fiber from sugarcane bagasse.pdf

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Textile Research Journal Article

Textile Research Journal Vol 80(17): 18461858 DOI: 10.1177/0040517510369408 The Author(s), 2010. Reprints and permissions:

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Preparation and Physical Properties of Regenerated Cellulose

Fibres from Sugarcane Bagasse

Ahmed Jalal Uddin, Atsushi Yamamoto,Yasuo Gotoh1, Masanobu NaguraFaculty of Textile Science and Technology, Shinshu

University, 3-15-1 Tokida, Ueda, Nagano 386-8567, Japan

Mahito Iwata2 Shinnaigai Textile Ltd., 2-6, 3-Chome, Bingo-Machi,

Chuo-ku, Osaka 541-0051, Japan

Conventional synthetic fibres are generally fabricated frompetroleum-based polymers and their large-scale consump-tion has generated serious environmental problems. As aresult, much attention has recently been devoted to thedevelopment of biodegradable and environmentally friendlyfibres for both apparel and industrial applications [1, 2].

Cellulose is one of the most abundant natural resourceson earth, and there has been extensive research on the pro-duction of fibre from this material. The history of cellulosefibre dates back to the 1860s, when the first rayon fibres

were commercialised.1

But the rayon process, which includedtoxic carbon disulfide treatments to block hydroxyl groupsof cellulose in order to prepare a spinnable solution, some-times caused ecological problems. Since then, manyattempts have been made to invent new solvents to directlydissolve cellulose. One solvent, N-methylmorpholine-N-oxide (NMMO) hydrate, has been successfully used in the

Abstract To produce cellulose regenerated fibreswith high mechanical properties at low cost, sug-arcane bagasse was chosen as a cheap raw mate-rial. In this study, bagasse was dissolved in N-methylmorpholine-N-oxide (NMMO) 0.9 hydrate,and fibres were prepared by the dry jet-wet spin-ning method by using dilute water/NMMO mix-ture as a coagulant, as is done in the productionof commercial lyocell fibre. The effects of othercoagulants, including water, methanol, isopropa-nol and ethanol, on the physical properties of thefibres were also investigated. Among these coagu-lants, fibres produced in ethanol and water/NMMOmixture exhibited the superior tensile strengthand initial modulus although had some NMMOtrapped in fibre matrix. After removal of NMMOby a simple heat treatment, much improvement inthe fibre structure and mechanical properties wasobserved. The cross-sectional morphology andsurface of these two fibres reveal the occurrenceof fibrillation due to their high degree of crystal-

linity and overall high molecular orientation. Thebagasse regenerated fibres produced in this studyhad a tensile strength of approximately 530 MPaand Youngs modulus of approximately 33 GPa,

which are comparable to those of commercial lyo-cell fibre.

Key words bagasse regenerated fibres, dry-jetwet spinning, structure-properties

1 Corresponding author: e-mail: [email protected]


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Preparation and Physical Properties of Regenerated Cellulose Fibres A. J. Uddin et al. 1847 TRJ

production of regenerated cellulose fibres. Lyocell fibresspun from cellulose solution in NMMO hydrate were firstinvestigated in the early 1980s [3, 4].

Though regenerated cellulose fibres are usually spun bythe traditional wet spinning method, the dry jet-wet spin-ning process with an air-gap was found to produce lyocellfibres with good physical properties [57]. Most dry jet-wetspun lyocell fibres have been commercially successful inthe apparel field due to their good mechanical properties,blendability with other fibres, and draping characteristics.In comparison with viscose rayon, they show excellentmechanical properties in the wet state [79]. The NMMOtechnology provides a relatively simple, resource-conserv-ing, and environmentally friendly method for producingregenerated cellulose fibre. The manufacturing process isdesigned to recover 99% of the solvent, which minimiseseffluent. Furthermore, the solvent itself is nontoxic and theeffluent is not hazardous [10, 11].

