WO2017023161A2

WO2017023161A2 - Biological membrane and hydrogel via carbamate process

Info

Publication number: WO2017023161A2
Application number: PCT/MY2016/000043
Authority: WO
Inventors: Binti Zakaria Sarani; Sin Yee Gan; Chin Hua Chia
Original assignee: Universiti Kebangsaan Malaysia
Priority date: 2015-08-06
Filing date: 2016-07-29
Publication date: 2017-02-09
Also published as: WO2017023161A3; CN107922509A

Abstract

The present invention provides a method of preparing cellulose based material comprising the steps of extracting cellulose from a lignocellulosic biomass by using a bleaching agent and an alkali solution to produce cellulose pulp, drying the cellulose pulp, preparing cellulose carbamate from the cellulose pulp, pre-cooling a cellulose solvent at a first temperature, dissolving the cellulose carbamate in the pre-cooled cellulose solvent to form a transparent cellulose solution, casting the transparent cellulose solution on a casting plate and immersing the casting plate in a coagulant until the transparent cellulose solution coagulates to form a cellulose membrane. Also, a method of preparing a hydrogel using the cellulose carbamate is disclosed.

Description

Title: Biological Membrane and Hydrogel via Carbamate Process Technical Field:

Embodiments of the present invention relate to a method of preparing cellulose based material and more particularly to a method of preparing cellulose based material from lignocellulosic biomasses and a method of preparing hydrogel from the lignocellulosic biomasses. Further, the method is inexpensive, efficient and environmental friendly. Background Art:

Lignocellulosic materials (LCMs) are the most abundant renewable biomass and mainly composed of cellulose, hemicellulose and lignin. LCMs have great potential as less expensive and renewable feedstock for different applications. Cellulose is the most abundant biopolymer that can be obtained from numerous LCMs resources. Kenaf is a species of plant which is considered as one of the most important commercially available fibre sources. Cellulose carbamate (CCs) synthesized from kenaf core pulp (KCP) has been gaining scientific and technical attention because of its natural biocompatible properties and its property to dissolve with ease in organic solvents.

Typically, pretreatment methods for cellulose are needed in order to change its structure and chemical composition. Numerous techniques for pretreatment of cellulose have been developed. Various techniques known in the art for the pretreatment of cellulose that involved liquid water under high temperature and pressure are autohydrolysis, hydrothermal treatment, hot compressed water(HCW), hydrothermolysis, liquid hot water (LHW), aquasolve process, aqueous processing and pressure-cooking in water.

In conventional method such as viscose process which is widely used for commercial preparation of rayon, cellulose prepared from either wood pulp or cotton linters is treated with sodium hydroxide (an alkali) and then with carbon disulfide (CS₂) results in a product called cellulose xanthate. Further, the cellulose xanthate is dissolved in sodium hydroxide and the alkaline cellulose xanthate forms a thick solution called viscose. Rayon yarn is made by forcing the viscose through tiny openings in a spinneret into an acid solution, which coagulates it in form of fine strands.

US 20130197275 Aldescribes a new type of alkoxylated farnesol alkoxylates based on farnesol or at least partially hydrogenated farnesol, directly linked to a propylene oxide block and it also describes a process for preparation of these alkoxylates. Further, these alkoxylates can be used in washing, rinsing, cleaning or finishing compositions, cosmetic compositions, compositions for papermaking, agrochemical compositions, fuel additives and solubilization auxiliaries in aqueous liquid systems. CA 1245180 A1 describes a process for manufacturing cellulose carbamate fibres or films. In the process, cellulose and urea are reacted at elevated temperature for producing cellulose carbamate followed by dissolving in an alkaline solution for producing a spinning solution. The spinning solution is spun in an acid precipitation solution to obtain fibres or films. The cellulose carbamate is subjected to a 0.05-10 Mrad radiation dose prior to dissolving in alkali. After being subjected to irradiation, the cellulose carbamate is in the form of loose fibres.

CN 102432894 B describes a formation of cellulose carbamate dissolved in a combination of solvent which can be used to prepare fibres and films. The solvent is an aqueous solution of sodium hydroxide and 6-10wt% zinc oxide containing 0.1-3 wt%. An amount of cellulose carbamate is dispersed in the solvent composition at -10 ~ -20°C for 3-5 hours. Alternatively liquid nitrogen can be used which reduces the freezing time interval drastically to 3-5 minutes. Thawing of the sample at a temperature without above 50°C and dissolving to obtain cellulose carbamate solution at high concentration of 4-15% by wt. is performed.

In particular at least one advantage of the conventional method for producing cellulose using pretreatment is that it results in improved accessibility to cellulose structure due to physical changes in the cellulose such as increase in pore size and accessible area.

While conventional method of producing cellulose can provide various advantages, such as those described above, conventional methods are limited in various other matters such as requirement of a long reaction time, high temperature, catalysts and organic solvents. Further, the conventional method such as viscose process produces a lot of toxic gases like CS2, H₂S and heavy metal salts thereby causing pollution. Furthermore, the process is carried out without delay from beginning to give product as the intermediate (viscose) produced is unstable. Also, these methods are not environmental friendly and cost-effective. Accordingly, there remains a need in the prior art to have an improved method of preparing cellulose based material which overcomes the aforesaid problems and shortcomings. However, there remains a need in the art for a method of preparing a cellulose based material, such as cellulose membrane. Further, it must facilitate rapid dissolution of cellulose thus reducing reaction period. Also, it should be an efficient and environmental friendly method. Disclosure of the invention :

Embodiments of the present invention aim to provide a method of preparing cellulose based material, such as cellulose membrane. The proposed method facilitates rapid dissolution of cellulose using microwave irradiation. Further, the method accelerates organic reactions with cellulose solvents and thus reduces reaction period from hours to minutes. Also, the method is inexpensive to process and simple as compared with the conventional methods. The present invention is provided with a method of preparing cellulose based material by performing the steps as mentioned in claim 1. The invention may additionally be performed by performing the steps of claim 1 in any appropriate order.

In accordance with an embodiment of the present invention, the method of preparing cellulose based material comprising the steps of extracting cellulose from a lignocellulosic biomass by using a bleaching agent and an alkali solution to produce cellulose pulp, drying the cellulose pulp, preparing cellulose carbamate from the cellulose pulp, pre-cooling a cellulose solvent at a first temperature, dissolving the cellulose carbamate in the pre-cooled cellulose solvent to form a transparent cellulose solution, casting the transparent cellulose solution on a casting plate and immersing the casting plate in a coagulant until the transparent cellulose solution coagulates to form a cellulose membrane.

In accordance with an embodiment of the present invention, the method of preparing cellulose based material further comprising the steps of preparing a metal oxide-graphene oxide nano-composite, mixing the metal oxide-graphene oxide nano-composite into the transparent cellulose solution to form an interaction mixture, coagulating the interaction mixture in the coagulant and regenerating a highly porous structure of a metal oxide-graphene oxide nano-composite cellulose membrane. In accordance with an embodiment of the present invention, the method of preparing cellulose based material further comprising the steps of preparing a plurality of solid particulates, adding the plurality of solid particulates into the transparent cellulose solution to form a cellulose solution mixture, dispersing the cellulose solution mixture into the coagulant and regenerating the cellulose solution mixture to form a plurality of cellulose beads.

