DESC:Field of Invention
The present disclosure relates to microcrystalline cellulose having a morphological form selected from the group consisting of serrated, hollow, multi-lobal and flat, and a process for preparing said microcrystalline cellulose.

Background
Microcrystalline cellulose, also known as MCC, is obtained from cellulose, and primarily consists of crystalline aggregates. Microcrystalline cellulose is a purified, partially depolymerized cellulose which is presented as a white, odorless, flavorless powder made up of porous particles. Microcrystalline cellulose demonstrates properties such as non-toxicity, biocompatibility, biodegradability, high mechanical strength, and low density, etc. making it suitable for use as a binder, filler, disintegrant, diluent, reinforcing agent and lubricant in food, cosmetic, pharmaceutical, medical and polymer composites’ industry.
It is known to prepare microcrystalline cellulose using different techniques, such as chemical process, reactive extrusion, high-pressure homogenization, and steam explosion. However, the known techniques only provide microcrystalline cellulose having a spherical or rod shape. This morphology of microcrystalline cellulose results in lower surface area restricting the applications of microcrystalline cellulose.

Summary
The present disclosure relates to microcrystalline cellulose having a morphological form selected from the group consisting of serrated, hollow, multi-lobal and flat.
The present disclosure also relates to a process for preparing aforesaid microcrystalline cellulose. Said process comprises subjecting cellulosic fibers having a morphological form selected from the group consisting of serrated, hollow, multi-lobal and flat, to controlled acid hydrolysis, and filtering the resultant mixture to obtain microcrystalline cellulose.

Brief Description of Drawings
Figure 1 shows the optical image of: (A) regular viscose fibers, (B) hollow viscose fibers, (C) tri-lobed viscose fibers, and (D) flat viscose fibers, used to prepare microcrystalline cellulose in accordance with an embodiment of the present disclosure;
Figure 2 shows the scanning microscopy images (SEM) of microcrystalline cellulose obtained from regular viscose fibers, hollow viscose fibers, tri-lobed viscose fibers, and flat viscose fibers, in accordance with an embodiment of the present disclosure.
Figure 3 shows the schematic- major axis and minor axis, for measurement of aspect ratio of microcrystalline cellulose of various morphological forms.

