Mechanical properties of glass/palmyra fiber waste sandwich composites

Transcription

1 Indian Journal of Engineering & Materials Sciences Vol. 12, December 2005, pp Mechanical properties of glass/palmyra fiber waste sandwich composites R Velmurugan a* & V Manikandan b a Department of Aerospace Engineering & Composite Technology, Indian Institute of Technology, Chennai , India b Dr Sivanthi Aditanar College of Engineering Tiruchendur , India Received 21 October 2004; accepted 20 September 2005 Uses of natural fibers as reinforcement in polymers have gained importance in the recent years due to the eco-friendly nature. This paper deals with the mechanical properties of the composites made up of palmyra fiber waste [pfw] and the pfw/glass fiber hybrid composites. Composite plates were prepared with 30%, 38%, 45%, 50%, 58%, 65% and 70% wt of fiber waste. Tensile, flexural, shear and impact properties were studied. Composites with wt% fibers showed marginal improvement in flexural strength. Tensile strength was decreased and there was considerable improvement in shear and impact properties than that of resin. The properties of the natural fiber reinforced composites can be improved by hybridizing with high strength synthetic fibers such as glass. In this study, the palmyra fiber waste was hybridized with glass fiber in the polyester matrix. Samples were prepared by sandwiching the fiber waste between chopped strand glass fiber mats by varying both glass fibers and waste material content, keeping total fiber content as 60% by weight. Specimens were cut as per ASTM standards and tested in Instron universal testing machine. Mechanical properties of the composites were found to be increased with increase in the amount of glass fiber in the hybrid. Hybrid composites containing 48% waste, 10% glass fiber showed good reinforcement effect than the composites reinforced with 11 wt % glass fiber. The resin used was isophthalic roof light resin, the catalyst and accelerator were methyl ethyl ketone peroxide (MEKP) and cobalt napthanate, respectively. IPC Code: C03C14/00 Polymers are used in large number of application due to their light weight. Use of biodegradable fibers as reinforcement in polymer matrix has been under research in the recent years. Natural fibers such as coir, jute, ramie, banana, oil palm, hemp, palmyra, and sisal as reinforcement in polymer matrix had been reported by several researchers 1-8. Natural fibers are easily available, low cost, low density, non-abrasive nature and biodegradable. The use of natural fibers as reinforcement in the composites gives good opportunities for the effective utilization of agricultural byproducts. These can be molded into flat plates and used as a substitute for building materials. Kazuya et al. 9 studied the tensile properties of bamboo based polymer composites and reported that there was an improvement in tensile strength and modulus by 15% and 30% than that of matrix. Composite material based on wood fiber and nylon was reported by McHenry et al. 10. Increase in tensile strength and modulus was observed in wood fiber/nylon matrix composites and decrease in tensile strength in wood fiber/pp matrix composites, with increase of wood fiber content. *For correspondence ( rvel@iitm.ac.in) Interspersing the two or more kinds of fibers in a common matrix forms the hybrid composites. Dispersed fiber, dispersed fiber ply, fiber skin and core, fiber skin non-fiber core are the different forms of hybrids often used. The properties of the hybrid composites depend upon length and fiber content of the individual fiber, the arrangement of the fibers in the matrix, the fiber matrix interfacial bonding and the strength of the fibers. The mechanical properties of the natural fiber composites can be improved by hybridizing the glass fibers with natural fibers. Sreekala et al. 11 reported the effect of hybridization of glass fibers with oil palm fiber-reinforced composites. Nikhil Gupta et al. 12 studied the hybridization effect of fly ash in glass fiber reinforced epoxy on compressive and impact properties. Thwe et al. 13 reported the effect of environmental aging on mechanical properties of bamboo glass fiber reinforced hybrid composites. Palmyra fiber is a natural fiber obtained from Palmyra (Borassus flabellifer) tree. Fibers are available in the leaf stem base and leaf stem of the palmyra tree. They are separated by hand beating or crushing mechanically and then by removing the pith using the device called comber. The fibers are dark

