WO2002016478A1 - Cellulosic films and uses thereof - Google Patents

Cellulosic films and uses thereof Download PDF

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Publication number
WO2002016478A1
WO2002016478A1 PCT/EP2001/009744 EP0109744W WO0216478A1 WO 2002016478 A1 WO2002016478 A1 WO 2002016478A1 EP 0109744 W EP0109744 W EP 0109744W WO 0216478 A1 WO0216478 A1 WO 0216478A1
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WO
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Patent type
Prior art keywords
film according
film
preceding
equal
greater
Prior art date
Application number
PCT/EP2001/009744
Other languages
French (fr)
Inventor
Alan Smith
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Ucb, S.A.
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    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08JWORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G
    • C08J5/00Manufacture of articles or shaped materials containing macromolecular substances
    • C08J5/18Manufacture of films or sheets
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D61/00Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis, ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/002Forward osmosis, direct osmosis
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D71/00Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06Organic material
    • B01D71/08Polysaccharides
    • B01D71/10Cellulose; Modified cellulose
    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08BPOLYSACCHARIDES; DERIVATIVES THEREOF
    • C08B1/00Preparatory treatment of cellulose for making derivatives thereof, e.g. pre-treatment, pre-soaking, activation
    • C08B1/003Preparation of cellulose solutions, i.e. dopes, with different possible solvents, e.g. ionic liquids
    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08JWORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G
    • C08J2301/00Characterised by the use of cellulose, modified cellulose or cellulose derivatives
    • C08J2301/02Cellulose; Modified cellulose

Abstract

Self supporting cellulosic film produced by dissolving cellulose having a viscosity number as determined by the viscometric test SCAN-CM 15:88 of greater than or equal to about 400 in a solvent therefor to form a solution containing less than or equal to about 15% by weight of cellulose, and extruding the solution into a precipitation bath whereby the film is produced.. These films are useful in producing products with increased strength combined with increased porosity such as bags for rehydration by osmosis.

Description

CELLULOSIC FILMS AND USES THEREOF

The present invention concerns cellulosic films and their production, and it further concerns containers produced therefrom, for example for use in the purification of contaminated water - by osmosis.

The supply of microbiologically safe drinking water has been an ongoing problem in many parts of the world. Although osmotically driven rehydration has been scientifically known from the mid 1700's, many techniques have been used over the years to solve the problem of providing safe drinking water from contaminated water using osmosis.

Water purification devices in the form of osmotic bags have been proposed for use in humanitarian applications, amongst others. These bags, which include a cellulosic membrane, rely on the hydrophilic nature of cellulose to wet out sugars inside them. This in turn generates osmotic pressure allowing a flow of water to the inside of the bags, the pore size of the cellulose structure being sufficiently small to prevent bacteria and viruses entering the bags. It is therefore, possible to use such bags to generate clean water for a range of different medical, food and/or drinks products, from a contaminated water source. Such bags are, for example, described in EP0360612-A (Hampshire Technical Services).

In addition to being able to effect osmotic filtration, acceptable flux rates and/or hydration times are required for such bags. One proposal for overcoming this problem is to use a cellulose film with a relatively open structure, a secondary membrane coating with a less open structure being applied to the inside of the bag. The open structure of the cellulose film increases water transport across the cellulose membrane, whilst the coating prevents dialysis of sugars from the bag, thus maintaining osmotic pressure to increase the hydration rate of the contents of the bag. Typical hydration times are from 2 to 8 hours, depending on the particular application.

Prevention of sugar dialysis using a secondary membrane can also enable a solution to be obtained having a desired concentration of sugar when the contents of the bag have been hydrated, and it allows hydration to take place in any external volume of water. This is described more fully in WO 98/00034.

Prevention of dialysis of smaller salt molecules from the bags is also desired, and one proposal hitherto for overcoming this is to construct the bag in two sections with dry salts (or food, or milk powder) in an upper compartment which is protected by a waterproof coating which prevents wetting during hydration. After hydration, these bags are inverted, breaking a central "smart" seal, and the contents of the upper compartment can then be thoroughly mixed with the sugar solution in the lower compartment. This is described more fully in WO 98/41458.

