A new nano ceria reinforced epoxy polymer composite

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A new nano ceria reinforced epoxy polymer composite

  1. 1. INTERNATIONAL JOURNAL OF ADVANCED RESEARCH INInternational Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –6480(Print), ISSN 0976 – 6499(Online) Volume 3, Number 2, July-December (2012), © IAEME ENGINEERING AND TECHNOLOGY (IJARET)ISSN 0976 - 6480 (Print) IJARETISSN 0976 - 6499 (Online)Volume 3, Issue 2, July-December (2012), pp. 248-256© IAEME: www.iaeme.com/ijaret.asp ©IAEMEJournal Impact Factor (2012): 2.7078 (Calculated by GISI)www.jifactor.com A NEW NANO-CERIA REINFORCED EPOXY POLYMER COMPOSITE WITH IMPROVED MECHANICAL PROPERTIES Siddhant Datta1*, B.M. Nagabhushana2, R. Harikrishna2 1 Department of Mechanical Engineering, RV College of Engineering. Bangalore. India-560 059 2 Department of Chemistry, MS Ramiah Institute of Technology. Bangalore. India-560 054 (*Corresponding author: email-siddhant.datta@gmail.com) ABSTRACT This study deals with enhancement of mechanical properties of Epoxy matrix using nano- Ceria (CeO2) as particulate reinforcement. Nano-Ceria with 10-20nm crystallite size was prepared by solution combustion method using Citric acid as fuel. Epoxy matrix was a standard diglycidyl ether of bis-phenol A (DGEBA) cured with aliphatic amine hardner. Nano-Ceria was dispersed in epoxy resin by manual stirring followed by sonication at 20 Khz for 15 minutes. Amine hardner was added to the sonicated mixture and rectangular polymer composite slabs of 10x8x1.5 cm3 were cast using releasing agent coated glass moulds. Effect of varying wt% of nano-ceria filler on mechanical properties of the matrix was studied. Flexural strength, Compressive strength, Vicker’s Microhardness and Density were tested for polymer slabs varying in wt% of nano-ceria filler from 0 to 3 wt%. Polymer nano-composite sample containing 0.25 wt% nano-ceria exhibits 42% increase in flexural strength. Sample with 0.5 wt% nano-ceria shows increase of 42.7% in compressive strength. Microhardness increased by 29% for the sample with 1 wt% of nano-ceria. All tests were carried out according to ASTM standards. As the wt% of nano-ceria increased the mechanical properties showed improvement till a maximum value and then these properties deteriorated with further increase in nano filler content. However, density continued to increase with increase in wt% of nano-Ceria. Keywords: Epoxy, Nano-ceria, Sonication, Mechanical properties, Nano-composite. 1. INTRODUCTION Epoxy resins are well established thermosetting matrices of advanced composites, displaying a series of interesting characteristics like good stiffness and specific strength, dimensional stability, chemical resistance, ease of processing and also strong adhesion to the embedded 248
  2. 2. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –6480(Print), ISSN 0976 – 6499(Online) Volume 3, Number 2, July-December (2012), © IAEMEreinforcement [1]. Epoxy resin is widely used as host matrix for fabricating Fiber ReinforcedPolymers (FRP) with higher strength to weight ratio than steel. Commonly used Fibers in epoxybased FRPs are glass fiber, kevlar fiber, carbon fiber etc. The use of particulate fillers has beenproven to improve the material properties of epoxy resins. Building on the fact that the micro-scaled fillers have successfully been synthesized with epoxy resin, the nano-scaled fillers arenow being considered to produce high performance composite structures with further enhancedproperties. Nano filler reinforced epoxy matrix can also provide superior host matrix for FRPcomposites. Improvements in mechanical, electrical, and chemical properties have resulted inmajor interest in nanocomposite materials in numerous automotive, aerospace, electronics andbiotechnology applications [2]. Various kinds of ceramic materials, e.g. SiC, Montmorillonite clay, Al2O3, SiO2, WO3 andZrO2, have been used to reinforce polymers. Superior properties of metal oxides such as highrefractoriness, hardness, compressive strength, modulus of elasticity, thermal resistance and wearresistance make them suitable for use as reinforcement material in polymer matrices [3,4].Incorporating ultra-fine particles of metal oxides can significantly improve mechanical propertiesof the host matrix by