GB2070508A - Producing Shaped Articles of Regenerated Cellulose - Google Patents

Abstract

A method of producing shaped articles e.g. fibres and fibres of regenerated cellulose comprises dissolving in organic solvents O- trimethylsilyl (O-TMS) celluloses of the general formula <IMAGE> wherein n denotes the mean average degree of polymerisation and stands for the numerical values 30 to 3,000 and R means hydrogen or trimethylsilyl provided that the degree of substitution amounts to 1 to 3, converting the solution into shaped articles, quantitatively desilylating the articles either slmultanesouly or in a subsequent working step in the presence of at least stoichiometric amounts of water, preferably in an acidic medium and, if desired, subjecting the products obtained to an after-treatment.

Description

SPECIFICATION Improvements In or Relating to a Method of Producing Shaped Articles, in particular Fibres and Films, of Regenerated Cellulose The invention relates to a method of producing shaped articles, in particular fibres and films, of regenerated cellulose.

The production of regenerated cellulose fibres hitherto has been effected primarily according to the socalled viscose or copperoxide-ammonia method, the rayon fibres or rayon-staple fibres producible by these methods having valuable utilisation properties.

These methods give, however, rise to problems with respect to the recovery of the chemicals used as well as to environmental protection. A particular problem is the load by waste water and the nuisance caused by the smell of hydrogen sulphides and non-reacted carbon bisuiphide, when applying the viscose method.

The invention aims at avoiding these disadvantages and has as its object to provide a method by which the production of shaped articles of regenerated cellulose, which have utilisation properties that are at least comparable to the fibres so far produced of regenerated cellulose, is possible without creating problems of environmental protection; furthermore, it is the object of the invention to make feasible an almost complete recovery of the initially used chemicals, and their recycling.

This object is achieved according to the invention in that O-trimethylsilyl (O-TMS) celluloses of the general formula

wherein n denotes the mean average degree of polymerisation (DP) and stands for the numerical values 30 to 3,000, preferably 200 to 2,000, and R means hydrogen or trimethylsilyl, provided that the degree of substitution (DS), i.e. the number of trimethylsilyl groups present at an average per anhydroglucose unit, amounts to 1 to 3, preferably 1.0 to 1.7, are dissolved in organic solvents, the solution is converted into shaped articles and the articles, either simultaneously or in a subsequent working step, are quantitatively desilylated in the presence of at least stoichiometric amounts of water, preferably in an acidic medium, and that the products of regenerated cellulose obtained, if desired, are subjected in a known manner to an aftertreatment, such as drawing, washing, drying, aviving, dyeing, or delustering.

For producing fibres, the solution of the O-trimethylsilyl celluloses either is transformed into shaped fibres according to the dry-spinning method by evaporating the solvent and desilylation with an acidic reagent or is spun into a regenerating bath according to the wet-spinning method.

With wet-spinning, for this purpose advantageously a solution of approximately 16% by weight of an O-TMS cellulose having a DP of about 400 and a DS of about 1.5, with a viscosity of between 30,000 and 32,000 cP in dimethylacetamide (DMA) or dimethylformamide (DMF) is spun into an aqueous regenerating bath containing 0.25 g of sulfuric acid/i and, if desired, also one or more salts, such as Na2SO4.

There are studies belonging to the prior art on the production of trimethylsilyl cellulose derivatives, yet the silylated products known so far have been used as coating materials or have been transformed into shaped articles exclusively by preserving their silylation degree. These O-TMS celluloses have not been suited for spinning their solutions according to the conventional wet-spinning method, for instance, into aqueous spin baths.

