Field of the invention

This invention relates to the production of cellulosic polymer materials from cellulose and in particular to the treatment of cellulose to increase its solubility in various solvents and to increase its rate of reaction in esterification reactions . The invention also relates to cellulosic polyrrler solutions prepared from the treated cellulose and to uses of the solutions .

Cellulose is an abundant natural raw material and is widely used in the production of fibres and films . Cellulose is generally regarded as an insoluble material, being soluble only in esoteric solvents such as tertiary amine N-oxides. There is a demand for solutions of cellulose polymer materials in more easily handled solvents .

Background art

The usual process for making cellulosic fibres and films is the viscose process in which cellulose is treated with aqueous alkali to form alkali cellulose and then reacted with carbon disulphide to form a solution of alkali cellulose xanthate, which is extruded into an acidic bath to regenerate the cellulose in its extruded shaped form.

Cellulose esters, produced by the esterification of the hydroxyl groups in the cellulose molecule, are widely used in industry, particularly in the production of fibres, films, coatings and moulded articles. Cellulose acetate, for example, is dry spun to form fibres and cast from solution to form film, and it is used as a thermoplastic moulding material. Cellulose nitrate and cellulose acetate butyrate are used in coatings and lacquers .

The hydroxyl groups of cellulose can also be etherified . Cellulose can for example be reacted with monochloroacetic acid or a salt thereof in an aqueous alkaline solution to produce carboxymethyl cellulose. GB-A- 2094802, for example, describes such a process using an aqueous ethanolic solution to prepare fibrous carboxymethyl cellulose. That reference includes a comparative experiment carried out in the absence of ethanol in which the degree of carboxymethyl substitution achieved is 0.03-0.04 carboxymethyl group per anhydroglucose unit; this is not regarded as a

useful result, since the reference seeks to achieve a higher degree of substitution. GB-A-2220881 and US-A-4579943 also describe carboxymethyl cellulose fibres for use as absorbent materials .

GB -A- 1224390 describes a method of producing aluminium carboxymethyl cellulose from a water-soluble alkali metal carboxymethyl cellulose of degree of substitution 0.4 to 0.9. The aluminium carboxymethyl cellulose is practically insoluble in water but is soluble in aqueous alkali.

JP-A- 1-207457 describes a disposable hygienic sheet containing more than 30 wt% alkali-soluble carboxymethyl cellulose fibre with a degree of substitution 0.25 to 0.4. The fibre can be put into a flush toilet with alkali solution and flushed without blocking the drain.

Disclosure of the Invention

In a process according to the invention for the preparation of a cellulosic polymer solution, cellulose is reacted with a carboxymethylating agent to form a Ughtly carboxymethylated cellulose having a degree of substitution such that it is not soluble in water, and the lightly carboxymethylated cellulose is dissolved in a solvent .

According to another aspect of the invention a process for the preparation of a cellulose ester by reacting cellulose with an esterifying agent is characterised in that the cellulose is first reacted with a carboxymethylating agent to form a lightly carboxymethylated cellulose , and the Ughtly carboxymethylated ceUulose is reacted with an esterifying agent to form a cellulose ester.

The cellulose starting material is usually wood pulp , although other cellulosic raw material can be used . The pulp can be any of the types used in the ceUulosic fibre or ceUulose acetate industry, for example sulphite pulp or sulphate pulp such as that sold as "dissolving pulp" to the viscose rayon industry or kraft pulp, including prehydrolysed kraft pulp, thermomechanical pulp or cotton linters . The pulp can for example be "high viscosity" pulp or normal or "low viscosity" pulp . It can for examaple comprise ceUulose of average degree of polymerisation about 700 to 1000 or ceUulose of average degree of polymerisation about 300 to 700. The pulp can

be treated in the form of compressed pulp sheets or in the form of flock.

The carboxymethylating agent preferably comprises monochloroacetic acid or a salt thereof used in conjunction with a strong alkaU, that is an alkaU whose IN solution has a pH above 13. The alkah and the monochloroacetic reagent are preferably appUed from aqueous solution . The strong alkaU is preferably an alkaU metal hydroxide such as sodium hydroxide or potassium hydroxide . The monochloroacetic acid is preferably used in salt form, usuaUy the salt corresponding to the alkaU used, for example sodium monochloroacetate with sodium hydroxide. The alkaU and monochloroacetate salt may be used in approximately equimolar amounts, for example at a molar ratio of 0.8 : 1 to 1.2 : 1. For sodium hydroxide and sodium monochloroacetate this corresponds to a weight ratio of 1 : 1.3 to 1 :3.5. Alternatively, the alkaU can be used in molar excess, for example at a molar ratio of alkaU to monochloroacetate salt of up to 6 : 1 , preferably up to 4 : 1 , for example about 3 : 1 , particularly if the Ughtly carboxymethylated ceUulose is to be dissolved in or reacted with an alkaline solution . If monochloroacetic acid is used, the molar ratio of alkaU to monochloroacetic acid is preferably at least 2:1.

The alkaU and the monochloroacetic acid or its salt are preferably appUed to the ceUulose simultaneously. They can alternatively be appUed sequentially, in which case it is preferred but not essential that the alkaU is appUed to the ceUulose first followed by appUcation of the monochloroacetic reagent .

Various procedures can be used for applying the alkaU and monochloroacetic reagents to the ceUulose . The ceUulose can for example be immersed as a slurry in a solution of the reagents. The concentration of reagents in the solution is preferably in the range 5 to 50%, for example 10 to 35%, by weight. This is the total concentration of the alkaU and the monochloroacetic reagent; for example a 25% by weight reagent solution may contain 12.5% by weight sodium hydroxide and 12.5% by weight sodium monochloroacetate or alternatively 7% by weight sodium hydroxide and 18% by weight sodium monochloroacetate . The concentration of ceUulose in the slurry is preferably at least 1%, most preferably at least 3 or 5%, by weight measured as dry pulp . It is preferred that there is sufficient Uquid to form a slurry rather than a mass of wet wood pulp; the concentration of wood

pulp in the slurry is usually below 25%, preferably below 20%, measured by weight of dry pulp, for example a slurry containing 7 to 15% by weight of dry pulp . The pulp is preferably wetted with water, for example at a weight ratio of dry wood pulp to water of 1 : 1 to 1 :3, before contact with the carboxymethylating agent. The slurry is preferably agitated whUe in contact with the carboxymethylating agent.

The pulp is preferably mixed with both carboxymethylating reagents to form a slurry at low temperature, which is usually below 25 °C and preferably below 10°C and may be 0°C or below, for example -10°C, so long as it is above the freezing temperature of the solution. The temperature of mixing is most preferably in the range -2°C to 5°C, for example 2°C. The slurry is then preferably filtered, preferably under pressure, and pulp wet with the solution of carboxymethylating reagents is recovered . The ratio of dry wood pulp to Uquid in the pulp after filtering is preferably 1 : 1.5 to 1 :3 by weight, and the carboxymethylating reagents can for example be present at a total concentration of 12 to 60% by weight based on wood pulp soUds, for example 15% by weight sodium hydroxide and 15% by weight sodium monochloroacetate. This pulp wet with reagent solution can be heated, for example at a temperature of 80-120°C, by passage through an oven or a bed of pulp on a conveyor. Heating generally dries the pulp as weU as causing the carboxymethylation reaction.

