WO2020129089A1

WO2020129089A1 - Method for preparation of cellulosic nanospheres from waste sugarcane bagasse pith fibers

Info

Publication number: WO2020129089A1
Application number: PCT/IN2019/050943
Authority: WO
Inventors: Mandeep Singh; Vikas Pahal
Original assignee: Mandeep Singh; Vikas Pahal
Priority date: 2018-12-21
Filing date: 2019-12-20
Publication date: 2020-06-25

Abstract

The present invention provides a method for preparing cellulose nanospheres with spherical morphology (SNCs) from defibrillated MFCs of waste sugarcane bagasse pith fibers using high shear mechanical treatment and without using highly concentrated chemical reagents. These SNCs are a class of CNCs that possess uniform spherical morphology, larger specific surface area, high porosity and numerous free surface hydrophilic groups. These characteristics reportedly make SNCs a promising nanomaterial in application areas such as biomedicine, nanocomposites and drug delivery.

Description

METHOD FOR PREPARATION OF CELLULOSIC NANOSPHERES FROM

WASTE SUGARCANE BAGASSE PITH FIBERS

FIELD OF INVENTION

The present invention discloses a method for direct preparation of cellulosic nanospheres from microfibrillated cellulose (MFCs) of bagasse pith fibers.

BACKGROUND PRIOR ART

Nanocrystalline cellulose have one of the strongest predilections as a unique natural biopolymer that will record a steep growth in next two decades with applications spanning across numerous industrial sectors. For an instance, the production of advanced organic materials with nanocellulose can possess potential to replace metals in automotive industry and therefore the said sector has been envisioned to show exponential growth in its use by the year 2025. The cost effectiveness, economic viability, renewability and rising ecological barriers have further moved various other sectors including packaging, biomedical, food industry and electronics to plan leap steps towards utilization of this non-toxic nanomaterial in most innovative and productive manner (Garcia et al. , 2016).

Nanocellulose is one of the few renewable biopolymers on earth that possess intrinsic crystalline and natural structures under nanoscale. Available abundantly, the native nanomaterial acts as strength building constituent of the ligno-cellulosic biomass. The morphology and dimensions of this cellulosic material strongly depends upon their source of origin and method of isolation (Siro and Plackett, 2010; Klemm et al , 2011). Nanocrystalline cellulose is that part of the cellulose which when isolated from woody or non-woody sources, the obtained cross-sectional dimensions, degree of crystallinity and morphology, classifies it into two types; nanowhiskers of cellulose (NWCs, CNWs, NCCs or CNCs) and nanofibrillated cellulose (NFCs or CNFs).

The intrinsic nanostructures of cellulose are responsible for some of the extremely attractive properties like mechanical strength and low bulk density (aboutl .6 gg/cc). A pure CNC isolated from hard wood pulp has been reported to be exhibiting elastic modulus of nearly 150 GPa and a tensile strength of nearly 10 GPa (Habibi, Lucia and Rojas, 2010; Siro and Plackett, 2010). The other quintessential physical and chemical characteristics like large surface area, high aspect ratio, non-toxicity, low thermal expansion and good optical properties co-evince it as an important material with broader application area like in development of bioplastics, as a replacement for petroleum plastics.

The availability of large number of free hydroxyl groups rendering on the surface of nanocellulose further provide possibilities of modification to the surface of nanomaterial for achievement of desired applications in the field of biomedicine, drug delivery, hydrogel systems, nanofilters for water and air purification, protein immobilization drug and metallic reaction templates (Gardner et al. , 2008; Missoum, Belgacem and Bras, 2013).

The chemical and mechanical treatments of ligno-cellulosic fibers (LFCs) or natural fibers (NFs) may yield defect-free, highly crystalline nanostructures called CNCs or NFCs depending upon their morphology. The obtained morphology is highly acute to the type of method used as well as raw source of cellulose. The obtained NFCs are usually reported to be 2-3 Onm thick in diameter and extends up to several hundred nanometers in length with crystallinity up to 90% pure. These fibers form strong spaghetti like entangled network with high agglomeration tendency due to large number of hydrophilic groups on their surface. These nanofibers mostly exist as microfibrillated bundles (MFCs) in their raw source completely covered and bind with the impurities (lignin, hemicellulose, pectin) forming a larger bundle called LFCs or NFs.

