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Potential of Jamaican banana, coconut coir and bagasse fibres as composite materials
M A TE RI A L S C H A RAC TE RI ZA T ION 5 9 ( 2 00 8 ) 1 2 7 3–1 2 7 8
Potential of Jamaican banana, coconut coir and bagasse fibres as composite materials Nilza G. Jústiz-Smith⁎, G. Junior Virgo, Vernon E. Buchanan University of Technology, Jamaica, School of Engineering, 237 Old Hope Road, Kingston 6, West Indies, Jamaica
AR TIC LE D ATA
ABSTR ACT
Article history:
This paper presents an evaluation of the alternative use of three Jamaican natural cellulosic
Received 10 February 2006
fibres for the design and manufacturing of composite materials. The natural cellulosic fibres
Received in revised form
under investigation were bagasse from sugar cane (saccharum officinarum), banana trunk
20 September 2007
from the banana plant (family Musacae, genus Musa X para disiaca L), and coconut coir1
Accepted 23 October 2007
from the coconut husk (family Palm, genus coco nucifera). Fibre samples were subjected to standardized characterization tests such as ash and carbon content, water absorption,
Keywords:
moisture content, tensile strength, elemental analysis and chemical analysis. The banana
Fibres
fibre exhibited the highest ash, carbon and cellulose content, hardness and tensile strength,
Composites
while coconut the highest lignin content.
Material strength
1.
Introduction
Centuries ago primitive man frequently used natural cellulosic fibres mainly as construction materials, clothing and as source energy [1]. In recent years, spurred by societal needs to ensure a more comfortable way of life, new technologies have been developed to produce various types of synthetic materials. The evolution of synthetic materials has seen its use in industrial processes as reinforcement of composite materials; the most common of which is fibreglass. There are, however, many advantages and disadvantages associated with the use of synthetic fibres. These fibres have been found to increase the mechanical strength of the composite and enhance other properties such as their thermal and electrical conductivities, which are germane to the composite material industry. Nevertheless, the main concerns are the lack of environmental soundness, the composites' high densities and their relatively low modulus of elasticity. These disadvantages have forced governments and private organisations to invest millions of dollars in the research and development of the use of natural
© 2008 Published by Elsevier Inc.
cellullosic fibres as a viable alternative to synthetic composites [2]. The global trends indicate that the marketplace is leaning towards natural fibre use because of various societal concerns. It is environmentally sound, i.e. renewable, recyclable [3,4] and it has a very low raw material cost. Due to the natural alignment of the carbon–carbon bonds within the structure of these organic fibres it is expected that their linear chained polymers would possess significant strength and stiffness. Over the last decade, there has been increased interest in the sourcing of cheaper raw materials used in the automotive and aerospace industries [2] and natural fibre composites have maintained a position at the top of the list. There is a wide range of biomass natural fibres that are prevalent in commercial applications. We see them being utilised in industries producing ropes and canvases [4–6]. Industrial use of lignocellulose fibre is well established especially in the form of wood for paper pulp and the manufacture of fibreboard [7]. The annual global production of lignocellulosic fibres from crops is about 4 billion tonnes, of which 60% comes
⁎ Corresponding author. Tel.: +1 876 977 4363; fax: +1 876 977 2267. E-mail addresses: [email protected] (N.G. Jústiz-Smith), [email protected] (G.J. Virgo), [email protected] (V.E. Buchanan). 1 Coir – a stiff, coarse fibre from the outer husk of a coconut. 1044-5803/$ – see front matter © 2008 Published by Elsevier Inc. doi:10.1016/j.matchar.2007.10.011
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from agriculture and 40% from forests. In comparison, annual world production of steel is currently around 0.7 billion tonnes and plastic is about 0.1 billion tonnes [4]. Plant fibre can be combined with other materials such as plastics, glass and metals to form a new material. The formation of a composite structure is dependent on the fibre and its matrix. The fibres are responsible for the strength and stiffness while the matrix provides the orientation that bonds the fibres. Also, the properties of plant fibres can be modified through the application of heat treatment and chemical technologies. At the end of these processes, the resulting materials should have more favourable characteristics than their original components [4,6].
3.
Methodology
3.1.
Sample Collection and Preparation
Samples of the three fibrous materials were collected from several locations and sorted: sugar cane (bagasse) samples were obtained from St. Catherine, at the Sugar Company of Jamaica, Bernard Lodge Division and the coconut of the Dwarf species from a Kingston, St. Andrew residence and banana of the Gross Mitchell species from a farm in St. Mary. The banana fibre strands were separated by retting while the coconut fibres were simply cut from the fruit using a sharp knife.