In accordance with an embodiment of the present invention, the step of extracting cellulose comprising the steps of bleaching the lignocellulosic biomass by the bleaching agent to remove dissolved lignin, treating the bleached lignocellulosic biomass with the alkali solution and washing the treated lignocellulosic biomass with distilled water to obtain the cellulose pulp. In accordance with an embodiment of the present invention, the step of preparing cellulose carbamate comprising the steps of milling the lignocellulosic biomass to form the cellulose pulp, immersing the cellulose pulp into a urea solution, subjecting the mixture of cellulose pulp and the urea solution to microwave irradiation, immersing the mixture of cellulose pulp and the urea solution in an ice bath to stop a reaction between the mixture of cellulose pulp and the urea solution and obtaining the cellulose carbamate, subjecting the cellulose carbamate to centrifugation to remove excess urea and vacuum-drying the cellulose carbamate.

In accordance with an embodiment of the present invention, the cellulose carbamate is vacuum-dried at a temperature of 80°C to 100°C for 12 to 24 hours. Preferably, at a temperature of 80°C for 2 hours. In accordance with an embodiment of the present invention, the alkali solution is 2% to 6 % (w/v) NaOH solution. Preferably, the alkali solution is 2% (w/v) NaOH solution.

In accordance with an embodiment of the present invention, the cellulose pulp is dried at a temperature of 105°C for 24 hours.

In accordance with an embodiment of the present invention, the cellulose solvent is selected from, but not limited to, a group consisting of mixed aqueous sodium hydroxide (NaOH) and urea solution, a mixed aqueous lithium hydroxide and urea solution and any combinations thereof. In accordance with an embodiment of the present invention, the mixed aqueous lithium hydroxide and urea solution; and water are mixed in a ratio of 4.6:15. In accordance with an embodiment of the present invention, the first temperature is in the range of -12°C to -15°C. Preferably, the first temperature is of -13°C.

In accordance with an embodiment of the present invention, the cellulose carbamate is dissolved in the pre-cooled cellulose solvent in an amount of 3% to 7 % by weight for 5 mins.

In accordance with an embodiment of the present invention, the cellulose carbamate; mixed aqueous sodium hydroxide (NaOH) and urea solution; and water are mixed in a ratio of 7:12:81.

In accordance with an embodiment of the present invention, the transparent cellulose solution is yellowish in color. In accordance with an embodiment of the present invention, the casting plate is, but not limited to, a glass plate.

In accordance with an embodiment of the present invention, the coagulant comprises an acidic solution. The acidic solution is dilute sulfuric acid (H₂S0₄). Further, the dilute sulfuric acid (H₂S0₄) has a concentration of 0 to 12% (v/v). In accordance with an embodiment of the present invention, the cellulose membrane is washed with distilled water and air dried at room temperature or in an IR Dryer. In accordance with an embodiment of the present invention, the transparent cellulose solution is stirred vigorously at a temperature between -13°C to 5°C before mixing the metal oxide-graphene oxide nano-composite.

In accordance with an embodiment of the present invention, the metal oxide-graphene oxide nano-composite is selected from, but not limited to, a group consisting of silver-graphene oxide nano-composite, magnetite (Fe₃0₄), titanium dioxide (Ti0₂), silver nanoparticles and graphene oxide.

In accordance with an embodiment of the present invention, the plurality of solid particulates was prepared by a chemical co-precipitation. The chemical is selected from, but not limited to, a group consisting of ferrous, ferric chloride and alkali hydroxide. Further, the alkali hydroxide comprises NaOH.

In accordance with an embodiment of the present invention, the plurality of solid particulates are, but not limited to, magnetite (Fe₃0₄) particles.

In accordance with an embodiment of the present invention, the plurality of cellulose beads are selected from, but not limited to, a group consisting of magnetic cellulose beads, silver-graphene oxide nano-composite, magnetite (Fe₃0₄), titanium dioxide (Ti0₂), silver nanoparticles and graphene oxide beads. In accordance with an embodiment of the present invention, the lignocellulosic biomass is selected from, but not limited to, a group consisting of kenaf core powder, kenaf pulp, cotton linter and oil palm pulp (EFB, OPT, frond). In accordance with an embodiment of the present invention, the bleaching agent is sodium chlorite. Further, the sodium chlorite has a concentration of 1.7 % (w/v).

In accordance with an embodiment of the present invention, the step of bleaching is performed at a temperature between 70°C to 80°C for 2 to 6 hours. Preferably, at a temperature of 80°C for 4 hours.

In accordance with an embodiment of the present invention, the step of treating the bleached lignocellulosic biomass with the alkali solution is performed at a temperature between 70°Cto 80°C for 2 to 6 hours. Preferably, at a temperature of 80°C for 3 hours.

Embodiments of the present invention aim further to provide a method of preparing a hydrogel using a lignocellulosic biomass by performing the steps as mentioned in claim 38. The invention may additionally be performed by performing the steps of claim 38in any appropriate order.

In accordance with an embodiment of the present invention, a method of preparing a hydrogel using the cellulose carbamate comprising the steps of dissolving the cellulose carbamate in a mixed alkali and urea solution to form a mixture, stirring the mixture to obtain a transparent cellulose solution, subjecting the transparent cellulose solution to centrifugation, adding a cross-linking agent to the transparent cellulose solution and stirring the mixture of transparent cellulose solution and cross-linking agent to form the hydrogel. In accordance with an embodiment of the present invention, the mixed alkali and urea solution is NaOH or LiOH solution.

In accordance with an embodiment of the present invention, the transparent cellulose solution is centrifuged at 10,000 rpm for 5 mins at a temperature of 5°C.

In accordance with an embodiment of the present invention, the cross-linking agent is, but not limited to, Epichlorohydrin (ECH). While the present invention is described herein by way of example using embodiments and illustrative drawings, those skilled in the art will recognize that the invention is not limited to the embodiments of drawing or drawings described, and are not intended to represent the scale of the various components. Further, some components that may form a part of the invention may not be illustrated in certain figures, for ease of illustration, and such omissions do not limit the embodiments outlined in any way. It should be understood that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the invention is to cover all modification/s, equivalent/s and alternative/s falling within the scope of the present invention as defined by the appended claim. The headings used herein are for organizational purposes only and are not meant to be used to limit the scope of the description or the claim. As used throughout this description, the word "may" is used in a permissive sense (i.e. meaning having the potential to), rather than the mandatory sense (i.e. meaning must). Further, the words "a" or "an" means "at least one" and the word "plurality" means "one or more" unless otherwise mentioned. Furthermore, the terminology and phraseology used herein is solely used for descriptive purposes and should not be construed as limiting in scope. Language such as "including," "comprising," "having," "containing," or "involving," and variations thereof, is intended to be broad and encompass the subject matter listed thereafter, equivalents, and additional subject matter not recited, and is not intended to exclude other additives, components, integers or steps. Likewise, the term "comprising" is considered synonymous with the terms "including" or "containing" for applicable legal purposes. Any discussion of documents, acts, materials, devices, articles and the like is included in the specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention.

