METHOD OF DISSOLVING MICROCRYSTALLINE CELLULOSE

Abstract

The present invention discloses a method of dissolving microcrystalline cellulose (MCC) in DMSO. The prior arts disclose the method of dissolving cellulose in two or more solvent system, however the present invention claims the usage of DMSO as a single solvent system for dissolving microcrystalline cellulose. Briefly, microcrystalline cellulose is dissolved in DMSO in a temperature range of 70 – 130 °C for a time duration ranging from 1- 8 hours in a hydrothermal vessel with the maximum solubility being observed as around 40 % in a 1 % solution of MCC in DMSO. The resulting solution was quite stable up to more than 30 days.

Specification

Description:FIELD OF THE INVENTION
The present invention relates to a method of dissolving microcrystalline cellulose. More specifically, the present invention relates to a method of dissolving microcrystalline cellulose in a single solvent system.
BACKGROUND OF THE INVENTION
Cellulose is the most abundant natural polymer on the earth. Conventionally its main resource is wood and cotton plants, however lignocellulosic waste has also been worked out for the extraction of cellulose. Cellulose is diversely applicable for various purposes, such as in boards, paper, textile, etc. Looking at its wide range of applications and huge demand, waste fabric has also been explored as the potential feedstock for the extraction of cellulose under energy efficient conditions [Singhal et al., 2023].
Cellulose is a thermally stable material with appreciable crystallinity, which has a good water retention value. However, due to the existence of interlinked chains in its structure, cellulose possesses sufficient hydrophobicity, which makes it water insoluble. Solubility of cellulose remains a difficult task in other solvents also due to its interlinked structure.
To enhance its functionalization and applicability, the dissolution of cellulose has always been an area of interest for the researchers.
US7828936B2: A method for dissolving cellulose in which the cellulose based raw material is admixed with a mixture of a dipolar aprotic inter-crystalline swelling agent and an ionic liquid at a temperature of 25° C. to 180° C. for a time sufficient to dissolve the cellulose based raw material. The molar ratio of dipolar aprotic inter-crystalline swelling agent to ionic liquid is 0.05 to 1.5 moles of dipolar aprotic inter-crystalline swelling agent to 1 mole of ionic liquid. Dipolar aprotic Inter-crystalline swelling agents do not include imidazole-based agents or amine-based agents (Abstract).

AU2007323223A1: The invention relates to a method for dissolving the components of gel forming materials suitable for use in wound care comprising the steps of admixing said components with an ionic liquid. The ionic liquid may be selected from the group of tertiary amine N-oxides, N, N-dimethyl formamide/nitrogen tetroxide mixtures, dimethyl sulphoxide/paraformaldehyde mixtures and solutions of limium chloride in N, N-dimethyl acetamide or N-methyl pyrrolidone. (Abstract)
2016 Jiang et al. (2016). "Bamboo cellulose fibers," BioResources 11(2), 4536-4549: A novel, efficient, and direct blend of solvents, tetrabutylammonium acetate/dimethyl sulfoxide (TBAA/DMSO), was used for the dissolution and regeneration of bamboo pulp. Regenerated fibres were successfully prepared by a wet spinning process. The bamboo pulp without any pretreatment was readily soluble in the solvent under mild conditions. The dissolution process was observed using a confocal laser scanning microscope (CLSM). Rheological properties of the cellulose solutions at various concentrations were investigated. The regenerated fibres prepared by coagulation in ethanol were characterized with scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), and an electronic tensile tester. The SEM images showed that the regenerated fibres possessed a smooth surface and circular cross-section, and the XRD and FT-IR results revealed that the fibres exhibited a cellulose II structure. The thermostability and mechanical properties of the fibres was also investigated. (Abstract)
The prior arts mentioned herein discusses various modes of dissolving of cellulose. However, the methods mentioned supra, are either not efficient or are too expensive.
Thereby, to overcome the drawbacks, there exists a need in the art to develop a method for dissolving of microcrystalline cellulose.

