Title of Invention

A PROCESS FOR PREPARATION OF CELLULOSE FRACTIONS

Abstract

The invention relates to a process for preparation of cellulose fractions. In the process fractionation of cellulose into different molecular weight fractions is carried out by dissolving cellulose in lithium chloride/N,N-dimethyl acetamide solvent system and using water as a non solvent for regeneration of different molecular weight fractions and the different molecular weight fractions of cellulose.

Full Text

This invention relates to a process for preparation of cellulose fractions. This invention particularly relates to a process for fractionation of cellulose into different molecular weight fractions by dissolving cellulose in lithium chloride/N,N-dimethyl acetamide solvent system and using water as a non solvent for regeneration of different molecular weight fractions and the different molecular weight fractions of cellulose prepared thereby. Although cellulose is the most abundant renewable organic raw material in nature, the transformation of cellulose to many end use applications has been limited, mainly because of its unique physical properties and complex morphology. To get maximum conversibility of cellulose to different derivatives, the reactions are generally carried out in a homogeneous medium by dissolving cellulose in various solvent or solvent systems like cupriethylene diamine, cadoxene, SO3/dimethyl formamide, SO3/dimethyl sulfoxide, paraformaldehyde/dimethyl sulfoxide, lithium chloride/N,N-dimethyl acetamide, lithium chloride/N-methyl-2-pyrrolidinone etc. Again it is known that, the physical properties of a saynthesized polymer depend on the molecular weight of the polymer(s) used for synthesis. In case of cellulose, the average molecular weight varies from 10,000 to 2,00,000 and the characteristics of polymer obtained from cellulose vary according to the molecular weights of original cellulose taken for synthesis/derivatization of cellulose. Depending on the molecular weights, some properties of the prepared compounds such as solubility in solvents, plasticity, heat stability etc vary accordingly. The high molecular weight cellulose fractions can be used for producing cellulose acetates and such other cellulose esters, which can be employed for producing films and plastics having high strength and heat resistant properties. So also, cellulose ethers like hydroxy ethyl cellulose and that type of modified esters, with high viscosity can be produced for use in oil drilling operations where stability and viscosity are of prime requirements, It has therefore,become essential to fractionate cellulose into different fractions according to their molecular weights for synthesizing derivatives for different end uses. Numerous literatures are available on fractionation of cellulose. To quote a few, E. Sjoholm et al (E. Sjoholm, K. Gustavsson, J. Kolar, B. Pettersson; Chemistry & Technology of Bleaching, pp 246-250, August 31, 1994) described the molecular weight distribution of cellulose by size exclusion chromatography by dissolving hard wood kraft pulp in lithium chloride/N,N-dimethyl acetamide solvent system. M.J. Teodorovic (M.J. Teodorovic, Acta. Polym., 42, 9, 458-461, 1991) described the molecular weight distribution of an alkalized sample of regenerated cellulose which was determined by size exclusion chromatography using diluted cadoxene as the solvent. Similarly the paper by Kennedy and Rivera (J.F. Kennedy, Z.S. Rivera, Cellulose Chem. Technol., 24(3), 319-325, 1990) dealt with the molecular weight characterization of underivatized cellulose by gel permeation chromatography using lithium chloride/N,N-dimethyl acetamide as solvent system. The main drawbacks of the above technique of fractionation are that the processes can not be used for large scale separation of cellulose fractions. The most widely used methods for fractionation of polymers are (1) addition of a non-solvent to the solution of polymer, (2) elimination of solvent by evaporation and (3) by lowering the temperature of the system. These methods are popular because they are based upon very simple operations and donot require equipments. In addition they can be applied to small scale as well as large scale experiments. In the light of this, H. Sihtola et al (H. Sihtola, E. Kaila and L. Laamanen, J. Polym. Sci. 23, 809, 1957) fractionated cellulose dissolved in cupriethylene diamine using propanol as a precipitant. Jayme and Neuschaffer (G. Jayme and K. Neuschaffer, Makromol Chem., 23, 71, 1957) and Guzman et al (G.M. Guzman, E. Riande, J.M. Perena and A.G. Urena, Eur. Polym. J., 10, 537, 1974) described dissolution of cellulose in cadoxene and then fractionation by adopting regeneration technique. In the above known processes of dissolution, the cellulose chain degrades to certain extract. So, the molecular weights of various fractions of cellulose found after fractionation in fact, do not represent the actual molecular weights of original cellulose. Recently, lithium chloride/N,N-dimethyl acetamide was found to be a true solvent for dissolution of cellulose in which cellulose could be dissolved without any degradation (A. El-Kafrawy, J. Appl. Polym. Sci. 27, 2435, 1982). It is, therefore, needed to develop a suitable process for fractionation of cellulose into different molecular weight fractions by dissolving cellulose in a cellulose non-degrading solvent system like lithium chloride/N,N_dimethyl acetamide. The main objective of the present invention is therefore, to develop a new process for fraction of cellulose by dissolving cellulose in lithium chloride/N,N-dimethyl acetamide solvent system using water as a non solvent or precipitant. Another objective of this work is to fractionate the high molecular weight fractions by adding an experimentally known amount of water, which can be utilized for different end uses