The hitherto known silylated products have been soluble merely in apolar solvents, having a mean degree of substitution (DS) of 2 to 3, mostly over 2.5. The following methods of producing silylated cellulose derivatives were already proposed: G. Keilich et al. (Makromol. Chem. 120 (1968), 87-95) for the first time produced, among others, 2,3,6-tris-0-methylsilyl cellulose of native cotton cellulose having a mean-weight average polymerisation degree (DPw) of about 5,800. After bucking the cellulose was reacted in pyridine under nitrogen with a 0.5% aqueous NaOH solution containing an excess of trimethylchlorosilane.The resulting tris-0-trimethylsilyl cellulose (O-TMS cellulose, I) was soluble only in apolar solvents, such as n-hexane and cyclohexane, and precipitable from these solutions with ethanol. Tetrahydrofuran (THF), dioxane, benzene, toluene and chloroform merely cause a swelling of (I). Keilich et al. also found out that this O-TMS cellulose is considerably less sensitive to hydrolysis than e.g. O-TMS glucoses. Thus, the hydrolysis of a TMS group per unit in the O-TMS cellulose takes place by K2CO3 in methanol only after 75 minutes at 500C. A complete desilylation under these conditions occurs only after three hours of boiling under reflux.

O-TMS celluloses which are also soluble in aliphatic and aromatic, if desired chlorinated, hydrocarbons and which contain 2 to 3 O-TMS groups per anhydroglucose unit are products from the method according to U.S. patent No.3,418,312, according to which cellulose is added to a mixture of trimethylchlorosilane, a mono or disaccharide, a solvent and a tertiary amine.

U.S. patent No. 3,418,313 relates to the production of O-TMS celluloses having the same solubility properties by the addition of pure trimethylchlorosilane-prepared by reacting hexamethyldisilazane with anhydrous hydrogen-chloride-to a mixture of cellulose, a tertiary amine, and a solvent.

According to U.S. patent No. 3,432,488 organosilylated celluloses having a degree of substitution (DS) of between 2 and 3 are obtained by the reaction of a cellulose material with an organosilylamide and/or a silazane in N-alkylpyrrolidone or hexamethyl phosphoric acid triamide; the actually produced O-trimethylsilyl celluloses had a DS of 2.6 and 2.73.

K. Bredereck and Colleagues (Makromolekulare Chem. 126 (1969), 139-146) equally used Ntrimethylsilylacetamide as a silylating agent in tetraline or cyclohexanon for cellulose regenerated from cellulose acetate or native cellulose. When reacting cellulose in an N-trimethylsilylacetamide melt, a DS of 2.95 was obtained. The unusual stability of the O-TMS celluloses against hydrolysis is stressed also by these authors.

J. Nagy et el. (Period. Polytechn. Chem. Eng. 18, 91--98, 1972) chose hexamethyldisi!azane in pyridine in the presence of catalytic amounts of trimethylchlorosilane for the silylation of cellophane used as a model substance. The product obtained was soluble in toluene. In this publication the discrepancy of bibliographical data referring to the solubility behaviour of cellulose derivatives silylated with trialkylchlorosilanes in organic solvents was pointed out.

R. E. Harmon and Colleagues (Carbohydrate Research, 31(1973)407-409) reacted various polysaccharides with hexa-methyldisilazane in formamide at 700C and, among others, obtained tris-0trimethylsilyl cellulose by precipitating the reaction products with anhydrous acetone, which cellulose was soluble in benzene, toluene and chloroform.

The invention makes possible, for the first time, the shaping and the regeneration of cellulose by processing O-trimethylsiiyl celluloses with the defined mean average degree of polymerisation and the defined degree of substitution, dissolved in organic solvents, i.e. high-silylated reaction products in apolar solvents and low-silylated reacted products in polar solvents. Therein, when using highly polar aprotic solvents, concentrations of up to about 30% by weight depending on the DP, and when using apolar or low polar solvents, concentrations of up to 10% by weight depending on the DP, may be reached.

As solvents for silylated celluloses, dimethylformamide (DMF), dimethylacetamide (DMA), Nmethylpyrrolidone (NMP), dimethylsulphoxide (DMSO), tetrahydrofuran (THF), aliphatic and aromatic hydrocarbons as well as chlorinated hydrocarbons are interesting above all. As precipitating agents for silylated celluloses in case of wet-spinning, alcohols, such as methanol, ethanol and butanol are suitable, besides water, for high-silylated celluloses, for instance also acetone.

The desilylation occurs particularly rapidly in aqueous acids, such as sulphuric acid, hydrochloric acid, acetic acid, but also in acidic alcohols, wherein salts and other electrolytes may be added for a more rapid coagulation.

