WO1987004194A1

WO1987004194A1 - Modified liber plant fibres and method for obtaining them

Info

Publication number: WO1987004194A1
Application number: PCT/FR1986/000443
Authority: WO
Inventors: Serge Chaunis; Pierre Monzie; Jean Prunier; Marc Ferrari; Michel Sotton; Alain Satta
Original assignee: Institut Textile De France; Centre Technique De L'industrie Des Papiers, Carto
Priority date: 1985-12-27
Filing date: 1986-12-23
Publication date: 1987-07-16
Also published as: FR2592400A1; CN86108934A; KR940005920B1; CN1015652B; EP0253828B1; JPS63502520A; EP0253828A1; BR8607038A; EP0253828B2; DE3675213D1; FR2592400B1; KR870006241A

Abstract

Modified liber plant fibres, particularly flax, characterized by an enhanced fineness, a reduced quantity of non cellulosic materials, an at least as much ordered crystalline structure of the cellulose. They may be obtained by subjecting the fibres to a hydrolysis treatment in water vapor at high pressure during a limited period of time, followed by a sudden expansion to atmospheric pressure, and by a washing treatment. Application to textile linen fibres.

Description

MODIFIED LIBERIAN VEGETABLE FIBERS AND PROCESS FOR OBTAINING SAME.

The present invention relates to modified bast fibers, in particular flax, usable in particular in the textile industry; It also relates to a process for obtaining such fibers.

"Liberian vegetable fibers" means fibers from the plant liber, such as those of flax, hemp, jute, kenaf, ramie, etc., or of families such as alfa, sisal, that is to say -to say αe fibers having a similar structure in fibrous bundles with cements.

In the following description and claims, reference will be made more particularly to flax fibers, these being preferred, but not limiting.

In the technical rod of flax, the fibers are arranged in bundles of elementary fibers at the periphery of the rod between the bark and the wood. There are thirty to forty elementary fibers per bundle, associated with each other by organic cements (pectins, hemicellulose, lignin ...). In the various processes, mechanical or chemical, used to extract the fibers intended for example for the textile industry, one obtains what one commonly calls the technical fibers which are assemblies of elementary fibers, because cements do not have not been completely eliminated during the different transformation phases. These fibrous linens, by their own constitution, have a finesse which is dependent on the presence of the bundles of elementary fibers and still contain a large proportion of non-encrusting materials. cellulosic.

We have already tried to increase the fineness of this fibrous linen and to decrease its content of non-cellulosic materials, by chemical degumming and bleaching treatments.

Effectively compared to unbleached fibrous flax, degummed and bleached flax, hereinafter called bleached flax, has greater finesse, but still has a non-negligible number of bundles in the process of cleavage and sometimes intact; it also has less encrusting matter, as can be seen from infrared spectroscopy and differential enthalpy analysis, but it still has a significant part. But in the opposite direction, it can be seen that bleaching degrades the crystalline structure of the cellulose.

Now we have found a modified Liberian vegetable fiber, in particular of flax, which, compared to the present unbleached or bleached fibers, have a greater fineness, a lower quantity of non-cellulosic materials and a crystal structure at least as ordered.

These modified textile fibers according to the invention are, after carding and before spinning, essentially made up of elementary fibers, possibly with some remains of bundles but in negligible proportion compared to the constitution of bleached fibers and even more so unbleached, in particular linen. It is this preponderance of elementary fibers which gives them a standard fineness index significantly lower than that of other unmodified fibers: at least thirty percent lower than unbleached flax and at least fifteen percent lower compared with bleached linen.

The preferred modified fibrous linen, according to the invention, is characterized by a very high purity of the cellulose, marked both by a small residual amount of non-cellulosic encrusting materials and by a crystal structure which is not degraded, or even improved by the treatment. that she suffered. The residual quantity of non-cellulosic encrusting materials is determined by various analyzes, either direct, for example the measurement of the total mass of extractable sugars after gentle hydrolysis and assayable by ion exchange chromatography, or indirect, for example the measurement of the number of ketone groups, significant of encrusting materials such as lignin and pectins, by infrared spectroscopy, that is to say comparative for example the examination of fine sections by transmission electron microscopy and the examination of the shape of so-called depolymerization peaks in analysis differential enthalpy. The non-cellulosic encrusting materials of flax include various compounds which, upon hydrolysis, generate sugars such as galactose, xylose, arabinose, rhamnose, mannose, glucose; pectins; lignin.

The preferred modified fibrous linen, according to the invention, has a significantly lower residual sugar content than that of unbleached and bleached linen; indeed, the dosage of these sugars by the ion exchange chromatography technique after flax attack for four hours with molar sulfuric acid at 105ºC revealed that the total mass of sugars extracted from flax modified according to invention was at least half as important as that extracted from unbleached or bleached flax. It was also noted that as regards the mass extracted from galactose it was at least three times less important in the case of linen modified according to the invention.

