Chapter 3 Extraction of nanocellulose fibrils from banana, pineapple leaf fibre (PALF), jute and coir fibres by steam explosion process Part of this chapter has been published in Carbohydrate Polymers journal as Extraction of nanocellulose fibrils from lignocellulosic fibres: A novel approach; Abraham et al. Carbohydrate Polymers. 2011, 86, 1468– 1475 Another part of this chapter has been published in Carbohydrate Polymers journal as Environmental friendly method for the extraction of coir fibre and isolation of nanofibre; Abraham, et al, Carbohydrate Polymers. 2013, 92, 2, 1477-1483.
Summary This chapter describes a simple process to obtain an aqueous stable colloid suspension of cellulose nanofibrils (CNF) from various lignocellulosic fibres. For the preliminary analysis we have studied four different fibres: banana (pseudo stem), jute (stem), pineapple leaf fibre (PALF) and coir (fruit). To study the feasibility of extracting cellulose from these raw fibres we have adopted steam explosion technique along with mild chemical treatment. These processes included usual chemical procedures such as alkaline extraction, bleaching, and acid hydrolysis but with a very mild concentration of the chemicals. The chemical constituents of the fibre in each processing step were determined by ASTM standard procedures. Morphological and spectroscopic analyses of the fibres were carried out and it was found that the isolation of cellulose nanofibres occurs in the final step of the processing stage. The chapter introduces an environmental friendly method for the effective utilisation of coir fibre by adopting steam pre-treatment. The retting of the coconut bunch makes strong environmental problems which can be avoided by this method. Steam explosion has been proved to be a green method to expand the application areas of lignocellulosic fibres.
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3.1 Introduction Most
lignocellulosic
biomass
is
comprised
mainly
of
cellulose,
hemicellulose, and lignin. Due to its heterogeneity and crystallinity, however, direct utilisation of biomass by microbes is extremely slow. Efficient separation of constitutive biomass components constitutes one of the major obstacles to the efficient utilisation of renewable resources. However, such separation is mandatory for its effective utilisation in the current nanotechnological field and of the various pre-treatment technologies for the isolation of nanocellulose from raw fibres, steam explosion is an attractive choice. Since plant-based cellulose nanofibres have the potential to be extracted into fibres thinner than bacterial cellulose, many researchers have been extensively studying the extraction of nanofibres from wood and other plant fibres. We used mild acids with low concentration (5% oxalic acid) which overcome toxicity, with no degradation of cellulose. Here we report on an efficient extraction of cellulose nanofibres from natural fibres like banana, pineapple leaf fibre (PALF), jute and coir as they exist in the cell wall, by a mild chemical treatment followed by very simple mechanical treatment. In the four studied fibres, coir fibre obtained from coconut husk and is one of the major underutilized raw material. It is composed of cellulose nanofibre which constitutes 32-43% of its dry weight [1]. Total world coir fibre production is 250,000 tonnes per year and out of it, 80% of the fibre is contributed by the coastal region of India [2]. The raw fibres have been reported to be used in the field of polymer composite application [3]. Efforts are going on for exploring wider export markets for coir and coir products but still most of the raw coir fibre remain underutilized. Judged from the
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increase in production and employment, the progress has been rather slow and exports in physical terms have remained mere or static. Another major issue is related to the pollution originated during the retting and processing of raw coir fibre [4]. One of the striking features of southern India is the continuous chain of lagoons or backwaters existing along the coastal region. The backwaters support rich and diverse life forms and provide crucial nurseries for shrimps and fishes as well as habitat for oysters, clams and mussels which later enrich the ocean. The shallow fringes of the backwaters and the channels drawn from them are used for retting of coconut husk. It adversely affects the productivity of the backwaters and is harmful to marine fisheries. The retting process is brought about by the pectinolytic activity of micro organisms especially bacteria, fungi and yeasts degrading the fibre binding materials of the husk and liberating large quantities of organic matter and chemicals into the environment, including pectin, pentosan, tannins, polyphenols, etc. Consequently hydrogen sulphide, phosphate and nitrate contents increase while dissolved oxygen and community diversity of plankton decrease in the ambient waters during the retting process. Here we report a novel environmental friendly method to use the raw coir fibre as they exist in the coconut husk, and thereby avoiding the retting steps of the coir fibre. Fig. 3.1 shows the schematic representation of the whole processes for the effective utilisation of coir fibre
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Fig. 3.1 Schematic representation of the green method for the effective utilisation of coir fibre
3.2 Results and discussions 3.2.1 Isolation of cellulose nanofibres from raw fibres Isolation of nanocellulose from raw fibres was done by steam explosion coupled with chemical treatments as described in 2.2.1. The four stage process leads to the isolation of cellulose nanofibres from the raw fibres. The alkali treatment removes a certain amount of lignin, hemicellulose, wax and oils covering the external surface of the fibre cell wall, depolymerizes the native cellulose structure, defibrillates the external cellulose micro fibrils and exposes short length crystallites. The alkali treated fibre is then subjected to steam explosion treatment. The steam-treated material is then obtained by rapid depressurisation of the vessel causing the material to expand (explode) into a stainless steel cyclone. Hence, this sudden pressure drop (explosion)
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can disrupt or defibrillate the pre-treated material whose structure has been softened through alkali treatment followed by high pressure steaming. Bleaching of the steam exploded fibre was done to complete elimination of the remaining cementing materials from the fibre. Hemicellulose is a water soluble polysaccharide. Lignin is a complex organic compound with alkali soluble character. Hence the percentage of lignin decreases from raw fibre to bleached fibre. After cellulose was isolated, acid hydrolysis was carried out in order to produce cellulose nanofibrils. Oxalic acid will react with sodium derivative of the fibre to form the pure cellulose. The samples were further broken down into leaner fragments by the sonicator. The slurry obtained after the sonication exhibited a remarkably high viscosity. It suggested that the synthesis of homogeneous dispersion of hydrophilic cellulose nano fibrils in water from natural fibres has been accomplished. The process provided high turbulence and shear that created the efficient mechanism of reduction in size nano cellulose level. 3.2.2 Chemical analysis The chemical constituents in the fibres at different processing stages are determined as per the ASTM standard described in 2.2.2. Table 3.1 describes the chemical composition of banana, PALF and jute fibres at different processing stages.
