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Characterization of new cellulosesansevieria ehrenbergii fibers forpolymer compositesT.P. Sathishkumar a , P. Navaneethakrishnan a , S. Shankar b & R.Rajasekar aa Department of Mechanical Engineering , Kongu EngineeringCollege , Erode , Tamilnadu , Indiab Department of Mechatronics Engineering , Kongu EngineeringCollege , Erode , Tamilnadu , IndiaPublished online: 17 Jul 2013.
To cite this article: Composite Interfaces (2013): Characterization of new cellulosesansevieria ehrenbergii fibers for polymer composites, Composite Interfaces, DOI:10.1080/15685543.2013.816652
To link to this article: http://dx.doi.org/10.1080/15685543.2013.816652
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Characterization of new cellulose sansevieria ehrenbergii fibers forpolymer composites
T.P. Sathishkumara*, P. Navaneethakrishnana, S. Shankarb and R. Rajasekara
aDepartment of Mechanical Engineering, Kongu Engineering College, Erode, Tamilnadu, India;bDepartment of Mechatronics Engineering, Kongu Engineering College, Erode, Tamilnadu, India
(Received 26 April 2013; accepted 15 June 2013)
Natural cellulose fibers were newly identified from the sources of sansevieria ehren-bergii plant. These fibers were extracted using the mechanical decortication process.The hierarchical cell structure of the plant and fibers was analyzed using scanningelectron microscope, optical microscope, Fourier transforms infrared, and X-ray dif-fraction. The density and diameter of the fibers were found to be approximately0.887 g/cm3 and 10–250 μm, respectively. The various chemical compositions wereanalyzed and compared with other natural fibers. The thermal stability of the fiberwas examined through thermogravimetric analysis/differential thermogravimetricanalysis (DTG). The maximum peak temperature was obtained at 333.02 °C in DTGcurve. The raw fibers exhibited a tensile strength of 50–585MPa, an elongation atbreak of 2.8–21.7%, a Young’s modulus of 2.5–7.5GPa, and a correctedcompliances Young’s modulus of 2.5–7.8GPa.
Keywords: sansevieria ehrenbergii; chemical composition; infrared spectroscopy;X-ray diffraction; thermal stability
1. Introduction
Over the past two decades, polymer-based materials reinforced with various naturalfibers have been established everywhere from academic and industrial point of view.Environmental consciousness, legislation, and energy consumption have inspired aca-demics and industrial researchers working in the area of cellulose fibers and fiber-rein-forced composite. More than 1000 species of cellulose plants are being available infibers forms and few of them are investigated to prepare the reinforced composite. Thenatural fiber composites have attractive features likes low cost, light-in weight, moder-ated strength, high specific modulus, moderate mechanical properties, easy to handle,and lack of health hazards compared to synthetics fiber composite. Structure of the fiberis framed with natural chemicals such as cellulose, hemicellulose, lignin, pectin, wax,pentosen, and silica. The cellulose fiber-reinforced composites have been significantlyused for industrial components, construction material, automobile parts, and home appli-ances. The traditionally available natural fibers have been used for making ropes, bedsheet, covers, clothes, etc. These cellulose fibers, such as petiole bark, rachis, rachilla,spatha, root, palmyrah, talipot,[1,2] sisal,[3–5] sansevieria cylindrica,[6] sea grass,[7]coconut tree leaf sheath,[8] bamboo,[9] coir and banana,[5,9] curaua,[9,10] vakka, date,
*Corresponding author. Email: [email protected]
Composite Interfaces, 2013http://dx.doi.org/10.1080/15685543.2013.816652
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palm,[11] okra,[12] elephant grass,[13] pineapple leaf fiber,[2,14] abaca leaf fiber, san-sevieria rifasciata, sisal leaf, cocount husk, kenaf bast, ramie bast,[14] rice husk andphormium tenax,[15] kenaf,[15,16] wheat straw,[17] cotton,[18] flax and hemp,[15,18]jute,[18,19] abaca, bagasse, alfa, piassava, date palm, henequen, isora, oil palm [9,19]and softwood kraft [20] were extracted using various fiber-retting process, and also thestructural morphology of natural plants and fibers was analyzed using scanning electronmicroscopy (SEM). The chemical compositions, and physical, thermal, and mechanicalproperties of natural fibers were discussed with Fourier transforms infrared (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA)/differential thermogravimetric(DTG), and tensile testing. These fibers have been reinforced with polymer matrix toprepare the composites using various manufacturing process.
In the present study, the newly identified sansevieria ehrenbergii fibers (SEFs) areextricated from sansevieria ehrenbergii (SE) plant. The physical, chemical, mechanical,and thermal properties have been investigated through FTIR, XRD, TGA/DTG, and ten-sile testing. The effects of fiber lengths on tensile properties such as strength, modulus,and elongation at break, corrected compliances Young’s modulus, and Weibull modulushave been investigated.