Detailed Description
To promote an understanding of the principles of the disclosure, reference will now be made to embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended, such alterations and further modifications in the disclosed composition and method, and such further applications of the principles of the disclosure therein being contemplated as would normally occur to one skilled in the art to which the disclosure relates.
It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the disclosure and are not intended to be restrictive thereof.
Reference throughout this specification to “one embodiment” “an embodiment” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Thus, appearances of the phrase “in one embodiment”, “in an embodiment” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.
The present disclosure relates to a process for preparing microcrystalline cellulose. Said process comprises subjecting cellulosic fibers having a morphological form selected from the group consisting of serrated, hollow, multi-lobal and flat, to controlled acid hydrolysis, and filtering the resultant mixture to obtain microcrystalline cellulose, said microcrystalline cellulose having the morphological form of the cellulosic fibers.
The present inventors found that when a cellulosic fiber having a definite morphology is subjected to the disclosed process the resultant microcrystalline cellulose retains the morphology of the cellulosic fibers used to prepare the microcrystalline cellulose. The microcrystalline cellulose obtained using the disclosed process has a morphological form of serrated, hollow, multi-lobal and flat, depending on the morphological form of cellulosic fibers.
In accordance with an embodiment, the controlled acid hydrolysis is carried out by treating cellulosic fibers with a mineral acid at a temperature ranging between 20 to 80oC. In accordance with an embodiment, the controlled hydrolysis is carried out for a period ranging between 5 minutes to 12 hours. The temperature and time-period of hydrolysis can be varied depending on the desired morphology and physical properties of microcrystalline cellulose. In some embodiments, the hydrolysis is carried out at a temperature of 25-35°C for 5 to 6 hours. In some embodiments, the hydrolysis is carried out at a temperature of 40°C for 45-60 minutes. In some embodiments, the hydrolysis is carried out at a temperature of 50°C for 15-30 minutes.
In accordance with an embodiment, the cellulosic fibers and mineral acid are treated in a w/w ratio of 20:1 to 5:1. In some embodiments, the cellulosic fibers and mineral acid are treated in a w/w ratio of 10:1.
In accordance with an embodiment, the cellulosic fibre is a viscose fibre having the morphology selected from the group consisting of serrated, hollow, multi-lobal and flat. Said viscose fibre can be obtained from commercial sources or can be obtained using any known process.
In accordance with an embodiment, viscose fibers with a serrated morphology are obtained using the standard viscose process (Woodings C 2001) The standard viscose process comprises the steps of: a) preparation of viscose dope by steeping, pressing, shredding, maturing, dissolution and ripening, b) spinning of viscose dope using coagulation bath comprising of sulphuric acid, zinc sulphate and sodium sulphate. After fibre regeneration, the fibers are subjected to a washing treatment for removing excess chemicals and impurities to obtain regular viscose fibers having serrated morphology.
In accordance with an embodiment, viscose fibers having a hollow morphological form are obtained by preparing viscose dope with 2% sodium carbonate, followed by regeneration in spin bath. Such fibers can also be prepared using the process described in EP3315659A1, the contents of which are incorporated herein by reference.
In accordance with an embodiment, multi-lobal and flat cellulosic staple fibers are obtained by spinning of a spinning solution through a spinneret with multi-lobal spinneret holes as disclosed in EP301874 B1, the contents of which are incorporated herein by reference. Cellulosic fibers of a "Y"-shaped cross-section are prepared using the process described in GB-A-2 085 304, the contents of which are incorporated herein by reference.
In accordance with an embodiment, the controlled acid hydrolysis is carried out using a mineral acid selected from the group consisting of hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid. In accordance with an embodiment, the mineral acid has a concentration in a range of 30-75%. In some embodiments, the mineral acid has the concentration of 55%.
After completing the controlled hydrolysis, the obtained solution is quenched with water followed by centrifugation. This solution is then washed with water and neutralized to remove traces of acid. In accordance with an embodiment, neutralization is carried out using a base selected from the group consisting of sodium carbonate, sodium bicarbonate, sodium hydroxide potassium hydroxide and ammonium hydroxide.
After neutralization, additional steps are taken for isolating the microcrystalline cellulose, such as filtration of the solution containing microcrystalline cellulose, purification by means of washing operations with purified water. The filtration can be carried out using any known means and process for filtration. In some embodiments, the filtration is carried out using centrifugation.
In the next step, the filtered microcrystalline cellulose is subjected to drying, grinding and classification according to particle size.
The microcrystalline cellulose obtained using the disclosed process has a morphological form selected from the group consisting of serrated, hollow, multi-lobal and flat.
The disclosed microcrystalline cellulose has an average particle diameter in a range of 11 to 35 µm and an average particle length in a range of 85 to 190 µm. In some embodiments, the disclosed microcrystalline cellulose has the average particle diameter in the range of 26 to 35 µm and average particle length in the range of 120 to 190 µm.
The disclosed microcrystalline cellulose has a degree of crystallinity in a range of 65 to 80%. In some embodiments, the disclosed microcrystalline cellulose has the degree of crystallinity in the range of 72 to 76%.
It will be apparent to those skilled in the art that various modifications and variations can be made to the method/process of the present disclosure without departing from the scope of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the method/process disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalent.

Examples:
Example 1: Preparation of regular Viscose Staple Fibre (VSF)
Viscose dope was prepared by a standard viscose process including the steps of steeping, shredding, aging, xanthation, dissolution, and ripening. In the first step, dissolving grade pulp was steeped in an 18% caustic solution for 20 minutes and pressed to remove excess alkali. Alkaline cellulose, noted as alkacell, in form of cake is shredded to break crumbles. This shredded alkacell was aged in a maturing drum for 50 minutes at 30°C followed by addition of CS2 under vacuum to form cellulose xanthate. Cellulose xanthate was mixed with cold alkaline water to dissolve followed by ripening for 12 hours to make viscose dope.
Further, viscose dope was filtered using 35-micron mesh and deaerated to remove air bubbles. The deaerated viscose dope is used for regular viscose fibre spinning. Viscose was spun with a spinneret with 60-micron capillary and 250 holes. The fibers were regenerated into a spin-bath comprising 120 g/l of H2SO4, 10.5 g/l of ZnSO4, and 355 g/l of Na2SO4. The spin-bath temperature was maintained at 50°C and stretch of 68% was provided to fibers between the two gadgets. Fibers were collected on a roller. Finally, fibers were cut into 38 mm length and washed with dilute acid, alkali and further washed with hot water. Washed fibers were treated with H2O2 to carry out bleaching followed by treating diluted acetic acid. Finally, these fibers were dried in an oven at 105°C for 20 minutes. The morphology of fibre was assessed by optical microscopy and is shown in Figure 1(A). The morphology of regular viscose fibre indicated serrated shape.
Example 2: Preparation of Hollow Viscose Staple Fibre (H-VSF)
Example 1 was repeated but by adding 2% sodium carbonate in viscose dope. During fibre spinning in acidic spin-bath, sodium carbonate reacts with sulphuric acid producing carbon dioxide which gets trapped during regeneration of viscose fibers and leaves a void, resulting in hollow cellulosic fibers. The morphology of fibre was assessed by optical microscopy, which indicated a bubble or hollow shape as shown in Figure 1(B).
Example 3: Preparation of Tri/multi-lobal Viscose Staple Fibre (T-VSF)
Example 1 was repeated but with specialized spinneret having three-lobed shape, to obtain cellulosic fibers having tri/multi-lobal morphological form. The morphology of fibre was assessed by optical microscopy, which indicated a tri-lobal shape as shown in Figure 1(C).