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Table 3.1 Constituents of the banana, PALF and jute fibres in different stages Cellulose (%)
Hemicellulos e (%)
Lignin (%)
Moisture content (%)
Raw banana fibre
69.9
19.6
Raw PALF
75.3
13.3
Raw jute fibre
68.3
15.4
Raw coir fibre
39.3
2
5.7 4.8 10.7 49.2
9.8 9.1 10.1 9.8
Steam exploded banana fibre
88.3
6.9
2.9
10.1
Steam exploded PALF
89.8
4.9
1.5
9.5
Steam exploded jute fibre
86.7
4.3
3.5
10.4
Steam exploded coir fibre
57.4
-
30.9
8.8
Bleached banana fibre
96.8
0.2
Bleached PALF
97.3
0.2
Bleached jute fibre
97.3
-
Bleached coir fibre
88.3
-
0.2 0.3
9.3 8.9 9.6 8.5
3.2.2.1 Banana fibre It has been found that the percentage of crystalline cellulose in the banana fibre increases when treated with NaOH followed by steam explosion process. The fine structure of banana fibre is composed of crystalline and amorphous regions. The amorphous regions easily absorb chemicals such as dyes and resins, whereas the compactness of the crystalline regions makes it difficult for chemical penetration [5]. The modification of banana fibres by alkali involves the removal of the surface impurities and the swelling of the
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crystalline region. The common trend from the observation is the gradual decrease of amorphous components like lignin and hemicellulose from raw fibre to bleached fibre. The lignin will react with NaClO2 and dissolve out as lignin chloride. The percentage increase of the pure cellulose component with each processing step is another main observation. Raw banana fibre has ~70% of cellulose content and it increased to 97% at the bleached stage. The hemicelluloses present in the raw fibre (~20%) is almost absent in the bleached fibre (~0.2%). The absence of the cementing materials in the final processing step is the main observation of the chemical estimation of the various stages of banana fibre. Moisture content of the banana fibre shows a small increase from raw (9.8%) to steam exploded fibre (10.1%) and then a decrease (9.3%). This is due to the increase in percentage of cellulose content during the process and the easy of accessibility of the water molecules in to the interior part due to the swelling of the fibre. Acid hydrolysis of cellulose leads to hydrolytic cleavage of glycosidic bond between two anhydroglucose units. Thus the amorphous portion gets dissolved by acid hydrolysis, leaving behind the crystalline regions. Acid hydrolysis followed by mechanical treatment results in disintegration of the cellulose structure from micro into nanofibre form [5]. 3.2.2.2 Pineapple leaf fibre PALF fibre shows highest crystalline cellulose percentage in the four studied fibres. The orientation of the nanocellulose in the raw fibre is much more regular in PALF when compared to other studied fibres. The fine structure of cellulose materials is composed of crystalline and amorphous regions. The modification of PALF by alkali treatment involves the removal of the surface impurities and the swelling of the crystalline region. The common trend from
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the observation is the gradual decrease of amorphous components like lignin and hemicellulose from raw fibre to bleached fibre which is evident from the Table 3.1. The raw jute fibre has 68% of cellulose content and it is increased to 97% in the bleached stage of the fibre. The bleached fibre is pure white in colour is free from other non-cellulosic components. The lignin will react with NaClO2 and dissolve out as lignin chloride. Moisture content shows a gradual increase from raw (9.1%) to steam exploded fibre (9.5%) and then a decreasing tendency at bleaching stage (8.9%). During alkali treatment, the swelling of the fibre takes place, which also promote the absorption of moisture by capillary action. The alkali treatment of the fibre will lead to the swelling which facilitate the accommodation of water molecule inside the fibre structure. Since in pure cellulose, each unit has three free –OH groups, the moisture absorption rate decreases due to the strong hydrogen bonds in between the crystalline cellulose molecules. 3.2.2.3 Jute fibre Jute fibre shows a moderate crystalline cellulose percentage (68.3%) in the four studied fibres. The structure of jute fibre is composed of crystalline and amorphous regions which are clear from its SEM analysis in Fig. 3.6. The amorphous regions easily absorb chemicals such as dyes and resins, whereas the compactness of the crystalline regions makes it difficult for chemical penetration [5]. The alkali treatment of the jute fibre involves the removal of the surface impurities and the swelling of the crystalline region of the fibre. The common trend of the gradual decrease of amorphous components like lignin and hemicellulose from raw fibre to bleached fibre is also applicable to jute fibre. The lignin content of the raw jute is 15% by weight and it reacts
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with NaClO2 and dissolves out as lignin chloride. The increase of the pure cellulose component with each processing step of the jute fibre is another main observation and at the bleaching stage it is 97% by dry weight. Jute also following the general trend of gradual increase of moisture content from raw to alkali treated fibre. As discussed earlier, the swelling of the fibre and by the capillary action the alkali treated fibre will facilitate the water absorption. The increase in percentage of cellulose content during the process also has some contribution. Since in pure cellulose, each unit has three free –OH groups with strong intra and intermolecular hydrogen bonds, the moisture absorption rate decreases. 3.2.2.4 Coir fibre Table 3.1 describes the chemical composition of the coir fibres at different processing stages as well as the moisture content. Chemical constituents of fibres were determined according to ASTM standards as described in the experimental section 2.2.2. The raw coir fibre is mainly composed of cellulose (~40%), lignin (~45%) and other components. Upon alkali treatment, the lignin starts to dissolve out and increases the relative percentage of cellulose components. It is clearly demonstrated in the data presented in the table. The structure of coir fibre is composed of crystalline and amorphous regions where the later dominate over due to the higher percentage of lignin. The amorphous regions easily absorb chemicals such as dyes and resins, whereas the compactness of the crystalline regions makes it difficult for chemical penetration [6]. The alkali treatment of the coir fibres involves the removal of the surface impurities and lignin, the swelling of the crystalline region, and alkalisation of the peripheral hydroxyl groups. The common trend from the observation is the gradual decrease of amorphous
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components like lignin and hemicellulose from raw fibre to bleached fibre. The lignin will react with NaClO2 and an oxidative fragmentation of lignin takes place and some part of lignin will dissolve out as lignin chloride. The percentage increase of the cellulose component (39.3 to 93.7%) and decrease of the lignin components (49.2 to 0.3%) with each processing steps are the main observation. Moisture content shows an increase from raw to alkali treated fibre and then a gradual decrease. During alkali treatment, the swelling of the fibre takes place, which promote the absorption of moisture by capillary action. The alkali treatment of the fibre will lead to the swelling which facilitate the breakdown during acid hydrolysis. During every processing step, there is an increase in the percentage of crystalline cellulose content. Since most hydroxyl groups in the final stage are bonded by intra and inter molecular hydrogen bonding, moisture absorption decreases. 3.2.3 FT-IR analysis The FTIR analyses of the fibres at different processing stages are determined as per the procedure described in 2.2.7. The infrared spectra of cellulose, hemicellulose and lignin [7] were studied in the literature. The three materials are mainly composed of alkanes, esters, aromatics, ketones and alcohols, with different oxygen-containing functional groups. Infrared transmittance spectra with main observed peaks of the banana, PALF and jute fibres in different stages are shown in Table 3.2. All the FTIR spectra were developed after carefully drying the samples, however the water adsorbed in the cellulose molecules is very difficult to extract due to the cellulose-water interaction.