getting uniformly embedded in the thoroughly cross linked chains of thethermoset-polymer. Metal oxide nanoparticles possess high surface area to volume ratio whichincreases interfacial interaction between nano-reinforment and host polymer matrix, thus betteradhesion between resin and filler is achieved. These nanoparticles present good wettabilty withthe thermoset-polymer and fill in the small gaps between cross-linked polymer chains providingthe chains with high resistance to deformation under stress. Nanoparticle reinforcements canreduce thermal expansion coefficient and increase thermal and wear resistance of the host matrix.By uniformly distributing these nano-reinforcement particles in epoxy resin the reinforcementmaterial can impart superior mechanical properties to every region of the host matrix in auniform manner [5,6]. The nanoparticles present high tendency to agglomerate under the influence of Vander Val’sforces. Agglomeration of these particle in the host matrix can result to reduced interfacialinteraction between resin and reinforcement. Non uniform dispersion of the reinforcement causesthermal stresses in the matrix around agglomerated nano particles due to unevenly distributedcoefficient of thermal expansion within the composite matrix. Many methods can be used toinfuse nanoparticles inside polymers including ultra-sonication bath, probe sonicator, high shearmixing by ball milling, high speed stirrer etc [7]. In this study the nano-CeO2 reinforced epoxy slabs were fabricated and fiber reinforcementswere not added in order to clearly analyze the effect of lab synthesized nano-CeO2 particles(crystsllite size 10-20nm) on mechanical properties of epoxy resin matrix. Sample slabs withwt% of nano-CeO varying from 0 to 3wt% were fabricated and mechanical properties namelyflexural strength, compressive strength, microhardness and density were tested. 2. EXPERIMENTAL 2.1 Materials used The matrix used in this work is a commercially available analar grade of diglycidyl ether ofbis-phenol A ((4-(2,3 epoxypropoxy) phenyl) propane), abbreviated as DGBEA, was obtainedfrom Huntsman Advanced Materials under the commercial name Araldite AY 105. Along with 249
  3. 3. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –6480(Print), ISSN 0976 – 6499(Online) Volume 3, Number 2, July-December (2012), © IAEMEepoxy resin an aliphatic polyamine hardner commercially known as Aradur HY 951 was alsoobtained from the same company. Nano-CeO2 powder synthesized by Solution Combustionmethod was used as reinforcement material. 2.2 Synthesis of nano-CeO2 particles. Nano-CeO2 particles were synthesized by dissolving cerium nitrate (Ce(NO3)3.6H2O) andcitric acid (C6H8O7) in minimum quantity of double distilled water in a pyrex dish. The solutionis then placed in a pre-heated Muffle furnace maintained at 400±10°C. Solution boils anddehydration takes place followed by decomposition and evolution of gases. Then spontaneouscombustion occurs with enormous swelling and porous product, CeO2 is obtained. Solution takes5mins in Muffle furnace till the bright sparks throughout the pyrex dish are seen which indicatethe occurrence of spontaneous combustion and formation of nano-Ceria. The theoretical equationof the combustion of redox mixture for the formation of CeO2 nanopowder using citric acid fuelcan be represented by: 2Ce(NO3)3 (aq) + C6H8O7 (aq) → 2 CeO2 + 6CO2 (g) + 4H2O (g) + 9 N2 (g)........................ (1) 2.3 Characterization of nano-CeO2 by PXRD, FTIR and SEM. The powder XRD patterns of CeO2 samples were obtained using a Philips PW/1050/70/76 X-ray diffractometer which was operated at 30 kv and 20 mA using CuKa radiation with nickelfilter at a scan rate of 20/min. The surface morphology of the powders was examined usingJEOL (JSM-840A) scanning electron microscopy (SEM). FTIR spectra were recorded using aNicollet IMPACT 400 D FTIR spectrometer in the range 4000-400 cm-1 using KBr pellet. 2.4 Fabrication of polymer nano composite slabs. Nano-Ceria filler was added to epoxy resin and stirred manually in a beaker using a glass rodfollowed by Sonication. Sonication of the mixture was done using a Probe-type Ultrasonicprocessor at 20 Khz frequency for a duration of 15 minutes. On/Off pulse was set to 10s to avoidover heating of the resin. Sonicated mixture was allowed to cool down following whichpolyamine hardner was added to cure the resin. This mixture was poured into rectangular mouldsof dimension 10x8x1.5 cm3 and allowed to cure at room temperature for 48 hours. Resin tohardner weight ratio was kept 10:1 as specified. 