Pulp material containing more than 90% -cellulose iscalled high -cellulose pulp, and pulp containing morethan 20% hemicellulose is called high hemicellulose pulp[12]. The cellulose of lyocell is usually derived from pulpwith only high -cellulose pulp content, which is obtainedfrom hardwood trees such as oak and birch. These treesrequire vast areas of land and many years to grow. Conse-quently, although the pulp of these trees guarantees a highfibre yield, the cost of producing the pulp material is rela-tively high [13]. In this context, a cheaper source of pulpwith high hemicellulose content would reduce the cost oflyocell fibres. Recent investigations reported that the yieldof lyocell fibres produced from high and low hemicellulose

content was approximately equal because most of the cel-lulose and hemicellulose can be converted into fibre in thelyocell process [14, 15]. Moreover, higher hemicellulosecontent correlates with a smaller fibril aggregation size[1618]. Thus, the hemicellulose serves as a regulator forthe close association of cellulose and hemicellulose. Thisassociation increases the stability of the fibril aggregation[19, 20] that ultimately leads to the increase in fibrillationresistance of lyocell fibres [21, 22].

Bagasse is a fibrous residue that is left after the crushingof sugarcane stalks. Essentially, bagasse is a waste product,and so annual production of approximately 100 milliontons requires additional disposal costs. Currently, some of

the bagasse is burned in the furnaces of sugar cane mills toprovide heat and to generate power or steam. These proc-esses generate toxic dioxins [23]. Bagasse pulp is also usedto make several grades of paper: newspaper, writing paper,toilet tissue, paper towels, glassine, etc. Even so, an excessof bagasse exists, and this excess is deposited on emptyfields, altering the landscape. Bagasse contains, on aver-age, 49% moisture, 49% fibre and 2% soluble solids. Thecomposition the fibrous part of bagasse is 50% cellulose,30% hemicellulose, 18% lignin and some inorganic com-pounds [24].

The main objective of our research is to prepare regen-erated cellulose fibre with high mechanical properties froma cheaper source of raw material. Fibres were preparedfrom sugarcane bagasse by following conventional lyocellprocessing, which entails dry jet-wet spinning usingN-meth-ylmorpholine-N-oxide (NMMO) 0.9 hydrate as a solvent. Inthis study, the influence of other types of coagulants on themechanical properties of fibres was investigated. First, adilute water/NMMO mixture and only water were used ascoagulants. Then, to inhibit the rapid coagulation in water,alcoholic coagulants miscible with the solvent NMMO-water, such as methanol, isopropanol and ethanol, werealso examined in order to obtain a high spin-draw ratio.

Experimental

Materials

Bagasse was supplied by Okinawa Sugarcanes ResearchCorporation in Japan.A commercial lyocell fibre sample(diameter, 20 m) used for making apparel was receivedfrom the Shinnagai Textile Ltd., Japan to compare themechanical properties of this sample with those of our pre-pared fibres.

NMMO hydrate was purchased from Tokyo ChemicalIndustry Co. Ltd., Japan. The 50 wt% aqueous NMMOsolution (approximately 4.8 mol/L) was condensed toNMMO 0.9 hydrate in an evaporator with a vacuum at120C.

Alkali Treatment of Bagasse Prior toSpinning

To extract lignin and inorganic compounds, bagasse wereagitated at 80 rpm and temperature 90C for 24 h in an alkalisolution of concentrations of 3, 5, 7 and 10 wt% NaOH. Theelimination of lignin was confirmed by Fourier TransformInfrared (FT-IR) Spectroscopy. The reduction of inorganicmaterials after alkali treatment was examined by Thermo-Gravimetric Analysis (TGA) and Scanning Electron Micro-scopy/Energy Dispersive X-ray (SEM/EDX).

Preparation of Spinning SolutionThe spinning solution was prepared by combining 40 mlNMMO 0.9 hydrate (solvent), 4 g bagasse (cellulose), 10mg propyl gallate (antioxidant) and 10 mg sodium dodecyl-sulphate (surfactant) in a flask and stirring the solution in astatic rotary mixer at 50 rpm at 120C for 2.5 h.

Dry Jet-Wet Spinning

Dry jet-wet spinning was carried out with an air gap of 15mm through a single-hole spinneret of diameter 0.5 mm.