We have found that the appUcation of pressure to the slurry of wood pulp in reagent solution, for example the use of a pressing step when contacting the pulp with the carboxymethylating agent and /or when filtering the slurry, can produce a treated pulp of superior properties in terms of dissolving completely in a solvent. AppUcation of pressure is thus preferred, although not essential, when complete dissolution of the Ughtly carboxymethylated wood pulp is required . The degree of pressure appUed can, for example, be that typicaUy used in a filter press, in which a pressure of 1 to 2 tonnes is appUed in a 12.5 cm diameter press, or it can be higher; pressures up to 10 times this level, for example 10 tonnes in a 12.5 cm diameter filter press, can give improved solution properties. It is beUeved that the appUcation of pressure may cause more thorough penetration of the reagents into the pulp and hence more uniform carboxymethylation of the wood pulp throughout the pulp fibres rather than merely at the surface of the pulp fibres . Increased pressure squeezes more

reagent solution out of the pulp slurry, so that the ratio of reagents to pulp is reduced during the treating step in which the carboxymethylation reaction takes place. This may cause a sUght reduction in the overaU degree of carboxymethylation of the ceUulose of the pulp but the carboxymethylated pulp nevertheless dissolves subsequently to form a more uniform solution.

The reagent solution pressed out from the slurry can be recirculated to treat a fresh batch of wood pulp. It is preferably kept cold (below 20° C, preferably below 5°C and most preferably 0 to 2°C or even colder) to prevent any reaction between the alkaU and the monochloroacetatic reagent .

The pulp wet with carboxymethylating agent which is separated from the slurry is preferably heated to aUow the carboxymethylation reaction to take place . The pulp is for example heated to a temperature of at least 50°C and preferably at least 80°C up to the boiling point of the solution, for example up to 120°C. The time of heating can, for example, be about an hour at 50°C or at least 1 minute and preferably 2 to 10 minutes at 100°C.

In an alternative procedure to slurrying the pulp in water, sheets of cellulose pulp can be steeped in a solution of the carboxymethylating agent. The sheets are preferably heated at 50-100°C in a subsequent process step.

As an alternative to heating the pulp after separation from the slurry or steeping solution, the pulp can be heated whilst it is in contact with the solution of carboxymethylating agent, for example in the form of a slurry or sheets steeped in the solution. The temperatures and times of heating are generally as stated above. This process is less preferred because side reactions can take place between the alkaU and the monochloroacetic reagent at elevated temperatures, so that recirculation or reuse of the carboxymethylating agent solution is made more difficult .

For many end uses it is preferred that any excess carboxymethylating agent is washed from the treated pulp, for example by water washing. The washing takes place after the heating step .

In an alternative process, the carboxymethylation reaction can be carried out in an alcohol as solvent. Ethanol is the preferred alcohol, for example in the form of industrial methylated spirits . Wet wood pulp of soUds

content 25 to 50% by weight is preferably treated with an alcohoUc solution of sodium hydroxide and sodium monochloroacetate, for example a solution containing 10 to 30% by weight of each reagent. The reaction in alcohol is preferably carried out at 45 to 75°C for 0.5 to 6 hours, for example at 60°C for 2 hours . The Ughtly carboxymethylated cellulose produced is separated from the alcohoUc reagent solution after the reaction and is preferably washed with water to remove the alcohol. If the pulp fibres of the Ughtly carboxymethylated cellulose are wet with alcohol rather than water, they may not dissolve in an aqueous alkaUne solvent.

The conditions of carboxymethylation are generally such as to produce a Ughtly carboxymethylated ceUulose which is not soluble in water, that is it has a degree of substitution (D. S . ) of less than about 0.4 carboxymethyl group per anhydroglucose unit. The preferred degree of substitution for most uses is generaUy much less than this, for example 0.25 or less, most preferably 0.20 or below. The degree of substitution is generaUy at least 0.02 and preferably at least 0.04 to achieve a significant increase in solubiUty and reactivity of the ceUulose. For many uses a degree of substitution of from 0.07 up to 0.15 is most suitable . For uses in which high absorbency in the end product is desirable, a higher degree of substitution may be preferred, for example up to 0.30, most preferably 0.15 to 0.25.

The Ughtly carboxymethylated cellulose is soluble in a wider range of solvents than ceUulose itself.

According to one aspect of the invention, a solution of a ceUulosic polymer in a solvent is characterised in that the ceUulosic polymer is a Ughtly carboxymethylated ceUulose having a degree of substitution such that it is not soluble in water and the solvent is not a solvent for ceUulose .

Aqueous alkaU is one example of a type of solvent which is a solvent for the Ughtly carboxymethylated cellulose but is not a solvent for ceUulose . The aqueous alkaU can for example be a solution of sodium hydroxide, potassium hydroxide, Uthium hydroxide, ammonium hydroxide or a substituted ammonium hydroxide, for example a quaternary ammonium hydroxide such as tetramethylammonium hydroxide. The concentration of the alkaU is generaUy in the range 0.5N to ION, preferably 1.5N to 5N. One preferred solvent is an aqueous solution of sodium hydroxide of

concentration at least 5% by weight, preferably at least 7%, up to 20%, preferably up to 15%, by weight. Lightly carboxymethylated cellulose wiU dissolve in such solutions at concentrations of up to 12% by weight or even up to 15% or 16% by weight. Higher concentrations of sodium hydroxide can be used but may tend to degrade the cellulose, leading to a reduction in mechanical properties . The solvent can alternatively be a solution of an alkaU metal alkoxide .

The D . S . of the Ughtly carboxymethylated ceUulose dissolved in aqueous alkaU is preferably up to 0.15 for most uses, for example for forming shaped articles such as fibres or film or for coating. At a D . S. greater than 0.15 the solution tends to form two layers, of which the upper layer contains more highly carboxymethylated cellulose and the lower layer less highly carboxymethylated ceUulose.

The Ughtly carboxymethylated cellulose and the aqueous alkaU or other solvent are preferably agitated as they are mixed together to disperse the carboxymethylated cellulose fibres . Mixing can for example be carried out by a turbine mixer or other high- shear mixer, in a screw extruder, preferably a twin-screw extruder, in a ploughshare mixer or in a thin-film evaporator such as that sold under the trademark "Filmtruder" . Mixing is preferably carried out at low temperature, generally at a temperature above the freezing point of the solvent but below 30°C and preferably below 20°C, for example in the range -15° C to +10° C . Mixing may be carried out in two zones at different temperatures, for example a first mixing zone at above 0°C such as 10 to 20°C and a second zone at below 0°C such as -10 to -5°C. Mixing may be carried out in two different types of mixer used successively, for example initial mixing in a high- shear mixer may be foUowed by mixing in a screw extruder. Mixing of the Ughtly carboxymethylated cellulose and aqueous alkaU initially forms a homogeneous slurry containing ceUulose fibres . Further mixing, particularly at low temperature, causes the fibres to swell and break down, forming a substantially uniform solution.