The other analyzes, either indirect or comparative, all lead to the conclusion that the flax modified according to the invention overall contains a smaller amount of non-cellulosic encrusting materials. The value of the absorption ratio of the ketone group (C = 0) to that of the group (CH ₂ ), by infrared spectroscopy, is considerably less for that modified flax according to the invention than that obtained for unbleached flax and slightly lower than that obtained for bleached linen. In transmission electron microscopy, the fine sections of unbleached linen show a very apparent concentric ring structure; this structure is slightly weakened for bleached flax, on the other hand, for flax modified according to the invention, this annular structure has almost disappeared, only one or two rings closest to the lumen persist. In differential enthalpy analysis, the so-called depolymerization peak has a very great intensity in the case of linen modified according to the invention, an average intensity in the case of bleached linen, whereas it cannot be evaluated in the case of linen. ecru, this being no doubt due to the superposition of different peaks.

The modified fibrous linen according to the invention has a crystalline structure which has not been altered by the treatment undergone, unlike bleached linen. Indeed, by different fractometry of X-rays, it is observed on the one hand that the rate of crystallinity compared to a sandard of amorphous cellulose is the same for the unbleached, bleached and modified linens according to the invention, but on the other hand share that the size of the crystallites which decreases by more than ten percent during bleaching is of the same order or even greater in the linen modified according to the invention by compared to unbleached linen.

The modified flax according to the invention can be obtained by subjecting a dyed flaxseed under a treatment of hydrolysis by steam at high pressure for a limited time, followed by a sudden expansion at atmospheric pressure, then at a subsequent wash. According to a particular mode, the hydrolysis treatment takes place at a pressure of the order of thirty bars for a duration of the order of ten seconds.

The modified flax according to the invention can also be obtained by subjecting a dyed flaxseed to a first treatment consisting of impregnation with a basic or acid solution, then to a hydrolysis treatment in water vapor at a pressure lower, for example of the order of fifteen bars, for a slightly longer time, for example of the order of ninety seconds, followed by a sudden expansion at atmospheric pressure, then a subsequent washing. According to a particularly advantageous mode, the impregnation solution of the first treatment is an alkaline solution containing from four to six percent by weight of soda.

The invention will be better understood thanks to the description which will be given of a comparative embodiment of four short fiber linens: an unbleached linen, a bleached linen and two modified linen according to the invention and attached photos and curves in which :

- Figures 1 to 4 are photos under light microscopy of the four linens in question, respectively: unbleached linen (Figure 1), bleached linen (Figure 2), modified linen A (Figure 3), modified linen B (Figure 4). - Figures 5 to 8 are photos in microscopy electronic transmission of the four linens, respectively: unbleached linen (Figure 5), bleached linen (Figure 6), modified linen A (Figure 7), modified linen B (Figure 8).

- Figures 9 to 12 are the differential enthalpy analysis curves of the four flaxes: unbleached flax (Figure 9), bleached flax (Figure 10), modified flax

A (figure 11), modified linen B (figure 12).

Unbleached short fiber flax is a flax which, after scutching, has undergone a mechanical refining treatment, using different materials such as fine openers. This ecru short fiber flax is an industrially produced flax and has been marketed for several years. It is used by the textile industry for the production of threads containing flax mixed with synthetic fibers, these threads always being a minority in flax, with a proportion in flax which generally does not exceed twenty five percent.

The bleached flax used is a mechanically refined flax, as above, which has been subjected to a degumming and bleaching treatment known as four quarters, representative of the purest products existing on the market.

The first modified flax according to the invention, hereinafter called modified flax A, was obtained from a flax. underwater scorch, which was introduced into a reactor, after having been cut into lengths of seventy millimeters, then subjected to a hydrolysis treatment in steam at 30 bars of pressure for a period of ten seconds; at the expiration of this period, the opening of the discharge port of the reactor causes a sudden expansion on passage from high pressure to atmospheric pressure and therefore the ejection through said orifice of flax into a tank containing slightly alkaline water (0.4% soda) where it is washed and then rinsed.

The second modified flax according to the invention, hereinafter called modified B flax, was obtained from an under-rye dye flax, which, cut into lengths of 70 millimeters, underwent a first impregnation treatment with a alkaline solution containing 4% by weight of soda. The flax thus impregnated was introduced into the reactor as above and subjected to a hydrolysis treatment in steam at 15 bar pressure for ninety seconds. The subsequent operations are the same as for modified flax A.

All the comparative tests which will now be described were carried out using the materials (unbleached flax, bleached flax, modified linen A and B) after carding on a conventional card, and before the spinning proper.