2 564 INDIAN J. ENG. MATER. SCI., DECEMBER 2005 brown and length of mm. During the separation of these fibers from leaf stem base a large quantity of fibrous waste is obtained (Fig. 1), which has no further use. It contains pith and poor strength short fibers of length ranging from 30 to 100 mm. These fiber wastes take a long time to decay in the environment and when burnt (which is the usual method of disposal) in the open environment, create environmental pollution. Hence, it is essential that these wastes are used in some form for different applications. Palmyra fiber separations have been carried out for long years in southern parts of Tamil Nadu and few places in Andhra Pradesh. The fiber needed for this study was collected from Shri Arumugam Fiber Industries, Trinelveli, Tamil Nadu. In the present study, the above waste material is used in combination with chopped strand glass fiber mat in polyester resin to make hybrid composites. Detailed investigations on the use of this palmyra fiber waste as reinforcement and the effect of glass fiber weight fraction on the mechanical properties are carried out. Experimental Procedure Specimen preparation Composite plates were prepared by varying the content of the palmyra fibrous waste (pfw) in the matrix to study the reinforcement effect of fibrous waste. The fibrous material was spread uniformly by manual process and compressed by applying a load of 20 ton in a hydraulic compression machine to get a single mat of thickness about 5 mm. This mat was placed in a mould of mm, polyester resin (isophthalic roof light resin) mixed with accelerator (methyl ethyl ketone peroxide (MEKP)) and catalyst (cobalt naphthanate 2% concentration) of 1.5% ml was added in it, mixed properly and then the mould was closed. Composite plates were prepared with 30%, 38%, 45%, 50%, 58%, 65% and 70% by weight of the fibrous waste. Another set of composite specimens were prepared by sandwiching the fibrous wastes between chopped strand glass fiber mats. The weight fraction of the glass fiber was about 7% by weight. The palmyra fiber waste was sandwiched between the chopped strand glass fiber mats. To study the effect of the glass fiber content, composite plates were prepared by varying the content of both glass fiber and fibrous wastes by keeping the total weight of the fiber content constant. For sandwich type composites, the fiber waste material was compressed first, and then sandwiched between the glass fiber mats, and then placed in the mould. The liquid resin mixed with catalyst and accelerator was poured on the mat and the mold was closed. Four identical test specimens were prepared for each test and subjected to different tests. Results and Discussion Tensile properties The tensile strength of the composites depends upon the strength of the fiber, matrix, fiber matrix interaction and the fiber length. Rectangular specimens of 10 mm wide with gauge length as 50 mm were cut from the plate as per ASTMD standards and tested in Instron Universal Testing Machine with cross head speed of 2 mm/min. The results are shown in Figs 2 and 3. The neat resin without any reinforcement had 33 tensile strength and modulus of Incorporation of 30 wt% of fibrous material resulted in 14 tensile strength and modulus of 750. As the fiber content was increased the tensile strength and Fig. 1 Palmyra fiber wastes Fig. 2 Variation of tensile strength with pfw content