The concentration of Ughtly carboxymethylated ceUulose in solution in aqueous alkaU is preferably in the range 0.5% or 1% up to 15% or 16% by weight. Lower concentrations within this range generally form fluid solutions for uses such as coatings . Higher concentrations, such as those above 6% by weight and particularly those above 8 or 10% by weight, form

highly viscous solutions , which retain their shape on extrusion and can be used to make shaped articles such as fibres or films . The concentration of alkaU in the aqueous solution is preferably in the range 2 to 15% by weight. In general, we have found it difficult to dissolve any substantial amount of Ughtly carboxymethylated ceUulose (particularly that having a D. S. of 0.1 or less) in aqueous alkaU having a concentration of less than 5% by weight alkaU . However , more concentrated solutions can be diluted without causing precipitation of the cellulosic material from solution . If solutions having a low concentration of alkaU such as 2.5 to 5% by weight are required, for example as coating solutions , they can conveniently be formed by dissolving the Ughtly carboxymethylated ceUulose in a more concentrated alkaline solution followed by dilution with water. For example, a solution of 6 to 8% by weight Ughtly carboxymethylated cellulose in 10% by weight aqueous sodium hydroxide can be dUuted with one to three times its volume of water to form a solution containing 1.5 to 4% by weight Ughtly carboxymethylated ceUulose and 2.5 to 5% by weight sodium hydroxide . On the other hand, the most convenient way of producing a solution containing a high proportion of Ughtly carboxymethyl ceUulose, which solution is highly viscous, may be to prepare a solution of lower concentration and then carry out mixing whilst removing water from the solution, for example in a thin-film evaporator such as a "FUmtruder" . By this means, solutions initially containing 8 to 10% by weight Ughtly carboxymethylated ceUulose can be concentrated to 11 to 14% by weight or even higher.

The solution of Ughtly carboxymethylated ceUulose in alkaU is useful as a coating composition. It is particularly useful as a coating for paper and can also be used as a coating, impregnating or bonding agent for non- woven or woven fabrics or as a coating for plastic film, masonry or leather. The concentration of the ceUulosic polymer in the solution is preferably at least

0.5% by weight and up to 10% by weight; for example solutions of ceUulosic polymer concentration 1 to 6% by weight have been successfuUy used to coat paper. The ceUulosic polymer solution can be appUed to the final sheet of paper, but since the coating generally needs to be dried the ceUulosic polymer solution is preferably appUed to the paper before the final drying step of the paper. In the production of paper, pulp fibres are wet laid on a foraminous belt to form a sheet which is compacted and dried, initially by dewatering through the foraminous belt and subsequently by heated roUs .

The cellulosic polymer solution can be appUed to the paper at any stage in

the process after the pulp fibres have been laid on the belt . Treatment with the cellulosic polymer solution strengthens the paper; maximum strengthening may be achieved if the cellulosic polymer solution is appUed at a relatively early stage during drying and compacting of the paper sheet, before the sheet has been fully dried. In particular, maximum wet strength of the paper (almost equal to its dry strength) is achieved if the paper undergoes a heating step at above 100°C after appUcation of the cellulosic polymer coating solutio . This heating can conveniently be that carried out by the heated rolls used in the paper drying process, which generaUy are at a temperature of over 140°C, for example 160°C . Treatment with the cellulosic polymer solution also improves the surface smoothness of the paper; for maximum smoothness the ceUulosic polymer solution is preferably appUed at a relatively late stage in the drying of the paper sheet. If desired, the paper sheet can be coated with ceUulosic polymer solution at more than one stage during its manufacture, in which case ceUulosic polymer solutions of the same or different concentration can be used. For example, a Ught initial coating can be appUed to stabiUse the paper foUowed after drying by a heavier coating, which may for example be appUed from a more concentrated solution, to give the desired smooth surface, for example for food wrapping. It is generaUy preferred to treat the coated paper sheet briefly with an acidic material, for example a dUute aqueous acid such as 1 to 50% by weight aqueous sulphuric acid, to neutraUse the excess alkaU in the cellulosic polymer solution. Such an acid washing step is preferably carried out immediately after drying and is a brief surface washing to neutraUse the alkaU, forming a water-soluble alkaU metal salt which is washed away, leaving the Ughtly carboxymethylated ceUulose deposited on the paper surface. Paper coated with a solution of cellulosic polymer in alkaU according to the invention is particularly suitable for use in food wrapping and for other wrapping uses. The solution of Ughtly carboxymethylated ceUulose in alkaU can replace the viscose (ceUulose xanthate solution in alkaU) currently used for coating paper for such uses, for example as described on page 171 of "Sausage Casing Technology" by E. Karmas, pubUshed by Noyes, 1974, with the advantage that handling and recovering of carbon disulphide can be avoided . Paper for filtration can also be improved by coating with such a solution .

Thus , according to a further aspect the invention is directed towards paper having at its outer surface a layer of non-fibrous Ughtly

carboxymethylated cellulose having a degree of substitution of 0.02 to 0.15 carboxymethyl group per anhydroglucose unit .

The solution of Ughtly carboxymethylated cellulose in alkaU can be appUed to fabrics as an antistatic coating. The fabric can be a woven, knitted or non-woven fabric and may be formed from natural, e. g. cotton, man-made, e. g. regenerated cellulose or cellulose acetate, or synthetic, e. g. nylon, polyester, polyolefin or acryUc, fibres . After treatment with the cellulosic solution in alkaU the fabric is preferably treated with an aqueous acidic solution, for example a bath of 1 to 20% by weight aqueous sulphuric acid , to neutraUse the alkaline solution on the fabric and to ensure that the Ughtly carboxymethylated cellulose is deposited from solution onto the fabric. The fabric is preferably subsequently water washed to neutraUty. The cellulosic solution can for example be appUed to stockings and tights to reduce static discharge or it can be coated on upholstery, laboratory coats and other fabrics used in clean rooms or computer rooms or locations where a spark of static electricity is a fire hazard . It can also be used to coat staple fibre fabrics, for example cotton or rayon fabrics, to give a fabric which wUl not shed lint, for medical uses such as use in operating theatres . The concentration of Ughtly carboxymethylated cellulose in the solution used is preferably 4 to 9% by weight if forming a coating to remain on the surface of the fabric or 1.6 to 6% by weight when impregnating the fabric.

The ceUulosic polymer solution can also be used as a bonding agent for nonwoven fabric . Many nonwoven fabrics are formed by dry-laying fibres as a web on a support and applying a bonding agent to increase the strength and coherence of the fibrous web . The fibres can for example be deposited from air suspension as a random web or can be in the form of a carded web or continuous tow which is cross-lapped . The ceUulosic polymer solution can be appUed to the dry web by spray or Uck roller and acts as an effective bonding agent for the fibres . The bonded fabric is preferably treated with an aqueous acidic solution to neutraUse the alkaUne solution before drying the treated web . The concentration of the ceUulosic polymer solution is preferably 1 to 8% by weight, with lower concentrations in this range being preferred if uniform penetration of the bonding agent through the fabric is desired. A relatively viscous solution within the above concentration range can be appUed to one surface if non-uniform distribution of bonding agent

is required; a nonwoven fabric which is to be embossed by a heated patterned roll can for example have a higher concentration of bonding agent at the surface which is to contact the embossing roU. Alternatively, a nonwoven fabric having an even distribution of the cellulosic polymer solution can be embossed . Any type of fibres can be used in the nonwoven fabric, for example any of the natural, man-made or synthetic fibres mentioned above. The cellulosic polymer solution may be particularly advantageous for bonding a nonwoven fabric formed from cellulosic fibres such as cotton or regenerated ceUulose fibres . For some products, particularly personal sanitary products, manufacturers desire to avoid the use of synthetic polymers. Use of the ceUulosic polymer solution of the invention as bonding agent aUows production of a bonded nonwoven fabric which is 100% ceUulose.

