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Investigation of flexural and water absorption behaviour of epoxy hybrid composites.


Now-a day's reinforced composites are used in variety of structural applications such as automobile, spacecraft, aircraft & buildings etc. The performance of polymer composites depends not only on the selection of components but also depends upon the interface between them. Natural fibres divided into two categories. They are plant fiber and animal fiber. Natural fibres play an important role in developing high performing biodegradable 'green' composites which will be a key material to solve the present environmental problems. Natural fibres offer many attractive technical and environmental qualities when used as reinforcements in polymer composites. The mechanical properties of natural fibre composites are much lower than those of the synthetic fibre composites. In order to improve the reactive hydroxyl groups and the rough surface for adhesion with polymeric materials, plant fibres need to undergo physical and/or chemical treatment to modify the surface and structure. Though the synthetic fibres have very good mechanical properties, their disadvantage is difficult recycling. Another advantage of synthetic fibre is their moisture repellence, whereas poor resistance to moisture absorption made the use of natural fibre reinforced composites less attractive. Hence to avoid the advantage of natural and synthetic fibres, they can be combined in the resin matrix to produce hybrid composites that take full advantage of the best properties of the constituents, A Review about natural and manmade cellulose fibre reinforced plastics and possible applications. Magurno. et al [2] studied the oil replacement of glass mats with hemp mats in a typical fitting used in pipeline of chemical plants. Saheb. et al [3] studied the natural fibre composites with special reference to the type of fibres, matrix polymers, treatment of fibres and fibre matrix interface. Kalia et al [4] studied the Pre-treatment of natural fibres and their application as reinforcing material in polymer composite and an overall review and study of various natural fibres, Flavio de Andrade Silva et al. [5] studied the Sisal fibre composite reinforced with long unidirectional fibres. Cicala, Cristaldi et. Al [6] The physical and mechanical behaviour were studied and scanning electron microscope is used for investigating the microstructure. Vijayaramnath et. al [7] investigated the mechanical behaviour of Abaca-Jute hybrid composites and found that hybrid composites has better property than mono fiber composites were studied. The study of banana fibre reinforced epoxy composite and their mechanical properties are evaluated. Composite samples with different fibre volume fraction are prepared by hand layup method. Venkateshwaran et al [8] studied the tensile, flexural, impact and water absorption test were carried out using banana epoxy composite material. Also sisal fibre is added additionally and properties were reviewed. Muthuvel et al [9] Studied the process of hybridisation of glass fibres with natural fibres for applications of aerospace and natural industries. Harish, S., et al [10] Development of Colr composites and their mechanical properties are evaluated. SEM analysis is done on fractured surfaces for qualitative analysis and their interfacial properties are compared with glass fibre epoxy. Vijaya Ramnath [16-19] investigated the mechanical behaviour of hybrid campsites using banana, jute, abaca and flax, concluded that hybrid composite has better mechanical properties. Also suggested that fiber orientation having impact on finer strength. Hence it is concluded that hybrid composites offers a attractive mode for fabricating products with reduced cost, high specific modulus, strength, corrosion resistance and in many cases excellent thermal stability.


Sisal fibres for this work are collected from local sources. Epoxy glass fiber and hardener are purchased from covai seenu company Pvt Ltd. The natural fibres are subjected to alkali treatment. For that, the alkali tabulates are purchased from scientific company, erode. Sisal and glass fibres are shown in the fig 1 & 2.

3. Methods And Processing Of Fibres:

3.1. Fibre Treatment:

Treating of fibres comprises two times bleaching. Here the sisal fibres are chopped up to 5mm and it is subjected to alkali treatment for two hours. After the treatment the fibre was washed in water and allowed to dry in atmospheric temperature up to 38[degrees]C.



4. Preparation Of Hybrid Composites:

Different combinations of composites such as (50:50, 45:55, 40:60, 30:70) were selected to do hybrid composites of sisal/glass/epoxy laminates in the form of chopped fibres. Chopped sisal /glass are mixed with the epoxy resin based upon the weight ratio. Hand lay up technique was used to prepare the hybrid composites as shown in the fig 3. The mechanical properties of the composites are improved due to the addition of glass fibre along with sisal fibre in the matrix. The glass fibre skin-sisal fibre core construction exhibits better mechanical properties than dispersed construction.


5. Tests:

In this work, flexural and water absorption characteristics are studied.