Cellulose nanowhiskers (CNWs) or nanocrystals (CNCs) are usually rod or cylindrical crystallites that are up to 95% pure with amorphous parts remaining almost absent (Klemm et al. , 2011; Moon et al. , 2011). These CNCs can be directly obtained from microcrystalline cellulose (MCCs) of biomass using acid hydrolysis treatment. When obtained from plant or agricultural sources, these CNWs possess diameter between 3-60nm and length extending up to 100-200nm while in volania (a sea plant), CNWs with diameter 20nm and length 1000- 2000nm can be obtained. Tunicates (a sea animal) can also produce CNWs with diameter 10- 20nm and length 500-2000nm and bacteria can produce CNWs with diameter 10-50nm and length 100-1000nm.

Spherical nanospheres of cellulose (SNCs) are another class of CNCs that has recently intrigued global attention due to their potential in development of super-capacitors for advanced electronics and inks for 3D bio-printers. The uniform spherical morphology, larger specific surface area, high porosity and numerous free surface hydrophilic sites has also reportedly made SNCs a promising nanomaterial in application areas such as biomedicine, nanocomposite fabrication and drug delivery (Carrick, Wagberg and Larsson, 2014; Xu and Zhang, 2015; Yu et al, 2017).

Generally, cellulose nanowhiskers are obtained (rod or cylindrical crystallites) using acid hydrolysis treatment of non-crystalline cellulosic biomass. The methods developed in 1940s and 1950s mostly employ use of highly concentrated acid minerals for reaction. A similar treatment can also be used for production of cellulose nanospheres. But, use of the above treatment for CNWs production is still a matter of great concern mainly due to difficulty of economic acid recovery and disposal of large amount of salt. For example, as per reported data, approximately 9 kg of H₂SO₄ is wasted for production of 1 Kg of CNWs. The subsequent neutralization of acid further produces 13kg of Na₂SC>₄ per Kg of CNWs whose disposal is a major problem today (Lu and Hsieh, 2010; Chen et al. , 2016).

The CNWs so produced with high concentration of H₂SO₄ are low in thermal stability due to presence of sulphate groups in the material due to reaction with the acids. The presence of sulphate groups further impose difficulty in functionalization (surface modification) of CNWs. However, sodium exchange during neutralization of the nanomaterial reduces this effect to some extent, but it still limits the use of nanomaterial for application in the grand market of nanocomposites.

The preparation methods of SNCs are yet complicated and widely under development. These methods usually employ high concentration of acids such as chemical acid hydrolysis (cone. H2SO4 treatment) or mixed acid hydrolysis (e.g. H2SO4/HCI treatment) combined with ultrasoni cation, multi-step acid hydrolysis, microbial hydrolysis and enzymatic hydrolysis under ultrasoni cation or mechanical treatments (Meyabadi etal. , 2014; Yan, Yu and Yao, 2015; Chen et al, 2016; Perez-Madrigal, Edo and Aleman, 2016).

Nevertheless, the conventional methods of hydrolysis used for preparation of SNCs are quite time-consuming and utilize highly concentrated chemical acids for the main reaction. Further, most of the reported works have produced SNCs with diameter in the range of 10-125nm using common H2SO4 and H2SO4/HCI acid hydrolysis methods and 40-100 nm using enzymatic hydrolysis of waste cotton fibers. The time of these reactions reported to be spanned from 16hrs to 175hrs with the yield concentration from 12.3% to 54%. Mostly applied to microcrystalline cellulose (MCCs) of a raw source, production of SNCs using hydrolysis methods possess different problems like non-uniform size distribution, irregular spherical morphology, low yield and poor thermal stability.

