The new approach to improve the impact property of coconut fiber reinforced epoxy composites using sodium laulryl sulfate treatment

Transcription

1 132 Journal of Scientific & Industrial Research J SCI IND RES VOL 72 FEBRUARY 2013 Vol. 72, February 2013, pp The new approach to improve the impact property of coconut fiber reinforced epoxy composites using sodium laulryl sulfate treatment A Karthikeyan 1*, K Balamurugan 2 and A Kalpana 3 1 Department of Mechanical Engineering, K.S.R College of Engineering, Tiruchengode , Tamil Nadu. 2 Institute of Road and Transport Technology, Erode , Tamil Nadu. 3 Department of Chemistry, Sri Sarada College for women, Salem , Tamil Nadu, India. Received 06 June 2012; revised 31 October 2012; accepted 26 December 2012 The present paper aimed at to investigate the effect of chemical modification of coconut fibers by Sodium Lauryl Sulfate (SLS) treatment in order to use them as reinforcement in epoxy resin. The coconut fibers were treated with 2%, 4%, 6%, 8% and 10% concentration of SLS, separately for 10 days respectively. For each group of the coir fibers the length was 10, 20 and 30mm. The modified coconut fibers were evaluated by using Scanning Electron Microscopy (SEM). The coconut fiber was used as a reinforcement and epoxy as a matrix to fabricate the composites by hand lay-up technique. The Impact strength of SLS treated fiber reinforced epoxy composite was measured with various fiber lengths and compared with NaOH treated fiber reinforced epoxy composites. The SLS treated epoxy composites provided better improvement in the impact strength about 6% when compared with NaOH treatment. Keywords: coconut fiber, sodium lauryl sulfate, fiber length, impact strength, scanning electron microscopy Introduction There is an increasing environmental consciousness and awareness for sustainable development, which has raised interest due to the advantages of natural fibers like low cost, low density, unlimited and sustainable availability and low abrasive wear of processing machinery 1. The use of natural fibers reduces weight by 10% and lowers the energy needed for production by 80%, while the cost of the component is 5% lower than the comparable fiber glass-reinforced component 2. For the past few years, there has been a renewed interest in using synthetic fibers as reinforcement materials, to some extent in the plastic industry. This resurgence of interest may be attributed to the increasing cost of plastics and the environmental aspects associated with using renewable and biodegradable materials 3. A strong fibermatrix interface bond is critical for high mechanical properties of composites. A good interfacial bond is required for effective stress transfer from the matrix to the fiber whereby maximum utilization of the fiber strength in the composite is achieved 4. Good interfacial *Author for correspondence karthirajme@gmail.com adhesion is generated by a combination of fiber modification and matrix methods. Treated fiber has a higher tensile modulus and greater flexural modulus than do untreated fiber composites 5. Modification to the fiber also improves resistance to moisture induced degradation of the interface and the composite properties 6. In addition, factors like processing conditions/techniques have significant influence on the mechanical properties of fiber reinforced composites 7. Mechanical properties of natural fibers, especially flax, hemp, jute and sisal, are very good and may compete with glass fibers in specific strength and modulus 8,9. A number of investigations have been conducted on several types of natural fibers such as kenaf, hemp, flax, bamboo, and jute to study the effect of these fibers based on the mechanical properties of composite materials Coir is an abundant, versatile, renewable, cheap, and biodegradable lignocellulosic fiber used for making a wide variety of products 14. Coir has also been tested as filler or reinforcement in different composite materials Coir fiber polyester composites were tested as helmets, as roofing and postboxes 19. The coir fiber loading ranging from 9 to 15 wt%, have a flexural strength of about 38 MPa. Coir polyester composites with untreated and

2 KARTHIKEYAN et al: THE NEW APPROACH TO IMPROVE THE IMPACT PROPERTY OF COCONUT FIBER 133 treated coconut fibers, and with fiber loading of 17 wt%, were tested in tension, flexure and notched Izod impact 20. Although the untreated fibers showed better mechanical performance, the composites with treated fibers, possessed moderate increase in the values of mechanical properties. Alkali treatment is also reported for coconut fibers 21,22. Treated fiber polyester composites, with volume fraction ranging from 10% to 30%, shows better properties than composites with untreated fibers, but the flexural strength of these composites was consistently lower than that of the bare matrix. A maximum value of 42.3MPa is reported against a value of 48.5MPa for the neat polyester. Acetylation of coconut fibers increases the hydrophobic behaviour, which in turn increases the resistance to fungi attack and also increases the tensile strength of coir polyester composites 23,24. However, the fiber loading has to be fairly high, 45 wt% or even higher, to attain a significant reinforcing effect when the composite is tested in tension. Moreover, even with high coconut fiber loading fractions, there is no improvement in the flexural strength 24. From these results, it is apparent that the usual fiber treatments reported so far did not significantly change the mechanical performance of coir polyester composites. Few investigations have also been made on the effect of fiber treatments on the performance of coir-polyester composites 25,26. Although a great deal of work has been done on coconut fiber reinforced polymer composites and also the limited work has been done on the effect of mechanical behavior of coconut fiber reinforced epoxy composites with SLS treatment. Keeping in view the above facts, the present investigation has been introduced with the newer chemical treatment using SLS for surface modification of fibers. Experimental details Material The coconut husks were soaked in the tap water container for 5 months. This process is called retting, which can partially decompose the pulp on the shell, allowing the fiber to be removed from the husk easily. After retting, the husks were beaten with a hummer. Coir fibers were removed from the shell and separate with a comb. After drying in the room temperature (RT), the coir fibers were combed in a carding frame to further separate the fibers in to an individual state. Coir fibers were treated in SLS solutions (Conc. 2, 4, 6, 8 &10%) at RT (27-29 ) for 10 days. After alkali treatment, the fibers Table 1 Effect of fiber length on impact property of untreated coir fiber Fiber Length in mm Impact Energy in KJ/m were immersed in the distilled water for 1hr to remove the residual SLS. Preparation of Epoxy & Hardener Epoxy LY556 resin of density g/cm 3, chemically belonging to the epoxide family which was used as a matrix and mixed with hardener HY951 of density g/cm 3 and it is used to prepare the composite plate. The solution was mixed with 10:1 by weight percentage. The resin and hardener was purchased from Covai Seenu & Company, Coimbatore, Tamil Nadu, India. Fabrication of Composites The treated coir fibers were first chopped in to the length of approximately 10, 20, and 30mm. The components of the epoxy resin were mixed manually. The moulds are cleaned and dried before applying the epoxy. The concentration of fibers added was 30 wt% of the final mass of the composite. The mixture was pressed for a curing time of 24hrs. After the curing process, the samples were cut in to required sizes prescribed in the ASTM standards. Impact Strength The impact test was carried out by using Charpy impact tester. The specimens were cut from the fabricated composite plates in accordance with ASTM D-256. A minimum of five specimens were tested in each case to obtain an average value of impact strength in KJ/m 2 were reported. Results and discussions Impact energy of untreated and NAOH fiber composites Under this investigation the properties of untreated and NaOH treated coir fiber reinforced epoxy composites with different fiber lengths are shown in Table 1. It indicates that the resistance to impact loading of coir fiber reinforced epoxy composites improves with increase in fiber length 27. The impact performance of fiber-reinforced epoxy composites depends on many factors including the nature of constituent, interface bond