3.2.
2.
Natural Cellulosic Fibres
A fibre is defined as ‘any of the threads or filaments forming animal or vegetable tissue and textile substances' [8]. The fibre cells found in natural fibres are very long in relation to their width [7] having in their cell walls a matrix or the homogeneous lattice structure of lignin and hemicellulose, with embedded cellulose micro fibrils [9]. The layered cell wall contains varying amounts of each constituent. They are classified broadly as lignocelluloses containing 85% or more cellulose, hemicellulose and lignin, and non-lignocelluloses possessing no lignin. Each constituent makes its own contribution to the properties of the fibres [7]. Cellulose is a natural polymer and its structure serves as a carbon reservoir. Cellulosic fibres have a higher Young's modulus when compared to thermoplastic material; hence, they contribute a higher increment of stiffness to the composite [4,10,11]. The high lignin content also allows the fibre to be resistant to rotting under wet and dry conditions and to have a better tensile strength [11]. Plant fibres are often seen as waste produced in the agricultural sector and investigation of these industries in Jamaica show them as an abundant source of raw material that can be transformed into profitable, useable products. Based on these investigations, three natural fibres were selected from the agriculture sector, namely, bagasse from the sugar industry, banana trunks from the banana industry and coconut husk from the coconut industry. The main characteristics of the most important plant fibres however, are described in terms of their mechanical properties such as tensile strength, hardness, chemical/biological composition such as lignin, cellulose, hemicellulose, pectin and ash and microscopic features [6,7]. The present research aims to provide the necessary information about the major physical, chemical and mechanical characteristics of Jamaican natural cellulosic fibres such as banana, coconut and bagasse. The fibre diameter, ash, carbon, moisture content, and water absorption were the parameters chosen to physically characterise these fibres. In the case of chemical/biological composition; the lignin, cellulose and hemicellulose contents were determined. The tensile strength tests were performed to evaluate the fibres' mechanical properties. Other elemental analyses were also performed to quantify silicon, aluminium, calcium, magnesium and sodium content.
Fibre Characterization
The fibres were characterized on the basis of their physical and chemical properties.
3.2.1.
Physical Properties
a. Determination of diameter and microstructure A metallurgical microscope, complete with image analyser software was used to determine the diameter and microstructure of the three fibres. The microstructure determination included both longitudinal and cross-sectional area measurements. Single fibre strands were horizontally positioned in a special clamp and placed on the table of the microscope. An appropriate resolution was determined in order to clearly identify the specimen. A total of 20 strands were analysed for each fibre. Diameter values were taken at different points of each strand and the standard deviation determined. In order to obtain an image of the cross-section of the fibre several strands were cut and placed in a vertical position in a clamp on the table of the microscope. This was repeated for all fibre types and the results recorded. Images were also taken using the Wild M3C Defect Microscope (Model: Leica DC 500) fitted with a digital camera. b. Moisture content The fibre samples were dried in an oven at 110 °C to a constant weight. The moisture content was calculated from the change in weight of the dried sample [12]. c. Ash and carbon content The ASTM standard method E1755-01 [13] was used to determine the mineral content and other inorganic matter (called ash content) as well as the carbon content of the biomass. d. Water absorption Water absorption was evaluated by using the Water Absorption 24 Hour or Equilibrium ASTM standard test D570 [14]. It involved determining the amount of water absorbed under specified conditions. Table 1 – Diameter of cellulosic fibres Fibres
Average diameter(μm) Maximum Minimum Mean Standard deviation
Banana Coconut Bagasse
271.74 511.9 519.4
177.89 307.35 313.35
225.53 396.98 399.05
33.18 67.93 76.75
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that is insoluble in acid. Pre-treatment with acid removes the acid-soluble components followed by solvent extraction of the residual insoluble compounds to leave the lignin as the final residue. b. Cellulose content In the case of cellulose content fibre samples were oxidised using successive solutions of sodium hydroxide at different molalities, filtered and dried, and the difference in weight recorded as cellulose content [16].
Fig. 1 – Micrographs of longitudinal section of fibre strands.
e. Tensile strength Individual fibres were used to determine tensile strength using the Chatillon TCM 201 tensile machine.
3.2.2.
Chemical Properties
a. Lignin content This determination was based on the ASTM Test Method D1106-96 [15] for acid-insoluble lignin in wood. The method involves the determination of the lignin content of wood
Fig. 2 – Micrographs of cross-sectional area of fibres strands.