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1848 Textile Research Journal 80(17)RJRJ

The extrusion temperature was 100C. The injection speedwas approximately 4.0 m min1. Coagulation took place inwater, methanol, isopropanol, ethanol and water/NMMOmixture (10 wt%) at room temperature (20C) with a 2-mcoagulating bath followed by a water wash. It should benoted that we previously spun bagasse fibres in water/NMMO coagulants of various NMMO concentrations (0%to 50%) and the water/NMMO (10 wt%) mixture showedthe best results in terms of physical properties. The entirestudy will be reported in a future paper. For simplification,the water/NMMO mixture (10 wt%) coagulant will hereaf-ter be referred to as the water/NMMO coagulant in thispaper.

The prepared fibres were taken up at their maximumpossible speeds, between 35 and 70 m min1 depending onthe coagulants. The spin-draw ratio df/d0was determinedby measuring the cross-sectional diameter of the solutiondope at the spinneret exit (df) over the fibre cross-sectionaldiameter at the take-up point (d

0).

Spun fibres were dried in an oven at 30C for 24 h in thepresence of silica gel to absorb water.

Hot drawing and heat treatment of fibres were carriedout with a hand-operated drawing apparatus into a hot oven.

Measurements

Structure characterization

Birefringence was obtained by measuring the refractiveindices parallel and perpendicular to the fibre axis by an

Interphako Interference Microscope, Carl Zeiss JENALtd., Germany. During each measurement, five fibre speci-mens were taken from five different locations and thenaveraged.

Wide-angle X-ray diffraction (WAXD) measurementswere obtained by a Rigaku Rotorflex RU-200B diffracto-meter using Ni-filtered Cu-K radiation operated at 40 kVand 150 mA (wavelength 1.542 ). The degree of crystallin-ity was determined from the ratio of crystalline scatteringversus total scattering, and the amorphous contribution wasestimated by polynomial approximation [25]. The angle ofpreferred orientation with respect to the fibre axis wasdetermined from the most intense reflection peak of equa-

torial diffraction (with the overlapping 110/200 plane at 2= 22.6) [26, 27]. Curves derived from the azimuthal scanswere fitted onto the profiles of the mathematical modelinvestigated with Gauss functions [28], as shown in eq. (1),whereIo is the peak intensity, o is the azimuthal angle atIo,and is the peak width. Hermans crystal orientation func-tions,fc, were then obtained with eq. (2):

(1)

(2)

where

The density of the fibres was determined on smallpieces of fibres by a floatation method at 25C using a mix-ture of carbon tetrachloride (CCl4) and n-heptane as thereference solution. Each density value represented theaverage of three measurements.

SEM was conducted with an Hitachi S-2380N after

sputtering the samples with platinum (Pt). SEM-EDX wasanalyzed with an Hitachi S-3000N attached with an EnergyDispersive X-ray (EDX) analyzer, Horiba EX 200-SE.

TGA was performed using a ThermoPlus II TG-DTA8120 from room temperature to 600C in air at a scan rateof 10C min1. The weight of each sample was 5 mg.

FT-IR measurements were performed by the FTIR-8600PC, Shimadzu Ltd., Japan.

Fibrillation of fibres was carried out by taking 10 fibresof 20 mm length. Fibres were immersed in distilled waterat room temperature (20C) and sonicated for 15 min on aBranson ultrasonic sonifier 2510 OJ-DTH followed bymagnetic stirring for 1 hr.

Mechanical properties

The tensile properties of filament fibres (40 mm gaugelength) were measured in Tensilon Model RTC-1250A,Japan at a crosshead speed of 40 mm min1. The experi-mental results represent the average of 10 individual meas-urements.

Dynamic mechanical properties

The dynamic viscoelastic properties were measured by an

ITK Co. DVA-225 instrument at a frequency of 10 Hz andheating rate of 10C min1 on fibres of 20-mm length.

Results and Discussion

Alkali Treatment of Bagasse

Several types of regenerated cellulose fibres (e.g., rayon,acetate, triacetate and lyocell) are manufactured from

I( ) Io o

--------------

2

exp=

fc3 2cos 1

2--------------------------------=

2cos

I( ) 2cos sin d

0

2

I( ) sin d0

2

------------------------------------------------=


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purified wood pulp. To remove the lignin and inorganiccompounds, bagasse was subjected to agitation with alkali(NaOH) solutions of different concentrations (3, 5, 7 and10 wt%).