3 134 J SCI IND RES VOL 72 FEBRUARY 2013 Fig 1 (a) & (b) Scanning Electron micrograph of untreated coir/epoxy specimen after impact testing. Fig 2 (a)-sem image of the coir fiber before alkali treatment, (b) 2% of NaOH treatment. between fiber and matrix, alkali treatment with different concentrations, construction and geometry of the composite and test conditions. The impact failure of the composite occurs by factors like matrix facture, fiber/ matrix de-bonding and fiber pull out. The figure 1 shows the SEM picture of untreated fiber reinforced epoxy composites after impact test. The fiber pull out is clearly visible in this composite 27. The lower impact strenght of the untreated coir fiber epoxy composite specimen was due to poor interface bonding. However adhesion was improved by surface modification of fiber. Due to NaOH treatment, the fiber surface was modified. The figures 2(a) & (b) shows the images of the coir fiber before and after the NaOH treatment respectively. From figure 2(a) one may see that the surface of the coir fiber is covered with a layer of substance, which may include pectin, lignin and other impurities. The surface is not smooth, spreaded with nodes and irregular strips. Due to this, there is no mechanical bonding between the fiber and matrix. The important modification done by alkaline treatment is the disruption of hydrogen onding in the network structure, thereby increasing surface roughness. After the NaOH treatment, most of the lignin and pectin are removed resulting in a rough surface specified in figure 2(b). These would increase the mechanical bonding between the fiber and matrix. From the figure 3, it was known that as chemical concentration increases, the fiber diameter decreases. This would be detrimental to the fiber strength. Fig 3 NaOH treatment versus Diameter of the fiber Fig 4 Impact characteristics of coir fiber with SLS treatment Impact Energy of SLS Treated Fiber Composites Six different types of composites [N1 {NaOH treated coir fiber with 10mm length},n2 {NaOH treated coir fiber with 20mm length}, N3 {NaOH treated coir fiber with 30mm length}, S1 {SLS treated coir fiber with 10mm length}, S2 {SLS treated coir fiber with 20mm length} and S3 {SLS treated coir fiber with 30mm length}]. The figure 4 shows the characterizations of the composites which reveals that the SLS treatment has significant effect on the impact strength. The SLS treated fiber gives the maximum impact strength along with increased fiber length. The SLS treated fiber the lignin and pectin are removed resulting in a rough surface. It may also be notified that there are rows of pits on the surface. These

4 KARTHIKEYAN et al: THE NEW APPROACH TO IMPROVE THE IMPACT PROPERTY OF COCONUT FIBER 135 would increase the mechanical bonding between the matrix and the coir fiber in the composite fabrication. A decreased trend is seen in the fiber lignin content with increased chemical concentrations. The SLS removes less amount of lignin content from the fiber as compared to NaOH. It is clearly observed that SLS led to an increase in amorphous cellulose content at the expense of crystalline cellulose as compared to NaOH. The NaOH solution reacts with the fiber causing greater amount of lignin, pectin to leach out 28. The NaOH treatment clearly shows that increase in chemical concentration with decrease in the fiber strength. Deterioration power is high in NaOH because of greater PH value, whereas in case of SLS the PH value is less as compare to NaOH, so deterioration is less in SLS solution. The SLS does not reduce much fiber strength as compared to NaOH. After the alkali treatment, a rough fiber surface resulted, which might improve the adhesive ability of the fiber with the matrix. It is clearly indicates that the bonding capacity between the fiber and the matrix was fair. The fiber diameter indicates that the strength of the fiber was good due to SLS treatment. SLS and NaOH both gives good bonding capacity. Even-though the cost of NaOH is lower than SLS, the NaOH treatment reduces the fiber strength drastically as compared to SLS treatment. Conclusion In this investigation, the effect of fiber length as well as SLS treatment of coir fiber on impact property was studied. It has been concluded from this study that i) the SLS treated fiber showed better impact property (28KJ/ m 2 ) with 30mm fiber length; ii) the fiber length increases with increase in impact strength; iii) the NaOH reduces the fiber strength drastically as compared to SLS and iv) the surface modification by SLS has improved the impact property than alkali. 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