Composites: Part A 45 (2013) 153161Contents lists available at SciVerse ScienceDirect

Composites: Part A

journal homepage: www.elsevier .com/locate /composi tesaCharacterization of blue agave bagasse fibers of Mexico

Satyanarayana Kestur G. a,, Thais H.S. Flores-Sahagun b, Lucas Pereira Dos Santos b, Juliana Dos Santos b,Irineu Mazzaro c, Alexandre Mikowski c,d,1

a PIPE/Department of Chemistry, Federal University of Parana (UFPR), Centro Politcnico, Jardim das Americas, P.B. No. 19081, CEP: 81531-980, Curitiba, PR, BrazilbDepartment of Mechanical Engineering, Federal University of Parana (UFPR), Centro Politcnico, Jardim das Americas, P.B. No. 19011, CEP: 81531-980, Curitiba, PR, BrazilcUniversidade Federal do Paran, Centro Politcnico, Departamento de Fsica, P.O. Box 19091, CEP: 81504-990, Curitiba, PR, BrazildUniversidade Federal de Santa Catarina, Centro das Engenharias da Mobilidade, CEP: 89218-000, Joinville, SC, Brazil

a r t i c l e i n f oArticle history:Received 6 November 2011Received in revised form 1 July 2012Accepted 1 September 2012Available online 9 October 2012

Keywords:A. FibersB. Mechanical propertiesB. MicrostructuresD. Thermal analysis1359-835X/$ - see front matter 2012 Elsevier Ltd.http://dx.doi.org/10.1016/j.compositesa.2012.09.001

Corresponding author. Present address: Anandaemy Road, Bikasipura, ISRO Layout, Bangalore 560 06135x3012; fax: +91 80 26614357.

E-mail addresses: kgs_satya@yahoo.co.in (S. Kgmail. com (T.H.S. Flores-Sahagun), santoslucas4@hojulianastos@hotmail.com (J. Dos Santos), mazzaromikowski@joinville.ufsc.br (A. Mikowski).

1 Universidade Federal de Santa Catarina, Centro daCEP: 89218-000, Joinville, SC, Brazil

2 Throughout this paper the word bagasse when usunless otherwise mentioned.a b s t r a c t

This paper presents physical, chemical, thermal and tensile properties of Mexican cooked blue agavebagasse fibers extracted from this plant. The fibers are 1012 cm long and 592.34 lm in diameter. Theelliptical cells in the fiber are regularly arranged with varying lumen size. The cellulose and lignin con-tents of the fiber are 73.60% and 21.10% respectively. Fibers showed decreasing average values of ultimatetensile strength and constant values of Youngs modulus and average % strain values with increasingmean gauge length and decreasing mean diameter. Above results are discussed in the light of various fac-tors that affect the properties. These fibers are found to be thermally stable due to their higher values ofcrystallinity and lignin. Main aim of this work is to characterize these partially degraded fibers with aview to find possible uses for such fibers such as compostable and biodegradable composites of cornstarch/cooked blue agave residues.

2012 Elsevier Ltd. All rights reserved.1. Introduction 1.1. Background, status of characterization and usesSignificant efforts in recent years to develop composites rein-forced with plant materials have prompted study of the structureand properties of various plant fibers. The heightened awarenessof the need to preserve and recycle natural resources has enlargedthe range of plant fiber resources [14] for such applications. Thereasons for such studies include renewability and abundant avail-ability of plant fibers, and stringent environmental regulations,have been mentioned elsewhere [5,6]. There has been specificcharacterization of individual plant fibers including those of Brazilorigin by the authors themselves such as coir and sisal [14,712]as well as part of studies on composites [5,6]. Extending their workon characterization of lignocellulosic fibers, the authors havestarted research on the characterization of two of the fibers ob-tained from Mexico, This paper deals with the blue agavebagasse12 fibers (Agave tequilana).All rights reserved.

Kuteera, G001, Insight Acad-, India. Tel.: +91 80 26622130

estur G.), tsydenstricker@tmail.com (L.P. Dos Santos),@fisica.ufpr.br (I. Mazzaro),

s Engenharias da Mobilidade,

ed refers to blue agave fiberA. tequilana (also termed A. tequilana or Agave Americana L asused by Bessadok et al. [12] or blue agave is native to Mexico. A.tequilana Weber azul is a succulent plant (Fig. 1a) that spreadsradially and is 1.21.8 m tall at maturity.

It is mainly used to produce the distilled spirit tequila, since un-der Mexican law, only the blue agave, which has an intense bluecolor, can be used to produce tequila [1316]. Commercially, theimportant part of A. tequilana Weber azul for tequila productionis the stem (Fig. 1b) commonly termed head or pin, the Span-ish word for pineapple, which it resembles. It is also reported thatafter the agave juice is obtained, a fibrous waste is left after cook-ing the head.

It should be noted that these cooked blue agave bagasse pilesare seen in the tequila industrial plant from which the fibers arealso extracted, which are used in this study. On the other hand,the raw blue agave stem is extracted from the fields and go bytruck to the tequila facilities where the sweet juice is extractedand the bagasse is the residue. From this, fibers (called bagassecomposed of fiber and pith) are obtained after shredding, millingand extracting the juice from the cooked agave heads.