In this disclosure, whenever a composition or an element or a group of elements is preceded with the transitional phrase "comprising", it is understood that we also contemplate the same composition, element or group of elements with transitional phrases "consisting of, "consisting", "selected from the group of consisting of, "including", or "is" preceding the recitation of the composition, element or group of elements and vice versa. Description of drawings and best mode for carrying out the invention:

So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may have been referred to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawing illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. These and other features, benefits and advantages of the present invention will become apparent by reference to the following text figure, with like reference numbers referring to like structures across the views, wherein:

Fig. 1 is a flow chart illustrating a method of preparing cellulose based material in accordance with an embodiment of the present invention.

Fig. 2 illustrates FTIR spectra of kenaf samples from (a) KCP and (b) K/U-4.5 wt% CCs in accordance with an embodiment of the present invention.

Fig. 3 illustrates SE images of (a) KCP, (b) KCP in urea solution and (c) K/U-4.5 wt% CCs in accordance with an embodiment of the present invention.

Fig. 4 illustrates FESEM images of regenerated kenaf membrane samples (a) KCP, (b) K/C-0.9 wt%, (c) K/C-2.8 wt% and (d) K/C-4.5 wt% in accordance with an embodiment of the present invention.

Fig. 5 illustrates XRD patterns of kenaf samples from (a) KCP, (b) regenerated K/U-4.5 wt%, (c) regenerated K/U-2.8 wt%, (d) regenerated K/U-0.9 wt% and (e) regenerated KCP in accordance with an embodiment of the present invention.

Fig. 6 illustrates a TEM image of dispersion of graphene oxide (GO) in a CC-GO membrane in accordance with an embodiment of the present invention.

Fig 7 illustratesFT-IR spectra of (a) GO, (b) KCP, (c) CC pulp, (d) CC membrane and (e) CC-G04 in accordance with an embodiment of the present invention.

Fig. 8 illustrates XRD patterns of (a) GO, (b) CC pulp, (c) CC membrane and (d) CC-G04 in accordance with an embodiment of the present invention.

Fig. 9 illustrates cellulose II crystalline form of CC-GO membranes with different loading of GO, (a) CC-G01 , (b) CC-G02, (c) CC-G03 and (d) CC-G04 in accordance with an embodiment of the present invention.

Fig. 10 illustrates surface (magnification, 50 x) and cross-section (magnification, 2 kx) FESEM images of (a, b) CC membrane, (c, d) CC-G01 , (e, f) CC-G02 and (g, h) CC-G03 and (ij) CC-G04 membrane in accordance with an embodiment of the present invention.

Fig. 11 illustrates typical stress-strain curves of (a) CC membrane, (b) CC-G01 , (c) CC-G02, (d) CC-G03, (e) CC-G04 membranes in accordance with an embodiment of the present invention.

Fig. 12 illustrates TG curves of (a) CC membrane and (b) CC-G04 in accordance with an embodiment of the present invention.

Fig. 13 illustrates DTG curves of (a) CC membrane and (b) CC-G04 in accordance with an embodiment of the present invention.

Fig. 14 illustrates XRD patterns of cellulose hydrogel samples in accordance with an embodiment of the present invention. Fig. 15 illustrates transparency of the cellulose hydrogel samples in accordance with an embodiment of the present invention.

Fig. 16 illustrates physical appearance of (a) cellulose hydrogel and FESEM images (b) to (f) of cellulose hydrogel samples in accordance with an embodiment of the present invention.

The present invention is described hereinafter by various embodiments with reference to the accompanying drawing, wherein reference numerals used in the accompanying drawing correspond to the like elements throughout the description. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiment set forth herein. Rather, the embodiment is provided so that this disclosure will be thorough and complete and will fully convey the scope of the invention to those skilled in the art. In the following detailed description, numeric values and ranges are provided for various aspects of the implementations described. These values and ranges are to be treated as examples only, and are not intended to limit the scope of the claims. In addition, a number of materials are identified as suitable for various facets of the implementations. These materials are to be treated as exemplary, and are not intended to limit the scope of the invention.

Embodiments of the present invention aim to provide a method of preparing cellulose based material, such as cellulose membrane. The present invention is able to provide an alternative method of preparing cellulose based material to replace the conventional method of preparing cellulose membranes using toxic gases. The disclosed method does not involve the use of any toxic gases. The method increases solubility of cellulose using microwave irradiation. Further, the method accelerates organic reactions with cellulose solvents and thus reduces reaction period from hours to minutes. The cellulose membrane obtained from the proposed method has anti-bacterial properties. Also, the proposed method is inexpensive, efficient and environmental friendly.

Figure 1 is a flow chart (100) illustrating the method of preparing cellulose based material in accordance with an embodiment of the present invention. At step 102, as shown in Figure 1 , cellulose is extracted from a lignocellulosic biomass by using a bleaching agent and an alkali solution to produce cellulose pulp. The lignocellulosic biomass is selected from, but not limited to, a group consisting of kenaf core powder, kenaf pulp, cotton linter and oil palm pulp (EFB, OPT, frond).

In accordance with an embodiment of the present invention, the step 102, involves bleaching of the lignocellulosic biomass by the bleaching agent to remove dissolved lignin. The bleached lignocellulosic biomass is treated with an alkali solution. Further, the treated lignocellulosic biomass is washed with distilled water to obtain the cellulose pulp.

In accordance with an embodiment of the present invention, the step of bleaching the lignocellulosic biomass by the bleaching agent is performed at a temperature between 70°C to 80°C for 2 to 6 hours. Preferably, at a temperature of 80°C for 4 hours. Further, the step of treating the bleached lignocellulosic biomass with the alkali solution is performed at a temperature between 70°C to 80°C for 2 to 6 hours. Preferably, at a temperature of 80°C for 3 hours.

In accordance with an embodiment of the present invention, the bleaching agent is, but not limited to, sodium chlorite. Further, the sodium chlorite has a concentration of 1.7 % (w/v). Furthermore, the alkali solution is 2% to 6 % (w/v) NaOH solution. Preferably, the alkali solution is 2% (w/v) NaOH solution. At step 104, the cellulose pulp is dried at a temperature of 105°C for 24 hours.

At step 106, cellulose carbamate is prepared from the cellulose pulp. In accordance with an embodiment of the present invention, the step

106, involves milling of the lignocellulosic biomass to form the cellulose pulp and the cellulose pulp is immersed into a urea solution. The mixture of cellulose pulp and the urea solution is subjected to microwave irradiation. The mixture of cellulose pulp and the urea solution is immersed in an ice bath to stop a reaction between the mixture of cellulose pulp and the urea solution and the cellulose carbamate is obtained thereafter. Further, the cellulose carbamate is subjected to centrifugation to remove excess urea and the cellulose carbamate is vacuum-dried at a temperature of 80°C to 100°C for 12 to 24 hours. Preferably, at a temperature of 80°C for 12 hours. At step 108, a cellulose solvent is pre-cooled at a first temperature. Further, the first temperature is in the range of -12°C to -15°C. Preferably, the first temperature is of - 3°C. In accordance with an embodiment of the present invention, the cellulose solvent is selected from, but not limited to, a group consisting of mixed aqueous sodium hydroxide (NaOH) and urea solution, a mixed aqueous lithium hydroxide and urea solution and any combinations thereof. The mixed aqueous lithium hydroxide and urea solution; and water are mixed in a ratio of 4.6:15. Further, the cellulose carbamate; mixed aqueous sodium hydroxide (NaOH) and urea solution; and water are mixed in a ratio of 7:12:81.

