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Extraction and tensile properties of natural fibers: Vakka, date and bamboo
Composite Structures 77 (2007) 288–295 www.elsevier.com/locate/compstruct
Extraction and tensile properties of natural fibers: Vakka, date and bamboo K. Murali Mohan Rao a
a,*
, K. Mohana Rao
b
Department of Mechanical Engineering, V.R. Siddhartha Engineering College, Vijayawada 520 007, AP, India b P.V.P. Siddhartha Institute of Technology, Vijayawada 520 007, AP, India Available online 7 October 2005
Abstract This paper aims at introducing new natural fibers used as fillers in a polymeric matrix enabling production of economical and lightweight composites for load carrying structures. An investigation of the extraction procedures of vakka (Roystonea regia), date and bamboo fibers has been undertaken. The cross-sectional shape, the density and tensile properties of these fibers, along with established fibers like sisal, banana, coconut and palm, are determined experimentally under similar conditions and compared. The fibers introduced in the present study could be used as an effective reinforcement for making composites, which have an added advantage of being lightweight. 2005 Elsevier Ltd. All rights reserved. Keywords: Fibers; Mechanical properties; Natural fibers
1. Introduction Vegetable fiber is one of the varieties of natural fibers obtained from stems, leaves, roots, fruits and seeds of plants. Vegetation is exploited for its ability to yield fibers directly from wild or natural forms. However, from commercial and technological points of view, cotton, kenaf, sisal, flax, palm, coir, arecanut and banana fibers acquire utmost significance, since reinforced plastics, strings, cords, cables, ropes, mats, brushes, hats, baskets and fancy articles such as bags are manufactured with those fibers. All the ligno-cellulosic based natural fibers consist of cellulose micro-fibrils in an amorphous matrix of lignin and hemi-cellulose. These fibers consist of several fibrils, which run all along the length of the fiber: each fibril exhibits a complex layered structure made up of a thin *
Corresponding author. Tel.: +91 866 2583179; fax: +91 866 2582672. E-mail address: kmmr55@rediffmail.com (K.M.M Rao). 0263-8223/$ - see front matter 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.compstruct.2005.07.023
primary wall encircling a thicker secondary layer and is similar to that of a single wood fiber. The fibers considered in the present analysis are treated as single units at the macro level as shown in Fig. 1. Roystonea regia (Oreodoxa regia), popularly known as Royal palm which is locally called vakka, a native of West Indies and neighbouring parts of tropical America, has been cultivated in India [1]. An attempt to explore this tree for its fiber has not been taken up yet. In the present investigation, its fibers have been identified and found to be a potential reinforcement. The date, botanically known as Phoenix sylvestris [2], the new name of which is Arecaceae, belongs to Palmaceae family. The fiber is picked from the dried leaves called leaf stalk fibers referred to hereafter as date (L) or from the netted structure called amplexicaul fiber referred to hereafter as date (A). The netted structure is the sheathing leaf base, which surrounds the stem. As far as the characteristics are concerned, bamboos are tall, perennial, arborescent grasses, belonging to the Bambusae, a tribe under Graminae. Earlier, the fracture
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289
Fig. 1. Cross-sections of various fibers.
properties of bamboo culms and nodes have been studied [3]. Bamboo is a typical natural composite material, and the fibers are distributed densely in the outer surface region, and sparsely in the inner surface region. It is evident that the fracture toughness of the bamboo culm depends on the volume fraction of fibers. The bamboo has multi-nodes and functionally gradient structure, macroscopically as well as microscopically [4–10]. The effect of the absorption of water on mechanical properties of bamboo has also been studied [11]. Okubo et al. [12] undertook an in-depth analysis into the mechanical properties of polypropylene composites using bamboo fiber, extracted by steam explosion technique. The tensile strength and modulus of the polypropylene based composites increase about 15% and 30%, respectively due to better impregnation and reduction of the number of voids, compared to those of fibers that were mechanically extracted. Thwe and Liao [13] examined the effect of fiber content, fiber length, bamboo to glass fiber ratio, and coupling agent (maleic anhydride polypropylene) on tensile and flexural properties of bamboo fiber reinforced polypropylene (BFRP) and bamboo-glass fiber reinforced polypropylene hybrid composite (BGRP). It was shown that hybridization with synthetic fibers is a viable approach for enhancing the mechanical properties and durability of natural fiber composites. Thwe and Liao [14] carried out an extensive survey on the durability of BFRP and BGRP subjected to hygrothermal ageing and fatigue behaviour under cyclic tensile load. The authors concluded that BGRP shows a better resistance to environmental ageing than BFRP. An unreinforced polypropylene has a longer fatigue life
than BFRP and BGRP composites at the specified cyclic load levels. In comparison to BFRP, the BGRP that is a hybrid composite presents a better fatigue resistance. An analysis by Ismail et al. [15] on the effect of a silane coupling agent (Si69) on curing characteristics and mechanical properties of bamboo fiber filled natural rubber composites highlighted various aspects of this phenomenon. It was concluded that the presence of a silane coupling agent, Si69 improves the adhesion between the fiber and rubber matrix and consequently enhances the tensile strength, tear strength, hardness and tensile modulus. Ismail et al. [16] examined the curing characteristics and mechanical properties of bamboo fiber reinforced natural rubber composites, as a function of fiber loading, and phenol formaldehyde and amethylenetetramine bonding agents. It was concluded that adhesion between the bamboo fiber and natural rubber can be enhanced by the use of bonding agents. As a result, the tensile modulus and hardness of composites increase with increasing filler loading and the presence of bonding agents. Yao and Li [17] carried out a thorough investigation into the preparation and flexural properties of bamboo fiber reinforced mortar laminates. The laminate was a sandwich plate combined with reinforced bamboo plate and extruded PVA fiber reinforced mortar sheet. The results of the investigation show that the flexural strength values can be improved to greater than 90 MPa for laminates with reformed bamboo plate on the bottom, which formed a tension layer and the fiber-reinforced mortar sheet on the top that acts as compressive layer. Among the well-known natural fibers (jute, coir, straw, banana, etc.), bamboo has low density and high
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mechanical strength. The specific tensile strength and specific gravity of bamboo are considerably less than those of glass fibers. However, cost considerations make bamboo an attractive fiber for reinforcement. The present work provides extraction procedures for vakka, date and bamboo fibers. Date fiber is extracted from leaf stalks and amplexicaul. The bamboo fiber is extracted by retting and manual extraction, and chemical extraction procedures. The chemical and mechanical extraction procedures of bamboo are referred to here as bamboo (C) and bamboo (M), respectively. The crosssectional shapes of the fibers are investigated and circular cross-section fibers are identified for tensile testing of fibers. The picnometric procedure has been employed for determining the densities of various fibers. The tensile properties of vakka, date and bamboo are experimentally determined along with a reinvestigation of sisal, banana, palm and coconut fibers. The tensile properties of vakka, date and bamboo fibers are compared with those of the established fibers like sisal, banana, palm and coconut.