Optical microscopy

The examination in light microscopy of the unbleached flax illustrated in Figure 1 (magnification 520) clearly shows the presence of a large number of fiber bundles either intact (1) or in the process of cleavage (2) Bleached flax (Figure 2 ) (magnification 325) still has bundles in the process of cleavage (2) and sometimes intact (1) The modified lines A and B almost exclusively contain only elementary fibers (3) with perhaps some remains of bundles (4 ) in the case of modified flax A.

Standard fineness index

The measurement of the standard fineness index (IFS) is carried out from a pad of material of constant mass, which is compressed in a mold under a predetermined pressure. We measure, in millimeters of propy alcohol lique, the pressure drop ΔH undergone by a gas flow passing through a pad thus molded, and the IFS is obtained by the following equation:

The values obtained for the four flaxes are respectively 23.2 for unbleached flax, 17.2 for bleached flax, 13.8 for modified flax A, and 11.3 for modified flax B, with, in all tests, a coefficient of variation of 2 or 3%.

Ion exchange chromatography

The flax is first attacked for four hours with molar sulfuric acid at 105º, then the extract obtained is analyzed according to the chromatographic analysis method for sugars developed by the Boulogne laboratory of the Textile Institute of France. and described in the Scientific Bulletin of the Textile Institute of France volume 6, Nº23, third quarter 1977. This method makes it possible to calculate in percentage the total mass of the extracted sugars, after the action of controlled hydrolysis carried out by sulfuric acid molar. These sugars are representative of hemicelluloses and pentosans available in technical flax. These are in particular arabinose, xylose with the weakest glycosidic bonds, galactose, rhamnose, mannose and glucose. The values obtained, as to the total mass of sugars extracted as a percentage compared to the mass of flax analyzed, are respectively 8.5% for unbleached flax, 11% for bleached flax, 2.9% for modified flax A and 3% for modified flax B.

The values obtained, with regard to the mass of galactose extracted as a percentage relative to the mass of flax analyzed, are respectively 3.0% for unbleached flax, 3.5% for bleached flax, 0.4% for modified flax A and 0.6% for modified flax B. Infrared spectroscopy

The flax sample is reduced to powder and then pelletized with anhydrous potassium bromide before recording its absorption spectrum. In the spectra obtained, the peak linked to the absorption of the ketone group (C = 0), at a wave number of 1730 cm ^-1 , shows variations according to the linens, which can be related to the presence in addition or less inlay material, including lignin and pectins. To further quantify these variations, an index defined as the ratio of absorption (C = 0) to absorption (CH ₂ ) was calculated.

The values of this index, obtained with the four linens, are respectively 0.635 for unbleached flax, 0.639 for bleached flax, 0.344 for modified flax A and 0.264 for modified flax B.

Transmission electron microscopy

Flaxseed is successively treated with a 0.1 M solution of sodium periodate for one hour at 20 ° C, with a saturated thiocarbohydrazide solution for one hour at 20 ° C and with an osmium tetraoxide solution for 12 hours at 20ºC. After rinsing with water and drying, the flax is included in an epoxy resin and cut into fine sections with an ultramicrotome before observation on an electron microscope.

The photos obtained for the four lines (Figures 5 to 8) allow the following observations. Unbleached linen (Figure 5) (magnification: 11,000) has a structure in concentric rings very characteristic of encrusting materials. In bleached linen (Figure 6) (magnification: 9000), there is a weakening of the annular structure, but which nevertheless remains very present. In contrast, in the modified linens A and B (Figures 7 and 8). (magnification 11,000), the annular structure has almost disappeared; sometimes only one or two rings nearest the lumen, that is to say the core of the fiber, persist.

Differential enthalpy analysis

The measurement is made by linear temperature rise, at a rate of 20 ° C. per minute, from 1 to 5 milligrams of material under a flow of nitrogen and by recording the difference between the temperatures of the crucible containing the material and a witness crucible. The so-called depolymerization peak is significant both by the temperature at which it is located, and by its intensity.

The comparison of the curves corresponding to the four linens shows that the unbleached linen is clearly different from the others by the shape of its curve, which does not allow to correctly assess the intensity of the depolymerization peak, this being probably due to a superposition of peaks. The temperature of the depolymerization peak of unbleached flax is 375ºC (Figure 9).

Bleached linen has a depolymerization peak of medium intensity, placed at a temperature of 369 ° C (fig. 10).

Modified flax A has a high intensity peak at 373.5 ° C (Figure 11), and modified flax B has an even greater peak at 378.5 ° C (Figure 12).

X-ray diffractometry Flax is cut into segments of 80 microns, disoriented and pelletized under a pressure of 350 kg / cm2. The recording of the diffracted spectrum is done in an angular domain 20 from 10 to 40 °. Measuring the areas of the diffracted peaks makes it possible to assess the crystallinity of the sample compared to an amorphous cellulose standard. Values. obtained are substantially the same for the four flaxes, the crystallinity being 40% for unbleached flax and the modified flaxes A and B, and 39% for bleached flax.