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3.2.3.1 Banana fibre From the Table 3.2 it is clear that the banana fibre shows the characteristic peaks of C=O stretching and the vibration of the aromatic ring due to lignin at 1736 cm-1 and 1247 cm-1 respectively. Lignin presented characteristic peaks in the range 1200–1300 cm-1corresponding to the aromatic skeletal vibration. In addition, due to the presence of functional groups such as methoxyl –O–CH3, C–O–C and aromatic C=C, peaks in the region between 1830 cm-1and 1730 cm-1was observed [8]. The peak corresponding to 1640 cm-1 has been reported to be due to the -OH bending [9] of adsorbed water and the cellulose components. The peak present at 1730-1740 cm-1 in the spectrum corresponding to the raw fibres is the presence of C=O linkage, which is a characteristic group of lignin and hemicellulose, at 1765–1715 cm-1. Another possibility is that carboxyl or aldehyde absorption could be arising from the opened terminal glycopyranose rings or oxidation of the C–OH groups. Alkali treatment reduces hydrogen bonding due to removal of the hydroxyl groups by reacting with sodium hydroxide. This results in the increase of the -OH concentration, evident from the increased intensity of the peak between 3300 and 3500 cm-1bands compared to the untreated fibre [9,10].
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Table 3.2 Infrared transmittance peaks (cm-1) of the fibres in different stages FTIR(cm- 1) —OH
C—H
C=O
Absorbed
Spectra [%T] stretching vibration stretching water
C—H
Aromatic ring
stretching vibration of lignin
C—C stretching
Raw banana
3400
2923
1736
1638
1369
1247
1029
Raw PALF
3432
2922
1738
1617
1372
1238
1020
Raw jute
3381
2919
1736
1376
1245
1019
2924
1735
1625
1369
-
1020
2922
1738
1617
1372
2919
1736
1633
1376
2922
-
1607
1370
-
1019
Bleached PALF 3492
2920
--
1655
1353
-
1022
Bleached jute
2924
--
1607
--
Steam exploded 3397
1633
banana fibre Steam exploded 3424
-
1022
PALF Steam exploded 3346
-
1019
Jute Bleached
3467
banana fibre
3316
-
1019
From the FTIR analysis of the banana fibre it has been concluded that there is a reduction in the quantum of binding components present in the fibres due to the process of steam and chemical treatment. The raw banana fibres have a characteristic peak in between 1736 cm-1and 1247 cm-1. These peaks are chiefly responsible for the hemicellulose and lignin components. These characteristic peaks are completely absent in the final bleached banana fibre.
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3.2.3.2 Pineapple leaf fibre In the PALF fibre the lignin presented characteristic peaks at 1238 cm1
corresponding to the aromatic skeletal vibration. In addition, due to the
presence of functional groups such as methoxyl –O–CH3, C–O–C and aromatic C=C, peaks in the region between 1830 cm-1and 1730 cm-1was observed [11]. The peak corresponding to 1617 cm-1 is due to the -OH bending and the peak present at 1738 cm-1 in the raw PALF spectrum is for the presence of C=O linkage, which is a characteristic group of lignin and hemicelluloses [9]. Another possibility is that carboxyl or aldehyde absorption could be arising from the opened terminal glycopyranose rings or oxidation of the C–OH groups. Alkali treatment reduces hydrogen bonding due to removal of the hydroxyl groups by reacting with sodium hydroxide. This results in the increase of the -OH concentration, evident from the increased intensity of the peak between 3300 and 3500 cm-1bands compared to the untreated fibre [9, 10]. It is reported that in most lignified plant cells lignin and hemicellulose are deposited between the micro fibrils to give an interrupted lamellar structure and without the removal of these noncellulosic components, the cellulose I to cellulose II transformation will be restricted. With the treatment of NaOH and bleaching agents, the lignin is removed and in this case also the degree of crystallinity goes on increasing. This may be due to the removal of lignin which acts as a cementing material and on delignification, an ordered arrangement of the crystalline cellulose in the structure takes place. From the FTIR analysis of the PALF, it has been concluded that there is a reduction in the quantum of binding components (lignin and hemicelluloses) present in the fibres due to the process of steam and chemical treatment. The
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raw fibres have a characteristic peak in between 1730-1740 cm-1and 12001300 cm-1. These peaks are chiefly responsible for the hemicellulose and lignin components. These characteristic peaks are completely absent in the final bleached cellulose fibre. 3.2.3.3 Jute fibre The main peaks of the FTIR spectra of the jute fibre is shown in Table 3.2. The –OH stretching of the cellulose components of the jute fibre gives a peak at 3381 cm-1 whose intensity is lower than the banana fibre and PALF. This is due to the strong binding between the cellulose, hemicelluloses and lignin. Lignin present in the jute fibre gives characteristic peaks at 1245 and 1736 cm-1corresponding to the aromatic skeletal vibration and carbonyl group. It is clear from the spectra that these peaks are completely absent in the bleached fibre. In addition, due to the presence of functional groups such as methoxyl –O– CH3, C–O–C and aromatic C=C, peaks in the region between 1830 cm-1and 1730 cm-1was observed [11]. All the FTIR spectra were developed after carefully drying the samples, however the water adsorbed in the cellulose molecules is very difficult to extract due to the cellulose-water interaction. The peak present at 1736 cm-1 in the spectrum corresponding to the raw fibres could be due to the presence of C=O linkage, which is a characteristic group of lignin and hemicellulose. Another possibility is that carboxyl or aldehyde absorption could be arising from the opened terminal glycopyranose rings or oxidation of the C–OH groups. Alkali treatment reduces hydrogen bonding due to removal of the hydroxyl groups by reacting with sodium hydroxide. From the FTIR analysis of jute fibre, it has been concluded that there is a reduction in the quantum of lignin and
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hemicellulose present in the raw fibres due to the process of steam and chemical treatment. The raw fibres have a characteristic peaks at 1736 cm1
and 1245 cm-1. These peaks are chiefly responsible for the hemicellulose
and lignin components respectively. These characteristic peaks are completely absent in the final bleached cellulose fibre. 3.2.3.4 Coir fibre The FTIR analyses of the coir fibre at different processing stages are determined as per the procedure described in 2.2.7. Fig.3.2 gives the FT-IR spectrum of coir fibre at different processing stages. As discussed in chemical analysis, the main components in the coir fibre are cellulose, hemicellulose and lignin. These three components are mainly composed of esters, aromatic ketones and alcohols, with different oxygen-containing functional groups. Klemm, Erdtman and Oh have reported on the infrared spectra of cellulose, hemicellulose and lignin [1, 7, 12-13]. Lignin present in the coir fibre gives characteristic peaks at 1240, 1650 and 1740 cm1
corresponding to the aromatic skeletal vibration and carbonyl group. It is
clear from the spectra that these three peaks are completely absent in the bleached fibre. The peak present at 1650 cm-1 in the spectrum corresponding to the raw fibres is due to the presence of C=O linkage, which is a characteristic group of lignin and that at 1740 cm-1 is hemicellulose. Another possibility is the carboxyl or aldehyde absorption arising from the opened terminal glycopyranose rings or oxidation of the C–OH groups. Alkali treatment reduces hydrogen bonding due to removal of the hydroxyl groups by reacting with sodium hydroxide [11]. This results in the decrease of the OH concentration, evident from the decreased intensity of the peak between 3300 and 3320 cm-1bands compared to the untreated fibre [9]. Since the bleached fibre is crystalline cellulose, its spectra gives the transmittance of
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the three hydroxyl groups. The exposed hydroxyl group of the cellulose is clearly seen from the increased intensity of the 3315 cm-1 peak. The three hydroxyl functional group present in the cellulose structure is primarily responsible for this peak in addition to aromatic hydroxyl groups present in the lignin and the water absorbed by moisture sorption in the case of raw and steam exploded fibres.