2.3. Date (A) The fiber is collected from amplexicaul, the sheathing leaf base, which surrounds the stem. It has a netted in structure, which is covered by soft or ground tissues. The amplexicaul is carefully collected from the tree. It is dried in shade at room temperature for a period of two days in order to remove any excess moisture content. The pulp (parenchyma) which is present on the individual fiber is removed by combing. Finally, the fiber is scraped to remove the pulp completely. 2.4. Bamboo (M)
Sisal, banana, coconut and palm fibers are collected from various local sources, and vakka, date (L), date (A), bamboo (C) and bamboo (M) fibers are extracted.
The node portions and very thin layer of exodermis (bark) of the bamboo are removed and the rest of the hollow cylindrical portion of culm is taken for extracting the fiber. The cylindrical portion of culm is peeled in the longitudinal direction to make strips of 0.5–1.5 mm thick and about 10 mm width. The strips are bundled and are kept in water for three days in order to soften them. After removing these strips from the water, they are beaten gently in order to loosen and to separate the fiber. The resulting fiber bundle is scrapped with sharp edged knife and combed. The process of combing and scrapping is repeated until individual fibers are separated.
2.1. Vakka
2.5. Bamboo (C)
The source of this fiber is the foliage of the tree, which falls on to the ground, when it ripens. It contains leaves with their stem in the form of a sheath. The sheath is separated from leaves and leaf stem and dried for two to three days in shade. It is then immersed in a water-retting tank for 15 days. The sheath contains layers of fiber throughout its thickness. In the first 15 days, the top layers on either side of the sheath loosen. Then, these layers are removed, washed and immersed in another water-retting tank for three more days. Later, they are removed, hand rubbed and rinsed in sufficient water. The water retting process takes 18–25 days to extract fibers completely. The fiber extraction is simple and economical, and requires no other process, since, the gums present in the sheath dissolve in water completely.
The manually decorticated bamboo fibrous strips are dried off in the sun. These strips of fiber removed from the culms contain tissues and gums. After decorticating, the dry fiber is extracted by means of a chemical process of decomposition called degumming, in which the gummy materials and the pectin are removed. The method of degumming designed by Gangstad et al. cited by Maiti [18] has been taken as a basis for chemical extraction. The chemical extraction process yields about 33% of fiber on weight basis.
2. Fiber extraction
2.2. Date (L) The pinnate leaves and surface layers of the stalks are chopped off with a knife and the resulting stems are dried in the shade for five days. The stems are beaten with a thick round mallet until the fleshy matter is dusted off. The resulted fiber is kept in a water retting tank for three days. Then, the fibers are removed and scraped with sharp knife to remove any foreign matter.
3. Fiber testing An oven of size 450 · 450 · 450 mm (model—CIC12) is used to dry the fibers. The oven has an automatic temperature control unit with an operating range 50– 300 C. An electronic weighing machine (0.0001 g accuracy) is used to weigh the fibers. The percentage of moisture present per unit weight of each variety of fiber is evaluated. The fiber density is measured by the picnometric procedure. The experimental results for various fibers are enumerated in Table 1. The diameter of the fiber was determined by the Fresnel diffraction method using a He–Ne laser as the mono-
K.M.M Rao, K.M. Rao / Composite Structures 77 (2005) 288–295 Table 1 Percentage moisture present in the fiber on weight basis at normal atmospheric condition and densities of various fibers Percentage moisture present in the fiber at normal atmospheric conditions
Density (kg/m3)
Vakka Date (L) Date (A) Bamboo (M) Bamboo (C) Palm Coconut Banana Sisal
12.09 10.67 09.55 09.16 10.14 12.08 11.36 10.71 09.76
810 990 960 910 890 1030 1150 1350 1450
800
600 Stress (MPa)
Name of the fiber
291
400 Bamboo (M) Banana Sisal Vakka
200
0 0.0
1.0
2.0
3.0 % Strain
4.0
5.0
6.0
Fig. 2. Stress vs. % strain of various natural fibers.
4. Discussion 4.1. Extraction of fibers The vakka fiber was extracted using a simple water retting process. It was observed that foreign matter (lignin, gums, etc.) was dissolved/separated in water within 15 days. Hand washing process results in complete separation of fibers from the foreign matter. The leaf sheath
600 500 Stress (MPa)
chromatic light source. The diffraction pattern consists of alternate bright and dark fringes surrounding a central bright fringe. By measuring the fringe width, the diameter of the fiber is obtained. The process is repeated for different angular rotations of the fiber such as 0, 45, 90 and 135, and the mean diameter is calculated. A plot for the periphery of the fiber is drawn using the package CATIA-5.0, and is shown in Fig. 1. The ultimate values of strength and percentage of strain in tension are obtained for five fiber specimens and the average of these is used to calculate tensile strength and modulus. Typical numerical values are presented in Table 2. in which the specific tensile strength and modulus of various fibers are also presented. The stress vs. percentage strain is shown graphically in Figs. 2–4.
400 300 Bamboo (M) Date (L) Vakka Bamboo (C)
200 100 0 0.0
0.5
1.0
1.5
2.0 2.5 % Strain
3.0
3.5
4.0
Fig. 3. Stress vs. % strain of various natural fibers.