2. Natural fiber materials
Natural plant of SE commercially called as snake grass plant belongs to the family ofdracaenaceae. It is a flowering plant which grows in Northeastern Africa, Tanzania,Saudi Africa, and South India and it was discovered by Schweinf Ex Baker in OlduvaiGorge. It has been traditionally used for various purposes such as leaf for antiseptic andnatural bandage, fibers for rope-making, baskets, roofs, and clothes, and it is used as ahome garden at Vijayamangalam (Figure 1).
2.1. Structure of SE leaves and its fiber
SE is known as Blue sansevieria, Sword sansevieria, Oldupai or East African WildSisal. It is a catus and succulent plant, and a native of Olduvai Gorge in Northern Tan-zania. The structure of this plant consists of four to six leaves in dark green color and
Figure 1. SE natural plant.
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approximately 100–200 fibrils in a bundle. It grows in a fan shape with long stiff leaveswrapped nearly into a sword pattern with sharp spine ending. These leaves are about500–1500mm long and 20–40mm wide, and they grow in tight clusters in closer prox-imity amongst themselves. A leaf consists of a sandwich natural composite containingapproximately 8% fiber, 1% cuticle, 12% dry matter, and 81% water.
2.2. Extraction process for SEFs
The natural plant fibers are extracted by adopting various retting process like mechani-cal retting (by hammering or decorticator), chemical retting (boiling with chemicals),steam/vapor retting, and water/microbial retting process.[4,8,13] The SEFs are extractedfrom the SE leaves and they yield strong white elastic long fibers which have been usedfor many purposes. In the process of fiber extraction, leaves of SE are plucked manu-ally and the nodes and culms of the leaves are trimmed by knife. The sand particles areremoved by water.
The mechanical decorticator consists of two rollers. The gap between these rollersof 5mm has been maintained for fiber extraction. The leaves are fed in between therotating rollers. The fibers are found to be adhering to the SE stem. The external layersof fibers such as gums and skin of stems are removed by continuous feeding of leavesin between the rotating rollers. The fibers separated from the stem are washed thor-oughly with water and dried under the sun light for 48 h [21] to remove water contentfrom the fibers surface. These fibers are denoted as SEFs. The extracted fibers length isaround 500–1500mm and it can be chopped into various lengths for experimentation.This extraction is a very simple process; it requires less manpower and energy con-sumption; and is very economical.
2.3. Physical analysis of SE plant and its fiber
The aim of this section is to analyze the cross-section of SE leaves and fibers, and theirmicrostructural characteristics and density of the fiber. SEM and optical microscope(OP) are used to analyze the cross-section of the SE leaves and fibers. The image ofprimary and secondary wall of the leaf and fibers is taken for calculating the dimension.The cross-sectional area of the fibers is approximately round in shape and is used tocalculate the strength of the fiber. The average cross-section diameter is calculated fromthe 1000mm fiber length which is cut into 10 sections of 100mm each.
The density of the SEFs is obtained using pycnometer for solids with toluene(known as Toulon) as the immersion liquid.[13] Initially, the fibers are dried for 48 h inair tight nonhygroscopic desiccator containing calcium chloride. Before measuring thedensity of the fibers, they are initially impregnated in toluene for 2 h to remove themicrobubbles present in the fibers. The density of the toluene (qTÞ is 0.8669 g/cm3 at20 °C. The fibers are chopped into length of 10mm and kept into the pycnometer. Thefollowing formula is used to calculate the SEF density (qSEFsÞ.[11]
qSEFs ¼m2 � m1
ðm3 � m1Þðm4 � m2Þ� �
qT ð1Þ
where m1 is the mass of the empty pycnometer (kg), m2 is the mass of the pycnometerfilled with chopped fibers (kg), m3 is the mass of the pycnometer filled with toluene (kg),and m4 is the mass of the pycnometer filled with chopped fibers and toluene solution (kg).
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2.4. Chemical analysis of the SEFs
2.4.1. Cellulose content
The cellulose content of plant fiber has been measured by Kurshner and Hoffer’smethod.[6,22] The bundle of fibers was washed in distilled water for removing theimpurities present on the fibers surface and dried in an oven at 80 °C for 24 h. The sam-ples of crushed fibers (150mg) were hydrolyzed with a mixture of ethanol and 95%nitric acid. This bundle of fibers was taken from the mixture and kept in oven for dry-ing at 60 °C until constant weight. The cellulose content with a corresponding insolublefraction of samples was weighted. The hemicellulose was measured according to stan-dard NFT 12-008.