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Fig. 3 – Micrographs of natural cellulosic fibres (Wild M3C). c. Metal element content Analysis was performed to determine the quantity of silicon, aluminum, magnesium, sodium and calcium present in all three fibrous materials. The AAnalyst 300 Atomic Absorption Spectrometer was used to analyze the samples. Lithium Tetraborate fusion was used to prepare the samples for silicon analysis [17,18]. During this procedure samples were weighed and lithium tetraborate added, inserting mixture in a Sybrone/thermolyne muffle furnace at 1000 °C for 15 min, where fusion occured. The bead was placed in a baker with distilled water and 10 ml concentrated hydrochloric acid over a period of approximately 15 min under medium heat until digestion is completed. The solution was then diluted to an appropriated volume for atomic absorption determination. Dry ash method was used for the other metallic ions [17–21]. Samples were dried at 150 °C for 4 h in an oven and then milled to powder. The powder was placed in a cold furnace, increasing temperature gradually to 500 °C for more than 4 h. The ash was then dissolved in a solution of 20% hydrochloric acid. Results were reported in weight percentages for both methods.
4.
Results and Discussions
4.1.
Physical Properties
The diameter of each fibre strand from the same species showed varying values due to the inconsistency produced by nature as
shown in Table 1. The table reflects the mean and standard deviation for a population of 20 fibres taken from each type of material. Plant and soil type, usage and climatic conditions may be the cause of these deviations in diameters of the fibres. It is noticed that both bagasse and coconut fibres have similar values whilst the diameter of banana is significantly smaller. Additionally, the values obtained for the diameter of the banana fibres were comparable with the 80 to 250 μm diametral ranges reported in the literature [2]. Micrographs of fibres in the longitudinal position showed residue on the surfaces of the fibres (Fig. 1). This was pronounced in images obtained with the metallurgical microscope. In the case of bagasse, the residue was mostly pith. From the microstructure of the vertical cross-sectional area (Fig. 2), it was observed that the single strand of the coconut fibre had a hollow section. Closer examination of this hollow section in the Wild M3C Defect microscope showed striations that resembled smaller fibre strands as is evident in Fig. 3. This suggests that the ‘single’ strand is actually a series of micro fibres, called a fibre bundle. Table 2 illustrates the physical properties (moisture, ash, carbon and water absorption content) determined for the fibres. For moisture content, banana showed the largest value of 85.6%, followed by bagasse 52.2%, then coconut 27.1%. These values were indicative of the processing that each fibre underwent prior to disposal. Banana and bagasse are continuously exposed to the elements of nature, and based on the time of recovery and nature of the material showed higher moisture content, as expected. Bagasse results from a process
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Table 2 – Physical properties of cellulosic fibres Fibre
Moisture Ash Carbon Water Tensile content content content absorption strength (wt.%) (wt.%) (wt.%) (wt.%) (MPa)
Banana Coconut Bagasse
85.6 27.1 52.2
8.3 5.1 4.5
50.9 51.5 53.0
40 169 235
142.9 138.7 29.6
of intense crushing and squeezing of sugarcane to extract the sucrose and generally retains a moisture content of 45 to 50% after the process is complete [22]. Hence, the moisture content is expected to be within the value measured in this study. The moisture content is related to mechanical properties of the fibre in such a way that the mechanical properties can be significantly reduced for a high value of moisture content [10]. This was observed from the results obtained in this study. Table 2 shows that the ash content (solid residue left after combustion) of banana has the highest value of 8.3%, and is followed closely by coconut (5.13%) then bagasse (4.5%). This ash content gives an indication of the carbon content of each fibre. Higher ash content results in lower carbon content; thus, the data obtained showed bagasse with the highest carbon content of 53%. The importance of this result is specifically useful as it provides the composite material with lightweight, high strength and favourable stiffness [10]. The coconut and banana fibres reveal tensile strength values comparable to that reported in the literature [2,6] although in the case of the coconut fibre mean value was smaller than 175 MPa. Previous studies have revealed comparable results between synthetic and natural fibres' physical and mechanical characteristics such as tensile strength [23].
Table 4 – Metal elements a present in natural cellulosic fibres (wt.%) Fibre
Al3+
Ca+
Mg+
Na+
Si+ 4
Banana Coconut coir Bagasse
0.14 0.03 3.89
5.72 2.44 3.87
1.77 0.76 1.32
0.28 2.53 0.97
1.41 2.56 27.0
a
As shown in Table 3, banana fibres possessed 43.46% of cellulose within its structure while bagasse and coconut showed similar values of 30.27% and 32.65%, respectively. The cellulose content accounts for the high tensile strength of composite materials [4]; hence, any material fabricated from these fibres should show this mechanical property and may be used in application where strength is important.
4.3.