With the wet-spinning method the precipitation at first may take place in pure water or alcohol, the desilylation may then occur in a second bath with sulphuric acid, drawing being possible to take place both during precipitation and desilylation, if desired, with the temperature of one or both baths being elevated. It is, however, also possible to spin and draw directly into an acidic regenerating bath, if desired at an increased temperature, wherein the temperature may again be varied. Similar variants are possible also with the dry-spinning method. Here, the desilylation may be carried out either during spinning by acidic steam or afterwards in an acidic water bath at different temperatures and degrees of drawing.

Since the parameters are variable in many respects, it is possible, similar to the viscose method, to produce a paliet of fibres having different property profiles, which in turn are particularly suited for different applications.

The trimethylsilanol initially forming during the hydrolysis of the O-TNOS celluloses immediately condenses under acidic conditions to hexamethyidisiloxane and water:

Hexamethyldisiloxane is completely insoluble in water, precipitates as upper phase and is therefore easy to separate.

By the reaction with HCI, trimethylchlorosilane can again be prepared of hexamethyldisiloxane, which is then again available for the silylation of celluloses. On the other hand, hexamethyidisiloxane could be used also for other technical fields of application. An example therefor would be the preparation of linear polysiloxanes terminated by trimethylsiloxy groups, which can be used for the production of silicone caoutchoucs. Hexamethyldisiloxane has an agreeable smell and moreover is physiologically harm less.

The method according to the invention therefore not only is anti-pollutive-no problems related with waste air or waste waters will arise-but also is very beneficial from the aspect of the rawmaterial balance, making feasible the production of regenerated cellulose fibres of a large range of variation and of a high quality.

In the following working directions, the production of silylated celluloses that are suited for the method of the invention are described.

Working Direction 1 Production of O-trimethylsilyl Cellulose with DS 1.46 Into a three-necked flask having a volume of 100 ml and equipped with a stirrer, an introduction tube and a methanol dry-ice bath, 2 g (12.34 mmole) of cellulose are fed and 50 ml ammonia dried over solid KOH and calcium chips are condensed in. Thereafter, the mixture is allowed to swell for another 1/2 to 1 hour at this temperature. Now 4 g (37.04 mmole) of trimethylchlorosilane are dropped in and the mixture is allowed to react over night at the same temperature. The ammonia is evaporated by slowly heating the mixture, the final residues being removed during 3 to 4 hours by applying a water-jet vacuum with a drying cartridge filled with KOH being interposed. If there is still too much ammonia, the hydrolysis and precipitation may take place already during the subsequent dissolving process.

By the addition of DMA, the silyl cellulose is dissolved and the insoluble ammonium chloride is removed by centrifugation. The product is precipitated with water, sucked off, and washed free of chloride with water. If it is not washed free of chloride, the silyl cellulose is at least partially hydrolysed during subsequent drying in a high-vacuum.

Yield: 3 g (90 /0 of theory), Si: 15.3%, DS: 1.46.

Working Direction 2 Production of O-trimethylsilyl Cellulose with DS 2.65 Into a three-necked flask having a capacity of 100 ml and equipped with a stirrer and a reflux cooler being in connection with the surrounding atmosphere via a drying tube, 2 g (12.34 mmole) of cellulose and 50 ml of anhydrous pyridine are fed, the mixture being heated till boiling under reflux for four hours. Thereafter, 6 g (55.6 mmole) of trimethylchlorosilane are dropped in at room temperature, the flask content being stirred for three hours. By the addition of methanol, the swelling of the silyl cellulose is reduced and the silylated substance is washed with methanol after sucking off.The crude product thus obtained is dissolved in petroleum ether and mixed with about 0.1 g of sodium carbonate in order to neutralise slight amounts of pyridiniumhydrochloride that are still present and which otherwise would suffice for hydrolysing the silylated cellulose. The solution is centrifuged or pressure filtered and the O-TMS cellulose is precipitated from the resulting clear solution with ethanol. After drying a white product is obtained which is soluble in apolar solvents, such as hydrocarbons, or in tetrahydrofuran, methylene chloride, chloroform and carbon tetrachloride.