Figure 1 shows the FT-IR curves of the original(untreated) and alkali-treated bagasse. The original bagassesample exhibits the IR bands at approximately 1740, 1604,1515 and 1240 cm1 which correspond, respectively, to thecarbonyl group of carboxyl and ester group, C=C aromaticring of lignin, aromatic ring of lignin, and C-O stretching oflignin [29]. These bands disappear for alkali-treatedbagasse, even at the alkali concentration of 3%. But thetreatment of bagasse with 10 wt% NaOH is necessary toremove the inorganic matters as described below.

The remaining matter of the alkali-treated bagassewere studied by TGA. To ascertain the presence of inor-ganic matter after alkali treatment, original and alkali-treated bagasse specimens were heated to 600C and keptfor 2 h until the hemicellulose, cellulose and lignin werecompletely degraded, since they degrade at 180C, 340C

and 420C, respectively. After TGA scans were finished,the weights of the remaining inorganic materials weremeasured. Figure 2 plots the weight reduction of inorganicmatter as a function of alkali concentration. As seen in Fig-ure 2, the removal of inorganic matter apparently reaches asaturation level after treatment with 10 wt% NaOH. In theSEM-EDX study, EDX identified inorganic materials con-taining potassium, silica, calcium and a small amount ofiron.

Characteristics of Bagasse Fibres Preparedin Different Coagulants

Physical Appearance

The physical appearance of the bagasse fibres prepared invarious coagulants was observed and all fibres showed thesilky sheen of commercial lyocell fibres, irrespective of the

coagulant used.

Structure Development

The structural parameters of bagasse fibres obtained in dif-ferent coagulants are listed in Table 1 according to theirmaximally achieved spin-draw ratio. In this table, it is seenthat the fibre diameter (measured in SEM) becomes thinnerwith the increase in spin-draw ratio, which directly influ-ences the structural parameters of fibres. Among all fibres,the water/NMMO and ethanol coagulated fibres show com-paratively better structural parameters, such as the degreeof crystallinity (Xc), lattice spacing (d) (measured when theintense peak corresponds to overlapping 110/200 plane at

2 = 22.6), crystal orientation (fc) and birefringence (n).The n and Xc values for these two fibres are very close,butfc andd are different. In the case of the water/NMMOcoagulated fibre, Xc value is seemingly lower, although itpossesses the highestfc and n among all fibres.

The densities of the 100% crystalline sample (c) and100% amorphous sample (a) for cellulose were reportedas 1.620 and 1.415 gcm3, respectively [30]. But the densityvalue of the water/NMMO coagulated fibre was found tobe 1.43 gcm3, which is very close to the density ofa of cel-lulose; this result does not match the other structural

Figure 1 FT-IR spectra for origi-

nal (untreated) and alkali-treated

bagasse.


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parameters of that fibre, such asXc(56%), fc(0.81) and n(19.3 103). Then, the low density value of this fibre wasinvestigated by SEM and FT-IR (described later) and thiswas attributed to the remaining NMMO in the fibre along

with the formation of an interfibrillar free volume or micro-voids during spin drawing. Such interfibrillation and theresultant low density value of fibres were found in our previ-ous work for highly crystallised and highly oriented polypro-pylene (PP) fibres, when the PP fibre was drawn by laser-heated drawing to its highest draw ratio [31]. For that reason,in our present study we calculated the degree of crystallinityof all bagasse fibres from their respective WAXD profiles.

The WAXD images of these fibres are shown in Figure 3.The WAXD images show that crystal order improves withincreasing spin-draw ratio. As shown by the structural

parameters obtained in Table 1, the WAXD images ofwater/NMMO and ethanol coagulated fibres show highercrystallinity and crystal orientation. Methanol coagulatedfibres indicate comparatively lower crystal orientation. Iso-

propanol and water coagulated fibres show the lowest crys-tal parameters and an obvious amorphous halo.

