Review ArticleABSTRACT
Use of natural fiber as reinforcement is a burgeoning field of research because of the ease of procuring raw materials, bio-degradable and environment friendly nature along with mechanical properties of the resulting composites that are comparable to synthetic fiber-reinforced composites. Areca owing to these very reasons along with low cost, light-weight further advocated by its tensile strength has pervaded the field of composite manufacturing. Different natural fibers have been used by many researchers for the development of bio-composites, but areca leaf fibers as a feasible fiber have seldom been researched or spoken about. The development and study of mechanical behavior of a natural fiber reinforced epoxy composite of areca fiber with different configuration of areca fiber orientation has been discussed herein. The factors considered for areca fibers have been young’s modulus, specific modulus, tensile strength, and specific modulus, and are found to be greater than those for the popular coir fiber. Another important aspect considered is the sheath fiber angle of orientation of the composite.
Keywords: Composites; Natural Fibers; Fiber Orientation; Mechanical Properties; Experimental Analysis
Introduction
Since the past decade there has been a steady increase in research for natural fiber reinforced composites because of its potential to replace synthetic fiber reinforced plastics at lower cost with improved sustainability in various engineering applications and industries. The age of composites began when there was a need for high strength to weight ratio in components that demanded high performance and efficiency, which invited the developments of various polymer matrix composites with a variety of fiber reinforcements such as carbon fiber, glass fibers, aramid, natural fibers, hybrid, etc. Considering the factor of environmentally friendly materials and the need to produce various sustainable engineering and industry-oriented components, natural fiber composites play an important role. Natural fibers [1] play an inevitable role as a reinforcement agent because of their good mechanical properties and bio-degradable nature [2] and it is found abundantly all over the world. Many natural fibers like jute, kenaf, sisal, hemp, bamboo, areca, pineapple [3], banana [4] and coir hold the position of key materials in many areas of research because of their availability and cost effectiveness to develop an inexpensive reinforcing material. Use of different natural fibers as a reinforcement agent in composite materials, has given us an array of properties that can be used advantageously for various applications. It has been found that natural fiber reinforced composites possess resistance to electricity, good thermal insulating [5] property and also provide good corrosion resistance. The past research works on volume fraction shows that the tensile strength of natural-polymer composites increases with increase in volume fraction of the fiber [6]. It has been shown in the study of the tensile characteristic of the untreated areca sheath composite that the longer the fiber length more is the strength of the composite [6]. Considering the fact that chemical treatment of the fibers [7] will bring out the changes in its mechanical properties it is found that by alkali treatment of the areca nut fiber shows enhanced mechanical strength than the untreated fibers [8]. Curing time of the composite also plays a vital role in determining the full potential strength of the composite.
From the work done by Srinivasa Chikkol Venkateshappa [8] it is evident that the strength of the composite increases as the curing time of the composite increases. Other mechanical properties such as impact strength, hardness and flexural strength of the areca fiber composite were studied in which the influence of volume fraction [9], post curing time and alkali treatment for effective bonding were considered. From the research work by SC Venkateshappa it is found that the flexural strength increases with increase in fiber loading percentage and comparing to the untreated fiber, there has been a significant increase in flexural strength for the alkali treated fibers [10,11]. The results drawn from the research work done by C.V. Srinivasa is it found that the impact strength increased with the post curing time [12] and it is also shown as the curing time increased the alkali treated composites became brittle [12]. This research is focused on the tensile property of the non-chemically treated areca fiber sheaths which is water soaked, hot pressed and compressed into the thickness of 2.5 mm to 3 mm, which is commonly available in India as areca fiber plates and using this as reinforcing agent in epoxy polymer composite to study its tensile properties and effects of the different combinations of the orientation angles of the fiber which influences the tensile property of the composite (Figure 1).
Figure 1.
