscosity data of uncured DGEBA/BE blends as a function of temperature is presented in Fig. 1. As can be seen as the BE content increased, the viscosity of the resin increased as well. This is due to the brominated element with the higher molecular weight added to the lower molecular weight DGEBA.
Dynamic Mechanical Thermal Analysis
The Loss tangent (Tan delta), obtained from the DMA analysis, as a function of temperature for the three hardener-cured systems are presented in Fig. 2. The maximum of the Tan Delta values corresponding to the [T.sub.g] are given in Table 2. In TETAcured systems, the addition of the BE lead to an increased [T.sub.g] for 20 and 60 wt% BE containing blends and a slight decrease in [T.sub.g] of the 40 wt% system. For both PEA4-cured and DDScured systems, results from DMA showed an increase in [T.sub.g]. The maximum increase of [T.sub.g] for DGEBA based systems are observable for 60 wt% BE in PEA4-cured epoxy from 91[degrees]C up to 108[degrees]C and from 187 to 216[degrees]C for 30 wt% BE in DDS-cured epoxy. The increase in [T.sub.g] can be attributed to an antiplastization effect of the BE resin. Anti-plasticizing effect is related to stiff and polar additives which limit the molecular motion by reducing the free volume for crosslinked epoxies [24, 32], In the current study, one can consider the BE resin as a reactive anti-plasticizer due to the bromine that is introduced to the epoxy backbone and network. The four bromine atoms on the bisphenyl unit inhibit the mobility of the system that results in higher stiffness compared with DGEBA epoxy. In addition, the high electronegativity of the bromine atom may form dipole-dipole interactions with the epoxy causing a reduction of free volume. Hence, higher [T.sub.g] values were observed . Furthermore, the heights of the tan delta damping curves of the epoxy TETA-cured and PEA4-cured, (Fig. 2a and b) are increased upon addition of BE. This suggests that the BE resin contributes to the energy dissipation process of the crosslinked networks. Thus, it can be concluded that BE functions as a typical toughener. An opposite behavior was obtained for DDScured epoxy systems (Fig. 2c). The magnitude of the tan delta damping curve was slightly reduced upon the addition of BE which indicates a restricted segmental motions in the case of BE blends cured by DDS. Hence, it was concluded that the composition of curing agent constitutes an effective means to control adhesive properties.
Flexural strength and elongation results of TETA-cured systems are presented in Table 3. The incorporation of BE resin in the DGEBA resin has a substantial effect on the flexural properties. The cured BE containing blends have shown an improvement in flexural strength, with a maximal 24% increase for 50 wt% BE system compared with the control. Furthermore, flexural elongation of cured BE blends exhibited similar values compared with the control. These results indicate that adding the BE resin to systems cured by TETA substantially toughen the resins, this is in line with the higher area under the stressstrain curves of BE containing systems showed in Fig. 3a. Moreover, the flexural modulus values of systems cured by TETA show a remarkably higher flexural modulus values, with up to 4.76 GPa at 50 wt% BE as compared with 3.38 GPa for the control system. The flexural strength and flexural modulus of the BE blends cured by TETA were increased at no expense on [T.sub.g], which is an outstanding finding in this study.
Tensile strength, strain, and Young's modulus of DGEBA/ BE blends cured by PEA4 and DDS are summarized in Tables 4 and 5, respectively. Stress-strain curves from the average values of strength and elongation are described in Fig. 3. PEA4 is a polyether amine containing oxypropylene units contributing to flexibility and ductility of the crosslinked network. Distinctively, DDS is composed of benzene and sulfone groups which account for rigidity and brittleness in the network. The different hardener's composition explains the higher elongation level and lower tensile strength of PEA4-cured systems as opposed to DDScured systems. In both hardener systems, the tensile strengths of the BE blends are higher than the reference DGEBA. These results are in agreement with the rigidity of the cured BE systems and it confirms the anti-plastization effect. At 40 wt% BE content, the PEA4-cured system displayed a remarkably increased elongation at break (Fig. 3b), from 8.3 to 13.5%. In DDS-cured systems (Fig. 3c), significant improvement in elongation was obtained with 50 wt% BE, from 3.8 to 5.9%. Simultaneously, in both systems, a reduction of Young's modulus is evident. The increase in elongation and reduction in modulus implies on an increase in toughness , The increased toughness conforms with the increase in the area under the stressstrain curves of BE containing systems compared with DGEBA.