OBJECTS OF THE INVENTION
The principal object of the present invention is to overcome the disadvantages of the prior art.
An object of the present invention is to provide a method for dissolving microcrystalline cellulose.
Another object of the present invention is to provide a single non-toxic solvent for dissolving microcrystalline cellulose.
The foregoing and other objects, features, and advantages of the present invention will become readily apparent upon further review of the following detailed description of the preferred embodiment as illustrated in the accompanying drawings.
SUMMARY OF THE INVENTION
The technique for dissolving microcrystalline cellulose is the subject of the current invention. The current invention pertains, more precisely, to a procedure for dissolving microcrystalline cellulose in a single solvent system.
An aspect of the present invention discloses the usage of DMSO as a single solvent system for dissolving microcrystalline cellulose. Briefly, microcrystalline cellulose is dissolved in DMSO in a temperature range of 70 - 130 °C for a time duration ranging from 1- 8 hours in a hydrothermal vessel with the maximum solubility being observed as around 40 % in a 1 % solution of MCC in DMSO. The resulting solution was quite stable up to more than 30 days.
While the invention has been described and shown with reference to the preferred embodiment, it will be apparent that variations might be possible that would fall within the scope of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The following description includes the preferred best mode of one embodiment of the present invention. It will be clear from this description of the invention that the invention is not limited to these illustrated embodiments but that the invention also includes a variety of modifications and embodiments thereto. Therefore, the present description should be seen as illustrative and not limiting. While the invention is susceptible to various modifications and alternative constructions, it should be understood, that there is no intention to limit the invention to the specific form disclosed, but, on the contrary, the invention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the invention as defined in the claims.
In any embodiment described herein, the open-ended terms "comprising," "comprises," and the like (which are synonymous with "including," "having" and "characterized by") may be replaced by the respective partially closed phrases "consisting essentially of," consists essentially of," and the like or the respective closed phrases "consisting of," "consists of, the like.
As used herein, the singular forms "a," "an," and "the" designate both the singular and the plural, unless expressly stated to designate the singular only.
The present invention relates to a method of dissolving microcrystalline cellulose. More specifically, the present invention relates to a method of dissolving microcrystalline cellulose in a single solvent system.
Dissolution of cellulose is a challenge, which creates hurdle in evaluating its various characteristics and applications. While exploring its different parameters in the laboratory, we attempted to dissolve cellulose in different solvent systems reported in the literature. All the solvent systems were the mixtures of two or more solvents in a specific ratio, which were not very useful for evaluating few of its properties, like viscosity. For example, dimethylsulfoxide (DMSO) has been used in combination with other additives/ solvents, such as nitrogen dioxide (N2O4), tetrabutylammonium fluoride (TBAF), paraformaldehyde, liquid zwitter ions, tetraethylammonium hydroxide (TEOAH), and ionic liquids [Heinze and Köhler, 2010; Remsing et al., 2008; Olsson and Westman, 2013; Sirviö and Lakovaara, 2021]. DMSO alone has not been used for dissolving cellulose to the best of our knowledge. Additionally, the requirement of multiple solvents for dissolving cellulose was tedious task as this needed very meticulous mixing of the solvents and intensive reaction conditions. So, in order to simplify the process, we tried to explore a single solvent for the dissolution of cellulose, which can minimize the efforts and cost of the process along with protecting the environment.
The present invention offers DMSO as a novel solvent, which has not been explored so far as a stand- alone solvent for the dissolution of cellulose. DMSO is derived from dimethyl sulfide and is a relatively polar aprotic solvent (Fig. 1). It has been used as co-solvent for the dissolution of cellulose, where it helps in decreasing the viscosity of the solution [Voronova et al., 2006]. DMSO acts as a hydrophobic solvent, in which various molecules of DMSO remain held together by S=O dipoles in an antiparallel manner due to electrostatic interactions (Fig. 2). The existence of S=O bonds in DMSO offers hydrogen bonding between its oxygen atoms and the hydroxyl groups of cellulose (Fig. 3). The intermolecular hydrogen bonding between the two supports the dissolution of cellulose in DMSO.

Fig. 1. Structure of DMSO


Fig. 2. Antiparallel arrangement of DMSO units

Fig. 3. H-bonding between cellulose and DMSO

Microcrystalline cellulose (MCC) is a purified and partially depolymerized cellulose made of glucose units connected by ß-1,4 glycosidic bonds, which was discovered by Battista and Smith in 1955 and first commercialized in 1963 with the brand name of Avicel®. (Thoorens et al., 2014)

The method of producing microcrystalline cellulose comprising:
(a) a. pre-processing of biodegradable waste material to obtain size reduced biodegradable waste material; (b) hydrolysing the size reduced biodegradable waste material using mineral acids to obtain a hydrolysed product, wherein the acid hydrolysis is performed by adding 5-50 % solution of mineral acids to the pre-processed biodegradable waste material and carrying out the reaction for 2-30 days under natural weathering conditions, wherein the natural weathering condition is sunlight during daytime and low temperature during evening and night time; and (c) post-processing the acid hydrolysed product to obtain the cellulosic material, wherein the cellulosic material is microcrystalline cellulose.