Filaments can be spun from certain solutions of the Ughtly carboxymethylated ceUulose in solvents which are not solvents for ceUulose , for example solutions in aqueous alkaU.

Thus , a process according to another aspect of the invention for the production of ceUulosic filaments by extrusion of a solution of a ceUulosic polymer through a spinneret into a bath in which the extruded filaments soUdify is characterised in that a solution of at least 6% up to 14 or 15% by weight Ughtly carboxymethylated cellulose in aqueous alkaU (such as 5 to 20% by weight sodium hydroxide) is extruded into an aqueous acidic bath to form filaments of Ughtly carboxymethylated cellulose. The concentration of Ughtly carboxymethylated ceUulose in the extruded solution is preferably at least 7% by weight, particularly 8 to 12% by weight. The aqueous acidic bath generally contains 7 to 20% by weight of a strong acid such as sulphuric acid and preferably also contains 10 to 30% by weight of an alkaU metal salt thereof, although the salt is not essential. The bath can, for example, be an acid regenerating bath of the type used in viscose rayon manufacture, which typically contains by weight 10% sulphuric acid, 23% sodium sulphate and 1% zinc sulphate. After passing through the acid bath the filaments are water- washed to neutraUty and dried .

Filaments produced by the above process are generaUy not as strong or regular as viscose rayon fUaments or filaments formed from a cellulose solution in a tertiary amine oxide, but they have a higher water absorbency

and are valuable for use in absorbent personal products . Because the filaments are highly water-absorbent, care must be taken in drying the filaments to avoid adhesion of the filaments during drying. The filaments may be passed through a bath of a water-miscible organic solvent such as ethanol before drying. The filaments are preferably cut to staple length, for example 3 to 40 mm . The Ughtly carboxymethylated fibres are preferably used in combination with other fibres , for example ceUulosic fibres such as cotton or regenerated cellulose , including multi-limbed ceUulose fibres . The Ughtly carboxymethylated fibres can be intimately mixed with said other fibres, for example by carding or air-laying the fibres together to form a web of mixed fibres , or the Ughtly carboxymethylated fibres can be used as a layer, for example a non-woven fabric, of Ughtly carboxymethylated fibre sandwiched between layers of said other fibres . The proportion of Ughtly carboxymethylated fibre in a blend with ceUulosic fibres for absorbent products can for example be at least 5% by weight and up to 95% by weight. The Ughtly carboxymethylated fibre can also be used at simUar levels in conjunction with fluffed wood pulp in absorbent products .

Solutions of the Ughtly carboxymethylated cellulose can also be cast or extruded to form film. According to another aspect of the invention, a process for the production of cellulosic film by extrusion of a solution of a cellulose polymer through a sUt die into a bath in which the extruded film soUdifies is characterised in that a solution of 6 to 14 or 15% by weight Ughtly carboxymethylated cellulose in aqueous alkaU (containing for example 5 to 20% sodium hydroxide by weight) is extruded into an aqueous acidic bath to form a film of Ughtly carboxymethylated cellulose . The preferred concentrations of Ughtly carboxymethylated ceUulose and alkaU (preferably sodium hydroxide) in the extruded solution are as stated above for extrusion of filaments . The composition of the aqueous acidic bath is also generaUy within the ranges quoted above, although for film formation a somewhat higher concentration of acid may be preferred compared to fibre formation. The solution can for example be extruded into an aqueous solution of 14% by weight sulphuric acid and 18% sodium sulphate, which is a typical bath used for the production of regenerated cellulose fUm from viscose, although a bath of similar acid content but with less or no sulphate salt wiU also serve to soUdify the film.

Films can be produced by the above process which have a dry

strength substantially equal to that of known regenerated ceUulose film but which are substantially more hydrophiUc.

The above process for making film and /or filaments has the advantage over known processes for making regenerated cellulose film and filaments that it does not involve the use and recovery of the hazardous chemical carbon disulphide.

The solutions of Ughtly carboxymethylated cellulose according to the invention can be shaped to form products other than fibre or film. For example , a solution in aqueous alkaU can be extruded through an annular die into an aqueous acidic coagulating bath, for example a bath comprising 5 to 20% by weight sulphuric acid and optionally up to 25% by weight sodium sulphate, to form a tubular food casing. The process used is very simUar ,to that used in the production of sausage casings from viscose as described for example in US-A-2999756, but without the need to recover carbon disulphide. A solution of Ughtly carboxymethylated cellulose in aqueous alkaU can also be formed into a shaped article by casting a thin film (up to 2 mm thick) on a former or in a mould and treating the cast film with an aqueous acidic solution to at least partially precipitate the ceUulose from solution before removing the cast film from the former or mould. The solution used in such a casting process preferably has a concentration of at least 7% by weight cellulosic polymer, most preferably 8 to 10% by weight.

When the Ughtly carboxymethylated cellulose is dissolved in an aqueous solution of a quaternary ammonium hydroxide , coagulated fUaments and film can be produced not only by extrusion into an aqueous acid bath but alternatively by extrusion into water. For example, carboxymethylated cellulose having a degree of substitution of about 0.10 can be dissolved at 10 to 12% by weight in an 18 to 30% by weight solution of tetramethyl- ammonium hydroxide to form a viscous solution which can be extruded through a spinneret or die into water to form fUaments or fUm.

AlkaUne solutions of the Ughtly carboxymethylated ceUulose can also be used to make ceUulosic sponges . The solution can, for example, be mixed with a blowing agent such as sodium bicarbonate or carbonate which is activated by acid, and a sheet or portion of the resulting material is contacted with a bath of an aqueous acidic solution, for example 7 to 20% by

weight aqueous sulphuric acid optionally containing an alkaU metal sulphate . The acid reacts with the alkaU so that the dissolved cellulose material is coagulated , while the acid simultaneously reacts with the sodium carbonate to generate carbon dioxide gas which foams the cellulose material as it is being coagulated. The resulting sponge comprises an expanded matrix of Ughtly carboxymethylated ceUulose . The carboxymethylation of the ceUulose renders the sponge more hydrophiUc and water-absorbent than conventional viscose sponges .

When producing sponges , the D . S . of the Ughtly carboxymethylated cellulose may be higher than that used when producing coatings, films or fibres . The D. S . for producing sponges can be up to 0.35 or even up to 0.40 but is preferably in the range 0.10 to 0.30, especiaUy 0.12 to 0.25, so that the Ughtly carboxymethylated ceUulose is not soluble in water. A higher D. S . generally leads to a more absorbent sponge, although the mechanical properties may be somewhat poorer.

The ceUulosic sponge preferably contains fibres which are added to the alkaUne solution of Ughtly carboxymethylated ceUulose before acid regeneration . The fibres used are preferably ceUulosic fibres , for example Tencel (Registered Trade Mark) solvent-spun ceUulose fibres , viscose rayon fibres or cotton fibres, although other types of fibre such as acryUc or polyolefin fibres can be used. The proportion of fibres used is generaUy at least 5% and preferably at least 10% up to 60% or even 100%, by weight based on the weight of Ughtly carboxymethylated cellulose in the solution; a particularly preferred proportion is in the range 20 to 50% by weight. The diameter of the fibres is preferably similar to that of fibres used in apparel, for example fibres of 0.5 to 5.0 decitex per filament . The fibre staple length is generaUy in the range 1 to 100 mm and preferably below 15 mm, for example 2 to 12 mm. The fibres improve the wicking and rate of water uptake of the sponge and give a more natural appearance and texture to the sponge.