Yield: 3.75 g (85% of theory), analysis: Si: 21%, DS: 2.65.

The method according to the invention will now be explained in more detail by way of the following examples: Example 1 140 g of O-trimethylsilyl cellulose having a DS of 1.45 and a DP, determined according to the copper-ethylenediamine ("Cuen") method, of 400 were dissolved in 800 g of DMA and the solution was filtered. The clear solution obtained was extruded into an aqueous spin bath containing 50 g of Na2SO4/l and 0.25 g of H2SO,/l through a 200-hole precious-metal nozzle with a hole diameter of 0.06 mm by compressed air. The fibre bundle obtained was pulled out of the spin bath with the help of a godet and drawn by 21% in a second bath containing hot water of a temperature of 700C.The fibres obtained were aftertreated for 10 minutes in cold, diluted sulphuric acid containing 1 g of H2SO,/l afterwards were washed with cold water and then with hot water, avived and dried at 700C. They had a titer of 0.95 dtex and exhibited a conditioned fibre strength of 14.5 cN/tex at an elongation of 17.8% as well as a wet strength of 6 cN/tex at an elongation of 11%. The wet module was 35 cN/tex.

Example 2 Like Example 1, however with the difference that the filtered spinning solution was extruded by compressed air through a 1,053-hole precious-metal nozzle with a hole diameter of 0.04 mm into an aqueous spin bath that contained 50 g of Na2SO,/l and 0.25 g of H2SO4/l. The fibre bundle obtained was pulled out of the spin bath with the help of a godet and drawn by 21% in a second bath of water.

The fibres obtained, which were aftertreated as in Example 1, had a titer of 0.70 dtex and exhibited a conditioned fibre strength of 15.1 cN/tex at an elongation of 16.8% as well as a wet strength of 6 cN/tex at an elongation of 14%. The wet module was 52 cN/tex.

Example 3 Like Example 1, however with the difference that the filtered spinning solution was heated to a temperature of 750C and was extruded by compressed air through a 1,053-hole precious-metal nozzle with a hole diameter of 0.06 mm into an aqueous spin bath containing 50 g of Na2SO,/l and 0.25 g of H2SO4/l. The fibre bundle obtained was pulled out of the spin bath with the help of a godet and was drawn by 43% in a second bath of water. The fibres, which were aftertreated as in Example 1, at an average had a titer of 1.75 dtex and exhibited a conditioned fibre strength of 14.0 cN/tex at an elongation of 19.6% as well as a wet strength of 5 cN/tex at an elongation of 16%. The wet module was 46 cN/tex.

Example 4 90 g of O-trimethylsilyl cellulose having a DS of 1.40 and a DPCUEN of 830 were dissolved in 910 g of DMA and the solution was filtered. The solution obtained was heated to a temperature of 750C and extruded through a 200-hole precious-metal nozzle with a hole diameter of 0.06 mm into an aqueous spin bath containing 50 g of Na2SO,/l and 0.25 g of H2SOJI. The fibre bundle obtained was pulled out of the spin bath with the help of a godet and was drawn by 50% in a second bath of water. The fibres obtained, which were aftertreated as in Example 1, had a titer of 3.0 dtex and exhibited a conditioned fibre strength of 1 6.5 cN/tex at an elongation of 13% as well as a wet strength of 7.5 cNAex at an elongation of 10%. The wet module was 65 cN/tex.

Example 5 1 80 g of O-trimethylsilyl cellulose having a DS of 1.48 and a DPCUEN of 200 were dissolved in 820 g of DMA and the solution was filtered. The solution obtained was extruded through a 200-hole precious-metal nozzle with-a hold diameter of 0.06 mm into an aqueous spin bath containing 50 g of Na2SO4/l and 0.25 g of H2SO,/I. The fibre bundle obtained was pulled out of the spin bath with the help of a godet and was drawn by 32% in a second bath of water. The fibres obtained, which were aftertreated as in Example 1, had a titer of 4.1 dtex and exibited a conditioned fibre strength of 12.8 cN/tex at an elongation of 25.3% as well as a wet strength of 5 cN/tex at an elongation of 14%. The wet module was 26 cN/tex.