Fiber Properties
As the areca sheath fibers are initially obtained in an anhydrous state it is mainly composed of 66.08% of α- cellulose, 7.40% of hemicellulose and 19.59% of lignin [13] which mainly contributes to the bond strength. In addition, it also comprises of minor constituents such as pectic matters and fatty and waxy matters that contributes in a relatively low matter to the bond strength, it is resistive to electric discharges and can be degraded with the action of fungus and bacteria, thus making the areca sheath fiber a biodegradable material. The properties of the fiber sheath that was obtained due to pure tensile failure have been determined. Sheath as a whole comprises of infinite number of fibers, it is evident from the results that the strength taken along the direction of the fiber will be more than the strength taken along the normal direction of the fiber. Taking the density of the sheath, the specific modulus young’s modulus and the specific strength of the sheath fiber are calculated accordingly.
Areca Fiber Reinforced Epoxy Polymer Composite
In making of areca sheath reinforced epoxy composite, the volume fraction of the fiber, chemical treatment of the fiber and the curing time for the composite plays an important role. In this paper the volume fraction of fiber to composite is 75% and it is kept constant through the whole process, no chemical treatment is done to the areca sheaths and the curing time for the preparation of each individual specimen is kept constant. The composite specimen was made according to the tensile standard ASTM D638 in which five composites were prepared. Within every composite the angular orientation of the sheath fiber is changed with respect to the x-coordinate, within the fiber layers of the composite [14]. The Young’s modulus results for various combinations of different orientation of fiber layers within a composite. The data from the obtained results shows that the composite which had the sheath fiber orientation 90°-90°-90° has the highest young’s modulus value. Comparing the fiber orientations 90°-90°-90° and 90°-0°- 90°, young’s modulus value of 90°-0°-90° composite decreased because of the zero-degree orientation of the fiber which was less effective in taking up the force applied on the composite. Comparing the fiber orientation 45°-90°-45° and 45°-0°-45°, even though the inter-angular difference between the adjacent layer is 45°, the 90° orientation of the fiber sheath increased the young’s modulus of the overall composite [15].
As the fiber angle approaches zero the young’s modulus decreased because comparing to the individual fiber properties for the 0° oriented fiber, as the load is applied along the perpendicular direction to the fiber orientation, transverse young’s modulus comes into the play with yields a lesser young’s modulus value than the longitudinal one. Comparing the models 45°-0°-45° and 30°- 60°-30° the young’s modulus value is the least from the model 30°- 60°-30°, as the majority fiber sheath angle is two layers of 30° in this case and it holds a least angular difference the orientation and the x-axis its local strength when resolved to the global strength, it’s strength is much lesser when compared the 90° oriented fiber’s global stress. So it is observed from this that the angle of orientation of the reinforcing fiber plays an important role in determining the overall Young’s modulus of the composite in which the global strength of the composite increased as the angular orientation with reference to the x-axis increased. As the load increased, the first failure occurred in the fiber sheath that had less fiber angle orientation with respect to the x-axis, it was followed by the corresponding fiber sheath that had minimum angle of orientation [7,9].
Conclusion
The Young’s modulus and the tensile strength of hot pressed, non-chemical treated areca sheath fiber was evaluated experimentally and its specific modulus was found to be 55.5% more than that of coir and 39.79% greater than that of medium density fiber board which is an engineered wood product commonly used for domestic appliances. Composites with different orientation in the sheath fiber angle were prepared and tensile test was performed, in which it was observed that the composite that had the sheath fiber orientation as 90°-90°-90° had the highest strength and its young’s modulus was estimated to be 1.798 GPa. The maximum elongation for the composite before the first failure of the specimen occurred was evaluated. Composite with sheath fiber orientation of 90°-90°-90° had the highest elongation of about 11.6% of its original length. As the sheath fiber angle of orientation in a composite decreased, there was a significant reduction in the young’s modulus value, the extension of the total composite also reduced. Composite that had least fiber orientation witnesses less longitudinal young’s modulus and it failed easily under loading and this effect was also felt in a significant manner in the composite. The composite that had 90°-90°-90° orientation of fiber gave the advantage to withstand higher strength when the load was applied only along the longitudinal direction of the sample. If the loading is of bidirectional in nature the composite with fiber orientation 45°- 90°-45° can be used as the optimum one because the 45° oriented fiber enhances the composite strength when load is applied in the inclined direction with reference to the longitudinal axis.
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