Flexural strength and stiffness of epoxy resin matrix and lemon umbrella house sawdust particle composites
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https://www.eduzhai.net International Journal of Composite M aterials 2013, 3(4): 108-113 DOI: 10.5923/j.cmaterials.20130304.04 Bending Strength and Stiffness of a Particulate Composite Material Manufactured with Epoxy Matrix and Corymbia Citriodora Sawdust Hélder Rafael Santos Pascoal1, Sergio Luiz Moni Ribeiro Filho1, Geraldo Roberto de Sousa1, Francisco Antonio Rocco Lahr2, André Luís Christoforo1,* 1Department of M echanical Engineering, Federal University of São João del-Rei (UFSJ), São João del-Rei, 36307-352, Brazil 2Department ofStructural Engineering, Schoolof Engineeringof SãoCarlos (EESC/USP), São Carlos, 13566-590, Brazil Abstract This research had as objective the development of particu late co mposite materials in epo xy matrix reinforced with Corymbia citriodora sawdust. The evaluated properties were bending modulus of elasticity (MOE) and bendingstrength (MOR). The resin volu met ric fraction over wood sawdust was the only variab le factor at experimental design, consisting 45% and 65% in fractions. The thickness of specimens for the bending test was 4mm, defined at preliminary studies. Were fabricated two panels by investigated fractions, with 200×200mm d imensions, under a press pressure of 3 MPa, and made at amb ient temperature, in d ifferent t imes. Fro m these panels, were extracted the specimens test with dimensions and specifications established by American Standard ASTM D790: 2010. Fro m results obtained from analysis of variance, concluded that variation of sawdust fraction present a significant behavior at response-variables, presenting the best results the materials manufactured with 45% of epo xy resin. Keywords Particu late Co mposite, Sawdust, Mechanical Characterization 1. Introduction Due the necessity of materials with properties that satisfyan ever more demanding market, the utilizat ion of composite materials is growing in last years. As examples, may be mentioned its use at automotive, aeronautic and civil construction. Composite materials are mu ltiphasic materials that show superior properties them their ind ividual phases, providing a synergic effect, and can be div ided in t wo types: Reinforced with part icles and rein forced with fibers. Among particulate reinforced co mposites, reinforced with natural fibers are focus at currently developed research, especially wood sawdust, due the growing concern about environment questions. La Mantia define these materials, which use natural resources, like green co mposites.The using of sawdust like reinforced assists to decrease the quantity of spoilage gener ated in sawmills and furniture producers[3, 4]. Assumpção et al.studied the effect of sawdust addition in mechanical p roperties of poly meric matrix co mposites. Were investigated two factors: Partic le size (10/20 US-Tyler and 100/ 200 US-Ty ler) and mass of sawdust fraction (40%, * Corresponding author: firstname.lastname@example.org (André Luís Christoforo) Published online at https://www.eduzhai.net Copyright © 2013 Scientific & Academic Publishing. All Rights Reserved 60% and 80%), leading to six d istinct experimental conditions. Were evaluated apparent density, bending modulus of elasticity and bending strength. For both develo ped tests, were manufactured five specimens and two replicates. The authors concluded that using 60% of sawdust with part icle size of 100/200 US Ty ler presented substantial improvements in every mechanical propert ies, being observed decrease in the composites manufactured with particles size fro m mash 10/20 US-Tyler. Hisham et al.investigated the effect caused in mechani cal properties: bending modulus of elasticity and bending strength modulus, in composites manufactured with epoxy resin and reinforced with part iculate wood sawdust or wood chips. In this research, epoxy resin was used at 14% in weight of the sawdust. Test specimens were handmade, using open casting process. The bending test confirmed the good mechanical behavior fro m co mposites, having both showed similar results. Concluded that this kind of composite can be used as anoptionatfurnitureproduction. Norashikin et al.investigated the performance of biodegradable composite films of ch itosan, starch and wood sawdust fibers. The main objectives were the manufacture and characterization of morphological and physical properties of this material. The specimens were prepared using casting method, using sawdust as reinforcement and starch as matrix. For