A number of studies [12,1321], though not systematic, havebeen reported (including some patents) on this plant looking intovarious aspects such as harvesting the plant, management, eco-nomic aspects, process for obtaining the fibers from leaves ofthe plant characterization and possible utilization of parts (e.g.leaves obtained after the extraction of juice) and other byprod-

http://dx.doi.org/10.1016/j.compositesa.2012.09.001mailto:kgs_satya@yahoo.co.inmailto:tsydenstricker@gmail.commailto:tsydenstricker@gmail.commailto:santoslucas4@hotmail.commailto:julianastos@hotmail.commailto:mazzaro@fisica.ufpr.brmailto:mikowski@joinville.ufsc.brhttp://dx.doi.org/10.1016/j.compositesa.2012.09.001http://www.sciencedirect.com/science/journal/1359835Xhttp://www.elsevier.com/locate/compositesa

Fig. 1. Photographs of (a) Mexican agave tequilana (blue agave) plantationshowing cutting operation to get the stems. (b) Stems lying in a factory from whichfibers are extracted. [Reproduced from (a) http://www.royalresortsnews.com/wp-content/uploads/2010/10/agave-farming-tequila-mexico.jpg (b) http://a1.sphotos.ak.fbcdn.net/hphotos-ak-snc6/226087_10150320505500861_709255860_9667455_3138674_n.jpg] (Accessed on 20th October 2011). (For interpretation ofthe references to colour in this figure legend, the reader is referred to the webversion of this article.)

154 S. Kestur G. et al. / Composites: Part A 45 (2013) 153161ucts [17]. Limited studies on the tensile properties of these fibersincluding the effect of surface treatments on these properties arealso reported [13,15] including one such study on the fiber bun-dles obtained from Tunisia with and without the chemical treat-ment of the fibers [12]. Another study has reported on thepreparation and characterization of composite of this fiber in highdensity polyethylene with and without esterification as reinforce-ment [21].

While many patents are available describing the utilization ofsub-products of blue agave leaves, other uses of the fibers are alsoreported [17,22,23], which include possible production of goodquality fiber from commonly discarded leaves after obtaining thepia and as reinforcements in thermosetting resins. While manyof these attempts are at laboratory stage without enough informa-tion to evaluate their feasibility, there is continuous research tofind alternative uses for this fiber. This has been the subject ofmany researchers, since 40% (on wet weight basis) of the total blueagave consumed corresponds to the residual bagasse, most ofwhich is treated as waste and hence thrown into fields, which isnot a value added use [12,13].

Further, it is also reported [17] that these plants would provideimportant economic status in the future with considerable devel-opment opportunities.

From the foregoing, the following becomes evident: (i) the blueagave fibers is produced in Mexico as a byproduct of one of theirmost important beverage industry; (ii) scanty and scattered datais reported on the properties along with some potential beneficialeconomic aspects of this waste; (iii) there is no report from one re-search group on the characterization of cooked blue agave bagasseextracted from the stem (head or pia) obtained from Mexicoalthough there are some papers about the use of the bagasse fiberas reinforcements in composites without mentioning whetherthese fibers were obtained from tequila factory where the fibers re-main stored in piles whereby degradation process of the fibersinevitably could have occurred and (iv) despite all these, a seriousenvironmental problem is posed by the waste blue agave leavesthat are left in the field after harvesting the heads for tequila pro-duction, even when some quantity of these are used for fiberextraction. Considering all these, a systematic study is undertakenwith the objectives to characterize the blue agave bagasse fiber ex-tracted from the stem base, which are obtained from one majorcountry. These include chemical composition, density, structureand morphology; thermal as well as tensile properties of these fi-bers, which were supplied by a tequila industry in Mexico. Itshould be understood that this kind of study may pave the wayfor finding suitable applications for such fibers obtained from leftout of cooked blue agave bagasse from the Tequila productionand thus, the fibers might have undergone a degradation processin the storage step.

2. Experimental

The agave bagasse fibers used here were obtained from a tequi-la factory in the city of Tequila, Jalisco state, Mexico. The fiberswere obtained in the tequila industry as follows: after the cookingof the agave stem (pia), the sweet agave juice obtained goes to thefermentation process, while the fibrous waste called bagasse isleft in the field forming big mountains until transportation bytrucks. As a residue, no special care is taken to avoid its partial deg-radation and so, the material undergoes some degradation processbefore these fibers are used for any application.

They were light brown in color. The dimensions (length anddiameter) were measured using a projection (optical) microscope,which could read up to 2nd decimal point. The morphology studieswere carried out on the received fibers using both optical and scan-ning electron microscopes. For the optical microscopy study, thespecimens were prepared using a mixture of polyester resin with2% catalyst and 2% initiator poured into a mold into which a bunchof fibers was kept vertically until the resin set. After curing, thesamples were ground successively using silicon carbide papers ofgrit size ranging from 220 to 600 mesh sizes. Then the specimenswere polished with a sylvet cloth mounted on disk polisher usingdiamond paste (6, 3 and 0.25 lm size). The polished specimenswere observed in reflected light using a Leica DMRX optical micro-scope. For electron microscopy, fiber samples were mounted onbrass studs and after gold coating were observed under a JEOLscanning electron microscope (model JSM 6360 LV) at 15 keVand current of 0.65 A.

