Organic compounds -- part of the class 532-570 series – Organic compounds – Carbohydrates or derivatives
Reexamination Certificate
2000-09-25
2003-04-29
Wilson, James O. (Department: 1623)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carbohydrates or derivatives
C536S124000, C536S127000
Reexamination Certificate
active
06555678
ABSTRACT:
The present invention relates to a process for the preparation of a regenerated cellulose fibre or yarn.
For greater clarity, the name “yarn” will be used for the products obtained by the process of the invention, this term denoting, for the requirements of the present description and for the assessment of the scope of the invention, products such as continuous yarns, fibres or rovings, with round or shaped cross sections and with any count.
Regenerated cellulose yarns have been produced for a very long time from a solution of a cellulose derivative such as xanthogenate, in a basic medium. This solution is spun with passage through a coagulation bath and then treatment to decompose the xanthogenic functional group and to regenerate the hydroxyl functional groups of the cellulose. However, this process, which uses carbon disulphide as xanthogenation agent, is very punishing to the environment and generates a great deal of effluent.
More recently, other processes have been provided, including the process known under the name Lyocell, which consists in dissolving the cellulose in an organic solvent, N.MMO (N-methylmorpholine oxide). The solvent is recovered after spinning in spin baths.
Provision has also been made for a process known as the “carbamate” process, which consists in manufacturing a cellulose derivative, cellulose carbamate. This carbamate is obtained by reaction of cellulose with urea. The cellulose carbamate is subsequently dissolved in a sodium hydroxide solution and then spun at low temperature. The cellulose is regenerated by raising the temperature and giving off ammonia.
The latter process is currently in development (see article by A. Urbanowski published in “Chemical Fibers International” of September 1996, pages 260 to 262).
These novel processes, in particular the Lyocell process, require wet spinning. In addition, the fibres obtained by the Lyocell process have different technical characteristics from those of conventional cellulose fibres obtained by the xanthogenation process, as is described in the article by P. A. Koch which appeared in the journal Man-Made Fiber Year Book of September 1997, p. 41 to 47.
A particular aim of the present invention is to provide a process for the manufacture of regenerated cellulose yarns which respects the environment and which makes it possible to obtain yarns which are similar with regard to properties to Viscose or Rayon yarns obtained by the conventional carbon disulphide process.
Another aim of the invention is to provide a process for the manufacture of a regenerated cellulose yarn which makes it possible to carry out the spinning in a molten medium. The latter characteristic makes it possible to improve the profitability of the process as the melt-spinning rates are markedly higher than those of the dry or wet spinning processes.
To this end, the invention provides a process for the manufacture of a regenerated cellulose yarn which consists in spinning a solution of a cellulose derivative or the said cellulose derivative in the molten state through at least one die hole and in then regenerating the cellulose by treatment of the yarn obtained, characterized in that it consists:
in synthesizing a silylated derivative of the cellulose by reaction with a silylating agent,
in extracting the said silylated derivative of the cellulose from the synthesis reaction mixture,
in spinning the said silylated cellulose derivative, dissolved or brought to the molten state, through at least one die hole,
in treating the said yarn with a desilylating agent, in order to regenerate the cellulose and to recover a siloxane,
in regenerating the silylating agent from the siloxane recovered in the stage of regeneration of the cellulose.
According to the invention, the cellulose suitable for synthesizing the silylated cellulose can be of plant (wood, cotton, and the like) or animal origin. It can have a variable degree of polymerization DP, for example of between 100 and 5000. The DP of the cellulose is chosen according to the mechanical properties desired for the cellulose yarn to be manufactured.
Cellulose derivatives can also be used to synthesize silylated celluloses, in particular amorphous cellulose derivatives, which are more reactive, such as those substituted by organic radicals with a low degree of substitution DS (less than 1).
The term “degree of substitution DS” should be understood as meaning the mean number of substituted hydroxyl groups per anhydroglucose unit. As each anhydroglucose unit comprises three accessible hydroxyl groups, the maximum degree of substitution DS is equal to 3.
In a preferred embodiment, the process applies particularly to the silylation of polysaccharides, in particular of cellulose, activated by treatment under pressure with ammonia and then explosion of the ammonia-impregnated polysaccharide according to the process disclosed in Patent Application WO 96/01274 or by reduction in pressure of the ammonia atmosphere as disclosed in Patent Application DE 19 51 10 61.
A compound for insertion or for inclusion between the polysaccharide fibres or chains can be added during the phase of activation by ammonia. Thus, this compound, added with the ammonia, preferably dissolved or dispersed in liquid ammonia, is uniformly distributed in the cellulose structure during the stage of pressure reduction or of explosion and keeps the polysaccharide chains separated from one another. The presence of this insertion compound renders the hydroxyl groups of the polysaccharide more accessible.
Mention may be made, by way of examples, as insertion compounds, of primary alcohols, secondary alcohols, phenols, ethers, acetals, ketones, &bgr;-keto esters, amides, sulphamides, esters, urea derivatives, amino acids, steroids, mono-, di- or oligosaccharides and/or an aromatic compound comprising a heteroatom. The preferred compound of the invention is ethylene carbonate.
The process of the invention applies even more particularly to celluloses partially substituted by organic groups and more advantageously to cellulose esters or ethers exhibiting a degree of substitution DS of less than 1, advantageously of less than 0.7. These celluloses exhibit a low degree of crystallization, which renders the hydroxyl groups accessible.
According to a novel characteristic of the invention, the silylating agent corresponds to one of the following general formulae:
in which:
n is between 0 and 20 inclusive
R
1
which can be identical or different, represent linear or branched alkyl radicals comprising from 1 to 12 carbon atoms or aromatic radicals
R
2
which can be identical or different, represent linear or branched alkyl radicals comprising from 1 to 12 carbon atoms or aromatic radicals
R represents an alkyl, aralkyl, aryl or alkylaryl radical or radicals of following general formulae:
in which:
R
3
, R
4
, R
5
, R
7
and R
8
, which can be identical or different, represent the hydrogen atom or an alkyl group comprising from 1 to 4 carbon atoms
R
6
represents an alkoxy group or an alkyl group comprising from 1 to 4 carbon atoms,
X represents a radical of following formula (V):
in which:
U represents a carbon, nitrogen, oxygen or sulphur atom,
T represents a carbon, nitrogen, sulphur or phosphorus atom,
V represents an oxygen, sulphur or nitrogen atom, and
T is other than U and than V.
According to another preferred characteristic of the invention, the silylation reaction is carried out in the presence of an organic swelling agent having a high dipolar moment which is advantageously higher than that of the alkoxy functional group of the silylating agent of formula (I). This swelling agent improves the accessibility of the hydroxyl groups of the cellulose. This swelling action is of use in particular when the cellulose has not been subjected to a prior activation treatment, such as activation by ammonia or substitution of a portion of the hydroxyl groups by organic radicals.
Mention may be made, as suitable swelling agents, of N-methylpyrrolidone (NMP), dimethylacetamide (DMAC), N-methylmorpholine oxide (NMMO) or dimethylforma
Allandrieu Christian
Gambut Lucile
Karrer Philippe
Karstens Ties
Mignani Gerard
Burns Doane Swecker & Mathis L.L.P.
Rhodia Acetow
White Everett
Wilson James O.
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