contains about 65% of fiber and 35% foreign matter. The process is simple and results in an excellent quality of fiber, on par with any other exploited fibers. Since, the fiber grows in the sheath longitudinal direction, a continuous and uniform, 1–1.5-m long fiber is obtained. The fiber is slightly glazed and white in colour. The surface condition of the fiber is not as smooth as that of coconut fiber, so that the fiber is expected to have better adhesion property with polymers. Hence, the fiber could be used as a better reinforcement in polymeric composites. Large size composite components could be made
Table 2 Tensile properties of various natural fibers Name of the fiber
% Tensile strain
Average tensile strength (MPa)
Average tensile modulus (GPa)
Specific tensile strength (MPa/(kg m 3))
Specific tensile modulus (MPa/(kg m 3))
Vakka Date (L) Date (A) Bamboo (M) Bamboo (C) Palm Coconut Banana Sisal
3.46 2.73 24.00 1.40 1.73 13.71 20.00 3.36 5.45
549 309 459 503 341 377 500 600 567
15.85 11.32 1.91 35.91 19.67 2.75 2.50 17.85 10.40
0.6778 0.3121 0.4781 0.5527 0.3831 0.3660 0.4348 0.4444 0.3910
19.56 11.44 1.99 39.47 22.10 2.67 2.17 13.22 7.17
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600
Stress (MPa)
500 400 Bamboo (M) Coconut Date (L) Palm Vakka Date (A)
300 200 100 0 0
5
10
15 % Strain
20
25
30
Fig. 4. Stress vs. % strain of various natural fibers.
with these fibers as potential reinforcement material in polymeric composites, since the fiber is long enough. The date (L) fiber was extracted by a simple and economical water retting processes. The raw material is abundantly available and renewable, and is presently being wasted. It was observed during the extraction process that about 35% of the fiber was extracted from leaf stalks. In spite of scraping many times, the cellulose fiber is not completely free of lignin. The fiber is extracted to the length required from the leaf stalks i.e., about 1.5 m long. The surface condition of the fiber is rough enough to develop a better interface bond when used as reinforcement in polymeric composites. Date (A) fiber is extracted through a purely manual extraction process. It was observed that 50% of foreign matter drops off from the amplexicaul sheath during pulling and collecting of the fibers. The quality of the fiber is dependent on the number of times the fibers are scrapped. The extracted fiber is like coconut fiber with a smooth surface condition. The fiber is 100–300 mm long, depending on the size of the sheath. This fiber has not been used for any specific purpose so far. However, it could be used as reinforcement in making composites. The quality of bamboo (M) fiber is excellent compared to bamboo (C) fiber. The fiber-breaks along the length of bamboo (M) fiber are much less compared to bamboo (C) fiber. The quality of bamboo (M) fiber largely depends on the process of scraping the surface of the fiber. Despite the expensive chemical extraction process, the bamboo (C) fiber results in a large number of break-ups along the length; apart from leaving out some quantity of lignin with the fiber which ultimately weakens it. The geometrical variation and diameter of bamboo, date, coconut, vakka, banana, palm and sisal fibers were examined. The observations from the Laser beam equipment enunciate large variations in the cross-sectional shapes of vakka fiber in a single sheath. Various shapes
such as circular, lobed, elliptical and their combinations have been identified (Fig. 1). The large variation in the shape of the cross-section in a single sheath of vakka fiber is attributed to the fact that the sheath is a compact composite lamina with unidirectional cellulosic fibers and a lignin matrix. The variation in compactness and the location of fiber in a sheath would result in growing the fiber with different cross-sectional shapes. The variation in the dimensions of a single fiber along its length were found to be much less. However, the population of circular cross-section fibers is more than other shapes, but they are smaller in size. The mechanical properties of fibers are measured by selecting the diameter of fibers in the range of 0.175–0.25 mm. The fiber population below 0.175 mm and above 0.25 mm is much less in a single sheath. The population of circular cross-sectional fibers of date (L) and date (A) fibers is very large and the variation of their diameters is less. However, the diameters of fibers extracted from amplexicaul are large compared to those of leaf stalk. The diameter of date (L) fiber varies between 0.1 and 0.7 mm. The diameter of date (A) fiber varies between 0.15 and 0.95 mm. Date (L) fibers of diameter below 0.155 mm and above 0.3 mm and date (A) fibers below 0.17 mm and above 0.6 mm is less abundant. Two methods are used to extract the bamboo fibers; one by manual extraction and the other by a chemical extraction process. The diameters of the bamboo fibers extracted by both the methods vary between 0.09 and 0.4 mm. The highest concentration of fiber diameter is between 0.2 and 0.35 mm. Fibers with diameter of 0.09–0.2 and 0.35–0.4 mm are available in low concentrations. 4.2. Density and percentage moisture in the fibers The density of fibers is measured by the picnometric procedure. The densities of various fibers are given in Table 1. In general, the densities of various natural fibers are likely to vary depending on the process of fiber extraction, age of the plant, moisture present in the fiber, soil condition in which the plant has grown, etc. However, the table gives a relative measure of the densities between the fibers considered. The densities of vakka, date and bamboo are comparable to those of well-established fibers like sisal, banana and coconut. The density of various fibers varies between 810 and 1450 kg/m3, which are much less in comparison to the density of Glass fiber (2500 kg/m3). The density of different fibers increases in the order of vakka, bamboo (C), bamboo (M), date (A), date (L), palm, coconut, banana, and sisal (Table 1). Hence, these fibers could be used as reinforcement for making composites with an added advantage of being lightweight, renewable and biodegradable.
