Epoxy Resin Blend

Article pubs.acs.org/IECR

New Materials from Maleated Castor Oil/Epoxy Resin Blend Reinforced with Fly Ash Dipa Ray,*,† Subhankar Ghorui,‡ N. R. Bandyopadhyay,‡ Suparna Sengupta,§ and Tanusree Kar⊥ †

Department of Polymer Science & Technology, University of Calcutta, 92 A.P.C Road, Kolkata 700009, India School of Materials Science and Engineering, Bengal Engineering and Science University, Shibpur, Howrah 711103, India § Calcutta Institute of Engineering and Management, Tollygunge, Kolkata 700040, India ⊥ Department of Materials Science, Indian Association for the Cultivation of Science, 2A and B Raja S.C Mallick Road, Kolkata 700032, India ‡

ABSTRACT: Maleated castor oil (MACO) was prepared and blended with epoxy resin in 1:1 weight ratio. The prepared MACO-epoxy blend was characterized for its viscosity. Fly ash (10 wt %) was incorporated both in the 1:1 blend matrix as well as in the 100% epoxy resin matrix. Then curing was done by condensation polymerization reaction using 10 wt % of diethylene triamine (with respect to the total resin) in suitable reaction conditions. An interpenetrating cross-linked network was formed within the matrix between MACO and the epoxy molecules. The resultant MACO/epoxy blend matrix reinforced with fly ash showed significant enhancement in impact strength and damping properties compared to that of epoxy. The morphologies of the fabricated biocomposites were studied by scanning electron microscope.

1. INTRODUCTION Epoxy resins are used extensively as adhesives and as a matrix for fiber reinforced composite materials because of their good thermal, mechanical, and adhesive properties, excellent solvent resistance, and high dimensional stability. Current demands for high performance materials have increased the usefulness of epoxy resins as structural adhesives and as the matrix resin for advanced composites. Both of these applications demand high strength, high modulus, and good adhesion characteristics in the epoxy resins. However, such uses require good fracture resistance and impact strength, which epoxy resin does not generally exhibit. A major drawback of epoxy resins is their inherent brittleness (having low fracture energy, ranging from 80 to 200 J/m);1−3 that is, they easily fail under impact because of highly crosslinked structure,1 and this has led to extensive research efforts to improve their low toughness. Various methods are utilized to modify epoxy resins to improve their toughness. Based on the structure−property relationships, the traditional chemistry approaches have been (i) chemical modification of a given rigid epoxy backbone to a more flexible backbone structure (ii) lowering the cross-link density by increasing the molecular weight of the epoxy monomers and/or (iii) decreasing the functionality of the curing agents. The most common approach is the incorporation of the dispersed toughening phase(s) in the cured epoxy matrix. The second phase includes rubbers, thermoplastics, and hard inclusions such as silica, glass beads, etc. Among them, the most successful systems have been the rubber-modified epoxy resins. In a study, epoxy resin was blended with epoxidized natural rubber (ENR) via an in situ epoxidation method and the obtained ENRs contained epoxide groups with various mole ratios.4 The impact strength of epoxy resin was improved by blending the resin with ENRs, owing to presence of rubber globular nodules. Tensile strength and Young’s modulus were © 2012 American Chemical Society

found to be decreased with an increasing amount of epoxide groups in ENR and also with an increasing amount of ENR in the blends, and flexural strength and flexural modulus of the blends were mostly lower than that of the epoxy resin. The synergic effect of acrylate liquid rubber with a pendant epoxy group and bisphenol A on the toughness of the epoxy resins was reported by some researchers.5 The addition of bisphenol A enhanced the impact strength and elongation at break of the epoxy resin, that is, increased the ductibility of epoxy resin matrix. A maleated depolymerized natural rubber (MDPR) was blended with the diglycidyl ether of the bisphenol A (DEGBA) type epoxy in different ratios, by keeping the epoxy resin component as the major phase.6 The addition of MDPR to epoxy resin did not significantly alter the glass transition temperature (Tg) value of the neat epoxy resin, resulting in an increase in the elongation at break and flexural strain to failure values. The Izod impact strength values of the epoxy/MDPR blends were higher than the impact strength value of the unmodified epoxy. Epoxy resins based on diglycidyl ether of bisphenol A and varying content of hydroxyl terminated polybutadiene (HTPB) were cured using a polyamide curing agent to modify the epoxy matrix by liquid rubber to improve its toughness.7 Different mechanical properties were evaluated. The morphological evolution of the toughened networks was examined by scanning electron microscopy (SEM). A new polyurea copolymer was developed for toughening epoxy.8 By varying the starting materials, two types of polyurea Received: Revised: Accepted: Published: 2603