3 VELMURUGAN & MANIKANDAN: GLASS/PALMYRA FIBER COMPOSITES 565 Fig. 3 Variation of stress with displacement of pfw reinforcement in resin from 30% to 70% of loading and with 7% of glass fiber mat. Fig. 4 Variation of tensile modulus with pfw content and 7% glass fiber mat hybrid modulus values had also increased up to 58-65wt% and then dropped. From the tested results it was seen that the tensile strength decreased up to 38wt% and then showed slight increase for the composites containing fiber up to 58%. No improvement in tensile strength was observed due to the incorporation of fibrous waste. Generally, the tensile strength initially drops up to a certain amount of fiber and then increases. This minimum volume of fiber is known as the critical volume above which the fiber reinforces the matrix. When the amount of fibers is not enough to restrain the matrix, large stress will be developed at low strains and the distribution of these stresses will not be uniform. But, after the minimum volume the fibers are sufficient to restrain the matrix, the stress distribution will be uniform and therefore the fiber starts reinforcing the matrix. A similar trend was reported by Geethamma et al. 14 in their studies on short coir fiber natural rubber composites. Another reason for the low strength may be due to the presence of poor strength fibers of length ranging from 30 to 100 mm. The stress in the shorter fiber may never reach its breaking strength and they only act to deflect propagating matrix crack. In the case of long fibers, fiber failure may occur. Once the fiber breaks, then propagating micro crack can not be effectively deflected and hence results in lower strength. Thew 13 observed similar lower strength in bamboo fiber polyester composites. The variation of tensile modulus with fiber waste wt% is shown in Fig. 4, which shows that there is a decrease in tensile modulus. Fig. 5 Variation of flexural strength with pfw content and 7% glass fiber mat hybrid Flexural, shear, and impact properties Standard specimens of 10 mm 65 mm size were cut from the plate and tested in three point bending with a cross head speed of 2 mm/min as per ASTM D The results are shown in Fig. 5. The neat resin without fiber reinforcement had flexural strength of 40. With 58 wt% of fiber waste reinforcement the flexural strength was almost close to that of neat resin and with 65wt% reinforcement the strength increased by 5% than that of resin. The flexural strength of 30% by weight of fibrous waste reinforcement was 27 and it continuously increased with increase of fiber up to 65wt% to the value of 42.2 and decreased to for 70%wt of fiber as shown in Fig. 5. Four specimens on each

4 566 INDIAN J. ENG. MATER. SCI., DECEMBER 2005 wt% were tested and their average results were presented. Shear specimens with length as six times of its thickness were cut from the plates and short beanbending test was conducted as per ASTM standard D2344/D2344M-00e1. The result of the shear test is shown in Fig. 6. For the addition of 30% by weight of the fibrous waste was found to be dropped to 3.3 and then it was seen to have increased continuously due to fiber addition up to 58% by weight, remains constant up to 65% by weight and then dropping steeply to 1.86 for 70%wt of the fiber. The value decreased on further addition of waste material because of poor wetting by the resin. It was observed that the shear strength of polyester matrix was 4. The observed shear strength of 5.93 for 58% of fibrous waste was 43% more than that of the resin. The initial lowering of flexural and shear strength than that of resin is in accordance with the rule of mixture, i.e., when the volume fraction of the reinforcing fibers is lower than the critical quantity, the fibers acts as flaws in the matrix 2. Similar observation was noticed in several studies The impact property of a material is its capacity to absorb and dissipate energies under impact or shock loading. The impact energy observed by the composites was studied by pendulum type Izod impact testing machine of Karl Frank Gmbih 53568, on unnotched specimens as per ISO and the results are shown in Fig. 7. Considerable improvement on impact strength was observed (Fig. 7) by the incorporation of waste material in the polyester resin. 30% by the weight of the waste in the composites showed impact strength of 1.05 J/cm 2, which was twice the value of resin. The impact strength increased with the increase in the fiber content and reached maximum of 3.58 J/cm 2, which was about 8 times than that of the resin that had occurred for 65% of palmyra fiber waste as reinforcement. From this study it was observed that the wt% composites exhibited improved mechanical properties. The neat resin had very low impact resistance. Fiber reinforcement increased its impact strength significantly. The impact energy level of the composites depends upon several factors such as nature of the component, geometry, fiber arrangement and fiber matrix interface. Presence of fiber in the matrix requires high energy to initiate crack and hence there is increase in impact strength. The decrease in impact value at high fiber content may be due to the presence of too many fiber ends within the composites, which could cause crack initiation 1. Addition of 10 g of glass fiber, which accounts for 7% weight of total composites, improved the mechanical properties considerably. There was a marginal improvement in mechanical properties due to the addition of 10g of glass fiber with 30wt% fiber waste. Addition of 10 g (7% by weight) of glass fiber with 58wt% improved the tensile strength by 22 %, flexural strength by 122% and shear by 117% than that of neat resin. When the results were compared with the resin filled fibrous waste, there was an improvement of 71% in tensile, 114% in flexural, Fig. 6 Variation of shear strength with pfw content and 7% glass fiber mat hybrid Fig. 7 Variation of impact strength with pfw content and 7% glass fiber mat hybrid