Alternative uses of the alkaUne solutions of Ughtly carboxymethylated ceUulose are those where a thickened alkaUne solution is required; for example the solution can be used as a paint stripper or in leather softening.

The cellulosic material thickens the alkaline solution sufficiently so that it remains in contact with the substrate to be treated for these uses. High

concentrations of alkaU, generally in the range 2N to ION, can be used since degradation of the cellulosic material is not important . The concentration of Ughtly carboxymethylated cellulose to achieve the required viscosity is generally in the range 4 to 15% by weight.

For some uses it may not be necessary that the Ughtly carboxymethylated cellulose dissolves completely in the alkaUne solution, provided that a substantial amount (at least 25%, and preferably at least 50%) does so . The resulting dispersion or slurry of Ughtly carboxymethylated cellulose fibres in a viscous solution of Ughtly carboxymethylated ceUulose preferably contains at least 8%, and most preferably at least 12%, by weight cellulosic material. Most preferably, at least 65% by weight of the Ughtly carboxymethylated cellulose, for example 75 or 80%, is dissolved in the solution. The dispersion or slurry can be produced using the same or a sUghtly lower concentration of alkaU than is necessary to achieve complete dissolution of the ceUulosic material. Preferably, the conditions of mixing are changed so that less vigorous agitation is used and there is no mixing step at low temperature. Contact of the aqueous alkali and Ughtly carboxymethylated ceUulose pulp at ambient temperature, for example 20 to 30° C, tends to dissolve most of the ceUulosic material read y but to leave undissolved pulp fibres . The concentration of cellulosic material in solution should be sufficient that the viscosity of the solution is sufficient to maintain the Ughtly carboxymethylated ceUulose pulp fibres in suspension. The total concentration of ceUulosic material in the dispersion can be up to 25% by weight, preferably up to 20%. The dispersion can, for example, be cast or extruded to form film which is treated with aqueous acid to coagulate the dissolved cellulosic material. The resulting opaque fUm comprises fibres of Ughtly carboxymethylated ceUulose in a non-fibrous fUm matrix of Ughtly carboxymethylated ceUulose. The fibres reinforce the film, increasing the tear strength in particular.

The dispersion of Ughtly carboxymethylated ceUulose fibres in an alkaline solution of Ughtly carboxymethylated cellulose can also be used to make sponges by mixing with a blowing agent and coagulating the ceUulosic material by acid , using the process described above . The dispersion can be used without added fibres since the dispersed cellulose pulp fibres perform to a large extent the role of fibres in wicking and in improving the appearance and texture of the sponge. Most preferably the dispersion is

used with added fibres, particularly fine ceUulosic textile fibres . The combination of the cellulose pulp fibres of the dispersion and the added fibres comes closer to reproducing the texture and appearance of natural sponge than added fibres alone .

The Ughtly carboxymethylated cellulose also has enchanced solubiUty in solvents which are solvents for cellulose, such as tertiary amine N- oxides, for example N-methylmorphoUne N-oxide, N,N-dimethylethanolamine N-oxide, N,N-dimethylcyclohexylamine N-oxide, N-methyl- piperidine N- oxide, triethylamine N-oxide or N,N-dimethylbenzylamine N-oxide. A process for preparing a cellulose solution in tertiary amine N-oxide with a minor amount of water and spinning the resulting solution to form lyoceU cellulose fibres is described in US-A-4246221 and US-A-4416698. The pulp, tertiary amine oxide and excess water are mixed for an hour and subsequently processed in a thin-film evaporator, for example a "FUmtruder" , or a "Readco" continuous processor. When the Ughtly carboxymethylated ceUulose is dissolved in tertiary amine N-oxide using this process, less mixing energy is required to enable the pulp to dissolve, and higher concentrations of ceUulose in solution can be spun by air-gap spinning into an aqueous bath as described in US-A-4246221. The process of US-A-4246221 and US-A-4416948 may need to be modified to include a dewatering step in which the fUaments are dewatered by a water-miscible organic solvent such as ethanol before being dried to avoid adhesion of the filaments during drying. Such a dewatering step is generaUy necessary if the overaU level of carboxymethylation of the ceUulose dissolved in the amine oxide solvent is 0.1 or above, and may be preferred if the overall level of carboxymethylation is 0.05 or above. The Ughtly carboxymethylated ceUulose fUaments produced have aesthetic properties such as handle and mechanical properties such as tensUe strength and extensibiUty which are close to those of lyoceU ceUulose fUaments produced without carboxymethylating but have increased water absorbency. The degree of substitution of the Ughtly carboxymethylated ceUulose for use in this process can , for example , be up to 0.20 , preferably up to 0.15. The degree of substitution is generally at least 0.02 and preferably at least 0.05. Lightly carboxymethylated cellulose pulp can be co-dissolved with unsubstituted pulp in the tertiary amine N-oxide if desired to give a desired overall level of carboxymethylation, for example 5 to 50% by weight Ughtly carboxymethylated cellulose with 95 to 50% non-carboxymethylated cellulose .

Mixtures using up to 20% of the Ughtly carboxymethylated ceUulose are particularly preferred, since filaments formed from such mixtures have increased absorbency compared to normal lyoceU fibres without being so absorbent that they need to be dewatered by an organic solvent before drying and without significant loss of tenacity .

The Ughtly carboxymethylated fibre thus produced can be used in various products . It can, for example, be used in absorbent personal products such as tampons, disposable diapers, sanitary napkins or incontinence pads . The Ughtly carboxymethylated fibre can be used alone or in combination with other fibres, for example ceUulosic fibres such as cotton or regenerated cellulose fibres, for example multi-limbed ceUulose fibres as described in EP-A-301874. The Ughtly carboxymethylated ceUulose fibre of the invention can also be used in garments such as underwear or sportswear to give increased absorbency and comfort . For such uses , the Ughtly carboxymethylated ceUulose fibre may be blended with another fibre , preferably a ceUulose fibre such as viscose rayon, including multi-limbed viscose, or cotton, but alternatively a synthetic fibre such as polypropylene or polyester .

Another type of solvent in which the Ughtly carboxymethylated cellulose will dissolve but which is not a solvent for ceUulose is an aqueous solution of a thiocyanate salt, particularly a thiocyanate salt with a monovalent cation such as alkaU metal or ammonium. The concentration of the aqueous thiocyanate solution is preferably at least 25%, most preferably at least 40%, by weight, up to a near saturated solution. Fibres and films can be formed by extrusion of the solution of ceUulosic material in concentrated thiocyanate solution into water or into a dUute aqueous solution of the thiocyanate salt, preferably having a concentration of less than 15%, most preferably less than 10%, by weight. The concentration of ceUulose material in the solution which is extruded can for example be 6 to 16% by weight.

The Ughtly carboxymethylated ceUulose wiU dissolve readily in solutions of ammonium thiocyanate or substituted ammonium thiocyanate.

Dissolution in aqueous sodium thiocyanate may require heating of the sodium thiocyanate solution, for example at 80 to 100°C. An alternative method of forming a solution of Ughtly carboxymethylated cellulose in aqueous sodium

thiocyanate is by adding ammonium thiocyanate to a solution of the Ughtly carboxymethylated cellulose in aqueous sodium hydroxide, for example a solution in 5 to 20% by weight aqueous sodium hydroxide.. The sodium hydroxide and ammonium thiocyanate react to form sodium thiocyanate and ammonia. The amount of ammonium thiocyanate added can be zero up to saturation without causing the cellulose to precipitate; however, a substantially stoichiometric amount is preferred to form a solution comprising predominantly sodium thiocyanate and Ughtly carboxymethylated cellulose .