Fig. 3.2 FTIR spectra of coir fibre The successive treatments lead to the exposure of the three hydroxyl groups which is gradually increased from raw fibre to bleached fibre. These hydroxyl groups are tightly bound by intermolecular hydrogen bonding which gives a reduced moisture absorption in the final crystalline cellulose fibre. Acid hydrolysed fibre gives a spectrum similar to that of the bleached fibre since their chemical compositions are identical. In addition, due to the
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presence of functional groups such as methoxyl –O–CH3, C–O–C and aromatic C=C, peaks in the region between 1250 cm-1and 1600 cm-1was observed [11,9] in the raw and steam exploded fibre. But the destruction of the lignin-cellulose complex during alkali treatment and bleaching steps facilitate the hydrogen bonding by enhancing the cellulose-cellulose interaction. The increased intensity of the peak at 1000 cm-1 and the appearance of the new peak at 1320 cm-1 are due to the isolated cellulose components. From the FTIR analysis it has been concluded that there is a reduction in the quantum of binding components present in the fibres due to the process of steam and chemical treatment. The raw fibres have a characteristic peak in between 1240-1740 cm-1and at 1240 cm-1. These peaks are mainly due to the hemicellulose and lignin components. 3.2.4 X-ray diffraction analysis The XRD analyses of the fibres at different processing stages are determined as per the procedure described in 2.2.8. The effect of various treatments on the crystallinity of the fibres was also calculated. Table 3.3 shows the values of the crystallinity index obtained by Eqn.3.1 in the case of variously treated fibres. The crystallinity index of the fibre can be calculated using the Eqn.3.1 Crystallinity index = {(I crystalline – I amorphous)/ I crystalline} 100
Eqn. 3.1
It is reported that in most lignified plant cells lignin and hemicellulose are deposited between the micro fibrils to give an interrupted lamellar structure and without the removal of these noncellulosic components, the cellulose I to cellulose II transformation will be restricted. With the treatment of NaOH and bleaching agents, the lignin is removed and in this case also the degree of crystallinity goes on increasing. This may be due to the removal of lignin
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which acts as a cementing material and on delignification, an ordered arrangement of the crystalline cellulose in the structure takes place. The removal of surface impurities on banana fibres is advantageous in fibre– matrix adhesion, as it facilitates both mechanical interlocking and the bonding reaction due to the exposure of the hydroxyl groups to chemicals such as resins and dyes. Alkali treatment of the natural fibre will lead to the swelling of the fibre and subsequent increase in the absorption of moisture. With an increase in acid concentration up to 10%, a gradual increase in the crystallinity was observed. However when the acid concentration was increased to 20%, a decrease in the concentration of the pure cellulose was found showing that at high concentration the pure cellulose will degrade. The trend is same in all fibres which we studied (banana, pineapple leaf fibre jute and coir). We can also see that the percentage crystallinity is of the order PALF>Banana>Jute>coir. This order agrees with the values of cellulose content determined in these samples. The crystallinity was found to vary depending on the conditions applied. The maximum crystallinity was obtained when acid hydrolysis was carried out to the bleached fibre. In natural cellulose fibres, the regions of intermediate order in the structure play an important role in the determination of the degree of crystallinity. From the peak intensity of the variously treated fibres that were observed, it has been found that acid hydrolysis changes the fibre diameter as well as the crystallinity. It could be noticed that cellulose was present in the form of cellulose I, and not cellulose II, which arises from the fact that there is no shift of the main peak upon alkali treatment [14]. In case of jute fibre during acid treatment, the pure cellulose is isolated more when the concentration of the oxalic acid increases up to 20 %. Moreover, in the process of hydrolysis,
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the hydronium ions could penetrate into the amorphous regions of cellulose, promoting the hydrolytic cleavage of glycosidic bonds and finally releasing the individual crystallites [15]. Table 3.3 The crystallinity index of the fibres Material
Crystallinity index (Ic)
Raw banana fibre
10.5
Raw PALF
11.3
Raw jute fibre
9.1
Raw coir fibre
2.1
Steam exploded banana fibre
54.1
Steam exploded PALF
63.7
Steam exploded jute fibre
52.9
Steam exploded coir fibre
22.9
Bleached banana fibre
83.8
Bleached PALF
89.3
Bleached jute fibre
82.6
Bleached coir fibre
72.3
It is reported that in most lignified plant cells lignin and hemicellulose are deposited between the micro fibrils to give an interrupted lamellar structure and without the removal of these noncellulosic components, the cellulose I to cellulose II transformation will be restricted. It is well-known that cellulose has four polymorphs, cellulose I, II, III, and IV, which are distinguishable by X-ray diffraction [15]. Cellulose I is the crystal form of native cellulose. Cellulose II is generally formed in regenerated cellulose or alkali treated cellulose. The cellulose present in the raw fibres are in cellulose I and upon