2.4.2. Lignin content
The insoluble solution of the lignin content of the SEFs was determined based onKlason lignin of APPITA P11s-78 method.[22,23] The samples of crushed fibers(300mg) were hydrolyzed with 72% of sulfuric acid in an ultrasonic bath for 1 h at acontrolled temperature of 30 °C. The treated sample was mixed with a solvent solutionof methylene chloride (CH2Cl2) and placed in autoclave at 125 °C for one hour anddried. Then, sample was cooled and the lignin was filtered through retentate. Thepercentage of lignin content was obtained by following expression:
IL ¼ WLignin
WFiber� 100 ð2Þ
where IL is the insoluble lignin content (%), WLignin is the oven dry weight of the insol-uble lignin or Klason lignin (g), and WFiber is the oven weight of the fiber (g).
2.4.3. Wax content
The SEFs wax content was determined by Conrad method with Soxhlet extraction.[6]The received SEFs were preconditioned before wax extraction took place. The bundleof fibers was washed in distilled water for removing the impurities in the fibers surfaceand dried in an oven at 80 °C for 24 h. Then, the chopped fiber of 10mm was kept inethanol solution for 6 h. The solution-wetted fiber was transferred to separator funnel.After that, the chloroform was added for wax extraction from the substance such aswaxes, fats, resins, photosterols and nonvolatile hydrocarbons, low-molecular-weightcarbohydrates, salts, and other water-soluble substance. The purified water was addedfor separating the chloroform and other substances. Then, the chloroform was evapo-rated by heating the funnel and leaving the wax. The percentage of wax content wasmeasured by following expression:
%WAX ¼ WFiber �WWax
WFiber
� �� 100 ð3Þ
where %WAX is the percentage of wax content, WFiber is the oven weight of the fiber(g), and WWax is the weight of the wax extracted from the raw fiber.
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2.4.4. Ash content
Initial weight of the sample fibers was measured for quantifying the ash content. Thefibers were kept inside the colorimeter at 250 °C. The result of heating was obtained asfiber ash. The percentage of ash content was measured by weighting the sample.
2.4.5. Percentage of moisture content
The moisture content of the fiber was obtained by normal weight loss method. Twentygrams of fibers were weighted and kept in the oven to dry at 100 °C. During dryingprocess, the weight of the fibers bundle was measured until the constant weight wasobtained. The constant weight was obtained at 100 °C for 4 h 30min. The followingexpression was used to calculate the percentage of moisture content in the fibers.[22]
%M ¼ WBefore drying �WAfter drying
WBefore drying
� �� 100 ð4Þ
where %M is the percentage of moisture content, WBefore drying is the weight of the fiberbefore drying (g), and WAfter drying is the weight of the fiber after drying (g).
2.5. FTIR test
FTIR spectroscopy analysis of the SEFs was recorded using a Perkin Elmer SpectrumRXI FTIR spectrometer. The spectrum was identified with scanning rate of 30 scans perminutes. The total wave number region was recorded from 500 to 4000 cm�1 at roomtemperature of 30 °C and relative humidity of 65%. The bundle of fibers was choppedapproximately 2–3mm and ground into powder form using mortar and pounder. Thepowder was mixed with KBr matrix and pelletized using pressurization. The pellet wasused to record the spectra.
2.6. XRD analysis
The wide angle XRD spectra of the SEFs was recorded with a Rigaku X-ray diffrac-tometer Dmax 2500. An X-ray tube produced monochromatic Cu Kα radiation. Thissystem had a rotating anode generator with angle powder goniometer. It was operatedat 40 kV and 150mA. The reflection mode at a scan speed of 4 °C/min with high inten-sity spectrum of SEF was identified and it estimated the crystallinity indices. All sam-ples were scanned in 2h angle of 5–50°.
2.7. Thermogravimetric analysis
The thermograms of the steam SEFs were recorded on a Perkin Elmer TGA-7 instru-ment in nitrogen atmosphere at a heating rate of 10 °C/min in the temperature range of50–200 °C. About 10mg of the sample fiber was heated from 30 to 200 °C at a rate of5 °C/min, followed by an isothermal setup to 200 °C for 20min. The flow rate of nitro-gen gas was 30mL/min. During this test, the weight loss in terms of temperature wasrecorded as graphs. This test was obtained at controlled atmospheric condition with65% RH and 30 °C.