2.5 Flexural test. Three Point Bending test was used to determine the flexural strength of the polymercomposites containing different wt% of nano-ceria. Specimens with dimensions 80x10x4 mm3were prepared for Three point bending test according to ASTM D-790-2010 standard. 2.6 Compression test. Compressive strength of the polymer composite samples was determined using UniversalTesting Machine (UTM). Compression test was carried our according to ASTM D-695-2002standard and specimens of dimensions 10x10x4 mm3 were prepared for this test. 250
  4. 4. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –6480(Print), ISSN 0976 – 6499(Online) Volume 3, Number 2, July December (2012), © IAEME July-December 2.7 Microhardness test. Microhardness of polymer composites was determined using Vicker’s Microhardness testerwith a diamond pyramid indenter. Load of 300g was applied for a duration of 20s and diagnols d 20of the indentation were measured with an Optical Microscope with a Micrometer attachment in Microscopethe eye piece.Formula used: …………………………......(2) …………………………..... Where ‘F’ is Load applied in N, ‘d’ is the average diagonal of indentation and ‘HV’represents Vickers Hardness Number. 2.8 Density test. Density was determined using displacement method with distilled water at 23°C. Test wasperformed according to ASTM DD-792-1998 standard. 3. RESULTS AND DISCUSSIONS 3.1 Characterization 3.1.1 Powder X-Ray Diffraction of nano Ray nano-CeO2 powder. Figure 1 PXRD pattern for as-formed nano-ceria Fig. 1 gives the PXRD patterns of the as as-prepared CeO2 sample, diffraction peaks, dcorresponding to cubic fluorite structure (JCPDS: 43 1002) are clearly observed. By applying the 43-1002)Scherrer’s formula [8] to the full width at half maximum of the diffraction pe peaks, the meancrystallite sizes was calculated as 10 10-20 nm. 251
  5. 5. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –6480(Print), ISSN 0976 – 6499(Online) Volume 3, Number 2, July-December (2012), © IAEME 3.1.2 Scanning Electron Microscopy of nano-CeO2 powder. Figure 2 SEM image of nano-ceria Fig 2 shows the SEM photographs of as prepared CeO2. The nano particles are agglomerated,and fluffy with porous morphology. The agglomeration of nanoparticles is usually explained as acommon way to minimize their surface free energy. The voids and pores present in the sampleare due to large amount of gases produced during the combustion synthesis. 3.1.3 FTIR analysis of nano-CeO2. Figure 3 FTIR spectra of nano-ceria Fig. 3 shows the FTIR spectra of as formed CeO2 nanopowder. The peak appearing at 400 -1cm , can be ascribed to the Ce-O vibration of the CeO2 nanopowder. The weak absorption peakat 3421 cm-1 corresponds to the -OH group of water adsorbed on the surface of the CeO2 powder. 252
  6. 6. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –6480(Print), ISSN 0976 – 6499(Online) Volume 3, Number 2, July-December (2012), © IAEME 3.2 Mechanical properties 3.2.1 Flexural test Flexural tests of the samples reveal improvement in the bending strength of epoxy matrix dueto addition of nano-ceria. Maximum increase of 42% in bending strength was shown by thesample containing 0.25 wt% of nano-ceria. Flexural strength of pure epoxy sample was 64.4Mpa and increased with increase in wt% of nano-ceria till a maximum value of 91.5 Mpa wasobtained for 0.25 wt% sample. Increase in wt% nano-ceria beyond 0.25% resulted in decrease inflexural strength and sample with 3 wt% ehibited lowest flexural strength of 57.6 Mpa. Relation of flexural strength to wt% of nano-ceria is shown in Fig4. Increase in flexuralstrength due to addition of nano-CeO2 till 0.25wt% can be attributed to resistance to crackinitiation and crack growth offered by nano-ceria particles bonded strongly in the spaces betweenpolymer chains. Due to extremely high surface area of nano-particles they adhere strongly to theepoxy matrix and fill in extremely small gaps between polymer chains owing to their nano size.The high strength of ceramic reinforcement is transmitted uniformly throughout the matrix whenreinforcement is dispersed uniformly at nano scale level.