The density of the fibers was determined as per the standardABNT NBR 11931, which is similar to ASTM D 1505 and ASTM D792 where the density of the fibers is estimated by the density gra-dient method used for polymeric materials. In this method, chloro-form having density of 1484 kg m3 and methylene chloridehaving density of 1330 kg m3) were used as solvents. The method,in short consists of immersion of a portion of the sample in a bea-ker containing a mixture of miscible solvents of different densities.Then, volume of each solvent used is measured and the beaker isfilled until the fibers stay floating at the center of the liquid mass(density of the fiber is equal to that of the liquid mass). Then, withthe known volumes and density values of the solvents, the densityof the fiber is calculated.

For tensile testing of the fibers, the procedure followed was thatthe fibers 50 mm in length were cut and mounted on a piece of

http://www.royalresortsnews.com/wp-content/uploads/2010/10/agave-farming-tequila-mexico.jpghttp://www.royalresortsnews.com/wp-content/uploads/2010/10/agave-farming-tequila-mexico.jpghttp://a1.sphotos.ak.fbcdn.net/hphotos-ak-snc6/226087_10150320505500861_709255860_9667455_3138674_n.jpghttp://a1.sphotos.ak.fbcdn.net/hphotos-ak-snc6/226087_10150320505500861_709255860_9667455_3138674_n.jpghttp://a1.sphotos.ak.fbcdn.net/hphotos-ak-snc6/226087_10150320505500861_709255860_9667455_3138674_n.jpg

S. Kestur G. et al. / Composites: Part A 45 (2013) 153161 155hard cardboard with a central window. Then the cardboard wasgripped by an Instron machine (model 5565) and the sides of thecardboard were cut before applying the final load. Stressstraincurves of the fibers were obtained using 1 kN load cell (having pre-cision of 0.02 N) and cross-head speed of 5 mm/min. All the testswere carried out at room temperature (25 C) and relative humid-ity of 43% with an average minimum load of 0.02 N and maximumof 2.43 N. Because of the variations in diameter of the fibers alongtheir length and also between fibers, three sets of fibers weretested with each set having a narrow diameter range. At least 10samples were used for each set. From the stressstrain curves ob-tained, the average Youngs modulus (YM), ultimate tensilestrength (UTS) and% elongation were evaluated for each set. To cal-culate the strength values, the values of the force (F) and the areaof the curve were used, while the% elongation was calculated usingthe standard method with monitoring the extension through thedisplacement shown without the use of the extensometer.

For chemical analysis, the fibers were chopped using knives.The fibrous residues were sieved into different fractions (20, 35and 60 mesh) and separated. The initial mass of material beforethe grinding was determined (170 g). Fibers of 35 mesh size wereused for the determination of chemical composition, as this frac-tion was the largest. All determinations were carried out in tripli-cate using 25 g of the fibers and average values are listed.

Moisture content of the fibers was determined as per Standard:TAPPI T212 om-02 and using the equation:

Min% W f Wo 100=Wo 1

where M is the moisture content and Wf and Wo are the weights ofthe fibers in wet and dry conditions. All experiments were per-formed in triplicate.

The ash content of the fibers was determined as per TAPPI T211om-02 standards and calculated using the equation:

Ash% A 100=B 2

where A is the mass of ash and B is the original mass of the fibersample.

The TAPPI T207 cm-99 standard was followed for the determi-nation of soluble products in cold/hot water. Solubility in coldwater or hot water was then calculated using the equation:

S% P P1=P 100 3

where P is the initial mass of the sample, P1 is the mass after the testand S is the percentage of soluble products in cold/hot water.

Solubility in 1% NaOH solution as per TAPPI T212 om-02 stan-dard determines the degree of attack of the lignocellulosic materi-als by fungi or other deleterious agents. Also, this is important dueto the wet nature of the residue and possible degradation duringtransportation. According to the standard mentioned above, low-molecular-weight carbohydrates consisting mainly of hemicellu-lose and degraded cellulose in wood and pulp are extracted byhot alkali solutions. In the case of wood, its solubility could indi-cate the degree of fungus decay or of degradation by heat, light,oxidation, etc. With the decay or degradation of wood, an increasein the percentage of the alkali-soluble material occurs. Further, theextent of cellulose degradation during any chemical process (pul-ping and bleaching, etc.) is indicated by the solubility of pulp,which has been related to strength and other properties of pulp.Accordingly, Solubility in 1% NaOH solution was determined asper the standard mentioned and using the equation also used fordetermining the solubility in water mentioned above.

Following the TAPPI T204 cm-97 and TAPPI T264 cm-97 stan-dards a mixture of ethanol/toluene was used to extract fats,greases, some resins and gums, while hot water was used to ex-tract tannins, gums, sugars, starches and colored materials. Theamount of extracts (%) was obtained using an equation mentionedin the standards (TAPPI T204 cm-97 and TAPPI T264 cm-97) simi-lar to the one used for% soluble in water, with P being the initialmass of the sample, P1 the mass after extraction and S the percent-age soluble in ethanol/toluene. The material resulting from the to-tal extracts was then used to determine the lignin content.