At step 110, the cellulose carbamate is dissolved in the pre-cooled cellulose solvent to form a transparent cellulose solution. Further, the cellulose carbamate is dissolved in the pre-cooled cellulose solvent in an amount of 3% to 7% by weight for 5 mins. Furthermore, the transparent cellulose solution is yellowish in color.

At step 112, the transparent cellulose solution is casted on a casting plate. Further, the casting plate is, but not limited to, a glass plate.

At step 114, the casting plate is immersed in a coagulant until the transparent cellulose solution coagulates to form a cellulose membrane. In accordance with an embodiment of the present invention, the coagulant comprises an acidic solution. The acidic solution is dilute sulfuric acid (H₂S0₄). Further, the dilute sulfuric acid (H₂S0₄) has a concentration of 0 to 12% (v/v).

In accordance with an embodiment of the present invention, the cellulose membrane is washed with distilled water and air dried at room temperature or in an IR dryer.

In accordance with an embodiment of the present invention, the method of preparing cellulose based material further comprising the steps of preparing a metal oxide-graphene oxide nano-composite, mixing the metal oxide-graphene oxide nano-composite into the transparent cellulose solution to form an interaction mixture, coagulating the interaction mixture in the coagulant. Further, a highly porous structure of a metal oxide-graphene oxide nano-composite cellulose membrane is regenerated.

In accordance with an embodiment of the present invention, the transparent cellulose solution is stirred vigorously at a temperature between -13°C to 5°C before mixing the metal oxide-graphene oxide nano-composite. Further, the metal oxide-graphene oxide nano-composite is selected from, but not limited to, a group consisting of silver-graphene oxide nano-composite, magnetite (Fe₃0₄), titanium dioxide (ΤΊΟ2), silver nanoparticles and graphene oxide.

In accordance with an embodiment of the present invention, the method of preparing cellulose based material further comprising the steps of preparing a plurality of solid particulates, adding the plurality of solid particulates into the transparent cellulose solution to form a cellulose solution mixture, dispersing the cellulose solution mixture into the coagulant and regenerating the cellulose solution mixture to form a plurality of cellulose beads. In accordance with an embodiment of the present invention, the plurality of solid particulates was prepared by a chemical co-precipitation. The chemical is selected from, but not limited to, a group consisting of ferrous, ferric chloride and alkali hydroxide. Further, the alkali hydroxide comprises NaOH. In accordance with an embodiment of the present invention, the plurality of solid particulates are, but not limited to, magnetite (Fe₃0₄) particles and the plurality of cellulose beads are selected from, but not limited to, a group consisting of magnetic cellulose beads, silver-graphene oxide nano-composite, magnetite (Fe₃C>4), titanium dioxide (Ti0₂), silver nanoparticles and graphene oxide beads.

In accordance with an embodiment of the present invention, a method of preparing a hydrogel using the cellulose carbamate is provided. The cellulose carbamate is dissolved in a mixed alkali and urea solution to form a mixture. The mixture is stirred to obtain a transparent cellulose solution and thereafter, the transparent cellulose solution is subjected to centrifugation. Further, a cross-linking agent is added to the transparent cellulose solution and the mixture of transparent cellulose solution and the cross-linking agent is stirred to form the hydrogel. In accordance with an embodiment of the present invention, the mixed alkali and urea solution is NaOH or LiOH solution. The transparent cellulose solution is centrifuged at 10,000 rpm for 5 mins at a temperature of 5°C. Further, the cross-linking agent is, but not limited to, Epichlorohydrin (ECH).

In accordance with an embodiment of the present invention, the hydrogel has highly porous structure and is transparent. Further, upon freeze dry, the hydrogel has excellent absorbance properties. Hereinafter, an example of the present invention will be provided for more detailed explanation.

Examples

Example 1

Materials and Methods

1. Preparation of dried cellulose pulp

The dried cellulose pulp was prepared by using a kenaf core pulp (KCP). The KCP was bleached using four stages bleaching method (DEED) where process 'D' composed of 1.7% sodium chlorite at 80°C for 4hours and process Έ' is an alkaline treatment on KCP with 2%-6% NaOH solution at 80°C for 3hours. Preferably, 2% NaOH solution was used for alkaline treatment. After every single stage performed, the KCP sample was washed until neutral, to remove the bleaching chemicals and dissolved lignin from the KCP sample prior to entering the next stage. Then, the KCP sample was dried at 105°C for 24hours to form the dried cellulose pulp. 2. Preparation of Cellulose Carbamate (CC) from Kenaf core pulp (KCP)

10 g of KCP was milled and immersed into a urea aqueous solution containing 2g /6g /10g of urea in 200 ml H₂0 separately. Therefore, the weight percentage for urea content were 0.9 wt%, 2.8 wt% and 4.5 wt% in each KCP/urea aqueous solution and later were referred as K/U-0.9 wt%, K/U-2.8 wt% and K/U-4.5 wt% respectively. Each mixture was stirred at 25°C for 30 min and placed in desiccators which were connected to a vacuum pump giving rise to a vacuum condition for 30 min. The vacuum pump was then turned off and allowed atmosphere forces the urea aqueous solution to penetrate into KCP for 30 min. The mixture was later poured into a reaction flask and was heated in a microwave reactor at the power set at 380 W for different reaction time which was10 min, 20 min and 30 min. The microwave reactor is a multimodal microwave apparatus (Electrolux-EMM1908S) that has been equipped with a condenser to prolong the microwave irradiation. Therefore, the CCs K/U-0.9 wt%, K/U-2.8 wt% and K/U-4.5 wt% with different urea content were formed at different reaction time. In each case, whenever reaction time reached, the mixture in the reaction flask was immersed instantly in an ice bath to stop the reaction. The obtained kenaf cellulose carbamate (CC) was washed with deionized water using both vortex shaker and centrifuged to remove the excessive urea. The kenaf CC was then vacuum-dried at 80°C for 12 hours.

3. Preparation of cellulose membranes from KCP and CC

An analytical grade of lithium hydroxide monohydrate (υθΗΉ₂0) (Sigma Aldrich), urea (Sigma Aldrich) and 98.8% sulfuric acid (Sigma Aldrich) were used for the preparation of cellulose membranes. A LiOH/urea aqueous solution with the weight ratio of 4.6:15 was prepared and frozen at 13°C for 6 hours. The 3wt% of each raw KCP and kenaf CCs (K/U-0.9 wt%, K U-2.8 wt% and K/U-4.5 wt%) which was produced in 10 min reaction time were dissolved using rapid dissolution method. The cellulose samples were dissolved in the LiOH/urea aqueous solutions and the cellulose solutions were stirred vigorously for 5min. Upon stirring, a transparent cellulose solution is obtained in a dissolution of KCP and slightly yellow transparent cellulose solution is obtained which is caused by the dissolution of kenaf CCs (K/U-0.9 wt%, K/U-2.8 wt% and K/U-4.5 wt%). The cellulose solution and undissolved cellulose were separated using centrifugation method. Only soluble cellulose solution was used to form cellulose membrane. The cellulose membranes were formed by casting each soluble KCP solution and soluble kenaf CCs solutions (K/U-0.9 wt%, K/U-2.8 wt% and K/U-4.5 wt%) on a glass plate and immersed in diluted sulfuric acid (H2SC ) until the membranes coagulate. All of membranes were then immersed and washed in deionized water bath for three days to eliminate the residue of unreacted LiOH and urea. A portion of the membrane samples were freeze dried for 48 hours and stored in desiccators for further characterization.