July 11, 2011 January 13, 2012 January 18, 2012 January 18, 2012 dx.doi.org/10.1021/ie201472u | Ind. Eng.Chem. Res. 2012, 51, 2603−2608

Industrial & Engineering Chemistry Research

Article

(Polyurea-1 and Polyurea-2) were synthesized which were subsequently compounded with epoxy. The first report on secondary phase separation in a liquid rubber/epoxy system was made in 2010,9 and though the modification of epoxies by synthetic rubber has been extensively reported, there were no serious attempts before this using liquid natural rubber. The secondary phase morphologies of hydroxylated liquid natural rubber (HLNR) modified epoxyanhydride system was analyzed by SEM, and the effects of secondary phase morphologies on the mechanical properties were evaluated. Some modified vegetable oils were also used to increase the toughness of epoxy resin. Patel et al.10 brominated castor oil by bromine liquid followed by amino functionalization. The resultant amino-functionalized castor oil (ACO) was used as a curing agent for epoxy resin. Chen et al.11 investigated the thermal stability, impact, and flexural properties of epoxy resins/ epoxidized castor oil (ECO)/nano-CaCO3 ternary systems. They varied the weight content of ECO from 5 to 20 wt %, and the weight content of nano-CaCO3 was kept at 1 wt %. They reported an improvement in thermal stability and mechanical property by the addition of ECO and nano-CaCO3. In a recent strudy, Chen et al.12 has reported the preparation, damping, and thermal properties of potassium titanate whiskers filled castor oil-based polyurethane/epoxy interpenetrating polymer network composites. Thus, attempts have been made, in various ways, to increase the toughness and damping property of epoxy-based composites. Such thermosetting resins, either modified or unmodified, can be reinforced with fly ash to develop some new value-added, cost-effective products.13,14 In a recent work, Altaweel et al.15 have characterized amine containing silicone (ACS) modified epoxy resin composites with fly ash and Cenospheres as fillers. They investigated their mechanical and microstructural properties. In another study by Singla et al.,16 the mechanical properties of an epoxy resin−fly ash composite was reported. In our previous work,17 we reported the properties of MACO and unsaturated polyester (UPE) resin blend matrix reinforced with 10 wt % fly ash. Incorporation of 5 wt % MACO in UPE enhanced impact and damping properties significantly. In our present work, the main objective was to prepare a new tough material from epoxy resin and MACO blend, having high impact strength and high damping property with low brittleness. Replacing 50 wt % of epoxy resin in a material by 50 wt % by MACO means the material becomes greener and sustainability of the product increases. Fly ash was used as filler to enhance the properties further and reduce the cost. First, maleated castor oil (MACO) was prepared and blended with epoxy resin in 1:1 weight ratio. The biocomposites were fabricated from MACO/epoxy blend and fly ash filler, which is an environmentally hazardous, industrial byproduct. Epoxy resin, epoxy/ fly ash composites, epoxy/MACO (1:1 weight ratio) blend, and epoxy/MACO/fly ash composites were prepared using diethylene tetramine (DETA) curing agent, and were examined for their flexural, impact, and dynamic mechanical properties. The fracture surfaces were investigated under scanning electron microscope (SEM) to determine the blend morphology.

Table 1. Sample Code and Chemical Composition of the Samples

a

sample code

epoxy

E EF EM EMF

100 100 50 50

MACO

fly ash 10

50 50

10

DETA (wt%)a 10 10 10 10

With respect to matrix weight.