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2.8. Single-fiber tensile test
The SEFs were chopped into various lengths for testing the tensile properties. Accord-ing to the ASTM D3822-01,[6] the tensile test of single fibers was performed by uni-versal tensile test machine of INSTRON 5500R in South Indian Textile ResearchAssociation (SITRA), Coimbatore, Tamil Nadu, India. Twenty samples of single fiberwere tested for each fiber gage length such as 10, 20, 30, 40, and 50mm. In testing,the individual fiber was clamped with a pneumatic gripper, the cross-head speed of fibertesting was 0.1mm/min and the strain rates were on the order of 0.6–0.15/s. A 1.0 kNload cell was used to measure the load vs. displacement curve (tensile strain) of fiber atvarious gage lengths and dates were recorded as graph. The average value of the tensilestrength, strain, modulus, and elongation at break was obtained. All tests were con-ducted at ambient temperature of 21 °C and humidity of about 65%. Finally, therecorded dates were taken for analysis to calculate the tensile properties of fiber.
The testing compliance of the loading and gripping systems is calculated by obtain-ing the force vs. displacement behavior of the fiber at various gage lengths.[4,24] Thetotal cross-head displacement (δt) during fiber testing is expressed using the followingexpression:
dtF
¼ 1
EA
� �Lþ C ð5Þ
where F is the applied force, L is the gage length (GL), E is the Young’s modulus ofthe fiber, A is the cross-sectional area of the fiber, and c is the machine compliance. Aplot of δt/F vs. GL yields a straight line of slope 1/(EA) and intercept in y axis, whichis the compliance (c) of the load train.
2.9. SEM and OP
The fibers cross-section in longitudinal and transverse directions was obtained usingSEM and OP. The image of transfer section of SE leaf was taken by a SEM model ofJEOL JSM-6390. The following specifications were used for scanning the image: (a)resolution (3.0 nm (Acc V 30 kV, WD 8mm, and SEI)), (b) magnification (5X (WD48mm or less)), and (c) electron gun (accelerating voltage: 0.5–30 kV and filament:pre-centered tungsten hairpin filament). The cross-area and diameters were obtained bythese images.
3. Results and discussion
3.1. Macrostructural analyses of SEF leaf and its fibers
Figure 2 shows that the transverse section of SE leaf consists soft and hard tissues, andthe fibers are arranged in the soft tissue of the plant (Figure 2(A) and (B)). Fibers aregrown from base of the plant which is classified as structural and arch fiber. The struc-tural fibers provide strength and stiffness for the SE leaf and are found in the peripheryof the leaf (Figure 2(A)). The cross-section of the structural fibers is found in semi-elongated circular shape. The arch fibers are usually found in the middle of the leaf(Figure 2(B)). The structure fibers present in the middle of the plant are of higher diam-eter and also found more in numbers. The structure fibers are nearer to green layer ofthe plant (Figure 2(C)). The diameter of the fibers is small and they are found less in
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numbers. The structural fibers are very important because they never split duringthe extraction process. The skin (green layer) of the plant does not have fiber(Figure 2(D)).
3.2. Physical properties of fiber
Some literature reports assumed the fiber are in circular cross-section. The SEFs have asemi-elongated circular shape, the OP is used to measure the diameter of the fiber (10samples) at four points with equal spacing through a 100mm of 1000mm-long fibers.The fiber diameter is almost 20–250 μm. But, the image analysis from an SEM
Figure 2. SEM image of cross-section of SE leaf and fiber: (A) and (B) middle of the SE plantat transfer section; (C) and (D) image of near to green layer; and (E) and (F) the longitudinalcross-section of fiber.
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micrograph is used to measure the area of fiber in precise method. The area of the fiberhas measure at four points with equal spacing through a 40mm SEFs which resulted invalues of 0.012, 0.016, 0.018, and 0.0215mm2 respectively. Therefore, measuring thearea of tensile-tested fiber at the fractured end resulted in more accurate determinationof the average area. For example, the area of the fractured end was 0.011, 0.0141,0.017, and 0.020mm2 respectively.
Figure 3 shows the longitudinal section of SEFs. The cross-sections of fibersare measured by OP along the length of the fiber at various locations. The fibercross-sections varied with varying fiber length. The images of the fiber arepostprocessor to Image ‘J’ software for determining the fiber diameters (20–240 μm).
The density of various natural fibers is given in Table 1. The density may vary withvarious fibers which are due to various climatic conditions, plant growth rate, and planttissue. The density of SEF is 0.887 g/cm3 as measured. The SEF has less density com-pared to sisal, flax, oil palm, hemp, jute, sea grass, agave fiber, etc. and more densitythan petiole bark, elephant grass, abaca leaf, elephant grass, etc. The weight of the com-posites can be determined by the fiber density. The low density fiber has been rein-forced with matrix, which leads to less weight composite. The SEF is a low densityfiber. SEF-reinforced polymer composites can be used for light-weight applications.This low density is in the construction of thermal and acoustic insulation using panelsreinforced with SEFs.