Metal (Ion) Content
The elemental analysis performed on the natural fibre aimed to determine the percentages of sodium, calcium, magnesium, aluminum and silicon. Table 4 presents the results of the metal element analyses performed for all cellulosic fibres. The presence of these trace elements in the fibres increases their brittleness; consequently, very low values are preferred. The values determined, although relatively low except for the silicon in the banana fibre, were higher than the readings obtained by other researchers [24,25].
5. 4.2.
Elements are present in the form of ions.
Conclusion
Chemical Properties
Table 3 shows the results of the chemical analyses performed on the fibres. The results were similar to other investigations [2,4,6]. The coconut coir fibre had the highest lignin content of 59.4% while bagasse and banana had 13% and 9%, respectively. Rai, Jha and others [10] reported similar values for the lignin content of bagasse, banana and coconut coir from their investigations. Studies conducted on Indian cellulosic fibres accounted for cellulose/lignin content ratio of 65/5 for banana and 43/45 for coir [2]. Jamaican cellulosic fibres displayed ratios of cellulose/lignin of 44/9, 33/59 and 30/13 for banana, coconut and bagasse, respectively, as shown in Table 3. Lignin within the structure is responsible for the rigidity of the fibres owing to its high molecular weight and three-dimensional polymer structure [10]. In previous studies carried out by other researchers [1,2], the lignin content was higher than the cellulose content for the coconut fibre, which is consistent with the result obtained for the Jamaican fibres studied. Table 3 – Chemical properties of natural cellulosic fibres Fibre Banana Coconut coir Bagasse
Lignin (wt.%)
Cellulose (wt.%)
Hemicellulose (wt.%)
9.00 59.40 13.00
43.46 32.65 30.27
38.54 7.95 56.73
Based on the results obtained there is potential for the use of Jamaican natural cellulosic fibres that goes beyond the scope of their restricted uses in interior and structural components. The uses of these fibres are driven solely by their environmental attributes and inexpensive nature. With respect to technical advancement, emphasis in this area will allow for further exploitation of local agricultural resources for local needs. Further studies are being conducted to enhance the chemical and mechanical properties of natural cellulosic fibres by chemical modification to promote bonding at the fibre-matrix interface [1,2,4,24,25].
REFERENCES [1] Rowell RM. The state of art and future development of bio-based composite, Science and Technology towards the 21st century. In: Hadi YS, editor. Proceedings: the fourth Pacific Rim Bio-based Composite Symposium; 1998. Bogor, Indonesia. [2] Biswas S, Mittal A, Srikanth G. Development of natural fibre composites in India, News & Views, TIFAC. New Delhi: DST; 2005. [3] Ditchfield C. Australian Hemp Resource and Manufacture, Paper presented at the Bast Fibrous plant today and tomorrow – Breeding. St. Petersburg: Molecular Biology and Biotechnology Beyond 21st Century Symposium; January, 1997.
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[4] Rowell RM, Sanadi AR, Caulfield DF, Jacobson RE. In: CArvalho FX, Frollini E, editors. Utilization of natural fibers in plastic composites: Problems and opportunities, Lignocellulosic-. University de Janeiro; 1997. p. 23–51. [5] Walsh PJ. Carbon fibres. In: Miracle DB, Donaldson SL, editors. Composites. ASM Handbook, vol. 21. ASM International; 2001. [6] Eichhorn SJ, Baillie CA, Zafeiropoulos N, Mwaikambo LY, Ansell MP, Dufresne A, et al. Current international research into cellulosic fibers and composites. J Mater Sci 2001;36:2107–31. [7] Reed A, Williams P. Thermal processing of biomass natural fibre wastes. Int J Energy Res 2004;28:131–45. [8] Fowler HW, Fowler FG, Thompson D, editors. The Concise Oxford Dictionary Ninth Edition. Oxford: Oxford University Press; 1995. [9] Cahn RW, editor. Encyclopedia of Materials Science and engineering Supplementary, vol. 2. Oxford: Pergamon Press; 1990. [10] Rai A, Jha CN. Natural fibre composites and its potential a building materials. Express Text 2004. [11] Sun J, Sun X, Zhao H, Sun R. Isolation and characterization of cellulose from sugarcane bagasse. Polym Degrad Stab J 2004;84:331–9. [12] ASTM Test Method D2216-05, Moisture Content determination.