The effect of the curing conditions for BE containing blends and DGEBA resin was evaluated using Shore D hardness. Shore D values of all cured systems (Tables (3-5)) are relatively similar in and above the range mentioned in the literature for rigid epoxies [34, 35],
The results of shear loadings of the bonded metal-to-metal specimens of DGEBA and BE containing blends, cured by PEA4 and DDS, are summarized in Fig. 4. Figure 4a shows the lap shear strength of PEA4-cured systems. The shear strength of all cured systems slightly decreased with the addition of BE exhibiting a mixed mode failure. Accordingly, at 20 wt% BE system the shear strength decreased by 5%, but within the range of standard deviation, in comparison to DGEBA. Above 20 wt% BE content the shear strength decreased by 10%. As presented in Fig. 1, the BE blends are highly viscous compared with the control, in particular at the low curing temperature used in systems with PEA4 curing agent. The high viscosity gives rise to difficulties in application of the adhesives and may limit the wettability which in tum causes voids formation when spreading the viscous blend over the adherend surface. Lakshmi et al.  investigated the shear strength of a DGEBA system compared with, BE system. They reported that DGEBA resin with lower molecular weight than BE exhibited higher shear strength. Although BE blends gave reduced tensile shear strength with the PEA4-cured systems, no negative effect on the DDS-cured BE blends was observed (Fig. 4b), possibly due to the relatively high-temperature curing conditions of these systems compared with PEA4-cured systems which reduce the viscosity and enhance the wetting of the adherends. Slight increase in shear strength of 50 and 70 wt% BE blends commensurate to the increase in rigidity of these systems. Furthermore, the higher rigidity is further expressed in significant higher [T.sub.g] values and in reduction of tan delta.
The effect of BE on the neat DGEBA fracture morphology cured by TETA was studied using high-resolution SEM microscopy. Figures 5a and b exhibits a typical fracture surface morphology of a neat epoxy system, characterized by smooth surface and longitudinal fracture lines. A remarkable difference was obtained in surface morphology for BE blends, cured by TETA. As can be seen in Fig. 5c and d, the 40 wt% BE systems show multiple nodules surrounded by many bowing fracture lines, indicating that the BE resin promoted ductile deformation of the matrix. With 60 wt% BE, the nodular morphology was formed as well (Fig. 5e). A magnified image of the 60 wt% system, presented in Fig. 5f revealed that the observed cracks tend to bow a few micrometers from the center of the nodule. This unique morphology was also reported in earlier studies as a toughening mechanism of crack bowing during crack propagation [36, 37]. Nodules were defined in earlier studies as inhomogeneous network formation in bulk epoxies , Lange  has investigated the interaction of a crack front with inhomogeneous brittle composite. He suggested that crack length increases when a crack front interacts with inhomogeneities; the crack length increases and both the fracture energy and the strength of the brittle material might be increased. Lange's hypothesis could be referred to the above mentioned results for the increased flexural strength of TETA-cured BE blends (Table 3). In addition, Racich et al.  investigated the nodulation in epoxy resins. They reported that nodules are characterized by higher crosslinking density and higher modulus compared with bulk epoxy [38, 40-42]. Thus, it can be assumed that a high content of the stiff BE molecules caused the formation of nodular zones.