morphological characterization, was used atomic force microscopy and concluded that composite International Journal of Composite M aterials 2013, 3(4): 108-113 109 has a regular structure. Thermal properties were measured using thermogravimetry and differential calorimetry, and revealed that composites presented a little d ifference between fusion and degradation temperatures. Machadoet al. studied mechanical, thermal and rheological properties of Poli-3-hydro xybutyrate (PBH), consisting in a biodegradable thermoplastic, and PBH used as polymeric matrix with sawdust reinforcement. The specimens were manufactured via casting injection process. Concluded that incorporation of sawdust increased the crystalinity degree, crystallization temperature and hardness of co mposites. The best proportion found of PBH/Sawdust among studied (90/ 10, 80/ 20, 70/ 30) was 70/30. Vitoriano and Felipe studied the influence of wood sawdust in mechanical properties of poly meric matrix composites. Were used Jatobá Hymenaea SP wood sawdust, fro m sawmills. Was performed a granulo metriccharacterizat ion of particles. Sawdust was used as load in orthophthalic polymeric matrix, accelerated and homogenized, then added to sawdust, and composite was leaked into a rectangular mo ld. Were manufactured four panels with different mass fractions. After cured, to density test, were extracted five specimens fro m each panel, totaling 20 samples and, for bending test, were used 7 specimens, totalizing 28 samples to determinate bending strength, bending modulus of elasticity and apparent density, in order to verify the influence of sawdust levels in these properties. Concluded that the increase of mass level of sawdust resulted in reduced density and mechanical properties evaluated. Redigh ieri and Costap roposed utilizat ion of reforesta tion wood sawdust (Eucalyptus) instead Pinus wood, traditionally used, andlow density polyethylene as matrix (LDPE) to manufactured composites. The LDPE, functionali zed with maleic anhydride (PE-g-MA)was used at sawdust treatment to improve adhesion between matrix and disperse phase. Were fabricated test specimens, using sawdust treated with PE-g-MA and without treatment. Then were perfo rmed bending and water absorption tests, concluding that PE-gMA worked as compatibilizing agent, imp roving adhesion between matrix and sawdust particles, optimizing its mechanica l properties and decreasing water absorption. Pedieu e Ried l evaluated the use of outer bark of wh ite birch in external surfaces of a 3-layers composite panel,due its hydrophobic characteristics to decrease water absorption. External layers were made with these particles, vary ing its fraction in three levels and, at internal layer, were used coarse wood particles orfibers. Were manufactured four panels for each evaluated condition, amounting 24 panels. Panels with wood particles in its core showed improvements in mechanical and physical properties, satisfying internal use requirements for particu late panels. The best condition was obtained from panel with 45% of outer bark particles and 55% of wood particles in core, due the best dimensional s tab ility . According Jaeger and Ziger, due shortage of traditional raw materials like Pinus, has been occurring a growing Eucalyptus consumption. Therefore, at some p laces it’s already used a mixture of Eucalyptus with another wood species to increase raw material. In this research, was proposed to compare co mpensated PinusTaeda panels (1) and Pinus Taeda mixed with Eucalyptus Dunnii(2) performance. Each panel was composed by nine sheets, only of Pinus Taeda, in case (1), and intercalated sheets of Pinus Taedaand Eucalyptus Dunnii in case (2). In this last, the central sheet was an E. Dunni sheet. Were performed bending tests at parallel and perpendicular direct ions and shear tests in glue lines.At shear tests, were used dry test specimens and also after two pretreatments, in hot water and in cold water to verify the possibility of use in exte rnal areas. In cold water treat ment, was lost 16% of (1) specimens because they unbonded. In hot water treat ment, 26% of (1) specimens and 23% of (2) were discarded.With this research, the authors concluded that mixture of Eucalyptus Dunnii with Pinus Taeda decrease the performance of the materials produced, and the panel wh ich was used just Pinus Taeda showed higher bending modulus of elasticity and bending strength in both cut directions, however, the wood mixtu re presented lower problems about panels swelling afterhaving been immersed in water. Najafiet al. studied water absorption in p lastic-wood