[13] ASTM standard method E1755-01, Ash content and Carbon content. [14] ASTM standard test D570, Water Absorption 24 Hour or Equilibrium. [15] ASTM Test Method D 1106-96, Lignin content determination. [16] Pessoa Jr A, Manchilha IM, Sato S. Acid hydrolysis of hemicellulose from sugarcane bagasse. Braz J Chem Eng 1997;14(3). [17] Yule J, Swanson G. At Absorpt News 1969;8:30. [18] Ingamells C. Anal Chim Acta 1970;52:323. [19] Everson R. Zinc contamination from rubber products. At Absorpt News 1972;11:130. [20] Heckman M. Collaborative study of copper in feeds by atomic absorption spectrophotometer. JAA 1971;54:666. [21] Jeffery PG, Hutchison D. Chemical methods of rock analysis. 3rd ed. Oxford: Pergamon Press; 1983. [22] Hugot E. Handbook of Cane Sugar Engineering. New York: Elsevier Publishing Company; 1986. [23] Justiz-Smith N, McCalla B. Alternative use of natural fibres in Jamaica. J Arts Sci Technol 2004;1:35–41. [24] Hornsby P, Hinnrichsen E, Tarverdi K. Preparation and properties of polypropylene composites reinforced with wheat and flax straw fibres. J Mater Sci 1997;32:443–9. [25] Barbero E. Introduction to Composite Materials. London: Taylor & Francis; 1998.
Potential of Jamaican banana, coconut coir and bagasse fibres as composite materials Nilza G. Jústiz-Smith⁎, G. Junior Virgo, Vernon E. Buchanan University of Technology, Jamaica, School of Engineering, 237 Old Hope Road, Kingston 6, West Indies, Jamaica
AR TIC LE D ATA
ABSTR ACT
Article history:
This paper presents an evaluation of the alternative use of three Jamaican natural cellulosic
Received 10 February 2006
fibres for the design and manufacturing of composite materials. The natural cellulosic fibres
Received in revised form
under investigation were bagasse from sugar cane (saccharum officinarum), banana trunk
20 September 2007
from the banana plant (family Musacae, genus Musa X para disiaca L), and coconut coir1
Accepted 23 October 2007
from the coconut husk (family Palm, genus coco nucifera). Fibre samples were subjected to standardized characterization tests such as ash and carbon content, water absorption,
Keywords:
moisture content, tensile strength, elemental analysis and chemical analysis. The banana
Fibres
fibre exhibited the highest ash, carbon and cellulose content, hardness and tensile strength,
Composites
while coconut the highest lignin content.
Material strength
1.
Introduction
Centuries ago primitive man frequently used natural cellulosic fibres mainly as construction materials, clothing and as source energy [1]. In recent years, spurred by societal needs to ensure a more comfortable way of life, new technologies have been developed to produce various types of synthetic materials. The evolution of synthetic materials has seen its use in industrial processes as reinforcement of composite materials; the most common of which is fibreglass. There are, however, many advantages and disadvantages associated with the use of synthetic fibres. These fibres have been found to increase the mechanical strength of the composite and enhance other properties such as their thermal and electrical conductivities, which are germane to the composite material industry. Nevertheless, the main concerns are the lack of environmental soundness, the composites' high densities and their relatively low modulus of elasticity. These disadvantages have forced governments and private organisations to invest millions of dollars in the research and development of the use of natural
© 2008 Published by Elsevier Inc.
cellullosic fibres as a viable alternative to synthetic composites [2]. The global trends indicate that the marketplace is leaning towards natural fibre use because of various societal concerns. It is environmentally sound, i.e. renewable, recyclable [3,4] and it has a very low raw material cost. Due to the natural alignment of the carbon–carbon bonds within the structure of these organic fibres it is expected that their linear chained polymers would possess significant strength and stiffness. Over the last decade, there has been increased interest in the sourcing of cheaper raw materials used in the automotive and aerospace industries [2] and natural fibre composites have maintained a position at the top of the list. There is a wide range of biomass natural fibres that are prevalent in commercial applications. We see them being utilised in industries producing ropes and canvases [4–6]. Industrial use of lignocellulose fibre is well established especially in the form of wood for paper pulp and the manufacture of fibreboard [7]. The annual global production of lignocellulosic fibres from crops is about 4 billion tonnes, of which 60% comes
⁎ Corresponding author. Tel.: +1 876 977 4363; fax: +1 876 977 2267. E-mail addresses: [email protected] (N.G. Jústiz-Smith), [email protected] (G.J. Virgo), [email protected] (V.E. Buchanan). 1 Coir – a stiff, coarse fibre from the outer husk of a coconut. 1044-5803/$ – see front matter © 2008 Published by Elsevier Inc. doi:10.1016/j.matchar.2007.10.011
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from agriculture and 40% from forests. In comparison, annual world production of steel is currently around 0.7 billion tonnes and plastic is about 0.1 billion tonnes [4]. Plant fibre can be combined with other materials such as plastics, glass and metals to form a new material. The formation of a composite structure is dependent on the fibre and its matrix. The fibres are responsible for the strength and stiffness while the matrix provides the orientation that bonds the fibres. Also, the properties of plant fibres can be modified through the application of heat treatment and chemical technologies. At the end of these processes, the resulting materials should have more favourable characteristics than their original components [4,6].