4. Preparation of highly porous metal oxide-graphene oxide nano-composite cellulose membrane (CC-GO membrane)

A NaOH/urea aqueous solution at the weight ratio 7 wt% NaOH : 12 wt% Urea : 81 wt% H₂0, was prepared and stored at low temperature -13 °C for 6 h. Firstly, 4 wt% of each CC sample was dissolved in the alkaline aqueous solution at -13°C using rapid dissolution method. The slight yellow transparent cellulose solution was then stirred vigorously for 5 min to form a heterogeneous mixture. The mixture was then centrifuged to remove the undissolved cellulose and the cellulose solution was used to form CC membrane. The CC-GO membrane was prepared by adding GO into the cellulose solution and stirred vigorously for 30 min in an ice-salt bath. A series of mixed CC-GO solutions were obtained and the mass ratios of GO/CC were 0, 1 , 2, 3 and 4 wt%. The cellulose membrane was formed by casting each CC-GO solution on the glass plate and thickness of membrane was in the range of 0.086-0.095 mm. Then, the glass plate was immediately immersed into 5 wt% H2SO4 aqueous coagulant solution for 5 min to obtain the CC-GO membrane. The CC-GO membrane was then immersed in deionized water bath for three days to remove the acid coagulant and excess NaOH/urea. A subset of membrane sample was freeze dried for 48 h for further characterizations. The CC-GO membranes were produced with the mass ratios 0, 1 , 2, 3 and 4 wt% of GO/CC and were labeled as CC membrane, CC-G01 , CC-G02, CC-G03 and CC-G04, respectively. 5. Preparation of cellulose beads

Magnetite (Fe₃0₄) particles were prepared by a chemical co-precipitation. The magnetite (Fe₃0₄) particles were added into the transparent cellulose solution to obtain a resulting cellulose solution mixture.

The cellulose solution mixture was dispersed into the diluted sulfuric acid (H₂S0₄) and the cellulose solution mixture was regenerated and resulted in the formation of cellulose beads.

6. Preparation of cellulose hydrogel

A LiOH/urea aqueous solution with the weight ratio 4.6:15 was prepared and frozen at 13°C for 6 h. The 3 wt% of each raw KCP and kenaf CCs (K/U-0.9 wt%, K/U-2.8 wt% and K/U-4.5 wt%) which was produced in 10 min reaction time were dissolved using rapid dissolution method. The kenaf cellulose solution was stirred for 5 min to obtain the yellowish transparent cellulose solution. The transparent cellulose solution was subjected to centrifugation at 10,000 rpm for 5 min at 5°C to remove air bubbles and to separate the dissolved and undissolved cellulose solutions. Epichlorohydrin (ECH) solution (5 %) was then dropped carefully into soluble cellulose solution for a cross linking process and stirred until the hydrogel was formed. The obtained hydrogels were washed with deionized water to remove the excess LiOH and urea. A portion of the hydrogel sample was freeze dried for 48 hours and stored in a desiccator for further characterization. .

7. Characterizations

The kenaf CCs and KCP samples were characterized by FT-IR to observe the functional groups in the CCs (PerkinElmer Spectrum 400 FT-IR). Nitrogen content of CCs was examined using Kjeldahl method conducted at

UNIPECS dn. Bhd. Morphology of KCP, bathed-in-urea KCP and CCs has been analyzed under a scanning electron microscopy (SEM, Supra 55 VP Zeiss).

Morphology and pore size of regenerated cellulose membranes were measured using a scanning electron microscope (Zeiss/Supra 55VP). Phase and crystallinity index for raw KCP, CC and regenerated cellulose membranes were characterized using X-ray diffraction (Bruker Axs D8 Advance).

Results

1. FTIR spectra of KCP and CCs

Figure 2 (a) displays the FTIR spectra of KCP and figure 2 (b) displays the FTIR spectra of K/U-4.5 wt% CCs wit O min reaction time. Both KCP's and CCs' spectra exhibit a transmittance peak at 2904.19 cm-1 due to the stretching of N-H functional group in urea. Spectrum of the KCP showed the transmittance peaks at wavelength 1641 cm-1. In comparison of KCP, CCs' spectrum showed two distinct transmittance peaks at wavelengths 1665.86cm-1 and 1626.12cm-1 , which is assigned to stretching vibration of the carbonyl (C=0) in the base of urethane. These two peaks indicated the formation of CCs from cellulose and urea as described in Eq. (1 ).

Cell-OH + HNCO > Cell-0-C-NH₂ + NH₃ (1)

O

Therefore, an efficient formation of CCs via the microwave reactor process has been demonstrated qualitatively in this study.

2. Morphology of KCP and CCs

Figure 3 shows the SEM micrographs of the (a) raw KCP, (b) KCP in urea solution and (c) K/U-4.5 wt% CCs that was produced under microwave reactor withIO min reaction time. Raw KCP as shown in figure 3(a) displayed a smooth and compact surface which did not have any external fibrillation or formation of fibrils. In figure 3(b), the fibre structure had changed visibly as it was immersed in urea solution. The observed relative density of cellulose was reduced which helped the urea to penetrate into the fibres and reacted with cellulose easily. Figure 3(c) displayed SEM micrographs of K/U-4.5 wt% CCs with 10 mins reaction time. In figure 3(c), the fibres swelled significantly and the surfaces of CCs become loosed. These properties and changes in the morphology and structure of cellulose fibres might give rise to high diffusion and good swelling properties which is important in a chemical reaction, solubility and spinnability of CCs.

3. Morphology of regenerated cellulose membranes from KCP and CCs

Figure 4 presents four FESEM micrographs of regenerated kenaf membranes from KCP and CCs produced in 10 min reaction time such as K/C-0.9 wt%, K/C-2.8 wt% and K/C-4.5 wt%. The regenerated kenaf membrane from KCP in figure 4 (a) displayed a wavy and disordered image, which might be due to the reducing of cellulose crystallinity after dissolution in urea-alkaline aqueous system. There were few curve-structured nanoparticles which appeared to form thicker bundles of aggregates and which were known to have a general tendency to aggregate in parallel with one another. Figure 4 (b), (c), and (d) displayed the regenerated CCs membranes formed from different percentage of urea composition. These figures showed that, as the percentage of urea used to produce CCs increased, the pore size of its regenerated cellulose membrane also increased. The nitrogen content during the formation of CCs and its solubility might have affected the morphology of its regenerated cellulose membrane, since the increase in urea content enhances the substitution of nitrogen within CCs molecule. The pore size of the regenerated CCs membranes was found to be in a range between 100.5 nm and 725.8 nm as shown in the figure 4 with the scale of 1 pm.

4. XRD patterns and crystallinity index of regenerated cellulose membranes from KCP and CCs

Figure 5 shows the XRD patterns of (a) raw KCP, (b) regenerated KCP membranes and regenerated CCs membranes of (c) K/U-0.9 wt%, (d) K/U-2.8 wt% and (e) K/U-4.5 wt% at 10 min reaction time. The diffraction pattern of KCP native cellulose was identical with that of typical cellulose I structure, with a sharp peak at the angle 22.2° and a wide peak between angles 14.7° and 16.3°. The sharp 2 Θ showed peak at the angles approximately 12.2°, 19.8° and 20.9°and signified the formation of cellulose II in all regenerated cellulose membranes.