3.3. Analysis of chemical composition of fiber
The chemical composition of the fiber influences its properties. The cellulose contenthas an important influence on the mechanical properties of the natural fiber such as ten-sile strength, modulus, and elongation at break. The various chemical compositions ofvarious natural fibers are listed in Table 2. The SEFs contain 80% cellulose, which is2.5, 7.5, 12, 12.7, 18.8, 29, and 53.8% greater than sisal, hemp, jute, flax, oil palm,kenaf and coir fibers, which is 3.8, 11.11% less than banana and cotton which is equalto sansevieria cylindrica and pineapple leaf fibers.
The SEFs also contain 11.25% of hemicellulose, 7.8% of lignin, 0.45% of wax, and10.55% of moisture. The hemicellulose of SEFs is less compared to all other fiber. Thelignin content influences the fiber structure, properties, and morphology. It is less than
Figure 3. The optical image of the longitudinal section of SEFs.
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kenaf, jute, oil palm, pineapple leaf fibers, and some other fibers, and also greater thanflax, sea grass, sansevieria cylindrica, banana, agave, and some other fibers. The waxcontent in raw fiber affects the interfacial bond between the fiber and the matrix duringcomposition preparation. However, SEFs contain less wax content than kenaf, jute,hemp, phormium tenax, nettle, and oil palm fibers, and it is greater than agave and san-sevieria cylindrica fiber. Therefore, to improve the interfacial bonding between the SEFsand resin, chemical treatment of the fiber has to be done in order to remove the waxand moisture content.
3.4. Fourier transform infrared spectroscopy
Figure 4 shows the FTIR spectrum of wave number 1500–400 cm�1 of raw SEF. TheFTIR spectrum of SEF shows absorption bands of various chemical groups of lignocellu-lose fiber components such as cellulose, hemicellulose, and lignin. The various principalcomponents are alkenes, phenolic hydroxyl group, aromatic groups, β-glucosi linkages,and various functional groups containing oxygen (ester, ketone and alcohol).[25]
Table 1. Physical and tensile properties of raw SEF and various natural fiber.
Fiber nameDensity(g/cm3)
Diameter(μm)
Gagelength(mm)
Tensilestrength(MPa)
Tensilemodulus(GPa)
Elongation(%)
Petiole bark [1,2] 0.69 250–650 – 185.52 15.09 2.1Spatha [1,2] 0.69 150–400 – 75.66 3.14 6Vakka [11] 0.81 175–230 100 549 15.85 3.46Elephant grass [13] 0.817 70–400 50 185 7.40 2.5Abaca leaf fiber
[14]0.83 114–130 10 418–486 12–13.8 –
Sansevieriaehrenbergii
0.887 20–250 10–50 50–585 1.5–7.67 2.8–21.7
Sansevieriarifasciata [14]
0.89 83–93 10 526–598 13.5–15.3 –
Bamboo [9] 0.91 240–330 100 503 0.35–0.91 1.40Sansevieria
cylindrica [6]0.915 230–280 10–40 585–676 0.2–11.2 11–14
Date [11] 0.99 155–250 100 309 11.32 2.73Palmyrah [1,2] 1.09 20–80 43 180–215 7.7–20 7–15Palm [11] 1.03 400–490 100 377 2.75 13.71Coconut or coir [8] 1.15 100–450 100 500 2.5 20Agave [24] 1.20 126–344 – – – –Henequen [9,19] 1.20 – – 430–570 11.1–16.3 3.7–5.9Bagasse [20] 1.25 200–400 – 290 11 –kenaf bast [14] 1.31 65–71 10 427–519 23.1–27.1 –Pineapple leaf
[2,14]1.32 53–62 10 609–700 23.7–30.3 0.8–1.6
Banana [5,9] 1.35 60–250 150 600 17.85 3.36Curaua [9,10] 1.40 170 10 158–729 – 5Sisal [3,4] 1.45 50–300 50 530–640 9.4–22 3–7Hemp [15,18] 1.48 – – 550–900 70 2–4Jute [18] 1.3–1.5 40�350 60 393–773 10–30 1.5–1.8Flax [15,18] 1.4–1.5 – – 345–1500 27.6–80 0.2–3.2Sea grass [7] 1.50 5 – 453–692 3.1–3.7 13–26.6Oil palm [9,19] 1.55 – 248 3.2 25
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Table 2. Chemical compositions of raw SEF and various natural fibers.