3.
Methodology
3.1.
Sample Collection and Preparation
Samples of the three fibrous materials were collected from several locations and sorted: sugar cane (bagasse) samples were obtained from St. Catherine, at the Sugar Company of Jamaica, Bernard Lodge Division and the coconut of the Dwarf species from a Kingston, St. Andrew residence and banana of the Gross Mitchell species from a farm in St. Mary. The banana fibre strands were separated by retting while the coconut fibres were simply cut from the fruit using a sharp knife.
3.2.
2.
Natural Cellulosic Fibres
A fibre is defined as ‘any of the threads or filaments forming animal or vegetable tissue and textile substances' [8]. The fibre cells found in natural fibres are very long in relation to their width [7] having in their cell walls a matrix or the homogeneous lattice structure of lignin and hemicellulose, with embedded cellulose micro fibrils [9]. The layered cell wall contains varying amounts of each constituent. They are classified broadly as lignocelluloses containing 85% or more cellulose, hemicellulose and lignin, and non-lignocelluloses possessing no lignin. Each constituent makes its own contribution to the properties of the fibres [7]. Cellulose is a natural polymer and its structure serves as a carbon reservoir. Cellulosic fibres have a higher Young's modulus when compared to thermoplastic material; hence, they contribute a higher increment of stiffness to the composite [4,10,11]. The high lignin content also allows the fibre to be resistant to rotting under wet and dry conditions and to have a better tensile strength [11]. Plant fibres are often seen as waste produced in the agricultural sector and investigation of these industries in Jamaica show them as an abundant source of raw material that can be transformed into profitable, useable products. Based on these investigations, three natural fibres were selected from the agriculture sector, namely, bagasse from the sugar industry, banana trunks from the banana industry and coconut husk from the coconut industry. The main characteristics of the most important plant fibres however, are described in terms of their mechanical properties such as tensile strength, hardness, chemical/biological composition such as lignin, cellulose, hemicellulose, pectin and ash and microscopic features [6,7]. The present research aims to provide the necessary information about the major physical, chemical and mechanical characteristics of Jamaican natural cellulosic fibres such as banana, coconut and bagasse. The fibre diameter, ash, carbon, moisture content, and water absorption were the parameters chosen to physically characterise these fibres. In the case of chemical/biological composition; the lignin, cellulose and hemicellulose contents were determined. The tensile strength tests were performed to evaluate the fibres' mechanical properties. Other elemental analyses were also performed to quantify silicon, aluminium, calcium, magnesium and sodium content.
Fibre Characterization
The fibres were characterized on the basis of their physical and chemical properties.
3.2.1.
Physical Properties
a. Determination of diameter and microstructure A metallurgical microscope, complete with image analyser software was used to determine the diameter and microstructure of the three fibres. The microstructure determination included both longitudinal and cross-sectional area measurements. Single fibre strands were horizontally positioned in a special clamp and placed on the table of the microscope. An appropriate resolution was determined in order to clearly identify the specimen. A total of 20 strands were analysed for each fibre. Diameter values were taken at different points of each strand and the standard deviation determined. In order to obtain an image of the cross-section of the fibre several strands were cut and placed in a vertical position in a clamp on the table of the microscope. This was repeated for all fibre types and the results recorded. Images were also taken using the Wild M3C Defect Microscope (Model: Leica DC 500) fitted with a digital camera. b. Moisture content The fibre samples were dried in an oven at 110 °C to a constant weight. The moisture content was calculated from the change in weight of the dried sample [12]. c. Ash and carbon content The ASTM standard method E1755-01 [13] was used to determine the mineral content and other inorganic matter (called ash content) as well as the carbon content of the biomass. d. Water absorption Water absorption was evaluated by using the Water Absorption 24 Hour or Equilibrium ASTM standard test D570 [14]. It involved determining the amount of water absorbed under specified conditions. Table 1 – Diameter of cellulosic fibres Fibres
Average diameter(μm) Maximum Minimum Mean Standard deviation
Banana Coconut Bagasse
271.74 511.9 519.4
177.89 307.35 313.35
225.53 396.98 399.05
33.18 67.93 76.75
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that is insoluble in acid. Pre-treatment with acid removes the acid-soluble components followed by solvent extraction of the residual insoluble compounds to leave the lignin as the final residue. b. Cellulose content In the case of cellulose content fibre samples were oxidised using successive solutions of sodium hydroxide at different molalities, filtered and dried, and the difference in weight recorded as cellulose content [16].