like preparation of cellulose esters fro highly thermo stable films and membranes. Accordingly, the present invention provides a process for preparation of cellulose fractions which comprises; preparing a solution of cellulose in NN-dimethyl acetamide in presence of lithium chloride, adding water to the above said solution, heating the solution upto 75°C followed by cooling to room temperature to give precipitate, separating the precipitated cellulose and filtrate by conventional method, adding water to the filtrate and repeating one time the sequence of heating cooling and separating the precipitated cellulose and to get different fractions of cellulose, drying the precipitated cellulose by conventional method. In an embodiment of the present invention, the cellulose used is obtained from different sources selected from bamboo, cotton linter and cotton. In another embodiment of the process, drying of filtered cellulose may be effected by conventional method such as in hot air ciruclating over. In yet another embodiment of the present invention, the precipitated cellulose may be separated by centrifugation, filtration. In still another embodiment of the invention, the cellulose solution may be prepared in N,N-dimethyl acetamide in presence of lithium chloride in the range of 2.5 to 7.5 g. The present invention, therefore, provides an improved process for fractionation of cellulose from dilute solutions of cellulose prepared in lithium chloride/N,N-dimethyl acetamide solvent system, by addition of cold distilled water, the process for which as a whole consists of the following steps. i. Preparation of dilute solution of cellulose in lithium chloride/N,N-dimethyl acetamide solvent system by adding cellulose to the solvent system and then following heating and cooling sequences ii. dropwise addition of non-solvent i.e. cold distilled water to the cellulose solution under vigorous stirring and then heating to certain degree of temperature and then cooling the system to room temperature iii. separation of the precipitated fraction of cellulose from the above system by centrifuging the contents in a centrifuge for certain duration of time iv. separation of the precipitated portions by decanting out from the centrifuge tube v. again, reprecipitation of the filtrate from step iv with addition of cold distilled water and then heating and cooling as in step ii and then repeating the centrifugation and decantation steps vi. further continuing the proces with the filtrate to isolate fractions of dissolved cellulose vii. drying of the filtered cellulose fractions in a hot air circulating oven. The present invention further provides a process for producing cellulose fractions of different molecular weights, which comprises the powdering of high purity pulp cellulose (92% α-cellulose and above) and dissolution in lithium chloride/N,N-dimethyl acetamide solvent system wherein 0.5-1.5 g of powdered cellulose which was passed through 50-70 BS sieve prefereably 60 BS sieve was added to 50-150 ml. of N,N-dimethyl acetamide preferably 1 g of powdered cellulose to 100 mi. of N,N-dimethyl acetamide taken in a round bottomed flask, fitted with a short path condenser. The flask was then heated to a temperature of 140-155°C, prefereably 150°C for about 15-30 minutes, preferably 26 minutes. Then 2.5-7.5 g of lithium chloride, preferably 5 g of lithium chloride was added to it and the system was again heated to 155-175°C, preferably 165°C for 5-10 minutes, preferably for 8 minutes which was then cooled to room temperature and stirred overnight for complete dissolution upon which to the 100 ml. of cold diluted cellulose solutions 5-10 ml., preferably 7 ml. of cold distilled water is added dropwise from a burette and the diluted cellulose solution was then heated to 50-75°C, preferably 60°C and then cooled to room temperature, when the precipitate appeaed which was then separated by centrifuge at a speed of 2000-3000 rpm, preferably at 2500 rom for 5-15 minutes, preferably for 10 minutes . The supernatent liquid part of the centrifuge tube was separated by decantation and then to the supernatent liquid separated, 1.5-3.0 ml, preferably 2.0 mL of cold distilled water was added and then heated to 60°C and then cooled, when precipitate appeared, which was then centrifuged as above to separate out the second fraction of cellulose. The supernatent liquid from this fraction, was then separated and the third fraction of cellulose was precipitated by adding just 0.2 mL of water. The third fraction was also separated by centrifugation. All the three fractions so collected were then added to cold distilled water separately and kept at low temperature for overnight, whereafter the fractions were filtered off and dried at 70-80°C, preferably at 75 °C in an air circulating electrical oven. The following example are given to illustrate the invention. The examples should not, however, be construed to limit the scope for this invention. Example - I Preparation of cellulose solution : cellulose (95% pureα-cellulose 1 g made from bamboo) N,N-dimethyl acetamide l00mL Lithium chloride 5 g 1 g of sieved cellulose (+100 British Standard, BS, sieve) was taken in a round bottomed flask, to which 100 mL N,N-dimethyl acetamide was added. The system was then heated to 150°C for 26 min. and afterwards 5 g lithium chloride was added to it. The temperature was then raised to 165°C and kept at that temperature for 8 min. The system was then cooled to room temperature (27°C) and stirring continued for 24 h for complete dissolution of cellulose. Fractionatton and separation of cellulose fractions : Cold distilled water was added to the cellulose solution by drops to the extent of 7 mL, when turbidity appeared in the solution. The system was then heated to 60°C followed by cooling to 25°C (Room temperature). The precipitate was separated by