Fiber nameCellulose
(%)Lignin(%)
Hemicellulose
(%)Pectin(%)
Wax(%)
Moisture(%)
Ash(%)
Sansevieriaehrenbergii
80 7.8 11.25 – 0.45 10.55 0.6
Kenaf [14] 45–57 21.5 8–13 0.6 0.8 6.2–12 2–5Jute [18] 61–71.5 11.8–13 17.9–22.4 0.2 0.5 12.5–13.7 0.5–2Hemp [15,18] 70.2–74.4 3.7–5.7 17.9–22.4 0.9 0.8 6.2–12 0.8Phormium tenax [15] 45.1–72.0 11.2 30.1 0.7 0.7 10 –Flax [15,18] 64.1–71.9 2.0–2.2 64.1–71.9 1.8–2.3 1.7 8–12 –Agave [24] 68.42 4.85 4.85 – 0.26 7.69 –Bamboo [9] 26–43 1–31 30 – – 9.16 –Sea grass [7] 57 5 38 10 – – –Sisal [3,4] 78 8 10 – 2 11 1Sansevieria cylindrica
[6]79.7 3.8 10.13 – 0.09 3.08 –
Oil palm [9,19] 65 17.5 10.12 – 4 – –Henequen [9,19] 60 8 28 – 0.5 – –Coconut tree leaf
sheath [8]27 27.7 14 – – 4.7 –
Piassava [9] 28.6 45 25.8 – – – –Cotton [18] 82.7–90 – 3 – 0.6 7.85–8.5 –Rice husk [15] 38–45 – 12–20 – – – 20Coniferous [22] 40–45 26–34 – – – – –coir 37 42 – – – 11.36Banana [5,9] 83 5 – – – 10.71
Figure 4. FTIR spectra of raw SEF.
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A broad absorption band in between 3600 and 3100 cm�1 (attributed to cellulose Iβ) cor-responds to the characteristic of O–H stretching vibration and hydrogen bond of thehydroxyl groups.[26] The absorption bands between 3786 and 3457 cm�1 belongs to thestretching vibrations of the phenolic hydroxyl group in the lignin components and hydro-xyl group of the glucopyranose unit in the cellulose. The two sharp peaks near at 2945and 2855 cm�1 are the characteristic bands for the C–H stretching vibration from CHand CH2 in cellulose and hemicellulose components. A small absorption peaks at1636 cm�1 belong to C=O stretching vibration of the alpha keto carboxylic acid in ligninor ester group in hemicellulose. The CH2 symmetric bending band is absorbed at a peakof 1482 cm�1.[24] This represents the hemicellulose xylene, wax, and impurities. Thepeaks at 1385 cm�1 belong to C–O stretching vibration of the acetyl group in lignin andhemicellulose. The bending vibration C–H and C–O group of aromatic ring of hemicell-ulos and lignin shows peaks at 1122 and 1035 cm�1 stretched vibration.[6] Also, the β-glucosi linkages present in cellulose and hemicellulose which is absorbed at 840 cm�1
stretching vibration.
3.5. TGA and DTG
The TGA/DTG vs. temperature curves of the raw SEF thermal process are shown inFigure 5. The temperatures used for the analysis range from 30 to 500 °C. The weightloss may be associated with dehydration as well as degradation of lignin content infiber. This process occurs in the temperature range from 50 to 230 °C. The temperaturerange from 233 to 352 °C leads to higher weight loss which decomposes the cellulose.Almost all cellulose content of the SEF is decomposed at the temperature of 360 °C.Normally, the moisture content of the fiber is associated with the thermal stability of
Figure 5. TGA/DTG curve of raw SEF.
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the fiber. The weight loss may be associated with loss of water in the natural fiber.[6,16,24] In DTG curve, the initial peak observed at 60 °C for SEF corresponds to theheat of evaporation of water from the fiber. The second peak of the SEF observed at333 °C is due to the thermal depolymerization of hemicellulose and the cleavage of theglycosidic linkage of cellulose. In DTG curve, the third peak of the SEF observed at450 °C is due to the thermal depolymerization of wax and other substance in the fiber.This peak is associated for calefactive rate. The temperature of SEF in onset degrada-tion and peak degradation is lower compared to coconut leaf sheath,[8] Okra,[12]Kenaf, [16] and Agave americana.[24] The moisture content of okra, coconut leafsheath, and agave americana fiber is low compared to SEF. In raw SEF, the moleculesare not closely packed, which leads to more penetration of water in the fibers. This ulti-mately decreases the thermal stability of the fiber. The higher value of moisture contentin SEF needs to pre-dry and chemically treat them before making composites.