Fig. 1 – Micrographs of longitudinal section of fibre strands.
e. Tensile strength Individual fibres were used to determine tensile strength using the Chatillon TCM 201 tensile machine.
3.2.2.
Chemical Properties
a. Lignin content This determination was based on the ASTM Test Method D1106-96 [15] for acid-insoluble lignin in wood. The method involves the determination of the lignin content of wood
Fig. 2 – Micrographs of cross-sectional area of fibres strands.
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Fig. 3 – Micrographs of natural cellulosic fibres (Wild M3C). c. Metal element content Analysis was performed to determine the quantity of silicon, aluminum, magnesium, sodium and calcium present in all three fibrous materials. The AAnalyst 300 Atomic Absorption Spectrometer was used to analyze the samples. Lithium Tetraborate fusion was used to prepare the samples for silicon analysis [17,18]. During this procedure samples were weighed and lithium tetraborate added, inserting mixture in a Sybrone/thermolyne muffle furnace at 1000 °C for 15 min, where fusion occured. The bead was placed in a baker with distilled water and 10 ml concentrated hydrochloric acid over a period of approximately 15 min under medium heat until digestion is completed. The solution was then diluted to an appropriated volume for atomic absorption determination. Dry ash method was used for the other metallic ions [17–21]. Samples were dried at 150 °C for 4 h in an oven and then milled to powder. The powder was placed in a cold furnace, increasing temperature gradually to 500 °C for more than 4 h. The ash was then dissolved in a solution of 20% hydrochloric acid. Results were reported in weight percentages for both methods.
4.
Results and Discussions
4.1.
Physical Properties
The diameter of each fibre strand from the same species showed varying values due to the inconsistency produced by nature as
shown in Table 1. The table reflects the mean and standard deviation for a population of 20 fibres taken from each type of material. Plant and soil type, usage and climatic conditions may be the cause of these deviations in diameters of the fibres. It is noticed that both bagasse and coconut fibres have similar values whilst the diameter of banana is significantly smaller. Additionally, the values obtained for the diameter of the banana fibres were comparable with the 80 to 250 μm diametral ranges reported in the literature [2]. Micrographs of fibres in the longitudinal position showed residue on the surfaces of the fibres (Fig. 1). This was pronounced in images obtained with the metallurgical microscope. In the case of bagasse, the residue was mostly pith. From the microstructure of the vertical cross-sectional area (Fig. 2), it was observed that the single strand of the coconut fibre had a hollow section. Closer examination of this hollow section in the Wild M3C Defect microscope showed striations that resembled smaller fibre strands as is evident in Fig. 3. This suggests that the ‘single’ strand is actually a series of micro fibres, called a fibre bundle. Table 2 illustrates the physical properties (moisture, ash, carbon and water absorption content) determined for the fibres. For moisture content, banana showed the largest value of 85.6%, followed by bagasse 52.2%, then coconut 27.1%. These values were indicative of the processing that each fibre underwent prior to disposal. Banana and bagasse are continuously exposed to the elements of nature, and based on the time of recovery and nature of the material showed higher moisture content, as expected. Bagasse results from a process
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Table 2 – Physical properties of cellulosic fibres Fibre
Moisture Ash Carbon Water Tensile content content content absorption strength (wt.%) (wt.%) (wt.%) (wt.%) (MPa)
Banana Coconut Bagasse
85.6 27.1 52.2
8.3 5.1 4.5
50.9 51.5 53.0
40 169 235
142.9 138.7 29.6
of intense crushing and squeezing of sugarcane to extract the sucrose and generally retains a moisture content of 45 to 50% after the process is complete [22]. Hence, the moisture content is expected to be within the value measured in this study. The moisture content is related to mechanical properties of the fibre in such a way that the mechanical properties can be significantly reduced for a high value of moisture content [10]. This was observed from the results obtained in this study. Table 2 shows that the ash content (solid residue left after combustion) of banana has the highest value of 8.3%, and is followed closely by coconut (5.13%) then bagasse (4.5%). This ash content gives an indication of the carbon content of each fibre. Higher ash content results in lower carbon content; thus, the data obtained showed bagasse with the highest carbon content of 53%. The importance of this result is specifically useful as it provides the composite material with lightweight, high strength and favourable stiffness [10]. The coconut and banana fibres reveal tensile strength values comparable to that reported in the literature [2,6] although in the case of the coconut fibre mean value was smaller than 175 MPa. Previous studies have revealed comparable results between synthetic and natural fibres' physical and mechanical characteristics such as tensile strength [23].