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The moisture present in various fibers at normal atmospheric condition i.e., 28 C and 50% relative humidity are also listed in Table 1. The moisture present in the fiber is likely to change depending on the atmospheric condition, type of fiber, age of plant, soil condition in which the plant has grown and the method and duration of preservation. The percentage of moisture present in the fiber on a weight basis at normal atmospheric conditions varies from 9.16 to 12.09. 4.3. Cross-section shapes of fibers Optical laser beam equipment is used to investigate the shape of the cross-sections of bamboo, banana, coconut, date, palm, sisal and vakka fibers. The crosssection dimensions of the fibers are measured at different degrees of orientation of the fiber cross-section and the results are shown in Fig. 1. It can be seen from the diagrams of various fiber cross-sections, that all the fiber cross-sections are approximately circular except vakka fiber. The cross-sections of the vakka fiber vary in different shapes, i.e., from circular to oval depending on the location of the fiber in the sheath. It is observed that their size varies from 0.01 to 1.2 mm in a single sheath. It was observed that the magnitude of laser beam diffraction is dependent on the curvature of the cross-section and the fiber variety. Hence, the test gives relative shapes of the fiber rather than the actual cross-section area. The fibers of circular cross-section are graded and selected for tensile testing of fibers. However, the cross-sectional areas of fibers under consideration are determined by measuring their diameters by digital micrometer with an accuracy of 0.001 mm. 4.4. Tensile strength of fibers The tensile test method ASTM-D3379-75 was been used to test bamboo (M), bamboo (C), banana, coconut, date (L), date (A), palm, sisal and vakka fibers. The diameters of bamboo (M) fibers selected are between 0.24 and 0.33 mm and that of bamboo (C) 0.235– 0.326 mm, banana 0.06–0.08 mm, coconut 0.101–0.161 mm, date (L) 0.155–0.251 mm, date (A) 0.175–0.269 mm, palm 0.405–0.487 mm, sisal 0.055–0.085 mm and vakka 0.175–0.232 mm. The average breaking strain, tensile strength and tensile modulus of some fibers are recorded in Table 2. The behaviour of different fibers under tensile load is plotted in Figs. 2–4. The following observations are made with regard to their mechanical behaviour. The plots of stress vs. percentage strain of various fibers are approximately linear (Figs. 2–4). The ultimate tensile strain of different fibers increases in the order of bamboo (M), bamboo (C), date (L), banana, vakka, sisal, palm, coconut and date (A). The increase of ultimate tensile strength of different fibers is in the sequence
293
of date (L), bamboo (C), palm, date (A), coconut, bamboo (M), vakka, sisal and banana. The ascendance in the tensile modulus of different fibers is in the sequence of date (A), coconut, palm, sisal, date (L), vakka, banana, bamboo (C) and bamboo (M). Amada et al. [4] estimated the tensile strength, modulus and bulk density of bamboo bundle sheaths at various location of culm with the rule of mixture. The report shows that the tensile strength, modulus and density of matrix is 50 MPa, 2 GPa and 670 kg/m3, and that of fiber is 610 MPa, 46 GPa and 1160 kg/m3, respectively. Nogata and Takahashi [6] estimated the tensile strength, YoungÕs modulus and density of bamboo matrix is 25 MPa, 2 GPa and 1360 kg/m3, and that of pure fiber is 810 MPa, 55 GPa and 1050 kg/m3, respectively using rule-of-mixtures. Deshpande et al. [19] explored the compression moulding technique (CMT) and roller mill technique (RMT) for extracting the bamboo fiber and determined their tensile properties. The maximum and average tensile strength of bamboo fiber extracted by CMT is 1000 and 645 MPa, and that of RMT is 480 and 370 MPa, respectively. The diameter of bamboo fibers extracted by CMT varies between 0.05 and 0.4 mm, and that of RMT, 0.05–0.1 mm. The tensile properties measured in the present work are well compared with various earlier investigators [3–8,12,17,19], though the method of extraction of bamboo fiber is different. The process of chemical extraction reduces the tensile strength and modulus, but increases percentage strain compared to the mechanical process of bamboo fibers (Fig. 3). Date (L) fiber is equally strong but flexible when compared to bamboo (C) fibers. The tensile strength and modulus of sisal fiber estimated by a number of authors [20–22] vary from 347 to 700 MPa and from 7 to 22 GPa, respectively. The maximum strain percent and diameter of fibers presented by different authors vary between 3–14 and 0.05–0.3 mm, respectively. Geethamma et al. [20] estimated the tenacity and elastic modulus of banana fiber, and are in the range 529– 759 MPa, and 8–20 GPa, respectively. The percentage elongation at break of banana fiber varies from 1.0 to 3.5. The diameter of banana fibers varies between 0.08 and 0.25 mm and having the density 1350 kg/m3. Sisal and banana fibers could be compared with various other fibers, since their composites are exploited to large extent. Banana fibers are stiffer and stronger than sisal fibers (Fig. 2). Bamboo fibers are stiffer but weaker than banana and sisal fibers. Vakka fibers are stiffer than sisal but less than that of banana. Vakka fibers are equally strong compared to banana and sisal fibers (Fig. 2). Geethamma et al. [20], Paul et al. [21] and Romildo et al. [22] estimated the physical and mechanical properties of coconut fiber. The diameter of coconut fiber
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varies between 0.1 and 0.53 mm. The density of coconut fibers is 1150 kg/m3. The moisture content in the fiber varies between 10% and 15.85%. The tensile strength and modulus vary between 108–252 MPa and 2.5– 6 GPa, respectively. The percentage elongation at the break is measured to be between 15 and 40. Coconut fibers are stronger and less stiff than those of palm fibers. Date (L) fibers are stiffer and weaker than palm fibers (Fig. 4). The physical and mechanical properties of sisal, banana and coconut fibers reinvestigated in the present work concur with the observations of earlier investigators. The specific tensile strength and modulus of various fibers are also listed in Table 2. The specific tensile strength of different fibers decreases in the order of vakka, bamboo (M), date (A), banana, coconut, sisal, bamboo (C), palm and date (L). The decrease of specific tensile modulus of different fibers is in the sequence of bamboo (M), bamboo (C), vakka, banana, date (L), sisal, palm, coconut and date (A). It is worth mentioning that vakka fiber, being introduced in the present study, is the best of all the fibers considered in terms of specific tensile strength. The date (A) fiber is next to bamboo (M) fiber in terms of specific tensile strength. Hence, these fibers could be included in the list of reinforcements in composites for the design of lightweight materials. Considering the specific tensile modulus, the vakka fiber shows superior characteristics among the well-established conventional natural fibers like banana, sisal, etc. However, bamboo (M) and bamboo (C) supersede vakka fiber in specific tensile modulus. The specific tensile strength of date (L) is very close, and could be well compared with banana fiber. The specific tensile strength of date (A) is well comparable with that of date (L) fiber. However, the large variation in the percentage tensile strain of date (A) and date (L) fibers resulted in a large variation in their specific tensile modulus. All the above exploited fibers in the present study could be used as reinforcement materials in polymeric composites, depending on the application.
5. Conclusions Vegetation associated with agriculture and forestry is a large source for extracting fibers, which has been largely under utilised. Fibers that can be extracted from the vegetation with water retting process are inexpensive. The process of extraction of vakka fiber is simple and results in an excellent quality of fiber, comparable to any of the presently explored fibers. Large polymeric composite components could be made of these fibers, since the fiber is long enough and uniform. Low density and high strength of vakka fiber proves to be attractive factors for the fabrication of lightweight materials.
As far as the extraction process is concerned; cost, fiber strength, and fiber length, the bamboo (M) fiber has been shown to be excellent when compared to bamboo (C) fiber. The densities of these newly introduced fibers are less than that of well-established natural and synthetic fibers. Hence, it can emphatically be stated that the fibers considered herein deserve to be included in the list of natural reinforcements in composites for the design of lightweight materials.
Acknowledgements The authors gratefully acknowledge the financial support extended by the All India Council for Technical Education, IG Sports Complex, IP Estate, New Delhi, India, (F. No. 8017/RDII/BOR/TMAT 049/Rec. 416) under Thrust Area Programme in Technical Education to carryout the Research project.