Solutions of an acrylonitrUe polymer in an aqueous thiocyanate solution are used commercially for wet spinning acryUc fibres. In one process according to the present invention, an acrylonitrUe polymer and Ughtly carboxymethylated ceUulose (preferably of D.S. 0.03 to 0.20) are dissolved together in an aqueous solution of a thiocyanate salt to form a spinning dope and are extruded through a spinneret into water or a more dUute aqueous thiocyanate salt solution to produce fUaments comprising the acrylonitrUe polymer and the Ughtly carboxymethylated ceUulose. The concentrations of thiocyanate salt in the spinning dope and in the more dilute regenerating solution can for example be in the ranges quoted above .

The acrylonitrUe polymer used in the above process is preferably a polymer containing at least 85% by weight acrylonitrUe units , as is known for spinning acryUc fibres . The acrylonitrUe polymer can contain up to 15% by weight of a plasticising comonomer, for example 2 to 12% by weight of methyl acrylate or other alkyl ester. The acrylonitrUe polymer may also contain an acidic comonomer conferring dyeabiUty, for example itaconic acid or 2- acrylamido-2-methyl-propane sulphonic acid or methaUyl sulphonic acid, generally used at 0.5 to 2.5% by weight.

It may be preferred that the same solvent is used for the acrylonitrUe polymer and for the Ughtly carboxymethylated ceUulose, that is to say that both are dissolved in aqueous ammonium thiocyanate before mixing or both are dissolved in aqueous sodium thiocyanate before mixing. In an alternative procedure starting from a solution of Ughtly carboxymethylated ceUulose in sodium hydroxide, ammonium thiocyanate is added to a solution of acrylonitrUe polymer in aqueous sodium thiocyanate. The amount of ammonium thiocyanate used is preferably approximately stoichiometric with

respect to the sodium hydroxide in the Ughtly carboxymethylated ceUulose solution. The solution of Ughtly carboxymethylated cellulose in aqueous sodium hydroxide is then mixed into the acrylonitrile polymer solution. The sodium hydroxide and ammonium thiocyanate react, resulting in a solution of acrylonitrile polymer and Ughtly carboxymethylated cellulose in aqueous sodium thiocyanate, which can be used as a spinning dope.

Filaments can thereby be produced having properties in general similar to those of known acryUc fibres . The fUaments retain the thermoplastic nature of the acrylonitrile polymer so that they can be crimped if required by methods known for acryUc fibres . The fUaments have increased dimensional stabiUty at high temperature due to the presence of the cellulosic polymer and also have increased moisture absorbency and comfort due to the presence of the Ughtly carboxymethylated ceUulose . The Ughtly carboxymethylated ceUulose preferably forms 5 to 50% by weight of the filaments, for example 10 to 25%.

A solution of Ughtly carboxymethylated ceUulose, for example a solution containing 2 to 10% by weight of the ceUulosic material, can be used as an adhesive. In particular, it can be used to bond or laminate layers of regenerated cellulose film, such as oriented, particularly biaxiaUy oriented, film which is difficult to bond . A preferred adhesive for this purpose is a solution of Ughtly carboxymethylated ceUulose in aqueous alkaU which has been modified by the addition of a thiocyanate . The thiocyanate is generaUy used at a less than stoichiometric amount with respect to the alkaU in the solution, for example it can be used at 4 to 25% by weight based on sodium hydroxide in the solution. One adhesive which has been successfuUy used is a solution containing 7% Ughtly carboxymethylated ceUulose, 10% sodium hydroxide and 1% ammonium thiocyanate, by weight. This can be appUed to a film by a doctor blade before laminating the films by nip roUers . The resulting laminate can, if desired, be treated with aqueous acid to neutraUse the alkaU and precipitate the Ughtly carboxymethylated ceUulose which forms a secure bond between the films , forming an aU- ceUulose film laminate . A solution of Ughtly carboxymethylated cellulose in alkaU without added thiocyanate is less effective as an adhesive for highly oriented regenerated ceUulose films, but other additives can be used in place of the thiocyanate, for example urea, boric acid, or a borate or a phosphate.

When the Ughtly carboxymethylated cellulose is to be reacted with an esterifying agent, the degree of substitution of the carboxymethylated cellulose is preferably up to 0.20, most preferably up to 0.10, and is preferably at least 0.02 and most preferably at least 0.04. The Ughtly carboxymethylated cellulose has an enhanced rate of reaction with esterifying agents and forms cellulose esters having enhanced solubiUty in various polar solvents .

One example of an esterifying agent with which the Ughtly carboxymethylated ceUulose pulp can be reacted is an acylating agent, for example an acyl chloride or a mixture of an alkanoic acid and the anhydride of an alkanoic acid, to produce a ceUulose alkanoate. UsuaUy, the preferred alkanoic acid is acetic acid and the anhydride is acetic anhydride to produce cellulose acetate. A catalyst, generally sulphuric acid, is preferably used in the acylation reaction. The ceUulose is preferably fuUy reacted to form Ughtly carboxymethylated ceUulose triacetate (having a D . S . of 0.02 to 0.20 carboxymethyl ether group and 2.8 to 2.98 acetate ester groups) . This is soluble in chloroform or methylene chloride and can be dry spun from methylene chloride to form fibres . For most uses the triacetate is partiaUy hydrolysed by water at the end of the esterification reaction, forming Ughtly carboxymethylated cellulose acetate having a D. S. of 0.02 to 0.20 carboxymethyl ether group and 2.0 to 2.5 acetate ester groups. This is soluble in acetone and can be dry spun to form fibres or cast from solution to form film, or it can be used as a thermoplastic moulding compound. Mixed ceUulose esters can be produced by using an alkanoic acid with the anhydride of a different acid or by using a mixture of alkanoic acids with an anhydride or a mixture of anhydrides with an acid. CeUulose acetate butyrate and cellulose acetate propionate, for example, are both useful in forming plastic fUm by thermoplastic extrusion or by casting from acetone solution.

Cellulose ester products formed from the Ughtly carboxymethylated cellulose retain their thermoplastic nature but have the advantage of being more hydrophUic. For example, ceUulose acetate filaments having greater abiUty to absorb moisture can be produced, leading to more comfortable fabrics when used in apparel.

The Ughtly carboxymethylated cellulose can alternatively be reacted

with an inorganic esterifying agent, for example carbon disulphide, to produce cellulose xanthate useful in forming viscose fibres and fUm . Viscose is an aqueous solution of sodium cellulose xanthate . It is typically prepared by treating cellulose pulp with aqueous sodium hydroxide solution to form alkaU cellulose . The alkaU cellulose is aged in air to aUow oxidative degradation to take place so that the molecular weight of the ceUulose chains is reduced to a desired level. The aged alkaU cellulose is then reacted in a xanthation step with carbon disulphide to form sodium cellulose xanthate. The sodium ceUulose xanthate is then dissolved in water or dUute aqueous sodium hydroxide solution to form viscose. The viscose is subjected to a number of further processes, including blending, fUtration and deaeration. The viscose concurrently undergoes chemical changes known as ripening. The processed and ripened viscose is then extruded through a suitable die into an aqueous acidic bath to form regenerated cellulose articles such as fibres or films, which are subsequently washed and dried.

