Plastic and nonmetallic article shaping or treating: processes – Formation of solid particulate material directly from molten... – With subsequent uniting of the particles
The present invention relates to a process for the preparation of mixtures of cellulosic fibers and microfibers.
In the present text and the claims attached hereto, cellulosic microfibers are understood to mean fibers based on cellulose or alloys of cellulose, whose fineness is less than 1 dtex (which generally corresponds to an equivalent diameter of said fibers smaller than 10 &mgr;m).
The process of the invention is based on the technique of disintegrating a spun solution by a jet of fluid. Similar or like techniques have been carried out in the prior art.
They have been more widely developed within the framework of the preparation of synthetic microfibers. For example, Application FR-A-2 331 632 describes the manufacture of fibrils or microfibers of polypropylene.
In the domain of cellulosic fibers, a process based on said technique of disintegrating is proposed in U.S. Pat. No. 3,114,747. Said process, to Applicants' knowledge, has never been developed and does not allow preparation of microfibers within the meaning of the invention. It consists in coagulating droplets of viscose in the stream of a liquid regenerating agent; said viscose being introduced, through orifices, in said stream at an angle of 90 degrees. In said process, a veritable shear of the extruded viscose is employed. In a first analysis, it may be considered that the process of the invention constitutes an improvement to said process according to U.S. Pat. No. 3,114,747, improvement with a view to obtaining finer fibers.
Furthermore, U.S. Pat. No. 3,785,918 describes a process, based on a different technique, which does allow the preparation of cellulosic microfibers. This process is not strictly speaking carried out with a die. According to this process, the regenerating liquid is injected in a first tube while the viscose flows in a second tube, coaxial to the first and having a larger diameter than that of the first tube. Said viscose is sheared by said liquid, from the inside.
The process of rupturing cellulosic solutions, according to the invention, makes it possible to obtain mixtures of cellulosic fibers which contain cellulosic microfibers and which are therefore very hydrophilic. It is also interesting in that it allows the continuous preparation of non-woven materials.
Said process of the invention, for the preparation of mixtures of cellulosic fibers and microfibers, comprises:
the preparation of a cellulosic solution;
the extrusion (or spinning) of said solution through the hole(s) of a die;
the disintegration of said solution when it comes out of said hole(s) by projecting a liquid or gaseous fluid in a direction making an angle less than or equal to 75 degrees with the axis of said die; said fluid being neutral or adapted to regenerate or precipitate, only partially, the cellulose;
the reception in a cellulose regeneration or precipitation bath, of the dispersion generated at the disintegration step;
the recovery of the mixture of fibers and microfibers, more or less bonded, obtained in said bath.
In characteristic manner, according to the present invention, an extruded (spun) cellulosic solution is broken up and the particles of solution resulting from said break-up are drawn with a fluid, which is neutral or adapted only to regenerate or precipitate said particles partially. According to the invention it is not suitable to coagulate said particles at the disintegration step (even less to block the hole(s) of the die) by using a fluid capable of regenerating or precipitating said solution instantaneously. Said particles must be previously drawn. This is why the fluid used is a neutral fluid or one only adapted to regenerate or precipitate said particles partially. Said fluid is chosen (nature) for and/or carried out under conditions (temperature, concentration) such that, even if it is capable of regenerating or precipitating said particles, it can only do so partially.
Furthermore, drawing is possible, in any case optimalized, insofar as said fluid is not responsible for a real shear of the extruded solution. It is projected at an angle much smaller than 90 degrees, and even at a virtually zero angle.
According to the invention, the disintegration of an extruded solution, on leaving a die, is therefore effected under very particular conditions.
To supply the die, at whose outlet the disintegration as described above is effected, any cellulosic solution capable of being extruded (and from which the cellulose can be recovered by regeneration or precipitation) is suitable. Within the scope of the invention, the following are recommended:
solutions of cellulose,
solutions of cellulosic derivatives,
solutions of cellulose alloy or of mixture based on cellulose,
solutions of alloy of cellulosic derivatives or of mixture based on cellulosic derivatives.
According to the invention, mixtures of cellulosic fibers and microfibers may therefore be prepared from solutions of the material constituting them (solutions of cellulose or of cellulose alloy, called true solutions from which the cellulose or a cellulose alloy will then be precipitated) or from solutions of precursors of said material (solutions of cellulosic derivatives or of alloys of cellulosic derivatives; said cellulosic derivatives then having to be regenerated into cellulose).
The nature of cellulosic solutions which may be extruded and disintegrated when drawn according to the invention are specified hereinafter:
It may therefore be question of true solutions of cellulose and in particular of solutions of the type as used industrially at the present time, for the production of cellulosic fibers by simple spinning: solutions of cellulose in N-methyl N-oxide morpholine (MMNO). Such solutions contain, in practice, from 3 to 12% by weight of cellulose and are solid at temperatures lower than 80° C. With such solutions, the process of the invention must therefore be carried out at temperatures higher than 80° C. Only said solvent MMNO is used industrially at the present time, but other solvents of the cellulose in fact exist, described in the literature and in particular in “Cellulose Chemistry and its applications”, Chapter 7, p. 181-200, edited by T. P. Nevell and S. Haig Zeronian (Ellis Horwood Limited—John Wiley & Sons), among which may be cited: pyridine, dimethylsulfoxide (DMSO) taken alone or mixed with formaldehyde; dimethylformamide (DMF) taken alone or mixed with nitrogen oxides (ex. N
/DMF); methylamine, hydrazine . . . as well as inorganic solvents such as lithium, zinc chlorides; calcium trithiocyanate; sulfuric, phosphoric, trifluoroacetic acids; bases such as sodium, lithium, copper hydroxides and in particular cuprammonium liquor or cupriethylenediamine hydroxide, used in the past for manufacturing “copper rayon” . . . Solutions of cellulose based on said solvents may be extruded (spun) and disintegrated when drawn in accordance with the process of the invention, to generate cellulosic fibers and microfibers.
It may also be question of true solutions of alloy of cellulose, i.e. a mixture of cellulose and of another material dissolved in a suitable solvent. Such alloys have been described in the literature and in particular in U.S. Pat. Nos. 4,041,121, 4,144,079, 4,352,770 and 4,302,252, in Polymer, 1991, Volume 32, No. 6, p. 1010-1011 and Macromolecules, 1992, 25, p. 589-592. The following may for example be extruded and disintegrated with drawing in accordance with the invention: a cellulose-polystyrene mixture in carbon sulfide, a cellulose-polyvinylalcohol mixture in dimethylsulfoxide (DMSO) . . .
It may also be question of solutions of cellulosic derivatives. According to this variant, the cellulose has been transformed, upstream, into a soluble derivative which, according to the invention, is extruded, disintegrated and re-transformed into cellulose, so-called regenerated into cellulose. Viscose constitutes an example of such solutions of cellulosic derivatives. It is question of a xanthate of cellulose in solution in sodium hydroxide. It is obtained in conventional manner by preparation, from cellulose (Cel
Acordis Fibres (Holdings ) Limited
Nixon & Vanderhye P.C.
Theisen Mary Lynn
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