An osmotic bag currently available commercially from UCB under the trademark Cellopore (TM) has been validated for exclusion of bacteria and viruses by Public Health Laboratories in the United Kingdom, and by the International Centre for Diarrhoeal Disease Research, Bangladesh (ICDDR,B). It has also been proven to meet the sugar and salt concentrations for Oral Rehydration Solutions set out by the World Health Organisation (WHO).

Nevertheless, there is a desire for improved osmotic bags, there being two factors where improved performance might be achieved, namely increased flux rates (porosity), to reduce fill time, and increased strength, to prevent damage in transit and use. Other features such as any of those described herein may also be used as well as or instead of these factors to provide improved films and bags made therefrom.

The current osmotic bags produced by UCB, S.A. referred to above are made from cellulose film produced by the conventional viscose process. Whilst such films perform satisfactorily when used to construct these bags, bags with enhanced properties, preferably providing new or improved solutions to one or more of the problems described herein, require cellulosic films with different properties.

According to the present invention there is provided a self supporting cellulosic film produced by dissolving cellulose having a viscosity number of greater than or equal to about 400 in a solvent therefor to form a solution containing less than or equal to about 15% by weight of cellulose, and extruding the solution into a precipitation bath whereby the film is produced.

The invention further provides osmotic bags produced using self supporting cellulosic films produced in accordance with the present invention.

The viscosity number of the cellulose used to produce films of the present invention is preferably greater than or equal to about 500, more preferably greater than or equal to about 600, especially greater than or equal to about 800 and more especially greater than or equal to about 1000. As used herein, viscosity number refers to the mean degree of polymerisation of the cellulose as determined by the viscometric test SCAN-CM 15:88. The solution of cellulose in a solvent which is extruded into the precipitation bath preferably contains less than or equal to about 10% w/w of cellulose, and more preferably less than or equal to about 6% w/w of cellulose.

The solvent used to dissolve the cellulose is preferably an amine N-oxide, and more preferably an N-alkyl cyclic N-oxide, for example N-methyl-morphline-N-oxide (subsequently referred to herein as NMMO). Numerous processes for forming solutions of cellulose in NMMO are described in the patent literature.

The precipitation bath is preferably at a temperature of from 20 to 80°C, and more preferably from 50 to 80°C.

When a tertiary amine oxide is used as the solvent for the cellulose, the precipitation bath preferably contains from 20 to 50% w/w of a tertiary amine oxide.

Films produced in accordance with the present invention will usually have an average thickness of up to about 2 mm.

Films in accordance with the present invention can be produced with a pressure flux (PF) of greater than or equal to about 8.0 l/m2/hr, this being measured as the volume of water passing through a supported sample of film with which the water is in contact when a pressure of 5.5 bar is applied to the water. The PF is more preferably greater than or equal to about 10.0 l/m2/hr.

Films in accordance with the present invention preferably have a tensile index measured in the transverse direction (TI-TD) of greater than or equal to about 40 kPa, and more preferably greater than or equal to about 70 kPa.

Films in accordance with the present invention can be made having a permeability with a molecular weight cut off such that micro-organisms are substantially prevented from passing through them.

The present invention still further provides articles, components thereof and/or consumables therefor, made from films of the present invention. Examples of such articles, components thereof and/or consumables therefor include containers for the supply of aqueous media by osmotic rehydration; devices suitable for dialysis; and film panels. Articles, components thereof and/or consumables therefor in accordance with the present invention can be produced by incorporating films of the invention into the structure of an article, component thereof and/or consumable thereof in a suitable manner so the film can act effectively (optionally as a semi-permeable membrane) in situ.

The invention yet further provides for the use of a film in accordance with the present invention in the manufacture of articles, components thereof and/or consumables therefor which are in accordance with the present invention. Such uses include improving the osmotic flux rate and/or porosity (and hence reduce fill time) of an article, component thereof and/or consumable therefor which otherwise has a particular tensile strength. A particularly preferred use of films in accordance with the present invention is in an osmotically rehydratable container.