5 VELMURUGAN & MANIKANDAN: GLASS/PALMYRA FIBER COMPOSITES % impact and 58% in shear. The results of tensile, flexural shear and impact test are shown in Figs 4-7. Reinforcement effect of glass fiber in sandwich construction To study the effect of glass fibers on mechanical properties, specimens were prepared with glass fiber alone by varying the fiber wt% and also sandwiching the waste fiber between glass fiber mats by varying both glass fiber and waste material content, keeping the total fiber content as 60% by weight. In the previous study it was observed that composites with 58-65wt% exhibited better mechanical properties. Hence, the total amount of waste material and glass fiber content was kept as 60% by weight for the present study. Tensile properties Standard tensile specimens were prepared according to the ASTMD and subjected to tensile loading in Instron Universal Testing Machine at crosshead speed of 2 mm/min. Four specimens were tested in each variety and the average values were considered. The tensile properties of the glass fiber composites are given in Table 1 in which the properties were found to increase with increased glass fiber content. This increase in strength was due to the presence of high strength glass fiber along with pfw in the matrix. The tensile strength and tensile modulus of glass fiber/palmyra fiber waste material sandwich composites are shown in Figs 8 and 9. Both the tensile strength and modulus values increased with increased glass fiber content. Composites with glass fiber of 11% by wt had tensile strength of 41.5 and modulus of , whereas composites containing 48% of fiber wastes and 10% glass fiber exhibited tensile strength, and modulus of 45.3 and 1175 Mpa, respectively. From the results it is clear that the improvement in tensile strength and modulus is due to the hybrid effect. From the tested specimen of the skin core sandwich construction, it was observed that at a low glass fiber content the core failed first followed by glass. Hence, a wider separation on core material was seen (Fig. 10). At high glass fiber content a similar crack on the core was observed but there was not much of a glass fiber breakage as was seen in the previous case Fig. 8 Variation of tensile and flexural strength of pfw/glass hybrids Fig. 9 Variation of tensile and flexural modulus with pfw/glass hybrids Table 1 Mechanical properties of glass fiber composites Glass fiber, wt % Tensile strength, Tensile modulus, Flexural strength, Flexural modulus, Shear strength, Impact strength, J/cm

6 568 INDIAN J. ENG. MATER. SCI., DECEMBER 2005 Fig. 10 Specimens showing the core failure under tensile loading Fig. 13 Variation of shear strength of pfw/glass hybrids Fig. 11 Figure showing the skin de-lamination under tensile loading Fig. 12 SEM picture of specimen subjected to uniaxial tension (a) with 60wt% Palmyra fiber waste, (b) with 48 wt % pfw and 10wt% glass (Fig. 11). In all the tested specimen the glass fiber delamination and pull out were observed. Fig. 12 shows SEM picture of the tensile specimens subjected to uniaxial tension. Fiber fracture and fiber pullout are seen on the fractured surface of the specimen. It is also observed that there is no significant elongation of the fiber and brittle mode of failure is seen (Fig. 12a). Fig. 12b shows the tensile fracture surface of the sandwich type hybrid composites reinforced with 48 wt% Palmyra fiber wastes and 10 wt% glass fiber. Glass fiber fracture is seen on the top and bottom layers and the Palmyra fiber fracture in the core. A good fiber matrix interface is also observed. The fracture surface shows a few resin rich pockets and fiber pullout in these resin rich pockets. Flexural, shear and impact properties Flexural specimens as per ASTM D were prepared and subjected to three point bending with the crosshead speed of 2 mm/min. Figs 8 and 9 showed the flexural strength and modulus of glass fiber/pfw hybrid composites. Flexural strength and modulus were seen to increase with the increase of glass fiber content. Composites with glass fiber of 22% by wt showed a flexural strength of 71 and modulus of Composites containing 48% fiber waste, 10% glass fiber and 42% resin showed a bending strength of and modulus of Hence, it was clear that the core material increased the bending properties. Specimens were cut from the plate with length equal to six times that of the thickness and subjected to shear loading. Fig. 13 shows the variation of shear