5.1. Flexural Test:

Flexural strength is one of the important mechanical properties of the composites. For a composite to be used as the structural material it must possess higher flexural strength. The flexural strength and modulus of sisal / glass hybrid fibre reinforced composites were calculated. It is clearly seen from the table 2 that flexural strength and flexural modulus increases with glass fibre content. From the table, it is observed that the flexural properties of the sisal fibre reinforced composites were considerably lower than those for the glass fibre reinforced composites and hence, as the glass fibre is added to the sisal in the hybrid composite, the properties were improved.

Model calculation:

Flexural strength ([??]UF) = 3PmaxL / 2bh2 =57.76 Mpa

Flexural Modulus (EF) = mL3 / 4bh3 =7.6Mpa

5.2. Moisture Absorption Test:

The effect of water absorption on glass-sisal fibbers reinforced hybrid composites were investigated in accordance with BS EN ISO 62: 1999. The specimens were dried in an oven at 500[degrees]C and then they were allowed to cool till they have reached the room temperature. The specimens were weighed to an accuracy of 0.1 mg. Water absorption tests were conducted by immersing the composite specimens in distilled water in plastic tub at room temperature for different time durations. Once in 24 hours, the specimens were taken out from the water and all surface water was removed with a clean dry cloth and the specimens were reweighed to the nearest 0.1 mg. The specimens were weighed regularly from 24 hours to 672 hours exposure, at an interval of 24 hours. The moisture absorption was calculated by the weight difference. The percentage weight gain of the samples was measured at different time intervals. Similarly, the specimens were immersed in water at 100[degrees]C to determine water absorption at a higher temperature. For this test, the specimens were placed in a container of boiling water. After 30 min of immersion, the specimens were removed from the boiling water, cooled in water for 15 min at room temperature then removed and weighed to the nearest 0.1 mg. The weight of the samples was measured at different time intervals up to 40 h of exposure until the water content reached saturation. The moisture absorption was calculated by the weight difference.

Weight of water content = (Wf-Wi)

% of water absorption = (Wf-Wi/Wi) x 100

Dry weight of the sample (Wi) = 3.5 gm

Weight of wet sample (Wf) = 3.94 gm

Weight of the water content = 3.94 - 3.5 =0.4 gm


6.1 Flexural test results:

For this test the specimen is prepared for ASTM: is 3.2mm x 12.7mm x 125mm (0.125" x 0.5" x 5.0") and for ISO is 10mm x 4mm x 80mm. The result of flexural test is shown in Table 2 and in figure 4. From the table it is clear that flexural strength with increase in fiber content.


6.2. Moisture Absorption Test results:

Test specimens are immersed in distilled water at a specified temperature for 24 hours. Testing is most commonly done at 23[degrees]C (73.4[degrees]F).




The glass fibber-sisal fibber core construction exhibits better mechanical properties than dispersed construction. Moisture absorption studies were conducted and the results were presented as a function of square root of time. Addition of glass fibber with sisal fibber in the matrix decreases the moisture absorption of the composites were studied.


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(1) G. Yuvaraj, (2) Dr. B. Vijaya Ramnath, (3) G. Hemanth raagavendiran, (4) R. Karthikraja

(1) Sairam Engineering College, Chennai, India.

(2) Sairam Engineering College, Chennai, India.

(3) Sairam Engineering College, Chennai, India.

(4) Sairam Engineering College, Chennai, India.

Received 25 April 2016; Accepted 28 May 2016; Available 5 June 2016

Address For Correspondence:

G. Yuvaraj, Sairam Engineering College, Chennai, India.

Table 1: properties of fibres

fiber type   density   tensile    E         Elongation   Moisture
             g/cc      strength   Modulus   at break %   Absorption
                       (MPa)      (GPa)                  (%)

E-Glass      2.54      1051       73        3
Sisal        1.42      700        35        2.9          11

Table 2: Flexural test results

Sample    Weight          Flexural    Flexural
          percentage of   strength    Modulus
          Sisal & Glass   (Mpa)       (Gpa)

S1        50:50           59.76       7.6
S2        45:55           56.15       7.38
S3        40:60           53.84       6.92
S4        30:70           53.10       6.21
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Author:Yuvaraj, G.; Ramnath, B. Vijaya; Raagavendiran, G. Hemanth; Karthikraja, R.
Publication:Advances in Natural and Applied Sciences
Date:May 30, 2016
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