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alkali treatment, we are expecting a polymorphic modification of the crystalline state of the samples from cellulose I to cellulose II [16]. It is reported that the crystalline transformation in natural fibres are occur with an alkali concentration of up to 32% (8 N) and we in the present case only 2% of NaOH was used. Alkali treatment followed by steam explosion in the extraction process permits the accessibility of chemicals and steam to the peripheral part of the fibres resulting in the dissolution of cementing materials from the raw fibres. The lower concentration of alkali and the limited accessibility to the cellulose molecules reduces the crystalline transformation of cellulose polymorphs. Some transformation occur in the PALF fibre which has highest cellulose content and this polymorphic change is visible from the shift in the main peak of the XRD of steam exploded PALF to left compared to that of the raw fibre diffractogram. However, this transformation is not retained up to the final stage of the extraction process since upon oxalic acid treatment the cellulose II is again converted to cellulose I which is evident from the nanocellulose XRD. It has been concluded from the X-ray diffractograms that as banana, PALF and jute fibres undergo steam explosion, bleaching and further acid hydrolysis there is a decrease in the fibre diameter. As the acid concentration is increased there is decrease in the fibre size. 3.2.4.1 Banana fibre Figure 3.3 (a) shows the X-ray diffraction analysis of the various processing stages of banana fibres. The XRD graphs of studied fibres show that they are in a crystalline nature. In raw banana fibre, crystalline cellulose components are oriented in the matrix of lignin, hemicellulose, pectin etc. During chemical treatment the cementing materials (matrix) will be dissolved, and the remaining pure crystalline particles isolated. That particles show
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increasing orientation along a particular axis, due to its similarity in shape. This pure crystalline particles show increasing orientation along a particular axis as the fibres are treated under different processing conditions. On removing the noncellulosic constituents of the fibres by chemical treatment, the degree of crystallinity and crystallinity index will change. The fibre constitutes crystalline and amorphous regions. The degree of crystallinity, i.e., the amount of crystalline cellulose present in a cellulosic fibre cannot be exactly defined, as neither the crystalline portions are perfect crystals nor the noncrystalline portion completely disordered. Alkalization of banana fibres changes the surface topography of the fibres and their crystallographic structure. Apart from truly crystalline and truly amorphous, there are some regions of intermediate order where the molecular configuration is liable to change by the chemical treatment. XRD analysis of the alkali acid treated banana fibre also revealed an overall increase in the crystallinity index with each processing stage. An improvement in the order of the crystallites as the cell wall thickens upon alkali treatment [10] is already reported.
Fig. 3.3 (a) XRD of banana fibre
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3.2.4.2 Pineapple leaf fibre Figure 3.3(b) gives the X-ray diffraction analysis of the PALF and they are in crystalline nature with two peaks, one broad peak at 2θ=17o and a strong peak at 2θ=22o. In raw fibre, crystalline cellulose components are oriented in the matrix of lignin, hemicellulose, pectin etc. During alkali treatment the cementing materials (matrix) will be dissolved, and the remaining pure crystalline particles isolated which is clear from the increased intensity of the fibre. That particles show increasing orientation along a particular axis, due to its similarity in shape. This pure crystalline particles show increasing orientation along a particular axis as the fibres are treated under different processing conditions. On removing the noncellulosic constituents of the fibres by chemical treatment the degree of crystallinity and crystallinity index will change. Both are increasing and the raw fibre has a crystallinity index of 11.3 and its steam exploded counterpart has a value of 63.7 which is clear from Table 3.3. The fibre constitutes crystalline and amorphous regions. The degree of crystallinity, i.e., the amount of crystalline cellulose present in a cellulosic fibre cannot be exactly defined, as neither the crystalline portions are perfect crystals nor the noncrystalline portion completely disordered. Alkalization of PALF changes the surface topography of the fibres and their crystallographic structure. Upon alkali treatment of the PALF an improvement in the order of the crystallites as the cell wall thickens [10] which lead to regular arrangement of the cellulose molecules. Alkali treated followed by steam exploded fibre shows a shift in both peaks to left suggesting a crystallographic transformation. Bleached PALF shows a splitting of the broad peak in to two also support the same. It is clear from
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the Table 3.1 that the raw PALF possess highest cellulose percentage (75%) when compared to other studied fibres. Moreover it is easy to extract the nanofibres from this raw fibre and is more susceptible to crystallographic conversion in the presence of mild alkali (2%) coupled with strong mechanical treatment (steam explosion). But in the final acid hydrolysed stage the fibres returned to their original crystallographic structure which is clear from the Fig. 3.3 (b)
Fig. 3.3 (b) XRD of PALF 3.2.4.3 Jute fibre Figure 3.3 (c) shows the X-ray diffraction analysis of the jute fibres at various processing stages and the graphs show that they are in a crystalline nature. The crystalline nature of the fibre gives two peaks, one broad peak at 2θ=15o and a strong peak at 2θ=22o. The XRD graphs of the jute fibres are different from the other fibres by the reduction of the fist broad peak which is at 2θ=15o. The effect of steam explosion coupled with alkali and acid treatments on the fibre structure is clearly envisaged by XRD. In raw jute
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fibre, crystalline cellulose components are embedded in the matrix of lignin, hemicellulose, pectin etc. During alkali treatment, the matrix materials react with sodium hydroxide and to dissolve along with the formation of traces of the sodium salt of the cellulose. The steam explosion facilitates the ease of access of the alkali in to the inner part of the raw coir by defibrillation of the fibre. More over it will lead to the swelling of the fibre and subsequent increase in the reacting surface area of the fibre. Alkalization of plant fibres changes the surface topography of the fibres and their crystallographic structure. From the figure it is clear that the raw jute fibres possess some crystallinity and this crystallinity keeps on increasing gradually with processing stages. Treatment of the fibres with 2% alkali and successive bleaching processes removed the lignin completely. During the bleaching step, the lignin dissolves out as lignin chloride and the cellulose component is left behind intact.
