EFFECT OF WOOD PARTICLE SIZE ON TENSILE STRENGTH IN CASE OF POLYMERIC COMPOSITES

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1 8th International DAAAM Baltic Conerence "INDUSTRIAL ENGINEERING April 2012, Tallinn, Estonia EFFECT OF WOOD PARTICLE SIZE ON TENSILE STRENGTH IN CASE OF POLYMERIC COMPOSITES Terciu, O. M.; Curtu, I. & Teodorescu-Draghicescu, H. Abstract: The paper presents experimental research results and aspects o mechanical characteristics o composite materials reinorced with wood sawdust, subjected to tensile stress. Sawdust, as wood waste resulting rom sawing, is an important material resource, natural and renewable. The research sought to determine the inluence o particle size on mechanical properties o composite. Like any other natural product, lignocelluloses materials are characterized by high diversity and variability o their properties, which are relected on structures which incorporate them. Key words: composites, wood sawdust, tensile tests, polymeric resin, particle size. 1. INTRODUCTION In recent years there are concerns or the production o wood structures and other materials. To achieve these, one o the requirements is to have compatibility between wood properties (mechanical, chemical) and the other materials that will allow obtaining a new product, with uniorm structure and deault properties. Wood combined with other materials has multiple beneits and utilities, becoming a subject o active research area, with new ideas that are to be examined and then developed [1, 2]. The changes that occur during execution o the composite, both or natural ibres and or other components, allow obtaining superior properties o its own, which must be properly identiied and used [3]. Experimental studies in the literature have pursued aspects o the structural composition o lignocelluloses materials, namely: the proportion o components, compatibility between components and types and characteristics o the matrix used [4]. Lignocelluloses ibres have a number o advantages and disadvantages compared with traditional glass ibres used to reinorce composite materials. Their ecological character, biodegradability, low cost, non-abrasive nature, sae handling, use with various possibilities as illers, processing with low power consumption, important speciic properties, low density and a large number o types o ibre are very important actors or their acceptance in markets where a large volume o materials is needed such as automotive industry. However certain disadvantages, such as the tendency o agglomeration during manuacture, low resistance to moisture and quality changes due to the seasons o growth, reduce the potential or these ibres [5, 6]. An optimal cost composite can be obtained by embedding in its component the waste rom other manuacturing processes or recycled materials. The waste sawdust is an important resource o raw material. A report by FAOSTAT (Food and Agriculture Organization o the United Nations) shows that the amount o wood o dierent species cut by sawmills in Europe in the year 2010 is about million m 3 [7]. The sawdust losses resulting rom sawing processes are between 5-11% o the total log volume. At a minimal loss value o 5% results in a volume o 6.27 million m 3 sawdust. So sawdust is an important 747

2 renewable raw material and can be used in other areas moreover than heating. 2. MATERIALS AND METHODS Composite materials are made o polyester resin and oak wood particles. The mechanical characteristics o the polyester resin without reinorcing are shown in table 1. Characteristics Value Unit o measure Tensile strength MPa 50 Tensile modulus MPa 4600 Tensile elongation % 1.6 Flexural strength MPa 90 Flexural modulus MPa 4000 Impact strength P4J mj/mm² Volume shrinkage % Table 1. Mechanical characteristics o the polyester resin used For these determinations have been used three types o materials using dierent grains o wood particles: 1 2 mm, mm and mm. In igure 1 can be seen that most part o the particles resulting rom the sawing process are o the sizes mentioned above. Fig. 2. Particle separation device and types o particles results An important parameter o composites is the ratio o components. In this study we used ibre volume raction which is deined as: mw V Wm mw (1) Where: V is the volume raction o ibres; W is the weight o ibres; W m is the weight o matrix; is the density o ibres and m is the density o matrix. To determine the volume o a certain quantity o particles is very important to know their density. It is known that wood is a porous structure consisting o wood cell membrane and cell lumena as can be seen in igure 3. Fig. 1. Data results rom a granulometric analysis o oak sawdust Particle separation was achieved by sieving, resulting three types o particles shown in igure 2. Fig. 3. Micrographs o spruce wood structure (1000x): a cross section; b radial section [8] 748

3 Oak density is between g/cm 3, but wood substance density (without cellular gaps) o the same wood species varies in the range g/cm 3. Pycnometer method by measuring the mass o liquid displaced by a certain amount o wood particles was used to determine the particle density. The liquid used or these determinations was Petrosin. For each size range o wood particles were analyzed three amounts o wood particles. The average values determined or dierent types o grains can be seen in igure 4. Fig. 5. Types o specimens tested: a. specimens with 1 2 mm wood particles; b. specimens with mm wood particles; c. specimens with mm wood particles The equipment used is a tensile test machine with constant speed o 1 mm per minute, provided with specimen ixing devices. In order to measure the speciic elongation o the specimen was used an extension measuring instrument. Specimens ixing in tensile test machine and method o breaking them can be seen in igure 6. Fig. 4. Oak wood particle density or dierent sizes determined by pycnometer method Knowing the density o wood particles can calculate their volume, respectively the volume raction o ibre reinorcement. To determine the eect o wood particle size on mechanical properties o the composite, tensile tests were perormed. Tensile test is known to be the most important and commonly used static test due to the procedure s simplicity on obtaining the strength and stiness characteristics. The specimens have the speciic shape and dimensions o tensile test composite materials reinorced with ibre, according to ASRO SR EN ISO 527 and were made by directly-moulded. Fibre volume raction o wood particles was 20% or all three types o specimens. The three types o samples can be seen in igure 5. Fig. 6. Tensile testing devices and specimens: 1 composite material specimen with dierent wood particle sizes (a.1 2 mm; b mm; c mm); 2 extension measuring instrument; 3 tensile test machine jaws 3. RESULTS AND DISCUSSION Ater processing the machine data, tensile tests diagrams load-extension were made, as presented in igure 7, 8 and