Table 1 shows the crystallinity index of raw KCP, the regenerated KCP membrane and regenerated CCs membrane. The regenerated kenaf membrane samples were formed from the dissolution of 3 wt% KCP and 3 wt% CCs (K/U-0.9 wt%, K/U-2.8 wt% and K/U-4.5 wt% with 10 min reaction time) respectively. The crystallinity index (%) of raw KCP was higher than that of all other regenerated kenaf membranes. A downward trend was observed between the crystallinity index of CCs membrane and the percentage of urea content supplied in the formation of CCs. This observation might be related to the resulting nitrogen content and the solubility trend among CCs samples.

Table 1 Crystallinity index of KCP and the regenerated kenaf membranes. 5. Nitrogen content of KCP and CC

Weight percentage of nitrogen in KCP was found to be 0.3 wt%. The nitrogen content of CC was found to be 5.6 wt% which had increased up to 5.3 wt% of nitrogen content with the aid of microwave treatment. The possible chemical reaction of KCP with urea in microwave irradiation in order to form cellulose carbamate is shown in Eq. (2).

6. Dispersion of graphene oxide (GO) in CC-GO

Figure 6 illustrates a TEM image of dispersion of graphene oxide (GO) in CC matrix (transparent cellulose solution). TEM sample was prepared by placing a droplet of the dilute CC-GO aqueous solution on a carbon grid. Wrinkle GO in low-magnification image was observed. Suspension of GO in CC is important for good dispersion in the cellulose carbamate matrix. As shown in figure 6, exfoliation of GO was achieved in CC matrix and the GO was homogeneously dispersed in the CC matrix.

7. FT-IR analysis of a highly porous metal oxide-graphene oxide nano composite cellulose membrane (CC-GO membrane)

Figure 7 shows the FT-IR spectra of (a) GO, (b) KCP, (c) CC pulp, (d) CC membrane and (e) CC-G04 membrane containing 4 wt % GO. The FT-IR measurement was carried out to confirm successful oxidation of graphite to GO and to reveal the interactions between CC and GO. In GO spectrum, wide and intense peaks in the range of 3354 and 3257 cm^-1 were observed that signifies O-H stretching vibrations. Occurrence of transmittance band at approximately 1630 cm^-1 was attributed to C=C bonding for aromatic rings of the GO carbon skeleton structure or the deformation vibrations of the O-H band of intercalated water molecules. Other C-0 functionality such as C-O-C can be seen at 1245 cm^-1. CC pulp spectrum displayed a transmittance peak at 2904 cm^"1 due to stretching of N-H functional group in urea. Spectrum of KCP depicted the transmittance peak at wavelength 1650 cm^"1. Compared to that of KCP, CC pulp spectrum showed two distinct transmittance peaks at wavelengths 1666 and 1626 cm^"1 , which corresponds to stretching vibration of the carbonyl (C=0) in urethane base. These two peaks indicated the formation of CC from KCP and urea. The peaks located at 1639 and 1647 cm^"1 for CC membrane and CC-G04 respectively were attributed to carbonyl amide group. For CC-G04, broadened peak of C-0 stretching vibrations appeared at 3349 cm^"1 and its changes in relative intensity implied the disturbance of hydrogen bonds in CC.

8. XRD study of the CC-GO membrane

Figure 8 illustrates the XRD patterns of (a) GO, (b) CC pulp, (c) CC membrane and (d) CC-G04 membrane containing 4 wt % GO. Typical 2Θ peak of GO occurred at 9.9° corresponded to (0 0 1) peak which was due to oxygen-rich groups on both sides of GO sheets and water molecules trapped between the sheets. The CC pulp showed a typical crystalline form of cellulose I by three distinct peaks at 14.8°, 16.4° and 22.4°. The CC membrane and CC-GO regenerated membrane samples(CC-G01 ,CC-G02, CC-G03 containing 1 wt %, 2 wt% and 3 wt% GO, respectively) exhibited diffraction peaks at 2Θ = 12.1°, 19.9°, and 21.1° which corresponded to diffraction of (110), (110) and (200) planes and preserved the cellulose II allomorph. Therefore, it proved that both the CC membrane and CC-GO membrane samples were in cellulose II crystalline form, while the diffraction angles of CC-GO membrane samples were almost similar to that of the CC membrane. However, for the CC-G04, the (0 0 1) peak which represented GO did not appear. It might be an indication to exfoliation and uniform dispersion of GO in the CC matrix, as shown in figure 6. Moreover, the CC-G04 membrane was black in colour and showed a sign of GO reduction to some extent in the cellulose solvent of NaOH/urea.

Figure 9 (a) to (d) displays the cellulose II crystalline form of the CC-GO membranes at different loading of GO. The crystalline structure of the CC-GO membranes was cellulose II as CC had been dissolved in NaOH/urea and recrystallized in a new form. Crystalline structure of cellulose II is generally formed by the treatment with NaOH solution (mercerization) or by dissolution of cellulose and subsequent regeneration, in order to form regenerated cellulose products. Effect of GO on the CC is similar to alkalization of cellulose in NaOH/urea solvent, which might be advantageous for disruption of strong intermolecular hydrogen bonding of the CC.

Table 2 shows the crystallinity index of the CC pulp, CC membrane and CC-GO membranes at different GO content. As shown in Table 2, the CC pulp had the highest crystallinity index (61.27 %) as compared to all the CC-GO and CC membranes. Due to the incorporation of GO, the CC-GO membranes showed lower crystallinity index than neat CC membrane having crystallinity index of 58.06 %. As the GO loading increased from 1 to 4 wt%, crystallinity index of the CC-GO membranes decreased from 55.85 to 47.01 %. This was due to the contribution of the amorphous state in GO which interrupted the aggregation and crystallinity in the CC matrix. The addition of GO decreased the crystallinity index of the cellulose carbamate (CC) membrane because of more hydrogen bonding between GO and cellulose molecules, which hindered the molecular movement of cellulose. This might also be due to the interaction between GO and CC that had weakened the strong intermolecular hydrogen bonding in CC and eventually dislocated the crystallinity index in the CC-GO membranes. As the GO loading increased, constrained movement of the CC molecules caused the reduction in crystallinity index of the CC-GO membranes. Therefore, introduction of GO reduced the crystallinity index of CC membrane and the increased GO loading reduced the crystallinity index of the CC-GO membranes.

Table 2 Crystallinity index of cellulose membrane samples.

9. Structure and morphology of the CC-GO membranes

FESEM images in Figure 10 showed the surface and cross-section of the CC-GO membranes at different GO loadings (from 0 to 4 wt%). As shown in figure 10 (a) and (b), surface and cross-section of the CC membrane at 50 x and 2 kx magnification illustrated a homogeneous mesh structure, which attributed to the self-aggregation tendency of cellulose in alkaline solution and penetration of coagulants during coagulation process. Rough surface and cross-section of CC-GO membranes with the presence of GO were also displayed in figure 10 (c) and (d) for CC-G01 , (e) and (f) for CC-G02, (g) and (h) for CC-G03, (i) and (j) for CC-G04 at 50 x and 2 kx magnification, from which wrinkle GO can be identified. Moreover, the surface of CC-GO membranes exhibited high level of homogeneity which indicated that CC and GO were completely unified in the CC-GO membrane.