Further, the pre-processing of biodegradable waste material comprising the steps of: (a) cleaning biodegradable waste material to obtain cleaned biodegradable waste material; and (b) shredding the cleaned biodegradable waste material into smaller sizes to obtain shredded biodegradable waste material followed by pulverizing to further reduce the size of the shredded biodegradable waste material to obtain the pre-processed biodegradable waste material.

Moreover, the post processing comprising the steps of: (a) filtering the acid hydrolysed product using vacuum pump to obtain filtered product and washing the filtered product using fresh water until reaching neutral pH to obtain washed product;
(b) drying the washed product at a temperature of 120 °C for 6-12 hours for completely removing water and moisture from the waste material to form a dried product; (c ) grinding the dried product in a grinder with stainless steel blades to obtain grinded product; and (d). passing the grinded product through a sieve mesh having a mesh size of 100-500 microns to obtain the cellulosic material.

The waste material was selected from cloth, fabrics, lignocellulosic material, wood chips, hardwood, soft wood, corn hulls, soy hulls, oat hulls, corn stalks, corn cobs, bagasse, wheat straw, oat straw, rice straw, barley straw, paper, cardboard, or combinations thereof, whereas the mineral acid was selected from the group comprising of sulfuric acid, hydrochloric acid, nitric acid, trifluoroacetic acid, formic acid or combinations thereof.

Process of dissolution:
Microcrystalline cellulose (MCC) was mixed with DMSO and was heated in hydrothermal vessel at 70°C to 130°C for varying time durations (1 - 8 h).

The inventors have used 1 % solution of microcrystalline cellulose (MCC), prepared by dissolving its 0.1 g in 10 mL of DMSO.

The solubility was determined by weight difference method. In this method, a 1 % solution of MCC in DMSO was taken in hydrothermal vessel and it was heated in the hot air oven for pre-determined temperature and time. After this, the vessel was allowed to stand for 3 - 4 h in order to release the pressure. Followed by this, the solution present in the hydrothermal vessel was filtered through a pre-weighed G3 crucible, for which the weight was already made constant. During this process, the MCC dissolved in DMSO was collected as filtrate, while undissolved MCC was collected over the crucible. The crucible with undissolved MCC was dried in hot air oven at around 130°C until constant weight. Crucible was cooled in desiccator and weighed again. Percentage of dissolved MCC was calculated using following equation:
Solubility of MCC (%) = x 100

Filtrate obtained in the above step was kept undisturbed and observed for the appearance of any turbidity in order to understand the stability of the solutions.

Solubility and stability of the solution of MCC in DMSO was observed. Results are mentioned in table-1.
Table-1. Solubility of MCC in DMSO and stability of resulting solutions.

Reaction Time (h) Solubility (%) Stability of
solution (days)
1 13 1
2 15 1
3 18 1
4 20 2
5 24 2
6 25 - 30 30
7 30 - 40 > 30
8 20 > 30

Maximum solubility was observed as around 40 % in a 1 % solution of MCC in DMSO. The resulting solution was quite stable up to more than 30 days.

