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Nanocellulose 56Nishtha Singh, Sonal Upadhyay, and Nidhi Mishra
ContentsIntroduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1366Differences Among Cellulose and Nano Cellulose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1366Applications of Nano Cellulose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1366Different Methods of Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1367Chemical Methods of Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1367Synthesis Processes for Nanocellulose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1370Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1381References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1381
AbstractCellulose being the most ample natural-based polymer has been recently nano-structured in the form of potential nanocellulose. Cellulose fibers at nanoscalealso known as nanocellulose or cellulosic nanoparticles have been preparedutilizing various procedures. These serve as distinctive constituents basedon which materials are produced with enhanced potential and performance.Basically, based on the procedures involved for the production, these have beenclassified into two categories – microfibrillated cellulose and nanocrystals ofcellulose. They have the full potential to be an eco material. This chapterhighlights the synthesis and significance of nanocellulose as environmentalfriendly, biodegradable, and recyclable nanoparticle making them potential can-didates for various applications and processing of other polymer composites atnanoscale.
N. Singh · S. Upadhyay · N. Mishra (*)Applied Science Division, Indian Institute of Information Technology,Allahabad, Uttar Pradesh, Indiae-mail: [email protected]; [email protected]; [email protected]
# Springer Nature Switzerland AG 2019L. M. T. Martínez et al. (eds.), Handbook of Ecomaterials,https://doi.org/10.1007/978-3-319-68255-6_146
1365
KeywordsNanocellulose · Synthesis · Biodegradable · Polymer · Hemicellulose · Lignin ·Nanofibers · Nanocrystals · Filtration · Centrifugation
Introduction
The emerging and ever-increasing demand of ecological materials, depletion ofsources like petroleum, and environmental concerns have led to provocative explora-tion of green materials that are environment compatible. Cellulose, a renewableresource, exists in hemp, rice husk, sugarcane bagasse, wood, cotton, and othermaterials based on plants. β-1,4-Glucopyranose units form cellulose. Cellulose hasprimary hydroxyl group at C-6 position and secondary hydroxyl groups at C-2 and C-3positions, having a molecular formula of (C6H10O5)n. These occur mainly in fourforms – cellulose I, cellulose II, cellulose III, and cellulose IV. Unit cell of crystal ofcellulose I is parallel while being antiparallel in cellulose II. These are restored by anatural process commonly acknowledged as photosynthesis. Nano cellulose has beenfound with interesting properties like high stiffness and tensile strength and excellentbiodegradability. Depending on the source of derivation of cellulose and pre-pro-cessing methodology, highly refined nanocellulose could be extracted. These method-ologies include physical processes like hominization using pressure or ultrasonicprocess, chemical procedure like hydrolysis by acid, and biological procedure likeenzymatic hydrolysis [1]. Cellulose microfibrils and cellulose nano crystals have beenobtained. The significant properties like chemical resistance, ability to be recycled, andhydrophilic nature have brought nanocellulose for various applications in comparisonwith cellulose. These cellulosic nano crystals have high refractive index and aspectratio along with low density. They show certain property of rheology due to theirreactive surface and specific surface area. nanocellulose can be obtained from manyplant products like sugarcane bagasse, sisal fibers, rice husk, maize straw, etc. Thischapter provides insight to some of the techniques and methodologies for obtainingnanocellulose from these products [2].
Differences Among Cellulose and Nano Cellulose
Cellulose being an organic compound has a molecular formula of (C6H10O5) and isfound in plants, algae, etc., while nanocellulose is synthesized by physical, chemical,and biological methods from cellulose. Cellulose fiber has a diameter of 10–50 μm,and nanofibers have a diameter which is less than 0.1 μm [3].
Applications of Nano Cellulose
As paper filler: Fibrillated cellulose can be used as fillers in paper as cellulose hasmore strength and more amounts can be added as filler thus reducing the productioncost. Low amount of energy is required for drying purpose as there is less cellulose
1366 N. Singh et al.
throughout the thickness. This paper has improved properties of low porosity,low translucency, and high printing quality. And the transportation is more effi-ciently done.
Surface coating: Nanocellulose has found application in surface coating.Coating formulations which are starch based have been filled with zinc oxide andcellulose nanofibrils for antibacterial paper. This paper shows bactericidal activityagainst gram-negative bacteria and gram-positive bacteria. Concentration of cellu-lose nanofibers influenced the adhesive property.