We observed the SEM images of the fractured cross sec-tions of fibres, presented in Figure 4. The images of thewater/NMMO, methanol and isopropanol coagulatedfibres indicate some fibrillation. It is well known that duringthe spinning of lyocell fibres, crystallization occurs and crys-talline regions are separated by amorphous regions but heldtogether by hydrogen bonds. At a high spinning speed, thecrystals orient and the fibre fibrillates, tearing the hydrogenbonds in the amorphous regions [32]. Such inherent phe-

Figure 2 Inorganic materials (%)contained in original and alkali-

treated bagasse measured by TGA.

Table 1 Structural parameters of bagasse fibres prepared in various coagulants.

CoagulantSpin-draw

ratiodf/d0

Fibrediameter

(m)

Fibre density(gcm3)

Degree ofCrystallinity*,

Xc (%)

LatticeSpacing, d

()

Degree ofcrystal

orientation, fc

Birefringencen 103

Water/NMMO 17.5 38 1.43 56 4.272 0.81 19.3

Ethanol 17 40 1.53 60 4.235 0.71 19.0

Methanol 12.75 43 1.51 58 4.238 0.65 17.1

Isopropanol 10.5 48 1.48 56 4.263 0.60 16.5

Water 8.75 52 1.41 48 4.303 0.45 12.2

* Xc measured from WAXD


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Figure 3 WAXD images of bagasse fibres prepared in various coagulants.

Figure 4 SEM images of fractured cross sections of bagasse fibres prepared in various coagulants.


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nomenon of lyocell fibre spinning was also observed in ourpresent work. However, water/NMMO coagulated fibrebears some indication of the remaining NMMO in the fibrematrix. The ethanol coagulated fibre was expected to showfibrillation due to its higher structure parameters (Table 1 andFigure 3); instead, it shows a skin-core structure. This is pos-

sibly due to the fact that the core of this fibre was not prop-erly coagulated because of its hard skin and some NMMOwas trapped in the core part of fibre. The SEM image of thewater coagulated fibre also does not show any fibrillation.Since NMMO is a strongly hygroscopic substance [33], thusthe solvent NMMO might have instantly extracted from thefibre towards water while entering into the water coagulat-ing bath. This fact might cause the very fast coagulation andlowest spin-draw ratio of the water coagulated fibre (Table 1)that ultimately results in the lowest structural parameters(Table 1 and Figure 3).

Correlation of Mechanical Properties with FibreStructure

Figure 5 shows the typical stress-strain curves of the fibres indifferent coagulants. For all fibres, the shape of the stress-strain curves expresses an initial linear portion, a yield point,

and a region of low or high slope up to rupture. Several ten-sile properties such as tensile strength, initial modulus, andelongation at break, evaluated from the stress-strain curves,are summarised in Table 2. In close agreement with the struc-tural development, the tensile properties of water/NMMOand ethanol coagulated fibres also show remarkable improve-ment in comparison to other coagulated fibres. Water/NMMO fibre shows the highest tensile strength with tough-ness and the ethanol fibre shows the highest initial modu-lus. Methanol and isopropanol coagulated fibres showsomewhat lower tensile properties, whereas the water coag-

Figure 5 Typical stress-strain cur-

ves of bagasse fibres prepared in

various coagulants.

Table 2 Mechanical properties of bagasse fibres prepared in various coagulants.

CoagulantTensile Strength

(MPa)Initial Modulus

(GPa)Elongation at break

(%)

Water/NMMO 427 10 (30) 13 1 (909) 15 2

Ethanol 394 8 (26) 21 2 (1372) 4.3 1

Methanol 349 7 (23) 13 1 (861) 10 1.5

Isopropanol 349 9 (24) 17 2 (1149) 11 1.8

Water 247 6 (18) 10 1 (709) 9.3 1.6

Note: The values in parentheses are in cN/tex.