[4] Presence of air bubbles in matrix canform crack initiation sites under bending stresses, formation of these air bubbles can be reducedby addition of reinforcement since reinforcement material can fill in void spaces. Figure 4 Flexural strength vs Wt% of nano-ceria The decrease in flexural strength when wt% is increased beyond 0.25% is due to absence ofenough resin in some regions to bond with surplus reinforcement material which results inweaker regions in the matrix. Higher content of nanoparticles can hinder uniform curing of theresin and result in non uniform cross linking of the epoxy network. At higher wt% there is apossibility of agglomeration of nano-reinforcement in different regions of the matrix resulting innon uniform dispersion of reinforcement material [7,9]. Thermal stresses can be induced inregions around agglomerated nano-particles at the time of curing since there is a mismatch ofthermal expansion coefficient of nano-ceria reinforcement and epoxy matrix. 253
  7. 7. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –6480(Print), ISSN 0976 – 6499(Online) Volume 3, Number 2, July-December (2012), © IAEME 3.2.2 Compression test Compression tests reveal increase in compressive strength of epoxy matrix with increase inwt% of nano-ceria from 0 to 0.5 %. Compressive strength of pure-epoxy sample was 368 Mpawhich increased to a maximum value of 525 Mpa for 0.5wt% sample. Increase in wt% beyond0.5% caused decrease in compressive strength and 3 wt% showed compressive strength of 406Mpa. This trend is shown in Fig 5. Figure 5 Compressive strength vs Wt% of nano-ceria Increase in compressive strength with increase in wt% of nano-ceria till 0.5wt% is a result ofhigh strength of CeO2 nanoparticles which is transmitted uniformly to the host matrix due tovery high interfacial area between resin matrix and nanoparticles assists in transfer of physicalstress. Nanoparticles are uniformly dispersed in the matrix and occupy spaces between polymerchains decreasing mobility of the chains and increasing resistance of matrix to deformation andcrack growth. Possibility of air bubbles reduces by addition of nano-ceria filler thus preventingcrack initiation due to void spaces in the matrix. Decrease in compressive strength on increasingwt% beyond 0.5% was observed. This decrease can be due to agglomeration of nanoparticles andlack of resin material to accommodate high content of nano-ceria. Region around agglomeratednanopaticles develops thermal stresses during curing cycle due to mismatch of thermal expansioncoefficient between resin host matrix and nano-ceria aggregate [11]. Cracks can initiate in suchregions with stress concentrations present due to poorly dispersed reinforcement or lack of resinmaterial to bond high content of reinforcement. 3.2.3 Vicker’s Microhardness test Microhardness of pure epoxy slab was 268.66 HV/0.3Kg and increased to a maximum valueof 347.62 HV/0.3Kg for 1 wt% slab. Composite slabs with low filler content (0.1 and 0.25 wt%)do not exhibit considerable change in microhardness. Increase in nano-ceria content above 0.25wt% showed increment in microhardness till maximum value was achieved at filler loading of 1wt%. When filler loading was increased beyond 1 wt% a decrease in microhardness is observedand value drops down to 319.85 HV/0.3Kg for 1.5 wt% slab. Decreased mobility of polymerchains due to hard ceramic nano filler can be the reason for high microhardness exhibited byslabs at high filler content [10,12]. Higher surface area of nano-ceria reinforces larger volume ofresin matrix and stress can be transferred to nanoparticles more efficiently owing to high 254
  8. 8. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –6480(Print), ISSN 0976 – 6499(Online) Volume 3, Number 2, July-December (2012), © IAEMEinterfacial area between resin and nano-Ceria. Trend of Microhardness with wt% of nano-ceria isgiven in Fig 6. Figure 6 Vickers Microhardness vs Wt% of nano-ceria More than 1 wt% nano-ceria content resulted in drop in microhardness value but still slabs with1.5 and 3 wt% possessed significantly higher microhardness than pure epoxy slab. High hardnessof ceramic filler contributes to the increase in microhardness but high content of nano-ceriaresults in its non uniform distribution and formation of aggregates. This can lead to non uniformreinforcement of host matrix and hindrance in curing of matrix in regions where nano-ceriaaggregates are present. 