In another approach, immuno-selective nanotheranostics application of SNCs was explored for therapeutic drug delivery (Carrick, Wagberg and Larsson, 2014). For this, SNCs were prepared in the size range of 160-170 nm. The entire methodology of preparation of SNCs was followed in a three-step protocol consisting of a complete dissolution of pure cellulosic pulp in a lithium chloride/N, N-dimethylacetamide solution, emulsification of the obtained cellulosic solution and then microfiltration of the final emulsified solution. Though, time of the reaction, stability, yield concentration and economic viability was not mentioned but synthesis of perfectly spherical morphology was an achievement of this work.

The SNCs produced so far using most common chemical acid hydrolysis methods possess low thermal stability as well as poor spherical uniformity. The stability of nanospheres mostly depends upon their crystallinity which is usually lower than their raw source because of accumulation of sulphate groups in SNCs due to reaction with H₂SO₄. An irregular spherical morphology further yields problems in impregnation of drug elements for therapeutic and drug delivery applications.

The pith fibers of sugarcane bagasse used in this work are an economical source of production of SNCs. These are renewable and natural agricultural residues that are abundantly available. Sucrose (polysaccharides) and bagasse are two major by-products of sugarcane that are produced every year. Bagasse is a heterogeneous material that consist of two parts rind and pith, where, the rind forms outer hard part of bagasse, while pith fibers form soft inner parts. The bagasse fibers (rind and pith) have been extensively used for production of biofuels and isolation of cellulose pulp for application in paper industry, building materials and bio composite production. However, research work on individual pith fibers are limited till date (Gao et al, 2014; de Oliveira et al. , 2016; Niu et al. , 2017).

Bagasse piths are mainly parenchyma material (visceral flesh) which is a ground tissue of non- woody structure. Derived from the core of a plant, parenchyma cells can be distinguished from the others due to their thin cell wall (1.7- 5 m). Bulk of the soft parts of plants, internal segments of leaves, flowers and fruits are made up of parenchyma cells but not their epidermis or veins. Sugarcane Bagasse mostly contains about 30-40% pith fibers that are further composed of 40-55% cellulose, binding and padding components such as hemicellulose (25- 28%), lignin (20-25%), impurities like ashes (5-7%) and 0.5-2% other extractives (Sanjuan el al., 2001; de Oliveira et al. , 2016; Kathiresan and Sivaraj, 2016; Niu et al, 2017).

The predominant feature of the pith fibers is their unique 3D porous honeycomb structure formed by parenchyma cell wall that functions mainly as nutrient absorbent (sucrose) in sugarcane. The length of pith fibers is usually longer than straw fibers and possess high concentration of carbon elements due to which it is now considered to be a suitable natural material for development of carbon nano-sheets for electrode materials to enhance electronic conductivity, surface wettability and pseudo-capacitance. The pith fibers have been also found to possess tremendous scope in adsorption of heavy alkali metals and fabrication of hydrogel systems.

The available methods of hydrolysis for preparation of SNCs is a time-consuming task and involves use of highly concentrated reagents for the main reaction. The present invention thus overcomes the aforesaid limitations of the prior art and provides a green method employing use of the sugarcane waste bagasse pith fibers for fabrication of cellulosic nanospheres using high shear homogenizer and without using concentrated H₂SO₄ solution. The resulting cellulosic nanospheres possess uniform spherical morphology, larger specific surface area, high porosity and numerous free surface hydrophilic groups.

OBJECTIVES OF THE INVENTION

An important objective of the present study is to provide a green method for fabrication of cellulosic nanospheres from waste sugarcane bagasse pith fibers.

Another important objective of the present invention is to provide cellulosic nanospheres with perfectly spherical morphology.

SUMMARY

The present invention provides cellulose with perfectly spherical morphology (SNCs) using high shear mechanical treatment of defibrillated bagasse pith fibers (MFCs) in distilled water.