Figure 6a-f depicts typical SEM micrographs of fractured surfaces of DGEBA and BE blends cured by PEA 4. Figure 6a contains representative images of neat DGEBA. A number of fracture line patterns were detected in Fig. 6a and rather smooth and flat fractured surface was found in Fig. 6b which is the magnified image of the marked square in Fig. 6a. With 40 wt% BE, more and rougher fracture lines were observed as can be seen in Fig. 6c. In the high magnification (Fig. 6d), the smooth patterns were replaced by many fine ridges due to the effect of the BE resin. This implies that the BE resin promotes ductile deformation of the matrix, corresponding to the enhancement of tensile strength and elongation as shown in Fig. 3b. Fig. 6e shows the fracture surface of a sample containing 60 wt% BE resin, the observed morphology indicates a large number of short and rougher fracture lines and flat surface compared with the 40 wt% BE sample. This implies that 40 wt% BE containing blend is more efficient in promoting ductile fracture than 60 wt% BE blend. This conclusion is in agreement with the reduced elongation of the 60 wt% sample as previously shown in Fig. 3b and Table 4.
Figure 7a-f presents SEM micrographs of the fractured surfaces of DGEBA and BE blends, cured with DDS. The BE component in the blend comprises 50 wt% BE (Fig. 7c) and 70 wt% BE (Fig. 7e). The fractured surfaces of all blends, including the control, presented an abundance of nodular structures (Fig. 7b, d, and f), representative to epoxy cured with DDS , A magnified image of the 50 wt% BE specimen (Fig. 7d) exhibited rougher fracture surface area compared with 70 wt% BE specimen. The increase in elongation to break that presented in Fig. 3b can be attributed to the rough fracture surface of 50 wt% BE blend.
DGEBA-BE blends, cured with aliphatic curing agent (TETA), etheramine curing agent (PEA4), and aromatic curing agent (DDS) were investigated. The effect of BE containing resins cured with TETA showed a moderate increase in [T.sub.g] of about 9[degrees]C at 60 wt% BE. In 20-70 wt% BE containing blends, [T.sub.g]'s of BE-modified epoxy systems significantly increased from 91[degrees]C to a maximum of 108[degrees]C for PEA4-cured epoxy and from 187[degrees]C to a maximum of 216[degrees]C for DDS-cured epoxy, with no loss of strength and elongation. [T.sub.g] improvement at BE containing resins was attributed to a limited molecular motion and reduction in free volume of the cross-linked network due to the presence of four bromine atoms on the aromatic rings. Moreover, TETAcured systems showed that flexural strength and modulus of BE blends were enhanced compared with DGEBA while maintaining flexural elongation. SEM of TETA-cured systems demonstrated that the addition of BE resin completely changed the fracture morphology from a typical smooth DGEBA surface to a rough surface exhibiting multiple nodules. The tortuous crack propagation contributed to the toughening mechanism manifested in increased flexural strength of TETA-cured BE blends. The 40 wt% and 50 wt% BE blends of PEA4-cured and DDS-cured systems, respectively, showed superior strength, elongation and improved toughness. SEM characterization of PEA4-cured systems showed that 40 wt% BE containing resin have a much rougher fracture surface than DGEBA, indicating ductile fracture. The shear strength of all PEA4-cured systems decreased moderately with the addition of BE exhibiting a mixed mode failure. As opposed to PEA4 cured systems, DDScured blends did not exhibited any negative effect on shear strength with the addition of BE.
The study of the BE and DGEBA blends demonstrated the potential of using these material systems as toughened and enhanced thermally stable structural adhesive and composites.
[1.] E. M. Petrie, Epoxy Adhesive Formulations, Vol. 30, McGraw Hill Professional, USA, 91 (2005).
[2.] J. P. Pascault, R. J. J. Williams, Epoxy Polymers: New Materials and Innovations, John Wiley & Sons, Weinheim, 222 (2009).
[3.] C. May, Epoxy Resins: Chemistry and Technology, 2nd ed., CRC Press, New York (1987).
[4.] G. Daun, L. Wittenbecher, M. Henningsen, D. Flick, J. P. Geisler, J. Schillgalies, E. Jacobi, U.S. Patent, 2730744 (2009).
[5.] C. Sinturel R. Thomas, Micro and Nano Structure Epoxy and Rubber Blends, John Wiley & Sons, Weinheim, 74 (2014).
[6.] J. A. Kent, Kent and Riegel's Handbook of Industrial Chemistry and Biotechnology, Springer Science & Business Media, New York (2007).