This can result in reduced damage in transit and/or use of articles, components thereof and/or consumables therefor having a given osmotic flux rate and/or porosity.

It is believed that cellulosic films produced in accordance with the present invention are in general inherently stronger than prior art films, such as those produced by known methods for preparing cellulose film (such as conventional viscose and standard NMMO processes), this being combined with improved porosities. The result is films having particular use as semi-permeable membranes, for example in osmotic bags. Furthermore, a balance of strength and porosity characteristics can be achieved over a much wider range with films of the invention compared with prior art films, for example those produced by a conventional viscose process.

Films of the present invention are produced by extruding solutions of the required concentration of cellulose in a suitable solvent through a slot die into a suitable regeneration bath where the cellulose film is produced. If desired, a gas can be blown on to the extrudate before it enters the regeneration bath, for example air, ethanol, i-propanol, or acetic acid. If desired, the films produced can be subjected to stretching across the width of the films, that is in the transverse direction (TD) to the direction of extrusion, for example as described in WO 98/49224.

Films in accordance with the present invention prepared using the method described in WO 98/49224 but with the cellulose having a viscosity number of 450 or more, and the solution of cellulose in NMMO containing not more than 15% by weight of cellulose, had strengths and porosities which made them particularly suitable for the production of osmotic bags although their particularly good porosities combined with high tensile strengths also made them suitable for other end uses.

Increasing the temperature of the precipitation bath in steps of 10°C from 20°C to 80°C resulted in increases in the porosity of the films.

Changes in the NMMO concentration in the precipitation bath from 20% to 40% w/w led to increases in the porosity of the films produced. Changes in the temperature of the bath in general had a greater effect on the strength and porosities of the films than mere changes in NMMO concentrations in the bath.

Films in accordance with the present invention can be treated with a softener, for example after washing.

Increasing the DP of the cellulose and/or reducing the concentration of the cellulose in the NMMO with the precipitation bath maintained at a temperature of 25°C resulted in an increase in pressure flux.

The TD tensile strengths of the films were similar to or higher than those of known viscose films, and the MD strengths of some films of the present invention were at least double those of known viscose films.

Stretching of the regenerated cellulose films in the precipitation bath can increase the TD tensile strength of the films significantly compared with analogous viscose films whilst substantially maintaining or even improving their MD strengths.