Fig. 3.3 (c) XRD of jute fibre
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3.2.4.4 Coir fibre The XRD analyses of the coir fibre at different processing stages are determined as per the procedure described in 2.2.8.Fig. 3.3 (d) shows the Xray diffraction analysis of the coir fibre at various processing stages. The effect of steam explosion coupled with alkali and acid treatments on the fibre structure is clearly envisaged by XRD. In raw fibre, crystalline cellulose components are embedded in the matrix of lignin, hemicellulose, pectin etc. During alkali treatment, the matrix materials react with sodium hydroxide and to dissolve along with the formation of traces of the sodium salt of the cellulose. The steam explosion facilitates the ease of access of the alkali in to the inner part of the raw coir by defibrillation of the fibre. More over it will lead to the swelling of the fibre and subsequent increase in the reacting surface area of the fibre. Alkalization of plant fibres changes the surface topography of the fibres and their crystallographic structure. From the figure it is clear that the raw coir fibre has almost zero crystalline nature and the crystallinity keeps on increasing gradually with processing stages. The zero crystallinity of the raw fibre reveals that each crystalline cellulose component is embedded within amorphous lignin components and upon the gradual removal of the lignin by various treatments, the cellulose components tend to form an ordered arrangement. Treatment of the fibres with 2% alkali and successive bleaching processes removed the lignin completely. During the bleaching step, the lignin dissolves out as lignin chloride and the cellulose component is left behind intact. The final cellulose component has two crystalline peaks, the first at 2θ value of 10 and the other at 2θ value of 22. These are the characteristic peaks of cellulose components isolated from natural fibres.
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Fig. 3.3 (d) XRD analysis of coir fibre As can be seen, the overall shape of all diffraction patterns is quite similar except untreated raw coir fibre. The baseline of the raw coir fibre diffraction pattern is almost flat, suggesting a higher content of amorphous material in the sample. On removing the noncrystalline constituents (lignin & hemicellulose) from the fibres by chemical treatment, the degree of crystallinity and crystallinity index will change with a positive shift. Degree of crystallinity of the fibre goes on increasing in both the processing stages. This may be due to the removal of lignin which acts as a cementing material and on delignification, an ordered arrangement of the crystalline cellulose in the structure takes place. By successive experiments, we found that 10% oxalic acid is an optimum concentration fine at the acid hydrolysis step to get a dispersion of cellulose in nanometre dimension. It has been concluded from the X-ray diffractograms that as the raw coir fibres undergo steam explosion, bleaching and further acid hydrolysis there is a decrease in the fibre diameter as well as an increase in the crystallinity.
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3.2.5 Morphological analysis by SEM The Scanning electron microscopic (SEM) analyses of the fibres at different processing stages are done as per the procedure described in 2.2.9. 3.2.5.1 Banana fibre Figure 3.4 (a), 3.4 (b), 3.4 (c) and 3.4 (d) shows the SEM micrographs of the untreated raw, 2% alkali treated, steam exploded and bleached banana fibre respectively. The SEM of the raw fibre in Fig. 3.4 (a) shows a rough surface and the diameter of the single fibre is 250-350 µm. The alkali treated fibre in the 3.4 (b) shows that the cementing materials are getting washing out at this stage. The removal of the surface impurities along with defibrillation is clear from the figure. The alkali treated followed by steam exploded fibre shown in Fig. 3.4 (c) proves the clear demonstration of the defibrillation and depolymerisation of the fibre. Bleached fibre is composed of several microfibrils with diameters in the range of 5–12µm. Each elementary fibre shows a compact structure; exhibiting an alignment in the fibre axis direction with some non-fibrous components in the fibre surface [17]. It was previously shown that during the alkali treatment most of the lignin and hemicellulose were removed.
Steam explosion further removed the
amorphous materials (lignin, hemicellulose, tannin, pectin etc) from the inner part of the fibre via depolymerisation and defibrillation. Lignin is rapidly oxidized by bleaching agent. Lignin oxidation leads to lignin degradation and thereby to the formation of hydroxyl, carbonyl and carboxylic groups, which facilitate the lignin solubilisation in an alkaline medium [18]. The final bleached form shown in Fig. 3.4 (d) is purely white in colour and the average diameter is 5-10 µm.
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Fig. 3.4 (a) SEM of raw r banana fibre
Fig. 3.4 (c) Steam exploded banana fibre
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Fig. 3.4 (b) Alkali treated banana fibre
Fig. 3.4 (d) Bleached banana fibre
3.2.5.2 Pineapple leaf fibre Fig. 3.5 (a), 3.5(b), 3.5(c) and 3.5(d) shows s the SEM micrographs rographs of the raw, 2% alkali treated, steam exploded and bleached PALF respectively. The SEM of the raw fibre 3.5 (a) shows a rough surface and the diameter of the single le fibre is 250-350 250 350 µm. The individual fibre bundles are arranged with an order which is clear from this figure. The alkali treated fibre 3.5 (b) shows that the surface of the fibre is much more smooth due to the removal of the cementing materials. The removal oval of the surface impurities along with defibrillation is clear from the figure. The alkali treated followed by steam exploded fibre shown in 3.5 (c) again proves the defibrillation and
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depolymerisation of the fibre. The final bleached form of the fibre shown in Fig. 3.5 (d) is purely white in colour and the average diameter is 5-10 5 10 µm.
Fig. 3.5 (a) SEM of raw aw PALF
Fig. 3.5 (c) Steam exploded PALF
Fig. 3.5 (b) Alkali treated PALF
Fig. 3.5 (d) Bleached PAL LF
3.2.5.3 Jute fibre Fig. 3.6 shows the SEM micrograph of the jute fibre at different processing stages. Fig. 3.6 (a), 3.6 (b), 3.6 (c) and 3.6 (d) shows s the SEM micrographs rographs of the raw, 2% alkali treated, steam exploded and bleached jute fibre
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respectively. Jute fibre also follows the trend observed for banana and PALF in the SEM analysis of the various stages of the fibre. Fig. 3.6 (a) shows the SEM micrograph of the untreated raw jute fibre. The fibre surface appears to be smooth due to the presence of waxes and oil. The raw fibre diameter is 50-100 µm where thousands of microfibrils are bound together in the matrix of lignin and hemicelluloses. Fig. 3.6 (b) is the alkali treated fibre and the arrangement of cellulose microfibrils are clearly seen in this picture. The removal of cementing materials, primarily lignin, from the surface of the raw fibre occurs during this step. Fig. 3.6 (c) represents the SEM of fibres subjected to steam treatment after alkali treatment. During the steam explosion with alkali, the hemicellulose is hydrolyzed and become water soluble. The steam explosion facilitates the ease of access of alkali to the interior part of the fibre. The clear demonstration of the defibrillation by steam explosion is seen in this figure. Figure Fig. 3.6 (d) shows the SEM micrograph of the bleached jute fibre. The lignin gets depolymerized and dissolved out at this step which is evident from the chemical analysis. As a result, defibrillation of the fibre occurs because of the removal of the cementing materials which can be seen from the SEM micro photograph.
