Compositions: coating or plastic – Coating or plastic compositions – Carbohydrate or derivative containing
Patent
1997-03-21
1997-12-30
Brunsman, David
Compositions: coating or plastic
Coating or plastic compositions
Carbohydrate or derivative containing
1062003, 1062175, 264561, C08L 102, C08L 500, C09D10102, C09D10500
Patent
active
057025150
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to methods of stabilising solutions of polysaccharides such as cellulose useful as spinning or casting dopes for making shaped polymer articles such as fibres and films.
Tertiary amine N-oxides (which may also be referred to for convenience as amine oxides) in hydrated form are susceptible to degradation, particularly at elevated temperatures and at certain lower levels of hydration, both of which conditions are conditions which favour the dissolution of organic polymers such as polysaccharides in the amine oxides. Degradation results in a loss of amine oxide, which is an expensive solvent, and degradation can give rise to discolouration of the solvent and any polymer dissolved in it. It is also known that amine oxides may decompose exothermally at elevated temperatures. It is further known that polysaccharides such as cellulose dissolved in an amine oxide solvent may degrade (suffer reduction in molecular weight) at elevated temperatures.
In the manufacture of fibres and film, it is usually desirable to employ as high a polymer concentration in the spinning dope as is compatible with suitable spinning viscosities. It is also often desirable to utilise a polymer of high molecular weight in the production of fibres and film with superior mechanical properties. Dope viscosity increases with increasing polymer concentration and molecular weight, but it decreases with increasing temperature. In general, the difficulty and expense of processing a dope rise with increasing viscosity. Accordingly, it is frequently desirable to operate at elevated temperature for reduced dope viscosity, subject to technical constraints such as the thermal stability of the dope. It is an object of the invention to provide solutions of polysaccharides in amine oxides which have improved thermal stability and can be processed at high temperatures.
BACKGROUND ART
The manufacture of shaped polymer articles by extrusion of a solution of cellulose in a tertiary amine N-oxide into an aqueous coagulating bath is described for example in U.S. Pat. No. 4,246,221, the contents of which are incorporated herein by way of reference. Such a process may be referred to as a solvent-spinning process.
EP-A-47,929 discloses that the degradation of cellulose in solution in amine oxide can be reduced by including in the solution a compound containing at least four carbon atoms and two conjugated double bonds and two hydroxyl or primary, or secondary amino groups. Examples of suitable compounds include ascorbic acid, pyrogallol, gallic acid and its esters, especially its propyl ester, hydroquinone and p-phenylenediamine. To prevent degradation of the cellulose the solution does not need to contain more than 0.5 percent by weight of the compound in question based on the weight of the amine oxide, 0.01 percent if the compound is propyl gallate. The solution may include non-solvents for cellulose such as water, lower alcohols, dimethyl formamide, dimethyl sulphoxide and high-boiling amines.
DD-A-158,656 discloses that the degradation of cellulose in solution in amine oxide can be diminished by including in the solution up to 10 percent by weight of a substance capable of reducing the amine oxide. Suitable reducing agents include nitrogenous compounds such as amines, urea, hydroxylamine and hydrazine; reducing sulphur compounds such as sulphite, thiosulphate, dithionite, thiourea and elemental sulphur; and reducing C--, H-- and O-containing compounds such as aldehydes and reducing sugars.
DISCLOSURE OF THE INVENTION
According to the invention there is provided a solution of a polysaccharide in a hydrated tertiary amine N-oxide, characterised in that it contains (1) an aromatic compound containing a benzene ring bearing at least two substituents selected from the group consisting of hydroxy, groups, primary amino groups and secondary amino groups and (2) a sulphur-containing compound containing an --SH group or an anion thereof or a precursor of such a compound, provided that the said sulphur-containing com
REFERENCES:
patent: 2179181 (1939-11-01), Graenacher et al.
patent: 4246221 (1981-01-01), McCorsley, III
patent: 4426228 (1984-01-01), Brandner et al.
patent: 5354371 (1994-10-01), Wykes et al.
Brunsman David
Courtaulds Fibres (Holdings) Limited
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