Both soluble and insoluble lignin contents were determined asper the TAPPI T222 om-02 standard. The amount of soluble ligninwas then calculated using the equation [24]:

CLS 4:53 A215 A280=300 4

where CLS is the lignin concentration in the sample in g L1; A215 isthe absorption by solution at 215 nm and A280 is the absorption bysolution at 280 nm.

On the other hand, the cellulose fractions (a, b and c) of the blueagave fiber were determined as described in the TAPPI T203 cm-99standard.

X-ray diffraction (XRD) studies were carried out using a Shima-dzu diffractometer (Model XRD-7000), with monochromatic Cu Karadiation (k = 1.5418 ), at operating conditions 40 keV and 20 mAto determine the crystallinity of the fiber following regular diffrac-tion method. For this, a sample was prepared by cutting a smalltransversal piece (0.51 mm), to make a sample with volume of100 mm3, seeking to obtain the best random distribution fromthe fibers to estimate the crystallinity index. The measurementwas done with slits from 1 and the equipment was operated at40 keV and 20 mA.

Thermogravimetric analysis (TGA) was carried out in a MetlerToledo instrument (Model SDTA 851) with a heating rate of20 C/min. In this case, two atmospheres were used. The first onewas nitrogen (inert) atmosphere, which prevents combustion andallows the degradation of components to take place one by oneand thus making it possible to identify the degradation regions ofthe fiber components, while under atmosphere of air/oxygen boththe reactions occur at the same time similar to oxidative atmo-sphere, since it is not possible to separate the different degradationprocesses of the fiber components such as hemicellulose, celluloseand lignin, because all the reactions would be very complex andthey would be overlapped in the temperature ranges of these reac-tions [9,10]. Finally, the samples were maintained at 800 C for 10more minutes. Experimental conditions used are: nitrogen (50 mL/min) in the range of 40600 C and air (50 mL/min) from 600 to800 C, after which the samples were maintained at 800 C for afurther 10 min.

Differential scanning analysis (DSC) was performed in a MetlerToledo instrument (Model 822e) in the range of 40550 C at aheating rate of 10 C/min in a nitrogen atmosphere at a pressureof 104 Pa.3. Results

It should be noted that the fibers characterized for various prop-erties in this paper are those fibers obtained from tequila factory(as explained in Section 2), where the fibers (cooked bagasse) re-main stored in piles whereby degradation process of the fibersinevitably could have occurred and mostly discarded as waste.In view of this, the properties determined show differences fromthose reported earlier on these types of fibers (these were raw,but not cooked ones). From the point of view of the readers, whoare new to this field of lignocellulosic fibers and hence may notbe aware of various factors that affect the properties of the fiber,detailed explanation is given in the next Section 4 to help themin understanding the observed results. In view of this, all the re-sults obtained in this study are described with the detailed discus-sions even though it may be often found to be redundant.

156 S. Kestur G. et al. / Composites: Part A 45 (2013) 1531613.1. Density

The density of the fiber was found to be 880 kg m3, which ishigher than that reported earlier (740 kg m3) for this fiber [12],but lower than that reported for other types of agave fibers [25].

3.2. Morphology studies

Fig. 2 shows a histogram of the sizes of blue agave bagasse fi-bers according to sieving. It can be seen that 32.9%, 47.8% and19.3% of the fibers sieved through mesh sizes of 20, 35 and 60respectively were retained in sieve size 0.85 mm, 0.43 mm and0.21 mm respectively. As can be seen from the figure, some fibersare very thick and others quite thin. Thus, each sieve retainedthe fibers according to their size, although during sieving the fibersmay pass from one sieve to another vertically (lengthwise). Thevery thick ones could have any size, but were mostly retained in20 mesh size.

Furthermore, Fig. 3 shows a cross section (Fig. 3a) and longitu-dinal sections (Fig. 3b and c) of this fiber. It can be seen from Fig. 3athat thick walled cells are closely packed and have irregular lumen.Fig. 3b is a scanning electron micrograph of a longitudinal sectionof the fiber, similar to that observed in many plant fibers, showingthe longitudinal arrangement of a large number of fibrils, withbinding and pithy material in between. Some surface defects arealso evident, which might have occurred during the extraction pro-cess. At higher magnification (Fig. 3c), one can see the internalstructure showing the helical winding of microfibrils. Averagelength of the fibers was found to be 1012 cm.

3.3. Chemical composition

Table 1 summarizes the complete chemical analysis of blueagave fiber residues (bagasse) determined in the present study. Itcan be seen that the ash content obtained [5.30%] is higher thanthat reported (2%) for fiber from raw heads without cooking [13],but, is lower than that reported (8.8%) for the cooked material[20]. On the other hand, the insoluble lignin content obtained issimilar to that reported for uncooked raw heads [13], while it ishigher than that reported [20] for the cooked material [7.2%].