centrifuge with a speed of 2500 rpm for 10 minutes. The supernatent solution in the centrifuge tube was separated by decantation. The first fraction thus separated was then mixed with 100 mL cold distilled water and kept at low temperature for overnight. Then it was filtered and dried in an air circulating oven at 70°C till properly dried. The separated supernatent liquid was then taken and cold distilled water was added to it dropwise till 2 mL water was added, when again turbidity appeared. As before it was heated to 60°C and then cooled to 27°C and centrifuged with the same speed and time. The second fraction thus separated by decantation was then mixed with cold distilled water and kept at low temperature. Then it was filtered and dried in an air circulating oven at 70°C till properly dried. To the decanted solution, again 0.2 mL cold distilled water was added when precipitation occured. This solution was again centrifuged to recover the third fraction of cellulose. When desired fourth and fifth fractions could be also recovered to obtain fractions of low molecular weights. Example - II Preparation of cellulose solution : Cellulose (96.5% rayon grade cellulose - 1.5 g made from cotton linter) N,N-dimethyl acelamide - 150 mL Lithium chloride - 5.0 g 1.5 g of rayon grade pulp cellulose was sieved through 100 mesh sieve (B.S. sieve) to which 150 mL N,N-dimethyl acetamide was added. The system was then heated to 150°C to 26 min and afterwards 5.0 g lithium chloride was added to it. The temperature was then raised to 170°C and kept at that temperature for 10 min. The system was then cooled to room temperature (25-27°C) and stirring continued for 24 h for complete dissolution of cellulose. Fractionation and separation of cellulose fractions : 10 mL cold distilled water was added to the cellulose solution by drops, when turbidity appeared in the solution. The system was then heated to 60°C followed by cooling to 27°C (Room temperature). The precipitate was separately centrifuged with a speed of 2500 rpm for 10 min. The supematent solution was spearated by decantation. The solid in the centrifuge tube was then mixed with 100 mL of cold distilled water and kept overnight at low temperature in a refrigerator. Then, the portion was filtered in a Whatman 40 filter paper and dried in air circulating oven at 70°C till properly dried. The separated supernatent liquid was then taken and cold distilled water was added dropwise till 3 mL water was added, when again turbidity appeared. As above, it was heated to 60°C and then cooled to 27°C and centrifuged as before. The solid was separated and dried. To the supernatent liquid again water was added dropwise to the extent of 0.5 mL, when precipitate appeared. This solution was again centrifuged to recover the third fraction of cellulose. When desired, fourth and fifith fractions could be recovered to obtain fractions of low molecular weights. Example - III Preparation of cellulose solution : Cellulose (92% pure high alpha cellulose made from Kenaf) - 1 g N,N-dimethyl acetamide - 1 00 mL Lithium chloride - 5 g The procedure of cellulose dissolution and fraction action and separation of cellulose fractions are same as in example - 1. Determination of molecular weights of fractions : Degree of polymerization (DP) and hence, the molecular weights of different fractions recovered above were calculated viscometrically by nitrating the cellulose samples (H. Tsuji, Z. Osono and K. Ono; Bull. Univ. Osaka, Pref. Ser B, (16) 89, 1965) and the data are given below along with their yield. Example I (95% alphacelulose made from bamboo): (Table Removed) Following the above procedure developed, the yields, DP and Mw of the cellulose fractions in Example II and III were found out and are given below : Example - II Example - III (Table Removed) The main advantages and the distinguishing features of the present invention are : i. By adopting the present invention, the fraction can be carried out with reproducible results i.e. by adding the same amount of water as standardized. Fractions of cellulose having equal or nearly equal molecular weights can be obtained on repeatition, from the same source of cellulose. ii. The process in the present invention is easy, simple and less laborious without involvement of sophisticated instruments, iii. The raw materials and chemicals used in the present invention are easily available. We Claim: 1. A process for preparation of cellulose fractions which comprises; preparing a solution of cellulose in N N-dimethyl acetamide in presence of lithium chloride, adding water to the above said solution, heating the solution upto 75°C followed by cooling to room temperature to give precipitate, separating the precipitated cellulose and filtrate by conventional method, adding water to the filtrate and repeating one time the sequence of heating, cooling and separating the precipitated cellulose and to get different fractions of cellulose, drying the precipitated cellulose by conventional method. 2. A process as claimed in claim 1, wherein the cellulose used is obtained from different sources selected from bamboo, cotton linter and cotton. 3. A process as claimed in claims 1-2, wherein the precipitated cellulose is separated by centrifugation, filtration. 4. A process as claimed in claims 1-3, wherein the cellulose solution is prepared in NN- dimethyl acetamide in presence of lithium chloride in the range of 2.5 to 7.5 g. 5. A process for preparation of cellulose fractions substantially as herein described with reference to the examples accompanying this specification.

Documents:

115-del-2001-abstract.pdf

115-del-2001-claims.pdf

115-del-2001-correspondence-others.pdf

115-del-2001-correspondence-po.pdf

115-del-2001-description (complete).pdf

115-del-2001-form-1.pdf

115-del-2001-form-19.pdf

115-del-2001-form-2.pdf

115-del-2001-form-3.pdf