Figure 1. Comparison of viscosity of epoxy, MACO, and MACOepoxy blends.

epoxy equivalent weight was 185−194 g/eq (average equivalent weight 190 g/eq, supplied) and the epoxide value as per ASTM 1652 was 0.515−0.540. The supplied viscosity @25 °C as per JIS K 7233 (86) was between 11000 and 14000 cP. The ASTM class ‘F’ fly ash (as per ASTM-C 618) was procured from Kolaghat Thermal Power Station, India, and had a particle size distribution as follows: 42 wt % of the particles had a particle size between 104 and 152 μm, 25 wt % were between 76 and 104 μm, and the rest were below that range. Diethylene triamine (Loba Chemie) (equivalent weight 20.63 g/equiv, supplied) was used for polycondensation of epoxy and epoxyMACO blend. The KOH and toluene used were SD. Chemicals products. 2.2. Sample Preparation. 2.2.1. Synthesis of Maleated Castor Oil (MACO). Maleic anhydride (MA) and castor oil (3:1 by mole) were reacted with continuous stirring at 125 °C temperature for 2.5 h. The reaction was continued for 2.5 h because the acid value reaches maximum between 2 and 2.5 h, which has already been reported in our previous work.17 After that, the molecules start to dimerize and the acid value starts to decrease. In this study, our objective was to keep the acid value high so that the MACO molecules could take part in the condensation reaction with the curing agent DETA. 2.2.2. Preparation of the MACO/Epoxy/Fly Ash Composites. The MACO/epoxy blend was prepared (1:1 weight ratio) and sonicated for 1 h at room temperature to eliminate entrapped air bubbles. A measured amount of fly ash (10% with respect to the total resin weight) was thoroughly mixed with the MACO/epoxy blend by mechanical stirring, followed by 30 min of sonication to eliminate the entrapped air and for effective dispersion of the filler. Then diethylene triamine (DETA) was added (10% with respect to the total matrix) to the MACO/epoxy/fly ash mix and mixed uniformly. To calculate the desired stoichiometric quantity of DETA with respect to 100 g of epoxy resin, the following formula

2. MATERIALS AND METHODS 2.1. Materials. Castor oil (medical grade) was purchased from Indian Drug House. Maleic anhydride (Loba Chemie) was used for the preparation of MACO. The epoxy resin used was an Aditya Birla Chemicals product, grade Y128. The supplied 2604

dx.doi.org/10.1021/ie201472u | Ind. Eng.Chem. Res. 2012, 51, 2603−2608


Article

Figure 2. Probable chemical reaction between MACO and epoxy using diethylene triamine.

was used:

the help of a DV-II+PRO Brookfield viscometer with a S-21 spindle between 22 and 24 °C temperature. 2.3.2. Characterization of Composites. Flexural tests of the composites were performed in an Instron 4303 instrument in accordance with ASTM D 790 with a crosshead speed of 1.5 mm/min (sample dimensions: length = 50 mm, width = 25 mm, thickness = 1.7 mm). The reported value of each set is the mean of five results. The Izod impact test of the composites was performed in accordance with ASTM D 256 in a WinPEN CEAST (S.p.A, Italy) impact tester (sample dimensions: length = 63 mm, width = 12.7 mm, thickness = 3 mm; impact energy of the pendulum = 2J), and the mean of at least six samples was reported for each set. Dynamic mechanical analysis (DMA) of the prepared composites was done by DMA Q800 V20.9 Build 27 instrument in flexural mode with 1 Hz test frequency. The fracture surfaces of the composites were examined with a scanning electron microscope using HITACHI-S-3400N. The fracture surfaces of the composites were examined with a field emission-scanning electron microscope (FE-SEM) using model-JEOL JEM-6700F.