There are also differences in the cellulose content obtained fromthe reported ones. The a cellulose content obtained in the presentstudy (49.43%) is lower than that reported (64.9%) when raw headswithout cooking were used [13], but it is higher than that reported[20] for cooked material (41.90%).53.98g

78.41g

31.60g

0102030405060708090

100

20 mesh 35 mesh 60 mesh

Fig. 2. Histogram of sieved blue agave fiber sizes. (For interpretation of thereferences to colour in this figure legend, the reader is referred to the web version ofthis article.)Similarly, the solubility in hot water is also higher than that re-ported by Iiguez-Covarrubias et al. (5.84%) for uncooked raw headfiber [20], while the ethanol/toluene extracts are comparable toethanol/benzene extracts (2.95% compared to 3.1%).

In the case of total lignin content, it is higher [21%] than that re-ported in fiber both from raw [1616.8%] and cooked heads [7.2%][13,20]. Also, all the values of chemical constituents are higherthan those reported earlier by Cedeo Cruz and Alvarez-Jacobs[18]. It is also interesting to note that while the total chemicalcomposition (cellulose content + lignin + ash) in the present studyadds to 100%, the same was not true in other studies [13,20],since many of the constituents were not given. In practice, the totalFig. 3. Morphology of Mexican blue agave fiber. (a) Scanning electron micrographof the cross section of blue agave bagasse fiber showing central lacuna and lumensin cells. (b) Longitudinal section of the fiber showing arrangement of cells withsome surface defects including the channels and defects.

Table 1Chemical composition of Mexican blue agave.

Content Present study (%)a

Moisture 10.1 0.05Ash 5.30 0.07Solubility in cold water 9.74 0.27Solubility in hot water 10.64 0.26Solubility in 1% NaOH 35.73 0.38Ethanol/toluene extracts 2.95 0.17Soluble lignin 5.12 0.40Insoluble lignin 15.98 1.20Total lignin 21.10 1.13Cellulose 73.60 0.01a-Cellulose 49.43 0.54b-Cellulose 15.21 1.26c-Cellulose 8.96 1.12

a All values are average of triplicates.

S. Kestur G. et al. / Composites: Part A 45 (2013) 153161 157of all the constituents determined by chemical analysis of lignocel-lulosic materials, such as the fiber studied here, should be 100%.Normally totals of 95102% are not uncommon [26] due to partialloss of a constituent, overlapping of some constituents in analysis,impurities present in residues and failure to account for some ofthe compounds present in the material.3.4. X-ray diffraction (XRD) studies

Fig. 4 shows the X-ray diffractogram of the fiber obtained in thisstudy. Several sharp peaks can be seen together. The crystallinityindex (Xc) of Mexican blue agave fiber was calculated at 2h valuesbetween 5 and 70 using the equation given below, following thereported method by Alexander [27]:

Xc Ic=Ic Ia 100% 5

where Ic is the scattering of crystalline portion and Ia is the scatter-ing of amorphous part. This method in brief is the one that is basedon the possibility of drawing a line between the spread of the crys-talline and amorphous material in a certain angular interval, wherethere is the amorphous halo and crystalline peaks. In the presentcase, a program Dxta Version 2.6 that comes with the analysis soft-ware of XRD Shimadzu equipment was used with delineation of theprofiles corresponding to diffraction of the crystalline portion (Ic)and also the scattering of amorphous part (Ia). The crystallinity ob-tained from the above is found to be 70% for the fiber.Fig. 4. X-ray diffractogram of Mexican blue agave fiber.On the other hand, a single fiber diffraction pattern showeddark wide concentric rings (halos) on the film coming from the fi-ber (not included due to poor quality of the figure). The Laue pat-tern obtained showed a pattern typical of cellulose fibers, whilesome points distributed on the film came from a very organizedcrystalline material, probably from internal microcrystalline impu-rities in the fiber. This confirmed that spots observed in the Lauemethod correspond to the sharp peaks observed in the diffracto-gram. However, it was not possible to identify symmetry of thepoints on the film, suggesting that the observed dark points mighthave come from different small crystallites distributed in the fiber.

3.5. Thermal studies

Fig. 5a and b present TGA and DSC data of the Mexican blueagave bagasse fiber. It may be noted that the TG analysis givesinformation about thermal stability of the fibers and compositionin terms of volatile substances, organic constituents and inorganicresidues. Accordingly, it can be seen from the TGA curve that thefiber undergoes mass loss at three different temperatures, viz.,10.8% starting at 80 C (moisture content in the fiber), 63.8% at360 C and finally 20% at 620 C.

Between 100 and 220 C, the blue agave bagasse fiber presentsthermal stability (see Fig. 5a) suggesting that these fibers can beused safely up to the maximum temperature of 220 C. This tem-perature can be taken as that for thermal stability of blue agave fi-ber, which is similar to that observed for Brazilian banana fibers,but slightly lower than those of sugarcane bagasse and spongegourd fibers (250 C). This high thermal stability may probablydue to its high value of crystallinity (70%) and high lignin content.