To carry out the crystallite size measurements, a strand of fibers is diffracted and the thickness of the diffracted lines is measured. One can thus calculate one of the mean dimensions of the smallest crystalline entity of the material. The line chosen corresponds to a 2% angle of 22.5 ° and relates to the crystalline plane 002 of the cellulose.

The sizes of the crystallites measured in a direction perpendicular to the crystal plane 002 are respectively 51.4 A for unbleached flax, 40.5 A for bleached flax, 54.5 A for modified A flax and 60 A for modified flax B.

The bleaching treatment degraded the crystal structure of the cellulose, while the flax according to the invention has a crystal structure as, or even more, ordered than unbleached flax.

Of course, given that the composition of a flax is a function of the climatic conditions which allowed its growth then its retting and its geographical origin, the figures given above are to be taken as orders of magnitude, because they could vary from year to year and from field to field. However, these figures clearly show the characteristics of the flax modified according to the invention compared to those of an unbleached flax and of a flax chemically treated according to traditional methods.

It should be emphasized that the material which served as a basis for the linen modified according to the invention is an under-rotted linen, for example a flax that was picked up prematurely in the case of rusting on the ground. Under-rotted flax, transformed in conventional processes, is always coarser than normally rotted flax, since the cements which bind the fibers together and the bundles between them could not be sufficiently degraded by the agents bacteriological retting. This is how a rotted linen always contains more encrusting materials than a normally rotted flax. It is therefore remarkable that a linen modified according to the invention can have such good characteristics, starting from a linen having such mediocre characteristics.

Modified flax A was used in spinning to produce a flax yarn mixed with synthetic fibers, for example acrylic fibers. Comparatively son of the same type was produced with a mechanically refined linecru, as described in the example embodiment above. It is observed that, for a 75% acrylic / 25% linen mixed yarn, the yarn produced from modified flax A is more regular than its counterpart produced from unbleached flax. Furthermore, it has been possible to produce with modified flax A a majority thread of flax, which is not possible in industrial market with unbleached flax.

The fibers treated according to the invention, in particular linen, can be used in all conventional textile applications, in particular in admixture with other natural or chemical fibers in the most varied proportions, but also for other applications.

Claims

CLAIMS 1 / Modified Liberian vegetable fibers, characterized in that, compared with the same unbleached unbleached fibers:. they have greater finesse,. they contain a lower amount of non-cellulosic materials,. and in that their cellulose is in a crystal structure at least as ordered.

2 / modified fibrous linen according to claim 1, characterized in that, compared to the unbleached and bleached fibrous linen, it has greater finesse, contains a smaller amount of non-cellulosic materials, and in that its cellulose is in a structure crystal clear at least as orderly.

3 / fibrous linen according to claim 2, characterized in that it has a standard fineness index lower by at least fifteen percent than that of a bleached linen and at least thirty percent than that of a linen unbleached.

4 / fibrous linen according to one of claims 2 and 3, characterized in that it consists, after carding and before spinning, essentially of elementary fibers.

5 / fibrous flax according to one of claims 2 to 4, characterized in that the total mass of its extractable sugars after gentle hydrolysis and which can be measured by ion exchange chromatography is at least twice less than the corresponding mass of a unbleached or bleached linen.

6 / fibrous linen according to one of claims 2 to 5, characterized in that the mass of galactose extractable after gentle hydrolysis and assayable by chromatography an ion exchange is at least three times less than the corresponding mass of unbleached or bleached linen.

7 / fibrous flax according to one of claims 2 to 6, characterized in that, with equal ini té tall cries, the size of its cellulose crystallites tied in X-ray diffractometry, is substantially larger than that of a flax off-white and much more generous than that of bleached linen.

8 / Fibrous flax according to one of the claims 2 to 7, characterized in that, in transmission electron microscopy, it has almost no apparent annular structure.

9 / A method for the manufacture of a fibrous linen according to one of claims 2 to 8, of the type consisting in subjecting a fiber plant to the action of steam under high pressure, then relaxing at atmospheric pressure and finally washing machine, characterized in that the fiber plant is a previously stained linen.

10 / A method according to claim 9, characterized in that the hydrolysis treatment takes place at a pressure of the order of trei.te bars for a period of the order of ten seconds.

11 / A method according to claim 9, characterized in that the flax undergoes a first treatment by impregnation with a basic or acid solution, and in that the hydrolysis treatment takes place at a pressure of the order of fifteen bars during a duration is in the order of ninety seconds. 12 / A method according to claim 11, characterized in that the pre-treatment solution is a solution containing from 4 to 6% by weight of sodium hydroxide.