[7.] C.R. Amaral, R.J. Sanchez Rodriguez, F. Gonzalez Garcia, L.P.B. Junior, and E.A. Carvalho, Polym. Eng. Sci., 54, 2132 (2014).
[8.] H. Dodiuk, S.H. Goodman, Handbook of thermoset plastics, 3rd ed., William Andrew, United States of America, 205 (2013).
[9.] J. Chenge, J. Li, and J.Y. Zhang, Express Polym. Lett., 3, 8 (2009).
[10.] L.A. Pilato, M.J. Michno, Advanced Composite Materials, Springer Science & Business Media, Germany, 14-15 (2013).
[11.] C. Gouri, R. Ramaswamy, and K.N. Ninan, Int. J. Adhes. Adhes., 20, 305 (2000).
[12.] A. Klingler, and B. Wetzel, Polym. Eng. Sci., 57, 579 (2017).
[13.] J.H. Hodgkin, G.P. Simon, and R.J. Varley, Polym. Adv. Tech., 9, 3 (1998).
[14.] S. Fellahi, N. Chikhi, and M. Bakar, J. Appl. Polym. Sci., 82, 861 (2001).
[15.] E.M. Woo, L.D. Bravenec, and J.C. Seferis, Polym. Eng. Sci., 34, 1664 (1994).
[16.] J. Zhang, C. Liu, J. Cheng, M. Miao, and D. Zhang, Polym. Eng. Sci., 0, 0 (2017).
[17.] G. Pritchard, Plastics Additives: An A-Z reference, Springer Science & Business Media, Dordrecht, 408 (2012).
[18.] G. Tripathi, and D. Srivastava, J. Mater. Sci. and Engin, 443, 262 (2007).
[19.] H. Dodiuk, S.H. Goodman, Handbook of thermoset plastics, 3rd ed., William Andrew, USA, 197 (2013).
[20.] T.H. Hsieha, A.J. Kinlocha, K. Masaniaa, A.C. Taylora, and S. Sprenger, Polymer, 51, 26 (2010).
[21.] S.M. Lee, Reference Book for Composites Technology, Vol. 1, CRC Press, USA, 86 (1989).
[22.] H. Zhang, L.A. Berglund, and M. Ericson, Polym. Eng. Sci., 31, 1057 (1991).
[23.] M. Opresnik, A. Sebenik, M. Zigon, and U. Osredkar, Thermochim. Acta, 178, 127 (1991).
[24.] N. Yokoyama, Y. Nonaka, T. Kurata, S. Saka, S. Takahashi, and T. Kasemura, J. Appl. Polym. Sci., 104, 1702 (2007).
[25.] H.N. Nae, J. Appl. Polym. Sci., 33, 1173 (1987).
[26.] A. Covacia, S. Voorspoelsb, M.A. Abdallahc, T. Geensa, S. Harradc, and R.J. Law, J. Chromatogr. A, 1216, 3 (2009).
[27.] M. Alaee, P. Ariasb, A. Sjodinc, and A Bergmand. Environ. Int, 29, 683 (2003).
[28.] H.R. Verma, K.K. Singh, and T.R. Mankhand, J. Cleaner Prod., 139, 586 (2016).
[29.] M. Xing, and F.-S. Zhang, Chem. Eng. J., 219, 131 (2013).
[30.] A.I. Balabanovich, a. Hornung, D. Merz, and H. Seifert, Polym. Degrad. Stab., 85, 713 (2004).
[31.] M.P. Luda, A.I. Balabanovich, M. Zanetti, and D. Guaratto, Polym. Degrad. Stab. 92, 1088 (2007).
[32.] E. Vassileva, and K. Friedrich, J. Appl. Polym. Sci., 89, 3774 (2003).
[33.] M.S. Lakshmi, B. Narmadha, and B.S.R. Reddy, Polym. Degrad. Stab., 93, 201 (2008).
[34.] L. L. Rosine, Advances in Electronic Circuit Packaging, Springer, Colorado, 2 (2013).