Further, it is reported that the estimation of the amount of bulkfree water in cellulose-based materials can be measured by thevaporization temperatures in DSC [28]. In the case of blue agavebagasse fibers, one endothermic peak was observed in DSC curve(Fig. 5b) at 89. 2 C, corresponding to the dehydration of fiber (inagreement in the range at which 10.8% mass loss observed inTGA curve). This is in contrast to only one peak observed at300 C for three Brazilian fibers (attributed to decomposition ofcellulose [11] and two endothermic peaks at 69.1 C and358.0 C) for bleached cellulose obtained from sugarcane [35]and at 126 C and 325 C for wood [29] corresponding to dehydra-tion and decomposition, respectively. In the present case, theamount of energy DH = 328.1 J/g was used during evaporation ofthis water.

3.6. Tensile property studies

It should be noted the fibers used in the present study are notthe same as those used by some of earlier researchers [1214,19,20] in that, present ones were received after the extractionfrom the blue agave leaves left in the field after the extraction ofjuice. Considering the large variation of gauge length and diameterof the fibers used (as-received only, but not cut) for the tensile test-ing, as shown in Fig. 6a and b, tensile properties were determinedin three groups of diameters (no relation to either fibrils or otherstructural aspects of fibers) of the same gauge lengths and differentgauge lengths with constant diameter, using the respective stressstrain curves. The typical stressstrain curve for Mexican blueagave fiber fibers is shown in Fig. 7, wherein the strain rate atthe point of maximum load is 0.09 min1 or 1.5 ms1. This is sim-ilar to that observed for banana fiber, showing continuous increasein stress with increasing strain until the maximum stress isreached, when it breaks.

The mean tensile properties were evaluated from such curves.The statistical treatment of these values is tabulated in Table 2.However, it may noted that the data shown (Youngs modulus

Fig. 5. (a) TGA and (b) DSC curves of Mexican blue agave fiber.

158 S. Kestur G. et al. / Composites: Part A 45 (2013) 153161and Tensile strength) in the table demonstrates these properties donot differ significantly with diameter of the fibers at 0.05 level withmeans are not significantly different as shown in the Tables 3a andb.

Further, it can be seen that the mean value of Youngs modulus(2.62.9 GPa) and % strain (1215) remain nearly constant for allthree sets. On the other hand, even though the mean ultimate ten-sile strength values decrease from 58.1 MPa to 41.5 MPa withincreasing mean gauge length (5198 mm) and decreasing meandiameter (426.6328.7 lm), as can be seen from Table 3b, it maybe assumed that this property also does not differ significantlyalthough diameter vs tensile strength showed inverse relationshipas observed by many others [9,10,35,36]. It thus becomes evidentthat the mean UTS values obtained in the present study are muchlower than those reported range of values earlier, but the meanvalues of YM and % strain are in comparable range with the re-ported range of values for the fibers with diameter range of 60140 lm [12].4. Discussions

It is well known that the properties of lignocellulosic fibers de-pend significantly on many factors, such as variety, climate, har-vesting and maturity, extraction process, and the experimentalconditions during testing, among others [18]. In addition, in thecase of fibers studied in the present investigations, other factorsto be considered include degradation occurred by the cooked blueagave bagasse thrown in the Tequila industrial plant (Remainstored in piles whereby degradation process of the fibers inevitablyoccurred), effect of variety and environment, etc. Accordingly, thedifferences in various properties studied in this investigation in re-

Fig. 6. Size distribution of Mexican blue agave fiber: (a) Length distribution. (b)Diameter distribution. (For interpretation of the references to colour in this figurelegend, the reader is referred to the web version of this article.)

Fig. 7. Typical stressstrain curve of Mexican blue agave fibers. (For interpretationof the references to colour in this figure legend, the reader is referred to the webversion of this article.)

S. Kestur G. et al. / Composites: Part A 45 (2013) 153161 159spect of blue agave bagasse fibers of Mexico and the earlier re-ported results on this fiber can be understood on the basis of abovementioned factors. Some details of this on each of the propertystudied are mentioned below briefly.

Thus, the difference in density values for the same type of blueagave fibers may be due to the fiber extraction processes used byBessadok et al. [12], who obtained the fibers from a pretreatmentof washed blue agave leaves of Tunisia origin by using a pectinasesolution followed by another washing followed by whitening usingbleach solution, the first washing being done by Milli-Q water for24 h at 25 C. On the other hand, the fibers used in the presentstudy obtained from Mexico were by cooking the stem followedby the extraction of the juice, resulting in the fibers (bagasse) fol-lowed by keeping the fibers for some period, during which likelyhood of degradation by fungi could have occurred.

Study of X-ray diffraction results of the fiber showing severalsharp peaks, which may be related to a material with less struc-tural organization and are associated with the fibers crystallinecharacter. This is probably due to some type of sugar or some othersubstance adhered during the fermentation process [21].

Similarly, the difference in various chemical constituents ob-tained in the present study such as cellulose, lignin and ash andthe previously reported by other workers [12,13,1820] in similarmaterial (blue agave fiber) may be due to various factors men-tioned above including geographic locations, harvesting and matu-rity of the plants, extraction process used for obtaining the fibers,and methodology used for chemical analysis [12,19,20,30]. Possi-ble degradation process undergone by the fibers analyzed couldalso be another factor [13,20]. In the case of difference in valuesfor solubility in hot water between the present study and earlierreported ones could also be due to natural resins, which are gener-ally insoluble thermosets.