⎛ equivalent weight of amine ⎞ ⎜ ⎟ × 100 ⎝ equivalent weight of epoxy resin ⎠ = {(20.63/190) × 100} = 10.8. On the basis of this calculation, a 10 wt % of DETA was used for curing the resins. It was poured in a mold and hot pressed at 70 °C in a compression molding machine for 2 h. Epoxy/fly ash composite was fabricated in the same way with 100% epoxy resin matrix. Apart from these two sets of composites, two more sets of samples were prepared devoid of any filler; one only epoxy resin cured with DETA and another, MACO/epoxy blend, cured with DETA. They were prepared following the same method as above without the addition of any filler. The sample codes and sample compositions are given in Table 1. 2.3. Characterizations. 2.3.1. Characterization of MACO. The viscosities of MACO, epoxy, and MACO-epoxy blends (with weight ratio of 1:1 and 3:2) were determined with 2605



Article

3. RESULTS AND DISCUSSION 3.1. Properties of MACO. The chemical structure of the prepared MACO was reported in our previous paper.17 Viscosity study (Figure 1) of the blends, prepared by mixing MACO with epoxy resin in different weight ratios (50% and 60% MACO incorporation), showed that the viscosity did not change significantly for the blend compared to that of the epoxy resin. This suggests that such blends will be highly useful from a practical point of view. 3.2. Properties of MACO-Epoxy/Fly Ash Composites. Epoxy and MACO molecules, when mixed with DETA, undergo curing and polymerization simultaneously. During in situ polymerization, the MACO molecules were cross-linked among themselves as well as with epoxy molecules (Figure 2) forming an interpenetrating cross-linked network, and the resulting chain entanglement showed great effect in the formed biocomposites’ properties. The flexural strength and modulus of the new materials (E, EF, EM, EMF) developed are shown in Figure 3 panels a

an adverse effect on the stress transfer characteristics at the interface, and the flexural was reduced. In Figure 3b, it was observed that incorporation of fly ash in both epoxy (EF) and epoxy/MACO matrices (EMF) increased the flexural modulus (by 22% and 36%, respectively) compared to that of epoxy. This observation indicates that the fly ash particles restricted the mobility of the polymer chains and modulus increased. But blending MACO with epoxy resin (EM) decreased the elastic modulus by 41% which can be ascribed to the increased flexibility imparted by MACO. Owing to the presence of long fatty acid chains in MACO, the impact properties of EM and EMF increased by nearly 335% and 265%, respectively, in comparison to the epoxy laminate E (Figure 4). Again, the significantly higher impact strength of

Figure 4. Impact strength of the composites.

EMF compared to that of EF (higher by nearly 265%) indicated good intermolecular bonding between MACO and fly ash particles, which was further confirmed by scanning electron micrographs. The dynamic mechanical analysis of the composites was done to study their properties under dynamic loading condition with rise in temperature. The storage modulus (E′) of the composites as a function of temperature is shown in Figure 5a. The E′ values of EM and EMF were much lower at room temperature than that of E and EF. This decrease in storage modulus value could be attributed to the presence of flexible MACO molecules in EM and EMF, which reduced the rigidity of the material under dynamic loading condition. The E′ values of E and EF decreased rapidly between 80 and 100 °C. The loss modulus values (E″) of EM and EMF were much higher than that of E and EF at room temperature and decreased steadily with rise in temperature (Figure 5b). This clearly indicates that the MACO molecules had some flexibility in room temperature also and contributed significantly in viscous dissipation at low temperature leading to a high loss value. E″ values of E and EF increased gradually with the rise of temperature and reached a peak around 90 °C. Epoxy molecules, having a rigid network structure, showed viscous dissipation at a higher temperature of 90 °C. The damping peaks (tan δ) of E and EF appeared at 118 and 122 °C, respectively (Figure 5c), while that of EM and EMF appeared at 92 and 93 °C, respectively. The reason for peak shifting and broadening could be the decrease of the cross-linking density of the epoxy, and molecular entanglements in the MACO/epoxy blend and the distribution of relaxation times of molecules in the blend becoming broader. A similar broadening of the peak has been reported in polyurethane-modified epoxy interpenetrating network.18

Figure 3. Flexural properties of composites: (a) flexural strength, (b) flexural modulus.

and b, respectively. The flexural strengths (Figure 3a) in E (38.6 MPa), EF (38.56 MPa), and EM (39.3 MPa) were almost equal and comparable, while this value was much lower (13.35 MPa) in the case of EMF. When epoxy is reinforced with fly ash particles, there is an interaction between the hydroxyl groups of epoxy resin and fly ash particles. But when MACO is incorporated in the matrix, the hydrophobicity of the matrix increases and the interfacial interaction is reduced. This indicated 2606



Article

Figure 6. The SEM micrographs of the fracture surfaces of the composites.