Advantages
The uniqueness of the present invention lies in utilizing dimethylsulfoxide (DMSO) as a single solvent for dissolving cellulose. The present invention offers an easy method for dissolving cellulose, which can facilitate its evaluation by different instrumental techniques. As compared to the existing solutions, the present system is advantageous as it proposes a system for solubility of cellulose, comprising only a single solvent instead of mixture of solvents. The use of single solvent is beneficial in terms of:
• Making the procedure simplified.
• Making the evaluations easy and more authenticated, as the existence of co-solvents may affect the precision levels of the observations and calculations. For example, while studying the viscosity of cellulose, mixture of solvents creates complexity in the system as the individual solvents are accompanied with different individual viscosities, and hence it becomes a requirement to determine the viscosity of the solvent mixture before applying it for calculations. This kind of problem is not encountered while working with a single solvent system.
• Efficiency of solvent: The proposed solvent is able to dissolve up to 40 % cellulose in its 1 % solution. The existing studies report the maximum dissolution of cellulose up to only 14 % at 100 °C using DMSO as a co-solvent with other solvents. One study has reported even up to 100 % dissolution also under specified conditions, but the chemicals applied in the procedures are very expensive (up to Rs. 40,000/Kg) [Shigemasa et al., 1990].
• Stability of the solution: The solution of MCC in DMSO is stable up to more than 30 days of duration, which offers it a good scope to be used for various purposes.
• Environment-friendly nature of solvent: The use of DMSO for dissolving cellulose is advantageous as DMSO is green and non-toxic organic solvent. It is biodegradable in nature in biological systems, where it converts to methyl sulfone and dimethyl sulfide [Nyamiati et al., 2021; Hawkesworth and Alder, 1999].
• Cost-effective: The overall process is economic as the requirement of co-solvents adds cost to the procedure.
References:
(1) Method and system for extracting a cellulosic material from waste material using energy-efficient process, Shailey Singhal, Shilpi Agarwal, Naveen Singhal, Application No. 202311008701, The patent office, Government of India, Nov. 2023.
(2) M.I. Voronova, T.N. Lebedeva, M.V. Radugin, O.V. Surov, A.N. Prusov, A.G. Zakharov, Interactions of water-DMSO mixtures with cellulose. Journal of Molecular Liquids 126 (2006) 124-129. https://doi.org/10.1016/j.molliq.2005.12.001
(3) Juho Antti Sirviö and Matias Lakovaara, A Fast Dissolution Pretreatment to Produce Strong Regenerated Cellulose Nanofibers via Mechanical Disintegration. Biomacromolecules 2021, 22, 3366-3376. https://doi.org/10.1021/acs.biomac.1c00466
(4) Heri Satria, Kosuke Kuroda, Yota Tsuge, Kazuaki Ninomiya, and Kenji Takahashi, Dimethyl sulfoxide enhances both cellulose dissolution ability and biocompatibility of a carboxylate-type liquid zwitterion. New Journal of Chemistry, 2013, 1-3. DOI: 10.1039/x0xx00000x
(5) Yoshihiro SHIGEMASA, Yutaka KISHIMOTO, Hitoshi SASHIWA, and Hiroyuki SAIMOTO, Dissolution of Cellulose in Dimethyl Sulfoxide. Effect of Thiamine Hydrochloride. Polymer Journal, Vol. 22, No. 12, pp 1101-1103 (1990)
Carina Olsson and Gunnar Westman, Direct Dissolution of Cellulose: Background, Means and Applications. In Cellulose - Fundamental Aspects, 2013. 10.5772/52144
(6) Heinze, T. and Köhler, S. (2010). Dimethyl Sulfoxide and Ammonium Fluorides Novel Cellulose Solvents. In: Cellulose Solvents: For Analysis, Shaping and Chemical Modification. American Chemical Society. pp. 103-118.
(7) Remsing, R.C., Liu, Z., Sergeyev, I. and Moyna, G. (2008). Solvation and Aggregation of N,N'- Dialkylimidazolium Ionic Liquids: A Multinuclear NMR Spectroscopy and Molecular Dynamics Simulation Study. The Journal of Physical Chemistry B, 112(25):7363-7369.
(8) R D Nyamiati, Y Rahmawati, A Altway and S Nurkhamidah, Effect of Dimethyl Sulfoxide (DMSO) as a Green Solvent and the Addition of Polyethylene Glycol (PEG) in Cellulose Acetate/Polybutylene Succinate (CA/PBS) Membrane's Performance. IOP Conf. Series: Materials Science and Engineering 1143 (2021) 012063. doi:10.1088/1757-899X/1143/1/012063
(9) Kathryn Hawkesworth and John F. Alder, Oxidation of dimethyl sulfide to dimethyl sulfoxide in liquefied petroleum gas prior to piezoelectric crystal detection. Analyst, 1999, 124, 153-156. https://doi.org/10.1039/A808931K
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While the present invention has been described with reference to embodiments, the embodiments are illustrative, and the scope of the invention is not limited to these embodiments. Many variations, modifications, additions, and improvements to the embodiments described above are possible. It is contemplated that these variations, modifications, additions, and improvements fall within the scope of the invention. , Claims:We Claim
1. A method for dissolving microcrystalline cellulose (MCC), the method comprising:
dissolving 0.1-0.3 mg of microcrystalline cellulose (MCC) in 10 ml of DMSO in a temperature range of 70 - 130 °C for a time duration ranging from 1- 8 hours in a hydrothermal vessel.
2. The method as claimed in claim 1, wherein 0.1 mg of MCC was dissolved in 10 ml of DMSO to obtain 1% solution of MCC.
3. The method as claimed in claim 1, wherein a method of determining solubility of the dissolved MCC, the method comprising:
(a) heating the 1 % solution of MCC in the hydrothermal vessel in a hot air oven and subsequently standing the heated 1 % solution of MCC for 3-4 hours for releasing pressure; (b) filtering the solution obtained in step a through a G3 crucible, wherein weight of the crucible was made constant; (c ) collecting of the dissolved MCC as a filtrate, wherein the undissolved MCC was collected over the crucible; (d) drying the crucible having the undissolved MCC at 130°C to achieve uniform weight (e ) cooling of the heated crucible with the undissolved MCC in a desiccator; (f) leaving the collected filtrate having the dissolved MCC obtained in step (c ) to study for turbidity over a course of time; and (g) calculating percentage of dissolved MCC.

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