Mechanical Properties of Short, Natural Fiber

Mechanical Properties of Short, Natural Fiber Hildegardia populifolia-reinforced Styrenated Polyester Composites A. VARADA RAJULU,* G. BABU RAO AND L. GANGA DEVI Department of Polymer Science and Technology Sri Krishnadevaraya University Anantapur 515 003, India SIDDA RAMAIAH, D. SHUBHA PRADA, K. SHRIKANT BHAT AND R. SHYLASHREE Department of Polymer Science and Technology S.J. College of Engineering Mysore 570 006, India ABSTRACT: Short, natural fibers belonging to the species Hildegardia populifolia were reinforced in styrenated polyester matrix. The mechanical properties of these polymer composites such as tensile modulus, compression strength at first deformation, flexural modulus, and izod impact strength were determined. The effect of alkaline treatment of the natural fiber on the mechanical properties of the composites has been reported. The fractured surfaces of these composites were investigated by scanning electron microscopic technique (SEM) to investigate the interfacial bonding between matrix and the reinforcement. The present work has been carried out in order to make partially biodegradable and eco-friendly composites. KEY WORDS: polymer composite, styrenated polyester, natural fiber, Hildegardia populifolia, mechanical properties, morphology, biodegradable composites.

INTRODUCTION polymer composites is increasing day by day because of their outstanding properties. The performance of a polymer composite depends not only on the selection of their components, but also on the interface between them. To meet the specific needs, some times it is necessary to modify the matrix and the reinforcement. In order to make the composites eco-friendly, natural fibers/fabrics have been used as the reinforcement [1–10]. The main aim of this study is to make environmental friendly composites. In the present paper the authors cross-linked the polyester resin using styrene and the resulting system was used as a matrix material. They also used the biodegradable natural fiber Hildegardia populifolia as the reinforcement material. The mechanical properties of the composites are studied. The effect of alkali treatment of the fibers has also been studied.

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Journal of REINFORCED PLASTICS

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COMPOSITES, Vol. 24, No. 4/2005

0731-6844/05/04 0423–6 $10.00/0 DOI: 10.1177/0731684405044896 ß 2005 Sage Publications

Downloaded from jrp.sagepub.com at UNISA Univ of South Africa on October 27, 2015

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EXPERIMENTAL Materials In the present work, polyester resin (Ecmos Corp. Ltd, Hyderabad), cobalt naphthanate as accelerator, methyl ethyl ketone peroxide as catalyst are used as matrix components. The styrene monomer is used as a cross-linking agent. The natural fabric Hildegardia populifolia with a thickness of 0.18 mm is used as the reinforcement. In order to protect the tree, the fabric is separated from its branches only as described elsewhere [11]. The extracted fabric is washed thoroughly with distilled water and allowed to dry in the Sun for seven days. This fabric is then cut to a length of 1–1.5 cm. These fibers are dried in the vacuum oven for one day prior to using them as reinforcement. Some quantity of the fiber is treated with 2% aqueous NaOH solution for half an hour to remove the soluble hemicellulose and lignin. After this, the fibers are washed with water, dried and used as the reinforcement. Sample Preparation The composite is fabricated in a glass mold of dimensions 150 30 3 mm. The mold cavity is coated with a thin layer of aqueous solution of polyvinyl alcohol, which acts as a good releasing agent. The polyester resin and styrene are mixed together. To this accelerator, cobalt napthanate and catalyst methyl ethyl ketone peroxide are mixed. The uncured matrix mixture is poured into the glass mold up to 1/4th of its volume. Over this the short cut fibers are sprinkled; to which another layer of matrix is poured. This is done till the complete mold is filled. The composite is made at a temperature of about 40 C. To ensure complete curing the composite and matrix sheets are post-cured at 65 C for 8 h. The same is repeated for reinforcement with alkali-treated fibers. Tensile Test The tensile modulus is measured using Instron UTM model: 1175 (UK). The test specimens with dimensions 100 15 3 mm are cut and used. The test is conducted at a speed of 2 mm/min. Flexural Test The flexural modulus at break of composites is measured using Instron UTM model: 4302 (UK). The test specimens with dimensions 120 12.5 3 mm are used for testing. The three-point loading system was used. The speed of testing was 0.01 in./in./min. Compression Test The compressive strength at first deformation is measured using Microtek tensometer provided with compression cage. The maximum load applied in the present work is 2000 kg. The test specimen dimensions were 10 10 10 mm.