[35.] W.F. Ernest, Epoxy resins, Curing agents, Compounds, and Modifiers, 2nd ed., Noyes Publications, Devon (1987).
[36.] F.F. Lange, Philos. Mag, 22, 0983 (1970).
[37.] M. Shneider, H. Dodiuk, S. Kenig, and R. Tenne, J. Adhes. Sci. Teehnol., 24, 1083 (2010).
[38.] C. Wehlack, W. Possart, J.K. Kruger, and U. Muller, Soft Mater., 5, 87 (2007).
[39.] J.L. Racich, and J.A. Koutsky, J. Appl. Polym. Sci., 20, 2111 (1976).
[40.] T.G. Rochow, Anal. Chem., 33, 1810 (1961).
[41.] R.M. Kessenikh, L.A. Korshunova, and A.V. Petrov, Polym. Sci. USSR, 14, 466 (1972).
[42.] Q. Le a, H. Kuan, J. Dai, I. Zaman, L. Luong, and J. Ma, Polymer, 51, 4867 (2010).
Lizzie Sheinbaum, (1) Maria Sheinbaum ((iD),1) Orli Weizman, (1) Hanna Dodiuk, (1) Shay Dichter, (2) Samuel Kenig (1)
(1) Department of Polymers & Plastics Engineering, Shenkar College of engineering design and art, Ramat-Gan 52526, Israel
(2) Department of Plastic Application Lab, Bromine Compounds Ltd., Israel Chemicals Ltd, Beer Sheva 84894, Israel
Correspondence to: M. Sheinbaum; e-mail: email@example.com Contract grant sponsor: Israel Chemicals Ltd. (ICL).
Published online in Wiley Online Library (wileyonlinelibrary.com).
Caption: FIG. 1. Effect of temperature on the viscosities of uncured DGEBA and BE blends at different ratios.
Caption: FIG. 2. DMA curves of the two epoxy systems cured (a) by TETA (b) by PEA4, and (c) by DDS.
Caption: FIG. 3. Stress-strain curves of the two epoxy systems, from flexural test, cured (a) by TETA and from tensile tests, cured by (b) PEA4, and (c) DDS.
Caption: FIG. 4. Lap shear adhesion strength of the two epoxy systems as a function of BE content, cured by (a) PEA4 and (b) DDS.
Caption: FIG. 5. SEM micrograph of fractured surface of DGEBA/BE blends: (a) DGEBA cured by TETA, (b) the magnified image of the small square in a, (c) 40 wt% BE blend TETA-cured system, (d) the magnified image of the small square in (c), (e) 60 wt% BE blend TETA-cured system, (f) the magnified image of the small square in (e).
Caption: FIG. 6. SEM micrograph of fractured surface of DGEBA/BE blends: (a) DGEBA cured by PEA4, (b) the magnified image of the small square in a, (c) 40 wt% BE blend PEA4 -cured system, (d) the magnified image of the small square in (c), (e) 60 wt% BE blend PEA4-cured system, (f) the magnified image of the small square in (e).
Caption: FIG. 7. SEM micrograph of fractured surface of DGEBA/BE blends: (a) DGEBA cured by DDS, (b) the magnified image of the small square in (a), (c) 50 wt% BE blend DDS-cured system, (d) the magnified image of the small square in (c), (e) 60 wt% BE blend DDS-cured system, (f) the magnified image of the small square in (e).