7 VELMURUGAN & MANIKANDAN: GLASS/PALMYRA FIBER COMPOSITES 569 Fig. 14 Variation of impact strength of pfw/glass hybrids Fig. 15 SEM picture of specimen subjected to impact load, (a) with 60wt% Palmyra fiber waste and (b) with 48wt% pfw and 10wt% glass strength as a function of relative wt% of glass fiber content (ratio of weight of glass fiber to the total fiber). Shear strength for 22wt% glass fiber composites was 13.6 and for the composites containing 48% of fiber waste and 10% glass fiber, it was 11.6 which was almost equal to 11wt% glass fiber polyester composites (12 ). From this experiment it is seen that the shear strength depended upon the bond strength between glass fiber, matrix, and the waste fiber core. The little reduction in shear value is due to the poor bonding between glass fiber and core material. Impact test was conducted as per ISO standard using Izod impact testing machine with 7.5 J hammer weight. Rectangular specimens of mm were cut from the plate and were subjected to impact testing. Fig. 14 shows the variation of impact strength of glass fiber skin and waste fiber core construction as a function of relative glass fiber content. Experimental observation shows that at low fiber content both core and glass fiber failures are observed. The impact strength of 11 wt% glass fiber composites is 2.97 J/cm 2 (Table 1) and for the hybrid composites, containing 10wt% of glass fiber it is 5.16 J/cm 2 (Fig. 13), Hence, the improvement in impact strength is about 90%. Fig. 15 shows the fracture surface of the impact tested specimens. Matrix fracture, crumbling of matrix, fiber fracture and weak interface in seen on the pfw composites (Fig. 15a). Fig. 15b shows the fracture surface of the sandwich type hybrid composites reinforced with 48 wt% Palmyra fiber wastes and 10wt% glass fibers. Glass fiber fracture is seen on the top and bottom layers and the Palmyra fiber and matrix fracture in the core. Conclusions Composite plates with the fibrous waste material content varying from 30 to 70% by weights were studied. Composites with wt% fiber waste had strength of 28 tensile, 42.2 flexural, 6 shear and 3.58 J/cm 2 impact. It was observed that the incorporation of pfw in the matrix imparted poor reinforcement effect in tensile, but there was an improvement in other mechanical properties such as shear, bending and impact. Sandwiching the 58wt% fibrous waste between glass fiber mats (7 wt%) improved the tensile, flexural, shear and impact properties. Composites with 7% by weight of glass fiber and 58 wt% improved the tensile strength by 22%, flexural strength by 122% and shear by 117% than that of neat resin which had tensile strength 32, shear strength 4 and impact strength 0.1 J/cm 2. Increasing the glass fiber content in the Palmyra fiber waste/glass hybrid composites in polyester matrix resulted in composites with improved mechanical properties. Moisture absorption studies on pfw/glass fiber polyester composites were carried out separately and observed that the composite absorbed 9.23% of moisture in 166 h, 5.57% of moisture in 154 h and 3.5% of moisture in 175 h for the composites with 50% pfw/10% glass fiber, 40% pfw/20% glass fiber and 30% pfw/30% glass fiber respectively. These Palmyra fiber waste and glass

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