The cross section of the CC-GO membrane sample displayed a 3D homogeneous porous structure of its freeze-dried samples whereas the CC membrane exhibited morphology with homogeneous porosity. As the GO content in CC membrane increased, the structure of the CC-GO membrane became more porous. The pore sizes of the cellulose network were in the range of two micrometer and the pore walls consisted of thin layers of stacked graphene sheets. The partial overlapping or coalescing of flexible GO had resulted in the formation of physical cross-linking sites in CC-GO membranes. Hence, the inherent flexibility of GO was a crucial part to build up the 3D macrostructures.

10. Mechanical Properties of the CC-GO membranes

Figure 11 presents the typical stress-strain curves of (a) CC membrane, (b) CC-G01 , (c) CC-G02, (d) CC-G03, (e) CC-G04 membranes, obtained from the uniaxial tension. The average tensile properties and standard deviations of all membranes are summarized in Table 3. The neat CC membrane without GO exhibited tensile modulus of 0.67 GPa, tensile strength of 26.4 MPa, and elongation at break of 4.8 %. In general, incorporation of GO into CC membrane remarkly improves the tensile modulus and strength but gradually weakens the elongation at break. It was noted that the modulus were 2.51 , 3.23, 3.71 , and 4.19 GPa for CC-G01 , CC-G02, CC-G03, and CC-G04 membranes, respectively. These values were corresponding to increase by about 275-525 % relative to the neat CC membrane. Similarly, as the GO/CC ratio was increased from 1 to 4 wt%, tensile strength of the CC-GO membranes increased from 40.8 to 50.9 MPa, which was around 1.5 to 2 times higher than the neat CC membrane. As the GO loading increased, the well-dispersed GO had higher opportunities of interaction with functional groups of CC chains as GO consists of a number of oxygen-containing groups in plane. Further, the elongation at break decreases from 4.8 (CC membrane) to 2.8 (CC-G01), 2.5 (CC-G02), 2.2 (CC-G03), and 2.1 % (CC-G04) because of the brittle nature of GO sheets.

Table 3 Tensile properties of cellulose membranes with different ratio of GO/CC. 1 1. Thermal properties of the CC-GO membranes

Thermogravimetry analysis (TGA) was conducted to reveal the effect of GO on thermal behaviors of CC membranes. The thermogravimetry (TG) and differential thermogravimetry (DTG) curves of the cellulose membranes were shown in figure 12 and figure 13, respectively. As shown in figure 12, char yield of the CC-G04 membrane at temperature beyond 350°C increased as GO incorporated into the CC. For example, at 500°C, the char yield of the CC membrane was about 53 wt% as shown in figure 12 (a), whereas CC-G04 cellulose membrane containing 4 wt% GO/CC ratio has char yield of about 56 wt% as shown in figure 12 (b).

Ti value is the initial decomposition temperature. T_max is the temperature with maximum decomposition rate, and T_f is the final decomposition temperature. From figure 13 (a) and (b), obtained readings for CC membrane without GO content were as following, T, = 240°C, T_max = 331 °C, and T_f = 376°C. For the CC-G04 membrane with 4 wt% GO/CC ratio, Ti = 255°C, T_max = 341°C, and T_f = 381°C were obtained. The T_max of the CC-G04 membrane was higher than that of the neat CC membrane, which indicated the occurrence of strong interaction between the CC and GO and resulted in improved thermostability in cellulose membranes. Hence, the TGA testing clearly showed that the CC-G04 membrane had enhanced the thermal stability compares to neat cellulose membrane.

12. X-ray diffraction of kenaf hydrogel

Figure 14 (a) to (f) shows the XRD diffraction patterns of all the cellulose hydrogels. The diffraction peaks at 2Θ = 14.9°, 16.3°, 22.6°and 34.5° can be assigned to cellulose crystal planes of (11 0), (1 1 0), (2 0 0) and (0 0 4), respectively. Figure 14 exhibited a shifted peak from cellulose I to cellulose II and therefore, proved the formation of cellulose II in cellulose hydrogel samples. 3. Transparency of kenaf hydrogel

The transparency of all the cellulose hydrogels is shown in figure15 (a) to (e). The light transmittance through KCP and CC hydrogels was measured by using an UV-vis spectrophotometer. The transmittances of ultraviolet and visible light of cellulose hydrogels were measured in wavelength range between 200 and 800 nm.

14. Morphology of regenerated kenaf hydrogel

Figure 16(a) depicts physical appearance of cellulose hydrogel. In comparison to cellulose membrane, the cellulose hydrogel, as shown in figure16 (a), was transparent, short cylinder and soft gel like. FESEM images of the cross section of the all cellulose hydrogel samples are shown in figure16 (b) to (f). All hydrogel samples had macro porous structure with bigger average pore size as the reaction time on cellulose increased. After carbamation process, the M_n of cellulose decreased and formed a less pack network, thus, this might cause the pore size of formed kenaf hydrogel to become bigger. This suggested that more water can be retained in the hydrogel at longer reaction time, leading to increase in the pores size. Conclusion

A method of preparing cellulose based material has been successfully performed by obtaining KCP, CC and metal oxide-graphene oxide nano composite cellulose membranes. The results have provided firm evident to prove the workability of this method, as a rapid dissolution method required only 10 mins to produce CCs from lignocellulosic biomass in presence of microwave irradiation. This method accelerates organic reactions with cellulose solvents and thus reduces reaction period from hours to minutes. Further, the method is inexpensive, efficient and environmental friendly. The cellulose membrane obtained from the proposed method has anti-bacterial properties. Also, the cellulose membrane technology has a great application in pharmaceutical or cosmetic industry, food preparations, building materials, varnishes, paints, coating compounds and polymers, drug delivery, optical media, bio membrane, separation, water treatment, adsorption and package. In addition, hydrogel has wide range of industrial applications such as hygienic products, drug delivery systems, cool dewatering, sealing, pharmaceuticals, food additives, separation of biomolecules or cells, tissue engineering and biomedical applications.

The exemplary implementation described above is illustrated with specific shapes, dimensions, and other characteristics, but the scope of the invention includes various other shapes, dimensions, and characteristics. Also, the method of preparing cellulose based materialas described above could be fabricated in various other ways and could include various other materials, including various other lignocellulosic biomasses, operating conditions, hydrogels, cross- linking agent etc. Similarly, the exemplary implementations described above include specific examples of lignocellulosic biomasses, operating conditions, hydrogels, cross- linking agent etc., but a wide variety of other such steps of fabrication could be used within the scope of the invention, including additional steps, omission of some steps, or performing process in a different order.

Various modifications to these embodiments are apparent to those skilled in the art from the description and the accompanying drawings. The principles associated with the various embodiments described herein may be applied to other embodiments. Therefore, the description is not intended to be limited to the embodiments shown along with the accompanying drawings but is to be providing broadest scope of consistent with the principles and the novel and inventive features disclosed or suggested herein. Accordingly, the invention is anticipated to hold on to all other such alternatives, modifications, and variations that fall within the scope of the present invention and appended claim.