Table 4 – Metal elements a present in natural cellulosic fibres (wt.%) Fibre
Al3+
Ca+
Mg+
Na+
Si+ 4
Banana Coconut coir Bagasse
0.14 0.03 3.89
5.72 2.44 3.87
1.77 0.76 1.32
0.28 2.53 0.97
1.41 2.56 27.0
a
As shown in Table 3, banana fibres possessed 43.46% of cellulose within its structure while bagasse and coconut showed similar values of 30.27% and 32.65%, respectively. The cellulose content accounts for the high tensile strength of composite materials [4]; hence, any material fabricated from these fibres should show this mechanical property and may be used in application where strength is important.
4.3.
Metal (Ion) Content
The elemental analysis performed on the natural fibre aimed to determine the percentages of sodium, calcium, magnesium, aluminum and silicon. Table 4 presents the results of the metal element analyses performed for all cellulosic fibres. The presence of these trace elements in the fibres increases their brittleness; consequently, very low values are preferred. The values determined, although relatively low except for the silicon in the banana fibre, were higher than the readings obtained by other researchers [24,25].
5. 4.2.
Elements are present in the form of ions.
Conclusion
Chemical Properties
Table 3 shows the results of the chemical analyses performed on the fibres. The results were similar to other investigations [2,4,6]. The coconut coir fibre had the highest lignin content of 59.4% while bagasse and banana had 13% and 9%, respectively. Rai, Jha and others [10] reported similar values for the lignin content of bagasse, banana and coconut coir from their investigations. Studies conducted on Indian cellulosic fibres accounted for cellulose/lignin content ratio of 65/5 for banana and 43/45 for coir [2]. Jamaican cellulosic fibres displayed ratios of cellulose/lignin of 44/9, 33/59 and 30/13 for banana, coconut and bagasse, respectively, as shown in Table 3. Lignin within the structure is responsible for the rigidity of the fibres owing to its high molecular weight and three-dimensional polymer structure [10]. In previous studies carried out by other researchers [1,2], the lignin content was higher than the cellulose content for the coconut fibre, which is consistent with the result obtained for the Jamaican fibres studied. Table 3 – Chemical properties of natural cellulosic fibres Fibre Banana Coconut coir Bagasse
Lignin (wt.%)
Cellulose (wt.%)
Hemicellulose (wt.%)
9.00 59.40 13.00
43.46 32.65 30.27
38.54 7.95 56.73
Based on the results obtained there is potential for the use of Jamaican natural cellulosic fibres that goes beyond the scope of their restricted uses in interior and structural components. The uses of these fibres are driven solely by their environmental attributes and inexpensive nature. With respect to technical advancement, emphasis in this area will allow for further exploitation of local agricultural resources for local needs. Further studies are being conducted to enhance the chemical and mechanical properties of natural cellulosic fibres by chemical modification to promote bonding at the fibre-matrix interface [1,2,4,24,25].
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[4] Rowell RM, Sanadi AR, Caulfield DF, Jacobson RE. In: CArvalho FX, Frollini E, editors. Utilization of natural fibers in plastic composites: Problems and opportunities, Lignocellulosic-. University de Janeiro; 1997. p. 23–51. [5] Walsh PJ. Carbon fibres. In: Miracle DB, Donaldson SL, editors. Composites. ASM Handbook, vol. 21. ASM International; 2001. [6] Eichhorn SJ, Baillie CA, Zafeiropoulos N, Mwaikambo LY, Ansell MP, Dufresne A, et al. Current international research into cellulosic fibers and composites. J Mater Sci 2001;36:2107–31. [7] Reed A, Williams P. Thermal processing of biomass natural fibre wastes. Int J Energy Res 2004;28:131–45. [8] Fowler HW, Fowler FG, Thompson D, editors. The Concise Oxford Dictionary Ninth Edition. Oxford: Oxford University Press; 1995. [9] Cahn RW, editor. Encyclopedia of Materials Science and engineering Supplementary, vol. 2. Oxford: Pergamon Press; 1990. [10] Rai A, Jha CN. Natural fibre composites and its potential a building materials. Express Text 2004. [11] Sun J, Sun X, Zhao H, Sun R. Isolation and characterization of cellulose from sugarcane bagasse. Polym Degrad Stab J 2004;84:331–9. [12] ASTM Test Method D2216-05, Moisture Content determination.
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