composites, made with sawdust and polymers (Po lyethylene and Polypropylene) rawor recycled.Th is components were mixed in weight fract ion of 50%. The panels were fabricated using compressing casting, with 2mm thickness and 15 cm x 15cm casts using a hydraulic hot press at 170° and 190° for polyethylene and polypropylene respectively. The water absorption was evaluated keeping the composite under water for several weeks.Were concluded that maximu m water absorption is bigger for co mposite manufactured with recycled poly mers, and saturation time decreases when it’s u s ed . Viannaet al. verify that thin wood particles can be efficiently used to substitute minerals charges and glass fibers, showing mechanical properties appropriate to engineering applications. However, the interfase between matrix and fiber consist in a problem to solve in the manufacture of th is kind of material. According Correa and Fonseca,wood composite preparationisnot a recentpractice. Since the 70’s, automobili stic industry uses wood sawdust as charges in thermoplastic, using this composite of polypropylene with wood part icles to produce a material co mmercially known by wodstock®. Maldas and Kokta observed the recyclable behavior of composites made with wood sawdust and polystyrene, measuring its mechanical p roperties and its dimensional stability under normal conditions (room temperature) and under extreme conditions, exposure to room temperature, water and boiling water, and in temperatures above 150°C and below -20°C. Results from untreated composites and after the several t reatments were co mpared. The recycled composites did not change significantly. Under all extreme conditions, thermoplastic co mposites presented superior mechanical p roperties and dimensional stability, even after recycling. 110 Hélder Rafael Santos Pascoal et al.: Bending Strength and Stiffness of a Particulate Composite M aterial M anufactured with Epoxy M atrix and Corymbia Citriodora Sawdust Due the good properties presented at previous studies and possibility of reutilize wood sawdust, whichis incorrectly discarded, this researchaimed to the evaluate thebending modulus of elasticity (MOE) and bending Strength (MOR), of particulate composite materials with epoxy matrix reinforced Corymbia Citriodora sawdust,allowing evaluate the influence of the volumetric fraction of resin (45% and 65%) in the mechanicalpropert ies. in smaller proportions the composites presented weak adhesion between phases. Initially, was necessary to define the mass of resin and sawdust for each fraction. Fro m total, resin mass was used 20% of hardener, as specified by manufacturer. After this, resin and hardener were mixed for about 5 minutes and then sawdust was added. Sawdust and resin were mixed until it was reached a homogeneous appearance(Figure 2). 2. Material and Methods The composite were manufactured and tested at the Materials Laboratory of theDepart ment of Mechanical Engineering of the Federal University of São João del-Rei, Brazil. The evaluated factor was volumetric fraction of resin over sawdust (45% and 65%) in mechanical p roperties: bending modulus of elasticity and bending strength modulus. To investigate the influence of resin fraction used on the response-variables, was used an analysis of variance (ANOVA), performed with aid o f Min iTabsoftware, version 14. The panelsproduced according the following steps: sawdust preparing, calculation of the quantityof sawdust and resin necessary, preparation of resin-sawdust mixture, panels fabrication, specimens cutting and preparation for tests. Samples ready, were performed bending tests. The sawdust used as reinforcement in co mposite was fro m Corymbia Citriodorawood specie.Sawdust was sieved in the size range 50-80 US-Tyler (Figure 1), had its moisture content controlled to 12%, accord ing to Brazilian standard ABNT NBR 7190, and went through a pycnometry test to determine its density, that was 1,57 g/cm³. Figure 2. Mixture of epoxy resin and sawdust 2.2. Panels Fabrication The panels fabricated were built with wood cast, covered with a mo ld release tissue (Armalon), with dimensions 200×200mm. This mo ld is detachable, being its edges fastened with screws that must be released to remove the plate after curing period. The mixture of resin and sawdust was placed in the mold (Figure 3), covering all its area with equals quantity. Figure 3. Mold For unifo rm pressing of material, was used a metallic plate (covered with Armalon). Mold was prepared and led to a hydraulic press, using a press pressure of 3 M Pa for 24hours at ambient temperature. Figure 1. Sieves and sawdust For mat rix was used epoxy resin and hardener fro m Resiqualy®, co mpany located at São Paulo city (Brazil-SP). According to manufacturer information, resin density is nearly 1,13 g/cm³. 2.1. Preparati on of Resin-sawdust Mixture According to preliminary studies performed, was determined that the best resin volume proportion, seeking to use the least amount of it, was between 45% e 65%, because Figure 4. Panelextracted from the mold After this, mold was taken out fro m press and International Journal of Composite M aterials 2013, 3(4): 108-113 111 dismounted to extract the panel. Figure 4 shows one of manufactured panels. 