Construction: Micro-cellulose fibrils and cellulose nanomaterials can be utilizedin concrete which would increase the toughness. Significance involves reduction involume of cement required, thus reducing labor cost and material cost therebyreducing the emission of corresponding greenhouse gas.
Energy: Devices converting chemical energy into electrical energy have beendefined as fuel cells. Nano cellulose-based nanocomposites have been utilized inmanufacturing of Li-ion battery, solar cells, and fuel cells [4].
Paint: Viscosity of coatings and paints can be modified by the use of nano-cellulose. It has been used as an additive in polyurethane paints and varnishes. Itprotects paints and varnishes from wearing away due to UV radiation. It providesprotection to the underlying materials. It extends the life of paints and varnishes andreduces the cost and burden on environment of replacing the coatings.
Personal care: Cosmetic cellulose nanomaterials have been used as rheologymodifier which is non-allergic and as hydrating agent. It has been also usedin cosmetics for coating like in eyelashes, nails, etc. With increasing demandsof natural cosmetic products, it has led to increased demands of cellulosenanomaterials.
Electronics: There is an ever-increasing demand of solar cells, transistors,and printed electronics in information and communication area. These requirethin Polymer films. This can be provided by nanocellulose which wouldprovide films that will have properties of high tensile strength, smoothness atnanoscale, low thermal expansion coefficient, and transparency (optical) [5, 6](Fig. 1).
Different Methods of Preparation
There are different processes of preparing nanocellulose which have beenhighlighted in Fig. 2.
Chemical Methods of Preparation
Nanocellulose can be prepared using a chemical process which involves differentchemical reactions and mechanisms. The method involves:
1. Acid hydrolysis: Preparation of cellulose nano crystals using hydrolysis ofcellulose by hydrochloric acid leads to flocculation of uncharged particles when
56 Nanocellulose 1367
dispersed in aqueous medium. On Hydrolysis with sulfuric acid, sulfonic groupsof negative charge are formed due to reaction with hydroxyl groups at the surface.Cellulose chains in noncrystalline portion when hydrolyzed by acid lead toaddition of proton to glucosidic oxygen or cyclic oxygen, which is trailed bysplitting of glucosidic bonds due to inclusion of water. As a result two short-chainfragments are produced, while principal backbone structure is preserved. Besides,
Nanocellulose
Food industry
Industrial
cosmetics
Textile industry
biosensors and
diagnostics
Health care
Fig. 1 Various applicationsof nanocellulose
Different processes of
preparing Nanocellulose
Mechanical methods:
1)Homogenization
2) Cryocrushing
3) Sonication
Chemical Methods:
1) Acid Hydrolysis
2) Catalytic hydrolysis
Fig. 2 Various methods of preparation of nanocellulose
1368 N. Singh et al.
splitting of chains of hydroxyl groups is partially esterified. Due to the presenceof sulfate groups, the surface of nanocrystals becomes negatively charged. Due tothis thermostability is compromised. Therefore, neutralization of sulfate groupwhich is done using sodium hydroxide is suggested [7] (Fig. 3).
2. Catalytic hydrolysis: Hydrolysis of amorphous domains while protecting thecrystallite stage is a challenge. Therefore, transition metals are used. Fe(III), Co(II), and Ni(II) are transition metals which can form coordination covalent bondswith water molecules which are six in number and form a metal ligand complex.Subsequently the ions of the complex were deprotonated to yield more H+ ions inthe solution which cleaved the glycosidic bond between the units of glucose, thusdegrading the glycosidic linkages. This process will be continued until thestabilization of the complex. Therefore, oxidation states of Fe(III), Co(II), andNi(II) have a significant role for generation of acidic state. The more the higherthe oxidation state, the more hydronium ions (H3O
+) will be produced to yieldstable state. Thus, this process helps in preparation of nanocellulose from cellu-losic fibers [9] (Fig. 4).