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Impact Strength The impact strength at break is determined using Izod Impact Tester (M/s. PSI–New Delhi, India). The dimensions of the specimen are 600 127 127 mm. This is measured directly in Joules. The impact strength is calculated by dividing the values obtained by the thickness of the specimen. For each test, ten samples are used and the average value is reported. Morphology of Composite For studying the interfacial bonding between the matrix and the reinforcement, the composite is tested by scanning electron microscopic technique SEM (JEOL JSM 840 (JAPAN)). The samples are brittle-fractured before testing by dipping in liquid nitrogen. The composite is gold-coated before subjecting it to SEM analysis. RESULTS AND ANALYSIS The tensile modulus, flexural modulus, compressive strength at first deformation, and impact strength of short, natural fibers Hildegardia populifolia-reinforced styrenated polyester composites are presented in Table 1. In this table, these values for the composites having untreated and alkali-treated fibers are included. For comparison, these values for the matrix are also presented in the same table. From the table, it is evident that the abovementioned mechanical properties are higher for the composites over those of the matrix, indicating good reinforcement by the natural fibers. The tensile modulus of the composites with untreated and alkali-treated fibers increased over that of the matrix by 11.8 and 15.6% respectively. It is also observed that the alkali treatment of the fibers enhanced the tensile modulus by 3.5%. Varada Rajulu et al. [12] have already reported that the surface of these fibers became rough on alkali treatment due to the elimination of hemicellulose and soluble lignin. The cleared micro-pores may thus facilitate good mechanical bonding between the fibers and the matrix. A similar trend was also observed in the compressive and flexural properties. The compressive strength of the composites with untreated and alkali-treated fibers increased over that of the matrix by 9.9 and 18.3% respectively. The alkali treatment of the fibers enhanced the compressive strength by 7.5%. The flexural modulus of the composites with untreated and alkali-treated fibers increased over that of the matrix by 4.6 and 6.9% respectively. Further, the alkali treatment of the fibers marginally enhanced the flexural modulus of the composites by 1.8%. The impact strength of composites with untreated and alkali-treated fibers is increased over that of the matrix by 75 and 51.5% respectively. However, by alkali treatment of the Table 1. Some mechanical properties of short, natural fiber Hildegardia populifolia–polyester composites.

Sample Matrix Composite with untreated fibers Composite with alkali-treated fibers

Tensile Modulus (GPa)

Compressive Strength at First Deformation (MPa)

Flexural Modulus (GPa)

Impact Strength (J/m)

5.14 5.78 5.97

104.31 114.73 123.36

4.3 4.5 4.6

26.0 45.6 39.4


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fibers, the impact strength of the composites decreased by 13.6%. Though the bonding between the matrix and the fibers is expected to increase by the removal of hemicellulose, in the present case the impact strength is found to decrease marginally. The elimination of the soluble lignin may be responsible for the slight decrease in this value. To probe the bonding between the matrix and the fibers the scanning electron micrographs of brittle-fractured composites with untreated and alkali-treated fibers are presented in Figures 1 and 2 respectively. When the untreated fibers were reinforced in the matrix, slight fiber pull out is observed from the micrographs. At higher magnification a

(a)

(b) Figure 1. Scanning electron micrographs of brittle-fractured composites of untreated short Hildegardia populifolia fibers–styrenated polyester at two magnifications – (a) 350; (b) 1200.


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(a)

(b) Figure 2. Scanning electron micrographs of brittle-fractured composites of alkali-treated short Hildegardia populifolia fibers–styrenated polyester at two magnifications – (a) 1000; (b) 1200.

thin layer of matrix skin formation is also observed. This may be due to the polar groups present in both the matrix and the cellulose fiber. However when the alkali-treated fibers were reinforced, the micrographs, (Figure 2) reveal better bonding between the matrix and the fibers. At higher magnification the micrographs reveal a thick layer of matrix skin formation on the fibers. The roughening of the surface and the clearing of the micro-pores in the fibers by alkali treatment may be responsible for such an observation.


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CONCLUSIONS The mechanical properties of the styrenated polyester matrix are improved by the short, natural fibers belonging to the species Hildegardia populifolia. Alkali treatment of the fibers further improved the mechanical properties. The microscopic investigation of the brittle-fractured composite samples revealed enhanced bonding between the matrix and the fibers. ACKNOWLEDGMENTS The authors (AVR and GBR) are thankful to UGC, India for the award of a Major Research Project. REFERENCES 1. Spidler, M., Pateman, R. and Hills, P.R. (1973). Composites, 4: 246. 2. Chand, N. and Rohatgi, P.K. (1987). Polymer, 23: 249. 3. Satyanarayana, K.G., Sukumaran, K., Kulakarni, A.G., Pillai, S.G.K. and Rohatgi, P.K. (1986). Composites, 17: 329. 4. Varma, K.K., Anantha, S., Krishnan, R. and Krishnamoorthy, S. (1989). Composites, 20: 383. 5. Jinda, U.C. (1986). J. Comp. Mater., 20: 19. 6. Madha, M.R., Raman, S., Pavithran, C., Prasad, S.V. and Rohatgi, P.K. (1983). J. Pure Appl. Ultrason., 5: 39. 7. Misra, S., Misra, M., Nayak, S.K. and Mohanty, A.K. (1998). Prof. National Seminar on Polymer Research in Academy, Industry and R&D Organizations, Calcutta, 42. 8. Hari, K.R,. Kumar Kurivilla and Thomas, S. (1999). J. Reinforced Plast. Com., 18: 290. 9. Chand, N. and Rohatgi, P.K. (1994). Natural Fibers and their Composites, Periodical Experts Book Agency, New Delhi. 10. Freddi, G., Tsukda, M. and Shiozak, H. (1999). J. Appl. Polym. Sci., 71: 1557. 11. Varada Rajulu, A., Li, X.H., Babu Rao, G., Ganga Devi, L. and Meng, Y.Z. (2004). J. Rein Plast Composites, 23: 217. 12. Varada Rajulu, A., Meng, Y.Z., Babu Rao, G., Ganga Devi, L., Mohan Raju, K. and Rama Krishna, Reddy, R. (2003). J. Appl. Polymer. Sci., 90: 1604.