When the ceUulose pulp is initiaUy Ughtly carboxymethylated according to the present invention, the Ughtly carboxymethylated pulp wiU react more readily with the aqueous sodium hydroxide solution and may dissolve in it. The resulting Ughtly carboxymethylated alkaU ceUulose reacts more readily with carbon disulphide, and a satisfactory viscose can be produced using a lower level of carbon disulphide. Reduction in the amount of added carbon disulphide reduces both the chemical cost of the process and the amount of emissions . It is weU known that the filterabiUty of viscose becomes worse as the amount of carbon disulphide added is reduced, with the consequence that the cost of fUtering the viscose increases, but this may be at least partiaUy avoided by the use of Ughtly carboxymethylated ceUulose pulp. The amount of carbon disulphide required to react with the alkaU cellulose to produce a satisfactory viscose is generally no more than 20% by weight based on the Ughtly carboxymethylated cellulose and may be as low as 15% or even 12% compared to amounts of over 25% by weight CS ₂ on cellulose generaUy required in known processes .

SimUar reductions in the amount of carbon disulphide required to form a satisfactory viscose for regenerated ceUulose film production can be achieved by the use of Ughtly carboxymethylated ceUulose . For both fibre and film, the product made from Ughtly carboxymethylated ceUulose has

equal dry strength and is more hydrophiUc than prior art material.

The invention is illustrated by the following Examples .

Example 1

Wood pulp produced from softwood by the sulphite process and sold as "dissolving pulp" was wetted with twice its weight of water. A 25% by weight aqueous solution of sodium hydroxide was mixed with a 25% by weight aqueous solution of sodium monochloroacetate at 2°C . 3 kg of wet wood pulp was slurried in 8 Utres of the mixed solution using a high-shear disperser. The resulting slurry was pressed in a filter press to retain a moist pulp of cellulose pulp content 35% by weight containing about 4% by weight sodium hydroxide and about 9% by weight sodium monochloroacetate based on cellulose . The moist pulp was heated by passage through a forced air oven at 100°C for 5 minutes, thereby drying the pulp and effecting the carboxymethylation reaction. The resulting dry pulp had a degree of substitution of 0.11 carboxymethyl group per anhydroglucose unit and contained some untreated NaOH. It was not soluble in water.

9.5% by weight of this Ughtly carboxymethylated cellulose pulp and 9.3% by weight sodium hydroxide peUets were dispersed in 81.2% by weight water in a "Hydisperser" turbine mixer at 20° C to form a homogeneous slurry in which some of the ceUulose material had dissolved and some remained as fibres . Mixing of the slurry was continued while it was cooled to -10°C and for 25 minutes at this temperature. The fibres present in the slurry swelled and broke down during this mixing, producing a solution of 9.0% by weight ceUulose in 9.8% by weight aqueous NaOH .

Example 2

The procedure of Example 1 was foUowed, but the slurry produced initially was fed to a twin-screw extruder at a feed rate of 12.6 kg/hour. The slurry was cooled to -14°C after entry into the extruder and held at no more than -11°C during its passage through the extruder. The residence time was 5 minutes and screw speed 50 rpm. The extruded product was passed through a 6 metre tube immersed in a water bath at 25°C and was collected at 15°C. A homogeneous solution, containing no fibres visible

under an optical microscope, was produced. A few swollen fibres were visible when the solution was examined under a more powerful microscope.

Example 3

The procedure of Example 2 was repeated using a feed rate of 4.4 kg/hour through the extruder (residence time 14 minutes, screw speed 40 rpm) . The extruded solution was more viscous than that of Example 2 and contained no detectable fibres .

The extruder was then fitted with a sUt die leading to an aqueous bath containing 14% by weight H ₂ SO ₄ and 18% by weight Na ₂ S0 ₄ . Clear film of Ughtly carboxymethylated ceUulose was produced.

Example 4

Lightly carboxymethylated ceUulose of degree of substitution 0.11 was produced as described in Example 1. This was dispersed in an aqueous sodium hydroxide solution to produce a clear solution containing 7.0% by weight Ughtly carboxymethylated ceUulose and 10% by weight NaOH.

The resulting solution was cast on a glass sheet and aUowed to dry. The sheet was then immersed in an aqueous bath containing 14% by weight H ₂ SO ₄ and 18% by weight Na ₂ S0 ₄ . A film of Ughtly carboxymethylated cellulose was produced which could be stripped from the glass . The film had a dry tenacity of 40 MPa, a wet tenacity of 6.8 MPa, a dry extensibiUty of 18% and a wet extensibiUty of 44%. The moisture content of the film after conditioning in air at 20° C and 65% relative humidity was 11% by weight.

Example 5

Sodium hydroxide and sodium monochloroacetate were each dissolved in ethanol (industrial methylated spirits) at 40% by weight and the solutions were mixed . Wood pulp wetted with twice its weight of water was dispersed in the mixed solution at a concentration of 10% by weight dry wood pulp soUds. The resulting slurry was heated to 60°C and held at this temperature for 2 hours to carry out the carboxymethylation reaction. The slurry was press filtered and the treated pulp was washed with water to

remove residual alcohol. The resulting carboxymethylated ceUulose pulp had a degree of substitution of 0.12. It could be dissolved in aqueous sodium hydroxide as described in Example 1 or Example 4.

Example 6 (a)

Wet wood pulp was dispersed in an aqueous solution containing 6.5% by weight NaOH and 19.2% by weight sodium monochloroacetate at a concentration of 15% by weight wood pulp soUds . The resulting slurry was filtered and the treated pulp was heated at 100°C for 30 minutes to produce a carboxymethylated cellulose pulp of degree of substitution 0.09.

This Ughtly carboxymethylated ceUulose was mixed with aqueous sodium hydroxide under high shear conditions to produce a solution containing 7% by weight Ughtly carboxymethylated ceUulose and 10% by weight NaOH. The solution was dUuted with twice its volume of water to produce a solution containing 2.3% by weight Ughtly carboxymethylated ceUulose and 3.3% by weight NaOH.

The diluted solution was sprayed onto a wet-laid manUa paper sheet which had been dewatered by suction but not dried . The paper was dried by passing around heated roUs at 120°C (residence time 5 minutes) . It was then sprayed with 1.5% by weight aqueous sulphuric acid (appUed to the same face as the ceUulosic solution) and redried. A tough smooth paper having a film of Ughtly carboxymethylated ceUulose at one surface was produced . The tensUe strength of the treated paper was 73.4 g/mm dry and 65.3 g/mm after wetting with water (compared to 35.1 g/mm and 1.2 g/mm respectively for the untreated paper) .

Examples 6(b) to 6(d)

The diluted solution of Example 6(a) containing 2.3% by weight Ughtly carboxymethylated cellulose and 3.3% by weight NaOH was appUed to manila paper using the general procedure of Example 6(a) but with different drying temperatures and a residence time of 3.5 minutes in each drying step. The concentration of the aqueous sulphuric acid spray was 1.8% by weight . The tensile strength (wet and dry) of the papers produced is shown in Table 1.