The NaOH solubility indicates that the agave fibrous residuewas subject to degradation. This is probably due to the fact thatthe analyzed residues were obtained from tequila production,where the head was cooked without any treatment and thus notcompletely dried, leading to degradation of its bagasse before theywere analyzed. Therefore, when these fibers are used, it should beknown that they are partially degraded fibers, without completedrying. In this respect, Iiguez-Covarrubias et al. [20] reported thatwet agave bagasse was subjected to degradation of organic mate-rial, following a first-order kinetic equation. The value obtained(35.73%) in this study is very high, considering that the acceptableamount of solubility in 1% NaOH is between 11.2% and 17.0%according to the TAPPI T212 om-02 standard.

Another factor that might have affected the chemical composi-tion of the fibers in the present study could be due to the time de-lay. For example, though the fibers were sun dried and transportedto Brazil from Mexico within 3 days of the cooking process, analy-sis of the fibers was carried out after several months, so during thisperiod probably the action of fungi and bacteria could have de-graded part of the material. This was indicated by the strong smellemanating from the fibers used for testing. Therefore, this poses animportant issue to be considered, if large amounts of agave resi-dues are used commercially, but at the same time it also importantto use these materials, which otherwise go waste.

In the case of thermal studies, it may be relevant here to pointout that a comparison of these results with those of bleached cel-lulose obtained from sugarcane [31], which are similar chemically,but different in water content, reveals different mass losses atabout similar temperatures although such comparison may notbe proper due to differences in experimental conditions. For exam-ple, Mulinari et al. [31] reported peaks and mass loss for their sam-ples of 4.7% at 62 C, 83.9% at 378 C of and 8.6%, at 613 Crespectively, attributing them to elimination of water, degradationof cellulose and lignin, respectively. Accordingly, observed resultsin the present study can also be understood on similar lines andalso as reported elsewhere [26,32] for lignocellulosic materials as

Table 2Statistical treatment of tensile properties.

Parameter Gauge length, L0 (cm) SD (cm) dia. (lm) SD (lm) YM (GPa) SD (GPa) TS (MPa) SD (MPa) Strain e (%) SD (%)

Mean 5.1 0.7 426.6 63.3 2.6 0.8 58.1 21.0 15 77.1 0.6 328.7 80.1 2.7 1.0 41.5 25.9 11 99.8 1.1 345.8 76.1 2.9 0.9 49.9 31.8 12 6

SD Standard deviation; dia: Diameter; YM: Youngs modulus; TS: Tensile strength.

Table 3Statistical treatment of tensile property data.

Data Mean Variance N

(a) One-way ANOVA: Youngs modulusA 2.62 0.64 8B 2.74 1.06 13C 2.92 0.84 10

(b) One-way ANOVA: tensile strengthA 58.09 440.75 8B 41.48 672.99 13C 49.92 1009.45 10

At the 0.05 level, the means are NOT significantly different.

160 S. Kestur G. et al. / Composites: Part A 45 (2013) 153161due to (i) elimination of water, (ii) degradation of cellulose and (iii)degradation of lignin respectively.

Beyond temperature of 220 C up to 600 C, observed massloss can be attributed to decomposition of different types of cellu-lose present in the fiber. Above the temperature of 600 C, degrada-tion of the fiber can be seen due to the breakage of bonds of ligninpresent in the fiber [33,34]. The above two mass losses can beattributed to oxidation of the fragments in the presence of air. Fur-ther, a residue of 6% can be seen from the Fig. 5a, probably ofmineral nature, which is similar (5.5%) to that in dry samples hav-ing 10% moisture content. Thus, it may be concluded that TGAcurves indicate about the moisture content of the fiber, thermalstability and ash content of the fiber.

The observed 10.8% water loss (see TGA curve) is that of the re-gained water as capillary water, which can be related to environ-mental humidity and temperature along with composition of thefiber [28]. In fact, the water content of blue agave bagasse fibers,calculated by the difference between the weight of the fiber beforeand after heating at 60 C until constant, was found to be 10.8%. Itshould also be noted that despite the fibers were dried before per-forming the test it would be difficult to eliminate the water contentcompletely from the fiber due to its hydrophilic nature, which ispresent even as structurally bound water molecules.

Therefore, this water is regained by other components of the fi-ber (soluble and insoluble lignin and very small amounts of amor-phous cellulose). This is because, in addition to high crystallinity ofthe fiber, total cellulose of bagasse is 74% with higher amount ofmore crystalline alpha-cellulose (polymer), than hemicellulosesand hence, the access of water (moisture) to its hydroxyls is muchmore difficult. These would lead to absorption of less moisture bythe fiber.

In the case of tensile properties, observed stressstrain curve isunderstandable since lignocellulosic fibers are natural polymersthat can show viscoelastic behavior, and the mechanical behaviorof polymers depends on the mobility of their macromoleculesand thus on time (speed of the tensile test) and temperature. Suchbehavior has been reported for many lignocellulosic fibers [810,35].