O
O
HOOH
HOOH
O
OH
n
OH
Cellulose
O
O
HOOH
OHO
OH
O
OH
n
OH
H+
OHH
Fast equilibrium H+
O
O
HOOH
OHO
OH
O
OH
n
OH
H+
OHH
H+
O
O
HOOH
HOHO
OH
O
OH
OH
OH +
O
O
HOOH
OHO
OH
O
OH
n
OH2+
SOHHO
OO
O
O
HOOH
OHO
OH
O
OH
n
SO3H
+ H2O
O
a
b
Fig. 3 (a) Mechanism showing Acid hydrolysis of cellulose chain. (b) Cellulose Nano crystalesterification process (From Lu and Hsieh 2010) [8]
56 Nanocellulose 1369
Synthesis Processes for Nanocellulose
Sugarcane bagasse: Industries like alcohol and sugar yield an ample amount ofsugarcane bagasse as residue every year which is being utilized for fuel and otherenergy-producing processes. These residues have been also employed for the pro-duction of paper and pulp. Their renewability and Biodegradability had led to theirprocessing for production of nanocellulose and microcrystalline cellulose. Majorityof the constituent of this biomass is the crystalline cellulose, and the other constit-uents include hemicellulose, lignin, minerals, etc. nanocellulose has been obtainedutilizing the hydrolysis by strong acid like sulfuric acid. Firstly, easily availablesugarcane bagasse was acquired and cleaned. The sugarcane bagasse was grounded
O
OO O
O
O
O
O
OO
O
O
O
OH
Cellulose hydrolysis inpresence of metal ions{M=Fe3+, Co2+, Ni2+}
OHHO
HO
HOM
M
HO
OH
OH
OH
OH O
OO
OH
[Fe(H2O)6]3+ + 3H2O [Fe(H2O)3(OH)3] + 3H3O+
[Co(H2O)6]2+ + 2H2O [Co(H2O)4(OH)2] + 2H3O+
[Ni(H2O)6]2+ + 2H2O [Ni(H2O)4(OH)2] + 2H3O+
Fig. 4 Catalytic hydrolysis for preparation of nanocellulose using transition metals (From Chenet al. [9])
1370 N. Singh et al.
and later dried in an oven at 60 �C for 16 h; 0.7% sodium chlorite solution wasutilized to bleach the grounded and dried sugarcane bagasse. The pH of 4 wasregulated by 5% acetic acid. To remove Lignin the mixture was boiled for 5 h. Aftercontinuous washing with distilled water, it was boiled with 5% sodium sulfitesolution (250 ml) for 5 h, thus removing Lignin completely and partially removingHemicellulose. The Hemicellulose was separated by boiling it with 17.5% sodiumhydroxide solution (250 ml) for 5 h. Using Filtration cellulose was collected andwashed with distilled water to make it neutral. After air-drying, 50 ml DMSO(dimethyl sulfoxide) is added in water bath maintained at 80 �C for 3 h, followedby filtration, washing, and air-drying. Hydrolysis using 60% sulfuric acid at 50 �Cfor 5 h is utilized for obtaining nanocellulose. Vigorous agitation is required.Fivefold water is added to the mixture, followed by cooling and then Centrifugationafter each washing. After five consecutive washing and Centrifugation, a colloidalsuspension is obtained. In ice bath the suspension was sonicated for 5 min and thenstored at 4 �C in a refrigerator [10] (Fig. 5).
China cotton, South Africa cotton, and Waste tissue paper: These materialswere mixed with 47% sulfuric acid and it is strongly stirred for 2 h at 60 �C. Thesuspension was centrifuged and washed with distilled water to decrease the concen-tration of acid. 0.5 N NaOH finally neutralized the suspension followed by washingwith distilled water. The nanocellulose suspension was stored in a refrigerator [11](Fig. 6).
Pineapple leaf fibers: Properties like high stiffness and specific strength areexhibited by PALF (pineapple leaf fiber). Fibrous cell bunches form the vascularbundle system, and the fibers are in the form of ribbons. The fibers are easilyavailable and inexpensive. It has a high cellulose content resulting in high mech-anical property. Pineapple leaves are by-product of pineapple cultivation.Bromeliaceae family plant Ananus cosomus after extraction yields lignocellulosicfiber by a process known as retting. For separation of nanofibres the method of steamexplosion is used which involves steaming at high pressure followed by decompres-sion at a rapid rate. Pineapple fibers were cut into pieces of size 10 cm. Furthertreatment followed placing the fibers in autoclave under 20 lb pressure for a durationof 1 h after fibers were treated with NaOH (2%) in a ratio of 1:10 (fiber to NaOH).After releasing the pressure immediately, the fibers were removed from autoclaveand NaOH was washed away with water. Mixture of acetic acid and NaOH was usedto bleach the mixture six times. Then the fibers were washed in distilled water anddried followed by treatment with 11% oxalic acid in an autoclave until pressure of20 lb is reached and then the pressure was released. This process was repeated foreight times. The nanofibrils were suspended in water and stirred with mechanicalstirrer for a duration of 4 h for 8000 rpm [12] (Fig. 7).