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ulant fibre possesses the lowest of all. These overall resultssupport the well-known fact that the higher the spin-drawratio (Table 1), the higher the tensile strength and modulus

The temperature dependence in mechanical propertiesis revealed by dynamic viscoelastic analyses. In Figure 6,

the temperature-dependent storage modulus (E) of all thebagasse fibres is illustrated. Considering the structuralparameters and tensile properties, the water/NMMO andethanol coagulated fibres are expected to show the highestE values across the entire temperature range. But the eth-anol coagulated fibre shows a strange E curve. A closerexamination of the E curve of this fibre indicates an increaseof between 50 and 105 C, may be due to the removal oftrapped ethanol/water. The curve then follows a sharpdecrease, perhaps due to the plasticising effect of remain-ing NMMO trapped inside the fibre during coagulation(later confirmed by FTIR as illustrated in Figure 7). SinceNMMO starts to decompose at around 170C, the curve

again turns towards an increasing trend. Unlike ethanolcoagulated fibre, the E curve of water/NMMO coagulatedfibre does not show such an unusual pattern though it alsohas some NMMO in its matrix (Figure 7). But the contentand the pattern of NMMO in water/NMMO and ethanolcoagulated fibres seem to be different. In the case of theethanol coagulated fibre, NMMO may become trapped inthe core part of fibre surrounded by its hard skin and soNMMO in the core part decomposes at 170 C as seen inits E curve. Such skin-core structure was found for isopro-panol coagulated NMMO-type cellulose fibre [27]. Unlike

the ethanol coagulated fibre, the water/NMMO fibre maynot have the skin-core structure as the solvent and thecoagulant in this case are the same, NMMO. In this case,NMMO may just randomly exist in fibre matrix and evapo-rate slowly with the gradual increase of temperature during

the measurement of storage modulus in dynamic mood.

NMMO Removal from the Fibre Matrix

The remaining NMMO in the water/NMMO and ethanolcoagulated fibres was investigated by FT-IR spectra. Asshown in Figure 7, the stretching bands at 1260 and 800 cm1,corresponding to the (-CN) and (-NO) stretching ofNMMO, were observed in these fibres. This finding is ingood agreement with our previous assumption. To elimi-nate NMMO from the fibres, both fibres were subjected tohot drawing and/or heat treatment. To do this, for the etha-nol coagulated fibre, the near melting temperature of

NMMO (170C), the lowest sagging point in its E curve(Figure 6), was selected. At 170C, this fibre could be drawnup to 1.2 times perhaps due to plasticising effect of NMMOand then kept for 5 min in that state with tension. In thecase of the water/NMMO coagulated fibre, the tempera-ture at 250C, at which E begins to drop (Figure 6), wasselected. This fibre could not be drawn even at a high tem-perature because it was already highly crystallised and ori-ented (Table 1) as well as fibrillated (Figure 4). Hence, thisfibre was only heat treated with tension for only 5 min at250C. The IR bands of NMMO for both fibres then disap-

Figure 6 Storage modulus of

bagasse fibres prepared in various

coagulants.


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peared (Figure 7), which confirmed the complete elimina-tion of NMMO from the fibres.

Characteristics of Fibres after NMMO Removal

Stress-strain curves of water/NMMO and ethanol coagu-lated bagasse fibres after NMMO removal are illustrated

in Figure 8 along with the curve of commercial lyocellfibre. The ethanol coagulated fibre exhibits a brittle modeof deformation behaviour with no apparent yield point,and a regime of sharply rising stresses until rupture. Con-versely, the water/NMMO coagulated fibre still shows ayield point and comparatively higher strain until rupture.The steeper initial slope for both fibres indicates their

Figure 7 FT-IR curves of water/

NMMO and ethanol coagulant

bagasse fibres, showing the elimi-nation of NMMO after heat treat-

ment.

Figure 8 Typical stress-strain

curves of water/NMMO and etha-

nol coagulated fibres after NMMO

removal in comparison with the

curve of commercial lyocell fibre.


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toughness, that is, their larger initial resistance to appliedstress.

The storage modulus curves (E) of these fibres areshown in Figure 9. The sagging part of the curve of the etha-nol coagulated fibre is completely eliminated after NMMOremoval. Moreover, after NMMO removal, the E values forboth the water/NMMO and ethanol coagulated fibres acrossthe entire temperature range have markedly increased. Theincrease in E suggests that high levels of molecular orienta-tion and crystallinity are achieved after NMMO removaland heat treatment.