Claims

Claims:

1. A method of preparing cellulose based material, comprising the steps of:

extracting cellulose from a lignocellulosic biomass by using a bleaching agent and an alkali solution to produce cellulose pulp;

drying said cellulose pulp;

preparing cellulose carbamate from said cellulose pulp,

pre-cooling a cellulose solvent at a first temperature;

dissolving said cellulose carbamate in said pre-cooled cellulose solvent to form a transparent cellulose solution,

casting said transparent cellulose solution on a casting plate; and immersing said casting plate in a coagulant until said transparent cellulose solution coagulates to form a cellulose membrane.

2. The method as claimed in claim 1 , further comprising the steps of: preparing a metal oxide-graphene oxide nano-composite

mixing said metal oxide-graphene oxide nano-composite into said transparent cellulose solution to form an interaction mixture;

coagulating said interaction mixture in said coagulant; and

regenerating a highly porous structure of a metal oxide-graphene oxide nano-composite cellulose membrane.

3. The method as claimed in claim 1 , further comprising the steps of: preparing a plurality of solid particulates;

adding said plurality of solid particulates into said transparent cellulose solution to form a cellulose solution mixture;

dispersing said cellulose solution mixture into said coagulant; and regenerating said cellulose solution mixture to form a plurality of cellulose beads.

4. The method as claimed in claim 1 , wherein said step of extracting cellulose comprising the steps of:

bleaching said lignocellulosic biomass by said bleaching agent to remove dissolved lignin;

treating said bleached lignocellulosic biomass with said alkali solution; and

washing said treated lignocellulosic biomass with distilled water to obtain said cellulose pulp.

5. The method as claimed in claim 1 , wherein said step of preparing cellulose carbamate comprising the steps of:

milling said lignocellulosic biomass to form said cellulose pulp;

immersing said cellulose pulp into a urea solution;

subjecting said mixture of cellulose pulp and said urea solution to microwave irradiation;

immersing said mixture of cellulose pulp and said urea solution in an ice bath to stop a reaction between said mixture of cellulose pulp and said urea solution and obtaining said cellulose carbamate;

subjecting said cellulose carbamate to centrifugation to remove excess urea;

vacuum-drying said cellulose carbamate.

6. The method as claimed in claim 5, wherein said cellulose carbamate is vacuum-dried at a temperature between 80°C to 100°C for 12 to 24 hours.

7. The method as claimed in claim 6, wherein said cellulose carbamate is vacuum-dried at a temperature of 80°C for 12 hours.

8. The method as claimed in claim 1 , wherein said alkali solution is 2% to 6% (w/v) NaOH solution.

9. The method as claimed in claim 8, wherein said alkali solution is 2% (w/v) NaOH solution.

10. The method as claimed in claim 1 , wherein said cellulose pulp is dried at a temperature of 105°C for 24 hours.

11. The method as claimed in claim 1 , wherein said cellulose solvent is selected from a group consisting of mixed aqueous sodium hydroxide (NaOH) and urea solution, a mixed aqueous lithium hydroxide and urea solution and any combinations thereof.

12. The method as claimed in claim 11 , wherein said mixed aqueous lithium hydroxide and urea solution; and water are mixed in a ratio of4.6:15.

13. The method as claimed in claim 1 , wherein said first temperature is in the range of -12°C to -15°C.

14. The method as claimed in claim 13, wherein said first temperature is -13°C.

15. The method as claimed in claim 1 , wherein said cellulose carbamate is dissolved in said pre-cooled cellulose solvent in an amount of 3% to 7% by weight for 5 mins.

16. The method as claimed in claim 11 , wherein said cellulose carbamate; mixed aqueous sodium hydroxide (NaOH) and urea solution; and water are mixed in a ratio of 7: 12:81.

17. The method as claimed in claim 1 , wherein said transparent cellulose solution is yellowish in color.

18. The method as claimed in claim 1 , wherein said casting plate is a glass plate.

19. The method as claimed in claim 1 , wherein said coagulant comprises an acidic solution.

20. The method as claimed in claim 19, wherein said acidic solution is dilute sulfuric acid (H₂S0₄).

21. The method as claimed in claim 20, wherein said dilute sulfuric acid (H₂S0₄) has a concentration of 0 to 12% (v/v).

22. The method as claimed in claim 1 , wherein said cellulose membrane is washed with distilled water and air dried at room temperature.

23. The method as claimed in claim 1 , wherein said cellulose membrane is washed with distilled water and dried in an IR dryer.

24. The method as claimed in claim 2, wherein said transparent cellulose solution is stirred vigorously at a temperature between -13°C to 5°C before mixing said metal oxide-graphene oxide nano-composite.

25. The method as claimed in claim 2, wherein said metal oxide-graphene oxide nano-composite is selected from a group consisting ofsilver-graphene oxide nano-composite, magnetite (Fe₃0₄), titanium dioxide (Ti0₂), silver nanoparticles and graphene oxide.

26. The method as claimed in claim 3, wherein said plurality of solid particulates are prepared by a chemical co-precipitation.

27. The method as claimed in claim 26, wherein said chemical is selected from a group consisting of ferrous, ferric chloride and alkali hydroxide.

28. The method as claimed in claim 27, wherein said alkali hydroxide comprises NaOH.

29. The method as claimed in claim 26, wherein said plurality of solid particulates are magnetite (Fe₃0₄) particles.

30. The method as claimed in claim 3, wherein said plurality of cellulose beads are selected from a group consisting of magnetic cellulose beads, silver-graphene oxide nano-composite, magnetite (Fe₃0₄), titanium dioxide (T1O2), silver nanoparticles and graphene oxide beads.

31. The method as claimed in claim 1 , wherein said lignocellulosic biomass is selected from a group consisting of kenaf core powder, kenaf pulp, cotton linter and oil palm pulp (EFB, OPT, frond).

32. The method as claimed in claim 1 , wherein said bleaching agent is sodium chlorite.

33. The method as claimed in claim 32, wherein said sodium chlorite has a concentration of 1.7 % (w/v).

34. The method as claimed in claim 4, wherein said step of bleaching is performed at a temperature between 70°C to 80°C for 2 to 6 hours.

35. The method as claimed in claim 34, wherein said step of bleaching is performed at a temperature of 80°C for 4hours.

36. The method as claimed in claim 4, wherein said step of treating said bleached lignocellulosic biomass with said alkali solution is performed at a temperature between 70°C to 80°C for 2 to 6 hours.

37. The method as claimed in claim 36, wherein said step of treating said bleached lignocellulosic biomass with said alkali solution is performed at a temperature of 80°C for 3 hours.

38. A method of preparing a hydrogel using said cellulose carbamate as claimed in claim 1 , comprising the steps of:

dissolving said cellulose carbamate in a mixed alkali and urea solution to form a mixture;

stirring said mixture to obtain a transparent cellulose solution;

subjecting said transparent cellulose solution to centrifugation;

adding a cross-linking agent to said transparent cellulose solution; and stirring said mixture of transparent cellulose solution and cross-linking agent to form said hydrogel.

39. The method as claimed in claim 38, wherein said mixed alkali and urea solution is NaOH solution.

40. The method as claimed in claim 38, wherein said mixed alkali and urea solution is LiOH solution.

41. The method as claimed in claim 38, wherein said transparent cellulose solution is centrifuged at 10,000 rpm for 5 mins at a temperature of 5°C.

42. The method as claimed in claim 38, wherein said cross-linking agent is Epichlorohydrin (ECH).