Figure 5. DMA analysis of composites: (a) storage modulus, (b) loss modulus, and (c) damping parameter.

The damping peaks were considered as the glass transition temperature (Tg) of the materials and they appeared due to segmental mobility in between the cross-links. This emergence of Tg at a higher temperature indicates a higher molecular rigidity in E and EF. It was very interesting to note that the tan δ values of EM and EMF (0.143 and 0.207, respectively, at 35 °C) were much higher than that of E and EF (0.0152 and 0.0248, respectively, at 35 °C) at room temperature. So for high damping application at room temperature, epoxy/MACO blend materials are superior to pure epoxy. Again, incorporation of fly ash in both epoxy and epoxy/MACO matrices shifted the Tg values to a higher temperature. These results indicate that the MACO/ epoxy blend and MACO/epoxy blend filled with fly ash can be utilized for various high damping and high impact applications. The morphology of the fracture surface of the composites (after Izod impact testing) was examined under SEM, shown in

Figure 7. The FE-SEM micrographs of the fracture surfaces of the composites.

Figure 6. For unmodified epoxy resin, an almost smooth glassy fractured surface with cracks was observed. The brittle fracture indicated its low impact strength. In the EF sample, the intermittent presence of fly ash particles within the matrix was seen, which might have increased the impact strength of the composite to a little extent (5% with respect to epoxy laminate E). The fractured surface of EM showed a typical uneven pattern 2607



Article

(8) Dai, J. B.; Kuan, H. C.; Du, X. S.; Daid, S. C.; Maa., J. Development of a Novel Toughener for Epoxy Resins. Polym. Int. 2009, 58, 838−845. (9) Mathew, V. S.; Sinturel, C.; George, S. C.; Thomas, S. Epoxy Resin/Liquid Natural Rubber System: Secondary Phase Separation and Its Impact on Mechanical Properties. J. Mater. Sci. 2010, 45, 1769−1781. (10) Patel, B. P.; Patel, H. S.; Patel, S. R. Modified Castor Oil as an Epoxy Resin Curing Agent. E-J. Chem. 2004, 1, 11−16. (11) Chen, J.-L.; Jin, F.-L.; Park, S.-J. Thermal Stability and Impact and Flexural Properties of Epoxy Resins/Epoxidized Castor Oil/NanoCaCO3 Ternary Systems. Macromol. Res. 2010, 18, 862−867. (12) Chen, S.; Wang, Q.; Wanga, T.,1; Pei, X. Preparation, Damping and Thermal Properties of Potassium Titanate Whiskers Filled Castor Oil-Based Polyurethane/Epoxy Interpenetrating Polymer Network Composites. Mater. Des. 2011, 32, 803−807. (13) Dipa, Ray; Gnanamoorthy, R Friction and Wear Behaviour of Vinylester Resin Matrix Composites Filled with Fly Ash Particles. J. Reinf. Plast. Compos. 2007, 26 (1), 1−5. (14) Dipa, Ray; Banerjee, S.; Mohanty, Amar K.; Manjusri, Misra Thermal and Electrical Behavior of Vinylester Resin Matrix Composites Filled with Fly Ash Particles. Polym. Compos. 2008, 29 (1), 58−62. (15) Altaweel, A. M. A. M.; Ranganathaiah, C.; Kothandaraman, B.; Raj, J. M.; Chandrashekara, M. N. Characterization of ACS Modified Epoxy Resin Composites with Fly Ash and Cenospheres as Fillers: Mechanical and Microstructural Properties. Polym. Compos. 2011, DOI: 10.1002/pc.21030. (16) Singla, M.; Chawla, V. Mechanical Properties of Epoxy Resin Fly Ash Composite. J. Miner. Mater. Charact. Eng. 2010, 9, 199−210. (17) Ghorui, S.; Bandyopadhyay, N. R.; Ray, D.; Sengupta, S.; Kar, T. Use of Maleated Castor Oil as Biomodifier in Unsaturated Polyester Resin/Flyash Composites. Ind. Crops Prod. 2011, 34, 893−899. (18) Chern, Y. C.; Tseng, S. M.; Hsieh, K. H. Damping Properties of Interpenetrating Polymer Networks of Polyurethane-Modified Epoxy and Polyurethanes. J. Appl. Polym. Sci. 1999, 74, 328−335.