Obtained mean UTS values for the blue agave fibers in the pres-ent study are much lower than those reported range of values ear-lier, but the mean values of YM and % strain are in comparablerange with the reported range of values for the fibers with diame-ter range of 60140 lm [12]. The differences between the obtainedmean UTS values and those reported earlier are understandable asdue to the fibers are from two different countries and also obtainedby different extraction processes in addition to state of the fibers(degradation during storing). Hence, the arguments stated earlierin respect of variations observed in the values chemical constitu-ents of the fiber holds good in this case also. In the case of Bessadoket al. [12] the fibers used could be fresh ones preventing any pos-sible degradation compared to the blue agave bagasse fibers usedin the present study thus having difference of time between theirproduction and testing. In fact, the high solubility in NaOH ob-tained in the chemical analysis suggested possible degradation ofthe fiber by fungi. Despite these variations, the fibers studied inthe present investigation have comparable reinforcement potentialas some of the other lignocellulosic fibers [58,25] and hence couldbe considered equally good for their use as reinforcements in poly-meric composites.

Despite lower tensile properties exhibited by these fibers, itwould be worthwhile to understand the purpose of this kind ofstudy, which highlights the benefits of characterizing cookedAgave even partially degraded bagasse that may still be used, forinstance, as reinforcement (as chopped fibers) in polymer (com-posites) based on properties exhibited by the fiber as explainedabove, which otherwise creates environmental problems. As a res-idue, no special care is taken to avoid its partial degradation and so,the material undergoes some degradation process before these fi-bers are used for any application. It should also be mentioned thatit is hard to dry fibers outdoors in the sun after harvesting becausehuge amounts (mountains) of bagasse are produced. On theother hand, it would be expensive to dry them using electricalheating. Even working with the present samples, we found it diffi-cult to dry the fibers properly since all of them were kept together.Therefore, it can be concluded that although utilization of these fi-bers may help prevent environmental problems from disposal oflarge amounts of waste, their drying method is an important con-sideration for the economic feasibility of their use. Hence, the char-acterization of the fiber as it is obtained (partially degraded) isappropriate because in theory it may be possible to think thatthe bagasse would be immediately dried and kept in conditionsthat could prevent its degradation till its use, but in practice thisis not the case. This is because tequila is expensive liquor, whilethe cooked agave bagasse is a byproduct, which is treated as awaste, while it should be valued in view of its properties, whichstill merit their uses.

5. Conclusions

Mexican agave cooked fiber (bagasse) extracted from the stemof the plant have been characterized for their density, chemicalcomposition, morphology, tensile and thermal properties.

The length of the fiber was found to be 1012 cm, with meandiameter of 592 lm and density of 880 kg m3.

The fibers contain 73.60% cellulose, 21.10% lignin and watercontent of 10.8%, comparable values with many other lignocel-lulosic fibers.

Morphological studies indicated that the fiber cells are regularlyarranged and are elliptical in shape with varying lumen size.

S. Kestur G. et al. / Composites: Part A 45 (2013) 153161 161 Crystallinity of Mexican agave bagasse fiber is found to be 70%. Tensile properties of these fibers indicated them to be in therange of some of the other lignocullulosic fibers suggestingthem to be potential reinforcements to develop compositessimilar to other similar fibers.

Mean values of Youngs modulus and % strain for three groupsof mean diameters (328, 345 and 426 lm) and mean gaugelengths (5.1, 7.1 and 9.8 cm) did not show much variation(2.62.9 GPa and 1215% respectively). On the other hand, ulti-mate tensile strength values for the same samples thoughshowed decreasing trend (from 58 MPa to 41 MPa), it may beassumed that this property also did not differ significantly whenthe standard deviations of these values are considered.

Thermal studies of Mexican agave fibers also indicated that thefiber is thermally stable probably due to its higher crystallinityand lignin content.

With the understanding of various properties particularly ten-sile and thermal properties, it should be possible for the useof these cooked fibers for incorporating in polymers includingbiodegradable ones. Thus, in view of abundant availability ofcorn and cooked blue agave residues are abundant in Mexico,a potential composite material, which could be compostableand biodegradable composites with corn starch and cookedblue agave residues could be produced there, whereby in addi-tion to value addition to the residues, employment generationcould be a possibility.

Acknowledgements

The authors thank Centro de Miscroscopia Eletrnica da UFPRfor their help for the SEM studies, CNPq for financial support forthis work and Prof. Graziela Muniz from Forest Engineering, UFPR,Curitiba-PR for permitting use their laboratory to carry out thechemical analysis of the fibers. One of the authors (Dr. KGS)sincerely thank Araucria Foundation, Curitiba for the financialsupport during the present work as well as the two organizations(BMS College of Engineering, Bangalore and Poornaprajna Instituteof Scientific Research, Bangalore) with which he is presently asso-ciated in India for their encouragement.

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Characterization of blue agave bagasse fibers of Mexico1 Introduction1.1 Background, status of characterization and uses

2 Experimental3 Results3.1 Density3.2 Morphology studies3.3 Chemical composition3.4 X-ray diffraction (XRD) studies3.5 Thermal studies3.6 Tensile property studies

4 Discussions5 ConclusionsAcknowledgementsReferences