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Extraction and tensile properties of natural fibers: Vakka, date and bamboo K. Murali Mohan Rao a
a,*
, K. Mohana Rao
b
Department of Mechanical Engineering, V.R. Siddhartha Engineering College, Vijayawada 520 007, AP, India b P.V.P. Siddhartha Institute of Technology, Vijayawada 520 007, AP, India Available online 7 October 2005
Abstract This paper aims at introducing new natural fibers used as fillers in a polymeric matrix enabling production of economical and lightweight composites for load carrying structures. An investigation of the extraction procedures of vakka (Roystonea regia), date and bamboo fibers has been undertaken. The cross-sectional shape, the density and tensile properties of these fibers, along with established fibers like sisal, banana, coconut and palm, are determined experimentally under similar conditions and compared. The fibers introduced in the present study could be used as an effective reinforcement for making composites, which have an added advantage of being lightweight. 2005 Elsevier Ltd. All rights reserved. Keywords: Fibers; Mechanical properties; Natural fibers
1. Introduction Vegetable fiber is one of the varieties of natural fibers obtained from stems, leaves, roots, fruits and seeds of plants. Vegetation is exploited for its ability to yield fibers directly from wild or natural forms. However, from commercial and technological points of view, cotton, kenaf, sisal, flax, palm, coir, arecanut and banana fibers acquire utmost significance, since reinforced plastics, strings, cords, cables, ropes, mats, brushes, hats, baskets and fancy articles such as bags are manufactured with those fibers. All the ligno-cellulosic based natural fibers consist of cellulose micro-fibrils in an amorphous matrix of lignin and hemi-cellulose. These fibers consist of several fibrils, which run all along the length of the fiber: each fibril exhibits a complex layered structure made up of a thin *
Corresponding author. Tel.: +91 866 2583179; fax: +91 866 2582672. E-mail address: kmmr55@rediffmail.com (K.M.M Rao). 0263-8223/$ - see front matter 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.compstruct.2005.07.023
primary wall encircling a thicker secondary layer and is similar to that of a single wood fiber. The fibers considered in the present analysis are treated as single units at the macro level as shown in Fig. 1. Roystonea regia (Oreodoxa regia), popularly known as Royal palm which is locally called vakka, a native of West Indies and neighbouring parts of tropical America, has been cultivated in India [1]. An attempt to explore this tree for its fiber has not been taken up yet. In the present investigation, its fibers have been identified and found to be a potential reinforcement. The date, botanically known as Phoenix sylvestris [2], the new name of which is Arecaceae, belongs to Palmaceae family. The fiber is picked from the dried leaves called leaf stalk fibers referred to hereafter as date (L) or from the netted structure called amplexicaul fiber referred to hereafter as date (A). The netted structure is the sheathing leaf base, which surrounds the stem. As far as the characteristics are concerned, bamboos are tall, perennial, arborescent grasses, belonging to the Bambusae, a tribe under Graminae. Earlier, the fracture
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289
Fig. 1. Cross-sections of various fibers.
properties of bamboo culms and nodes have been studied [3]. Bamboo is a typical natural composite material, and the fibers are distributed densely in the outer surface region, and sparsely in the inner surface region. It is evident that the fracture toughness of the bamboo culm depends on the volume fraction of fibers. The bamboo has multi-nodes and functionally gradient structure, macroscopically as well as microscopically [4–10]. The effect of the absorption of water on mechanical properties of bamboo has also been studied [11]. Okubo et al. [12] undertook an in-depth analysis into the mechanical properties of polypropylene composites using bamboo fiber, extracted by steam explosion technique. The tensile strength and modulus of the polypropylene based composites increase about 15% and 30%, respectively due to better impregnation and reduction of the number of voids, compared to those of fibers that were mechanically extracted. Thwe and Liao [13] examined the effect of fiber content, fiber length, bamboo to glass fiber ratio, and coupling agent (maleic anhydride polypropylene) on tensile and flexural properties of bamboo fiber reinforced polypropylene (BFRP) and bamboo-glass fiber reinforced polypropylene hybrid composite (BGRP). It was shown that hybridization with synthetic fibers is a viable approach for enhancing the mechanical properties and durability of natural fiber composites. Thwe and Liao [14] carried out an extensive survey on the durability of BFRP and BGRP subjected to hygrothermal ageing and fatigue behaviour under cyclic tensile load. The authors concluded that BGRP shows a better resistance to environmental ageing than BFRP. An unreinforced polypropylene has a longer fatigue life
than BFRP and BGRP composites at the specified cyclic load levels. In comparison to BFRP, the BGRP that is a hybrid composite presents a better fatigue resistance. An analysis by Ismail et al. [15] on the effect of a silane coupling agent (Si69) on curing characteristics and mechanical properties of bamboo fiber filled natural rubber composites highlighted various aspects of this phenomenon. It was concluded that the presence of a silane coupling agent, Si69 improves the adhesion between the fiber and rubber matrix and consequently enhances the tensile strength, tear strength, hardness and tensile modulus. Ismail et al. [16] examined the curing characteristics and mechanical properties of bamboo fiber reinforced natural rubber composites, as a function of fiber loading, and phenol formaldehyde and amethylenetetramine bonding agents. It was concluded that adhesion between the bamboo fiber and natural rubber can be enhanced by the use of bonding agents. As a result, the tensile modulus and hardness of composites increase with increasing filler loading and the presence of bonding agents. Yao and Li [17] carried out a thorough investigation into the preparation and flexural properties of bamboo fiber reinforced mortar laminates. The laminate was a sandwich plate combined with reinforced bamboo plate and extruded PVA fiber reinforced mortar sheet. The results of the investigation show that the flexural strength values can be improved to greater than 90 MPa for laminates with reformed bamboo plate on the bottom, which formed a tension layer and the fiber-reinforced mortar sheet on the top that acts as compressive layer. Among the well-known natural fibers (jute, coir, straw, banana, etc.), bamboo has low density and high
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mechanical strength. The specific tensile strength and specific gravity of bamboo are considerably less than those of glass fibers. However, cost considerations make bamboo an attractive fiber for reinforcement. The present work provides extraction procedures for vakka, date and bamboo fibers. Date fiber is extracted from leaf stalks and amplexicaul. The bamboo fiber is extracted by retting and manual extraction, and chemical extraction procedures. The chemical and mechanical extraction procedures of bamboo are referred to here as bamboo (C) and bamboo (M), respectively. The crosssectional shapes of the fibers are investigated and circular cross-section fibers are identified for tensile testing of fibers. The picnometric procedure has been employed for determining the densities of various fibers. The tensile properties of vakka, date and bamboo are experimentally determined along with a reinvestigation of sisal, banana, palm and coconut fibers. The tensile properties of vakka, date and bamboo fibers are compared with those of the established fibers like sisal, banana, palm and coconut.