Claims

1. A self supporting cellulosic film obtainable by dissolving cellulose having a viscosity number of greater than or equal to about 400 in a solvent therefor to form a solution containing less than or equal to about 15% by weight of cellulose, and extruding the solution into a precipitation bath whereby the film is produced.
2. A film according to claim 1 , in which the viscosity number is greater than or equal to about 500.
3. A film according to either claim 1 or 2, in which the viscosity number is greater than or equal to about 600.
4. A film according to any of the preceding claims, in which the viscosity number is greater than or equal to about 800.
5. A film according to any of the preceding claims, in which the viscosity number is greater than or equal to about 1000.
6. A film according to any of the preceding claims, in which the solution contains less than or equal to about 10% by weight of cellulose.
7. A film according to any of the preceding claims, in which the solution contains less than or equal to about 6% by weight of cellulose.
8. A film according to any of the preceding claims, in which the solvent comprises an aqueous tertiary amine oxide.
9. A film according to claim 8, in which the tertiary amine oxide comprises N-methyl- morpholine-N-oxide.
10. A film according to any of the preceding claims, in which the temperature of the precipitation bath is from 20 to 80°C.
11. A film according to claim 10, in which the temperature of the precipitation bath is from 50 to 80°C.
12. A film according to any of the preceding claims, in which the precipitation bath contains from 20 to 50% w/w of a tertiary amine oxide.
13. A film according to any of the preceding claims, in which an air gap exists between the solution as it is extruded and the bath in which the cellulose is precipitated.
14. A film according to claim 13, in which a fluid is blown into the air gap.
15. A film according to claim 14, in which the fluid comprises air, ethanol, i-propanol or acetic acid.
16. A film according to any of the preceding claims, which has been stretched transversely to the direction of extrusion after entering the precipitation bath.
17. A film according to any of the preceding claims, which has an average thickness of up to about 2 mm.
18. A film according to any of the preceding claims, having a pressure flux (PF) of greater than or equal to about 8.0 l/m2/hr.
19. A film according to any of the preceding claims, having a PF of greater than or equal to about 10.0 l/m2/hr.
20. A film according to any of the preceding claims, having a tensile index measured in the transverse direction (TI-TD) of greater than or equal to about 40 kPa.
21. A film according to any of the preceding claims, having a TI-TD of greater than or equal to about 70 kPa.
22. A film according to any of the preceding claims, which has a selective permeability with a molecular weight cut off such that micro-organisms are substantially prevented from crossing the film.
23. An article, component thereof and/or consumable therefor, which comprises a film as claimed in any of the preceding claims.
24. An article, component thereof and/or consumable therefor, as claimed in claim 23, in which the article is selected from at least one of the group consisting of:
(a) a container for the supply of aqueous media by osmotic rehydration;
(b) a device suitable for dialysis; and
(c) a film panel
25. A method of preparing an article, component thereof and/or consumable therefor as claimed in either claim 23 or claim 24, comprising the steps of:
(a) preparing a film as claimed in any of claims 1 to 22; and
(b) incorporating the film into the structure of the article, component thereof and/or consumable thereof in a suitable manner so the film can act effectively (optionally as a semi-permeable membrane) ]n situ.
26. Use of a film as claimed in any of claims 1 to 22, in the manufacture of an article, component thereof and/or consumable therefor as claimed in either claim 23 or 24.
27. Use of a film as claimed in any of claims 1 to 22, for the purpose of improving the osmotic flux rate and/or porosity (and hence reduce fill time) for an article, component thereof and/or consumable therefor as claimed in either claim 23 or 24 having a given tensile strength.
28. Use of a film as claimed in either of claims 25 to 26, for the purpose of improving the tensile strength (and hence reduce damage in transit and/or use) for an article, component thereof and/or consumable therefor as claimed in either claim 23 or 24 having a given osmotic flux rate and/or porosity.
29. Use of a film according to any of claims 1 to 22, in an osmotically rehydratable container.
PCT/EP2001/009744 2000-08-24 2001-08-23 Cellulosic films and uses thereof WO2002016478A1 (en)

Priority Applications (2)

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GB0020852A GB0020852D0 (en) 2000-08-24 2000-08-24 Cellulosic films and uses thereof
GB0020852.0 2000-08-24

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AU1215202A AU1215202A (en) 2000-08-24 2001-08-23 Cellulosic films and uses thereof

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4173613A (en) * 1976-07-16 1979-11-06 Rhone-Poulenc-Textile Process for producing cellulosic shaped articles
WO1998049223A1 (en) * 1997-04-25 1998-11-05 Lenzing Aktiengesellschaft Method for producing cellulose shaped bodies
EP0930016A1 (en) * 1998-01-20 1999-07-21 Viskase Corporation Method and apparatus for forming a cellulose article including solvent recovery means
US6019925A (en) * 1996-05-15 2000-02-01 Akzo Nobel Nv Method of making cellulosic dialysis membrane

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4173613A (en) * 1976-07-16 1979-11-06 Rhone-Poulenc-Textile Process for producing cellulosic shaped articles
US6019925A (en) * 1996-05-15 2000-02-01 Akzo Nobel Nv Method of making cellulosic dialysis membrane
WO1998049223A1 (en) * 1997-04-25 1998-11-05 Lenzing Aktiengesellschaft Method for producing cellulose shaped bodies
EP0930016A1 (en) * 1998-01-20 1999-07-21 Viskase Corporation Method and apparatus for forming a cellulose article including solvent recovery means

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