2.3. Bending Tests After the panels manufacture, specimens were p repared for bending test (Figure 5) toevaluate the MOE and MOR, cut using an electric saw, and dimensions and standardizations of test preconized by American standard ASTM D790. After cut, was necessary rigging the specimens to achieve exact dimensions. At the end of this process, dimensions of specimens to tests were 76,8 mm×12,7 mm×4 mm. Of each manufactured panel, were extracted 28 specimens, amounting 56 specimens for e xperimental condition. of the analysis of variance model. Table 2. P -Valuesfrom the response-variables evaluat ed Experimental factor Resin fract ion R² (Adj)[%] P-Values MOE MOR 0,003 0,007 89,15 83,01 Figure 6 and 7 show the main effects plots for the resin fraction on MOE and M OR, respectively. Mean of MOE (MPa) 1600 1500 1400 1300 1200 1100 93,54% 1000 900 800 45 65 Proportions of resin (%) Figure 6. Main effect plotsforthe MOE 40 Mean of MOR (MPa) Figure 5. Bending test 2.4. Scanning Electron Microscopy (S EM) After bending tests, a specimen of each condition was collected to be made a scanning electron microscopy, to verify particles homogeneity distribution at matrix phase. The photos were made using an electronic microscope from Hitachi brand, model TM 3000. 3. Results and Conclusions Table 1. Valuesofthe response-variablesevaluated Experimental condition CE1 (45%) CE2 (65%) MOE (MPa) 1578 ± 18 815± 13 MOR (MPa) 37,87± 4,6 20,10 ± 3,1 The mediu mvaluesand standard deviationsobtained for each response-variable per experimental conditionevaluated are presented in Table 1. Table 2 presents P-Values and R² coefficient for the response-variablese valuated. According Werkema and Aguiar, P-values smaller or equals 0,05 (95% of confidence) are significant. The Anderson-Darling normality testwas utilized to analyze residuals distribution obtained from ANOVA for each response-variableevaluated, being found P-values 0,71 and 0,36 for MOE and MOR, respectively, validating the use 35 30 25 88,60% 20 45 65 Proportion of resin (%) Figure 7. Main effect plotsfor theMOR As presented on Table 2, the variat ion of resin fraction was significant in both response-variables evaluated. Co mparing the results, it can be noted that in composites that used 45% of resin, the values of the bending modulus of elasticity and bending strength modulus were 93,54% and 88,60% respectively bigger than composites manufactured with 65% of resin content, as shown in Figure 6 and 7. Figure 8 and 9 show images obtained using SEM, fro m samples of composites with 45% and 65% of resin content, respectively, where can be noted the homogeneous distribution of particles, in both cases. After analyze the results, was possible to conclude that volumetric resin fraction presented significant variations in the bending modulus of elasticity and in the bending strength modulus. The best results were obtained using 45% of resin content. In this way, it can be concluded that sawdust works as a good reinforce for epo xy resin, since that be respected a minimu m limit , appro ximately 35% of resin content, 112 Hélder Rafael Santos Pascoal et al.: Bending Strength and Stiffness of a Particulate Composite M aterial M anufactured with Epoxy M atrix and Corymbia Citriodora Sawdust because, in this proportion, the adhesion between matrix and 2011. particles decreaseand can easethe mechanical properties of  S. Hisham, A. A. Faieza, N. Ismail, S. M . Sapuan,M . S. the composite materials. Ibrahim,“Flexural M echanical Characteristic of Sawdust and Chipwood Filled Epoxy Composites”, 8th International Conference on Composite Science and Technology, ICCST8, Kuala Lumpur, M alasya. 2011.  M . Z. Norashikin, M . Z. Ibrahim,“Fabrication and Characterization of Sawdust Composite Biodegradable film”, World Academy of Science, Engineering and Technology, v. 65, p. 864 – 868, United States. 2010.  M . L. C. M achado, N. C. Pereira,L. F. 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