Nanocellulose from beer industry residues: Beer industrial residue suspension(10%) for attainment of constant weight was boiled for 1 h and then dried at 105 �C.Then it was soaked overnight in 2% NaOH, followed by washing and treatment with12% NaOH and then autoclaving three times at 121 �C for a duration of 45 min toobtain pulp. At temperature of 105 �C, the pulp was washed and dried. For removalof lignin, treatment was done for 1 h at 75 �C by a solution of NaClO2 (3%) and
56 Nanocellulose 1371
CH3COOH (1.5%) two times. For removal of Hemicelluloses, the pulp was soakedin a 3% KOH solution for a night followed by treatment for a duration of 1 h at80 �C. NaClO2 (3%) and CH3COOH (1.5%) bleached the pulp (1 h at 75 �C)followed by drying at 105 �C. Hydrolysis of purified cellulose to 10% hydrochloricacid was done for durations of 2 h, 4 h, and 6 h at 80 �C. Washing was done bycentrifugation (three times) for 30 min at 4 �C and 6000 rpm. Neutralized cellulosewas subjected to ultrasonic treatment for dispersion for 15 min that yielded nano-cellulose [13] (Fig. 8).
Maize straw for preparation of Nanocellulose: Zea mays (maize straw) havehigh carbon to nitrogen ratio making them resistant to degradation from microor-ganisms in soil and thus decaying takes a longer time. Maize straw contains 28–44%of cellulose. Cutin, pectin, and others were removed by Soxhlet method utilizingethyl alcohol (2 h), deionized water (4 h), and hexane (2 h) and dried at 80 �C in an
Sugarcane bagasse grounded and dried
Add 0.7% sodium chlorite solution to bleach
Boil to remove lignin
After washing pH was regulated by 5% Acetic Acid
Hemicellulose was removed by boiling with 17.5% NaOH (250 ml)
Filteration cellulose was collected and washed with distilled water
Hydrolysis using 60%H2SO4
NanoCellulose
Fig. 5 Flowchart description of methodology of synthesis of nanocellulose using sugarcanebagasse
1372 N. Singh et al.
oven. It was then treated with NaOH (5% w/v). The suspension of straw (1:100straws to liquor ratio) was treated for 2 atm pressure at 121 �C in an autoclave fordurations of 15, 30, 45, and 60 min. The pulp was filtered and washing was donewith deionized water till the attainment of neutralization. H2O2 (2% v/v) and tetraacetyl ethylene diamine (0.2% w/v) was used to treat the pulp at 48 �C for 12 h wherestraw and liquor ratio is 1:25. The pulp was washed with deionized water. Dried pulpwas treated with acetic acid (80% in 1:33 ratio) and nitric acid (65% in 1:4 ratio) fora duration of 30 min while stirring at 120 �C. It was washed and filtrated in waterand ethyl alcohol. Purified cellulose was then treated with sulfuric acid (64%).While stirring the hydrolysis with acid was carried out for different durations of15,30,60,90,120,150, and 180 at temperature of 25 �C. Cold deionized water wasadded to stop the reaction. Ultrasonification for 15 min was done after Centrifugationfor 1 h at 3000 rpm [14] (Fig. 9).
Preparation from sisal fibers: The sisal fibers were washed with distilled waterand later dried in an oven for 24 h at 80 �C and then cut into 5–10 mm length. Fiberswere boiled in a mixture of toluene/ethanol (2:1 v/v) for 6 h in a Soxhlet. The fiberswere washed, filtered with ethanol for 30 min, and later dried. Removal of lignin isdone by treatment with NaClO2 (0.7% w/v) and boiling for 2 h and treating withNaHSO4 solution (5% w/v) followed with treatment by NaOH (17.5% w/v). Filter-ing and washing is done with deionized water and dried in vacuum. Nanofibres are
China Cotton, South Africa cotton , Waste tissue paper + 47% H2SO4 and strongly stirred
Centrifugation
Washed with distilled water
Neutralization of suspension with 0.5N NaOH
Nanocellulose suspension stored in refrigerator
Fig. 6 Flowchart description of methodology of synthesis of nanocellulose using China cotton,South Africa cotton, and waste tissue paper
56 Nanocellulose 1373
obtained by acid hydrolysis. This is done with sulfuric acid solution (60%) for30 min at 45 �C while stirring [15] (Fig. 10).