More specifically, the present invention provides a method for preparing cellulosic nanospheres (SNCs) directly from defibrillated MFCs of waste sugarcane bagasse pith fibers without using highly concentrated chemical hydrolysis treatment that are currently in use for such purpose such as hydrolysis treatment of a plant biomass with concentrated H₂SO₄ (up to 64%) solution. The resulting cellulosic nanospheres of the present invention thus possess a uniform spherical morphology diameter in the range of 30-85 nm.

The present invention employs mild acid hydrolysis treatment to the alkaline treated and bleached fibers using 0.1N HC1 solution in the process of preparing defibrillated MFCs from raw pith fibers of sugarcane bagasse.

The method of the present invention can also be used for simultaneous production of NFCs and SNCs from raw pith fibers of bagasse.

Such nanospheres of cellulose are of great importance in the field of emerging technologies due to their exclusive potential towards development of super-capacitors (electronics) and fabrication of ink for 3D bio-printers. These SNCs are a class of CNCs that possess uniform spherical morphology, larger specific surface area, high porosity and numerous free surface hydrophilic groups. These characteristics reportedly make SNCs a promising nanomaterial in application areas such as biomedicine, nanocomposites and drug delivery.

BRIEF DESCRIPTION OF TABLES AND FIGURES

Fig. 1 illustrates schematic of high shear homogenization process.

Fig. 2 depicts Fourier transform infrared spectroscopy (FTIR spectroscopy) of (a) raw pith fibers; (b) MFCs of raw pith fibers; (c) SNCs of raw pith fibers with demarcation of major peaks.

Fig. 3 shows FTIR spectra (overlapped) of (a) raw pith fibers; (b) MFCs of raw pith fibers; (c) SNCs of raw pith fibers.

Fig. 4 shows WA-XRD diffraction profiles of (a) raw pith fibers, (b) MFCs of raw pith fibers and (c) SNCs of raw pith fibers of bagasse with description of prominent peaks used for measuring and amorphous index.

Fig. 5 illustrates WA-XRD diffraction profile (overlapped) of (a) raw pith fibers; (b) SNCs of raw pith fibers.

Fig. 6 shows Field emission scanning electron microscopy (FESEM) images (a and b) of MFCs obtained after physico-chemical treatment of Raw pith fibers of bagasse.

Fig. 7 provides FESEM images (a and b) of NFCs of raw pith fibers obtained after initial passes of high shear homogenizer. Fig. 8 shows FESEM images (a and b) of SNCs of raw pith fibers of bagasse.

Fig. 9 shows High resolution transmission electron microscopy (HRTEM) images (a and b) of SNC of raw pith fibers of bagasse.

Fig. 10 provides Dynamic light scattering (DLS) of SNCs of raw pith fibers of bagasse.

Table 1 provides FTIR spectral band descriptions occurring in bagasse pith fibers.

DETAILED DESCRIPTION

The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the invention. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been described in detail below. It should be understood, however that it is not intended to limit the invention to the particular forms disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and the scope of the invention. In addition, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventors to enable a clear and consistent understanding of the invention. Accordingly, it should be apparent to those skilled in the art that the following description and embodiments of the present invention are provided for illustration purpose only and not for the purpose of limiting the invention as defined by the appended claims and their equivalents.

Features that are described and/or illustrated with respect to one embodiment may be used in the same way or in a similar way in one or more other embodiments and/or in combination with or instead of the features of the other embodiments.

It should be emphasized that the term“comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

The present invention provides a novel and green method for direct preparation of nanocellulose with spherical morphology (SNCs) from defibrillated MFCs of bagasse pith fibers.

In the present invention, defibrillated bagasse pith fibers (MFCs) were directly subjected to high shear mechanical treatment using homogenizer to obtain perfectly spherical nanocellulose. The acid hydrolysis in presence of mild HC1 solution (0. IN) was employed only to the bleached fibers in the process of preparation of defibrillated MFCs as a part of most common strategy followed to remove impurities from any cellulosic material such as wheat straw, rice straw and bagasse fibers.