The WAXD images of these fibres, shown in Figure 10,also clearly indicate the improvement in crystallinity and

crystal orientation after NMMO removal. Table 3 lists thestructural and mechanical properties of the water/NMMO

and ethanol coagulated fibres. The structural improvementsof the fibres have a strong correlation with their respectiveincrease in tensile properties. After NMMO removal, bothfibres show improved molecular structures, such as crystallin-ity, lattice spacing, crystal orientation and birefringence thatnoticeably enhance their mechanical properties and reduc-tion in elongation at break. The higher tensile strength andmodulus of ethanol coagulated fibre compared with water/NMMO coagulated fibre may be attributed to its highercrystallinity, crystal orientation, birefringence and smallercrystal lattice spacing. The SEM images of the fracture and

Figure 9 Storage modulus ofwater/NMMO and ethanol coagu-

lated fibres after NMMO removal in

comparison with the storage mod-

ulus of commercial lyocell fibre.

Figure 10 WAXD images of water/

NMMO and ethanol coagulated

bagasse fibres after NMMO removal

and heat treatment.


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surface of these fibres, shown in Figure 11 and Figure 12,respectively, demonstrate the higher fibrillation of ethanolcoagulated fibre in comparison with water/NMMO fibre.As shown in Table 3, the occurrences of higher fibrillationof the ethanol coagulated fibre can be attributed to its higherdegree of crystallinity, smaller lattice spacing and higher ori-

entation of both crystalline and non-crystalline regions of thefibre. Such fibrillation is generally observed for highly crys-tallised and highly oriented lyocell fibres [34, 35].

In this work, the tensile strength of 530 MPa and initialmodulus of 33 GPa are reported for bagasse regeneratedfibre. These values are comparable with those of the com-mercial lyocell fibre used in our study (tensile strength 486MPa and initial modulus 16 GPa) and those reported inrelated literature (tensile strength 525~600 MPa, and ini-tial modulus 8~18 GPa) [36, 37].

Conclusion

Sugarcane bagasse was dissolved in N-methylmorpholine-N-oxide (NMMO) 0.9 hydrate, and fibres were preparedby the dry jet-wet spinning method. We evaluated differentkinds of coagulating agents, including water/NMMO(10%), water only, methanol, isopropanol and ethanol andcompared the structures and properties of the resultingfibres. The fibres prepared in water/NMMO and ethanolcoagulant showed better physical properties even thoughthe solvent NMMO remains in the fibre matrix. Afterremoval of NMMO by heat treatment, further improve-ment in the structures and properties for these fibres wereachieved. The fractured cross-sections and surfaces ofthese fibres reveal the occurrence of fibrillation due tohigher crystallinity and molecular orientation.

Considering the structure and mechanical properties ofthe fibres prepared in this work, it can be concluded that

Table 3 Mechanical properties and structural parameters of water/NMMO and ethanol coagulated bagasse fibres after

NMMO removal by heat treatment.

CoagulantTensile

Strength,(MPa)

InitialModulus,

(GPa)

Elongation atbreak(%)

Degree ofCrystallinity, Xc

(%)

Lattice Spacing,d ()

Degree ofcrystal

orientation, fc

Birefringencen 103

Water/NMMO 502 (33.5) 26 (1733) 6 60 4.246 0.85 20.8

Ethanol 530 (35) 33 (2171) 2 69 4.218 0.88 23.2

Note: The values in parentheses are in cN/tex.

Figure 11 SEM images of fractured water/NMMO and ethanol coagulated bagasse fibres after NMMO removal by heat

treatment.


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sugarcane bagasse, which is generally considered as wasteproduct, can produce regenerated cellulose fibres withmechanical properties comparable to those of commerciallyocell fibre.

Acknowledgements

The authors are indebted for support of this work by theGrant-in-Aid for the Global COE program by the Ministry

of Education, Culture, Sports, Science and Technology ofJapan.

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Figure 12 SEM images of fibrillated water/NMMO and ethanol coagulated bagasse fibres after NMMO removal by heat

treatment.


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