Table 1

Effect of Drying Temperature After Padding (Residence Time 3.5 mins)

Drying Temp Concentration TensUe Strength °C % Acid g/mm

Dry Wet

Example 6(b) 180 1.8 72.2 77.5

Example 6(c) 160 1.8 110.2 91.8 Example 6(d) 140 1.8 97.9 67.3

Example 7 (a)

A solution of 7% by weight Ughtly carboxymethylated ceUulose in 10% by weight aqueous sodium hydroxide was produced as described in Example 6(a) and was dUuted with water to provide a solution of 3.5% by weight Ughtly carboxymethylated ceUulose in 5% by weight sodium hydroxide . This solution was appUed to paper, dried, treated with acid and re-dried using the process of Example 6(a) .

Example 7(b)

The process of Example 7(a) was repeated with the variation that the concentration of the aqueous sulphuric acid used to treat the ceUulose- coated paper was 1.0% by weight. The strength of the paper produced in Examples 7(a) and 7(b) is shown in Table 2.

Table 2

Effect of Drying Temperature After Padding (Residence Time 3.5 mins)

Drying Temp Concentration Tensile Strength

°C % Acid g/mm

Dry Wet

Example 7(a) 120 1.5 53.0 20.8

Example 7(b) 120 1.0 208.0 22.8

10 Example 8

A solution of 7% by weight Ughtly carboxymethylated ceUulose in 10% by weight aqueous sodium hydroxide was produced as described in Example 6(a) and was dUuted with water to provide a solution of 1.75% by weight Ughtly carboxymethylated ceUulose in 2.5% by weight NaOH . This solution 15 was appUed to paper, dried, treated with acid and re-dried using the process of Example 6(a) . The tensUe strength of the treated paper was 25.7 g/mm dry and 16.7 g/mm after wetting with water.

Example 9

Softwood pulp was treated with sodium hydroxide and sodium 20 monochloroacetate as described in Example 1 to produce a Ughtly carboxymethylated ceUulose pulp of D. S. 0.12 which was not soluble in water.

19.2g of this Ughtly carboxymethylated pulp was mixed with 180.8g 10% aqueous sodium hydroxide at 20° C to produce a dispersion in which most

25 of the pulp was dissolved but some remained as fibres. 6g of 6mm "Tencel" (Registered Trade Mark) solvent-spun ceUulose fibres was mixed into the dispersion. The dispersion was then mixed with a solution of 28g sodium bicarbonate in 175g 5% aqueous sodium hydroxide . The resulting dispersion contained 4.8% by weight Ughtly carboxymethylated ceUulose , of which about

30 80% was dissolved and about 20% was present as dispersed pulp fibres .

Portions of the dispersion were placed on shallow glass dishes and immersed in a bath of 14% aqueous sulphuric acid . The dispersion foamed and set , forming sponges comprising a network of Ughtly carboxymethylated cellulose having dispersed therein "Tencel" fibres and also undissolved fibres of Ughtly carboxymethylated cellulose . The sponge was washed with tap water until neutral and then washed with a 1% aqueous solution of "Trigol" (Trade Mark) softener.

When the sponge was subsequently immersed in water and aUowed to drain, it retained approximately 6 times its weight of water and had a texture simUar to that of natural sponge.

Example 10

Softwood pulp was treated with sodium hydroxide and sodium monochloroacetate as described in Example 1 to produce a Ughtly carboxymethylated ceUulose pulp of D.S. 0.12 which was not soluble in water . The pulp was washed with tap water until neutral, removing residual sodium hydroxide and also any water-soluble non-ceUulose impurities derived from the pulp .

The washed pulp was re- dried and was mixed with a concentrated aqueous ammonium thiocyanate solution to form a solution containing 7% by weight Ughtly carboxymethylated ceUulose and 70% ammonium thiocyanate.

This solution could be extruded through a spinneret into demineraUsed water to form fibres .

Example 11

A solution of 7% by weight Ughtly carboxymethylated ceUulose in 10% by weight aqueous NaOH was produced as described in Example 4.

An acryUc fibre dope was prepared by dissolving 13% by weight acrylonitrUe polymer (containing minor amounts of copolymerised methyl acrylate and 2-acrylamido-2-methyl-propane-sulphonic acid) in a 50% aqueous solution of sodium thiocyanate. 3.8g ammonium thiocyanate was dissolved in lOOg of this dope. 20g of the solution of Ughtly carboxymethylated ceUulose was mixed with the dope to form a stable dope

containing dissolved acrylonitrile polymer and Ughtly carboxymethylated cellulose .

The resulting dope was extruded through a fine nozzle into water and separately into a 5% by weight aqueous sodium thiocyanate solution, forming in each case filaments containing approximately 90% by weight acrylonitrUe polymer and 10% by weight Ughtly carboxymethylated ceUulose.

Example 12

An aqueous solution containing 2.3% by weight Ughtly carboxymethylated ceUulose and 3.3% by weight NaOH was prepared as described in Example 6. A woven cotton gauze was passed through the solution and was then passed through an aqueous acidic bath containing 5% by weight sulphuric acid to deposit the ceUulosic material on the gauze and the resulting material was washed in water to neutraUty and dried, producing a lint-free fabric suitable for medical uses, particularly use in operating theatres .

Example 13

The process of Example 12 was repeated using a hydroentangled non- woven fabric of 6 mm "Tencel" (Registered Trade Mark) lyoceU staple fibres in place of the cotton gauze . A lint-f ree fabric was produced .

Example 14

Lightly carboxymethylated ceUulose pulp having a degree of substitution of 0.10 was produced by a process according to Example 1. 15% by weight of the Ughtly carboxymethylated ceUulose was mixed with 75% by weight N-methyl morpholine oxide and 10% by weight water to produce a spinning dope consisting of a solution of ceUulosic polymer in the amine oxide /water mixture. The Ughtly carboxymethylated ceUulose dissolved much more readUy in the amine oxide/water mixture than does unsubstituted cellulose in the usual production of lyoceU fibre .

The spinning dope was spun into fUaments by air-gap spinning into cold water using the process of US-A-4416698. The fUaments were coUected

on a godet roll as described in US-A-4416698 but were then passed through a bath of ethanol (industrial methylated spirits) to dewater the filaments before drying.

The filaments produced had a tenacity of 34 cN/tex, which is simUar to that of normal lyoceU fibres , and a moisture regain of 15% by weight at 65% relative humidity / 20° C, which is higher than that of lyocell fibres, indicating increased absorbency of the fUaments and a superior comfort factor for garments prepared from them . The tenacity of the fUaments when wet was 19 cN/tex.

Example 15

The process of Example 14 was repeated using as starting material a "high viscosity" wood pulp of degree of polymerisation 950. This was carboxymethylated to a degree of substitution of 0.10 and spun into filaments as described in Example 14. The tenacity of the fUaments was 34 cN/tex dry and 17 cN/tex wet, their moisture regain was 17% and their initial modulus was 220 cN/tex.

Example 16

The process of Example 1 was repeated, but with an increased amount of water in the "Hydisperser" to produce a solution of 7% by weight Ughtly carboxymethylated ceUulose of degree of substitution 0.11 in 7% by weight aqueous NaOH. This solution was extruded at 30 m/min through a spinneret having 40 micron diameter jet holes using a back pressure of 690 kPa (100 psi) into a bath of 13% by weight aqueous sulphuric acid. The filaments produced were coUected by godet and dried. They had a weight of 5 to 6 decitex per fUament, a tenacity of 5 cN/tex and an extensibiUty of 28%. The fUaments were more water absorbent than conventional regenerated ceUulose fUaments. The tenacity of the fUaments is low but sufficient for use in a nonwoven disposable absorbent product.