More specifically, the present invention involves subjecting the defibrillated bagasse pith fibers (MFCs) to high shear mechanical treatment using homogenizer to obtain perfectly spherical nanocellulose. The present invention is considerably different from the currently available techniques for obtaining SNCs that employ highly concentrated chemical-based treatments which are considerably time consuming. As usually employed to microcrystalline cellulose (MCCs of a cellulosic source), most of these reactions use concentrated H2S04 (up to 64%) for reducing crystalline structures (rods or cylindrical shaped) of cellulosic material in to nano sized particles with spherical morphology. The present invention does not employ such process for size reduction of the cellulosic material, instead defibrillated bagasse pith fibers were directly subjected to high shear mechanical treatment using homogenizer for few minutes to obtain perfectly spherical nanocellulose.

In an embodiment, the present invention provides spherical nanocrystals of cellulose possessing amorphous index and percentage crystallinity index nearly 0.18 and 63% as estimated using following formulas.

Am = 0.5

and

%/_cr = 100

In which‘I_Arn’ is sum of intensities of peaks P₃ (2Q - 11° ) and P₅ (2Q ~ 25°) and _CR’ is sum of intensities of peaks Pi (2Q ~ 22°) and P₂ (2Q ~ 15°) as shown in figure 3. While, second equation is mainly attributed to crystalline and amorphous parts of cellulose I crystal at 2Q = 22.5° and therefore, I₀₀₂ represents intensity of peaks A and B of figure 6 that is Pi at 2Q = 22.5° and 7_arn’ is minima of A and B that is 2Q =18°.

Cellulose in XRD profile is observed with its major planes of diffraction 1 0 1, 101, 0 2 1, 0 0 2, and 0 4 0 that appears at about 14.8°, 16.7°, 20.7°, 22.5°, and 34.6° Bragg angles (20). Therefore, Pi and P2 represent Bragg angles at which prominent peaks of crystalline cellulose appears in the pattern. The scattering intensities of maxima and minima of these peaks were observed for measuring crystalline and amorphous content of the cellulosic material. The calculated amorphous index of SNCs was decreased from .51 of raw pith fibres to .18 that is more than 65% decrement in the amorphous content of the nanomaterial while the present invention provides SNCs possessing percentage crystallinity index about 63%.

The present invention results in high concentration of uniformly spherical SNCs possessing diameter in the range of 30-85 nm. The reported conventional methods that are currently in use employs acid hydrolysis, mixed hydrolysis or enzymatic hydrolysis treatments to MCCs of cellulosic content. But the present method technique liberates SNCs from MFCs of bagasse pith fibers instead of MCCs which further renders advantage of simultaneous preparation of SNCs and NFCs from bagasse pith fibers.

In an embodiment, the present invention discloses a process for fabrication of cellulosic nanospheres comprising: a) Treating raw bagasse pith fibers with 2% NaOH solution overnight;

b) Washing the fibers and providing alkaline steam explosion treatment in an autoclave while maintaining the fiber to liquor ratio at 1 : 10(w/v);

c) Bleaching with hydrogen peroxide at 60°C for about 4 hours and defibrillation of the bleached fibers using mild acid hydrolysis treatment to obtain microfibrillated aggregates of cellulose (MFCs);

d) Homogenization of MFCs using ultra high shear mechanical action in distilled water; and

e) Ultrasoni cation for about half an hour to facilitate segregation of the individual particles. In another embodiment, the homogenization is carried out at 11000 under ambient temperature 5-40°C for about 2 minutes.

In yet another embodiment, the steam explosion treatment in an autoclave comprises alkaline treatment of pith fibers with 4% NaOH sol. and multiple sudden depressurizations of the autoclave are caused once fiber solution reaches at 15 lb of pressure at temperature of about 115±5°C.

In another embodiment, defibrillation is carried out for about 4 hrs at 55°C using mild HC1 (0.1 N) solution under ultrasoni cation.

In yet another embodiment, the cellulosic nanospheres obtained by the process of the present invention have uniform spherical morphology, large specific surface area and several free surface hydrophilic groups.