Example 4: Preparation of Flat Viscose Staple Fibre (F-VSF)
Example 1 was repeated but with Flat fibre prepared using slit type spinneret, to obtain viscose fibre having flat morphological form. The morphology of fibre was assessed by optical microscopy, which indicated a flat fibre as shown in Figure 1(D).
The above fibers were used to form microcrystalline cellulose using the disclosed process.
Examples 5-8: Preparation of shaped microcrystalline cellulose- serrated microcrystalline cellulose (S-MCC), hollow microcrystalline cellulose (H-MCC), tri-lobal microcrystalline cellulose (T-MCC), flat microcrystalline cellulose (F-MCC):
Four experiments were conducted to form various morphological forms of microcrystalline cellulose. 5 grams of cellulosic fibers obtained in the above examples 1-4 was hydrolyzed with 55% H2SO4 in a beaker, keeping Fibre: H2SO4 ratio as 20:1 at 25-30 °C, then gradually increasing the temperature to 40°C and 50°C while stirring. While maintaining the concentration of sulphuric acid at 55 wt.%, to ensure hydrolysis, time and temperature were varied to alter the kinetics of hydrolysis. The specific conditions for hydrolysis- temperature, time-period used for each of the experiments have been summarized in Table 1. After completing the hydrolysis process, the obtained slurry was quenched with ice-cold water followed by centrifugation The solution was then washed with water and neutralized with 1.5 M Na2CO3 solution to remove traces of acid. After neutralization, the solution was again washed with water, followed by extraction of microcrystalline cellulose. The extracted microcrystalline cellulose was in powder form and was dried in vacuum oven at 80°C for 1hour.
The structure of this microcrystalline cellulose was assessed using scanning electron microscopy (SEM). Figure 2 shows the SEM images of cross-section of microcrystalline cellulose obtained in Examples 5-8.

TABLE 1: Hydrolysis treatment conditions to form microcrystalline cellulose from different precursor fibers
Example Samples Morphology of base fibre % H2SO4 Temperature ( °C) Time % Yield
Example 5 S-MCC-1 Serrated 55 25-30 6 hours 77.3
S-MCC-2 40 45 minutes 74.9
S-MCC-3 50 15 minutes 71.6
Example 6 H-MCC-1 Hollow 25-30 6 hours 74.6
H-MCC-2 40 45 minutes 79.5
H-MCC-3 50 15 minutes 75.8
Example 7 T-MCC-1 Tri-lobal 25-30 6 hours 75.3
T-MCC-2 40 45 minutes 76.0
T-MCC-3 50 15 minutes 74.4
Example 8 F-MCC-1 Flat 25-30 6 hours 75.1
F-MCC-2 40 45 minutes 76.2
F-MCC-3 50 15 minutes 75.0