Example 6 50 g of O-trimethylsilyl cellulose having a DS bf 2.65 and a DPCUEN of 400 were dissolved in 950 g of petroleum ether (60 to 900 C) and filtered. The solution obtained was extruded by compressed air through a 200-hole precious-metal nozzle with a hole diameter of 0.06 mm into a spin bath of ethanol.

The fibre bundle obtained was removed from the spin bath with the help of a godet and was drawn by 20% in a second bath containing 50 parts by volume of ethyl alcohol and 50 parts by volume of 1 N aqueous sulfuric acid. The fibres obtained were aftertreated in the same manner as described in Example 1 and exhibited substantially the same textile properties as those produced according to the preceding examples.

Example 7 50 g of O-trimethylsilyl cellulose having a DS of 2.65 and a DP of 400 were dissolved in 950 g of THF and filtered. The solution obtained was heated to 500C and extruded by compressed air through a 468-hole precious-metal nozzle with a hole diameter of 0.06 mm into an aqueous spin bath containing 200 g of Na2SO;i and 100 g of H2S04/l. The fibres obtained were aftertreated in the same manner as in Example 1 and exhibited substantially the same textile properties as those produced according to the preceding examples.

Example 8 Like Example 7, however with the difference that pure water having a temperature of 1 2 OC was used as the spin bath and that the fibre bundle, which was pulled out of the spin bath with the help of a godet, was drawn by 122% in a second aqueous bath containing 100 g of H2SO4/l. The fibres obtained were aftertreated in the same manner as described in Example 1 and exhibited substantially the same textile properties as those produced according to the preceding examples.

Example 9 (Dry-spinning) 1 80 g of O-trimethylsilyl cellulose having a DS of 1.46 and a DP of 400 were dissolved in 820 g of dimethylacetamide and the solution was filtered. The solution obtained was heated to 800C and dryspun from a 180-hole nozzle with a hole diameter of 0.15 mm in a spinning shaft according to working methods which are known in the art. The shaft temperature amounted to 1 800C. The spinning products were collected on spools and plied to form a thick ribbon. This ribbon was drawn by 50% in an aqueous bath containing 50 g of Na2SO4/l and 0.25 g of H2SO4/l. These fibres, which were aftertreated as in Example 1, had an average titer of 8.5 dtex and exhibited a conditioned fibre strength of 12.5 cN/tex at an elongation of 27% and a wet strength of 5 cN/tex at an elongation of 17%. The wet module was 22 cN/tex.

Claims (4)

Claims

1. A method of producing shaped articles, in particular fibres and films, of regenerated cellulose, which method comprises dissolving in organic solvents O-trimethylsilyl (O-TMS) celluloses of the general formula

wherein n denotes the mean average degree of polymerisation (DP) and stands for the numerical values 30 to 3,000, preferably 200 to 2,000, and R means hydrogen or trimethylsilyl provided that the degree of substitution (DS), i.e. the number of trimethylsilyl groups present at an average per anhydrogiucose unit, amounts to 1 to 3, preferably 1.0 to 1.7, converting the solution into shaped articles, quantitatively desilylating the articles, either simultaneously or in a subsequent working step, in the presence of at least stoichiometric amounts of water, preferably in an acidic medium, and, if desired, subjecting the products obtained of regenerated cellulose in a known manner to an aftertreatment, such as drawing, washing, drying, aviving, dyeing, or delustering.

2. A method according to claim 1 for the production of fibres, wherein the solution of 0trimethylsilyl celluloses either is converted into shaped fibres according to the dry-spinning method by evaporation of the solvent and desilylation with an acidic reagent, or is spun into a regenerating bath according to the wet-spinning method.

3. A method according to claim 2 for the production of fibres, wherein for wet-spinning a 1 6% by weight solution of an O-TMS cellulose having a DP of about 400 and a DS of about 1.5, and a viscosity of between 30,000 and 32,000 cP in DMA or DMF, is spun into an aqueous regenerating bath containing 0.25 g of sulfuric acid/l, and, if desired, also containing one or several salts, such as Na2SO4.

4. A method substantially as hereinbefore described with reference to the accompanying examples. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~