Preparation of Nano cellulose from rice husk: Rice husk constituents arecellulose, Hemicellulose, silica, and lignin. Rice husk was treated with KOH (3%w/v in ratio of 1: 12) and boiled for 30 min and left for a night. After filteringit was washed with distilled water, and hydrochloric acid (10%) was added.Silica precipitate was removed. Lignocellulose residue was treated with NaClO2
(1:50 ratio) for 2 h at pH 4, then treated with sodium bisulfite solution (5%) for 1 h atroom temperature, and later dried at 100 � 2 �C. NaOH (17.5%) was used to treatfor 8 h. The nanocellulose was obtained by treatment with sulfuric acid for 30 minwhile stirring. To obtain the neutralized pH, washing was done with deionized water.It was centrifuged and later dried using liophilizator [16] (Fig. 11).
From rubber wood fibers: Nanofibres of rubber wood were formed by twotreatments: (1) enzymatic and (2) ultrasonic. A solution of 3% was prepared bysuspending well-dried fibers (15 g) in deionized water (485 g). pH of 5 was
Pineapple Fibres were cut into pieces each of 10 cm
Treated with NaOH (2%)
Fibres placed in autoclave for 1 hr
Then washed with water
Bleached with mixture of Acetic acid+ NaOH
Washed with distilled water and then dried with 11% Oxalic acid in autoclave for 8 times
Nanofibrils formed were suspended in water
Fig. 7 Flowchart description of methodology of synthesis of nanocellulose using pineapple leaffibers
1374 N. Singh et al.
Beer industrial residue suspension boiled and dried
Soaked for overnight in NaOH
Washed and treatment with NaOH and autoclave
Pulp obtained was washed and dried
Treated with solution of NaClO2 and CH3COOH to remove lignin
Soaked in KOH solution to remove hemicellulose from pulp
Hydrolysis with HCl
Washed by centrifugation
Ultrasonic treatment
Nanocellulose
Fig. 8 Flowchart descriptionof methodology of synthesisof nanocellulose using beerindustry residues
56 Nanocellulose 1375
maintained by using buffer solution of CH3COOH and C2H3NaO2. Required oxi-dation of Lignin was obtained by using 6 U/g of enzymes. This enzymatic pre-treatment was carried at 40–65 �C. For best results, the whole process was kept at aspeed of 160 rpm for a duration of 24 h. After the process, the Filtration ofsuspension was done, and to cease the reaction, it was exposed for a night to heatat 60 �C. In chemical pretreatment, the residual Lignin was removed NaClO2
Using Soxhlet method utilizing ( ethyl alcohol+ deionised water + hexane) to remove Cutin,pectin from Zeamays
Treated with NaOH
Suspension was treated in Autoclave
Washed with Deionized water (DI)
Treated with H2O2 and tetra acetyl ethylene diamine and then washed with deionized water
Then treated with Nitric Acid and Acetic Acid
Washed with H2O2 and Ethyl alcohol
Treated with H2SO4 acid and then add cold DI to stop reaction
Ultrasonification
Nanocellulose
Fig. 9 Flowchart description of methodology of synthesis of nanocellulose using maize straw
1376 N. Singh et al.
(acidified) for 60 min at 75 �C. For removal of Hemicellulose and remaining starch,the sample was treated with KOH (3%) for 2 h at 80 �C and KOH (6%) for 2 h at80 �C. Neutralization of the sample was done by filtration and then washing withdeionized water. To prevent formation of hydrogen bonding, the sample throughoutthe treatment was kept in water-swollen state. Then the sample was put throughultrasonic treatment for 30 min to obtain nanofibers [17] (Fig. 12).
Sisal fibres washed with distilled water and then cut into 5-10 mm in length
Boil the fibres in mixture of toluene/ ethanol in soxhlet
After washing with ethanol removal of lignin is done by NaClO2
Boil and treat with NaHSO4 followed with treatment by NaOH
Then washed with deionized water
Acid Hydrolysis
Nanofibres
Fig. 10 Flowchart description of methodology of synthesis of nanocellulose using sisal fibers
56 Nanocellulose 1377
Cryocrushing: Cryocrushing is a least used method where microfibrils are ina range of 0.1–1 μm. This is a mechanical method for production of nanocellulose.In this fibers are first frozen at a low temperature which is in liquid nitrogen,followed by crushing in high speed. The forces and high shear turn them intopowders where they contain microfibrils. They are then dispersed in watersuspension. Nanofibres which are in the range of 10–100 nm are usually obtained(Fig. 13).