2.3. Date (A) The fiber is collected from amplexicaul, the sheathing leaf base, which surrounds the stem. It has a netted in structure, which is covered by soft or ground tissues. The amplexicaul is carefully collected from the tree. It is dried in shade at room temperature for a period of two days in order to remove any excess moisture content. The pulp (parenchyma) which is present on the individual fiber is removed by combing. Finally, the fiber is scraped to remove the pulp completely. 2.4. Bamboo (M)
Sisal, banana, coconut and palm fibers are collected from various local sources, and vakka, date (L), date (A), bamboo (C) and bamboo (M) fibers are extracted.
The node portions and very thin layer of exodermis (bark) of the bamboo are removed and the rest of the hollow cylindrical portion of culm is taken for extracting the fiber. The cylindrical portion of culm is peeled in the longitudinal direction to make strips of 0.5–1.5 mm thick and about 10 mm width. The strips are bundled and are kept in water for three days in order to soften them. After removing these strips from the water, they are beaten gently in order to loosen and to separate the fiber. The resulting fiber bundle is scrapped with sharp edged knife and combed. The process of combing and scrapping is repeated until individual fibers are separated.
2.1. Vakka
2.5. Bamboo (C)
The source of this fiber is the foliage of the tree, which falls on to the ground, when it ripens. It contains leaves with their stem in the form of a sheath. The sheath is separated from leaves and leaf stem and dried for two to three days in shade. It is then immersed in a water-retting tank for 15 days. The sheath contains layers of fiber throughout its thickness. In the first 15 days, the top layers on either side of the sheath loosen. Then, these layers are removed, washed and immersed in another water-retting tank for three more days. Later, they are removed, hand rubbed and rinsed in sufficient water. The water retting process takes 18–25 days to extract fibers completely. The fiber extraction is simple and economical, and requires no other process, since, the gums present in the sheath dissolve in water completely.
The manually decorticated bamboo fibrous strips are dried off in the sun. These strips of fiber removed from the culms contain tissues and gums. After decorticating, the dry fiber is extracted by means of a chemical process of decomposition called degumming, in which the gummy materials and the pectin are removed. The method of degumming designed by Gangstad et al. cited by Maiti [18] has been taken as a basis for chemical extraction. The chemical extraction process yields about 33% of fiber on weight basis.
2. Fiber extraction
2.2. Date (L) The pinnate leaves and surface layers of the stalks are chopped off with a knife and the resulting stems are dried in the shade for five days. The stems are beaten with a thick round mallet until the fleshy matter is dusted off. The resulted fiber is kept in a water retting tank for three days. Then, the fibers are removed and scraped with sharp knife to remove any foreign matter.
3. Fiber testing An oven of size 450 · 450 · 450 mm (model—CIC12) is used to dry the fibers. The oven has an automatic temperature control unit with an operating range 50– 300 C. An electronic weighing machine (0.0001 g accuracy) is used to weigh the fibers. The percentage of moisture present per unit weight of each variety of fiber is evaluated. The fiber density is measured by the picnometric procedure. The experimental results for various fibers are enumerated in Table 1. The diameter of the fiber was determined by the Fresnel diffraction method using a He–Ne laser as the mono-
K.M.M Rao, K.M. Rao / Composite Structures 77 (2005) 288–295 Table 1 Percentage moisture present in the fiber on weight basis at normal atmospheric condition and densities of various fibers Percentage moisture present in the fiber at normal atmospheric conditions
Density (kg/m3)
Vakka Date (L) Date (A) Bamboo (M) Bamboo (C) Palm Coconut Banana Sisal
12.09 10.67 09.55 09.16 10.14 12.08 11.36 10.71 09.76
810 990 960 910 890 1030 1150 1350 1450
800
600 Stress (MPa)
Name of the fiber
291
400 Bamboo (M) Banana Sisal Vakka
200
0 0.0
1.0
2.0
3.0 % Strain
4.0
5.0
6.0
Fig. 2. Stress vs. % strain of various natural fibers.
4. Discussion 4.1. Extraction of fibers The vakka fiber was extracted using a simple water retting process. It was observed that foreign matter (lignin, gums, etc.) was dissolved/separated in water within 15 days. Hand washing process results in complete separation of fibers from the foreign matter. The leaf sheath
600 500 Stress (MPa)
chromatic light source. The diffraction pattern consists of alternate bright and dark fringes surrounding a central bright fringe. By measuring the fringe width, the diameter of the fiber is obtained. The process is repeated for different angular rotations of the fiber such as 0, 45, 90 and 135, and the mean diameter is calculated. A plot for the periphery of the fiber is drawn using the package CATIA-5.0, and is shown in Fig. 1. The ultimate values of strength and percentage of strain in tension are obtained for five fiber specimens and the average of these is used to calculate tensile strength and modulus. Typical numerical values are presented in Table 2. in which the specific tensile strength and modulus of various fibers are also presented. The stress vs. percentage strain is shown graphically in Figs. 2–4.
400 300 Bamboo (M) Date (L) Vakka Bamboo (C)
200 100 0 0.0
0.5
1.0
1.5
2.0 2.5 % Strain
3.0
3.5
4.0
Fig. 3. Stress vs. % strain of various natural fibers.
contains about 65% of fiber and 35% foreign matter. The process is simple and results in an excellent quality of fiber, on par with any other exploited fibers. Since, the fiber grows in the sheath longitudinal direction, a continuous and uniform, 1–1.5-m long fiber is obtained. The fiber is slightly glazed and white in colour. The surface condition of the fiber is not as smooth as that of coconut fiber, so that the fiber is expected to have better adhesion property with polymers. Hence, the fiber could be used as a better reinforcement in polymeric composites. Large size composite components could be made
Table 2 Tensile properties of various natural fibers Name of the fiber
% Tensile strain
Average tensile strength (MPa)
Average tensile modulus (GPa)
Specific tensile strength (MPa/(kg m 3))
Specific tensile modulus (MPa/(kg m 3))
Vakka Date (L) Date (A) Bamboo (M) Bamboo (C) Palm Coconut Banana Sisal
3.46 2.73 24.00 1.40 1.73 13.71 20.00 3.36 5.45
549 309 459 503 341 377 500 600 567
15.85 11.32 1.91 35.91 19.67 2.75 2.50 17.85 10.40
0.6778 0.3121 0.4781 0.5527 0.3831 0.3660 0.4348 0.4444 0.3910
19.56 11.44 1.99 39.47 22.10 2.67 2.17 13.22 7.17
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600
Stress (MPa)
500 400 Bamboo (M) Coconut Date (L) Palm Vakka Date (A)
300 200 100 0 0
5
10
15 % Strain
20
25
30
Fig. 4. Stress vs. % strain of various natural fibers.