3.6. XRD analysis
The X-ray spectrum for raw SEF is shown in Figure 6. This spectrum shows two peakswhich are mostly distinct for a raw fiber. These two diffraction peaks indicate that theSEF is semi-crystalline. The two peaks found at 2h= 14.26° and 2h = 26.3°. This can beattributed to cellulose I and IV, both of which exhibit a monoclinic structure [18=26].The broadening of the peak at 2h = 14.26° is mostly of noncellulose materials likehemicellulose and lignin in the fiber. The peak at 2h= 26.3° is the content of α-cellulosein the fiber.[22] These peaks are attributed to the (1 1 0) and (2 0 0) crystalline planes.[26] The crystallinity index (CI) is measure of the crystalline cellulose using the follow-ing expression:
Figure 6. XRD analysis of SEF.
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CI ¼ H26:3 � H14:26
H26:3ð6Þ
where H26.3 is the height of the peak at 2h = 26.3°. H14.26 is the height of the peak at2h= 26.3 and it denotes the intensity of the amorphous peak in the crystallographicplanes. This calculation yields a CI value of 52.27%. It is higher than the cordia dicho-toma fabric [22] of 12.14% and lower than the sansevieria cylindrica of 60%.[6]
3.7. Tensile properties of SEFs
A total of 20 fibers are randomly chosen from a given bundle and tested for each GLof 10, 20, 30, 40, and 50mm. Figure 7 shows the tensile testing machine. The fiberends are hold between the pneumatic grippers and the load vs. displacement curve ismeasured. Figure 8 shows the tensile force vs. displacements curve measured for singlefiber with varying GL. The increase in GL of fiber leads to more fiber displacement.The 10mm GL has less displacement and carries higher tensile load. Increasing the GLdecreases the load carrying capability of fiber. This is due to increase in the number offlaw in the fiber. The fiber length exceeding 40mm does not significantly change in
Figure 7. Single-fiber tensile testing machine.
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displacement. This may be due to constant size of mean flaw in the fiber. The Young’smodulus is calculated in the elastic portion of the stress–strain curve and then correctedfor compliance by measuring the force vs. displacement at various gage lengths usingEquation (5) (Figure 9). These results are shown in Table 3. The GL of fiber does notinfluence the modulus of the fiber. The variability in the modulus for a given GL is dueto the changeability in the microstructure of SEFs by various climatic conditions andalso due to possible damage that occurred during the mechanical decorticator process.
Figure 8. Tensile force vs. displacements of various GL of fiber.
Figure 9. Displacement/forced of fibers vs. gage length (showing a linear relationship with aslope of 1/(EA)).
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A measured vs. corrected stress–strain response of the SEFs is used to quantify themachine compliance. At a given stress level, the measured machine compliance hascontributed in larger displacements. The displacement/force vs. GL is used to calculatethe machine compliance at two different levels. The slope of the line is also measuredfor calculating the modulus of the fiber at different GL. The modulus calculated fromthe corrected compliance curve is similar to the modulus calculated from the displace-ment/force vs. GL procedure. The tested fiber result of a nonlinear region following theinitial portion of the stress strain curve is observed. This may happen due to a collapseof the weak primary and secondary cell walls, and delamination between the microfibercells.[4] During the tensile testing of fiber, the strain-to-failure rate of the fibersdecreased with increasing the gage length of SEFs. This may be related to the size ofthe flaws, propagation of flaws in the entire volume of the fiber, and the number ofmicrocrack due to GL increments.
The tensile strength of the fiber does not depend on function of the GL as shown inTable 3. The Young’s modulus varies between 2.5 and 7.5GPa and the mean tensilestrength varies between 50 and 585MPa. The tested parameters influencing the resultsare as follows: precision of the instrumentation, gage length, strain rate, type of grips,and compliance of the machine. Increase in gage length affects the ductility of the fiber.Strength and modulus will not be affected as the mean flaws size controls the strength.During testing, the crack propagation is initiated as the largest flaws determines the duc-tility. The gage length increases the several flaws existed and the linkage between theflaws will be quicker during testing. It is found that the ductility is very low in thehighest gage length of 50mm. The mechanical behaviors of the SEFs are also depen-dent on source of plant, climate conditions, growth rate, age, types of processing, andthe fiber microstructure.
The SEFs exhibited variability in tensile strength which is quite characteristic of allnatural fibers. This changeability can be explained by distribution of defects within thefiber and fiber surface. Slight differences in microstructure associated with the differenttypes of SEFs could also result in some variability. Weibull statistic tool is used to rankthe relative fiber strength vs. probability of failure of the fibers to obtain a measure ofthe variability in fiber strength.[4] According to the Weibull analysis, the probability ofsurvival of a fiber at a stress (σ) is given by the following relation:
PðrÞ ¼ exp � rro
� �m� �ð7Þ
where σ is the fiber strength for a given probability of survival, and m is the Weibullmodulus. σo is defined as the characteristic strength. The higher the value of m, thelower the variability in strength. Ranking defined as the characteristic strength of thefiber strengths is performed by using an estimator given by:
Estimator ðE1Þ ) PðrÞ ¼ 1� i� 0:5
Nð8Þ
Estimator ðE2Þ ) PðrÞ ¼ 1� i
N þ 1ð9Þ
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Table
3.Sum
maryof
sing
le-fibertensile
prop
ertiesandWeibu
llmod
ulus
ofvariou
sestim
atorsof
SEF.