Rice husk +KOH and then boiled
Wash with Distilled water and HCl
Silica removed
Lignocellulose residue treated with NaClO2
Treated with sodium bisulphite solution
Treat with NaOH
Nanocellulose
Fig. 11 Flowchartdescription of methodology ofsynthesis of nanocelluloseusing Rice husk
1378 N. Singh et al.
Homogenization: In this process after refining and dilution of suspension ofcellulose fibrils, they are pumped through a valve at a high pressure. Closing andopening of these valves is done very rapidly leading to a drop in pressure along withforces affecting the fibers. Depending on the starting material being used, the numberof passes through the valve varies. High amount of microfibrillation is achieved dueto high pressure, shear, and forces [18] (Fig. 14).
Compression mechanical techniques: After removal of Lignin from cellulosematerials, they are placed in bed of stripes which is placed between two plates, andthen it is subjected to a load of 10 tons which is constant for time duration of 10 s.
Roller mechanical techniques: In this after removal of Lignin from cellulosicfibrils, the strips are forced in between two rollers of which one is fixed and other isrotating [19] (Table 1).
Challenges and future tendencies: The use of nanocellulose as bio-scaffold forinteraction of cells and nanocellulose is mysterious and also requires extensive invivo studies. The need of technology for preparation of films, composite of cellulose,
Solution of fibres + deionized water
Oxidation of lignin using enzymes and filtration done
Residual lignin removed using NaClO2
Hemicellulose and remaining starch was removed by using KOH at different concentration and temperature
Neutralization done by deionized water.
Ultrasonic treatment for 30 min
Nano fibres.
Fig. 12 Flowchart description of methodology of synthesis of nanocellulose using rubber woodfibers
56 Nanocellulose 1379
and nanocellulose can be a challenge. If nanocellulose is utilized in packagingindustry, then moisture should be diminished which is a challenge, and when appliedfor nanocomposites, then dispersion would be a challenge [20].
Nanocellulose has become a material of the future, with potential properties likestrength, renewability, biodegradability, barrier properties, and biocompatibility.Owing to these properties, Nano cellulose in today’s scenario and future haswidespread and promising applications in various fields of drug delivery, in theform of nanocomposites, or use in construction, personal care, etc. [21]
Fibres are frozen at low temperature
Then crushed at high speed
Turned into powders containing microfibrils
Fig. 13 Flowchartdescription of methodology ofsynthesis of nanocellulose byCryocrushing
Suspension of cellulose fibrils is refined and diluted
Then it is pumped through valve at high pressure
High amount of microfibrillation is achieved.
Fig. 14 Flowchartdescription of methodology ofsynthesis of nanocellulose byHomogenization
1380 N. Singh et al.
Conclusion
The need and demand for biodegradable and sustainable natural resources have ledto research for methods for production and use of nanocelluloses. Cellulose isbiodegradable, easily available, and cheap (relatively). Nanocellulose of differentshapes has been produced using different precursors and different methods (chem-ical and mechanical). These nanocelluloses with improved properties have wide-spread applications in the field of biomedical (surgical wounds, tissue engineering,etc.), in construction, in paints, and in other applications. Nanocelluloses have alsobeen used as polymer nanocomposites. Being easily available and economical, theuse of natural cellulosic fibrils outweighs the limitations associated with them.Taking into consideration environment cellulose which is biodegradable and naturalrenewal polymer is an attractive combination finding role in various applications.This chapter discusses various methods for production of nanocellulose, and alsofew applications have been mentioned.
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Table 1 Summarizationof the use of differentraw materials andmethods of preparationof nanocellulose
Raw materials usedMethods ofpreparation
Year andreference
Sugarcane bagasse Chemical method 2011
[7]
China cotton, South Africacotton, waste tissue paper
Chemical method 2013
[8]
Pineapple leaf fibers Chemical method 2010
[9]
Beer industrial residues Chemical andmechanical methods
2015
[10]
Maize straw Chemical andmechanical methods
2014
[11]
Sisal fibers Chemical method 2008
[12]
Rice husk Chemical method 2011
[13]
Rubber wood fibers Chemical andmechanical methods
2015
[14]
56 Nanocellulose 1381
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