with these fibers as potential reinforcement material in polymeric composites, since the fiber is long enough. The date (L) fiber was extracted by a simple and economical water retting processes. The raw material is abundantly available and renewable, and is presently being wasted. It was observed during the extraction process that about 35% of the fiber was extracted from leaf stalks. In spite of scraping many times, the cellulose fiber is not completely free of lignin. The fiber is extracted to the length required from the leaf stalks i.e., about 1.5 m long. The surface condition of the fiber is rough enough to develop a better interface bond when used as reinforcement in polymeric composites. Date (A) fiber is extracted through a purely manual extraction process. It was observed that 50% of foreign matter drops off from the amplexicaul sheath during pulling and collecting of the fibers. The quality of the fiber is dependent on the number of times the fibers are scrapped. The extracted fiber is like coconut fiber with a smooth surface condition. The fiber is 100–300 mm long, depending on the size of the sheath. This fiber has not been used for any specific purpose so far. However, it could be used as reinforcement in making composites. The quality of bamboo (M) fiber is excellent compared to bamboo (C) fiber. The fiber-breaks along the length of bamboo (M) fiber are much less compared to bamboo (C) fiber. The quality of bamboo (M) fiber largely depends on the process of scraping the surface of the fiber. Despite the expensive chemical extraction process, the bamboo (C) fiber results in a large number of break-ups along the length; apart from leaving out some quantity of lignin with the fiber which ultimately weakens it. The geometrical variation and diameter of bamboo, date, coconut, vakka, banana, palm and sisal fibers were examined. The observations from the Laser beam equipment enunciate large variations in the cross-sectional shapes of vakka fiber in a single sheath. Various shapes
such as circular, lobed, elliptical and their combinations have been identified (Fig. 1). The large variation in the shape of the cross-section in a single sheath of vakka fiber is attributed to the fact that the sheath is a compact composite lamina with unidirectional cellulosic fibers and a lignin matrix. The variation in compactness and the location of fiber in a sheath would result in growing the fiber with different cross-sectional shapes. The variation in the dimensions of a single fiber along its length were found to be much less. However, the population of circular cross-section fibers is more than other shapes, but they are smaller in size. The mechanical properties of fibers are measured by selecting the diameter of fibers in the range of 0.175–0.25 mm. The fiber population below 0.175 mm and above 0.25 mm is much less in a single sheath. The population of circular cross-sectional fibers of date (L) and date (A) fibers is very large and the variation of their diameters is less. However, the diameters of fibers extracted from amplexicaul are large compared to those of leaf stalk. The diameter of date (L) fiber varies between 0.1 and 0.7 mm. The diameter of date (A) fiber varies between 0.15 and 0.95 mm. Date (L) fibers of diameter below 0.155 mm and above 0.3 mm and date (A) fibers below 0.17 mm and above 0.6 mm is less abundant. Two methods are used to extract the bamboo fibers; one by manual extraction and the other by a chemical extraction process. The diameters of the bamboo fibers extracted by both the methods vary between 0.09 and 0.4 mm. The highest concentration of fiber diameter is between 0.2 and 0.35 mm. Fibers with diameter of 0.09–0.2 and 0.35–0.4 mm are available in low concentrations. 4.2. Density and percentage moisture in the fibers The density of fibers is measured by the picnometric procedure. The densities of various fibers are given in Table 1. In general, the densities of various natural fibers are likely to vary depending on the process of fiber extraction, age of the plant, moisture present in the fiber, soil condition in which the plant has grown, etc. However, the table gives a relative measure of the densities between the fibers considered. The densities of vakka, date and bamboo are comparable to those of well-established fibers like sisal, banana and coconut. The density of various fibers varies between 810 and 1450 kg/m3, which are much less in comparison to the density of Glass fiber (2500 kg/m3). The density of different fibers increases in the order of vakka, bamboo (C), bamboo (M), date (A), date (L), palm, coconut, banana, and sisal (Table 1). Hence, these fibers could be used as reinforcement for making composites with an added advantage of being lightweight, renewable and biodegradable.