In an embodiment, the cellulosic nanospheres have a diameter in the range of 25-120nm and preferably between 25-80nm.

In another embodiment, the cellulosic nanospheres have amorphous index of about 0.18 and crystallinity index of 63%.

Examples

Material

The pith fibers of sugarcane bagasse used in this work are an economical source of production of SNCs. These are renewable and natural agricultural residues that are abundantly available in northern India. Sucrose (polysaccharides) and bagasse are two major by-products of sugarcane that are produced every year. Bagasse is a heterogeneous material that consists of two parts rind and pith, where, the rind forms outer hard part of bagasse, while pith fibers form soft inner parts. The bagasse fibers (rind and pith) have been extensively used for production of biofuels and isolation of cellulose pulp for application in paper industry, building materials and bio-composite production. However, research work on individual pith fibers are limited till date (Gao et al, 2014; de Oliveira et al. , 2016; Niu et al, 2017). The chemicals sodium hydroxide (NaOH), hydrochloric acid (HC1) and hydrogen peroxide (H2O2) used for obtaining MFCs were supplied by Merck India Pvt. Ltd. A laboratory standard distilled water was also purchased for purpose of neutralizing the fibers after each treatment and preparing suspension of MFCs for homogenization.

Processing of Raw Bagasse Fibers

In the present work, raw bagasse pith fibers of length 1-2 cm were first kept in 2% NaOH solution overnight to get rid of ash and dust. On the next day, fibers were thoroughly washed with clear water and alkaline steam explosion treatment was given in 4% NaOH aqueous solution in an autoclave while maintaining the fiber to liquor ratio at 1 : 10 (w/v). The above process was then followed by bleaching with H2O2 at 60°C for 4 hours and defibrillation of the bleached fibers using mild acid hydrolysis treatment with HC1 solution (0.1 N). The acid hydrolysis was given for 4hrs at 55°C temperature under ultrasoni cation in order to obtain microfibrillated aggregates (MFCs) of raw pith fibers.

Homogenization of processed pith fibers

The MFCs of bagasse pith fibers were homogenized using ultra high shear mechanical action of dispersion emulsifier, which is essentially a specialized homogenizer that can operate up to 26000 RPM under ambient temperature 5-40°C. It is a pilot scale equipment designed to perform operation from small scale to industrial scale. As shown in figure 1, the major components of homogenizer consist of a rotor or impeller and a stator or stationary part that are used in container to generate high shearing forces. Equipped with high precision-machined holes or slots in stator and rotor exceptionally facilitates the inward and outward forces to take flux of solution in and out of the rotors. The high shearing operation can be carried out in multiple passes in order to subject the material in to large number of shearing events resulting in uniform particle distribution in narrow size range.

The above high shear mechanical treatment using homogenizer was given to the fine suspension of MFCs that was prepared in distilled water. The entire mechanical process was carried out in total 11 passes of homogenization at 11,000 RPM, where each pass was for duration of 2 minutes. Momentum of the inward and outward solution flux was also changed in order to allow adequate processing in every single pass. After completion of all passes, the prepared suspension of nanoparticles was instantly subjected to ultrasoni cation for half an hour in order to facilitate segregation of the individual particles.

Fourier transform infrared spectroscopy (FTIR)

The SNCs obtained by the process of the present invention are free of Sulphur. The FTIR spectra of SNCs shown in figure 2 and 3 exhibited absence of bands near 468cm ¹ (S-S stretching). Further, stability of bands near 1162 cm ¹ and 1111 cm ¹ indicate non-formation of functional groups containing C=S and S=0 stretching during reaction process. FTIR spectra of MFCs of pith fibers and its homogenized SNCs are also in close resemblance to each other as mechanical treatment has thoroughly remained inert and did not cause any chemical change during process of production of SNCs.