Fig. 3.6 (a) SEM of raw jute fibre
Fig. 3.6 (b) Alkali treated jute fibre
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Fig. 3.6 (c) Steam exploded jute fibre
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Fig. 3.6 (d) Bleached jute fibre
,
3.2.5.4 Coir fibre The SEM analyses of the coir fibre at different processing stages were done d as per the procedure described in 2.2.9. Fig. 3.7 shows the SEM micrograph of the coir fibre at different processing stages. Fig. 3.7 (a) shows the SEM micrograph of the untreated raw coir fibre. The fibre surface appears to be smooth due to the presence of waxes and oil. However, the presence of pores could be observed on the surface. Though coir fibre has high lignin content (49.2), thee moisture absorption capability is comparable (9.2%) with the other fibres. Fig. 3.7 (b) is the alkali treated fibre. The arrangement of cellulose fibres within the matrix of lignin is clearly seen in this picture. The removal of cementing materials, primarily primarily lignin, from the surface of the raw fibre occurs during this step. Fig. 3.7 (c) represents the SEM of fibres subjected to steam treatment after alkali treatment.
During the steam
explosion with alkali, the hemicellulose is hydrolyzed and become water wate soluble. The steam explosion facilitates the ease of access of alkali to the interior part of the fibre by swelling of the fibre. fibre. The clear demonstration of the defibrillation by steam explosion is seen in this figure. Figure Fig. 3.7 (d) shows the SEM micrograph icrograph of the bleached coir fibre. The lignin gets
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depolymerized and dissolved out at this step which is evident from the chemical analysis. As a result, defibrillation of the fibre occurs because of the removal of the cementing materials which can be seen seen from the SEM micro photograph.
Fig. 3.7 (a) SEM of raw r coir fibre
Fig. 3.7 (c) Steam exploded coir fibre
Fig. 3.7 (b) Alkali treated coir fibre
Fig. 3.7 (d) Bleached coir fibre
Bleached fibre is composed of several microfibrils with diameters in the range of 3–12µm. 12µm. Each elementary fibre shows a compact structure; exhibiting an alignment in the fibre axis direction with some non-fibrous non components in the fibre surface [17]. It was previously shown that during the chemical mical treatment (alkalization) most of the lignin and hemicellulose were
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removed. Mechanical treatment further removed the amorphous materials (lignin, hemicellulose, tannin, pectin etc) from the inner part of the fibre via depolymerisation and defibrillation. Lignin is rapidly oxidized by bleaching agent. Lignin oxidation leads to lignin degradation and thereby to the formation of hydroxyl, carbonyl and carboxylic groups, which facilitate the lignin solubilisation in an alkaline medium [18]. Fibre diameter was again reduced in the acid hydrolysis followed by steam explosion process and cellulose fibre with a diameter of less than 100 nm was obtained. Thus cellulose microfibrils of the original fibres were separated from each other to produce fibrils with diameters around 5–50 nm. The dispersed cellulose nanofibre within this nanometre dimension is clearly seen from the SEM image Fig. 3.8.
Fig. 3.8 SEM of cellulose nano dispersion
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3.2.6 The element detection analysis Element detection analysis was carried out by EDS technique of the scanning electron microscopic instrument in liquid nitrogen atmosphere which is described in 2.2.9. This analysis reveals the presence of various elements present in the focussed area of the fibre. A characteristic observation of the result is the weight percentage of the carbon and oxygen in the raw fibres. Pure cellulose has a higher weight percentage for oxygen than carbon. The untreated raw fibres of banana, PALF, jute and coir, there is a higher weight percentage for carbon than oxygen. The high percentage of the lignin content is responsible for the result. Lignin has an aromatic structure with very high carbon content than cellulose and hemicellulose. But in bleached fibres possess higher oxygen content than carbon due to pure isolated cellulose. The lignin decomposition and elimination is clearly demonstrated from the result obtained in the weight percentage of carbon and oxygen of the bleached fibre. All bleached fibres show a higher oxygen weight percentage than carbon. 3.2.7 Morphological analysis by SPM The scanning probe microscopy (SPM) analyses of the raw fibres of banana, PALF, jute and coir fibre and final isolated cellulose nanofibres are done as per the procedure described in 2.2.10. Fig. 3.9 (a), 3.9 (b), 3.9 (c) and 3.9 (d) shows the SPM micrographies of the raw banana, PALF, jute and coir fibre respectively. Each fibre is composed of several microfibrils with diameters in the range of 3–12µm. Each elementary fibre shows a compact structure; exhibiting an alignment in the fibre axis direction with some non-fibrous components in the fibre surface [17].
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Fig. 3.9 (a) SPM of raw banana fibre
Fig. 3.9 (c) SPM of raw jute fibre
Fig. 3.10 (a) SPM of banana nanocellulose;
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Fig. 3.9 (b) SPM of raw PALF
Fig. 3.9 (d) SPM of raw coir fibre
Fig. 3.10 (b) SPM of PALF nanocellulose
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It was previously shown that during the chemical treatment (alkalization) most of the lignin and hemicellulose were removed. Mechanical treatment (steam explosion) further removed the amorphous materials (lignin, hemicellulose etc) from the inner part of the fibre via depolymerisation and defibrillation. Fibre diameter was again reduced in the acid hydrolysis followed by steam explosion and pure cellulose fibre with a diameter of less than 100 nm was obtained. Thus cellulose microfibrils of the original fibres were separated from each other to produce fibrils with diameters around 5– 50 nm. The scanning probe microscopy (SPM) pictures show the final cellulose nano fibrils with diameters of 5–50 nm. Figure 3.10 (a), 3.10 (b), 3.10 (c) and 3.10 (d) shows the SPM image of the cellulose nano dispersions of banana, PALF, jute and coir fibre respectively. The nanofibres are separated in this height image since the sample was subjected to sonication just before the experiment was conducted to avoid the agglomeration. The fibres are dispersed randomly and are white in colour. SPM pictures show the final cellulose nano fibrils with diameters of 5–10 nm which supports the evidence for the isolation of individual nanofibres from raw fibres by this process. Acid hydrolysis of cellulose leads to hydrolytic cleavage of glycosidic bond between two anhydroglucose units. Thus the amorphous portion gets dissolved by acid hydrolysis, leaving behind the crystalline regions. Acid hydrolysis followed by mechanical treatment results in disintegration of the cellulose structure into nanocrystalline form. It was found that 1 kg of raw fibre gives 234gm of dry nanocellulose.