Observation: It was observed that the microcrystalline cellulose prepared in Examples 5-8 retained the morphology of cellulosic fibers prepared in Examples 1-4 respectively.
Figures 2(A), (B) and (C) depicts the cross-section of S-MCC-1, S-MCC-2 and S-MCC-3, respectively, prepared from VSF. These microscopic pictures indicate serrated and oval cross-section of S-MCC, similar to the morphology of VSF used to prepare the microcrystalline cellulose. Further, figures 2(D), (E) and (F) shows cross-section of H-MCC-1, H-MCC-2 and H-MCC-3, respectively, prepared from H-VSF. As observed from the micrographs of H-MCC, increase in hydrolysis temperature to 50oC leads to distortion of hollow cross-section while hollow structure is retained at lower hydrolysis temperature of 25oC and 40oC. Figures 2 (G), (H) and (I) shows the cross section of T-MCC-1, T-MCC-2 and T-MCC-3, respectively, at different hydrolysis conditions. As observed from cross-section of T-MCC, it is evident that lower hydrolysis temperature results in microcrystalline cellulose with retained tri-lobal shape whereas higher hydrolysis temperature results in distortion of tri-lobal morphology. T-MCC prepared using tri-lobal fibers at higher hydrolysis temperature show splitting of these lobes into individual fragments. Figures 2(J), (K)and (L) showed the cross section of F-MCC-1, F-MCC-2 and F-MCC-3, respectively, indicating distortion of flatness with increase in temperature for hydrolysis.
Additionally, as noted in Table 1, the yield of microcrystalline cellulose was observed to be similar for all types of cellulosic fibers and hydrolysis conditions. This indicates that optimization of hydrolysis conditions only alters the kinetics and not the extent of hydrolysis itself.
An aspect ratio of microcrystalline cellulose cross section was measured on SEM images. Figure 3 represents the schematics used for measuring the aspect ratio of microcrystalline cellulose and indicate difference in aspect ratio in microcrystalline cellulose prepared from shaped fibre with an optimized hydrolysis condition at different temperature and time. This was correlated with surface area and other properties of material. The aspect ratio of different microcrystalline cellulose has been provided in Table 2. S-MCC showed lowest aspect ratio of 1.8 whereas H-MCC was observed to have the highest aspect ratio of 12. T-MCC and F-MCC showed aspect ratio of 2.89 and 4.9 respectively.

Table:2 Aspect ratio (L/D) of microcrystalline cellulose

Sample Aspect ratio (L/D)
S-MCC 1.8
T-MCC 2.89
H-MCC 12
F-MCC 4.9

Industrial Applicability
The disclosed process can be used to prepare microcrystalline cellulose of various morphological forms including but not limited to serrated, hollow, multi-lobal and flat. Thus, using the disclosed process, it is possible to increase the surface area of microcrystalline cellulose.
The disclosed process is easy to scale and has low energy consumption, resulting in economical and environment friendly commercial process. Also, the disclosed process avoids high thermal carbonization for spheronization of microcrystalline cellulose for different applications.
The disclosed microcrystalline cellulose can be used as battery separators, liquid absorbers, pickering agent, water purification medium, bulking agent in pharmaceuticals, cosmetic applications etc.
,CLAIMS:1. A process for preparing microcrystalline cellulose, said process comprising:
subjecting cellulosic fibers having a morphological form selected from the group consisting of serrated, hollow, multi-lobal and flat, to controlled acid hydrolysis; and
filtering the resultant mixture to obtain microcrystalline cellulose,
said microcrystalline cellulose having the morphological form of the cellulosic fibers.

2. The process as claimed in claim 1, wherein the controlled acid hydrolysis is carried out by treating cellulosic fibers with a mineral acid at a temperature ranging between 20 to 80oC for a period ranging between 5 minutes to 12 hours.

3. The process as claimed in claim 2, wherein the controlled acid hydrolysis is carried out at a temperature of 25-35°C for 5 to 6 hours.

4. The process as claimed in claim 2, wherein the controlled acid hydrolysis is carried out at a temperature of 40°C for 45 to 60 minutes.

5. The process as claimed in claim 2, wherein the controlled acid hydrolysis is carried out at a temperature of 50°C for 15 to 30 minutes.

6. The process as claimed in claim 1, wherein the cellulosic fibers and the mineral acid are treated in a w/w ratio of 20:1 to 5:1.

7. The process as claimed in claim 1, wherein the cellulosic fibre is a viscose fibre.

8. The process as claimed in claim 1, wherein the controlled acid hydrolysis is carried out using a mineral acid selected from the group consisting of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid.

9. The process as claimed in claim 8, wherein the mineral acid has a concentration in a range of 30-75%.

10. The process as claimed in claim 1, wherein the resultant mixture is subjected to washing and neutralization, before filtration.

11. Microcrystalline cellulose having a morphological form selected from the group consisting of serrated, hollow, multi-lobal and flat.

12. The microcrystalline cellulose as claimed in claim 11, having an average particle diameter in a range of 11 to 35 µm and an average particle length in a range of 85 to 190 µm.

13. The microcrystalline cellulose as claimed in claim 11, having a degree of crystallinity in a range of 65 to 80%.