4 Fig. 7. Tensile tests diagrams or specimens with 1 2 mm wood particles Fig. 10. Stress-strain σ-ε curves recorded in tensile test or specimens with 1 2 mm wood particles Fig. 8. Tensile tests diagrams or specimens with mm wood particles Fig. 11. Stress-strain σ-ε curves recorded in tensile test or specimens with mm wood particles Fig. 9. Tensile tests diagrams or specimens with mm wood particles In igures 10, 11 and 12 strain-stress correlations or the three types o specimens can be seen. Fig. 12. Stress-strain σ-ε curves recorded in tensile test or specimens with mm wood particles 750

5 It may be noted that or the same category o specimens there is not a large dispersion o values. The absorbed energy required to produce a racture, per area unit or mechanical work done during the break, per area unit is equal with area under the curve σ = (r), as shown in igure 13. Fig. 15. Average tensile strength or the three types o specimens Fig. 13. Determining the energy absorbed by the specimen during tensile tests Tests have shown that the energy absorbed by the specimens reinorced with particles o size between mm is greater. The average values o energy absorbed or the three types o specimens can be seen in igure 14. Fig. 16. Average elongation o racture or the three types o specimens Although the use o smaller particles typically leads to an increase in mechanical properties, in this case it was ound that particles o size between mm have a greater length than particles o other sizes and this makes the tensile strength or this category to be greater. 4. CONCLUSION Fig. 14. Average values o energy absorbed or the three types o specimens Other properties such as tensile strength and elongation at racture are also higher or the specimens reinorced with particles o size between mm, as can be seen in igure 15 and 16. With increasing o oak particles sizes, density decreases ater the law: y 0.16ln x (2) Oak particles sizes o mm obtained by sawing are the majority representing a percentage o approx. 58% rom the total amount o sawdust. This percentage varies rom one species to another and depends on several actors such as wood density, moisture content at the processing, cutting regime etc. 751

6 Experimental tests have shown that long particles lead to increased resistance compared to those with comparable sizes (spherical or rectangular). Maximum strain energy resulted or specimens reinorced with particles sizes between mm. 5. ACKNOWLEDGEMENTS This paper is supported by the Sectoral Operational Programme Human Resources Development (SOP HRD), inanced rom the European Social Fund and by the Romanian Government under the contract number POSDRU/88/1.5/S/ REFERENCES 1. Bismarck, A.; Baltazar, A.; Jimenez, Y. & Sarikakis, K. (2006). Green composites as panacea? Socio-economic aspects o green materials, Available rom: Accessed: Curtu I., Stanciu A., Stanciu M. D., Savin A., Grimberg R., Research regarding the static behavior o layers rom structure o ROVING and MAT composite, in Proceedings o conerence The Eighth International Congress In Materials Science and Engineering ISSIM, 2011, Iasi, Romania, ISSN , p Stanciu M.D., Curtu I., Terciu O.M, Savin A., Cosereanu C., Evaluation o acoustic attenuation o composite wood panel through nondestructive test, in Annals o DAAAM or 2011 & Proceedings o the 22th International DAAAM Symposium Intelligent Manuacturing & Automation, Editor Katalinic B., 2011, ISSN , Cerbu C., Curtu I., Internal Factors that Acts on the Behaviour in Charpy Testing in the Case o the Glass/Wood Flour Epoxi Composite Materials, in Proceedings o the 8th International Conerence Wood Science and Engineering in the Third Millennium ICWSE2011, 2011, Brasov, Romania, ISSN , pp Terciu, O. M., Curtu, I., Cerbu, C., Stan, G. I., Research on mechanical properties o composites materials reinorced with lignocellulosic ibers, The 8th International Conerence Wood Science and Engineering in The Third Millenium, ICWSE 2011, 2011, Brasov, Romania, ISSN , pp ; 6. Terciu, O.M., Curtu, I., Cerbu, C., Stanciu, M.D., Mechanical properties o composites reinorced with natural iber abrics, In Annals o DAAAM or 2011 & Proceedings o the 22th International DAAAM Symposium Intelligent Manuacturing & Automation, Editor Katalinic B., 2011, ISSN , pp ; 7. Food and Agriculture Organization o the United Nations: [WWW] ( ). 8. Szmutku, M.B., Campean, M., Sandu, A.V., Microstructure modiications induced in spruce wood by reezing, Pro Ligno, 7, No. 4, 2011, ISSN-L , pp ADDITIONAL DATA ABOUT AUTHORS Terciu, O.M. / PhD. Student Eng. / Transilvania University o Braşov Faculty o Mechanical Engineering / 29 Eroilor Blvd., Brasov, Romania / phone/ax: / ovidiumihai.terciu@unitbv.ro Curtu, I. / Pro. Dr. Eng. / Transilvania University o Braşov Faculty o Mechanical Engineering / 29 Eroilor Blvd., Brasov, Romania / phone/ax: / curtui@unitbv.ro Teodorescu-Draghicescu H./ PhD. Assoc. Pro. / Transilvania University o Braşov Faculty o Mechanical Engineering / 29 Eroilor Blvd., Brasov, Romania / phone/ax: / draghicescu.teodorescu@unitbv.ro 752