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Fig. 3.10 (c) SPM of jute nanocellulose;
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Fig. 3.10 (d) SPM of coir nanocellulose
3.2.8 Dynamic light scattering cattering (DLS) and Zeta potential The Dynamic light scattering (DLS) and Zeta potential analyses of the nanocellulose isolated from coir fibre is done by the procedure described in 2.2.11. Dynamic light scattering was one of the most popular light scattering techniques because it allows particle sizing down to 1 nm dimension. Typical applications tions are emulsions, micelles, polymers, proteins, nanoparticles or colloids. For particle size distribution, the water suspended nanocellulose particles were diluted appropriately and analyzed in DLS particle size analyzer. The intensity of light scattered scattered in a particular direction by dispersed nanocellulose tends to periodically change with time. These fluctuations in the intensity vs. time profile are caused by the constant changing of nanocellulose positions brought on by Brownian motion. DLS instruments instrument obtain, from the intensity counts vs. time profile, a correlation function. This exponentially decaying correlation function is analysed for characteristic decay times, which are related to diffusion coefficients and then by the
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Stokes–Einstein equation, to a particle radius. The physical mechanism that is used to stabilize most aqueous nanocellulose particles systems is electrostatic repulsion. Gaussian size distribution of water suspended nanocellulose particles extracted from coir fibre is given in Fig. 3.11. The relative intensity is plotted against mean diameter in nanometer range. The result confirmed that the dimension of the nanocellulose particles are in the range of 4-100 nm with an average value of 37.8 nm. The standard deviation for the particle sizing is 2.1 nm (5.5%) with a Chi Squared of 2.114 for Gaussian summary. The linearity in particle size reduction is observed for dilute solution. The increase in the concentration of the suspension resulted in partial agglomeration. The colloidal nanocellulose particles of interest are charged, resulting in their mutual repulsion at extended distances. Ideally, the repulsive forces are sufficiently strong to prevent the nanocelluloses from diffusing close to each other, where shortrange van der Waals attractive forces dominate and lead to agglomeration.
Fig. 3.11
Gaussian distribution curve of nanocellulose fibre obtained from coir fibre
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Zeta potential (mV)
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Fig. 3.12 Zeta potential as a function of concentration (%) of coir nanocellulose suspension in 0.1 mM KCl electrolyte Zeta potential is due to the formation of the electric double layer between a solid substrate and a liquid electrolyte. Here it is a measure of the mobility distribution of the dispersion of charged nanocellulose particles as they are subjected to an electric field. The average zeta potential of nanocellulose prepared by acid hydrolysis is −18.3mV. Zeta potential measured as function of concentration of original aqueous coir nanocellulose suspension in 0.1 mM KCl electrolyte is shown in Fig. 3.12. Concern is that changing the electrolyte concentration with dilution may have also affected the results. It does appear that using a concentration of between 10 and 20% appears most promising for measuring zeta potential f (pH) tests. The negative charge on the surface of nanocellulose prepared by mild oxalic acid hydrolysis indicates the attachment of oxalate groups on its surface. The cellulosic surfaces generally show bipolar character with prevalent acidic contribution due to the proton of the hydroxyl functional group as well as of present carboxyl groups from oxalic acid.
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3.3 Conclusion The work reported in this chapter with the aim to suggest a simple and low cost method for the extraction of cellulose from various lignocellulosic fibres and preparation of nanocellulose fibrils from this extracted cellulose. The chemical composition of raw, steam exploded, and bleached fibres were determined. The percentage of cellulose components were found to be increased during steam explosion and the additional bleaching process for all the studied fibres. The lignin and hemicellulose components were found to be decreased from raw to the bleached fibres. Alkali treatment of the fibre will dissolve the non-crystalline particles from the lignocellulosic fibres. Steam explosion after alkali treatment of the fibre causes defibrillation and depolymerisation along with isolation of the crystalline cellulose particles. Steam explosion combined with acid hydrolysis has been found to be successful in obtaining fibres in the nano dimension from various plant fibres. A homogenous nanocellulose fibrils with a diameter of 5-40nm is obtained by this process. FTIR, XRD, TGA and morphological analyses clearly supports the isolation of nanocellulose fibrils. FTIR analysis show that there is a reduction in the quantum of binding components present in the fibres due to the process of steam and chemical treatment. The raw fibres have a characteristic peak in between 1730-1740 cm-1and 1200-1300 cm-1. These peaks are chiefly responsible for the hemicellulose and lignin components. These characteristic peaks are completely absent in the final bleached cellulose fibre. X-ray diffractograms show that as banana, PALF and jute fibres undergo steam explosion, bleaching and further acid hydrolysis, there is a decrease in the fibre diameter. As the acid concentration is increased there is decrease in the fibre size. The crystallinity of the fibre increases during each of these processing steps.
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Other interesting finding is the extraction of nanocellulose from raw coir fibre and thereby enhances its effective utilisation and to avoid the retting process of the coir fibre which makes strong environmental problems. Steam explosion has been found to be successful in obtaining fibres in the nano dimension from raw coir fibres even though it has 45-50% of lignin content. The FTIR analysis shows that there is a reduction in the quantum of binding components present in the fibres due to the process of steam and chemical treatment. The raw fibres have a characteristic peak in between 1240-1740 cm-1and at 1240 cm-1. These peaks are mainly due to the hemicellulose and lignin components. The X-ray results show that as the raw coir fibres undergo steam explosion, bleaching and further acid hydrolysis there is a decrease in the fibre diameter as well as an increase in the crystallinity. Homogenous cellulose nanofibrils with a diameter of 5-50 nm are obtained from coir fibre by this process. The zeta potential results show that the cellulosic surfaces have bipolar character with prevalent acidic contribution due to the proton of the hydroxyl functional group as well as of present carboxyl groups from oxalic acid which is used in the acid hydrolysis step of its isolation. By adopting this process it can now be concluded that we can easily isolate the nanocellulose from various lignocellulosic fibres. Out of the four fibres studied; pineapple leaf fibre is the best one for the preparation of nanocellulose fibrils when quality and the yield is concerned. But jute fibre is cheaply and abundantly available and the raw jute fibre has about 60-70% cellulose content. Hence for the production of nanocellulose with cost effectively; jute fibre is the potential candidate. The prepared nano cellulose fibrils will be a good reinforcement in the polymeric matrices where a large surface area and specific properties of nanotechnology is required
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