As shown in table 1, FTIR spectra of SNCs possessed number of distinguished features as compared to untreated raw pith fibers. The disappearance of transmittance bands around 1731, 1512, 1633, 1603, 1326, 1246, 833 cm ¹ are clearly visible in spectra of SNCs that indicates a complete removal of extraneous contents like lignin, sugar, pectin, hemicellulose and ash. The increase of band at 897 cm ¹ in bleached fibers and finally hydrolyzed MFCs indicates the typical structure of cellulose (due to b-glycosidic linkages of glucose ring of cellulose)

The SNCs thus produced can act as a strong absorbent for hydrogel applications. An improved intensity of bands around 2902 cm ¹ and 3700-3100 cm ¹ (-OH groups) is an important betoken of production of highly pure cellulosic SNCs with large number of surface hydroxyl groups. The band at 1641cm ¹ has further shown growth in terms of intensity and area, exhibiting enhanced capacity of SNCs to absorb water from its surroundings.

Wide-angle X-ray Diffraction (WAXRD)

The spherical nanocrystals of cellulose thus obtained possess amorphous index and percentage crystallinity index nearly 0.18 and 63% as estimated using following formulas. 4m = 0.5

and

%/_cr = 100

In which‘I_Arn’ is sum of intensities of peaks P₃ (2Q ~ 11°) and P₅ (2Q ~ 25°) and _CR’ is sum of intensities of peaks Pi (2Q ~ 22°) and P₂ (2Q ~ 15°) as shown in figure 4. While, second equation is mainly attributed to crystalline and amorphous parts of cellulose I crystal at 2Q = 22.5° and therefore, I₀₀₂ represents intensity of peaks A and B of figure 5 that is Pi at 2Q = 22.5° and 7_arn’ is minima of A and B that is 2Q =18°.

Cellulose in XRD profile is observed with its major planes of diffraction 1 0 1, 101, 0 2 1, 0 0 2, and 0 4 0 that appears at about 14.8°, 16.7°, 20.7°, 22.5°, and 34.6° Bragg angles (20). Therefore, Pi and P2 represent Bragg angles at which prominent peaks of crystalline cellulose appears in the pattern. The scattering intensities of maxima and minima of these peaks were observed for measuring crystalline and amorphous content of the cellulosic material. The calculated amorphous index of SNCs was decreased from .51 of raw pith fibres to .18 that is more than 65% decrement in the amorphous content of the nanomaterial while the present invention provides SNCs possessing percentage crystallinity index of about 63%.

Morphology

The present invention results in high content of uniformly spherical SNCs possessing diameter in the range between 30-85 nm. The reported conventional methods that are currently in use employs acid hydrolysis, mixed hydrolysis or enzymatic hydrolysis treatments to MCCs of cellulosic content. But the present method liberates SNCs from MFCs of bagasse pith fibers instead of MCCs that further render advantage of simultaneous preparation of SNCs and NFCs from bagasse pith fibers.

As shown in figure 6, FESEM images of defibrillated MFCs contains flaky and fibrous morphology which is an inherent microstructural characteristic of bagasse pith fibers. This is because of presence of two different tissues in pith fibers that is (i) translucent parenchymal cells and (ii) short epidermal fibers. The fibrous morphology of MFCs consist of microfibers in the diameter range between 15-20 m while the flakes or sheets of parenchyma cells had possessed thickness <2 m. Most of the sheets were curled and had sign of surface roughness that acknowledge the adequate eruption of impurities during procurement of MFCs from raw bagasse pith fibers.

The morphology of homogenized nano-particulate form of fibers was examined after certain incremental levels of homogenization corresponding to numbers of passes through homogenizer. After about 5 passes of 2-3 minutes each, the morphology of the MFCs had converted in to NFCs of bagasse pith fibers and after 11 passes the morphology transformed in to SNCs and large micro-sized aggregates of MFCs were no longer present. The final suspension was immediately put in to ultra-sonication for 90 minutes to gain stable spherical uniformity in the SNCs morphology.

The FESEM images of NFCs (figure 7) obtained in the first phase of homogenization were of thickness in the range between 40-90nm. The strong agglomeration tendency because of large number of free surface hydroxyl groups and inherent morphological characteristics of the bagasse pith fibers had turned NFCs in to sheet form during simple drying process. The existence of pores was also visible in the agglomerated sheets possessing circular radius in the range of 5-10nm approximately. These characteristics are excellent for a material for extending their application in developing advanced hydrogel systems.