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The moisture present in various fibers at normal atmospheric condition i.e., 28 C and 50% relative humidity are also listed in Table 1. The moisture present in the fiber is likely to change depending on the atmospheric condition, type of fiber, age of plant, soil condition in which the plant has grown and the method and duration of preservation. The percentage of moisture present in the fiber on a weight basis at normal atmospheric conditions varies from 9.16 to 12.09. 4.3. Cross-section shapes of fibers Optical laser beam equipment is used to investigate the shape of the cross-sections of bamboo, banana, coconut, date, palm, sisal and vakka fibers. The crosssection dimensions of the fibers are measured at different degrees of orientation of the fiber cross-section and the results are shown in Fig. 1. It can be seen from the diagrams of various fiber cross-sections, that all the fiber cross-sections are approximately circular except vakka fiber. The cross-sections of the vakka fiber vary in different shapes, i.e., from circular to oval depending on the location of the fiber in the sheath. It is observed that their size varies from 0.01 to 1.2 mm in a single sheath. It was observed that the magnitude of laser beam diffraction is dependent on the curvature of the cross-section and the fiber variety. Hence, the test gives relative shapes of the fiber rather than the actual cross-section area. The fibers of circular cross-section are graded and selected for tensile testing of fibers. However, the cross-sectional areas of fibers under consideration are determined by measuring their diameters by digital micrometer with an accuracy of 0.001 mm. 4.4. Tensile strength of fibers The tensile test method ASTM-D3379-75 was been used to test bamboo (M), bamboo (C), banana, coconut, date (L), date (A), palm, sisal and vakka fibers. The diameters of bamboo (M) fibers selected are between 0.24 and 0.33 mm and that of bamboo (C) 0.235– 0.326 mm, banana 0.06–0.08 mm, coconut 0.101–0.161 mm, date (L) 0.155–0.251 mm, date (A) 0.175–0.269 mm, palm 0.405–0.487 mm, sisal 0.055–0.085 mm and vakka 0.175–0.232 mm. The average breaking strain, tensile strength and tensile modulus of some fibers are recorded in Table 2. The behaviour of different fibers under tensile load is plotted in Figs. 2–4. The following observations are made with regard to their mechanical behaviour. The plots of stress vs. percentage strain of various fibers are approximately linear (Figs. 2–4). The ultimate tensile strain of different fibers increases in the order of bamboo (M), bamboo (C), date (L), banana, vakka, sisal, palm, coconut and date (A). The increase of ultimate tensile strength of different fibers is in the sequence
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of date (L), bamboo (C), palm, date (A), coconut, bamboo (M), vakka, sisal and banana. The ascendance in the tensile modulus of different fibers is in the sequence of date (A), coconut, palm, sisal, date (L), vakka, banana, bamboo (C) and bamboo (M). Amada et al. [4] estimated the tensile strength, modulus and bulk density of bamboo bundle sheaths at various location of culm with the rule of mixture. The report shows that the tensile strength, modulus and density of matrix is 50 MPa, 2 GPa and 670 kg/m3, and that of fiber is 610 MPa, 46 GPa and 1160 kg/m3, respectively. Nogata and Takahashi [6] estimated the tensile strength, YoungÕs modulus and density of bamboo matrix is 25 MPa, 2 GPa and 1360 kg/m3, and that of pure fiber is 810 MPa, 55 GPa and 1050 kg/m3, respectively using rule-of-mixtures. Deshpande et al. [19] explored the compression moulding technique (CMT) and roller mill technique (RMT) for extracting the bamboo fiber and determined their tensile properties. The maximum and average tensile strength of bamboo fiber extracted by CMT is 1000 and 645 MPa, and that of RMT is 480 and 370 MPa, respectively. The diameter of bamboo fibers extracted by CMT varies between 0.05 and 0.4 mm, and that of RMT, 0.05–0.1 mm. The tensile properties measured in the present work are well compared with various earlier investigators [3–8,12,17,19], though the method of extraction of bamboo fiber is different. The process of chemical extraction reduces the tensile strength and modulus, but increases percentage strain compared to the mechanical process of bamboo fibers (Fig. 3). Date (L) fiber is equally strong but flexible when compared to bamboo (C) fibers. The tensile strength and modulus of sisal fiber estimated by a number of authors [20–22] vary from 347 to 700 MPa and from 7 to 22 GPa, respectively. The maximum strain percent and diameter of fibers presented by different authors vary between 3–14 and 0.05–0.3 mm, respectively. Geethamma et al. [20] estimated the tenacity and elastic modulus of banana fiber, and are in the range 529– 759 MPa, and 8–20 GPa, respectively. The percentage elongation at break of banana fiber varies from 1.0 to 3.5. The diameter of banana fibers varies between 0.08 and 0.25 mm and having the density 1350 kg/m3. Sisal and banana fibers could be compared with various other fibers, since their composites are exploited to large extent. Banana fibers are stiffer and stronger than sisal fibers (Fig. 2). Bamboo fibers are stiffer but weaker than banana and sisal fibers. Vakka fibers are stiffer than sisal but less than that of banana. Vakka fibers are equally strong compared to banana and sisal fibers (Fig. 2). Geethamma et al. [20], Paul et al. [21] and Romildo et al. [22] estimated the physical and mechanical properties of coconut fiber. The diameter of coconut fiber
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varies between 0.1 and 0.53 mm. The density of coconut fibers is 1150 kg/m3. The moisture content in the fiber varies between 10% and 15.85%. The tensile strength and modulus vary between 108–252 MPa and 2.5– 6 GPa, respectively. The percentage elongation at the break is measured to be between 15 and 40. Coconut fibers are stronger and less stiff than those of palm fibers. Date (L) fibers are stiffer and weaker than palm fibers (Fig. 4). The physical and mechanical properties of sisal, banana and coconut fibers reinvestigated in the present work concur with the observations of earlier investigators. The specific tensile strength and modulus of various fibers are also listed in Table 2. The specific tensile strength of different fibers decreases in the order of vakka, bamboo (M), date (A), banana, coconut, sisal, bamboo (C), palm and date (L). The decrease of specific tensile modulus of different fibers is in the sequence of bamboo (M), bamboo (C), vakka, banana, date (L), sisal, palm, coconut and date (A). It is worth mentioning that vakka fiber, being introduced in the present study, is the best of all the fibers considered in terms of specific tensile strength. The date (A) fiber is next to bamboo (M) fiber in terms of specific tensile strength. Hence, these fibers could be included in the list of reinforcements in composites for the design of lightweight materials. Considering the specific tensile modulus, the vakka fiber shows superior characteristics among the well-established conventional natural fibers like banana, sisal, etc. However, bamboo (M) and bamboo (C) supersede vakka fiber in specific tensile modulus. The specific tensile strength of date (L) is very close, and could be well compared with banana fiber. The specific tensile strength of date (A) is well comparable with that of date (L) fiber. However, the large variation in the percentage tensile strain of date (A) and date (L) fibers resulted in a large variation in their specific tensile modulus. All the above exploited fibers in the present study could be used as reinforcement materials in polymeric composites, depending on the application.
5. Conclusions Vegetation associated with agriculture and forestry is a large source for extracting fibers, which has been largely under utilised. Fibers that can be extracted from the vegetation with water retting process are inexpensive. The process of extraction of vakka fiber is simple and results in an excellent quality of fiber, comparable to any of the presently explored fibers. Large polymeric composite components could be made of these fibers, since the fiber is long enough and uniform. Low density and high strength of vakka fiber proves to be attractive factors for the fabrication of lightweight materials.
As far as the extraction process is concerned; cost, fiber strength, and fiber length, the bamboo (M) fiber has been shown to be excellent when compared to bamboo (C) fiber. The densities of these newly introduced fibers are less than that of well-established natural and synthetic fibers. Hence, it can emphatically be stated that the fibers considered herein deserve to be included in the list of natural reinforcements in composites for the design of lightweight materials.
Acknowledgements The authors gratefully acknowledge the financial support extended by the All India Council for Technical Education, IG Sports Complex, IP Estate, New Delhi, India, (F. No. 8017/RDII/BOR/TMAT 049/Rec. 416) under Thrust Area Programme in Technical Education to carryout the Research project.
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