indicating exceptionally high impact strength of the EM composite. The morphology of EMF showed coated fly ash indicating considerable intercomponent bonding between fly ash particles and the matrix phase. A good compatibility between epoxy and MACO was evident from Figure 7. However, the fracture surfaces showed different features with and without MACO. The above results indicate that MACO (a green prepolymer) can be blended effectively with epoxy resin in 1:1 weight ratio to produce a high impact and high damping material. Fly ash can be used as filler into such matrix for enhanced property and reduced cost. Epoxy/MACO blends and epoxy/MACO/fly ash composites exhibit very good damping property at room temperature which can be explored for various applications.

4. CONCLUSION Maleated castor oil (MACO) was used in combination with epoxy resin in 1:1 weight ratio and this blend was reinforced with 10 wt % of fly ash particle. The impact strength of EM blend and EMF composite increased 315% and 265%, respectively, compared to that of epoxy laminate. The damping of EM and EMF composites were much superior to that of E and EF composites at room temperature. The SEM micrographs revealed a very good compatibility between epoxy and MACO (EM). There was also a good interfacial bonding between fly ash particles and EM blend. These results indicate that MACO can be blended effectively with epoxy to develop high impact and high damping materials, and these new materials will be greener and more sustainable.

■

AUTHOR INFORMATION

Corresponding Author

*Tel: +91-033-2350 1397. Fax: +91-033-2351 9755. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS Dipa Ray thanks the Department of Science and Technology (DST), Government of India, for granting the project.

■

REFERENCES

(1) Kang, B. U.; Jho, J. Y.; Kim, J.; Lee, S. S.; Park, M.; Lim, S.; Choe, C. R. Effect of Molecular Weight between Crosslinks on the Fracture Behavior of Rubber-Toughened Epoxy Adhesives. J. Appl. Polym. Sci. 2001, 79, 38−48. (2) Meister, J. J. Polymer Modification: Principles, Techniques and Applications; Marcel Dekker: New York, 2000. (3) Ting, R. Y. Epoxy Resins, Chemistry and Technology, 2nd ed.; Marcel Dekker: New York, 1988. (4) Chuayjuljit, S.; Soatthiyanon, N.; Potiyaraj, P. Polymer Blends of Epoxy Resin and Epoxidized Natural Rubber. J. Appl. Polym. Sci. 2006, 102, 452−459. (5) Kong, J.; Tang, Y.; Zhang, X.; Gu, J. Synergic Effect of Acrylate Liquid Rubber and Bisphenol A on Toughness of Epoxy Resins, Polym. Bull. 2007, 60, 229−236 (2008). (6) Kumar, D. K.; Kothandaraman, B. Modification of (DGEBA) Epoxy Resin with Maleated Depolymerised Natural Rubber. eXPRESS Polym. Lett. 2008, 2, 302−311. (7) Khalaf, E. S.; Hassanein, S. M.; Hadhoud, M. K. Investigation of Mechanical Behavior for a Selected Rubber-Modified Epoxy Adhesive. 13th International Conference on Aerospace Sciences and Aviation Technology, Cairo, Egypt, May 26-28, 2009; ASAT-13-CA-04. 2608


Epoxy Resin Blend

Recommend Documents