The sample of SNCs of bagasse pith fibers procured after last phase of high shear homogenization and after final ultrsoni cation exhibited fine production of spherical nanocellulose with high concentration. The FESEM images in figure 8 depicted SNCs with diameter in the range between 50-120nm while the wide size range had reduced considerably after ultrasoni cation with high concentration of SNCs in the diameter range <100nm as shown in HRTEM images shown in figure 9. There were clear traces of high concentration of SNCs produced with diameter in the range of 30-85nm.

The MFCs of bagasse pith fibers were homogenized using ultra high shear mechanical action of dispersion emulsifier, which is essentially a specialized homogenizer operating up to 26000 RPM under ambient temperature 5-40°C. It is a pilot scale equipment designed to perform operation from small scale to industrial scale. As shown in figure 9, the major components of homogenizer consist of a rotor or impeller and a stator or stationary part that are used in container to generate high shearing forces. Equipped with high precision-machined holes or slots in stator and rotor exceptionally facilitates the inward and outward forces to take flux of solution in and out of the rotors. The high shearing operation can be carried out in multiple passes in order to subject the material in to large number of shearing events resulting in uniform particle distribution in narrow size range.

The size distribution estimation conducted using dynamic light scattering (DLS) further reveals similar scenario and exhibits high concentration production of SNCs with maximum nanoparticles below lOOnm and within the range of 25-80 nm. The analysis also showed presence of particles which are probably remnants of sheet and fibrous like morphology of MFCs of bagasse pith fibers. These particles are in marginal percentage about 10-15% with size distribution at scale of several lOOnm. ADVANTAGES

The present invention offers the following advantages:

1. Cellulosic nanospheres possess uniform spherical morphology, larger specific surface area, high porosity and numerous free surface hydrophilic groups

2. Simultaneous preparation of SNCs and NFCs from bagasse pith fibers can be carried out. 3. Does not utilize conventional high concentration-based acid hydrolysis treatment of the fibers at any stage for production of SNCs

4. Spherical nanocellulose are promising candidates in nanocomposites, biomedicine and drug delivery.

5. The resultant product is free from any extraneous sulphate group as no H₂SO₄ is used in the entire process.

Claims

The Claims:

1. A process for fabrication of cellulosic nanospheres comprising:

a) Treating raw bagasse pith fibers with NaOH solution overnight;

e) Ultrasoni cation for about half an hour to facilitate segregation of the individual particles.

2. The process as claimed in claim 1, wherein the NaOH used in step a) of claim 1 is 2% NaOH solution and that used in the alkaline steam explosion of step (b) is 4% NaOH aqueous solution.

3. The process as claimed in claim 1, wherein the homogenization is carried out at 11000 under ambient temperature 5-40°C for about 2 minutes.

4. The process as claimed in claim 1, wherein the steam explosion treatment in an autoclave comprises alkaline treatment of pith fibers with 4% NaOH sol. and multiple sudden depressurizations of the autoclave are caused once fiber solution reaches at 15 lb of pressure at temperature of about 115±5°C.

5. The process as claimed in claim 1, wherein defibrillation is carried out for about 4 hrs at 55°C using mild HC1 (0.1 N) solution under ultrasonication.

6. The cellulosic nanospheres obtained by the process as claimed in claims 1 to 5, wherein the nanospheres have uniform spherical morphology, large specific surface area and several free surface hydrophilic groups.

7. The cellulosic nanospheres as claimed in claim 6, wherein the cellulosic nanospheres have a diameter in the range of 25-120nm.

8. The cellulosic nanospheres as claimed in claim 7, preferably having the diameter 25- 80nm.

9. The cellulosic nanospheres as claimed in claim 7, wherein the nanospheres have amorphous index of about 0.18 and crystallinity index of 63%.