3.2.4 Density test Minute increase in density was observed with increment in wt% of nano-CeO2 due to highdensity of Ceria particles. Density of pure epoxy casting was 1.19g/cm3 and sample with 3wt%of nano-CeO2 exhibited a density of 1.22g/cm3. Table 1 shows the trend of density of polymercastings with variation in wt% of nano-ceria. Table 1 Density with varying Wt% of nano-ceria Wt% of 0% 0.10% 0.25% 0.50% 1.0% 1.50% 3.0% nano-CeO2 Density 1.19 1.19 1.20 1.20 1.20 1.21 1.22 (g/cm3) 4. CONCLUSIONNano-ceria reinforcement synthesized by combustion method significantly improved themechanical properties of epoxy matrix. 42.6% increase in compressive strength, 42% increase inflexural strength and 29% increase in microhardness suggest that this nano-ceria reinforcedepoxy can be used as host matrix for fabricating better FRPs. Enhancement of mechanicalproperties uniformly throughout the polymer composite slabs at filler content lower than 1 wt% 255
  9. 9. International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –6480(Print), ISSN 0976 – 6499(Online) Volume 3, Number 2, July-December (2012), © IAEMEsuggests that sonication process successfully dispersed the nano-ceria particles in the resinmatrix. Negligible increase in density was observed when filler content increased from 0 to 3wt%. Since low nano-ceria content is needed to achieve this improvement in properties there isscope of accommodating additional reinforcement materials, e.g. carbon fiber, glass fiber, carbonnanotubes, into the epoxy host matrix.REFERENCES[1] Smrutisikha Bal. “Experimental study of mechanical and electrical properties of carbonnanofiber/ epoxy composites.” Journal of Materials & Design,Volume 31, Issue 5, May 2010,Pages 2406–2413[2] Renee´ M. Rodgers, Hassan Mahfuz, Vijaya K. Rangari, Nathaniel Chisholm, Shaik Jeelani.“Infusion of SiC Nanoparticles Into SC-15 Epoxy: An Investigation of Thermal and MechanicalResponse.” Macromolecular Materials and Engineering. Volume 290, Issue 5, 2005 Pages 423–429.[3] S.M. Mirabedini, M. Behzadnasab, K. Kabiri. “Effect of various combinations of zirconiaand organoclay nanoparticles on mechanical and thermal properties of an epoxy nanocompositecoating.” Composites: Part A 43 2012, Pages 2095–2106.[4] Peerapan Dittanet, Raymond A. Pearson. “Effect of silica nanoparticle size on tougheningmechanisms of filled epoxy.” Polymer Volume 53, Issue 9, 17 April 2012, Pages 1890–1905[5] Jae-Jun Park, Ki-Geun Yoon, Jae-Young Lee. “Thermal and Mechanical Properties ofEpoxy/Micro- and Nano- Mixed Silica Composites for Insulation Materials of Heavy ElectricEquipment”. Transactions on Electrical and Electronic Materials Vol. 12, Issue 3, 2011 pp. 98-101.[6] M. Sudheer, K. M. Subbaya, Dayananda Jawali, Thirumaleshwara Bhat. “MechanicalProperties of Potassium Titanate Whisker Reinforced Epoxy Resin Composites”. Journal ofMinerals & Materials Characterization & Engineering, Vol. 11, No.2 , 2012 pp.193-210.[7] Haydar Faleh, Riadh Al-Mahaidi, Luming Shen. “Fabrication and characterization ofnanoparticle reinforced epoxy.” Composites Part B: Engineering Volume 43, Issue 8, December2012, Pages 3076–3080[8] P. Klung, L.E. Alexander, X-Ray Diffraction procedure (Wiley, New York, 1954).[9] Y. X. Zhou, P. X. Wu, Z-Y. Cheng, J. Ingram, S. Jeelani. “Improvement in electrical, thermaland mechanical properties of epoxy by filling carbon nanotube” eXPRESS Polymer Letters 2008Vol.2, No.1 Pages 40–48.[10] Mir Mohammad Alavi Nikjea, Mohammad Reza Khanmohammadia, Amir BagheriGarmarudia and Moslem Haghshenasb. “Nanosilica reinforced epoxy floor coating composites:preparation and thermophysical characterization”. Current Chemistry Letters 1, 2012 Pages 13–20.[11] L.Merad, B.Benyoucef, M.J.M. Abadie and J.P. Charles. “Characteriazation and Mechanicalproperties of Epoxy resin reinforced with TiO2 nanoparticles.” Journal of Engineering andApplied Sciences 6(3): 2011 Pages 205-209.[12] Ali Allahverdia, Morteza Ehsanib, Hadi Janpoura, Shervin Ahmadib. “The effect ofnanosilica on mechanical, thermal and morphological properties of epoxy coating.” Progress inOrganic Coatings 75 2012. Pages 543–548. 256

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