Gageleng
th(m
m)Diameter
(μm)Tensile
streng
th(M
Pa)
You
ng’smod
ulus
(GPa)
You
ng’smod
ulus
corrected
forcompliance(G
Pa)
Strain-to-failure
(%)
Weibu
llmod
ulus
Areaof
the
fibermm
2
1060–240
317.65
±26
6.78
2.27
±1.13
2.57
±1.05
15.75±5.93
7.28
7.29
7.28
7.32
0.02
4±0.00
320
55–225
343.67
±24
2.99
3.29
±1.79
3.58
±2.11
9.05
±2.61
7.29
7.31
7.30
7.33
0.02
8±0.00
530
40–230
347.12
±23
0.12
4.07
±2.56
5.45
±1.19
7.53
±2.97
7.15
7.16
7.15
7.18
0.02
5±0.00
340
30–235
356.28
±26
7.27
5.55
±1.91
5.95
±1.17
6.81
±4.42
7.14
7.14
7.14
7.17
0.02
3±0.00
650
35–245
368.18
±19
8.58
6.37
±2.15
6.56
±1.73
5.25
±2.42
7.07
7.08
7.07
7.11
0.01
9±0.00
8
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Estimator ðE3Þ ) PðrÞ ¼ 1� i� 0:3
N þ 0:4ð10Þ
Estimator ðE4Þ ) PðrÞ ¼ 1� i� 3=8
N þ 0:25ð11Þ
where P(σ)i term is the probability of survival corresponding to the ith strength valueand N is the total number of fibers tested (N= 20). Substituting Equations (8–11) intoEquation (7) yields:
In In½E� ¼ m Inrro
� �ð12Þ
Thus, a plot of In In½E� vs. In rro
� �yields a straight line with slope of m. The Weibull
modulus for the SEF is higher than sisal fiber. Decreasing the Weibull modulus increasesthe GL of fiber. The Weibull modulus obtained from estimators may be varied with smallchanges. Silva et al. [4] obtained a Weibull modulus of 4.6–3.0 for 10–40mm fiberlengths for sisal fiber. Figure 10 shows the influence of GL on the Weibull modulus mwith estimator E2. Increasing the GL of SEFs resulted in a decrease in Weibull modulus.It can be seen from Figure 8 that the curves have different slope – they almost all inter-cept at the same point (e.g. they have the same mean strength, but little variation).According to Silva et al. [4], this behavior of different materials has the same meanstrength and different Weibull modulus can be obtained. The mean strength of the allmaterials can be controlled by mean defect size in the fiber, but the number of defects inincremental fiber length controls the Weibull modulus. Thus, the fibers with a lower GL(10mm) have less number of defects and the average defect size is same as increasing
Figure 10. Weibull distribution of the SEFs tensile strength for different gage lengths of E2.
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the fiber GL. The defect meant the flaw in the fiber and fiber surface. However, the fiberstrength is not affected by the fiber GL, but the ductility is affected by GL. This meansthat once a crack is formed at the largest flaw, how quickly this linkage between flawsoccurs determines the ductility of fiber. Increasing GL of SEFs leads to a large numberof flaws, the linkage between the flaws will be quicker which leads lower ductility (asabsorbed in the highest SEF GL of 50mm).
4. Conclusion
The structure and properties of the SEFs were studied. The SEM analysis showed themorphology of the plant and fibers was arranged in the plant. The diameter of the fiberalong longitudinal section was around 25–250 μm using optical microscopy and40–165 μm using SEM. Also, the diameter of the fibers of 20–240 μm was obtained fromtransverse section of the fibers using optical microscopy. The cross-sectional area of onethese fibers was 0.0215mm2. The physical density of the SE fiber was 0.887 g/cm3 whichhas been used to prepare light-weight composites materials. The XRD and FTIR analysesshowed that SEFs were semi-crystalline and Iβ cellulose was present in the fiber. The ten-sile strength of the fibers is independent of the gage length. The Young’s modulus of SEFscorrected for machine compliance was approximately 7.8GPa. The strain-to-failuredecreased from 2.8 to 21.7% when the gage length was increased from 10 to 50mm. TheWeibull modulus was decreased with respect to different estimator and decreased whenthe gage length was increased.
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