TABLE 1. Materials used in this study; characteristics and structures. Monomer Trade name Chemical formulation DGEBA DER 331 [formula not reproducible] BE F2200 [formula not reproducible] Triethylenetetramine TETA [formula not reproducible] Polyetheramine JEFFAMINE T-403 [formula not reproducible] (PEA4) Diaminodiphenyl DDS [formula not reproducible] sulfone Monomer Mw F DGEBA 374 2 BE 696 2 Triethylenetetramine 146 6 Polyetheramine 226 6 Diaminodiphenyl 248 4 sulfone F, functionality; Mw, molar weight (g/mol). TABLE 2. [T.sub.g] of DGEBA and BE blends cured by TETA, PEA4, and DDS. Materials, cured [T.sub.g] Materials, cured [T.sub.g] by TETA ([degrees]C) by PEA4 ([degrees]C) DGEBA 119 DGEBA 91 BE blend, 20 wt% 123 BE blend, 20 wt% 95 BE blend, 40 wt% 116 BE blend, 40 wt% 103 BE blend, 60 wt% 126 BE blend, 60 wt% 108 Materials, cured Materials, cured [T.sub.g] by TETA by DDS ([degrees]C) DGEBA DGEBA 187 BE blend, 20 wt% BE blend, 30 wt% 216 BE blend, 40 wt% BE blend, 50 wt% 212 BE blend, 60 wt% BE blend, 70 wt% 213 TABLE 3. Mechanical properties of DGEBA and BE blends cured by TETA. Materials, cured Flexural Modulus, Flexural strength, by TETA GPa MPa DGEBA 3.38 [+ or -] 0.13 137.9 [+ or -] 6.3 BE blend, 30 wt% 4.19 [+ or -] 0.11 164.2 [+ or -] 3.5 BE blend, 40 wt% 4.19 [+ or -] 0.17 159.7 [+ or -] 9.1 BE blend, 50 wt% 4.76 [+ or -] 2.13 169.8 [+ or -] 6.2 BE blend, 60 wt% 4.60 [+ or -] 0.30 171.2 + 8.3 Materials, cured Flexural Elongation, % Shore D Hardness by TETA DGEBA 5.0 [+ or -] 0.1 88.0 [+ or -] 1.9 BE blend, 30 wt% 5.2 [+ or -] 0.2 89.6 [+ or -] 0.9 BE blend, 40 wt% 5.4 [+ or -] 0.4 86.0 [+ or -] 0.7 BE blend, 50 wt% 4.8 [+ or -] 0.4 88.4 [+ or -] 0.6 BE blend, 60 wt% 5.2 [+ or -] 0.2 89.7 [+ or -] 0.8 TABLE 4. Mechanical properties of DGEBA and BE blends cured by PEA4. Materials, cured Young's Modulus, Tensile strength, by PEA4 GPa MPa DGEBA 1.8 [+ or -] 0.4 60.4 [+ or -] 0.8 BE blend, 20 wt% 1.8 [+ or -] 0.1 61.6 [+ or -] 2.3 BE blend, 40 wt% 1.5 [+ or -] 0.2 65.6 [+ or -] 3.0 BE blend, 60 wt% 1.3 [+ or -] 0.4 65.1 [+ or -] 2.9 Materials, cured Tensile Elongation, % Shore D Hardness by PEA4 DGEBA 8.3 [+ or -] 1.5 89.1 [+ or -] 2.9 BE blend, 20 wt% 5.4 [+ or -] 0.4 85.5 [+ or -] 1.1 BE blend, 40 wt% 13.5 [+ or -] 3.8 84.4 [+ or -] 3.6 BE blend, 60 wt% 6.7 [+ or -] 2.2 87.2 [+ or -] 1.9 TABLE 5. Mechanical properties of DGEBA and BE blends cured by DDS. Materials, cured Young's Modulus, GPa Tensile strength, MPa by DDS DGEBA 3.2 [+ or -] 0.8 82.9 [+ or -] 6.1 BE blend, 50 wt% 1.8 [+ or -] 0.1 91.3 [+ or -] 4.9 BE blend, 70 wt% 1.5 [+ or -] 0.2 88.7 [+ or -] 9.2 Materials, cured Tensile Elongation, % Shore D Hardness by DDS DGEBA 3.8 [+ or -] 0.5 90.2 [+ or -] 2.0 BE blend, 50 wt% 5.9 [+ or -] 0.9 90.1 [+ or -] 5.1 BE blend, 70 wt% 3.7 [+ or -] 0.9 92.1 [+ or -] 3.4
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|Author:||Sheinbaum, Lizzie; Sheinbaum, Maria; Weizman, Orli; Dodiuk, Hanna; Dichter, Shay; Kenig, Samuel|
|Publication:||Polymer Engineering and Science|
|Date:||Jan 1, 2019|
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